bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic viscosity of dilute solutions of poly(L‐glutamic acid)
Authors: Nakajima Haruhiko , Wada Yasaku 
Published: April 2003

AbstractThe dynamic viscosity η′ of a dilute solution of poly(L‐glutamic acid) (DP = 1370) in a mixed solvent made up of aqueous 0.2M NaCl and dioxane (2:1 by volume) is measured over the pH range 4.2–10 and in the frequency range 2–500 kHz. The frequency dependence of η′ in the helix region (low pH) is interpreted in terms of a model molecule consisting of n rigid helical segments connected by universal joints. The steady‐flow viscosity, relaxation time, and high‐frequency limiting viscosity at pH 4.75 (helical content 80%) are well explained by this model with n = 5. This value of n is consistent with that estimated from the nucleation parameter σ = 1.4 × 10−3 obtained from the relation between reduced steady‐flow viscosity and helical content. The high‐frequency values of η′ in the coil region (high pH) are fitted by Peterlin's theory. The internal viscosity seems to arise in part from the polyelectrolytic character of the molecule. An additional relaxation at low frequencies in the coil region is ascribed to rotation of molecules elongated by the electrostatic interaction. The lower value of reduced steady‐flow viscosity in the coil region in the mixed solvent compared with that in water is interpreted in terms of the lower degree of effective ionization and the selective solvation of water by the polypeptide. No anomaly is observed in the helix–coil transition region, indicating that the relaxation time for helix–coil equilibrium is less than 10−6sec.
Effect of molecular weight distribution on viscoelastic properties of polymers
Authors: Kurata Michio , Osaki Kunihiro , Einaga Yoshiyuki , Sugie Tsutomu 
Published: April 2003

AbstractThe effect of molecular weight distribution on mechanical properties of concentrated polymer solutions was studied by measuring creep compliance and complex modulus for solutions of binary blends of narrow distribution polystyrenes in chlorinated biphenyl. Two‐step plateaus in the rubbery plateau region, as reported for undiluted polymer blends, were observed for concentrated solutions provided the molecular weights of component polymers differed greatly. The nth order blending law (n = 1, 2, 3) of Bogue et al. was simplified in form to compare with experimental results. As far as the present version of simplification was concerned, the cubic blending law was better than the quadratic one in describing viscoelastic properties of polymer blends. The cubic blending law reproduced closely the magnitudes of viscoelastic functions such as loss modulus and relaxation modulus but it was not able to predict the two‐step plateaus, even when the ratio of molecular weights of components was as large as 10. It also provided a good approximation to reported results on the steady‐state compliance J for undiluted binary polymer blends and present results for solution blends. Since the cubic blending law in the simplified version was consistent with previous results on concentration dependence of the steady‐state compliance for concentrated solutions of narrow distribution polymers, it gave a unified expression for the steady‐state compliance of binary polymer blends and concentrated solutions of narrow distribution polymers.
Radiation crosslinking of elastomers. I. Polybutadienes
Authors: Pearson Dale S. , Skutnik Bolesh J. , Böhm Georg G. A. 
Published: April 2003

AbstractThe chemical and physical crosslink densities of irradiated polybutadiene were determined using a precise and consistent method. This method included the use of a statistical theory of crosslinking modified to include chain reactions and the use of Langley's theory for calculating the number of trapped chain entanglements. The number of crosslinks formed per unit radiation dose, G(X), was measured for a series of polybutadienes containing various isomeric forms of unsaturation. The physical crosslink density and the molecular weight between entanglements were determined from measurements of the compression modulus of swollen samples.
Stability of heterocharges in poly(methyl methacrylate) thermoelectrets. I. Effect of humidity on thermal current spectra
Authors: Vanderschueren J. 
Published: April 2003

AbstractThermoelectrets of poly(methyl methacrylate) were exposed to various atmospheres of known relative humidity between 0 and 100% and the thermal current spectra analyzed. The study of the decrease of the heterocharges as a function of the exposure time reveals important differences in stability between the three peaks of the spectrum; the two peaks appearing at low temperatures can be attributed to a uniform volume polarization, and the third peak observed at high temperature to a space charge polarization. The shift of the peaks indicates plasticization of the polymer by water vapor. This effect is reversible when the samples are exposed for a sufficiently long time to a drying atmosphere. The complex variations of the initial rise of the spectrum as a function of the exposure time show that the activation energy of the peaks probably depends upon the degree of hydration of the polymer.
A search for the mosaic block structure in polyethylene single crystals
Authors: Thomas E. L. , Sass S. L. , Kramer E. J. 
Published: April 2003

