bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crystallization of poly(vinylidene fluoride): Equilibrium melting point and heat of fusion of the α‐polymorph
Authors: Welch Gordon J. , Miller Robert L. 
Published: April 2003

AbstractSamples of poly(vinylidene fluoride) were crystallized either (a) isothermally at a series of temperatures, or (b) in the presence of varying amounts of diluent (dimethylphthalate or dimethylacetamide). The α‐polymorph was the only crystalline form present in these samples. Melting points of the first series (a) were determined by DSC and of the second (b) by dilatometry. The same equilibrium melting point for the α‐polymorph (178°C) was obtained from analysis of the two sets of data. A value of 1425 cal mole−1 (5.96 kJ mole−1) for the heat of fusion of this polymorph was obtained from analysis of the polymer–diluent melting data. The heat of fusion and the entropy of fusion calculated therefrom correlated well with corresponding values for other fluoroethylene polymers. Thus, the equilibrium melting point and the heat of fusion could be predicted for a fluoropolymer for which data have not yet been reported–poly(trifluoroethylene). The melting point predicted, 222°C, agreed remarkably well with that determined here for an experimental sample, thereby lending support to the empirical correlations. The heat of fusion of poly(trifluoroethylene) is, therefore, expected to be approximately 1300 cal mole−1.
Ionic transport in a sulfonated polystyrene–polyethylene copolymer
Authors: Crowley John L. , Wallace Richard A. , Bube Richard H. 
Published: April 2003

AbstractThe conductivity of a grafted copolymer composed of 21% sulfonated polystyrene and 79% polyethylene has been investigated as a function of temperature and absorbed moisture for membranes containing the monovalent counterions H+, Li+, Na+, K+, Rb+, Cs, and Ag+. The mobility of Ag+ was measured directly in an experiment analogous to that used for the mobility of F‐centers in alkali halides. The mobility and density of free counterions depend on the amount of absorbed water, but only the mobility and not the density of free counterions is a thermally activated process. Current is carried by both intrinsic counterions and, in samples containing absorbed water with greater than 1.5 V applied, by protonic carriers created when the absorbed water is electrolyzed. Thermal depolarization studies indicate that persistent polarization observed is the result of homogeneous volume polarization, due to the orientation of sulfonic acid side groups.
High resolution 1H‐NMR relaxation study of polyisobutylene in solution
Authors: Spěváček J. , Schneider B. 
Published: April 2003

AbstractFrom the temperature dependence of integrated intensities and from line widths in high‐resolution 1H‐NMR spectra, the relaxation times T1 and T2 of protons in CH2 and CH3 groups of polyisobutylene in CCl4 solution have been determined. Although the relaxation time T1 of methylene protons is determined mainly by intragroup interactions, intergroup interactions of two methyl groups from each two consecutive monomer units were found to contribute considerably to T1 of methyl protons. The Structure and mobility of polyisobutylene (PIB) molecules in solution is discussed on the basis of the relaxation time data.
Theory of epitaxial crystallization of S2N2 and (SN)x on alkali halide substrates
Authors: Mauritz K. A. , Hopfinger A. J. 
Published: April 2003

AbstractAn initial series of energy calculations is aimed at predicting the epitactic behavior of S2N2 as deposited from the vapor phase upon NaCl‐type alkali halide substrates and preferred orientation of molecular chains in the (SN)x polymerized phase. Although the preferred orientation of a single S2N2 molecule is identical for NaCl and NaF, the energetics of dimer formation on the surface greatly favor use of the latter substrate as a heterogeneous nucleation catalyst. Enhancement of dimer formation on NaF is due to a near match between S2N2–S2N2 equilibrium distance and substrate unit‐cell spacing. Furthermore, the (SN)x chain‐orientation tendency also appears to be a function of alkali halide type. On NaCl, the chain axis lies along the 〈110〉 surface direction above cationic rows, the plane of interatomic bonds being perpendicular to the surface. For NaF the axial direction is 〈100〉 with alignment between rows of alternating charge, with the molecular plane in this case parallel to the substrate surface. From the calculations it appears that primary Coulombic forces are not a significant factor in dictating the epitactic properties of monomer or polymer.
A theory of the stress‐induced crystallization of crosslinked polymeric networks
Authors: Gaylord R. J. 
Published: April 2003

