bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multiblock copolymers of styrene and isoprene. II. Microstructure and dilute solution properties
Authors: Corbin N. , Prud'Homme J. 
Published: April 2003

AbstractDilute solution properties of linear (SI)3 six‐block copolymers of styrene and isoprene are compared to those of random, two‐block, and three‐block copolymers of the same system. All the copolymers were prepared with sec‐butyllithium in benzene. The microstructure of the polyisoprene blocks is close to that of homopolyisoprene prepared under the same conditions. In contrast, the random copolymer shows a larger amount of trans‐1,4 isoprene units. The intrinsic viscosities of the copolymers in methylisobutyl ketone, a poor solvent for both polystyrene and polyisoprene, and in toluene, a good solvent for both homopolymers, are examined on the basis of the Fox–Flory relation for homopolymers. All the copolymers behave similarly in each solvent. In methylisobutyl ketone, the viscosity results indicate a random coil conformation with a small expansion owing to the extra repulsive interactions between the dissimilar units. In all cases, the heterocontact repulsive interactions are small and can be characterized by an interaction parameter χab close to 0.025. In toluene, the perturbation caused by the heterocontacts becomes negligible and the expansion factor αη can be predicted from a weighted average of those of the parent homopolymers of the same molecular weight as the copolymer.
Low‐temperature relaxations in styrene‐crosslinked polyester networks. II. The γ′ relaxation
Authors: Cook Wayne D. , Delatycki O. 
Published: April 2003

AbstractThe low‐temperature γ′ relaxation was found to originate in the diol units of a variety of crosslinked polyesters. The results were explained in terms of Boyer's Crankshaft model. As the polyester concentration in the networks increased, the γ′ relaxation shifted to higher temperatures and the intensity of the relaxation increased but not as rapidly as the diol concentration. This behaviour was interpreted in terms of an interaction of the relaxing species with the surrounding matrix.
Selective degradation of nylon 6,6. I. Description of the degradation technique and preliminary morphological characterization
Authors: Hughes Alfred J. , Bell James P. 
Published: April 2003

AbstractA technique for the selective degradation of amorphous regions in nylon 6,6 is reported. Samples of unoriented film and single‐crystal mats have been subjected to selective degradation by refluxing in hydrazine. Weight loss, viscosity‐average molecular weight, density, and small‐angle x‐ray scattering of these samples were monitored as a function of time of degradation. In addition, selected samples have been investigated by gel permeation chromatography (GPC) and transmission electron microscopy. Based on the results of these investigations it is concluded that the reported degradation technique is unique in that the debris is not monodisperse in molecular weight distribution. The Weight loss, density, small‐angle x‐ray scattering, and microscopy data demonstrate that the unordered or noncrystalline regions of the material are removed upon treatement. However, the relatively high molecular weight and broad molecular weight distribution of the debris indicate that regular folds at lamellar surfaces are intact after degradation treatment.
Low temperature relaxation in polypyromellitimide
Authors: Tanaka Takao , Shibayama Kyoichi 
Published: April 2003

AbstractThe effect of heat treatment at temperatures above 300°C on the low temperature relaxation of poly(4,4′‐oxydiphenylenepyromellitimide) (Kapton H‐film) was studied by wide‐line nuclear magnetic resonance (NMR), mechanical, and dielectric measurements. In the NMR line spectrum of the as‐received film, a narrow component above −60°C and a broad component which begins to narrow at about −100°C were observed. It is proposed that the narrow component is associated with absorbed water, because it disappeared in the heat‐treated film at 300°C in N2. On the other hand, the behavior of the broad component was not influenced by heating to 300°C in N2. Mechanical and dielectric loss peaks were observed at −75°C (11 Hz) and −65°C (1 kHz), respectively, in the as‐received film. These loss peaks did not change in intensity with heating to 300°C in N2. It is proposed that the mechanical and dielectric loss peaks corresponding to the narrowing of the NMR broad component are associated with the local‐mode motion of the diphenylether portion of the polypyromellitimide chain. It was found that crosslinks are formed by heating to 374°C in air through coupling of the diphenylether portions of the molecular chains. With the formation of crosslinks the dielectric loss peak shifted toward higher temperature and the intensity decreased through restriction of the local‐mode motion of the diphenylether portion of the molecular chain.
Radiation chemistry of polyethylene. XIV. Allyl radical decay kinetics in different types of polyethylene
Authors: Patel V. M. , Patel G. N. , Gvozdic N. , Hsu C. S. , Dole Malcolm 
Published: April 2003

