bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tensile stress and recoverable strain measurements on polystyrene melts. Interpretation of results in terms of rubberlike elasticity
Authors: Muller R. , Froelich D. , Zang Y. H. 
Published: April 2003

AbstractExtensional tests at constant strain rate \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document} have been carried out on polystyrene melts with different molecular weight distributions at various temperatures and strain rates. The true tensile stress is found to be well approximated by the sum of two contributions: (1) a neo‐Hookean expression involving the recoverable strain and (2) a contribution rapidly reaching a steady‐state value. Two experimental parameters can be defined: an elasticity modulus \documentclass{article}\pagestyle{empty}\begin{document}$ G(\dot \varepsilon ) $\end{document} from (1) and a viscosity \documentclass{article}\pagestyle{empty}\begin{document}$ \eta _{\rm v} (\dot \varepsilon ) $\end{document} from (2). It is further shown that time‐temperature equivalence applies not only to the stress but also to the recoverable strain and to G and ηv. The dependence of G and ηv on strain rate is then discussed. For high strain rates, G is close to the linear viscoelastic plateau modulus of PS melts and decreases with decreasing strain rate. The value of ηv is found to a good approximation to be equal to three times the shear viscosity taken at a shear rate equivalent to the elongational strain rate.
Isomorphic behavior of poly(aryl ether ketone) blends
Authors: Harris James E. , Robeson Lloyd M. 
Published: April 2003

AbstractBlends of various poly(aryl ether ketones) have been found to exhibit a range of miscibility and isomorphic behavior. This range is dependent on molecular weight; however, for poly(aryl ether ketones) with number‐average molecular weight of 20,000, this range is about ±25% difference in ketone content. All miscible blends exhibit isomorphism, and all immiscible blends exhibit no evidence of isomorphism. The dependence of the glass transition temperature Tg versus composition exhibits a minimum deviation from linearity whereas the melting temperature Tm versus composition exhibits a pronounced maximum deviation from linear behavior.The crystalline melting point versus composition for isomorphic blends is considerably different than for random copolymers with isomorphic units. Homopolymers and random copolymers exhibit a melting point that is a linear function of ketone content (increasing ketone content increases Tm). For blends, the melting point is essentially the same as that of the higher melting constituent until high levels of the lower melting constituent are present. The observed melting point versus composition behavior will be interpreted using classical theory to calculate the components of the liquid and crystalline phase compositions. As a miscible blend is cooled from the melt, essentially pure component of the highest melting point crystallizes out of solution, as predicted by calculated solid‐liquid phase diagrams. This occurs until the crystallization is complete owing to spherulitic impingement. At high concentrations of the lower melting constituent, lower melting points will be observed because the highest melting constituent will be depleted before the crystallization is complete.In many miscible blends involving addition of an amorphous polymer to a crystalline polymer, the degree of crystallinity of the crystalline polymer has been shown to increase. On the basis of evidence presented here, it is hypothesized that dilution by a miscible, amorphous polymer allows for a higher level of crystallinity.
Interaction parameters of polystyrene‐polyisoprene‐toluene systems at 45°c from gel permeation chromatography
Authors: Tseng Hsiao‐Show , Lloyd Douglas R. , Ward Thomas C. 
Published: April 2003

AbstractEquilibrium phase diagrams of narrow molecular weight distribution samples of polystyrene and polyisoprene in the presence of toluene at 45°C and 1 atm pressure were established by means of gel permeation chromatography. The polymer‐polymer interaction parameter was evaluated on the basis of the Flory‐Huggins approach. The influence of polymer molecular weight and polymer‐solvent interaction parameters on (i) the shape and location of the binodal curve, (ii) the location of the critical point, and (iii) the polymer‐polymer interaction parameter was investigated.
Moderately concentrated solutions of polystyrene. II. Integrated‐intensity light scattering as a function of concentration, temperature, and molecular weight
Authors: Hager B. L. , Berry G. C. , Tsai H.‐H. 
Published: April 2003

