bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics of fiber heat treatment. III Poly(butylene terephthalate) fibers
Authors: Peszkin Perla N. , Schultz J. M. , Lin J. S. 
Published: April 2003

AbstractSmall‐ and wide‐angle X‐ray scattering (SAXS and WAXS), shrinkage, and density experiments were performed on poly(butylene terephthalate) fibers which had been isothermally crystallized at different temperatures, and at constant tension, for times ranging from 100 to 1050 ms.A consistent correlation among WAXS, SAXS, and the kinetic results is demonstrated. Shrinkage results show that the crystallization process prevails over the chain‐re‐coiling process. Density measurements show that the rate of crystallization increases with temperature. Pinhole X‐ray photos show that the orientation of the chains within the crystals remains constant with time and temperature. WAXS diffractometer scans show the development of wide‐angle Bragg peaks.SAXS shows the development of small‐angle Bragg peaks, as the annealing time is increased. The two‐lobe arced pattern is the characteristic pattern. The value for long spacing ranged from 100 to 120 Å, increasing with temperature.
Response of the mean‐square optical anistropy of chain molecules to the imposition of excluded volume
Authors: Mattice Wayne L. , Saiz Enrique 
Published: April 2003

AbstractThe influence of the chain expansion produced by excluded volume on the mean‐square optical anisotropy has been studied in six types of polymers. The mean‐square optical anistropy for a specified configuration is calculated using the valence optical scheme. Realistic rotational isomeric state models are used for the configurational statistics of the unperturbed chains. Excluded volume is introduced by hard sphere interactions. Results obtained with chains of 100, 200, 300, and 400 bonds permit extrapolation to the behavior expected for much longer chains. The mean‐square optical anisotropy of polyethylene is insensitive to excluded volume. A similar conclusion was obtained several years ago in a study of chains confined to a tetrahedral lattice and weighted in a manner appropriate for the short‐range interactions in polyethylene.2 Different behavior is seen in poly(vinyl chloride), poly(vinyl bromide), polystyrene, poly(p‐chlorostyrene), and poly(p‐bromostyrene). The mean‐square optical anisotropy of these five vinyl polymers is sensitive to the imposition of excluded volume if the stereochemical composition is exclusively racemic. Much smaller effects are seen in meso chains and in chains with Bernoullian statistics and an equal probability for meso and racemic dyads.
Poly(chloropropylmethyl‐dimethylsiloxane)–polyurethane elastomers: Synthesis and properties of segmented copolymers and related zwitterionomers
Authors: Yu X. , Nagarajan M. R. , Li C. , Gibson P. E. , Cooper S. L. 
Published: April 2003

AbstractA series of polyurethane block copolymers based on hydroxybutyl terminated poly(chloropropylmethyl‐dimethylsiloxane) and poly(tetramethylene oxide) soft segments of molecular weights 2100 and 2000, respectively, were synthesized. The hard segments consisted of 4,4′‐methylenediphenylene diisocyanate (MDI) that was chain extended with either 1,4‐butanediol (BD) or N‐methyldiethanolamine (MDEA). The materials chain extended with MDEA were ionized using 1,3‐propane sultone. The weight fraction of the hard segments was in the range 0.30–0.45. The effect of mixed soft segments, chain extenders, and zwitterionization on the extent of phase separation and physical properties was studied by utilizing differential scanning calorimetry and dynamic mechanical, stress‐strain, and Fourier Transform Infrared spectroscopy experiments. All of these short segment block copolymers showed nearly complete phase separation. The zwitterionomer materials exhibited ionic aggregation within the hard domains. Although hard segment crystallinity or ionic aggregation did not affect the morphology, hard domain cohesion was important in determining the tensile and viscoelastic properties of these elastomers.
The heat capacity of solid and liquid polystyrene, p‐substituted polystyrenes, and crosslinked polystyrenes
Authors: Judovits Lawrence H. , Bopp R. C. , Gaur U. , Wunderlich Bernhard 
Published: April 2003

