bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic polarized infrared studies of stress relaxation and creep in polypropylene
Authors: Wool R. P. , Statton W. O. 
Published: April 2003

AbstractA new technique was developed to study the molecular mechanics of highly oriented polypropylene during stress relaxation and creep. The polarized infrared spectrum was recorded while the polymer was under load. Stress relaxation effects were investigated during the two‐stage process of fast decay followed by a slower “dynamic equilibrium” decay by examining the stress‐sensitive 975‐cm−1 band and the orientation‐sensitive 899‐cm−1 band. In the fast decay region, the aligned chains became more highly overstressed and the nonaligned chains quickly relieved themselves of their initial overstress. These findings suggest an exchange of stress from nonaligned to aligned chain segments, without much orientation change. Also, a rupture of very highly overstressed aligned chains is though to occur. In the slow decay region, the aligned overstressed chains showed a relief of stress accompanied by some disorientation or helix distortion. Creep, however, appeared to occur via a process which involved all chains regardless of alignment. It was found that the number of highly stressed bonds increased with time at the expense of the intermediately stressed bonds. Very little change in overall orientation was noted, which probably explains the observed crazing and void formation.
Relationship between structure and transport in cellulose acetate desalination membranes
Authors: Sudduth R. D. , Rogers C. E. 
Published: April 2003

AbstractSeveral experimental techniques, including measurements of salt rejection, water flux, birefringence, and membrane opaqueness, were used to characterize the structure and performance of typical cellulose acetate desalination membranes. The results indicate that optimum salt rejection and water flux characteristics are related to the presence of molecular orientation effectively perpendicular to the membrane surface. An alignment‐type flow mechanism involving water contained within the oriented structure is consistent with the observed structural and transport phenomena. The various membrane fabrication procedures apparently have significant effects on the development of molecular orientation in the thin surface layers of the membrane.
The quantitative approach to the composition heterogeneity of the products of reactions of polymers
Authors: Noah O. V. , Litmanovich A. D. , Platé N. A. 
Published: April 2003

AbstractThe problem of describing the composition heterogeneity of the products of reactions of substituent groups on a polymer chain when there are interactions between neighboring groups is considered. A Monte Carlo simulation method and a modified first‐order Markovian approximation are proposed for obtaining composition distributions. The conditions of the mathematical experiment (the optimum length of the model chain and the size of the sample population) are found from a comparison of calculated parameters of the distribution of units with the exact values obtained by accurate analytical solution. These conditions depend upon the ratios k0:k1:k2 of rate constants for reaction of groups with neither, one, or both neighboring groups already reacted. The modified first‐order Markovian approximation gives results close to those of the Monte Carlo simulation for fairly long chains (100 units or more). Results are summarized graphically for calculations of the composition heterogeneity for various k0:k1:k2 ratios. As an example of the application of the suggested theoretical approaches the quaternization of poly‐4‐vinylpyridine with benzyl chloride is considered. The individual rate constants were found from experimental kinetic data. The functions of composition distribution calculated with these constants (k0 = 5.8 × 10−4 l mole−1 sec−1, k1 = k2 = 1.7 × 10−4 l mole−1 sec−1) were compared with experimental data obtained by gel permeation chromatography. Fairly good coincidence was found between experimental and calculated data. The satisfactory description of both reaction kinetics and composition heterogeneity by the same constants enables us to conclude that the neighboring group effect is dominant in this reaction.
In situ characterization of solution–grown polymer single crystals by light scattering and kerr effect
Authors: Picot C. , Weill G. 
Published: April 2003

AbstractSimultaneous measurements of light scattering and electric birefringence on a crystallizing solution of poly(ethylene oxide) (PEO) are shown to lead to the determination of the radius, thickness, and number of crystals at the early stages of the crystallization process.
Solution properties of polymers of pyridinium and ammonium methacrylates.
Authors: Stejskal Jaroslav , Beneš Milan J. , Kratochvíl Pavel , Peška Jan 
Published: April 2003

