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January 1 984

Polymer

Science and

Standards

Division

Annual Report 1983

P

U.S. DEPARTMENT

OF COMMERCE

National 3ureau

of Standards

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POLYMER SCIENCE AND STANDARDS DIVISION

Annual Report 1983

U. S. Department of Commerce

National Bureau of Standards

Polymers Bldg. (224), A305

Washington, DC 20234

(301) 921-3734

January 1984

Polymer Science

and Standards

Division

LESLIE E. SMITH, Acting Chief. Dr. Smith was born in New York. He

earned degrees in chemistry from Case

Institute of Technology and Catholic

University. Except for a three year period of graduate study, he has been

with NBS since 1964.

MARTIN G. BROADHURST,

Acting Deputy Chief. Dr. Broadhurst was born in Washington, D.C., and

earned degrees in physics at Western Maryland College and Pennsylvania

State University. After teaching at Pennsylvania State, he joined NBS in 1960.

ANTON PETERLIN, Assistant

Chief. Dr. Peterlin was born in Yugoslavia. He earned the M.S. in mathematics at the University of Ljubljana and Ph.D. in physics at the University of Berlin. From 1939 to 1960 he was professor of physics in Ljubljana and from 1949 to 1959 was head of the Josef Stefan Institute. Before joining NBS in 1973, he was

director of the Camille Dreyfus

Laboratory.

G. THOMAS DAVIS, Acting Group

Leader, Electrical Properties. Dr. Davis was born in Montour Falls, New York. He earned degrees in chemical engineering at Cornell

University and physical chemistry at Princeton University. Prior to joining NBS in 1964, he worked for Esso

Research and Engineering Co. and

taught at the University of Virginia.

BRUNO M. FANCONI, Group

Leader, Composites and Mechanical

Performance. Dr. Fanconi was born

in Merced, California. He earned

degrees in physical chemistry from

the University of California at Los

Angeles and the University of Washington. He joined the staff of NBS

in 1971.

ISAAC C. SANCHEZ, Group

Leader, Polymer Blends. Dr. Sanchez was born in San Antonio, Texas. He

earned degrees in physical chemistry

at St. Marys University (Texas) and

at the University of Delaware. Prior

to joining the NBS staff in 1977, he worked at the Xerox Research Laboratories and was on the Polymer

Science and Engineering faculty at the University of Massachusetts.

FRANCIS W. WANG, Acting

Group Leader, Chemical Performance

and Standards. Dr. Wang was born

in Peikang, Taiwan. He earned the

B.S. and M.S. in chemical engineering

at California Institute of Technology

and the Ph.D. in physical chemistry

at the University of California, in San

Diego. He joined the staff of NBS in 1972 after a postdoctoral period at the Polytechnic Institute of New

York.

JOHN A. TESK, Acting Group

Leader, Dental and Medical

Materials. Dr. Tesk was born in Chicago, Illinois. He holds the degrees of B.S., M.S. in Metallurgy

and Ph.D. in Materials Science from

Northwestern University. Prior to joining NBS in 1978, he was at the University of Illinois, Chicago, on

the staff at Argonne National Laboratory, Director of R&D with the Dental Division of Howmedica, Inc. and

Director of Education Services at IGT.

Table of Contents

Page

I. PREFACE .......................... i

II. POLYMER THEORY FOR STRUCTURE AND PROCESSING ............ 1

- Classification of Structure Inducing Transitions in Polymers

E. A. DiMarzio. . 1

“ Monte Carlo Modeling of the Kinetics of Polymer Crystal Growth

C. M. Guttman and E. A. DiMarzio. . 1

- Block Copolymers with Lamellar Morphology: Chain Dimensions in

Directions Parallel and Perpendicular to the Lamellae

E. A. DiMarzio. ....... ...... 2

- Translational Diffusion Constant of Linear and Branched Chains

C. M. Guttman 2

- Processes Involving Conformational Changes in Polymers

D. H. Reneker and J. Mazur 2

III. POLYMERS STANDARDS FOR PROCESS CONTROL AND EQUITY ..... 4

- Self-Calibrating Gel Permeation Chromatography; P. H. Verdier 4

- Critical Evaluation of Mark-Houwink Relation for Linear Polyethylene;

H. L. Wagner 4

- Characterization of Ultrahigh Molecular Weight Polyethylene; H. L. Wagner

and J. G. Dillon. . 5

- Characterization of Polyisobutyl Methacrylate; H. L. Wagner 6

- Dynamics of Polymer Chains; P. H.. Verdier and D. E. Kranbuehl 6

- Automated Liquid Size Exclusion Chromatography; J. D. Barnes and

F. L. McCrackin 7

- Span of an Adsorbed Polymer Chain in a Lattice Random Walk Model;

R. J. Rubin 7

- Monte Carlo Calculations of the Hydrodynamic Radii of Polymers;

F. L. McCrackin and C. M. Guttman 7

- Standards for Gas Transmission Measurements; J. D. Barnes 8

- A5TM Activities; J. D. Barnes 9

- Random-Walk Model of Chain' Polymer Adsorption. Behavior at Critical Energy

and Relation to Reflecting Boundary Condition; R. J. Rubin 9

- Expansion Factor of a Part of Polymer Chain in Good Solvent Measured by Small

Angle Neutron Scattering; C. C. Han, T. P. Lodge, E. J. Amis,

Y. Matsushita 9

- Temperature Dependence of Dynamic Light Scattering in the Intermediate

Momentum Transfer Region; T. P Lodge, C. C. Han, A. Z. Akcasu 9

- Dynamic Scattering from Bimodal Polymer Solutions; B. Hammouda, A. Z. Akcasu,

T. P. Lodge, C. C. Han 10

- Dynamic Light Scattering Measurements of Polystryrene in Semi dilute Solutions

E. J. Amis, C. C. Han and Y. Matsushita 10
IV. BLENDS PROCESSING

Page

11

- Forced Rayleigh Scattering; E. J. Amis and C. C. Han 11

- SANS and SAXS Studies on Molecular Conformation of a Block Copolymer in

Microdomain Space; H. Hasegawa, T. Hashimoto, H. Kawai , C. C. Han,

T. P. Lodge, A. J. Amis 12

- Novel Fluorescence Method for Polymer Blend Phase Diagrams; F. W. Wang and

R. E. Lowry 12

* Nonosecond Fluorimeter for Measurements of Polymer Phase Diagrams; F. W. Wang,

F. L. McCrackin, J. D. Barnes, and W. H. Grant 12

- Installation of a Laboratory for Polymer Synthesis; B. J. Bauer 12

- Digital Small Angle Scattering Camera; J. D. Barnes 13

- New Correlation Discovered for Surface Tension of Simple and Polymeric

Liquids; I. C. Sanchez 13

V. TESTS, STANDARDS AND CHARACTERIZATION FOR MANUFACTURING AND DURABILITY OF DENTAL

AND MEDICAL MATERIALS 14

- Dental Composite and Sealant Chemistry and Related Developments;

J. M. Antonucci , G. M. Brauer, R. L. Bowen, J. W. Stansbury,

R. E. Dehl , and N. W. Rupp 14

- Dental Adhesion Research; R. L. Bowen, G. M. Brauer, J. M. Antonucci,

J. W. Stansbury, D. W. Misra, E. Cobb, and J. M. Cassel 15

- Dental Cements; G. M. Brauer, J. M. Antonucci, and J. W. Stansbury .... 15

- Wear Mechanisms and Durability of Dental Composite Materials. Effect

of Degree of Cure; W. L. Wu, J. E. McKinney, E. E. Debelius,

and J. M. Cassel 16

- Porcelain Fused-to-Metals and Dental Ceramics; J. A. Tesk, W. deRijk,

H. R. Kase, G. Widera, D. L. Menis, and R. W. Hinman 17

- Dental Casting Alloys and Investments; J. A. Tesk, R. W. Waterstrat,

S. Hirano, R. W. Hinman, H. R. Kase, W. deRijk, and H. Argentar 18

- Dental Chemistry, Crystallography, and Preventive Treatments; W. E. Brown,

L. C. Chow, M. Mathew, S. Takagi , M. Tung, G. L. Vogel, T. M. Gregory,

C. M. Carey, B. Sieck, and C. Schreiber 19

- Clinical and Laboratory Investigation of Dental Amalgams, Composites and

Glass Ionomer Cements; N. W. Rupp, G. C. Paffenbarger, and

R. W. Waterstrat 20

- Characterization of Porosity in Porous Polymeric Implant Materials;

R. E. Dehl 21

- Surgical Bone Cement Modification; G. M. Brauer, J. A. Tesk, J. W. Stansbury,

W. L. Wu, and J. E. McKinney 21

- Dental and Medical Materials Standards; J. M. Cassel, J. A. Tesk, G. M. Brauer,

N. W. Rupp, and W. Derijk 22
VI. MECHANICAL DURABILITY OF POLYMERS

Page

23

- Molecular Processes Associated with Mechanical Deformation and Failure;

B. M. Fanconi , D. L. VanderHart, S. J. Kryder, J. R. Havens,

and K. L. DeVries 23

- The Morphology of Crystalline Polymers; F. A. Khoury, L. H. Bolz,

and J. Mazur. 27

- The Necking of Semi crystal line Polymers in Tension; L. J. Zapas and

J. M. Crissman. 29

- A Study of the Morphology and Mechanical Properties, and Their Dependence

on Thermal History and Processing of Ultra High Molecular Weight

Polyethylene; J. M. Crissman 30

- Information Handbook on Polymeric Materials Used in Orthopedic Devices;

J. M. Crissman and G. B. McKenna 31

- Instabilities in the Flow of Viscoelastic Fluids; R. W. Penn and

L. J. Zapas 31

- The Distribution of Stresses in Crazes at the Tips of Uniformly Extending

Cracks; E. Passaglia 32

- Physical Ageing in Polymeric Glasses Subjected to Large Deformations;

G. B. McKenna and A. J. Kovacs 33

- The Effect of Elastic and Plastic Deformation on the Solubility of

Ethyl Acetate Vapor in Polyvinyl i dene Fluoride (PVF-); J. C. Phillips

and A. Peterlin. 33

VII. PROCESSING AND RELIABILITY OF POLYMER COMPOSITES. 35

- Interlaminar Fracture of Composites; D. L. Hunston, G. W. Bull man, and

W. D. Bascom 35

- Failure Behavior of Particle Reinforced Polymer Composites; D. L. Hunston,

A. J. Kinloch, and S. S. Wang. 36

- Cure Monitoring in Polymers and Composites via Nondestructive Techniques;

D. L. Hunston, B. M. Fanconi, F. I. Mopsik, C. C. Yu, and H. Weisshaus . . 37

- Chemorheology in Polymerization Systems Initiated by Oxygen; D. L. Hunston

and G. W. Bullman 39

- Novel Excimer Fluorescence Method for In-Si tu Monitoring of Composite

Materials Manufacturing; F. W. Wang, R. E. Lowry, and W. H. Grant 39

- Analysis of Thermoset Resin Polymerization Kinetics; G. A. Senich,

R. E. Florin, and J. C. Phillips . 39

- Measurement of Photopolymerization of Polymers by Thermal Methods;

J. H. Flynn 40

VIII. ADDITIVE MIGRATION AND CHEMICAL DURABILITY OF POLYMERS 42

- Prediction of the Long Term Stability of Polyester-Based Recording Media;

D. W. Brown, R. E. Lowry, and L. E. Smith. 42
- Hydrolytic Degradation of Polyester Polyurethanes; W. Brown, R. E. Lowry,

and L. E. Smith 42

- Studies With Polyether Polyurethane Tubing; D. W. Brown, R. E. Lowry, and

L. E. Smith 43

- Solar Type Photolytic and Thermal Degradation of Plates of Poly(Methyl)

Methacrylate; B. Dickens 43

- Evaluation of IC-Encapsulants; S. S. Chang and J. R. Maurey 44

- Variable Heating Rate Thermal Analysis; J. H. Flynn 44

- Measurement of Additive Diffusion by Fluorimetry; F. W. Wang, B. F. Howell,

and F. L. McCrackin 44

- Migration of Low Molecular Weight Materials in Polymers Under Simultaneous

Swelling Conditions; C. M. Guttman and S. S. Chang 45

- Migration of Styrene Monomer From Polystyrene; S. S. Chang and

J. R. Maurey 45

- Chromotographic Studies of Migration From Polymers; G. A. Senich 46

- Solubilities and Partition Coefficients of BHT in Polyolefins and Various

Solvents; S. S. Change and J. R. Maurey 46

- Determination of Segmental Mobility by Picosecond Fluorescence Spectroscopy;

F. W. Wang, R. R. Cavanagh and W. H. Grant 46

IV. MICROSTRUCTURE AND PERFORMANCE OF DIELECTRIC PLASTICS 48

- Automated Dielectric Measurements; F. I. Mopsik 48

- Dielectric Properties of Polyvinyl idene Fluoride; A. J. Bur

and F. I. Mopsik 49

- Dielectric Loss Spectra of Polymers in the Microwave Region; A. J. Bur ... 50

- Conducting Polymers; C. K. Chiang 50

- Fast Ion Transport in Solid Polymers; C. K. Chiang, G. T. Davis, C. A. Harding,

and T. Takahashi 51

- Structure and Performance of Piezoelectric Polymers; G. T. Davis and

M. G. Broadhurst 52

~ Polarization and Space Charge Studies; A. S. DeReggi and F. I. Mopsik. ... 52

- A Dynamic Polymer Pressure Transducer With Temperature Compensation;

A. J. Bur and S. C. Roth 53

- Acoustic Sensors; A. S. DeReggi 53

- Spontaneous Polarization in Ferroelectric Polymers; A. S. DeReggi, S. C. Roth,

G. T. Davis, and M. G. Broadhurst 54

X. OTHER DIVISION ACTIVITIES 55

- Invited Talks 55

- Seminars for Staff and Guests 73
Page

Technical and Professional Committee Participation and Leadership 80

Publications . . . 87

Special Reports.. .............................. 95

Books 95

Consulting and Advisory Services ...... ........... 95

External Recognition . 96

New SRMs 96

Patents. ................... ... 96

Industrial Interactions 96

Formal Visits. ....... 97
*
POLYMER SCIENCE AND STANDARDS DIVISION (563)

Leslie E. Smith, Acting Chief

Martin G. Broadhurst, Deputy Chief

Bo A. Hyde, Secretary

Although synthetic polymers have been used as materials for technology during only three

quarters of a century, they have left little of our economy, technology, industry, science, and

culture untouched. We have moved rapidly into an age in which an evergrowing number of humanity's

needs are served by polymers. The volume currently produced exceeds that of steel and forms the

basis of industries which add over $106 billion of value by manufacturer (a measure of the relative

economic importance of manufacturing among industries) and provides 3.3 million jobs. Recent

summaries show that polymers and polymer composites research already accounts for about 47 percent

of the total industrial R&D expenditure for metals, polymers, and inorganic materials. Among these

materials, polymers also constitute about 40 percent of the value added by manufacturer, 45 percent

of the jobs, 49 percent of the number of scientific publications, and 42 percent of the American

Society for Testing and Materials (ASTM) standards.

Polymers have been shaped by intellectually sophisticated research which has been recognized by

a number of Nobel Prizes. The resulting materials have contributed to national industrial

productivity through their economy, ease of fabrication, and useful properties such as low density,

corrosion resistance, and toughness. Polymers are energy efficient; the largest volume polymer,

polyethylene, uses 29 percent of the energy per unit volume required by steel for conversion from raw to refined material and yields further savings in processing and shipping. In fact, studies

have shown that for every barrel of oil used to make plastic products, approximately one barrel is

saved in comparison with the use of the next best alternative material. These characteristics have

enabled polymers to contribute to increased national economic strength both by creating entirely new products and by substituting for other materials in existing products.

Polymers have entered a widening range of increasing sophisticated and demanding applications.

Polyvinyl idene fluoride films are used as piezoelectric transducers in high fidelity sound systems,

biomedical imaging devices and infrared sensors. Structural parts of aircraft are constructed from

composites with a polymer matrix and sometimes a polymer reinforcement. Polyurethane elastomers are used to pump blood in circulatory assist devices. The list of such examples is very long, and

includes trends for the increased use of polymers in packaging, construction, transportation,

national security, electronics, information handling, clothing, electrical appliances, energy,

dentistry and medicine. Since polymer science and technology is on the steep part of the learning

curve, these trends create many new needs for scientific concepts, measurements, standards, and data

that can be used to ensure their reliable performance in the use, processing, and other phases of

the material cycle. The programs of the Division are aimed at the fundamental scientific basis of

these needs.

To identify the key needs with the best prospects for payoff, the managers of the Polymer

Science and Standards Division make structured visits to industrial and Government laboratories.

Visited sites include Bell Laboratories, E. I. DuPont de Nemours, Inc., 3M, Army R&D Command,

General Motors Corporation, Martin Marietta, and Lawrence Livermore Laboratories. Surveys have been

conducted in the areas of durability, composites, and processing. Research Associates, working on joint NBS- industrial projects in polymers were sponsored by ten organizations during the past year

including General Electric Research Laboratories, Exxon Chemical Co., Martin Marietta, Arco Chemical

Co., and the American Dental Association. These and other contacts with research associates,

experts in industry, trade associations, standards associations, guest workers, Government, and

academia ensure that the Division's efforts are directed toward fostering the effective use of

polymers in solving generic national problems. These include the growth of the economy, national

security, efficient Government, materials utilization, and conservation of critical materials.

Current activities are associated into areas concerned with phase behavior and characterization

methods for polymer blends, processing and reliability of composites, long-term research on the

scientific basis for mechanical reliability in load-bearing applications, chemical durability,

lifetime prediction, migration of protective additives, characterization methods, standards for

molecular composition and performance properties, dielectric properties, and reliable dental and

medical materials. Substantial cooperative efforts are conducted with research associates from a number of industries, universities, and Department of Defense, the National Institutes of Health,

the American Dental Association (ADA), the Food and Drug Administration, and the Bureau of Engraving

i
and Printing (BEP). All these efforts lead the staff of the Division into an examination of the

scientific basis of those properties which are of concern to people who use, design, and produce

useful polymer objects. This work helps society capture, in safe and satisfying ways, the benefits

of the increasingly widespread application of polymers.

FY83 SIGNIFICANT ACCOMPLISHMENTS

POLYMER STANDARDS FOR PROCESS CONTROL AND EQUITY

o A high performance liquid size exclusion chromatograph laboratory has been established for

the determination of the molecular weight and molecular weight distribution of polymer

samples. The apparatus has been automated and may be operated at temperatures up to

150 °C. A microcomputer system for automated data collection and reduction has been in

routine use during FY83. To date approximately 3,000 chromatograms have been collected

and analyzed.

o A new Research Associate Program has been established with the ARCO Chemical Company. The

objective of this program is to establish the feasibility of applying size exclusion

chromatography to samples of ultra high molecular weight polyethylene and other high

molecular weight polyolefins.

o A critical evaluation of the Mark-Houwink parameters used in determination of the

molecular weight of linear polyethylene has been carried out. Literature values of these

parameters for six polyethylene solvents, commonly used for viscosity and size exclusion

chromatography measurements, were critically evaluated. A report has been written giving

the recommended values of the Mark-Houwink parameters.

o Measurements of the cooperative diffusion coefficient and center of mass translational

diffusion coefficient as a function of concentration and molecular weight have been made

by dynamic light scattering. The observed molecular weight and concentration dependences

are not in full agreement with scaling law predictions.

o The anisotropic expansion of a polymer chain has been investigated by small angle neutron

scattering. Deuteration of different portions of a polystyrene chain enables the

determination of the expansion factor for these different portions.

BLENDS PROCESSING

o Construction and testing of a Forced Rayleigh Scattering instrument has been completed.

The method permits rapid determination of the extremely low diffusion rates commonly

encountered in polymers. It will be particularly useful for studies of the kinetics of

phase separation of polymer blends. This instrument uses two crossing coherent laser

beams to generate interference patterns in a specimen by exciting photochromic labels on polymers. When the laser is turned off, diffusional processes cause the interference

pattern to decay. The diffraction of a second laser beam of different wave length is used

to "read" the diffusion controlled dissipation of the interference pattern. The

alternating line pattern looks like a holographic grating to the second laser. Since the

spacing of the grating is between 1 and 10 pm, diffusion coefficients as small as 10 10 cm2 /s can be determined quickly by monitoring the intensity decay of the

diffraction.

o A review paper entitled "Bulk and Interface Thermodynamics of Polymer Alloys" was published in the 1983 issue of Annual Review of Materials Science .

o Fluorescence energy transfer has been used to investigate the phase behavior of ternary

blends of PMMA, PEMA, and PVF2. In this method the constituent polymers are chemically

labeled with a small number of "acceptor" and "donor" chromophores. The fluorescence

intensity of the donors will be reduced by the acceptors whenever the donor and acceptor

chromophores are separated by small distances as in a homogeneous mixture. Phase

separation increases the average distance between donors and acceptors and, therefore,

reduces the efficiency of the energy transfer. This method can also be used to monitor

the phase separation process as a function of time.
o A new two-dimensional x-ray detector is being installed for SAXS measurements which will

facilitate the study of spinodal decomposition in blends,

o NBS and the Society of Plastics Engineers (SPE) have instituted a joint program to provide

data on the thermodynamics and nonequilibrium phase behavior of polymer blends and related

systems. NBS will be responsible for the overall guidance of the technical aspects of the

program with the aim of assuring reliability of the data evaluations and will provide a center for coordination with other data compilation centers.

o A new correlation has been discovered for the surface tension of simple and polymeric

liquids [J. Chem. Phys . , 79: 405; 1983]. This correlation relates the surface tension of

a liquid to its isothermal compressibility and mass density. It has been shown to be

applicable to quantum liquids, hydrogen bonding liquids, and polymeric liquids.

TESTS, STANDARDS, AND CHARACTERIZATION FOR MANUFACTURING AND

DURABILITY OF DENTAL AND MEDICAL MATERIALS

o Clinical observations in outside laboratories combined with our clinical and laboratory

results revealed a potential short term laboratory observation which may reduce the need

for long term clinical studies to evaluate the durability of new alloy systems.

Dimensional changes of restricted and unrestricted amalgam specimens correlated directly

with the clinical observations of durability using three widely accepted but markedly

different alloys. If this correlation continues to be consistent for other alloys, 4 to 8

month i_n vitro data can be used to predict 3 year clinical data.

o The characterization of porosity in two porous polymeric implant materials is being

continued, at the request of the Office of Medical Devices (FDA). A method of preparing

histograms of mercury porosimetry data has been devised, leading to the conclusion that

the distribution of pore radii in the materials is log-normal. The pore volume percentage

and pore size (mean intercept length) have been measured for both materials by the method

of quantitative microscopy. This work is important to establish reliable and accurate

methods for characterizing the porosity of implant materials.

o Polymeric resins in commercial dental composites cured at the i_n situ temperature 37 °C

have been found to be undercured, and are thus susceptable to polymeric softening by

certain solvents present in the oral environment. Increasing the degree of cure by

increasing the cure temperature has been found to increase the i_n vitro wear resistance of

commercial composites presoaked in certain food simulating chemical liquids. Although

this method of increasing the degree of cure may be impractical for i_n situ restorations,

the wear results imply the incorporation of more flexible chain polymers and a mismatch

between solubility parameter values of resin and common oral solvents to achieve more

durable composites.

o Most of the modern dental alloys are based on nickel. Since there is some concern over

latent carcinogenicity and allergic sensitization from nickel alloys, the use of titanium

as a potential substitute is promising. A major impediment to the widespread use of

titanium alloys is their poor castability under dental laboratory conditions. A recent

accomplishment of NBS is the production of a successful titanium alloy casting using a magnesium oxide investment.

o Dental cements with superior physical properties have been prepared by incorporating

cement and composite components into a new hybrid material. The lack of polymerization

inhibition by the recently developed hexyl vani llate-EBA-ZnO cements allows the addition

of monomers and reinforcing fillers to the cement formulation. The extremely high

strength, low solubility, and excellent adhesion of the resulting cements indicate their

application as durable, intermediate restoratives.

o A tooth structure conserving procedure for bonding composite restorative materials to

dentin has been developed which utilizes brief applications of a cleanser mordant aqueous

solution of ferric oxalate, a surface active comonomer and coupling agent. The difficulties in bonding to dentin have been serious obstacles to the successful placement of

many restorations. Tensile tests on restorations using this technique revealed frequent

cohesive failure in the composite and occasionally, in the dentin.

iii
o The chemical resistance and overall durability of the polymeric matrices currently used in

dental composite restorative materials is a significant factor limiting their service

life. The use of low surface energy polymeric binders based on the highly fluorinated

oligomeric multifunctional methacrylate, PFMA, is a feasible method of enhancing the

hydrophobicity , oleophobicity, stain resistance and chemical stability of dental

composites. A variety of hydrocarbon and fluorocarbon diluent comonomers have been used

with PFMA to yield composites with good mechanical properties, reduced microleakage, and

extremely low water sorption.

o A new technique for determining the water sorption of composites and sealants by near- infrared spectroscopy was developed and appears to be a more sensitive method for

measuring water uptake than the standard gravimetric procedure. In contrast to the latter

method which requires immersion of relatively large specimens in water, long equilibration

times, and the measurement of small changes in large numbers, the near-IR method has the

following advantages: (1) thin specimens (< 100 pm) which have short equilibrium times

are used, (2) comparative measurements after immersion in water versus simple exposure to

atmospheres of 100% relative humidity can be made, and (3) the time dependent water

sorption behavior of the specimen may be easily monitored.

o In addition to their utility in dental composite materials, we have found that polythiols

such as pentaerythri tol tetra(3-mercaptoproprionate) , PETMP, reduce. the setting times of

denture base materials while improving the esthetics and color stability of the cured

product. When used in modest quantities in liquid component (e.g. methyl methacrylate

plus amine accelerator) of a commercial surgical bone cement formulation, it was shown to be effective in reducing the peak temperature of the exotherm without adversely affecting

dough and setting time or the compressive strength of the cured cement. A more moderate

peak temperature is desirable in surgical bone cement since it reduces the chance of

inflammatory or other adverse responses in contiguous tissues.

o Conventional polycarboxyl ate cements are based on the acid-base reaction of a poly(al kenoic acid), e.g. poly(acrylic acid), and a basic powder (e.g. ZnO). Ionically

crossl inked polymeric matrices are formed that are rigid and hydrophilic . We have

explored the feasibility of obtaining less rigid and hydrophobic dental cements by the

reaction of liquid dimer (DA) and trimer (TA) acids with a variety of basic powders (e.g.

ZnO, MgO, CaO, etc.). Many of these cements have shown excellent resistance to brittle

failure and very low solubility both in water and lactic acid solutions. The versatile

nature of cements obtained from DA and TA with different base components suggests many

potential dental applications.

o Dental cement formulations in which syringate esters have partially or completely replaced

the structurally similar hexyl vanillate ingredient have been evaluated. These new cements maintain the highly desirable physical properties obtained with the

vanillate-EBA-ZnO cements. Since syringic acid has been shown to significantly inhibit

caries formation, the syringate cements might also be caries-reducing.

o A simple technique for evaluating castability of dental alloys was developed at NBS. The

castability value, c

v

, of several alloys was determined. It was found that the same simple mathematical expression could be used to express c

y as a function of alloy casting

temperature and mode temperature for each alloys at a 99.5 percent confidence level.

o A relatively easy to use test specimen/methodology was developed for characterizing

porcelain fused-to-metal (PFM) bond strength. It was found that a cumulative failure plot

using Weibull distribution analysis shows clear distinctions between systems; such

distinctions are not apparent from comparing the means of failure strengths in the

different systems.

MECHANICAL DURABILITY OF POLYMERS

o Mechanical failure in fatigue of ultra high molecular weight polyethylene has been

associated with a critical concentration of chain scissions. The number of chain

scissions at failure has been found to be dependent on the initial molecular weight.

Approximately twice as many chain scissions are required to produce failure in a polyethylene of twice the initial molecular weight.

iv
o The structure of ultrahigh modulus polyethylene is characterized by carbon-13 nuclear

magnetic resonance. The profile of relaxation times indicates the presence of three

. components , and the intermediate component is identified with interfacial material. It can be concluded that a significant contribution to the heat of melting arises from this

region. Time constants for the long component vary significantly with sample preparation.

An interpretation of their differences is that cold drawing produces crystallites which

contain more crystal defects than in melt crystallization.

o A detailed investigation of inhomogeneous deformation has been completed on quenched

samples of isotactic polypropylene under a wide variety of stress and strain histories in

uniaxial extension. Using the data, a surface of isochrones of stress versus strain was constructed from which it was possible to predict the point at which inhomogeneous

deformation will occur for other strain histories. It has been shown that the predicted

behavior is consistent with a theory recently developed in our laboratory.

o The stress in the craze at the tip of a uniformly moving crack has been shown to be a function of the derivative of the displacement under the assumption that the craze

thickens by a drawing process. The stress is thus identified as the drawing stress. The

stress distributions have been obtained from theoretical analysis and show a peak at the craze tip and one at the crack tip, in agreement with experimental observations.

o The physical ageing behavior of polymethyl methacrylate glasses has been investigated as a preliminary to a larger program to measure dilatometrically the volume changes of polymer

glasses subjected to increasing torsional deformation after various thermal treatments.

The results revealed significant discrepancies as compared to previous studies and models

of physical ageing in polymer glasses. In the linear viscoelastic range, the relaxation

isotherms, measured at increasing ageing times, cannot be superimposed by mere shifting

along the time axis below some critical temperature range. Such effects may be accounted

for by a change in the shape of the short time relaxation spectrum with increasing ageing

time.

PROCESSING AND RELIABILITY OF POLYMER COMPOSITES

o The compressive strength of continuous fiber reinforced composites is sensitive to the

delamination damage. There is a need to develop polymer matrix materials with improved

resistance to both initial damage and subsequent growth of this damage into delamination.

In addition, design data are needed to predict the growth rate of delamination. The

effect of sample lay-up pattern on interlaminar fracture behavior has been studied and

guidelines for specimen design have been formulated. Investigations of the temperature

and rate dependence of interlaminar fracture of brittle and tough polymer matrix materials

as well as composites made from these materials revealed that the effects were negligible

in the composites in contrast to the behavior for the resins alone.

o An extensive study was performed to examine the viscoelastic fracture behavior of a rubber-modified epoxy. Rubber modification is one way of improving the brittle nature of

polymer matrix materials. Based on these studies, a mechanism for toughening has been

formulated. The mechanism involves both dilatation via cavitation in the rubber particles

or at the particle-matrix interface and shear plastic flow of the epoxy matrix.

o Time domain dielectric spectroscopy has been applied to the post curing of vinyl ester

matrix materials. The measurements were carried out on the recently developed time domain

dielectric spectrometer which has the capability to measure the dielectric properties of a material over a very wide range of time (or frequencies) in a single experiment.

Preliminary studies have shown that it is possible to follow changes in molecular

mobilities that would otherwise be very difficult to detect because they appear only in

the very low frequency range. This type of information is particularly useful since the

final degree of cure is often a critical parameter in processing.

o A novel excimer fluorescence technique has been developed for monitoring i_n situ and

nondestructively the processing of components made of fiber-glass-reinforced composite

materials. The method monitors the resin viscosity that must be carefully controlled

during processing to avoid high rejection ratios of these components.

v
o Rapidly curing thermoset matrix resins could greatly reduce processing time and permit a large increase in the volume of fabricated composite output. Radiation initiated

polymerization is being examined as a method for obtaining rapid cure. An experimental

program to measure the overall rate and determine reaction kinetics is in progress. The

effects of initiator structure, concentration, and solubility, reactant concentration,

fiber thickness, reaction temperature, and radiant intensity are being studied. This

program is providing a better understanding of the chemistry that occurs during processing

of thermoset polymers, and is aiding in the identification of materials for particular

applications.

ADDITIVE MIGRATION AND CHEMICAL DURABILITY OF POLYMERS

o A method for predicting the useful lifetime of archival films made of polyethylene terephthalate) has been developed. The prediction was based on newly measured

kinetic data on the hydrolytic degradation of this polymer. The results provide realistic

estimates of when poly(ethylene terephthalate) archival films should be recopied.

o The relative contributions of thermal and photolytic degradation in a common solar glazing

material poly(methyl methacrylate), PMMA, were elucidated. Sheets of PMMA were exposed to

controlled environments and the molecular weight was measured as a function of depth. The

results show the importance of oxygen in reducing molecular weight, and of unpolymerized

raw material in converting the initial products of degradation into a form more sensitive

to oxygen attack.

o A theoretical model has been developed to explain the complicated but important case of

migration of an additive from a polymer into a solvent that swells the polymer. The model

relates the non-Fickian migrant loss behavior to the non-Fickian sorption behavior. The

predictions of the model for the very short time and the very long time agree with the

limiting behavior seen in experiments.

o Extraction experiments and concentration profile experiments have been carried out using

fluorimetry to determine the diffusion coefficients of additives in low-density

polyethylene. An experimental value for the diffusion coefficient of 3-tert-buty-4-

hydroxyanisole (BHA) in polyethylene at 30 °C, in the absence of a solvent, has been

determined.

o Picosecond fluorescence spectroscopy has been used to determine the segmental mobility of

methacrylate polymers and pyrenelabeled alkanes. This measurement is one way of

determining the kinetics of resin curing in polymer composites.

MICROSTRUCTURE AND PERFORMANCE OF DIELECTRIC PLASTICS

o The time domain dielectric spectrometer recently developed at NBS is being transferred to

the user community. Through the Research Associate program, the General Electric Co. is

reproducing the instrument for their laboratory and the IMass Corp. will produce the

instrument for sale. The main features of the instrument have been described in a manuscript submitted for publication in the Review of Scientific Instruments.

o The speed and accuracy of dielectric measurements afforded by the time domain dielectric

spectrometer have been used to study the influence of crystal phase and orientation on the

dielectric properties of polyvinylidene fluoride. These relaxations are expected to provide information useful in predicting the performance and durability of the polymer as

a piezoelectric and pyroelectric transducer. The spectrometer has also been used to follow changes which occur during post-cure of epoxy resin composites and to differentiate

between morphologies which exist in some polymer blends.

o Copolymers of vinyl idene fluoride and trifluoroethylene containing 52 to 78 mole percent

VDF have been examined as ferroelectrics. The ferroelectric to paraelectric transition

temperature increases with VDF content and involves a crystal -crystal transition which is

similar for all compositions. Favorable piezoelectric response can be obtained even without mechanical orientation and polarization reversal occurs over a narrow range of

electric field near 400 kV/cm. This work was done cooperatively with Bell Laboratories.

vi
o The thermal pulse technique for measuring space charge and polarization distribution has

been successfully applied to films of polyvinyl idene fluoride, fluorinated ethylene

propylene copolymer, and nylon-11 in cooperative work with 3M, Bell Laboratories, and

Naval Ocean Systems Command.

o Piezoelectric polymer sensors which compensate for the pyroelectric response arising from

adiabatic heating of the polymer or its surroundings are being developed under a contract

with the Air Force. The Building Research Division will evaluate the gauges as pressure

transducers in a variety of soil environments as a part of the contract.

o A Research Associate agreement between NBS and Alta Technology Inc. has been reached. The

work will focus on the performance of piezoelectric polymer arrays with special emphasis

on minimizing cross-talk between elements. The polymer properties required for

non-propagating acoustic modes will be specified and experimental arrays will be developed

and evaluated.

o Rigorous upper and lower bounds for the dielectric constant of a semi crystal line polymer

containing anisotropic crystals has been calculated. The model has been applied to polyvinlyidene fluoride and found to be in good accord with data resulting from different

processing such as orienting and poling.

o Ionic conductivity in polyethyl eneoxide to which Nal has been added has been found to

exhibit a maximum at a salt concentration far below that where a crystalline complex

between the polymer and salt first appears. Conduction in non-crystalline regions rather

than specific pathways within the crystal as frequently proposed has important

consequences in guiding further research on ion transport in polymers.

In the following pages, the activities of the Division are presented formally in eight tasks, each

described separately:

POLYMER THEORY FOR STRUCTURE AND PROCESSING

POLYMER STANDARDS FOR PROCESS CONTROL AND EQUITY

BLENDS PROCESSING

TESTS, STANDARDS, AND CHARACTERIZATION FOR MANUFACTURING AND DURABILITY OF DENTAL AND MEDICAL

MATERIALS

MECHANICAL DURABILITY OF POLYMERS

PROCESSING AND RELIABILITY OF POLYMER COMPOSITES

ADDITIVE MIGRATION AND CHEMICAL DURABILITY OF POLYMERS

MICROSTRUCTURE AND PERFORMANCE OF DIELECTRIC PLASTICS

vii

POLYMER THEORY FOR STRUCTURE AND PROCESSING

Processing routes, particularly those involving phase transitions, can produce a wide range of

microstructures which must be controlled to optimize desirable properties. An improved scientific

basis for characterization of molecular aspects of polymer molecules and their conformational

behavior will provide industry with tools to control processing and for nondestructive evaluation.

