bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of the crystalline phase on the molecular mobility of PVDF
Authors: Teyssedre G. , Bernes A. , Lacabanne C. 
Published: April 2003

AbstractDielectric relaxation and pyrocurrent of PVDF were studied by thermostimulated current spectroscopy. The transition spectrum of the material was investigated by differential scanning calorimetry. Two well‐resolved relaxation peaks have been observed in the temperature range [−100–100°C]. The molecular mechanisms of these phenomena have been discussed, based on a comparative study of α‐PVDF. and β‐PVDF. The β relaxation mode is located at −41°C in α‐PVDF and is slightly shifted toward higher temperatures in the stretched material. This mode has been ascribed to the dielectric manifestation of the glass transition (Tg) of PVDF. It is comprised of two components corresponding to the free and constrained amorphous phases, respectively, in the order of increasing temperatures. The αc transition/relaxation has been associated with molecular motions in the crystalline/amorphous interphase. At higher temperatures, a compensation phenomenon corresponding to cooperative movements liberated at the Curie transition has been observed in β‐PVDF. © 1993 John Wiley & Sons, Inc.
Water‐induced micellar structures of block copoly(oxyethylene‐oxypropylene‐oxyethylene) in o‐xylene
Authors: Wu Guangwei , Zhou Zukang , Chu Benjamin 
Published: April 2003

AbstractWe previously reported the water‐induced micelle formation of copoly(oxyethylene‐oxy‐propylene‐oxyethylene), Pluronic L64, in o‐xylene. The micellar properties could be controlled by varying the water to EO ratio (Z) in micelles. in micelles. In this paper, laser light scattering, transient electric birefringence (TEB), and synchrotron small‐angle x‐ray scattering (SAXS) were used to study the micellar structure at different Z values. Both TEB and SAXS results further confirmed the micellar shape transition from that of a sphere to a nonspherical shape. A comparison between TEB and dynamic light‐scattering results as well as the SAXS experiments showed an ellipsoidal shape for micelles when Z > 1.3 with the oblate being the more reasonable form for fitting all the experimental parameters. The degree of asymmetry appeared to be not high. © 1993 John Wiley & Sons, Inc.
Model experiments for the interfacial reaction between polymers during reactive polymer blending
Authors: Scott Chris , Macosko Chris 
Published: April 2003

AbstractBilayer film Fourier transform infrared (FTIR) model experiments are designed to provide a well‐defined interface for study which can be probed by infrared spectroscopy during the interdiffusion and reaction of two reactive polymers. This provides a model experiment to determine the kinetics and extent of reaction between functionalized polymers during reactive polymer blending. This type of experiment provides data on the reaction at a stagnant interface which is necessary for the analysis of the interface while it is simultaneously undergoing deformation. It is also useful as a screening or preliminary experiment on reactive blending systems in that the extent of reaction may be followed for different systems at different temperatures. Experiments reported here trace the reaction of a styrene–maleic anhydride copolymer with two different amine terminated polymers. Results are obtained for the interdiffusion and reaction of a styrene‐maleic anhydride copolymer with two amine terminated polymers: a butadiene‐acrylonitrile copolymer and Nylon 11. The kinetics from these experiments include contributions due to both interdiffusion and chemical reaction. The chemical reaction kinetics may be isolated from the diffusion kinetics by performing experiments on well‐mixed systems which are prepared by casting films of the polymer mixtures from a mutual solvent. © 1994 John Wiley & Sons, Inc.
Effects of solvent and electrolyte on the electrochromic behavior and degradation of chemically prepared polyaniline‐poly(vinyl alcohol) composite films
Authors: Morita Mitsuyuki 
Published: April 2003

