bluuebunny/crossref_metadata_2025 huggingface dataset:
Angular dependence of 1H‐ and 2H‐NMR spectra of H2O and D2O absorbed in cellulose acetate film
Authors: Matsumura Kazunori , Hayamizu Kikuko , Nakane Takashi , Yanagishita Hiroshi , Yamamoto Osamu
Published: April 2003

1H‐ and 2H‐NMR spectra of H2O and D2O absorbed in cellulose acetate films were observed while changing the angle between the plane of the film and the magnetic field. 1H‐NMR spectra show dipolar splittings that vary depending on the angle. The splitting has a maximum when the surface of the film is perpendicular to the magnetic field. From the angular dependence of the dipolar splitting, it is recognized that the proton‐proton dipolar axis of water molecules tends to orient perpendicularly to the surface of the film. 2H‐NMR spectra that show quadrupolar splittings also indicate that the quadrupolar axis tends to orient perpendicularly to the film. The so‐called bound water and free water in the film can exchange rapidly on the NMR time scale, so that the line width and the splitting of the NMR spectra become smaller as the amount of water in the film increases. From the temperature dependence of line widths, the apparent reorientational activation energy of water molecules in the film is estimated to be 25 kJ/mol from 1H‐NMR and 31 kJ/mol from 2H‐NMR.
Influence of chemical structure on nonelastic mechanical properties in polystyryl‐pyridine resins
Authors: Caux X. , Coulon G. , Escaig B.
Published: April 2003

We propose a micromechanical characterization of the chemical structure (i.e., the state of cure) of polystyryl‐pyridine (PSP) resin. The nonelastic work‐hardening rate K is measured in the preyield stage during compression tests at constant strain rate. The nonelastic deformation is analyzed from a metallurgical point of view; the parameter K varies as the inverse of the nucleation rate for dislocations and thus is a measure of the ability of the material to deform plastically. The comparison with high‐resolution solid‐state carbon‐13 NMR experiments shows that, at room temperature, the ability of PSP resin to deform plastically depends mainly on the degree of crosslinking, whatever the length of prepolymer molecule; however, at high temperatures (T = 200°C) it is affected by the length of prepolymer molecule during curing, whatever the degree of crosslinking. Plastic deformation of PSP resin is easier at 200°C than at room temperature. The longer the duration of curing, the better the mechanical properties at high temperatures; PSP resin readily deforms plastically and has a sufficiently high elastic modulus.
Mössbauer spectroscopy of Fe2+‐complexed poly(N‐propylpyrrole‐sulfonate)
Authors: Auric P. , Bidan G.
Published: April 2003

The polymer obtained by chemical oxidation of N‐propylpyrrole‐sulfonate (PPS) with Fe(ClO4)3 is studied through elemental analysis and Mössbauer spectroscopy. From elemental analysis data this polymer appears to be composed of a polypyrrolic backbone with side chains of alkylsulfonate pendant groups. These sulfonate groups are mainly in the form of iron salts that act as a dopant of the poly(PPS). Mössbauer spectra of iron‐complexed poly(PPS) has been analyzed as functions of temperature, water content, and applied magnetic field in order to characterize the iron environment. Nearly 95% of the iron ions are ferrous ions in different environments. The spectra of a dried sample or a fully hydrated one, which are recorded at a given temperature, were fitted by using identical isomer‐shift values but two different distributions or quadrupole doublets (the Q.S. evolution with temperature was the same). The Debye temperature of the two samples has the same value, but the recoil‐free fraction falls to zero somewhere above 340 K for a dried sample and near 290 K for the fully hydrated material. These results suggest that the additional water molecules that act as a solvate layer mainly change the lattice properties and that the Fe2+ ions are probably linked to the SO‐terminated side chains of the backbone. These high‐spin Fe2+ ions are in the fast relaxation limit at 4 K without external field and have anisotropic magnetic properties under high applied fields. No clusters or dimers have been detected.
FTIR studies of PMR‐15 polyimides
Authors: Garcia Dana , Serafini Tito T.
Published: April 2003

Fourier‐transform infrared spectroscopy (FTIR) shows that during the curing of PMR‐15 polyimide, formation of an anhydride intermediate occurs prior to the formation of polyamic acid, suggesting that its origin is the diester diacid starting material, as has recently been proposed by Johnston and coworkers. These results disagree with some previous literature reports that have attributed formation of the anhydride to a degradation pathway of polyamic acid and confirm the validity of a recently published paper by Johnston and coworkers.
Polydispersity effects in polymer self‐diffusion measured by small‐angle neutron scattering
Authors: Finerman T. , Crist B.
Published: April 2003

The small‐angle neutron scattering (SANS) method for measuring the self‐diffusion coefficient D has been analyzed for effects of polydispersity in degree of polymerization for the case of linear polymers diffusing by reptation. Polydispersities corresponding to Mw/Mn = 1.0−10 were considered. It is shown that in all cases a meaningful effective diffusion coefficient De can be obtained from the short time recovery of the SANS intensity. This quantity De ≤ 1.3 D(Mw), where D(Mw) is the diffusion coefficient of a monodisperse polymer having molecular weight M = Mw. The method relies on SANS intensities extrapolated to zero scattering angle; realistic extrapolation is shown to give rise to quite acceptable errors on the order of 0.05 De.
Fiber spinning from the nematic melt. IV. Effect of P oxybenzoate crystallinity on the spinning and fiber properties of the copolyester of polyethylene terephthalate and p‐oxybenzoate
Authors: Muramatsu Hiromochi , Krigbaum W. R.
Published: April 2003

