bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental investigation of the concept of molecular migration within sheared polystyrene
Authors: Whitlock L. Ronald , Porter Roger S. 
Published: April 2003

AbstractSeveral important aspects of the flow in polymer melts through capillaries remain unexplored. This paper examines experimentally one such effect associated with the radial shear‐stress gradient in capillaries. During capillary melt flow of a polymer with a wide molecular weight distribution, migration of the large molecules away from the region of highest shear stress, i.e., at the capillary wall, has been predicted but only modestly investigated. This effect has the potential to produce a molecular weight spectrum over the cross section of extruded polymer. Studies of distribution in shear were conducted on a well‐characterized wide‐distribution polystyrene (M̄w = 234,000). An Instron Rheometer equipped with a long capillary (length/diameter ratio of 66.7) was used to perform the extrusion at temperatures of 160–250°C. A solvent coring procedure was used to dissolve away concentric layers of polymer from the extrudate for molecular weight analyses. The method has been shown to cut clean sections without selective extraction. Values of M̄w, M̄n and M̄w/M̄n were calculated from complete molecular weight distribution data obtained by calibrated gel permeation chromatography. For a wide range of shear rates and temperatures, no evidence for molecular fractionation was observed. Shear degradation of this polymer was found to be small. However, at high shear rates at 250°C, evidence indicating extensive shear‐induced thermal degradation was found. No evidence for oxidative degradation at the extrudate surface was found at either low or high shear rates at this temperature.
Mass and momentum transfer in polymers. I. Effects of equilibrium vapor sorption on tensile creep of an amorphous polymer
Authors: Machin D. , Rogers C. E. 
Published: April 2003

AbstractDiffusion and tensile creep measurements were made for systems of poly(‐n‐butyl methacrylate) (PBMA) and sorbed ethanol, MEK, or benzene at 23°C. Rates of penetration of an inert spherical indenter into PBMA also were investigated and compared with the tensile creep behavior of the polymer. Creep measurements for various volume fractions of penetrant sorbed at equilibrium revealed that master curves, resulting from a time‐concentration superposition procedure, could be constructed for each penetrant. At long times, these master curves, particularly that for ethanol, show deviations from the corresponding time‐temperature superposition master curve. These deviations are interpreted in terms of probable long‐range entanglement coupling governed in part by the partially specific nature of polymer‐penetrant interactions. Parameters calculated by a free‐volume theory, describing both diffusion and tensile‐creep data, indicate that MEK is a more efficient plasticizing agent than the other penetrants and requires less local free volume for diffusion. Analysis in terms of the free volume concept was not attempted for the case of ethanol, where specific polymer‐penetrant interactions are more important.
Direct analysis of small‐angle equatorial x‐ray scattering from fibrous systems. II. Methods of extracting physical parameters describing the scattering system
Authors: Harget P. J. , Krimm S. 
Published: April 2003

AbstractSmall‐angle equatorial x‐ray scattering from fibrous systems is often complicated by the effects of morphological organization and/or heterogeneities as well as by macromolecular structure and organization influencing this same region of scattering space. In previous work it was shown that closed form mathematical expressions could be obtained for the Patterson function, without prior assumptions about the scattering system, when the intensity data were purposely truncated. In this paper the use of these expressions to extract the physical parameters describing the scattering system is demonstrated by application to a model system. The expressions are also expanded to include lattice distortions and long range coherency. A second approach is presented for cases when the coherence is small, and finally the use of higher‐resolution data is discussed.
Growth stages in epitaxial crystallization of poly(γ‐benzyl L‐glutamate)
Authors: Rybnikar F. , Geil P. H. 
Published: April 2003

