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NBS

PUBLICATIONS

Imtitute for Materials Science and Engineering

POUTMERS

NAS-NRC

Assessment Panel

January 20-21 , 10B7

NBSIR 86-3437

U.S. Department of Commerce

National Bureau of Stendards

-OC

inn

.1156

H6-3437

1986 -

Technical Activities

1986
X-ray pole figure diagram of the 200 reflection from an oriented

polyethylene film. The figure was taken on a highly automated x-ray apparatus recently constructed at NBS that is available to industrial and academic users.
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RESEARCH

INFORMATION CENTER

Institute for Materials Science and Engineering i>u.

/.

T if

L E. Smith, Chief

B. M. Fanconi, Deputy

NAS-NRC

Assessment Panel

January 20-21, 1987

NBSIR 86-3437

U.S. Department of Commerce

National Bureau of Standards
POLYMERS DIVISION

CHIEF

Leslie E. Smith

Phone: (301) 975-6762

'Deputy chief , ‘r f

I

'

• '

. ' Bruno. M,. Fanconi t ; ’*'^7 Phone: (301) 975-6770

'

ASSISTANT CHIEF

Martin G. Broadhurst

Phone: (301) 975-6765 : <. ,

GROUP LEADERS

Electrical Properties

G. Thomas Davis

Phone: (301) 975-6725

Chemical Performance & Standards

Francis W. Wang

Phone: (301) 975-6726

Mechanical Performance

Bruno M. Fanconi

Phone: (301) 975-6770

Polymer Composites

Donald L. Hunston

Phone: (301) 975-6838

Polymer Blends

Charles C. Han

Phone: (301) 975-6771

Dental & Medical Materials

John A. Tesk

Phone: (301) 975-6801 ,
Polymers

Division

LESLIE E. SMITH, 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.

BRUNO M. FANCONI, Deputy

Chief. 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.

MARTIN G. BROADHURST,

Assistant 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.

G. THOMAS DAVIS, 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.

FRANCIS W. WANG, 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.

DONALD L. HUNSTON, Group

Leader, Polymer Composites. Dr. Hunston was born in Springfield,

Ml. He earned degrees in mathematics and chemistry at Kent State University. Prior to joining NBS in 1980, he was a Postdoctoral Fellow at Northwestern University and worked

in the Chemistry Division at the Naval Research Laboratory.

JOHN A. TESK, 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 Uni\ersity. 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 ICT. CHARLES C. HAN, (;roup Leader,

Polymer Blends. Dr. Llan was born

in Szuchuan, China. He earned his B.S. in chemical engineering at National Taiwan University, M.S. in physical chemistry at the University

of Houston and his Ph.D at the University of Wisconsin. He joined

the staff of NBS in 1974. mfi ^

BRUNO M. FANCONI, (iroup

Leader, Mechanical Performance.

TABLE OF CONTENTS PAGE

INTRODUCTION iii

RESEARCH STAFF vii

TECHNICAL ACTIVITIES 1

ELECTRICAL PROPERTIES 1

FY 86 Accomplishments 1

Automated Dielectric Measurements 2

Piezoelectric Polymers 3

Thermal Pulse Measurement of Space Charge 4

Polymer Dielectric Phantoms 5

Ionic Conduction in Polymers 5

Liquid Crystalline Polydiacetylenes for Non-linear Optics 6

POLYMER STANDARDS AND CHEMICAL PERFORMANCE 8

FY 86 Accomplishments 8

Standard Reference Materials & Data 9

Molecular Characterization 12

MECHANICAL PERFORMANCE OF POLYMERS 19

FY 86 Accomplishments 19

Characterization of Polymer Structure & Deformation Processes. . . 20

Mechanical Properties Measurement and Modeling 27

Mechanical Durability of Polymeric Materials 32

PROCESSING AND RELIABILITY OF POLYMER COMPOSITES 34

FY 86 Accomplishments 35

Cure Monitoring & Process Control for Thermosetting

Polymers & Their Composites 35

Analysis of Structure in Polymers & Their Composites 42

Performance of Polymers & Their Composites 45

POLYMER BLENDS 49

FY 86 Accomplishments 49

Experimental 50

Theory 51

SAXS & Pole Figure Facilities 54
DENTAL AND MEDICAL MATERIALS 56

FY 86 Accomplishments 56

Dental Composite & Cement Sealant & Adhesion Chemistry 57

Wear, Durability, Clinical Studies & Related Properties of Dental

Composites, Amalgams, Cements, & Glass-Ionomer Cements 59

Dental Alloys, Ceramics, Metrology, & Analysis 60

Calcium Phosphate Chemistry, Biochemistry, Structure &

Clinical Implications 61

Medical Materials & Improved Surgical Bone Cement 63

OUTPUTS/ INTERACTIONS 64

Publications 64

Technical & Professional Committees: Leadership Activities. ... 70

Industrial & Academic Interactions 75

Associated Activities 78

ORGANIZATIONAL CHARTS 81

ii

I
INTRODUCTION

POLYMERS DIVISION

Leslie E. Smith, Chief

Bruno M. Fanconi, Deputy Chief

The Polymers Division is responsible for providing standards, measurements, and

fundamental concepts of polymer science to assist U.S. industries that produce,

process, or use polymers as an essential part of their business. Plastics,

elastomers, and synthetic fibers now form the basis of industries that add over

$100 billion of value by manufacture to the U.S. economy and these industries

are growing rapidly relative to other basic materials industries. This growth

rate is due primarily to the extreme versatility of synthetic polymers, whose

wide range of possible properties offer opportunities for scientists to create

innovative materials for nearly any new product. The polymer industry has

vigorously pursued these opportunities and continues to introduce new polymers,

process methods, and applications at a high rate. Examples of these new

applications include trends for the increased use of polymers in packaging,

construction, transportation, national security, dentistry, and medicine. The

Division's programs are structured to deliver outputs that meet current needs

as well as prepare for the changing needs of the industry over the next decade.

The organization of the Division consists of three property-oriented Groups and

three material-oriented ones. The Groups concerned with electrical, chemical,

and mechanical performance of polymers concentrate on the relationship of

polymer structure to properties and especially on the measurement of the

response of polymers to electrical, chemical, or mechanical stress. The

programs of these Groups focus on the use of fundamental science to provide

standards, measurement methods, and solutions to technological problems.

The Polymer Blends Group is responsible for providing fundamental data and

concepts related to the development and processing of blends. Polymer blends

are one effective way for domestic polymer producers to respond to competitive

pressure from foreign producers with access to very inexpensive feedstocks.

New products can be tailored to meet specific market requirements by blending

two or more polymers, without abandoning present production facilities and

without the large capital expenditures necessary to produce a totally new

polymer. The principal industrial need in this field is for a fundamental

science base to underlie the design and processing of new blends. This incudes

needs for measurement methods to produce data for polymer phase diagrams,

measurement methods and data on the microstructure of phase-separated blends,

data on polymer diffusion and the kinetics of phase separation, and theoretical

models that accurately describe the thermodynamics and kinetics of blends.

Although only about 10% of polymer production is now used in polymer matrix

composites, the current and potential impact of these materials on other

industries is dramatic. Military and aerospace uses of advanced composites are already large and diverse, amounting to about 40% of all advanced polymer

composites. In the next ten years, advanced composites are predicted to have

an annual value of over $10 billion and many other markets in the civilian

sector will certainly expand. By the year 2000, the automotive industry may

iii
well be the largest single market for polymer composites with potential

applications in structural components of the frame and suspension as well as in

body panels. Many other opportunities exist in the construction, machinery,

and electronics markets.

Two major factors have Inhibited the growth of composites in these mass

markets: inability to process the materials inexpensively and reliably; and

uncertainty about the performance of these anisotropic materials under complex

loads, particularly at failure. The Composites Group has programs aimed at

solving some of the measurement and basic science aspects of these two

problems. More efficient processing will come from automated manufacture aided

by appropriate feedback control sensors. The identification of materials

properties that can be monitored and development of measurement methods

suitable for process control are major objectives of the Group with additional

support from the NBS Non-Destructive Evaluation program.

Failure behavior of composites is very complex and the fundamental science of

heterogeneous materials is not advanced enough to be confident of predictions

based on much less than prototype testing. Important new work has focused on a fundamental understanding of the structure of crosslinked epoxy networks and

measuring the response of these networks to deformation. Small angle neutron

scattering has been vitally useful to these studies and the results are illustrative of the kind of leap forward in understanding that is made possible

by this NBS facility.

The Dental and Medical Materials Group is a model of effective private sectorgovernment cooperation. For over sixty years the American Dental Association

(ADA) and NBS have worked together to improve dental materials and devices.

Virtually all the major materials used by dentists in the United States today

have been developed or influenced by this joint program which includes the

National Institutes of Dental Research, and foreign guest workers in the most

comprehensive program of its kind anywhere in the world.

Each of these programs is described in more detail in this report. The report

is organized into the six Groups as follows:

ELECTRICAL PROPERTIES

POLYMER STANDARDS AND CHEMICAL PERFORMANCE

MECHANICAL PERFORMANCE OF POLYMERS

PROCESSING AND RELIABILITY OF POLYMER COMPOSITES

POLYMER BLENDS

DENTAL AND MEDICAL MATERIALS

These Groups have made a number of significant accomplishments during the past

year. Some of these are summarized below with references to the section of the

report where more information about the work may be found.

• An interpenetrating network of low molecular weight poly (ethylene oxide)

containing dissolved salts and an epoxy resin has been demonstrated to

perform well as a solid electrolyte. The dissolved salt forms mobile

cross-links within the normally liquid PEG and apparently prevents it from

phase-separating (pg. 5)

.

iv
• A synthetic phantom which has the same dielectric heating characteristics

as living tissue has been designed for the Food and Drug Administration.

Organic salts are dissolved in an ethylene carbonate-propylene carbonate

mixture and thickened with fumed silica or by cross-linking a methacrylate- terminated polyethylene glycol. Interfacial polarization is

simulated by incorporating 1.5 pm-thick flakes of poly (ethylene

terephthalate) (pg. 5).

• A series of three poly (methyl methacrylate) Standard Reference Materials

are being produced with support from the Navy and the Office of Standard

Reference Materials. These SRM's will be used for quality control of

antifouling paints and as calibrating materials for the analysis of

acrylic polymers. For SRM 1489, the highest molecular weight polymer in

the series, a certificate has been issued certifying both the limiting

viscosity number and the number-average molecular weight. The number

average molecular weight of SRM 1488 with intermediate molecular weight

has also been determined (pg. 10)

.

• Two linear low density polyethylenes used in gas piping (one with, and the

other without pigment) have been characterized for certification as Standard Reference Materials, with support from the Gas Research Institute

and the Office of Standard Reference Materials. Such standards will be

useful not only to the gas distribution and associated industries but also

to the rest of the scientific community (pgs. 24,32).

• A novel method, called Fluorescence Recovery After Photobleaching, has

been applied to rapidly determine the diffusion coefficients of polymers

in solutions. The diffusion of a polystyrene in dilute and semi-dilute

solution has been measured over a concentration range from 0.02 g/ml to

0.3 g/ral. In the low-concentration regime the diffusion coefficient has

been found to be inversely proportional to the one-half power of polymer

concentration, and in the semi-dilute regime, the seven-fourth power of

concentration. These results agree well with a recent theory (pg. 13)

.

• A nuclear magnetic resonance technique has been developed and applied to

determine the partitioning of chain ends and branches between the

crystalline and non-crystalline regions of polyethylenes. Side groups

(branches) in polymers can greatly affect mechanical properties and

performance. A major problem in predicting such effects is that branches

may be concentrated in regions of crystalline polymers (p. 22)

.

• The molecular mechanism for large strain deformations in epoxies has been

shown by neutron scattering experiments to be at variance with current

knowledge concerning the deformation mechanisms in rubbers, and other

cross-linked polymers. In epoxies cured with short chain amines the

average distance between crosslinks in the molecular network stays

unchanged even when the macroscopic strain reaches values up to 30%. This

result suggests that the deformation mechanism is either defect controlled

or unfolding of the network (pg. 42).

V
• Viscosity changes during cure have been correlated in model materials with

the results from four measurement techniques that have on-line potential:

ultrasonics, fluorescence, photo-bleaching, and dielectrics. Both

similarities and differences have been highlighted as a critical first

step toward evaluating the potential of these measurement methods. Proper

control of viscosity is the single most important factor in efficient

composite processing (pg. 35).

• The molecular weight dependence of the binary interaction parameter, X,

has been obtained for polystyrene/poly (vinylmethylether) blends using

small angle neutron scattering. This has been used in conjunction with a temperature jump light scattering technique to obtain the mutual diffusion

coefficient of this polymer blend system above and below the critical

point. The critical slowing down, and the analytical continuity of free

energy and diffusivity have been demonstrated quantitatively for the first

time (pg. 50)

• Blends of poly (vinylidene fluoride) (PVF2 ) and poly (ethylacrylate) have

been used in their compatible region to study the crystallization process

and morphology of PVF2 . The structures formed evolve from single crystal

lamellae to more complex aggregates and eventually to spherulites. The

morphology has been studied as a function of PVF2 concentration (pg. 51)

• Flexible prepolymer monomers and bulky diluent monomers (based on vinyl

thermosetting silyl ethers) were synthesized that yield high filler

content dental composites with reduced water uptake, adequate mechanical

strength, and excellent esthetics (pg. 57).

• The susceptibility of glass ionomer cements to brittle fracture and

degradation under acidic conditions has been reduced by the incorporation

of water-soluble or water compatible vinyl resin systems (pg. 57)
RESEARCH STAFF

Antonucci, Joseph H.

Barnes, John D.

Bauer, Barry, J.

Blosser, Richard L.*

Bowen, Rafael L.*

Brauer, Gerhard M.

Briber, Robert J.

Brown, Walter E.*

Bur, Anthony J.

Carey, Clifton M.*

Chang, Shu Sing

*Research Associate

• Synthetic and polymer chemistry

• Dental composites and cements

• Antioxidants

• Gas and vapor transport in polymers

• X-ray scattering

• Computer applications in polymer

measurements

• Polymer synthesis

• Neutron, x-ray and light scattering

• Adhesion measurements

• Adhesion

• Dental composites

• Biocompatibility

• Synthetic and polymer chemistry

• Dental composites and cements

• Adhesion

• Orthopedic materials

• Structure and morphology of polymers

• Electron microscopy

• X-ray scattering

• Solution chemistry of calcium

phosphate (CAPH) compounds

• Biological CAPH compounds

• Atherosclerotic plaque

• Dielectric properties of polymers

• Piezoelectric, pyroelectric polymers

• Polymeric transducers

• Dental plaque

• Microanalytical analysis techniques

• Thermal properties of polymeric

materials

• Electronic packaging

• Polymer phase transitions

• Precision electrical and temperature

measurements

vii
Chiang, C. K.

Chow, Laurence C.*

Crissman, John M.

Davis, G. Thomas

Dehl, Ronald E.

DeReggi, Aime S.

de Rijk, Valdemar G.

Dickens, Brian

Di Marzio, Edmund A.

^Research Associate

• Electrical properties of polymeric,

ceramic and organic materials

• AC electrical impedance spectroscopy

• Calcium phosphate compounds

• Dental and biomedical cements

• Solution chemistry

• Topical dental fluorides

• Mechanical behavior

• Environmental stress-cracking

• Failure and fracture of polymers

• Piezoelectricity in polymers

• Polymer crystallization

• X-ray diffraction of polymers

• Ionic conduction in polymers

• Surface analysis

• Porosity measurements

• Ellipsometry

• Bonding of polymers & composites

• Polarization-depth profiles in

polymers

• Space charge in dielectrics

• Ferroelectric polymers

• Polymeric piezo- & pyroelectric devices

• Clinical dentistry

• Ceramic materials

• Expansion characteristics of solids

and semi-solids

• Kinetics of thermal degradation

of polymers

• Photodegradation of poly (methyl

methacrylate)

• Curing of thermosetting resins

including printing inks

• Statistical mechanics of polymers

• Phase transitions

• Glasses

• Polymers at interfaces

viii
Eanes, Edward D.*

Eidelman, Naomi, N.*

Fanconi, Bruno. M.

Fowler, Bruce 0.*

Giuseppetti, Anthony A.*

Gregory, Thomas M.*

Guttman, Charles M.

Han, Charles C.

Hailer, Arthur W.*

Howell, Barbara F.

Huns ton, Donald L.

• Structure of bones and teeth

• Calcium phosphate compounds

• Effects of biological molecules on precipitation of calcium phosphates

• Liposome studies

• Atherosclerotic plaque

• Infrared & Raman spectroscopy of polymers

• Structure of polymers

• Polymer fracture

• Process monitoring of polymer composites

• Laser Raman structural analysis of

calcium phosphates

• Casting of dental alloys

• Titanium alloys

• Calcium phosphate compounds

• Surface chemistry

• Solution properties of polymers

• Diffusion of small molecules into

polymeric systems

• Semicrystalline polymer chain

configurations

• Kinetics of polymer crystal growth

• Polymer blends

• Polymer characterization

• Small angle neutron scattering

• Static and quasi-elastic light scattering

• Chemical reactions, chemical analysis

• Electron microscopy

• Spectrophotometry

• Light microscopy

• Adhesion science and technology

• Fracture behavior of polymers

• Processing & failure behaviors of

composites

• Flow behavior of dilute high polymer

solutions

• Macromolecule-small molecule binding

*Research Associate
Johnston, Allen, D.*

Khoury, Freddy A.

Kryder, Samuel J.

Lowry, Robert E.

Mathew, Mathai*

Maurey, John R.

McCrackin, Frank L.

McKenna, Gregory B.

McKinney, John E.

Misra, Dwarika N.*

^Research Associate

• Nuclear magnetic resonance

• Mossbauer studies

• Chemical adhesion

• Crystallization, structure and

morphology of polymers

(including polymer blends)

• Analytical electron microscopy of

polymers

• Wide angle and small angle x-ray

diffraction

• Structure and mechanical property

relationships

• Electronic circuit design & construction

• Electronic troubleshooting & repair

• Applications of fluorescence

spectroscopy to polymeric systems

• Synthesis of chromophore-labeled

polymers

• Crystallography

• Calcium phosphate compounds

• Ultracentrifugation

• Rayleigh light scattering

• Osmometry

• Densimetry

• Refractometry

• Monte Carlo computer simulations

• Ellipsometry analysis

• Size exclusion chromatography

• Nonlinear viscoelasticity

• Molecular rheology

• Physics of polymer glasses

• Rubber elasticity

• Tribology of dental composites,

cements and alloy

• Surface chemistry

• Adhesion

• Chemisorption

X
Mopsik, Frederick L.

Passaglia, Elio

Penn, Robert W.

Phillips, Joseph C.

Reneker, Darrell H.

Roth, Steven C.

Rubin, Robert J.

Rupp, Nelson W.*

Schen, Michael A.

• Dielectric measurements and behavior

• Automated measurement design

• Computerized data analysis & programming

• Electrical properties of polymers

• Fracture and crazing

• Linear viscoelasticity

• Crystallization theory

• Rheology

• Properties of polymers & composites

• Statistical analysis

• Viscosity & normal stress measurements

• Environmental effects on transport &

mechanical properties

• Curing of thermoset resins including

printing inks

• Crystallographic defects in polymers

• Polymer structure

• Electron microscopy of polymers

• Vibrational spectroscopy of polymers

• Piezoelectric polymer transducersfabrication and applications

• Vacuum deposition of metals

• Calibration of polymer transducers

• Statistics of polymer chain configurations

• Theory of Brownian motion

• Random walk models with traps

• Polymers near surfaces

• Clinical dentistry

• Amalgams

• Direct golds

• Dental standards

• Composites

• Titanium castings

• Microleakage

• Dentin adhesives

• Living polymer synthesis

• Polymers for non-linear optics

• Molecular electronics

*Research Associate
Schreiber, Carol J.*

Setz, Louise E.*

Sieck, Barbara*

Smith, Leslie E.

Stansbury, Jeffrey W.

Takagi, Shozo*

Tesk, John A.

Tomazic, Branko*

Tung, Ming, S.*

VanderHart, David L.

Venz, Sabine*

Verdier, Peter, H.

*Research Associate

• Topical dental fluorides

• Adhesion

• Chemical analysis

• Calcium phosphate compounds

• Chemical analysis

• Adsorption of polymers

• Polymer degradation reactions

• Synthetic chemistry

• Polymers and polymer composites

• Polymerization expanding monomers

• Crystallography

• X-ray diffraction

• Calcium phosphate compounds

• Casting of alloys

• Strength of dental systems

• Thermal expansion & properties of

dental materials

• Finite element studies

• Porcelain-metal system

• Atherosclerotic plaque

• Biological calcium phosphate compounds

• Biological solution chemistry of

calcium phosphate compounds

• Equilibrium studies

• Measurement of orientation in

polymer fibers and films

• Solid state NMR of polymers

• Measurement of pol]nner morphology

on the 1-10 nm scale

• Clinical dentistry

• Dental composites

• Dental polymers

• Polymer solution properties

• Polymer chain dynamics in solution

• Statistical analysis of data

• Error estimation

• Computer simulation of polymer

chain dynamics

xii
Vogel, Gerald L.*

Wagner, Herman L.

Vang, Francis W.

Waterstrat, Richard M.*

Wu, Wen-li

Zapas, Louis J.

*Research Associate

• Dental plaque, biological solution

chemistry of calcium phosphates

• Micro analytical techniques

• Dilute solution properties of

polymers

• Molecular parameters

• Limiting viscosity number

• Size exclusion chromatography

• Osmotic pressure

• Photophysics and photochemistry

of polymers

• Fluorescence spectroscopy

• Thermodynamic and frictional

properties of macromolecules

• Dental metallurgy

• Metallurgical phase diagrams

• Structure of alloy phases

• Neutron and x-ray scattering

• Electron microscopy

• Mechanical behavior of polymers

and composites

• Continuum mechanics & Rheology

• Non-linear mechanical behavior

of polymers

• Static fatigue of plastics

• Finite elasticity (rubbers)

xiii
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ELECTRICAL PROPERTIES

The goal of the task on electrical properties is to carry out long-range

research involving the interaction of electric fields with polymers. Such

research provides the basis for new or improved measurements which will lead to

higher performance of polymers in existing applications or to entirely new

applications. The program includes research on high voltage insulation, ionic

conduction, piezoelectricity, pyroelectricity, and electro-optic phenomena.

Results in the form of data, measurement techniques, and scientific concepts

are communicated to funding organizations in the form of technical reports. In

most cases, the results are also published in archival journals, presented

orally at scientific meetings, discussed with visitors, and shared with

research associates who come to work with us. In some cases, the research

results in a measurement system which is delivered to the sponsor.

The measurement of dielectric constant and dielectric loss as a function of

frequency and temperature has long been used to probe the molecular motions in

polymers. Development of a time domain dielectric spectrometer at NBS has

extended the ability of these measurements to follow dielectric properties

which evolve with time, since data for a wide frequency range can be obtained

in an interval of time comparable to the reciprocal of the minimum frequency of

interest. Also, an automated system which measures dielectric constant and

loss at a series of fixed frequencies between 100 Hz and 10^ Hz is being used

to infer DC conductivity of polymer systems where polarization becomes a problem.

A thermal pulse technique which has proven useful for measuring polarization as

a function of position across a thin film of polymer has been improved to

increase sensitivity and resolution so that the distribution of charge can now

be measured. The role of trapped charge, leading to locally high electric

fields, is being examined for its effect on dielectric breakdown in cable

insulation.

Examples of new electric applications of polymers are piezoelectrics,

pyroelectrics, solid electrolytes, and electro-optics. NBS has made

significant contributions to the understanding of the mechanisms responsible

for piezoelectric and pyroelectric properties of polymers. Details of these

models are being refined and transducers using polymer piezoelectrics are being

developed for specific applications. Research continues on the dissolution of

salts and the transport of ions in polymers such as polyethylene oxide and

linear polyethylene imine. Of particular interest is the diffusion of Li* as determined by neutron depth profiling. The concept of an interpenetrating

network for ionic conduction has been reduced to practice by employing a low

molecular weight PEO and an epoxy resin. A new effort within the group is

directed toward the synthesis and evaluation of new polymers for electrooptical properties.

FY 86 Significant Accomplishments

• The sensitivity and resolution of space charge distribution in polymer

films using the thermal pulse technique has been greatly improved by using

a dye laser to provide a short pulse of intense heat.