We have previously reported two studies of the rheology and fiber properties of one sample of the copolymer of polyethylene terephthalate having 60 mol% of p‐oxybenzoate (PHB) units. The DSC curve of that sample exhibited crystalline melting transitions, and the sample appeared to contain PHB blocks. Here we compare those results with observations for a second sample that, although nominally the same polymer, appears to be more random because it exhibits little PHB crystallinity. We had previously reported that the flow of the copolymer containing PHB blocks was non‐Newtonian at all temperatures, and that it exhibited a thermal history effect. We find the flow of the more random polymer is Newtonian above the melting temperature, and the melt viscosity of the more random copolymer exhibits no thermal history effect. Fibers were spun from the more random copolymer with a capillary rheometer using a capillary having a length/diameter ratio of 14.1 and a shear rate at the wall of 6.4 sec−1. Spinning temperatures were 250, 260, and 280°C, and the spin draw ratio was examined as a variable. The initial modulus increased with spin draw ratio but exhibited no dependence upon the spinning temperature. For the copolymer containing PHB blocks, the initial modulus increased as the spinning temperature was raised. These differences are due to the larger amount of PHB crystallinity in the more blocky sample. When chips of the more random sample were heated for 1 h at 235°C, the melt viscosity increased and the initial modulus of the fibers decreased. These changes are due to the crystallization of longer PHB blocks produced by melt interchange.
Two‐dimensional NMR characterization of propylene copolymers
Authors: Cheng H. N. , Lee G. H.
Published: April 2003

Newly developed two‐dimensional NMR techniques are used to characterize homopolypropylene and copolymers of propylene with ethylene and butylene. Both homonuclear and heteronuclear shift‐correlated experiments have been attempted. The most useful technique for the copolymers is 13C‐1H shift correlation, whereby the one‐dimensional 1H‐NMR spectra of these copolymers are completely interpreted for the first time. Although the 1H resonances are heavily overlapped, the use of a computerized “analytical” approach permits pertinent information to be obtained from the one‐dimensional 1H‐NMR spectra.
The onset of chain folding in ultralong n‐alkanes: An electron microscopic study of solution‐grown crystals
Authors: Organ S. J. , Keller A.
Published: April 2003

Crystallization of extremely pure n‐C198H398 from dilute solution is investigated by electron microscopy and differential scanning calorimetry. This long‐chain alkane is capable of crystallizing in the extended form or of folding once or twice and thus provides useful insights into the fundamental process of chain‐folded crystal growth. Crystallization conditions that give rise to the different crystal types are identified by measuring the variation in dissolution temperature with crystallization temperature and crystallization time. Examples of each type of crystal are examined in the electron microscope using various techniques. From shadow length measurements we find the crystals to have thicknesses corresponding to integer fractions of the extended chain length, in agreement with previous findings on this and similar materials. However, contrary to all past experience with polyethylenes, refolding was found to occur while in the solvent. This refolding, which here takes place isothermally, also occurs in integral steps, with wider implications discussed. The crystal morphologies are similar in many respects to those obtained from polyethylene; in particular the crystals containing once‐folded chains are often lozenge shaped with the folds along {110} growth planes, thus producing clearly defined sectorization made visible by several techniques. Electron diffraction studies show that the chains are substantially perpendicular within the crystals in all cases. In addition, differences in surface regularity between the different crystal types revealed by decoration techniques are discussed.
Molecular weight relations for crosslinking of chains with length and site distribution
Authors: Miller Douglas R. , Macosko Christopher W.
Published: April 2003

Many polymer networks are formed by crosslinked polymer chains through reactive sites distributed along the chains. How these sites are distributed as well as the chain length distribution can have a significant effect on properties like the gel conversion and molecular weight. Previous treatments have used simplifying approximations. In this paper we eliminate these approximations and derive computational formulae for weight average molecular weight and gel point for polymer chains of any length and reactive site distribution. Three types of crosslinking are considered: direct coupling of chains (homopolymerization), direct coupling through propagation, and coupling through copolymerization with small monomers.
Molecular weight dependence of mechanical properties of poly(p,p′‐oxydiphenylene pyromellitimide) films
Authors: Volksen W. , Cotts P. , Yoon D. Y.
Published: April 2003

The mechanical properties, i.e., Young's modulus, elongation, and tensile stress, were determined as functions of the molecular weight for films of poly(oxydi‐p‐phenylene pyromellitimide) prepared by thermal cyclization of the precursor poly(amic acid). The molecular weights of the samples were controlled by the monomer stoichiometry employed for the solution condensation of pyromellitic dianhydride and p,p′‐oxydianiline. Weight‐average molecular weights were determined by light scattering of the precursor poly(amic acid) as well as the fully cyclized polyimide. The elongation‐at‐break is most sensitive to the molecular weight, undergoing a rapid increase at Mw ⋍ 8000 and reaching a limiting value of about 60% for Mw > 20,000.
Craze growth and healing in polystyrene
Authors: McGarel Owen J. , Wool Richard P.
Published: April 2003