AbstractA diffraction contrast study with the aid of an image intensifier was undertaken to obtain direct evidence for the existence of a mosaic block structure in polyethylene single crystals grown by self seeding under isothermal conditions. Dark‐field microscopy indicates that the crystals do not contain a mosaic block structure. High‐resolution electron diffraction confirms that the crystal is coherent (i.e., mosaic block‐free) over regions of several thousands of Angstroms. It is concluded that a mosaic structure on the scale of ∼300 Å does not exist in polyethylene single crystals grown under carefully controlled conditions from dilute solutions. Possible reasons for previous results that indicate the presence of a ∼300 Å mosaic block structure are discussed.
Dynamic viscosity of dilute aqueous solutions of poly(acrylic acid) at frequencies of 2–500 kHz
Authors: Okamoto Hideho , Nakajima Haruhiko , Wada Yasaku 
Published: April 2003

AbstractThe dynamic viscosity of aqueous solutions of poly(acrylic acid) at a polymer concentration of ca. 0.15 g/100 ml has been measured at frequencies from 2 to 500 kHz as a function of degree of polymerization P, degree of neutralization α, and salt (NaCl) concentration Cs. Relaxation spectra have been obtained from the dynamic viscosity. The spectra in the short relaxation time region can be approximated by the Zimm theory for the conformational relaxation of nonionic polymers. The maximum relaxation time τ1 of the Zimm spectra is proportional to P2 and depends rather moderately on α and Cs. Increased deviation is found, however, in the long relaxation time region, in particular for high values of P and α and low values of Cs. The major part of the deviation is interpreted in terms of rotational relaxation of a molecule as a whole. The rotational relaxation time τR is proportional to P3 and increases with increasing α and decreasing Cs. The remaining part of the excess spectra located between τ1 and τR is ascribed to the deviation of the conformational relaxation from the Zimm theory arising from ionization of the polymer.
Quasichemical approach to crosslinked polymer solutions and the swelling equation for polycondensation networks
Authors: Dušek K. 
Published: April 2003

AbstractThe change of free enthalpy and the chemical potential of solvent for mixing of solvent with crosslinked structures formed by stepwise reactions of the polycondensation type has been derived by an adaptation of the quasichemical equilibrium method. Each monomer unit is supposed to bear a different number of crosslinkable contact points, the coupling of which gives rise to chemical bonds, and of uncrosslinkable contact points, involved in interactions with the solvent, which may be of different type. The results are used to analyze the effect of network topology on the parameters of the swelling equation, particularly on a parameter characterizing the network composition. This parameter may be obtained from analytical data or by using the crosslinking statistics; and model calculations show how it varies with monomer conversion.
Low‐frequency dielectric behavior of poly(vinylidene fluoride)
Authors: Uemura Shinsaku 
Published: April 2003

AbstractAn explicit mechanism is described for the anomalous increase in dielectric constant and dielectric loss at low frequencies and high temperatures for poly(vinylidene fluoride) containing ionic impurities. Relations are proposed for the ionic contributions, εi″ and εi″, to the dielectric constant and dielectric loss:

where v0 and D0 are the concentration and the diffusion coefficient of the mobile ions at infinite temperature, q is the charge of an ion (in cgs electrostatic units), l is the distance between electrodes, k is the Boltzmann constant, T is the absolute temperature, Ed is the apparent activation energy for diffusion of the ions, and W is the dissociation energy of the ionic impurities. From the slopes of curves of log εT′ versus 1/T and log ε″T versus 1/T for poly(vinylidene fluoride), energies Ed = 34 kcal/mole and W = 342 kcal/mole were obtained.
Surface tension of polymer mixtures and copolymers
Authors: Schwarcz Andor 
Published: April 2003