1
• A synthetic phantom which has the same dielectric heating characteristics

as living tissue has been designed for the Food and Drug Administration.

Organic salts are dissolved in an ethylene carbonate-propylene carbonate

mixture and thickened with fumed silica or by cross-linking a methacrylate- terminated polyethylene glycol. Interfacial polarization is

simulated by incorporating 1.5 pm-thick flakes of poly (ethylene

terephthalate)

.

• An interpenetrating network of low molecular weight poly (ethylene oxide)

containing dissolved salts and an epoxy resin has been demonstrated to

perform well as a solid electrolyte. The dissolved salt forms mobile

cross-links within the normally liquid PEO and apparently prevents it from

phase-separating.

Automated Dielectric Measurements

F. I. Mopsik

The recent development of a time-domain dielectric spectrometer has continued

to receive attention. This instrument measures the charge response of a dielectric to an applied voltage step for times from 10 ps to 3000 s and

transforms the data into the frequency domain for frequencies from .0001 Hz to

10 kHz. A commercial version of the instrument is actively being developed by

IHASS, Inc., Hingham, MA through the Research Associate program at NBS and is

nearing completion. A further development has been the signing of a Research

Associate agreement by GE Research Laboratory in Schenectady, NY to facilitate

transfer of a copy of the instrument for use in their laboratory.

The instrument's sensitivity, accuracy and frequency range has allowed it not

only to be used in relaxation studies on PVDF and the study of epoxy resin cure

but in routine relaxation time studies on other polymers as background

information for other work. Measurements have been made on polycarbonate,

SURLYN and ULTEM to clarify their behavior.

Cure Monitoring in Epoxy Resin Systems

The development of the dielectric spectrometer and an A-C conductivity system

has allowed an intensive study into the use of dielectric measurements for

monitoring the cure of epoxy resins. Several different resins cured with

imidazole showed that a 50 Hz conductance measurement can readily follow the

curing reaction of the resin system. Cross comparisons were made with

measurements of viscosity, ultrasonic elastic constant, and exotherm on common

samples. These studies demonstrated that the conductance could follow the

curing reaction into the final state at least as well as the other techniques.

Furthermore, the conductance data was not simply related to viscosity and could

show features, such as an initial ion-forming reaction, that were not readily

apparent in other measurements. Also, controlled studies on mixed resin aged

at room temperature demonstrated that a conductance measurement could be used

to monitor the state of mixed resin systems quite readily. This could prove of

great value in establishing cure cycles a priori and the suitability for use of

mixed resin.

2
Preliminary measurements were made on an epoxy-diamine system. This system had

a much lower initial conductance and, for the first time, evidence of dipolar

relaxation was seen. This was indicated by the appearance of a conductance

maximum toward the end of the cure reaction. Measurements with the dielectric

spectrometer were typical of a relaxation process. These measurements were

also useful in showing the limitations in interpreting the data due to sample

evolution on a time scale approaching the measurement frequency. With the

development of a new, faster changing temperature control system, this work

will be continued and cross-compared with other measurement methods. Also,

measurements on higher temperature, commercial resin systems will be made.

Piezoelectric Polymers

S. C. Roth, A. J. Bur, and M. G. Broadhurst

The development of piezoelectric polymer gauges with a protective layer of

polyetherimide has been concluded with the delivery of 15 calibrated gauges to

Eglin AFB. The inert layer of glassy polymer protects the piezoelectric

polyvinylidene fluoride from damage when imbedded in soil containing sharp

particles and delays the temperature rise due to adiabatic heating when used to

measure pressure changes in air. Complications arise for times longer than

about 2 ms which are believed to be associated with mechanical relaxation in

the protective layers.

Another research project is directed toward measurement of piezoelectric

response to shear in piezoelectrically active polymers and development of

methods to enhance such response for specific transducers. According to

current models in which molecular dipoles are aligned preferentially normal to

the electrode surface of polymer thin films, shear stresses are expected to

produce negligible charge response at the electroded surface. If dipoles could

be aligned parallel to the electroded surface, shear response is expected to be

much larger. Attempts to align dipoles in an electric field parallel to the

surface have been unsuccessful and the present approach involves poling thick

films of polymer and then slicing and depositing electrodes on what were the

edges of the specimen.

A cooperative mean-field model has been analyzed for pyroelectric properties.

The model assumes that the orientation of independent molecular chain segments

in the crystalline phase of PVDF and its ferroelectric copolymers can be

determined from a six-site rotational potential energy function where the

energy of a site is linear with occupation probability. The potential function

is chosen to give the infrared-observed vibrational frequency of 70 cm~^, and a barrier height of about 12 kT suggested by dielectric relaxation rates. A sixfold cosine function meets both with requirements. Analytical solutions for

the case of no applied electric field yield a first order ferroelectric

transition. The remanant polarization and disorder contribution to the

pyroelectric coefficient were calculated for the ferroelectric phase. The

model predicts that for PVDF more than half of the pyroelectric response is

secondary and due to thermal expansion in the thickness direction while changes

in the order parajneter with temperature make up the remainder. Surprisingly,

the primary response occurs much later (milliseconds) than the secondary

3
response (microsecond) because the dipolar reorientation accompanying the

disorder process involves rotation over large (-^12 kT) energy barriers. This

result seems quite consistent with existing data and offers a satisfactory

alternative to the popular reversible crystallization theory of pyroelectricity

in PVDF.

Thermal Pulse Measurement of Space Charge

A. S. DeReggi

The measurement of the distribution of space charge across the thickness of

dielectrics has been advanced by replacing the flash lamp which served as a thermal pulse source by a pulsed dye laser. The dye laser can deliver thermal

pulses with shorter duration (-vl ps vs 50 ps before) and higher power (up to 1 MW vs ^'30 kW before) . Evaporation of the electrodes on the sample now limits

the energy per pulse rather than the output capability of the source itself.

The shorter pulse duration has increased the spatial resolution of the

measurements. Prior measurements on polyvinylidene fluoride (PVFz) poled at room temperature had shown that ferroelectric switching occurred more readily

in the central parts of a sample than near the surfaces, although it appeared,

within the resolution then available, that finite polarization extended to the

surfaces. New measurements with increased resolution show now that the

polarization in similar samples falls to essentially zero within ^1 pm of the

surfaces. The inhibition of switching near the surfaces is not understood

presently although electrode constraints could be an explanation.

Ferroelectric switching is believed to occur through a 60° dipole rotation

accompanied by a displacive transformation of the unit cell of the polar

crystal phase. The displacement requires an extension of the unit cell by

nearly 2% in a direction perpendicular to a face diagonal. Any restriction on

this displacement could prevent poling.

During this FY, space charge measurements in new dielectrics for electric power

cable insulation have continued under the sponsorship of the Electric Power

Research Institute. The NBS task is to gain an understanding of charging

phenomena and the kinetics controlling its distribution. These factors affect

the internal electric fields and their distribution, and hence are thought to

affect long term aging behavior and dielectric failure. Furthermore,

identification of materials with tendencies to accumulate charge of opposite

signs might help guide the development of compatible blends of these materials

which might remain electrically neutral. In a coordinated effort also

involving a research team at the U. of Connecticut, the blend polyethylene and

a Zn-ionomer Surlyn'*’” has been investigated. The U. of Connecticut team

prepared samples one composition (80% PE) and performed thermally stimulated

current studies, while NBS was responsible for space charge measurements and

theoretical modeling. In the initial stages of this work, the effects of

charging voltage, charging temperature, charging time and electrode materials

were investigated. Space charge measurements showed dependence on the

variables cited, but many of the observed effects were judged to depend on the

sample history. The procedure of annealing samples was not appropriate for the

blend due to phase separation. Studies on annealed Surlyn samples were carried

out with charging voltages of up to 800 V/mil and charging temperatures of room

4
temperature and of 60 °C, the nominal allowed operating temperature of power

cables. The charging behavior for short charging times (up to tens of minutes)

was found to vary among samples, which showed hetero charge in some cases and

homocharge in other cases. However, for long charging times (hours or days)

all Surlyn samples exhibited similar behavior in that they showed accumulation

of charge of negative sign with a nearly uniform accumulated charge

distribution. Even samples which showed heterocharge initially (those charged

for short-to-intermediate time intervals) , exhibited a nearly uniform negative

charge distribution after aging times of several days at room temperature. The

samples studied had very high resistivities between room temperature and 60 ®C.

Estimates of the Maxwell relaxation time at 60 ®C give a few hours. It is

reasoned, therefore, that the Maxwell relaxation time is a natural parameter

separating the different charging behavior at long and short times.

Furthermore, given enough time, all samples achieve the same charge equilibrium

state.

Polymer Dielectric Phantoms

M. G. Broadhurst, C. K. Chiang, and G. T. Davis

A synthetic phantom has been designed which has the same dielectric heating

characteristics as living tissue so that testing can be done using it rather

than live subjects. This material is needed by the Food and Drug

Administration (FDA) and biomedical instrument makers for testing and

calibrating devices that subject human tissue to high-frequency electromagnetic

radiation.

The FDA's Center for Devices and Radiological Health asked MBS to help design a more stable material than the presently used aqueous biopolymer-based phantoms.

The synthetic phantom is a mixture of four components, chosen to provide the same electrical properties as the corresponding components in live muscle.

These components are: 1) ethylene and propylene carbonate, organic solvents

with dielectric constants similar to water; 2) tetraethylammonium

tetraf luoroborate, an organic salt to provide conductivity similar to

biological electrolytes; 3) 1.5-micrometer-thick poly (ethylene terephthalate)

flakes to provide interfacial polarization similar to that found at cell walls;

and 4) fumed silica, a thickening agent to provide mechanical stability. The

resulting composite is more stable to drying and biological attack and can be

used over a wider frequency range than existing phantoms. It also has a lower

heat capacity and thermal diffusivity that should improve the sensitivity of

temperature distribution measurements inside the material during

electromagnetic heating experiments.

Ionic Conduction In Polymers

B. J. Bauer, C. K. Chiang, R. M. Briber, and G. T. Davis

A new type of polymeric electrolyte has been developed based on interpenetrating polymer networks (IPNs) . Polymeric films that have high ionic

conductivity have many applications such as in all polymeric batteries. The

conductivity of salt-polymer systems is limited by the glass transition

temperature of the polymers. Low molecular weight polymers such as

5
polyethylene oxide (PEO) have higher conductivities, but they are liquids that

cannot form films.

IPNs have been synthesized that have two co-continuous phases. One is a crosslinked epoxy phase that provides strength and dimensional stability. The other

phase is a low molecular weight PEO (MW = 400) with dissolved salt which gives

high conductivity (as high as lO"'* S/cm). This is an order of magnitude better

than previous one-phase films.

Transmission electron microscopy shows a two phase structure with the size

scale ranging from 0.1 to 0.5 microns. The conductivity of the films is

constant up to 35% (by wt.) epoxy and then drops exponentially. The optimum

mechanical and electrical properties come around 35% epoxy. Films made with

cross-linked poly (methyl methacrylate) as the support phase have similar

properties. A patent is pending on these polymeric electrolytes.

As part of our program on solid electrolytes, preliminary measurements of the

diffusion coefficient of Li* in poly (ethylene oxide) have been performed using

neutron depth profiling in cooperation with personnel from the Center for

Analytical Chemistry at the NBS reactor. The technique is based upon the

nuclear reaction in which a lithium 6 nucleus captures a neutron and decays

immediately to yield a triton particle and an alpha particle, each of known

energy. Energy of each particle is dissipated as a known function of distance

in the polymer medium. A measurement of the number of particles as a function

of energy can be converted to concentration of ®Li as a function of depth

within the polymer - up to about 50 pm from the surface closest to the

detector. The initial experiments involved pressing a 100 pm - thick film of

PEO against a thick film of PEO containing 10 mole percent of LiC104 and

following the appearance of Li in the thin film by counting the emerging a and

T particles in increments of 30 minutes over a period of 20 hours. The

concentration of Li in the thin film was then measured much less frequently

over the next four weeks. From a time-lag analysis, the diffusion coefficient

of Li in the "pure" PEO was found to be 4x10- ® cm^/sec. The equilibrium

concentration of Li implies that the salt is entirely in the non-crystalline

regions and that crystallinity is not reduced if maintained at room

temperature.

Liquid Crystalline Polvdiacetvlenes for Non-Linear Optics

M. A. Schen

For optical based telecommunications and signal processing, a strong need

exists for non-linear optical materials which can be fabricated into switching,

logic, and phase conjugated devices. Currently, for example, second and third

order phenomena are being exploited for frequency doubling and tripling using

ceramic semiconductors such as GaAs and LiNbOa . It is now evident, though,

that organic compounds containing n-electron systems can offer intrinsic non- linear susceptibilities v<“>d exceeding those of known inorganic structures.

Specifically, polydiacetylenes (PDA) have been shown to exhibit exceptionally

large picosecond scale response times, phase matching, high laser damage

threshold energies, and optical transparency throughout much of the visible and

6
near infra-red regions. These factors are responsible for making PDA a likely

candidate for future devices.

Nearly all disubstituted diacetylene monomers, once polymerized, form

insoluble, unprocessable polymers. For this reason, many optical studies have

been performed on as-polymerized single crystals or organized LangmuirBlodgett multilayers. Examples of soluble PDA's do exist, such as 1,4-

tetramethylene butoxycarbonylmethylurethane diacetylene (4BCMU) andl,4-

tetramethylene-p-toluenesulfonate diacetylene (PTS-12) . During reprecipitation

of 4BCMU from solution, inter-side chain hydrogen bonding introduces side chain

organization which in turn influences backbone conformational order and

gelation occurs. Gelation has not been observed in PTS-12.

The objective of this research is to prepare a new class of disubstituted

diacetylene monomers which, after solid state polymerization, will be soluble,

processable, and exhibit liquid crystalline (LC) behavior in the bulk. In

essence, a new level of side chain molecular ordering will be introduced into

PDA compositions. This will be accomplished by preparing side chain LC

architectures analogous to the methacrylate based LC polymers explored by

Ringsdorf et al.

7

POLYMER STANDARDS AND CHEMICAL PERFORMANCE

The objective of this task is to provide to the polymer industry standard

reference materials (SRM's) as well as measurement methods and data for

predicting the lifetimes of polymers used in high volume or critical

applications.

Polymeric SRM's certified for molecular weight are needed by the polymer

industry to calibrate gel permeation chromatographs (GPC's) 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 processibility and its end-use properties.

Improved techniques for polymer characterization and better understanding of

polymer solution properties are essential to the efficient production of

polymeric SRM's. Consequently, experimental and theoretical studies of

polymer-solution properties are actively pursued in this task.

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 short-term methodologies for

predicting service life."

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

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.

FY 86 Significant Accomplishments

• A series of three poly (methyl methacrylate) Standard Reference Materials

are being produced with support from the Navy and the Office of Standard

Reference Materials. These SRM's will be used for quality control of

antifouling paints and as calibrating materials for the analysis of

acrylic polymers. For SRM 1489, the highest molecular weight polymer in

the series, a certificate has been issued certifying both the limiting

viscosity number and the number-average molecular weight. The number

8
average molecular weight of SRM 1488 with intermediate molecular weight

has also been determined.

• Two linear low density polyethylenes used in gas piping (one with, and the

other without pigment) have been characterized for certification as Standard Reference Materials, with support from the Gas Research Institute

and the Office of Standard Reference Materials. Such standards will be

useful not only to the gas distribution and associated industries but also

to the rest of the scientific community. A certified value of the melt

flow rate for the polyethylene with pigment has been obtained.

• A novel method, called Fluorescence Recovery After Photobleaching, has

been applied to rapidly determine the diffusion coefficients of polymers

in solutions. The diffusion of a polystyrene in dilute and semi-dilute

solution has been measured over a concentration range from 0.02 g/ml to

0.3 g/ml. In the low-concentration regime the diffusion coefficient has

been found to be inversely proportional to the one-half power of polymer

concentration, and in the semi-dilute regime, the seven-fourth power of

concentration. These results agree well with a recent theory.

• The diffusion coefficients of two fluorescent dyes in polystyrene

solutions have been measured over a wide concentration range by the

technique of fluorescence recovery after photobleaching. In all cases,

the diffusion coefficient decreases with polymer concentration more slowly

when the molecular weight is 18,000 than when the molecular weight is

110,000 or 500,000.

• Changes in fluorescence spectra occur during the formation of polyimide

polymers from poly (amide-acid) . These changes can be measured in-situ and

non-destructively to monitor the course of imidization.

Standard Reference Materials and Data

F. W. Wang, C. M. Guttman, P. H. Verdier, H. L. Wagner, and J. R. Maurey

Work in this subtask proceeds primarily along two lines: Production of polymer

standards; Critical evaluation of experimental data on polymers. The linear

low density polyethylene standards currently under development, which are partly supported by the Gas Research Institute, will aid in the development of

polyethylene gas pipes with improved properties. The poly (methyl methacrylate)

standards currently in production will aid the Navy, which is partially

supporting their production, in the development of long-lived antifouling

paints for ships' hulls. In addition, both kinds of standards will be

generally useful in the plastics and related industries, both for equipment

calibration and as materials for research. The critical evaluation of

literature data on the relationships between limiting viscosity number and

molecular weight for atactic polystyrenes will aid in materials

characterization in this important segment of the plastics industry.

Development of a self-calibrating gel permeating chromatograph should

eventually result in substantial reductions in the cost of producing polymer

Standard Reference Materials, and should allow much more detailed

characterization of polymeric materials than has thus far been practical.

9
Characterization of Gas Research Institute Polyethylene

Polyethylene is widely used for piping in gas distribution systems. It has

been recognized lately that better coordination of research and development

activities facilitating comparison of techniques and test data would result if

a single well characterized resin were available to all research workers in the

gas distribution and associated industries. Such a resin should be available

from a single supplier over a number of years. As a result the Gas Research

Institute and OSRM are supporting work on the characterization of two "linear

low density" polyethylenes used in gas piping, one with pigment, the other

without. The unpigmented resin has been designated SRM 1496; the pigmented,

SRM 1497. This new type of polyethylene is considerably higher in molecular

weight than any of the polyethylene SRM's now available. Such a standard would

be useful to the rest of the scientific community because there is a growing

need for higher molecular weight polyethylene standards.

The melt flow rate, a widely used measure of polymer processing properties, has

been measured for SRM 1497 by ASTM method D1238-82 under three standard test

conditions. The value obtained under one of these, called the melt index

condition, will be certified. The other two melt flow rates will be given as supplemental information. Studies preliminary to the certification of the

limiting viscosity number of SRM 1496 in 1,2,4-trichlorobenzene at 130 ®C are under way. Future plans include estimation of the distribution in molecular

weight of both materials by gel permeation chromatography as supplemental

information, and measurement of a molecular weight of SRM 1496 for

certification.

Poly (methyl methacrylate) Standard Reference Materials

Three poly (methyl methacrylate) polymers with molecular weights of

approximately 8,000, 30,000, and 120,000, which are designated SRM 1487, 1488,

and 1489 respectively have been blended and bottled. They have been examined

by NMR to check chemical identity and tacticity. The uniformity of the

materials has been checked by capillary viscometry measurements.

Capillary viscometry measurements have been used to determine the limiting

viscosity number (intrinsic viscosity) of SRM 1489 in toluene at 25 °C. The

number average molecular weight has also been determined by membrane osmometry

in toluene at 25 ®C for both SRM 1488 and 1489. A certificate has been issued

for SRM 1489 certifying both the limiting viscosity number and the number

average molecular weight.

Revalldatlon of Polyethylene Standard Reference Materials

For a variety of reasons, it was deemed desirable to have a measure of

assurance that the materials presently available for sale as three of our polyethylene Standard Reference Materials (SRM's) have not changed

significantly since their original certification. Accordingly, we have

measured melt-flow rate and limiting viscosity number under the same conditions

as those used for the original certification of SRM 1475 Linear Polyethylene

(Whole Polymer) and SRM 1476 Branched Polyethylene (Whole Polymer) . For both

10
properties and both SRM's, the differences between the values measured now and

those originally certified are too small to provide significant evidence for

any change in these materials. A similar comparison, using only limiting

viscosity number, will be carried out for SRM 1482 Linear Polyethylene (Narrow

Molecular Weight Distribution)

Critical Evaluation of Mark-Houwlnk Constants for

Poly (methyl methacrylate)

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

molecular weight, which largely determines processibility and performance

properties. Since absolute determinations of molecular weight are time

consuming and are not made routinely, relative methods, such as solution

viscosity and size exclusion chromatography (also called gel permeation

chromatography) are used instead.'

The limiting viscosity number (intrinsic viscosity) , [rj] , and the molecular

weight, M, are related, empirically, by a simple power law:

[nl = KM«

where K and a are the empirically determined Mark-Houwink parameters, which

depend on the specific solvent and temperature. An incomplete compilation of

these data can be found in the handbooks, but a critical assessment is not yet

available. Yet these data are used extensively to obtain molecular weights as well as to calibrate size exclusion chromatography columns. Detailed

examination of the literature revealed that many of the determinations of K and

a were made by indirect rather than by absolute measurements of molecular

weight, or by the use of whole polymers rather than fractions, leading to large

uncertainties. Determinations such as these were rejected in favor of direct

determinations of molecular weight by absolute methods such as light scattering

or osmotic pressure.

Review papers for linear polyethylene and atactic polystyrene have been

published previously. This past year the literature for poly (methyl

methacrylate) has been critically examined and the K and a values for a variety of solvents used for viscosity and size exclusion chromatography

measurements have been recommended. These are acetone, benzene, chloroform 2-

butanone, and tetrahydrofuran, as well as for some less frequently used

solvents. The values for the coefficient K in the relation [q] = KM°-® for

several theta solvents are also reported.

The results of this evaluation have been submitted for publication in the

Journal of Physical and Chemical Reference Data.

Self-Calibrating Gel Permeation Chromatography

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

11
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.

Sample preparation and filtering procedures have been developed which permit

injection of calibrants directly into the light-scattering detector, bypassing

the GPC columns.

Molecular Characterization

F. W. Wang, C. M. Guttman, P. H. Verdier, R. E. Lowry, J. H. Shibata,

and E. S. Wu^

^University of Maryland, Baltimore County

Work in this subtask concerns the development of improved methods for

characterizing polymeric materials, and the development of fundamental concepts

related to the solution properties of polymers. Fluorescence measurements of

polymer diffusion and polymer-polymer interactions will provide data that are needed for heat-joining of polymers, for designing polymerization reactors, and

for producing molecular ly reinforced composites. Since almost all polymers in use contain additives to maintain and enhance their useful properties, the

experimental study of diffusion of small molecules in entangled polymers will

provide the data needed for predicting the lifetimes of polymers containing

additives. The theoretical studies of translational diffusion constants and

chain-molecule dynamics will yield fundamental concepts that will not only

guide the experimental work on polymer-solution properties but also give

insight on the processibility and the end-use properties of polymeric

materials. Finally, the fluorescence techniques developed for diffusion

12
measurements and for characterizing the formation of polyimide polymers have

been used to monitor in-situ the cure of epoxy resins and polyimide polymers as described elsewhere in the report.

Diffusion of Polymers in Semi-Dilute Solutions by Photobleaching Method

Verification of theories of self-diffusion and reptation in semi-dilute

solutions has been hampered by the lack of a rapid method for determining the

diffusion coefficient of polymers. We have applied a novel method, called

Fluorescence Recovery After Photobleaching (FRAP) , to rapidly measure the

diffusion coefficient of a polystyrene polymer in semi-dilute solutions [1]

.

The measurements cover nearly two decades of concentration and also extend to

the low-concentration regime. These results agree with a recent theory [2]

which predicts that self-diffusion coefficient varies inversely with sevenfourths power of concentration in the semi-dilute regime, and varies inversely

with the one-half power of concentration in the low-concentration regime. In

collaboration with Prof. E. -S. Wu of the University of Maryland, Baltimore

County, we are now using the FRAP method to measure the diffusion of polymers

in both a theta and a good solvent, as a function of shape, concentration, and

molecular weight.