Better specifications for polymers in industrial and defense applications will also result.

Basic features of phase transitions in polymers are modeled in ways that incorporate the

kinetics of the transition. Included are phase transitions relevant to polymer blends, composites,

and glasses. Both transitions that occur in single molecules and those that occur in collections of

molecules are addressed.

The usefulness of gel permeation chromatography and quasi elastic light scattering for molecular

characterization and processing is enhanced by work describing the relation between branching of

polymer molecules and these measures of molecular size.

The mechanical behavior at long times of classes of high volume polymers, particularly in the

fiber form, were modeled. The conformational and vibrational behavior of defects which rotate and

translate the polymer chain were calculated.

Classification of Structure Inducing Transitions in Polymers

E. A. Di Marzio

Phase transitions in polymers constitute a rich subject area. There are more transitions

occurring in polymer systems than in any other subject area. This is because the nature of the

fundamental unit, which is the molecule, can be infinitely varied in its complexity (chain length

being only one degree of complexity). The following transitions and phases occurring in polymers

have been treated by the author: crystals, liquid crystals, liquids, glass transition, Helix-Random

Coil transition, collapse transition, the transition associated with adsorption onto a surface, and

finally polymerization which can be viewed as a transition. These various transitions can be made

to couple to one another giving a hierarchy of structures involving feedback and control. An

attempt is being made to describe each of the transitions with a simple mathematical treatment that

captures the physical basis of the transition. This will facilitate treatments which couple the

various transitions to one another.

Phase transitions are useful to processing science because a slight change in one of the

control variables (examples: temperature, pressure, affinity, shear rate) can result in a sudden

appearance of structure. The profusion of structure inducing phase transitions in polymer systems

warrants study.

Monte Carlo Modeling of the Kinetics of Polymer Crystal Growth

C. M. Guttman and E. A. Di Marzio

A Monte Carlo simulation of polymer crystal growth from the melt was completed this year. This

two-dimensional model approximates growth of a polymer crystal using the model of laying down full

stems one at a time. The model allows us to explore the growth of polymer crystals over a wide

range of temperatures. More particularly the model extends theoretical studies into the region of

temperature most used in polymer processing. The simulation was developed to obtain quantitative

estimates of the accuracy of previous approximate mathematical approaches. We were able to show

that analytical expressions previously developed for growth at small undercoolings were very

accurate. However, in the high undercooling regions— those of most interest from the point of view

of processing—we showed the analytical expressions were not at all accurate. Furthermore, previous

analytical developments made no predictions on the effects of detailed geometric structures on the

surface. We showed that the traditional site on site model does not produce space filling polymer

crystals at high undercooling. A hexagonal lattice model of the crystal yields space filling

crystals but does not show the rapid upsweep observed experimentally at high undercoolings. Only if we allow growth on a hexagonal lattice and growth on more than one growth plane does the Monte Carlo

model mimic the experimental data well.

The requirements of this Monte Carlo model are consistent with earlier modeling the small angle

neutron scattering (SANS) on highly undercooled polymer crystals where we found it necessary to

invoke a two-growth plane model to explain the SANS data.

1
Block Copolymers with Lamellar Morphology: -Chain Dimensions in

Directions Parallel and Perpendicular to the Lamellae

E. A. Di Marzio

The packing entropy (arising from competition for space) is dependent on the orientation of

molecules. In block copolymers the chains are stretched out in the direction perpendicular to the

planes of the lamellae. The packing entropy contributes a term that results in a shrinking of the

transverse dimensions. Quantitative estimates are made. The result is a substantial improvement

over existing treatments which predict a negligible shrinking in the transverse direction. The

experimental data seem to show a shrinkage even larger than what we predict. The effect on dissolved homopolymers is described. Block copolymers (chemical blends) can be used to stabilize

polymer blends.

Translational Diffusion Constant of Linear and Branched Chains

C. M. Guttman

With the advent of experimental equipment in which both static and quasi -el as tic light

scattering may be done on the same sample, the ability to obtain both a radius of gyration and a hydrodynamic radius on the same system is possible. For branched chains this offers the hope of

obtaining structural information about branching heretofore unavailable. Sipce the character and

details of the branching of a polymer molecule determine its processability as well as its ultimate

physical properties and mechanical strength, such information on branching is invaluable.

One theory currently available to relate these two quantities to the polymer structure is the

Kirkwood Riseman theory of the translational diffusion constant in solution. However there has been

found to be a discrepancy between the experimental value of the translational diffusion coefficient

of polymer molecules, both branched and unbranched, in dilute solution and that obtained from

Kirkwood Riseman theory using an analytical Gaussian model of the chain. The discrepancy is

15 percent for linear chains and nearly 50 percent for the ideal star branched chains studied.

Current work at this laboratory approaches this problem in two ways. In one, the hydrodynamic

radius is computed using the Kirkwood Riseman formulation for both linear and branched chains

created by a computer simulation in which both excluded volume and interaction energies are

included. These calculations have shown that about half of the 15% deviation found between theory

and experiment previously was attributable to these corrections for linear chains. Currently work

on branched chains is in progress.

In a second approach analytical modeling was done on chains in which local chain structure but

not excluded volume is taken into account. Earlier work showed that the analytical model currently

available which is used to compare theory and experiment shows a very slow approach to its large

molecular weight, M, limit. It is only in this limit that the Gaussian theory and experiment can be

meaningfully compared. Thus corrections to the large M values used to compare with experiments were

not possible even for polymers of high molecular weight. In this effort analytical modeling of

chains with local structure and stiffness was done and the first two corrections to the large M limit of the hydrodynamic radius of the chains were computed exactly. It was shown that the effect

of chain structure on each of these three terms was different. Thus the simple ideas of statistical

length used earlier were found to need improvement.

Processes Involving Conformational Changes in Polymers

D. H. Reneker and J. Mazur

Polyethylene fibers offer the possibility of very high modulus and strength since the backbone

bonds are very strong and the cross sectional area of the molecule is small. Achievement of these

exceptional properties requires alignment of the molecules, so they must move past each other and

eliminate unfavorable molecule conformations during processing. To maintain the high strength, the

molecules must not slide along their axes after the fiber is formed. In this work molecular scale

processes which are involved in the formation and mechanical deformation of fibers are modeled as a basis for processing methods to produce strong, stable polymer fibers.

2
The molecular vibrations associated with crystallographic defects in polyethylene called

dispi rations, disci i nations, dislocations, and twist boundaries were modeled. These defects provide

mechanisms for translating the polymer chain along its axis or rotating it. Characteristic

vibrations associated with the defects may make it possible to observe the presence and behavior of

defects by examining the vibrational spectrum of polyethylene.

It was found that the above crystallographic defects have a lowest longitudinal frequency in

the range of 85 to 105 cm 1 associated with motions of the ends of the defect region parallel to the

chain axis. The ends may simultaneously twist or move sideways, but the longitudinal motion is

dominant. This defect vibration may couple to any of a large number of normal vibrational modes of

the polyethylene crystal. This coupling tends to split the lowest longitudinal frequency of the

defect into a band of frequencies. The longitudinal vibration of the defect has a reasonably high

predicted Raman intensity, so probably contributes to the Raman spectrum either as a broad band or

an increase in the background intensity in the range of 85 to 105 cm 1

. The defect regions have

other characteristic vibrational modes at lower frequencies. These modes have displacements which

are transverse to the chain axis, both twist and shear. The low frequency transverse modes do not

contribute to the Raman spectrum, but some may be infrared active. It appears that vibrational

spectroscopy can provide information needed to characterize crystallographic defects in

polyethylene.

The transport of polymer molecules in the melt, which is fundamentally involved in the

processing of polymers, proceeds by the motion of segments of a molecule. This gives rise to a relatively rapid process which produces local rearrangements and a slower process which ultimately

moves the center of mass of the molecule over macroscopic distances. In cooperation with scientists

in the Polymer Science and Standards Division, and the Jozef Stefan Institute in Ljubljana, the

diffusion of polymer molecules in the melt is observed using magnetic resonance measurements of spin

echo in a magnetic field gradient. The interactions of adjacent molecules seem to play an unexpectedly important role in controlling the time evolution of the molecular transport process.

This was observed by measuring the transport in mixtures of polyethylene and paraffin. The data

indicate that velocity correlations persist for surprisingly long times and that unusually long

times are required for the magnetic dipolar interactions of the protons on the molecule to average

to zero. These experiments promise new and fundamental insight into the kinematics of entangled

melts of flexible polymer molecules.

3
POLYMER STANDARDS FOR PROCESS CONTROL AND EQUITY

This task provides standard reference materials (SRMs) to the $30 B/year synthetic polymers

producing industry. Molecular weight SRMs are used extensively in industry to calibrate gel

permeation chromatographs (GPCs) which are used routinely to measure polymer molecular weights and

molecular weight distributions. The latter are the most important physical properties in

determining a polymer's processability and its ultimate performance. Gas transmission and rubber

SRMs are used in process control applications.

Improved characterization techniques are essential to providing improved SRMs. A fundamental

knowledge of polymer solution properties such as osmotic pressure, viscosity, diffusional behavior,

and scattering power is essential to this goal. As a consequence, a majority of the activities in

this task involve experimental and theoretical studies of polymer solution properties. As a spinoff

of our characterization activities, this task also provides data and concepts which are useful in

polymer processing.

Self-Calibrating Gel Permeation Chromatography

P. H. Verdier

Gel permeation chromatography (GPC) is a widely accepted technique for estimating the molecular

weight distribution (MWD) of high polymers. However, the usefulness of the conventional GPC

apparatus is limited by the need to provide calibrants for each polymer measured of known molecular

weight over the entire molecular weight range in which the MWD is significantly different from zero. The calibration depends, among other things, upon the chemical nature, degree of branching, etc., of

the polymeric material so that each new material requires a fresh calibration. The so-called

"universal calibration" hypothesis, while useful, is limited to comparisons of polymers of similar

shape and, in any event, is inadequate for quantitative determinations. Some instruments, one of

which is commercially available, attempt to circumvent the need for calibrants by adding a single-angle light scattering detector to the usual concentration-sensitive detector. However, this

does not allow the extrapolation to zero scattering angle which is required, in principle, to relate

scattering intensity to molecular weight. In addition, qualitative information on the variation of

scattering with angle, normally required to give assurance that meaningful results are being

obtained, is not available.

A light-scattering detector for the GPC has been designed and built which measures, in real

time, scattered intensity as a function of scattering angle. The apparatus is controlled by a dedicated minicomputer in a way that allows scattering to be measured as a function of both

scattering angle and concentration. Continuous monitoring of the variation of scattering with angle

while the chromatogram is being obtained allows immediate identification of difficulties such as association, microgel formation, etc., which would affect the validity of the molecular weights

obtained, an important consideration for work on new and unstudied materials. In addition to molecular weight, the mean-square radius (radius of gyration) can be obtained as a function of

molecular weight, at least in the higher ranges of molecular weight, providing useful information

for the characterization of branched polymers. The second virial coefficient, a measure of

polymer-polymer interactions of both current and continuing interest to solution-properties

theorists, can also be obtained as a function of molecular weight.

During the current year, a series of tests of the instrument has been carried out. Excessive

quantities of stray light were found at very small scattering angles, due apparently to the

inevitable mismatch in index of refraction between the solvent employed (tetrahydrofuran) and the

entrance window of the scattering cell. While these effects can be calibrated out, they materially

reduce the accuracy of the final results. A new scattering cell has therefore been designed, with

cell geometry which minimizes detection of entrance-window scattering and with improved internal

blackening and decreased cell volume. Improved controls for alignment of the scattering cell have

also been designed. Fabrication of the new components is expected to be completed by the end of

FY83.

Critical Evaluation of Mark-Houwink Relation for Linear Polyethylene

H. L. Wagner

One of the most important physical properties of a polymer is its average molecular weight

which largely determines its processability and its performance properties. Since absolute

4
determinations of molecular weight are time consuming and are not made routinely, relative methods,

such as solution viscosity or size exclusion chromatography (GPC), are used instead.

The limiting viscosity number (LVN) or the intrinsic viscosity— and the molecular weight, M, are related by a simple power law:

LVN = [r|] = KM

a

where K and a are empirical constants which depend on the specific solvent and the temperature. An

incomplete compilation of these data can be found in handbooks, but a critical assessment is not

available. Yet these data are used extensively to obtain molecular weights as well as to calibrate

size exclusion chromatography columns.

Detailed examination of the. original literature revealed that many of the viscosity

determinations used to obtain K and a were made with whole polymers rather than fractions so that

the values of these parameters depend on the molecular weight distribution. In other cases the

absolute molecular weights of the fractions were determined indirectly from viscosity measurements

in a solvent with known values of K and a. By measuring the viscosity of these same fractions in a second solvent, values of K and a for this solvent may now be determined using the molecular weights

measured in the first solvent. Such an indirect determination using the molecular weights measured

in the first solvent. Such an indirect determination adds to be uncertainty. Determinations such

as these were rejected in favor of direct determinations of molecular weight by absolute methods

such as light scattering and osmotic pressure for narrow molecular weight distribution samples.

After reviewing and evaluating all the papers dealing with a particular polyethylene solvent,

the best Mark-Houwink parameters for that solvent were chosen. This was done for each of six

solvents commonly used for viscosity and size exclusion chromatography measurements. These solvents

are: decalin, 1,2,4 tri chlorobenzene, m 1-chloronaphthalene, tetralin, o-dichlorobenzene, and xylene.

In addition, the K values for several theta solvents (a = 0.5) were compiled. A report has been

written giving the results of this evaluation and the recommended values of the Mark-Houwink

parameters.

Characterization of Ultrahiqh Molecular Weight Polyethylene

H. L. Wagner and J. G. Dillon

Ultrahigh molecular weight polyethylene (UHMWPE), one of the most extensively employed surgical

implant materials, is usually characterized for specification and control by limiting viscosity

number (intrinsic viscosity) rather than by a direct measurement of molecular weight such as light

scattering. The viscosity may be measured at zero shear rate in the low shear viscometer developed

in this laboratory, or by a relatively simple measurement in a high shear rate capillary viscometer,

which must then be empirically corrected for shear rate. For many polymers an empirical

Mark-Houwink relation is available for relating the molecular weight to the limiting viscosity

number. Such a relation exists for ordinary commercial polyethylene, but not for UHMWPE, although

it is often assumed the same relation holds. To determine the Mark-Houwink parameters for these

higher molecular weights, fractions of varying molecular weights are required as well as a method

for measuring their molecular weights.

Two fractionations were carried out using the stir crystallization technique to give 17

fractions with zero shear rate viscosities ranging from 9 dL/g to 50 dL/g. A special procedure was necessary to dissolve some of th'e higher molecular weight fractions. Using the uncertain

Mark-Houwink equation derived from data for lower molecular weight fractions, an integral

distribution curve was obtained for the whole polymer. Although this results in some uncertainty in

the absolute values of molecular weight, the general features of the curve are of interest. The

molecular weight of the bulk of the material lies between 700,000 and 10 million. There is a suggestion of a bimodal distribution peaking at 1.1 million and 4.5 million. A report in the

literature indicates that Ziegler-Natta type polyethyl enes , such as this sample, have very narrow distributions and in the same paper some possible reasons for this are put forth. This does not seem to be true of this sample which appears to be broad, possibly because it may be a blend of two

polymers, as indicated by the bimodal distribution curve.

Liquid size exclusion chromatography (GPC), is a very convenient, indirect, method of

determining molecular weight and molecular weight distribution of polymers with molecular weight

5
species of no greater than several hundred thousand. Recently, column manufacturers have developed

new columns which they claimed would surpass this limit. To determine whether one such column set

could separate UHMWPE, a very dilute solution was injected at the highest possible temperature,

148 °C. Although instrument problems were encountered, it was nevertheless evident that a large

fraction of the polymer eluted at the exclusion limit and was not separated. Because the exclusion

limit is about 1 million for polyethylene, it was concluded that the whole polymer contains a substantial amount of material greater than this molecular weight. Since it is also possible that

some degradation occurred, no determinations of the lower molecular weight components were made. A sample of one of the lower molecular weight fractions with a limiting viscosity number of 11.5 was also run, and although no instrument problems were encountered, it was evident that a substantial

portion of the fraction was also eluted beyond the exclusion limit. Since a molecular weight

distribution could not be obtained for even this relatively low fraction, no further attempt was made to inject any other higher molecular weight fractions.

Pennings has examined by electron microscopy the structures formed during hydrodynamic

crystallization, the fractionation process used here, and found a "shish-ke-bab" structure. He

believes the fibrils are the high molecular weight constituents crystallizing first and the

overgrowths are the lower molecular weight species which crystallize subsequently.

Since the fractions cannot be characterized by size exclusion chromatography, with the columns

now available it will be necessary to measure their molecular weight by light scattering. A low

angle laser light scattering apparatus will shortly be available for this purpose.

Characterization of Polyisobutyl Methacrylate

H. L. Wagner

The Chemical Systems Laboratory at Aberdeen Proving Grounds has asked the National Bureau of

Standards (NBS) to consolidate and evaluate the data on the characterization of poly isobutyl

methacrylate carried out by two commercial laboratories. A review of the data indicated that interlaboratory agreement was poor and that in the development of a polymer or process it would be best

for control purposes to have the characterization performed in a single laboratory. The

reproducibility of limiting viscosity numbers (intrinsic viscosities) was much poorer than usual in

the one laboratory in which it was carried out.

Some experiments were also conducted by NBS on the dependence of viscosity on shear rate of a sample of polyisobutyl methacrylate with a molecular weight of about 1.5 million. This was found to

be negligible in the solvent tributyl phosphate.

Dynamics of Polymer Chains

P. H. Verdi er and D. E. Kranbuehl

The dynamic behavior of polymer chains is important to improving both characterization and

processibility of polymers. The principal methods used to estimate molecular weight, and in

particular gel permeation chromatography, the only method available at present for estimating

distribution in molecular weight, are dynamical, nonequilibrium experiments which depend in part

upon the relaxation of polymer chains in dilute solution. In its present state, the theory of these

systems does not allow the calculation of molecular weight directly from measured quantities; a series of calibrants of known molecular weight is required. Improvements in the theory could reduce

or even remove the need for calibrants, allowing the determination of molecular weight distribution

of polymers for which calibrants are not available.

The processibility and the final characteristics of both plastics and elastomers depend in

large part upon the relaxation behavior of the high-polymer chains of which these materials are primarily composed. More realistic theoretical treatments of polymer melts and elastomers, which

must start with more realistic treatment of the dynamical behavior of the individual chains, will

lead to more efficient processing and better fabricated end products. A major shortcoming of the

present theory is its inability to treat chain entanglements in a realistic way. Present work is

aimed primarily at the study of entanglement effects, using a combination of analytical and computer

simulation techniques. The simulation results provide data on simple model systems and serve to guide the development of better theoretical treatments.

6
Work in this area is proceeding along two main lines. First, as a step in the direction of

investigating melt properties, simulation studies are being carried out of systems of many

interacting chains, with chain densities spanning the range from dilute solutions to concentrated

solutions and melts. An initial set of studies of these systems has been completed and the results

analyzed. As the concentration increases from the dilute-solution limit, entanglement effects cause

the chain relaxation times to increase dramatically. The results are consistent with the wellestablished free volume theory, with a slight modification to take account of chain connectivity.

These results will be published during the coming year. Second, a series of studies is under way to assess the magnitude of artifacts due to the simple move rules employed and to constraining the

chains to lie on space-fixed lattices. Perhaps surprisingly, removing the requirement that the

chains lie on lattices appears to increase the effects of excluded volume and entanglement upon

chain relaxation times.

Automated Liquid Size Exclusion Chromatography

J. D. Barnes and F. L. McCrackin

A microcomputer system for automated data collection and reduction has been in routine use during FY83. To date approximately 3,000 chromatograms have been collected and analyzed. The

studies that have used the system most extensively have been concerned with monitoring the

degradation of poly(methyl methacrylate) as subjected to various photolytic and thermal oxidative

stresses for research programs in the Center for Building Technology and the Center for Fire

Research.

Areas requiring further effort include the generation of calibration curves defining the

functional dependence of hydrodynamic volume on elution volume, the characterization of the

background which must be subtracted 'from the chromatograms, and data management techniques for

handling the large quantities of raw data and analytical results that are obtained. Enhancements to

the software that will provide for easier user interaction with the graphically displayed data are currently being designed.

Techniques for dealing with data off line have been developed in order to allow users to

analyze their data without interfering with the data collection process.

Span of an Adsorbed Polymer Chain in a Lattice Random Walk Model

R. J. Rubin

Recently [1] the probability density of the span, or extent, of an N-step adsorbed polymer

chain in the direction normal to the solution surface was derived in deGennes* model [2] for weakly

adsorbed chains. The corresponding probability of the span has now been derived in a discrete

lattice random walk model of an adsorbed polymer chain [3]; and a paper reporting results is in

preparation. It is noteworthy that in both models the following two measures of thickness of an adsorbed polymer chain have a different N-dependence. The average span is proportional to InN and

the scale length of the exponential step density distribution [3] is independent of N. Although the

foregoing results are derived in models which ignore the effect of excluded volume, we conclude that

the average span increases at least as rapidly as InN in models where self-intersections are

excl uded.

[1] R. J. Rubin and G. H. Weiss, J. Chem. Phys. 78, 2039 (1983).

[2] P. G. de Gennes, Rep. Prog. Phys. 32, 187 (1969).

[3] R. J. Rubin, J. Chem. Phys. 43, 2392 (1965).

Monte Carlo Calculations of the Hydrodynamic Radii of Polymers

F. L. McCrackin and C. M. Guttman

The inverse radius (1/R) of single polymer chains on a cubic lattice and on a face centered

lattice were computed. These chains were created by a Monte Carlo simulation in which both excluded

volume and energetics of interaction were taken into account. Values of 1/R are calculated for

various values of the energy of interaction. Thus the effect of going from good solvent to a theta

solvent is modeled. The hydrodynamic radius of the polymer chain is computed from the values of 1/R

using Kirkwood- Riseman theory and compared to experimentally obtained hydrodynamic radii. The

7
hydrodynamic radii obtained from the Monte Carlo simulation are shown to be in better agreement with

the experimental data obtained at the theta point then those hydrodynamic radii computed for

Gaussian coils.

The 1/R and the radius of gyration obtained from the Monte Carlo calculations are fit as a function of both N and temperature to a modification of the deGennes blob model of the polymer

chain. The fit is found to be reasonably good.

Analytical calculations of 1/R as a function of the chain length N for chains in which the

local structure of the chain is taken into account but in which no excluded volume has been included

have been developed. This was done to see if the better agreement of the Monte Carlo is the result

of some details of local structure which are in the Monte Carlo model but not in the Gaussian coil

models. Analytical models developed so far suggest that the deviation between the Monte Carlo and

the analytical models at the theta point is not a result of such local structure but rather a result

of the effect of the excluded volume.

The inverse radii of two interacting chains have been computed and are being interpreted as the

properties of polymers in dilute solution.

Standards for Gas Transmission Measurements

J. D. Barnes

Gas transport properties of polymeric materials are the major determinant of suitability for

end use in a great variety of applications ranging from food and beverage packaging, industrial gas

separation processes, and sterilization of medical devices, to substrates and packages for

semiconductor products. Gas molecules are useful as probes of materials properties at the

microstructural level. The measurement system for gas transport properties has suffered from a lack

of reliable standards.

NBS is addressing these needs by developing improved measurement technology and by characterizing polymeric materials for use as Standard Reference Materials (SRMs). The revised certificate

for SRM 1470 has been released for transmission to users of the material.

During the recertification process for SRM 1470 it was observed that a mathematical 'model based

on the permeation of a gas obeying ideal Fickian diffusion failed to properly predict the transition

to steady-state permeation behavior for C02 in SRM 1470. Efforts to construct appropriate numerical

solutions to the transport equation for systems exhibiting partial immobilization in their gas

transport properties has been initiated in an attempt to provide a better fit to the experimental

data. It is expected that this activity will lead to a better understanding of- transport processes

in cases where the diffusing species appear to exhibit a weak binding to polymer matrix.

The users of SRM 707, Standard Reference Material for Water Vapor Transmission Rate, have been

forced to consider needs for new standards because it was not possible to replace the SRM when

supplies became exhausted. The original (1972) certification of the SRM was based on measurements

using ASTM E96, a cup test. Improved methods for measuring water vapor transmission in thin films

have been developed since 1972.

The material used in SRM 707 was similar to SRM 1470, and it has also become clear that this

material is sensitive to water vapor and thus may not be an appropriate choice for a water vapor

transmission SRM.

Dr. J. D. Barnes has been working with representatives of the Office of Standard Reference

Materials and ASTM Committees F2, D20, and C16 to identify the state of the measurement art in the area of water vapor transmission in plastic films, to identify the needs for new standards, and to

identify materials that might be suitable for SRMs.

The efforts involve: (1) an interlaboratory test program for which NBS is devising the protocol

and analyzing the results, (2) identification of test methodology that is suitable for

characterizing the water vapor transmission properties of materials to the necessary precision and

accuracy, and (3) screening measurements on candidate materials to evaluate their suitability as SRMs.

8
ASTM Activities

J. D. Barnes

J. D. Barnes serves as Chairman of ASTM Subcommittees F~2. 93 and D-20.I3. These subcommittees

I provide assistance in matters relating to the design of experiments for evaluating the precision of

test methods for the parent ASTM Committees. This assistance takes the form of approval of

round-robin protocols, critique of precision statements, and statistical education for task group

leaders. Current projects include an interlaboratory test program for Water Vapor Transmission

measurements, an interlaboratory test program for evaluating oxygen tfif fusion into package

assemblies, and defining the proper form for formulating the standard deviation in ASTM test

methods.

f Computer programs for analyzing the results of interlaboratory test programs have been

1 developed and are currently being field-tested by several task groups in Committee D-20. We expect

to document these programs for general distribution so that ASTM task groups will have suitable

j- tools for carrying out analyses of interlaboratory test programs using ASTM E-69X, Standard Practice

for Conducting and Analyzing Interlaboratory Test Programs for Studying the Precision of Test

Methods.

Random-Walk Model of Chain Polymer Adsorption. Behavior at Critical

Energy and Relation to Reflecting Boundary Condition

R. J. Rubin

It is found that there are subtle differences between the set of energyweighted random walks

generated in the random-walk model of polymer chain adsorption at the critical energy and the

corresponding set of random walks generated in the presence of a reflecting boundary. These subtle

differences have their analog in the lattice model of self-avoiding random walks at the theta-point

where volume exclusion of monomers is exactly compensated by monomer-monomer attraction in the limit

of large N.

Expansion Factor of a Part of Polymer Chain in Good Solvent Measured by

Small Angle Neutron Scattering

C. C. Han, T. P. Lodge 1

, E. J. Amis2, Y. Matsushita3

Assistant Professor, University of Minnesota

2 Research Associate, University of Wisconsin

Assistant Professor, Nagoya University

The radii of gyration of deuterium labeled parts in polystyrenes with narrow molecular weight

distributions in good solvent (carbon disulfide) were determined by small angle neutron scattering

(SANS); The expansion factors of the labelled parts were calculated from the observed radii of

gyration and their unperturbed ones which were estimated from the unperturbed radius of

i gyration-molecular weight relationship of polystyrene in literature. The expansion factors of the

labelled parts were smaller than those of the whole chains, but were larger than that of a whole

i chain with the same molecular weight as that part. This result is reasonable compared with a Monte

! Carlo calculation in literature and also with the perturbation theory.

Temperature Dependence of Dynamic Light Scattering in the Intermediate

1 Momentum Transfer Region

T. P. Lodge 1

, C. C. Han, A. Z. Akcasu2

Assistant Professor, University of Minnesota

2 Professor, University of Michigan

Dynamic light scattering measurements have been made on dilute solutions of very high molecular

weight polystyrenes in cyclohexane at 35.4 °C, 45.0 °C, and 55.2 °C. The data have been analyzed in

|* terms of the first cumulant Q(q) of the dynamic structure factor S(q,t), with particular emphasis on

- the intermediate momentum transfer region (R - 1 << q « £=

x ), for which theoretical predictions

yield Q(q) ~ q

3

. The temperature dependence of the magnitude of Q(q) is examined in terms of a

*

9
"modified blob" model for the equilibrium distribution function and the preaveraged Oseen tensor

description of hydrodynamic interaction. The temperature dependence of the experimental results is

found to be in very good agreement with the theoretical calculations, although the magnitude of Q(q)

at each temperature falls consistently slightly below (~ 15 percent) the theory, as reported

previously for both good solvent and theta conditions.

Dynamic Scattering from Bimodal Polymer Solutions

Be Hammouda1

, A. Z. Akcasu2, T. P. Lodge3, C. C. Han

Research Associate, University of Michigan

2 Professor, University of Michigan

Assistant Professor, University of Minnesota

Dynamic scattering matrix S(q,t) for scattering from multimodal systems is formulated and

explicit results in the case of bimodal systems are presented in the small-q limit. The total

dynamic scattering function is expressed, in this limit, as a weighted sum of two exponentials with

decay rates r x and r2

. Both the decay rates and the weighting factors are calculated in terms of

the concentrations and molecular weights of the two components. The dependence of the apparent

diffusion coefficient „ on concentrations of both components are calculated and the results are app # compared to the experimental data for polystyrene (M^ = 1.79 x 10s and 1.05 x 106

) in cyclohexane at

the theta point. The magnitude of the interference effect on the concentration dependence of D is studied quantitatively. The concentration dependence of the apparent diffusion coefficient and

the collective diffusion coefficient in a single component system is expressed in terms of the pair

correlation function for polymer molecules.

Dynamic Light Scattering Measurements of Polystyrene in Semidilute

Solutions

E. J. Amis 1

, C. C. Han and Y. Matsushita2

Research Associate, University of Wisconsin

Assistant Professor, Nagoya University

Measurements of the cooperative diffusion coefficient D c and a center of mass translational

diffusion coefficient, D

g have been made by dynamic light scattering for the polystyrene-cyclohexane

theta system as a function of molecular weight and concentration. For semidilute solutions we observe D

g « N

2 c3 which is in agreement with the predictions from scaling arguments for the self

diffusion coefficient. On the other hand, if the cooperative mode is interpreted by D c

<* Nx

c^, the

results of 0 < x < 0.7 and 0 < y < 0.5 are in disagreement with scaling predictions of D

c « N°c 1

. The assumptions and potential shortcomings of the blob model which is used in the derivation of the

power law predictions and the dynamic scattering equations is examined. In addition, we have

obtained monomeric friction coefficients from the D

s results within the framework of Doi -Edwards

model. A comparison is made of the concentration dependence of the monomeric friction coefficient

from the present data to that from similar experiments on a good solvent (tetrahydrofuran) system

which have been discussed in last years annual report and from shear relaxation modulus measurements

on the polystyrene in Aroclor 1248.

10
BLENDS PROCESSING

Blends are a relatively new commercial development which represent one of the most rapidly

growing fields in the U.S. synthetic polymer industry. Blending- two or more polymers provides an inexpensive means of developing materials with improved properties and performance. By blending

existing polymers, industry can avoid the expense of both new synthesis plants and new government

approval tests. Further, properties can be tailored to performance specifications by blending. For reasons such as these, blends have already become nearly 20 percent of the U.S. production. Their

use as engineering materials is projected to triple between 1982 and 1987.

There is strong industrial interest with many companies involved. General Electric has formed

a new blends center and Exxon has sent a Research Associate to the Polymer Science and Standards

Division to work on blends. In response to expressions of need from the plastics community, the

Society of Plastics Engineers, Inc., together with its Engineering Properties and Structure Division

and the National Bureau of Standards (NBS), have agreed to institute a joint program to provide data

on the thermodynamics and nonequilibrium phase behavior of polymer blends. NBS will be responsible

for the overall guidance of the technical aspects of the program with the aim of assuring

reliability of the data evaluations, and will provide a center for coordination with other data

compilation centers.

A characteristic of most blends is that they spontaneously separate into phases of different

compositions. This phase separation markedly affects the useful physical properties. Industrial

development of blends is hindered by an inadequate knowledge of the fundamental factors that govern

the kinetics of phase separation during processing. Proper process control requires a knowledge and

understanding of phase separation kinetics which are dependent on diffusional processes, interfacial

phenomena, and the underlying thermodynamics. The activities of this task are focused on measurement methods, data, predictive models, and general theoretical descriptions that will form a scientific basis for optimizing control of blend processing.

NBS has five experimental facilities which, taken as whole, represent a unique combination of

tools for the study of phase separation kinetics in polymer blends: small-angle neutron scattering

(SANS), Forced Rayleigh Scattering (FRS), small -angle x-ray scattering (SAXS), fluorescence energy

transfer techniques, and electron microscopy. The only other SANS facility in the United States is at Oak Ridge; there are only two other FRS instruments in the world being used to study polymeric

systems; fluorescence methods are relatively new and unexploited. After adding the two-dimensional

x-ray detector (1984), the NBS SAXS facility will be one of the finest in the world. NBS possesses

state-of-the-art facilities in imaging and analytical electron microscopy.

Forced Rayleigh Scattering

E. J. Amis 1 and C. C. Han

Research Associate, University of Wisconsin

A Forced Rayleigh Scattering instrument has been designed. Most mechanical and optical parts

have been fabricated, installed, and tested. In this technique a split laser beam is recombined at

a small crossing angle on a sample which includes a trace of polymer labeled with a photochromic

dye. This "writing" beam is pulsed to produce an interference pattern which bleaches a holographic

grating in the sample. A second laser beam "reads11 this pattern and is diffracted by the grating.

As the labeled polymers diffuse in the sample, the grating is destroyed and thus, by measuring the

intensity decay of the diffracted beam, the tracer diffusion coefficient of the labeled species can

be obtained. Since the distance scale of this tracer method is very small (typically several orders

of magnitude smaller than macroscopic tracer methods) it is possible to measure extremely small

diffusion coefficients such as those expected for polymer molecules in concentrated solutions and

melts. Recent theories of dynamics in concentrated solutions and melts should be tested by this

experiment. Preliminary tests of the instrument have been very encouraging. Computer interface,

automatic grating spacing adjustment, and temperature controlled sample chamber have been designed.

This instrument can be used for in situ diffusion measurement of phase decomposition kinetics.

11
SANS and SAXS Studies on Molecular Conformation of a Block Copolymer in

Microdomain Space

H. Hasegawa 1

, T. Hashimoto2

, H. Kawai 3

, C. C. Han, T. p. Lodge4

, A. J. Amis 5

Assistant Professor, Kyoto University

Associate Professor, Kyoto University

3 Professor, Kyoto University

4 Assistant Professor, University of Minnesota

5 Research Associate, University of Wisconsin

Small angle neutron scattering (SANS) technique is used in conjunction with small angle xray

scattering (SAXS) technique to extract the "molecular scattering" from a set of "matched" lamella

microphase separated polystyrene/ polyisoprene samples. This set consists of five samples with

different blending ratios of (PS/PI) and (deuterated PS/PI) two block copolymers which have almost

identical chain length and composition.

The periodical scattering pattern from both SAXS and SANS have been used to interpret the

lamella microphase structure. The molecular scattering extracted from SANS results at different

PS/PI to dPS/PS ratio and from the orientation factor obtained from SAXS show an anisotropic pattern

which gives chain expansion in the direction perpendicular to the lamella interface and contraction

in the direction parallel to the interface.

The expansion is expected from current theoretical understanding but the contraction has not

been predicted so far.

Novel Fluorescence Method for Polymer Blend Phase Diagrams

F. W. Wang and R. E. Lowry

The reliable measurement of polymer blend phase diagrams assumes greater importance as more polymer-polymer blends are used both in the replacement of other materials and in new applications.

Calorimetric and dynamic mechanical methods, which are often used for phase-diagram determination,

have been found to be unreliable in some cases. Furthermore, these methods cannot be used if the

glass-transition temperatures of the constituent polymers are relatively close to each other.

The fluorescence quenching method determines phase diagrams by measuring the intimacy of mixing

of the constituent polymers at the molecular level. The constituent polymers are chemically labeled

with either a small quantity of chromophores or a small quantity of quenchers. The fluorescence

intensity of the chromophores will be reduced by the quenchers only when the chromophores and the

quenchers are well mixed and separated by small distances. The fluorescence intensity will be much

smaller for a single-phase blend than for a two-phase blend. This method was successfully

demonstrated for two-phase blends made from poly(methyl methacrylate) and poly(ethyl methacrylate).

