bluuebunny/crossref_metadata_2025 huggingface dataset:
Viscosity behavior of poly(glyceryl methacrylate) in the presence of borate and phenylboronate ions
Authors: Keita G. , Ricard A. , Audebert R.
Published: April 2003

The viscosity behavior of polyelectrolyte solutions induced by borate or phenylboronate complexation with poly(glyceryl methacrylate) (PGM) has been investigated. In dilute solutions borate ions can form monodiol (1/1) complexes and didiol (2/1) intramolecular complexes. Both types of complex are anionic. Thus, the polymer is characterized by the existence of charged sites on the chain and loops formed by intramolecular complexation. On the contrary, phenylboronate can only give monodiol 1/1 complexes. In the presence of passive salt, the charges are screened. By addition of borate ion to a PGM solution, a decrease of the initial polymer viscosity due to loop formation is first observed, then the anionic charges fixed on the chain by complex formation induce an expansion of the polyelectrolyte and the viscosity of the solution increases. The situation is different for the PGM‐phenyl boronate system, where no intramolecular crosslink is present. In this case the viscosity of the solution increases with phenyl boronate concentration. But for a fixed complexing ion concentration it will tend to that of the neutral polymer when NaCl is added. ©1995 John Wiley & Sons, Inc.
Retardation of dissolution and surface modification of high‐modulus poly(ethylene) fiber by the synergetic action of solvent and stress
Authors: Vaykhansky L. E. , Cohen Y.
Published: April 2003

Retardation of dissolution of highly oriented polyethylene fibers exposed to solvent under a constant tensile force has been investigated in comparison to free conditions. Beyond a critical value of the applied force, the time for dissolution increases sharply by several orders of magnitude. This effect is significant only in fibers with high initial orientation. It is attributed to the existence of a network of oriented crystallites. We have utilized this effect for surface modification of highly oriented PE fibers, by exposure to solvent at different temperatures and applied stress. At a relatively low load the action of the solvent displays pronounced effects: roughening of the fiber surface, formation of a nonoriented crystalline phase, enhancement of adhesion to epoxy resin with some loss of strength. ©1995 John Wiley & Sons, Inc.
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

Nylon 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

Attenuated 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

Morphology 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

The 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

Several 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

The 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

Pyrene‐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

Positron 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

Theoretical 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

The 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

In 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

Conjugated 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

A 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

Water 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

Interdiffusion 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

Soluble, 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

Molecular 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.
Solid state 13C NMR study of hexa(methoxy methyl)melamine and melamine‐formaldehyde selfcondensates
Authors: Andreis M. , Koenig J. L. , Gupta M. , Ramesh S.
Published: April 2003

The structure and molecular dynamics of self‐condensation products of three different melamine resins based on hexa(methoxy methyl)melamine are studied by 13C NMR in the solid state. The application of direct (DP) and cross‐polarization (CP) pulse sequences shows that uncured and cured melamine resins are motionally heterogeneous systems, with the mobile and rigid parts consisting of the same basic structural units. Viscous lightly cured samples based on commercial melamine‐formaldehyde resins contain low‐molecular weight species which act as plasticizers. In these resins, three motionally different methyl groups are observed. Their existence is confirmed either by spectral deconvolution or by fitting the experimental signal intensities to the cross‐polarization dynamics with the assumption of two cross‐polarization‐transfer rates. Fast cross‐polarizing rigid methyl groups are accompanied with the spinning sidebands. On the basis of DP and CP relaxation measurements, quantitative results for three major structural units are calculated. Problems concerning the 14N‐13C quadrupolar interactions and quantitative analysis are discussed. ©1995 John Wiley & Sons, Inc.
A nuclear magnetic resonance study of toluene‐polyisobutylene solutions. 2. Vrentas‐Duda theory
Authors: Bandis Athinodoros , Inglefield Paul T. , Jones Alan A. , Wen Wen‐Yang
Published: April 2003

The self‐diffusion coefficients of toluene in polyisobutylene have been analyzed using the Vrentas‐Duda free volume diffusion model. The diffusion coefficients were determined at different temperatures and concentrations, using the pulsed field gradient nuclear magnetic resonance technique. The data were satisfactorily described by the model and the size of the polymer jumping unit was extracted. Comparisons were made with the Fujita free volume theory and the Fujita free volume parameters were extracted from the Vrentas‐Duda free volume parameters. From the diffusion data that now available, it can be concluded that for most polymers the jumping unit is about 1.5 times the polymer monomer molecular weight. The activation energy of the toluene diffusion in polyisobutylene is compared with the activation energies of other penetrants in the same polymer. The diffusion data presented in this work show that the energy per mole required to overcome the attractive forces which constrain a diffusing species to its neighbors should be considered to be zero, in order to be able to extract the free volume parameters (from viscosity and diffusion data) with an acceptable uncertainty. ©1995 John Wiley & Sons, Inc.
Synthesis and characterization of poly(vinylcyclohexane) derivatives
Authors: Gehlsen Mark D. , Weimann Peter A. , Bates Frank S. , Harville Steven , Mays Jimmy W. , Wignall George D.
Published: April 2003