AbstractThe decay kinetics of the chain allyl free radical has been studied in the following morphological forms of polyethylene (PE): Marlex bulk film, hydrogenated PE, and extended‐chain PE. Coupled with previous work on single‐crystalline PE it can be seen that the decay rate is greater the more amorphous the sample. In the Marlex bulk film and hydrogenated PE the decay can be interpreted in terms of a simultaneous fast and slow decay process by means of our Q‐function equation, but with rising temperature the decay approximates a single rate process. With extended‐chain PE the allyl decay rate does not become appreciable until the melting range is approached. The fraction of allyl radicals decaying by the slow process is 2 to 10 times greater than the fraction of fast decaying radicals. The ratio of the fast decay rate constant to that of the slow rate constant is greater for the bulk Marlex film than for the hydrogenated PE. All ratios decrease with rising temperature. For times up to about 150 min the allyl decay in the extended‐chain PE accurately follows a single second‐order decay law with a time‐independent diffusion controlled reaction rate constant.
Dependence of cooperative relaxation of amorphous polymers on diluent concentration
Authors: Havlíček I. , Ilavský M. , Hrouz J. 
Published: April 2003

AbstractThe Adam–Gibbs molecular theory, which describes the temperature dependence of relaxation phenomena in the main transition region in terms of the configurational entropy of a system, has been extended to include the effect of concentration of a low‐molecular‐weight compound on the viscoelastic behavior of concentrated polymer solutions. The concentration dependence of relaxation times in the polymer–diluent mixture leads to an expression of the concentration dependence both of the shift factor in the Williams–Landel–Ferry (WLF) equation and of the glass transition temperature Tg of the mixture. The constants of the WLF equation and the concentration dependence of Tg are given in terms of a difference between the specific heats of the liquid and glass ΔCp of the equilibrium temperature T2 of the second‐order transition, and of the parameter Δμs/k, which includes the chemical potential Δμ and the configurational entropy s of the smallest cooperatively rearranging region. The resulting relationships also predict the temperature dependence of the constants of the concentration WLF equation. Good agreement was found between theory and the viscoelastic and Tg data on the systems poly(vinyl acetate) + diethyl phthalate, poly(methyl methacrylate) + diethyl phthalate and polystyrene + dibutyl phthalate. This finding indicates that the configurational entropy, at least in the first approximation, is responsible for the concentration dependence of relaxation phenomena in concentrated polymer solutions.
Dielectric loss of high‐density polyethylene below 4.2°K
Authors: Yano Okimichi , Kamoshida Takaya , Sekiyama Shigehiro , Wada Yasaku 
Published: April 2003

AbstractDrawing of oxidized high‐density polyethylene (HDPE) and subsequent annealing greatly reduce the low‐temperature dielectric loss when the electric field is applied perpendicular to the draw direction. This supports our model (J. Polym. Sci. Polym. Phys. Ed., 15, 43 (1977)) of the proton moving parallel to the c axis of the PE crystal. A particular antioxidant (Ionox 330) in unoxidized HDPE induces a dielectric loss with a frequency and temperature dependence which differs from that for the loss in oxidized HDPE. The antioxidant loss seems to be an overlapping of tunneling and a thermal activation process. The possibility that the hydroperoxide group in the PE crystal is the origin of the loss in oxidized HDPE was theoretically examined in a manner similar to that used for the hydroxyl group in the previous paper. Results suggest that the hydroperoxide group is less probable than hydroxyl as the origin of the low‐frequency loss in HDPE.
Influence of pressure and chemical structure on the thermal conductivity of vitreous poly(alkyl methacrylates). II. Relation to free volume
Authors: Frost R. S. , Barker R. E. , Chen R. Y. S. 
Published: April 2003