1. F. W. Wang, R. E. Lowry, and E. -S. Wu, Polymer, 26, 241 (1985).

2. W. Hess, Macromolecules 1£, 1395 (1986).

Translational Diffusion Measurements of a Conducting Polymer in the Melt

The unusually high ionic conductivity observed in polyethylene oxide (PEO)

complexed with inorganic salts has stimulated considerable activity in the

development of polymeric solid electrolytes. Fundamental questions concerning

the specific interactions between PEO and the inorganic salts remain. We plan

to investigate these specific interactions by measuring the translational

diffusion coefficient of polymer complexed with salt in the melt. Diffusion

measurements will be performed on our newly acquired fluorescence

photobleaching apparatus. Narrow molecular weight distribution samples of

f luorescently labeled PEO are prepared by our standard labeling method. The

translational diffusion coefficients as a function of added salt, molecular

weight of polymer, and temperature will be compared with existing conductivity

data.

Diffusion of Small Molecules in Entangled Polymers

In collaboration with Professor E. -S. Wu of the University of Maryland

(Baltimore County) , we have used the technique of fluorescence recovery after

photobleaching (FRAP) to measure the diffusion of fluorescent dyes in

polystyrene solutions. The fluorescent dyes used are Dil-C6(3), l,l'-dihexyl3 , 3 , 3

' , 3 ' -tetramethylindocarbocyanine perchlorate , and similarly structured

DiICl(3), which has two methyl groups instead of two hexyl groups. The large

dynamic range of the FRAP technique together with the large viscosity of the

solvent diethyl phthalate makes it possible to measure the diffusion

coefficient over a wide concentration range, from 0.05 g/ml to 0.8 g/ml. The

molecular weights of the polymers used are 17,500, 110,000, and 498,000.

13
We have found that, in all cases, the logarithm of the diffusion coefficient

decreases linearly with the ratio of the volume of the polymer to the volume of

the solvent. For both Dil-Cl(3) and Dil-C6(3), the magnitude of the slope for

17.5 K polystyrene polymer is substantially smaller than those for 110 K and

498 K polystyrene polymers. For the latter two polymers, the slopes are the

same within the experimental uncertainties. These results suggest that the

characteristic volumes of Dil-Cl(3) and Dil-C6(3) depend on whether the polymer

forms an entangled network or not, and are greater in entangled solutions.

Translational Diffusion Constant Linear and Branched Chains

With the advent of experimental equipment in which both static and quasielastic 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 ability offers the hope of obtaining

structural information about branching heretofore unavailable. Since 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 relating the radius of gyration to the hydrodynamic radius 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 a polymer molecule in

dilute solution and that obtained from Kirkwood Riseman theory using an analytical Gaussian model of the chain. The discrepancy is 15% for linear

chains and nearly 50% for the ideal star branched chains studied.

Current work at this laboratory approaches this problem in various 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 can be explained by this modeling. Also, Monte Carlo chains have

been created in which corrections only up to the second cluster integral or the

second virial coefficient are included in the modeling. Such chains at the

theta point are akin to the so called "true" self-avoiding walks. The

importance of the third and higher cluster terms on properties like radius of

gyration and hydrodynamic radius for both linear and branched Monte Carlo

chains is being investigated.

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 for large M values

used to compare with experiments were not possible even for polymers of high

molecular weight. Currently analytical work is being pursued in which both

local structure and long range exclusion is taken into account in the same

theory.

14
Characterization of Polylmlde Polymers by Fluorescence Spectroscopy

Polyimide polymers are important In electronics and associated industries

because they have properties suitable for photoresists and thermally stable

insulators. We have used the fluorescence technique to monitor the formation

of a polyimide polymer from 2,2-bis (4-phenoxyanilino)hexafluoropropane and a dianhydride like 3,3' ,4,4'-benzophenone-tetracarboxylic dianhydride (BTDA) or

2, 2-bis (3 ' ,4'-dicarboxyphenyl)hexafluoropropane dianhydride (6F) . Preliminary

results show that the fluorescence spectrum of the poly (amide-acid) overlaps

the spectra of the diamine and the dianhydride when the excitation wavelength

is 355 nm. However, the formation of the polyimide polymer from the

poly (amide-acid) is accompanied by red shifts in the excitation and the

emission spectra. Therefore, the formation of the polyimide polymer can be

monitored by measuring the increase in the fluorescence intensity at 550 nm

when the sample is irradiated at 480 nm.

In collaboration with scientists from AT&T, we have initiated a project to

monitor the formation of polyimide polymer from p-diaminobenzene and 3, 4,3', 4'-

biphenyl-tetracarboxylic dianhydride. The formation of the polyimide polymer

from the poly (amide-acid) is accompanied by red shifts in the excitation and

emission spectra. Therefore, the formation of the polyimide polymer can be

monitored by measuring the increase in the fluorescence intensity at 560 nm when the sample is irradiated at 460 nm.

Fluorescence Spectroscopy of Rod-like Polymers

Recently, heterocyclic rod-like polymers, exhibiting thermal and oxidative

resistance as well as superior mechanical properties, have attracted

considerable interest. The high strength of these polymers arises from their

ability to achieve a high degree of molecular order during film or fiber

processing. Such order arises from the high degree of rigidity that these

polymers show as well as the degree of interaction the polymers have with

themselves and the surroundings. Even in solution, the polymers show

anisotropic liquid crystalline states as well as isotropic states. In all

states the polymers seem to exhibit a fully extended configuration.

In cooperation with the Materials Laboratory of the Air Force Wright

Aeronautical Laboratories (AFWAL) we are developing fluorescence methods to

study single chain and multiple chain properties of these systems. By looking

at the time-resolved fluorescence intensities from dilute solutions of the

polymers, we hope to provide an estimate of the torsional rigidities of these

polymers which we expect will relate directly to their performance properties.

From studies of the fluorescence of the solutions of these polymers as a function of concentration, we hope to characterize the polymer-polymer

interactions as well as the degree of order in the various phases.

We have measured the excitation and emission spectra of a dilute solution of

poly (p-phenylene benzbisthiazole) (PBT) in methanesulfonic acid. We have also

measured these spectra for a dilute methanesulfonic acid solution of 2,6-

diphenylbenzo(l,2-d:4, 5-d' )bisthiazole (hereafter referred to as tbisthiazole) , a model compound of PBT. We have found that the emission

spectrum of the PBT solution has its most intense band at 466 nm when the

15
excitation wavelength is any of the following wavelengths: 270 nm, 320 nm, and

440 nm. The emission band for the PBT solution occurs at longer wavelength

than the one for the t-bisthiazole solution at 416 nm, indicating that the

phenyl and the heterocyclic moieties in PBT are highly conjugated.

Because PBT films, and blends containing PBT are often cast from

methanesulfonic acid, they inevitably contain some residual acid. It is

therefore important to study the effect of protonation on the emission spectrum

of t-bisthiazole (the model compound of PBT) in chloroform containing varied

amounts of trif luoroacetic acid (TFA) . We have found that as the concentration

of TFA increases, a broad structureless band at 460 nm appears and increases in

intensity at the expense of the structured band at 416 nm. However, as the

concentration of TFA is further increased, the intensity of the band at 416 nm increases while that at 460 nm decreases and nearly disappears when the solvent

is 100 percent methanesulfonic acid.

In collaboration with Drs. Ted Heilweil and Rich Cavanagh of the Molecular

Spectroscopy Division, we have also measured by picosecond spectroscopy the

lifetimes of electronically excited PBT in methanesulfonic acid, and tbisthiazole in chloroform containing varied amounts of TFA. The lifetime for

PBT was found to be 130 ps. The lifetime for t-bisthiazole was 120 ps in pure

chloroform, increased to 185 ps in chloroform containing 2% of TFA, but

decreased to 142 ps in pure TFA.

Evanescent Wave Induced Fluorescence Spectroscopy of Adsorbed Polymers

The importance of adsorption to problems in areas such as adhesion,

flocculation, chromatography, and biological fouling has spurred considerable

interest in the adsorption of macromolecules. Theories detailing the

adsorption of linear chains onto surfaces using computer simulation methods

based on a partition function approach and using analytical methods based on scaling theory are described in the literature. In comparison to theoretical

results, experimental results on polymer conformation at the liquid/solid

interface are scarce.

We plan to probe the conformation of adsorbed polymers by the technique of

evanescent wave induced fluorescence. In this experiment, a polymer solution

is in optical contact with a solid substrate. Laser light is coupled into the

substrate at an angle appropriate for total internal reflection at the polymer

solution/substrate interface. The index of refraction of the substrate must be

greater than the index of refraction of the polymer solution for total internal

reflection to occur. Concomitant with total internal reflection is the

creation of an evanescent wave in the interfacial region. The evanescent wave

penetrates the polymer solution with an intensity that decays exponentially

with distance normal to the interface. The decay rate depends on the internal

reflection angle, the indices of refraction of the solid and solution, and the

wavelength of light. When polymers labeled with a fluorescent dye adsorb on the surface of the substrate, chromophores near the surface will be

preferentially excited by the evanescent wave. By measuring the fluorescence

intensity as a function of penetration depth of the evanescent wave, the

concentration gradient of chromophores normal to the surface can be obtained.

16
Ve have installed a thin film optical waveguide as our substrate. A waveguide

has two advantages over a prism. The fluorescence signal is enhanced due to

the numerous internal reflections and the determination of the reflection angle

is more precise due to the discrete guided wave modes. Preliminary experiments

have confirmed the generation and detection of fluorescence induced by the

evanescent wave. Solutions of polystyrene that are f luorescently labeled

exclusively at the ends will be studied to determine the extension of polymer

tail ends from the surface of the waveguide. The chemistry of labeling a polystyrene chain with a fluorescent group has been established. In addition,

the molecular weight characterization of end labeled polystyrene will be

accomplished by a gel permeation chromatography apparatus installed

specifically for this study.

Fluorescence Studies of Polymer Solutions

Current interest in solution properties of polymers focuses on the shape of the

polymeric chain in dilute solutions and the chain's interactions with itself,

with other chains, and with solvent. The fluorescence quenching study provides

information on many of these properties. The chemistry of attaching

fluorescent and quenching groups to a polystyrene chain has been worked out and

chains with varying concentrations of fluorophores and quenchers have been

made. Preliminary experiments on the properties of single chains in solution

have been done. Theoretical development establishing the relationship between

the fluorescence properties of isolated chains or two chains in solution and

other chain properties is being carried out in connection with the experimental

studies. Our long range plan is to study the interchain properties of the

polymer in more concentrated systems so we will be able to obtain properties of

polymers in blends.

Dynamics of Polymer Chains

The dynamic behavior of polymer chains is important to improving both

characterization and processibility of polymers. The principal methods used to

estimate molecular weight, in particular gel permeation chromatography, the

only method available at present for estimating the 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 highpolymer 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 excluded

volume and chain entanglement effects in a realistic way. Present work is

aimed primarily at the study of these effects, using a combination of

17
analytical and computer simulation techniques. The simulation results provide

data on simple model systems and serve to guide the development of better

theoretical treatments.

We have completed a study of the effects of varying the lattice and the

elementary move rules upon the dynamical behavior of bead-stick models both of

polymer chains constrained to remain on three-dimensional lattices and of

chains not so constrained. The chain-length dependence of the effects of selfentanglement and excluded volume upon long relaxation times depends upon the

presence or absence of lattice constraints, but appears to be independent of

the type of lattice used. The behavior of the translational diffusion

constants roughly parallels that of the long relaxation times. A paper

describing these results has been submitted for publication.

18

MECHANICAL PERFORMANCE OF POLYMERS

The approximate 8% annual growth of polymeric materials results from

substitution for other materials owing to enhanced properties at reduced costs,

the expanded need for all materials due to growth in population and economic

activity, as well as new products that rely on unique properties of polymers.

Important to wider use and acceptance of plastics is a firmer understanding of

performance limitations and processes that affect durability. Full

exploitation of plastics has not been realized due to the lack of adequate data

and models upon which to design for long-term use and to tailor materials for

specific applications.

The objectives of this task are to provide data, test methods, and standards

for evaluation of long-term mechanical performance of polymeric materials and

determination of those factors that limit performance. The approach is to

identify and analyze principal failure mechanisms of commercially important

thermoplastics and elastomers under mechanical stress, to determine the effects

of chemical structure and fine structure morphology on mechanical properties

and failure mechanisms, and to develop constitutive relationships that serve as the basis for accelerated test methodology and lifetime prediction.

The approach to development and verification of predictive models of mechanical

performance is: (1) identify the principal molecular mechanisms and processes

associated with deformation and failure and establish their relationships with

molecular structure and fine texture; (2) evaluate models for degradation of

mechanical properties and for extrapolating short-time measurements to predict

long-term performance; and (3) model mechanical properties and failure using

time dependent constitutive equations.

Joint programs on performance of plastics have been established with other

government agencies which are fostering the use of plastics in areas of

national concern. A joint program with the Air Force is applying advanced

characterization techniques to elucidate the structure of molecular composites

formed by combining rigid-rod polymers with thermoplastic matrix materials.

This project is concerned with establishing the relationships among the

molecular structure, fine texture, mechanical properties, and performance of

these materials. Test methods for evaluating the performance of elastomers

used in tank track pads are under development in a joint project with the U.S.

Army Tank & Automotive Command.

FY 86 Significant Accomplishments

• A nuclear magnetic resonance technique has been developed and applied

to determine the partitioning of chain ends and branches between the

crystalline and non-crystalline regions of polyethylenes . Side

groups (branches) in polymers can greatly affect mechanical

properties and performance. A major problem in predicting such

effects is that branches may be concentrated in regions of

crystalline polymers.

• A joint project with the Gas Research Institute is producing standard

polyethylene materials and components of gas distribution plastic

19
piping and joints. The standards are to be used in laboratory

studies by the gas utilities Industries on mechanical properties and

long term performance of polyethylene components. Mechanical

properties characterization was conducted on the standard materials

to ensure uniformity throughout the large sample of polyethylene

piping and joints which are to be made available through the NBS SRM

program.

• The physical aging of polymer glasses and their failure behavior

under conditions of tensile creep is under investigation. It has

been observed that the creep response curves did not agree with

recent predictions and a method has been developed to predict long

term failure behavior using short time tests.

Characterization of Polymer Structure and Deformation Processes

B. M. Fanconi, B. F. Howell, F. A. Khoury, G. B. McKenna, D. H. Reneker,

D. L. VanderHart, E. Perez^

^Fellow, Institute de Plasticos y Caucho, Madrid, Spain

Knowledge of the molecular mechanisms and structural changes associated with

deformation during and subsequent to processing polymeric materials not only

provides the basis for development of test methods for prediction of long-term

performance and for quality control, but also provides insights into the

selection, processing, and design of materials with improved mechanical

properties and performance. A major part of the Group's effort is the

development and utilization of advanced techniques to elucidate the structure

of polymers from the molecular level to microstructure. Vibrational

spectroscopy and solid state nuclear magnetic resonance are used to determine

the chemical and physical structures of semicrystalline and amorphous polymers,

as well as molecular composites. Calculational approaches are used to predict

the spectral signatures of polymers as a function of conformations determined

from energy minimization calculations. In particular, the minimum energy

conformations of lattice defects thought to be involved in mechanisms

associated with mechanical deformation as well as other physical processes are analyzed. Associated with these calculations is an experimental program to

produce single extended polymer molecules, or small polymer fibers on substrates which are suitable for investigation by tunneling electron

microscopy. The size scale of such specimens are similar to those treated in

calculations. Construction of a tunneling electron microscope is well under

way. This microscope will be used to investigate the architecture of

copolymers and branch distribution in polymers. Better methods are needed to

measure branching in polymers as this aspect of molecular structure, such as in

linear low density polyethylenes, can lead to enhanced mechanical properties.

Major improvements have been made in the nuclear magnetic resonance

instrumentation. The 200MHz spectrometer has been equipped with a new computer

system, and deuterium NMR capability has been acquired. The 60MHz instrument

has been upgraded with a new computer, and a superconducting magnet is under

procurement. The completion of these instrumental modifications will upgrade

our NMR capability to state of the art.

20
A project was initiated in this fiscal year to investigate the structure and

mechanical behavior of physical polymer gels. These materials, formed from

solution, obtain their properties through physical molecular contacts, rather

than chemical linkages, as for example, in polymer networks. The mechanical

properties of these gels are sensitive to the state of aggregation and, through

modeling, provide a means of assessing various structural models. It has been

shown that the mechanical properties are sensitive to the amount of solvent

present in the gel, an aspect that heretofore had not been known.

The Morphology of Crystallizable Polymers: The Development of Spherulitlc

Structures in Polymers

Upon being cooled from the molten state, polymers crystallize in the form of

spherulitic structures which evolve progressively from lamellar chain-folded

single crystal precursors. Fully developed spherulites consist of a radiating

array of long, narrow (on the order of 1pm) lamellae. The reasons why the

single crystal precursors degenerate into spherulites remain to be fully

elucidated. A central feature of the phenomenological theory of polymer

spherulite growth advanced in the mid-1960s was the role played by segregated

"impurities" (low molecular weight chains, atactic chains). The main postulate

of the theory was that the segregation of impurities at the lateral growth

faces of the precursor lamellar crystals gives rise to cellulation at these

faces and hence to a breakdown of coherent lamellar growth. As indicated in a later review and discussion, the theory did not specifically account for a salient feature of the transitional morphological changes manifested in the

evolution of the precursor crystals into spherulites, namely the profuse

splaying of lamellae. Furthermore, the role of impurity segregation in the

evolution of spherulites has been questioned of late with particular reference

to the formation of isotactic polystyrene spherulites. A main difficulty

confronted in the study of the fine structural details of the early transient

stages of evolution of spherulites in bulk polymer, with the object of

determining the nature of the growth processes involved in their evolution, is

that these structures are relatively inaccessible to direct electron

microscopical examination except in very thin films in which the threedimensional pattern of development of the spherulites is seriously obstructed.

Recent work in this laboratory has led to the observation that it is possible

to "excise" isotactic polystyrene (IPS) spherulites at various stages of

development from bulk polymer. This capability stems from the fact, discovered

in some exploratory experiments, that whereas amorphous IPS dissolves readily

in amyl acetate, crystalline IPS does not do so. Because the glass transition

temperature of IPS is fairly high (Tg about 90°C) , the polymer can be readily

quenched to the amorphous state by rapid cooling. Accordingly, the growth of

spherulites in bulk polymer samples can be arrested at different shapes of

development by rapidly cooling partially crystallized samples to room temperature. Addition of excess amyl acetate to such samples, which contain

the spherulitic structures dispersed in a matrix of amorphous polymer, results

in the dissolution of the matrix. The crystalline aggregates remain in

suspension in the solvent and can thus be conveniently isolated for examination

either with a transmission or a scanning electron microscope depending on their

thickness. Such a study is currently being pursued.

21
Partitioning of Chain Ends and Branches Between the Crystalline and

Non-crystalline Regions of Melt-Crystallized Polyethylenes

The experiments utilize a) proton-carbon cross-polarization (CP) techniques, b)

the differentiation in the carbon spectra of crystalline and non-crystalline

carbon resonances, and c) reasonable assumptions about proton-proton spin

diffusion in order to establish the morphological position of defects such as chain ends or branches.

Results of the partitioning studies can be summarized as follows; 1) In

several samples which were slowly cooled (1® per minute) from the melt, the

concentration of chain end methyl and terminal groups in the crystalline

regions fell to 76% and 62%, respectively, of the original overall average

concentration. This means that these end groups are preferentially, but not

severely, excluded from the crystalline regions. Also, these results imply

that the ratio of crystalline to non-crystalline concentrations is very much a function of the total crystallinity.

As to the branch concentrations in the crystalline regions, in the systems

which have been analyzed fully to date, the methyl branch concentration (4.2

branches per 1000 carbons) is 37% of the average overall branch concentration

whereas this percentage is 16% in a sample of hydrogenated polybutadiene (17

branches per 1000 carbons) and less than 10% in an ethylene/butene copolymer

(2.6 branches per 1000 carbons). Thus, it is clear that ethyl branches are more excluded from the crystal than methyl branches, which, in turn, are more

excluded than methyl and vinyl end groups. A rather surprising result has been

obtained recently on an ethylene/hexene linear copolymer having butyl branches.

In this material, the crystalline region seems to contain a higher

concentration of butyl branches, relative to the overall average, than was found for ethyl branches. We are currently pursuing certain questions about

the test methodology used for butyl branches. The polyethylenes with branches

having four or more carbons present a problem in the analysis since resonances

of the methyl carbons from chain ends and branches are superimposed. These

resonances are distinct for methyl and ethyl branched polyethylene.

We have also looked at samples which were exposed to ionizing radiation. One

set of samples was sealed in vacuum and placed in a gamma-ray source. Two

other samples of ultrahigh molecular weight LPE were subjected to rather

intense electron beam irradiation under nitrogen. No differences in reaction

chemistry were observed with the two kinds of irradiation. The production of

methyls and interior vinylenes along with the early disappearance of any

terminal vinyls was observed. Also a loss of crystalline perfection was indicated. Some crystallinity could be restored by annealing; however, the

partitioning of defects such as the interior vinylenes was unaffected by

annealing as one would expect if chains were highly cross-linked, i.e. if a carbon in a crystalline environment was forced to remain in a crystalline

environment

.

22
Spin Diffusion at Natural Abundance

The object of this work is to examine spin exchange in crystalline

materials having natural abundance populations of nuclei. A strong

motivation for this work was the recognition that due to the dilute nature of

the 13C spins (1.1% at natural abundance), spin exchange interactions should be

weak and governed by statistical distributions. Therefore, spin exchange

should be a reasonable probe over distances of 0.5-lnm during times of 1-lOOs.

This technique was successfully applied to cellulose in which polymorphy was demonstrated by the lack of spin exchange between certain resonances.

In linear polyethylene, a temperature-dependent spin-exchange rate was observed. The only explanation for this is that internuclear distances between

nuclei are time dependent, i.e. the chains are being transported through

the crystal lattice, even at room temperature. Through modeling, a crude

estimate of transport rates was obtained. The chain transport inferred from

the data was not consistent with uniform transport described by unbounded

diffusive motion. Failure of this model might be attributed either to a wide

distribution of crystalline stem lengths or to the bounded nature of chain

transport in the crystalline lattice.

Polystyrene Gels

Isotactic polystyrene (i-PS) gels exhibit unusual mechanical behavior and

observations in other laboratories claimed evidence for a new crystalline phase

in the gels, periodicities of the order of 300nm, and PS/solvent complexes.

We investigated these gels at ambient temperatures using both and proton

NMR to test the various structural models. From the proton NMR and from the

stoichiometry of the original solutions, we concluded that 46% and 52% of the

i-PS appeared rigid on a time-scale of 10 microseconds in gels made up of 25%

by weight PS in cis- and trans-decalin, respectively. In gels made from 10% by

weight PS, the fraction of PS which appeared rigid increased to 51% and 64% in

cis- and trans-decalin, respectively. The increase in the rigid fraction with

decreasing initial concentration of PS is evidence that points of condensation

are more widely separated at lower concentrations and that a larger fraction of

the total chain length is identified with each condensation site.

The NMR experiments performed on the gels are more qualitative because

cross polarization techniques were employed in the absence of a detailed

knowledge of the proton relaxation dynamics. Cross-polarization techniques

were required in order to obtain sufficient sensitivity. The carbon spectra of

non-spinning gel samples indicated that the proton-decoupled linewidth of the

i-PS carbons was very similar to that of the i-PS glassy solid, which, in turn,

is close to the linewidth of the crystalline solid. Thus, the more rigid PS

chain segments in the gels exhibit mobility similar to the normal condensed

phases of PS. The other important finding from the CP experiments was that the

broader resonances did not include any unusually larger contribution in the

aliphatic region where decaline (in any possible PS/solvent complex structure)

23
would appear. It is, therefore, not likely that there is any PS/solvent

complex in the more rigid PS regions. For this conclusion we also cite the

motional rigidity indicated by the PS linewidth. If a complex existed, then

the packing would probably contain more free volume so that more PS chain

mobility would be expected.

These findings significantly restrict the models available for describing the

gel phase. A fringed micelle model seems reasonably consistent with the NMR

data but inconsistent with periodicities of the order of 300nm in the following

naive sense: Suppose the sites of PS condensation were distributed on a cubic

lattice having periodicity x. Then the characteristic domain dimension of this

condensed phase would be close to x/2 in the 25% gels (approximately 1/8 of the

total volume is solid PS) . If the periodicity is 300nm, then the condensed

phase would be 150nm across. Such a large dimension should yield a condensed

PS phase identical to the normal condensed phases. Moreover, if this phase

were crystalline, WAXS should reveal this —but WAXS reveals no crystalline

peaks. Furthermore, proton dipolar relaxation times in the gels are significantly shorter than in the glass or crystal. Therefore, a small (less

than lOnm) domain size is suggested.

