bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solubilities of volatile solutes in poly(vinyl acetate) from 125 to 200°C
Authors: Liu D. D. , Prausnitz J. M. 
Published: April 2003

AbstractGas‐liquid chromatography (GLC) was used to measure Henry's law constants for ethylene, ethane, carbon dioxide, sulfur dioxide, methyl chloride, vinyl acetate, isopropyl alcohol, methyl ethyl ketone, and acetone in liquid poly(vinyl acetate) in the region 125 to 200°C. Retention‐time differences were measured relative to nitrogen and corrections for nitrogen's finite solubility were applied; these corrections are significant when measuring the solubilities of sparingly soluble solutes by the GLC method. The effect of GLC column diameter is discussed.
The concentration and pressure dependence of the diffusion of dichlorodifluoromethane in poly(dimethyl siloxane)
Authors: Assink Roger A. 
Published: April 2003

AbstractThe diffusion of dichlorodifluoromethane in poly(dimethyl siloxane) as a function of concentration and pressure was measured by nuclear magnetic resonance (NMR) pulsed‐field‐gradient techniques. The pressure dependence of diffusion could be treated phenomenologically by an activation volume description where the activation volume of 20.9 cm3/mol is only a fraction of the penetrant's molar volume. A free‐volume theory, modified to include the effects of pressure, was used to analyze both the pressure and concentration dependence of diffusion. The functional form of the equation was obeyed very well although it was necessary to assume that the fractional freevolume of penetrant was more than twice its expected value. This discrepancy was interpreted to mean that the motions of the penetrant molecules are weakly coupled to the polymer lattice.
Melting and internal motion in highly alternating copolymers of ethylene and carbon monoxide
Authors: Starkweather Howard W. 
Published: April 2003

AbstractThe melting point of the 1:1 copolymer of ethylene and CO is 244°C. It falls rapidly as the percent CO is reduced indicating that the heat and entropy of fusion are 0.60 kcal and 1.15 e.u./mol of chain atoms, respectively. These are lower than the values for polyethylene. Dynamic mechanical measurements showed loss peaks at −100° and 25°C. The low temperature γ‐relaxation which is also seen in dielectric data appears to be a local mode relaxation with an activation energy of about 12 kcal/mol. The room temperature relaxation is associated with a large decrease in the modulus and a large increase in the dielectric constant. It is probable that the low entropy of fusion is due in part to extensive motion in the crystal.
Kinetics and mechanism of the quaternization of poly(4‐vinyl pyridine) with 1‐bromopropane
Authors: Boucher E. A. , Mollett C. C. 
Published: April 2003

AbstractThe kinetics of the quaternization of poly(4‐vinyl pyridine) with 1‐bromopropane in sulfolane has been studied in the temperature range 308–348°K with data points covering the whole conversion range. The results have been analyzed according to the neighbouring‐group model with rate constants k0, k1, and k2 for reaction of pyridyl groups with zero, one, and two already reacted neighbors. Allowing for limiting reaction at about 95%, the experimental results substantiate the model with K = k1/k0 = 0.80 ± 0.03, and L = k2/k0 = 0.37 ± 0.03, which are independent of temperature. The temperature dependence of k0 values gives an activation energy of 66.22 ± 4.20 kJ mol−1. It is still not possible to decide whether steric or electrostatic factors are responsible for K and L values less than unity. Other systems are mentioned where side reactions occur.
Thermodynamic fluctuations and light scattering from monodisperse polymer solutions
Authors: Cohen Claude 
Published: April 2003

AbstractAn expression for the free energy of a monodisperse polymer solution which incorporates volume changes upon mixing is obtained from a two‐component van der Waals model. When contributions to the thermodynamic quantities from the hard‐core interactions are neglected, expressions similar to those of Flory–Huggins–Debye for the spinodal and critical conditions are obtained. Partial molecular volumes instead of the pure molecular volumes appear in these expressions. The thermodynamic fluctuations of the system, which cause the Rayleigh and Brillouin light scatering, are also expressed in terms of the parameters of the polymer solution in a simple fashion. A limitation to the standard Debye procedure of associating the excess scattering to the solute concentration fluctuations is pointed out.
Deformation band studies of oriented polyethylene and polyethylene terephthalate
Authors: Duckett R. A. , Goswami B. C. , Ward I. M. , Zihlif A. M. 
Published: April 2003