AbstractA quantitative model for the pressure dependence of the thermal conductivity K in glassy polymers is presented. By extending the hole theory of liquids to temperatures below the glass transition temperature, an equation of state is obtained and an expression for the pressure dependence of the thermal conductivity is then formulated from a consideration of the anharmonicity associated with the segmental vibrations. The resulting equation ΔK/K = γGf0[1−exp(−p/B*)], where γG is the Grüneisen parameter, f0 is the fractional free volume, and B* = kTg/V0, is compared with experimental results for the poly(alkyl methacrylates).
Concentration and temperature dependence of the refractive index increment of a polystyrene sample in trans‐decalin
Authors: Roots Jaan , Nyström Bo 
Published: April 2003

AbstractThe refractive index increment of macromolecules in solution has been observed to be a function of concentration, temperature, molecular weight, wavelength of light, and solvent. Most of the studies have been performed in dilute or semidilute solutions, and therefore the concentration dependence of the refractive index increment was too small to be accurately observed. This study was performed on solutions of polystyrene in trans‐decalin at mass fractions, w2, from 0.01 to 0.11 and at 436 and 546 nm wavelengths. The concentration and temperature dependence of the refractive index increment were measured, and comparisons were made with previous theories.
Fine structure of polyethylene prepared by γ‐ray‐induced polymerization in various solvents. III. Selective degradation with ozone
Authors: Arai Hidehiko , Yamaguchi Koichi , Mitomo Hiroshi , Kuriyama Isamu 
Published: April 2003

AbstractOzone‐degradation products of polyethylenes prepared by γ‐ray‐Induced polymerization in ethyl alcohol, t‐butyl alcohol, and 2,2,5‐trimethylhexane were analyzed by gel permeation chromatography (GPC). The ozonized polymers show two discrete peaks in the GPC traces, and the ratio of molecular weights corresponding to the peaks is close to 1:2, suggesting that these polymers are composed of folded‐chain crystals similar to solution‐grown single crystals. The peak profiles, however, are broad and the peaks in the chromatograms shift concertedly toward lower molecular weight in the course of degradation. These findings suggest that the fold surfaces of the polymers are coarse and that there is no unique crystalline core containing a regularly folded layer. The long period estimated from small‐angle x‐ray measurements increases with increasing polymerization temperature, but scarcely varies with the solvent type. This implies that when crystallization occurs during polymerization, kinetic factors may have no great effect on crystallization.
Conformation of poly(isoprene‐gstyrene) in dilute solution
Authors: Hadjichristidis N. , Roovers J. 
Published: April 2003

AbstractA detailed description of the synthesis of a model poly(isoprene‐g‐styrene) is given. From light scattering measurements the real radius of gyration of the polyisoprene is backbone is found to be smaller than that of the polystyrene branches. The core‐and‐shell conformation of graft copolymers in dilute solution in good solvents, which was proposed for poly(styrene‐g‐isoprene), is supported by these results.
Infinite‐dilution viscoelastic properties of sodium poly(styrene sulfonate)
Authors: Rosser Robin W. , Nemoto Norio , Schrag John L. , Ferry John D. 
Published: April 2003

AbstractThe storage and loss shear moduli G′ and G″ of dilute solutions of two samples of sodium poly(styrene sulfonate) with molecular weights (M) of 3.28 × 105 have been measured. The Birnboim–Schrag multiple‐lumped resonator technique was used in the frequency range 100–8000 Hz, and the intrinsic moduli were obtained by extrapolation to infinite dilution. Measurements were performed over the temperature range from 1.0 to 25.0°C in aqueous solvents containing from 0 to 60% by weight glycerol and from 0.001 to 0.005M added salt. The large intrinsic viscosities indicated high extension of the polymer, and the frequency dependences of G′ and G″ were matched well by hybrid relaxation spectra combining rodlike and coil‐like behavior. In a solvent containing 0.001M sodium ion and no glycerol, the end‐over‐end rotational relaxation times for the two molecular weights corresponded to proportionality to the 1.7 power of M. With increasing molecular weight, ionic strength, and/or glycerol concentration, the polyelectrolyte appeared to become less extended, and its behavior more nearly coil‐like.
Small‐angle x‐ray scattering by nylon 6
Authors: Matyi R. J. , Crist B. 
Published: April 2003