Estabishing Connections Between Butyl Side Branches and Resistance to Slow

Crack Growth in Linear Low Density Polyethylene

The behavior of side branches is important in understanding the useful

properties of linear low density polyethylene, particularly one with a concentration of a few branches per 100 main chain carbon atoms that has been

found to have superior crack resistance in critical applications such as pipe

for the distribution of natural gas. Such pipes are expected to last for many

decades and it is essential to understand their behavior in order to control

the processing that leads to stable, safe, and uniform quality pipe for this

large scale operation. The work is being done in consultation with the Gas

Research Institute.

A working hypothesis suggests that the interactions between the butyl group and

the polyethylene crystal alter or prevent the chain transport mechanisms which

lead to crack formation. This hypothesis is very difficult to investigate

experimentally because the important type of cracks may form slowly over a period of years.

The processes by which the butyl branches lead to crack resistance can be

modeled with the help of crystallographic defects and the observable

morphological features of the polyethylene in the pipe.

Side branches, from methyl groups to butyl groups and even longer, can be

accommodated in the crystal and even diffuse through it. We have calculated

the energy required to place a butyl side branch in the crystal. Barriers to

movement along paths involving defect motion appear to be low enough that the

defect can move by utilizing energy available from macroscopic strain fields or from forces transmitted along the chain. It is reasonable to expect that such

forces can move the side branch without necessarily causing the chain to break.

This possibility is being investigated by computer modeling of the

24
conformations of the chains in a crystal in the immediate vicinity of an incorporated side chain.

Ethyl branches can be accommodated by smooth bending of the surrounding chains,

without the introduction of gauche dihedral angles. Butyl and longer branches

require that the adjacent chains bend around the branch and this requires a row

of jog like conformations with gauche bonds in some of the chains.

This row of jog-like conformations has been recognized as an ordinary screw

dislocation loop with properties that have been investigated in metal crystals,

except that in polymers the dislocation line encircles only one plane of

molecules. The introduction of a few other defects for which specific energies

and motional properties are or can be defined allows the problem to be treated

in terms of the defects rather than requiring the calculation of the detailed

conformations of many chains. This produces a tremendous simplification of

the problem and opens the possibility of developing realistic and tractable

models for the molecular scale processes in the vicinity of a growing crack

tip.

Origin of the Longitudinal Acoustic Mode in Polyethylene

In crystalline polyethylene in the forms often used, a single molecule passes

from crystalline regions with long all-trans segments through regions with

folds or other conformations. The longitudinal acoustic mode vibrations

provide information about this structure. The effects of the non-trans regions

on the frequency of the observed longitudinal acoustic mode were investigated

by calculating the behavior of a polyethylene chain in a lattice with

periodically spaced crystallographic defects or folds.

The defects considered are the dispiration loop, the disclination loop, the

dislocation loop (all loops encircle only one chain) , folds with nearest

reentry to the crystal in multiple fold systems and chain twist boundaries. The

atomistic models examined are much more extensive than those considered

previously and, as a result, required large computational power. The force

field and the lattice geometry, together with minimum energy calculations,

determine other physical parameters relevant to the model, such as moduli of

crystalline and defect segments, longitudinal stresses at the boundaries, and

force and mass perturbations.

The longitudinal acoustic mode frequencies were found to be inversely

proportional to the sum of the length of the all-trans segment and to a quantity 2 A which represents the masslike effect of the defect region on the

LAM vibration. Delta was found to have a value of 3.75 ± .25 angstroms. The

internal structural details of the defects and the conformations of adjacent

chains are relatively unimportant, as long as minimum energy conformations of

the defect region are used.

25
Vibrational Spactra of Dafecta in Cryatalline Polyathylana

Polyethylene in useful forms like molded objects, films or ultra high strength

fibers is known to contain a significant fraction of the polymer in

conformations which do not have the all-trans arrangement of the perfect

crystal. Vibrational spectroscopy promises to provide information for the

characterization of these conformations.

To investigate this possibility, the spectrum of polyetheylene crystals

containing crystallographic defects in their minimum energy conformations was calculated and compared with experimentally observed spectra. This was done

for folds, dispirations, disclinations, dislocations, and twist boundaries.

Each defect produces many new bands in the vibrational spectrum of

polyethylene. In many frequency regions, two or more defects contribute to the

intensity of observed bands. There are a few bands which are characteristic of one defect or another, but such bands are generally weak and close in frequency

to other bands. In ordinary experimental spectra, the result is that most of

the vibrations associated with the defects contribute to a broad background.

An important exception is the defect associated bands which fall at a frequency

that lies in a gap between dispersion curves of the crystal. Twist boundaries

have such a vibration. It is observed experimentally, particularly in rapidly

cooled samples.

Correlation spectroscopy provides the possibility of separating and observing

some of the defect associated modes. Other relevant information may be gleaned

from the spectra of crystalline cyclic alkanes where known non-trans

conformations exist, or from molecules which contain alkane sequences as branches, as do some biological molecules, or as blocks in a linear copolymer.

An interesting example of this class is a triblock of an alkane sandwiched

between two f luoro-alkane segments investigated by workers at IBM, San Jose.

We predicted a band associated with the twist of the alkane segment which was subsequently found in the infrared spectrum.

We are now cooperating with workers at Oak Ridge National laboratory in the

development of molecular dynamics calculational techniques for determining the

spectra of defect conformations of polyethylene chains. This offers the

possibility of studying the widths of the bands associated with particular

frequencies and of characterizing the interactions between vibrations with

nearby frequencies but different normal coordinates and other non-linear

processes in a more informative way than conventional vibrational analysis

permits.

Small Polymer Fibers, Thin Polymer Films, and Single Polymer Molecules

The scanning tunneling microscope offers the possibility of producing images of

polymer molecules on a conducting substrate. A microscope for this purpose is

now being constructed with the help of workers in the Physics Department of the

University of California at Santa Barbara.

A repertoire of techniques for producing very small fibers, thin layers of

polymers and isolated polymer molecules has been developed. Thin films or

26
networks of polymer molecules suitable for examination in a transmission

electron microscope have been prepared on carbon films thinned by exposure to a glow discharge in oxygen until they contain small holes or cracks across which

the polymer is stretched. Ruthenium tetra-oxide techniques for staining the

polymer molecules have been developed. High resolution, high magnification

transmission electron microscope techniques that produce resolutions under 10

angstroms have shown that films and networks produced by different polymers

(polyethylene, polyetheretherketone, polystyrene, polyisobutylene, poly gamma

benzyl glutamate) have different characteristic features, although fundamental

limits of the performance of the transmission electron microscope do not allow

individual polymer chains to be imaged in detail.

A program written at Arizona State University for calculating the image of a known molecular structure was installed in the Cyber 855 and is being used to

investigate the images expected for the known transfer function parameters of

the electron microscope. The program calculates a 128 by 128 pixel image of a sample containing several layers of atoms by a method that is equivalent to

solving the time independent Schrodinger equation by the Cowley-Moodie method

and calculating the effects of parameters including spherical and chromatic

aberration, defocus, electron wavelength, radius of the objective aperture,

specimen thickness, beam divergence and sample orientation. The program

provides increased capability to interpret polymer structure from micrographs,

where the images are complicated by changes in the sample produced by the

electron beam, the presence of heavy atoms used to decorate the chains, and the

presence of a substrate to support the chains.

A very efficient method for producing through focus pictures needed to

interpret the electron microscope images was developed. It involves tilting

the sample so that different parts of the field of view have different amounts

of defocus. Since the most useful contrast is obtained at a particular but

difficult to achieve level of defocus this technique has proven to be efficient

and useful for these samples.

Precipitation of polyethylene samples spanning molecular weights from around

52,000 to over 5 million showed that the molecules interacted and formed

network like features at concentrations as low as 10~® gm/ml for the 5 million

molecular weight polyethylene, while the critical concentration predicted

theoretically at which the random coils in solution would be expected to

overlap is about 10 times higher at each molecular weight. This is consistent

with reports in the literature that measurements of elongational flow show

evidence of molecular interactions well below the critical concentration.

Mechanical Properties Measurement and Modeling

J. M. Crissman, G. B. McKenna, L. J. Zapas, J.-M. Guenet^ , P. Stockmayer*

,

G. Sleater® , P. A. Pella® , J. C. Humphreys®

1 Centre de Recherches sur les Macromolecules, Strasbourg, France

^Institute for Polymer Testing and Polymer Science, Univ. Stuttgart,

West Germany

®Gas and Particulate Science Division, MBS

27
The mechanical performance and behavior of polymeric systems covers a modulus,

G, range including the gel-like state (G^lOKPa) , rubbery state (G“lMPa)

,

semicrystalline polymers (G“.3GPa) and the glassy state (G“lGPa) . Members of

the Polymer Division staff are conducting research to characterize

relationships between the molecular and continuum physics of appropriate

polymer systems as used to model mechanical properties.

On the basis of investigations of the mechanical behavior of polymeric systems

which exhibit a variation of over 5 orders of magnitude in modulus, major

contributions are being made to the understanding of the molecular and

continuum physics required to predict and/or describe the mechanical

performance of macromolecular materials.

A Reduced Variable Approach to Relating Creep and Creep Rupture In PNMA

The description of the viscoelastic and creep rupture behavior of polymers

subjected to large stresses has received considerable attention. Kinetic and

reaction rate models, which have successfully described the failure behavior of

polymers subjected to monotonically increasing loading histories, appear to be

unsuitable when the loading history is more complicated. Similarly, there have

been several successful attempts to correlate the nonlinear viscoelastic

response of polymer glasses under monotonic loading histories using the concept

that the applied stress, or strain, simply shifts the viscoelastic spectrum

along the time axis. That is, the creep, or stress relaxation, curves at

different stress (strain) levels can be superposed to form a master curve by a shift, aa, along the log time axis.

In addition to the consideration of the time dependent behavior of polymers, it

is know that the mechanical response of polymeric glasses is also dependent

upon the thermal history to which they have been subjected. It has been shown

that, to a first approximation, the effect of a change in the volume of the

glass is to shift the viscoelastic spectrum along the time axis. This

phenomenon is generally referred to as physical aging.

While much work has been done to describe either the failure behavior of

polymers or the effects of stress, strain, or volume on their viscoelastic

response, little work has been directed toward studying both aspects

simultaneously. We have begun a program designed to address both the issue of

physical aging in polymeric glasses and their failure behavior under conditions

of tensile creep. In the initial stage of this work the creep behavior at

relatively large stresses has been examined for specimens of polymethyl

methacrylate (PMMA) which were subjected to two widely different thermal

histories. Specimens were prepared from one sheet of commercial grade PMMA

which is known to have been manufactured more than five years prior to its use. Tensile specimens prepared from the sheet were divided into two sets. One set was used as-received (aged at room temperature for five years) . The second set was heated above the glass transition temperature to 120®C and held at that

temperature for one hour, and then removed from the oven and allowed to cool

rapidly in air to room temperature. This heat treated (rapidly cooled) set was stored at room temperatures for at least one week prior to mechanical testing.

Creep tests were then done for a range of applied engineering stresses of from

30 to 60 MPa. All experiments were done at 22.5 ± 1°C in a room where the

28
relative humidity was maintained between 40 and 50 percent. Except at the very

smallest loads, the creep experiments were continued until fracture occurred.

It was found that when represented in terms of the creep strain the data

obtained at different stresses could be superposed onto mastercurves by a shift

along the time axis with no vertical shift required. The shift factors along

the time axis were found to be the same for both sets of creep curves, the only

difference being that the entire mastercurve for the rapidly cooled specimens

was shifted to shorter times by a factor of 2.5 relative to the mastercurve for

the well aged specimens. On log - log coordinates a plot of the horizontal

shift factors versus applied stress yielded a straight line over the entire

range for which data were obtained. A log - log plot of time to failure versus

applied stress also resulted in a straight line over the range of data for

which the specimens actually failed. In the absence of unknown environmental

effects such plots should be useful to predicting a lower bound to the long

time failure behavior of PMMA under tensile creep rupture conditions.

When represented in terms of the creep compliance, superposition of the two

sets of curves is still possible, but now requires a vertical shift, the shift

factors along the time axis being the same as before. The vertical shift

required was found to be simply the ratio of the stress corresponding to the

curve being shifted to that of the reference curve (bs = Oa/ar).

The master curves were also examined to determine whether the creep response

could be fitted with a fractional exponential function where the exponent is

equal to about one third. It was found that the data could not be fit using a single fractional exponential, irrespective of the exponent. Rather it was found that all the data could be fitted within an error of 5-7 percent using

the sum of two fractional exponentials. In this case the only difference

required in the fitting parameters between the two mastercurves was a factor of

2.5 in the horizontal shift factors.

Additionally, in theories of crack growth a relationship is used which states

that the time to failure for creep at constant stress multiplied by the strain

rate at failure should be a constant. An important observation here in that

regard is that the strain at failure was found to be essentially constant (10-

12% strain) for nearly all the specimens tested. This fact taken with the

observations that the shape of all the creep curves were the same and the

vertical shifts required to superpose the compliance data were equal to the

ratio of the applied stress to the reference stress implies that such a relationship is true for the two preparations of PMMA under investigation here.

Finally it is suggested that in systems for which it is true that the product

of the time to failure and the strain rate at failure is a constant, the

reduced variable approach described in this paper can be used to predict the

long time failure behavior of polymeric glasses using short time tests.

29
Conitltutlve Equation for Non-linear Viscoelastic Behavior of Incompressible

Materials

In an attempt to overcome some of the inadequacies of the BKZ theory on the

description of the non-linear behavior of isotopic materials, we derived a new constitutive equation. For the case of simple shearing flow the shear stress

012 (t) is given by the following expression

t t t 012 (t) = - / H^(x(t)-X(T) , t-T)dT + / F*(X(t)-X(T),t-T) /

— 00 —00 J where X(t) and X(t) are the shear strains at times t and t.

There is a characteristic time ti , which depends on the material. If a material has been in a strained condition for time greater than ti , then it can

be considered as being at rest for all time.

This equation has been successfully applied to already published data.

Characterization of the Nonlinear Viscoelastic Behavior of Epoxy and Rubber

Toughened Epoxy Resins

Cast cylinders of an epoxy and its CTBN rubber toughened analogue have been

tested in single step stress relaxation in torsion at constant length. Both

torque and normal force responses were measured at times from 0.1 to 3,355s and

at strains of X=0.0025 to X=0.08. While both materials exhibit nonlinear

behavior in the torque response at »2-3% strain the modulus G(t) of the

untoughened resin decreases more rapidly than does that of the CTBN modified

material. Data were obtained on various two step stress relaxation experiments

and the behavior were analyzed with the new constitutive equation.

Non-linear Shear Behavior of a Polyieobutylene Solution

Single and multistep stress relaxation experiments were obtained on a 15%

polyisobutylene solution (B-200) in Opanol. Some of the wiring and pickup

transducers were changed on the Rheometrics Mechanical Spectrometer, so that

input signals and the responses could be accomplished with the aid of a computer. This minimized errors on the introduction of the steps due to

overshooting, and cut the time of the introduction of the step by a factor of

20. The data were analyzed with our new constitutive equation. The three

functions were evaluated for times ranging from .2 to 1000 sec and shear

strains from .5 to 20. All the terms for strains greater than 1 were highly

non-linear. The characteristic time for this solution at 25®C is about 5,000

seconds, while the stress in a stress relaxation experiment at 1000 sec after

the introduction of the step was about 500 smaller than its value at t=.2 sec.

As yet, we do not have a molecular explanation for this persistent memory on

the previous strain history.

30
The Effect of X-Rays on the Polycarbonate Substrate of X-Ray Calibration

Standards

In a new type of X-ray calibration standard issued by the National Bureau of

Standards (NBS) , thin uniform layers of silica-based glasses containing

certified amounts of specific elements are deposited by ion beam coating on a polycarbonate (PC) film substrate. The PC substrate was selected primarily

because it was essentially free of trace elements. This substrate is stable

when exposed to relatively low intensity X-rays from secondary target emitters

in energy dispersive (EDX) spectrometers. However, PC films irradiated with

primary X-rays in a wavelength dispersive (WDX) spectrometer show radiation

damage, such as color changes in the film (from milky white to brown),

embrittlement, and, in some cases, splitting along the parallel striations

visible on one side of the film.

As radiation damage will affect the service life of calibration standards, it was necessary to determine the effect of X-rays on the physical strength of the

PC film substrate (no problems with the glass coatings on the substrate were

observed) . Specimens for tensile measurements were cut from the polycarbonate

film used as the calibration standard substrate.

In the manufacturing process, the membranes are prepared by a solvent casting

technique and are stretched by a factor of 3:1 in the machine direction. The

film is therefore partially crystalline and has anisotropic mechanical

properties in the machine versus the cross-machine direction. Striations,

parallel to the machine direction, are visible on one side of the film.

Tensile test specimens were cut both parallel and perpendicular to the machine

direction based upon the orientation of the striations. The specimens were cut

from the filter membranes before irradiation; after irradiation films were

often too fragile to cut.

Specimens were irradiated in both WDX and EDX spectrometers. In the WDX

spectrometer the specimens were exposed to unfiltered direct radiation from a chromium-target X-ray tube operated at tube powers (kV x mA) from 3-0.2 kW. In

the EDX spectrometer the specimens were exposed to secondary target emitters

(either molybdenum or germanium) excited by a tungsten-target X-ray tube

operated at 40kV and 30 mA.

Two tensile properties were measured: (1) the strain at break, and (2) the

stress at break. The value of each property depended upon whether the specimen

was cut parallel or perpendicular to the machine direction. With the exception

of the stress at break for specimens cut perpendicular, the effect of X-rays on the measured property was cumulative: specimens irradiated with the same X-ray

tube energy (kW-min) , no matter what the irradiation time, the tube power, or the tube voltage, showed approximately the same tensile change. For specimens

cut parallel to the machine direction, both the stress at break and strain at

break showed a steady decrease with irradiation until, at an energy of 100 kWmin, the value of either property was approximately one-half that of the

unirradiated material.

31
Specimens cut perpendicular to the machine direction exhibited a different

behavior. Irradiation had no effect on the measurement of stress at break:

all specimens, unirradiated or irradiated, had the same stress at break, 35

MPa (standard deviation, 2 MPa). At an energy of 100 kW-min the strain at

break was approximately one-fourth that of the unirradiated polycarbonate.

The tensile measurements show that primary X-rays will degrade the PC film.

The greater change in strain at break with irradiation for specimens cut

perpendicular to the machine direction suggest that the deterioration in

mechanical properties will be greater in this direction. In using calibration

standards with a PC substrate it is suggested that a standard be handled with

extreme care once irradiation has begun, and that a record be kept of

cumulative X-ray tube energy to which the standard has been exposed.

Mechanical Durability of Polymeric Materials

D. L. VanderHart, G. W. Bullman, J. M. Crissman, K. M. Flynn, G. B. McKenna

The objectives of this Subtask are to develop measurement methods and models of

long term mechanical performance and to conduct joint projects with other

government agencies on mechanical durability issues of concern to those

agencies. Joint activities with other agencies provide opportunities to

evaluate various approaches to mechanical durability on materials with known

performance histories.

The durability of rubber tank track pads has been of concern to the Army, and a joint project has been established to develop predictive methods for

performance. The failure behavior of filled rubbers under static and dynamic

loads is being investigated.

Reference Standard Polyethylene Resins and Piping Materials

The Gas Research Institute is sponsoring a program at MBS to provide reference

materials for use in research pertaining to natural gas distribution systems.

In addition to the pigmented and unpigmented polyethylene resins, described

elsewhere in this report, this program includes the procurement and

characterization of piping and joints prepared from the pigmented resin.

Piping in three sizes (1.27, 5.08, and 10.16 cm diameter) and two types of tee

joints have been received and characterization of these materials is underway.

Tensile tests and/or density measurements have been done on each size of piping

and each type of joint.

From the 1.27 and 5.08 cm diameter pipe ten specimens were prepared by cutting

rings from five different locations along one 25cm long section. Each ring was then cut in half. From the 10.16 cm diameter pipe, five specimens were cut

from one ring section. Density measurements were then made with the

displacement method using degassed distilled water at 22®C. The average

density for all 25 specimens was found to be 0.938 g cm"® with a standard

deviation of 0.001 g cm"®. The experimental error using this method is

estimated to be no greater than ± 0.001 g cm"®. These measurements indicate

that there is no significant difference in density among the three sizes of

pipe.

32
One butt tee joint and one socket tee joint were also examined for uniformity

in density. Six specimens were taken at different locations from one butt tee

joint and six from one socket tee joint. For the six pieces from the butt tee

joint, the density ranged from 0.928 to 0.939 g/cm® , whereas, for the socket

tee joint, the range was from 0.921 to 0.940 g/cm® . In both cases the lowest

densities recorded were for the pieces taken nearest the point on injection and

the highest values were obtained for the pieces taken from a point on the

inside wall well away from the point of injection. Two tensile properties, the

yield stress and strain at yield, were examined for two of the three different

sizes of pipe. The largest diameter pipe was not included due to a lack of

load capacity in our test machine. Six pieces of the 1.27 cm (0.5 in) diameter

pipe and four pieces of the 5.08 cm diameter pipe were selected at random from

the two lots of pipe. In order to obtain a measure of the specimen to specimen

variability within the two lots of pipe, 10 specimens of the 1.27 cm diameter

pipe and 6 specimens of the 5.08 cm diameter pipe were tested at one strain

rate (81% per min). The average yield stress for the ten specimens of 1.27 cm diameter pipe was 16.4 MPa with a Standard Deviation of 0.15 MPa. The strain

at yield was found to be essentially the same for all ten specimens (e=0.125).

For the larger diameter pipe, the average yield stress was 17.4 MPa with a standard deviation of 0.2 MPa, while the strain at yield was the same for the

six samples tested (0.127) and only slightly higher than for the smaller

diameter pipe.
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PROCESSING AND RELIABILITY OF POLYMER COMPOSITES

One of the most rapidly growing areas in the materials field is polymer based

composites. Their high specific strength and stiffness combined with their

versatility in the manufacture of complex parts given them tremendous potential

for applications in many diverse areas ranging from transportation to

construction. For advanced composites, growth rates of 16 percent per year and

higher are frequently cited. To maintain this growth rate, however, it will be

necessary to overcome major problems in two areas. First, there is a need to

make processing more rapid and reliable. Second, improvements must be made in our ability to predict performance, particularly long term durability.

To achieve these goals, it is essential that the underlying science base, which

is currently rather weak, be significantly strengthened. The Composites Task

is responding to this need by conducting long range, basic research to provide

industry and other Government agencies with test methods, materials property

data, and predictive models in the area of composite processing and

performance.

The overall objective in this Task is to establish the scientific basis for the

relationships between the generic parameters associated formulation and

processing and the properties important in the performance of the final

material. The programs in this Task are divided into three highly interrelated

areas: processing, structure, and performance. Projects in the first subtask

deal with the development of new process monitoring techniques and the

application of these techniques to the study of model systems. This provides

both new measurement methods for process monitoring and a better understanding

of the events that occur during processing. The second subtask area seeks to

bridge the gap between processing and performance by developing techniques to

determine the structure of the fabricated material. Both macro-structure (i.e.

flaws, defects, phase separated domains, etc.) and micro-structure (the

molecular network) are of interest, but most of the work during the past year

has focused on the use of neutron-scattering techniques to study the molecular

network in epoxies. These techniques are now being applied to the analysis of

materials whose processing and performance properties are also being examined.

The third subtask focuses on the determination of performance properties for

polymers and their composites. The major efforts in this area during the past

year have been studies of fiber-matrix bonding and failure behavior of high

fracture energy polymers and their composites.

To assist in conducting this broadly based effort, the Task utilizing a number

of cooperative programs as well as the assistance of experts who, in some

cases, have spent time working in the Division during the last year. A major

new aspect of this cooperation was the initiation of an Institute wide

Colloquium Series on Composite Materials which brought many world renown

scientists to NBS for discussions. The cooperative efforts involve programs

with NASA Langley Research Center, the Department of Treasury, and the

industrial research laboratories at Hercules, Hexcel, and Texaco. In addition,

joint programs were conducted with Drs. A. J. Kinloch at Imperial College

(London) and R. S. Stein at the Univ. of Massachusetts. Guest workers and

visiting scientists during the last year have included Mr. A. Gilat from the

34
Ministry of Defense in Israel and Ms. Weijie Su from the Shanghai Institute of

Pharma and Tech, in China.

