bluuebunny/crossref_metadata_2025_split huggingface dataset:
Identification and quantitative analysis of the intermediate phase in a linear high‐density polyethylene
Authors: Cheng Jinlong , Fone Matilda , Reddy Vijay N. , Schwartz Kenneth B. , Fisher Howard P. , Wunderlich Bernhard 
Published: April 2003

AbstractThe observation of chain conformation and mobility in polyethylene by solid‐state 13C magic angle spinning (MAS) nuclear magnetic resonance (NMR) permits unambiguous identification and quantitative analysis of an intermediate phase. The carbon‐carbon bonds in the intermediate phase adopt, on the average, an all‐trans conformation and are more mobile than in the crystalline state (room temperature rate of reorientation ≈ 107 Hz). Comparisons of crystallinities by differential scanning calorimetry, wide‐angle x‐ray diffraction, and NMR support the high orientation of the intermediate phase and suggest a lower heat of fusion than for the crystals. Results from 13C spin‐lattice relaxation and 1H spin diffusion show that the mass fractions are ≈ 20% and the domain sizes ≈ 36 Å. Both change with crystallization and annealing conditions. © 1994 John Wiley & Sons, Inc.
High field electrostrictive response of polymers
Authors: Zhenyi Ma , Scheinbeim Jerry I. , Lee Jar Wha , Newman Brian A. 
Published: April 2003

AbstractIt is well known that electrostrictive strains are proportional to the square of the applied electric field. It therefore appeared reasonable to assume that for some polymeric materials, a large acoustic thickness response, dT, \[
\left( {d_T = \frac{{dS}}{{dE}}} \right)
\] might be obtained by application of high dc bias fields, ∼ 20 MV/m, to a film while driving the film with an ac signal to access the high slope region of the electrostrictive strain vs. applied field curve. Previous studies of crystallizing poly(vinylidene fluoride) (PVF2) from solution under high electric fields have demonstrated that gel‐like samples of PVF2 with high content of the plasticizer tricresyl phosphate (TCP) could be subjected to electric fields as high as ∼ 100 MV/m. Using this type of heavily plasticized PVF2 dT values ∼ 4 Å/V were obtained. Values of 9 Å/V were obtained for a certain class of thermoplastic elastomer (i.e., a polyurethane). These dT values are considerably greater than those obtained from conventional piezoelectric ceramic materials. In addition, large elastic strains (> 3%) were observed as a function of applied dc field. © 1994 John Wiley & Sons, Inc.
Structure and property development in poly(p‐phenylene terephthalamide) during heat treatment under tension
Authors: Lee K.‐G. , Barton R. , Schultz J. M. 
Published: April 2003

AbstractThe evolution of several structural characteristics during isothermal heat treatment of poly(p‐phenylene terephthalamide) was studied. In this work, heat treatment was interrupted after different treatment times, with the specimens immediately quenched to room temperature. These specimens were then characterized by tensile testing, wide‐ and small‐angle x‐ray scattering, and optical microscopy. Structural parameters obtained from these measurements relate to crystal perfection (via the paracrystalline axial distortion parameter), axial crystallite size, transverse crystallite size, degree of chain misorientation, and degree of pleating. Structural and mechanical parameters were then plotted against heat‐treatment time to obtain kinetic isotherms for each parameter. The kinetics of the removal of chain misorientation parallels that of tensile modulus increase under all conditions. Of the other structural parameters, only the kinetics of pleat removal mimics that of modulus change, indicating that pleat removal is the effective cause of increased chain alignment and thereby of increased axial stiffness. ©1995 John Wiley & Sons, Inc.
The effect of stoichiometry on chain segment and ion mobility in partially polymerized epoxy systems
Authors: Bidstrup Sue Ann , Simpson Joycelyn O. 
Published: April 2003