AbstractHeat capacities were measured for poly(4‐methylstyrene) [300–500K], poly(4‐fluorostyrene) [130–350K], poly(4‐chlorostyrene) [300–550K], poly(4‐bromostyrene) [300–550K], poly(4‐iodostyrene) [300–550K] and poly(styrene‐co‐divinylbenzene) with 1, 2, 4, 8, and 12 wt.% divinylbenzene (technical grade) [300–550K]. Polystyrene and poly(α‐methylstyrene) data were found to match the ATHAS data bank collections. Crosslinking causes no significant change in heat capacity, but substitution does. The heat capacities in the solid state are evaluated using approximate group and skeletal vibration spectra. Glass transitions are discussed, and full thermodynamic functions (Cp, H, S, G) can be calculated for amorphous, crystalline, and deuterated polystyrene as well as poly(α‐methylstyrene). Glassy polystyrene has an entropy of 7.5 J K−1 mol−1 at absolute zero. Changes of the heat capacity at the glass transition are explained and are predicted to go to zero for 50% poly(styrene‐co‐divinylbenzene) at about 550K.
Structure investigation of poly(p‐phenylene vinylene)
Authors: Granier Thierry , Thomas Edwin L. , Gagnon David R. , Karasz Frank E. , Lenz Robert W. 
Published: April 2003

AbstractElectron diffraction patterns of highly oriented poly(p‐phenylene vinylene) films obtained by the soluble polymeric precursor route are interpreted on the basis of a monoclinic unit cell containing two monomer units: c (chain axis) = 0.658 nm, a = 0.790 nm, b = 0.605 nm, α ≃ 123°. The molecules are nearly perfectly oriented along the stretching direction but exhibit partial axial translational disorder.
Stress‐optical behavior of cycloaliphatic polyesters
Authors: Riande E. , Guzmán J. 
Published: April 2003

AbstractStress‐strain‐birefringence measurements were carried out on elastomeric networks of poly(oxymethylene‐1,4‐cis‐cyclohexylenemethyleneoxysebacoyl) at several temperatures between 5 and 80°C. The dependence of both the birefringence Δn and the true stress f/A on temperature was found to be linear for T > 30°C; for T < 30°C an anomalous increase in the birefringence and a sharp decrease in the stress was observed. This behavior suggests that crystallinity is developed in the strained networks at low temperatures, and the crystallites are oriented in the direction of the elongation. Values of the optical configuration parameter Δa ranged from 9.15 to 8.28 in units of 1024 cm3 in the temperature range studied. The value at 40°C of 1024Δa, obtained from experiments performed on swollen networks, amounted to 7.47 cm3. These results suggest that intermolecular interactions enhance the birefringence of the strained networks. The quantities Δa and d In Δa/dT were calculated by using the valence optical scheme. Although the calculations reproduce the temperature coefficient fairly well, the theoretical values of Δa are smaller than the experimental ones. The agreement between theory and experiment is better assuming that the CH2CH2COOCH2 segment is freely rotating.
The effect of plasticization on craze microstructure
Authors: Brown H. R. , Njoku N. G. 
Published: April 2003

AbstractThe structure of crazes in plasticized polystyrene has been studied by means of small‐angle x‐ray scattering and optical interference microscopy. Addition of plasticizer causes a rapid increase in the mean fibril diameter D and a slow decrease in the craze fibril volume fraction vf. The crazing stress σc was also measured and it was found that the product Dσc is independent of plasticizer concentration. These results are shown to be consistent with the entanglement model for controlling vf and the meniscus instability model of craze thickness growth.
The heat capacity of solid poly(p‐xylylene) and polystyrene
Authors: Kirkpatrick Donald E. , Judovits Lawrence , Wunderlich Bernhard 
Published: April 2003

AbstractThe constant‐pressure heat capacity Cp of poly(p‐xylylene) (PPX) has been measured from 220 to 625 K by differential scanning calorimetry. The constant‐volume heat capacities Cv of both, PPX and its isomer polystyrene (PS) have been interpreted in the light of literature data on full normal‐mode calculations for PS and estimates from low‐molecular‐weight analogs for PPX for the 39 group vibrations. Nine skeletal vibrations were used in this discussion with characteristic temperatures θ1 and θ3 of 534.5 and 43.1 K for PS. It was also possible to calculate a heat capacity contribution of a phenylene group within a polymer chain. Single 48‐vibration θ1 temperatures of 3230 K for PS and 2960 K for PPX are sufficient to describe Cv above 220 K. Below 140 K, PS heat capacity shows deviations from the Tarasov treatment.
The relationship between microstructure and mode of fracture in polyhydroxybutyrate
Authors: Barham P. J. , Keller A. 
Published: April 2003