FY 86 Significant Accomplishments

• The capability to measure the complex events which occur during processing

has been developed using a variety of techniques. Several model systems

have been successfully examined with multiple techniques including one example where six different measurement methods were utilized. This is

far beyond the capabilities previously available either at NBS or elsewhere and demonstrates a unique facility that will be exploited in

future studies.

• Viscosity changes during cure have been correlated in model materials

with the results from four measurement techniques that have on-line

potential: ultrasonics, fluorescence, photo-bleaching, and

dielectrics. Both similarities and differences have been highlighted

as a critical first step toward evaluating the potential of these

measurement methods. Proper control of viscosity is the single most

important factor in efficient composite processing.

• The molecular mechanism for large strain deformations in epoxies has

been shown by neutron scattering experiments to be at variance with

current knowledge concerning the deformation mechanisms in rubbers,

and other cross-linked polymers. In epoxies cured with short chain

amines the average distance between crosslinks in the molecular

network stays unchanged even when the macroscopic strain reaches

values up to 30%. This result suggests that the deformation

mechanism is either defect controlled or unfolding of the network.

• It has been shown that the fracture energy of rubber-modified epoxies

is loading rate and temperature dependent, but simple viscoelastic

modeling can be used to obtain empirical parameters that depend only

on the material. It has been suggested that the volume fraction of

phase separated rubber is the critical factor in determining the

fracture energy. The empirical parameters of our viscoelastic model

can not be correlated with volume fraction alone, and thus new failure models are needed.

Cure Monitoring and Process Control for Thermosetting Polymers and Their

Composites

S. S. Chang, B. Dickens, B. M. Fanconi, K. M. Flynn, D. L. Hunston, F. I.

Mopsik, J. C. Phillips, F. Wang, and A. C. Lin

The precise monitoring and control of the cure process is an important factor

for manufacturing reproducible products that possesses properties suitable for

each practical application. The properties of the resin are strongly

influenced by the degree of cure and to a lesser extent by the rate and the

path of the curing process. It is important therefore to develop cure monitoring techniques both for the laboratory, so cure cycles can be developed,

and for on-line applications, so the processing can be monitored and

35
controlled. This is particularly important in the manufacturing of large

laminated items where the development of on-line or in-situ cure monitoring

techniques will not only provide precise control of the curing process but also

increase efficiency and reduce waste by minimizing post-process inspection and

reducing rejection rates.

The goal of the NBS program is to support the scientific and industrial

communities by: (1) developing improved cure monitoring techniques, (2)

maintaining a wide variety of such techniques for the evaluation and

calibration of new methods, and (3) studying simple systems with multiple

techniques to increase our basic scientific understanding of processing events

and to develop models for process control.

During previous years, this program has developed or improved a wide variety of cure monitoring techniques which can be classified in terms of the properties

measured:

Mechanical and Transport Properties

Viscosity

Dynamic mechanical properties — torsional braid analysis

Ultrasonics

Thermal Properties

Calorimetry — Differential Scanning Calorimetry

Electrical Properties

Conductance/Resistance

Dielectric Properties

Optical Properties

Spectroscopy — Fourier-Transformed Infrared Spectroscopy, — Fluorescence Spectroscopy

Other Chemical and Structural Properties

Neutron Scattering — network structure in deuterated materials

Chromatography —Size Exclusion Chromatography for molecular volume

In the past year, a new technique, photo-bleaching, was developed (see below),

and a number of improvements have been made in the instrumentation or experimental procedure for other monitoring methods. These advances are summarized below together with some of the more interesting results obtained

through the application of these techniques.

VISCOSITY. For the viscosity measurements, a new computer program has been

developed to more fully automate the instrument. Shear rates are now

automatically adjusted to fully utilize the digitization range of the viscosity

measurement

.

ULTRASONICS. In the ultrasonic measurement, we have successfully developed a technique to apply a thin layer of silicone release agent to facilitate the

removal of the cured resin from the quartz substrate rod without causing

damage. Experiments show this does not effect the cure results.

DSC. In differential scanning calorimetry, the heat of the cure reaction can

be measured in either isothermal or scanning modes. For thermally stable

materials, however, the cure may continue for long periods of time even at the

36
highest measurement temperature (200-250 C) . Thus an integration of the area

of the exothermic peak for a scanning curve may not be sufficient to indicate

the total heat of reaction. As an alternative the heat can be more

reproducibly defined by closing the thermodynamic cycle, i.e., by ending the

measurement on the products at the same temperature as the measurement started

on the reactants. The degree of cure for any time or path can then be

estimated by normalizing the heat released to the maximum exotherm, since the

amount of heat released during the cure is directly proportional to the number

of bonds formed.

DIELECTRICS. The use of the time-domain dielectric spectrometer and

conductance measurements at 50Hz to monitor cure were described in the previous

report. During the past year several experiments have been performed to

compare the conductance results with viscosity measurement made during cure on

the same material. For the most part the conductance was a strong inverse

function of viscosity, but features were also observed that were unique to the

dielectric measurements. For example, the amine cured system shown in Figure 1

exhibited in the conductance curve (ID) a dipolar relaxation after gelation.

This obviously could not be seen in the viscosity data (lA) . In another system

(epoxy cured with ethylmethylimidazole) , the conductance was found to increase

during the early phases of cure where the viscosity was also increasing. This

clearly indicates the presence of an ion-forming reaction in the cure chemistry. Clearly a simple interpretation of conductance as a measure of

viscosity can be misleading.

FLUORESCENCE. In fluorescence spectroscopy we have demonstrated the use of

viscosity sensitive fluorescent molecules as probes for the local

microviscosity and the use of a photobleaching technique to determine the

diffusion coefficients for a fluorescent dye. In the first technique the

fluorescent intensity of an excimer-forming dye decreases with increased

viscosity due to a reduction in the excimer formation. Alternatively, the

fluorescent intensity of another type of dye is enhanced with increased

viscosity due to a reduction in the excited state electronic energy lost

through non-radiative processes. An example of the latter case is shown in

Figure 1C where the fluorescence is ratioed to that for a viscosity insensitive

dye. In the photobleaching experiment, the dye is rendered inactive in a small

region by high intensity radiation at an appropriate frequency. The

fluorescence in this region is then monitored as it returns to normal by

diffusion of the unbleached dye into the sampling volume. The time constant

for this change is related to the diffusion constant. By repeating this

process, changes during cure can be monitored. An example of this is shown in

Figure IB. For all of these methods an effort is underway to use a light-pipe

or a wave-guide to excite and monitor the fluorescence in the interior of the

material thus giving an in-situ monitoring device.

Comparisons of Results from Different Methods

The most important and exciting aspect of the work during the past year has

been the application of many measurement techniques to characterize the same model systems. By comparing the results, the sensitivity and the applicability

of individual methods may be assessed. In Figure 1, the results for curing a diglycidyl ether of Bisphenyl-A (DGEBA) type epoxy, DER 332, with bis-(p37
aminocyclohexyl) methane, BPACM, at 45 C are given for measurements of

viscosity, fluorescence intensity, fluorescence recovery after photobleaching,

reaction exotherm (DSC), ultrasonic attenuation and conductance at 50Hz.

As shown in Figures lA and 1C, the fluorescence, the viscosity, and the

diffusion coefficient from the photobleaching measurements are highly sensitive

to the initial stage of cure. The fluorescence intensity measurement is made

with the probe molecule, l-(4-dimethylaminophenyl)-6-phenyl-l,3,5-hextriene,

normalized to the intensity of a viscosity insensitive molecule, 9,10,

diphenylanthracene (Figure lA) . The diffusion coefficient is measured with the

probe molecule, l,l'-dihexyl-3,3,3' ,3'-tetramethylindocarbocyanine perchlorate

using the photobleaching experiments (Figure 1C) . Interestingly, the increase

in the diffusion constant is similar in magnitude to the change in viscosity.

The diffusion constant curve is not smooth and its structure may provide useful

information.

The isothermal release of the heat for the curing reaction is shown in Figure

IB. As the sample was prepared by melting the BPACM and then mixing it into

DGEBA, the curing reaction has already progressed to some extent during the

mixing process. Consequently, the DSC thermogram picks up the reaction at a particular degree of cure. The maximum cure at 45 C is about 75% of a fully

cured sample at high temperatures, estimated from separate DSC measurements or from heat released in a post-cure process. Both fluorescence measurements also

indicate that the reaction starts off at a reasonable rate. The viscosity

curve shows a similar pattern although there is a 10 minutes delay to reach 45

C. The conductance curve. Figure ID, can not be evaluated in this way because

temperature equilibrium requires 20 minutes or more (equipment modification has

now eliminated this problem). The ultrasonics curve, Figure 1C, on the other

hand, has a different shape, but clearly it does not indicate an induction

period as might be suspected. Additional studies are now underway to examine

this comparison more fully.

Both DSC and dielectric measurements can be used to determine the age or the

effect of storage for the sample, i.e. the degree of pre-reaction before the cure process. For example, the conductance curves for three samples, DGEBA

catalyzed by 2-ethyl-4-methylimidazole, aged at 23 C are shown in Figure 2,

where each curve is shifted in time to match the later part of the cure process

(the conductance of each sample is also shifted by an arbitrary amount to

separate the curves for clarity) . The time shift can be used to construct a cure curve for 23 C. Both DSC and dielectric measurements yield identical

curing time constants for the cure reaction at room temperature for both this

system and the amine system discussed above.

38
EPOXY

332/BPACM,

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39

Figure

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Cure

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Viscosity,

Fluorescence

Ratii

Diffusion

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via

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experiment,

ultrasonic

attenuation

change

in

shear

wave

reflection

technique,

heat

generation

via

DSC,

and

conductance

at

50

Hz.
1IiiIiIIIIfIIIiiIi oo

inoooofOooCsJ ooo o$ootoo8 w

Ijj

O 0^ o 3 - o

40

Figure

2:

Conductance

measurements

of

cure

(at

55C)

for

samples

of

an

epoxy-catalyst

system

aged

before

cure

for

various

times

at

room

temperature.
The discussion above describes a few of the comparisons that have been made in

this task among the various cure monitoring techniques. The availability of

this variety of measurement methods is a unique capability that will be

exploited in the future. Although work on the development of new measurement

methods and the improvement of existing techniques will continue, the major

emphasis will now shift to the comparison of data from multiple techniques for

simple materials. The focus will be on the selection and use of well

characterized systems that exemplify the common cure mechanisms. A second area

of work will be the development of models to describe and interrelate the cure monitoring results. Such models are necessary for process control and for data

analysis since on-line monitoring will inevitably be limited to only one technique.

Investigation of Curing for Intaglio Ink

As an example of the practical applications of the techniques and expertise

developed in the studies discussed above, one project in this task is

developing measurement techniques to aid in the design, production, and use of

intaglio inks. This work is in cooperation with the Bureau of Engraving and

Printing (Department of Treasury)

.

Intaglio inks are complex mixtures of some ten ingredients. The dispersion of

the solid phases in the liquid phase is critical to the cure behavior. A

sedimentation technique using turbidity has been developed to monitor the break

up and dispersion of the solid aggregates during the mixing and milling

operations in ink production.

The size of the polymerizing resin molecules has a strong bearing on the rate

of cure. In air-dry resin systems, oxygen in the air is a reactant. For small

resin molecules, oxygen diffusion may be the factor limiting the rate of

setting of the ink. Molecular size of oligomers and pre-polymers is

conveniently measured with size exclusion chromatography (SEC) . New SEC

computer programs have been written for a laboratory computer systems. These

programs characterize molecular size in terms of hydrodynamic volume, since the

usual intaglio vehicle is a mixture of materials and therefore the molecular

weight distribution cannot be determined. Newly procured materials can be

compared automatically with previously procured batches. Changes in molecular

size of polymerizing resins can be followed. These programs are being used to

monitor ink cure in conjunction with tests which follow the viscosity of the

curing ink as a function of time.

New water-soluble and water-dispersible electron-beam polymerizing resins are being synthesized from poly (ethylene glycol) /bisphenol A/acrylate sequences.

The important parameters in terms of the cure behavior and properties of the

resulting films are the viscosity of the resins, the molecular size, and the

number of polymerizing groups per resin molecule.

41
Analysis of Structure in Polymers and Their Composites

W. L. Wu, B. J. Bauer, J. Prahinski, J. T. Fossett, E. Debelius, W. Su,

D. L. Hunston, H. Yang^ , R. S. Stein^ and H. G. Waddill*

1 Polymer Research Institute, Uniyersity Massachusetts, Amherst, MA

2 Texaco Chemical Company, Austin, TX

The determination of structure in thermoset resins and their composites is a vital step in relating processing and formulation parameters to performance.

During the past year, neutron scattering was the main technique used to address

the structure problem, and some of the results and progress will be described

in this section.

Molecular Response to Large Strain Deformations

The molecular mechanisms associated with large deformations in crosslinked

polymers has been a subject of extensive research. Most of these efforts,

however, have concentrated on those materials with rather low crosslink

densities such as rubbers. Neutron scattering has been the main research

technique for determining the molecular response to the deformation process.

The junctions within the crosslinked materials were found to deform following a scheme closely predicted by a phantom network model. For those materials of

high crosslinking density such as epoxies, however, no experimental results

about the changes in the molecular dimension have been reported using any

direct measurement methods.

Based on our previous experience in the determination of the molecular network

structure of epoxies using neutron scattering techniques, it is apparent that

the epoxies composed of partially deuterated diglycidyl ether of Bisphenal A

and difunctional amines of poly (propylene oxide) are the ideal candidates for

the deformation study. The average distance between crosslinks can easily be

calculated from the positions of the scattering peaks. As a result, a program

along these lines has been initiated. All the specimens were deformed in the

pure shear mode, and a pair of aluminum jigs were used to keep the specimens in

their deformed state during the scattering measurements.

For those epoxies containing a 2000 molecular weight amine, the average

distance between the crosslinks along the amine chain was found to be 4.3 nm

and the distance along the epoxy link was 1.7 nm. The maximum amount of

deformation before sample rupture was about 50%. Within this strain limit, the

amine chains were found to elongate with the macroscopic strain. The amount of

the stretch of the amines was far less than what is predicted by the junction

affine model.

As the molecular weight of the amine decreased to 400, the average distance

between the crosslinks along the amine decreased to about 1.7 nm while the

distance along the epoxy chain was unchanged. For the low molecular weight

amine, the maximum strain before sample failure was 30%. Surprisingly, within

this strain limit, no change in the distance between crosslinks along either

the amine or the epoxy chains was observed.

The glass transition temperature of the epoxy containing the low molecular

weight amine was found to be 70C. In order to ensure that the molecules were

42
in equilibrium with the macroscopic strain, the following experiment was also

conducted. While maintained in the deformed state the sample was heated to

90C, which was 20C above its glass transition temperature, for 20 minutes. The

neutron scattering measurements were conducted on this deformed and heated

specimen. Once again, the average distances between crosslinks within this

deformed and heated sample remained identical to those in the undeformed

specimens.

The above observation is striking and may also have important implications in a practical sense since most of the thermosetting resins used as composite

matrices have distances between crosslink points that are less than those in

the 400 molecular weight amine system. In light of this observation, the

question that needs to be addressed is what parts of the molecular network are deformed in a specimen with a macroscopic strain up to 30% since major portions

of the molecular network do not deform. There are at least two possible

explanations for the above observation. The first is a defect-control model.

This hypothesis would propose that the deformation is concentrated in some localized defect regions while major portions of the molecular network are located outside these defects. The analog of this defect model in metals or other crystalline materials is dislocation theory. The generation and movement

of the dislocations accommodate the macroscopic strain while the lattice

dimensions of the crystals remain unchanged. For this hypothesis, the

unanswered question in the case of epoxies is the nature of the defects. A

second possible explanation for the neutron results is that the deformation

mechanism involves the unfolding of the molecular networks; however, the

prerequisite for such a mechanism is that the average network within a bulk

sample must be topologically two dimensional. In fact, this is true for the

samples tested to date but would not be true for all epoxies. Experiments are now underway to elucidate the deformation mechanisms in greater detail. Amines

and epoxies with different functionality and composition are included in this

work to establish the generality of the findings.

Network Structure Revealed in a Solvent Swollen State

The molecular network structure of epoxy specimens made of protonated

diglycidyl ether of Bisphenol A and linear diamines of poly (propylene oxide) were investigated using neutron scattering technique. Deuterated acetone was used to swell these epoxies to provide the scattering contrast. The molecular

weight of the diamine was the experimental variable in the present work.

The swelling ratio as well as the scattering intensity in the small q (<0.18 A“

1) region for these epoxies were found to increase with the average molecular

weight of the amines. Specimens were also prepared using two amines of

different molecular weight, and found to be between the values obtained from

the single amine containing specimens. A clear scattering maximum was observed

only in the epoxy which contained the two amines of different molecular weights

in equal mole ratio. This observation suggests the existence of a regular

spacing between regions of different swelling ratios within an average

molecular network.

A molecular model with a regularly alternating block structure was chosen to

account for this observed maximum. A semi-quantitative comparison showed that

43
K

K

K

M

M

R

i

the scattering data on an absolute scale agreed quite well with the theoretical

result. The homogeneity of swelling, hence the homogeneity of the molecular

network, has also been studied and compared successfully with the observed

scattering intensities.

Relation Between Network Structure and Fracture Toughness

The fracture toughness is one of the major properties that needs to be enhanced

for most thermoset resins. Composites using brittle resins as matrix materials

are often susceptible to inter-laminar failure. The study of the molecular

mechanisms of deformation in epoxies, as reported at the beginning of this

section, is aimed at understanding the deformation processes which lead to

fracture. In the present section, some of the preliminary results of our work

on the relation between the fracture toughness and the network structure will

be discussed.

For certain compositions, the toughness of the resins depends on the curing

condition. For example, precuring the reaction mixtures at a temperature well

below the glass transition temperature of the fully cured material followed by

a normal cure procedure results in a tougher material for several formulations

tested here. Such results have been observed in epoxies containing mixtures of

400 and 230 molecular weight amines. The network structures of the samples

with different toughness but with identical composition were investigated using

neutron scattering technique.

Deuterated acetone was chosen as the swelling agent. The swelling ratios for

the samples with different toughness were found to be the same; however, a significant difference in the network structure manifested in the swelling

process was revealed by the neutron scattering results. The correlation length

calculated from the excess scattering intensity of the d-acetone swollen

samples showed a strong dependence on the curing process. For materials

subjected to a precuring cycle, hence with higher toughnesses, the correlation

lengths were greater than those for the corresponding brittle samples.

One possible interpretation asserts that the excess scattering in the swollen

epoxies originates from some network defects. The correlation lengths

determined are then a measure of the size of these defects. This hypothesis

suggests that the toughness of materials would be related to the size of the

network defects. This conjecture is consistent with the results reported in

the beginning of this section, namely, the deformation of the epoxies may be a defect-controlled process.

44
Performance of Polymers and Their Composites

R. E. Dehl, E. Passaglia, G. W. Bullman, K. M. Flynn, A. Gilat^ , E. Lin,

A. J. Kinloch,2 w. D. Bascom,^ N. J. Johnston,** R. J. Moulton,®

C. K. Chiang, and D. L. Hunston

* Ministry of Defense, Israel

2 Imperial College, London, England

^Hercules, Inc., Magna, Utah

^NASA Langley Research Center, Hampton, Virginia

®Hexcel Inc., Dublin, California

In studies of composite materials the measurement of performance properties is

almost always a critical element. Consequently, the development of test

methods and reference data is of great importance. During the last year, work

in this area has focused in four areas: delamination, toughening mechanisms,

characterization of tough resins, and fiber-matrix adhesion in composites. In

most of the projects the objective was to understand the performance properties

of the polymeric system in terms of the constituent properties and the

processing/fabrication involved.

Delamination

In recent years, there has been a great deal of interest in composite

delamination, i.e., the growth of cracks between layers of fibers either in the

polymer that holds the fibers together or at the fiber-polymer interface.

These cracks, which can grow from impact damage, substantially reduce the

mechanical performance of a composite, particularly in compression. To design

composites with more resistance to delamination, however, requires a better

understanding of the failure processes involved and the factors that influence

them. Previous work in the Composite Group has examined the relationship

between delamination resistance and matrix resin toughness for a wide range of

materials subjected to mode-I loading. A clear correlation was established,

and the effects of other variables such as fiber-matrix adhesion were identified.

During the past year the mode-I results have been further refined with test

results for a number of new systems. In addition, the studies were extended to

include delamination tests in mode-II loading using the edge notched flexure

specimen. As part of this effort, experiments were performed to examine the

effects of the precracking method on the calculated fracture energy. This is

important for the mode-II test because the crack growth is unstable. Different

thickness shims were inserted into the specimen before fabrication to create

precracks with known crack tip radii. In addition some specimens were wedged

open to advance the crack beyond the insert, and thus create a sharp precrack.

The fracture tests conducted on these specimens indicated that the sharp

precracks gave the best results with the lowest fracture energies and least

scatter. The blunt precracks not only gave high fracture energies, as would be

expected based on previous work in this program and elsewhere, but also showed

extremely wide scatter indicating a lack of reproducibility. Even the thinnest

shim (5 pm) was found to be unacceptable. Consequently, only sharp cracks can

be used to produce valid results in this test geometry.

45
These mode-II studies are now continuing with an examination of the correlation

between fracture energies of various resins and their composites. As with

other studies in the area, our preliminary results show increases in composite

fracture energies for mode-II loading relative to mode-I loading, with the

largest increases for the most brittle matrices. More systems must be

examined, however, before a complete quantitative can be established.

Toughening Mechanisms

The generation of high fracture energy polymer systems for improved adhesives

and composites is a major industrial goal. To assist this effort, basic

studies of toughening mechanisms are being conducted in this subtask. A

critical part of this work is the analysis of the deformation mechanisms

present for toughened thermosets, and how these mechanisms relate to the

morphology involved. Toughened thermosets are generally two phase systems

consisting of an elastomeric phase dispersed as particles in a glassy thermoset

phase. Properties such as toughness depend on the details of this morphology

in ways that are, at present, only vaguely known.

As part of this program, an electron microscope technique for the analysis of

morphology was developed by A. J. Kinloch (Imperial College) and applied to

characterize a variety of systems whose fracture properties were also studied.

The results show that the fracture behavior could not be correlated in a unique

way with the volume fraction of the elastomeric phase as had been proposed

previously in the literature. The major problem with such a correlation is

that the fracture energies are loading rate and temperature dependent, and so different relationships are obtained for different test conditions. By using a simple viscoelastic approach, the rate and temperature dependence could be

modeled for each material tested with an empirical equation whose parameters

are then material constants independent of test conditions. Even these

parameters, however, could not be correlated with volume fraction alone. In

fact, samples with different distributions of elastomer particle sizes but

similar volume fractions gave quite different fracture properties.

Consequently, a simple comparison based on volume fraction will not correlate

results for different morphologies, and thus more study is needed before

meaningful relationships can be established.

Fracture Properties of Tough Composite Matrix Materials

Future composite materials will use tough matrix resins such as rubber modified

epoxies among the thermosets and poly (aryl ether ether ketone) (PEEK) among

the thermoplastics. These matrix materials improve the performance of the

composite particularly with regard to the delamination problem discussed above.

However, the quantitative evaluation of resistance to crack growth in bulk

resin samples is difficult for such very tough polymers. Since they are non- linear materials whose deformation involves plasticity and non-linear

viscoelasticity, the customary means of linear elastic fracture mechanics do

not work very well. One possible way of characterizing such materials is by

the use of the so-called J-integral. The J-integral may be described as the

force on a crack and the deformation zone around it, and has been shown to

apply rigorously to non-linear elastic materials. It can be measured by

46
determining the energy required to advance a crack, and has been successfully

used to characterize the resistance to crack growth of tough steels.

An experimental program to use J-integral methods for determining the fracture

resistance of tough polymer composite matrix materials has been initiated. The

first work will be on rubber modified epoxies with possible subsequent

extension to thermosets.

Fiber-Matrix Bonding In Polymer Composites

Thermoplastic polymers offer great promise as composite matrix materials

because of their superior toughness, high temperature performance, and ease of

fabrication. As reported last year, however, delamination studies of carbon

fiber reinforced thermoplastics conducted in this program have shown poor

fiber-matrix bonding, and this prevents them from achieving the full potential,

particularly in load-bearing applications where delamination is a problem.