It was shown that addition of poly(vinyl idene fluoride) turns the above two-phase system into a single-phase system.

Nanosecond Fluorimeter for Measurements of Polymer Phase Diagrams

F. W. Wang, F. L. McCrackin, J. D. Barnes, and W. H. Grant

The nanosecond fluorimeter for measurements of polymer phase diagrams by the energy transfer

technique is being installed by the vendor. The fluorimeter has been interfaced to the computer in a simple way.

We are now developing a computer program to treat the data from the fluorimeter. Further, we

are preparing a more sophisticated interface between the fluor-i meter and the computer.

Installation of a Laboratory for Polymer Synthesis

B. J. Bauer

A laboratory has been established for polymer synthesis. Polymerizations by all standard

techniques can be used in sample preparation. Special emphasis has been placed on anionic

12
polymerization. A high vacuum line has been designed and constructed. It is capable of production

of small amounts 10 g) of model polymers such as blocked, branched, functionally terminated, or network polymers.

Digital Small -Angle Scattering Camera

J. D. Barnes

. The Polymer Science and Standards Division has identified a need for improved capabilities in

the collection and analysis of small -angle x-ray scattering data. A new facility, which essentially

duplicates the one at the National Center for Small -Angle Scattering (Oak Ridge National

Laboratory), is being designed and constructed.

|; The NBS camera will use a two-dimensional position sensitive x-ray detector to collect data on

an array of up to 128 x 128 picture elements (pixels) with 16-bit resolution at each pixel. The

data collection hardware and software are functionally equivalent to those being employed on the

small angle neutron scattering instrument in the NBS Reactor Radiation Division.

We will use an existing 12 kW rotating-anode generator as the x-ray source. The beam path

supporting and positioning hardware is being redesigned to provide better mechanical stability than

is found on the Oak Ridge machine. The alignment adjustments will be computer controlled in order

to facilitate careful monitoring and control of these functions by the user. The monochromator

system is being redesigned to eliminate the need for large movements of the beam path when changing

the x-ray wavelength.

Given the need to observe subtle qualitative features in the data, considerable emphasis is

being placed on graphical display of the data. A separate computer is being installed to provide

interactive data analysis using color graphics without interfering with the data collection process.

-

This computer will also be used to apply detector sensitivity corrections, to desmear the data, to

derive correlation functions, and to calculate appropriate integrals over the corrected scattering

functions.

It is expected that these capabilities will provide powerful tools for use in such studies as morphology of semi crystal line polymers, kinetics of phase transitions, deformation processes, crack

formation in glassy polymers and composities, and studies of phase behavior in polymer blends.

New Correlation Discovered for Surface Tension of Simple and Polymeric

Liquids

I. C. Sanchez

A new equation has been derived which relates the surface tension (ct) to a liquid's isothermal

compressibility (k) and mass density (p). This new correlation is

a = (AqP/k ) 1/2

where A

q is a constant that has some interesting properties. First, it is temperature independent

in the normal liquid range (water is a notable exception). Second, it is an invariant for a wide

class of organic liquids that includes aliphatic and aromatic hydrocarbons, alcohols, amines, acids,

as well as other oxygen and nitrogen containing organics. It is also invariant among the diatomic

elements (except hydrogen) and among the heavy noble elements. For polymeric liquids A

q is

temperature independent, but varies by about a factor of 2 among several chemically different

polymers. It is remarkable that hydrogen, methane, and polyethylene all have the same value of A . Third, if the Lennard-Jones force constants are known for a liquid, A

q can be estimated

theoretically for this pair potential. That this correlation exists suggests that the force

constants are not independent, but are coupled in a special way--a property that heretofore had not

been recognized.

j

13
TESTS, STANDARDS AND CHARACTERIZATION FOR MANUFACTURING AND DURABILITY

OF DENTAL AND MEDICAL MATERIALS

The objective of this research is to provide basic materials science, engineering and test

methods which may be used by sectors of the health care industry for the development of new or improved materials, delivery systems and standards.

Materials research efforts support development of materials and techniques which will provide

adhesion and increased durability and wear resistance of composite restoratives, decrease marginal

microleakage, and add to the knowledge available for the development and use of less costly

alternatives to gold casting alloys and dental porcelains. The understanding of the structure and

physical chemistry of calcium phosphates as they relate to biological systems is being advanced for

the development of new or improved preventive stomatological treatments (applications for other than

oral diseases are also considered). Techniques for characterization of low modulus, porous

polymeric implant materials are being investigated and analyzed. Methods for modifying surgical

bone cement to improve durability and performance of bone cement- imp! ant systems are being pursued.

Dental Composite and Sealant Chemistry and Related Developments

J. M. Antonucci , G. M. Brauer, R. L. Bowen1

, J. W. Stansbury,. R. E Dehl

,

and N. W. Rupp 1

Research Associate, American Dental Association

In an effort to significantly enhance the in vivo performance and durability of dental

composite and sealant materials, several types of dental resin systems are under development which

are designed to yield polymers having the following desirable characteristics: (a) Minimal or zero polymerization shrinkage from monomer systems, (spiro monomers which expand slightly on polymerization also are being synthesized). Composites based on these types of dental resins should

have improved marginal adaptation and adhesion to tooth structure, (b) Improved chemical stability

including minimal residual vinyl unsaturation. The inclusion in the resin system of relatively

small quantities of multi-functional chain transfer agents (e.g. , polythiols such as pentaerythritol-tetra (3-mercaptopropionate) , PETMP have been shown to be effective in reducing the

residual vinyl content of the polymer. Composites based on PETMP also exhibit improved esthetics

and color stability. (c) Minimal sorption of water and other oral fluids. Excessive sorption of

fluids by composites and sealants results in plasticization and/or chemical disintegration which

contributes to a reduction in the service life of these materials. Composites based on the use of a low surface energy resins such as the highly fluorinated oligomeric multifunctional methacrylate,

PFMA, with several conventional diluent comonomers (e.g., 1,6-hexamethylene dimethacrylate,

1,10-decamethylene dimethacrylate, neopentyl dimethacrylate, etc.) had good mechanical properties,

improved marginal adaptation and extremely low water sorption. Composites based on PFMA also

exhibit excellent esthetics and color stability. Such composites are expected to resist staining

and plaque accumulation.

A method for determining the water sorption of composites and sealants by near-infrared

spectroscopy was developed and appears to be a more sensitive technique for measuring water uptake

than the standard gravimetric method. In an effort to improve the shelf life of dental composite

and sealant materials, the use of initiator systems based on the relatively stable cumene hydroperoxide rather than the usual benzoyl peroxide has been investigated. The need for a more

stable ambient temperature initiator system is especially critical to the needs of the military

where storage conditions are more severe than those encountered in ordinary clinical usage. It was found that PETMP is an effective promotor for the radical decomposition of cumene hydroperoxide.

This initiator system offers promise for the formulation of dental composite and sealant materials

of enhanced storage stability.

PETMP also has found utility in reducing the setting times of denture base materials while

improving the esthetics and color stability of the cured material. When used in modest amounts in

the liquid portion (e.g., methyl methacrylate) of one surgical bone cement it is effective in

reducing the peak temperature of the exotherm without adversely affecting dough, and setting times

or the compressive strength of the cement. A more moderate exotherm is desirable in surgical bone

cement since it reduces the chance of inflammatory or other adverse responses in tissues contiguous

to the cement.

14
Dental Adhesion Research

R. L. -Bowen 1

, 6. M. Brauer, J. M. Antonucci , J. W. Stansbury, D. W. Misra1

, E. Cobb2

, and J. M. Cassel

Research Associate, American Dental Association

2 Guest Worker, Georgetown University School of Dentistry

Effective bonding to tooth enamel is presently achieved by means of acid-etch treatments.

Similar treatments for bonding to dentin have proved ineffective, and are often contra-indicated.

Adhesive systems and methodologies that would bond effectively not only to dentin but also to enamel

without the necessity of removing sound hard tissue are being investigated.

Certain alkyl cyanoacrylates, which polymerize anionically at ambient temperatures, had been

shown to initially form strong bonds to dentin. However, these bonds weakened significantly on exposure to water. In an effort to stabilize and maintain the good initial bond strength to dentin,

a functional alkyl cyanoacrylate, which is capable of crosslinking with itself and/or copolymerizing

with dental resins has been synthesized. Preliminary studies have shown this cyanoacrylate to be a highly reactive monomer. Evaluation of its bonding potential to dentin will be carried out in the near future.

Another unique approach for a tooth-structure conserving bonding procedure has recently been

developed which utilizes brief applications of a cleanser mordant aqueous solution of ferric

oxalate, a surface- active comonomer and a coupling agent. The surface-active comonomer is either

NTG-GMA, or NPG-GMA, the adducts of glycidyl methacrylate with N(p-tolyl) glycine and

N(phenyl )glycine, respectively. The coupling agent is PMDM, the diadduct of pyromellitic anhydride

and 2-hydroxyethyl methacrylate. Scanning electron microscopy evidence shows that the iron oxalate

solution alters the surface layer. The surface-active comonomer and the coupling agent then provide

molecules which are bound to the altered surface and yield the capability of copolymerizing with

subsequently applied resin of the composite material. With enamel surface the average tensile bond

strength was 13.5 MPa, about the same as obtained with the acid-etch technique. With dentin,

tensile bond strength averaged 13.1 MPa (range, 10.2 to 18.2 MPa). In addition to an adhesive mode

of failure, the fractured surfaces exhibited frequent cohesive failure in the composite and

occasional cohesive failure in dentin. The biocompatibility of this promising adhesive bonding

system is undergoing evaluation prior to clinical trials.

Dental Cements

G. M. Brauer, J. M. Antonucci, and J. W. Stansbury

Dental cements with good biocompatibility, improved mechanical properties and resistance to

erosion on exposure to the chemical environment are needed. With the exception of cements based on aqueous solutions of poly(acryl ic) or similar poly(al kenoic) acids none have shown significant

adhesion to tooth structure. Because of the hydrophilic character of these latter cements, there is some question of their long term durability in the oral cavity, especially with patients having

hyperacid oral conditions.

Two approaches have been initiated to develop more hydrophobic, tough cements with adhesive

potential to various substrates.

One approach is based on enhancing the strength and chemical resistance of current cements

based on zinc oxide-eugenol (Z0E)-2-ethoxybenzoic acid (EBA) by replacing the eugenol with esters of

vanillic acids. Cements based on n-hexyl vanillate (HV) and EBA have been shown to have higher

strength and lower solubility than currently used EBA-ZOE cements. In contrast to ZOE containing

cements, the HV-EBA cements do not inhibit free radical polymerization, adhere strongly to non-precious metals, porcelain, and composites, and can be formulated with methacrylate monomers to

yield composite cements of even higher strength and lower solubility. Work to modify the newly

developed hexylvanillate (HV), o-ethoxybenzoic acid (EBA), and zinc oxide (ZnO) dental cement for

intermediate restorative applications has led to the synthesis of several new types of vanillate

esters. Substitution of the difunctional decamethylene divanillate for the monofunctional HV in a cement formulation yielded stronger and less soluble materials. Enhanced physical properties were

also obtained for cements which included methacryloyl ethyl vanillate; a compound capable of free

radical induced polymerization as well as the normal ZnO chelating reaction. Hybrid cement

15
composites arising from powders containing ZnO and benzoyl peroxide treated glass along with liquids

consisting of HV-EBA and various monomethacrylates have been evaluated. These formulations yielded

cured cements which exhibit extremely high strength and low solubility. In addition, they demonstrated excellent adhesion to a wide range of substrates.

The incorporation of esters of syringic acid, a potential caries reducing agent, as a complete or partial replacement for HV in cement formulations has been investigated. Cement products

obtained with ZnO have had more than adequate physical properties, however, a study of any

cariostatic qualities of these cements remains to be done.

To date, all of the preliminary biocompatibility results have indicated that hexyl vanillate

elicits equivalent or milder tissue responses than eugenol.

These newly developed materials show great promise as intermediate restoratives, luting base,

endodontic cement, crown and bridge cement and as a cement for repairing fractured porcelain. The

second appraoch to a more durable dental cement is based on the development of nonaqueous

polycarboxyl ate cements.

Conventional polycarboxyl ate cements are based on the reaction of aqueous solutions of

poly(acrylic acid), or similar poly(al kenoic acids), with a basic inorganic powder (e.g. , zinc

oxide, magnesium oxide, ionomer glasses). The acid-base reaction that occurs on admixture of the

aqueous polyacid and the base powder yields ionically crosslinked polymeric matrices that are rigid

and hydrophilic in nature. The feasibility of obtaining less rigid and more hydrophobic dental

cements by the reaction of the commercially available dimer (OA) and trimer (TA) acids with a variety of basic powders (e.g., Ca(0H) 2 , ZnO, etc.) is being explored. DA and TA are moderately

viscous liquid polycarboxyl ic acids of high molecular weight possessing a unique chemical structure

of a bulky, flexible, hydrophobic core which terminates in 2 or 3 hydrophilic carboxyl groups

(-C02 H), respectively. The relatively low carboxyl content, large size hydrophobic nature of these

acids should result in dental materials of excellent biocompatibility.

Cements having clinically acceptable setting times, and good physical and mechanical properties were obtained from base powders containing calcium hydroxide, magnesium oxide and zinc oxide. DA admixed with Ca(0H) 2 in a powder/liquid ratio (by weight) of 1.5 gave a fast-setting cement (3 min.)

with 24-hr compressive (CS) and diametral tensile strengths (DTS) of 25 and 4 MPa, respectively.

This DA-Ca(0M) 2 cement had a low water solubility of only 1.5 percent after 24 hours at 37 °C; the

water after this period of storage was alkaline (a condition which should protect pul pal tissues

from acid attack and stimulate secondary dentin formation). Under compressive loading (crosshead

speed = 1 mm/min) specimens of this cement do not fracture but show significant deformations. A TA-Ca(0H) 2 cement behaved similarly. The addition of 17 percent tricalcium phosphate to a DA-Ca(0H) 2 formulation (P/L=2) gave a material that hardened in 7 min. and deformed only slightly

under the same compressive stress (CS=32, DTS=6 MPa). The absence of brittle failure is indicative

of the non-friable nature of these cements. Thus far, the strongest DA-Ca(0H) 2 cement was one consisting of a base powder with equal parts of Ca 3 (P04 ) 2 , Ca(0H) 2 , and MgO (P/L=2); CS=41; DTS=6

MPa. The energy absorbing nature of all these Ca(0H) 2 cements coupled with their low solubility and

alkaline character suggests their use as cavity liners, endodontic sealers, impression materials,

etc. The strength and solubility characteristics of these Ca(0H) 2 cements are superior to those

currently available.

DA and TA with micronized zinc oxide (P/L = 7) yielded tough, extremely hydrophobic cements

(setting time = 7.5 min) CS = 50, DTS = 7 MPa) which may find use as temporary and intermediate

restoratives. Because these cements do not inhibit the polymerization of composites they are amenable to the formulation of hybrid composite-cement materials. The setting mechanism of these

novel polycarboxyl ate cements involves primarily chain extension through the formation of multidivalent metal carboxylate linkages. The versatile nature of cementitious materials obtained from

DA and TA with different base components suggests a wide range of potential dental applications.

Wear Mechanisms and Durability of Dental Composite Materials. Effect

of Degree of Cure

W. L. Wu, J. E. McKinney, E. E. Debelius, and J. M. Cassel

Since clinical evaluations on dental restoratives require three to five years, it is necessary

to develop and utilize appropriate laboratory tests to obtain reliable durability assessments in a

16
reasonable period of time. Microdefect analyses involving a photographic silver staining process

and small angle x-ray scattering reveal the extent of damage in both jji vivo and in vitro worn

materials. On in vivo worn restoratives the results from these techniques revealed subsurface

damage on both stress and nonstress bearing surfaces. Accordingly, it is believed that the oral

chemical environment plays a very important role in the degradation of composite restorations.

Earlier laboratory tests have shown that the wear resistance decreased markedly after certain food

simulating liquid chemicals diffused into the composite specimens. In particular, those presoaked

in a 75 percent/25 percent ethanol -water solution revealed the greatest extent of subsurface damage

and wear (pin and disc). At this concentration the solubility parameters of the solvent and BIS-GMA

polymer (used as matrix) are assumed to be proximate.

FTIR measurements revealed a degree of cure of only about 65 percent for a BIS-GMA-TEGDMA

polymer cured at the in situ temperature 37 °C. Increasing the degree of cure is expected to

improve the wear resistance and durability of the composites. In recent work the degree of cure was increased by elevating the cure temperature. Although this method may not be practical for in situ

restorations, it affords an evaluation of the influence of the degree of cure on material

properties. Wear and hardness measurements were conducted on three kinds of commercial dental

composites: conventional (large particle reinforcing filler), visible liqht activated, and a microfill. Specimens cured at temperatures up to 80 °C were soaked in water and the 75 percent/25

percent ethanol -water solution for one week. Subsequent wear and hardness measurements on the water

soaked specimens revealed no significant changes with cure temperature. With the ethanol soaked

specimens, however, considerable improvement with increasing cure temperature was observed in the wear and hardness of all of the composites. With the 80 °C cured specimens, no significant

difference was observed between wear of the water and ethanol soaked specimens.

With cross-linked polymers the degree of cure is apparently limited by the elevation of the

glass transition temperature Tg during the curing process. At a certain point during the cure the

viscosity becomes so large that the reactive groups cannot become proximate and are used up in other

ways, thus terminating the cure. In order to obtain more knowledge of the behavior of this process,

we have initiated a series of low frequency vibration measurements to follow the isothermal curing

of dental polymers at different temperatures. Companion FTIR measurements will be made to relate Tg

to the degree of cure. The information obtained from these measurements will be used to evaluate

the potential of new dental polymers under development at NBS.

The diffusion processes of water and other food simulating chemicals into dental composites

have been monitored quantitatively using a CAHN electrobalance. Fickian type diffusion is observed

for water as a penetrator, and the diffusion coefficient of water is not suppressed by the presence

of the fillers. Class-II diffusion is found for other liquids which swell the dental resins. The

presence of fillers in this case decrease the extent of swelling significantly.

Porcelain Fused- to-Metals and Dental Ceramics

J. A. Tesk, W. deRijk1

, H. R. Kase2, G. Widera3, D. L. Menis 1, and

R. W. Hi naan4

Research Associate, American Dental Association

2 Guest Worker, University of Gottingen, W. Germany

3 Guest Worker, University of Illinois, Chicago, IL

4 Guest Worker, U. S. Navy

Porcelain fused-to-metal (PFM) restorations often fail by cracking of the porcelain or delamination of the porcelain veneer. A major cause of this failure is thought to lie in the

thermomechanical induced residual stress from firing of the system at high temperatures. Another source of failure lies in attainment of a poor porcelain-to-metal bond; this can frequently be

attributed to a lack of proper process control (technique variations) and/or to lack of a chemical

compatibility between alloy and porcelain.

To characterize the PFM bond strength, a four point bending beam composite (BBC) has been

developed. Simple BBC theory is utilized to calculate failure stress. For modulus ratios of two,

(approximately that of metal to porcelain for nonprecious alloys^ the calculated stress is within 6

percent of that calculated from a finite element model of the system. Up to four interfaces are provided for PFM bond failures. Fractures occur within porcelain or at interfaces. It has been

found that a cumulative failure plot using Wei bull distribution analysis shows clear distinction

17
between systems; such interactions are not significantly apparent from the means of failure

strengths alone. As the system and analysis is developed it is expected that industry will begin to adopt it as it provides more information with fewer samples in less time than other tests currently

employed and is capable of characterizing PFM systems according to several parameters.

To characterize the residual stress of PFM and, therefore, stress compatibility, the change in

gap of a porcelain veneered split metal ring is being employed. The rationale for this has been

developed. A finite element model which describes the gap as a function of thermal history and

material properties is nearing completion. Ultimately, it is expected that the ability to calculate

gap changes which correspond to experimentally determined changes will lead to definition of the

stress within the system. Correlation with clinically/experimentally observed failure of the

porcelain is expected to lead to delineation of the limits of stress which can be imposed on each

combination of porcelain and alloy. Use of a tensile stress failure criteria should also provide a means for calculation of thermal expansion compatibility between porcelain and alloy, thereby

providing a method which may be used by industry for development of new materials/techniques,

quality control and for use in development of standards.

An important consideration in calculation of thermal stress compatibility is the elastic

modulus of the materials involved and their temperature dependencies. The moduli of porcelain have

been determined and hysteresis between heating and cooling shows evidence of some microcracking.

Generally, the modulus of the porcelain decreases about 1 percent per each 100 °C increase in

temperature with moduli ~ 70 GPa near 23 °C.

New compositions of ceramic materials that can function as veneers for dental prostheses have

been formulated. These materials are formed from solutions. Fusion temperatures in the 710 °C to 750 °C have been obtained. Several of these materials have adequate thermal expansion and good

chemical durability.

Mathematical analysis has shown that the fusion temperature of the modified aluminosilicates

can be predicted as a function of the constituent oxide concentrations.

In addition it has been found that the firing of dental porcelains beyond the mature fire does

not increase chemical durability.

Dental Casting Alloys and Investments

J. A. Tesk, R. W. Waterstrat 1

, S. Hirano2

, R. W. Hinman3, H. R. Kase4, W. deRijk1

, and H. Argentar5

1 Research Associate, American Dental Association

2 Guest Worker, Tsurumi University, Japan

3Guest Worker, U. S. Navy

4 Guest Worker, University of Gottingen, W. Germany

5 Private Collaborator

Because of superior properties and/or lower costs, dental alloy systems other than gold are being used and introduced at a high rate. Most of the newer alloys are based on nickel and an increasing percentage of palladium based alloys are appearing. Although the use of nickel based

alloys has not to date produced an obvious problem of biocompatibility, concern over potential

latent carcinogenecity and allergic sensitization has not abated. For this reason, titanium based

alloys offer some characteristics which are appealing as they may be expected to be non-toxic,

durable and strong. A major impedment to their widespread use lies in the need to find a way to successfully cast these alloys under dental laboratory conditions. Recent work at NBS with

magnesium oxide investments has produced a successful casting which has not been unduly contaminated

fa y the investment, as evidenced by the surface finish and non-brittle nature. The production of a ^Hes of castings for evaluation of clinical potential will be undertaken in the near future.

As the desire for new alloys continues, a method for evaluating the castability and the effects

r

J’

f element additions as functions of alloy casting temperature and mold temperature is needed to aid

processing quality control and development.

. A simple technique has been developed for these purposes; it involves the use of a polyester

1 pattern. The percentage of completely cast grid segments is used as a castability value, C

v

.

18
Because the standard deviation (SD) of C , is a function of C it is convenient to use a . . v v transform

of C

v

, (Cyt ) to mathematically represent as a function of temperature. It has been found that

for six alloys investi gated * the same function is capable of describing C at the 99.5 percent

confidence level.

cvt = a + b V

2 V

where a and b are constants, characteristic of each alloy

T

a = alloy casting temperature in terms of superheat above the

solidus; = the mold temperature in degrees celcius

2/3 + Vc'TToo

v 2/3 + Vl-C

v/100

A graph of vs C

y provides a convenient way of obtaining the inverse transform.

The next step in the program is to represent the contribution of various elements to

castability, as a function of temperatures.

Dental Chemistry, Crystallography, and Preventive Treatments

W. E. Brown 1

, L. C. Chow1

, M. Mathew1, S. Takagi 1

, M. Tung 1, G. L. Vogel 1, T. M. Gregory 1

, C. M. Carey 1

, B. Sieck1, and C. Schreiber1

Research Associates, American Dental Association

The relationship between C

v ^ and C

v is

C

vt =

Fundamental studies on the chemical properties and crystallographic structures of tooth and

bone minerals and other biologically important calcium and phosphate containing compounds are conducted. The information obtained is applied to the development of improved caries preventive

techniques. Work conducted under this project includes studies on topical fluoridation, mechanisms

of biomineralization, caries mechanisms, calcium phosphate cements, crystal structures of

biominerals, and x-ray magnification microradiography.

Work continues on the new procedure for topical fluoridation which involves treating the tooth

with solutions that form dicalcium phosphate dihydrate (DCPD) in the enamel to make it more reactive

towards fluoride. A cooperative fluoride-uptake and caries-score study was carried out with

investigators at NIDR using the rat model. The DCPD pretreatment considerably increased the

permanently-held fluoride content of teeth and produced the lowest caries score. However, due to

the relatively large standard deviations, the caries score was not significantly different from the

fluoride treatment alone. Our present procedure requires two treatments, DCPD-forming solution

followed by fluoride solution. By incorporating into the DCPD-forming solution a complex fluoride

which does not react with calcium ions, the procedure may be reduced to a single treatment. Initial

laboratory results showed that SiF^2 ions served well for this purpose. Based on the above

principle, a patent application was filed: "Composition and Methods for Topically Fluoridating

and/or Mineralizing Dental Enamel."

We have long advocated the view that octacalcium phosphate (OCP) participates as a precursor in

the formation of tooth and bone mineral. There is growing evidence that in biological

calcifications OCP is formed first, then hydrolyzes to a nonstoichiometric hydroxyapatite. A procedure was developed in our laboratory by which these two processes can be separated and studied

individually to determine the effects of physiologically active components on the rates of these two

mineralization processes which form tooth, bone, and pathological mineral deposits such as those in

atherosclerotic plaque.

Caries Mechanisms : The work on caries mechanisms has been expanded to include studies on four

levels: (1) theoretical considerations which focus on the fact that the relative rates of diffusion

of ions into and out of the lesion can be important parameters affecting the rate of caries

19
progression, (2) bench-scale experiments using a two-compartment diffusion cell to test the major

principles of the proposed caries model, (3) a computer simulation model which has produced results

in close agreement with the bench scale studies and allows us to survey rapidly the effects of a large number of variables, and (4) ultramicro-analytical studies on tooth sections to establish

quantitatively the events occuring within the enamel during artifically induced caries formation.

Results from the above studies have produced important new insights into the factors governing the

caries process.

Progress has been made on the development of cements that harden in water and form compositions

nearly identical to tooth and bone mineral. A method was developed which can produce cement

specimens with greater strengths and with pores if needed for bone implant applications. In collaboration with the Research Institute, a study to test the biocompatibility of the cement using

animal models has been initiated. A patent application, "Combinations of Sparingly Soluble Calcium

Phosphates in Slurries and Pastes as Mineralizers and Cements", was filed.

The crystallographic studies provide a structural base for understanding the chemistry of

biominerals and their interactions with dental materials. Crystal structures of Ca2 KH7 (P04 )*H2 0 has

been determined using x-ray and neutron diffraction data. Research on the structural studies of

octacalcium phosphate, Ca8 H 2 (P0 4 ) 6 -5H2 0 and its role in biomineralization and the surface and

colloidal properties of apatites continue to be a major activity.

A new study of the structural features in mineralized tissues using x-ray magnification

microradiography has been initiated. X-ray magnification microradiography is a new technique that was developed by the National Bureau of Standard's Metallurgy Division. Considerably better

resolution may be obtained by this technique than by standard contact microradiography. Preliminary

studies have clearly shown images of dentin tubules and special features of carious lesions.

Clinical and Laboratory Investigation of Dental Amalgams, Composites and

Glass Ionomer Cements

N. W. Rupp 1

, G. C. Paffenbarger1, and R. W. Waterstrat1

Research Associates, American Dental Association

The success or failure of dental restorations can be determined only after long term, greater

than two years, observations. The causes of failure relate to three categories: (1) the physical,

mechanical and chemical properties of the material; (2) the operator's selection of material, cavity

preparation and manipulation of the material; and (3) the patient's home care. Sorting out of the

factors contributing to the durability of restorations requires a careful combination of clinical

studies and laboratory analyses.

Amalgam restorations placed in our clinical study over nine years ago are continually being

observed. These, along with observations of ui vitro specimens made six years ago, show an interesting correlation within our laboratory and with observations reported from other laboratories. Unrestricted amalgam specimens, 4 x 8 mm cylinders, have been stored at 60 °C for six years

and their length and diameter measured and changes in dimensions recorded. Also, restricted

specimens have been compacted in cavities in a steel block, also stored at 60 °C for six years, and

the extrusion from the cavities measured. Currently we have the clinical data from an outside

laboratory for three alloys in common with our study. The clinical study reports the deterioration

of restorations directly in comparison with our yearly laboratory observations. When this data,

after six years, is plotted, there is a straight line from the fiducial reading. We are now searching for clinical reports on other alloys on which we have data to determine if the laboratory

data is consistently compatible. Also, we are studying the data to determine the shortest or earliest time period which can be observed in the laboratory that will predict long-term

deterioration of restorations. Clinical studies are expensive and time consuming. If the

laboratory test in a few months does predict what the long-term clinical studies finally show, then

patients, dentists, and manufacturers will be saved considerable money and time.

Composite restorations placed both i_n vivo and i_n vitro are being observed for margin staining

using commercial products recommended for bonding to dentin. Only those products having proof of

safety to the pulp are being used i_n vivo . Currently two brands of dentin bonding agents indicate

adequate bond strength to prevent gross margin leakage. When this is statistically confirmed, the

results will be published. This is necessary because the gingival margin of a composite restoration

rarely has sufficient enamel for bonding; thus the gingival margin is the first'area to break down

20
with stain and/or caries. As soon as the dentin bonding agent being developed in this laboratory

(Dr. R. L. Bowen) is determined to be biologically safe to use, it will be incorporated in a clinical

study.

Glass ionomer cement restorations are being placed in selected cavities. Some restorations

have been retained for over two years. This material can be used in gingival erosion cavities that

are extremely sensitive without grinding or removal of tooth tissue. The sensitivity is immediately

reduced and the restoration appears to be effective. The handling technique is extremely difficult

and is also being studied.

Characterization of Porosity in Porous Polymeric Implant Materials

R. E. Dehl

Porous synthetic bicmaterials are currently being used as implants, where they become

stabilized by the ingrowth of hard or soft natural tissues. Both the rate and the type of tissue

ingrowth are affected by the porosity of the materials, and it is important to be able to characterize the porosity by reliable and reproducible methods. In response to a request from the Office

of Medical Devices, Food and Drug Administration, a study is being conducted by the currently

existing methods for characterizing the porosity of two commercially available porous polymeric

implant materials, porous polyethylene and a composite of polytetrafluoroethylene and carbon.

In previous years, studies of the porous implant materials included measurements of the pore

volume and interconnecting pore size by mercury porosimetry; a quantitative analysis of the

stress-strain behavior of both materials, as it might affect the porosity measurements; and an estimation of the average pore "diameter" from measurements of the ratio of the specific pore volume

to the specific surface area. Error analysis- of the mercury intrusion experiment revealed

increasing accuracy of the measurement with increasing pressure, corresponding to smaller pores.

The shape of the volumeweighted pore size distribution curves were found to be approximately

log-normal

.

A major effort is now directed to the measurement of pore volume and pore size by quantitative

microscopy (stereology). Samples were prepared for optical analysis by filling the porous materials

with a liquid resin which hardened to allow the surface to be ground and polished. Under intense

overhead illumination, both materials revealed differences in reflectivity between the pore (resin)

phase and the polymer phase, thus permitting quantitative microscopic analysis of the pores. Thirty

photomicrographs of each of the materials, taken at random spots on the surface, were analyzed using

a transparent overlay grid. The pore volume fraction was determined by measuring the fraction of

grid intersects or "points" (P

p ), and the mean intercept length, a measure of pore "size", was determined from the ratio of P

p to N^, the number of pore line intercepts per unit test length.

A discussion has been prepared concerning • the advantages and disadvantages of each of the

porosity characterization techniques. The accomplishment of this project's objectives will be of

significance to the medical device industry and medical implant standards development, as well as to

the users of porous implant materials.

Surgical Bone Cement Modification

G. M. Brauer, J. A. Tesk, J. W. Stansbury, W. L. Wu, and J. E. McKinney

Surgical bone cement, while serving a necessary function in orthopedic practice, has several

shortcomings which become especially apparent in total joint replacements which require large

amounts of material. Improved biocompatibility, low exotherm temperatures during polymerization,

and more stable interfaces with bone and implant materials are some of the problems addressed in

this investigation.

In comparison with the commercial, surgical simplex material, bone cements with shorter setting

times, lower peak exotherms, and higher compressive strengths have been developed. With strength

values unaffected, maximum temperatures were significantly reduced for formulations containing small

quantities of pentaerythritol tetra (3-mercaptopropionate). A lowering of the peak exotherm was

also accomplished by the addition of high molecular weight methacrylate monomers such as

di cycl openteny 1 oxyethy 1 methacryl ate;

21
Radiopaque bone cements have been obtained through incorporation of pentabromophenyl

methacrylate as a comonomer in the powder portion of the formulation. Cements formulated with 5 to

10% of the brominated methacrylate are expected to have acceptable dough and setting times and the

copolymer should have improved physical properties since this eliminates the weakening effect of the

barium sulfate presently used as radiopaquing agent.

Dental and Medical Materials Standards

J. M. Cassel , J. A. Tesk, G. M. Brauer, N. W. Rupp 1

, and W. Derijk1

Research Associates, American Dental Association

Developments of standards for dental and medical materials is strongly supported by activities

on committees and subcommittees of ANSI MD 156 (Dental Materials, Instruments and Equipment) and

ASTM F-4 (Medical and Surgical Materials and Devices). Leadership roles are held as chairpersons of

ANSI MD 156, ASTM F-4, the USA TAG for ISOTC 106, Task group convenor for several working groups of

ISO TC 106 and by participation on the Executive Committee of the Medical Device Standards

Management Board of ASNI. Numerous standards have been reviewed, edited, revised and reaffirmed for

ANSI/ADA and ISO including standards for dental units, chairs, abrasives, burrs and alloys.

22
MECHANICAL DURABILITY OF POLYMERS

The rapid growth in the use of polymeric materials derives from substitution for other

materials, the expanded need due to population and economic growth, as well as new applications due

to the unique properties of these materials. Long-term mechanical performance is important in

critical applications. The realization of increased utilization is often limited by the lack of

data and models upon which to design for long-term use. Thus, the lack of adequate test methods and

data for evaluation of long-term mechanical performance not only restricts applications, but also

leads to over design which results in more expensive items and limits weight savings. Evaluation

and control during processing of material parameters that affect long-term performance should lead

to more durable materials and, hence, reliable performance for the intended service life.

The objective of this task is to provide data, test methods, and standards for evaluation of

long-term mechanical performance of polymeric materials. The approach is to identify and analyze

principal failure mechanisms of commercially important thermoplastics under mechanical stress in the

use environment, to determine the effects of chemical structure and fine structure morphology on mechanical properties and failure processes, and to develop constitutive relationships and models

for mechanical properties to serve as the basis for accelerated test methodology and lifetime

prediction. In addition, the influence of processing conditions on structure and morphology are elucidated.

The approach to development and verification of predictive models of mechanical performance

are: (1) establish dependence of the principal failure modes of inhomogeneous deformation and crack

initiation and growth on mechanical stress use environment and molecular structure and fine texture;

(2) identify the principal molecular processes associated with deformation and failure and relate

failure to molecular structure and fine texture; (3) evaluate the kinetic theory of bond rupture as

a model for degradation of mechanical properties and for extrapolation of short-term measurements

to predict long-time performance; (4) on the basis of (1), model failure by neck formation and

propagation using time-dependent constitutive relations that predict the onset of inhomogeneous

deformation:. from .baseline mechanical properties characterization; and (5) expand fracture mechanics

approach to viscoelastic materials to modelcraze and crack growth phenomena.

The National Bureau of Standards has established joint programs on mechanical performance with

other Federal agencies which are fostering the application of polymeric materials in areas of

national concern. For example, a joint program with the Defense Advanced Research Projects Agency

(DARPA) is concerned with development of molecular characterization techniques for mechanical

degradation as the basis for nondestructive evaluation methods. Joint projects are executed with

industries. An example is the project with Firestone Tire and Rubber Company on the effects of

processing on polyethylene terephthalate (PET) fiber structure and properties.

Molecular Processes Associated with Mechanical Deformation and Failure

B. M. Fanconi , D. L. VanderHart, S. J. Kryder, J. R. Havens, and

K. L. DeVries 1

1 College of Engineering, University of Utah

The elucidation of molecular processes and structure changes accompanying mechanical

deformation and failure not only provides the basis for development of test methods for long-term

performance and quality control, but also provides insight into the selection, processing, and

design of materials with improved mechanical performance and durability. The semicrystall ine

structures found in some commonly used polymeric materials present significant challenges to

characterization of molecular structure. Spectroscopic techniques involving 13 C nuclear magnetic

resonance (NMR) and FTIR spectroscopies are used to elucidate molecular conformations in disordered

material. Reorganization of polymer molecules during deformation affects mechanical performance and

identification of the molecular processes involved and the physical structures which result are the

aim of the studies.