The kinetics of craze growth and craze healing were studied by dark‐field optical microscopy in monodisperse molecular weight polystyrene (PS) that varied in molecular weight from 88,000 to 1,334,000. The following observations were made. (1) G1 the virgin growth rate, decreased rapidly with increasing molecular weight until Mn ∼ 200,000 and then remained constant. (2) G1 decreased with increasing craze density. (3) The growth rates of approaching craze tips decreased when the craze tips overlapped, and the effect was less for crazes whose parallel growth paths were greater than 40 μm apart. (4) Complete craze healing was observed by comparison of the nucleation times, τ2, and growth rates, G2, of healed individual crazes with the craze kinetics of the virgin sample. (5) The extent of healing was characterized using four cases in which τ and G were measured as a function of healing time, temperature, constant stress, and molecular weight. (6) Craze healing times were found to increase with molecular weight and were analyzed in terms of the modified molecular weight of the craze zone. (7) Significant bond rupture was determined to occur during crazing by comparison of healing times with stress relaxation and diffusion data. (8) Craze healing studies provide insight into both crack healing and fracture of glassy polymers.
Network parameters for crosslinking of chains with length and site distribution
Authors: Miller Douglas R. , Macosko Christopher W.
Published: April 2003

Polymer chains are crosslinked to form a network. The chains are polydispersed, with an arbitrary distribution of weight and functionality. Crosslinks may form in three different ways: direct coupling (homopolymerization), direct coupling with propagation, and coupling through copolymerization with small monomers. Various network parameters are calculated. We give computational formulae for gel point, weight fraction soluble, weight fraction pendant, weight fraction effective, concentration of effective junctions, concentration of effective network strands, and the entanglement trapping factor. These formulae give exact values for systems that previously have only been solved using simplifying approximations. Examples show that such simplification may lead to sizable errors in the computation of network parameters.
Thermodynamic and morphological studies of the solid‐state transition in copolymers of vinylidene fluoride and trifluoroethylene
Authors: Stack G. M. , Ting R. Y.
Published: April 2003

Copolymers of vinylidene fluoride and trifluroethylene are presently being considered for many piezoelectric applications. In contrast to the poly(vinylidene fluoride) homopolymer, a transition from the room temperature ferroelectric phase to a paraelectric phase has been observed in these copolymers. The temperature of this transition was determined by measuring the position of the endothermic peak observed in the differential scanning calorimeter. The rate of cooling from the paraelectric to ferroelectric phase was found to affect the temperature at which the transition occurred on subsequent heating. Changing the conditions under which molten polymer initially crystallized into the paraelectric phase had an even greater effect on the resultant transition temperature. In addition to the DSC studies, wide‐angle x‐ray measurements were performed on samples subjected to different thermal treatments. No significant differences were found in the x‐ray scans of these copolymers.
Depression of the crystal‐nematic phase transition in thermotropic liquid crystal copolyesters
Authors: George Eric R. , Porter Roger S.
Published: April 2003

The crystal‐nematic phase transition of a copolyester consisting of 20 mol% poly(ethylene terephthalate) and 80 mol% p‐hydroxybenzoic acid (PHB) was characterized by depression of the crystal‐nematic transition by the addition of a liquid crystal diluent. This copolyester contains blocks of crystalline PHB. Its transition behavior was compared with thatrandom copolyester with diluent of the same composition. From the extrapolated transition temperature depression data, the heat of transition per mole of p‐oxybenzoate was calculated as about 1.3 kcal/mol, with an entropy of about 2 cal/deg mol. This assumes that only the p‐oxybenzoate unit crystallized from the nematic state. The validity of the Flory‐Huggins model for this transition point depression was confirmed graphically by comparison with two different thermotropic‐liquid crystal polyesters. These results may represent the first reported crystal‐nematic temperatures and heats generated by the dilution method for liquid crystal copolyesters of this type.
Thermodynamic properties of chain liquid mixtures with strong, local interactions
Authors: Durning C. J. , Secor R. M.
Published: April 2003

This paper addresses the effect in chain liquids on thermodynamic behavior of a large charge in the strength of local interactions on mixing. We classified real systems according to the ability of the Flory equation of state (FES) theory to prodict the excess volume. The FES theory enables reliable estimates provided the mixture is nearly athermal and the pure components obey the Flory equation of state. These requirements arise from Flory's approximations for the lattice part of the configuration integral, ZL, and the cell part, ZC, respectively. We revised ZL without adding adjustable parameters by the quasichemical perturbation method to account for local ordering in the mixture because of a large change in the strength of binary interactions on mixing. The modification improves the predictions of the thermodynamic functions for systems where Flory's ZL is inadequate.
Primary and secondary pyroelectricity in highly oriented polyvinylidene fluoride
Authors: Nix E. L. , Nanayakkara J. , Davies G. R. , Ward I. M.
Published: April 2003

Measurements of the pyroelectric response in both free and constrained conditions are presented for low‐draw ratio, high‐draw ratio and voided form I polyvinylidene fluoride sheets. The results are used together with related data for the piezoelectric response and for the thermal expansion behavior to estimate the primary and secondary components of the total macroscopic pyroelectricity. For the high‐draw ratio and voided sheets the primary response was approximately 90% of the total pyroelectricity compared with 40% for the low‐draw ratio nonvoided sheet. It is proposed that the role of reversible temperature‐dependent crystallinity is more pronounced in the high‐draw samples. Previous NMR studies provide support for this conclusion.
A study of the mechanical anisotropy of high‐draw, low‐draw, and voided PVDF
Authors: Humphreys J. , Lewis E. L. V. , Ward I. M. , Nix E. L. , McGrath J. C.
Published: April 2003