AbstractPolyhydroxybutyrate (PHB) is a bacterially produced thermoplastic. Melt‐cast PHB sheets are usually quite brittle. We show that this brittleness is due to cracks within the spherulites. These cracks, which may be either radial or circumferential within the spherulites, depending on the crystallization temperature, form under conditions of no externally applied stress. When the material is strained the cracks grow and join together, leading to brittle failure. It is possible to produce ductile PHB sheets in two ways: first, the cracks may be “healed” by a cold rolling process; second, special crystallization conditions can be used to produce ductile sheets consisting entirely of crack‐free spherulites. The relevance of this work to the ductility of crystalline thermoplastic in general is discussed.
Ultrahigh‐molecular‐weight polyethylene: Raman spectroscopic study of melt anisotropy
Authors: Wunder Stephanie L. , Merajver Sofia D. 
Published: April 2003

AbstractThe Raman spectrum of ultrahigh‐molecular‐weight polyethylene (UHMWPE) has been obtained in the temperature interval 135–208°C, a region where optical anisotropy was observed to exist. On the basis of our spectroscopic evidence, we believe that ordered regions persist in the melt above the calorimetrically determined melting point, and that part of the polyethylene chain is in an enviroment which is similar to that of the orthorhombic crystal. These ordered domains disappear with increasing temperature, but no calorimetric phase transition is associated with this change. We postulate that the very long relaxation times associated with the highly viscous melt keep the polyethylene chains in ordered environments which persist until decreased viscosity at increased temperature allows long‐range segmental motion. Our evidence supports the view that the melt anisotropy of UHMWPE arises from oriented slowly melting superheated crystals and not from a smectic liquid‐crystalline phase.
Determination of dual‐mode sorption and mobility parameters from permeation experiments
Authors: Toi K. , Oba K. , Maeda Y. , Ito T. , Shirakawa T. , Ikemoto I. , Tokuda T. 
Published: April 2003

AbstractThe precise pressure dependence of apparent diffusion and permeation coefficients was measured by using a microcomputer system for collecting and treating permeation data for CO2 in glassy poly(ethylene terephthalate) below 1 atm between 15 and 40°C. The partial immobilization model was used to determine the dual‐mode sorption and mobility parameters. The curves calculated with these parameters were in excellent agreement with experimental data. These parameters were also compared with sorption parameters obtained from measurements at 30°C. There was a small difference between the values of the parameters obtained from these permeation data and those from sorption data which we had previously obtained. Relations between this difference and the method of determination of the parameters are discussed.
Second and third virial coefficients for binary polystyrene mixtures in benzene
Authors: Sato Takahiro , Norisuye Takashi , Fujita Hiroshi 
Published: April 2003

AbstractLight‐scattering second and third virial coefficients for benzene solutions (at 25°C) of two binary polystyrene mixtures, in which the molecular weight ratios of component fractions (essentially monodisperse) were 98 and 11.6, were determined as functions of polymer composition. The cross‐term virial coefficients A12 (for two different solutes 1 and 2), A112 (for two same solutes 1 and one solute 2), and A122 were evaluated from such functions. It was found that none of the existing theories for A12 yield a consistent and quantitative description of our experimental finding. No theory is yet available for A112 and A122, but the numerical values of these coefficients as estimated here are of interest in themselves.
Fundamental relationship between the nonequilibrium glassy state and yield stress of amorphous polymers
Authors: Chow T. S. 
Published: April 2003

AbstractThis paper reports the theoretical prediction and experimental verification of the connection between the yield stress of amorphous polymers and the physical aging phenomenon. The analysis reveals the existence of a fundamental relationship between the nonequilibrium glassy state and the thermally activated process controlling viscoelastic and plastic deformation. The results show that the volume relaxation and deformation kinetics share the same relaxation times, and that the activation energy for deformation below Tg is much smaller than previously mentioned in the literature. This indicates that the phenomenon of physical aging plays a very important role in the deformation and processing of polymers at low temperatures. The effect of quenching and annealing on the yield stress is described in terms of the mean energy of hole formation, the departure of volume from its equilibrium state, the distribution of hole energies, and lattice volume. The same set of molecular parameters obtained from the molecular kinetic theory of the glass transition and volume relaxation predicts the yield stress as a function of cooling rate, annealing time, temperature, and strain rate.
Films solidified from a lyotropic mesophase which retain the cholesteric structure
Authors: Watanabe Junji , Krigbaum W. R. 
Published: April 2003

