bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural relationships in blends of isotactic polypropylene and polymers with aliphatic sequences
Authors: Lotz B. , Wittmann J. C. 
Published: April 2003

AbstractBlends of isotactic polypropylene and polyethylene or polyamides often display highly unusual crystalline morphologies in which the chain axes of the helical and linear polymers are at large angles to each other. These crystalline morphologies are explained on the basis of a specific epitaxial relationship that rests on the existence, in the (010) plane of iPP, of rows of methyl groups nearly 5‐Å apart. The structural basis of all the observed morphologies is the parallel alignment of the aliphatic segments of the PE or polyamides and of the iPP methyl rows (or vice versa) and matching of the near 5‐Å distances between PE or PA chains and iPP methyl rows. The implications of this unusual epitaxial relationship with respect to the apparent “universality” of polymer nucleating agents are examined.
Blends of a chlorinated poly(vinyl chloride) with a polyurethane
Authors: Garcia Dana 
Published: April 2003

AbstractBlends of a 67% chlorinated poly(vinyl chloride) with a low‐molecular‐weight polyurethane are partially miscible over the 0–80% urethane compositional range. A single, composition‐dependent glass transition temperature is observed from both DSC and dynamic mechanical measurements. The blends exhibit a cocontinuous morphology with domain sizes varying from 0.15 to 1.5 μm. These results point out that the relation between miscibility characteristics and domain size is a complex one, not only dependent upon the degree of miscibility, but also on the nature of the blend components and the test method used. Thus the domain size for a certain degree of miscibility is not a universal constant as was previously believed. The melt rheology of the blends as a function of composition is strongly “positive deviating” from the log additivity rule and fits a simplified version of the McAllister model. The strongly “positive deviating” rheological behavior of the blends is most likely a result of the cocontinuous morphology which makes the system behave as a highly entangled network.
A dielectric study of secondary relaxations and the “memory effect” in two compatible polystyrene blends
Authors: Pathmanathan K. , Johari G. P. , Faivre J. P. , Monnerie L. 
Published: April 2003

AbstractDielectric permittivities and loss tangents of 10 and 30% poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO)–polystyrene (PS) blends and 10 and 25% poly(vinyl methyl ether) (PVME)–polystyrene blends have been measured from 80 to 360 K at 1 and 10 kHz. The PPO‐PS blends have two secondary relaxations below Tg and the PVME‐PS blends have three regions. All blends have a β process which appears near 290 K, is independent of PPO or PVME concentration, and is associated with the local modes of motions of PS chains. It is suggested that the β process of PS allows a dipolar reorientation of the PPO or PS chain segments by creating more favorable surroundings for the motions of the latter. The effect of physical aging in the PPO‐PS blend is substantial but the “memory effect” is significantly less. This is due to the lower contribution to tanδ from the β process of the blend.
Hydrogen bonding in polymer mixtures
Authors: Kwei T. K. , Pearce Eli M. , Ren Fan , Chen J. P. 
Published: April 2003

AbstractThe enthalpy–infrared frequency shift correlation for simple acids and bases is extended to study hydrogen bonding in polymer systems. The acidity of a polymer is calibrated by comparing the shifts in hydroxyl absorption frequency of the acidic polymer when mixed with a series of bases with the corresponding spectral shifts of known acids with the same bases. The basicity of a polymer is calibrated by measuring the hydroxyl frequency shifts of known acids when mixed with the basic polymer. For polymers containing carbonyl groups, the shift in carbonyl absorption is also a measure of basicity. The acidity and basicity constants obtained for polymers are in good agreement with the values for small‐molecule analogs. The enthalpies of hydrogen bond formation in polymer mixtures are calculated from the acidity or basicity constants.
Chain retraction, length fluctuations, and small‐angle neutron scattering in strained polymer melts
Authors: Viovy Jean Louis 
Published: April 2003

