bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrical and differential scanning calorimetry studies of poly(ethylene oxide) complexed with alkaline‐earth thiocyanates
Authors: Fontanella John J. , Wintersgill Mary C. , Calame J. P. , Andeen Carl G. 
Published: April 2003

AbstractAudio‐frequency dielectric relaxation measurements and differential scanning calorimetry studies have been performed on poly(ethylene oxide) (PEO) complexed with calcium and barium thiocyanate. The measurements were performed over the temperature range 5.5‐300 K. The relaxation spectrum for the complexed material consists of two peaks. The activation enthalpy for the peak corresponding to the γ relaxation of pure PEO depends upon the size of the dopant cation. The activation enthalpy for the second peak is independent of the nature of the dopant cation and is very similar to that observed for the αc relaxation observed in pure PEO. Furthermore, the room‐temperature electrical conductivity of the complexed materials is much smaller than that for pure PEO and hence very much less than for PEO‐complexed with alkali‐metal salts. However, above Tg the conductivity rises rapidly and is larger for the barium‐thiocyanate‐complexed PEO than for the calcium‐complexed material. Finally, the DSC studies show that one effect of the ions is to shift the glass transition to higher temperatures.
The effect of transcrystallinity on the behavior of fibers in polymer matrices
Authors: Huson M. G. , McGill W. J. 
Published: April 2003

AbstractSingle copper fibers embedded in a polypropylene matrix along part of their length will, on application of a tensile load, break in the absence of transcrystallinity adjacent to the fiber, or pull out of the polymer matrix in the presence of a transcrystalline zone. It is shown that the transcrystalline zone allows thinning of the fiber in the matrix up to the point at which compressive forces created by the shrinkage of the polymer around the fiber on cooling are removed and fiber pullout occurs.
Molecular weight dependence of healing and brittle fracture in amorphous polymers above the entanglement molecular weight
Authors: Adolf Douglas , Tirrell Matthew , Prager Stephen 
Published: April 2003

AbstractA model based on chain entanglements is developed to predict the molecular weight dependence of the fracture stress for brittle, amorphous polymers. It is then used in conjunction with the reptation model of polymer diffusion to predict the time and molecular weight dependence of the fracture stress in the closely related healing problem. Theoretical predictions are found to be in close agreement with experimental data.
Investigation of ion binding in ionic polysaccharide solutions using Tb(III) as a luminescent probe
Authors: Crescenzi V. , Brittainc H. G. , Yoshinoc N. , Okamoto Y. 
Published: April 2003

AbstractThe luminescence properties of a series of lanthanide‐substituted ionic polysaccharides have been examined in an attempt to learn about the nature of interactions between the metalions and the polymers. Emission and excitation spectra were obtained for Tb(III) complexes with carboxymethyl cellulose, Sclerox S‐1.0, alginate, polygalacturonic acid, amylose sulfate, dextran sulfate, and i‐carrageenan. Studies of the chirality associated with the metal‐ion binding sites were performed through the use of circularly polarized luminescence spectroscopy. It was learned that the lanthanide ions could form complexes with polysaccharides in the electrostatic manner of polyelectrolytes, and that specific ligating groups could further influence the metal‐ion binding characteristics.
The thermal diffusivity of natural rubber
Authors: Brown R. A. , Yahya Razak Abd. Samad Bin 
Published: April 2003

AbstractMeasurements of thermal diffusivities of peroxide‐cured and sulfur‐cured rubbers, over the range 0–100°C and 0–75 phr of carbon, are described. They are based on the asymptotic time dependences of heating and cooling curves, recorded following quenching of the samples into baths at various temperatures. The diffusivities are shown to depend linearly on both temperature and carbon content, to reasonable accuracies over the ranges studied. Some theory bearing on measurement techniques is presented.
Model copolymers of ethylene with butene‐1 made by hydrogenation of polybutadiene: Chemical composition and selected physical properties
Authors: Krigas T. M. , Carella J. M. , Struglinski M. J. , Crist B. , Graessley W. W. , Schilling F. C. 
Published: April 2003