AbstractSolidified cholesteric films of α‐helical poly(γ‐methylL‐glutamate) and poly(γ‐benzylL‐glutamate) were prepared by casting from solutions of the lyotropic cholesteric mesophase. Colored films can be prepared in this manner, so the cholesteric structure is retained with a pitch corresponding to a visible wavelength. Their iridescent colors can cover the full range of the visible spectrum, and the colors remain unchanged for years. Although the films are similar in optical properties to those of fluid cholesteric phases, the temperature dependence of the color is quite different. On stretching, the film undergoes a permanent deformation, and the iridescent color is shifted toward the blue. Ift0is the initial film thickness and Δtis the change in thickness after stretching the film, the relative change in pitch, −ΔP/P0, of the cholesteric structure increases linearly with −Δt/t0in the range −Δt/t0> 0.10. This reduction of the pitch is attributed to a decrease in the number of pseudonematic layers in the span of one pitch, which may be interpreted in terms of delamination using an angle‐ply model of the cholesteric structure.
Elasticity of model poly(oxypropylene) networks
Authors: Andrady Anthony L. , Llorente Miguel A. 
Published: April 2003

AbstractThe equilibrium stress‐strain properties and the swelling behavior of moderately cross‐linked model networks of poly(oxypropylene) were studied. Results were in general agreement with the theory of rubber elasticity due to Flory. However, data on the highly cross‐linked networks (M̄c ≈ 725) could not be satisfactorily described by the recent theories of elasticity or swelling. This is believed to be primarily due to the marked non‐Gaussian character of the very short network chains and the substantial chemical modification of the polymer by the cross‐linking moiety which inevitably occurs at high cross‐link densities.
Morphologies and mechanical properties of pet films crystallized under high strain rates
Authors: Petermann J. , Rieck U. 
Published: April 2003

AbstractThe morphologies of highly oriented PET films, crystallized in a longitudinal flow gradient, were examined using transmission electron microscopy, differential thermal analysis, thermomechanical analysis, birefringence measurements, and mechanical tensile tests. The morphology in the as‐drawn state of the samples consists of oriented single micellar blocks which are embedded in the amorphous matrix. Annealing above 180°C causes a morphological transformation into lamellalike crystals, which are formed by lateral crystallization, preferably at the sidefaces of the micellar blocks. An interpretation of the mechanical behavior is given in accordance with the morphological model.
Dielectric properties of thermooxidized poly(vinyl formal)
Authors: Aoki Hiroyuki , Suzuki Tsutomu 
Published: April 2003

AbstractAn investigation was made of the correlation between changes in dielectric properties (110 Hz–4 MHz, 213–443 K) of poly(vinyl formal) and chemical structure during thermooxidation. As thermooxidation proceeds, the loss peak of the αa relaxation is displaced to higher temperature and cannot be detected in this temperature range. On the other hand, two loss peaks are observed in the region of the β relaxation and can be assigned to local motion of the main chain (βlocal) and end groups (βend). These two β relaxations are closely correlated with changes in chemical structure: the former is attributed to cleavage of the formal ring, formation of unsaturated bonds and cross‐linking; and the latter is assigned to aldehyde end groups. A good correlation exists between the total dielectric relaxation strength of the β relaxation and changes in carbonyl concentration. The carbonyl dipole moment is calculated as 2.68D by the Frölich‐Onsager equation. Thus, it is clear that carbonyl groups formed by thermooxidation have a strong influence on the dielectric properties.
A dielectric study of chain motions in poly(vinyl methyl ether)
Authors: Pathmanathan K. , Johari G. P. 
Published: April 2003

AbstractThe dielectric permittivity and loss of poly(vinyl methyl ether) (mol. wt. 30,000) have been measured from 12 Hz to 100 kHz at temperatures from 77 K to 320 K. Two relaxation processes, γ and β, are observed at T < Tg (245 K), and one above Tg. The Arrhenius plots of the γ and β processes have activation energies of 20 and 41 kJ mole−1 respectively. The relaxation rate of the α process is described by the Vogel‐Fulcher‐Tamman equation or the William‐Landel‐Ferry equation. The relaxation rates of γ and β processes evaluated from the isochrones differ from those evaluated from the isothermal spectrum. The features of chain motions observed are similar to those in other polymer and rigid molecular glasses.
Properties of iodine complexes of monosubstituted polyacetylenes
Authors: Petit Michel A. , Soum Alain H. , Leclerc Mario , Prud'Homme Robert E. 
Published: April 2003