AbstractDeformation bands formed at the yield point in tensile tests on oriented high‐density polyethylene have been studied by optical microscopy and wide‐angle x‐ray (WAXS) diffraction. The observations of the rotation of the optical extinction direction are shown to obey a simple scheme proposed previously by us: the principal directions of the refractive index ellipsoid within the deformation bands are everywhere parallel to the principal axes of the plastic strain ellipsoid, zero strain referring to the isotropic state. This result is similar to that obtained previously for polyethylene terephthalate (PET) and polypropylene despite the much higher crystallinity obtained with polyethylene. Independent measurements of the molecular reorientation in the deformation bands made using wide‐angle x‐ray scattering broadly confirm the optical measurements. The results taken together suggest that the material within the band, whether crystalline or not, becomes realigned about the new direction of maximum elongation as if controlled by the deformation of an effective molecular network.
Some elastic and thermoelastic properties of two organophosphazene polymers
Authors: Mark J. E. , Yu C. U. 
Published: April 2003

AbstractSamples of the alkoxyphosphazene polymer [P(OCH3)2N]x and the aryloxyphosphazene polymer [P(OC6H5)(O‐p‐C6H4C2H5)N]x were crosslinked using γ‐radiation. The resulting elastomeric networks were characterized, in elongation, with regard to both their stress‐strain relationships and their stress‐temperature (“thermoelastic”) properties. Values of the ratio 2C2/2C1 of Mooney–Rivlin constants used to characterize the stress‐strain isotherms were found to be similar to those of other elastomeric networks of comparable degree of crosslinking. The thermoelastic data show the energetic component of the retractive force to be positive for the alkoxy polymer, but negative for the aryloxy polymer. Although it is not difficult to suggest a possible molecular explanation for some of these thermoelastic results, a definitive interpretation would require reliable information on the conformational characteristics of the skeletal bonds in the polyphosphazene chain.
Diffusion in polymer—solvent systems. I. Reexamination of the free‐volume theory
Authors: Vrentas J. S. , Duda J. L. 
Published: April 2003

AbstractThe free‐volume theory describing diffusion in polymer–solvent systems is reexamined. Calculation of the specific free volume for such systems is discussed, and equations are presented for the determination of the self‐diffusion coefficients of the polymer and the solvent. Conditions under which the mutual diffusion coefficient can be deduced solely from free‐volume considerations are clarified, and a more general version of the free‐volume diffusion theory proposed by Fujita is presented. The further restrictions needed for the theory of Fujita are discussed, and it is concluded that these additional restrictions are responsible for failures of the Fujita theory.
Internal viscosity in the dynamics of polymer molecules
Authors: Macinnes D. A. 
Published: April 2003

AbstractWe consider the internal viscosity (IV) of polymer molecules in solution, and investigate how the IV might depend on solvent viscosity η0. From the Kirkwood model of a polymer, we derive in a nonrigorous manner two equations containing an IV, one equation valid for low η0 and the other for high η0, and we show that in these respective cases the coefficient of the IV is independent of η0 and linearly dependent on η0.
Light scattering from crystalline superstructure in tubular‐extruded polybutene‐1 films
Authors: Hashimoto Takeji , Todo Akira , Murakami Yukinobu , Kawai Hiromichi 
Published: April 2003

AbstractLight scattering from polybutene‐1 films prepared by tubular extrusion was studied in order to investigate its crystalline superstructure and the deformation mechanism. Analysis of the light‐scattering patterns together with electron micrographs, indicate the existence of sheaflike crystalline superstructures. The sheaves are aligned nearly side by side with their axes preferentially oriented perpendicular to the machine direction. The Hv scattering patterns exhibit a “butterfly” appearance. Analysis of the patterns in terms of scattering and azimuthal angles at which the scattering intensity is a maximum yields information on the size and shape of the sheaflike texture. The information should be of importance in studies of anisotropic crystal growth caused by molecular orientation in the melt and of the deformation mechanism of the texture. The deformation behavior should be representative of that of different parts of spherulites, at least qualitatively; the deformation of the texture along the machine and transverse directions corresponds to deformation of equatorial and meridional regions of a spherulite, respectively.
TSC and dielectric study of multiple relaxations in poly‐L‐proline
Authors: Guillet Jacques , Seytre Gérard , Chatain Daniel , Lacabanne Colette , Monpagens Jean Claude 
Published: April 2003