AbstractThe electron microscope study of the isothermal epitaxial crystallization of PBLG on 001 cleavage surface of NaCl or KCl from 0.01% chloroform solution with various n‐octane contents has shown that the epitaxial growth process could be divided in two stages. In the first stage a rapid growth of a lamellar layer 20–40 Å thick could be observed; the PBLG molecules in αhelix conformation are oriented along <110> substrate directions. The dimensions and perfectness of alignment of these lamellae along the <110> direction depends on the molecular weight of the PBLG. In the second stage of PBLG epitaxial crystallization the relatively slow thickening of some initial lamellae takes place and one can observe many types of secondary structures. With increasing thickness of the epitaxial structures and increasing molecular weight of the PBLG the degree of orientation in relation to <110> substrate direction diminishes. The two growth stages in PBLG epitaxial crystallization are related to different kinds of orienting and attracting forces of the alkali halide substrate.
Elastic and thermoelastic behavior of cis‐polybutadiene crosslinked in the swollen state
Authors: De Candia F. , Amelino L. , Price C. 
Published: April 2003

AbstractSamples of cis‐polybutadiene were cross‐linked in the presence of decalin at values of ϕr (the volume fraction of rubber) ranging from 0.25 to 0.50. After the diluent had been removed, a study was made of the force‐extension and thermoelastic behavior of the networks. Within experimental error, the ratio of the Mooney‐Rivlin constants 2C2/2C1 was found to be zero for networks prepared at low ϕr (0.25 and 0.30) but started to increase towards the conventional value at higher ϕr. The quantity fe/f was found to be independent of the ratio 2C2/2C1 and of the extension ratio α; the average value of fe/f was found to be 0.11.
Analysis of anisotropy in dielectric absorption due to defects in the polyoxymethylene crystal
Authors: Tanaka Akira , Ishida Yōichi 
Published: April 2003

AbstractThe dielectric absorption due to terminal polar groups localized in defect regions of polyoxymethylene crystals shows an anisotropy relative to an applied field. An attempt to interpret this anisotropy has been made by applying the barrier theory of Hoffman. The potential energy map for the rotation of the terminal polar group calculated from conformational analysis gives two minima. The angle between the dipole moment of the terminal OH and the fiber axis calculated in terms of the two conformations corresponding to the potential energy minima is in good agreement with results from infrared dichroism. This agreement is considered as evidence that the conformational analysis is reliable for estimating the potential energy minima required in the calculation according to the barrier theory. The barrier height obtained by the conformational analysis and the anisotropy calculated from the components of the dipole moments for the terminal polar group in terms of the barrier theory are in qualitative agreement with the experimental data.
Steady flow measurements on moderately concentrated solutions of poly(sodium acrylate)
Authors: Sakai Mototsugu , Noda Ichiro , Nagasawa Mitsuru 
Published: April 2003

AbstractShear stress P21 and normal stress P11 –P22 functions of moderately concentrated aqueous solutions of sodium poly (acrylate) were measured under steady shear flow at various shear rates \documentclass{article}\pagestyle{empty}\begin{document}$\dot \gamma$\end{document} with a Weissenberg rheogoniometer. The compliance function Js = (P11 – P22)/2P212 is found to vary with shear rate. The double logarithmic plot of Js versus
\documentclass{article}\pagestyle{empty}\begin{document}$\dot \gamma$\end{document} can be superposed with respect to molecular weight at constant concentrations of added neutral salt and polymer. These reduced plots differ markedly as the concentration of added salt is varied but converge to a single line at high shear rates.
Viscoelastic properties and flow of narrow distribution polybutadienes and polyisoprenes
Authors: Vinogradov G. V. , Ya. Malkin A. , Yanovskii Yu. G. , Borisenkova E. K. , Yarlykov B. V. , Berezhnaya G. V. 
Published: April 2003

AbstractThe dynamic shear modulus and the flow rate through capillaries under constant pressure and under constant velocity of the piston, have been measured for polybutadienes and polyisoprenes of narrow molecular weight distribution with molecular weights ranging, respectively, from 3.8 × 104 to 5.8 × 105 and from 1.06 × 105 to 6.02 × 105. The phenomena of the discontinuous increase of volume flow rate and self‐oscillatory flow regime at critical rates of deformation have been considered in detail. It is proposed that these phenomena are due to the induced transition of the polymer from the fluid to the high‐elastic state at higher deformation rates. As a result, an inference has been made that polybutadienes and polyisoprenes with a narrow molecular weight distribution in the high‐elastic state, behave in certain respects as crosslinked polymers incapable of displaying fluidity. The quantitative relationships among the viscoelastic characteristics measured under dynamic regimes, the parameters determining the critical flow regimes, and the molecular weights of polybutadienes and polyisoprenes have been worked out.
Thermally induced phase separation of polystyrene‐poly(vinyl methyl ether) mixtures
Authors: Bank M. , Leffingwell J. , Thies C. 
Published: April 2003