AbstractThe temperature dependence of steady‐shear viscosity and ionic conductivity were measured for a series of unreacted mixtures and partially cured, ungelled samples of diglycidyl ether of bisphenol‐A (DGEBA) and an amine cross‐linking agent, diamino diphenyl sulfone (DDS). Six stoichiometric ratios of epoxide groups to amine hydrogens were examined. Free volume expressions were used to model the temperature dependence of the conductivity and viscosity for the unreacted DGEBA‐DDS mixtures. In addition, these expressions were combined to successfully correlate changes in viscosity and conductivity during the DGEBA‐DDS polymerization prior to gelation. It also was demonstrated that the change in weight average molecular weight during polymerization could be interpreted from the dielectric data. Through studying variations in the stoichiometry, it was possible to examine the effects of changes in chemical structure and ion concentration on the fitted parameters in the free volume models. The inherent ion transport factor (ζ0) was found to be inversely proportional to the concentration of ions in the test samples. The fractional free volume for segmental motion (B) was found to increase with an increase in the glass transition temperature and to be a function of the rigidity of the polymer. ©1995 John Wiley & Sons, Inc.
Evolution of nanometer voids in polycarbonate under mechanical stress and thermal expansion using positron spectroscopy
Authors: Xie L. , Gidley D. W. , Hristov H. A. , Yee A. F. 
Published: April 2003

AbstractPositron Annihilation Lifetime Spectroscopy (PALS) measurements were conducted on polycarbonate subjected to either thermal expansion or to tensile and compressive strains. It was found that thermal expansion affected both the nanometer hole size and the hole number density, whereas mechanical stress affected mainly the size of existing holes, and did not generate or eliminate holes in the quasielastic deformation region. The effect of stress on yield and postyield behavior of this glassy material was also investigated. The deduced hole volume fraction of this polymer at 25°C was 6.8 ± 0.5% from the thermal expansion experiment and 7.2 ± 1.2% from the mechanical loading experiment. When the specimen was under compression, the hole volume fraction was found to continuously decrease. This can be considered as evidence of the inability of the free volume concept in explaining the yield behavior of glassy polymers. ©1995 John Wiley & Sons, Inc.
Charge effect of the cation on the structure and the molecular mobility of polymer electrolytes
Authors: Bartolotta A. , Di Marco G. , Lanza M. , Carini G. 
Published: April 2003

AbstractA study of the thermal and mechanical characteristics of polyethylene oxide‐Fe(SCN)3 complexes shows the existence of structures which can be described by considering a crystalline phase of pure polyethelene oxide (PEO) and an amorphous phase of PEO with dissolved salt. Increasing salt contents decrease the content of crystals, favoring the formation of complexes with a high degree of noncrystallinity as a result of strong polymersalt interactions which tend to enhance the distortion degree of the polymeric skeleton. The microscopic homogeneity of the complexes is also confirmed by the presence in the thermal and mechanical spectra of single glass transitions, which shift to higher temperatures with increasing salt content. Two molecular relaxations are present in the mechanical behavior of these systems, the γ‐and the αa‐processes at low and high temperatures, respectively, and show a relaxation strength which increases with decreasing degree of crystallinity of the polymer up to a X ∼ 0.10 molar fraction. Both relaxations exhibit a marked nonexponentiality which has been well accounted for in terms of a gaussian distribution of relaxation times for the γ‐process and of the Kolrausch‐Williams‐Watt exponential function for the αa‐process. In the glassy region, the elastic modulus E' reveals a linear temperature dependence which has been interpreted as arising from the anharmonicity of vibrational modes. Increasing noncrystallinity of the system gives rise to an increase of the anharmonicity parameter, which has been ascribed to the influence of the “free volume” in determining the thermal expansivity. ©1995 John Wiley & Sons, Inc.
Membrane formation by isothermal precipitation in polyamide‐formic acid‐water systems I. Description of membrane morphology
Authors: Cheng Liao‐Ping , Dwan An‐Hwa , Gryte Carl C. 
Published: April 2003

AbstractAliphatic polyamides (Nylon‐66 and a Nylon‐6, ‐66, ‐610 terpolymer) were isothermally precipitated from formic acid solution by immersing in an aqueous nonsolvent bath or a solvent/nonsolvent mixture. Depending on the composition of the polymer solution and nonsolvent bath, phase separation by nucleation and growth can be initiated for a liquid‐liquid phase separation process, a crystallization process or a combined process. Under certain conditions, crystallization of Nylon‐66 results in a membrane with a uniform skinless microporous structure that was rapidly wetted by water. In contrast, liquid‐liquid phase separation produces a polyamide film with largely unconnected cellular voids that is as a result not wetted by water. © 1995 John Wiley & Sons, Inc.
A thermally stimulated discharge currents study of the molecular motions in two polysiloxane side‐chain liquid crystalline polymers
Authors: Mano João F. , Correia Natália T. , Moura Ramos Joaquim J. , Fernandes Anabela C. 
Published: April 2003