AbstractA non‐Gaussian theory of the stress‐induced crystallization of polymeric networks is presented. It is predicted that for uniaxial extension of crosslinked polyethylene, a perfectly oriented, extended‐chain crystal is formed initially, changing to one‐fold crystal oriented perpendicular to the stretch direction at low extension and to a two‐fold crystal having nearly perfect orientation at high extension. The stress is predicted to decay initially and then to rise as the network chains switch from an extended‐ to a folded‐chain morphology, the rise being delayed and finally suppressed by additional crosslinking. The final, equilibrium birefringence is calculated and found to be negative at low extension and positive at high extension. The initial rate of crystallization is calculated using irreversible thermodynamics and is found to increase with extension and decrease with increasing crosslinking and temperature. All of the theoretical predictions are in qualitative agreement with experiment.
Poly(styrene sulfonic acid)–poly(vinylidene fluoride) interpolymer ion‐exchange membranes. I. Preparation and characterization
Authors: Gryte Carl C. , Gregor Harry P. 
Published: April 2003

AbstractHighly porous interpolymer ion‐exchange membranes have been prepared from poly(styrene sulfonic acid), PSSA and poly(vinylidene fluoride) PVdF using a casting solvent of dimethylformamide and hexamethylphosphoramide. The membranes have been characterized by their water content, concentration potential, ionic conductivity, and their hydraulic permeability. An estimation of the porosity of the membranes has been made from the relative conductance of the potassium and the tetrabutylammonium ions in the film. This porosity has been compared with that derived from a consideration of the water flux through a Poiseuille‐type pore.
Effect of solvent on depolarized light scattering in dilute polymer solutions
Authors: Fortelny I. 
Published: April 2003

AbstractAn optical model of a system in which both polymer segments and solvent molecules are described as point dipoles has been used to calculate the intensity of light depolarized in scattering. The final expression consists of six terms, the physical meaning of which is briefly discussed. An approximation procedure has been worked out for the calculation of two interaction terms due to deviations of the local field in solution from the Lorentz–Lorenz field; the terms have been calculated for simple models of flexible and rigid molecules. Their dependence on molecular weight appears to be approximately the same as the intrinsic anisotropy of the polymer molecule; their contribution is nonzero even for a solvent isorefractive with the polymer.
Crystallization and melting of polyethylene under high pressure. III. Mixed crystallization of two kinds of extended‐chain crystals
Authors: Maeda Yoji , Kanetsuna Hisaaki 
Published: April 2003

AbstractThermal behaviors of extended‐chain crystals of polyethylene formed during various crystallization processes and conditions under about 5000kg/cm2 were studied by high‐pressure dilatometry and differential scanning calorimetry. The experiments indicate that by isothermal crystallization at small undercoolings for prolonged periods, the products show two endothermic peaks in the melting region of the usual extended‐chain crystals. This means of the presence of a bimodal lamellar thickness distribution in the extended‐chain crystals. A phase diagram has been made for pressures up to 5000 kg/cm2. The experimental results confirm the existence of two kinds of extended‐chain crystals, i.e., ordinary extended‐chain and highly extended‐chain crystals, as suggested previously by the authors.
On the modulus of particulate‐filled composites: Application of van der Poel's equation
Authors: Dickie Ray A. 
Published: April 2003

AbstractApplication of the van der Poel equation (as recently corrected and simplified by Smith) to modulus‐composition data on polymer composites is discussed. The van der Poel equation is in good agreement with experimental results on systems for which the ratio of filler to matrix modulus is either much less than or, if the filler particles are large enough, much greater than unity. For these systems, it is shown that the van der Poel equation is essentially equivalent to an empirically modified form of the Kerner equation. Discrepancies between the van der Poel equation and experimental modulus values for the remaining systems are analyzed in terms of an effective volume fraction veff. A functional form for veff found to be in agreement with experimental results on several systems is: veff = vf + k′(vf/d)2/3 where vf is filler volume fraction, d is filler particle size, and k′ is an empirical parameter. For the systems studied, k′ ranges between 0.28 and 1 μm2/3.
Craze initiation of glassy polymers under the action of crazing agent
Authors: Kitagawa M. 
Published: April 2003