Consequently, there is a need to improve the adhesion between fibers and

thermoplastics.

In the case of carbon fiber reinforced epoxies, it has often been found

beneficial to precoat the fibers with an epoxy prepolymer (called asizing) in

order to improve bonding in the composite. In the same way, it may be

postulated that appropriate coatings might improve the performance of

thermoplastic composites. Currently at NBS studies are underway to determine

the effect of polymer and metal coatings on the adhesion of carbon fibers to

thermoplastic materials. Polymer coatings are being applied by vapor phase

polymerization (through cooperation with scientists at the Naval Research

Laboratory) and by electrodeposition from monomer solutions, while metal

coatings are being applied by scientists in the Metallurgy Division using an electroless process. After a careful study of all established tests to

evaluate fiber-matrix bonding, the "critical length" measurement was selected.

In this test a single fiber is embedded in a coupon of the desired resin, and

the coupon is then stretched parallel to the fiber axis causing the fiber to

break into ever shorter length segments. Eventually the segment lengths become

too short to transfer sufficient load into the fiber to cause rupture. This

minimum length, or parameters derived from it, provide a measure of the

fiber-matrix bonding. In the initial experiments this technique was used to

evaluate epoxy coupons with coated and uncoated fibers. This provides an important test to determine if the coatings decreased the already good adhesion

normally found with epoxies. Some early results for studies with each of the

coatings is given below. Work planned for the future will extend these

experiments to thermoplastic resins.

Carbon fibers, coated by vapor-phase polymerization of butene, were examined

first. It was found that the coated fibers adhered about as well to the resin

as uncoated fibers. There was however a greater scatter in critical lengths

which could indicate some damage to the fibers resulted from the coating

process. If so, this would complicate the interpretation of the results.

Experiments to independently measure the strengths for coated and uncoated

fibers are now underway.

47
Carbon fibers coated with Cu and Ni films have also been studied with the

critical length test. The results suggest that the bonding with the coated

fibers was not dramatically inferior to that for the uncoated fibers. The

failure mechanism was different, however, in that fiber appears to break while

the coating does not. This limits the accuracy of the comparison with uncoated

fibers, and may suggest that the coating-fiber bond could be improved. Further

work is planned with coatings that scientists in the Metallurgy Division

believe will give better adhesion to the fiber.

Experiments were also conducted on carbon fibers coated by electropolymerization of ruthenium ion-labelled 4-vinyl pyridine. One reason for

selecting this material is the ability to characterize certain aspects of the

coating by electrochemistry using the ruthernium. The polymer was grown onto

the fibers by a slow current-cycling process, in an effort to produce a uniform

coating and maximize adhesion to the carbon surface. Identification of the

polymer was made by comparison of its FTIR spectrum to that of a similarly

grown coating on a flat platinum surface where the coating could be identified

by other analytical techniques. Preliminary critical length measurements in

epoxy resin have clearly shown that the bonding was not decreased by the

coating.

48
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POLYMER BLENDS

Approximately 15 to 20% of the estimated 47 billion pounds of plastics to be

produced in the United States during 1986 will be polymer blends. In the same way that stainless steels are alloys of iron, chromium, and nickel to make

metal resistant to corrosion, polymer blends are a mixture of two or more

polymers to create plastic alloys with new properties. Mechanical properties,

flame retardance, processability, as well as many other polymer properties can

be improved by blending.

While the blending of low cost polymers is a relatively inexpensive way to

produce materials with new properties, most polymers fail to form a homogeneous

phase during the blending process. In a majority of instances, the

heterogeneous blend has poorer mechanical properties, but in a small number of

cases large and favorable synergistic effects are obtained. For example, the

impact resistance (toughness) of a heterogeneous polymer can sometimes be

increased by an order of magnitude whereas such synergism is never observed in

a homogenous blend. The properties of a heterogeneous blend are dependent on the details of the microstructure and interfacial tension between phases. The

key to understanding how to produce desirable heterogeneous blends is a better

knowledge of the fundamental factors that control the blend morphology,

interfacial adhesion and the relationship between the kinetics (rates of

separation) and the thermodynamics (static properties) of polymer blends.

Two research techniques, small angle neutron scattering (SANS) and temperaturejump light scattering (TJLS) , are being used to obtain basic information for

predicting the conditions under which polymers are miscible and therefore will

form a homogeneous phase and for controlling the rate of demixing and the size

of phase separated microdomains if the polymers are immiscible. These methods

allow phase diagrams to be determined and the phase separation kinetics to be

studied. In addition to these two methods. Forced Rayleigh scattering (FRS)

,

small-angle X-ray scattering (SAXS) , and electron microscopy are also used in

polymer-blend studies.

FY 86 Significant Accomplishments

o The molecular weight dependence of the binary interaction parameter,

y, has been obtained for polystyrene/poly (vinylmethylether) blends

using small angle neutron scattering. This has been used in

conjunction with a temperature jump light scattering technique to

obtain the mutual diffusion coefficient of this polymer blend system

above and below the critical point. The critical slowing down, and

the analytical continuity of free energy and diffusivity have been

demonstrated quantitatively for the first time.

o Blends of poly (vinylidene fluoride) (PVFz) and poly (ethylacrylate)

have been used in their compatible region to study the

crystallization process and morphology of PVF2 . The structures

formed evolve from single crystal lamellae to more complex aggregates

and eventually to spherulites. The morphology has been studied as a function of PVFa concentration.

49
o A theory for the dynamics of phase separation of block copolymers

into ordered lamellar microdomains has been developed. The time

dependence of the scattering function after the system is quenched

into the microphase spinodal region has been calculated. The

similarities and differences between block copolymers and binary

blend systems have been analyzed.

Experimental

C. C. Han, B. J. Bauer, F. L. McCrackin, R. M. Briber, F. A. Khoury,

J. Clark, Y. Matsushita^. T. Sato^ , Q. Tran-Cong^ , Pei Sung'*,

M. Okada'* and Taihyun Chang®

* Nagoya University, ^osaka University, University, “FDA, “Tokyo

Institute of Technology, ®University of Wisconsin

Experimental Study of Thermal Fluctuations in the Spinodal

Decomposition of Polymer Blends

The kinetics of spinodal decomposition of a binary polymer system of

polystyrene/poly (vinylmethylether) near its critical composition has been

studied by the temperature jump light scattering technique. The results

indicate that the linearized theory of the Cahn-Hilliard-Cook type which

includes the thermal fluctuation term describes the polymer system very well in

the early-time and shallow-quench region. The virtual structure factor, Sx (q)

,

which is a consequence of including the thermal fluctuations, has been obtained

for the first time. For experiments of deeper quench, the virtual structure

factor becomes small in our experimental q range, and the time dependent static

structure factor, S(q,t), reduces to the original Cahn-Hilliard type.

Application of a Photodimerizable Probe to the Forced Rayleigh Scattering

Technique for Measurement of Self-Diffusion of Polymer Chains

A new type of photochromic compound, a bis-9-anthryl methyl ether (BAME) , is

introduced as a potential probe for the Forced Rayleigh Scattering (FRS)

technique. Upon irradiation with U.V. light (- 360 nm) , BAME undergoes

intramolecular dimerization which involves a large refractive index change in

the visible region. The dimerization process is known to be essentially

irreversible in the absence of short U.V. (- 250 nm) light at room

temperatures and above. A derivative of BAME is synthesized and chemically

attached to polystyrene chains. Some photochemical properties of the BAME

labeled polystyrene have been reported together with the results of a preliminary diffusion measurement of polystyrene by the FRS technique.

Structure and Morphology of MDI/BDO Based Polyurethane Materials

Polyurethanes are random block copolymers consisting of alternating sequences

of hard and soft segments of variable length along the chain. The hard and

soft segments separate to form hard and soft segment domains. In the case of

copolymers containing less than about 50% hard segments the hard segment

domains act as physical crosslinks for the soft segment matrix. The size,

shape and structure of these hard segment domains are believed to play a

50
crucial role in determining the physical properties of such polyurethanes. We

have begun work, in cooperation with the Food and Drug Administration, on characterizing the hard segment morphology of a series of polyurethanes based

on 4'4'-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (EDO) as the hard

segment. These polyurethanes are important as insulating materials for

pacemakers as well as other biomedical applications. Initial work has

indicated that the polyurethanes in the as-received state are only poorly

microphase separated. This was determined by small angle x-ray scattering and

electron microscopy. An increase in phase separation can be observed after

annealing at elevated temperatures (140 °C) or after soaking in acetone.

Future work will examine the time dependence of the change in the phase

separation during annealing. In addition. Wide Angle X-ray Scattering (WAXS)

has been used to study the changes in morphology with deformation. Unlike most

semicrystalline polymers, the MDI/BDO repeat unit undergoes a chain

conformation rearrangement from a contracted form to the fully extended form on deformation. In addition, WAXS indicates that the transition between the two

chain conformations (each of which exhibits a distinct crystal structure in

annealed samples) is continuous with the d-spacing associated with the monomer

repeat units shifting continuously to lower angles (larger d-spacing values)

with increasing deformation.

The Morphology of Blends of Poly (vinylidene Fluoride) and

Poly (ethyl acrylate)

In the previous year we performed extensive cloud point and melting point

temperature measurements in order to determine the phase diagram for this

system. This year we have characterized the morphology of PVF2 crystallized

from blends in the composition range where the melt is compatible (single

phase) . Crystallization experiments were done as a function of temperature and

composition. As the PVF2 concentration increases from 0.5 wt% to 15wt% the

structures formed evolve from single crystal lamellae to more complex

aggregates, and eventually to spherulites. The phenomenon of twisting of

lamellae, begins to appear in blends at about 5wt% PVF2 crystallized at

150 °C. In blends containing 15wt% PVF2 crystallized at 150 °C where distinct

spherulites are formed, periodic branching of the lamellae along the radial

growth direction of the spherulite is observed. This branching has the same period as the lamellar twist observed in the spherulites with polarized light.

Future work will involve studying the small angle x-ray scattering of the

single phase melt as a function of temperature as the cloud point is approached

in order to measure the correlation length and, possibly, the interaction

parameter, y.

Theory

E. A. Di Marzio, P. Van der Schoot^ , R. J. Rubin, I. C. Sanchez,

F. L. McCrackin, M. Olvera de la Cruz, J. A. Marqusee, E. Passaglia,

C. M. Guttman and M. Mansfield^

^Agricultural University, Netherlands, ^Michigan Molecular Institute

51
Oltff Ttmptrtture of Polymer Rings

The glass temperature Tg of a bulk polymer consisting of polymer rings has been

predicted using the Gibbs-Di Marzio theory of glasses. The predictions were

found to be in accord with experimental data of S.J. Clarson, K. Dodgson and

J.A. Semiyen (Polymer 2^, 930 (1985)). An interesting feature is that Tg of

rings rises as we lower the temperature. This is opposite to the behavior for

linear systems. It is now possible by mixing linear and ring systems to have a polymer blend whose glass temperature is independent of molecular weight.

Estimation of the Amount of Adjacent Reentry in Polymer Crystallization

We have developed a treatment of polymer chain folded crystallization in which

stems are incorporated into the crystal by both adjacent and non-adjacent

reentry. By defining certain stages of partial incorporation of a molecule as separate species, we have been able to adapt a kinetic transfer matrix

technique derived previously to solve the problem of the growth of multicomponent chains to the solution of the present problem. A prescription is

given for obtaining the relative amounts of adjacent and non-adjacent reentry

as a function of the forward and backward rate constants for stem

incorporation. The difficult problem of determining the rate constants as well

as the actual numerical calculations are also being addressed.

Models of the Crystal-amorphous Interface

The presence of a surface near a polymer molecule is shown to invalidate the

concept of universality. It is shown that one cannot scale the properties of

polymers near a surface. One is forced to use molecular models for the loops

of segments near a surface. Previous lattice model results are shown to retain

their validity. In particular, the bound of 2/3 for the amount of tight

folding is shown to be valid.

Spatially Dependent Orientational Packing Entropy

The orientation dependent packing entropy near a surface has been previously

calculated only for the case of non-spatially varying density and orientation.

Experimental data however show that orientation is a function of depth in

membranes. An attempt is being made to determine if these orientation effects

can be incorporated into pre-existing lattice models, such as the very

successful Sheut jens-Fleer treatment. The basic formulae for orientation

dependent probabilities of stepping between adjacent lattice sites have been

obtained and a minimization procedure for determining their actual values is

being formulated.

The Dimensions of Block Copolymers

A diblock copolymer has a thickness which varies as the 2/3rds power of the

molecular weight. The original treatment which obtained this law is

generalized by incorporating the entropy of packing for ordered systems (the

2/3rds law implies that the molecules are stretched perpendicular to the

lamellar surfaces and therefore ordered.) It is found that the dimensions can vary from the 2/3rds to the first power of the molecular weight.

52
Diffusion-Controlled Rates of Relaxation and of Chemical Reaction

[Work Undertaken in Internal Sabbatical Program in Collaboration

with Members of the Thermophysics Division, 774]

This sabbatical program was devoted to the study, in model systems, of: 1) the

concentration dependence of the rate of diffusion-controlled reactions, and 2)

the diffusion-controlled rate of relaxation in the presence of traps. Among

problems of current interest which fall in these categories are: growth of

colloidal or aerosol particles, precipitation, catalysis, fluorescence

quenching, combustion of fuel droplets, and transport and relaxation processes

in disordered materials.

Two related investigations in the area of diffusion-limited reactions have been

carried out.

A) Lattice model simulations in one- and two-dimensions of random-walking

chemically reacting species in the presence (and in the absence) of traps have

been carried out in collaboration with J. Hubbard, J. Rasaiah, and S.-H. Lee.

A mean field theory solution of the nonlinear reaction equations has been

developed which can qualitatively account for the results of the numerical

model simulations.

B) A one-dimensional discrete lattice model of diffusion-limited chemical

reaction has been treated exactly. Our solution is analogous to that obtained

by D.C. Torney and H.M. McConnell in the continuum limit. Exact results for

the discrete lattice model serve as bench marks for the numerical simulations

in A)

.

Computer Simulation of Phase Changes in Polymer Solutions

A polymer solution is simulated by many excluded volume chains on a cubic

lattice. The effect of temperature is simulated by varying the attractive

energy between the segments of the chains. The changes of the radii of

gyration, mean-square end-to-end distance and diffusion coefficient with

temperature and concentration of the solution has been calculated. The change

of clustering size of polymer chains with temperature has been observed. These

calculations will be extended to the case of two types of chains to represent

blends and possibly to the case of copolymers.

Chain Configurations In Lamellar Semicrystalline Interphases

The nature of chain configurations at the crystal/amorphous interface of

semicrystalline polymeric materials is not yet well understood. A lattice

theory has been developed which allows one to predict the degree of adjacent

reentry, the orientational order parameter and the mean lengths and types of

amorphous configurations. The theory permits systematic levels of

approximation for correlations among neighboring bonds along the chains subject

to the interfacial constraints. For freely flexible chains, a sharp interphase

is found with approximately 73% of the chains which emerge from the crystal

reentering at sites which are immediately adjacent. The mean lengths of

amorphous walks and loops are found to be significantly longer than predicted

by random walk statistics. These predictions agree with recent Monte Carlo

simulations.

53
Coagulation and Late Stage Phase Separation

A simulation and analysis of a one-dimensional coagulating system has been

performed. Since coagulation of droplets is an important mechanism for

coarsening in phase separation, we have determined what features of binary

phase separation are exhibited by a system whose dynamics are governed solely

by coagulation. We find the droplet size grows as and the scattering

function develops a well defined peak which grows in intensity and shifts to

smaller wavevectors with time. Furthermore, the scattering function is shown

to have a scaling or self-similar form which is also characteristic of late

stage spinodal decomposition. The droplet size distribution is also shown to

obey a scaling relation. These results are explained by mean field type

arguments.

Microphase Separation Dynamics

Block copolymers microphase separate into ordered domains of the size of the

radius of gyration of the polymer. A theory for the dynamics of the formation

of lamellar domains from the disordered state is being developed. The

scattering function in the disordered phase has a broad peak which upon

quenching into the microphase spinodal region grows exponentially in time and

then plateaus to its new equilibrium value. Contrary to the case of binary

phase separation, no shift in the peak position is seen. For shallow quenches

the dynamics is dominated by fluctuations with wavevectors corresponding to the

maximum in the scattering function. Using a Landau expansion of the free

energy, the time dependence of the scattering function is determined in the

linear region (exponential growth) and the non-linear region (plateauing) for

this microphase separation.

SAXS and Pole Figure Facilities

J. D. Barnes and L. Ouzts

Small Angle X-ray Scattering Camera

The 10 meter small angle X-Ray camera is being used in a "breadboard"

configuration. Under the guidance of Dr. Chris Vonk we have calculated all of

the parameters for a three pinhole design to minimize parasitic scattering.

The major beam path elements have been fabricated and installed, except for the

beam stop mount and the beam monitor mount. Some experimentation is needed to

establish the optimum geometry for the monitor detector, scatterer, beam

combination.

Additional beam path components which have not yet been designed or purchased

include an Fe-55 source for checking uniformity of detector response, the

automatic sample changer, and a suitable automatic inserter for the Fe-56

source. These will be completed as early as possible in FY 87.

54
Initial Operation

Small angle scattering images have been obtained. These indicate that there is

adequate intensity and resolution for operation of the system at a resolution

of 1000 angstroms. Dr. Fred Mopsik has assisted us with a comprehensive

evaluation of the noise characteristics of the detector. The grounding of the

circuit elements in the detector was reworked to minimize pickup due to ground

loops. This improved the detector resolution noticeably. We have devised and

tested procedures for calibrating the positional response of the detector and

we have found this to be adequate and reliable. We are working on calibrating

the detector sensitivity as a function of image position. We have observed

minor amounts of non-uniformity that may be attributable to non-uniformity of

wire spacing in the cathode planes. These effects do not interfere with

qualitative interpretation of the data, but they are important for quantitative

work.

Polymers Division staff are being encouraged to prepare specimens and use the camera. There are a number of specimens of anisotropic semicrystalline

polymers, polymer networks, copolymers, and polymer blends that are awaiting

evaluation.

Operation ka A User Facility

Operation as a full-scale user facility is dependent upon completing the

automatic controls for the beam path, including safety interlocks for detector

protection, automatic beam stop positioning, and automatic sample changing.

The primary problems in this area involve computer interfacing and software

development.

X-Ray Generator Upgrade

We have procured a turbomolecular vacuum pump for use with the Rigaku Denki 12

kW generator. Installation will be done in early FY 1987. This upgrade will

allow the generator to operate with a cleaner vacuum, which should increase

reliability at high power levels.

X-ray Pole Figure Facility - Interest From Outside NBS

The software developed for orientation measurements by NBS has been provided to

workers at the Army Materials Research Command and the University of Dayton

Polymer Research Institute. Graduate students from Washington University and

workers from Picatinny Arsenal also made use of the facility during FY 1986.

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. Although no current effort is in progress on diagnostic systems

or therapeutic equipment, plans do include these activities for the future.

Materials-research efforts are aimed at development of materials and techniques

for promoting adhesion of restorative materials to tooth dentin and enamel.

Novel approaches are pursued for reducing marginal leakage of restorations via

utilization of adhesives and durable space occupying materials for use in

cavity preparations. These include new composite resin formulations with

reduced polymerization shrinkage and more resistance to attack by oral fluids

as well as macroscopic bulky space fillers bonded to cavity walls. Strong,

more durable, versatile dental cements are also explored as are methods for

improving properties of surgical bone cement such as durability, radiopacity,

and coupling between the bone-metallic implant system. New tissue adhesives

are being explored. Testing of retrieved biodegradable bone plates was conducted. Studies of calcium phosphate compounds for endodontic sealants,

bone augmentation, or caries-reducing agents are being investigated. The basic

chemistry of precipitation of calcium phosphates is explored as it relates to

formation of mineral deposits such as bone, teeth; and atherosclerotic plaque

is also under investigation.

Theoretical and experimental studies of stresses within bonded dental systems

are explored with the objectives of defining the most compatible materialproperty combinations and geometric designs for porcelain-to-metal, tooth-toresin, resin-to-f iller bonding and so forth.

Techniques for characterizing casting processes and effects of variables

including alloy compositions are being studied with a view toward improved

alloys and processing methods.

FY 86 Significant Accomplishments

• A promising procedure has been developed for bonding to bone. An

isocyanate containing copolymeric liquid provides a stronger, more

permanent, water-resistant material than other bone adhesives.

• Dental crowns cast from pure titanium have been placed in several patients

in an ongoing clinical study. Methods to achieve greater dimensional

accuracy in these castings are being explored with emphasis on compounds

that produce a permanent expansion of the investment mold material.

• Tests of retrieved fiber reinf orced-biodegradable implant bone plates for

the U.S. Army Institute for Dental Research showed significant

deterioration in mechanical properties within two days of implantation.

The results pointed to directions to be taken for improved performance.

• Flexible prepolymer monomers and bulky diluent monomers (based on vinyl

thermosetting silyl ethers) were synthesized that yield high filler

56
content dental composites with reduced water uptake, adequate mechanical

strength, and excellent esthetics.

• The susceptibility of glass ionomer cements to brittle fracture and

degradation under acidic conditions has been reduced by the incorporation

of water-soluble or water compatible vinyl resin systems.

• Interfacial bonding of dental composites in the presence of water has been

enhanced by the use of a newly synthesized multifunctional silane coupling

agent

Dental Composite and Cement Sealant and Adhesion Chemistry

J. M. Antonucci, E. Asmussen^ , R. L. Blosser^ , R. L. Bowen^ , G. M. Brauer,

E. E. Cobb^ , H. lizuka^, A. D. Johnston^ , R. W. Penn, N. W. Rupp^

,

L. E. Setz2 , J. w. Stansbury, A. Sugawara** and S. Venz®

^The Royal Dental College, Copenhagen, Denmark

^American Dental Association Health Foundation, Paffenbarger Research Center

(ADAHF/PRC) at NBS

3 Dental School, Georgetown University, Washington, DC

‘‘Nihon University, Tokyo, Japan

'’Dentsply International, Milford, DE

Vinyl-based thermosetting composites, are increasingly used in stress-bearing

applications traditionally reserved for amalgam fillings. However, they are deficient in wear resistance, color stability and margin adaptability. The

oral environmental resistance (OER) of polymer-based dental materials is a significant factor in determining their in vivo performance. To enhance the

OER two complementary approaches are being pursued. One is to increase the

degree of polymerization and crosslink density by the synthesis and formulation

of flexible, multifunctional methacrylates (e.g., silicon-containing monomers)

and flexible chain transfer agents (e.g., polythiols). The other approach

involves designing resin systems that have low solubility parameters. We have

synthesized and formulated resin systems that yield composites containing

significant amounts of fluorocarbon or siloxane segments in the matrix phase

and still have acceptable mechanical properties. Composites using a siloxanecontaining resin showed improved OER and acceptable strength. Emphasis also is

directed to monomer systems that have minimal (preferably zero or slightly

positive) changes in volume on polymerization and that have rheological

properties that permit high filler loadings. A novel type of dental resin

system was formulated based on recently synthesized silyl ether derivatives of

BIS-GMA. These silyl ether multifunctional methacrylates have both low

viscosity and excellent wetting characteristics which lend themselves to the

preparation of composites of high filler content. Composites with adequate

strength, excellent esthetics and low water sorption were formulated using

these silyl ether monomers. The long-term hydrolytic stability and potential

for "self-healing" of these unique types of matrices are under investigation.

A series of spiro orthocarbonate monomers which undergo free radical, double

ring-opening polymerization with expansion in volume has been synthesized. By

varying the degree and pattern of substitution, the melting points of the spiro

57
monomers and the mechanical properties of the resulting polymers can be

tailored to meet different formulation requirements. When applied to dental

composites, the incorporation of spiro monomers into conventional dental

resins yielded composites which exhibited a 30 percent decrease in

polymerization shrinkage along with a 250 percent increase in micromechanical

retentive adhesive strength.

A major deficiency of dental composites, is their less than optimal interfacial

bonding phase which also may contribute to their relatively low service life in

aggressive environments such as the mouth. A study of different types of

silane agents and techniques, led to the following conclusions: (1) For silane

agent types, the order of increased bonding effectiveness is methacryl > mercapto > dimethylamino. (2) Integral blending, which aids in filler loading,

is not as effective as presilanization. (3) Dual silanization techniques

utilizing both integral blending and presilanization appears to be the most

effective method of promoting interfacial bonding. (4) The tranverse strength

test is a more sensitive test for evaluating interfacial bonding than the

diametral tensile strength test. (5) A newly synthesized multifunctional

silane coupling agent, having increased potential for bonding to both the

matrix and siliceous filler as well as the capability of forming a more

hydrophobic polysiloxane, yielded composites with enhanced hydrolytic

stability.