AbstractThe technique of thermally stimulated depolarization currents was used to study the dipolar relaxation mechanisms in two side‐chain liquid‐crystalline polysiloxanes. The studied polymers have the same mesogenic side‐group, but they differ in the number (or density) of side groups attached to the main chain. In both cases three different relaxations were observed: one in the vitreous state, one in the liquid crystalline phase, and the glass transition relaxation. The features of those thermally stimulated discharges are discussed and some suggestions are made concerning the attribution of those discharges at the molecular level. © 1995 John Wiley & Sons, Inc.
Polyurethane cationomers III: Oxygen permeation
Authors: Chan Wu‐Chung , Chen Show‐An 
Published: April 2003

AbstractDynamic oxygen permeation measurements at 20–70°C on films cast from solutions and emulsions of three series of polyurethane (PU) cationomers based on MDI, HDI, and TDI that are the subject of Parts I and II of this series were made by Barrer's vacuum technique. For the MDI system, films cast from solutions of ionized PU exhibit permeation coefficients P that are higher at 20–40°C (below the glass transition temperature Tgh of the hard domains) than at 50–70°C (above Tgh) by factors of about 5 and 40. This is the opposite of what is observed for normal homopolymers and un‐ionized PU. This phenomenon is attributed to the continuous/dispersed morphology of these films. At the low temperature, oxygen molecules diffuse through the continuous phase (soft domains) only. But at the high temperature, oxygen molecules diffuse through soft domains and subsequently through hard domains, leading to an increase in diffusion pathlength. For films cast from the PU emulsions, such a drop in P was not observed because the hard domains were partially inverted from the dispersed phase to a continuous phase that gives an interwoven morphology. Such morphology allows oxygen molecules to diffuse through soft and phase‐inverted hard domains simultaneously. For the HDI and TDI systems, P and D vs. 1/T plots show no zone of discontinuity. This is attributed to a Tgh that is lower than or close to the permeation temperature. © 1995 John Wiley & Sons, Inc.
Chemical modification of butyl rubber. II. Structure and properties of poly(ethylene oxide)‐grafted butyl rubber
Authors: Ikeda Yuko , Kodama Kazutoshi , Kajiwara Kanji , Kohjiya Shinzo 
Published: April 2003

AbstractPoly(ethylene oxide)‐grafted butyl rubbers (IIR‐g‐PEOs), which were synthesized from potassium salt of polyethylene glycol monomethyl ether (PEGM) and chlorinated butyl rubber, were found to behave like thermoplastic elastomers. The poly(ethylene oxide) (PEO) content of these amphiphilic polymers was ca. 10 wt %, and their PEO lengths were 750, 2000, and 5000, respectively. The grafted segments of PEO in butyl rubber (IIR) aggregated to form the PEO domains in IIR matrix. At constant PEO content, the longer the PEO segment length, the larger the size and the crystallinity of PEO domains became. This PEO domain worked as a cross‐linking site and a reinforcing filler. The degree of swelling in water of IIR‐g‐PEO film that was prepared from PEGM‐5000 was largest, but its emulsification ability was smallest among them. © 1995 John Wiley & Sons, Inc.
Prediction of polymer PVT behavior using the group contribution lattice‐fluid EOS
Authors: Parekh Vipul S. , Danner Ronald P. 
Published: April 2003

AbstractA scheme has been developed using the group contribution lattice‐fluid equation of state (GCLF‐EOS) to predict the pressure‐volume‐temperature (PVT) behavior of polymers in the amorphous state. The model requires only the structure of the molecule as input information. Prediction results with an average error of 2% have been obtained for a wide variety of polymers. A table of 23 different group contributions is presented. With this set of group parameters, the GCLF‐EOS can be applied in the prediction of equation of state properties of a wide variety of homopolymers, random copolymers, and polymer blends. © 1995 John Wiley & Sons, Inc.
Thermal diffusion and molecular weight calibration of poly(ethylene‐co‐vinyl acetate)s by thermal field‐flow fractionation
Authors: Jeon Sun Joo , Lee Dai Woon 
Published: April 2003