AbstractSolution properties of poly[1(2‐hydroxyethyl)pyridiniumbenzene sulfonate methacrylate] and poly[1(2‐hydroxyethyl)trimethylammoniumbenzene sulfonate methacrylate] were studied. Within a certain concentration range of some added low molecular weight electrolytes, phase separation occurs. The dependence of intrinsic viscosity on molecular weight was determined and the steric factor estimated for both polymers. For nonaqueous solvents, an extrapolation of the dependence of the refractive index increment of the polymer on the refractive index of the solvent leads to an apparent refractive index of the polymer, different from the refractive index determined directly by the immersion method. Some peculiarities of light scattering in solutions with no electrolyte added are mentioned.
Craze and crack growths in polycarbonate
Authors: Kitagawa M. , Motomura K. 
Published: April 2003

AbstractCraze and crack growth have been studied in polycarbonate. The results are correlated by a stress intensity factor derived from fracture mechanics. A new model taking creep into account is proposed to explain the experimental results. Theoretical predictions derived from the model are compared with experimental results. Fair agreement is obtained.
Flow properties of branched polydisperse polymers
Authors: Graessley W. W. , Shinbach E. S. 
Published: April 2003

AbstractViscosity and normal‐stress difference as functions of shear rate were examined for poly(vinyl acetate) samples with various degrees of random branching in diethyl phthalate solution. At moderate concentration (c = 0.17 g/ml) the viscosities were depressed by branching, in fair accord with the Bueche theory. However, at higher concentrations (c = 0.35 g/ml) the data showed a progressive trend in the direction of viscosity enhancement by branching, a characteristic which has been observed by other workers in undiluted branched polymers. Accompanying viscosity enhancement was an increase in the temperature coefficient of viscosity, an increase in recoverable compliance (estimated from steady‐state normal‐stress data) and an early onset in the shear rate dependence of viscosity.
Relaxations in the transition region of crosslinked polyesters. I. The β relaxation
Authors: Cook W. D. , Delatycki O. 
Published: April 2003

AbstractThe glass transition region of styrene‐crosslinked poly(1,2‐propylene phthalate fumarate) was studied using a torsion pendulum. The region was composed of two separate relaxations. The major relaxation was the glass transition of the whole network, while the minor relaxation, at a lower temperature, was ascribed to the polyester segments between the crosslinks. A comparison was made between these relaxations and these observed in related polyester networks.
Theory of the local mode relaxation in the glassy state of polymers
Authors: Hayakawa Reinosuke , Wada Yasaku 
Published: April 2003

AbstractThe local modes refer to vibrational motions of the main chain in the glassy state which are thermally excited with a relatively large amplitude and are consequently strongly damped into relaxational motions by the intermolecular viscous force. This paper describes a theory of strengths of the dynamic mechanical and dielectric local mode relaxations, in the latter of which the correlation of dipole arrangement along the main chain is considered. The results are compared with the observed strength and its dependence on temperature and pressure, in particular for the dielectric β relaxation of poly(vinyl chloride). Satisfactory agreement is obtained between theory and experiment.
Dilute solution rheology of flexible macromolecules (bead–rod model)
Authors: Acierno D. , Titomanlio G. , Marrucci G. 
Published: April 2003

AbstractThe rheological behavior of dilute solutions of flexible macromolecules is studied by means of a freely jointed multiple bead–rod model. The solution of the equations describing the mechanics of the system is obtained by means of a numerical procedure, which applies to arbitrary flow conditions. The case of the transient stress in uniaxial elongational flow is developed in some detail. A comparison with bead–spring models shows both quantitative and qualitative differences which are briefly discussed.
Cryoscopy on sulfuric acid solutions of a heterocyclic polymer (BBB) and related compounds
Authors: Berry Guy C. , Eisaman Paul R. 
Published: April 2003

AbstractCryoscopic measurements have been carried out on solutions in sulfuric acid of a heterocyclic polymer, its monomers, and certain of its oligomers. The polymer, BBB, is prepared by the polycondensation of 1,4,5,8‐naphthalenetetracarboxylic acid (NTC) with 3,3′‐diaminobenzidine (DAB). The results show that the polymer, its oligomers and one of its monomers, DAB, are all extensively protonated in sulfuric acid, whereas its other monomer is not. The degree of protonation appears to be greater for the polymer than for its low molecular weight oligomers.
Plasticization of poly(dimethyl siloxane) by high‐pressure gases as studied by NMR relaxation
Authors: Assink Roger A. 
Published: April 2003