The mechanical anisotropy of oriented PVDF sheet is examined using a variety of experimental techniques. The mechanical behavior is similar to that observed previously for low‐density polyethylene and nylon and consistent with a parallel lamellar crystalline structure. The s31 compliance is reduced in magnitude by drawing to higher draw ratio, but the reduction in the piezoelectric coefficient d31 is less marked, suggesting that the piezoelectric response cannot be related solely to dimensional changes under stress. Drawing to high draw ratio increases the s33 compliance, and this is further increased by introducing voids. The corresponding d33 piezoelectric coefficient is not changed significantly by drawing to high draw ratio, or by the introduction of voids, again indicating that the piezoelectric behavior relates to factors other than dimensional changes.
A strip resonance technique for measuring the ultrasonic viscoelastic parameters of polymeric sheets with application to cellulose
Authors: Pankonin B. , Habeger C.
Published: April 2003

An acoustic strip resonance apparatus that measures the viscoelastic response of polymeric sheets over the temperature range of 100–400°K and at frequencies from 20 to 100 kHz is described. This is a computer‐controlled instrument which uses the resonant frequency and the quality factor of standing waves in strips to calculate the ratio of complex Young's modulus to density. Results are presented for cellophane and paper samples. These are consistent with measurements reported by others at lower frequencies. That is, (1) a single predominant secondary relaxation process which corresponds to the γ relaxation occurring at 200°K and 1 Hz is found in dry samples at 260°K and 60 kHz; (2) as moisture is added, the γ relaxation weakens and a higher temperature, β, relaxation appears; and (3) at low temperature, moisture addition initially increases the mass specific Young's modulus. The effects of methanol on the viscoelastic parameters of cellulose were also measured and found to be similar to those of water.
Interpretation of light scattering from supermolecular structures in liquid systems by master curves
Authors: Dautzenberg H. , Rother G.
Published: April 2003

By a detailed analysis of light scattering curves, a more complete characterization of colloidal particles may be achieved. For this purpose, a fitting procedure based on theoretical master curves of models of polydisperse systems of homogeneous spheres and Gaussian coils is presented. The use of a suitable logarithmic distribution function makes it possible to separate the influence of polydispersity from that of particle size on the shape of the scattering curve. A double logarithmic plot of master curves reduces the fitting procedure to translations of the experimental curves. The reliability and accuracy of this procedure are demonstrated by light scattering results on solutions of a polyelectrolyte complex with variation of salt content.
Optical properties of poly‐diacetylene monolayers
Authors: Collins Michael A.
Published: April 2003

The topochemical polymerization of diacetylene molecules as monolayers in situ on a Langmuir trough is described via the visible absorbance of the polymer products. Possible differences in the product structure between crystal or multilayer polymerizations and that in monolayers is investigated for two monomers. Significant differences in the visible, infrared, and resonance Raman spectra are reported and a strong dependence of visible absorbance on surface pressure is described.
Cholesteric hydroxypropylcellulose solutions: Microscopy and small‐angle light scattering
Authors: Meeten G. H. , Navard P.
Published: April 2003

Polarized optical microscopy and small‐angle light scattering (SALS) are used to investigate the cholesteric phase of aqueous hydroxypropylcellulose (HPC) solutions. The results suggest a polygonal focal conic rather than the recently proposed parabolic focal conic morphology. Measurements of the polygonal domain size show it to decrease with increasing HPC concentration.

Depolarized SALS gives clover‐leaf patterns, whose maximum of intensity at 45° is related to the domain size.
Latent energy of deformation of bisphenol A polycarbonate
Authors: Adams G. W. , Farris R. J.
Published: April 2003

The thermodynamic behavior of poly(bisphenol A carbonate) (PC) during uniaxial cold drawing and the properties of the drawn polymer were examined. Isothermal deformation calorimetric measurements were made during the drawing process. The deformation calorimeter measures heat, work, and internal energy changes for deformation. It was found that PC exhibited nonideal plasticity with approximately 50–80% of the work of deformation dissipated as heat. The remainder of the work of deformation was stored as a latent internal energy change. The value of the internal energy change was dependent on strain rate at 20°C but was not strongly dependent on temperature in the range 20–65°C. Thermomechanical measurements on cold‐drawn PC samples demonstrated striking behavior at temperatures far below the glass transition temperature Tg. Stress‐temperature experiments showed that the stress increased for uniaxially constrained samples, and this stress increase began at temperatures just above the deformation temperature. Additional experiments indicated that the changes which took place during cold drawing were physical in nature and were thermoreversible. These changes in physical properties are related to those which occur due to physical aging below Tg.
Effect of combined pressure and temperature changes on structural recovery of glass‐forming materials. I. Extension of the KAHR model
Authors: Ramos A. R. , Kovacs A. J. , O'Reilly J. M. , Tribone J. J. , Greener J.
Published: April 2003