AbstractHydrogenation of polybutadienes with from 8 to nearly 100% vinyl content was used to prepare a series of model copolymers of ethylene and butene‐1 with uniform microstructures and narrow molecular weight distributions. They range from readily crystallizable to completely amorphous, depending on the frequency of ethyl side branches (2–50 per 100 skeletal carbons). Melting temperature, secondary transition temperature, density, plateau modulus for the melt, and elastic modulus for the solid were obtained as functions of branch content. The effect of crystallinity on the secondary transition and modulus of the solid is discussed.
Phase transitions in mesophase macromolecules. V. Transitions in poly(oxy‐1,4‐phenylene carbonyl‐co‐oxy‐2,6‐naphthaloyl)
Authors: Cao Miao‐Yong , Wunderlich Bernhard 
Published: April 2003

AbstractThe copolymer system HBA (4‐hydroxybenzoic acid) and HNA (2,6‐hydroxyhaphthoic acid) has been studied mainly by means of differential scanning calorimetry. Heat capacities for the two homopolymers and three copolymers are reported from 175 to 650 K. The heat capacities are additive with composition. The whole copolymer system represents an example of a mesophase intermediate between the liquid‐crystalline and the condis‐crystalline state with a small amount of crystallinity. The disordering transitions (520–620 K) have a eutecticlike phase diagram. The transitions to the isotropic states occur above the decomposition temperatures (600–700 K). The glass transitions (377–434 K) show normal changes in heat capacity (31–34 J/K mol), but are broadened to as much as 200 K.
The effect of pressure on the mechanical properties of polymers. IV. Measurements in torsion
Authors: Moonan W. K. , Tschoegl N. W. 
Published: April 2003

AbstractStress relaxation was studied in torsion under superposed hydrostatic pressure using a newly constructed device. Two materials, a styrene–butadiene rubber and a butadiene rubber, were studied in the range from −60 to 30°C at pressures up to 500 MPa. The time–temperature–pressure superposition of the data can be described by the FMT form of the free‐volume theory which uses input from relaxation experiments at high pressure. The applicability of the Havlíček–Ilavský–Hrouz form of the Adam–Gibbs theory was also examined. This theory, which does not require information from high‐pressure relaxation experiments, offers less flexibility than the FMT theory and is less successful in predicting superposition. The data are also examined in light of an adaptation of the Simha–Somcynsky equation of state to the free‐volume theory. Prediction of the effect of pressure by the theory requires a single adjustable parameter. It was possible to calculate the free‐volume parameters of several polymers without use of information from high‐pressure experiments.
Crystallization in oriented poly(ethylene terephthalate) fibers. I. Fundamental aspects
Authors: Desai P. , Abhiraman A. S. 
Published: April 2003

AbstractThe nature of crystallization‐ and mobility‐induced changes during annealing of melt‐spun poly(ethylene terephthalate) precursor fibers of a range of orientations has been examined. The kinetics of crystallization and the accompanying orientational changes have been studied under conditions of constant, low tensile stress, with the accompanying dimensional changes and under a constraint against shrinkage in length, with the stress developed being monitored. The effects of precursor orientation and externally imposed constraints on the course of the fundamental crystallization and orientational relaxation processes are revealed. Oriented crystallization has been shown to have a significant effect on the stress developed and on the dimensions of oriented precursor fibers, with a strong tendency to spontaneously extend as a consequence of the reorientation of crystallizing segments predominantly along the preferred fiber direction. The sequence in which crystallization and major orientational relaxation, if any, occur is found to have a profound effect on the structure and thus the deformability of oriented fibers after annealing above the glass transition temperature.
Relaxation of chemical potential and a generalized diffusion equation
Authors: Jäckle Josef , Frisch Harry L. 
Published: April 2003

AbstractThe effect of slow structural relaxation in a solvent of high viscosity on the chemical potential driving the diffusion of penetrant molecules is described by a generalized diffusion equation with a memory term. The linearized version of this equation is solved for some special cases, and the correlation function of concentration fluctuations in thermodynamic equilibrium is calculated. As a result of the memory term, for very slow relaxation two different stages of the diffusion process can be distinguished.
Energy absorption in polymer crazing
Authors: Pang S. S. , Zhang Z. D. , Chern S. S. , Hsiao C. C. 
Published: April 2003

