bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dilation of polyethylene by sorption of carbon dioxide
Authors: Hirose Takuji , Mizoguchi Keishin , Kamiya Yoshinori 
Published: April 2003

AbstractThe dilation of low‐density polyethylene accompanied by the sorption of CO2 was measured by microscopy under pressures up to 50 atm at temperatures from 25 to 55°C. The dilatometry measurement, which is also applied to the determination of the thermal expansion coefficient, is directly performed by a cathetometer. The dilation of LDPE by sorbed CO2 is linear with concentration. The buoyancy correction is described for the CO2 sorption isotherms in LDPE. The partial molar volume of CO2 in LDPE, calculated from the dilation and the sorption isotherms, is almost independent of temperature.
Topotactic transitions of the tetramer of P‐acetoxybenzoic acid
Authors: Volksen W. , Geiss R. , Economy J. 
Published: April 2003

AbstractThermal and electron diffraction studies of single crystals derived from the tetramer of p‐acetoxybenzoic acid have revealed the presence of two consecutive crystallographic transformations, i.e., topotactic transitions. Thus, differential scanning calorimetry of the oligomer indicated two irreversible phase transitions, an endotherm followed by an exotherm, between 150 and 180°C, in addition to the crystal‐to‐nematic transition at 260°C. Electron diffraction analysis further elucidated the transformation occurring during thermal treatment of the original oligomer. Hence it could be shown that the solution‐crystallized material (α form) underwent a solid–solid phase transition to the β modification at a temperature corresponding to the observed endotherm. This β form then converted to a more stable modification (β′ form) which represented a superlattice structure derived from the β modification.
Crystallizing crazes: The probable source of solvent stress cracking resistance in a polyester/polycarbonate blend
Authors: Kambour R. P. , Chu C. , Avakian R. W. 
Published: April 2003

AbstractThe addition of a miscible phthalate polyester to BPA polycarbonate results in a remarkable improvement in stress cracking resistance in strong swelling agents. Comparative measurements of solvent craze initiation resistance, craze strengths, degrees of swelling, and crystallization behavior have been made. The results indicate that the improvement in cracking resistance probably results from stabilization of the craze fibrils by crystallization of the polyester before and/or during fibril formation.
Poly(m‐phenylene disulfide): Antimony pentafluoride doping and infrared spectroscopy
Authors: Bertinelli F. , Bizzarri P. Costa , Casa C. Della , Saltini S. 
Published: April 2003

AbstractPoly(m‐phenylene disulfide) treated with SbF5 gives an unstable blue‐black material. Heating of doped samples at 155°C leads to some stabilization to ambient conditions; doped and heated pellets exhibit a conductivity of 10−9 and 10−5 S/cm for vapor and liquid doping, respectively. To investigate backbone modifications, polymer powders have been treated with large amounts of liquid SbF5 and an analysis of the IR spectra of the extracted samples has been tried in comparison with that of pristine polymer. Evidence for SbF ion has been found in the IR spectra of the complexes.
Use of blocked electrodes in thermally stimulated depolarization current measurements
Authors: Topića M. 
Published: April 2003

AbstractThe use of blocked electrodes in thermally stimulated depolarization current (TSDC) measurements has been studied on phenol–formaldehyde novolac resin blocked by one or two Teflon foils. The measurements were performed after polarization at different temperatures Tp separately for the Teflon and the resin. Blocking decreases the effectiveness of a nominal polarizing field and suppresses the background current. It is explained here for the first time that the charge released from the charged Teflon interferes with the conductivity relaxation peak of the resin. The influence of the blocking is very dependent upon Tp, and this dependence is specific in regard to the type of current peak. The application of blocking at different Tp is recommended for the determination of the origin of peaks in TSDC measurements.
Theoretical study of sequence distributions in polydienes. I. Statistical treatment
Authors: Wang Zhiyu , Yan Deyue 
Published: April 2003

AbstractIn this paper, the sequence distribution of polydienes is studied systematically by means of statistics. The discriminants for Bernoullian and various Markovian processes are obtained. In addition, the condition of statistical stationarity and a series of relationships among frequencies of occurrence of sequences with different lengths are given. When the polydiene consisting of only two structural units is taken into account, the statistical treatment of this paper degenerates into that for vinyl polymers.
Theoretical study of sequence distributions in polydienes. II. Non‐steady‐state analysis of a bernoullian process
Authors: Yan Deyue , Wang Zhiyu 
Published: April 2003