AbstractThe molecular relaxation behavior of poly(dimethyl siloxane) (PDMS) exposed to various gases pressurized to 207 megapascals (MPa) was investigated by pulsed nuclear magnetic resonance spectroscopy. For a gas of low solubility, such as helium, the gas acts only as a pressurizing medium allowing the effect of pressure on the glass transition to be determined. For gases of high solubility the gas acts not only as a pressurizing medium but also as a plasticizing agent, expanding the polymer lattice and increasing the frequency of molecular motions. The plasticizing effect of argon was found to increase the temperature dependence of the molecular correlation frequency.
Mechanism of formation of shish kebab structures
Authors: Nagasawa Toshio , Shimomura Yasushi 
Published: April 2003

AbstractTo describe the characteristic crystalline structure of polyolefins, Pennings first proposed a model consisting of a combination of an extended chain crystal (a “shish”) and folded chain crystals (“kebabs”). In Pennings' model the “shish” forms first during a crystallization process under stress and then later the “kebabs” overgrow this “shish” structure epitaxially. Because we had some doubts about such a mechanism, we undertook a series of experimental studies on linear polyethylene, particularly in regard to the crystallization process from a solution under shear. Our conclusion is that the crystals grow first by a screw dislocation mechanism, like whiskers, and then later these are deformed by the shear stress to form the shish kebab structures.
Crystallization kinetics of polyethylene under high pressure
Authors: Kyotani Mutsumasa , Kanetsuna Hisaaki 
Published: April 2003

AbstractThe kinetics of isothermal crystallization of polyethylene under high pressures ranging from 840 to 5300 kg/cm2 has been studied dilatometrically. The crystallization rate estimated from the half‐time of the overall transformation increases markedly with pressure. The Avrami exponent n becomes smaller with increasing pressure. Values of n ≈ 2 for the crystallization at 840 and 1950 kg/cm2, and n ≈ 1 at 5100 and 5300 kg/cm2 were obtained. Differential scanning calorimetry and electron microscopy data are presented. It is concluded that extended‐chain crystals grow rapidly, predominantly in one dimension, at high pressure. Relations between log k and Tm/T(ΔT) and Tm2/T(ΔT)2 are nearly linear. Here, k is the crystallization rate constant from an Avrami equation, ΔT = Tm – T, Tm is the melting point, and T is the temperature of crystallization. From the dependence of the slope of the straight line on the crystallization pressure it is concluded that the surface energy of crystal nuclei decreases with increasing pressure.
A systematic experimental study of moiré patterns in the electron image of solution‐grown polyethylene crystals
Authors: White J. R. 
Published: April 2003

AbstractA systematic study of solution‐grown polyethylene crystals in the electron microscope using dark‐field imaging in several diffracted beams has warranted a detailed analysis of the moiré patterns recorded. Direct proof for the existence of tilt moiré patterns has been obtained for the first time, while parallel and tilt patterns have been positively distinguished. Consideration of the formation conditions and properties of moiré patterns in dark field has been extended to include interference between an electron beam diffracted in both participating crystals with one diffracted in only one of them. Examples of moiré patterns depending thus on double diffraction have been identified.
Pressure and temperature effects on the vibrational frequencies of crystalline polymethylenes. I. Infrared‐active rocking modes
Authors: Wu Che‐Kuang 
Published: April 2003

AbstractThe energy level dispersion, along the chain wave vector, of infrared‐active methylene rocking modes has been measured as a function of pressure to 40 kbar for a number of polymethylenes. They are crystalline polyethylene and n‐paraffins C23H48, C24H50, C28H58, and C29H60. The crystalline factor‐group splitting of each chain mode is observed at various pressures, for those polymethylenes which have orthorhombic or monoclinic structures. The effects of crystal structure, intermolecular force field and intramolecular force field on the observed energy levels as well as on the crystalline factor‐group splittings are discussed A hydrogen–hydrogen nonbonded repulsion potential has been calculated as a function of interatomic distance rH••H for 2.3 Å < rH••H < 3.0 Å from the observed volume dependence of the factor‐group splittings of methylene rocking modes. It is shown that the dynamic potential wells along the normal coordinates of the rocking modes are harmonic up to room temperature.
Morphology and fold length of single crystals in linear aliphatic polyesters
Authors: Kanamoto T. 
Published: April 2003