AbstractPast differential scanning calorimetry and dielectric relaxation measurements have established that polystyrene (PS)‐poly(vinyl methyl ether) (PVME) mixtures exhibit a degree of compatibility when cast from toluene, whereas they are incompatible when cast from chloroform or trichloroethylene. The present study reports that toluene‐cast mixtures can be phase‐separated by thermal treatment at temperatures exceeding 125°C. This is true for samples containing 20–80 wt‐% PS. The temperature of phase separation varies with heating rate; isothermal heating times needed to cause phase separation increase rapidly as the temperature approaches 125°C. Reversibility of the phase separation process depends upon such factors as cooling rate, annealing time, treatment temperature, and thermal history. By annealing and/or slow cooling, all thermally phase‐separated mixtures have been brought back to their original state of compatibility. That is, there is no evidence for true irreversiblity of phase separation in thermally treated samples. Quench‐cooled samples remain phase‐separated indefinitely at room temperature, but this is attributed to rapid cooling below the glass transition of the PS. Chloroform‐cast and trichloroethylene‐cast mixtures have not been brought to a compatible state by thermal treatment, even after lengthy annealing and slow cooling steps.
Far‐infrared spectra of piezoelectric polyvinylidene fluoride
Authors: Luongo J. P. 
Published: April 2003

AbstractPoly(vinylidene fluoride) (PVF2) is currently used to form piezoelectric films. The PVF2 molecule can exist in more than one stable conformation and it has electrically polar groups making the polymer amenable to the electrification processes involved in the formation of the piezoelectric film. The two crystalline forms of PVF2 are distinguishable by far‐infrared spectroscopy. Polarized far‐infrared spectra (1000‐50 cm−1) of uniaxially oriented PVF2 show changes in the strong perpendicular dichroism in a number of absorptions before and after being made piezoelectric. The dichroism is attributed to a structural rearrangement from a staggered trans‐gauche‐trans‐gauché conformation to a planar zig zag conformation. In the latter conformation the permanent dipoles are oriented approximately at right angles to the surfaces of the film and result in an electrically polarized film.
Light scattering by anisotropic elliptical objects
Authors: Finkelstein R. S. , Sarko A. 
Published: April 2003

AbstractThe small‐angle light scattering in Hv and Vv modes is calculated for elliptical disks with the use of an elliptical coordinate system. The method is general for all degrees of ellipticity, from a circular disk to rodlike extensions, and permits the definition of any desired dipole orientations. The solution is obtained by computer‐assisted numeric integration. Two models are considered, an “elliptical” one an “affine deformation” one differing in the orientation of scattering dipoles. The calculated patterns show a significant dependence of the distribution of the scattered intensity on the size and the elliptical axial ratio in both models, permitting the determination of both the size and the degree of ellipticity of the disk from its patterns. In addition, the differences between the calculated results for the two models are sufficiently large to permit the selection of the experimentally appropriate model, at least within the range of moderate degree of ellipticity.
Crystallite size in drawn and then annealed polypropylene
Authors: Morosoff N. , Sakaoku K. , Peterlin A. 
Published: April 2003

AbstractCrystallite sizes have been obtained from the breadth of equatorial x‐ray reflections from polypropylene samples subjected to a draw ratio of 6 at 21°C and then annealed at 155°C, 140°C, and 120°C, respectively. For all samples it was found that the ratio of the dimension of the crystallite perpendicular to the {110} planes to that perpendicular to the (040) plane is a constant. The ratio of the lateral crystallite size to the meridional long period was also found to be constant, independent of annealing temperature. In contrast, the thickness of the crystallites in the direction parallel to the draw direction, as calculated from the meridonal long period and density data, was not proportional to the lateral crystallite size.
Effect of heat treatment on the morphology and structure of crystals, powders, and fibers of polyacrylonitrile and saran
Authors: Boucher E. A. , Langdon D. J. , Manning R. J. 
Published: April 2003

