bluuebunny/crossref_metadata_2025_split huggingface dataset:
A study of thermodynamic behavior of polystyrene solutions in benzene at moderate concentrations by sedimentation equilibrium
Authors: Chu Sung Gun , Munk Petr 
Published: April 2003

AbstractThe method of sedimentation equilibrium was used to obtain values of the thermodynamic interaction coefficient χ as a function of concentration. Five samples of polystyrene with molecular weights ranging from 36,000 to 1,750,000 were studied in benzene over the concentration range up to the volume fraction equal to 0.03. The experimental data were used to test the theory of Koningsveld et al. (Macromolecules, 7, 73, 1974). This theory predicts that the interaction term in the free enthalpy of mixing may be split into one term common for all molecular weights and another term, which depends on molecular weight and vanishes exponentially at high concentrations. It is concluded that the functional form proposed by the theory gives a fair description of experimental data. However, the phenomenological coefficients obtained from the experiment differ significantly from the values predicted by the theory.
Influence of pressure and chemical structure on the thermal conductivity of vitreous poly(alkyl methacrylates). I
Authors: Barker R. E. , Chen R. Y. S. , Frost R. S. 
Published: April 2003

AbstractThe influence of pressure on the thermal conductivity K of four vitreous poly(alkly methacrylate) polymers has been measured by steady state techniques. The measurements were made under pressures up to 2 kbar and over a temperature range between 173 and 300°K. For each member of the homologous series, K was found to increase with applied pressure. Shifts in thermal conductivity transition temperatures (attributed to glass transition phenomena) of 25, 26, and 16°C per kbar of applied pressure were observed for poly(methyl methacrylate), poly(ethyl methacrylate), and poly(n‐isobutyl methacrylate).
Flow‐induced crystallization of poly(ethylene terephthalate) melts in a capillary die: Formation and properties of the crystalline toroid
Authors: Griswold Phillip D. , Cuculo John A. 
Published: April 2003

AbstractAn unusual crystalline aggregate, which is toroidal in shape, has been formed at the entrance region to capillary dies during the high‐pressure extrusion of poly(ethylene terephthalate) melts in an Instron capillary rheometer. The toroidal remnant was discovered in capillary dies removed from the rheometer after the occurrence of oscillating flow. Detailed observations of the rheological factors involved in the formation of the crystalline toroid were made. Examination of recovered entrance plugs disclosed that the crystalline toroid was a hard, stagnant zone which throttled the bulk flow of polymer melt into the capillary during the extrusion experiments. Hot‐stage optical microscopy, differential scanning calorimetry, and wide‐angle x‐ray techniques were used to initiate a structural study of the crystalline toroid. The toroid contained clusters of fibrous crystals which persisted to high temperatures. The fibrous clusters were randomly oriented in a matrix polymer which melted normally. Based upon the rheological and structural evidence, a mechanism of crystalline toroid formation is proposed.
Solid‐state relaxations in poly(ethylene oxide). II. Study using the spin‐labeling technique
Authors: Lang M. C. , Noël C. , Legrand A. P. 
Published: April 2003

AbstractPoly(ethylene oxide) (PEO) was spin‐labeled with 3‐chlorocarbonyl‐2,2,5,5‐tetramethylpyrroline‐1‐oxyl. Correlation times were calculated from 173 to 375°K. For estimating slow‐motion rotational correlation times three models were used: Brownian diffusion, “moderate jump” diffusion, and “large jump” diffusion. Analysis of the changes in the extrema separation and spectra shape with temperature strongly suggests the presence of β and γ processes in solid poly(ethylene oxide). The Brownian diffusion model gives, for the γ relaxation, an activation energy of 8 kcal mole−1 which is in good agreement with that found using dielectric relaxation measurements.
Polarized Raman scattering of concentrated solutions of poly(dimethyl siloxane) in benzene
Authors: Thornley P. W. , Shepherd I. W. 
Published: April 2003