AbstractWith the aid of the non‐steady‐state kinetic method, the sequence distribution of polydienes conforming to a Bernoullian process is treated theoretically. The expressions for sequence length distribution, the probability functions, and other structural parameters are derived in closed form. The results obtained show that at the beginning of polymerization all the parameters mentioned vary with reaction time, monomer conversion, and the ratio of initial concentrations of monomer to initiator, but monotropically approach their respective limits which are identical with those derived from statistics.
Infrared absorption study of organic polyiodide chain complexes
Authors: Oza A. T. 
Published: April 2003

AbstractStudy of infrared absorption spectra of α‐cyclodextrin and its KI‐I2 and HI‐I2 complexes and those of Coumarin and its KI‐I2 complex reveals changes in the spectra of α‐cyclodextrin and Coumarin in the range 400–1800 cm−1. New bands in the COC stretching range are caused by charge transfer interactions of iodine with oxygen atoms in α‐cyclodextrin and Coumarin. Other changes in the spectra are ascribed to hydrogen bonding between water molecules and cyclodextrin molecules, water of crystallization, and structural effects.
Photophysical properties of N‐acylated linear polyethylenimine and dehydroalanine main‐chain polymers containing carbazole or pyrene groups in side chains
Authors: Arora Kartar S. , Overberger C. G. , Johnson G. E. 
Published: April 2003

AbstractA comparison of the UV absorption spectra of a carbazole‐substituted N‐acylated linear polyethylenimine (PEI) (5, 6) with its monomer (1, 2) and dimer (3, 4) model compounds shows the presence of local conformational order of the carbazole groups in 3, 5, and 6 since these compounds exhibit hypochromism. The UV absorption spectra of carbazole‐substituted N‐acrylated dehydroalanine main‐chain polymer (PDA) (12, 13) and monomer (10, 11) model compounds indicate that the extent of local conformational order of the carbazole groups is reduced in 12 and 13 compared to that in 5 and 6. The UV absorption spectra of a pyrene‐substituted PEI (9) and PDA (15) and those of their monomer model compounds (7, 14) indicate that the extent of local conformational order of the pyrene groups is greater in 9 than in 15 and furthermore the pyrene‐substituted polymers (9, 15) show more local conformational order than analogous carbazole‐substituted polymers (5, 12). The emission spectra of 5 and 12 show carbazole monomer emission, while those of 9 and 15 are dominated by pyrene excimer emission. The formation of excimer emission is more efficient in 9 than in 15. Fluorescence lifetime measurements indicate interactions of excited carbazole groups in 5 and 13 but not in 12. The quenching of carbazole fluorescence by dimethyl terephthalate is more efficient in 5 than that in 12, indicating more efficient transfer of electronic energy in 5. These measurements show that the PEI main‐chain polymers are conducive to interactions of the pendant groups.
A study of molecular motion in a liquid‐crystalline copolyester by broad‐line nuclear magnetic resonance
Authors: Clements J. , Humphreys J. , Ward I. M. 
Published: April 2003

AbstractBroad‐line nuclear magnetic resonance (NMR) measurements have been carried out for the proton resonance in an oriented liquid‐crystalline copolyster prepared from 4‐hydroxybenzoic acid (HBA) and 2‐hydroxy‐6‐naphthoic acid (HNA). The Second moments were determined as a function of the angle γ between the specimen orientation direction and the static magnetic field. The low‐temperature NMR results are consistent with a rigid structure of random copolymer chains arranged on a hexagonal lattice. As the temperature is raised the NMR signal changes and can be modeled very satisfactorily by considering that there is free rotation of the benzene ring residues about the 1‐4 substitution direction. At more elevated temperatures the observed NMR spectra are consistent with rotation of both HBA and HNA groups.
Effect of pressure on phase behavior in polymer blends of poly(2,6‐dimethyl‐1,4‐phenylene oxide) and poly(styrene‐co‐p‐fluorostyrene) copolymers
Authors: Maeda Yoji , Karasz Frank E. , MacKnight William J. , Vuković R. 
Published: April 2003