AbstractThe thermally stimulated current (TSC) technique has been used to perform a detailed study of the complex relaxation modes observed in poly‐L‐proline II. Each mechanism has been resolved into elementary processes, each well described by using the assumption of a single relaxation time following an Arrhenius equation. This resolution allows us to predict the complex dielectric constant for temperatures between 77 and 400°K and frequencies between 10−6 and 104 Hz. In the range where experimental results are available, the predicted energy losses are in very good agreement with those measured by DC transient experiments, the pendulum technique without contacting electrodes, and the AC bridge. We discuss the probable origin of the various relaxation modes. The relaxation observed at the highest temperature may be attributed to electrons trapped at the boundaries between paracrystalline and crystalline regions. From the changes in the relaxations caused by bound water, we conclude that there are two types of water interacting with the macromolecular substrate. With increasing water content, the relaxation modes observed may first be due to water tightly bound between two carbonyl groups of adjacent chains and second, to increased stiffness of the poly‐L‐proline chain from more mobile water.
Solubility of ethylene in liquid, low‐density polyethylene to 69 atmospheres
Authors: Cheng Y. L. , Bonner D. C. 
Published: April 2003

AbstractEthylene solubility in low‐density polyethylene has been measured using the piezoelectric sorption method from 0 to 69 atm at 126, 140, and 155°C. The measured solubility data indicate lower ethylene solubility in polyethylene at a given temperature and pressure than a previously published extrapolation of infinite‐dilution results. The data are interpreted using the Flory–Huggins solution theory.
Studies on the α and β forms of isotactic polypropylene by crystallization in a temperature gradient
Authors: Lovinger Andrew J. , Chua Jaime O. , Gryte Carl C. 
Published: April 2003

AbstractSamples of isotactic polypropylene (PP) were zone‐solidified in temperature gradients up to 300°C/cm at growth rates down to 3 μm/min. Oriented α‐type spherulites were obtained only by nucleation. While β nucleation is extremely rare, the β phase is easily initiated by growth transformations along the oriented α front. Since the β phase was found to grow considerably faster than the α phase, the α‐to‐β transformation points diverge across the sample, interrupting growth of the oriented α fibrils. This causes subsequent nucleation to yield teardrop‐shaped α spherulites.Differential scanning calorimetry (DSC) studies of zone‐solidified PP show the β‐phase to be favored by slow growth rates, high temperature gradients, and large degrees of superheat in the melt—all of which tend to suppress nucleation. Differential thermograms of largely β‐PP obtained at a heating rate of 1°C/min show the actual melting and recrystallization of the β spherulites into the α form.
On the connectivity of modified glass networks
Authors: Holliday L. 
Published: April 2003

AbstractThe concept of network connectivity is applied to inorganic oxide glasses of hybrid structure. In order to describe these materials which are ripe for investigation, a new terminology is put forward. By using this terminology, some new lines of research can be readily identified. The way in which the physical properties of these novel materials will change with structure is discussed in broad terms, with particular reference to the glass transition temperature.
Temperature dependence of the dynamic mechanical properties of filled polymers
Authors: Lee Biing‐Lin , Nielsen Lawrence E. 
Published: April 2003