AbstractIntegrated‐intensity light scattering data are reported for moderately concentrated solutions of polystyrene in benzene and in cyclopentane. The benzene system is one for which the second virial coefficient A2 is large; data obtained over the range 0.5 < A2Mc < 30, with c the polymer concentration, are analyzed in terms of the (extrapolated) intensity at zero angle and the angular dependence of the intensity. The former is discussed in terms of power law representations based on scaling relations, which are found to represent the data. The latter is discussed in terms of the dependence of the chain dimensions on concentration. With cyclopentane, the behavior is similar for temperatures for which A2 is near its maximum, but for T near either ΘU or ΘL, for which A2 is zero or small, the angular dependence of the scattering is distinctly different, with the intensity exhibiting a maximum as a function of scattering angle.
Brillouin scattering of oriented films of poly(vinylidene fluoride) and poly(vinylidene fluoride) ‐poly( methyl methacrylate) blends
Authors: Wang C. H. , Liu Q.‐L. , Li B. Y. 
Published: April 2003

AbstractTemperature dependent Brillouin scattering studies of PVF2 films stretched to various stretch ratios have been carried out. Elastic constants for unstretched and stretched films have been obtained as functions of temperature. The elastic constant C33 of the stretched films has a greater temperature dependence than that of unstretched films. To elucidate the effect of the surrounding amorphous matrix on the Brillouin spectrum of semicrystalline PVF2 film, we carried out Brillouin scattering studies of films made from blends of PVF2 and PMMA.
Crystal structure of nylons 2/3/3 and 1,3
Authors: Puiggalí Jordi , Muñoz‐Guerra Sebastián 
Published: April 2003

AbstractThe crystal structures of two polyamides, poly(glycyl‐β‐alanyl‐β‐alanine) (nylon 2/3/3) and poly(methylene malonamide) (nylon 1,3), have been investigated by x‐ray diffraction and electron microscopy. Crystallization of nylon 2/3/3 from a solution in a mixture of water and formic acid yields lamellar single crystals exhibiting a triangular habit. Doughnut‐shaped morphologies diffracting as single crystals are obtained in the crystallization of nylon 1,3. A helical structure of the type known as polyglycine II is found for both polyamides. In such a structure, chains are intermolecularly linked by hydrogen bonds giving a hexagonal lattice of a = 4.79 Å. Insufficient data are available to determine precisely the conformation of the chains. We assume a threefold helix having c = 35.2 Å and c = 18.0 Å for nylon 2/3/3 and nylon 1,3 respectively. No sign of the layered structure familiar in polyamides has been detected for these polymers throughout the experiments made in the present study.
Morphological heterogeneity of polymer fibers which do not reveal small‐angle x‐ray reflections
Authors: Slutsker Leonid I. 
Published: April 2003

AbstractFor many aliphatic and wholly aromatic polymer fibers, meridional small‐angle x‐ray reflections (SAXR's) are not observed. The morphological features which give rise to this effect have Received little attention in the literature. It is sometimes speculated that this is evidence of a morphological homogeneity along the fiber axis (no fluctuation of electron density–no long periods), ignoring other possible reasons (morphology is heterogeneous but very irregular or the maximum intensity of SAXR (Imax) is low and SAXR cannot be observed against the background of diffuse scattering.) Fibers with homogeneous crystalline morphology should have an elastic modulus Ef close to that of the crystallites Ecr along the polymer chains over a broad range of stresses. But, as was found in this work for the overwhelming majority of such nonreflection fibers (including Kevlar aramid fibers) there is a considerable difference between Ecr and Ef (for some nonreflection fibers the ratio Ecr/Ef is on the order of 10). This means that their morphology is heterogeneous along the fiber axis and contains “weaker” intercrystalline regions. This heterogeneity appeared to be regular enough to give rise to SAXR, as determined from the appearance of SAXR during elastic extension and after the beginning of pyrolysis in some nonreflection fibers. Thus, it was concluded that the lack of observable SAXR for these fibers is a result of the weakness of Imax relative to the diffuse scattering. Support for this statement is seen in the analysis of the decrease of Imax to zero with increasing draw ratio for poly(vinyl alcohol) fibers. The key factors influencing the decrease of Imax in this case were found to be the decrease of fibril diameter (fibril splitting), an increase of the dispersion of the long periods and some possible decrease in the density difference between crystalline and amorphous regions. The particular combinations of such factors can be different for each particular case of missing SAXR and are discussed in this paper.
Sorption of a finite amount of swelling solvent in a glassy polymer
Authors: Cohen Donald S. , Goodhart Charles 
Published: April 2003