AbstractThe effect of pressure on the miscibility of blends of poly(2,6‐dimethyl‐l,4‐phenylene oxide) (PPO) with a random copolymer of styrene and para‐fluorostyrene, P(S‐co‐p‐FS), has been studied by high pressure differential thermal analysis (HPDTA). P(S‐co‐p‐FS) copolymers less than 36 mole % p‐FS are miscible with PPO in all proportions irrespective of pressure up to 200 MPa, using the customary criterion of a single calorimetric glass relaxation. P(S‐co‐p‐FS) copolymers containing 40 to 50 mole % p‐FS undergo phase separation upon annealing at elevated temperatures, indicating the existence of a lower critical solution temperature (LCST). In these blends, pressure displaces the phase boundary associated with the LCST to higher temperatures causing an apparent increase in polymer miscibility. The phase diagram for the blend of PPO and P(S‐co‐p‐FS) containing 46 mole % p‐FS, shows that the critical composition at about 50 wt % PPO does not change with pressure, but the consolute temperature Tc increases with increasing pressure. The pressure dependence of the LCST (dTc/dP) of this system is about 0.35°C/MPa.
Structure and properties of polypropylene crystallized from the glassy state
Authors: Hsu C. C. , Geil P. H. , Miyaji Hideki , Asai Kenjiro 
Published: April 2003

AbstractGlassy isotactic propylene (PP) films of thickness up to 0.3 mm were obtained by an ultraquenching technique. The structure and properties of the as‐quenched and subsequently crystallized samples were characterized by various techniques. Electron microscopy indicates the glass has no structure larger than 25 Å. X‐ray diffraction shows PP crystallizes from the glass into a smectic structure at ca. −20°C and then transforms to monoclinic microcrystals at ca. 40°C; a nodular structure (80 to 100 Å in diameter) was observed on the surface. The transformation temperature increases with the film thickness. Annealing above the α‐relaxation temperature results in an increase in the nodule size. A correspondence was found between the diameter of the nodules observed on the surface and long spacings obtained by small‐angle X‐ray scattering from the bulk. Dynamic mechanical spectra show the presence of two relaxation‐like peaks at ca. −10°C and 10°C for the as‐ultraquenched samples. X‐ray scattering, differential scanning calorimetry (DSC), and torsion pendulum measurements show PP crystallizes from the glass at a temperature, depending on the rate of heating, that corresponds to the lower relaxation peak temperature.
Initial relaxation times in dynamic light scattering from once‐broken rod molecules in solution
Authors: Moro Keiji , Fujiwara Masako 
Published: April 2003

AbstractInitial relaxation times determined by the initial decay rate of the time correlation function of scattered light are calculated for the once‐broken rod model (two rigid rods of equal length connected by a universal joint) following the Fujiwara–Saito theory. The coefficient C describing the initial angular dependence of the first cumulant of the correlation function is also calculated. The results are compared with Pecora's results based on the Yu–Stockmayer theory for this model; and it is shown that the Fujiwara–Saito theory gives reasonable results.
Properties of polyelectrolytes: Maleic acid‐vinylpyrrolidone copolymers. I. Viscometric behavior in dilute solution
Authors: Rios Hernan , Gargallo Ligia , Radić Deodato 
Published: April 2003

AbstractThe viscometric behavior of maleic acid‐vinylpyrrolidone copolymer systems p(MA–co–VP) were studied in dilute solution. The weight‐average molecular weights of fractionated copolymers were determined by gel permeation chromatography. Viscometric relations were determined in aqueous salt solutions and in organic solvents. Two theta‐conditions were found for p(MA–co–VP): in 0.968 M Na2SO4, and in a DMSO/acetone mixture, 35.6/56.4 (v/v) at 25°C. The conformational and thermodynamic parameters KΘ and B were evaluated from viscosity data in good solvents using the Stockmayer–Fixman and Berry extrapolations. A linear variation of B with the salt concentration was observed. The electrostatic (Be) and nonelectrostatic (Bo) contributions to B were estimated. It was found that Be > Bo, and this was attributed to the hydrophylic nature of p(MA–co–VP) copolymers. The latter would reflect a greater influence of the electrostatic interaction on the hydrodynamic behavior of this polymer. The electrostatic (α), and the nonelectrostatic lim →∞(α3 − 1) contributions to the expansion factor α were determined. It was found that α is a function of (M̄w/Cs)1/2, as is predicted by the Fixman theory.
Micromechanics of a craze zone at the tip of a stationary crack
Authors: Bevan L. , Doell W. , Koenczoel L. 
Published: April 2003