AbstractWe propose a possible explanation for an apparent contradiction between the Doi–Edwards (DE) theory and time‐resolved small‐angle neutron scattering experiments. The original DE theory predicts that a chain in a melt subjected to a step‐elongation undergoes a reduction of its dimensions in both the parallel and perpendicular directions to the strain axis, before returning to an isotropic conformation by reptation. In the present paper, we propose a crude model to compare the relative effect of retraction and of the chain length fluctuations, introduced later by Doi to explain the M power law of viscosity of polymer melts. We show that length fluctuations are able to screen retraction in most experimental situations available to small‐angle neutron scattering, whereas that is not the case for viscoelasticity. Quantitative predictions are consistent with the experimental data presently available.
Infrared spectroscopy of ethylene–vinyl chloride copolymers
Authors: Bowmer T. N. , Tonelli A. E. 
Published: April 2003

AbstractThis paper continues an investigation into the ethylene–vinyl chloride copolymers prepared by partial reduction of poly(vinyl chloride). The infrared spectra of the copolymers have been obtained and the individual resonances assigned. Each infrared band has been quantitatively analyzed in terms of peak position (cm−1) and intensity, and correlations with the sequence microstructure (dyad, triads, etc.) have been determined. The infrared resonances have been found to be sensitive to long sequences; i.e., (V)x or (E)x where x ≥ 10. Sequences of up to 10–15 monomer units were seen to affect the position (cm−1) and intensity of CH stretching and bending frequencies. Methylene rocking bands between 850 and 700 cm−1 were observed to be sequence dependent with V(E)xV resonanting at 860, 750, or 730 cm−1 for x = 0, 1 and 2, or ≥3, respectively. The CCl stretching resonances, which are well known for their conformational complexity in pure PVC, were found to be dominated by sequence length effects reducing to two bands at 665 and 610 cm−1 characteristic of and isolated CHCl unit in a long methylene chain.
Energy transfer in polymers and nitroxide decay during photolysis
Authors: Bauer D. R. , Briggs L. M. , Gerlock J. L. 
Published: April 2003

AbstractWhen polymeric materials doped with nitroxides of the 2,2,6,6‐tetramethylpiperidine type are exposed to light, the nitroxide concentration decreases. The two mechanisms for the decrease of the nitroxide are the reaction of nitroxide with free radicals produced during photolysis of the polymer to form amino ethers and the abstraction of hydrogen atoms by excited‐state nitroxides to form hydroxyl amines. Excited‐state nitroxides can be formed in two ways: by direct absorption and by energy transfer. In this paper, the effect of energy transfer on the rate of decay of the nitroxide signal is studied, and measurements of nitroxide decay are used to probe energy transfer in crosslinked polymeric coatings. A simple kinetic scheme is used to interpret nitroxide decay during photolysis of both solutions and polymers containing benzophenone. These results are used to show that the slope of the line relating nitroxide decay rate to nitroxide concentration is essentially determined by energy transfer from a coating‐based chromophore to nitroxide. The nitroxide decay assay is also used to study the effectiveness of a benzotriazole ultraviolet light absorber as a quencher.
Interpretation of differences in temperature and pressure dependences of density and concentration fluctuations in amorphous poly(phenylmethyl siloxane)
Authors: Ngai K. L. , Fytas G. 
Published: April 2003

AbstractDifferences in the temperature and pressure dependences of the relaxation times of a slow diffusional process and the α structural relaxation pose an interesting problem. This feature, observed by dynamic light scattering in amorphous poly(phenylmethyl siloxane), is related to another basic feature of lack of thermorheological simplicity discovered by Plazek in polystyrene, poly(vinyl acetate), and amorphous polypropylene. A quantitative explanation based on the predictions of a general coupling theory of relaxations has been found. The coupling theory also predicts the Kohlrausch fractional exponential time correlation function exp[−(tτ*)1−n] at long times, as observed by photon correlation spectroscopy, and crossover to an exponential time dependence exp–(t/τ0) at short times, as frequently assumed in Brillouin scattering. An additional relation between τ* and τ0 predicted by the theory is confirmed also by the experimental data.
Thermoreversible gelation of cellulose acetate solutions studied by differential scanning calorimetry
Authors: Altena F. W. , Schroder J. S. , Van De Huls R. , Smolders C. A. 
Published: April 2003