FTIR is used to determine relationships between the number of chain scissions produced by

mechanical stress, stress history, the useful service life, and molecular weight and its

distribution.

23
Chain Scission and Mechanical Durability of Polyethylene

Previous work on ultra high molecular weight polyethylene (UHMWPE) had established that

mechanical failure was associated with a critical concentration of chain scissions [1]. The number

of chain scissions was determined from changes in end group concentrations as found from infrared

spectroscopic analysis. During the past year, the effects of the initial molecular weight and the

fatigue test frequency on the number of chain scissions at failure have been examined. In addition,

the relationship between the growth in end group concentration and fractional lifetime has been

establ i shed.

Spectroscopic investigations have been carried out on a second UHMWPE with a manufacturer's

reported molecular weight of 2xl0 6

, or one-half the value of the material used in the aforementioned

study. For this material it was found that failure occurred at a mechanically induced chain rupture

concentration of about lxl0 18 /cc instead of 2xl0 18 /cc. This finding suggests that the original

molecular weight is a determining factor in the level of molecular damage that can be tolerated

before failure occurs. Whether the relationship between initial molecular weight and concentration

of chain ruptures at failure is linear needs to be verified by further experiments.

The effect of fatigue test frequency on the concentration of chain scissions at failure has

been investigated. The increase in chain scission concentration with test frequency is similar to the observed [2,3] increase in free radical concentration at failure of nylon-6 fibers with

increasing strain rate. The latter results were interpreted in terms of competing processes. At

high strain rates relaxation times for slip or uncoiling of molecules may be too slow to relieve

over-stressed molecular segments with the result that more chain scissions occur. A competing

process is the higher rigidity at the higher strain rates which means a smaller strain at fracture,

and fewer over-stressed chains. Alternately, the weak dependence on test frequency may be caused by

a slight rise in sample temperature as the fatigue frequency increases. Although according to the

kinetic theory of chain scission the probability of chain rupture increases with increasing

temperature the critical concentration would also be expected to rise due to a greater probability

for free radical termination reactions as a result of more molecular mobility. The extent of free

radical propagation reactions would decrease at higher temperatures and damage zones formed would

net be of sufficient dimensions to coalesce into the microvoids that are the precursors to macroscopic failure.

The finding that macroscopic failure occurs at a critical concentration of chain ruptures

suggests that monitoring the buildup in end group concentrations may serve as the basis for lifetime

prediction. In order to assess the potential of this approach the increase in chain scission

concentration during the course of a fatigue-to- failure test has been examined.

In this experiment the test specimens were subjected to a predetermined number of stress

cycles, removed from the mechanical tester, and placed in the interferometer for infrared

spectroscopic analysis. The specimens were then returned to the mechanicaT tester for another

series of stress cycles, and the entire process repeated unt'il the specimens failed. During the

initial stress cycles the chain scission concentration increased only slightly. This was followed

by a rapid rise to about 60 percent of the concentration at failure after which it rose linearly

with the number of stress cycles until macroscopic failure.

The growth in the chain scission concentration with the number of stress cycles has been

measured for specimens fatigued at 0.002 and 0.01 Hz and a peak stress of 35 MPa. These experiments

yielded a similar behavior with fractional lifetimes. Thus, the general features of the rise in

chain scission concentrations appear to be independent of the fatigue test frequency.

The fatigue experiments that have been carried out are constant peak stress tests. During the

fatigue experiment the initially isotropic test specimen is elongated and preferential chain axis

orientation in the direction of the applied stress occurs. The sample morphology is transformed

from spherulitic texture to fiber morphology. The number of highly stressed molecules would be

expected to change as these morphological changes occur. Thus, the rise in chain scission

concentrations may correlate more directly with the imposed strain than the number of stress cycles

in a fatigue experiment. Furthermore, the behavior of chain scission concentration with the first

few cycles in fatigue is very similar to the strain induced increase in free radical concentration

[2], or degradation of molecular weight [4]. The dependence of the chain scission concentration on strain has been examined. No discernible change in the aldehyde band (1735 cm- 1

) is observed up to draw ratios of about 5. The polymer specimens were strained in a manually operated stretching frame

24
and it has not been possible to strain at levels which would produce chain scissions withoutfracturing the tensile specimen. After fracture, a sizable increase is observed in the 1735 cm- 1 band indicative of the occurence of chain scission processes.

[1] Fanconi , B. M. Annual Report 1982, Polymer science and standards division. Nat. Bur. Stand.

(U.S.) NBS1R 82-2607, March 1983.

[2] Kausch, H. H. ; DeVries, K. L. Int. J. Fract. 11: 727; 1975.

[3] Williams, M. L. ; DeVries, K. L. Proc. of the Fifth Inti. Congress on Rheology, 3: S. Onogi , ed.

Tokyo: Univ. of Tokyo Press.

[4] Shen, L. N. J. Poly. Sci. Poly. Lett. Edn. 15: 615; 1977.

Examination of Drawn PET Fibers by Solid State NMR

The motivation of this joint project with Firestone Tire and Rubber Co. is to better understand

molecular organization in polyethylene terephthalate (PET) fibers so as to effect better control of

fiber shrinkage during processing in tire reinforcement applications.

Two questions are under current investigation:

The first is related to the presence of tie chains which are important in understanding the

modulus of these materials since these are the links which connect the crystals. In particular, the

sensitivity of 13 C NMR techniques to the structure and mobility of such chains is under

i nvestigation.

In a matrix of ordered as well as disordered chains, criteria must be established which

differentiate NMR signals from tie chains from those of other structural components. This is not a straightforward problem. Nevertheless, the following criteria were adopted:

(a) Chain orientation close to the draw direction

(b) Mobility in excess of crystalline chain mobility

(c) Spatial proximity to the non-crystalline or disordered chains

In the 13C spectrum (non-spinning), resonance positions indicate orientation, excess mobility

is indicated by the rotation of the aromatic rings in the polymer backbone (about their 1,4 axes),

and a crude proton rotating frame relaxation selection (in the presence of spin diffusion) indicates

whether these mobile, oriented chains are primarily found in regions of orientational disorder. The

chains which satisfy all three criteria are a minor fraction of the total number and annealing

diminishes the number of chain segments having these characteristics. Possible interpretations of

this diminishing population are (a) incorporation of tie chains into growing crystals, (b) densification of molecular packing in the non-crystalline regions, and/or (c) relaxation of orientation

with annealing. Since the amount of orientational relaxation is small according to the spectra,

process (c) cannot be the dominant one. Each of these explanations, however, ought to create its own signature on the modulus.

The second emphasis in the PET studies is to examine morphological changes which occur upon

annealing. Spin diffusion measurements using proton NMR give information about domain size,

particularly when domains are in the 4 to 10 nm size range as they are believed to be in these PET

fibers. Last year preliminary studies of spin diffusion were carried out. This year, largely due

to the efforts of John Havens, a post-doctoral associate, multiple pulse experiments have been

initiated. In these experiments, which are experimentally very difficult, spin diffusion can be

manipulated by turning it on and off. The thinking behind these experiments is that sharp

magnetization gradients can be prepared between regions of different relaxation times by allowing

relaxation to occur while quenching spin diffusion. Then with a well-defined initial condition,

spin diffusion is allowed to occur for different periods of time. Finally, after these times, the

status of the system can be monitored without spin diffusion occurring, so that the status of the

system does not change during "read out." This version of the experiment is much superior to former

efforts on PET. Early results tend to verify what was observed in a more qualitative way before,

namely, that the domain sizes are not changing by more than 40 percent upon post annealing. These

results support the idea that extensive solid-state chain mobility does not exist during annealing

in PET as it does in polyethylene, for example. Thus efforts at controlling shrinkage, i.e. , controlling morphology, are better focussed on the initial solidification and crystallization

process.

25
Characterization of Ultrahigh Modulus Polyethylene

Work in collaboration with Ian Ward at the University of Leeds and Dr. Bernard Meurer from CRM,

Strasbourg, France, is concerned with drawn and undrawn polyethylene. Efforts were focussed on

r measuring 13 C longitudinal relaxation times, T-. The typical profile of relaxation indicates three

-*• r components having short (5.5 s), intermediate (10-130 s) and long (300-500 s) characteristics T s. In particular, in a drawn sample, the intermediate component always shows good chain orientation

relative to the draw direction, and thus this component is a candidate for tie chains (orientation,

mobility in excess of the crystalline chain mobility). Unfortunately, the third criterion used to identify tie chains in PET, namely, spatial proximity to the disordered regions, is a harder

criterion to apply in polyethylene and attempts have not been successful in this regard. At

present, therefore, the amount of intermediate component is being identified primarily with

interfacial material. A melt- (or pressure-) crystallized isotropic sample is found to have 15 to

35 percent less intermediate component than a cold-drawn (at 100 °C) material. Moreover, in the

samples studied, a sample with a draw ratio of 10 has more intermediate component than one whose

draw ratio is 20. It is also found that the amount of long relaxing (crystalline) material

underestimates crystallinity when compared with normal measures, i.e., DSC. At the same time, the sum of the long and intermediate components overestimates crystallinity. Furthermore, the high

pressure crystallized sample, which has lamellar widths of a few hundred nanometers, shows 15

percent intermediate and no short component. For this latter sample, which by density or DSC one would label as 95 percent crystalline, the 15 percent seems high. It, therefore, seems reasonable

to assign the major portion of the intermediate component to regions near the fold surface of a crystal. It can be concluded that a significant contribution to the heat of melting arises from

this region.

The time constants for the long relaxing (crystalline) components vary considerably.

Unfortunately, the mechanism of this very slow relaxation is not fully understood. In the isotropic

samples there seems to be a definite dependence on lamellar thickness, but comparable lamellar

r thickness in drawn versus isotropic samples do not yield comparably long T^s. An interpretation of

this difference is that cold drawing produces crystallites which contain more crystal defects than

in melt crystallization. Whether this ultimately will affect creep is possible, but not known.

Quantitative Determination of the Monoclinic Crystalline Phase in Polyethylene

Under certain circumstances of mechanical deformation, the monoclinic crystalline phase appears

in polyethylene. This phase can be detected easily by x-ray wide angle techniques, however, the

quantitative determination of the relative amounts of monoclinic and the usual orthorhombic

crystalline forms in polyethylene is a more difficult task using x-ray techniques. Solid state 13 C NMR provides a way of distinguishing these two crystalline phases. Moreover, it has been

demonstrated in a ultrahigh molecular weight sample that the ratio of spectral intensities is the

true ratio of amounts of these phases present. It has also been argued that the NMR technique, when

reasonable care is taken, will give very good quantitative results, no matter what the history of

the sample preparation is.

Investigation of Cellulosic Materials Used in Papermakinq

This work was partly sponsored by the Bureau of Engraving and Printing (BEP). The remaining

work was undertaken in collaboration with Professor Rajai Atalla of the Institute of Paper

Chemistry.

The work sponsored by BEP was a continuation of efforts to examine changes in cellulose-water

interactions and changes in microstructure which occur during mechanical beating of pulps used in

papermaking. In addition, any comparisons of different raw materials, notably cotton and wood

cellulose, are important because BEP is looking for cheaper substitutes for currency paper which now utilize primarily cotton and linen celluloses.

Previous 13 C NMR studies of cotton and wood pulp had pointed to the conclusion that wet beating

did not change the microstructure of the elementary fibril, i.e., there was no significant increase

in surface area which could be attributed to wet beating. Certain possible distortions of the NMR

spectra, which could reflect on the validity of these conclusions, were recognized at that time and

part of this year's effort was to investigate whether these spectral distortions were significant.

26
The results of those experiments suggest that no significant intensity distortion occurs between the

spectra of the wet and wet beaten materials, be they cotton or wood pulp. However, relaxation time

evidence suggests that the wood pulp has picked up paramagnetic impurities which shorten its

relaxation times so that the relative signal strength of the surface resonances compared to

crystalline interior resonances is smaller by the order of 10 percent in the wood pulp relative to

the cotton. Thus, whereas some distortions exist which increase the relative intensities of the

interior crystalline resonances compared with the remaining resonances, the surface area changes due

to wet beating in any of these materials, are correctly monitored and are undetectable.

With regard to the interaction of cellulose and water, one of the interesting results is the

similarity (within 15 percent) of magnetization transfer rates between water and the cellulose

matrix in the wood pulp compared with the cotton. In the magnetization transfer experiments, proton

spin magnetization is prepared to be non-zero only in the water as an initial condition. Then, due

to proton chemical exchange, or dipolar spin exchange, some of the magnetization from the water

moves into the cellulose. In the wet and wet beaten samples, the amount of water protons is well i r» excess of the number of cellulose protons, so magnetization transfer occurs in the presence of a largely constant water magnetization. The rate of transfer, normalized to the amount of cellulose

present, might then be approximately related to surface area. The wood pulp was found to have a transfer rate in both the wet and wet beaten preparations about 15 percent higher than that in the

cotton preparation. If these rates reflect relative surface areas, this is a surprising result,

particularly from the point of view that the non-freezing water in the wood pulp was measured to be

SO percent higher than that of cotton. This would suggest that on average, some non-freezing water

is not in contact with the surface, or perhaps that the few percent residual lignin in the wood pulp

modifies the water/cellulose interaction in such a way that even though water does not freeze,

magnetization transfer rates are partially inhibited.

The work carried out jointly with Professor Atalla focussed on the use of magic-angle spinning

techniques for obtaining 13 C spectra in order to investigate heterogeneity of crystal structure in

native celluloses. The interesting result of this work is that native cellulose appears to be a crystalline composite of two different forms. The exact nature of the differences is not defined by

the NMR. The possibility that this heterogeneity may also be reflected as heterogeneity in

mechanical properties or in water-cellulose interactions could have significant consequences in

dictating end-uses of these various native celluloses.

The Morphology of Crystalline Polymers

F. A. Khoury, L. H. Bolz, and J. Mazur

Investigations on the morphology of crystalline polymers during the past year have been mainly

in the areas outlined below.

The Effect of Uniaxial Extension on the Fine Structure of Ultra High

Molecular Weight Polyethylene (UHMWPE )

This work is sponsored by the Bureau of Medical Devices of the Food and Drug Administration.

It is part of a study of the relation between the fine structure and the mechanical properties of

UHMWPE. This polymer is used in the manufacture of several types of orthopedic protheses.

The deformation of compression molded specimens of UHMWPE (M.Wt. 2xl06 -4x 106

) when they are stretched uniaxially i*s characterized by the following features [1,2]: (1) In contrast with lower

molecular weight polyethylenes (e.g., M.Wt. 1x10s

) the specimens do not exhibit any gross necking.

(2) The stretched specimens contract substantially when they are released under zero tension. For

example, specimens made from polymer of M.Wt 2x10s which were stretched to strains of 0.25 and 3.0

at room temperature had residual strains of 0.1 and 1.9 respectively 24 hours after they were

released. (3) For initial strains of up to 3, deformation does not occur uniformly throughout the

specimens. This feature is associated with the retention of a memory of the "grain-like" character

of the raw polymer in the molded samples, even though the polymer is heated to 60 °C above its

melting point during the molding process. Evidence derived from light and scanning electron

microscopical studies indicates that regions corresponding to the boundaries between the original raw polymer "grains" deform preferentially. (4) The weight percent crystallinity of unstretched

specimens (which varies slightly with molecular weight) is close to 60 percent, and the unit cell

structure in the crystalline regions is the commonly observed orthorhombic structure. The majority

of the crystallites in deformed specimens (stretched/ released) having residual strains in the range

27
0.1 to 2.9 are also orthorhombic. These specimens also contain a small fraction of the metastable

monoclinic crystalline phase of polyethylene.

Current investigations are aimed at determining the fine structural changes which occur during

the initial stretching of specimens to various strains, and upon subsequent contraction when the

tension is released. The manifestation of polymorphism (i.e., the occurrence of the monoclinic

crystalline phase in addition to the orthorhombic phase) and the progressive changes in orientation

of orthorhombic and monoclinic phases during stretching up to a strain of 1.0 has been examined

using wide angle x-ray diffraction.

The following are among the features observed: (a) The lowest strain at which the occurrence

of the monoclinic phase was observed was 0.05. (b) At a strain of 1.0 the distributions in the

angle of inclination of the chain axis in the orthorhombic and monoclinic crystallites relative to

the stretching direction are peaked at inclinations of about 36° and 30°, respectively, (c) A substantial decrease in the content of monoclinic phase occurs in all the samples stretched to strains in the range 0.05 to 1.0 when they are released and allowed to contract under zero stress.

(This has also been found to be the case in specimens stretched to a strain of 3.0).

Small angle x-ray diffraction and electron microscopy are being applied to examine the changes

in morphology (texture) associated with the changes in crystalline orientation and the manifestation

of. polymorphism mentioned above. The application of 13 C

' NMR as a method for determining

quantitatively the relative amounts of the orthohombic and monoclinic phases in UHMWPE is described

elsewhere in this report.

The Morphology of Polyethylene Crystals Grown From Solution

A study of the effects of crystallization temperature and molecular weight on the lateral

growth habits and the aspect ratio r (r = ratio of the dimensions of the lamellae parallel to the

[010] and [100] directions) in polyethylene crystals grown from 0.01 percent solutions in heptyl

acetate and dodecanol at temperatures in the range 95 °C to 120 °C has been completed. Scanning

transmission electron microscopy coupled with electron diffraction are currently being used to determine the nature of the non-planar conformation of the crystals whose aspect ratios vary between

1.6 to 6 depending on solvent, crystallization temperature and polymer molecular weight. Interest

in these crystals stems from their usefulness as models (admittedly idealized ones) for the

constituent lamellae in polyethylene spherulites grown from the molten state [3]. One of the

objectives of our current work is to determine whether the relationship between crystals having a particular aspect ratio and the corresponding crystal conformation is unique or whether it varies

with the molecular weight of the polymer.

The Energies of (110) and (200) Folds in Polyethylene Crystals

The energies of (110) and (200) folds in polyethylene crystals are ’of interest in the

elucidation of the origins of two features of the morphology of solution-grown crystals and that of

the constituent lamellae in melt grown spherulites namely: (1) The occurrence of fold staggering

resulting in the formation of hollow pyramidal, tent-like or otherwise non-planar lamellae, and (2)

the dependence of the lateral growth habits of the lamellae on the crystallization conditions. The

feature of interest in the latter context is the dependence of the aspect ratio r (r = ratio of the

dimensions of the lamellae parallel to the [010] and [100] directions) in the crystals on the

crystallization conditions. The ratio r is governed by the ratio of the growth rates normal to the

(110) and (200) faces. The higher that ratio the higher r.

As an initial step in examining the possible relationships between the above mentioned features

and the (110) and (200) fold energies, minimum energy calculations for models of such folds were previously carried out for the following cases assuming adjacent reentry: (a) (110) folds

surrounded by and interacting with kindred folds situated in the same and in adjoining (110) planes,

lamella surface (001); (b) (200) folds surrounded by kindred folds situated in the same and

adjoining (200) planes, lamella surface (001); (c) (200) folds surrounded by kindred folds packed in

a staggered manner, i.e. , lamella surface (201).

Calculations have now been completed for three models of staggered (110) folds, namely for the cases in which the lamella surface is (112), (111), and (312). The results expressed in kcal/mole

of fold are summarized in Table I in which we confine ourselves to giving data for the energetically

most favorable among the various models we have considered for each type of unstaggered or staggered

folds containing 7 methylene groups in the fold.

28
Table I

(110) Fold Energy (kcal/mole of fold) (200) Fold Energy (kcal/mole of fold ) (001)

surface (unstaggered) 5.66 (001) surface (unstaggered 8.68

(112) surface 17.49 (201) surface 7.54

(111) surface 6.73

(312) surface 7.73

As can be seen from this table staggering results in a lowering of the energy of (200) folds.

This is not the case however in the (110) folds. Since, for example, the folds in the distinct

constituent (200) and (110) sectors in polyethylene crystals grown from xylene are staggered, this

latter result is unexpected and remains unexplained at present.

Comparison of the energies of (110) and (200) folds is also of interest in connection with the

known effects of crystallization temperature on the lateral growth habits of polyethylene crystals,

for the following reason.

When the crystallization temperature is increased, the aspect ratio r of the crystals becomes

larger, i.e.

,

the ratio of the growth rates normal to (110) and (200) faces increases with

crystallization temperature. An analysis [4] of the variation of r with temperature for crystals

grown from solution in xylene in terms of the kinetic theory of polymer crystal growth, has led to

the result that the ratio of the end (fold) surface free energies, cr20°/a110

, associated with (200)

and (110) folds should

bg greater than urrjty. a^S/cr11# was found to be between 1.1 and 1.3 depending on the growth regime assumed. The models of staggered folds which correspond most closely to

those in the crystals whose growth habits were used as a basis for the above-mentioned analysis are

the [(110), (312) surface] and the [(200), (201) surface] models. The results of the fold energy

calculations for those folds would have been consistent with the results of the analysis of the

crystal habits had the energy of the latter type of (200) fold been greater than that of the [(110),

(312) surface]. As can be seen from Table I, this is not the case. The calculated energies for

these two types of folds are very nearly equal. The energy of the (110) fold is in fact ~ 0.2

kcal/mole higher than the (200). A possible explanation of the apparent discrepancy between the

results of the fold energy calculations and the analysis of crystal habits is that (i) statistical

variations from the regular type of stagger assumed in the fold energy calculations occur in the

crystals and (ii) that these variations give rise to deviations from the calculations based on the

idealized models.

[1] McKenna, G. B. ; Khoury, F. A.; Crissman, J. M. Nat. Bur. Stand. (U.S) NBSIR 81-2209; 1981.

[2] Crissman, J. A.; Khoury, F. A.; McKenna, G. B. Nat. Bur. Stand. (U.S.) NBSIR 82-2493; 1982.

[3] Khoury, F. A. Faraday Disc. Chem. Soc. 68: 404; 1979. [4] Passaglia, E. ; Khoury, F. A. in

press.

The Necking of Semi crystal 1 ine Polymers in Tension

L. J. Zapas and J. M. Crissman

In tensile tests on polymeric bars the initial motion of homogeneous uniaxial extension can change to inhomogeneous motion called "necking." The occurrence of a neck is influenced by

environmental factors such as temperature, pressure, and ambient atmosphere, as well as material

related properties such as molecular weight, molecular weight distribution, and specimen preparation

history which may be important in determining the degree of crystallinity. Although the phenomenon

of necking is readily observed in most semi crystall ine polymers, it can also occur under certain

conditions in glassy polymers. Until quite recently most of the published work was concerned with

studies of the necking process in polymers in which the deformations involved were accomplished with

a hard machine where the specimens were extended at constant rate of clamp separation.

More recently, Zapas and Crissman [1-3] reported the results of uniaxial creep experiments

under constant load for different polyethyl enes under varied loads and temperatures. Several of

these experiments lasted for months before necking was observed. A graphical procedure was proposed

for estimating the time t

£

of first departure from the initial spatial homogeneous motion induced in

a tensile creep specimen; t

c often preceded by a constant factor the time at which the neck became

easily visible. Zapas and Crissman considered that necking in polymers occurred due to an instability arising from the non-linear viscoelastic behavior of the specimen.

29
f e55i« Bri of \zv £

j who er:

ded the

£

d\szx znszz ss zsxss a^7««Mss:

oTt~t=f

h history.'

bdt “ d°dS

^ *" eXpla"ati °" for “a TMon of tho^noc"! whTch depend!

s:esM

^

Tt^hj^ dKsr. ^HFSf'pr-zv

betwaen the ihstability theory of Bernsteih ahd Zapas and the experimental resoUs ” COnSlstenc5'

References

rin £ a

?as ’ » Crissman, J. M. Poly. Eng. & Sci. 19(2): 104- 1979

[2] Cnssman, J. M. ; Zapas, L. J. Poly. Eng. &Sci. 19(2): 99; 1979

L3J Z

Dap?

S

’cl;' J ‘C L ^Ir5 ?

3"’ J - M * Durab ility of macromolecular materials.

K. K. tby, Ed. ACS Symp. Series, No. 95: 301; 1978.

[4] Bernstein, B. ; Zapas, L. J. J. Rheol. 25: 83; 1981.* [5] Ericksen, J. L. Elasticity 5: 191; 1975.

[6] B7er ^

ei ^6

2* ’ Kearsley> E- A.; Zapas, L. J. Trans. Sco. Rheol.

A_ Study of the Morphology and Mechanical Properties, and Thpir Dependence

fthyl'ene

3 HlSt° ry and Processing of Ultra High Molecular Weight Pol^

J. M. Crissman

orthopedic SMS ifeUml" ?“

“tUrd ° f 3

tim^depeodent processes wh^ch Result

1

* fronf^

v

! ^ ^J a ^’^^a^cTVail^rehhdepends 'upon

SSKS,* spherul Ue

r «

Polymer Science and Standards Division 1981 and isV Annual PeportI

P ^ ' S C°"ta 'mad 1n the

elsewhere^n thuX?^’0®' ° f “h1Ch haVe bee" StUd1ad duH "9 the Paat

^ a "» summarited

r;iwhere g(cr)

experiments

temperature

(Kcr,^) = (const)g(cr)t, 1/3

, is a function of stress alone and t x is the

carried out at elevated temperature indicate

is increased.

duration of the creep step. More recent

that the exponent of t x decreases as the

30
Another important area of study, and one which relates to the performance of the polymeric

component of surgical implants, is the influence of y-irradiation on the mechanical properties of

UHMWPE. For purposes of sterilization, the UHMWPE components of prostheses are routinely subjected

to relatively low levels of y-irradiation (2 to 4 Mrad). y-irradiation can produce both crosslinks

and chain scissions. Whether or not a particular property is enhanced or diminished will depend

upon which of the mechanisms is dominant. In normal lower molecular weight polyethyl enes it is

known that radiation increases the tensile modulus and yield stress whilst reducing creep. The

creep and recovery behavior of y- irradiated UHMWPE is being investigated in uniaxial extension for

specimens having radiation dosages in the range 1 to 6 Mrad. It is found that for applied stresses

in the range expected in clinical use (2 to 4 MPa) a dose of 3 Mrad is sufficient to noticeably

reduce the amount of creep. On the other hand, it is also found that does of from 3 to 6 Mrad are sufficient to significantly reduce the environmental stress-crack resistance of UHMWPE from the

value in air.

Information Handbook on Polymeric Materials Used in Orthopedic Devices

J. M. Crissman and G. B. McKenna

A project is underway to write a materials handbook on the principal polymeric materials used

in surgical implants. This work is being done for the FDA, Bureau of Medical Devices, as part of

task 80-01 NBS-BMD Interagency Agreement. Included in the handbook will be sections on raw materials characterization, processing, and characterization of morphology and mechanical properties

of fabricated forms of polymer. The intended audience for the handbook includes the FDA/BMD staff,

resin manufacturers, fabricators, medical researchers, and surgeons.

Instabilities in the Flow of Viscoelastic Fluids

R. W. Penn and L. J. Zapas

The rates of production of many polymer processing operations are limited by the onset of flow

instabilities. Such operations include filament extension processes (the instability is referred to

as "draw resonance") and die extrusion processes (the instability is generally termed "melt

fracture"). Bernstein and Zapas have shown how such instabilities can be related to the time

dependent, constitutive behavior of non-linear viscoelastic materials [1]. Their analysis involves

the behavior of the material in both a "hard device" where the strain is imposed and one observes

the stress and in a "soft device" where the stress is imposed and one observes the strain. In a typical hard device experiment one subjects a specimen to a constant rate of strain at zero time and measures the stress. In the range of high strain rate approaching unstable flow the stress

increases to a maximum and then decays to a steady state value [2]. This behavior was adequately

described by the BKZ fluid [3] but in light of discrepancies between BKZ behavior and the behavior

of these fluids in other strain histories, it becomes of interest to study them in a soft machine

and to obtain a better description of their behavior.

In the current work a Rheometrics Mechanical Spectrometer has been modified so that it can be

operated in torque control. This required the addition of a more stable torque transducer. The

output of this transducer was sent to the "external" input on the position control card and the

position feed back signal was interrupted on that card. Outputs from the torque and position

transducers were linearized and amplified to levels compatible with our digital data acquisition and

control system. The servo-system was tested and optimized with standard Newtonian fluids. At

constant stress these fluids show only a constant strain rate and zero recovery on removing the

stress.

Shear creep and recovery measurements were obtained in cone and plate geometry on a 19.3

percent solution of polyisobutylene 1-100 in cetane at various shear stresses approaching the range

of flow instability. At these high values of stress, the rate of shear ceases to be a monotonic

function of time. It starts off at a large value on application of the step in stress. It then

goes through a minimum before approaching a steady state value. Significant recovery is observed on reducing the stress to zero.

The creep and recovery cannot be correlated using non-linear Boltzman-like superposition. A one dimensional mathematical description is being developed which will correlate the creep and

recovery data. It is a description of a fluid and is properly time invariant. The strain is

31
expressed as the sum of two integrals. The kernal of the first is a non-linear function of the

value of the instantaneous stress. The second is a non-linear functional of the history of the rate

of shear.

[1] Bernstein, B. ; Zapas, L. J. J. Rheol. 25(1): 83; 1981.

[2] Zapas, L. J. ; Phillips. J. C. J. Rheol. 25(4): 405; 1981.

[3] Bernstein, B. ; Kearsley, E. A.; Zapas, L. J. Trans. Soc. Rheol. 7: 391; 1963.

The Distribution of Stresses in Crazes at the Tips of Uniformly

Extending Cracks

E. Passaglia

The work reported in the last report (Polymer Science and Standards Division 1982 Annual

Report) has been brought to a conclusion. It was shown there that in a craze at the tip of a uniformly moving crack, the stress at a point p in the craze is a function of the derivative of the

displacement at that point, under the assumption that the craze thickens by a drawing process. The

stress is thus identified as the drawing stress. Specifically, if 3. is the displacement, and p and

q are normalized coordinates within the craze, then

3p 2it Q J

a(n) (p/n) dn/p-n (D

where C

g is the plane strain compliance. Since the stress is a function of the displacement

derivative, which is equivalent to the draw rate, an integral equation for the stress is obtained in

the following manner.

Over fairly wide ranges of draw rates, the drawing stress of many polymers, is linear in the

logarithm of the draw rate [1], i.e. ,

a

D = ar + CT S 1og s/£

r where e is the draw rate, o

r is the drawing stress at the draw rate er

, and a

g is the rate

coefficient. Denoting the integral in Eq. (1) by I, we obtain as the equation to be solved

°(p) = a

r + as log (3)

where the reference draw rate is arbitrarily chosen to be at the mid point of the craze.

A computer algorithm has been developed to solve this equation. The following assumptions are entered into the solution.

(1) The value of the stress at the craze tip is kept constant to represent the yield stresses.

(2) The value of the stress at the mid point of the craze is treated as a parameter, and solutions

for various values obtained, i.e., for a(0.5)/a(0) from 0.5 to unity.

(3) The value of the rate coefficient is also treated as a parameter and solutions have been

obtained for a

s /ar ranging from 0.03 to 0.3, which covers the range for most polymers.

The stress distributions obtained all show a peak at the craze tip and one at the crack tip, in

agreement with the observations of Kramer [23 - The heights of the peaks are determined by both the

chosen stress at the mid point and the value of the rate coefficient, with the latter largely

determining the height of the peak at the crack tip.

(1] Ward, I. M. Mechanical properties of solid polymers. John Wiley

N.Y. , 1971.

[2] Kramer, E. J. Advances in Polymer Sci. 50: 1983.
Physical Ageing in Polymeric Glasses Subjected to Large Deformations

G. B. McKenna and A. J. Kovacs 1

x Centre de Recherches sur les Macromolecules (CRM), 67083 Strasbourg, France

Upon isobaric cooling through their glass transition range undercooled liquids, including

rubbery polymers, are known to depart from their thermodynamic equilibrium [1]. Non-equilibrium

glassy structures are intrinsically unstable, since they spontaneously evolve towards their

equilibrium structure which depends on temperature alone [2]. This approach towards structural

equilibrium is clearly reflected by the time dependence of the volume and enthalpy of the glass as well as its mechanical (viscoelastic) properties.

The purpose of the present work is to investigate the ageing behavior of polymethylmethacrylate (PMMA) as a preliminary to a larger program to measure dilatometrically the volume

changes of polymer glasses subjected to increasing torsional deformation after various thermal

treatments. Such an attempt should lead, in fact, to some important conclusions (both from

practical and fundamental viewpoints) about the viscoelastic behavior of glasses at moderate and

large deformations as a function of their thermal and mechanical histories.

The results obtained on the ageing behavior of PMMA reveal a few, though significant,

discrepancies as compared to the general picture emerging from previous investigations [3,4]. In the linear viscoelastic range, the relaxation isotherms, measured at increasing ageing times, cannot

be superposed by mere shifting along the time axis below some critical temperature range (60 ° < T_

< 80 °C). This critical temperature range decreases, however, as the deformation increases. Such

effects may be accounted for by a change with increasing ageing time in the shape of the relaxation

spectrum at short times [5].

Furthermore, the shift rate for the torque relaxation function decreases much more rapidly with

increasing deformation’ than does that of the normal force relaxation function. This difference in

shift rates for the torque and normal force responses increases with decreasing temperature, and

implies that the molecular processes controlling the torque (shear) response are less sensitive to

changes in structure (free volume) during ageing than are those determining the normal force

response. A complete understanding of these phenomena requires simultaneous (as opposed to

parallel) measures of the changes in volume, torque and normal force induced by a given deformation

under systematically varied thermal histories. Such . investigations are currently underway at CRM in

Strasbourg using the apparatus described in last year's Polymer Science and Standards Division

annual report [6].

[1] Simon, F. Erg. Exakt. Naturwiss. 9: 222; 1930.

[2] Kovacs, A. J. Fortsch. Hochpolym. Forsch. 3: 394; 1963.

[3] Struik, L. C. E. Physical aging in amorphous polymers and other materials. Elsevier,

Amsterdam, 1978.

[4] Chapter 8 in ref. 4. [5] Kovacs, A. J. ; Stratton, R. A.; Ferry, J. D. J. Chem. Phys. 67: 152; 1963.

[6] Polymer science and standards division annual report. Nat. Bur. Stand. (U.S.) NBSIR 82-2607,

March 1983.

The Effect of Elastic and Plastic Deformation on the Solubility of

Ethyl Acetate Vapor in Polyvinyl i dene Fluoride (PVF£)

J. C. Phillips and A. Peterlin

The transport of liquids into semi crystal! ine polymers has been known to be influenced by the

strain deformation of the polymeric material. Often, the diffusivity and solubility of gases and

vapors in the strained material are also dramatically reduced from those of the unstrained material.

The extent of the reduction of these transport properties depends on the strain level e, the vapor

pressure p, and the elongation time t^. According to the fractional free volume theory (FFV), the

solubility S=c/p (c=equi librium concentration; p=pressure) of the permeant is proportional to the

elastic deformation.

33
Strain recovery measurements were performed in air at 24 °C and in an IR cell at 30 °C as a function of ethyl acetate vapor pressure. The experiments in air were done by elongating the film

on a stretching frame, holding the film at this elongation for a time t^ and then releasing the

film. The decrease in length was followed as a function of time with a cathetometer.

In the IR cell the experiments in the vapor environment were performed by first sorbing the

vapor to saturation and then straining the sample. The sample was held at this strain for a time t^

and the stress was manually nulled to obtain strain recovery as a function of time. From the strain

recovery/time curve, the elastic and plastic components of the total strain were obtained by

extrapolation of the curves to t=o.

The IR cell was also used to obtain solubility data as a function of strain and pressure. The

experimental procedure consisted of stretching the sample and admitting the vapor to the sample

chamber of the IR cell at some time t after stretching. The carbonyl band of liquid ethyl acetate was monitored as a function of time to determine the amount of the liquid adsorbed by the polymer

film. From the sorption curve, the equilibrium solubility, S, was determined from the IR equilibrium absorbance. The results indicate that the FFV concept applies reasonably well to the

PVF2 /ethyl acetate system under uniaxial deformation.

34
PROCESSING AND RELIABILITY OF POLYMER COMPOSITES

The great emphasis on light-weight, energy-efficient materials is producing a rapid growth of

composites as a high payoff application of polymers. The addition of a reinforcement, either

particles or fibers, to polymers can dramatically improve their performance, and as a result they

can be utilized in a wide range of generic applications where the requirements are beyond the

capabilities of simple polymers. This expanded potential has led to increased usage in diverse

areas ranging from transportation to construction. In addition to their light-weight, major factors

behind the expanded applications of composites include versatility in fabrication, high corrosion

and fatigue resistance, and the potential to significantly reduce the need for critical materials

such as cobalt and chromium whose limited supply is of critical concern to the national interest.