AbstractContact angles θ of liquids of different polarity were measured on a series of mixtures of solid high polymers and a series of copolymers. The mixtures were composed of an alternating poly(ethylene‐co‐maleic anhydride) (EMA), and its addition product with n‐octadecylamine, poly(ethylene‐co‐N‐n‐octadecylmaleamic acid) (EOM). The co‐polymers were composed of the same monomeric units as the mixtures. The surface tension γs of EOM, calculated from θ by the Good‐Fowkes‐Owens‐Wendt treatment, decreased slightly with increasing molecular weights and then reached a limiting value. Plots of γs against EOM concentration indicated large negative excess surface tension of the units with lower surface tension, EOM, in both series studied. For the mixture series, γa first sharply decreased with the EOM concentration; then it reached a limiting value, the γs of pure EOM, at a very low EOM concentration. This indicates phase separation of the two polymers, and the thickness of a monomolecular surface layer was calculated from these data. For the copolymers, γs varied logarithmically with the EOM concentration. Throughout the whole concentration range, the data fitted the equation developed by Belton and Evans for ideal mixtures.
Relationship between dielectric behavior and molecular conformation of polyisobutylene in the rubbery state
Authors: Tanaka Akira , Ishida Yoichi 
Published: April 2003

AbstractIn order to elucidate the relationship between the dielectric main‐chain relaxation and molecular structure in rubbery polymers, we studied polyisobutylene, which is free from complicating factors such as stereoregularity, branching, isomerism, and crystallinity. On the basis of the known conformation in the crystal and conformations deduced in solution and in the glassy state, we assumed several probable conformations in the rubbery state, and estimated the motional units in terms of the modified Adam—Gibbs theory. A computer simulation based on the above results leads to the conclusion that the local conformation in the rubbery state retains a regularity similar to that in the crystal.
Glass and melting transitions of copolymers of tetrafluoroethylene with propylene and isobutylene
Authors: Brown Daniel W. , Lowry Robert E. , Wall Leo A. 
Published: April 2003

AbstractCopolymers of tetrafluoroethylene and propylene were prepared that contained 30–65 mole‐% of the former. Reactivity ratios of tetrafluoroethylene‐ and propylene‐ended radicals are 0.008 and 0.06, respectively, resulting in formation of highly alternating copolymers. The glass temperatures, Tg, were determined using a differential scanning calorimeter. Values ranged from 260 to 275°K. A plot of Tg versus composition has a low maximum centered about the equimolar composition. Copolymers of tetrafluoroethylene and isobutylene were prepared that contained 30–56 mole‐% of the former. Reactivity ratios of tetrafluoroethylene‐ and isobutylene‐ended radicals are 0.005 and 0.021, respectively. The glass temperatures of these copolymers range from 257 to 313°K. A higher maximum at the equimolar composition is obtained when Tg is plotted versus composition. Isobutylene‐containing copolymers having 45–54 mole‐% tetrafluoroethylene are crystalline. Melting temperatures range from 416 to 476°K and have their maximum value at the equimolar composition. It is thought that long sequences of alternating units behave as a third entity in these copolymers, the other two being nonalternating units of the two monomers. Unless inhibited, ionic homopolymerization of isobutylene can be appreciable, sometimes resulting in the polymer having two Tg.
Crystal orientation in a semicrystalline polymer in relation to deformation of polymer spherulites. III. Small‐angle light scattering
Authors: Nomura Shunji , Matsuo Masaru , Kawai Hiromichi 
Published: April 2003

AbstractSmall‐angle polarized light scattering from a deformed three‐dimensional spherulite is formulated on the basis of the deformation model proposed in Part II of this series. The intensity distribution of scattered light is discussed chiefly for the cross‐polarization condition, the so‐called Hv polarization, as a function of elongation of the spherulite. In the undeformed state, the scattered intensity distribution forms the typical fourleaf clover pattern, and the intensity decreases with increasing fraction of crystals oriented randomly (type R crystals) within the crystal lamellae of the spherulites. In a system composed of type R crystals and folded‐chain crystals (type B crystals) within the lamellae, the four‐leaf pattern moves to the horizontal zone near the equator with increasing elongation of the spherulite, and, simultaneously, extends to some extent to the vertical zone near the meridional direction as a parameter measuring the ease of lamellar untwisting increases. In a system composed, in addition to type R and type B crystals, of crystals transformed from type B to type Ca and type Cr due to tilting and unfolding of polymer chains, respectively, within the crystal lamellae an eight‐leaf pattern appears, even at small elongation up to about 30%. Each lobe of the eight‐leaf pattern undergoes a characteristic change with increasing elongation. In both systems, the scattered intensity increases with sharpening of orientation distribution of crystals within the crystal lamellae.
Diffusion of monoanionic dyes in nylon
Authors: Komiyama Jiro , Iijima Toshiro 
Published: April 2003

