bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rheology of concentrated solutions of helical polypeptides
Authors: Kiss Gabor , Porter Roger S. 
Published: April 2003

AbstractRheological studies were carried out on concentrated m‐cresol solutions of two helical synthetic polypeptides; poly‐γ‐benzyl‐L‐glutamate (PBLG; molecular weight, 150,000) and poly‐ϵ‐carbobenzyloxy‐L‐lysine (PCBZL; molecular weight, 200,000). Steady shear measurements were made over a range of 0.01–16,000 sec−1 to obtain steady shear viscosity and first normal stress difference. Dynamic viscosity and dynamic storage modulus were measured both by oscillatory shear between cone and plate and also by an eccentric rotating disk device over frequency ranges of 0.1–400 and 0.1–63 rad/sec, respectively. The concentration ranges were such that both liquid crystalline and isotropic solutions were investigated. The previously reported observations of an apparent negative first normal stress difference within a defined range of shear rate for liquid crystalline solutions were confirmed for the PBLG and PCBZL solutions. At high shear rates the peaks in plots of steady shear viscosity against concentration were profoundly suppressed but peaks in first normal stress difference versus concentration were not. The observation of liquid crystalline order in PCBZL/m‐cresol solutions at room temperature constitutes evidence that the inverse coil‐helix transition temperature is lower in concentrated solutions than in dilute solutions. The critical concentration for formation of the liquid crystalline phase was higher for PCBZL than for PBLG, despite a higher axial ratio, due to helix flexibility.
Etude diélectrique de trois copolymères ethylène—monoxyde de carbone
Authors: Decossas Françoise , Moliton André , Marchal Eve 
Published: April 2003

AbstractDielectric absorption measurements are made on three ethylene‐carbon monoxide copolymers containing 2.3, 8.7, and 18 CO per 1000 CH2 at frequencies ranging from 1 kHz to 1 MHz throughout the 90–373°K temperature range. Mean values of the activation energies of the γ, β, and α relaxations are found to be, respectively, 11.5, 41.5, and 31 kcal/mole from measurements done at fixed frequency by varying the temperature and 27 kcal/mole for the α relaxation as obtained from measurements at steady temperatures with drifting frequencies. The interaction energy of the CH2 unit in the crystalline polyethylene chain with its neighbors is calculated on the basis of the chain rotation model as well as of the rotation‐translation model proposed by Hoffman et al. It seems that their αc models accounting for the molecular origin of the α relaxation have to be rejected. It is further shown that the sharp decrease of permittivity for high temperature (above 330°K at 1 kHz) is only due to the marked decrease of the density of polyethylene with increasing temperature.
Crystallinity of bulk polyacetylene
Authors: Akaishi Tsukasa , Miyasaka Keizo , Ishikawa Kinzo , Shirakawa Hideki , Ikeda Sakuji 
Published: April 2003

AbstractThe fine structure of bulk trans‐polyacetylene (PA) was investigated by x‐ray diffraction. The degree of crystallinity 0.81, determined by Ruland's method, was significantly higher than the value for linear polyethylene. The disorder parameter k was 5, which is much larger than the value for polyethylene. These results led us to propose that PA crystals are more disordered than PE crystals owing to the higher rigidity of PA chains. Small‐angle x‐ray diffraction indicated that the crystal morphology is of the extended‐chain type rather than lamellar. All results obtained in this work showed that the fine structure of PA bulk is such as to facilitate electrical conduction of bulk PA.
Crystallization and morphology of melt‐solidified poly(vinylidene fluoride)
Authors: Lovinger Andrew J. 
Published: April 2003

AbstractCrystallization of poly(vinylidene fluoride) (PVF2) from the melt yields two types of spherulites. The first consists of large, highly birefringent, and tightly banded spherulites of the α‐form, which are seen at all temperatures. The second type, termed mixed, crystallizes with a newly reported unit cell which appears to be the correct one for γ‐PVF2, but may contain inclusions of a different form (probably α‐PVF2); it is seen only at relatively high temperatures and frequently exhibits irregular or disorganized birefringent and morphological features. In thin films, some mixed spherulites contain regions of single‐crystal‐like aggregates which are grown parallel to the substrate and appear essentially nonbirefringent between crossed polars. Mixed spherulites frequently undergo transformations at their growth fronts leading to initiation of α‐growth. These transformations are associated with the generally higher growth rate of α‐spherulites which may exceed that of their mixed counterparts by almost seven times. However, with increasing temperature this difference in growth rates is progressively reduced and ultimately reversed.
Thermoplastic urethane elastomers. VI. Dilute solution properties in various solvents
Authors: Seefried C. G. , Koleske J. V. , Critchfield F. E. , Pfaffenberger C. R. 
Published: April 2003