AbstractRaman depolarization (ρ) measurements have been made over the temperature range 20 > T > 60°C for solutions of poly(dimethyl siloxane) (mol wt 7.7 × 104 and 2.0 × 104) for several concentrations up to 100%. The band studied was the highly polarized methyl stretch at 2907 cm−1. Computer calculations of the probability pt of a rotational isomer being trans allow the ρ values to be related to ΔG, the free energy of mixing. ΔG is plotted as a function of concentration and minima are observed at 60 ± 3% (mol wt = 7.7 × 104) and 70 ± 3% (mol wt = 2 × 104).
Properties of polyethylene modified with phosphonate side groups. I. Thermal and mechanical properties
Authors: Weiss R. A. , Lenz R. W. , MacKnight W. J. 
Published: April 2003

AbstractLow‐density polyethylene was modified by the inclusion of phosphonate ester pendent groups by using an oxidative chlorophosphonylation reaction followed by esterification of the polyethylene poly(phosphonyl chloride) with an alcohol. Two different types of phosphonate esters were prepared: dimethyl phosphonate from the reaction with methanol and a phosphonate graft copolymer from the reaction with hydroxy‐terminated poly(ethylene oxide) (PEO). For the latter, oligomers with molecular weights of 350 and 750 were used. For each type of phosphonate, a series of polymers were prepared with pendent group concentrations ranging from 0 to 9.1 substituents per 100 carbon atoms. The modified polymers were characterized by infrared spectroscopy, differential scanning calorimetry, and by measurement of the tensile modulus. Infrared spectroscopy proved to be useful for determining if the polymer modification reaction resulted in entirely phosphonate ester pendent group substitutions or if unesterified phosphonic acid groups were also present. The polymers prepared in this investigation exhibited no infrared absorbances arising from phosphonic acid groups. The presence of phosphonate ester groups resulted in a decrease of crystallinity with increasing phosphonate concentration and with the exception of the polymers containing 9.1 PEO–phosphonate grafts per 100 carbon atoms, the effect of phosphonylation on the melting temperature of the polymers was consistent with Flory's theory for the melting point depression of random copolymers. The tensile modulus measured from a constant uniaxial elongation experiment decreased with increasing phosphonylation. The behavior of all three phosphonate series was identical and could be attributed to the effect of decreasing polymer crystallinity.
Dynamics of chain molecules. Intramolecular diffusion controlled reactions for a pair of terminal reactive groups
Authors: Perico Angelo , Cuniberti Carla 
Published: April 2003

AbstractThe first order intramolecular rate constant for the reaction between the terminal groups of flexible macromolecules is calculated in the partial draining case, following the theory formulated by Wilemski and Fixman for diffusion controlled reactions. Substantial differences with respect to the nondraining and free‐draining limits are evidenced, and it is shown that the rate constant in the partial‐draining case has relevant contributions from all the modes of the bead‐spring chain. The effects of chain flexibility and hydrodynamic interaction in macromolecules of increasing molecular weight are examined. The effective diffusion constant of the end groups increases with both the flexibility and the length of the chain. Numerical results for polystyrene (PS) and polydimethylsiloxane (PDMS) are presented and employed to calculate the relative quantum yield for fluorescence quenching. For highly flexible chains, like PDMS, quenching effects are expected in a range of molecular weight well above the limit of validity of the bead‐spring model. On the contrary, for more rigid polymers, like PS, the quenching can be observed only at molecular weights lower than this limit. The calculated behavior is compared with some experimental results recently obtained by the authors.
Solution grown isotactic polystyrene crystals. II. Kinetics of thermal changes by x‐ray diffraction
Authors: Overbergh N. , Sadler D. M. , Keller A. 
Published: April 2003

AbstractThe present paper is a study of the annealing, melting, and recrystallization behavior of solution grown isotactic polystyrene crystals in order to elucidate changes both in total lamellar thickness and in the thickness of the crystalline “core” as a function of temperature. The lamellar thickness was obtained from x‐ray long spacings and the core thickness from the broadening of appropriate reflections, both assessed by a high sensitivity x‐ray detector system able to produce records within a few minutes during time dependent processes. The x‐ray results were correlated with differential scanning calorimetry (DSC) measurements. On heating, first the usual annealing effects with little net melting were observed, but on increasing the temperature large changes in long spacing, which were reversible with temperature, were seen accompanied by only small changes in crystal core thickness. The second effect was found to be associated with a substantial degree of melting. Even after heating above the temperature where complete melting was indicated by DSC, the recrystallization rate was found to decrease as the melt temperature was increased and to be much faster than on cooling from the usual melts. Strikingly, this recrystallization was accompanied by a decrease in long period with time even under isothermal conditions. It is inferred that the memory of the preceding crystalline stack is preserved throughout the melting range and even beyond this, far into the molten state. This “seeding” effect is intrinsic to the polymer even if its nature cannot be specified. The principal effects in question can then be explained by envisaging that randomly placed lamellas gradually disappear within the stack on melting and successively reappear on crystallization during cooling. These ideas agree well with previous work on reversible long spacing changes in polyethylene (see ref. 9) and are likely to be of wider generality for melting and recrystallization phenomena in systems having stacked lamellar morphologies.
The effect of thermal stress on the thermal expansion coefficient and glass transition temperature of glass fiber–polymer composites
Authors: Kajiyama T. , Yoshinaga T. , Takayanagi M. 
Published: April 2003