AbstractWe study the time history of a diffusing front when a polymer is exposed to a finite amount of penetrant which becomes used up. A class of polymers is considered for which slow molecular relaxation occurs only at or near the glass‐gel interface with instantaneous relaxation both ahead of and behind the progressing front. We show that the position of the penetrant front versus time undergoes a long smooth transition from standard Fickian t1/2 behavior to exponential time decay onto a final equilibrium position attained when all the penetrant is used up.
Compatibility of coils and rods bearing flexible side chains
Authors: Ballauff M. 
Published: April 2003

AbstractWe present a theoretical treatment of nematic‐isotropic phase equilibria in mixtures which consist of random coils and comblike polymers, the latter components being composed of a rigid backbone and flexible side chains. The mixing partition function is evaluated by using the Flory lattice model. The comblike component is characterized by the axial ratio xr of its rigid main chain and the number of flexible side chains z, each containing m segments. The coiled component is described by its number of segments xc. The net exchange energy of mixing is assumed to be zero; i.e., we consider athermal solutions. It is shown that the flexible side chains attached to the rigid main chains markedly enhance the compatibility in the isotropic phase. If the ratio of the volume fraction of the side chains to the volume fraction of the main chains is high enough, there is even a finite range of concentration where the random coils mix homogeneously with the comblike component. This is in contrast to mixtures of rods and coils, which have been shown by Flory to be incompatible over nearly the full range of composition. These conclusions hold true only when ordered states are involved. For comblike polymers with flexible backbones mixed with random coils in isotropic melts, the resulting free energy of mixing is given by the familiar Flory‐Huggins expression.
Ultrasonic and hypersonic dispersion in polysiloxanes
Authors: Onabajo A. , Dorfmüller Th. , Fytas G. 
Published: April 2003

AbstractWe report ultrasonic attenuation and velocity measurements on poly(dimethylsiloxane) (PDMS), poly(phenylmethyl siloxane) (PPMS), and copolymer poly(dimethyl phenylmethyl siloxane) in the temperature range of 10–50°C and frequency 0.3–45 MHz. The present data complement previously reported Brillouin spectra at hypersonic frequencies. Whereas the ultrasonic velocity u0 is virtually independent of frequency, the ultrasonic absorption exhibits strong dispersion which can be ascribed to the viscoelastic normal mode relaxation. The ultrasonic attenuation data for PPMS at low temperatures display an additional relaxation process related to localized segmental motion. This mode is also responsible for the relatively large dispersion of the sound velocity and attenuation in the gigahertz frequency range accessible to the Brillouin scattering experiment. The extended information, which can be extracted by studying hypersonic dispersion, is discussed in detail.
A study of the acoustic mode structure of oriented poly(ethylene)
Authors: Cavanaugh David B. 
Published: April 2003

AbstractThe low‐frequency acoustic vibrational modes of solid poly(ethylene) (PE) oriented by stretching and hydrostatic extrusion are studied with Brillouin spectroscopy. The experimental results evidence a damping of the longitudinal acoustic mode propagating in the direction parallel to the orientation axis of the samples. The results are discussed in terms of the theoretically derived acoustic dispersion relations for the PE crystal.
Fiber spinning from the nematic melt. II. Effect of thermal history on spinning of the copolyester of polyethylene terephthalate and p‐oxybenzoate
Authors: Muramatsu Hiromochi , Krigbaum W. R. 
Published: April 2003

AbstractFibers were spun from the nematic phase of the copolymer of polyethylene terephthalate having 60 mol % of p‐oxybenzoate units. A capillary rheometer was used for spinning with a shear rate at the wall of 6.4 sec−1, and capillary (length/diameter) ratio of 14.1. The spinning temperature was varied from 250° to 300°C and, at each temperature, the spin‐draw ratio was examined as a variable. Spinning was performed under two conditions. When spinning from the melt without preheating, the initial modulus of the fibers increased with spin‐draw ratio and increased with increasing spinning temperature for a fixed spin‐draw ratio. In the second case, the melt was preheated and then cooled to the desired temperature before spinning the fibers. The preheating temperature was 280°C for spinning at 250°C, and 300°C for spinning at 280°C. Preheating increased the fiber modulus to the value obtained by spinning at the preheating temperature. A reduction of the viscosity due to the melting of poly(p‐hydroxybenzoic acid) (PHB) crystallites produces better orientation and higher modulus. However, with increasing spin‐draw ratio, the modulus of the preheated fibers decreased to the values expected for the spinning temperature. This decrease in modulus is due to recrystallization of PHB in the threadline.
Studies of magnetic resonance phenomena in polymers. II. Molecular motions in poly(methyl methacrylate) as studied by spin‐probe and spin‐label methods
Authors: Tsay Fun‐Dow , Gupta Amitava 
Published: April 2003