AbstractEffects of solvent and electrolyte on the electrochromic behavior and degradation of polyaniline in nonaqueous aprotic media, as well as its electrochemical redox and degradation mechanisms, were investigated with chemically prepared polyaniline‐poly (vinyl alcohol) composite films and polyaniline homogeneous films. Visible and FT‐IR absorption spectra of the polyaniline films, oxidized electrochemically at various polarization potentials, showed that the mechanisms in aprotic media involved two successive oxidation processes. In contrast to aqueous systems, the higher oxidation process involved further anion insertion without deprotonation, and the degradation was due to partial formation of the electrochemically inactive quinonediimine structure at excessive polarization potentials. From investigations of solvent and electrolyte effects, it is suggested that the electrochromic behavior and degradation of polyaniline are influenced by the electron‐donating and accepting ability of solvents, acceptor strength of electrolyte cations, and the nucleophilic character of electrolyte anions. It was also suggested that some anions like $\[ PF_6^ - , BF_4^ - , \] and $
$\[ CIO_4^ - , \] $
as well as protons, are constrained in the PVA matrix by specific electrostatic interactions and steric effects to improve the stability of polyaniline in the highly oxidized state. © 1994 John Wiley & Sons, Inc.
Mechanical properties of unsaturated polyester resins in relation to their chemical structure. I. Secondary relaxations and local motions
Authors: Melot D. , Escaig B. , Lefebvre J. M. , Eustache R. P. , Lauprêtre F. 
Published: April 2003

AbstractDynamic mechanical spectroscopy has been combined with high‐resolution solid‐state 13C NMR to characterize the molecular motions responsible for the γ and β secondary relaxations in unsaturated polyester networks. In DEG networks the 7γ transition is assigned to restricted phenyl group rotation in the styrene cross‐links whereas the motion of molecular groups in the vicinity of the residual maleic double bonds account for the β transition. © 1994 John Wiley & Sons, Inc.
Short branch effects on the creep properties of the ultra‐high strength polyethylene fibers
Authors: Ohta Yasuo , Sugiyama Hiroshige , Yasuda Hiroshi 
Published: April 2003

AbstractShort branch (methyl branch) effects on the creep properties of the ultra‐high strength polyethylene fibers were investigated. The temperature and the stress dependence of creep rates of several high‐strength polyethylene fibers having different branch contents, which were prepared by blending of two polymers of highly and less branching, was evaluated according to a model described by Ward and Wilding, and the activation energies and the activation volumes were calculated in terms of their methyl branch contents and tensile moduli. The creep rates of ultra high strength fibers are strongly influenced by their methyl branch contents. The typical branching sample with ca.6 CH3 units per 1000 CH2 units shows ca. 1/20 lower creep rate than that of the less branching (1.0 CH3 per 1000 CH2) fiber sample at the room temperature. The activation energies of creep rate obtained by those highly branching samples are higher than those of lesser branching samples; the difference is nearly proportioal to their branch contents. Wide‐angle x‐ray diffraction results showed that the dimension of a‐axis of unit cell increases in proportion to their branch contents. These results imply that the creep mechanism of ultra‐high strength polyethylene fibers is dominated by chain slippage in the crystalline part, and also imply that some amount of methyl branch sites can be incorporated in the crystalline part in proportion to the branch content and those incorporated branch sites hinder the slippage motion of molecular chains in crystalline part, which results in the extreme lower creep rate. © 1994 John Wiley & Sons, Inc.
Experimental study of molecular entanglement in polymer networks
Authors: Gent A. N. , Liu G. L. , Mazurek M. 
Published: April 2003

AbstractElastomeric molecular networks have been prepared by endlinking polydimethyl siloxane molecules having functional chain ends, both in the presence of an unreactive polymeric diluent and in the undiluted state. Values of tensile (Young) modulus were found to be in good agreement with the simple molecular theory of rubberlike elasticity for networks prepared in a highly diluted state. For concentrated systems the modulus was anomalously high, however. The discrepancy can be attributed to chain entanglements. A second interpenetrating network was introduced into networks formed in the diluted state by replacing the diluent polymer by reactive polymer, which was then gelled in situ. The modulus of these combined networks was much higher than the sum of the moduli of the constituent networks, implying a large contribution from molecular entanglements. © 1994 John Wiley & Sons, Inc.
Effects of an electrostatic field on crystallization of poly(vinylidene fluoride)
Authors: Sajkiewicz Pawel 
Published: April 2003

