bluuebunny/crossref_metadata_2025_split huggingface dataset:
Novel preferred orientation in injection‐molded nylon 6‐clay hybrid
Authors: Kojima Yoshitsugu , Usuki Arimitsu , Kawasumi Masaya , Okada Akane , Kurauchi Toshio , Kamigaito Osami , Kaji Keisuke 
Published: April 2003

AbstractNylon 6‐clay hybrid (NCH) is a molecular composite of Nylon 6 and uniformly dispersed silicate monolayers of montmorillonite. In this study the preferred orientation of montmorillonite and Nylon‐6 crystallites in a thick (3 mm) injection‐molded bar of NCH has been investigated using x‐ray diffraction and electron micrography (TEM). It is clear that this bar has a triple layer structure consisting of surface, intermediate, and middle layers which have different preferred orientation. In the surface layer both the silicate monolayers and the chain axes of Nylon‐6 crystallites are parallel to the bar surface though the latter are randomly oriented within the plane. In the intermediate layer the silicate monolayers remain parallel to the bar surface but the Nylon‐6 crystallites rotate by 90° so that the chain axes would be perpendicular to the bar surface or the silicate monolayers. In the middle layer the silicate monolayers are randomly oriented around the flow axis of the NCH bar while remaining parallel to it, and the Nylon crystallites are randomly oriented around the flow axis while keeping their chain axes perpendicular to the silicate monolayers. It may be concluded that such preferred orientation of Nylon 6 crystallites is induced by the clay because the crystallites in the pure Nylon 6 bar have no preferred orientation. ©1995 John Wiley & Sons, Inc.
Effects of hydrophilic and hydrophobic counterions on the Coulombic interactions in perfluorosulfonate ionomers
Authors: Cable Kevin M. , Mauritz Kenneth A. , Moore Robert B. 
Published: April 2003

AbstractAttenuated total reflectance FTIR spectroscopy was used to compare the influence of hydrophilic and hydrophobic counterions on the vibrational behavior of the sulfonate and perfluoroether groups in 1100 equivalent weight (EW) Nafion® and 808 EW Dow perfluorosulfonate ionomer membranes. For dry, Na+‐form membranes, the infrared band attributed to the —SO3− symmetric stretching vibration was found to shift to higher frequencies with an increase in the degree of neutralization. In contrast, neutralization with tetrabutlyammonium ions caused the —SO3− vibrational band to shift to lower frequencies with increasing neutralization. This behavior is attributed to a diminished polarization of the —SO3− groups by the hydrophobic and diffusely charged TBA+ cations, relative to the strong polarization observed with Na+ ions. Vibrational bands attributed to perfluoroether groups in close proximity to the sulfonate groups were also found to be influenced by Coulombic interactions within the clusters. The frequency shifts of these bands followed a trend that was virtually identical to that observed for the —SO3− symmetric stretch. This behavior is attributed to a combination of through‐space, dipolar field effects, and through‐bond inductive effects, from the neighboring ionic groups. In Nafion®, the ether groups directly attached to the backbone are shielded from the Coulombic interactions within the clusters, while the ether groups within three bonds of the terminal ionic groups are very sensitive to the state of polarization of the sulfonate anion. ©1995 John Wiley & Sons, Inc.
Spinodal phase separation in semi‐interpenetrating polymer networks—polystyrene‐cross‐polymethacrylate
Authors: De Graaf Leontine A. , Beyer Jenö , Möller Martin 
Published: April 2003

AbstractMorphology control in semi‐interpenetrating polymer networks has been achieved by means of a two‐step process, separating morphology formation and polymerization/crosslinking. Phase textures formed during spinodal liquid/liquid demixing of a solution of atactic polystyrene in methacrylate monomers were arrested by thermoreversible gelation of the polymer‐rich phase as this phase passed its glass transition temperature. The phase separated structure was permanently stabilized by low‐temperature crosslinking ultraviolet (UV) polymerization of the methacrylate monomer, and studied by transmission electron microscopy. Thus, it was directly observed how the initial demixing process depended on the initial viscosity of the polymer solution and the mode of quenching. Arrest of the earliest stage of spinodal demixing resulted in separated domains of 0.05–0.08 μm thickness, which were separated by a distance of the spinodal wavelength λ. A cocontinuous network only developed in a relatively late stage of demixing. ©1995 John Wiley & Sons, Inc.
Gelation of micellar solutions of diblock‐copoly (oxyethylene/oxybutylene) in aqueous K2SO4. An investigation of excluded volume effects
Authors: Deng Nan‐Jie , Luo Yun‐Zhu , Tanodekaew Siriporn , Bingham Nicole , Attwood David , Booth Colin 
Published: April 2003