AbstractA thermoplastic urethane elastomer prepared from a polycaprolactone diol, 4,4′‐diphenylmethane diisocyanate, and 1,5‐pentanediol was fractionated and the solution properties of the fractions were characterized in terms of viscosity and sedimentation. Mark‐Houwink relations were established for data obtained at 30° in various solvents:

In dimethylacetamide, tetramethylurea, and N‐methyl pyrrolidone, the value of Kθ increased systematically in the range (1.7 to 2.0) × 10−3. Lower values of Kθ were obtained in dimethylformamide (0.8 × 10−3) and meta‐cresol (0.9 × 10−3). The molecular expansion coefficients in the various solvents were approximated from the experimental viscosity data. Short‐range interactions between the solvent molecules and polymer chains are suggested as possible causes for differences in the hydrodynamic parameters.
Quantitative determination of mesomorphic regions in oriented polymers from wide‐angle X‐ray diffraction
Authors: Lemanska Gizela , Narebska Anna 
Published: April 2003

AbstractA method for quantitative characterization of the noncrystalline region in poly(ethylene terephthalate) (PET) fibers based on x‐ray wide‐angle diffraction data is elaborated. The procedure consists in a computational resolution of the diffracted intensity into individual peaks for 010, 110, and 100 planes and into isotropic and anisotropic components of diffuse scattering. The results show that the content of mesomorphic regions in the noncrystalline part of PET fibers with draw ratio of λ = 3.0 varies from 12% to 32% depending on the temperature of heat treatment.
Characterization of polyethylene shish‐kebabs by small‐angle X‐ray scattering
Authors: Van Hutten P. F. , Pennings A. J. 
Published: April 2003

AbstractSmall‐angle x‐ray scattering has been used to characterize a variety of polyethylene fibers of the so‐called shish‐kebab type. These fibers are aggregates of elementary fibrils each consisting of a backbone with a lamellar overgrowth. Intense scattering is due to voids between the lamellae giving rise to a “Bragg maximum” reflecting the ordering of lamellae along the backbones. It can be described by rather broad distributions for both the interlamellar spacings and the lamellar thicknesses. This is shown by comparing experimental scattering curves with SAXS patterns calculated on the basis of the theory for one‐dimensional scattering of linearly ordered lamellar systems, using the general paracrystalline model. A negative exponential distribution for the center‐to‐center distance of the lamellae, characteristic of a random nucleation process, apparently cannot be employed for the description of these shish‐kebab morphologies. From a discussion on the discrepancies between experimental and theoretical scattering curves it is concluded that the fibers may be inhomogeneous with respect to the statistics of lamellar ordering. This may be due to the nonisothermal character of the crystallization process.
Ellipsometric study of the adsorption of comb‐branched polystyrene onto a metal surface
Authors: Kawaguchi Masami , Takahashi Akira 
Published: April 2003

AbstractThe adsorption of well‐characterized comb‐branched polystyrene onto a chrome plate from cyclohexane solution at the θ temperature has been studied by ellipsometry. Both the adsorbance of the polymer and the extension of the adsorbed layer are compared with values for the linear polystyrene of the same molecular mass. The adsorbance is higher than that of the linear polystyrene, whereas the extension of the adsorbed layer is smaller, reflecting the higher segment density of the branched polymer. The extension tb of the branched polymer is given approximately tb = tlg, where tl is the extension of linear polystyrene of the same molecular mass and g is the ratio of the radii of gyration of the branched and linear polymers. The ratio of the adsorbances Ab/Al of branched and linear polymer is approximately equal to g. These results indicate that the comb‐branched polymer is adsorbed as a slightly distorted randam coil with extension and adsorbance governed primarily by the experimental gs factor.
Piled‐lamellae structure in polyethylene film and its deformation
Authors: Tagawa Takashi , Ogura Kazumichi 
Published: April 2003