AbstractIodine complexes of six monosubstituted polyacetylenes with methyl, ethyl, propyl, pentyl, t‐butyl, and phenyl substituents have been characterized by electronic spectroscopy. UV spectra allow the determination of the nature and the amount of active species, and photoelectronic spectra confirm the nature of these species. These measurements indicate the presence of iodine in the I and I2 forms. The concentration of I is low (0.12–4.0 mol%), and it depends on the nature of the substitutent, but this amount does not decrease when the films are left under vacuum. On the other hand, the adsorption of ε high concentration of iodine is possible; this adsorption is governed by a diffusion mechanism and is reversible. Iodine doping leads to a cis‐to‐trans isomerization of the polymers, except for poly(3‐3‐dimethyl‐1‐butyne), which can be isomerized to the cis or to the trans form, depending on the solvent employed. Electrical properties of polymer I complexes are also reported. Conductivities of about 10−4 Ω−1 cm−1 are obtained for all polymers in the presence of an excess of iodine.
Influence of structural and morphological factors on the mechanical properties of the polyethylenes
Authors: Popli Rakesh , Mandelkern Leo 
Published: April 2003

AbstractForce‐length relations at ambient temperature have been determined for a set of polyethylenes which represent a wide range in molecular weight and molecular constitution. Taking advantage of previous work from this laboratory, samples have been prepared in such a manner that the important independent structural variables can be identified and isolated and their influence on the different aspects of the deformation process assessed. Partial melting‐recrystallization processes appear to play an important role. For the linear polymers there is a direct influence of molecular weight. The influence of molecular weight manifests itself in the structure of the interlamellar zone which has a major influence on the initial modulus as well as the ultimate properties. Copolymers and branched copolymers display quite different behavior. The most striking difference is the invariance of the ultimate properties with molecular weight, branching, and level of crystallinity. From the set of experimental results that are presented the molecular factors involved in the deformation process can be sorted out. It becomes quite evident that all of the basic structural regions, characteristic of semicrystalline polymers, contribute to the observations. Focus solely on the changes in the crystallite, in analogy to the deformation of small‐molecule crystalline systems, is inadequate in the case of crystalline polymers.
Large edge‐excitation red shift for a merocyanine dye in poly(vinyl alcohol) polymer matrix
Authors: Al‐Hassan Khader A. , El‐Bayoumi M. Ashraf 
Published: April 2003

AbstractThe observed large edge‐excitation red shift of the fluorescence of a merocyanine dye in a polyvinyl alcohol polymer matrix is explained in terms of a matrix that is rigid enough at room temperature to prevent complete equilibration between different solvation sites.
Thermal properties of thermotropic polyesters with rigid chains
Authors: Kyotani Mutsumasa , Yoshida Katsumi , Ogawara Kaoru , Kanetsuna Hisaaki 
Published: April 2003

AbstractThe relationship between chemical structure and thermal properties of three polyesters composed of rigid backbone units,
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and
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here X = Br (A), Y = Cl (B), and Y = Methyl (C), was studied by differential scanning calorimetry, x‐ray diffraction, and polarized‐light microscopy. The effect of annealing on the polyesters was also investigated. Polymer A forms an anisotropic melt phase at temperatures above 280°C, but decomposes at temperatures in the range of the anisotropic melt phase. The thermal properties of polymer B are very similar to those of polymer C. Anisotropic‐isotropic melt transitions were observed at temperatures below 400°C in both heating and cooling runs for polymers B and C. These two polymers do not decompose thermally up to 400°C. A polymer with chlorine as a substituent on the hydroquinone ring in the main chain shows a wider range of temperatures at which the anisotropic melt phase exists. Quenched films of the polymers are very poorly crystalline or almost amorphous. Textures observed in anisotropic melt phases are largely preserved in the quenched films. The temperatures of the crystal‐anisotropic melt and anisotropic‐isotropic melt phase transitions become higher with annealing.