AbstractThe marked effects of chemical structure on the morphology of single crystals in linear aliphatic polyesters have been investigated. Drawn fibers and solution‐grown crystals of poly(ethylene sebacate), poly(hexamethylene sebacate), and poly(decamethylene 1,16‐hexadecanedicarboxylate) have been studied by small‐angle and wide‐angle x‐ray diffraction. Electron microscopy, and broadline NMR provided supplementary information.The crystal disorder due to irregularity in the cross section of the molecule due to ester groups along the chain direction increases with increase of the methylene sequence length in the chemical repeat unit. On the basis of the x‐ray data and electron microscopy, it is proposed that the nature of the fold surface of single crystals of a given polymer, especially a choice of (001) or (hkl) fold surface (flat lamellae or hollow pyramidal crystals), is determined by energetic competition effects between fold geometry and unit cell symmetry. A smooth increase of the long period with increasing crystallization and annealing temperature seems to be general behavior even when a pronounced stepwise increase might be anticipated.
Morphology of polytetrafluoroethylene prepared by radiation‐induced emulsion polymerization
Authors: Seguchi Tadao , Suwa Takeshi , Tamura Naoyuki , Takehisa Masaaki 
Published: April 2003

AbstractThe original morphology of polytetrafluoroethylene prepared by radiation‐induced emulsion polymerization was studied by electron microscopy. The morphology depends on molecular weight, which in turn depends on polymerization conditions, especially the emulsifier concentration. The molecular weight decreases with increasing emulsifier concentration. The morphology changes with molecular weight roughly as follows: fibrils below 105, rods between 105 and 5 × 105, and granular particle above 106. The crystallinity is high for all morphologies.
Thermal activation parameters for large strain deformation of polyethylene and polycarbonate
Authors: Wu W. , Turner A. P. L. 
Published: April 2003

AbstractExperiments were performed to determine the effects of strain rate, temperature, and pressure on the flow stress of polyethylene and Lexan polycarbonate deformed in shear. The results were analyzed to determine the activation enthalpy and the shear and dilatation activation volumes of the rate‐limiting mechanism of the deformation process. Results show that the activation event involves a volume containing several monomer units and that this volume must dilate by as much as 7% during the activation event. The activation enthalpy was approximately 2.5 × 10−12erg for polyethylene and 1.1 × 10−12erg for polycarbonate. The rate‐limiting mechanism for polyethylene seemed to be unchanged by plastic strains of up to 250%.
Non‐Newtonian behavior in steady flow over the range from the lower to the upper Newtonian region for polystyrene solution
Authors: Ito Yoshio , Shishido Shunsuke 
Published: April 2003

AbstractGraessley's entanglement theory of viscosity modified by a frictional viscosity parameter ηfric is applied to data on solutions of polystyrene in diethyl phthalate at various concentrations and different temperatures. All the data modified give a single master curve over the entire rates of shear, as obtained previously with polydimethyl‐siloxanes of various molecular weights and their solutions of various concentrations. The zero‐shear viscosity η0, the upper Newtonian viscosity η∞, and ηfric are compared. Three activation energies for flow are estimated from η0, η∞ and ηfric, and are compared. The result suggests that the flow behavior in the upper Newtonian region is much more dependent on ηfric than on the entanglement viscosity term ηent. The ratio of zero‐shear entanglement viscosity ηent,0 to ηfric can be used as a measure of the non‐Newtonian behavior of the present solutions. Non‐Newtonian behavior of the investigated polymer solution becomes appreciable at about ηent,0/ηfric = 2.5. These results are in agreement with previous conclusions based on comparison between η0, η∞ and ηfric for polydimethyl‐siloxanes and their solutions.
Formation of kink bands by compression of the extrudate of solid linear polyethylene
Authors: Shigematsu Kazuyo , Imada Kiyohisa , Takayanagi Motowo 
Published: April 2003