The KAHR model of structural relaxation has been extended to include the effects of pressure upon the retardation times of glass‐forming materials. The previously used methodology is applied with a continuous distribution of retardation times of the fractional exponential form. Several forms of the pressure dependence are examined. The combined temperature and pressure changes on structural recovery of glasses are addressed in this paper.
Effects of ionizing radiation on epoxy, graphite fiber, and epoxy/graphite fiber composites. Part II: Radical types and radical decay behavior
Authors: Seo K. S. , Fornes R. E. , Gilbert R. D. , Memory J. D.
Published: April 2003

Electron spin resonance (ESR) investigations of line shapes and radical decay behavior have been made on an epoxy based on tetraglycidyl diaminodiphenyl methane (TGDDM)/diaminodiphenyl sulfone (DDS), T‐300 graphite fiber, and T‐300/5208 (graphite fiber/epoxy) composites after irradiation with Co60 γ‐radiation or 0.5 MeV electrons. Two kinetically distinct radical species are found in the irradiated epoxy as the temperature is raised beyond 120 K following irradiation of samples at 77 K with Co60 γ. One has been termed a fast‐decaying species and the other a slow‐decaying species. The ratio of fast‐decaying/slow‐decaying radicals increases as the decay temperature rises. The fast‐decaying radicals at room temperature are attributed largely to alkyl type radicals residing in regions of relatively low crosslink density, while the long‐lived radicals are attributed to radicals residing in the highly crosslinked regions of the epoxy. A large concentration (ca. 1020 to 1021 spins/g) of unpaired electrons was found in unirradiated graphite fiber which masked the ESR spectral change in irradiated composites.
Effects of thermal treatment on biaxially oriented poly (ethylene terephthalate). III. Creep behavior following various thermal histories
Authors: Vallat M.‐F. , Plazek D. J. , Bhushan B.
Published: April 2003

Elongational creep measurements were carried out on a biaxially oriented poly (ethylene terephthalate) (PET) film parallel to, orthogonal to, and at 45° to the principal optic axis. Measurements made after various thermal treatments which were intended to stabilize the physical state of the PET were shown to be ineffective. Samples were annealed at 140°C for 12 days and aged at 95°C for over 24 days before measurement without success. Thermal cycling between 41 and 91°C which was also employed to stabilize the mechanical response also failed. Significant deceleration of the creep rate caused by densification of amorphous regions of the samples during storage below the glass temperature Tg is illustrated. Because of physical aging below Tg and morphological changes occurring above Tg during the various thermal treatments and histories, time‐scale shift factors were found to be not unique.
Simulations on radiation‐cured polyethylene
Authors: Galiatsatos V. , Eichinger B. E.
Published: April 2003

Simulations of the simultaneous crosslinking and chain scission reactions that are induced in bulk amorphous polyethylene by irradiation have been implemented with a computer. A detailed study of the various defect structures in the network is reported, to show that dangling ends have the highest population among these defects, especially at higher crosslink densities. The calculated sol fractions compare very favorably with previously published experimental studies. We find that there is about 1 chain scission for every 9 crosslinked units, i.e., one scission per 4.5 crosslinks. This is fewer scissions than had previously been deduced by application of the Charlesby‐Pinner method.
Solubility and miscibility of poly(ethyl oxazoline)
Authors: Lin Pinyen , Clash C. , Pearce Eli M. , Kwei T. K. , Aponte M. A.
Published: April 2003

The solubility of poly(ethyl oxazoline) in aqueous solutions was studied. The cloud point temperatures decreased in the presence of sodium chloride but increased by the addition of tetrabutylammonium bromide or dioxane. Solution‐cast films of blends of the polymer and poly(acrylic acid) were miscible, but mutual precipitation occurred in water, methanol, and dioxane. The compositions of the complexes correspond in most cases to simple molar ratios of the interacting groups. The glass transition temperatures of the complexes are higher than the values for blends of the same compositions, and the high values are attributed to hydrogen bonds acting as physical crosslinks. Complex formation also occurs when the polymer is mixed with a styrene‐acrylic acid copolymer and with low weight polymers containing phenol groups.
Counterion selectivity in cationic polyelectrolytes
Authors: Boussouria B. , Ricard A. , Audebert R.
Published: April 2003

Chloride ion activity coefficients in aqueous solutions of several cationic copolymers have been determined using ion‐selective electrodes in both the absence and the presence of simple univalent and divalent salts. Without added salt, the activity coefficient depends on the polymer concentration. It increases with increasing concentration of the added salt. The extent of interaction between counterions and polyions at a given polymer concentration, as estimated form chloride anion activity, is greater for bivalent than for univalent anions. Experimental data are in good agreement with theory. Selective interaction of anions with the ammonium copolymers has also been evidenced by viscometry. The selectivity follows the orderFor organic anions, in addition to electrostatic interactions, hydrophobic effects, which depend on the structure of the copolymer, play a significant role.
Plastic deformation of polytetramethylene oxide. I. Influence of molecular weight distribution, crystallinity, and structure
Authors: Kretz M. , Meurer B. , Lotz B. , Weill G.
Published: April 2003