AbstractThis paper deals with the formation of crazes that may be caused by an external load on glassy polymers wetted with kerosene. First, the orientation of crazes has been determined when applying a uniaxial tension to a specimen of cold‐rolled polyvinyl chloride sheet at various angles to the rolling direction. The critical stress for craze initiation in poly(methyl methacrylate) and polyvinyl chloride rods has been investigated under combined tension–torsion loading. It is shown that: (1) in an anisotropic, as well as an isotropic polymer, the direction of crazes is perpendicular to that of the maximum strain calculated by taking into account the internal stress due to rolling; and (2) under the action of a crazing agent, crazing may occur even under the pure torsional load, i.e., in the absence of dilatational stress.
Characterization of polystyrene networks by small‐angle neutron scattering
Authors: Benoit H. , Decker D. , Duplessix R. , Picot C. , Rempp P. , Cotton J. P. , Farnoux B. , Jannink G. , Ober R. 
Published: April 2003

AbstractPolystyrene networks prepared by anionic polymerization have been characterized by small‐angle neutron scattering. Two kinds of systems have been examined:(A) networks with labelled branch points allowing characterization of the spatial distribution of crosslinking points; (B) networks containing a low proportion of chains labelled with perdeuterated polystyrene in order to characterize the conformation of individual elastic chains of the polymeric network. The dependence of the results on swelling and uniaxial extension is discussed.
Environmental effects on the mechanical properties of reconstituted collagen hollow fiber membranes
Authors: Viswanadham R. K. , Agrawal Dinesh C. , Kramer Edward J. 
Published: April 2003

AbstractThe lateral swelling, changes in length and tensile stress–strain curve of reconstituted collagen hollow fibers, crosslinked with uv irradiation, were measured as a function of the pH and ionic strength of their aqueous environment. From pH 5 to pH 10 the lateral swelling and length are constant; at lower and higher pH the lateral swelling increases rapidly while the fiber shrinks in length. Corresponding to these changes, a pronounced toe develops in the stress–strain curve and extends to a higher strain in more acid (or basic) media. This toe is attributed to the straightening of a microcrimp in the collagen fibrils; the microcrimp is accentuated by the repulsion between the charged fibrils in acid or basic media. Direct small‐angle x‐ray evidence of these microcrimp structure changes at low pH is presented. Increasing the ionic strength of an acid solution by adding NaCl decreases the lateral swelling, increases the length, and decreases the extent of the toe on the stress–strain curve. These changes result from an increased screening of the charge on neighboring fibrils at higher ionic strengths thus decreasing the repulsion between fibrils and the resulting microcrimp. Although the zigzag elastica model of the crimp developed by Diamant et al. [Proc. Roy. Soc., Ser. B, 180, 293 (1972)] provides a good empirical fit to the stress–strain data, it is shown to be inappropriate where the crimp results from repulsive forces between fibrils. A new model taking these forces into account is developed and is shown to be in reasonable agreement with the experimental results.
Effects of diluent on molecular motion and glass transitions in polymers. II. The system polyvinylchloride–tetrahydrofuran
Authors: Adachi Keiichiro , Ishida Yoichi 
Published: April 2003

AbstractDielectric measurements, differential thermal analyses, and density measurements are reported on concentrated solutions of polyvinylchloride in tetrahydrofuran. The relaxation processes observed between 80 and 400°K have been classified into four types. From the analysis of experimental data, the primary process at the highest temperature and the process at the lowest temperature are assigned, respectively, to segmental motion of the polymer and motion of the solvent. Activation plots for the primary process conform to the Vogel–Tamman equation. The dielectric glass‐transition temperature T'g (defined as the temperature at which the dielectric relaxation time is 100 sec) determined with this equation agrees well with the glass‐transition temperature Tg from thermal analysis. Therefore, Tg can be represented by an expression of the form

The parameters of the Vogel–Tamman equation A and B are nearly independent of concentration, whereas To depends strongly on concentration. The dipole moment per monomeric unit calculated from the experimental data changes with concentration and exhibits steep increments around 30% and 90% by weight. The width of the distribution of the relaxation time also increases with the concentration. The results were compared with those for the system polystyrene–toluene studies in the same way.
Dipole moments of poly(ethylene oxide) and poly(hexamethylene oxide) chains
Authors: Riande E. 
Published: April 2003