AbstractSmall‐angle x‐ray scattering (SAXS) of isotropic or uniaxially oriented nylon 6 was investigated as a function of thermal and mechanical history. In addition to the peak position and linewidth of the SAXS maximum, the integrated SAXS intensity was measured. It was found that the radial intensity distributions of isotropic or arced patterns are controlled to some extent by the small width of the semicrystalline macrolattice, rendering the conventional long period and line shape analysis inapplicable to these patterns. A two‐dimensional analysis is possible with well‐oriented fibers; the major structural changes which are seen in fibers after annealing above 190°C are associated with melting and recrystallization. Extensive cold drawing and subsequent annealing cause rather modest (ca. ∼30%) changes in the integrated SAXS intensity. These effects are consistent with the generation of homogeneous interfibrillar regions during the latter stages of plastic deformation. On annealing a quenched film on nylon 6, the transformation of the crystals from a pseudohexagonal to a monoclinic habit occurs above 170°C.
Four‐center photopolymerization. A heterogeneous topochemical solid‐state reaction
Authors: Meyer Wolfgang , Lieser Günter , Wegner Gerhard 
Published: April 2003

AbstractThe four‐center solid‐state photopolymerization of distyrylpyrazine (DSP) and of 2,6‐naphthalene bis(acrylic acid‐2,4‐dichloro phenyl ester) (NBA–DCP) was investigated by x‐ray and microscopic techniques. In both cases the polymer grows as a separate product phase topotactically well arranged with respect to the monomer matrix. In the case of polymerization of DSP the space group of the monomer (Pbca) is not maintained but the polymer phase has space group P21ca. Nucleation and growth of the polymer phase was observed by light and electron microscopy. Nucleation occurs at defect sites. The polymer grows at different rates in different crystallographic directions which were identified by electron diffraction in the case of DSP. Polymerization thus occurs in the transition region between monomer crystal and product phase and not in the bulk of the crystal so that the four‐center‐type photopolymerization is best described as a heterogeneous solid‐state reaction.
A thermodynamic approach to the stress‐induced crystallization in cross‐linked rubbers
Authors: Wu W. L. 
Published: April 2003

AbstractThe thermodynamic treatment of crystallization phenomena in a prestretched rubber was undertaken. Emphasis was put on defining conditions for the thermodynamic stability of the extendedor folded‐chain crystal structure. The extended‐chain structure is found to be stable thermodynamically at temperatures higher than the isotropic melting point of un‐cross‐linked polymer T in the stretched state, while the folded chain one is not. Below T, the stretch ratio of the network structure determines which crystal structure is more stable. The relation among the critical stretch ratio for the extended/folded crystalline structure transition, temperature, and molecular weight is also discussed. The crystallinity predicted by this work becomes zero at a temperature of T, the isotropic melting point of a cross‐linked system. The value of T decreases with increasing cross‐link density, and this is consistent with the experimental data reported in the literature.
First‐order perturbation calculations of intrinsic viscosities of flexible linear and ring polymers with excluded volume: Comments on the papers of Fujita et al.
Authors: Shimada Jiro , Yamakawa Hiromi 
Published: April 2003

AbstractIt is shown that the first‐order perturbation coefficient C1 of the cubed viscosity‐radius expansion factor α of nondraining flexible chains with excluded volume may be evaluated without great labor and with sufficient accuracy by solving numerically the Kirkwood–Riseman‐type integral equations with a digital computer. The value 1.18 for C1,r obtained for ring chains is in good agreement with the corresponding value of Norisuye and Fujita, while the value 1.14 for C1,l obtained for linear chains is appreciably smaller than the corresponding value 1.29 of Fujita et al. despite the fact that the starting equations are the same. However, it is shown that the calculated value of C1,l of Fujita et al. is incorrect. Thus, the present result that C1,l < C1,r is consistent with the earlier conclusion of Yamakawa and Tanaka derived in the Zimm–Hearst scheme.
On the structure of glassy polymers. VI. Electron microscopy of polycarbonate, poly(ethylene terephthalate), poly(vinyl chloride), and polystyrene
Authors: Meyer M. , Vander Sande J. , Uhlmann D. R. 
Published: April 2003