AbstractThe thermal expansion coefficients of glass fiber–polymer composites were calculated applying the solid cylindrical model taking into account the interaction effects among the glass fibers. The stress and displacement in the composite model were determined as functions of the thermal stress. It was found theoretically that the deviation of the thermal expansion coefficient from the linear mixture relationship based on volume additivity appeared at around Tg + 20 K upon cooling. The thermal expansion coefficient of the composite was also found to be markedly dependent on the dispersion state of the glass fibers. An expression for the difference in the Tg of the matrix resin in the composite from that in the unloaded resin was obtained on the assumption that the volume change of the matrix resin caused by mixing was compensated by free volume expansion. The experimental results obtained by differential scanning calorimetry (DSC) measurements were found to agree well with the theoretically predicted ones.
Small‐angle light scattering from thin polymer films: Multiple scattering from samples with rodlike morphology
Authors: Lévesque Denis , Prud'homme Robert E. 
Published: April 2003

AbstractHartel's theory for multiple scattering has been generalized to the case of small‐angle light scattering (SALS) by polymers having a roadlike morphology. It is shown that multiple scattering tends to make the scattering tends to make the scattering patterns more diffuse and leads to an underestimation of the size of the units (rods) measured from such patterns. The error induced by neglecting multiple scattering has been estimated at 10% for a transmittance of 75% and at 22% for a transmittance of 50%. A correction method based on Hartel's procedure is suggested.
Crystallization of polydioxolan. II. Morphology and melting properties
Authors: Prud'homme Robert E. 
Published: April 2003

AbstractPolydioxolan samples crystallized between 25 and 35°C present two optical phases when viewed on the polarizing microscope. These phases, termed central and external phases, form a spherulite. It is shown in this paper that the central phase of the two‐phase spherulite melts at about 63°C, and is made of modification III crystals. The external portion of the two‐phase spherulites melts at a lower temperature, around 59°C, and is composed of modification II crystals. Differential scanning calorimeter (DSC) melting curves, photomicrographs, and x‐ray results are presented to prove these assertions.
Influence of chemical modification (bromination) on structure and charge transport in poly(N‐vinylcarbazole)
Authors: Griffiths C. H. , Okumura K. , Van Laeken A. 
Published: April 2003

AbstractBromine has been randomly substituted in the 3 or 6 position of the pendant carbazole group of poly(N‐vinylcarbazole) using N‐bromosuccinimide in chlorobenzene solution. X‐ray diffraction indicated that this substitution interferes with the interchain interactions in the amorphous polymer eliminating the unusual degree of chain parallelism and destroying the ability to crystallize. Charge carrier photogeneration and mobility measurements show that holes are still the majority carrier in the bromine‐substituted polymer but both generation and mobility are substantially reduced compared to the unsubstituted polymer. It has not been possible to separate the influence of pendant group electronic structure from that of bulk chain conformation in this modification of the polymer photoconductive properties.
Mechanical behavior of a highly oriented polyethylene rod
Authors: Crissman John M. , Zapas Louis J. 
Published: April 2003

AbstractDynamic mechanical and single step stress relaxation data are presented for a highly oriented linear polyethylene rod as produced by a high pressure extrusion technique. The results indicate that both major relaxation processes normally observed in unoriented polyethylene are virtually absent in torsion, whereas they are present in flexure. Stress relaxation in torsion data show a very highly nonlinear behavior when compared to similar data for an unoriented polyethylene rod.
Crystallization and melting of the system isotactic polystyrene + poly(2,6‐dimethyl phenylene oxide)
Authors: Berghmans H. , Overbergh N. 
Published: April 2003