Polytetramethylene oxide with a planar zig‐zag structure similar to polyethylene can be obtained with narrow molecular weight distributions. The plastic deformation of samples differing in molecular weight, molecular weight distribution, crystallinity, and structure has been studied. The degree of crystallinity of the undeformed annealed samples, as studied by NMR and DSC, leads to a value of the enthalpy of melting ΔHm = 167 J g−1, supporting the lower of two previously reported values. The low natural draw ratios and low Young's modulus of the drawn samples, together with the effect of blending a small amount of high molecular weight material into a low molecular weight sample, highlight the role of the flexibility and of the high molecular weight tail of the distribution in the plastic deformation process. The stress required for the propagation of the neck and the tensile strength are found to be linear functions of, respectively, the natural and maximum draw ratio.
Viscoelastic behavior and order‐disorder transition in mixtures of a block copolymer and a midblock‐associating resin
Authors: Kim Jinhwan , Han Chang Dae , Chu Sung Gun
Published: April 2003

The viscoelastic behavior and order‐disorder transition in mixtures of a block copolymer and a midblock‐associating resin were investigated. The block copolymers investigated were polystyrene‐block‐polysioprene‐block‐polystyrene (SIS) copolymers (Shell Development Company), specifically Kraton D‐1107, with the block molecular weights 10,000S‐120,000I‐10,000S, and Kraton D‐1111, with the block molecular weights 15,000S‐100,000I‐15,000S. The midblock‐associating resin investigated was a resin polymerized from C5 hydrocarbon, referred to as Piccotac 95BHT (Hercules Inc.), which is an aliphatic hydrocarbon containing considerable amounts of cyclic structures, with a weight‐average molecular weight of 1,100 and a glass transition temperature Tg of 43°C. In the investigation, mixtures of the block copolymer and Piccotac 95BHT were prepared with toluene as solvent. Temperature scans of the samples were made to obtain information on dynamic storage modulus G′, dynamic loss modulus G″, and loss tangent tan δ, using a Rheometrics dynamic mechanical spectrometer. It was found that Piccotac 95BHT decreased the plateau modulus G0N and increased the Tg of the polyisoprene midblock of the SIS block copolymer in the mixture. This experimental observation led to the conclusion that Piccotac 95BHT associates (or is compatible) with the rubbery polyisoprene midblock of the SIS block copolymer. The order‐disorder transition behavior of mixtures of SIS block copolymer and Piccotac 95BHT was also investigated by a rheological technique proposed by Han and Kim (Ref. 21). The order‐disorder transition temperature Tr (i.e., the temperature at which the ordered microdomain structure of the block copolymer completely disappears) of the SIS block copolymer decreased steadily with increasing amount of Piccotac 95BHT in the mixture. With the information determined on Tr, a phase diagram for the mixture was constructed, showing the boundary between the mesophase and homogeneous phase in the mixture. The phase diagram is in qualitative agreement with the theoretical predictions of Whitmore and Noolandi (Ref. 28).
Solubility parameters of poly(vinylidene fluoride)
Authors: Bottino A. , Capannelli G. , Munari S. , Turturro A.
Published: April 2003

The solubility behavior of poly(vinylidene fluoride) (PVDF) in about 50 liquids was investigated. The results were input to a computer program to obtain a three‐dimensional representation of the polymer solubility region in the Hansen space; the values of dispersion, hydrogen bonding, and polar components of the total solubility parameter δt,P were evaluated. The latter was also estimated from limiting viscosity number data in the eight solvents found. Both experimental methods gave δt,P values in very good agreement. Comparisons among our findings, the literature, and calculated results are discussed.
The role of differential scanning calorimetry and X‐ray diffraction in identifying crystal continuity in highly oriented samples of die‐drawn polypropylene
Authors: Taraiya A. K. , Unwin A. P. , Ward I. M.
Published: April 2003

X‐ray diffraction and differential scanning calorimetry studies of die‐drawn polypropylene have indicated the presence of a crystalline structure which does not identify with any of the usual crystallographic forms and has a melting point slightly below that of the monoclinic a form. The melting of this structure is stress sensitive and shows the superheating effect expected from the melting of an extended chain structure, whose chain ends are physically constrained. It is postulated that this structure bridges the gaps between adjacent monoclinic crystal blocks and provides the framework necessary to maintain mechanical stability at temperatures well above that of the glass transition. Moreover, together with taut tie molecules, this structure is considered to be the main source of the high material stiffness.
Rheology of a miscible polymer blend
Authors: Roland C. M.
Published: April 2003

Difference spectra of blends of cis‐1,4‐polyisoprene and atactic poly(vinylethylene), obtained from the measured FTIR spectra of the pure components and the blends, indicate that mixing of these polymers is not accompanied by any specific chemical interactions. Miscibility in this system arises solely due to the small combinatorial entropy of mixing. The conformation and configuration of the polymer chains in the blends are, therefore, identical to those in the pure melts. As a consequence it was found that the entanglement density of the blends varied monotonically with composition. This variation, however, was not in accordance with predictions based simply on the mechanical interaction density. The principle rheological effect of miscible blending was a large change in the monomeric friction coefficient, which arises from the strong dependence of free volume on composition. The zero shear viscosity and the terminal relaxation time of the blends reflected this change in local chain mobility. Empirical relations, which have previously been proposed for the properties of miscible polymer mixtures, were found to be without merit in describing the obtained experimental results.
Theoretical stress–strain isotherms for elastin model networks
Authors: Debolt L. C. , Mark J. E.
Published: April 2003