AbstractThe mean‐square dipole moments of poly(ethylene oxide) and poly(hexamethylene oxide) chains have been determined from dielectric constant measurements on dilute solutions of the polymers in benzene. The values obtained are in good agreement with those predccted using the rotational isomeric state models for these chains. In addition, the unperturbed dimensions of poly(hexamethylene oxide) have been calculated as a function of molecular weight, using the isomeric state theory.
Mechanical relaxations in some ionene polymers. II. Influence of counterions and absorbed water
Authors: Tsutsui Tetsuo , Tanaka Ryuichi , Tanaka Takehide 
Published: April 2003

AbstractSix 6,10‐ionenes with different counterions were prepared by ion exchange reactions in aqueous solutions. The counterions were Br, I, CIO4, BF4, SCN, and B(C6H5)4. The dynamic mechanical properties of these polymers were investigated by use of a torsional braid analyser. Three relaxations α (25–140°C), β (−30–0°C), and γ (−140–120°C) were observed at the frequencies of 0.3–0.8 Hz. The temperature of the α and β relaxations were largely dependent on the size of counterions, but those of the γ relaxations had little variation. The effects of electrostatic forces in the polymers on each relaxation was discussed. The influence of absorbed water on the α, β, and γ relaxations was examined. The absorbed water in the polymers greatly depressed the temperature of the α relaxations and this phenomenon was interpreted to be the result of the specific hydration on ionic portions.
Rapid small‐angle and wide‐angle x‐ray studies of crystallization behavior in polymers
Authors: Schultz J. M. 
Published: April 2003

AbstractSmall‐angle and wide‐angle x‐ray scattering measurements, using a position‐sensitive detector, were made during melt‐crystallization of linear polyethylenes and PEO–PS–PEO triblock copolymer. The scattering measurements indicated that the triblock copolymer grew by the enlargement of regions in which lamellae are regularly stacked. During primary crystallization at higher temperatures similar behavior is observed in two linear polyethylenes. At lower temperatures, changes in the shape of small‐angle scattering curves during the primary stage of crystallization indicate that amorphous gaps within the lamellar stacking become filled in. During secondary crystallization at higher temperatures new crystallites appear to grow between those formed in the primary stage. Concurrent decrease of the overall scattered intensity leads to the conclusion that secondary crystallization has two components: crystallization of new lamellae behind the spherulite growth front and the thickening of existing lamellae.
The effects of cyclic loading on polymers in a glassy state
Authors: Bouda V. , Zilvar V. , Staverman A. J. 
Published: April 2003

AbstractThe effects of cyclic loading on several physical properties of some polymers have been investigated. The results indicate that internal damping, shear modulus, heat capacity, and density of poly(methyl methacrylate) and alkali‐polymerized polyamide 6 in the glassy state undergo changes during cyclic loading well before the appearance of crazes. It is suggested that cyclic loading induces a nonuniform volume contraction in the structure of the material.
Photon correlation spectroscopy of crosslinked polystyrene networks in the swollen state: Influence of macromolecular polydispersity
Authors: Munch J. P. , Candau S. , Hild G. 
Published: April 2003

AbstractWe report measurements of the correlation function of light scattered from thermally excited longitudinal fluctuations in crosslinked polystyrene networks at equilibrium. In order to investigate the influence of the polydispersity of linear chain elements between successive branch points, we synthesized a network by means of anionic block copolymerization, using a mixture of two “precursor” polystyrenes of different molecular weights to initiate polymerization of a small amount of divinyl‐benzene (DVB). The correlation function for fluctuations having a wave vector K, has the form of an exponential decay, exp (−Γ). The decay rate is given by Γ = D′K2, where D′ represents the diffusion constant of longitudinal modes of the network. We also present measurements of the correlation function of light scattered from gels prepared by anionic block copolymerization of styrene and DVB with only one “precursor” polystyrene and by a free‐radical process. In the latter case, the gels should have a wide distribution of linear chain lengths between branch points.
Processing of semicrystalline polymers by high‐stress extrusion
Authors: Kolbeck A. G. , Uhlmann D. R. 
Published: April 2003