AbstractThe finite element method is applied to contours (measured by interferometry) of craze zones in front of stationary crack tips in polymethylmethacrylate (PMMA) in order to compute the stress distribution. The stress along the craze zone has its maximum at the crack tip, being about twice that predicted by the Dugdale model; and it decreases at first sharply and then more gradually, being almost constant as the craze tip is approached. Stress distributions, in a growing craze at the still stationary crack tip, at various times can be combined in a normalized curve. Craze stresses relax with time as the craze continues to propagate in a stable manner. When the specimen is unloaded, the craze stress is compressive near the crack tip, but is tensile at the craze tip and for most of the craze length. Analysis of measurements made during a loading cycle establishes minimum stress intensity levels at which no fibrils are in compression. The levels are different for increasing and decreasing loads, and it is found the craze stresses are tensile for most of the cycle. Throughout the cycle, there is an excellent correlation between the average craze stress and the theoretical stress predicted by the Dugdale model.
High‐melting bisphenol‐A polycarbonate from annealing of vapor‐induced crystals
Authors: Jonza James M. , Porter Roger S. 
Published: April 2003

AbstractPolycarbonate is known to crystallize thermally, but only slowly and to a limited (25%) extent. The melting points reported exhibit a wide variation. We have found that the melting temperature of polycarbonate may be drastically increased by employing a sequence of vapor‐induced crystallization and annealing treatments. The crystals formed by the treatment with organic vapor act as a nucleation or precursor state for further crystallization into larger, more perfect lamellae. An initial peak melting temperature of 195°C has been annealed up to 239°C, and then to 295°C by a double‐heat treatment. This sample is 60% crystalline, based on heat‐of‐fusion calculations. An equilibrium melting point of 335°C has been obtained for PC from an extrapolation of reciprocal lamellar thickness.
Prediction of thermodynamic properties of polymer solutions by a group‐contribution method
Authors: Patwardhan Ashutosh A. , Belfiore Laurence A. 
Published: April 2003

AbstractThe Flory–Huggins lattice‐theory expression for solvent activity in a polymer‐solution is commonly used to calculate the thermodynamic interaction parameter χ with the aid of experimental data from vapor pressure osmometry. This expression assumes that χ is independent of composition. However, experimental data for a variety of polymer‐solvent mixtures indicate that χ exhibits an appreciable concentration dependence. A group contribution method, UNIFAC (UNIQUAC Functional‐Group Activity Coefficients) incorporating the free‐volume correction of Oishi and Prausnitz is used to predict the dependence of χ on solvent concentration. Agreement with previously reported experimental data is within 15%. Calculated values of χ obtained from the Flory–Huggins expression for solvent activity and from the corresponding Gibbs free energy of mixing (which does not assume that χ is independent of composition) are compared. Calculations based on the Gibbs free energy of mixing predict a somewhat larger value of χ relative to those based on solvent activity. The specific Gibbs free energy of mixing for polystyrene‐solvent mixtures is calculated using the UNIFAC model, and is found to represent qualitatively the phase equilibrium behavior. Quantitative discrepancies are observed, however, for the polystyrene‐acetone system in light of the actual experimental solubility reported by Suh and Clark (20). Most of the thermodynamic predictions for polymer‐solvent systems investigated herein are correlated qualitatively with the relative mismatch between solubility parameters of both components.
The effects of morphological transitions on hydrogen bonding in polyurethanes: Preliminary results of simultaneous DSC–FTIR experiments
Authors: Koberstein Jeffrey T. , Gancarz Irena , Clarke Thomas C. 
Published: April 2003