AbstractThe total energy absorbed by a craze during its development in creep is analyzed and calculated on the basis of a time‐dependent theory of crazing. Experimental measurements of the craze length have been utilized in the energy calculations. For polystyrene the initial energy absorption in the craze region is found to be several hundred times that in the uncrazed medium. This ratio decreases sharply in a short period of time to about 50 to 1 and less and remains low afterward. For polycarbonate, somewhat similar behavior has been found. The initial strain energy absorption by crazing is about 200 times that in the uncrazed region. The energy ratio reduces rapidly to about 55 to 1 and tends to level off thereafter. However, in general, the amount of strain energy absorbed does increase as a function of time, as it should.
A study of the gas barrier properties of highly oriented polyethylene
Authors: Holden P. S. , Orchard G. A. J. , Ward I. M. 
Published: April 2003

AbstractMeasurements of permeability and diffusivity have been undertaken for the gases helium and oxygen in a range of highly oriented polyethylene films. The solubilities deduced for both gases are proportional to the amorphous volume fraction, showing that the noncrystalline regions are the transport medium in all instances. The changes in diffusion coefficient are more complex. A large reduction in diffusion coefficient is observed with increasing draw ratio, and this is particularly marked in the case of the larger oxygen molecule, where significant differences are also observed for different grades of polymer and different drawing conditions. These changes in diffusion coefficient are discussed in the light of previous studies of diffusion in polymers and present knowledge of the changes in structure produced by drawing.
Crystallization of poly(m‐xylylene adipamide) induced by sorption of water
Authors: Inoue Kazuo 
Published: April 2003

AbstractSorption of water in quenched amorphous poly(m‐xylylene adipamide) has been studied at 50°C. The sorption process is nearly Fickian at low humidity. At relative humidities higher than about 58%, however, extremely abnormal behavior, such as a decrease in moisture uptake and a change in appearance from transparent to opaque, is found. From x‐ray diffraction analysis, these changes can be attributed to crystallization. Thermal analysis of moistened samples confirmed that the crystallization is due to a drop in crystallization temperature caused by sorption of water. From the relation between the reduction in moisture uptake and the increase in volumetric crystallinity, it is proposed that the change in moisture uptake is caused by the exclusion of water from the crystalline phase.
Crystallization of bisphenol‐A polycarbonate induced by organic salts; physical aspects. I. Crystallization rate, melting behavior, and morphology
Authors: Bailly Ch. , Daumerie M. , Legras R. , Mercier J. P. 
Published: April 2003

AbstractThe presence of organic acid salts in bisphenol‐A polycarbonate (PC) completely modifies the crystallization mechanism, the melting behavior, and the morphology of the polymer. Organic salts are not ordinary nucleating agents for PC since they react with the polymer, producing metal phenoxide chain ends. On reaction, abundant instaneous nucleation is induced. The seeds are likely to be polymer crystalline fragments preexisting in the melt. The phenoxide chain ends significantly increase the growth rate of the crystalline phase. Melting points and enthalpies of fusion are unusually high, suggesting a high degree of crystalline perfection. Thick multilamellar crystals, which are likely to contain chains in extended configuration, are observed by electron microscopy. No trace of spherulitic morphology is found. The chemical instability of PC containing ionic chain ends is also shown to seriously affect the crystallization rate, the maximum degree of crystallinity, and the melting point.
Spectroscopic characterization of acetylene‐terminated sulfone resin
Authors: Koenig Jack L. , Shields Carl M. 
Published: April 2003

AbstractFourier‐transform infrared spectroscopy was used to characterize the thermal polymerization of the acetylene‐terminated (AT) resin, bis[4‐(3‐ethynylphenoxy)phenyl]sulfone. Spectral processing techniques (including the method of factor analysis) were utilized in the analysis of the infrared data. The degree of cure was quantitatively monitored as the resin was thermally polymerized. Factor analysis indicated that only one reaction product is spectroscopically distinguishable. Further band analysis indicated the formation of predominantly trans conjugated polyene structures. No evidence for cyclotrimerization was found.
Percolation and effective‐medium theories for perfluorinated ionomers and polymer composites
Authors: Hsu William Y. , Berzins Talivaldis 
Published: April 2003