Although composite materials have great potential, the same multicomponent composition that is

responsible for their high performance also gives rise to numerous problems with regard to

processing and reliability. Since the composite field is still at an early stage of development,

many of these problems can be directly attributed to a lack of basic knowledge and adequate test

methods. In response to this need, a new Task was initiated in 1982. The objectives were to carry

out long range research to provide industry and other Government agencies with test methods,

materials property data and failure prediction models that are essential if the full potential of

these materials is to be achieved. In line with the two primary problem areas mentioned above, two

major thrusts were developed and these continue to be the basis for the composites effort. The

first seeks to gain a better understanding of the basic science involved in processing and

fabrication of these materials while the second addresses the development of the basic science

concepts, methods, and data needed to assist in improving durability and enhancing the capability

for failure predictions.

Task programs have been developed to address both areas of concern. A number of projects are studying cure, i.e.

,

the chemical reactions that occur during processing and represent the most

important factor in successful fabrication. The work combines a variety of nondestructive

measurement techniques so that a thorough understanding of the processes involved can be developed.

The potential for employing one or more of these techniques for real time on-line control of cure is

also being addressed. The second major thrust area concerns the failure behavior of both particle

and fiber reinforced polymers. Special emphasis is placed on the development of techniques, such as x-ray scattering, which can provide information about the state of the material before and during

failure. The programs seek to understand the basic failure mechanisms in polymers and how these

mechanisms are transferred into composites.

To assist in conducting this broadly based effort, the task is utilizing a number of

cooperative programs as well as the services of experts who spent time working in the Division

during the last year. The cooperative efforts involve programs with NASA Langley Research Center,

the Department of the Treasury, and the industrial research laboratories at Hercules and Hexcel. In

addition, the joint research program with Dr. A. J. Kinloch of the Waltham Abbey Research Laboratory

of the Ministry of Defense in England on the failure behavior of particle reinforced composites is

continuing. Finally, foreign guest workers from Israel, Mrs. H. Weisshaus, and Taiwan, Mr. C. Yu„

have actively participated in these Task programs during the last year.

Interlaminar Fracture of Composites

D. L. Hunston, G. W. Bullman, and W. D. Bascom1

x HercuVes, Inc., Graphite Fiber Aerospace Division, Magna, UT

A major area of concern in the use of continuous-fiber reinforced composites is delamination,

that is, the growth of cracks between the layers of fibers. Delamination can substantially reduce

the performance of composites in numerous ways but compression strength is particularly sensitive to

this type of damage. The conventional polymeric matrix resins, i.e., the material that binds the

fiber together, are very brittle and therefore subject to damage particularly when loaded by impact.

This damage involves matrix cracks which can easily grow into large areas of delamination. The

problems this can generate in practical applications have led to a widespread interest in developing

polymeric matrix materials with improved resistance to both initial damage and subsequent growth of

this damage into delamination. In addition, there is a need to develop design data that can be used

to predict the growth rate of delamination. Unfortunately, although a number of test methods are now being used, few if any have been developed to the extent that they can provide the quantitative

information that is needed.

35
In response to this problem, a joint program has been established among researchers at NBS,

NASA Langley, the University of Illinois, and several composites manufacturers. As part of this

program, NBS is examining the double cantilever beam test method for determining interlaminar

fracture. The tests employ specimens with either rectangular or triangular geometries. A precrack

is generated between fiber layers in the specimen and an increasing load is applied perpendicular to the precrack so that subsequent crack growth occurs between the layers of fibers. The critical

value at which this crack growth begins is noted and converted to a fracture energy using

appropriate equations.

During the past year, the effects of sample lay-up pattern on interlaminar fracture behavior

have been studied and guidelines for specimen design have been formulated (1). In addition,

preliminary experiments were performed to determine the effects of loading rate and temperature on interlaminar fracture behavior. With brittle matrix resins both the resin itself and the composite

exhibit only small variations with changes in these variables over the ranges that are of interest.

Tough resins, on the other hand, have a significant rate and temperature dependent fracture energy.

The decrease in fracture energy with decreasing temperature and increasing cross-head speed is

particularly important because a major concern with composites is damage resulting from impact

loads. As a result, tests were conducted on selected samples of woven fabric reinforced composites

using the double cantilever beam. The results are shown in Table I. These data indicate that,

unl.ike the resin itself, the interlaminar fracture energy tioes not decrease with decreasing

temperature and increasing cross-head speed over this range of conditions. In fact, if a trend

exists, it's in the opposite direction. These preliminary results are encouraging but much more work

needs to be done before the effects of temperature and loading history can be understood and predicted.

Work currently in progress is examining these questions and extending the study to unidirectional

composite specimens.

[1] D. L. Hunston and W. D. Bascom, Composite Technology Rev. , submitted.

2 Table I: Fracture Energy (kJ/m )

Fracture Energy at Cross-Head

Temperature Speed (mm/s)

°C 0.008 0.04 0.8

40 1.7 1.8 1.8

24 1.7 1.7 1.9

0 1.7 1.9 2.0

-25 1.9 2.1 2.4

Failure Behavior of Particle Reinforced Polymer Composites

D. L. Hunston, A. J. Kinloch 1

, and S. S. Wang2

Ministry of Defense, PERME, Waltham Abbey, Essex, England

2 Dept. of Theoretical and Applied Mechanics, University of Illinois,

Urbana, IL

Most of the polymers used in stuctural application are inherently brittle and must be

reinforced or toughened. One empirically developed method that has proven to be quite successful is

the incorporation of small particles of a softer material in a matrix of the brittle polymer.

Although composite materials of this type often have very high fracture energies their failure

behavior is usually quite complex and involves large viscoelastic effects.

In an effort to gain a fundamental understanding of the failure behavior of such materials, NBS

is currently studying two different model systems: a polysulfone filled with polytetrafluoroethylene particles and an epoxy filled with epoxy/polybutadiene particles. The first system

is of interest to the Navy for certain sealant applications while the second serves as a model for

most commercial structural adhesives. The program focusses on developing test methods for such

materials and studying the mechanisms of failure. This is a joint program involving scientists from

the Ministry of Defense (Waltham Abbey Laboratory) in England and the University of Illinois.

36
During the past year an extensive study was performed to examine the viscoelastic fracture

behavior of an rubber-modified epoxy. Based on these results a mechanism for toughening was

formulated. This mechanism involves both dilatation via cavitation in the rubber particles or at

the particle-matrix interface and shear plastic flow of the epoxy matrix. This mechanism explains

all of the observed fractographic features over a wide range of test temperatures and cross-head

speeds [1]. A two parameter failure criterion was then proposed and this criterion fits all of the

failure data over the complete range of conditions studied [2].

The investigation also studied the failure behavior of these materials in adhesive bonds. The

well known dependence of fracture energy on bond thickness was examined and a qualitative

explanation was formulated based on an interaction between the size of the crack tip deformation

zone and the bond thickness. By using this picture, the optimal bcjid thickness could be predicted

with a time/temperature dependent elasticplastic model [3]. The quantitative form of the bond

thickness dependence, however, could not be predicted and thus even a modified fracture energy

approach has not provided a unique failure criterion. By using a nonlinear elastic-plastic

constitutive equation in a finite element analysis, an effort was made to use a "J" integral

approach to address this problem. The results suggest that even this more general approach does not

provide a unique criterion for failure. Consequently, more fundamental studies are required before

the failure behavior of rubber-modified epoxy adhesives can be understood and predicted.

[1] Kinloch, A. J. ; Shaw, S. J. ; Tod, D, A.; Hunston, D. L. Polymer; in press.

[2] Kinloch, A. J. ; Shaw, S. J. ; Hunston, D. L. Polymer; in press.

[3] Hunston, D. L. ; Kinloch, A. J. ; Shaw, S. J. ; Wang, S. S. Proc. Inti. Symp. on adhesive joints;

in press.

Cure Monitoring in Polymers and Composites via Nondestructive Techniques

D. L. Hunston, B. M. Fanconi , F. I. Mopsik, C. C. Yu 1

, and H. Weisshaus2

1 Chun-Shan Inst, of Science & Technology, Taiwan

2 Armament Development Authority, Haifa, Israel

The rapidly expanding use of polymers in structural applications has generated much interest in

the new field of polymer processing with chemically reacting (i.e. , polymerizing) materials. The

commercial importance of these polymer systems combined with the general lack of knowledge in this area has produced an urgent need to investigate the basic science of processing with reacting

polymers and to develop nondestructive test methods to explore this area. These needs include both

laboratory test techniques which permit the study and optimization of the processing reactions and

on-line techniques that can be used to monitor and adjust processing variables.

A fundamental approach to this problem, however, requires a variety of measurement techniques

since important events occur on the molecular level, the morphological level, and the mechanical

properties level. The approach taken in the program currently underway in the Polymers Division is

addressing this difficulty by combining techniques from three different areas: spectroscopy,

di electrometry, and mechanical properties characterization. The spectroscopic technique (Fourier

transform infrared measurements) has the potential to examine curing (polymerization) reactions at a molecular level indicating what the reactions are and how rapidly they proceed. The mechanical

characterization technique involves the ultrasonic test method developed previously in the NDE

program, [1,2]. In this method an ultrasonic shear wave is propagated in a thin quartz strip that

is coated with the sample to be tested. By measuring the wave in the quartz, information related to

the mechanical properties of the coating can be obtained. Consequently, this method provides data

directly relevant to processing and performance. The dielectric experiments, which utilize the

unique NBS time domain dielectric spectrometer, provide information on mobilities at a morphological

level, i.e., a size scale intermediate to the other two methods. By combining these three

techniques, it will be possible to obtain a much more complete understanding of the transformations

that occur during reactive processing of polymers.

During the past year a feasibility study was conducted to determine if all three of these

techniques could be used to monitor cure in similar chemically reacting polymer systems. These

tests confirmed that such measurements could be made and thus demonstrated that an indepth development of each technique as a cure monitoring tool would be advantageous. In previous years the

ultrasonic technique has been shown to be a valuable cure monitoring device which has a unique

capability to nondestructive! y follow changes that occurred during the curing of polymers in thin

films or restricted layers. In addition to this the technique has the potential for quantitatively

37
determining mechanical properties. Over the past year this latter capability has been implemented.

Since no other technique can provide equivalent measurements the only way to validate this

capability for highly viscoelastic materials is to compare the results from the ultrasonics test

with extrapolated values obtained by applying time- temperature superposition to low frequency data

from torsional oscillation experiments on a thermorheologically simple material. Such tests were

conducted using a polyvinyl chloride plastisol and the results are shown in Table I. In light of

the large extrapolations involved (5 decades), the agreement between the two sets of results is

excellent.

Method

Table I

Shear Storage

Modulus (MPa)

Shear Loss

Modulus (MPa)

Ultrasonic Tests 0.70 1.8

Estimate from Superposition 0.78 2.1

The successful development of this technique has led to a desire by a number of other groups to

implement a similar device for addressing their particular problems. For example, NBS is currently

constructing such a device for the Bureau of Engraving and Printing so they can use it to study

drying of printing inks [2].

The Fourier transform infrared studies of thermally initiated curing of vinyl ester systems was reported previously [3]. During the past year infrared studies have been extended to UV initiated

cure systems. These systems are desirable as it is not necessary to mix components to initiate the cure reaction. Thus, time available for fabrication is not limited as it is for the two component

systems that are presently in use.

Vinyl ester systems containing UV initiated accelerators were examined as a function of the

initial UV exposure. Somewhat surprisingly, the subsequent degree of cure (post curing) behavior of

the UV initiated systems was not substantially different from that of the thermally induced curing

resins. What is measured by the FT-IR technique is the remaining unreacted double bonds. Based on our results mixing of the two component systems was reasonably complete and the substantial amount

of unreacted groups cannot be attributed to a nonuniform distribution of initiators.

Subsequent work will focus on the relationship between the functionality of the reactive

monomers, gel point, curing temperature and glass transition temperature of the incompletely cured

material. The glass transition temperature effectively determines the maximum useable temperature

of the system. This temperature is given by the temperature of cure in low functionality systems.

It is anticipated that increasing the functionality will lead to a higher use temperature for a given curing temperature.

Future work in this program will also focus on the development of the time domain dielectric

spectrometer as a cure monitoring device. This instrument, which was developed at NBS, has the

capability to measure the dielectric constant of a material over a very wide range of times (or

frequencies) in a single experiment. Preliminary studies on the latter phases of cure have shown

that this capability makes it possible to follow changes in molecular mobilities that would

otherwise be very difficult to detect because they appear only in the very low frequency range.

This type of information is particularly useful since the final degree of cure is often a critical

parameter in processing. As a result further development of this technique is highly desirable and

will be a major goal next year.

[1] Hunston, D. L. ; Cure monitoring of thermosetting polymers by an ultrasonic technique, Review of

Progress in Quantitative Nondesstructive Evaluation, D. 0. Thompson, ed. p. 1711, Plenum Press,

1983.

[2] Hunston, D. L. ; Relationship between mechanical properties and performance of inks as the basis

for quality control techniques. Nat. Bur. Stand. (U.S.) NBSIR 83-2691, April 1983. [3] Annual

Report of the Polymers Science and Standards Division, Nat. Bur. Stand. (U.S.) NBSIR 82-2607,

March 1983.
Chemorheology in Polymerization Systems Initiated by Oxygen

D. L. Hunston and G. W. Bullman

Many commercially important coatings dry via cure reactions that are initiated by oxygen and

polymerize through double bond reactions. To study these important systems, however, a means must

be found to expose all of the sample to oxygen. Experiments conducted at NBS have developed a test

method to accomplish this. In this technique, the sample is placed on a 2 roll mill. The thin film

generated on the mill maximizes the exposure to oxygen while the mixing action between the 2 rolls

constantly renews the outer surface thus preventing the formation of an outer crust.

In one set of experiments, the mill was heated to 80 °C, and periodically small amounts of the

sample were removed and tested for mechanical properties. In this way, the rheological changes

associated with the cure reactions could be followed. One particularly useful measurement was the

steady flow shear viscosity. If this parameter is measured at a series of shear rates, the results

can be analyzed in terms of an initiation time followed by an exponential growth in viscosity with

time (linear relationship in a log-linear graph). The slope of the best fit straight line and the

intersection between this line and a horizontal line at the zero time viscosity value can then be

used to characterize the early phase of the cure reaction in these systems [1].

[1] Hunston, D. L. ; Rushford, J. L. ; Newitt, W. R. ; Vaudreuil, B. A. Chemorheology of Thermosetting

Polymers, C. May, Ed., ACS Symp. Series; in press.

Novel Exciaer Fluorescence Method for In-Si tu Monitoring of Composite

Materials Manufacturing

F. W. Wang, R. E. Lowry, and W. H. Grant

We have developed a novel excimer fluorescence method that can be adopted for monitoring in

situ and nondestructive^ the manufacture of components made of fiberglass-reinforced composite

materials. The need to monitor and control the processing variables in the manufacture of these

composite components becomes pressing as they become widely used in critical aerospace applications.

The excimer fluorescence method monitors the resin viscosity that must be carefully controlled

during processing if the rejection rates of these components are to be reduced.

The excimer fluorescence method determines the resin viscosity by measuring the fluorescence

properties of a trace amount of an excimer- forming probe dissolved in the resin. Each of the

chromophores attached to the probe molecule can fluoresce as an isolated excited chromophore or combined intramolecularly with another chromophore in the ground state to form an excimer that

fluoresces at its characteristic wavelengths. Since the rate of excimer formation depends on the

medium viscosity, this viscosity can be determined from the ratio of the fluorescence intensities of

the excimer and the isolated chromophore, when the resin is continuously illuminated. This method

was successfully used to monitor the viscosity changes of samples of methyl methacrylate undergoing

polymerization.

This excimer fluorescence method can even be used to determine the resin viscosities of

inhomogeneous or irregularly-shaped samples. For example, it has been successfully used to monitor

the viscosity change of a methyl methacrylate sample filled with fiberglass. This insensitivity to

inhomogeneity or irregular geometry, is important for ijn situ monitoring of the curing of composite

structures in the factory environment.

Analysis of Thermoset Resin Polymerization Kinetics

G. A. Senich, R. E. Florin, and J. C. Phillips

Composite parts are produced from thermoset resins by molding or laminating operations which

generally require either a long time in a closed mold or press at a high temperature and pressure or

a lengthy post-cure outsSde the mold, again at high temperature. These long times for thermal

polymerization or curing, on the order of one to several hours, restrict the rate of production of

composite articles. Rapitfly curing thermoset matrix resins could greatly reduce processing time and

permit a large increase in the volume of fabricated composite output.

39
Radiation initiated polymerization is one method for obtaining the rapid cure of a thermoset

composite matrix. The most common radiation sources used to induce curing reactions are electron

beams (EB) and ultraviolet (UV) light. Since the energy imparted by UV radiation is much less than

for EB, special excitable molecules referred to as photoinitiators must be added to insure that

exposure to UV light yields the desired chemically reactive species. Additional methods of

promoting polymerization by radiation include infrared (IR), microwave, and high frequency curing.

It has been estimated that of all the radiation curing methods, IR has the broadest potential for

use although, at present, EB and UV are exploited commercially to a much greater extent. Many

industrial procedures utilize radiation and radiation curing, some for treating thin films and

coatings and others for bulk articles. They include such diverse commercial processes as cross- linking of wire insulation, rubber tires, and dental fillings, preparation of resists for

microelectronic device fabrication, setting coatings and printing inks, and sterilizing medical

supplies.

The science and technology of curing organic materials with radiation is the subject of a review prepared as a background for further research [1]. Included are discussions of definitions

of the curing process, motivations for exploiting curing with radiation, basic principles of the

interaction of various forms of radiation with matter, and kinetic schemes for polymerization and

oxidation, chain reactions which can be initiated by molecular species excited by the aforementioned

interations. Various radiation sources, the equipment necessary to affect a radiation cure, and

• resin systems suitable for use with these sources are considered, and some practical problems unique

to each radiation method are indicated.

The application of radiation curing to industrial operations is discussed, with particular

emphasis given to processes which employ relatively thin films, such as inks and coatings.

An experimental program to measure the overall rate and determine reaction kinetics of

thermoset curing reactions is in progress. The principle thermosetting systems of interest,

epoxies, acrylated oligomers, and unsaturated polyesters/acrylics, are being initiated with UV and

IR radiation as well as by more conventional thermal means. The effects of initiator structure,

concentration, and solubility, reactant concentration, film thickness, reaction temperature, and

radiant intensity are being studied. FTIR spectroscopy is being used to determine the extent of

reaction of the participating chemical functional groups as curing progresses. Viscometric

techniques at a variety of shear rates are employed to measure the increase in sample molecular

weight while polymerization is taking place. Results from these experiments are being coordinated

with the findings from photopolymerization measurements on identical materials by thermal analysis

methods to provide a more complete explanation of the bulk polymerization kinetics of these rapidly

curing thermoset resin systems. Novel methods for studying the kinetics of rapid curing, such as monitoring the mechanical property changes of a UV- irradiated film on a substrate by ultrasonic

shear wave propagation, are also being employed. This program is providing a .better understanding

of the chemistry that occurs during processing of thermoset polymers and is aiding in the

identification of materials for special applications, such as rapidly curing thermosets suitable for

use as ink vehicles or repair formulations for the quick mending of composite parts.

[1] Senich, G. A.; R. E. Florin. Radiation curing of inks and coatings.

Nat. Bur. Stand. (U.S.) NBSIR 83-2722; June 1983.

Measurement of Photopolymerization of Polymers by Thermal Methods

J. H. Flynn

Considerable interest and activity has been exhibited in the past few years in polymerization

reactions initiated by visible and ultraviolet light. Areas in which applications of photocuring

are of interest include the ink, coatings, and dental fillings industries where techniques of rapid cure which avoid excessive heating and solvent removal are desirable.

Differential Scanning Calorimetry (DSC) is being used to monitor the kinetics of these

photocure processes. This technique is particularly well suited for these investigations as the

amplitude of a DSC trace is a robust measurement of the rate of cure and the area beneath the trace measures the enthalpy of reaction.

40
The effects of light intensity, initiator concentration, temperature, specimen thickness, etc. upon the polymerization kinetics are being investigated for several industrially important resin”

initiator systems. A post irradiative “dark" reaction has been detected and it is also being

investigated.

Variable induction periods and other anomalies becloud the initial phases of these reactions.

Therefore, a technique of analysis has been adapted to these conditions which obtains kinetic

parameters from derivative data in which the initial concentrations of reactants may remain unknown.

By this method, the amplitude of the DSC trace, dq/dt, is represented by the equation

dq/dt = k(q

Q

-q)

n

, where q is the enthalpy and t, the time. The rate constant, k, and reaction

order, n, are determined from an appropriate function of dq/dt vs. time, after an approximate value

of n has been estimated from tables in which ratios of times to reach fractions of completion are given for values of n. These analyses permit the determination of parameters for the relationship

between rate and the factors influencing it, to be used in modeling mechanism.

The low thermal conductivity of polymeric materials is a chronic problem in the treatment of

their kinetics as often heat flow becomes a rate-limiting factor. A simple, novel method has been

developed to determine the thermal conductivity of polymer sheets by DSC. The slope (or intercept)

of the melting peak of a metal placed on top of the polymer specimen and the slope (or intercept) of

its melting peak in a bare pan are determined. Theory of heat flow in DSC has been developed so that the thermal resistance and time constants for thermal flux in the polymer specimens can be

determined from these data. The method holds promise of becoming a simple, quick, and

nondestructive method for thermal conductivity measurements of thermally insulative sheet materials.

Data from these new techniques are being applied to modeling the kinetics of

photopolymerization reactions in close conjunction with work on the investigation of thermoset resin

polymerization kinetics by infrared spectroscopy and rheological property measurements, which is

also being undertaken -in the Polymer Science and Standards Division.

41
ADDITIVE MIGRATION AND CHEMICAL DURABILITY OF POLYMERS

The most promising areas of growth in polymer markets are in construction, transportation, and

electrical systems where long-term durability is essential to competitive performance. To compete

successfully in these markets, our country needs scientific research on the mechanisms by which

polymeric materials are degraded because of environmental and other imposed stresses. In fact, a recent National Research Council report states, "Mechanistic data on degradation are essential (1)

in identifying possible stabilization processes to slow degradation, and (2) in developing shortterm methodologies for predicting service life."

Research this year on degradation mechanisms and rates includes investigations of the

hydrolysis of polyester polyurethanes, the degradation of polyurethane tubings in media simulating

body fluids, and the long-term stability of polyester-based recording media. In addition, we have

carried out a collaborative program with the Building Materials Division to investigate the kinetics

and mechanism of the photodegradation of PMMA, a polymer widely used for solar cover plates.

Protective additives are needed for fabrication and long-term use of most polymers. In use, these additives inevitably diffuse through the polymer to some extent and may migrate out of the

polymer entirely. The polymer is then left with poorer properties or made more vulnerable to degradation and failure. This is a major failure mode of polymers, and lifetime prediction methods

must explicitly include the rates of additive diffusion along with the rates of the inhibited and

uninhibited degradation reactions. The number of commercially usable polymer- additive combinations

is too large to be considered efficiently on a case-by-case basis. The emphasis in this task is,

therefore, on the development of general principles or models of diffusion that are applicable to

the widest range of generically important systems. In addition, knowledge of the general principles

which control diffusion through solid polymers is important to the design and evaluation of improved

additive systems. Work this year on the migration of additives includes measurements of diffusion

rates by solvent extraction and by inverse chromatography and investigations of slow diffusion in

solid polymers by fluorimetry.

Prediction of the Long Term Stability of Polyester-Based Recording Media

D. W. Brown, R. E. Lowry, and L. E. Smith

The stability of poly(ethylene terephthalate) is being studied for the National Archives in

order to predict its long term behavior as the base for film and magnetic tape. The project is

supposed to last for four to five years. A report has been written that contains results of the

second year's work. Film base, photographic film, and electrographic film are being aged at several

temperatures and relative humidities, RH. Acid contents, mechanical properties, and molecular

weight have been measured at intervals. The rate of increase in acid content, k, provides a useful measure of the degradation rate. Data for films aged between 115 and 55 °C at’ 100 percent RH obey

the equation Ln k = 39.3 - (14000A), where k is in percent/day and T is the absolute temperature.

The water content is included in k, which is approximately proportional to RH. Lifetimes of the

films appear to be equal to 69.3/k days. Extrapolation of 25 and 20 °C gives 400 and 900 years for

the lifetime at 100 percent RH. A more sensitive analytical method than now used will be required

to make useful measurements of acid content at 35 °C, even after samples have been aged for five

years. Two films have always failed before the others. The short-lived films might well be stored

with others, since failure of the former would warn of the approaching failure of the latter.

Magnetic tapes are also being aged, primarily to study the binder that holds the magnetic oxide

to the substrate. Binder on five brands of tape that were aged at 60 °C become cross-linked at RH of zero and 11 percent, changed little at 30 percent RH, but degraded at 100 percent RH. The binder

on tapes aged at 85 °C and 100 percent RH first degraded severely and then appeared to cross- linx

slightly. Badly degraded binder was not gummy but was easily detached from the substrate. Model

binder aged at 85 °C and 100 percent RH eventually became brittle.

Hydrolytic Degradation of Polyester Polyurethanes

D. W. Brown, R. E. Lowry, and L. E. Smith

A manuscript entitled "Equilibrium Acid Concentrations in Hydrolyzed Polyesters and Polyester

Polyurethanes" was prepared and submitted to the Journal of Applied Polymer Science. Conclusions

are the same as those in last year's report: namely, that equilibration does not set a practical

42
limit to the hydrolytic degradation of thermoplastic polyurethane elastomers and that chemical rate

constants calculated in the conventional manner appear to increase with the relative humidity.

Attempts were made to develop a general mechanism to fit data from the hydrolytic degradation

of polyester diols in the presence of different concentrations of carbodi imide, an hydrolysis

stabilizer. These . were not very successful, despite allowing for possible hydrolysis of the

carbodiimide, hydrolysis of the acyl urea produced in the reaction of acid with carbodiimide, and

uncatalyzed and acid-catalyzed ester hydrolysis. More data will be obtained with polyester

polyurethanes before making additional attempts to modify the mechanism.

Studies With Polyether Polyurethane Tubing

D. W. Brown, R. E. Lowry, and L. E. Smith

Polyether polyurethane tubing is used for electrical insulation on pacemaker leads implanted in

blood vessels. Failure of this tubing has been reported in the literature but the causes and the

exact nature of the failure are in dispute. The Bureau of Medical Devices is sponsoring an i_n vitro

aging study of the tubing to help guide their investigation of the extent and causes of any problem

with the tubing.

Samples of tubing have macroscopic and microscopic irregularities that are indicative of

orientation gradients. It is not known if these can lead to failure. There were too many

irregularities to avoid incorporating some in any piece more than a few centimeters long, so samples were prepared without trying to select regions with and without the irregularities. Some samples were stretched on glass or Teflon rods in order to accelerate the aging. Extension ratios in the

circumferential and axial directions were of the order of four and two, respectively. Other samples were bent into small radius bends to. induce stresses. Eight different media were used, including

air, water, Ringer's solution, bovine serum, and several mixtures containing lipids, bile salts, and

hydrogen peroxide. The degradation was followed by measuring the molecular weight by gel permeation

chromatography. The active media were water, Ringer's solution, and hydrogen peroxide. Only the

hydrogen peroxide solutions affected unstretched samples. Comparison of results from samples on glass and Teflon rods indicated that the glass was chemically active, since degradation on the

Teflon was only one third as great.

These experiments are being repeated using fewer media and a greater variety of stretching

conditions. Only Teflon rods are being used to stretch the samples.

Solar Type Photolytic and Thermal Degradation of Plates of Poly(Methyl

Methacrylate )

B. Dickens

A joint program between the Polymer Science and Standards Division of the Center for Materials

Science and the Building Materials Division of the Center for Building Technology has provided a chemical mechanism for the destructive, effect of sunlight on a transparent glazing material. This

information explains the deleterious effects of oxygen, unpolymerized raw material and high

temperature, and is an important step in the achievement of estimates of lifetimes in service.

The mechanical properties of polymers are dependent on the lengths of the chain-like polyme-r

molecules which must be above a certain value to confer useful properties. As damage processes

reduce the average molecular weight of the polymer molecules, the polymeric material approaches and

eventually reaches a condition in which it fails to maintain its function. Thus the effect of

damage processes can be followed via measurements of molecular weight.

Plates of poly(methyl methacrylate), PMMA, were exposed at various temperatures and over a series of times to radiation with a solar-type spectrum. The specimens were sectioned parallel to

the plate surface and analyzed by gel permeation chromatography to give precise estimates of the

changes in molecular weight of the material. Changes were also followed using Fourier transform

infrared spectroscopy, ultraviolet spectroscopy, and fluorescence spectroscopy and fluorescence

lifetime measurements.

The results show the importance of the role of oxygen in reducing molecular weight, and of

unpolymerized raw material in essentially converting the initial products of degradation into a form

43
which is more sensitive to oxygen. Calculations based on the diffusion and consumption of oxygen

during irradiation have lead to the discovery of a decrease in the protective nature of the

so-called cage effect of the polymers with temperature. This discovery has important ramifications

in that the protective nature of the cage effect can also be changed by plasticizing agents such as water, which is taken up readily in small amounts by PMMA. Further work on the effect of water and

temperature cycling on the damage rates will begin soon. The long term aim of the program is to

correlate molecular weight changes with the significant factors in the service environment so that

changes in molecular weight in service polymers can be predicted. In this way, changes in the

mechanical properties can be predicted and estimates of service life given.

Evaluation of IC-Encapsulants

S. S. Chang and J. R. Maurey

Various chemical, electrical, mechanical, and thermal properties of thermosetting polymeric

encapsulation systems for microelectronic circuits were evaluated. These properties were evaluated

along with the characteristics of UV erasable programmable read-only memories and electrically

erasable programmable read-only memories.

Variable Heating Rate Thermal Analysis

J. H. Flynn

The isoconversional method for determining energies of activation is used extensively for

kinetic analysis of thermoanalytical experiments at a constant heating rate. Its popularity is due

mainly to its capability of yielding activation energies without the necessity of one positing what

often turns out to be incorrect models for the reaction mechanism. The use of Doyle's linear

approximation of the temperature integral in this method introduces sizable errors in the

calculation of the activation energy under certain conditions. The size and nature of these errors

have been reviewed and a procedure has been developed for correcting them. These corrections have

been found to be significant for cases where the activation energy is less than 100 kJ/mol.

Examples of such cases include heterogeneous catalysis, biological reactions, and reactions wnere

the rate limiting step is the diffusion of small molecules through their evaporation from a condensed phase.

Measurement of Additive Diffusion by Fluorimetry

F. W. Wang, B. F. Howell, and F. L. McCrackin

Antioxidants and other additives are added to polyolefins and other plastics to improve the

useful properties and to extend the service life of plastics by preventing or retarding degradation.

The effectiveness of these additives depends not only on their chemical properties but also on their

ability to remain in the plastics throughout the intended lifetime under various end-use conditions.

The basic physical quantities which control the retention of additives in plastics are their

diffusion coefficients and solubilities. Thus, measurements of diffusion coefficients and

solubilities are important for effective design of additive-polymer systems.

We have carried out, by fluorimetry, both extraction experiments and concentration-profile

experiments to determine the diffusion coefficients of additives in low-density polyethylene.

In an extraction experiment, a plane sheet of polymer with uniform concentration of a fluorescent additive is immersed in a limited amount of well-stirred solvent. Then, the amount of

the additive extracted by the solvent is determined at various times by fluorimetry. The diffusion

coefficients of an amine antioxidant, N,N'-diphenyl-p-phenylenediamine (DPPD), and a substituted

thiophene UV screener, 2,5-di (5-tert-butyl-benzoxazoiyl )thiophene (Uvitex OB) in low-density

polyethylene have been determined from extraction experiments.

At the beginning of a concentration profile experiment, twenty polyethylene films without

additive, 4 mils thick and 1.5 inches in diameter, were stacked in the center of a diffusion device.

A porous teflon disc which was 1.5 inches in diameter and filled with a fluorescent additive was then placed above and below the stack and served as a reservoir of additive. The assembly was clamped between two heavy aluminum plates and the whole assembly was then placed in a nitrogen

filled chamber at 30 °C. As time passed, the additive diffused from the teflon discs into the

44
polyethylene films. At the end of an experiment, the polyethylene films were separated, and the

concentration of the additive in each film was determined by fluorimetry. The raw data thus

obtained were the values of concentration as a function of position after a fixed length of time.

By comparing the concentration profile with master curves obtained by solving the diffusion equation

with boundary conditions, we can determine the solubility and the diffusion coefficient of the

additive in polyethylene. In this way, we have obtained a preliminary value for the diffusion

coefficient of 3-tert-butyl-4-hydroxyanisole(BHA) in polyethylene at 30 °C.

Migration of Low Molecular Weight Materials in Polymers Under

Simultaneous Swelling Conditions

C. M. Guttman and S. S. Chang

Additives are placed in polymer films to enhance their properties, improving the polymer's

chemical stability as well as the polymer's mechanical properties. The loss of the additives from

the polymer films into liquids in contact with the polymers not only causes degradation of the films

properties but also often contaminates the liquids causing uncertain health hazards. Thus the loss

of additives out of polymer films is an important area of study.

In earlier work in this laboratory Chang and coworkers have shown that the mass loss of an additive from a semi crystal! ine polymer into a solvent that swells the polymer does not obey Fick's

law. They found that at early times of the extraction experiment, the amount of the additive

extracted into the solution at time t, M(t), increases as the square root in time. At intermediate

times, M(t) increases more rapidly (almost linearly) with time. Finally, at later times, M(t) again

increases like the square root of time before the final approach to equilibrium. The diffusion

coefficient at long times is found to be much larger than that observed at earlier times. In contrast, Chang found that mass loss of additives from polymers into solvents which do not swell the

polymer followed normal Fickian behavior.

Current work is directed at the development of a theoretical model to explain the mass loss

into solvents which swell the polymer. The model being studied relates the non-Fickian migrant loss

behavior to the non-Fickian sorption behavior. In particular, we assume that the migrant diffuses

with diffusion constant D x in the swollen region and with diffusion constant D2 in the unswollen

region. is greater than 02. We assume that the swelling front is sharp and moves proportional

to time (type two diffusion). Thus it is necessary to solve the one dimensional diffusion equation

in which there are two regions each having a different diffusion constant and in which the width of

each of the regions changes as a function of time.

Exact analytical solutions for such a problem have so far not been possible. However,

asymptotic solutions for very short time and for very long times show the limiting behavior seen in

the experiments. Furthermore, an approximate analytical solution has been produced which show most

of the general features of the experimental data of Chang. In these studies the velocity of

swelling was estimated from swelling data on polyethylene obtained by Rodgers et al. and D t and D2 obtained from the data of Chang. Currently a numerical solution to the problem is being undertaken.

Migration of Styrene Monomer From Polystyrene

S. S. Chang and J. R. Maurey

The migration of styrene monomer from polystyrene into various solvents has been observed by

radioactive tracer techniques. The content of styrene in the polymer is nominally 0.4 percent.

n-Heptane distorts the sample quickly and therefore should not be considered as a food-oil

simulating solvent, although it may be used effectively to characterize the styrene content of the

sample.

Most other experiments involving corn oil and ethanol ic solvents took more than one month

before reaching equilibrium extraction. For corn oil at 30 °C, less than 10 percent of styrene was extracted even after one year. In these experiments, the migration behavior may be described by two

Fickian regions, with the longer-time diffusion coefficient greater than the initial diffusion

coefficient.

45
The behavior of migration under the influence of solvent swelling for both glassy and

semi crystal 1 ine polymers is being modeled in collaboration with C. M. Guttman.

Chromatographic Studies of Migration From Polymers

G. A. Senich

The method of polymer analysis termed inverse phase gas chromatography (IGC) differs from

conventional gas chromatography in that a polymer of interest is employed as a stationary phase

which sorbs various volatile organic species, often referred to as probes. The experiment involves

injecting the probe and a gaseous marker into a flowing carrier gas stream which propels the

substances through a column containing the polymer, coated on an inert support packed within the

column. The time lag between injection and elution of the probe vapor peak and its standard

deviation characterize the polymer-probe interactions, which are strongly influenced by the carrier

gas flow velocity. The steady-state probe distribution reached between vapor and polymer phases at

low flow rates allows polymer-probe thermodynamics to be studied. A steady-state distribution is

not reached at high flow rates where the kinetics of polymer-probe interactions are accessible and

the probe diffusivity in the polymer can be obtained. The probe concentration in the polymer is

normally very low and the technigue lends itself to determinations of the degree of migration of

trace additives, oligomers, and polymerization residues from polymers.