AbstractMelt crystallization of poly(vinylidene fluoride) (PVF2) under a static electric field was studied by optical microscopy. For most crystallization temperatures a mixture of α and γ spherulites was obtained. The growth rate of the spherulites was measured in the plane perpendicular to the direction of the field. The effect of an electric field on the growth rate of the γ spherulites corresponds in a qualitative way with the dependence predicted theoretically for the primary nucleation of the nonpolar form. It is shown, that the growth rate of γ spherulites is always reduced by the electric field. This reduction was larger the lower the undercooling. In the case of γ spherulites the interpretation of the results is more complicated. Both the morphology and the growth rate of γ spherulites under an electric field depend on electrode configuration. An increase of the growth rate of γ spherulites in an electric field was detected only when the sample was in direct contact with both electrodes. Under these circumstances, γ spherulites nucleate and grow at the PVF2‐positive electrode interface; and the increase of the growth rate is higher the lower the undercooling, and is greater in comparison with the decrease found for the nonpolar α phase. The reason for the sensitivity of the morphology of the γ form to the electrode configuration is not completely clear. © 1994 John Wiley & Sons, Inc.
Roll‐Casting of block copolymers and of block copolymer‐homopolymer blends
Authors: Albalak Ramon J. , Thomas Edwin L. 
Published: April 2003

AbstractAn improved technique for casting highly oriented films of block copolymers from solutions subjected to flow is presented. Polymer solutions were rolled between two counter‐rotating adjacent cylinders while at the same time the solvent was allowed to evaporate. As the solvent evaporated, the block copolymers microphase separated into globally oriented structures. Using this method known as ‘roll‐casting’ we present in this paper a study of the morphology of polystyrene‐polybutadiene‐polystyrene (PS/PB/PS) triblock copolymer cast with and without additional high molecular weight homopolymers. The pure copolymer films consisted of polystyrene cylinders assembled on a hexagonal lattice in a polybutadiene matrix in a near single‐crystal structure. Blends of copolymer with high molecular weight polystyrene and/or polybutadiene, phase separated into ellipsoidal regions of homopolymer embedded in an oriented block copolymer matrix. Annealing the films resulted in conversion of the homopolymer regions to spheres accompanied by some misalignment of the copolymer microdomains. The morphology of these films as revealed by TEM is discussed. A brief discussion of the flow field that develops in the experimental system is also presented and its similarity to the flow field of our previous work is shown. © 1994 John Wiley & Sons, Inc.
FTIR and X‐ray study of polymorphs of nylon 11 and relation to ferroelectricity
Authors: Balizer E. , Fedderly J. , Haught D. , Dickens B. , Dereggi A. S. 
Published: April 2003

AbstractNylon‐11 polymorphs have been studied by x‐ray diffraction and by infrared spectroscopy. A γ or γ‐like phase of Nylon‐11 was produced by treating the metastable δ' phase with gaseous HCl or DCl and then exposing the resulting complex (amidonium salt) to 100% RH H2O or D2O vapor. An oriented form of the γ or γ‐like phase results from treatment of the oriented δ' phase, but stretching of the unoriented γ or γ‐like phase, obtained by treatment of the unoriented δ' phase, induces a transformation to the α phase stable at room temperature. The use of DCl and D2O produced highly deuterated samples with Fermi resonances indicating the relative strengths of the hydrogen bonds are weakest in the α phase, intermediate in the δ' phase and strongest in the γ or γ‐like phase. © 1994 John Wiley & Sons, Inc.
Toughening of a highly cross‐linked epoxy resin by reactive blending with bisphenol A polycarbonate. I. FTIR spectroscopy
Authors: Abbate M. , Martuscelli E. , Musto P. , Ragosta G. , Scarinzi G. 
Published: April 2003

AbstractA highly cross‐linked thermosetting epoxy resin was modified by a reactive blending process carried out in the presence of bisphenol A polycarbonate (PC). Prior to the curing process the PC component was dissolved at high temperature in the uncured epoxy matrix. FTIR investigation of this reactive mixture demonstrated the occurrence of physical and chemical interactions among the blend components. Isothermal kinetic measurements performed by FTIR spectroscopy showed that the presence of PC does not affect the overall curing mechanism but decreases both the initial reaction rate and the final conversion of reactants. © 1994 John Wiley & Sons, Inc.
The effect of thermal annealing on the thermal properties and molecular weight of a segmented polyurethane copolymer
Authors: Hu Wenchun , Koberstein J. T. 
Published: April 2003