AbstractThe micellization and gelation properties of oxyethylene/oxybutylene diblock copolymers E40B10 and E41B8 in aqueous K2SO4 solutions were investigated. The thermodynamic and hydrodynamic volumes of the micelles in salt solutions of various concentrations up to 0.4 mol dm−3 were determined by static and dynamic light scattering, respectively. The related changes in the gelation behavior of concentrated micellar solutions of the copolymers were explained as thermodynamic (excluded) volume effects. The thermodynamic volumes of micelles measured in moderately concentrated solution were used successfully to predict the critical gel concentrations of concentrated solutions. ©1995 John Wiley & Sons, Inc.
Elastomers having high functionality cross links viewed as bimodal networks. An alternative interpretation in terms of bimodal chain‐length distributions
Authors: Sharaf M. A. , Mark J. E. 
Published: April 2003

AbstractSeveral groups have now prepared poly(dimethylsiloxane) networks of high cross‐link functionality by end‐linking vinyl‐terminated chains by means of SiH groups in siloxane oligomers (CH3)3SiO[SiHCH3O]xSi(CH3)3. The elongation moduli of these networks were generally found to be considerably larger than the values predicted from the functionality and number density of the cross links (based on the stoichiometry of the end‐linking reaction). Not all the SiH groups in an oligomer are used in the end‐linking reaction, however, and the segments between cross‐links can themselves act as short network chains. The connectivity of these short chains to the long ones, in what is essentially a bimodal distribution, has been neglected in analyses to date. They are taken into account in the present analysis, giving much better agreement between experiment and theory. The stress‐strain behavior for such very short chains can be characterized by the use of Monte Carlo methods and the Fixman‐Alben non‐Gaussian distribution. This alternative analysis seems useful in reproducing the experimental observations, but further experimental and theoretical will be required to remove some remaining ambiguities. © 1995 John Wiley & Sons, Inc.
Conformations of polymer chains in voids with an external electric field by Green's function methods
Authors: Chen X. , Burns J. 
Published: April 2003

AbstractThe statistical conformations of a length of polymer chain, such as DNA, trapped in a void within a gel under the influence of an external electric field, have been studied by the method of Green's functions. Based upon a rectangular box approximation for the void shape, the method gives an explicit analytical expression for the end‐to‐end distance (Rx) as a function of applied field strength, number of chain segments coiled within the void, and size of a chain segment. Results of calculations show that the field compresses the entrained coil into more compact configurations, as would be expected. Such compression is believed to affect the electrophoretic mobility of a long chain molecule like DNA in a dilute gel. © 1995 John Wiley & Sons, Inc.
Characterization of the ground state pyrene complex in ethylene‐propylene copolymer solutions
Authors: Jao Tze Chi , Mishra Munmaya K. , Rubin Isaac D. , Duhamel Jean , Winnik Mitchell A. 
Published: April 2003

AbstractPyrene‐labeled functionalized ethylene‐propylene (EP) copolymer was prepared by grafting 1‐pyrenebutyrylhydrazine onto EP copolymer through maleic anhydride pendants. The EP copolymer contained 60 mol % ethylene; its weight‐average molecular weight (Mw) was 148,000. The pyrene‐labeled amide functionalized EP copolymer, PA‐EP(60/40), was made to simulate the amine functionalized EP copolymers that are commonly used as dispersant additives in motor oils. UV absorption spectra, fluorescence emission and excitation spectra, and fluorescence decay profiles of the pyrene were studied to determine the copolymer conformation and dynamics in methylcyclohexane and tetrahydrofuran (THF). The pyrene fluorescence characteristics of PA‐EP(60/40) were highly dependent on the solvent. The dependence of fluorescence emission intensity on the excitation wavelength was large in methylcyclohexane and moderate in THF. A frequency shift of about 2 nm was observed between the excitation spectrum obtained with the emission line at 377 nm and that at 550 nm in the methylcyclohexane solutions, but no shift was found in the corresponding tetrahydrofuran solutions. The ratios of the preexponential factors (a21/a22) of the excimer decays obtained in both methylcyclohexane and THF solutions were different from −1.0. However, the deviation of the excimer formation process from the Birks scheme is small in THF but large in methylcyclohexane. In addition, the Huggins constants obtained from intrinsic viscosity measurements of the PA‐EP(60/40) copolymer solutions suggest that copolymer aggregation occurs in methylcyclohexane but not in THF. H‐bonding between two pyrene‐containing pendants is apparently the main driving force for the formation of the ground state pyrene complex. THF is found to be effective in inhibiting the H‐bonding formation. © 1995 John Wiley & Sons, Inc.
Thermal variation of free‐volumes size distribution in polypropylenes. Probed by positron annihilation lifetime technique
Authors: Ohko Y. , Uedono A. , Ujihira Y. 
Published: April 2003