AbstractA theory has been developed to explain the jump in the relative modulus of filled polymers near the glass transition temperature Tg and the subsequent decrease in relative modulus at temperatures above the glass transition temperature. The theory is based upon the concept that there are some particle–particle contacts in doublets and in agglomerates containing a larger number of particles. Below Tg motion of particles at the contact points is possible because of the high modulus of the polymer. At Tg particle–particle motion mostly ceases because of the low modulus of the polymer. At higher temperatures, the mismatch in the coefficients of expansion allows some motion to occur at points of contact and slippage may occur at the polymer–particle interfaces, so the modulus decreases. It is shown theoretically and experimentally that both the elastic modulus and the mechanical damping depend upon the nature of the surface of the particles.
Solid‐state thermal polymerization of 2,4‐hexadiyne‐1,6‐diol
Authors: Bloor D. , Stevens G. C. 
Published: April 2003

AbstractThe solid‐state thermal polymerization of 2,4‐hexadiyne‐1, 6‐diol has been studied by a variety of methods. Pure monomer heated under vacuum or in an inert gas atmosphere is found to polymerize readily, unlike material heated in air. X‐ray diffraction reveals that samples anneal during polymerization. Initially, a long chain polymer is formed, but above 20% conversion a less perfect product is obtained. Measurements suggest a complex molecular rearrangement during the nonideal phase of polymerization. Possible models for this process are discussed.
On the electrical polarization of polymer single crystals in suspension
Authors: Leute U. 
Published: April 2003

AbstractA model is proposed for the electrical polarization that causes the orientation and, hence, the electric birefringence of a suspension containing single crystals of a poly(ethylene oxide)–polystyrene diblock copolymer or a poly(ethylene oxide) homopolymer. It serves to describe how an electric dipole moment lying in the plane of the single crystal can be induced by protons migrating in poly‐(ethylene oxide). The resulting Kerr effect is calculated up to saturating fields, and the observed dispersion of the polarization in high frequency fields is explained as a space charge relaxation phenomenon. The estimated relaxation time agrees satisfactorily with published experimental data.
X‐ray structure determination of isotactic poly(2‐vinylpyridine)
Authors: Puterman M. , Kolpak F. J. , Blackwell J. , Lando J. B. 
Published: April 2003

AbstractThe structure of isotactic poly(2‐vinylpyridine) has been determined from x‐ray fiber data utilizing rigid‐body least‐squares refinement techniques. The polymer exists as a threefold helix with three chains passing through a hexagonal unit cell having the dimensions a = b = 15.49 Å and c = 6.56 Å (fiber axis) and space group P31 or P32. The asymmetric unit consists of three monomeric units (one in each chain), resulting in three crystallographically independent chains in the unit cell. The results show that two of the chains are interlocked through pyridine ring interactions whereas the third chain is less restricted. A statistical structure is proposed in which any two chains in the unit cell can be interlocked, provided they have the same sense. Such a situation permits a completely statistical structure in which half the chains in any crystallite are oriented upward and the other half downward.
Proton magnetic resonance studies of the phase structure of bulk‐crystallized linear polyethylene
Authors: Kitamaru R. , Horii F. , Hyon S.‐H. 
Published: April 2003

AbstractThe broad‐line proton NMR spectra of melt‐crystallized samples of polyethylene covering a very wide range in molecular weight have been analyzed in terms of contributions from three components: (1) a crystalline region with crystals of orthorhombic form; (2) a noncrystalline region with liquid‐like character which produces a Lorentzian contribution to the spectrum; and (3) an intermediate region in which the rotation of methylene groups about C—C bonds is partly hindered. The relative mass fractions as well as the character of these components depend greatly on the molecular weight. Samples of low molecular weight (e.g., ⩽30,000) are predominantly composed of lamellar crystalline regions with a minor amount of interfacial regions and no liquid‐like interzonal regions. As the molecular weight increases beyond 45,000, an interzonal region with a liquid‐like character associated with a higher molecular mobility is produced. Above a molecular weight of 100,000, this liquid‐like character becomes pronounced with an increase in molecular mobility in the interfacial region.
Models for spin relaxation in dilute solutions of randomly coiled polymers
Authors: Jones Alan Anthony , Stockmayer Walter H. 
Published: April 2003