Another objective of this subtask has been to synthesize specific monomers or oligomers and to prepare suitable formulations using these compounds as ingredients in adhesives to bond to dentin in an aqueous environment. Thus,

the dimethacrylate ester of 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-

cyclohexene-l,2-dicarboxylic acid as well as a series of oligomers of

isocyanatoethyl methacrylate (IBM) or m-isopropenyl-a,a-dimethylbenzyl

isocyanate (TMI) with ethyl acrylate, butyl methacrylate or hydroxyethyl

methacrylate (HEMA) were synthesized. The urethane methacrylate of IBM or TMI

with HEMA were also prepared. The isocyanato containing monomers or oligomers

reacted with bone, but only slowly with dentin. However, glutaraldehyde

treated dentin bonded strongly to dental composites using these isocyanato

containing oligomers. The bond strength obtained was of the same magnitude as that obtained with ferric oxalate, a surface active agent and a diadduct of

HEMA and pyromellitc anhydride (see below) or with glutaraldehyde-HEMA treated

dentin. The composition of the monomeric ingredients can be easily modified to

provide relatively high molecular weight compounds with low volatility. A low

rate of diffusion into tissues by these adhesives is expected to result in a low degree of toxicity. The biocompatibility will have to be established.

Non-eugenol containing dental cements based on vanillate or syringate esters,

o-ethoxybenzoic acid (EBA) and zinc oxide, have been developed in this

laboratory. These materials do not dissolve in an aqueous environment and have

superior mechanical and adhesive properties compared to presently used cements.

Extensive studies conducted recently have shown the biocompatibility of these

luting agents to be equal to or better than that of commercial cements.

Limited clinical studies to determine their effectiveness have been initiated

elsewhere. Toxicological investigations of modified formulations (containing

acrylic monomers) for temporary fillings are underway at three universities.

68
The feasibility of utilizing halato polymers derived from the acid-base

reaction dimer acid (DA) and trimer acid (TA) with various inorganic bases as dental cements has been established. (See Polymers Division Report for 1985.)

Hybrid composite cements with enhanced mechanical strength can be formulated

using a variety of dental resins and initiator systems.

A thin layer of cement is used for the complete closure of the margin of crowns

and inlays and for retention of the restoration. Film thickness (FT) and

retention of zinc phosphate, polycarboxylate and ionomer cements were determined as a function of power-liquid (P/L) ratio. The relationship between

FT or P/L ratio and retention is complex and depended on the type and brand of

cement. Venting lowered FT and increased retention. Results should assist in

developing improved techniques for placing inlays or cast crowns.

Previous studies showed that acidified aqueous solutions of ferric oxalate, a surface-active compound, and a dimethacrylate coupling agent prepared tooth

surfaces for strong adhesive bonding with dental composite resins. The bond

strength obtained are much greater than those possible with present commercial

products and may eliminate the need to cut away healthy dentin for mechanical

retention of esthetic filling materials. Laboratory studies have shown that

aluminum oxalate can be substituted for ferric oxalate, with potential

improvements in color stability in vital teeth. Biocompatibility studies of

the simplified aluminum oxalate system are underway.

A new activity is the development of inserts for composite restorations. The

development of esthetic inserts may be a means to overcome deficiencies with

composites. Prototypic inserts have been developed and used in cavities in

extracted teeth. Another new activity is designed to develop polymeric

protective coatings for tooth crown and root surfaces. These coatings must

have durable adhesive bonding to both enamel and dentin, and recent discoveries

have been promising. Patents are pending on some of the innovations just

described.

Recent experiments on diametral tensile test specimens of dental composites

have failed to reproduce evidence of a size effect in accord with Weibull

Failure Statistics. Our best explanation for this negative result is that the

polymerization reaction is very sensitive to temperature and that the

temperature rise due to the exothermic polymerization can be expected to be

quite different in the different sized specimens.

Wear, Durability, Clinical Studies and Related Properties of Dental

Composites, Amalgams, Cements, and Glass-Ionomer Cements

J. M. Antonucci, R. L. Bowen^ , W. de Rikj* , A. A. Giuseppetti^

,

J. E. McKinney, N. E. Rupp^ , R. W. Penn, and R. W. Waterstrat^

1 ADAHF/PRC

2 Dental School, University of Maryland, Baltimore, MD

Wear measurements have been extended to include glass-ionomer cements. Glass

ionomer cements are noted for their adhesion to tooth structure. They also are noted for their propensity toward brittle fracture and for their erodible

59
nature especially in acidic environments. One approach to ameliorating the

excessive brittle nature of the glass ionomer cement is to incorporate a water

soluble, somewhat flexible vinyl resin capable of blending with, or even interpenetrating, the glass ionomer network during the dual curing process.

Using an aqueous, compatible, free radical initiator system (e.g., hydrogen

peroxide and ascorbic acid) with a water soluble monomer such as 2-hydroxyethyl

methacrylate, hybrid cement composites were prepared which not only have a "rubber toughened" nature as evidenced by their improved diametral tensile

strength and resistance to catastrophic failure but exhibit greater resistance

to acidic penetrants.

Castings of titanium crowns have been made for dental patients and are being

observed periodically for wear of the opposing tooth and the Titanium as well

as for other subjective responses. It is too early to determine if wear on the

opposing tooth is significant.

In vitro tests are continuing for microleakage at composite-tooth interfaces.

The method of application and the techniques for placing various materials are being studied in order to be able to advise dentists on the preferred

techniques.

Investigation was completed on the reduction of dentinal hypersensitivity by

means of an clinical hydroxy apatite precipitating paste.

Composite restorations with enhanced polymerization were retrieved following

clinical testing and were evaluated and assessed with low power microscopy.

Results showed that the wear was virtually indistinguishable from the controls.

This may be due to a factor which could off set the expected enhanced

durability, i.e., additional polymerization shrinkage may have made margins

more susceptible to failure because of an increased marginal gap.

Dental Alloys, Ceramics. Metrology, and Analysis

J. M. Antonucci, K. Asaoka^ , R. L. Bowen^ , W. de Rijk^, A. A. Giuseppetti^

,

R. W. Hinman^ , J. E. McKinney, 0. Okuno® , R. W. Penn, and R. W. Waterstrat^

^Tokushima University School of Dentistry, Tokushima, Japan

2ADAHF/PRC

'^Dental School, University of Maryland, Baltimore, MD

‘‘Naval Dental Clinic, San Diego, CA

'•Tokyo Medical and Dental University, Tokyo, Japan

Research on the effects of investments on the casting of dental alloys

continued. It was found that batch variations of the same investment affect

only the magnitude of the castability value, Cv . (See Polymers Division Report

for 1985) and the temperature dependence is unaffected. Each brand of

investment produces different magnitudes and temperature dependence of Cv for a given alloy composition. A surface and chemical analysis of investment

patterns is under way.

A two dimension finite element program was developed for evaluating residual

stress in dental porcelain. This program allows for variable cooling rates.

60
It also Incorporates the effects of cooling rate on the glass transition

temperature, and the effects of temperature on the elastic modulus, shear

viscosity and coefficient of thermal expansion of porcelain, as well as evaluating the temperature distribution during cooling. Results are being

analyzed, but at this point it can be stated that the incorporation of a temperature-dependent elastic modulus affects the results to only about one percent

.

Work is continuing on exploring various ways to inpart a permanent expansion to

the investment mold materials which are used in casting titanium dental

appliances. A proprietary mold expander that has been partially successful for

this purpose was identified at NBS as the mineral "kyanite". Kyanite is an inexpensive and abundant aluminum silicate (Al2Si03) which occurs in nature as

a metastable high-pressure phase. When heated to 1400 ®C it begins to

decompose into the equilibrium phases (Mullite plus Silica) and this

transformation is accompanied by a density decrease of about 20 percent.

Experiments are now under way to develop a better understanding of the firing

reactions and to find ways of inhibiting the shrinkage and simultaneously

retarding the tendency toward cracking of the mold which also limits the

effectiveness of the expander. The initial experiments on setting expansion of

dental casting investments with multidirectional strain gauges were completed.

Two computer facilities were installed for the group; one is a terminal that is

connected to the Cyber facility through the NBS net. This facility has been

used principally for finite element analysis of porcelain-fused-to-metal

systems. The other is an IBM PCAT which is being used principally for data

reduction and for the analysis of Weibull fracture statistics. By analyzing

samples taken randomly from known Weibull distributions, it is now possible to

evaluate the confidence intervals for the estimates of parameters for PFM and

other experimental samples. Parameters can be estimated for both two and three

parameter Weibull distributions by maximum likelihood techniques. The

resulting data can be plotted along with the best fitting distribution

function.

Calcium Phosphate Chemistry, Biochemistry, Structure and Clinical

Implications

W. E. Brown^ , C. M. Carey^ , L. C. Chow^ . N. Eidelman^ , E. D. Eanes^

,

B. 0. Fowler^ , T. M. Gregory^ , A. W. Hailer^ , M. Mathew^ , D. N. Misra^

,

B. A. Sieck^ , S. Takagi^ , B. Tomazic^ , M, S. Tung^ , and G. L. Vogel^

lADAHF/PRC

^National Institutes of Dental Research (NIDR) at NBS

A ultramicro analysis system developed in this laboratory specifically for oral

research has been used to study the degree of saturation of human enamel

mineral in plaque samples recovered from individual tooth sites. The results

of this study indicates that human dental plaque, in the absence of sucrose or other food substances, is supersaturated with respect to all pure calcium and

phosphate phases. This demonstrates the existence in plaque fluid of

substances which prevent crystallization or restrict crystal growth. There is

61
no trend in the data which would account for the known site, specificity of

caries.

A calcium phosphate cement development during the previous report period was evaluated both morphologicaly and functionally in vivo using a rat tibial

implantation model. Both prefabricated and paste forms of the cement were

used for bone implantation. Preliminary data provided an attractive biological

profile for this new material which includes (1) no systemic toxicity, (2) no inflammatory response, (3) no foreign body response, (4) good dimensional

stability of the implant, and (5) evidence of soft tissue and bone ingrowth

into the voids in the material.

Application of CaHP04-2H20 (DCPD) -forming solutions has been shown to increase

substantially the enamel reactivity toward fluoride (F) . The effectiveness of

a variation of this treatment procedure, in which the DCPD-forming solution was replaced by a viscous carboxymethylcellulose gel containing monocalcium

phosphate monohydrate (MCPM) , was evaluated using extracted human molars. The

MCPM gel has advantages over the DCPD-forming solution because the treatment

agent can readily be delivered to specific sites where the tooth needs the

protection most.

Several mathematical models have been proposed to describe the diffusion

process during caries lesion progression. A study in which a diffusion cell

comprising two compartments separated by a membrane of known ion

permselectivity was used as an experimental model to study how the dynamics of

diffusion affect dissolution and precipitation of hydroxyapatite and other

sparingly soluble calcium phosphates. The results suggest that the rate of

caries progression may be significantly reduced by making the tooth surface

highly anion permselective.

There is growing evidence that biomembranes play an important role in

initiating and/or controlling mineral deposition during the early states of

calcification in such vertebrate hard tissues as cartilage, dentin, and bone.

In particular, the first mineral crystals formed in these tissues are often

associated with the membrane surfaces of submicron size, extracellular

structures known as matrix vesicles. Synthetic lipid vesicles (liposomes)

previously developed by us as models for studying matrix vesicle calcification

were employed during the period covered by this report to investigate the role

that various biomolecules found in matrix vesicle membranes may be in

regulating this type of biomineralization. The membrane biomolecules most

extensively investigated to date have been the acidic phospholipids,

phosphatidic acid and phosphatidylsevine. Results suggest that their function

in vivo is to control rather than to initiate mineral deposition processes in

matrix vesicles.

The manner in which precipitation was initiated played a crucial role in

determining the size apatite crystals can attain in physiological-like

solutions. Crystals formed by seeded growth were much larger than crystals

formed in spontaneously precipitated reactions. The data suggest that the

formation of amorphous precursor phases, may be a more critical factor in

delimiting crystal size than such solution conditions as the degree of

supersaturation.

62
High resolution mlcroradiographlcs of "dental specimens" of various thicknesses

were also investigated using synchrotron radiation from the NBS Material

Science beamline x-23A, National Synchrotron Light Source at Brookhaven.

Results from these studies indicate that this technique has promise of allowing

one to follow the structural changes accompanying the formation,

demineralization and remineralization of hard tissues in realtime or quasi

realtime.

The calcium phosphate solubility properties in serum and the nature of the

mineral phases in cardiovascular plaques are being investigated. The

combination of data from these two sources clearly indicates that octacalcium

phosphate is a precursor in formation of pathologic mineral deposit. This new

insight into the mechanism of formation of mineral promises eventual control of

pathological mineralization.

Medical Materials and Improved Surgical Bone Cement

G. M. Brauer, J. W. Stansbury, C. Lee^ R. W. Penn and J. A. Tesk

^Sichuan Medical College, Chengdu, Peoples Republic of China

A biocompatible tissue adhesive bonding to bone would find many applications in

orthopaedics. Oligomers or copolymers of 2-isocyanatoethyl methacrylate (lEM) or m-isopropenyl a,a-dimethylbenzyl isocyanate (TMI) have been synthesized.

These low molecular weight liquids containing pendant isocyanate and ester

groups were obtained on reacting lEM or TMI with ethyl acrylate, butyl

methacrylate (BMA) or other acrylic monomers. Shear and tensile strength on bone treated with dil. aq. glutaraldehyde and then with either a solution of

(1) lEM, (2) TMI, (3) lEM-TMI-BMA or (4) TMI-BMA bonded to polymerizable

dimethacrylate was determined. The tensile adhesion of bone cemented with

these compositions varied from 80 to 101 kg/cm^ yielding stronger more

permanent bonds than 2-cyanoacrylates or other adhesives previously suggested

for the cementation to bone. On thermocycling for one week between 5® and 55®

C

HzO, bond strength from 75 to 90 kg/cm^ were obtained indicating that there is

little deterioration of the bond on prolonged water exposure. Subject to their

biocompatibility, compositions containing the oligomers of lEM or TMI should be

most useful as adhesives for mineralized tissues.

Homogeneous, radiopaque bone cements incorporating 10% pentabromophenyl

methacrylate have been formulated. Such materials had excellent physical

properties, but the storage stability of their monomeric solution was inadequate. To overcome this, poly (methyl methacrylate-co-pentabromophenyl

methacrylate) has been prepared. Evaluation of cured bone cements using this

copolymer are under active investigation.

We have developed instrumentation to test experimental biodegradable bone

plates in a project for the Army Institute of Dental Research. Results of the

initial tests are that the bone plates degrade too rapidly. After one day of

implantation, the original properties had degraded significantly and at the end

of one week the plates had fragmented and were unsuitable for testing (hence,

unsuitable as structural implants)

.

63
OUTPUTS / INTERACTIONS

Publications

Barnes, J. D.; Clark, E. S. An automated apparatus for x-ray pole figure

studies of polymers, in Computer Applications in the Polymer Laboratory,

Theodore Provder, Ed., ACS Symp. Series, Vol 313, 1986.

Barnes, J. D.; Dickens, B.; McCrackin, F. L. Software for data collection

and analysis from a liquid size exclusion chromatograph, in Computer

Applications in the Polymer Laboratory, Theodore Provder, Ed., ACS Symp.

Series, Vol. 313, 1986.

Ubrich, J. M.; Chiekh, F. B.; Halary, J. L.; Monnerie, J.; Bauer , B. J.;

Han, C. C. Molecular weight effects on the phase diagram of polystyrenepoly (vinylmethylether) blends. Macromolecules 19: 210; 1986.

Bowen, R. L.; Chalkley, M. W. Research in improved composites, in Anterior

Restoratives, 1986, A Parameswaran and B. P. Rajan, Eds., The Federation

of Operative Dentistry, Madras, India, pp. 1-12.

Bowen, R. L.; Misra, D. N. Complexes of iron cations with n- phenylglycinate or oxalic acid. J. Dent. Res. 65(3): 41; 1986.

Brauer, G. M.; Antonucci, J. M. Dental applications (of polymers) in

Encyclopedia of Polymer Science and Engineering, Wiley Interscience, NY.

Vol. IV., 1986, p. 698.

Brauer, G. M.; Stansbury, J. W.; Flowers, D. Modification of cements

containing vanillate or syringate esters. Dent. Mat. 2: 21; 1986.

Brauer, G. M.; Steinberger, D. R.; Stansbury, J. W. Dependence of curing

time, peak temperature, and mechanical properties on the composition of

bone cement, J. Biomed. Matl. Res. 20: 839; 1986.

Briber, R. M.; Thomas, E. L. The crystal habit and morphology of

poly (butylene terephthalate) and related copolymers. Polymer 27: 66; 1986.

Broadhurst, M. G.; Chiang, C. K.; Davis, G. T. Dielectric phantoms for

electromagnetic radiation, NBSIR 86-3356, April 1986.

Brown, W. E.; Chow, L. C.; Effects of neutral salts in a bench-scale

Caries model. J. Dent. Res. 65(9): 1116, 1986.

Bur, A. J.; Barnes, J. D.; Wahlstrand, K. J. A study of thermal

depolarization of polyvinylidene fluoride using x-ray pole-figure

observations. J. Appl. Phys. 59(7): 2345; 1986.

64
Carey, C.; Gregory, T.; Rupp, N. W.; Tatevossian, A.; Vogel, G. L. The

driving forces in human dental plaque fluid for demineralization and

remineralization of enamel mineral. In Factors Relating to

Demineralization and Remineralization of the Teeth, S. A. Leach, Ed. IRL

Press Ltd., Oxford, England, 1986, pp. 163-173.

Chang, S. S. Book Review: Heminger/Hoehne Calorimetry-Fundamentals and

Practices. J. Therm. Anal. 31: 217; 1986.

Chiang, C. K.; Davis, G. T.; Harding, C. A.; Takahashi, T. Polymeric

electrolyte based on poly (ethylene imine) and lithium salts. 4th Inti.

Conf. on Solid State Ionics, 18 & 19: 300; 1986.

Crissman, J. M. Creep and recovery of a linear high density polyethylene

and an ethylene-hexene copolymers in the region of small uniaxial

deformations. Poly. Eng. Sci., 1986.

Crissman, J. M.; Wang, F. W.; Guttman, C. M.; Maurey, J. R.; Wagner, H. L.

Reference standard polyethylene resins and piping materials, NBSIR 86-

3318, February 1986.

Dickens, B.; Hunston, D. L.; Phillips, J. C.; Bullman, G. W. Study of

intaglio ink mixing and cure and ingredients, NBSIR 86-3303, January 1986.

Martin, J. W.; Dickens . B.; Waksman, D.; Bentz, D. P.; Bird, W. E.;

Embree, E.; Roberts, W. E. Thermal degradation of poly (methylmethacrylate)

at 5QOC to 125<>C. J. Appl. Poly. Sci., 15(3): 256-279; 1986.

Di Marzio, E. A.; Sanchez, I. C. On the origin of non-exponential decay

processes in amorphous systems with special application to polymers. Proc.

of Conf. on Transport and Relaxation Processes in Random Materials held at

NBS, 1986.

Weiss, G. H.; Di Marzio , E. A.; Gaylord, R.J. First passage time densities

for random walk spans. J. Stat. Phys. 42: 567; 1986.

Gaylord, R. J.; Weiss, G. H.; Di Marzio , . E. A. Non-equilibrium mechanical

response of a cross-linked network. Macromolecules 19: 927; 1986.

Fanconi, B. M. Trends in polymer development and analytical techniques.

Proc. of the Inti. Conf. on Polymer Characterization, USGPO, p. 87, 1986.

Fanconi, B. M. ; Wang, F. W.; Hunston, D. L.; Mopsik, F. I. Cure monitoring

for polymer matrix composites, in Matls. Characterization for Systems

Performance and Reliability, eds. J. W. McCauley and V. Weiss, Plenum

Publishing, 1986, p. 275.

Flynn, J. H.; Dunlap, L. A. Gradients in horizontal tube furnaces,

Thermochimica Acta 105: 215; 1986.

65
Guttman, C. M. Relationship of the unweighted Rosenbluth and Rosenbluth

walk to a polymer chain at the theta point. Macromolecules 19(3): 833;

1986.

Han* C. C.; Okada, M.; Muroga, Y.; McCrackin, F. L.; Bauer, B. J.; TranCong, Q. Static and kinetic studies of polystyrene poly (vinylmethylether)

blends. Poly. Eng. Sci. 26(1): 3; 1986.

Han, C. C.; Sanchez, I. C. Dynamics of phase separation in polymer blends.

Physics Today 39: S66; 1986.

Yang, H.; Stein, R. S.; Han . C. C.; Bauer, B. J.; Kramer, E. J.

Compatibility of hydrogenated and deuterated polystyrene. Poly. Comm. 27:

132; 1986.

Howell, B. F.; Reneker, D. H. Morphology of small polymer fibers and

single molecules. Poly. Matl. Sci. Eng. 54: 557; 1986.

Hunston, D. L.; Dehl, R. E.; Wu, W-L. Polymer composites-challenges and

research trends. Mech. Eng. 108: 52; 1986.

Hunston, D. L.; Dickens, B.; Phillips, J. C. Drying behavior studies on intaglio inks. Poly. Matls. Sci. Eng. 54: 53; 1986.

Khoury, F. A.; Crissman, J. M.; Barnes, J. D.; Fanconi, B. M.; Wagner, H.

L.; Guttman, C. M.; Maurey, J. R.; Harding, C. A.; Bolz, L. H. A

comparative study of the structure and mechanical properties of

polyethylene films used in heavy lift balloons, NBSIR 86-3353, 1986.

Marqusee, J. A.; Dill, K. Chain configurations in lamellar semicrystalline

polymer interphases. Macromolecules 19: 2420; 1986.

McKenna, G. B. Durability testing of tank track rubber compounds under

cyclic loading, NBSIR 86-3302, January 1986.

McKenna, G. B.; Hinkley, J. A. Mechanical and swelling behavior of

well characterized polybutadiene networks. Polymer 27: 1368; 1986.

McKenna, G. B.; Zapas, L. J. On the small strain behavior of peroxide

crosslinked natural rubber. Rubber Chem. Tech. 59(1): 130; 1986.

McKenna, G. B.; Ngai, K. L.; Plazek, D. J. Differences in the molecular

weight and the temperature dependences of self-diffusion and zero shear

viscosity in linear polyethylene and hydrogenated polybutadiene. Polymer,

26: 1651-1653; 1985.

McKinney, J. E.; Wu, W.-L. Chemical softening and wear of dental

composites. J. Dent. Res. 64(11): 1326 (1985).

Misra, D. N. Adsorption of benzoic acid on pure and cupric ion-modified

hydroxyapatite: implications for design of a coupling agent to dental

polymer composites. J. Dent. Res. 65(5): 706; 1986.

66
Misra, D. N. Water on apatites. Calcif. Tiss. Int. 38; 333; 1986.

Paf fenbarger , G. C.; Rupp, N. W. A history of the international

association for dental research Vilmer Souder award in dental materials,

with a short biography of Wilmer Souder, Dent. Mater. 2: 49; 1986.

Passaglia, E. Economic effects of corrosion and other degradative

processes, Enc. of Matls. Sci. Eng., Pergamon Press, NY, 1986.

Passaglia, E.; Di Marzio, E. A. Growth regimes and the time development of

lateral habits in polyethylene crystals. Polymer 27: 510; 1986.

Passaglia, E. The economic effects of degradative process on materials,

ACS Symp. on Degradation of Materials Caused by Acid Rain, ACS Symp. Ser.

318 (Pergamon Press, NY) 1986.

Penn, R. W. A recording dilatometer for measuring polymerization

shrinkage. Dent. Mater. 2: 78; 1986.

Roth, S. C. Development of piezoelectric polymer gauges for measuring

pressure on intaglio printing prress, NBSIR 86-3400, June 1986.

Rupp, N. W. Composites - aktueller stand, Phillip Journal 2: 86; 1986.