AbstractPositron annihilation lifetime measurement was applied to the study of free‐volume properties in three kinds of polypropylene as a function of temperature in the range of 25–180°C at thermal equilibrium. Positron lifetime data for polypropylenes were analyzed with a Laplace inversion technique in order to obtain continuous positron annihilation lifetime (PAL) distributions. At each temperature, four distinct PAL distributions were recognized. The distribution of the longest lived component was associated with a pick‐off annihilation of ortho‐positronium (o‐Ps) trapped in free‐volume of amorphous region, which grew bigger as the temperature increased. The hole radius distributions of free‐volumes were estimated from the results of o‐Ps lifetime distributions. A detailed analysis showed a mean radius of free volumes was 0.34 nm at room temperature and that was 0.42 nm near the melting point for each specimen. The distributions of hole radii of free volumes were found to be broader after thermal treatments. The relaxation of free volumes was attributed to the thermal equilibrium and the evacuation of included molecules in free volumes. © 1995 John Wiley & Sons, Inc.
Design of miscible polyolefin copolymer blends
Authors: Fredrickson Glenn H. , Liu Andrea J. 
Published: April 2003

AbstractTheoretical guidelines are established for designing miscible blends of amorphous polyolefin copolymers. On the basis of calculations for an athermal and incompressible model of copolymer melts, limits are placed on the compositions and structural differences between blend components that are consistent with thermodynamic stability of a single liquid phase. Specific cases analyzed include binary blends of random copolymers containing short branches and blends of graft polymers with long flexible branches, either periodically or randomly placed. The predictions are shown to be in good agreement with recent experimental studies of miscibility in model polyolefin copolymer blends. © 1995 John Wiley & Sons, Inc.
Viscoelastic properties of dilute nematic mixtures containing cyclic and hyperbranched liquid crystal polymers dissolved in a nematic solvent
Authors: Chen Fu‐Lung , Jamieson A. M. , Kawasumi M. , Percec V. 
Published: April 2003

AbstractThe twist and bend viscosities of dilute solutions of cyclic and hyperbranched liquid crystal polymers (LCP) dissolved in low molar mass nematic solvents were determined via dynamic light scattering analysis. These results were compared to those of linear chains with similar chemical repeat structures. The nematic solvent used was 4′‐pentyloxy‐4‐cyanobiphenyl (50CB). The cyclic LCP oligomers, Cy TPB10, have a mesogenic group, 1‐(4‐hydroxy‐4′‐biphenyl)‐2‐(4‐hydroxyphenyl) butane, separated by flexible decamethylene spacers. The twist viscosity of the cyclic Cy‐TPB10 oligomers increases with molecular weight more strongly than the linear, TPB‐10, suggesting that the hydrodynamic behavior of Cy‐TPB10 is closer to that of a rigid rod than TPB10. Surprisingly, the intrinsic bend viscosity [ηbend] of Cy‐TPB10 decreases with molecular weight, in contrast to the positive dependence for linear TPB10. This may reflect the higher strain energy in the smaller ring sizes. The hyperbranched LCP, TPD‐b‐8, is also based on the mesogen 10‐bromo‐1‐(4‐hydroxy‐4′‐biphenyl)‐2(4‐hydroxyphenyl) decane but with octyl groups at the chain ends. We compare the viscoelastic behavior of dilute nematic solutions of TPD‐b‐8 in 50CB against that of a linear main‐chain LCP, TPB7, with the same mesogenic group but with heptamethylene spacers. The viscometric properties of TPD‐b‐8/50CB and TPB7/50CB are quite different. The results suggest that each chain is prolate (i. e., R∥ > R⊥) but that TPD‐b‐8 has a smaller chain anisotropy than that of TPB7. © 1995 John Wiley & Sons, Inc.
High temperature thermal field‐flow fractionation of polyethylene and polystyrene
Authors: Pasti Luisa , Roccasalvo Salvatore , Dondi Francesco , Reschiglian Pierluigi 
Published: April 2003