AbstractCopolymer characterization is accomplished with respect to measurement of thermal diffusion coefficient (DT) and molecular weight determination by thermal field‐flow fractionation. The examined copolymers are the eight poly(ethylene‐co‐vinyl acetate)s [P(E‐V)] having different compositions of vinyl acetate ranging from 25 to 70% and the molecular weight from 110,000 to 285,000, and three polyvinyl acetate standards as component homopolymer. The carrier solvents are tetrahydrofuran, toluene, and chlorobenzene which have different viscosities and thermal conductivities. Measured DT values vary from 1.36 × 10−8 to 5.97 × 10−8 cm2/(s . K) which are dependent on the composition of copolymers and types of carriers. These values increase linearly with the increase of weight percent of vinyl acetate. It is possible to estimate DT values of polyethylene from the extrapolated intercept in the plots of DT vs. vinyl acetate wt % of copolymer. Tetrahydrofuran is found to be the appropriate carrier solvent for the separation of P(E‐V) copolymers since DT varies greatly with the increase of wt % in THF. Attempts are made to correlate the measured retention data with molecular sizes of copolymers for the construction of the molecular weight calibration curve. Good correlations (r2 ≥ 0.931) are found in which D/DT values of polymers vary inversely with the product of hydrodynamic volume by weight ratio of vinyl acetate. Based on this relationship, the unknown molecular weight of copolymer sample can be determined from component homopolymers for which standards are readily available. © 1995 John Wiley & Sons, Inc.
Rheological and mechanical properties of antiplasticized and rubber‐toughened bisphenol A polycarbonate
Authors: Kambour R. P. , Caraher J. M. , Fasoldt C. L. , Seeger G. T. , Sowa N. M. , White D. M. 
Published: April 2003

AbstractThe addition of a high‐Tg aromatic diluent to bisphenol A polycarbonate (PC) reduced Tg and melt viscosity while raising elastic modulus and yield stress substantially. Ultimate tensile elongation and impact toughness were badly affected. However, the addition to these antiplasticized blends of a small amount of a rubber modifier restored impact toughness and elongation but left the blend with increased melt fluidity and ambient stiffness re: neat PC. The key to this rebalancing of the properties of PC was found to be the disappearance of the plane strain crack instability that is a hallmark of the neat resin. The deformation mechanism in all the rubber‐containing blends in all failure tests, regardless of geometric constraint and strain rate was found to be shear flow alone. The large plastic zone seen at the plane strain crack tip appears to involve rubber particle cavitation as well. © 1995 John Wiley & Sons, Inc.
Impedance spectroscopy of reactive polymers. 2. Multifunctional epoxy/amine formulations
Authors: Bellucci Francesco , Valentino Maio , Monetta Tullio , Nicodemo Luigi , Kenny Jose , Nicolais Luigi , Mijovic Jovan 
Published: April 2003

AbstractDielectric measurements were utilized to follow the advancement of cure in a bifunctional and a tetrafunctional epoxy/amine formulation. In deferance to earlier dielectric studies of cure, complex impedance was measured and used to calculate ionic resistivity. By using complex impedance we were able to separate, according to their frequency dependence, the contributions to overall polarization from electrode blocking layers, mobile charge carriers, and dipole relaxations. At any stage of cure, there is a unique frequency at which ionic resistivity can be singularly measured. Our approach does not involve trial‐and‐error frequency search, it measures dielectric response in real time, and is conducive to the development of phenomenological models based on equivalent circuits. Values of ionic resistivity measured at different cure time and temperature were used to quantify the progress of cure. Excellent agreement was reported between the calculated values of normalized degree of cure obtained by dielectric and calorimetric measurements. It was suggested that apart from the extrinsic conductivity by ionic impurities, an intrinsic mechanism which involves the reactive molecules contributes to the overall ionic conductivity. © 1995 John Wiley & Sons, Inc.
Effects of humidity, imidization history, and thickness on water sorption behavior of poly(p‐phenylene biphenyltetracarboximide) films
Authors: Ree M. , Han H. , Gryte C. C. 
Published: April 2003