AbstractThermoreversible gels of cellulose acetate can be obtained by cooling concentrated cellulose acetate solutions in solvent‐nonsolvent mixtures of dioxane and water. Upon heating the gels, endothermic effects were observed with differential scanning calorimetry. The heat effects are ascribed to the melting of a crystalline phase consisting of cellulose triacetate units. The endothermic peaks appear only after long aging periods of up to several days. Melting points generally decrease and heats of melting increase with increasing polymer concentration and with increasing nonsolvent content. The maximum degree of crystallinity is estimated as 8%. The kinetic effects of varying the water content in the solvent mixture are discussed.
Heat capacities and entropies of liquid, high‐melting‐point polymers containing phenylene groups (PEEK, PC, and PET)
Authors: Cheng Stephen Z. D. , Wunderlich Bernhard 
Published: April 2003

AbstractThe heat capacity at constant pressure of liquid PEEK, poly(oxy‐1,4‐phenylene‐oxy‐1,4‐phenylene‐carbonyl‐1,4‐phenylene), has been measured by scanning calorimetry from 420 to 680 K, and that of PC, poly(4,4′‐isopropylidenediphenylene carbonate), from 325 to 610 K. These new data were combined with data‐bank data for PC and PET, poly(ethylene terephthalate), over wide temperature ranges. An addition scheme for liquid heat capacities of similar macromolecules has been obtained. In addition, values of absolute entropy, residual entropy for the glassy state, enthalpy, and Gibbs function are estimated for these three polymers. Both melting and glass transition temperatures have been confirmed. The heat capacity increases at the glass transition temperature have been determined by making use of previously calculated solid‐state heat capacities.
Interpretation of small‐angle x‐ray and neutron scattering data for perfluorosulfonated ionomer membranes
Authors: Kumar Satish , Pineri Michel 
Published: April 2003

AbstractIn small‐angle x‐ray and neutron scattering studies of ion‐containing polymers, it is observed that there is a maximum in the intensity and also an increase in the intensity at very low Q. Several ion clustering models have been proposed in the literature to explain the peak and the intensity increase. The SAXS data of Gierke et al. and the SANS data of Roche et al. are considered in this paper in order to elucidate the possible cluster morphology in perfluorosulfonated ionomer membranes. For these samples the occurrence of the SAXS peak is accounted for quantitatively; it is shown to arise from the interference between ionic aggregates (clusters), assuming them to be noninteracting hard spheres. In these calculations the volume fraction of the clusters (the cluster is assumed to be constituted of SO3−, a cation, and a swelling agent, which is water in the present case) is determined from water absorption values, equivalent weight, and from the density of the dry polymer. The size of the ionic clusters is chosen to match the calculated and observed peak positions. In these calculations it is assumed that all the ions are in clusters. The calculated peak value of the relative intensity invariant is found to be within ±15% of the experimentally observed intensity invariant for samples of different equivalent weight, and in different cationic form, soaked or boiled in water. Samples equilibrated at lower levels of humidity showed greater deviations. The deviations become smaller if either or both of two assumptions are made; that with a decrease in humidity (i) the percentage of clustering ions decreases, (ii) a fraction of the polymer chains is present in the clusters. This work gives credence to the thought that the small‐angle scattering peak in ion‐containing polymers is not a Bragg peak. This invalidates the conventional method of comparing the macroscopic and microscopic degrees of swelling. Previous SAXS work on dense groups of particles has neglected a term which is shown to be important at low angles. We found that this term is capable of qualitatively explaining the observed increase in intensity at low angles in perfluorosulfonated ionomers. The possibility of the presence of an intercluster potential, which can also contribute to the increase in intensity at these angles, is also discussed.
CO2 sorption in uniaxially drawn atactic polystyrene
Authors: Carfagna C. , Nicodemo L. , Nicolais L. , Campanile G. 
Published: April 2003

AbstractThe CO2 solubility in oriented and unoriented atactic polystyrene films has been investigated. Orientation does not change the nature of the sorption process; however, it decreases the level of solubility. Both the Langumir sorption term and the Henry's‐law contribution are affected by orientation. The decrease of solubility is correlated with an increase of density due to orientation. A simple experiment has been described to evaluate the depression of the glass transition temperature of polystyrene containing dissolved carbon dioxide.
Structure of the polyion complex between poly(sodium P‐styrene sulfonate) and poly(diallyl dimethyl ammonium chloride)
Authors: Oyama Hideko Tamaru , Frank Curtis W. 
Published: April 2003