The extent of migration of a sufficiently volatile material from a polymer into a contacting

substance (typically a solvent) can be estimated from data readily obtained by IGC studies using the

migrant or additive as the probe. The specific retention volume is obtained experimentally from the

time lag at slow carrier gas flow rates and is used to determine the polymer-migrant interaction

parameter. When combined with a measured or literature value of the solubility of the migrant in

the solvent, a calculation of the eguilibrium partition coefficient is possible. The latter is a direct measure of the fraction of the additive which can be expected to migrate from the polymer to the contacting medium. If the time over which migration can occur is short, an equilibrium

prediction may greatly exaggerate the degree of migration expected. A value for the diffusion

coefficient of the migrant in the polymer may then be obtained from the peak standard deviation of

IGC experiments and employed to estimate the degree of migration which will occur over the shorter

time period. Experimental determinations by IGC of the extent of migration of protective additives

from polymers are continuing. Both thermodynamic interactions and diffusion behavior are of

interest.

Solubilities and Partition Coefficients of BHT in Polyolefins and

Various Solvents

S. S. Chang and J. R. Maurey

BHT(3,5-di-t-Butyl-4-hydroxytoluene) is one of the most widely used antioxidants for

polyolefins and many other polymers. The solubility of BHT in aqueous media is generally in the ppm

level and therefore requires either sensitive chromatographic techniques or radiotracer techniques.

However, as BHT degrades readily in the presence of water, the true value of solubility in aqueous

media can only be estimated by extrapolating the observation to time zero. BHT is readily soluble

in many organic solvents, and is relatively stable in organic solution.

The solubility of BHT in polyolefin is a more controversial subject. The apparent solubility

of BHT in polyolefin is relatively small. However, there exist literature values indicating

moderate solubility from vapor absorption studies and very high solubility from diffusion studies.

We are attempting to solve this controversy through partition coefficient studies and direct

observation of the solubility in condensed phases.

Determination of Segmental Mobility by Picosecond Fluorescence

Spectroscopy

F. W. Wang, R. R. Cavanagh 1

, and W. H. Grant

1 Molecular Spectroscopy Division

The study of polymer- segment mobility is of practical as well as scientific interest. Such a study will on the one hand contribute to the design of polymeric reagents and on the other hand,

46
shed some light on "internal viscosity," an idea introduced by Kuhn some 35 years ago and yet still

argued about [1,2]. Therefore, we have started a project to measure polymer-segment mobility by

picosecond fluorescence spectroscopy.

An excimer is formed by the association of an excited molecule with another molecule in its

ground state. Such an excimer gives off a broad structureless fluorescence which has longer

wavelengths than the fluorescence of the isolated excited molecule. Excimers may also be formed

intramolecularly from molecules carrying excimer- forming groups. For example, excimer fluorescence

has been observed in dilute solutions of pyrene-labeled alkanes such as l,3- bis -(l-pyrene)propane

and 1, 10- bi_s-(l- pyrene) decane [3].

In a novel experimental technique for studying segmental mobility, the solution of an excimerforming oligomer or polymer is irradiated with pulses of light at 355 nm with pulse width of 27 ps. Since a pyrene excimer, for example, is formed by the diffusion-controlled reaction of an excited

pyrene group and a pyrene group in the ground state, the rise of pyrene-excimer fluorescence

intensity will be faster if the pyrene groups are attached to more mobile segments. Similarly, the more mobile the segments, the faster the decay of pyrene-monomer fluorescence intensity.

We have applied the picosecond fluorescence technique to measure the segmental mobility of

1,3- bi

s

-(l-pyrene)propane, l,10-bi_s-(l- pyrene) decane, copolymers of 1-pyrenyl methyl methacrylate and

methyl methacrylate, and poly(l-pyrenylmethyl methacrylate). We have found that the pyrene groups

of the pyrene-labeled homopolymer and copolymers are more mobile than those of the pyrene- labeled

al kanes.

[1] Ott, H. ; Cerf, R. ; Michels, B. ; Lemarechal , P. Chemical Physics Letters, 24, 323 (1974).

[2] Stockmayer, W. H. Pure Appl. Chem. Supplement, 8, 379 (1973).

[3] Zachariasse, K. A.; Kuhnle, W. Z. Physik. Chem. NF, 101 , 267 (1976).

47
MitKlWkUUUW: m MtUI-UUMANLk Ul- UILLLLIKIL PLAU1W

The goal of the task on electrical properties is to carry out long range research to provide

the basis for new or improved measurements and provide concepts and data which will lead to higher

performance in the electrical applications of polymers. The research encompasses a broad range of

generic applications from insulating materials with low loss to materials that conduct either

electrons or ions. An important part of the program includes research on polymers that can be made

to exhibit piezoelectric and pyroelectric properties which has led to new types of transducers and new measurement capabilities. Results of the research in the form of data, measurement techniques,

and scientific concepts go directly to funding organizations through written reports or in some cases by the delivery of a measurement system. The information is made available to interested

parties in the general public by publication in archival journals, by presentation at the meetings

of technical societies, through research associates who come to work with us, and by visits to our laboratories.

Polymers have long been used as electrical insulators where they have performed well. However,

higher demands are being made on their electric breakdown strength as the electric power companies

increase the voltage of power transmission, and make requirements for longer lifetime in more hostile environments as the trend to underground cables continues. A measurement technique

developed to probe the distribution of polarization in polymer films offers an opportunity to measure the distribution of charge in insulation film and thus provide information on the role of

non-uniform electric fields in determining the breakdown strength of polymers. The time-domain

dielectric spectrometer which was recently completed can be used to readily follow any changes in

dielectric loss as a polymer is exposed to use conditions.

Electric conduction in organic polymers is an exciting new area of solid state physics and

chemistry. It is generally agreed that a conjugated double bond structure along the polymer chain

is a necessary condition for conducting properties but the role of the "dopants" which must be added

to induce conductivity is still being investigated. The porous nature of polyacetylene, its ability

to be oxidized and/or reduced by "dopants" such as metals, and its resultant conducting properties

offer great opportunities for battery electrodes and electrochemical sensors. This field of

investigation requires data on molecular packing, dopant location, chemical changes with doping, and

charge carrier measurements to form a basis for modeling and predicting electrical properties. Fast

ion transport in polymers provides a basis for a large and growing class of important applications

including the production of chlorine and sodium hydroxide from the electrolysis of brine, hydrogen

production from low-head hydroelectric sources, solid electrolytes for fuel cells and batteries,

materials separation membranes and electrochemical sensors. These polymers differ from conducting

polymers referred to above because the carriers are ions, not electrons. In most applications it is

required that the current be carried entirely by ions participating in an electrochemical reaction

rather than electrons which essentially short circuit the cell. NBS work involves the preparation

of ion-conducting specimens, measurement of electrical properties, characterization of structure,

and relating the structure and properties to provide a basis for transport mechanisms at the

molecular level. These concepts will then guide the preparation of additional ion-transporting

films.

Research at NBS has made a significant contribution to the understanding of the mechanism

responsible for the piezoelectric and pyroelectric properties of some polymers. Applications for

these new transducers are continuing to grow and there is a need for predicting their long term

performance through an understanding of the mechanism whereby polarization is lost at elevated

temperatures. Factors influencing the stability such as poling conditions, crystal structure,

chemical structure, and molecular motions are being investigated. In addition to improving our understanding of these polymers, the polymeric transducers are being fabricated and employed in

instrumentation to solve measurement problems posed by other government agencies.

Automated Dielectric Measurements

F. I. Mopsik

This activity was undertaken to provide a more efficient, rapid, and at the same time highly

accurate and sensitive measuring system for measuring the dielectric constant and loss of dielectric

material at audio and subaudio frequencies.

48
The instrument, a dielectric spectrometer, records the transient electric charge response to a step change in applied voltage as a function of time from 5 ps to up to 3000 s. The charge response

is then numerically transformed into the dielectric constant and loss for an equivalent frequency

range from 10- 4 to 104 Hz. The basic accuracy of the instrument is 0.1 percent in tan 6 with

resolution in tan 6 to as low as 10 5

.

In FY83 the instrument was completed and operated successfully. Real time graphics have been

introduced so that the experimenter can monitor the course of the measurement while it is in

progress. This last feature was found to be necessary when longer measurement times are used. It also allows the rapid, graphical presentation of data for analysis and experimental guidance.

Experience in FY83 has shown the instrument to be reliable, easy to use, and a great improvement over older methods.

A paper on the instrument has been completed and submitted to Review of Scientific Instruments

for publication. Research associates from General Electric Company have started a transfer of the

technology to their laboratory for use in research. Another research associate program with IMASS,

Inc. has been started to produce a commercial version of the instrument.

Dielectric Properties of Polyvinyl idene Fluoride

A. J. Bur and F. I. Mopsik

This subtask directly supports the optimization of piezoelectric polymers for applications in

industry and Government. It concerns the definition of PVDF properties prior to poling which, after

poling, will yield highly active transducers with optimum ageing characteristics.

Using the dielectric spectrometer referred to above, the dielectric properties of PVDF were measured over a frequency range of 10 4 Hz from room temperature to 90 °C. The data at room temperature were supplemented by measurements on a high frequency bridge to extend the range to 10 8 Hz. At room temperature, four dielectric loss regions were observed: a high frequency loss at

106 Hz; a loss at 1 Hz; an intermediate loss region at 10- 2 - 10- 3 Hz; and a low frequency loss

region at frequencies less than 10 4 Hz. With the exception of the 1 Hz loss, which occurs only in

samples containing an unoriented a phase, the observed dielectric dispersions were present in all

samples regardless of' their preparation history. The 10 6 Hz dispersion is known to be associated

with the rubber-to-glass transition (Tg - -50 °C) and therefore is attributed to micro-Brownian

motion of molecules in the amorphous phase. Usually, in semicrystall ine polymers dispersions which

occur at frequencies lower than (or temperatures higher than) the rubber-to-glass transition are attributed to the crystalline phase. The situation with PVDF appears to be an exception to the

rule. For example, the 1 Hz dispersion and the 10 s Hz loss peaks are complementary, i.e. , a decrease in one results in an increase in the other. For an a phase sample, the 1 Hz peak decreases

in intensity upon orientation but its amplitude is absorbed into the dispersion at 10 6 Hz. This is

observed for both e

1 and e". Thus, the 1 Hz dispersion appears to be associated with the amorphous

phase. Its molecular mechanism has not been determined but we suggest that it is associated with

the interface between amorphous and crystalline phases. Previous assignment of this peak to a relaxation of the component of the dipole moment parallel to the main chain (p u ) in the a phase

crystal appears to be incorrect. The intermediate frequency loss region (10- 2 - 10- 3 Hz) differs in

magnitude for a and p phase samples and is attributed to the crystalline phase. The very low

frequency loss (less than 10- 4 Hz) contains a broad distribution of relaxation times and is not

entirely accounted for by DC conduction. At elevated temperatures conductivity dominates the

dispersion data in this frequency range but at room temperature a long-time relaxation is clearly

seen.

The dielectric samples have been characterized by x-ray and density measurements. From these

data, we are able to calculate the fractional component of the a phase, p phase and amorphous phase

in each sample. The data show that the amorphous fraction remained constant for all samples at 52

percent. Using x-ray orientation data for oriented a phase samples, the component of p lx which is

perpendicular to the axis of sample orientation was calculated. (This is the component which would

contribute to the dielectric dispersion). It was found to be too small to account for the 1 Hz

loss.
Loss bpectra of Polymers in the Microwave Region

A. J. Bur

This work was undertaken as a result of a direct request from the U. S. Army Civil Engineering

Laboratory. It consists of a review of dielectric loss data for polymers at microwave frequencies

and an elucidation of the molecular mechanisms which are responsible for microwave absorption.

Archival journals and laboratory reports were searched in order to obtain the available

microwave dielectric data. While the main focus of attention was the frequency range from 100 MHz

to 100 GHz, loss spectra outside this region were also reviewed because variations in temperature

can cause a shift of dielectric loss into or out of the microwave range. A large volume of data for

low loss polymers (polyethylene, polypropylene, and polytetrafluoroethylene), which are used in the

communications industry, was available for review. Other polymers, for which data were available

and which have significant loss at microwave frequencies, are: polystyrene, polyvinyl chloride,

polyvinyl idene fluoride, polymethyl methacrylate, polymethyl acrylate, polyoxymethylene,

polyethylene oxide, polypropylene oxide, polyacetylene, and polysulfur nitride. The origins of

microwave dielectric loss in polymers are categorized as: (a) dipolar absorption dispersions in

both crystalline and amorphous polymers; (b) dipolar losses due to impurities, additives or fillers

in a polymer material; (c) microwave absorption in conducting polymers (polyacetylene and polysulfur

nitride) for which the current carriers are electrons; and (d) photon-phonon absorption spectra

corresponding to the density of states in amorphous regions of a polymer material. Non-polar

polymers, such as polyethylene, have low dielectric loss at microwave frequencies. Amorphous or semicrystall ine polar polymers, which have a glass transition temperature less than -50 °C, can display large microwave loss at room temperature.

This review has been completed and a final report has been delivered to the Army.

Conducting Polymers

C. K. Chiang

The physical properties of polyacetylene, (CH)

x when doped closely resemble those of

conventional semiconductors. The chemical behavior of doped (CH)

x

is in many aspects analogous to that of insertion compounds. The highly conducting (CH)

x polymer can incorporate as much as 10 to 20 mol % of the dopants into its structure. The high conductivity and the ability to react with

large amounts of dopants make the (CH)

x a good candidate for electrode material. Studies on the

(CH)

x electrodes in liquid cells have been reported. In the past year we have studied (CH) x using

solid containing dopants, and on the use of the (CH)

x electrode in a solid state cell.

When polyacetylene acts as an electrode in a solid state cell, the electrode process is the

doping and undoping of the (CH)

x

. The solid state doping of (CH) x

is studied using a threeelectrode cell with two (CH)

x electrodes and a sodium electrode in the polyethylene oxide (PE0)

complex conductor arranged as follows:

(cn)

x Na

Na/PEO Complex x

( 1 )

where two polyacetylene electrodes are suitably arranged so that the ac impedance of (CH)

x can be

measured 1_n situ without removal from the cell. The doping process is started by connecting a negative voltage to both (CH)

x film electrodes and a positive voltage to the sodium electrode. The

current carried by sodium ions flows from the sodium electrode to both (CH)

x film electrodes. The

sodium ions arrive at the (CH) film and react with it electrochemically to form (CH-Na ) , where y

X Jr A

is the concentration of sodium ions in doped (CH)

x

- The total charge transferred during the process

is proportional to y. The effect of doping can be measured by the change of resistivity of the

doped (CH)

x film electrode, which is obtained from analyzing the ac impedance data.

5Q
The resistivity of (CH)

x

in the electrode before doping is lxlO6 ohm-cm. On doping with sodium

ions the resistivity increases initially. With further doping, the resistivity reaches a maximum

and then decreases slowly. At the end of the doping experiment the resistivity of (CH) decreases

by over three orders of magnitude. x

Our preliminary data indicate that the doping can proceed in a solid state cell. To examine

the electrode behavior the emf of Na/(CH) cell versus sodium concentration is measured using the

cell

x

In this case, the cell voltage for pure (CH)

x

is 2.7 volts and decreases with increasing dopant

concentration.

Li/TS2.

(CH)

x PEO-Nal Complex |Na

» for pure (CH)

x

is 2.7 vc The results resemble those reported for the highly successful insertion compound

Fast Ion Transport in Solid Polymers

C. K. Chiang, G. T. Davis, C. A. Harding, and T. Takahashi 1

1 Guest worker from Ube Industries, Japan

Polyethyleneoxide (PEO) with added alkali metal salts has been shown to exhibit unusually large

conductivities—especially at temperatures around 120 °C. A complex is formed between the polymer

and the salt which increases the melting point from 60 °C for PEO to the vicinity of 190 °C; the

exact temperature depends upon the particular salt. The formation of the high melting complex

imparts structural rigidity to films of the material at temperatures above the melting point of pure

PEO. There are also several reports in the literature that ascribe the mobility of the cation to a specific pathway of conduction along the interior of the 3/1 helical chain conformation which the

polymer assumes in the crystalline phase. The activation energy for conduction as obtained from

Arrhenius plots changes markedly at a temperature which is close to the melting point of the

uncomplexed polymer—becoming smaller at higher temperature. Understanding the mechanism of ionic

transport in this polymer is essential in guiding efforts to select or synthesize other polymers

which conduct in the solid state.

During the past year, we have started an experimental program in which we first duplicated the

results of previous investigators on preparing PEO- salt complexes by evaporation of a common solvent

but have also shown that crystals of PEO grown from dilute solution can be converted to a PEO-Nal

complex by exposing the crystals to a solution of Nal in amyl acetate. Evidence for the complex

comes from DSC and x-ray data. The thermal behavior of PEO-Nal mixtures as revealed by differential

scanning calorimetry (DSC) is dependent upon salt concentration and thermal history. Below 10 mole

percent Nal, only one endothermic peak appears at the normal melting point of PEO, i.e. , 60 °C. For

concentrations of 15 percent and greater, the first heating following evaporation of the solvent

exhibits a rather irregular trace with a broad endotherm in the vicinity of 190 °C. After having

been melted and cooled, subsequent traces show two endotherms, one near 60 °C and another near

190 °C which are regular and reproducible upon subsequent heatings. It has also been determined

that the Nal separates as a separate phase above the melting point of the complex.

DC conductivity is inferred from data on complex impedance measured over a wide range of

frequency or from 4- terminal DC measurements. By studying a wide range of Nal concentrations in PEO

rather than the "stoichiometric ratio" commonly employed, we have shown a maximum in conductivity at

low salt concentratiort (ca. 2 mole percent) which is below the level required to see any evidence

for the PEO-Nal complex. Therefore, the concept of a specific pathway for ionic conduction may not

be necessary to explain the transport process in this polymer.

With the aid of a guest worker from Ube Industries in Japan, we have synthesized linear

polyethyl eneimine (-CH2 CH2 NH-) and have shown that it too can form a high melting complex with Nal

but once melted, it does not reform upon cooling. Preliminary results on the conducting of the

PEI-Nal preparation indicates that it is not as good a conductor as the PEO counterpart but the

early results are very encouraging. We intend to convert this polymer to the quaternary ammonium

analog to examine the role of the groups on the nitrogen in influencing ion transport.

51
Structure and Performance of Piezoelectric Polymers

G. T. Davis and M. G. Broadhurst

The objectives of this task are to study the molecular motions, structural changes, and

electrical properties associated with the process whereby polymers are made piezoelectric.

Information gained from these studies will be used to optimize piezoelectric and pyroelectric

response with respect to both initial activity and long-term stability.

While piezoelectric and pyroelectric activity from polymers is comparable to that from good

ceramic materials, other properties of polymers often make them the preferred transducer material.

Some of the polymer properties which make them so useful include toughness, flexibility, low

density, broad band response, close acoustic impedance match to water, and ease of fabrication.

Requests for information from other Government agencies and from industries have remained numerous. Interest in this area of research continues at a high level in the U. S. as well as Japan, England,

and Europe. Many papers dealing with piezoelectric polymers were presented at the recent IEEE International Symposium on Applications of Ferroelectrics , a special conference on medical applications of piezoelectric polymers was held in Pisa, Italy and piezoelectric polymers was the subject

of a U. S. —Japan cooperative science seminar held in July of 1983.

Collaborative work on copolymers of vinylidene fluoride and trifluoroethylene has continued

with Bell Laboratories and the Institute of Physical and Chemical Research in Saitama, Japan.

Compositions containing 52, 65, 73, and 78 mole percent of vinylidene fluoride (VDF) have been

studied. A ferroelectric to paraelectric transition involving a change in chain conformation within

the crystal occurs in all of these compositions but the temperature of the transition increases with

increasing VDF content. Hysteresis between electric displacement and electric field shows that

these copolymers can be poled at much lower electric fields that the PVDF homopolymer and

piezoelectric activity can be comparable even without orienting the polymer chains prior to poling.

Phenomena related to ionic conduction and trapping of charge have been observed in these copolymers

when subjected to poling fields at temperatures of 70 °C or greater. A reduction in the magnitude

of polarization reversal occurs as a result of these charges but hysteresis is restored if the

copolymer is heated to the paraelectric phase and returned to room temperature. The influence of

such charges and the internal fields they create on the thermal stability of polarization is now being investigated.

Polarization and Space Charge Studies

A. S. DeReggi and F. I. Mopsik

The thermal pulse technique has been developed in this laboratory for studying the distribution

of permanent polarization across the thickness of a dielectric film. This measurement method has

provided key information in understanding the poling behavior of polymeric materials used as piezoand pyroelectric elements.

The method has been applied to the study of the poling of PVDF at room temperature. The

application of forward and reverse poling fields in sequence showed that the regions of the film near the surfaces require higher poling fields than the bulk of the film to achieve the same polarization. Typically the surfaces remain less poled relative to the center by approximately 15

percent at fields of 2 MV/cm. When a film was first poled to 2 MV/cm and reverse poled to -1 MV/cm,

the center was reverse poled but the surfaces still retained polarization in the original direction

with nearly zero mean polarization for the entire sample. A paper on these results has been

accepted for publication in Applied Physics Letters.

A study in collaboration with Professor Sidney Lang of Ben Gurion University has continued.

PVDF was poled at low fields at room temperature with A1 and Au electrodes to see if work function

changes in the electrode materials would influence the poling behavior. Previous work indicated

that this could be so. A detailed series of measurements showed that this was not the case but

apparent changes were due to the presence of a small amount of permanent polarization in the

original, nominally unpolarized film. The strength of this preexisting polarization varied randomly

among samples. Also, the two surfaces of the film were found not to be equivalent. These results

reinforce and amplify our previous results that the film is intrinsically nonuniform in its poling

behavior. A paper on these results has been accepted for publication in the Journal of Applied

Physics.

52
Because scientists in other laboratories are working on alternative approaches to the

measurement of polarization distributions, and have recently begun to publish data on these, there

is a need for comparison of the results of different methods. This need has led to a collaboration

with Bell Telephone Laboratories. Polarization distribution measurements on the same samples arc underway using both the thermal pulse and the acoustical pulse methods.

A Dynamic Polymer Pressure Transducer With Temperature Compensation

A. J. Bur and S. C. Roth

At the request of the U. S. Air Force, a pressure transducer using polyvinylidene fluoride

(PVDF) as the active element is being developed for the purpose of measuring dynamic pressures in

various soil environments underground.

Since underground pressure waves will be accompanied by adiabatic thermal effects, a transducer

with temperature compensation is being developed. The essential elements of this gage are: (a) the

active PVQF transducers; (b) a thermocouple having a short rise time; and (c) amplifiers which add

the transducer and thermocouple in the appropriate proportion in order to achieve compensation for- the temperature effects. Its construction involves laminating four sheets of 12 pm PVDF together.

The inner two sheets contain active areas 1 cm in diameter which are placed face-to-face with each

other and on which are deposited aluminum electrodes. The outer two layers serve as protection for

the inner two. A copper-constantan thermocouple junction, made with 75 pm (3 mil) wire, is placed

between the inner two sheets and within 2 mm of the active transducer area. For a pressure wave

which is also accompanied by a temperature pulse, the active PVDF will respond to both pressure and

temperature.

The thermocouple will respond to temperature only. By taking the output of the thermocouple

and amplifying it in proportion to the pyroelectric coefficient of the PVDF, the thermocouple

voltage can be used to correct the pressure wave signal from the transducer.

An amplifier has been constructed which can be used to achieve temperature compensation over

the frequency range from 1 Hz to 104 Hz. Sensitivity to temperature changes of 0.2 °C and pressure

changes of 1 psi (7x10? N/m2

) have been obtained.

After testing the transducer in different soil environments, we will deliver six transducers to

the Air Force.

Acoustic Sensors

A. S. DeReggi

The outstanding advantages of ferroelectric polymer transducers when used in hydrophones or in

biomedical sensors of various types include negligible perturbation of the acoustic field measured,

broad operating bandwidth, and mechanical flexibility. In addition, when polymers are used to make

monolithic arrays, their mechanical properties are favorable for achieving low crosstalk between

individual elements of the arrays.

To understand the general features of the performance characteristics which are peculiar to

polymeric transducers in terms of their material properties, we have considered the mixing of piezo

and pyroelectric effects in pressure measurements. This mixing arises from the large adiabatic

compressional heating coefficient which is typical of polymers. A paper on this topic has been

presented at the 1983 International Symposium on Applications of Ferroelectrics.

A collaboration with the Brown University Foundation and the University of Pisa which started

with a research associateship has had, as an outgrowth, the organization of the International

Symposium on Piezoelectricity in Biomaterials and Biomedical Devices. A paper on the biomedical

applications of piezoelectric polymers was presented at the meeting which took place June 20-23,

1983 in Pisa. It is anticipated that this first meeting will be followed by other meetings

initially at two-year intervals.

During this fiscal year, we have initiated a collaboration through a research associate

agreement with Alta Technology of Stamford, Connecticut. We have begun to study the factors

affecting crosstalk in polymeric transducer arrays, and to explore ways to minimize this coupling in

53
the design of high fidelity ultrasonic imaging arrays. One aspect of this work is aimed at

investigating the applicability of trapped energy mode concepts -in monolithic transducer arrays made

with polymeric active material. Previous work elsewhere has shown that useful levels of isolation

can be attained in monolithic transducer arrays made with ceramics if these arrays are operated in

the frequency range where trapped energy modes prevail.

Spontaneous Polarization in Ferroelectric Polymers

A. S. DeReggi , S. C. Roth, G. T. Davis, and M. G. Broadhurst

A method for measuring the pyroelectric response of polymers as a function of temperature while

the temperature is increased linearly with time has been developed at NBS. The technique provides a rapid means of determining the temperature at which polarization begins to decay and is being used

to establish the effects of poling variables and polymer morphology on the relative stability of

piezoelectric and pyroelectric properties.

Measurements of the sample polarization temperature dependence have been performed on PVDF and

on its copolymer with tetraf1 uoroethylene (TFE). In both cases the polarization has been found to go to zero when melting of the sample is complete, rather than at some transition temperature

distinct from the melting temperature. Measurements such as those described here must be done with

well characterized samples since the ferroelectric polymers, like other semi crystal line polymers,

may exhibit relaxation or melting behavior which depend on the prior mechanical and thermal history.

The extended range of temperature over which melting may occur, and the multiphase nature of PVDF

samples also must be considered in making the connection between the sample polarization and the

spontaneous polarization.

The measurements on biaxially oriented PVDF poled at 100 °C show a gradual loss of sample

polarization starting at 70 °C and extending throughout the remainder of the semi crystalline range

which finally melts at approximately 170 °C. There is no evidence of ferroelectric to nonferroelectric transition as reported by others, and no sign of impending precipitous polarization

decrease of the kind shown by analogous spontaneous magnetization of a ferromagnet near a Curie

point. Experiments with samples differing only in their poling treatment show generally similar

polarization versus temperature behaviors. These results suggest that the polarization loss

mechanism is not strongly influenced by the method of poling. Companion measurements of the angular

dependence of the x-ray scattering intensity have been performed in reflection as a function of

temperature from ambient temperature to the melting point. The results do not support an explanation "for the loss of polarization in terms of a gradual phase transformation from the polar

to antipolar phase (p-^a). Such a transformation was an admissible possibility since an or>p transformation occurs upon mechanically orienting PVF2 , and since a relaxation of mechanical

orientation could be expected on heating.

Future measurements are planned on the VDF-trifl uoroethylene copolymer at high VDF content. A structural -ferroelectric transition distinct from melting is observed i nr this system at a temperature which depends on composition and possibly on history. Extrapolation of the transition

temperature vs composition data to 100 percent VDF would place the transition in PVDF in the area of

its melting point. Future measurements also are planned for poly(vinyl fluoride) which is a semicrystall ine system with a single crystalline phase, in which transformation to alternate phases

should not exist.

54
Other Activities of the

Polymer Science and Standards Division

Invited Talks

The Role of Interlaboratory Test Programs

in Quality Assurance ASTM Symp. on Quality

Assurance in Plastics,

Nashville, TN

J. D. Barnes

March 1983

Computerized Data Acquisition and

Control for Gas Transmission

Measurements Digital Equipment

Corp. Users' Society (DECUS),

St. Louis, MO

J. D. Barnes

May 1983

Composite Resin Chemistry

International Symposium on Posterior Composite Resins,

Chapel Hill, NC

R. L. Bowen

October 1982

The Development of Composites &

Recent Innovations in Research Labs.

New Port Harbor Academy of Dentistry,

Newport Beach, CA

R. L. Bowen

October 1982

Direct Bonding to Dentin American

Dental Association Annual Meeting,

Las Vegas, NV

R. L. Bowen

November 1982

Adhesion of Restorative Materials

to Enamel and Dentin American Academy

of Plastics Research in Dentistry,

Northwestern Dental School, Chicago, IL

R. L. Bowen

February 1983

Mechanisms in the Bonding of Resins to Dentin

AADR, Cincinnati, OH

R. L. Bowen

March 1983

Adhesive Bonding of Various Materials to Hard Tooth Tissues

Symposium on Dental Adhesives,

3M, Kenora, Ontario

R. L. Bowen

June 1983

55
Some New Bonding Methods

Melbourne Materials Symposium,

Victoria, Australia

R. L. Bowen

August 1983

Composites-Past, Present and Future

Kerr Division of Sybron Corp.

Romulus, MI

R. L. Bowen

September 1983

Recently Developed Concepts in

Adhesive Bonding of Composites

to Dentin and Enamel 6th Annual

Greater Niagara Frontier Dental Meeting,

Buffalo, NY

R. L. Bowen

September 1983

Composites —Past, Present, and

Future Kerr Division of Sybron

Corporation,

Romulus, MI

R. L. Bowen

September 1983

Properties, Structure, Modeling

and Applications of Ferroelectric

and Paraelectric PVDS Polymers 1983

IEEE Inti. Symp. on Applications of

Ferroelectrics

Gaithersburg, MD

M. G. Broadhurst

June 1983

Physical Basis of Transducer

Properties in PVDF Inti. Symp. on Piezoelectricity in Biomaterials

and Biomedical Devices,

Pisa, Italy

M. G. Broadhurst

June 1983

Aspects of Modeling of

Ferroelectricity in PVDF

and Related Polymers NSF/

US/Japan Workshop on Piezoelectric Polymers,

Honolulu, Hawaii

M. G. Broadhurst

July 1983

The Gibbs-Duhem Equation and

Calcium Phosphate Systems ASDR,

Cincinnati, OH

W. E. Brown

March 1983

Acidic Calcium Phosphate Precurosor

in Enamel Formation Gordon Conference

on Calcium Phosphates,

Plymouth, NH

W. E. Brown

June 1983
Heat Capacity of Phenolic Resins

Symposium on Phenol ics Revisited,

75 Years Later,

Washington, DC

S„ S. Chang

August 1983

Simultaneous Dissolution and

Precipitation of Calcium Phosphate

in Gels AADR,

Cincinnati, OH

LoC„ Chow

March 1983

A Procedure for Bonding to

Both Dentin and Enamel AADR,

Cincinnati, OH

E. N„ Cobb

March 1983

Phase Transitions and Ferroelectric

Polarization in a Vinylidene FluorideTrifluoroethylene Copolymer

Hokaiddo University,

Sapporo, Japan

G. T. Davis

October 1982

Polarization Distribution in

Polymer Films University of Tokyo,

Tokyo, Japan

G„ T. Davis

October 1982

Phase Transitions and Ferroelectric

Polarization in a Vinylidene-fluorideTrifluoroethylene Copolymer Institute of

Phys. & Chem. Research,

Saitoma, Japan

G. T„ Davis

October 1982

Phase Transitions and Ferroelectric

Polarization in a Vinylidene-fluorideTrifluoroethylene Copolymer

Nagoya, Japan

G. T„ Davis

October 1982

Polarization Distribution in

Polymer Films Chung-Shan

Institute of Sci. & Technology,

Taiwan Republic of China

G. T. Davis

October 1982

Hysteresis in Copolymers of

Vinylidene Fluoride and

Trifluoroethylene East West

Convention Center,

Honolulu, Hawaii

G. T. Davis

July 1983

57
Polymeric Transduction Phenomena

and Their Role in Biomedical

Applications Inti. Symp. on Piezoelectricity in Biomaterials

and Biomedical Devices,

Pisa, Italy

A. S. DeReggi

June 1983

Porcelain to Metal Bond Strength

Measurements as Determined by the

Four Point Bending of a Composite

Beam ASDR,

Cincinnati, OH

W. G. de Rijk

March 1983

A Quantitative and Expedient

Test for Porcelain-to-Metal

Bond Strength, Symp. on Mechanical

Properties, Performance, and Failure

Modes of Coatings

NBS, Gaithersburg, MD

W. G. de Rijk

May 1983

Thermal and Photo lytic Degradation

of PMMA University of Aston,

Birmingham, UK

8. Dickens

December 1982

The Role of Fluorescence in

the Photo-Oxidation of Poly(methyl

methacrylate) John Dalton Institute,

Institute of Technology,

Manchester, UK

B. Dickens

December 1982

Degradation in Solar Cover

Plate Materials Centre

Scientifique et Technique

des Batiments,

Grenoble, France

B. Dickens

December 1982

Role of Oxygen Diffusion in the

Photodegradation of Polymethacrylates

Laboratorie de Photochemie, General Ecole

National e Superieure de Chimie,

Mulhouse, France

B. Dickens

December 1982

Mechanisms of Thermal and

Photo-Oxidation of Polymethacrylates

Centre de Recherches sur les Macromolecules,

Strasbourg, France

B. Dickens

December 1982
The Mechanism of Oxidation and

Role of Oxygen pi f fusion in the

Photolysis of Poly(methyl )Methacry1ate

Technische Uni vers i tat

,

Stuttgart, West Germany

B. Dickens

December 1982

Initiation of Degradation by

Photolysis, Especially in PMMA

Hahn-Meitner Institute,

W. Berlin, West Germany

Bo Dickens

December 1982

Thermal and Photodegradation of

Plates of PMMA Soc. of Plastics

Engineers, Mid-Hudson Section,

Poughkeepsie, NY

Be Dickens

March 1983

Solar Type Degradation of Plates

of PMMA Containing Monomer Rohm

and Haas Inc.