AbstractHigh‐resolution electron microscopy studies have been carried out on four glassy polymers examined in previous small‐angle x‐ray scattering (SAXS) investigations. The polymers include polycarbonate, poly(ethylene terephthalate), poly(vinyl chloride), and polystyrene. For all four polymers, both bright field and dark‐field observations indicate the general absence of microstructural features of a size down to the resolution limit of the electron microscope. Only “pepper and salt” features on a scale ca. 5 Å are seen as characteristic of the structures. These features reflect simple interferences as the resolution limit is approached, and are seen for single crystal and oxide glasses as well as for the polymers. The present results, taken together with structural information from light scattering, SAXS, and small‐angle neutron scattering, indicate that glassy polymers should be regarded as having rendom structures. The combined results are inconsistent with heterogeneous microstructures having regions of locally high order present in large volume fractions.
Vibrational spectra and normal coordinate analysis of isotactic poly(alkyl ethylene)s. I. Modification I of poly(ethyl ethylene) and its deuterated derivatives
Authors: Holland‐Moritz K. , Sausen E. 
Published: April 2003

AbstractA new calculation of the vibrational frequencies of poly(ethy1 ethylene) based on the actual molecular geometry was performed. The calculation takes into account new experimental data such far‐infrared spectra and Raman spectra of the stretched polymer, infrared spectra of poly(ethyl ethylene)‐(2,2;d2) (P‐4‐1‐d2) and poly(ethyl ethylene)‐(3,3,4,4;d4) (P‐4‐1‐d4), and Raman spectra of poly(ethyl ethylene)‐(1,3,3;d3) and poly(ethyl ethylene)‐(3,3,4,4;d4). Refinement produced a set of force constants; it is also applicable to poly(propyl ethylene).
Inverse gas chromatography of poly(cyclohexyl methacrylate)
Authors: Llorente M. A. , Menduiña C. , Horta A. 
Published: April 2003

AbstractInverse gas chromatography is applied to determine the glass transition temperature Tg of poly‐(cyclohexyl methacrylate). Both good and bad solvents for the polymer are used as molecular probes. Although the transition is clearly detected by both types of probes, only the nonsolvents yield a Tg in quantitative agreement with the value determined by differential scanning calorimetry. The relative depth of penetration of the probe in the polymer phase is calculated from retention volume data. Also, the height equivalent to a theoretical plate is calculated from peak halfwidths. Both calculated magnitudes show a temperature dependence which significantly differs from good to bad solvents. Some kind of diffusion‐limited penetration of the probe in the bulk of the glassy polymer may be responsible for the difference.
Theory of free volume in polymers
Authors: Rudnick J. , Taylor P. L. , Litt M. , Hopfinger A. J. 
Published: April 2003

AbstractA number of theoretical approaches to the problem of free volume in polymers are discussed. Because some questions in the Bueche approach remain unresolved, the lattice‐gas model was studied. Inconsistencies in the independent‐vacancy approximation led to consideration of a mean‐field model and then a precise Padé‐approximant solution, neither of which gave satisfactory agreement with experiment. Introduction of an internal pressure parameter to model the effects of the chainlike structure of polymers restores agreement with experiment.
Estimations of fold surface densities using space‐filling models
Authors: Harrison I. R. , Juska T. 
Published: April 2003

AbstractThe model of a tight‐fold adjacent reentry fold surface for polyethylene single crystals has been questioned, because it has been speculated that a tight‐fold surface should have a density approximating that of the unit cell (∼1.00 g/cm3). This would lead to an overall lamella density of close to unity. In contrast, the majority of measured values are in the range 0.96 to 0.97+ g/cm3. These lower values have been taken as evidence to disprove a tight‐fold–surface model. The present calculations made on space filling models of tight folds indicates a fold surface density on the order of 0.75 g/cm3. This produces no inconsistency between a tight‐fold model and accepted lamella density values. Further, calculated values of the weight fraction crystallinity of lamella, as a function of the number of carbons in the fold, limits this number to approximately 9 to 11 carbons per fold.