AbstractThe fine structure of polyethylene film has been investigated by using a high‐resolution scanning electron microscope equipped with a field emission source. The original film surface of a‐axis‐oriented blown polyethylene film and the surface of a necked region formed by drawing the film in the machine direction were observed. High magnification electron micrographs indicate that the basic unit of internal texture of this film consists of piled‐lamellae units, each pile containing three to ten lamellar crystal sheets. The piled‐lamellae unit acts as one body and does not separate into single lamellae during deformation. Many tie fibrils are formed between adjacent piled‐lamellae units, when the film is drawn in the machine direction. Although little attention has been given to this mechanism, it is important in deformation. This fact seems to be reflected in different shapes of the stress‐strain curves of films drawn the machine direction and perpendicular to it.
Molecular theory of piezoelectricity of α‐helical polypeptide
Authors: Namiki Koji , Hayakawa Reinosuke , Wada Yasaku 
Published: April 2003

AbstractA molecular theory of the piezoelectric constant of the α‐helical backbone of polypeptide is developed on the basis of fluctuation formalism. The piezoelectric constant, electric susceptibility, and elastic compliance of the α‐helix are calculated through the method of molecular lattice dynamics by use of normal‐coordinate analysis. Displacements of each atom due to the external stress exerted upon the backbone are also calculated. The piezoelectricity of the α‐helix is concluded to arise mainly from rotation of the CONH bond. The value of the piezoelectric constant of poly(γ‐benzyl‐L‐glutamate) film calculated from the above theoretical constants along with a composite theory is found to agree reasonably with experiment.
Molecular rheology of concentrated polymer systems. I
Authors: Doi Masao 
Published: April 2003

AbstractThe primitive chain model of Doi and Edwards is generalized to include the short‐time relaxation process. Stress relaxation after a sudden imposition of strain is studied in detail. It is shown that in the linear region (small strain) stress relaxation occurs in two steps, the relaxation of chain segments between the fixed entanglement points, and the relaxation of the entanglement points, in accordance with the conventional picture, whereas in the nonlinear region (large strain) there appears a new relaxation process between the above two. The characteristic time of this process is the Rouse relaxation time which the entire chain would have if there were no entanglements, and increases with the square of the molecular weight. This result is consistent with experimental observations.
Small‐angle X‐ray and neutron scattering studies of the morphology of ionomers
Authors: Roche E. J. , Stein R. S. , MacKnight W. J. 
Published: April 2003

AbstractPreliminary small‐angle neutron scattering (SANS) studies have been made of different ionomers in the dry state and after saturation with water. Scattering from the dry samples arises from differences in the neutron scattering cross sections of the ionic and nonionic units in the polymer. The SANS technique is complementary to previous small‐angle x‐ray scattering (SAXS) studies since the SANS contrast differences are generally quite different than those for SAXS. A quantitative comparison is made of SANS and SAXS intensities for a dry cesium salt of an ethylene‐methacrylic acid (E‐MAA) copolymer. For water‐saturated samples the technique of isotopic replacement can be used in conjunction with SANS since saturation can be effected with either H2O or D2O. In this case information about the chemical composition of the phases is obtained from an analysis of the intensity ratio I/I. Results are consistent with the presence of a separate phase containing water molecules and ions in a matrix of the nonionic units. A Guinier analysis gives a radius of gyration of 17 Å for a water‐saturated cesium salt of an E‐MAA copolymer.
Nylon‐6 α‐phase crystal: Chain repeat distance and modulus in the chain direction at low temperature
Authors: Miyasaka Keizo , Isomoto Tsuneyuki , Koganeya Hiroshi , Uehara Katsuhiko , Ishikawa Kinzo , Ogata Nobuo 
Published: April 2003

AbstractThe chain repeat distance in the α‐phase crystal of nylon‐6 was measured from −150 to 150°C. The distance increases with decreasing temperature, indicating that the chain is not a complete planar zigzag but is twisted at room temperature. The relation between the distance and temperature changes at about −110°C and again near 40°C. Both changes seem to be related to the mechanical dispersions of the material. Young's modulus in the chain direction is 270 GN/m2 at −150°C, or 14% less than the theoretical value given by Tashiro and Tadokoro for the planar zig‐zag structure. It is not possible to determine from the (0k0) diffraction intensities whether the amide or methylene moieties are the more important in the chain twisting.
Glass transition in polyacrylonitrile: Analysis of dielectric relaxation data
Authors: Gupta A. K. , Chand Navin 
Published: April 2003