AbstractIn this paper the high‐temperature thermal field flow fractionation method is exploited for the analysis of polyethylene (PE). The experimental apparatus set‐up, obtained by simply modifying a commercial instrument, is presented. The numerical procedure for deriving retention calibration plot versus molecular weight is discussed with reference to the specific polymer‐solvent pair, PE‐o‐dichlorobenzene (ODCB), here employed. Different methods for computing the physicochemical data set of the solvent, necessary for calibration, are compared. The selectivity of the checked PE‐ODCB system proves comparable with respect to the values currently found in thermal field‐flow fractionation (ThFFF) analysis. Differences are found between PE and polystyrene (PS) analysis in the same solvent. The conditions for high temperature ThFFF operation in PE analysis and their advantages are discussed with respect to the standard SEC technique for PE, PS, and PE‐PS copolymer analysis. Molecular weight distributions obtained by ThFFF of two PE commercial samples agree with those obtained by SEC. © 1995 John Wiley & Sons, Inc.
Phase behaviors and interactions of N‐alkylated polyanilines and ethylene‐co‐vinyl acetate blends
Authors: Zheng Wenyue , Levon Kalle , Taka Tapani , Laakso Jukka , Österholm Jan‐Eric 
Published: April 2003

AbstractConjugated polyanilines bearing long alkyl side chains (dodecyl PANi‐12 and octadecyl PANi‐18) were prepared for the purpose of obtaining well‐mixed conducting polymer blends with insulating flexible polymers. The miscibility of the polyanilines and ethylene‐co‐vinyl acetate copolymers (EV A20 with 20 wt % of vinyl acetate and EV A70 with 70 wt %) was significantly improved by long alkyl chains of the same hydrocarbon moieties as the ethylene segments in the matrix EV A, as demonstrated by microscopic observation. PANi‐18/EV A20 blends exhibit a lower critical phase separation temperature (LCST). In addition, the EV A crystallinity and the side‐chain crystallinity in the miscible blends were depressed, as shown by thermal analysis and x‐ray scattering. The comparison of three designed blend systems indicates that the miscibility of the polymers is determined by the hydrophobic interaction between the hydrocarbon units in the both components and by the hydrogen bonding. The solvatochromic phenomena for the blends at low miscible PANi compositions was detected by UV‐visible spectroscopy. The threshold conductivities exhibit sensitivity to the morphological structure of the polymeric blends, and was lowered by improved homogenous dispersion of the conducting phase. © 1995 John Wiley & Sons, Inc.
Conductivity studies of polymer electrolytes based on aliphatic polyesters
Authors: Kim Dong‐Won , Park Jung‐Ki , Gong Myoung‐Seon 
Published: April 2003

AbstractA series of aliphatic polyesters of sebacoyl chloride and poly(ethylene glycol) containing a different number of ethylene oxide groups was synthesized and characterized. These polyesters were complexed with lithium perchlorate to obtain a new class of polymer electrolyte. The relationships between the structure and properties of these polymer electrolytes were investigated. The main factor that affects the ionic conductivity in these systems was found to be the solvating capacity of the polyester for the lithium salt. These polymer electrolytes showed ionic conductivities up to 10−5 ˜ 10−4 S/cm at 25°C. The mechanical strength was improved by cross‐linking, and the cross‐linked polyester complexed with a LiCIO4 salt showed an ionic conductivity of 2 × 10−5 S/cm at room temperature. 7Li NMR spin‐spin relaxation and dielectric relaxation studies were also carried out to investigate the local environments and dynamics of ions in the polymer electrolytes. © 1995 John Wiley & Sons, Inc.
Water transport in a polyketone terpolymer
Authors: Mensitieri G. , Del Nobile M. A. , Sommazzi A. , Nicolais L. 
Published: April 2003

AbstractWater transport in a polyketone terpolymer was analyzed performing both sorption and permeation experiments. Water vapor sorption tests were conducted at four temperatures (35, 45, 55, and 65°C) and at several activities. The analysis of sorption isotherms revealed the occurrence of water clustering. A reduction of the endothermicity of mixing as the amount of sorbed water increased was observed which is consistent with significant association of penetrant molecules in the polymer. Permeation experiments performed at 35°C at upstream pressures ranging from 4 to 25 Torr showed evidence of a reduction in water diffusivity as function of sorbed water concentration which is a typical indication of penetrant aggregation. © 1995 John Wiley & Sons, Inc.
Interdiffusion of polymer chains and molecular dynamics in dried latex films
Authors: Richard J. , Wong K. 
Published: April 2003