AbstractThe influence of thermal annealing on molecular weight, microphase mixing, and multiple melting behavior of a segmented block copolyurethane is reported. The material studied contained 55% of hard segment consisting of 4,4'‐diphenylmethane diisocyanate and butanediol, and a poly (propylene oxide) diol of molecular weight 2000 as the soft segment. The thermal stability of the materials was influenced greatly by the order‐disorder transition, estimated to occur at ca. 191°C. Upon annealing above this temperature, molecular weight increased rapidly as a result of chain branching reactions. Microphase separation increased under these conditions, while the degree of hard segment crystallinity decreased. Annealing below the order‐disorder transition temperature resulted in relatively small molecular weight increases for short annealing times, but large increases for annealing times greater than one hour. Glass transition temperature data for these thermal treatments was consistent with upper critical solution temperature behavior and selective solubility by hard segment sequence length according to the Koberstein‐Stein hard microdomain model. The critical hard segment sequence for segregation was estimated (for 30 min annealing) to contain ca. 5 diisocyanate residues at 80°C, ca. 8 residues at 185°C, and increased slowly with annealing time. © 1994 John Wiley & Sons, Inc.
Electrical relaxation in in situ dried acid‐form nafion
Authors: Fontanella J. J. , Mclin M. G. , Wintersgill M. C. 
Published: April 2003

AbstractElectrical relaxation studies have been carried out on dried, acid‐form Nafion 117 (copolymer of tetrafluoroethylene and perfluoro 3,6‐dioxa‐4‐methyl‐7‐octenesulfonic acid and which has an equivalent weight of 1100). Significant electrical conductivity is found and the data are found to be non‐Arrhenius. The results are converted to the electrical modulus representation and a conductivity relaxation is observed. A stretched exponential is best‐fit to the conductivity relaxation and again, non‐Arrhenius behavior is observed for the peak position. Finally, at low temperatures, a new dielectric relaxation peak is found which has an activation enthalpy of about 0.57 eV (13 kcal/mol). This relaxation is analogous to the γ‐relaxation observed in mechanical relaxation studies. © 1994 John Wiley & Sons, Inc.
Physical aging studies in epoxy resins. I. Kinetics of the enthalpy relaxation process in a fully cured epoxy resin
Authors: Montserrat S. 
Published: April 2003

AbstractThe physical aging of an epoxy resin based on diglycidyl ether of bisphenol‐A cured by a hardener derived from phthalic anhydride has been studied by differential scanning calorimetry. The isothermal curing of the epoxy resin was carried out in one step at 130°C for 8 h, obtaining a fully cured resin whose glass transition was at 98.9°C. Samples were aged at temperatures between 50 and 100°C for periods of time from 15 min to a maximum of 1680 h. The extent of physical aging has been measured by the area of the endothermic peak which appears below and within the glass transition region. The enthalpy relaxation was found to increase gradually with aging time to a limiting value where structural equilibrium is reached. However, this structural equilibrium was reached experimentally only at an aging temperature of Tg‐10°C. The kinetics of enthalpy relaxation was analysed in terms of the effective relaxation time τeff. The rate of relaxation of the system given by 1/τeff decreases as the system approaches equilibrium, as the enthalpy relaxation tends to its limiting value. Single phenomenological approaches were applied to enthalpy relaxation data. Assuming a separate dependence of temperature and structure on τ, three characteristic parameters of the enthalpic relaxation process were obtained (In A = −333, EH = 1020 kJ/mol, C = 2.1 g/J). Comparisons with experimental data show some discrepancies at aging temperatures of 50 and 60°C, where sub‐Tg peaks appears. These discrepancies probably arise from the fact that the model assumes a single relaxation time. A better fit to aging data was obtained when a Williams‐Watts function was applied. The values of the nonexponential parameter β were slightly dependent on temperature, and the characteristic time was found to decrease with temperature. © 1994 John Wiley & Sons, Inc.
Physical aging and dye diffusion in polysulfone below the glass transition temperature
Authors: Zhang X. Q. , Wang C. H. 
Published: April 2003

AbstractThe effect of physical aging on the tracer diffusion coefficient D of camphorquinone in polysulfone is investigated. It is shown that if the sample is sufficiently annealed and physical aging is nearly complete, the temperature dependence of D will reflect the primary α‐relaxation process of the host polymer. In the temperature range between Tg (=185°C) and 165°C, D is found to be a function of time, and the time dependence of D is given by D = At−μ, with μ approximately equal to unity. © 1994 John Wiley & Sons, Inc.
Preparation of small poly(butylene terephthalate) spheres by crystallization from solution
Authors: Nichols Mark E. , Robertson Richard E. 
Published: April 2003