AbstractA study has been conducted on the solid‐state extrusion of three semicrystalline polymers:poly‐propylene (PP), poly(vinylidene fluoride) (PVDF), and high‐density polyethylene (HDPE). HDPE has been extruded in continuous lengths with area reductions up to 25× at temperatures substantially below the melting region. Such extrusion has been identified as a solid‐state process, since measurements of the temperature of the polymer during extrusion indicate the absence of significant heating due to deformation. In contrast, continuous lengths of PP and PVDF could not be obtained substantially below their melting temperatures, indicating that crystallization during extrusion is an important process for these polymers. Under severe extrusion conditions (low temperatures, high area reductions. etc.), all three polymers failed within the tapered region of the extrusion die. Two modes of failure have been identified, brittle fracture and, surprisingly, necking. Grid‐line distortion patterns and a highly simplified upper‐bound plasticity analysis both indicate that shear deformations are a major factor during high‐stress extrusion.
Dielectric loss of polyethylene below 4.2°K arising from proton tunneling
Authors: Yano Okimichi , Saiki Koichiro , Tarucha Seigo , Wada Yasaku 
Published: April 2003

AbstractThe dielectric loss of high‐density polyethylene (HDPE: melt‐crystallized films and single‐crystal mats), low‐density polyethylene (LDPE), and copolymers of ethylene and vinyl alcohol (PEVA) was measured at 1.5 to 4.2°K in the frequency range from 10 Hz to 10 kHz. Results for HDPE show dispersion curves almost corresponding to a single relaxation and are interpreted in terms of phonon‐assisted tunneling of the protons of hydroxyl groups which are accidentally attached to tertiary carbons (carbons with a short branch). Dispersion curves for LDPE and PEVA are quite broad, indicating a wide distribution of relaxation times. The loss level of PEVA passes through a maximum at 7.5% vinyl alcohol, suggesting that interaction between a couple of neighboring hydroxyl groups depresses the loss. A potential calculation for the rotation of a hydroxyl group in the orthorhombic lattice of polyethylene yielded a double‐minimum potential for the tunneling when the lattice is assumed to have a distortion which is acceptable from x‐ray analysis. The potential quantitatively explains the observed values of relaxation time and relaxation strength of HDPE. The concentration of hydroxyl groups in HDPE, which varies among the samples, is estimated to be of the order of 1016 cm−3.
On‐line viscometry combined with gel permeation chromatography. II. Application to branched polymers
Authors: Park Won S. , Graessley William W. 
Published: April 2003

AbstractGel permeation chromatography (GPC) combined with on‐line flow time measurements have been applied to the analysis of branching in polymers. Three sets of branched polymers were examined: polybutadienes lightly crosslinked by high energy radiation, a styrene‐divinyl benzene copolymer and several of its fractions, and polyvinyl acetates branched by polymer transfer reactions during polymerization. The reduction in intrinsic viscosity due to branching was determined for each GPC fraction of the polybutadiene samples. The branching frequency in these fractions was known from other information, so the results were used to establish a relationship between viscosity ratio G and the theoretical size ratio g. This relationship was then used to calculate the distribution of branching and Mw in the styrene copolymers and the polyvinyl acetates. The results were compared with independent information on these polymers. The agreement was generally good.
Raman depolarization measurements over the entire miscible range for polystyrene–cyclohexane and polydimethylsiloxane–benzene solutions: Determination of upper theta temperatures
Authors: Thornley P. W. , Shepherd I. W. 
Published: April 2003

AbstractRaman depolarization ratio measurements (ρ) have been made for 20% polydimethylsiloxane (PDMS) solutions in benzene and 10% Polystyrene (PS) solutions in cyclohexane over the temperature range 20 > T > 200°C. The bands studied were the 2907 cm−1 methyl stretch in PDMS and the 1002 cm−1 ring breathing mode in PS. The measured ρ are related to rotational isomeric state populations and a qualitative picture of the polymer conformation changes over much of their miscible ranges is described. Measurements of ρ for PDMS gum over the temperature ranges 20 < T < 200°C have been obtained and the upper theta temperature has been determined to be 171 ± 3°C for PDMS/benzene. Quantitative information about the variation of the polymer solvent interaction parameter χ can in principle be obtained.