AbstractAs part of a study of chemical and physical changes accompanying the formation of carbons by the pyrolysis of polymers, conventional electron microscopy, electron diffraction, and scanning electron microscopy techniques have been used to examine structural and morphological features of polyacrylonitrile (PAN) crystals, powder, and fibers, and of Saran and poly(vinylidene chloride) (PVDC) powder. Changes accompanying the heating of these polymers in air and in nitrogen have been investigated. PAN crystals grown from propylene carbonate were similar to those obtained by Klement and Geil. When heated in air at 220°C they retained their morphology, and electron diffraction gave the same reflections as PAN. On further heating to 400°C in nitrogen the morphology was retained, but the diffraction was lost. Crystals treated in nitrogen alone at 200°C showed morphology similar to that of the polymer. PAN powders and fibers retained discernable external features of their morphology on heating to 800°C. These results are discussed with reference to changes which take place when poly(vinylidene chloride) and Saran are heated in the range 150–180°C, which results in the loss of one hydrogen chloride per monomer unit, and are subsequently carbonized at 800°C. The development of pore structure and the adsorptive properties of Saran carbons are also discussed.
Glass transition temperature for epoxy‐diamine networks
Authors: Williams J. G. , Delatycki O. 
Published: April 2003

AbstractThe glass transition temperature of systems based on epoxy resin and a number of diamines has been determined by using a torsion pendulum. An equation relating composition and crosslink density with the glass transition temperature has been established which gives reasonable predictions of the glass transition temperatures for systems based on aliphatic or aromatic amines and methylated amines and for systems containing a monofunctional epoxy diluent. The equation may be used to predict Tg for systems with non‐stoichiometric quantities of curing agent and blends of amines. Deviation of the predicted and observed values for Tg is interpreted in terms of differences between definitions of Tg used by other workers and, also the occurrence of competing side reactions during polymerization which lead to additional crosslinks.
Studies of the morphology of emulsion‐grade polytetrafluoroethylene
Authors: Rahl Forrest J. , Evanco Michael A. , Fredericks Robert J. , Reimschuessel Annemarie C. 
Published: April 2003

AbstractTwo types of emulsion‐grade polytetrafluoroethylene particles have been studied. We refer to these as ribbons and rods. The ribbons consist of very thin ribbons or lamellae folded upon themselves a number of times. In typical emulsion‐grade material prepared at Allied Chemical, the unraveled ribbon measures about 3.25 μ in length, 0.25 μ in width, and 60Å in thickness. The folded ribbons, which form the particles, are about 0.5 μ long and 0.25 μ wide. Electron diffraction shows that the ribbons are single crystals with the chain axis parallel to the long axis of the ribbons thus forming extended chain crystals. This extended‐chain packing is consistent with the observed cleavage or fibrillation of the ribbons and with the molecular weight. The rods are formed in low–yield polymerizations. Electron diffraction also shows that the rods are single crystals with the chain axis parallel to the long axis of the rods. Striations parallel to the long axis are believed to result from stacking of parallel segments. Considerable bending of the long axis of rods is observed.
Surface tension of polymer solutions. IV. Three‐component mixtures
Authors: Gaines George L. 
Published: April 2003

AbstractThe lattice‐theory equations for the surface tensions of polymer solutions based on the parallel‐layer model have been tested for three‐component systems. Surface tensions of solutions of some low molecular weight polyisobutylenes and polydimethylsiloxanes in n‐heptane–tetralin mixtures and solutions of mixtures of the polymers in these solvents were measured at room temperature. The results are in good agreement with the theoretical calculations.
Four‐center type photopolymerization in the crystalline state. V. X‐ray crystallographic study of the polymerization of 2,5‐distyrylpyrazine
Authors: Nakanishi Hachiro , Hasegawa Masaki , Sasada Yoshio 
Published: April 2003