AbstractStoichiometric and nonstoichiometric polyion complex films were prepared from poly(sodium p‐styrene sulfonate) and poly(diallyl dimethyl ammonium chloride). X‐ray photoelectron spectroscopy revealed that the ionic groups in the complex are more ionized than in each component polymer. Fluorescence measurements showed that the complex had a main emission peak around 300 nm, whereas the peak for its original polyanion occurred at 324 nm. With the monomer and excimer peaks of the phenyl rings taken to be at 294 and 324 nm, respectively, the ratio of excimer to monomer emission intensities increased in proportion to the mole fraction of polyanion in the observed range 0.44–0.59. There was no discontinuity at the stoichiometric composition. Furthermore, the change in peak position shows that the local aggregation of phenyl groups in the polyanion was destroyed by complexation with the polycation through Coulombic forces. These results, together with the visual observation of the transparency of the films, mean that the mixing between polyanion and polycation chains in the polyion complex is on the molecular level and that this polymer alloy is miscible.
Thermodynamics of linear reversible deformation
Authors: Göuritz D. 
Published: April 2003

AbstractThe change in internal energy of a body on stretching can be determined by means of deformation calorimetry. Theoretically the changes in thermodynamic properties on stretching can be deduced from Hooke's law and the Thomson expression dQ = β0TL df, which gives the amount of heat dQ absorbed when the force is changed from f to f+df; β0 is the linear expansion coefficient of the isotropic specimen, T the absolute temperature, and L the length of the deformed specimen. This has been demonstrated here for the deformation of a metal, and of isotropic and oriented polyethylene.
Effects of tertiary amine accelerators on curing of epoxide resins
Authors: Shimbo Masaki , Nakaya Takashi , Takahama Takashi 
Published: April 2003

AbstractThe effects of seven tertiary amine accelerators on curing of bisphenol‐type epoxide resins using azelaic acid as a curing agent have been investigated. The structure of the cured resins is characterized and reaction and structure schemes are proposed. The reaction mechanism and the resulting structure of the resin depend on the basicity of the accelerator. With increasing accelerator basicity crosslinking in the cured resin increases. Characterization results indicate that the network structure consists of ether bonds or a mixture of ether and ester bonds; the linear structure consists of only ester bonds. The structure and, therefore, the properties of the cured epoxide resin may thus be regulated by selection of the amine basicity.
The dielectric β‐relaxation of poly(bis‐benzimidazobenzisoquinolinones)
Authors: Śamigasiewicz Stefan , Kowalski Bogdan 
Published: April 2003

AbstractThe dielectric relaxation of poly(bis‐benzimidazobenzisoquinolinones) has been studied in the frequency range from 101 to 105 Hz and at temperatures from −150 to +80°C. The data show that the relaxation is due mainly to diffusion of water in the polymer with simultaneous reorientation of water dipoles.
Tensile flow and stress–strain behavior over a wide temperature range for poly(butyl methacrylate) with a broad molecular weight distribution
Authors: Vinogradov G. V. , Dreval V. E. , Borisenkova E. K. , Kurbanaliev M. K. , Zabugina M. P. 
Published: April 2003

AbstractThe poly(butyl methacrylate) studied is a polymer with a normal molecular weight distribution and a relatively low molecular weight close to Mc, the critical molecular weight from the viscosity–molecular weight relation. The polymer was subjected to uniaxial extension and shear over a temperature range which included Tg. It was found that in the region of Tg an increase in applied stress is accompanied by a decrease both in the temperature shift factor aT and in the activation energy for relaxation and rupture of polymer melts. Close attention is given to the long‐term durability of the polymer. As is expected in the temperature range below Tg, its dependence on the stress is exponential, whereas at temperatures above Tg a power law fits the data. In the latter case a log‐log plot of the long‐term durability versus stress can be represented by two intersecting straight lines which can be replotted as a generalized straight line if the long‐term durability values are normalized by the viscosity.
Chain entanglement and viscoelastic properties of molten polymers
Authors: Ajji A. , Carreau P. J. , Schreiber H. P. , Rudin A. 
Published: April 2003