AbstractDielectric relaxation of polyacrylonitrile (PAN) samples, in which the presence of an amorphous phase is evidenced by x‐ray diffraction, has been studied over the temperature range 30–150°C and frequency range 102–105 Hz. These data as well as those reported by other authors, reveal several points useful to the understanding of the dielectric relaxations of PAN in relation to its structure. A glass transition in PAN is evidenced by at least two of the four data sets investigated; the third shows combined effect of two relaxations, whereas the fourth clearly shows a relaxation process different from the glass transition. The glass‐transition behavior of the dielectric relaxation data is confirmed by Williams‐Landel‐Ferry theory and a recent theory of Phillips, both of which lead to consistent conclusions.
Oriented cellulose films and fibers from a mesophase system
Authors: Chanzy H. , Peguy A. , Chaunis S. , Monzie P. 
Published: April 2003

AbstractCellulose mesophases were obtained by preparing concentrated solutions of cellulose (20–55%) in a mixture of N‐methyl‐morpholine N‐oxide (MMNO) and water. The anisotropy depends on four interconnected parameters: the temperature of the solution which, in general, must be lower than 90°C; the concentration of cellulose which must exceed 20%; a water content such that the mole ratio water/anhydrous MMNO is smaller than unity; and the degree of polymerization of the dissolved cellulose. The anisotropic cellulose solutions can readily be oriented during extrusion or casting thus giving fibers or films which upon regeneration exhibit high orientation.
Electron microscopy study of the structure of normal and abnormal poly(butylene terephthalate) spherulites
Authors: Roche E. J. , Stein R. S. , Thomas E. L. 
Published: April 2003

AbstractNormal and abnormal spherulites of polybutylene terephthalate cast from solution in HFIP were investigated by electron microscopy (CTEM and STEM). Both spherulite types crystallize in the α form. The crystallite is biaxial with its greatest polarizability directions Z and Y oriented along the molecular chain and perpendicular to it in the plane of the terephthalate residue. In the normal spherulites, the [210]* direction is parallel to the radius direction, so that both Z and Y directions are oriented tangentially (negative spherulites). In the abnormal spherulites, the [111]* direction is parallel to the radius, and this explains the observed abnormal light scattering pattern.
Nature of the penetrant jump length in diffusion within polymers
Authors: Pace R. J. , Datyner A. 
Published: April 2003

AbstractResults from two types of experiments, both on polyethylene, which allow, respectively, direct and indirect estimates of the magnitude of simple penetrant diffusion jump lengths are examined. In both cases the jump lengths inferred, for several small penetrants, are consistent with the values suggested by a recently proposed theory of diffusion in polymers.
Hydrostatic extrusion of linear polyethylene: Effects of extrusion temperature and polymer grade
Authors: Hope P. S. , Gibson A. G. , Ward I. M. 
Published: April 2003

AbstractThe hydrostatic extrusion behavior of linear polyethylene has been examined for two homopolymers of very different molecular weight characteristics and for a copolymer. Good unflawed extrudates could be obtained in all cases, and the extrusion behavior at a fixed temperature correlated well with the melt flow index. Although the maximum values of axial Young's modulus obtainable from the higher molecular weight homopolymer and the copolymer were lower than those possible for the lower molecular weight homopolymer, such materials do show improvements in creep behavior which could be advantageous. The effect of temperature on the extrusion behavior is discussed; the results suggest that for each grade of polymer there is an optimum temperature for effective extrusion, i.e., extrusion which gives optimum modulus enhancement. Finally, the melting behavior and the temperature dependence of the axial Young's moduli of the extrudates are considered in terms of our present knowledge of the structure of these high modulus materials.
Glass transition in semicrystalline polycarbonate
Authors: Wissler G. E. , Crist B. 
Published: April 2003