AbstractFrom glass transition Tg measurements on isotactic polystyrene (IPS)–poly(2,6‐dimethyl phenylene oxide) (PPO) blends, it was concluded that thoroughly annealed, freeze‐dried samples, or samples evaporated from solution at high temperature, are homogeneous. Without annealing, the freeze‐dried blends show two to three Tg's characteristic of the presence of different phases. The overall crystallization rate of these samples is much higher than that observed with annealed samples. The presence of dissolved PPO in annealed samples reduces the overall crystallization rate and the spherulitic growth rate, compared to IPS. The melting behavior of the blends is influenced by the extent of mixing of both polymers. Without annealing, isothermally crystallized, freeze‐dried blends show the same melting behavior as IPS (i.e., multiple melting). In homogeneous annealed samples the rate of reorganization is strongly reduced and multiple melting only occurs at low scanning rate (e.g., 1°C/min). This behavior is influenced by the crystallization temperature and by the composition of the blends. The addition of PPO has no influence on the relation between melting point and crystallization temperature and the same equilibrium melting point is found by extrapolation.
Longitudinal acoustic mode in polymers. II. Solution of the general composite perturbed elastic rod
Authors: Hsu S. L. , Ford G. W. , Krimm S. 
Published: April 2003

AbstractThe theory of the longitudinal vibrations of a composite rod with perturbing forces at the ends has been generalized by the inclusion of inertial effects at the ends of the rod. The frequencies have been calculated for both symmetric and asymmetric forces and masses. The problem of coupled rods has also been treated, and its relation to the isolated rod is shown. These results should be applicable to the study of longitudinal acoustic modes in long chain molecular systems.
Viscoelastic properties of entangled polymers. II. The interchain–intrachain entanglement model
Authors: Hong S. D. , Hansen D. R. , Williams M. C. , Shen M. 
Published: April 2003

AbstractOur earlier model of entangled chain dynamics represented the elastic effects at entanglement points as a coupling with the surrounding medium, which was propagated weakly to every other entanglement site on the parent chain. In this way, a great variety of linear viscoelastic phenomena could be successfully predicted, with the only significant deficiency being a quantitative failure in curve fitting the local minimum in dynamic loss modulus G″(ω). Here we introduce the “intrachain entanglement,” or the “internal entanglement,” in which the parent chain entangles directly with itself. Elastic forces between pairs of internal entanglements are assumed to be stronger than those with the medium (“external entanglement”). Predictions of the new model are compared with rheological data on monodisperse polystyrene. Good agreement is obtained between theory and experiment, including G″(ω).
Spectroscopic examination of chain conformation and bonding in poly(phenylene oxide)–polystyrene blends
Authors: Wellinghoff S. T. , Koenig J. L. , Baer E. 
Published: April 2003

AbstractUltraviolet and Fourier‐transform infrared spectroscopy are used to characterize the chain conformation of 2,6‐dimethyl poly(phenylene oxide) (2MPPO) in compatible 2MPPO‐polystyrene (PS) blends. Blending with PS increases the intramolecular energy of the 2MPPO. Atactic PS induces a greater distortion from the minimum energy conformation of 2MPPO than isotactic PS. The dispersion interaction between the phenyl ring of PS and the phenylene ring of 2MPPO is found to be quite strong. These large intermolecular forces are thought to supercede the increase in 2MPPO conformational energy and to be responsible for the blend compatibility.
Diffusion of long molecules through solid polyethylene. I. Topological constraints
Authors: Klein J. 
Published: April 2003

AbstractIt is proposed that the mobility of sufficiently long molecules undergoing translational diffusion through solid polyethylene is significantly reduced by tie molecules and fixed entanglements within the interlamellar regions of the matrix. The effect on the diffusion coefficient both of diffusant molecular length and of the host matrix morphology is considered, and a semiquantitative relation between them obtained. This indicates that the mobility of long diffusants is higher in polyethylene which has been cooled slowly from the melt than it is in quenched polyethylene, in marked contrast to the behavior of gaseous and other small diffusants.
Diffusion of long molecules through solid polyethylene. II. Measurements and results
Authors: Klein J. , Briscoe B. J. 
Published: April 2003