,

Bristol, PA

B. Dickens

May 1983

Biological Self Assembly Modeled

as Phase Transition Phenomena

Georgetown University,

Washington, DC

E. A. DiMarzio

October 1982

Phase Transitions in Polymers as Models for Self Assembly in Biology

Wash. Chapter of Alpha Chi Sigma, American University,

Washington, DC

E. A. DiMarzio

October 1982

Phase Transition in Polymers;

Their Use as Models for Self Assembly

in Biology University of Virginia,

Charlottesville, VA

E. A. DiMarzio

October 1982

Phase Transitions in Polymers;

Their Use as Models for Self

Assembly University of Maryland,

College Park, MD

E. A. DiMarzio

March 1983

The Proof of the Necessity of a Low

Temperature Equilibrium Phase in Polymer

Glasses Inti. Symp. on Structure and

Bonding in Noncrystalline Solids,

Reston, VA

E. A. DiMarzio

May 1983

59
Nature of the Glass Transition:

Configurational Entropy as a Unifying Concept for Glasses

Virginia Polytechnic Institute

and State University,

Blacksburg, VA

E. A. DiMarzio

July 1983

Crystal Structures and Disorders

in Polytetrafl uoroethylene

Georgia Inst, of Technology,

Atlanta, GA

R. K. Eby

October 1982

Crystal Structures and Disorders

in Polytetrafl uoroethylene

University of Cincinnati,

Cincinnati, OH

R. K. Eby

October 1982

Opportunities and Needs for NDE

and Accurate Service Life Prediction

of Polymers Joint Seminar for ASTM

for Nondestructive Testing,

Li nth i cum, MD

R. K. Eby

December 1982

Overview of the Polymer Science

and Standards Division Martin

Marietta Laboratories,

Baltimore, MD

R. K. Eby

January 1983

Opportunities and Needs for Research

on the Performance of Polymers 6th

Asilomar Conf. on Polymeric Materials,

Pacific Grove, CA

R. K. Eby

February 1983

Structures and Transitions in

Tetrafl uoroethylene Polymers

University of Utah,

Salt Lake City, UT

R. K. Eby

July 1983

Molecular Processes Affecting Mechanical

Durability of Polymers NBS Director's

Seminar Series,

Gaithersburg, MD

3. M. Fanconi

January 1983

Polymer Durability University of Utah,

Salt Lake City, UT

B. M. Fanconi

February 1983
Chain Scission and Mechanical

Degradation of Polymers American

Physical Society,

Los Angeles, CA

B„ M. Faneemi

March 1983

Thermal Degradation of Polymers

Macromolecular Section of the

Chemical Society of Vojvodina

Novi Sad, Yugoslavia

J. H. Flynn

September 1982

Prediction of Service Lifetimes of

Polymers by Thermogravimetry Macromolecular

Section of the Society of Chemistry and

Technology of Croatia,

Zagreb, Yugoslavia

J. H. Flynn

September 1982

Prediction of the Service Life of a Polymer by Thermogravimetry Symposium

on Polymer Characterization by Thermal

Methods, 1983 ACS Middle Atlantic

Regional Meeting,

White Haven, PA

J. H. Flynn

April 1983

Application of Corrections for the Slope

of the Doyle Approximation for the Logarithm

of the Temperature Integral to the Determination

of Activation Energy by the Isoconversional Method

North American Thermal Analysis Society 12 Conf./

38th Calorimetry Society Conf.,

Williamsburg, V

A

J. H. Flynn

September 1983

The Xsoconventional Method for Determination

of Energy of Activation at Constant Heating

Rates— Corrections for the Doyle Approximation

12th North American Thermal Analysis Society and

38th Calorimetry Conference,

Williamsburg, VA • J. H. Flynn

September 1983

Computer Simulation of a Diffusion

Controlled Model for Caries AADR,

Cincinnati, OH

T. M„ Gregory

March 1983

Some Remarks on the History and Development

of the ASTM E-37 Purity Method Symposium on Purity Determines by Thermal Analysis,

Baltimore, MD

C. M. Guttman

April 1983

61
Effects of Excluded Volume and Hydrodynamic Interaction

In Polymer Solutions Nagoya University,

Nagoya, Japan

C. C. Han

April 1983

Dynamic Light Scattering from Dilute and Semi dilute

Polymer Solutions Institute of Chemistry,

Beijing, China

Co C. Han

April 1983

Measurements of Block Chain Dimensions by

Small Angle Neutron Scattering Institute of Chemistry,

Beijing, China

C. C. Han

Apri 1 1983

Dynamic Light Scattering of Polystyrene from

Semi dilute Polymer Solutions Department of Chemistry,

Osaka University,

Osaka, Japan

C. C. Han

May 1983

Dynamic Light Scattering from Polymer

Solutions Kyoto University,

Uji, Japan,

C. C. Han

May 1983

Dynamic Light Scattering from Dilute Polymer Solutions

in the Intermediate q-region Kyoto University,

Kyoto, Japan

C. C. Han

June 1983

Light and Neutron Scattering from Polymers

Korean Standard Research Institute,

Daejeon, Korea,

C. C. Han

June 1983

Dynamic Light Scattering from Dilute

and Semidilute Solutions Kyushyu University,

Fukuoka, Japan

C. C. Han

June 1983

^nall Angle Neutron Scattering Measurements

of Portions of Polymer Chains Tokyo

Institute of Technology,

lokyo, Japan

C. C. Han June 1983

Internal Chain Expansions Measured by SANS

•okyo Metropolitan University,

fokyo, Japan

C. Han

June 1983

62
Polymer Diffusion and Frictional Coefficient

in Semi dilute Solutions Japan Fiber &

Textile Society,

Kyoto, Japan

C. Co Han

June 1983

Polymer Dimensions and Characterization

by Light and Neutron Scattering Dai cel Company,

Himejo, Japan

Co C. Han

June 1983

SANS Measurements of Block Chains at

NBS American Chemical Society Meeting,

Washington, DC

C. Co Han

August 1983

j Review of NBS Programs on Adhesion

and Adhesion Science NASA/DOD Workshop

on Adhesion and Adhesives,

Hyannis, MA

D. L. Hunston

October 1982

Nondestructive Evaluation of Polymer

Surfaces, Interfaces, and Films via

Ultrasonics Paint Res. Inst. Symp. at

the Annual Mtg. of the Federation of

Societies for Coating Technology,

Washington, DC

D. L. Hunston

November 1982

Failure Behavior of Polymer Adhesives

and Composites Bendix Corporation,

Columbia, MD

D. L„ Hunston

November 1982

The Double Cantilever Beam Test

for Interlaminar Fracture of

Composites ASTM D30 Meeting, Task

Group on Interlaminar Fracture Toughness,

San Francisco, CA

0. L. Hunston

Oecember 1982

Fundamentals of Adhesion Center

for Professional Advancement,

| Fast Brunswick, NJ

0- L. Hunston

January 1983

Roughening of Polymers for Improved

Romoosites and Structural Adhesives,

'- h **ical Society of Washington,

! J«h»ngton, DC

0 L - Hunoton
Mechanics of Adhesive Bond Failure

Center for Professional Advancement,

San Mateo, CA

0. L. Hunston

March 1983

Durability of Adhesive Bonds Center

for Professional Advancement,

San Mateo, CA

D. Lo Hunston

March 1983

Characterization of Interlaminar

Crack Growth with the Double Cantilever

Beam Specimen NASA Workshop of Tough Composites,

Hampton, VA

D. L. Hunston

May 1983

Failure Behavior of Elastomer-Modified

Epoxies Sandia National Laboratories,

Albuquerque, NM

D. L. Hunston

June 1983

General Rheology and its Applications

in Adhesion Workshop on Adhesion and

Adhesives, Kent State Univ.

Kent, OH

D. L. Hunston

June 1983

Viscoelastic Fracture of Adhesive

Joints Workshop on Adhesion and

Adhesives, Kent State Univ. , Kent, OH

D. L. Hunston

June 1983

Flow Fundamentals in Fluid Systems

Containing High Molecular Weight Additives

Workshop on Rheology for the Industrial Chemist,

Kent State Univ.,

Kent, OH

D. L. Hunston

June 1983

Fracture Behavior of Brittle Materials

Workshop on Rheology for the Industrial

Chemist, Kent State Univ.,

Kent, OH

D. L. Hunston

June 1983

Effects of Formulation on the Failure

Behavior of Rubber-Modified Epoxies Gordon

Research Conference on Thermosetting Polymers,

Meriden, NH

D. L. Hunston

August 1983

64
Failure Behavior of Rubber-Toughened Epoxies

in Bulk, Adhesives and Composite Geometries Symp. on Rubber Modified Thermoset Resins, American Chem. Soe„

,

Washington, DC

D. L. Hunston

August 1983

Scanning Transmission Electron Microscopy

of Polyethylene Crystals Workshop on the

Electron Microscopy of Polymers, Univ. of Mass.,

Danvers, MA

F. A. Khoury

June 1983

A Water Rich Calcium Phosphate AADR,

Cincinnati, OH

M. Mathew

March 1983

Simultaneous Measurement of Torque and

Normal Force Responses in Torsi on- An Efficient

Means of Testing Constitutive Equations Ecole

Superieure de Physique et de Chimie Industrie! les,

Paris, France

G„ B. McKenna

October 1982

An Outlook on the Rheology of High Polymers Saclay,

France

G. B. McKenna

October 1982

Nonlinear Viscoelastic Behavior of

PMMA in Torsion Ecole de Mines,

Nancy, France

G. B. McKenna

November 1982

Effects of Large Deformations on Aged

Polymer Glasses American Society of Mechanical Engineers,

Houston, TX

G. B. McKenna

June 1983

Simultaneous Measurement of Torque and

Normal Force Responses as Probes of Physical

Aging in Glassy Polymers VPI Summer Workshop

on Relaxation Effects in Disordered Systems,

Blacksburg, VA

G. B. McKenna

July 1983

Anomalies in the Physical Ageing Behavior

of PMMA 12th NATAS Annual Calorimetry Conference,

Williamsburg, VA

G. McKenna

September 1983

The Influence of Composition on the

Fusion Temperature of Experimental Dental

Porcelains Determined by Multiple Regression AADR,

Cincinnati, OH

D. L. Menis

March 1983

65
Absorption of N,N-dimethyl-p-amino-phenyl-acetic

Acid on Hydroxyapatite AADR,

Cincinnati, OH

D. N. Misra

March 1983

Relation Between Clinical Behavior and

Expansion of Three Amalgams AADR,

Cincinnati, OH

N. W. Rupp

March 1983

The Influence of the Polymer Morphology

on the Transport Properties 19th Annual

Meeting of the Society of Engineering Science,

Roll a, MO

A. Peterlin

October 1982

Relation Between Clinical Behavior and

Expansion of Three Amalgams AADR,

Cincinnati, OH

N. W. Rupp

March 1983

Dental School, Tufts University,

Boston, MA

N. W. Rupp

November 1982

Selection and Handling of Dental Materials

Eglin Air Force Base, FL

N. W. Rupp

October 1982

Cavity Preparation Modifications Made

Possible by the Acid Etch Technique,

Maryland State Oental Meeting,

Baltimore, MD

N. W. Rupp

October 1982

Selection and Use of Dental Materials

Scott Air Force Base, IL

N. W. Rupp

November 1982

Impression and Die Materials Naval Dental School,

Bethesda, MD

N. W. Rupp

December 1982

Esthetic Restorative Materials - New Developments

Naval Dental Center, Bethesda, MD

N. W. Rupp

February 1983

The Hazards to the Patient of Mercury in

Dental Amalgam Restorations American Association

of Dental Schools,

Cincinnati, OH

W. Rupp

Harch 1983

66
Recent Developments in Materials For

Operative Dentistry Dental School,

Georgetown University, Washington, DC

No Wo Rupp

March 1983

The Selection and Use of Dental Materials

for Removable Partial Dentures Veterans Administration,

Washington, DC

No W. Rupp

March 1983

The World of Dental Materials

Johns Hopkins University Center for

Materials Research

Baltimore, MD

N. W. Rupp

March 1983

Sealing the Gingival Margin of

Composite Restorations AADR,

Cincinnati, OH

N. W. Rupp

March 1983

Recent Developments in Esthetic

Restorative Materials East Central

Dental Society,

Champaign, IL

N. W. Rupp

May 1983

The Selection and Use of Dental Materials

Lackland Air Force Base, FL

No W. Rupp

May 1983

Recent Developments in Dental Materials

Office of the Surgeon General,

U.S. Air Force, Shreveport, LA

N. W. Rupp

September 1983

Selection and Manipulation of Dental

Materials Veterans Administration,

Washington, DC

N. W. Rupp

September 1983

Polymer Blends ARCO Chemical Co.

,

Newton Square, PA

I. Co Sanchez

February 1983

Statistical Thermodynamics of Polymeric Fluids

University of Maryland, College Park, MD

I. C. Sanchez

March 1983

67
On the Nature of Polymer Interfaces and

Interphases National Research Council of

Canada, Ind. Materials Res. Inst.,

Montreal , Canada

I. C. Sanchez

April 1983

Liquids: Surface Tension, Compressibility, and

Invariants Washington Area Statistical Physics Symp.

Gaithersburg, MD

I. C. Sanchez

April 1983

Bulk and Interface Thermodynamics of

Polymer Blends Inti. Symp. of Phase

Relationships and Properties of

Multicomponent Polymer Systems,

Capri , Italy

I. C. Sanchez

May 1983

On the Nature of Polymer Interfaces and

Interphases G. E. Research and Development Center,

Schenectady, NY

I. C. Sanchez

May 1983

On the Nature of Polymer Interfaces and

Interfaces Xerox Research Laboratories,

Webster, NY

I. C. Sanchez

May 1983

Center for Research on Macromolecules,

Strasbourg, France

G. A. Senich

September 1982

Inverse Phase Gas Chromatographic Studies of

Polymers Textile Institute of France,

Boulogne-Billancourt, France

G. A. Senich

September 1982

Studies of Polymer-Solvent Interactions by

Inverse Gas Chromatography: Thermodynamics and

Diffusion Eastman Kodak Company,

Kingsport, TN

G. A. Senich

October 1982

Studies of Polymer-Solvent Interactions by

Inverse Gas Chromatography: Thermodynamics and

Diffusion Polytechnic Institute of New York,

Brooklyn, NY

G. A. Senich

October 1982

Careers in Polymer Chemistry at Government

and Industrial Research Laboratories Howard University,

Washington, D.C.

G. A. Senich

October 1982

68
Migration from Polymers: Thermodynamics and

Diffusion by Inverse Gas Chromatography E. I du Pont de Nemours & Company,

Wilmington, DE

G. A. Senich

April 1983

Physical Chemistry Studies of Polymers by

Inverse Gas Chromatography Washington

Chromatography Discussion Group,

Rockville, MD

G. A. Senich

May 1983

Application of X-ray Magnifier to

Microradiography of Dental Specimens

A Preliminary Report AADR,

Cincinnati, OH

S. Takagi

March 1983

The World of Dental Materials

Johns Hopkins University,

Baltimore, MD

J. A. Tesk

March 1983

The Need for Beryllium in Dental

Casting Alloys Ann. Session Am. Assoc, of Dental Schools, Biomaterials Sec.

Cincinnati, OH

J. A. Tesk

March 1983

Hydroylsis of Amorphous Calcium Phosphate

(ACP) with an Intermediate State AADR,

Cincinnati, OH

M. S. Tung

March 1983

What Does Solid State 13C NMR

Reveal About the Microstructure

of Cellulose Institute of Paper Chemistry,

Appleton, WI

D. L. VanderHart

October 1982

NMR of Solids University of Florida,

Gainesville, FL

D. L. VanderHart

March 1983

NMR of Solid Polymers

University of Florida,

Gainesville, FL

D. L. VanderHart

March 1983

NMR of Solid Polymers

University of California,

San Diego, CA

D. L. VanderHart

March 1983
Studies of Microstructure in Native

Celluloses Using Solid State 13 C NMR Inti.

Dissolving and Specialty Pulp Conference,

Boston, MA

D. L. VanderHart

April 1983

High Resolution 13C NMR of Solid

Polymers Owens Corning Fiberglass,

Granville, OH

D. L. VanderHart

April 1983

NMR Studies of Oriented Polymers Case

Western Reserve University,

Cleveland, OH

D. L. VanderHart

April 1983

Native Cellulose: A Crystalline Composite

ACS National Meeting,

Washington, DC

D. L. VanderHart

August 1983

Combined 13 C and X H NMR Methods

for the Examination of Orientation

and Microstucture in Polymers 15th

Europhysics Conf. on Macromolecular Physics,

Hamburg, W. Germany

0. L. VanderHart

September 1983

Investigation of Microstructure by

Solid State NMR University of Stuttgart,

Stuttgart, W. Germany

D. L. VanderHart

September 1983

13NMR Methods for the Examination of

Orientation and Microstructure in

Polymers Europhysics Conference,

Hamburg, Germany

D. L. VanderHart

September 1983

Solid State NMR Studies of Cellulose

Centre d' Etudes Nucleaires de Grenoble,

Grenoble, France

0. L. VanderHart

September 1983

Low Shear Viscosity of Ultra High Molecular

Weight Polycohylene Arco Chemical Company,

Newtown Square, PA

H. L. Wagner

March 1983

70
fo

PPn?

atl0n

! ° f Fluorescence Techniques to Polymer Systems: Polymer Compatibility &

soc - ^Wscib

: ,,tyi

F. W„ Wang

May 1983

(^

e

r Si

Ud

: eS °n Chem1cal Durability of Polymers

oWxet- Ud - Hirakata p,as ««

^

F. W. Wang

May 1983

Applications of Fluorescence Techniques

and ? ymer Systems: Polymer Compatibility

Kyoto?

9

Japan

^ ^ F. W. Wang

May 1983

Applications of Fluorescence Techniques to olymer Systems: Polymer Compatibility & Segmental Mobility, Osaka University Toyonaka, Japan y>

F. W. Wang

May 1983

Some Studies on Chemical Durability of Polymers University of Tokyo *

Komaba Meguroku, Tokyo, Japan

F. W. Wang

June 1983

Applications of Fluorescence Techniques to o ymer Systems: Polymer Compatibility and egmental Mobility Research Institute of Polymers and Textiles,

Tsukuba, Japan

F. W. Wang

June 1983

°J ^"Kt-Polymer Compatibility

womaS';

Rs;

a

st;ra

e

n

Eunn

e^ri^nsfar Techni<,ue T°*°

Tokyo, Japan

F. W. Wang

June 1983

App!i cations of Fluorescence Techniques to

Comnst

emS " Additive Migration, Polymer

Institute of

V

^ ^ CuHn9 Kinetl‘ cs ChungShan institute of Science and Technology

LungTan, Taiwan yy$

F. W. Wang

June 1983

Applications of Fluorescence Techniques to Polymer Systems: Additive Migration Pollux compatibility, and Coring Kinases Refining and Manufacturing Research Center, Chinese Petroleum Corporation ese

Chia-Yi, Taiwan

F. W. Wang

June 1983

71
Progress in Characterization of Macromolecules

Gas Research Institute,

Evanston, IL

F. W, Wang

September 1983

Comparison of the Refractory

Metal-Noble Metal Phase Diagrams

T

5 -T 10 Materials Research Society,

Boston, MA

R. W. Waterstrat

November 1982

Idiosyncrasies of the Less Common Metals

Alloy Phase Diagram Workshop,

NBS

R. M. Waterstrat

January 1983

Small Angle X-Ray Scattering of Composites

University of Hamburg,

West Germany

W. Wu

October 1982

Small Angle Neutron Scattering of

Partially Segregated Polyethylene Blends

University of Hamburg,

West Germany

W. Wu

October 1982

Small Angle Neutron Scattering of Partially

Segregated Amorphous Polymeric Blends

University of Hamburg,

West Germany

W. Wu

November 1982

Wear and Degredation of Dental Composites

Free University of Berlin,

West Germany

W. Wu

November 1982

Chemical Factors Affecting Wear

Resistance of Dental Restorative

Composite Resins Royal Dental College,

Copenhagen, Denmark

W. Wu

December 1982

Random Phase Approximation to the

Paraclustering Phenomena of Polymer Blends

University of Hamburg,

West Germany

W. Wu

December 1982

Surface Breakdown and Laboratory Wear

of Dental Composites IADR,

Sydney, Australia

W. Wu

August 1983

72
Small Angle Neutron Scattering Study

of Polyethylene Deformation Process

ACS Conference,

Washington, DC

W. Wu

August 1983

Society of Rheology

Evanston, XL

L. J. Zapas

October 1982

The Necking of Semicrystall ine Polymers

in Tension University of Minnesota,

Minneapolis, MN

L. J. Zapas

March 1983

A One Dimensional Description of the

Behavior of UHMWPE in Tension at Several

Deformations University of Minnesota,

Minneapolis, MN

L. J. Zapas

March 1983

Seminars for Staff and Guests

Piezo and Pyroelectricity of PVDF/PMMA Blends

Dr. Bernd R. Hahn

Deutsches Kunststoff Institut,

Germany

October 1982

Electrical Breakdown in P.E. and its Morphology

Professor K. Yahagi

Waseda University, Tokyo, Japan

October 1982

Nonlinear Finite Element Analysis of

Radially Loaded Fiberglass Composite

Rings and Applications to Large Pressure Vessels

Professor S. G. Ladkany

Johns Hopkins University, Baltimore, MD

October 1982

Addition Polyimides

Professor (Mrs.) I. K. Varma

Indian Inst, of Technology,

New Delhi , India

November 1982

The Preparation and Properties of

Ultra High Modulus Polyolefins

Professor I. M. Ward

University of Leeds, Leeds, England

November 1982

AC Partial Discharge and Surface

Effects in Polymer Films

Professor W. J. Sarjeant

State University of New York at Buffalo, Amherst, NY

November 1982

73
Morphology and Toughness Comparison of

Two Amine Cured Rubber Epoxies

Or. Stephanie C. Kunz

Sandia Laboratories, Albuquerque, NM

November 1982

Polymer Surfactant Interactions

Dr. Pak S. Leung

Union Carbide Corp. , Terrytown, NY December 1982

The Silver Electrode:

Antibacterial Effects of Ostagenesis

Dr. Joseph Spadaro

State University of New York, Syracuse, NY

December 1982

Interfacial Structures of Composite Materials

Professor H. Ishida

Case Western Reserve University, Cleveland, OH

December 1982

Light Reflection by Dental Enamel

Dr. Roelf A. J. Groenhuis

NIDR, NIH, 8ethesda, MD

December 1982

Property Relationships in Miscible Polymers Blends

Professor Donald R. Paul

The University of Texas, Austin, TX

December 1982

Structure and Properties of Polydi acetylenes

Produced from Polyfunctional Diacelytene Monomers

Professor J. B. Lando

Case Western Reserve University, Cleveland, OH

December 1982

Associative Thicknesses

Dr. Barry Bauer

45 Broad St., Summit, NJ January 1983

Etched Cast Restoration: What We Don't Know

Dr. Van P. Thompson

University of Maryland Dental School, Baltimore, MD

January 1983

Conformational and Dynamic Properties of Olefin/

S0„ Polymers in Solution

Professor Walter H. Stockmayer

Dartmouth College, Hanover, NH February 1983

Recent Measurement of Polymer Interaction

Parameter by Scattering Methods

Professor Richard S. Stein

University of Massachusetts, Amherst, MA

February 1983

Injection Moulding of High Strength Polyethylene

Dr. R. K. Bayer

University of Kassel, West Germany

February 1983

74
Entropy Correlation Theory and Diffusion

Measurements for Oriented Polymers

Dr. R. E. Barker, Jr. University of Virginia, Charlottesville, Vk

February 1983

Characterization of Linear and Branched

Polyethylene by Laser Light Scattering

Professor Ben Chu

State University of New York at Stonybrook

February 1983

Diffusion Controlled Growth and Fractal Structure

Dr. Paul Meakin

DuPont Experimental Station, Wilmington, DE

February 1983

Cold-Drawing of Polymers

Professor Bernard Coleman

Carnegie-Mel Ion Univ. , Pittsburgh, PA March 1983

Nonlinear Viscoelasticity of Molten Plastics

Professor Johm M. Dealy

McGill University, Montreal, Canada

March 1983

Osteoinductive Materials from Bone Matrix

Dr. Karl Schmitd

University of Tuebingen, Tuebingen, W. Germany

March 1983

Long Chain Polymers as Substrates for

Biomedical and Organometal 1 ic Reactions

Dr. Harry All cock

Penn State University, University Park, PA

March 1983

Low Frequency Raman Scattering from

Vitreous and Molten B_0~

Professor George Walrafen

Howard University, Washington, DC

March 1983

Synthetic Techniques for Living Polymers

Dr. Barry Bauer

45 Broad St. , Summit, NJ

April 1983

Fluoridation of Enamel and Microleakage

Around Dental Amalgams

Dr Hugo Retif

University of Alabama, Birmingham, AL

April 1983

Influence of Combined Linear & Rotating

Motion on the Friction & Wear of Polymers

Dr. Brian Briscoe

Imperial College, London, England

April 1983

75
Xray Study of the Structure of

Liquid Crystalline Polyesters

Dr. John Blackwell

Case Western Reserve University, Cleveland, OH

April 1983

Descriptions of Diffusion of Small

Molecules in Polymer Blends

Professor Julio Ottino

University of Massachusetts, Amherst, MA

April 1983

New Polymer Structures and Their Properties

Professor Otto Vogl

Polytechnic Inst, of New York, Brooklyn, NY

April 1983

The Morphology of MDI/BDO Based Polyurethanes

Dr. Robert Briber

University of Massachusetts, Amherst, MA

April 1983

Biocompatibility of Dental Casting Alloys

Dr. Heiner

Weber University of Tuebingen, Tuebingen, W. Germany

May 1983

Radiation Chemistry of Polyethylene

and Crystalline Alkanes

Professor Joseph Silverman

University of Maryland, College Park, MD

May 1983

New Aspects of Electrical Conduction in Polymers

Professor Frank Karasz

University of Massachusetts, Amherst, MA

May 1983

Configuration of Immiscible Fluids with

Different Viscosities

Professor D. D. Joseph

University of Minnesota, Minneapolis, MN

May 1983

Endurance of Electrical Insulating Materials

for Combined Thermal Electrical Stress

Professor Luciano Simini

University of Bologna, Bologna, Italy

May 1983

Infrared Intensities: Theory and Applications

Dr. Giuseppe Zerbi

Institute of Macromolecular Chemistry, Milan, Italy

May 1983

Functional Representation of the

Castability of Dental Alloys

Dr. Susumo Hirano

Tsurumi University, Yokohania, Japan

May 1983

76
Curing Kinetics and Morphology of

High Temperature and Rubber Toughened Epoxy

Or. D. Hong

Jet Propulsion Laboratory, Pasadena, CA

May 1983

Corrosion Products of Dental Amalgams

Dr. Sally Marshall

Northwestern University, Chicago, IL

June 1983

Fourier Cross-Correlation Analysis of Impedance

Spectra of Solid State Electrolytic Cells

Dr. Alan D. Franklin NBS, Retired

June 1983

Thermodynamics, Kinetics, Morphology and Chemistry

of Calcium Phosphate Crystal Growth

Dr. E. D. Eanes

NIDR, NIH, Bethesda, MD

June 1983

Calcium Phosphate Inhibitors in Blood

Dr J. L. Meyer

NIDR, NIH, Bethesda, MD

June 1983

Hybrid Materials. and Their Applications

Dr. Hiroyuki Sasabe

Institute of Physical & Chemical Research, Saitama, Japan

June 1983

Photochemical Investigations of Polymers:

Charge Transfer Complexes in Polyolefins, Energy

Migration, Photoyel lowi ng of Epoxy Resins

Dr. N. S. Allen Manchester, United Kingdom

June 1983

LCST Behavior in Polymer Blends: Directional

Specific Interactions and Compressibility

Dr. Gerrit ten

Brinke University of Massachusetts, Amherst, MA

June 1983

Diffraction Studies of Craze Structures

Professor Hugh Brown

Case Western Reserve University, Cleveland, OH

June 1983

Scattering from a Polymer Solution and a Mixture of Polymers at an Arbitrary Concentration

Dr. Henri Benoit

Centre de Recherches sur les Macromolecules, Strasbourg, France

June 1983

Scattering from Copolymer Solutions

Dr. Henri Benoit

Centre de Recherches sur les Macromolecules, Strasbourg, France

June 1983

77
Piezoelectric and Ferroelectric Properties of

Vinylidenefluoride, Trifluoroethylene Copolymer

and its Application to Ultrasonic Transducers

Dr„ Hirogi Ohigashi

Toray Industries, Kamakura, Japan

June 1983

Some Recent SANS Results on Poly(di methyl si 1 oxane) Networks

Dr. Henri Benoit

Centre de Recherches sur les Macromolecules, Strasbourg, France

June 1983

Air Force Ordered Polymer Research Program

Dr. Wade Adams

Wright Patterson AFB, Dayton, OH

July 1983

The Microstructure and Deformation Behavior

of Highly Oriented Polyethylene Films

Dr. Wade Adams

Wright Patterson AFB, Dayton, OH

July 1983

Mechanisms of Network Formation

by Radical Copolymerization

Dr. Girard Hi Id

Centre de Recherches sur les Macromolecules, Strasbourg, France

July 1983

Crazing in Semi Crystalline Isotactic Polystryrene

Professor David T. Grubb

Cornell University, Ithaca, NY

July 1983

Theory of Critical Micelle Concentrations

in Block Copolymer Systems

Dr. L. Leibler

CNRS, Strasbourg, France

July 1983

Brownian Motions in Polymer Solutions and Melt

Dr. D. Richter

Institut fur Festkorperforschung, Julich, Germany

July 1983

Structural Studies on Conducting Polymers

by x-ray and Neutron Diffraction

Dr. C. Riekel

University of Hamburg, West Germany

August 1983

Molecular Studies on Rheology and Microphase

Separation of Block Polymers

Professor Takeji

Hashimoto Kyoto University, Kyoto, Japan

August 1983

Spinodal Decomposition of Polymer Blends

Professor Takeji Hashimoto

Kyoto University, Kyoto, Japan

August 1983

78
Structural Studies on Gels from

Isotactic Polystyrene

Professor Edward Atkins

Univeristy of Bristol, Bristol, England

August 1983

Overview of Theories for the Adsorption

of Homodisperse or Polydisperse Polymers

Dr. Gerard Fleer

DeBreyen 6, Wageningen, The Netherlands

August 1983

NMR Polymers

Professor R. Kitamaru

Institute for Chemical Research, Kyoto University, Japan

August 1983

Photoinitiation of Acrylic Resins

Dr. C. Decker

Laboratory of General Photochemistry Mul house, France

August 1983

Solid State Reaction and Its Use for the Syntheses of Novel

Organic Compounds, Conducting Polymers and Photopolymers

Dr. Hachiro Nakanishi

Research Inst, for Polymers and Textile, Ibaraki , Japan

September 1983

Time-Dependent Properties of Statically Deformed

Glassy Polymers: Dynamic Modulus and Gas Transport

Dr. Thor L. Smith

IBM Research Laboratory, San Jose, CA

September 1983

Kinetics of Decomposition and Crystallization

in Mixtures of PE and POM

Dr. B. J. Jungnickel

Deutsches Kunststofflnstitut, Darmstadt, Germany

September 1983

A Multi parameter Model for Structural Recovery in

Polymer Glasses and its Implications for their

Physical Properties

Professor A. J. Kovacs

Centre de Recherches sur les Macromolecules, Strasbourg, France

September 1983

Xray Studies of the Kinetics of Crystallization

and Recrystallization of Different Polymers

Dr. H. G. Zachmann University of Hamburg, Hamburg, West Germany

September 1983

The Modeling of Crystal Growth; Roughness of

Growth Faces and Nature of the Interfaces

Professor David Sadler

University of Bristol, Bristol, England

September 1983

Recent Neutron Scattering Experiments at JulichStructure,

Conformation and Diffusion of Polymers

Dr. M. Stamm

Institut fur Festkorperforschung, Julich, Germany

September 1983

79
Rutherford Backscattering and NBS Facility

Dr. Hans P. R. Frederikse

Inorganic Materials Division, NBS

September 1983

Enhancement of Polymer Miscibility

Through Specific Interaction

Dr. T. K. Kwei

Industrial Technology Research Institute, Taiwan

September 1983

Technical and Professional Committee Participation and Leadership

Academy of Operative Dentistry

N. W. Rupp, Councilor

American Academy of Gold Foil Operators

N. W. Rupp, Councilor

American Association for Dental Research/International Association

for Dental Research

R. L. Bowen

Member: Dental Materials Group

Wilmer Souder Award Committee

J. M. Antonucci

Member: Dental Materials Group

G. M. Brauer

Member: Dental Materials Group

J. M. Cassel

Member: Dental Materials Group

J. E. McKinney

Member: Dental Materials Group

W. G. deRijk

Member: Dental Materials Group

Student Research Committee

G. C. Paffenbarger

Member: Dental Materials Group

N. W. Rupp

Member: Dental Materials Group

W. Wu

Member: Dental Materials Group

J. A. Tesk

Member: Dental Materials Group

Group Representative: Executive Committee

W. E. Brown

Member: Biological Mineralization Research Award Committee

Mineralized Tissue Group, Councilor

L. C. Chow

Member: Mineralized Tissue Group

Nominating Committee

Teller

80
T. M. Gregory

Member: Mineralized Tissue Group

M<, Mathew

Member: Mineralized Tissue Group

S. Takagi

Member: Mineralized Tissue Group

M. S„ Tung

Member: Mineralized Tissue Group

American Association of Dental Research/Washington Section

J. A„ Tesk

Secretary-Treasurer

American Chemical Society

J. M. Antonucci

Member: Board of Managers

Advertising Editor

G. M. Brauer

Member: Meetings and Expositions Committee

Counci 1 or

American Dental Association

R. L. Bowen

Member: Biomedical Research Support Grant Committee

W. E. Brown

Member: Biomedical Research Support Grant Committee

American Dental Association Special Committee on the Future of

Dentistry

R„ L Bowen

Member: Research Working Group

American Dental Association Specifications Committee

W. E„ deRijk

Member: Subcommittee on Waxes (Specifications 4 and 24)

American Institute of Mining, Metallurgical, & Petroleum Engineers

R. M, Waterstrat

Member: Committee on Alloy Phases

American Institute of Physics

R. K. Eby

Chapter Editor, Physics Handbook

E. A. Kearsley

Member: Committee for Public Policy

American National Standards Committee, MD156, Dental Materials,

Instruments, and Equipment

R„ L. Bowen

Member: Subcommittee on Biological Evaluation of

Dental Materials, Secretary

Go M. Brauer

Member: Government Representative

Denture Resins, Chairman

Z-E Type Material

81
J. M. Cassel

Member: C054, Medical Devices Standards Management

Board, Executive Committee

No Wo Rupp

Member: Alloy for Dental Amalgams, Chairman

Dispensers for Alloys and Mercury, Chairman

Mercury for Dental Amalgam, Chairman

Mechanical Amalgamators, Chairman

J. A. Tesk

Member: Base Metal Alloys

C054, Medical Devices Standards Management

Board, Executive Committee

Dental Implants, Secretary

Dental Materials, Instruments, & Equipment, Chairman

Porcelain/Alloy Systems

USA TAG for ISO TC106, Chairman

American Physical Society

Division of High Polymer Physics

F. A. Khoury

Member: Committee on History of DHPP

I. Co Sanchez

Member: Division of High Polymer Physics, Chairman, 1983-84

Selection Committee, APS High Polymer Physics

Prize, 1983-84

American Society of Mechanical Engineers

R. Wo Penn

Member: Reinforced Thermoset Plastic Corrosion Resistant

Equipment

American Society for Testing and Materials

Committee on Research and Technical Planning

E. Passaglia

Member: Subcommittee on Research Chairman

D-2: Petroleum Products and Lubricants

L. J. Zapas

Member: D2.07 Flow Properties

D2.07A Newtonian Viscometry

D-ll: Rubber and Rubber—Like Materials

E. A. Kearsley

Member

G. B. McKenna

Member

D-20: Plastics

R. K. Eby, Chairman.

Member: D20.01: Executive Subcommittee

J„ D. Barnes

Member: D20.12

020.13

D20.19

D20.70

Olefin Plastics

Statistics, Chairman

Film and Sheeting

Analytical Methods

WG.07: Gas Permeability

82
H. L. Wagner

Member: WG.02 Liquid Size Exclusion Chromatography

WG.05 Molecular Weight Parameters, Chairman

J. Ho Flynn

Member: • D20.30: Thermal Properties

30.7 Fundamental Thermal Methods,

Chairman

D-30: High Modulus Fibers and Their Composites

D. 1. Hunston

Member

E-9: Fatique

G. B. McKenna

Member

R. W. Penn

Member

E-37: Thermal Measurements

S. S. Chang

Member: E37.01: Test Methods and Recommended Practices

E37.05: Thermophysical Properties

J. H. Flynn

Member: E37.03: Nomenclature and Definitions, Chairman

E37.90: Executive Subcommittee

E-45: Geothermal Energy and Resources

E. A. Kearsley

Member: E45.02: Materials

F-2: Flexible Barrier Materials

J. D. Barnes

Member: F02.30: Test Methods

F02.93: Statistical Matters, Chairman

WG.30.2: Barrier Methods, Chairman

F-4: Medical and Surgical Materials, and Devices

G. M. Brauer

Member: Executive Committee

F04.20: Resources

WG.01: Polymeric Materials, Chairman

J. M. Cassel

Member: F04.20: Resources

R.K. Eby

Member

G. B. McKenna

Member

Biomedical Research Support Grant

R. L„ Bowen

Member: 1982-1983 Review Committee

W. E» Brown

Member: 1982-1983 Review Committee

Applications of Ferroelectrics (ISAF), Gaithersburg, MD, 1983 IEEE Inti. Symp

M. G. Broadhurst

Member: Program Committee

83
Case Western Reserve University, Materials Research Laboratory

Advisory Board

R, K. Eby

Member

Chemical Society of Washington

J. Antonucci

Member: Awards Committee

G. M. Brauer

Chairman, Councilors Committee

Award Committee

B. F. Howell

President: 1983

G. Ao Senich

Chairman: Budget Committee

DECUS (Digital Equipment Users' Society)

Washington Area MIN- LSI Users'

J. D. Barnes

Chai rman

Eleventh NATAS Conference

J. H. Flynn

Symposium on Kinetics of Chemical & Physical Processes, Chairman

Geis Foundation for the Advancement of Dentistry

G. C. Paffenbarger

President

Member: Award Committee for Dental Editorial, Chairman

Award Committee for Oral & Maxillofacial Surgery,

Chairman

Award Committee for Periodomtology , Chairman

Government Interagency Panel on Adhesive Bonding Research

D. L. Hunston

Member

International Confederation for Thermal Analysis

J. H. Flynn

Member: Nomenclature Committee

Working Party on Symbols

International Council on Alloy Phase Diagrams

R. M. Waterstrat

Member

International Electrotechnical Commission

TC046, Cables, Wires, & Waveguides for Telecommunication

Equipment

L. J. Zapas

Member: WG.03: Measuring Methods of Polyethylene

TC061, Plastics

L. E. Smith

Member

International Standards Organization

TC106, Dental Materials and Devices

G. M. Brauer

Member: Task Force on Color Stability

84
N. W. Rupp

Member: Restorative Materials

WG.01: U. S. Delegation, Chairman

TG7: Alloys for Dental Amalgams,

Chairman

WG.06: Amalgamation Devices & Accessories,

Chairman

J. A. Tesk, USA Delegation, Chairman

TC150, Implants for Surgery, USTAG

J. M. Cassel , Chairman

TC150/SC2, Cardiovascular Implants for Surgery, USTAG

J. M. Cassel, NBS Representative

International Union of Pure and Applied Chemistry

J. H. Flynn

Member: 4. Macromolecular Division

4.2 Polymer Characterization and Properties

4.2.4 Working Party on Thermal Properties of Polymers

Macromolecules

E. A. DiMarzio

Member: Editorial Advisory Board

Molecular and Cellular Thermobiology (Journal)

B. Dickens

Member: Editorial Board

National Bureau of Standards Advisory Panel for Tariffs on Electron Microscopes Under Florence Agreement

F. A. Khoury, Member

National Bureau of Standards Committee on University of Maryland

Instructional Television System

E. A. DiMarzio, Member

National Bureau of Standards Research Advisory Panel

E. A. DiMarzio, Member

National Bureau of Standards Sigma Xi

B. F. Howell, President, 1982

Member: Executive Committee, 1983

National Center for Small Angle Scattering

C. C. Han

Member: Users Committee

National Health and Medical Research Council of Australia

G. C. Paffenbarger, Consultant

National Institute of Dental Research

R. L. Bowen

Member: Long Range Research Planning & State-of-the-Science

on Composites, Consultant

Panel on Restorative Materials Program

Review Committee for ADA

National Institutes of Health

L. C. Chow

Member: Oral Biology and Medicine Study Section

85
National Research Council

Panel on Polymer Science & Engineering

R. K. Eby, Member

Committee on Room Temperature Curing Resin Systems

B. M. Fanconi , Member

Panel on Civil /Navy Ocean Engineering

Task Group on Materials and Structure

Nondestructive Testing of NRC

R. K. Eby, Member

North American Thermal Analysis Society

J. H. Flynn

International Confederation for Thermal Analysis Councilor

Member: Awards Committee

Executive Committee

Ohio Dental Association

G. C. Paffenbarger

Member: Callahan Memorial Committee

Piezoelectricity in Biomaterials and Biomedical Devices, Inti. Symposium,

Pisa, Italy

M. G. Broadhurst

Member: Program Committee

Publication Committee

Polymer (Journal)

R. K. Eby, U. S. Associate Editor

Polymer Degradation and Stablility (Journal)

J. H. Flynn, Editorial Board Member

Polymer Physics Gordon Conference

E. A. DiMarzio, Chairman

Smithsonian Institution

American Academy of the History of Dentistry

Advisory Committe

G. C. Paffenbarger

Society of Plastics Engineers

R. K. Eby

Member: Selection Committee for SPE International

Award for Research, Chairman

G. B. McKenna

Member: Technical Publications

Society of Rheology

D. L. Hunston

Member: Committee on Education

Member: Site Selection Committee

J. E. McKinney, Member

E. A. Kearsley

Member: Executive Committee

G. B. McKenna

Member: Committee on Education

86
Symposium on Structure and Bonding in Noncrystall ine Solids

E. A. DiMarzio, Committee member

Technical Meeting of Digital Equipment Users' Society of "Database

Management in Small Systems"

J. D. Barnes, Chairman

Third Conference on Fractals in the Physical Sciences

R. J. Rubin

Member: Organizing Committee

Thermochi mica Acta (Journal)

J. H. Flynn

Member: Editorial Board

Twelfth North American Thermal Analysis Society, 38th Calormetry Society Conf.