AbstractPoly(p‐phenylene biphenyltetracarboximide) films with various thicknesses were prepared from the poly(amic acid) precursor by thermal imidization at 230–400°C for 1–10 h under a nitrogen atmosphere. The water sorption in the films was measured at 25°C over 22–100% relative humidity using a Cahn microbalance as a function of film thickness and thermal imidization history. The water diffusion in all the films followed nearly Fickian process despite the morphological heterogeneity due to the ordered and less ordered phases. The diffusion coefficient and water uptake varied in 0.85 × 10−10 − 7.50 × 10−10 cm2/s and 0.12–2.4 wt %, respectively, depending upon humidity, film thickness, and imidization history. Both diffusion coefficient and water uptake increased with increasing humidity, but decreased as imidization temperature and time increased. With increasing film thickness, the diffusion coefficient increased whereas the water uptake decreased. The water sorption behavior was interpreted with the consideration of morphological variations, such as polymer chain order, in‐plane orientation, and intermolecular packing order due to the film thickness and imidization history. © 1995 John Wiley & Sons, Inc.
A thermally stable polymer molecular composite
Authors: Roberts Michael F. , Jenekhe Samson A. 
Published: April 2003

AbstractA molecular composite of rigid‐rod poly(p‐phenylene benzobisthiazole) and flexible‐coil poly(benzimidazobenzophenantroline) has been prepared, characterized, and shown to be thermally stable to at least 300°C. These results suggest that stable miscible blends of rodlike and coil‐like polymers can be prepared by controlling the glass transition temperature of the flexible‐coil polymer. © 1995 John Wiley & Sons, Inc.
Isothermal cis‐trans isomerization behavior of polyacetylene films
Authors: Kyotani H. , Shimomura M. , Ito K. , Tanabe Y. , Zhang Y.‐X. , Akagi K. , Shirakawa H. 
Published: April 2003

AbstractIsothermal cis‐trans isomerization behavior was studied by differential scanning calorimetry for conventional Shirakawa polyacetylene (S‐PA) film and highly stretchable polyacetylene (hs‐x) films synthesized using catalysts aged at high temperature. The rate of isomerization is slower for S‐PA than for hs‐x. Kinetic results of isomerization are analyzed by a stretched exponential function with exponent n (0 < n < 1), which is different from the previously assumed single exponential function. An activation energy of 31 kcal/mol was obtained for all the samples. © 1995 John Wiley & Sons, Inc.
Phase behavior and miscibility limits in PC/hytrel blends
Authors: Gaztelumendi M. , Nazabal J. 
Published: April 2003

AbstractPolycarbonate of bisphenol‐A (PC)/copolyetherester (Hy) blends have been obtained by melt mixing over the complete composition range. After testing the lack of interchange reactions and degradation under the conditions studied, the miscibility state was studied by DSC and DMTA. The blends appeared to be miscible in the melt state. A fairly complex phase behavior was obtained in the solid state with Tg‐composition plots showing a single Tg at most of the compositions but very different after the first and second scans. This was attributed to the different crystalline content of the blends before the two scans. The presence of a Hy crystalline phase and a single PC/Hy amorphous phase in all the blends, with the exception of the 20/80 composition, was verified by DMTA. Several thermal treatments showed the presence of an immiscibility range and, thus, the presence of a UCST. A LCST, which in the case of the 50/50 and 40/60 blends would be at roughly 75°C, will also probably exist. © 1995 John Wiley & Sons, Inc.
Highly conducting solid electrolytes based on poly (ethylene oxide‐co‐propylene oxide)
Authors: Florjańczyk Zbigniew , Krawiec Włodzimierz , Wieczorek Władysław , Siekierski Maciej 
Published: April 2003

AbstractThe conducting properties of solid electrolytes comprising random poly(ethylene oxide‐co‐propylene oxide) (of 84 : 16 monomer units mole ratio) and lithium, sodium, potassium, cesium, and rubidium salts have been studied. The systems containing some lithium or sodium salts achieved conductivity levels as high as 10−5–10−4 S/cm at ambient temperature and greater than 10−3 S/cm at 100°C. However, the systems with rubidium and cesium salts exhibit conductivities a few orders of magnitude smaller. DSC studies show that the electrolytes studied are characterized by a high content of an amorphous phase (95–100%). It is suggested that the copolymer exhibits lower complexing abilities than that of poly(ethylene oxide), which results in a higher flexibility of electrolytes containing small cations and poor dissociation of the salts having large cations. © 1995 John Wiley & Sons, Inc.