AbstractThe diffusion coefficient for two diffusants of the type n‐(CH2)NX is measured, where N ≃ 25, 45 and X is a suitable label; the matrix is linear polyethylene cooled at two widely differing rates from the melt. The measuring technique used is a recently developed one based on infrared microdensitometry. The results indicate that these diffusants diffuse faster in the slowly cooled matrix, in marked contrast to the behavior of gaseous diffusants. They are in agreement with the predictions of the model developed in a previous paper (part I), in which the constraints imposed by interlamellar tie molecules on long diffusants were shown to be important.
On the interrelation between microstructure and physicochemical properties of some polyconjugate systems
Authors: Grigorovskaya V. A. , Basin V. E. , Khakimova D. K. , Lyubchenko L. S. , Cherepanova E. S. , Berlin A. A. 
Published: April 2003

AbstractSoluble oligoarylenes based on naphthalene and anthracene, and fractions of different molecular weights have been studied by electron microscopy. For the examined samples, a definite interrelation is ascertained between microstructure and physicochemical properties, such as density, x‐ray parameters, heat of solution, electron paramagnetic resonance (EPR) spectra, and dark conductivity. The molecular‐weight distribution of oligoarylenes is shown to decisively influence the degree of packing of macromolecules and their physicochemical properties. This allows interpretation of some anomalous properties of oligoarylenes in comparison with the first members of the corresponding homologous series.
Infrared dichroism of glassy polycarbonate at small strains
Authors: Jansson J‐F. , Yannas I. V. 
Published: April 2003

AbstractThe dichroism of the 889, 1364, and 3063 cm−1 infrared absorption bands of glassy, amorphous polycarbonate has been measured as a function of the strain in the range 0 to 2% at 23°C. The data obtained for these three bands superpose rather well over this strain range. Negligible dichroism is observed up to about 0.6% strain; above this level, the dichroic ratio increases in an approximately linear manner. Independent mechanical data, obtained under comparable conditions of time‐scale and temperature, are cited which show that a transition from approximately linear to marked non‐linear viscoelastic behavior occurs with glassy polycarbonate in the range 0.7 to 1.0% strain. The coincidence on the strain axis of a relatively abrupt increase in optical absorption anisotropy with a distinct change in Young's modulus is discussed in terms of a recent molecular theory of deformation of glassy polymers. It is suggested that the data are consistent with the view that the transition from linear to nonlinear viscoelastic behavior in glassy polycarbonate is marked by the onset of significant rotation around backbone bonds.
Extensional flow‐induced crystallization in polyethylene melt spinning
Authors: Nadkarni V. M. , Schultz J. M. 
Published: April 2003

AbstractPolyethylene was spun into a heated chamber, with the spin‐line temperature controlled in the range of 90–120°C. Within narrow limits, the stretch rate of the fiber was also controlled. Spin‐line and crystallization onset conditions were characterized. Characteristics of fibers as‐spun were measured via wide‐angle x‐ray scattering (WAXS), density, scanning electron microscopy, and differential scanning calorimetry. Spin‐line data indicate that elongational flow enhances crystallization rate and that time under spin‐line conditions is an important parameter. Analysis of WAXS data shows a typical “b‐axis radial” orientation, the details of which change with spin‐line parameters. This orientation is consistent with growth of lamellar crystals on extended‐chain fibrils (shishkebab model). Other physical data are also consistent with this microstructure. Microcamera x‐ray patterns show a similarity of microstructure generation in spinning and drawing.
Supramolecular structure of a high‐modulus polyaromatic fiber (Kevlar 49)
Authors: Dobb M. G. , Johnson D. J. , Saville B. P. 
Published: April 2003

AbstractThe supramolecular organization of the aromatic polyamide fiber Kevlar 49 has been studied using a combination of electron diffraction and electron microscope dark‐field image techniques. The dark‐field images derived using selected reflections from longitudinal sections exhibit axial banding of two main types having periodicities of 500 and 250 nm. Careful analysis, including tilting experiments, conclusively shows that the supramolecular architecture of these fibers consists of a system of sheets regularly pleated along their long axes and arranged radially.