AbstractThe crystallization of poly(butylene terephthalate) (PBT) from moderately dilute solutions of PBT in a diglycidyl ether of bisphenol‐A epoxy has been investigated. PBT dissolves in this epoxy approximately 35°C below its usual melting temperature of 227°C to form a one‐phase solution. Cooling this solution below 165°C leads to rapid crystallization of the PBT. The resulting mixture of liquid epoxy and crystalline PBT has a low viscosity and contains highly birefringent, individual PBT spherulites. The PBT spherulites have a narrow size distribution and a high surface‐to‐volume ratio. These particles are suggested to arise from a rapid crystallization that follows liquid–liquid phase separation. © 1994 John Wiley & Sons, Inc.
Local compositional fluctuations in PPO/HIPSand PPO/SBS blends
Authors: Li S. , Charles Dickinson L. , Chien James C. W. 
Published: April 2003

AbstractSolid‐state NMR relaxation has been used to explore the distribution of components in poly(phenylene oxide) (PPO) high impact polystyrene (HIPS) and PPO/poly(styrene‐b‐butadiene‐b‐styrene) (SBS) blends. The nuclear relaxation of PPO in the former system is single exponential for all compositions, but the relaxation of PS in the blend is simple exponential only when the PPO content is low but is otherwise nonexponential. The nuclear magnetization decay curves were analyzed in terms of statistical compositional fluctuation at the scale of spin diffusion distances of several nm. Distribution functions for nuclear relaxation and for blend composition have been derived. Extraction of low molecular weight occluded PS from HIPS resulted in blends having reduced homogeneity. Addition of low molecular weight PS enhanced homogeneity in both the PPO/HIPS and PPO/SBS blends. © 1994 John Wiley & Sons, Inc.
Liquid–liquid phase separation in linear low‐density polyethylene
Authors: Nesarikar A. , Crist B. , Davidovich A. 
Published: April 2003

AbstractThe issue of multiple equilibrium phases in compositionally heterogeneous random copolymers is studied with an ethylene‐butene copolymer representative of many linear low‐density polyethylenes (LLDPE). This material has a dispersed minority phase (volume fraction ƒβ ≈ 0.02) of highly branched, amorphous chains. A thermodynamic calculation of the equilibrium liquid state is done using the distribution of chain branching from temperature rising elution fractionation and the Flory‐Huggins interaction parameter χAB for linear and ethyl branched C4H8 repeat units. The calculation indicates that this copolymer is metastable, between the binodal and spinodal at a melt temperature of 150°C. The predicted volume fraction of the second phase, ƒβ = 0.016, is in good agreement with experiment. This work is the first to compare directly the observed and calculated two‐phase behaviors in a random copolymer. © 1994 John Wiley & Sons, Inc.
A high‐speed, high‐precision data acquisition and processing system for experiments producing steady‐state periodic signals
Authors: Winther Grethe , Parsons Donald M. , Schrag John L. 
Published: April 2003

AbstractA wide variety of experiments investigate the response of a sample to a steady‐state periodic excitation. We describe a computerized data acquisition and processing system for experiments of this type assembled from relatively inexpensive, commercially available components which has been optimized for highly precise determinations of the magnitude and relative phasing of drive and response signals having frequencies from 1 μHz to approximately 1 MHz. Through the use of timing control with a precision of 1 part in 109 and high speed on‐line signal processing, the system combines a very high rate of data acquisition with extended signal averaging times, enabling it to acquire an uninterrupted data stream consisting of at least 109 samples. Furthermore, the system acts as a digital filter which can be tuned to completely reject unwanted signals of any frequency other than the exact signal frequency. This allows accurate characterization of sample response even when obscured by other, extraneous signals of substantially larger magnitudes as long as they have at least somewhat different frequencies. Oscillatory experiments on very dilute polymer solutions, including oscillatory flow birefringence, dynamic viscoelasticity, oscillatory electric birefringence and dielectric measurements, are important examples of this type of measurement situation, in which the experiment depends critically on accurate determination of the magnitude and phasing of weak response signals, frequently under extremely poor signal‐to‐noise conditions. The system has an aggregate sampling rate of 1 MHz and up to four input channels. The potential for distortion of the results by aliasing frequencies may limit the input signal frequency to less than 500 kHz for one channel. © 1994 John Wiley & Sons, Inc.