AbstractLinear low‐density polyethylenes (LLDPES) and polypropylene (PP) have been recovered from solutions of varying initial polymer concentration. Melts of these polymers show significant reductions in viscosity and elasticity, and the effects are attributed to changes in the entanglement density of the polymer. Measurements of entanglement densities have been attempted from experimental values of the apparent zero‐shear melt viscosity. These indicate that solution treatments in trichlorobenzene at 135°C reduce the entanglement density more effectively in PP than in LLDPE. In all cases the observed effects are reversible by annealing at elevated temperatures. Analytic data point to entanglement changes as the true origin of changes in viscoelastic properties, since solution treatments produce no changes in molecular weights and weight distributions, and the samples tested are free of solvent residues.
Morphology of a phase‐separated and a molecular composite PBT/ABPBI polymer blend
Authors: Krause Stephen J. , Haddock Tim , Price Gary E. , Galen Lenhert P. , O'brien Joseph F. , Helminiak Thaddeus E. , Adams W. Wade 
Published: April 2003

AbstractThe structure and morphology of homopolymers and blends of rigid‐rod poly(p‐phenylene benzobisthiazole) (PBT) and semiflexible coil poly[2,5(6)benzimidazole] (ABPBI) were examined by wide‐angle x‐ray diffraction and scanning and transmission electron microscopy. When samples were processed from a solution where the total polymer concentration of 30% PBT/70% ABPBI blend was greater than a critical concentration, large‐scale phase separation occurred and 0.1–4 μm ellipsoidal particles were present in a ductile matrix. The ellipsoids were chiefly composed of aggregates of well‐oriented 10‐nm PBT crystallites, while the matrix material was chiefly ABPBI. When the concentration was less than a critical concentration, the solution was optically homogeneous. In processing of fiber and film samples from the homogeneous solution, large‐scale phase separation was inhibited by rapid coagulation in a water bath. After heat treatment, these samples were found to contain crystallites of both PBT and ABPBI with lateral dimensions of ordered regions no larger than 3 nm. The PBT homopolymer was dispersed in the matrix at the molecular level in ordered regions at a scale no larger than 3 nm, resulting in a rigid‐rod molecular composite. In the rigid‐rod molecular composite fiber both the molecular‐level dispersion and high orientation contributed to higher values of strength and modulus compared to the properties of a phase‐separated fiber. The strength and modulus of highly oriented fiber were only 25% higher than those of planar isotropically oriented film, suggesting that the level of dispersion of rod molecules is more important than orientation of the reinforcing phase in rigid‐rod molecular composites.
Ferroelectric order and phase transition in polytrifluoroethylene
Authors: Oka Yoshio , Koizumi Naokazu , Murata Yukinobu 
Published: April 2003

AbstractPolarization‐reversal currents and x‐ray profiles under a high dc field were measured on polytrifluoroethylene (PTrFE) samples prepared by melt crystallization at different cooling rates. The results for PTrFE were found to be analogous to those for copolymers of vinylidene fluoride and trifluoroethylene [P(VDF/TrFE)] with low VDF content. Slow‐cooled and quenched samples showed different x‐ray profiles but the same IR spectra. For the slow‐cooled samples, a polarization reversal was clearly observed as a peak in polarization current, offering evidence for ferroelectric order in PTrFE. The ferroelectric behavior was found to be unlike that of typical ferroelectric polymers. There are two processes in a polarization reversal, i.e., partial depolarization reversal, accompanied by crystalline phase transitions. It is noted that no ferroelectric order was observed for the quenched sample which, however, becomes pyroelectric by poling as revealed by our previous studies. We speculate on possible crystal structures of PTrFE based on the published structure models and the present results. The relation between the ferroelectricity and the previously reported pyroelectricity is also discussed.
Theory of relaxational interaction in linear polymers
Authors: Volkov V. S. , Vinogradov G. V. 
Published: April 2003

AbstractThe theory of nonlinear viscoelasticity of linear polymers is considered in the single‐molecule approximation. The dynamics of a macromolecule among similar molecules is studied with the use of the bead‐spring model. It is assumed that the surroundings of the molecule are equivalent to the simplest viscoelastic fluid with a single relaxation time. The viscoelastic drag force is determined by means of the relaxation equation. It is demonstrated that the viscoelasticity of the macromolecule's environment together with frame invariance leads to anisotropy of the mobility of the molecule. This proves to be of paramount importance in the description of nonlinear viscoelasticity of entangled polymers.