AbstractExtrudates of solid linear polyethylene prepared under proper pressure and temperature conditions have a high c axis orientation along the extrusion direction, with lamellar crystals and amorphous layers stacked alternately along the extrusion direction. Kink bands were formed by compressing the oriented extrudate at room temperature along the extrusion direction. Inspection of the kink bands by wide‐angle and small‐angle x‐ray diffraction and electron microscopy revealed that the fiber axis was rotated from the original axis direction by 70–75° and that the lamellar crystals were inclined to the fiber axis in the kink band by 55–60° and stacked nearly parallel to the kink boundary. The superstructural change during the formation of the kink band could not be interpreted in terms of uniform c axis shear alone. In addition to such a mechanism, it was necessary to take into account intermicrofibril and/or intercrystallite slip.
Deformational, swelling, and potentiometric behavior of ionized poly(methacrylic acid) gels. I. Theory
Authors: Hasa J. , Ilavský M. , Dušek K. 
Published: April 2003

AbstractBy using the model of a randomly coiled chain, a relation is derived describing the equilibrium stress–strain behavior of variously ionized polyelectrolyte gels swollen in solutions of a uni–univalent salt. The effect of the concentration of bound counterions calculated on the basis of the cylindrical model and the effect of the change of length of the statistical chain segment with the change in ionization of the gel on stress–strain, swelling, and potentiometric equilibria is discussed.
Pressure and temperature effects on the vibrational frequencies of crystalline polymethylenes. II. Lattice anharmonicity and the equation of state
Authors: Wu Che‐Kuange 
Published: April 2003

AbstractThe lattice anharmonicity of crystalline polymethylene is interpreted from the observed pressure and temperature dependence of Raman active interchain lattice frequencies of the n‐paraffins C23H48 and C44H90. The temperature dependence of the Lc′ interchain lattice frequency is separated into quasiharmonic and self‐energy shifts. The former is due to the volume dependence of the force constant of the oscillator. The latter is due to the anharmonicity of the dynamic potential, and is obtained as a function of volume and phonon population. The setting angle of the carbon skeleton is predicted to be temperature‐sensitive. While the potential surface of the crystal is asymmetric along the Lc′ normal coordinate, it is essentially symmetrical along the Tb′ coordinate.The well‐known Mie–Gruneisen equation of state is generalized to include anharmonicities of oscillators through the temperature dependence of their vibrational frequencies.
Partial molar excess free enthalpies of n‐alkenes in apiezon M and alkanes in squalane and polydimethylsiloxane, and the solution theories of prigogine and flory: An investigation by gas chromatography
Authors: Hammers W. E. , Bos B. C. , Vaas L. H. , Loomans Y. J. W. A. , De Ligny C. L. 
Published: April 2003

AbstractPartial molar excess free enthalpies (or excess chemical potentials) at infinite dilution were obtained over a large temperature range by gas chromatography. Data on n‐alkenes in Apiezon M are interpreted by the Prigogine–Patterson theory; data on normal and branched alkanes in squalane and polydimethylsiloxane (PDMS) are discussed in terms of the Prigogine–Patterson theory and the solution theory of Flory, Orwoll, and Vrij. For the alkane–PDMS systems heats of dilution and partial excess heat capacity data are given.The aim of this work is to get some insight in the applicability of these solution theories to mixtures of fluids, the properties of which may slightly violate the basic assumptions of these theories. It is shown that orientational order in and a large cross‐sectional chain diameter of the polymer solvent do not affect their applicability to the partical molar excess free enthalpies of apolar mixtures, whereas large dissimilarities between the force fields around the segments of the mixture components and/or dissimilar chain flexibilities detract from the applicability of these theories (alkanes in PDMS).Special attention has been paid to the effects of dissimilar size and shape of the segments of the mixture compounds on the magnitude of the interchange interaction parameter. It is shown that the multiple‐connected segment model after Lichtenthaler et al. does not warrant a reliable combinatorial contribution. Comparison of the interaction parameters obtained for n‐alkanes in n‐alkanes, Apiezon, squalane, and polyisobutylene and for branched alkanes in squalane reveals that the magnitude of this parameter is affected by small end‐effects due to the relative weakness of methyl‐methylene interactions.