AbstractModels for the interpretation of magnetic relaxation in a randomly coiled macromolecule in dilute solution are considered. Expressions are given for the spin‐lattice relaxation time and the nuclear Overhauser enhancement resulting from modulation of the dipole–dipole interaction by three specific independent and mutually competitive types of macromolecular motion. Overall molecular rotation is characterized by a single exponential correlation time and internal anisotropic rotation by the well‐known Woessner theory. A simple description of backbone motion is presented based upon a three‐bond crankshaft motion and the concept of limited coupling among backbone bonds. The resulting correlation function is numerically similar to that recently proposed by Valeur, Jarry, Gény, and Monnerie from a somewhat different standpoint. Representative calculations for appropriate ranges of the model parameters are made for a 13C nucleus relaxing by heteronuclear dipole–dipole interaction with a single 1H nucleus.
Phenyl group rotation in polystyrene and the nature of twofold anisotropic internal rotation
Authors: Jones Alan Anthony 
Published: April 2003

AbstractA review of the experimental evidence for phenyl group rotation in various polystyrenes and improvements in the interpretation of spin relaxation data for dilute solutions of randomly coiled polymers led to a new calculation of the correlation time for phenyl group rotation from nuclear magnetic resonance (NMR) data. Both 13C and 19F NMR data were reconsidered by using a model which includes motional modulation of the dipole–dipole interaction by overall rotatory diffusion, backbone rearrangements, and internal anisotropic rotation. The choice of a twofold potential to characterize local resistance to internal phenyl group rotation strongly influences the estimate of the rate of phenyl group rotation. The magnetic resonance data are found to be consistent with a correlation time for phenyl group rotation which is one to six times longer than the average correlation time for backbone rearrangement.
Measurement of pole figures and orientation functions for Valonia cellulose
Authors: Tanaka Fumio , Okamura Keizo 
Published: April 2003

AbstractThe x‐ray pole‐figure technique has been applied to the study of orientation in Valonia cellulose. It is found that the maximum of the orientation distribution of the (220) poles of crystallites in Valonia cell walls is precisely normal to the cell wall surface, and the pole population is denser in the longitudinal direction than in the transverse direction. The orientation is interpreted as a typical uniplanar‐axial orientation after Heffelfinger and Burton's classification: a uniplanar orientation in (220), and two types of uniaxial orientation in the (220) and (400) planes based on the unit cell parameters for Valonia cellulose. The degree of biaxial orientation of the (220), (220), and (400) plane normals as well as three principal crystallographic axes are shown by Desper's equilateral triangle plots.
Thermostimulated depolarization currents in thermorheologically simple materials
Authors: Solunov Ch. A. , Ponevsky Ch. S. 
Published: April 2003

AbstractA theory is presented which makes possible the calculation of the dielectric parameters for a distributed dipole relaxation from thermostimulated depolarization current (TDC) data. The theory is applicable to dielectrics which obey the time–temperature superposition principle, i.e., for thermorheologically simple materials. The shift factor, the activation energy, the dielectric relaxation strength, the density of the isothermal displacement current, and the distribution function of relaxation times of the β relaxation in poly(methyl methacrylate) are calculated. The TDC investigations were carried out over the temperature range of −136 to 90°C. The values for the activation energy U = 26.4 kcal/mole and the dielectric relaxation strength Δϵβ = 2 are in good agreement with values obtained from dynamic measurements. A criterion for checking the validity of the time–temperature superposition principle by TDC is suggested.
In vacuo photocurrent measurements of plasma polymerized styrene films
Authors: Morita S. , Shen M. , Ieda M. 
Published: April 2003

AbstractPhotoconductivity measurements were carried out on plasma polymerized styrene (PPS) in vacuo, in air, and in subsequently re‐evacuated conditions. Samples with two gold electrodes (Au‐PPS‐Au) and gold‐aluminum electrodes (Au‐PPS‐Al) were used. Positive short circuit photocurrents in the direction of illumination were observed in both types of specimens. In the case of Au‐PPS‐Au, photocurrent threshold was about 1.6 eV in vacuo for the virgin film, which is attributed to the energy of hole generation in bulk. Residual free radicals were assumed to be the acceptors in this mechanism. In the case of Au‐PPS‐Al, electron injection from aluminum was thought to be a more likely mechanism, with an estimated barrier height of approximately 2.6 eV.