A theoretical analysis was carried out for polypeptides composed exclusively of one of the three highly conserved repeat sequences present in the bioelastomer elastin. Conformational energy maps of the relevant amino acids were generated and a standard matrix method used. Various levels of intramolecular hydrogen bonding were studied, ranging from none to the inclusion of longer‐range hydrogen bonds implicated in stabilizing β‐bend conformations considered of importance owing to a Pro‐Gly pair present in each of the three repeat peptides. Monte Carlo techniques were used to evaluate the distribution functions of the end‐to‐end distance vector r, from which the modulus as a function of elongation was calculated. With minor exception, the resulting stress–strain isotherms for chains having degree of polymerization 5 and 10 showed little deviation from Gaussian behavior for elongation ratios up to 2.
T∥ from the temperature dependence of carbon‐13 NMR correlation times τc
Authors: Boyer Raymond F.
Published: April 2003

We demonstrate that carbon‐13 NMR average correlation times τc published by Dekmezian et al. as plots of log τc against reduced temperature, T/Tg, reach a visibly apparent asymptotic limit, (T/Tg)as, at about 1.21 for 9 amorphous polymers and 4 semicrystalline polymers; PIB and ethylene copolymers are exceptions. The average value of Tc/Tg is 1.21, where Tc is the carbon‐13 NMR collapse temperature reported by Axelson and Mandelkern. Log τc − T data can be linearized by the WLF equation or by the Vogel equation using a reference temperature, Tr ≡ Tc. Log f, versus T/Tg data can also be linearized by a hyperbolic equation method. All three methods yield an asymptotic frequency of 1 Hz or less, rationalizing why Tc (about 106 Hz) ≡ T‖ (f ≤ 1 Hz). Dielectric loss data analyzed by the Lobanov–Frenkel method confirm and define a T* (K) at a frequency of about 105−107 Hz at T‖ associated with local chain motion. A plot of Tc or T* against Tg (static) is linear, suggesting that Tc ≡ T* ≡ T‖. It is demonstrated that values of log f versus 1/T with f = 1/2πτc help to define the high‐frequency locus in relaxation maps for cis‐PI, PIB, and at‐PP.

The T‖ transition thus manifests itself in any of three ways: motion of the entire macromolecule in low frequency (1–1000 Hz) dynamic mechanical tests, an increase with temperature in Cp and in the coefficient of expansion in static measurements, and a high‐frequency local response in NMR and dielectric loss data. All three aspects are associated with the disappearance of interchain segment‐segment contacts at T‖, i.e., the “segmental melting” of Lobanov and Frenkel. Carbon‐13 NMR is a powerful tool for investigating T‖ dependence on structure in amorphous and crystalline polymers but is less satisfactory with ethylene copolymers. A linear correlation of Tc or Tas against Tg is demonstrated, where Tas is the asymptotic temperature from log τc versus T plots. This correlation can be used to define Tg in crystalline polymers if their Tc is known.
Dependence of the glass transition temperature of poly[N‐(n‐alkyloxy‐carbonyl‐methyl) Maleimides] and poly[N‐(5‐n‐alkyloxycarbonyl‐n‐pentyl) Maleimides] on n‐alkyl side‐chain length
Authors: Barrales‐Rienda J. M. , Mazón‐Arechederra J. M.
Published: April 2003

The glass transition temperature has been determined by a refractometric technique for two homologous series of poly[N‐(n‐alkyloxycarbonyl‐methyl) maleimides] (PEMIS 1) and poly[N‐(5‐n‐alkyloxycarbonyl‐n‐pentyl) maleimides] (PEMIS 5) with the outer part of the n‐alkyl side‐chain ranging in length from ethyl to decosyl for PEMIS 1 and from ethyl to decyl for PEMIS 5 and including only the even members of the series. The glass transition temperature is directly related to the number of methylene groups in the outer part of the n‐alkyl side‐chain (including terminal methyl) of the repeating unit. A semiempirical equation is presented that affords estimates of Tg that are in good agreement with the experimental data.
Effects of bond‐angle inversion on the statistical properties of poly(dimethylsiloxane)
Authors: Debolt L. C. , Mark J. E.
Published: April 2003

Evidence of only a low barrier to inversion in SiOSi sequences could be important with regard to the interpretation of the statistical properties of silicone polymers. The effects are estimated for the temperature coefficients of the unperturbed dimensions, dipole moments, and optical‐configuration parameter for poly(dimethylsiloxane).
Electron spin resonance studies of manganese(II) and copper(II) salts of poly(ethylene‐co‐methacrylic acid)s
Authors: Takei Miyuki , Tsujita Yoshiharu , Shimada Shigetaka , Ichihara Hisakatsu , Enokida Motohiro , Takizawa Akira , Kinoshita Takatoshi
Published: April 2003

The ionic interaction of poly(ethylene‐co‐methacrylic acid) ionomer neutralized with Mn2+ or Cu2+ was studied by ESR spectroscopy to explore the local structure in the ionic aggregate. ESR spectra of the ethylene ionomer were obtained as functions of degree of neutralization and temperature. The existence of both isolated and aggregated cations in the ionomer was confirmed by ESR. In addition, the formation of a Cu2+−Cu2+ dimer structure similar to the crystal structure of copper acetate monohydrate was found in ethylene ionomer containing the Cu2+. Cation‐cation interactions changed markedly around 70°C with increasing temperature, representing the onset of the motion of cations in the aggregated ionic structure.
On the dual mode gas transport model for glassy polymers
Authors: Petropoulos J. H.
Published: April 2003