AbstractThe diffusion of three monoanionic dyes [Orange II (C.I. Acid Red 7) and two chromium complex dyes] in nylon 6 is discussed on the basis of dye distribution obtained by the film‐roll method. Variations of the diffusion coefficients with dye concentration depend characteristically on the dye species and in one case show a maximum near the dye concentration stoichiometric to the amino endgroup concentration in the nylon. These concentration dependences are interpreted on the assumption of two thermodynamically distinct dye populations in equilibrium.
Dielectric properties of some semiconducting polyazophenylenes
Authors: Löfgren B. , Sipilä R. , Heleskivi J. 
Published: April 2003

AbstractThe dielectric properties of a series of semiconducting polyazophenylenes were studied as a function of temperature and molecular weight in the temperature range 293–600°K and for molecular weights between 5,100 and 62,800 at a constant frequency of 1 kHz. The compounds studied included poly‐2,4‐diaminotoluene, poly‐2,4‐diaminoanisole, and poly‐2,5‐diaminotoluene. The dielectric properties are presented in the usual way in terms of a complex dielectric constant ε* = ε′—jε″. Activation energies of relaxation processes were evaluated from the areas and widths of the dielectric loss factor, ε″, against reciprocal temperature at constant frequency. The dielectric activation energies were found to be roughly equal to the activation energies from the DC conductivity. This indicates that the conduction mechanism is based on rotational movements of molecules or parts of molecules.
Secondary crystallization of isotactic polystyrene
Authors: Lemstra P. J. , Schouten A. J. , Challa G. 
Published: April 2003

AbstractWhen isotactic polystyrene (i‐PS) is crystallized from the melt or from the glassy state at rather large supercooling an additional melting peak appears on the curve during scanning in a differential calorimeter. The overall rate of crystallization deduced from the total peak areas as a function of crystallization time did not fit the Avrami equation well. When we omit the area of the additional melting peak in the kinetic analysis a much better fit is obtained. We also observed that no lamellar thickening occurs during isothermal crystallization. In view of the low degree of crystallinity of i‐PS these results lead to the idea that a secondary crystallization process takes place within the amorphous parts of the spherulites resulting in this additional melting peak on the DSC curve. The large supercooling needed and the increase in peak area with increasing molecular weight make us suppose that intercrystalline links are probably responsible for the additional melting peak of bulk‐crystallized i‐PS. Electron microscopic studies of surface replicas of i‐PS support this view.
Stress, strain, and birefringence relations of swollen cis‐1,4‐polybutadiene crosslinked in solution
Authors: Ong C. S. M. , Stein R. S. 
Published: April 2003

AbstractStress–strain–birefringence relations are measured for a series of unswollen and swollen networks of cis‐1,4‐polybutadienes which differ both in the degree of crosslinking and in the volume fraction of rubber present during crosslinking. The stress optical coefficient (SOC), the Mooney–Rivlin constants C1, C2 and B1, B2 are calculated. Results show that the unswollen, solution‐vulcanized polymers have very low values of C2 and B2, but high SOC. Upon swelling with CCl4, the stress optical coefficients decrease considerably and agree well with the values obtained by Fukuda, Wilkes, and Stein, and by Ishikawa and Nagai. The networks prepared in solution exhibit different behavior from those crosslinked in dry state, suggesting that in order to understand the origin of deviations from kinetic rubber elasticity theory and the Kuhn–Grün birefringence theory, more consideration must be given to the effect of overall network topology on stress–strain–birefringence behavior.
Copolymers of ethylene with norbornene derivatives—dynamic mechanical properties
Authors: Wilson T. P. , Von Dohlen W. C. , Koleske J. V. 
Published: April 2003