AbstractThe intensity of the glass transition in semicrystalline polycarbonate was measured by differential scanning calorimetry and by thermally stimulated discharge of electrets. Solution‐cast and bulk‐crystallized samples possessing widely varying crystallinities and morphologies were investigated. It is shown that the intensity of the glass transition is governed by the extent of primary crystallization and is a linear combination of intensities from the bulk amorphous regions and from noncrystalline polymer within semicrystalline aggregates such as spherulites. The intensity of the glass transition within spherulites is about 0.1–0.3 as great as that in bulk amorphous regions. A three‐phase model incorporating two distinct types of noncrystalline polycarbonate is proposed to account for the properties of this polymer.
Free‐volume interpretations of self‐diffusion in ternary solutions: n‐Paraffin‐hexafluorobenzene‐cis‐4‐polybutadiene
Authors: Ferguson R. D. , von Meerwall E. 
Published: April 2003

AbstractSelf‐diffusion of both diluents in the systems n‐paraffin + hexafluorobenzene + cis‐4‐polybutadiene (paraffin = dodecane or hexatriacontane) has been measured at 80°C as function of both concentrations, using field‐gradient spin‐echo techniques (1H and 19F NMR). The data follow the free‐volume model in the form of the Fujita‐Doolittle equation, or the Vrentas‐Duda theory, extended to apply to ternary systems. It is found that the polymer molecular jumping segments are roughly equal in size to the diluent molecules or their jumping segments.
Morphology and melting behavior of semicrystalline poly(ethylene terephthalate). II. Annealed PET
Authors: Groeninckx G. , Reynaers H. 
Published: April 2003

AbstractAnnealing of poly(ethylene terephthalate) samples crystallized under isothermal conditions above the crystallization temperature has a marked influence on their morphology and results in increased thermal stability of the crystalline structure as indicated by the melting point increase of the samples. The morphological transformation processes induced by annealing are very complex and depend on the thermal history of the samples, i.e., crystallization temperature and heating procedure. Depending on the nature of the processes occurring during annealing, various parameters characterizing the semicrystalline state of the samples can be affected such as the degree of crystallinity, the long spacing, the thickness of amorphous and crystalline layers, the crystal perfection, the fold‐surface structure, and the mosaic structure of the crystalline lamellae. Annealing involves a solid‐state transformation of the original crystalline structure including crystal perfection without thickening or a melting followed by recrystallization with crystal perfection and crystal thickening. The combination of differential scanning calorimetric (DSC) measurements and small‐angle x‐ray scattering is a powerful analytical tool to detect morphological changes and helps in deciding on the processes which are involved in the transformation of the microstructure upon annealing.
Electron spin resonance study of copolymerization of hexafluoroisobutylene with vinylidene fluoride
Authors: Yue H. , Nelson G. , O'Brien K. , Chandrasekaran S. , Sibilia J. 
Published: April 2003

AbstractThe Copolymerization reaction of hexafluoroisobutylene (HFIB) and vinylidene fluoride (VF2) was studied using X‐band electron spin resonance (ESR) by applying a photo‐in situ method. Owing to the toxicity of HFIB monomer, the flow ESR method could not be directly applied without extensive modification. The observed ESR signal with 21‐line hyperfine structure was assigned to the copolymer radical with head‐to‐head configuration. Although the HFIB monomer radical possesses the same hyperfine pattern, the ambiguity has been removed by using CF3 as an initiator radical. Owing to the high steady‐state concentration of the observed copolymer radical with head‐to‐head configuration as well as the nature of the static photo‐in situ ESR method, we believe the actual molecular configuration for HFIB/VF2 copolymer must be head‐to‐tail. The observed hyperfine constant for AβF = 1.74 mT suggests that the geometry for HFIB/VF2 copolymer radicals with both head‐to‐head or head‐to‐tail configurations is possibly similar to that of (CF3)3C· radical. The small value for AβH indicates steric hindrance to rotation about the CαCβ bond, and this is also supported by the experimental results of nonalteration in linewidth during the temperature dependence study from −40 to about 90°C. Attempts to measure directly the monomer reactivities have been unsuccessful owing to the fact that not all the possible radicals were detected, but nevertheless the relative reactivities of VF2 and HFIB could be estimated. The relative reactivities of VF2 and HFIB monomers and the steric hindrance effect indicate that the conformation of the copolymer is head‐to‐tail; this has been further confirmed by infrared analysis.