AbstractThin films of spin‐probed and spin‐labeled poly(methyl methacrylate) (PMMA) have been examined by electron spin resonance (ESR) in the temperature range of 77–520°K. The rotational correlation times of nitroxides used as spin probes and labels have been determined as a function of temperature from which activation energies are also determined. The nitroxide rotational times are found to strongly correlate with local segmental and side‐chain motions of the host PMMA matrix. Five discrete molecular motions are detected in PMMA along with their activation energies as measured: side‐chain CH3 rotation (1 Kcal/mol), main‐chain CH3 rotation (2 Kcal/mol), ester side‐chain COOCH3 rotation around the CC bond (4 Kcal/mol), main‐chain CC bond rotation (6 Kcal/mol), and side‐chain OCH3 rotation around the CO bond (18 Kcal/mol). The activation energies determined by ESR are consistent with the potential‐energy barriers calculated theoretically for various rotations in PMMA. It is concluded that the probe and label rotational motions do respond to localized, small‐scale segmental and side‐chain motions of host polymers but are relatively ineffective in response to the large‐scale segmental motion with an activation energy larger than 20 Kcal/mol in the case of PMMA.
Complex refractive indexes for polymers over the infrared spectral region: Specular reflection IR spectra of polymers
Authors: Pacansky J. , England C. , Waltman R. J. 
Published: April 2003

AbstractA dispersion analysis is used to determine the complex refractive indexes over the infrared for the following polymeric systems: isotactic poly(methyl methacrylate), syndiotactic poly(methyl methacrylate), poly(2‐methyl‐1‐pentene)sulfone, poly(perfluoropropylene oxide), poly(pyromellitimide), poly(styrene), and poly(vinyl alcohol). These were combined with solutions of Maxwell's equations for electromagnetic radiation at interfaces in a FORTRAN computer code to model specular relection infrared spectra. Calculations and experimental data are compared to demonstrate the complicated nature of specular reflection and the ability of the modelling to simulate the observed spectra.
Transport of methylene chloride in poly(aryl‐ether‐ether‐ketone) (PEEK)
Authors: Grayson Michael A. , Pao Peter S. , Wolf Clarence J. 
Published: April 2003

AbstractThe sorption of methylene chloride in neat PEEK was investigated as a function of temperature, sample thickness, surface treatment, and thermal history. The solubility of H2CCl2 in neat PEEK is 23 wt.% and is independent of thickness. Both surface treatment and thermal annealing strongly affect the rate of penetration; the as‐Received material sorbs H2CCl2 more rapidly than abraded or annealed samples; however, the bulk solubility is independent of surface treatment. The sorption and desorption processes are considerably different, and the diffusion process is not simple Fickian Case I. The penetrant advances as a sharp front, suggesting a two‐step, relaxation‐controlled diffusion mechanism.
Effect of antiplasticization on gas sorption and transport. II. Poly(phenylene oxide)
Authors: Maeda Y. , Paul D. R. 
Published: April 2003

AbstractThe propensity for various diluents to cause antiplasticization of poly(phenylene oxide) was examined and compared with similar responses for polysufone. Of the diluents used, none resulted in significant stiffening of poly(phenylene oxide) at 35°C relative to what was observed for polysulfone in an earlier paper. However, these diluents did cause substantial reduction in gas sorption levels and permeability coefficients. The latter is consequently a more sensitive indicator of changes in molecular motions of glassy polymers caused by diluents. The permeability response of adding low molecular weight diluents is compared with that of adding a high molecular weight polymer, polystyrene, to poly(phenylene oxide). The data were analyzed and interpreted along lines used in the companion paper for polysulfone.
Effect of antiplasticization on gas sorption and transport. III. Free volume interpretation
Authors: Maeda Y. , Paul D. R. 
Published: April 2003