AbstractThe dynamic mechanical properties have been determined and the β relaxation temperatures Tβ have been located for a series of copolymers of ethylene with norbornene, methylnorbornene, dicyclopentadiene, and octahydrodimethanonaphthalene. The Tβ values show discontinuous changes with changing comonomer content. The several levels of Tβ observed apparently can be associated with the sequence of close multiplets of norbornane moieties ranging from isolated units through pairs to triads and higher. For isolated norbornane units Tβ is around 10°C, while for pairs of these units, probably separated by a C2H4 unit, it is 55°C. The size of the norbornene‐type comonomer has a small but measurable effect on these values of Tβ. The bearing of these results on the problem of defining a value of Tg for polyethylene is discussed.
Temperature dependence of viscosity–shear rate behavior in undiluted polystyrene
Authors: Penwell Richard C. , Graessley William W. , Kovacs André 
Published: April 2003

AbstractThe time—temperature superposition principle is well‐established for linear viscoelastic properties of polymer systems. It is generally supposed that the same principle carries over into nonlinear phenomena, such as the relationship between viscosity η and shear rate \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}. Guided by this principle and the forms of various molecular theories, one would expect that η—\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} data on the same polymer at different temperatures would superimpose when plotted as η/η0 versus \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}η0/ρT, η0 being the limiting viscosity at low shear rates, ρ the polymer density, and T the absolute temperature. Data on polystyrene melts, obtained in a plate‐cone viscometer, appear systematically to violate this principle in the range 140–190°. Such anomalies are absent in concentrated solutions of polystyrene. The trends are similar to those reported by Plazek in the steady‐state compliance of polystyrene melts near Tg, but they appear to persist to higher temperatures than the compliance anomaly.
The scattering of light by correlated assemblies of anisotropic rods in two dimensions
Authors: Prud'Homme Robert E. , Stein Richard S. 
Published: April 2003

AbstractThe scattering from an assembly of anisotropic rods having correlated orientation is calculated in terms of a correlation function expressing the probability of parallelism of orientation of their optic axes as a function of their separation. The scattering is dependent upon the product of a form factor for the scattering from an individual rod and an interference factor dependent upon this correlation function.
Tensile strength of polyurethane and other elastomeric block copolymers
Authors: Smith Thor L. 
Published: April 2003

AbstractProcesses that impart strength and toughness are discussed along with reinforcement by colloidal plastics to indicate that high strength, except under restricted test conditions, necessitates a dispersed phase. Thereafter the dependence of the nominal and true tensile strengths on the type, size, and concentration of polar segments in polyurethane elastomers is considered. Data are first examined on formulations devoid of plastic domains and then on those containing domain‐forming segments that result from the reaction of toluene‐2,4‐diisocyanate (TDI) with either toluene‐2,4‐diamine or 4,4′‐methylene‐bis‐(2‐chloroaniline) and from the reaction of 4,4′‐diphenyl methane diisocyanate (MDI) with 1,4‐butanediol (BD). Segments from TDI and either diamine give plastic domains that are especially effective for augmenting strength over an extended temperature range. Segments from MDI and BD are comparatively ineffective, although the formulation studied exhibits high strength at and below room temperature owing to strain‐induced crystallization. From data on various segmented and triblock elastomers, general conclusions are drawn regarding the dependence of strength on the characteristics of the domains and the matrix. For some six segmented and triblock elastomers, it is found that the true tensile strength is essentially independent of the weight fraction of domains provided it exceeds 0.20 or thereabouts.
The effect of densification on the mechanical properties of amorphous glassy polymers
Authors: Bree H. W. , Heijboer J. , Struik L. C. E. , Tak A. G. M. 
Published: April 2003

AbstractFour polymers, viz. polystyrene, polycarbonate, poly(methyl methacrylate), and poly‐(vinyl chloride), were cooled from the melt to room temperature under hydrostatic pressures of 30 and 1000 atm. Cooling under high pressure increased the density by 0.4–0.6%, and the effect of this has been examined for the torsional creep properties, the dynamic properties at 1 Hz, the Charpy impact strength, the thermal expansivity, and the torsional yield stress. It turned out that, in general, densification affects the thermomechanical properties only slightly.