AbstractPercolation and effective‐medium theories are applied to model the transport and elastic properties of perfluorinated ionomers. The composite nature of these polymers is emphasized. The effective‐medium theory is generalized to track continuously the evolution from lamellar to fibrillar morphology. The predicted dramatic difference in ion selectivity between lamellar and spherical morphology is verified quantitatively in perfluorinated ionomer blends. The limitations and potential improvements of the effective‐medium theory and its relationship to percolation theory are discussed. Applications of these theories to other multiphase polymer systems are also discussed.
Polymer migration in newtonian fluids
Authors: Jhon Myung S. , Freed Karl F. 
Published: April 2003

AbstractThe theory of Freed and Edwards is used to investigate polymer migration in nonhomogeneous flow fields with confined geometry. Polymer migration from the main flow originates in three effects: (i) nonhomogeneous flow‐field effect, (ii) the confined‐geometry effect, and (iii) the concentration effect. General correlation function formulas for these three effects are explicitly derived. Some specific examples are illustrated and solved by using the harmonic dumbbell and Rouse–Zimm models.
Sorption and diffusion of toluene in isotropic and oriented linear polyethylene
Authors: Ng H. C. , Leung W. P. , Choy C. L. 
Published: April 2003

AbstractSorption and diffusion of toluene vapor in linear polyethylene with mass‐fraction crystallinity between 0.48 and 0.82 and draw ratios λ up to 10 have been studied at 30°C. The sorbed concentration in the amorphous phase Ca is little affected by crystallinity, indicating that the free‐volume fraction is roughly the same for all isotropic samples. However, the diffusion path becomes more tortuous with increasing crystalline content, thereby leading to a sixfold drop in the zero‐concentration diffusion coefficient D0. Drawing has more drastic effects, reducing Ca and D0 by factors of 4 and 60, respectively, as λ increases to 10. These large changes result from the transformation of the initially spherulitic material into a fibrous structure, which is composed of aligned microfibrils with taut tie molecules lying on the outer boundaries. The effects of crystallinity and orientation on the concentration dependence of the diffusion coefficient are also discussed.
Conformational behavior of styrene–dymethylsiloxane block copolymers in dilute solution
Authors: Benchabane Mahmed , Van Leemput R. 
Published: April 2003

AbstractTo determine the behavior of a copolymer is dilute solution, a viscosity study has been performed on a polystyrene–polydimethylsiloxane block copolymer in three solvents presenting different thermodynamic conditions. The results are discussed in relation to a mixture of homopolymers and a segregated model. The unperturbed dimensions, obtained by the Stock–mayer–Fixman method, are intermediate between those of the parent homopolymers. The intrinsic viscosity measured in a good solvent, toluene, was close to the weighted averages of those of the corresponding homopolymers of equal molecular weight, but higher in decalin and in butanone, θ solvents for PS and PDMS, respectively. According to the low value obtained for the interaction parameter, the chain is slightly expanded as a result of the interactions between the unlike monomer units. Both segregation and random conformation would probably occur, depending on the quality of the solvent.
Morphological studies of liquid‐crystalline cellulose derivatives. II. Hydroxypropyl cellulose films prepared from liquid‐crystalline aqueous solutions
Authors: Nishio Y. , Yamane T. , Takahashi T. 
Published: April 2003

AbstractA morphological study of hydroxypropyl cellulose (HPC) was performed on solid films prepared by casting from a liquid‐crystalline aqueous solution at rest or under shear. Electron microscopic observations reveal that many round particles composed of stacked disks are densely packed in the interior of a quiescently cast HPC film, while on the film surface formation of fibrous textures is also noted. Shear‐deformed HPC films exhibit some interesting morphological features according to the shearing conditions. It is found by electron microscopy that the originally round particles become more and more elongated as shear stress increases. The resulting rodlike fibrillar entities are considerably aligned in the shear direction (SD), but form a banded structure with periodic discontinuities of molecular orientation distribution along the SD. A new mechanism of structural transformation is proposed in order to interpret these results.
An investigation of the effect of sample preparation on the thermal behavior and the small‐angle x‐ray scattering of a polyurethane block copolymer
Authors: Miller John A. , Cooper Stuart L. 
Published: April 2003