AbstractInterdiffusion of polymer chains across particle‐particle interfaces in latex films is one of the key issues, because this further coalescence process usually controls the cohesive strength of the films. Here we examined local dynamics of polymer chains within latex films and showed that it is related to the occurrence of particle coalescence. For this purpose, structural and dynamic micromechanical properties of partly cross‐linked polymer films from styrenebutadiene (SB) copolymer latexes were investigated. The gel fraction of the emulsion copolymers was varied within a large range (15–90%) by adding different chain transfer agents during the polymerization process. The structure of the films was determined using small‐angle neutron scattering (SANS) and transmission electron microscopy (TEM). A qualitative description of the mechanism that likely triggers further coalescence in latex films is given, based on critical disjoining pressure exerted by particle cores on interfacial membranes. In addition, from dynamic micromechanical analysis (DMA) spectra, a key molecular parameter reflecting local segmental mobility was derived. Average diffusion coefficients of polymer segments were calculated and shown to be consistently related to the occurrence of particle coalescence as evidenced from SANS and TEM structural investigations. Finally, the noncovalent physical intermolecular interaction loci, which act as cross‐link knots, were shown to play a significant part in the restriction of the coalescence process, increasing the state of constraints encountered by free chain segments embedded in the covalent network. © 1995 John Wiley & Sons, Inc.
Molecular weight characterization of soluble high performance polyimides. 1. Polymer‐solvent‐stationary phase interactions in size exclusion chromatography
Authors: Konáš Martin , Moy Thomas M. , Rogers Martin E. , Shultz Allan R. , Ward Thomas C. , Mcgrath James E. 
Published: April 2003

AbstractSoluble, fully cyclized m‐amino phenyl acetylene terminated polyimides based on several anhydride/diamine monomers were prepared in N‐methylpyrrolidine (NMP) and cyclized by solution imidization to controlled molecular weight. The polyimides and a polyamic acid precursor were successfully analyzed by size exclusion chromatography (SEC) utilizing online parallel coupled refractive index and differential viscometer detectors. The calculated Mnvalues were varied from 3,000 to 20,000 daltons. N‐methylpyrrolidone (NMP), tetrahydrofuran (THF), and chloroform served as mobile phases for the cross‐linked polystyrene gel packings. Normal retention behavior of the polyimides was observed in chloroform, THF, and NMP containing LiBr, or in NMP stirred over P2O5 before use. Values of Mark‐Houwink‐Sakurada exponents for narrow distribution linear polystyrene indicate that pure NMP and NMP with 0.06 M LiBr are good solvents for polystyrene standards at 60°C. In contrast, SEC behavior of polyimides in pure NMP leads to splitting of the peaks with the major portion observed to pass through the columns at the exclusion limit. In contrast to strong polymeric chain expansion of the polyamic acid in dilute solution, presumably due to a polyelectrolyte effect, no increase of intrinsic viscosity of polyimide samples in pure NMP was observed. This exclusion effect of polyimides analyzed in NMP is discussed in terms of possible ion‐exclusion from pores of the stationary phase. Differences in polystyrene calibration in NMP with or without additives and the temperature dependence of calibration curves in these mobile phases is discussed as well. ©1995 John Wiley & Sons, Inc.
Solid state 15N NMR study of 15N enriched melamine‐formaldehyde resins
Authors: Andreis M. , Koenig J. L. , Gupta M. , Ramesh S. 
Published: April 2003

AbstractMolecular dynamics and structure of uncured and cured melamine‐formaldehyde resins isotopically 15N enriched at amine sites were studied by solid‐state 15N nuclear magnetic resonance (NMR). Spectra recorded with direct (DP) and cross‐polarization (CP) pulse sequences reflect two motionally different regions arising from similar chemical structures. DP spectra of uncured resins at higher temperatures have narrow lines and the detection of slightly different structural units is possible. With increasing crosslinking resonances broaden and overlap and the direct detection of individual signals in cured resins is not possible. On the basis of variable contact time, variable spinning speed, and interrupted decoupling experiments three protonated and one nonprotonated group of signals are identified in the CP spectra for all samples. Short polarization‐transfer rates, TNH, for nonprotonated nitrogen in uncured and lightly cured samples reveal more effective hydrogen bonding in viscous and rubber‐like resins compared to the highly cured rigid resins. The rigid portions of the resins exhibit longer T1 and short T1ρ relaxation times, while the shorter T1 times and longer T1ρ times are associated with the more mobile portion of samples. ©1995 John Wiley & Sons, Inc.