Jo Ho Flynn

Session Chairman

U.S. Air Force

National Civilian Consultant to the Surgeon General

N. W. Rupp

U.S. Army

Medical R&D Advisory Committee

G. C. Paffenbarger

US/Yugoslav Science and Technology Program

Physico-Chemical Aspects of Urinary Stone Formation

W. E. Brown, Monitor

Thermal Degradation of Polymers

J. H. Flynn, Monitor

University of Virginia, Department of Materials Science

G. C. Paffenbarger, Consultant

University of Massachusetts Advisory Board of Polymer Research

Institute

R. K. Eby, Member

Washington Academy of Sciences

B. F. Howell

Member: Executive Committee

Washington Area MINC Users Group

J. D. Barnes, Chairman

Washington Philosophical Society

B. F. Howell

Member: Executive Committee (Member- at- large)

Younger Chemists Committee

Go A. Senich

Member: Activities Committee

Publ i cations

Bascom, W. D. ; Hunston, D. L. The fracture of epoxy and elastomermodified epoxy polymers, chapter 14 in Adhesion 6. Allen, K. W. edo London, England: Applied Science Publishers; 1982.

87
Bowen, R. L. ; Cobb, E. N. ; Rapson, J. E. Adhesive bonding of various

materials to hard tooth tissues: improvement in bond strength to dentin. J. Dent. Res. 61(9): 1070; 1982.

Bowen, R. L. ; Cobb, E. N. ; Setz, L. E. Adhesive bonding to dentin and

enamel. Dentistry 82: 11; 1982.

Bur, A. J. Resistivity of ultra drawn polyvinylidene fluoride. 1982

Annual Report, Conference Electrical Insulation and Dielectric

Phenomena; 156.

Bur, A. J. Dielectric loss spectra of polymers at microwave frequencies.

Nat. Bur. Stand. (U.S.) NBSIR 82-2603; December 1982.

Chen, T. M. ; Brauer, G. M. Solvent effects on bonding organo-silane

to silica surfaces. J. Dent. Res. 61: 1493; 1982.

Chow, L. C. ; Brown, W. E. An approach to remineralization via saliva.

Proc. of Third Annual Conference on Foods, Nutrition and Dental Health,

October 1979, Vol. 2 (Chicago, IL 1982).

Davis, G. T. Phase transition and ferroelectric polarization in a vinyl idene fluoride—trifluoroethylene copolymer. Polymer Preprints,

31(5): 937; 1982.

Dehl , R. E. On the characterization of porosity in PTFE-carbon composite

implant materials by mercury porosimetry. J. Biomed. Mater. Res. 16: 715;

1982.

Dermann, K. ; Rupp, N. W. ; Brauer, G. M. Effect of hydrophilic diluents on the properties of cured composites. J. Dent. Res. 61(11): 1250; 1982.

DiMarzio, E. A.; Guttman, C. M. Polymer crystallization: proper accounting

of a wider class of paths to crystallization- variation on a theme of point.

J. Appl . Phys. 53: 6581; 1982.

Eby, R. K. ; Davis, G. T. ; Wang, F. W. ; Broadhurst, M. G. ; Fanconi , B. M.

Sanchez, I. C. ; Tesk, J. A. Polymer science and standards division.

Kobunshi 31(11): 1026; 1982.

Han, C. C. ; Amis, E. J. Cooperative and self diffusion of polymers by

dynamic scattering in semidilute solutions. Polymer 23: 1403; 1982.

Matsushita, Y. ; Furakashi , H. ; Choshi, H. ; Noda, I.; Nagasawa, M; Fujimoto, T. ; Han, C. C. Polymer Journal (Japan) 14: 489; 1982.

McKinney, J. E. ; Wu, W. Relationship between surface damage and wear of

dental restorative composites. J. Dental Res. 61(9): 1083; 1982.

Mjor, I. A.; Hensten-Petersen, A.; Bowen, R. L. Biological assessments

of experimental cavity cleansers: correlation between in vitro and in

vivo studies. J. Dent. Res. 61(8): 967; 1982.

Paffenbarger , G. C. ; Rupp, N. W. ; Coyne, M. P. Dimensional changes of

four amalgams after five years of storage in air at 60, 37, and 23 C. J. Dent. Res. 61(12): 1427; 1982.

Paffenbarger, G. C. ; Rupp, N. W. ; Patel, P. R. Dimensional changes of a high-tin content amalgam. J. Dent. Res. 61(12): 1423; 1982.

Peterlin, A. Accordion type laser-raman scattering by polymers. J. Polym.

Sci. (Poly. Phys. Ed.): 20: 2329; 1982.

88
Senich, G. A. A review of the migration of food-contact organotin stabilizers

from poly(vinyl chloride). Polymer 23: 1385; 1982.

Takagi, S; Mathew, M. ; Brown, W. E. The structure of sodium strontium

phosphate nonahydrate. Acta Cryst. B38: 1408; 1982.

Wang, F. W. ; Howell, B. F. Fluorescence measurement of antioxidant migration

from low-density polyethylene into 1 -propanol. Proceedings of the ACS organic

coatings and applied polymer science symposium; 47: 41; 1982.

Wu, W. ; McKinney, J. E. Influence of chemicals on wear of dental

composites. J. Dental Res. 61(10): 1180; 1982.

Amis, E. J. ; Glinka, G. J. ; Han, C. C. ; Hasegawa, H. ; Hashimoto, T.

Lodge, T. P. ; Matsushita, Y. SANS measurements of block chains at NBS.

ACS Polymer Preprint 23(2): 1983.

Antonucci , J. M. ; Debelius, E. Extent of polymerization of dental

resins by differential scanning calorimetry. J. Dent. Res. 62(2): 121; 1983.

Barnes, J. D. Standard reference materials for gas transmission measurements

in "industrial gas separations". ACS Symposium Series No. 223, T. E. Whyte, Jr.,

C. M. Yon, and E. H. Wagener Eds., American Chemical Society, Washington, DC 1983.

Bowen, R. L. ; Nemoto, K. ; Rapson, J. E. Adhesive bonding of various materials

to hard tooth tissues; forces developing in composite materials during

hardening. JADA 106: 475; 1983.

Brauer, G. M. ; Stansbury, J. W. ; Argentar, H. Development of high-strength,

acrylic resin-compatible adhesive cements. J. Dent. Res. 62: 366; 1983.

Brown, W. E. ; Chow, L. C. Surface equilibria of sparingly soluble crystals.

Colloids and Surfaces 7: 67; 1983.

Brown, D. W. ; Lowry, R. E. ; Smith, L. E. Prediction of the long term

stability of polyester based recording media, Nat. Bur. Stand. (U.S.)

NBSIR 83-2750; July 1983

Clark, E. S. ; Eby, R. K. ; Piermarini, G. J. ; Block, S. The crystal structure

of polytetrafluoroethylene homo and copolymers in the high pressure phase.

Polymer Preprints, ACS Meeting, Washington, DC; August 1983.

Chang, S. S. ; Maurey, J. M. ; Pummer, W. J. Solubilities of two n-alkanes in

various solvents. J. Chem. Eng. Data 28: 187; 1983.

Crissman, J. M. ; Zapas, L. J. ; Khoury, F. A. Relationship between morphology

and mechanical properties of ultra high molecular weight polyethylene.

Third Annual report to the FDA, Bureau of Medical Devices, NBSIR 83-2696.

Crissman, J. M. ; Zapas, L. J. ; Mechanical behavior of isotactic polypropylene

subjected to various strain histories in uniaxial extension. Polymer 24: 351; 1983.

Crissman, J. M. A new test method for determining environmental stress-crack

resistance of ethylene based plastics. Testing and evaluation ASTM, 11(4): 223;

1983.

DeCandia, F. D. ; Perullo, A. Vittoria, V.; Peterlin, A. Mechanical and transport

properties of drawn low pressure low density polyethylene. J. Appl. Poly.

Sci. 28: 1815; 1983.

Dehl , R. E. Characterization of porosity in porous polymeric implant materials.

Nat. Bur. Stand. (U.S.) NBSIR 83-2645 (FDA); February 1983.

89
Dickens, B. ; Flynn, J. H. Thermogravimetry applied to polymer degradation

kinetics. Chapter 12 in Polymer Characterization, C. D. Craver, Ed., Adv.

in Chem. Series 203, ACS; Washington, DC; 209; 1983.

Eby, R. K. ; Davis, G. T. ; Wang, F. W. ; Broadhurst, M. G. ; Fanconi , B. M.

Sanchez, I. C. ; Tesk, J. A. Polymer science and standards division. Polyra.

News 9(4): 81; 1983.

Eby, R. K. ; Broadhurst, M. G. ; Davis, G. T. ; Wang, F. W. ; Fanconi, B. M; Tesk, J. A.; Sanchez, I. C. Polymer science and standards division 1982.

Nat. Bur. Stand. (U.S.) NBSIR 82-2607; 1983 March.

Farmer, B. L. ; Eby, R. K. Molecular packing in 15/7 "hexagonal" polytetrafluoroethylene. Proc. ACS Meeting, Polymer Preprints, Washington, DC;

August 1983.

Fanconi, B. M. Molecular processes affecting mechanical failure of polymeric

materials. Nat. Bur. Stand. (U.S.) NBSIR 83-2682; June 1983.

Flynn, J. H. The isoconversional method for determination of energy of

activation at constant heating rates—corrections for the doyle approximation.

J. Therm. Anal. 27; 92; 1983.

Fraker, A. C. ; Rutt, A. W. ; Bundy, K. J. ; Smith, J. D. ; Penn, R. W. ; Van Orden,

A.C. Studies of interface bondings on implant alloys, Nat. Bur. Stand. (U.S.)

NBSIR 83-2736.

Hansen, R. J. ; Hunston, D. L. Effects of fluid viscosity and viscoelasticity

on flow- gene rated waves on a compliant surface. 131: 161; 1983.

Hunston, D. L. Relationship between mechanical properties and performance of

inks as the basic for quality control techniques. Nat. Bur. Stand. (U.S.)

NBSIR 83-2691; 1983.

Hunston, D. L. ; Rushford, J. L. ; Newitt, W. R. ; Vaudreuil, B. A. Rheology

of cure for intaglio printing inks. Organic Coatings and Plastics Prep.

47: 513; 1983.

Hunston, D. L. ; Wang, S. S. ; Kinloch, A. J. Characterization of fracture

behavior of adhesive joints. Organic coatings and plastics Prep. 47: 408; 1983.

Hunston, D. L. Cure monitoring of thermosetting polymers by an ultrasonic

technique. Thompson, D. 0., ed. Review of Progress in Quantitative Nondestructive Evaluation; New York, NY: Plenum Publ. Co.: 1711; 1983.

Hunston, D. L. ; Rushford, J. L; Newitt, W. R. ; Vaudreuil, B. A. Rheology of

Cure for Intaglio Printing Inks, chapter 10 in Chemorheology in Thermosetting

Polymers. May, C. , ed. ; ACS Symp. Ser. 227; Washington, DC, 1983.

Kranbuehl , D. E. ; Verdier, P. H. Interpretation of quasi-elastic light

scattering data for flexible chains: model dependence. Polymer, 24: 383; 1983.

LeGeros, R. Z. ; Tung, M. S. Chemical stability of C0o + F- containing aptites.

Carries Res. 17:419; 1983.

Mabie, C. P. ; Menis, D. L; Whitenton, E. P. ; Trout, R. L. ; Metherate, R. S.

Ferry, C. H. Gel-route preparation of low fusing dental porcelain frit. J. Biomed. Mater. Res. 17(4): 691; 1983.

McKenna, G. B. ; Kovacs, A. J. Anomalies in the physical ageing behavior of

PMMA. Proc. 12th NATAS/38th Calorimetry Conf. , Williamsburg, VA; 1983.

90
McKenna, G. B. ; Kovacs, A. J. Anomalies in the physical ageing behavior of

PMMA, Polymer Preprints; 1983.

Metz, P. D. ; Tech, H„ ; VanderHart, 0. L. ; Wilhelm, W. G. Evaluation of

polyacrylonitrile as a potential organic polymer photovoltaic material.

Polymers for Solar Energy Utilization, ACS Symposium Series 220: 421; 1983.

Olsen, R. B. ; Hicks, J. C. ; Broadhurst, M. G. ; Davis, G. T. Temperature

dependent hysteresis study in polyvinyl idene fluoride; Appl . Phys. Lett. 43:127;

1983.

Perry, B. W. ; Doumas, B. T. ; Bayse, 0. D. ; Butler, T. ; Cohen, A.;

Fellow, W. ; Garber, C. C. ; Howell, B. F. ; Koch, T. ; Krishnamurthy, S.

Louderback, A.; McComb, R. B. ; Miller, D. ; Miller, R. R. ; Rand, R. W.

Schaffer, R. A candidate reference method for determination of bilirubin

in serum. Test for Transferability. Clin. Chem. 29: 297; 1983.

Peterlin, A. Polymer morphology & mechanics: the strength and stiffness

of polymers. New York, NY: Marcel Dekker, Inc.; 97; 1983.

Peterlin, A. Transport of small molecules in polymers, chapter in controlled

drug delivery, Bruck, S. ed. CRC Press I; 15; 1983.

Peterlin, A; Mechanical and transport properties of drawn semi crys tall ine

polymers. Chapter in the book The Strength and Stiffness of Polymers,

Zachariades, A. E. ; Porter, R. S. eds. M. Dekker, New York 97; 1983.

Phillips, J. C. Mechanical relaxation of liner materials in acetic acid,

Nat. Bur. Stand. (U.S.) NBSIR 82-2615 1983.

Rubin, R. J. ; Weiss, G. H. Limiting thickness of an adsorbed polymer chain

random flight model. J. Chem. Phys. 78: 2039; 1983.

Rubin, R. J. Span of an adsorbed chain in a lattice random walk model.

Bull. Am. Phys. Soc. 28(3): 473; 1983.

Sanchez, I. C. ; Poser, C. I. Surface thermodynamics of liquid polymers: theory.

Physicochemical aspects of polymer surfaces, Vol. I, K. L. Mittal, ed.

,

Plenum Press, New York; 173; 1983.

Sanchez, I. C. Liquids: surface tension, compressibility, and invariants.

J. Chem. Phys. 79: 405; 1983.

Sanchez, I. C. Bulk and interface thermodynamics of polymer alloys. Ann. Rev. Mat! . Sci. 13: 1983.

Senich, G. A.; Florin, R. E. Radiation curing of inks and coatings.

Nat. Bur. Stand. (U.S.) NBSIR 33-2722 1983.

Takagi, S. ; Mathew, M. ; Brown, W. E. A glaserite-type structure; calcium

tripotassium hydrogenbis(phospahte) , CaK3 H(P04 ) 2

. Acta Crystallogr. C39: 166;

1983.

Tesk, J. A.; Hinman, R. W. ; Widera, G. E; Holmes, A. D. ; Cassel , J. M. Effects

of porcelain/alloy interfacial diffusion zones on thermo-mechanical strain.

J. Dent. Res. 63(5): 585; 1983.

Tung, T. S. Surface properties of hydroxyapatite in fluoride solution. Colliods

and Surfaces 6: 283; 1983.

Tung, M. S. ; Brown, W. E. Characterization and modification of electrochemical

properties of teeth. J. Dent. Res. 62(1): 60; 1983.

91
VanderHart; Atalla, R. H. Studies of microstructure in native celluloses

using solid-state 13 C NMR. Preprints of the Inti. Dissolving and Specialty

Pulps Conference, Boston, Ma 1983.

Vogel, G. L. ; Chow, L. C. ; Brown, W. E. A microanalytical procedure for the

determination of calcium, phosphate and fluoride in enamel biopsy samples.

Caries Res. 17: 23; 1983.

Wagner, H. L. ; Dillon, J. G. A low shear, high temperature rotational viscometer: the viscosity of ultrahigh molecular weight polyethylene, in Polymer

Characterization, Adv. in Chem. Ser. 203, Craver, C. D. , ed. ACS, Washington,

DC 1983.

Wang, F. W. Applications of fluorescence techniques to polymer systems:

polymer compatibility and segmental mobility. Polymer Preprints, Japan

32(1): 79; 1983.

Weiss, G. H.: Rubin, R. J. Random walks: theory and selected applications,

Advances in Chem. Phys. 52: 363; 1983 (John Wiley & Sons, Inc., NY).

Wu, W. ; Cobb, E. ; Dermann, K. ; Rupp, N. W. A silver staining technique for

detecting margin leakage of dental composite restorations. J. Biomed. Matl

Res., 17: 37; 1983.

Wu, W. Small angle neutron scattering of partially segregated polymer blends,

Polymer 24: 43; 1983.

Wu, W; Cobb, W; Dermann, K. ; Rupp, N. W. Detecting margin leakage of dental

composite restorations. J. Biomed. Mater. Res. 17: 37; 1983.

Bowen, R. L; Cobb, E. N. A method for bonding to dentin and enamel. JADA;

in press.

Brauer, G. M. ; Stansbury, J. A. Dental cements containing esters of syringic

acid. J. Dent. Res. in press.

Broadhurst, M. G. Rigorous bounds for the calculated diectric constants of

ferroelectric polymers. Ferroelectrics ; in press.

Brown, W. E. ; Chow, L. C. ; Mathew, M. Thermodynamics of hydroxyapatite

surfaces. Croatica Chemica Acta; in press.

Brown, D. W. ; Lowry, R. E. ; Smith, L. E. Equilibrium acid concentrations

in hydrolyzed polyester diols and polyester polyurethanes, Polymer preprints;

in press.

Brown, D. W. ; Lowry, R. E. ; Smith, L. E. Equilibrium acid concentrations

in hydrolyzed polyesters and polyester polyurethane elastomers, J. of

Appl. Poly. Sci.; in press.

Chang, S. S. ; Pummer, W. J. ; Maurey, J. R. Fat-simulating and accelerating

solvents for polyolefins and MWD of solvent extracts of polyethylenes.

Polymer; in press.

Chang, S. S. Migration of low molecular weight components from polymers.

I. methodology and diffusion of n-octadecane in polyolefins. Polymer; in

press.

Chang, S. S. Specific heat of phenolic resins. ACS Polymer Preprints 24: in press.

Chang, S. S. Thermodynamic properties and glass transition of polystyrene.

J. Polym. Sci.; in press.

92
Dehl , R. E. Reply to "comments on 'on the characterization of porosity in

PTFE-carbon composite implant materials by mercury porosimetry'". J. Biomed.

Mater. Res.; in press.

DeReggi, A. S. Transduction phenomena in ferroelectric polymers and their

role in pressure transducers. Proc. of the 1983 IEEE Inti. Symp. on Applications of Ferroelectrics , Gaithersburg, MD; in press.

DeReggi, A. S. Polymeric transduction phenomena and their role in biomedical

applications; Inti. symp. on piezoelectricity in biomaterials and

biomedical devices, Pisa, Italy; in press.

Dickens, B. ; Marchal , J. Oxidation of polystyrene in solution. Polym.

Degrad. Stab. ; in press.

Dickens, B. Thermal degradation study of polyisobutylene using factor-jump

thermogravimetry. J. Thermal Anal.; in press.

Dickens, 8. Factor- jump thermogravimetry as applied to the study of polymer

degradation. Chapter in advances in fundamentals of polymer stability and

degradation. Jellinek, H. H. G. , ed. Elsevier, Publ.; in press.

Dickens, B. ; Martin, J. W. ; Waksman, D. Solar type photolytic and thermal

degradation of plates of poly(methyl methacrylate). Division of polymer

chemistry preprints; ACS 24; in press.

Dickens, B. ; Martin, J. W. ; Waksman, D. Thermal and photolytic degradation

of plates of poly(methyl methacrylate) containing monomer. Polymer; in press.

Fanconi, B. M. Fourier transform infrared spectroscopy of polymers-theory

and application, J. of Test, and Evaluation; in press.

Fanconi, B. M. Chain scission and mechanical failure of polyethylene, J. of

Appl . Phys. ; in press.

Flynn, J. H. ; Florin, R. Polymer degradation and pyrolysis mechanism, Chapter

4 in Pyrolysis and GC in Polymer Analysis, S. A. Liebman and E. J. Levy, eds.

Marcel Dekker, Inc., New York; in press.

Furukawa, T. ; Lovinger, A. J. ; Davis, G. T. ; Broadhurst, M. G. Dielectric

hysteresis and nonlinearity in a 52/48 mol percent copolymer of vinylidene

fluoride and trifluoroethylene; in press.

Guttman, C. M. Some remarks in the history and development of the ASTM E-37

purity method. Purity Determinations by Thermal Methods, ASTM Symp. Series;

in press.

Guttman, C. M. ; DiMarzio, E. A. Monte carlo modeling of kinetics of polymer

crystal growth-Regime III and its implications on chain morphology, J. Appl.

Phys.; in press.

Hammonda, B. ; Akacasu, A. Z. ; Lodge, T. P. ; Han, C. C. Dynamic scattering from

bimodal polymer solutions. I. apparent diffusion coefficient. Macromolecules;

in press.

Han, C. C. ; Amis, E. J. ; Matsushita, Y. Dynamic light scattering measurements

of polystyrene in semidilute theta solutions. Polymer; in press.

Hunston, D. L. ; Bascom, W. S. Effects of lay-up, temperature, and loading

rate in double cantilever beam tests of interlaminar crack growth. Composite

Technology Review; in press.

93
Hunston; D. L. ; Wang, S. S. ; Kinloch, A. J. Characterization of fracture

behavior of adhesive joints. Inti. Symp. on, Adhesive Joints; in press.

Kinloch, A. J. ; Shaw, s. J. ; Tod, A. A.; Hunston, D. L. Deformation and

fracture of rubber toughened epoxy: 1. microstructure and fracture studies.

Polymer; in press.

Kinloch, A. J. ; Shaw, S. J. ; Hunston, D. L. Deformation and fracture behavior

of a rubber toughened epoxy: 2. failure criteria. Polymer; in press.

Lang, S. S. ; DeReggi , A. S. ; Mopsik, F. I.; Broadhurst, M. G. Pre-existing

polarization and influence of electrode materials on PVF2 electrets as determined by thermal pulse and pyroelectric methods. J. Appl. Phys. ; in press.

lovinger, A. J. ; Furukawa, T. ; Davis, G.T. ; Broadhurst, M. G. Crystallographic changes characterizing the curie transition in three ferroelectric

copolymers of vinyl i dene fluoride and trifluoroethylene. 1. as-crystallized

samples; in press.

Lovinger, A. J. ; Furukawa, T. ; Davis. G. T. ; Broadhurst, M. G. Crystallographic changes in characterizing the curie transition in three ferroelectric

copolymers of vinyl idene fluoride and trifluoroethylene. 2. oriented or poled samples; in press.

Lodge, T. P. ; Han, C. C; Akcasu, A. Z. Temperature dependence of dynamic light

scattering in the intermediate momentum transfer region, Macromolecules; in press.

Ludeman, S. M. ; Shao, K-L; Zon, G. ; Himes, V. L. ; Mighel, A. D. ; Takagi , S. 0-iminyl esters of N, N-bis(2-chloroethyl )phosphorodiamidic acid, synthesis,

x-ray structure determination, and anticancer evaluation. J. Med. Chem. ; in

press.

McCrackin, F. L. ; Guttman, C. M. ; Akcasu, A. Z. Monte carlo calculations of

the hydrodynamic radii of polymers in theta and good solvents. Macromolecules;

in press.

McKenna, G. B. ; Zapas, L. J. Experiments on the small strain behavior of

cross! inked natural rubber I. torsion. Polymer; in press.

McKenna, G. B. ; Zapas, L. J. Experiments on the small strain behavior of

crosslinked natural rubber II. extension and compression. Polymer; in press.

Mopsik, F. I.; DeReggi, A. S. The poling behavior of polyvinyl idene

fluoride at room temperature. Appl. Phys. Lett.; in press.

Passaglia, E. ; Khoury, F. A. Crystal growth kinetics and the lateral habits

of polyethylene crystals; in press.

Peterlin, A.; DeCandia, F. ; Perullo, A.; Vittoria, V. Transport properties

of drawn isotactic polypropylene. Proc. Inti. Symp. on Polymers; in press.

Peterlin, A. Transport properties as an extremely sensitive indicator of the

status of the amorphous component in the elastically and plastically deformed

semicrystalline polymer. Proc. Inti. Symp. on Polymers; in press.

Phillips, J. C. ; Peterlin, A. Diffusion of ethylacetate in strained polyethylene.

J. Polym. Sci. (Polym. Sci. Ed.); in press.

Phillips, J. C. ; Peterlin, A.; Waters, P. F. Stress relaxation of polyvinyl idene

fluoride in ethyl acetate vapor, ACS Polymer Preprints; in press.

Phillips, J. C. ; Peterlin, A.; Waters, P. F. The effect of elastic and

plastic deformation on the solubility of ethyl acetate vapor in polyvinyl idene

fluoride (PVF2 ), ACS Polymer Preprints; in press.

94
Sanchez, I. C. On the nature of polymer interfaces and interphases, Polym.

Eng. Sci . ; in press.

Tung, M. S. ; Brown, W. E. An intermediate state in hydrolysis of amorphous

calcium phosphate. Calcif. Tiss. Xnterntl.; in press.

VanderHart, D. L. ; Atalla, R. H. Native celluloses as composites of two

distinct crystalline forms. Science; in press.

Wang, F. W. ; Lowry, R. E. ; Grant, W. H. In- situ monitoring of polymerization

reactions by excimer fluorescence technique. Organic coatings and applied

polymer science proceedings; in press.

Wang, F. W. ; Lowry, R. E. ; Grant, W. H. Novel excimer fluorescence method

for monitoring polymerization. 1. Polymerization of methyl mathacrylate.

Polymer; in press.

Waterstrat, R. M. The Hf-Os constitution diagram. J. of Less Common Metals;

n press.

Wignall, G. D. ; Wu, W. A SANS investigation into the role of melting and

recrystallization during solid state deformation of polyethylene. Polymer;

in press.

Wu, W. ; Fanconi. B. M. Post-curing of dental restorative resin, Polym.

Eng. and Sci.; in press.

Wu, W. ; Debelius, E. E. ; Moffa, J. F. ; Ellison, J. A. Subsurface damage

layer of in-vivo worn dental composite restorations. J. Dent. Res. ; in press.

Zapas, L. J. ; Crissman, J. M. The necking of semi crystal line polymers in

tension, Proc. of the workshop on instabilities and two phase systems,

March 1983; in press.

Zapas, L. J. ; Crissman, J. M. The creep and recovery behavior of ultra high

molecular weight polyethylene in the region of small uniaxial deformation.

Polymer; in press.

Special Reports

Cassel , J. M. ; Tesk, J. A.; Brauer, G. M. ; Antonucci , J. M.

Wu, W. ; McKinney, J. E. Properties and interactions of oral

structures and restorative materials. Annual report to National

Institute of Dental Research (NIDR); October 1982 to September 1983;

in press.

Books

Tesk, J. A. Solders and fluxes. Chapter in Dentists Desk Reference,

Materials, Instruments and Equipment, 2nd ed. , American Dental

Association Publications; in press.

Tesk, J. A.; Waterstrat, R. M. Physical metallurgy of dental casting

alloys, Sections, C, D, E, and F. Encyclopedia of Materials Science

and Engineering, Pergamon Press; in press.

Consulting and Advisory Services

NIDR Grant Proposal Reviewer

J. A. Tesk

American National Standards Institute

B. Dickens

95
External Recognition

Or. G. C. Paffenbarger

Research Associate, American Dental Association

Distinguished Service Award of American Dental Association

November 1982

Dr. G. C. Paffenbarger

Research Associate, American Dental Association

Guest of Honor at 39th Annual Dental Post-College Assembly

Dental Faculty and Dental Alumni Assoc., Ohio State University

April 1983

New SRMs

SRM 1470, Polyester Film SRM for Gas Transmission Measurements

J. D. Barnes, 1983

Patents

Cementitious Dental Compositions Which do not Inhibit Polymerization

G. M. Brauer, H. Argentar, and J. W. Stansbury

U. S. Patent #4,362,510

December 7, 1982

Method for Obtaining Strong Adhesive Bonding of Composites to

Dentin, Enamel and Other Substrates

R. L. Bowen

Filed January 10, 1983

Isotonic Monomer Formulations

R. L. Bowen

U. S. Patent «4, 373, 035

February 8, 1983

Compositions and Methods for Topically Fluoridating or Mineralizing Dental Tissue

W. E. Brown and L. C. Chow

Filed March 25, 1983

Industrial Interactions

Archival Technical Papers Coauthored with Industrial Employees

Bascom, W. D. ; Hunston, D. L. The fracture of epoxy and

elastomer-modified epoxy polymers. Chapter 14 in Adhesion

6. Allen, K. W. , ed. London, Applied Science Publishers, 1982.

Crissman, J. M. Participated in the 4th Annual Plastic Piping

Materials Workshop sponsored by the Gas Research Inst.,

Chicago, IL April 1983.

VanderHart, D. L; Atallas, R. H. Studies of microstructure

in native celluloses using solid-state 13 C NMR, Preprints

of the Inti. Dissolving and Specialty Pulps Conf . , Boston, 1983.

Hunston, D. L. ; Bascom, W. D. Effects of lay-up, temperature,

and loading rate in double cantilever beam tests of interlaminar crack growth, Composite Technology Review; in press.

VanderHart, D. L. ; Atalla, R. H. Native celluloses as composites

of two distinct crystalline forms, Science; in press.

96
Formal Visits

Rohm and Haas, Inc. /6/1/83/Discussed the research associate . program and expressed interest in collaborating with NBS in

further work on the photooxidation and thermal degradation

of poly(methyl methacrylate).

Feldmuhle Co. /5/10/83/Bonding test for forced- fused-tometal systems.

Shofu Dental Manufacturing/4/29/83/Testing amalgam, bonding

of composites to dentin, vanallate cements.

Nipon Silken Dental Co. /II /24/82/Casting of dental alloys,

effects of temperature and investments.

G. C. Dental Co. /10/18/82/Cl ini cal behavior of glass-ionomer

cements and new dental cements.

Bayer AG/3/22/83/Composite chemistry including acceleration, monomer and bonding to fillers.

ICI Pharmaceutical s/3/15/83/Composite resins, strength, wear,

filler loading, coupling agents.

Dentsply International/4/26/83/Pursue agreement for industrial

research associate.

Coe Laboratories/4/19/83/Dental composite and surgical bone

cement chemistry.

Howmedica Inc. /2/24/83/Modification leading to improvement

of bone cement-implant system.

Colgate Palmolive Co. /2/25/83/Fluoridation techniques in

development and fluoride-calcium phosphate chemistry.

Health Services Inti., Inc. /1/22/83/Information on dental

products for third world nations.

Bell Laboratories/l/20/83/0verview of Programs.

Sulzur Brothers/10/25/82/Discuss merits of bone cement

implant system as cementless orthopedic implants.

Martin Marietta/l/19/1983/0verview of Programs.

American Dental Association/2/28/83/0verview of Programs.

Gas Research Institute/5/24/83/0verview of Programs.

NBS-114A (REV. 2-80

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

PUBLICATION OR

REPORT NO.

NBSIR 84-2813

2. Performing Organ. Report No. 3. Publication Date

January 1984

4. TITLE AND SUBTITLE

Polymer Science and Standards Division Annual Report 1983

5. AUTHOR(S)

L. E. Smith, M. G. Broadhurst, G. T. Davis, F. W. Wang, B. M. Fanconi , J. A. Test

and I. C. Sanche z

6. PERFORMING ORGANIZATION (If joint or other than NBS, see in struction s)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

3. Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

NBS

Washington, DC 20234

10. SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FiPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most si gnificant information. If document includes a significant

bi bliography or literature survey, mention it here)

Although synthetic polymers have been used as materials for technology during only

three quarters of a century, they have left little of our economy, technology,

industry, science, and culture untouched. We have moved rapidly into an age in which

an evergrowing number of humanity's needs are served by polymers. The volume currently produced exceeds that of steel and forms the basis of industries which add over

$106 billion of value by manufacturer (a measure of the relative economic importance

of manufacturing among industries) and provides 3.3. million jobs. Recent summaries

show that polymers and polymer composites research already accounts for about 47 percent of the total industrial R&D expenditure for metals, polymers, and inorganic

materials. Among these materials, polymers also constitute about 40 percent of^the

value added by manufacturer, 45 percent of the jobs, 49 percent of the number of

scientific publications, and 42 percent of the American Society for Testing and Materials (ASTM) standards.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

Chemical durability, characterization; dental and medical materials; dielectric

plastics; performance; polymers; mechanical durability; migration.

13. AVAILABILITY

jy j Unlimited

r~] For Official Distribution. Do Not Release to NTiS

j | Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

| XI Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

110

15. Price

$ 13.00

USCOMM-DC 6043-PSO
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