AbstractThe effect of varying sample preparation parameters on the thermal behavior and on the small‐angle x‐ray scattering (SAXS) properties of a polyether polyurethane were investigated. The polyurethane studied was a methylene bis(p‐phenyl isocyanate) (MDI)/butanediol/poly(tetramethylene oxide) (PTMO) system synthesized in a 6/5/1 mole ratio by a two‐step solution polymerization. The PTMO had a nominal molecular weight of 2000. The samples were compression molded under different conditions for the SAXS experiments. The preparation parameters studied included molding time and temperature, sample thickness, and quenching rate from the molding temperature. The molding temperature has the greatest effect on the SAXS data. In this case the domain size was observed to increase as the molding temperature increased from 130 to 200°C. The thermal properties were also found to be strongly dependent on the molding temperature, as measured by differential scanning calorimetry (DSC). An endotherm related to the annealing that occurs during the molding process appears in each sample near the molding temperature. The other preparation parameters have little or no effect on the SAXS and thermal properties of this sample.
Mechanochemical reactions in an epoxy resin system
Authors: Grayson Michael A. , Wolf Clarence J. 
Published: April 2003

AbstractMechanical degradation of the MY720/Eporal (CIBA GEIGY) epoxy resin system was investigated by stress mass spectrometry. Resin coupons were strained to fracture in a unique mass spectrometer system in which the clamping jaws of an Instron tensile tester are located inside the ion‐source housing of a time‐of‐flight mass spectrometer. Several compounds are released at the instant of fracture. However, only one compound, SO2, is not an impurity in either the starting material or the cured resin. A sensitive gas‐chromatographic technique was used to search for SO2 indigenous to the starting material and the unstressed cured resin. The data indicate that SO2 is a mechanochemical reaction product generated during main‐chain bond cleavage of the glassy epoxy resin network.
Copolymers of tetrafluoroethene with chlorotrifluoroethene and with bromotrifluoroethene
Authors: Moggi Giovanni , Bonardelli Piergiorgio , Monti Claudio , Bart Jan C. J. 
Published: April 2003

AbstractTetrafluoroethene (TFE)–chlorotrifluoroethene (CTFE) and TFE–bromotrifluoroethene (BTFE) copolymers have been synthesized by solution copolymerization over the entire range of comonomer composition. Crystallinity data are reported and first‐ and second‐order transitions have been investigated by DSC. Glass transition temperatures of TFE‐CTFE copolymers vary in a nonlinear fashion in the range defined by the homopolymers conforming best to the Johnston equation; the behavior in the TFE‐BTFE system is more linear. Whereas TFE‐BTFE copolymers show a steep decrease of melting temperature at higher BTFE content, due to the amorphous character of the polymers, more regular behavior was found for TFE‐CTFE copolymers. Enthalpies of fusion are also reported. The results are discussed in relation to copolymer composition and structure and are compared with data on tetrafluoroethene–hexafluoropropene (FEP) fluorocarbon resins.
Molecular interactions in the poly(vinyl chloride)‐di‐n‐butylphthalate system determined by infrared spectroscopy
Authors: Benedetti Enzo , Posar Francesco , D'Alessio Aldo , Vergamini Piergiorgio , Pezzin Giovanni , Pizzoli Maria 
Published: April 2003

AbstractInfrared studies of the poly(vinyl chloride) (PVC)/di‐n‐butylphthalate (DBP) system are reported. Spectra of DBP in different solvents seem to be indicative of the ability of DBP to interact with PVC chains in the same way as with polyesters and of competitive interactions between DBP molecules and DBP with PVC. Plots of the width at half‐height of the carbonyl stretching vibration, measured at 25 and at −180°C, as a function of composition, show a sudden change of slope at about 60% PVC concentration by weight, indicating that above this polymer composition interaction between DBP and PVC dominates that between DBP molecules. This change corresponds to a “singularity” observed in the dependence of the glass transition temperature on composition.