AbstractChanges in crystal structure during polymerization and oligomerization of 2,5‐distyrylpyrazine have been investigated by x‐ray crystallography. The polymer and the oligomer as obtained are three‐dimensionally oriented, and the directions of the three axes of the resultant crystals coincide with those of the original crystal. The space group of the products also agrees with that of the monomer. It is concluded that the polymer and the oligomer crystals approximately duplicate the molecular arrangement in the monomer crystal. The polymerization mechanism is discussed on the basis of the crystal structures.
Low‐angle x‐ray scattering from crazes and fracture surfaces in polystyrene
Authors: LeGrand D. G. , Kambour R. P. , Haaf W. R. 
Published: April 2003

AbstractBoth crazes and fracture surfaces in glassy polymers produce a low‐angle scattering of x‐rays. Scattering patterns are anisotropic and often show considerable streaking. In the one case (polystyrene) studied extensively so far, detalied analysis suggests that the craze is approximated as a collection of spheroidal or irregular‐shaped voids surrounded by material with anisotropic density distribution arising from its orientation in the stress direction. The void dimension is about 90–115 Å and the specific internal surface area about 170 m2/cm3 of craze. These results and those from electron microscopic studies are reasonably consistent.
High‐temperature annealing of drawn nylon 66 fibers
Authors: Statton W. O. 
Published: April 2003

AbstractThe structure and morphology of highly oriented fibers were modified by thermal treatments at varying tensions. The structural changes were characterized by wide‐ and small‐angle x‐ray diffraction, broadline nuclear magnetic resonance, and electron microscopy of surface replicas. Increasing temperatures caused increases in local ordering, number of regular chain folds, mobile fraction or amount of fluidlike mobility, and surface recrystallization in localized areas. Each of these changes was also a function of the amount of tension on the fiber during the annealing; each change was maximized when the fiber was free to shrink but minimized when the fiber was stretched.
Crystallinity in poly‐N‐methyllaurolactam and copolymers
Authors: Shalaby S. W. , Fredericks Robert J. , Pearce Eli M. 
Published: April 2003

AbstractFully methylated nylon 12 was prepared by the hydrolytic polymerization of N‐methyllaurolactam. The polymer, with about 20% crystallinity, has a crystal structure different from that of nylon 12. The X‐ray diffraction patterns of copolymers of N‐methyllaurolactam and laurolactam were shown to be composition‐dependent. Copolymers containing up to 15% laurolactam units exhibited a crystal structure essentially the same as poly‐N‐methyllaurolactam. Copolymers containing from 20 to 50% laurolactam are transition structures, whereas copolymers containing more than 50% laurolactam units exhibit a crystal structure characteristic of polylaurolactam. DSC data on the homopolymers and copolymers are also reported.
Transitions and relaxations in poly(1,4‐phenylene ether)
Authors: Wrasidlo Wolfgang 
Published: April 2003

AbstractTransitions and relaxation phenomena in poly(1,4‐phenylene ether) were studied over temperature range from 100 to 800°K by applying a combination of calorimetric, dilatometric, dynamic mechanical, and dielectric techniques. Amorphous polymer, exhibiting no x‐ray crystallinity, is obtained only by quenching molten samples at extremely fast cooling rates (ca. 1000°C/sec) and by minimizing thermal gradients within specimens. A weakly active mechanical relaxation region with a loss maximum at 155°K of unknown origin was observed. The glass transition interval of completely amorphous polymer is characterized by a discontinuous jump in heat capacity of 2.76 cal/deg per chain segment occurring at 363°K (corrected for kinetic effects), and a fourfold increase in the coefficient of linear thermal expansion. Strongly active, dynamic mechanical relaxations occur in the Tg interval with a loss maximum at 371°K (f = 110 cps) and resulting in a drop in the dynamic storage modulus from 1011 to 109 dyne/cm2. Cold crystallization takes place just above Tg, to yield a polymer with an x‐ray crystallinity of 0.7 and a heat of crystallization of 270 cal/mole. The crystalline polymer shows a complex melt structure. Depending upon the thermal history, multiple endothermic peaks indicative of structural reorganizations occur just prior to fusion. Very high dielectric losses with a wide distribution of relaxation times were observed in the melt interval. The mechanical relaxation spectrum in this region is typical of viscous flow behavior.