The present paper is concerned with a detailed examination of the formalism and the physical basis of the dual mode mobility model used for the theoretical description of gaseous transport in glassy polymers in the light of recent theoretical and experimental work. It is shown that there are no really major differences among the original formulation of the model and later variants. A major modification becomes necessary, however, if the Langmuir sorption mode is assumed to exist in the form of patches or domains extensive enough to constitute a macroscopically recognizable phase rather than in the commonly accepted from of scattered individual adsorption sites. It is shown that the proper treatment of this case reduces to the familiar dual mode mobility formalism only under certain conditions. The interpretation of the experimental results thus far available is considered in some detail, and the usefulness of each of the aforesaid approaches in this respect is discussed.
Effect of tacticity on permeation properties of poly(methyl methacrylate)
Authors: Min K. E. , Paul D. R.
Published: April 2003

The effect of stereoregularity on gas permeation properties of poly(methyl methacrylate) (PMMA) was investigated. The gas permeability coefficients for He, H2, O2, N2, Ar, CH4, and CO2 at 35°C near atmospheric pressure have been measured for three different PMMAs. Apparent diffusion and solubility coefficients were obtained from time lag data, and these were compared with data for a commercial PMMA previously reported. The permeability, solubility, and diffusion coefficients increase as the content of syndiotactic sequences increases. These observations are consistent with more dense packing of the isotactic form in the glassy state that stems in part from its lower glass transition temperature. The transport behavior for a 50:50 isotactic/syndiotactic blend was also studied. These so‐called stereocomplexes exhibit permeation behavior comparable to other weakly interacting miscible blend systems.
Deformation of semicrystalline polymers via crystal–crystal phase transition
Authors: Saraf Ravi F. , Porter Roger S.
Published: April 2003

A classification is given of flexible, semicrystalline polymers based on the early stage deformation behavior in the solid state. The criteria of each category are discussed with experimental evidence from the literature on 17 polymers. The central aim of this classification is to point out the possibility of ductility induced during deformation. The understanding of the induced ductility in a given semicrystalline polymer suggests a systematic route to optimize solid‐state deformation processes for achieving high draw ratios.
Influence of the glass transition on solvent self‐diffusion in amorphous polymers
Authors: Vrentas J. S. , Duda J. L. , Ling H.‐C.
Published: April 2003

The free‐volume theory of diffusion is used to analyze the temperature dependence of solvent self‐diffusion coefficients both above and below the glass transition temperature at concentrations removed from the pure polymer limit. The glass transition can have a pronounced effect on the temperature dependence of solvent self‐diffusion coefficients at small solvent concentrations, but the theory predicts a decreased effect of the transition on the diffusion process with increasing solvent concentration.
The entropy of inhomogeneous polymer–solvent systems
Authors: Balsara Nitash P. , Nauman E. B.
Published: April 2003

The entropy of inhomogeneous polymer solutions has been evaluated using a lattice model. Previous models for polymer solutions considered only the enthalpic contributions, and a more complete expression for the free energy is obtained by adding the entropic term. The resulting expression is used to predict the characteristics of spinodal decomposition of polymer solutions and the interfacial tension between demixed polymer solutions. There is general improvement in the agreement between theory and experiment when the entropic effects are included.
Test of a model of stress‐dependent diffusion by means of combined colored tracer and birefringence profile measurements
Authors: Petropoulos J. H. , Sanopoulou M.
Published: April 2003

In the present paper we further test a model of stress‐dependent diffusion previously used with success to simulate the variation from Case I to Case II penetration kinetics in the system liquid methylene chloride‐uniaxially oriented cellulose acetate film, according to whether penetration occurs across or along the axis of preferred macromolecular orientation. Data on penetration rates, optical density profiles (using a colored tracer), and the corresponding birefringence profiles, characteristics of these penetration modes in the aforesaid system, are presented and compared with appropriate model uptake kinetic curves and penetrant concentration and compressive differential swelling stress profiles. It is shown that the salient features of the observed experimental behavior are in general accord with model predictions based on physically realistic assumptions.
Thermotropic polyesters of 4'‐hydroxyphenyl‐4‐hydroxybenzoate: A study of the transition temperatures
Authors: Kotek R. , Krigbaum W. R.
Published: April 2003

Polyesters based on 4'‐hydroxyphenyl‐4‐hydroxybenzoate and dichlorides of dibasic acids, prepared using a high‐temperature solution polycondensation in 1‐chloronaphthalene, exhibit enantiotropic nematic mesomorphism. The range of temperatures for the nematic phase Δ tN can be controlled by changing the number of methylene units in the repeating polymer unit. For n = 4, Δ tN = 97°C is the largest that can be obtained. Higher n leads to smaller values of Δ tN. When n = 12, the polyester exhibits only one single C‐I transition. For n > 12 a smectic mesophase can be expected in this system. Strezlecki and Liébert reported a wide range of temperatures of Δ tN (70–160°C) for the Sn polymers made by the transesterification of 4'‐acetoxyphenyl‐4‐acetoxybenzoate and the dicarboxylic acids. We believe the latter reaction occasionally involves the internal ester linkage in the monomer unit, producing a copolyester having a random distribution of hard segment lengths and changed polymer mesomorphic properties.