AbstractPrevious papers have shown that antiplasticization of polysulfone and poly(phenylene oxide) by low molecular weight diluents is accompanied by substantial reductions in permeability to gases like helium, carbon dioxide, and methane because of reduced mobility in the glass. These effects are not explained even qualitatively by the extent of volume contraction on mixing for these mixtures. However, as shown here, a simple free volume treatment provides an excellent correlation of these effects. Free volume was computed from measured specific volume and an estimate of the volume at the absolute zero of temperature of the material from a group contribution method. Application of this approach to the mechanical stiffening associated with antiplasticization is suggested. The basis and limitations of this analysis are discussed.
Role of matrix‐particle interface adhesion on fracture toughness of dual phase epoxy‐polyethersulfone blend
Authors: Raghava R. S. 
Published: April 2003

AbstractCompatibility or miscibility of a polyethersulfone (ICI: Victrex 100P) and a tetrafunctional epoxy (Ciba‐Geigy: MY‐720), cured with an aromatic anhydride, has been studied using scanning electron microscopy, x‐ray microanalysis, and dynamic mechanical spectroscopy. Fracture toughness of epoxy and a blend of epoxy and polyethersulfone has been measured using three point bend tests (ASTM: E‐399‐81). Fracture surfaces were examined by x‐ray microanalysis for detecting concentration of sulfur, present in polyethersulfone, in the matrix and precipitated phase. The influence of the morphology of the epoxy/polyethersulfone blend on its fracture toughness and toughening mechanism has been studied. Fracture toughness values of unmodified and modified cured epoxy resin were evaluated as a function of test temperature.
Response of polyisoprene and polybutadiene vulcanisates to double‐step retractions: Analysis by a disengagement process of pendant chains
Authors: Thirion Pierre , Monnerie Lucien 
Published: April 2003

AbstractThe influence of the molecular weight of the primary chains and of crosslinking density on the viscoelasticity of polyisoprene and polybutadiene vulcanisates has been examined by subjecting these materials to double‐step extensions in opposite directions. The stress peaks caused by these sudden retractions are well described by a model derived from the Curro–Pincus treatment of the disengagement pendant chains from a net of obstacles. These topological interactions do not appear to be derived from discrete chain entanglements but from diffuse interspersion effects between the pendant chains and the chemical junctions of the networks.
Nematogenic aromatic block copolymers of rigid and flexible units. II. Phase equilibria
Authors: Krigbaum W. R. , Shufan Zhang , Preston Jack , Ciferri A. , Conio G. 
Published: April 2003

AbstractThe solubility and mesophase behavior are investigated for block copolymers of poly(p‐benzamide) (PBA), the polyterephthalamide of p‐aminobenzhydrazide (PABH‐T), and PBA and poly(m‐phenylene isophthalamide) (MPD‐I) dissolved in N,N‐dimethylacetamide (DMAc) containing 3% LiCl. The block copolymers, whose synthesis and characterization were described in the previous paper in this series, included samples prepared by the two‐step and multistep copolycondensations. The first of these methods yields a considerable amount of the flexible homopolymer (PABH‐T) and also some of the rigid homopolymer. The flexible homopolymer can be removed from the block copolymer by extraction with dimethyl sulfoxide (DMSO), whereas precipitation may offer a way to remove the rigid homopolymer. The results observed for the block copolymers are compared with those for the homopolymers and mixtures of homopolymers. The apparent solubility of the PBA/PABH‐T block copolymers obtained by the two‐step method is unusually large but decreases toward the value observed for mixtures after the flexible homopolymer had been extracted with DMSO. Labile adducts involving PABH‐T and/or the block copolymer appear to be capable of forming a single mesophase. This offers a most interesting approach to the preparation of composite materials involving rigid and flexible polymers.
Polyethylene–isotactic polypropylene epitaxy: Analysis of the diffraction patterns of oriented biphasic blends
Authors: Lotz B. , Wittmann J. C. 
Published: April 2003

AbstractDiffraction patterns of oriented blends of isotactic polypropylene (iPP) and polyethylene (PE) published recently by several authors are analyzed on the basis of a unique epitaxial relationship between the iPP and PE crystal lattices. The contact planes are (100)PE and (010)iPP, and the PE chains lie at 50° to the iPP chain axis, parallel to the helical path of the iPP helices, which is formed by rows of side‐group methyls.