Smith, L. E.; Brown, D. W.; Lowry, R.E. Prediction of the long term

stability of polyester-based recording media. NBSIR 86-3474, November

1986.

Smith, L. E.; Fanconi, B. M. Polymers division technical activities. NBSIR

86-3437, November 1986.

Takahashi, T.; Davis, G. T.; Chiang, C. K.; Harding, C. A. Chemical

modification of poly (ethylene imine) for polymeric electrolyte. Solid

State Ionics 18 & 19; 321; 1986.

Tesk, J. A. Soldering of dental alloys. Dentist Desk Reference, 1986.

Tesk, J. A. The role of structure and composition on the physical and

biological properties of dental alloys. Review of literature for Inti.

Workshop on Biocompatibility, Toxicity and Hypersensitivity to Alloy

Systems Used in Dentistry, Univ. of Michigan Press, 1986.

Tesk, J. A.; Antonucci, J. M.; Brauer, G. M.; McKinney, J. E.; Penn, R.

W.; Venz, S.; lizuka, H.; Okuno, 0.; deRijk, W. Properties and

interactions of oral structures and restorative materials, NBSIR 86-3320,

February 1986.

Tesk, J. A.; Waterstrat, R. M. Dental base-metal casting alloys: physical

metallurgy. Encyclopedia of Matl. Sci. Eng. 1056; 1986.

67
VanderHart, D. L. Field-dependent C-13 chemical shifts in solids: a second-order dipolar perturbation. J. Chem. Phys. 84(3): 1196; 1986.

VanderHart, D. L.; Perez, E. A UMR method for determining the

partitioning of end groups and side branches between the crystalline and

noncrystalline regions of polyethylene. Macromolecules, 1986.

VanderHart, D. L.; Wang, F. W.; Eby, R. K.; Fanconi, B. M.; DeVries, K. L.

Exploration of advanced characterization techniques for molecular

composites. AFWAL-TR-85-4137, 1986.

VanderSchoot, P. Towards a theory for the orientation dependent packing

entropy of inhomogeneous polymer systems. NBSIR 86-3466, October 1986.

Wang, F. W.; Lowry, R. E.; Wu, E.-S.; Fanconi, B. M. Fluorescence methods

for cure monitoring of epoxy resins, Proc. of the 1985 Scientific

Conference on Chemical Defense Research, 573 (1986).

Wang, F. W.; Lowry, R. E.; Fanconi, B. M. Fluorescence monitoring of

viscosity and chemical changes during polymerization. Poly. Preprints

27(2): 306; 1986.

Waterstrat, R. M.; Giuseppetti, A. A. The Hafnium-Rhodium Constitution

Diagram. J. Less-Comm. Met. 119: 327; 1986.

Kuentzler, R.; Waterstrat . R. M. Electronic properties and stability of

the ordered structures of the V-Pd, Nb-Pd and Ta-Pd systems, J. LessCommon Metals, 120: 317; 1986.

Wu, W-L.; Bauer, B. J. Epoxy network structure (II). Polymer 27: 169;

1986.

Wu, W-L.; Bauer, B. J. Epoxy network structure (III). Macromolecules 19:

1613; 1986.

Antonucci, J. M. Resin based dental composites-an overview. Proc. of the

2nd Inti. Conf. on Polymers in Medicine, Capri, Italy, in press.

Kuo, J. S.; Antonucci . J. M. Evaluation of siloxane-containing dental

composites. J. Dent. Res. in press.

Bowen, R. L. Review of the paper: bonding agents and adhesives, by R. W.

Phillips, Proc. of the Inti. State of the Art Conf. on Restorative

Materials, in press.

Briber, R. M.; Khoury, F. A.; The phase diagram and morphology of blends

of poly (vinylidene fluoride) and poly (ethyl acrylate). Polymer, in press.

Quay, J. R.; Blackwell, J.; Briber , R. M.; Thomas, E. L. The hard segment

unit for MDI-BDO-based elastomers: a combined x-ray and electron

diffraction approach, in press.

68
Chang, S. S.; Maurey, J. M. Migration of low molecular weight components

from polymers. IV. Migration of styrene^ monomer from polystyrene.

Polymer, in press.

Chiang, C. K.; Bauer, B. J.; Briber, R. M.; Davis, G. T. Synthesis of

ionic conducting interpenetrating polymer networks, Poly. Comm., in press.

Crissman, J. M.; McKenna, G. B. A reduced variable approach to relating

creep and creep rupture in PMMA. J. Poly. Sci. in press.

Dehl, R. E. Studies of adsorbed polymers by ellipsometry. "Applied

Ellipsometry" , in press.

Schoch, K. F.; DeReqgi , A. S.; Roth, S. C. Apparatus for quasihydrostatic

measurement of piezoelectric dh coefficient, Proc. Conf. Applic. of

Ferroelectricity in Ferroelectics, June 1986.

Dickens, B.; Martin, J. W.; Waksman, D. Analysis of damage profiles in

poly (methyl methacrylate) in terms of oxygen diffusion and consumption.

Polymers Degradation and Stability, Elsevier Applied Science Publishers,

Barking, Essex, England, in press.

Di Marzio, E. A.; Guttman, C. M. The glass temperature of polymer rings.

Macromolecules, in press.

Di Marzio, E. A.; Passaglia, E. Calculations of the amount of adjacent re- entry in polymer crystallization, I. The Basic Equations, J. Chem. Phys.

in press.

Eidelman, N.,* Chow, L. C.; Brown, W. E. Calcium phosphate saturation

levels in ultraf iltered serum. Calc. Tiss. Inti., in press.

Fanconi, B. M.; Wang, F. W.; Lowry, R. E. Process monitoring of polymer

matrix composite using fluorescence probes. Review of Progress in

Quantitative Nondestructive Evaluation, Vol. 6, in press.

Mansfield, M.; Guttman, C. M.,* Di Marzio, E. A. Models of chain folding in

semicrystalline polymers. J. Poly. Sci., in press.

Okada, M.; Han , C. C. Experimental study of thermal fluctuation in

spinodal decomposition of a binary polymer mixture, J. Chem. Phys., in

press.

Tran-Cong, Q; Chang, T.,* Nishijima, Y.; Han, C. C. Application of a photodimerizable probe to the forced rayleigh scattering technique for

measurement of self-dif fusion of polymer chains. Polymer, in press.

Hunston, D. L.; Moulton, R. J.; Johnston, N. J.; Bascom, W. D. Matrix

resin effects in composite delamination: Mode-I Fracture Aspects. Proc.

ASTM Symp. of Tough Composite Materials, in press.

69
Bascom, W.; Boll, D. J.; Hunston , D. L.; Fuller, B.; Phillips, P. J.

Fractographic analysis of interlaminar fracture, Proc. ASTM Symnp. of

Tough Composites, in press.

Kinloch, A. J.; Hunston . D. L. The effect of volume fraction of dispersed

rubber phase on the toughness of rubber-toughened epoxy polymers. J. Matl.

Sci. , in press.

Marqusee, J. A. One dimensional coagulation: scaling and phase separation

dynamics, Phys. Rev. A, in press.

Marqusee, J. A.; Mulholland, G. W. "Comment on: On the applicability of

Smoluchowski ' s equation with a constant kernel to coalescence". J. Chem.

Phys., in press.

Mathew, M.; Brown, W. E. A structural model for octacalcium phosphatesuccinate double salt. Bull. Chem. Soc. Japan, in press.

McKenna, G. B.; Bullman, G. W.; Flynn, K. M.; Patt, J. Fatigue of a rubber

tank track compound under tensile loading. Proc. 32nd Sagamore Army

Materials Research Conf., in press.

McKenna, G. B.; Guenet, J. M. The concentration of the compression modulus

of isotactic polytyrene/cis-decalin gels, J. Poly. Sci., Phys. Ed., in

press

.

McKenna, G. B.; Hadziiaonnou, G.; Hild, G.; Strazielle, C.; Lutz, P.;

Rempp, P.; Kovacs, A. J. The molecular weight dependence of the zero shear

viscosity of cyclic polystyrene molecules in the melt. Macromolecules, in

press

.

McKenna, G. M. Plazek, D. J. The viscosity of blends of linear and cyclic

molecules of similar molecular mass. Poly. Comm., in press.

Whitman, D. J.; McKinney , J. E.; Hinman, R. H.; Heby, R. A.; Pelleu, G.

M. An in vitro comparison of the wear rates of acrylic resin, IPN, and

denture tooth materials. J. Prosth. Dent, in press.

Misra, D. N.; Bowen, R. L. Adsorption of PMDM, the adducts of pyromelletic

dianhydride with 2-hydroxyethylmethacrylate, on hydroapatite, Special

Edition Supplement to Journal of Colloid and Surfaces, in press.

Olvera de la Cruz, M.; Sanchez, I. C. Theory of micophase separation in

graft and star copolymers. Macromolecules, in press.

Olvera de la Cruz, M.; Sanchez, I. C. Microphase separation in block

copolymer/homopolymer blends. Macromolecules, in press.

Passaglia, E. Craze and fracture in polymers, J. Chem. Phys. Solids, in

press

.

70
Bundy, K. J.; Penn , R. W. Improvement of metal/bone cement interfacial

strength, J. Biomedical Matls. Res., in press.

Penn, R. W.; Craig, R.; Tesk, J. A. Diametral tensile strength and dental

composites. Dent. Matl., in press.

Perez, E.; VanderHart, D. L. Solid state nmr investigation of

polyoxetanes . Polymer, in press.

Register, R. A.; Sanchez, I. C. Compressibility and surface tension

relationships in molten salts and metals, J. Chem. Eng. Data, in press.

Register, R. A.; Sanchez, I. C- Compressibility, surface tension, and

chemical structure of organic liquids, J. Chem. Eng. Data, in press.

O'Sullivan, B.; Johnson, P.; Hesby, R.; Blosser, R.; Rupp , N. W.; Pelleu,

G. Bonding stregnths of a luting composite resin to dentin using different

bonding systems, J. Pros. Dent., in press.

Sanchez, I. C. Polymer phase separation. Enc. Phys. Sci. & Tech., in

press.

Hung, C.-C.; Shibata , J. H. Tarpey, M. F.; Jones, A. A.; Porco, J. A.;

Inglefield, P. T. Further studies of multiple nuclear spin relaxation and

local motions in dissolved l,l-dichloro-2,2-bis(4-hydroxyphenyl) -ethylene

polyformal. Anal. Chimica Acta, in press.

Takagi, S.; Mathew, M.; Brown, W. E. The crystal structures of natural

bobierrite and synthetic Mgs (PO4 )z

.

8 H2 O, American Mineralogist, in press.

Hirano, S.; Tesk, J. A. Hinman, R.; Argentar, H.; Gregory, T. Casting of

dental alloys mold and alloy temperature effects. Dent. Matl., in press.

Tesk, J. A. Review of the paper: casting metals by Kamal Asgar, J. Dent.

Res. , in press.

Vogel, G. L.; Chow, L. C.; Brown, W. E.; Carey, C. M. Ultramicro analysis

of the fluid in enamel during in vitro caries attack, I. hydrochloric

acid. Caries Research, in press.

Wang, F. W.; Lowry, R. E.; Fanconi, B. M. Novel fluorescence method for cure monitoring of epoxy resins. Polymer, in press.

Wang, F. W.; Wu, E. S. Cure monitoring of epoxy resins by fluorescence

recovery after photobleaching. Poly. Comm., in press.

71
Technical and Professional Committees: Leadership Activities

Academy of Operative Dentistry

N. W. Rupp, Past President

Alpha Chi Sigma

G. M. Brauer, Member, Awards Committee

American Academy of Gold Foil Operators

N. W. Rupp, President

American Association for Dental Research/International

Association for Dental Research

L. C. Chow

Member, Fellowship Committee

American Association of Dental Research - Washington Section

L. C. Chow, Vice President

American Chemical Society

G. M. Brauer

Member, Meetings and Expositions Committee

Councilor

B. F. Howell, Councilor

American Dental Association

R. L. Bowen

Member, Biomedical Research Support Grant Committee

American National Standards Committee, MD 166, Dental Materials,

Instruments, and Equipment

R. L. Bowen

Secretary, Subcommittee on Biological Evaluation of

Dental Materials

Member, Subcommittee on Direct Filling Resins

G. M. Brauer

Chairman, Subcommittee on Denture Resins

Member, Dental Materials, Instruments and Equipment

Member, Zinc Oxide-eugenol and Modified ZOE Cements Subcommittee

N. W. Rupp

Chairman, Group I Restorative Materials

Member, Subcommittee #1 - Alloy for Dental Amalgams

#6 - Mercury for Dental Amalgams

#29 - Fissure Sealants

#43 - Dispersers for Alloy & Mercury

#55 - Electrically Powered Amalgamators

72
J. A. Tesk

Chairman, Dental Materials, Instruments and Equipment

Member, Dental Implants Subcommittee

Chairman, USA TAG for ISO TC 106

Member, Porcelain Alloys Subcommittee

American National Standards Institute (ANSI)

J. A. Tesk

Member, Medical Devices Standards Management Board

American Physical Society

G. B. McKenna

Division of High Polymer Physics

Member, Publications Committee

I. C. Sanchez

Chairman and Organizers: Introduction to Theoretical Polymers

Physics" Short Courses to be presented prior to the 1986 March

Meeting of the APS

American Society for Metals

R. M. Waterstrat

Member, Alloy Phase Diagram Data Committee

American Society for Testing and Materials (ASTM)

G. M. Brauer

Member, Executive Committee, F-4 Medical and Surgical

Materials, and Devices

Chairman, Polymeric Materials Section

Member various task forces

Member, TAG/TC 150

C. M. Guttman

E-37 - Subcommittee on Thermal Analysis

Chairman, Task Group on Purity Standards and Methods

G. B. McKenna

Member, D-11 Rubber and Rubber-like Materials

Member, E-9 Fatigue

H. L. Wagner

Member: D20:70.05: Molecular Weight Parameters

Member: D20:70.02: Liquid Chromatography (Task Force on Size

Exclusion Chromatography)

D-2 Petroleum Products and Lubricants

L. J. Zapas

Member: D2.07 Flow Properties

D2.07A Newtonian Viscometry

73
Chemical Society of Washington

J. M. Antonucci

Member, Board of Managers

B. M. Brauer

Chairman, Councilors Committee

Chairman, Publications Committee

Member, Executive Committee

Member, Public Relations Committee

Member, Long Range Planning Committee

B. F. Howell

Member, Public Relations Committee

Conference on Transport and Relaxation Processes in

Random Materials, October 15-17, 1985, NBS

R. J. Rubin, Co-Chairman

Experimental NMR Conference

D. L. VanderHart

Member, Executive Board

Gordon Conference: Thermosetting Polymers

D. L. Hunston

Vice Chairman 1986

Chairman 1987

International Council on Alloy Phase Diagrams

R. M. Waterstrat

Member

International Standards Organization

TC106, Dental Materials and Devices

N. W. Rupp

Member, Restorative Materials

Chairman, SC. 01, U.S. Delegation

Chairman, ATG7, Alloys for Dental Amalgams

SC6 WG5 Electrically Powered Amalgamators

Macromolecules

E. A. Di Marzio

Member, Editorial Review Board

Metallurgical Society AIME

R. M. Waterstrat

Member, Committee on Alloy Phases

National Bureau of Standards Committee on University of Maryland

Instructional Television System

E. A. Di Marzio, Member

74
National Bureau of Standards Editorial Review Board

E. A. Di Marzio, Member

National Bureau of Standards Research Advisory Panel

E. A. Di Marzio, Member

National Center for Small Angle Scattering

C. C. Han

Member, Users Committee

National Science Foundation Advisory Board

Regional NMR Facility at Colorado State University

D. L. VanderHart

Office of Science and Technology Policy

D. H. Reneker

Executive Secretary, Committee on Materials (COMAT)

Plastics Institute of America

D. H. Reneker

Polymers Division Editorial Committee / R. J. Rubin, Chairman

Polymers Gordon Conference (West)

I. C. Sanchez, Vice-Chairman and Chairman

Elect, 1985-86

Society of Plastics Engineers

I. C. Sanchez

Member, Executive Board of the Engineering Properties

and Structure Division

Society of Rheology

G. B. McKenna

Member, Committee on Education

D. L. Hunston

Member, Committee on Education

Member, Site Selection Committee

U.S. Yugoslav Joint Scientific and Technological

Cooperative Program

W. E. Brown

NBS Member

VAMAS

C. C. Han

Member, Technical Working Party on Polymer Blends

D. L. Hunston

Member, Technical Working Party on Polymer Composites

75
visiting Committee for Lehigh University

D. H. Reneker

Member, Department of Metallurgy and Materials Engineering

Washington Academy of Sciences

B. F. Howell, Fellow

Member at Large

Member, Program Committee

Representative of the Philosophical Society of Washington
Industrial and Academic Interactions

Industrial

Work with the Gas Research Institute is leading to reference and standard

polyethylene resins, piping, and joints of th$ sort used in natural gas

distribution systems. These materials will facilitate test method development,

standardization of test methods, and inter-laboratory comparisons of test data.

It is anticipated that the standard PE materials will be widely used by other

sectors of the plastics industry.

A joint program is underway with Hercules, Hexcel, and NASA Langley Research

Center to study delamination in composite materials. Hercules and Hexcel are providing materials and some fracture surface analysis# NASA is characterizing

the samples, and NBS is determining the interlaminar fracture behavior. The

objective is to establish the relationship between the properties of the

composite and the behavior of its constituent materials.

Joint projects with Exxon, IBM, Eastman Kodak, and Armstrong World Inc. are concerned with polymer blends phase relationship and phase stabilization.

Research activities are directed to specific polymer blends of interest to

Exxon, IBM, and Eastman Kodak, to stabilization problems of concern to IBM and

Eastman Kodak and to the barrier material property and processing of Armstrong

World Inc. materials.

A joint project with scientists at the Almaden Research Laboratory of IBM and

the CRM - Strasbourg, France led to the publication of the manuscript "The

Molecular Weight Dependence of the Zero Shear Viscosity of Cyclic Polystyrene

Molecules in the Melt".

Research Associate agreements have been concluded with Westinghouse Electric

Corporation to transfer measurement techniques of compliant piezoelectrics,

with IMASS Corporation to transfer design of time domain dielectric

spectrometer for commercial development, and with General Electric Corporation

to duplicate time domain dielectric spectrometer for use in its corporate

research laboratories.

A joint research program has been established with Dr. T. T. Wang of the Bell

Laboratories to develop a technique for real-time, in-situ fluorescence

monitoring of the formation of polyimide polymers from poly (amide-acid)

polymers.

The American dental industries continued to display strong interest in and

support for the dental materials program. The research associate agreement

with Dentsply International was extended to its third year and another dental

manufacturer, Astron dental corporation, entered into a research associate

agreement. One dental manufacturer supplied special alloy for porcelain fusedto-metal strength studies and other provided a new composite for NBS scientific

research. Glass inserts for composite restorations have generated much

commercial interest. NBS-developed monomer for radiopaque polymers was trialsynthesized by one dental supplier.

77
Work continued with scientists at the Pulp and Paper Institute utilizing NMR to

characterize the solid state morphology of native cellulose. A paper has been

written on this work.

Industrial/Academic

A cooperative program has been established to investigate the network structure

of epoxy resins and other thermosets. Prof. R. Stein of the University of

Massachusetts and H. G. Waddill of Texaco are participating in this effort. A

postdoctoral Researcher from Prof. Stein's group has been assigned to work part

time at NBS to collect and analyze neutron scattering data from epoxies swollen

with deuterated solvent. Thermo-analysis of the epoxy samples to determine the

glass transition temperature has been carried out at the University of

Massachusetts. Texaco is providing the raw materials and other mechanical

measurements. The molecular weight determination of the curing agents and the

epoxy resins were also carried out at Texaco. The objective of this project is

to understand the basic network structure in highly crosslinked polymers and to

determine the relation among network structure, processing condition and

physical properties.

An NBS/Mobil/Univ. of Massachusetts joint project is concerned with

polystyrene/poly (p-methylstyrene) blends. Phase diagram and binary interaction

parameter between different monomers are being measured by SANS technique at

NBS. A second project is an NBS/GenCorp/Univ. of Kyoto joint effort on rubber/rubber blends. Questions of microstructure and isotope effects on the

miscibility and phase diagram are being addressed. For immiscible

rubber/rubber pairs, the mechanical blending/phase separation process will be

studied. This information is critically needed by the tire industry.

Academic

A joint research program is underway with Prof. E.-S. Wu of the University of

Maryland (Baltimore County) to measure, by fluorescence recovery after

photobleaching, the self-diffusion of polymers in entangled system as well as the diffusion of small molecules in entangled polymer solutions and in

plasticized polymers.

The failure behavior of toughened polymers is being studied in cooperation with

Dr. A. J. Kinloch at Imperial College. Scientists at NBS are determining the

fracture behavior while those at Imperial College are characterizing the

morphology of the same multiphase polymer systems. The ultimate objective is

the development of structure - property relationships for such materials.

A joint research program to study the conformation of block copolymers in

phase-separation systems has been established with Prof. J. Koberstein of

University of Connecticut. As part of this program, a graduate student is

conducting neutron scattering measurements on these polymers at NBS.

Work on the characterization of the mechanical response of cyclic polystyrenes,

in conjunction with the University of Pittsburgh, led to the publication of two

articles. NBS scientists furnished the sample and interpreted the data while

78
scientists at the University of Pittsburgh developed mechanical testing

equipment suitable for studies on very small amounts of material.

A collaborative effort has been initiated with the University of California,

Santa Barbara to build a tunneling electron microscope in the Polymers Division

at MBS. A first generation apparatus has been constructed and tested at NBS.

Collaborative programs with universities in the area of polymer blends include

single chain conformational and diffusional studies in polymer blends and

solutions with the Universities of Wisconsin and Minnesota. Also, we have an ongoing international collaboration program with Nagoya University, Japan which

is jointly sponsored by NSF/JSPS on the subject of block copolymers in

microphase-separation systems.

Guest scientists from six domestic and three foreign institutes are conducting

research on dental materials at NBS. A cooperative seminar series was established with the University of Maryland Dental School. Several finite

element modeling studies on dental material-tooth systems continue with the

University of Illinois, Chicago. One guest scientist from Georgetown

University is a key investigator on bonding of dental resins to dentin. Guest

scientists (residents) from the Naval Dental School work with several

investigators within the group. We acknowledge the cooperation of Professor E.

Horowitz from John Hopkins University, Professors L. Queral and M. Sadovnik

from the University of Maryland, and Dr. W. Pierce from Hershey Medical Center

on studies of cardiovascular plaque.

79
Associated Activities

Invited Talks

Division personnel presented a total of 108 invited talks on research

activities at the following types of organizations and symposia: industrial

laboratories, 12; international symposia, 9; universities, 34; topical symposia

11; national and government laboratories, 15; professional society meetings,

18; and Gordon Conferences, 9.

SRHs

The certificate for one of the poly (methyl methacrylate) SRMs has been issued

(SRM 1489) and the certificate for the other (SRM 1488) is being drafted.

These SRMs will be used by the polymers industry to calibrate instruments used

to measure the molecular weight and molecular weight distributions of acrylic

type polymers.

Patents

G. T. Davis, C. K. Chiang, J. M. Antonucci, and T. Takahashi, Polyethylene

Imine-Metal Salt Solid Electrolyte, US Patent No. 4,576,882, March 18. 1986.

80
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BIBLIOGRAPHIC DATA

SHEET (See Instructions)

1. PUBLICATION OR

REPORT NO.

NBSIR 86-3437

2. Performing Organ. Report No. 3. Publication Date November 1986

4. TITLE AND SUBTITLE

Polymers Division; Technical Activities 1986

5. AUTHOR(S)

L. E. Smith and B. M. Fanconi

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

national bureau of standards

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

Report & Period Covered

10/1/85 - 9/30/86

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, State, ZIP)

National Bureau of Standards

Institute for Materials Science & Engineering

Polymers Division, Gaithersburg, MD 20899

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 significant information. If document includes a significant

bibliography or literature survey, mention it here)

Technical Activities of the Polymers Division for FY 86 are reviewed. Included

are descriptions of the 6 Tasks of the Division, project reports, publications,

and other technical activities.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) National Bureau of Standards; Polymers Division; Review; Technical Activities

13. AVAILABILITY

PyI Unlimited

I I For Official Distribution, Do Not Release to NTIS

Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

102

15. Price

$ 16,95

USCOMM-OC 8043-P80
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