AbstractThe influence of morphological transitions on the hydrogen‐bonding behavior of polyurethanes is investigated by simultaneous measurements of Fourier‐transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The materials examined are a noncrystalline polyurethane hard segment, a crystallizable polyurethane hard segment, and a segmented polyurethane block copolymer containing crystallizable hard segments. Integrated absorbance data show that the hydrogen‐bonding behavior is insensitive to crystalline transitions within the hard segment microdomains, but that it does reflect morphological transitions in the block copolymer that are associated with intersegmental mixing. In addition, the spectral data show conclusive evidence for reversal of the urethane reaction at high temperatures.
The concentration dependence of the compression modulus of iostactic polystyrene/cis‐decalin gels
Authors: Guenet J. M. , McKenna G. B. 
Published: April 2003

AbstractNew results for isotactic polystyrene/cis‐decalin gels are presented that suggest that a simple fringed micellar model of the gel may not be appropriate. In measuring the room temperature compressive modulus of gels formed at −20°C, it was found that, not only do the gels exhibit significant stress relaxation but also that the isochronal modulus‐concentration diagrams exhibit abrupt changes in modulus (reduced stress) over narrow ranges in concentration rather than the smooth curves (straight lines) typical of swollen rubber and fringed micellar gels.
Analysis of trichroic infrared absorption in solids. I. Description of methods
Authors: Fina L. J. , Koenig J. L. 
Published: April 2003

AbstractInfrared absorption by polymeric solids is generally anisotropic due to orientational effects induced by industrial processing and fabrication. The isotropic‐equivalent or structure‐factor spectrum of a sample can be computed from the absorbances along the three principal axes of the absorption ellipsoid. Experimentally, this is accomplished by a tilting procedure which has been computer interfaced for precise angular control. The technique is applied to poly(vinyl acetate) (PVAc) and poly(ethylene terephthalate) (PET). The effects of refractive index dispersion, fringe distortion, reflection, and birefringence are evaluated in terms of the thickness direction calculation. Error spectra based on sample symmetry are generated, and the limits of accuracy of the tilting technique are established.
The role of chain scission in fracture of amorphous polymers
Authors: Willett J. L. , O'Connor K. M. , Wool R. P. 
Published: April 2003

AbstractWe have investigated the role of chain scission in glassy polymers by monitoring the molecular weight changes induced by microtoming thin slices of monodisperse polystyrenes. The changes in number‐average molecular weight allow determination of Nf, the number of bond scissions per unit area. It is found that Nf is independent of initial molecular weight and has the value 6.50 × 1013 scissions/cm2 at room temperature; Nf decreases with increasing temperature, suggesting that chain pullout increases with temperature. The work required to create unit surface area in polystyrene is several orders of magnitude greater than the energy required to break Nf bonds, indicating that plastic deformation plays a major role in deformation and fracture of glassy polymers.
Electrical conduction of poly(vinyl alcohol) films
Authors: Tawansi A. , Migahed M. D. , El‐Hamid M. I. A. 
Published: April 2003

AbstractPVA films (30–45 μm thickness) were prepared by casting. dc electrical measurements were done over the temperature range 293–353 K. Two different conduction mechanisms are suggested. The first one is ohmic and extends to 303 K. Above this temperature a space‐charge‐limited conduction mechanism, with protons as charge carriers, predominates. Dependences of the voltage‐reversion current temperature and field were investigated and were attributed to a clean‐up effect of charge carriers. The variance in the activation energy, calculated from the conductivity curves and from the mobility curves, led to a discussion of the origin of the charge carriers. No change in conductivity was observed for the PVA films irradiated with UV (of wavelength 365 nm) at 303 K, i.e., PVA is a photostable material under these conditions.
Fourier‐transform infrared study of orientation in pure and plasticized poly(vinyl chloride)
Authors: Theodorou M. , Jasse B. 
Published: April 2003

AbstractFourier‐transform infrared spectroscopy has been used for the study of orientation of pure and plasticized PVC. The results show that orientation is independent of experimental conditions (temperature, strain rate, plasticizer) in the homogeneous deformation range. Such behavior is explained by the existence of a fringe micellar‐type network with physical crosslinks. The network is partially destroyed during stretching. Furthermore, the orientation of the carbonyl group of the plasticizer is connected with PVC chain orientation.