Six nearly monodisperse substituted poly(styrene) homopolymers, poly(styrene) (PS), poly(2‐methylstyrene) (P2MS), poly(3‐methylstyrene) (P3MS), poly(4‐methylstyrene) (P4MS), poly(tertiary‐butylstyrene) (PtBS), and poly(α‐methylstyrene) (FαMS) were anionically polymerized and subsequently saturated using heterogeneous hydrogenation techniques to poly(vinylcyclohexane) (PVCH), poly(2‐methylvinylcyclohexane) (P2MVCH), poly(3‐methylvinylcyclohexane) (P3MVCH), poly(4‐methylvinylcyclohexane) (P4MVCH), and poly(tertiary‐butylvinylcyclohexane) (PtBVCH), respectively. In each case, except PαMS, the materials were saturated to > 99% conversion with no chain degradation. PS hydrogenations required the addition of small amounts of tetrahydrofuran to the reaction solvent cyclohexane to enhance miscibility and eliminate large‐scale chain degradation. Density gradient and differential scanning calorimetry (DSC) measurements were used to characterize the density and glass transition temperature, Tg, of the unsaturated and saturated polymers. Saturation reduces the density by 3% to 11% and changes Tg substantially. The greatest variation in Tg is obtained with the 3‐methyl substituted species where a 63°C increase is observed, while the highest measured Tg is 186°C for P2MVCH. Small‐angle neutron scattering (SANS) experiments on binary mixtures of hydrogenous and deuterium labeled PVCH derivatives provided a determination of bulk chain statistics. The statistical segment length is relatively insensitive to vinylcyclohexane ring substitution, except with P3MVCH where a 20% greater value is obtained. ©1995 John Wiley & Sons, Inc.
Polystyrene (1)/poly(butyl acrylate/amide type functional monomer) (2) two‐stage emulsion polymers. Synthesis and thermomechanical properties of latex films
Authors: Hidalgo M. , Cavaillé J. Y. , Guillot J. , Guyot A. , Perez J. , Vassoille R.
Published: April 2003

Polystyrene (PS) (1)/Poly (n‐butyl acrylate (BA)/amide type functional monomer) (2) structured latex particles were prepared through emulsion polymerization varying the hydrophilicity of the functional monomer employed. The second‐stage polymerization kinetics, the size and morphology of latex particles, and the location of the functional groups in the final latexes were studied, in order to relate them to the thermomechanical properties of films cast from these latexes. It has been shown that, as expected, increasing the hydrophobicity leads to a better homogeneity in the copolymer formed during the second‐stage polymerization, while the more hydrophilic functional monomer partly homopolymerizes in a separate phase. However, the functionalization by all the monomers used in this work, prevents the PS seed particles to form a continuous skeleton (percolated network). Further heat treatments at 140°C do not lead to the formation of a continuous PS phase as for pure BA/pure PS two‐stage particles. In addition, some thermally induced crosslinking effects are discussed in relation with the functional monomer location within the particles. © 1995 John Wiley & Sons, Inc.
Analysis of polyurethanes using core excitation spectroscopy. Part I: Model polyurethane foam polymers
Authors: Urquhart S. G. , Hitchcock A. P. , Leapman R. D. , Priester R. D. , Rightor E. G.
Published: April 2003

The C 1s, N 1s, and O 1s excitation spectra of model methylenediphenyldiisocyanate (MDI) polyurethanes with well known structures have been recorded using electron energy loss spectroscopy (EELS) in an electron microscope. These spectra are compared to the core excitation spectra of selected small molecule analogue species (recorded by gas phase EELS) in order to identify transitions characteristic of various structural components found in polyurethanes. A more detailed report on the small molecule analogue spectra is presented in the following article. Spectral features characteristic of the different structural components in polyurethanes are identified in the spectra of the model polymers. These can be used as the basis for chemical studies of micron or submicron sized segregated phases in flexible polyurethane polymers. © 1995 John Wiley & Sons, Inc.
Modelling the fractionation process in TREF systems: Thermodynamic simple approach
Authors: Borrajo Julio , Cordon Cristina , Carella José M. , Toso Susana , Goizueta Graciela
Published: April 2003

A simple thermodynamic model, based on an extension of Flory‐Huggins theory, is applied to temperature rising elution fractionation (TREF). Dependence of the fractionation process on melting temperature, melting enthalpy, average crystallinity, average crystallizable sequence length, and polymer‐solvent interaction parameter is predicted. Results from the model fit experimental TREF data, and correctly predict number‐average branch points for TREF fractions. © 1995 John Wiley & Sons, Inc.
Elastic modulus of the crystalline regions of cellulose polymorphs
Authors: Nishino Takashi , Takano Kiyofumi , Nakamae Katsuhiko
Published: April 2003

The elastic modulus El of the crystalline regions of cellulose polymorphs in the direction parallel to the chain axis was measured by x‐ray diffraction. The El values of cellulose I, II, IIII, IIIII, and IVI were 138, 88, 87, 58, 75 GPa, respectively. This indicates that the skeletons of these polymorphs are completely different from each other in the mechanical point of view. The crystal transition induces a skeletal contraction accompanied by a change in intramolecular hydrogen bonds, which is considered to result in a drastic change in the El value of the cellulose polymorphs. © 1995 John Wiley & Sons, Inc.
Physical aging in poly(ethylene naphthalene‐2,6‐dicarboxylate) in relation to sorbed water, enthalpic relaxation, and mechanical properties
Authors: Rueda D. R. , Varkalis A. , Viksne A. , Baltá Calleja F. J. , Zachmann H. G.
Published: April 2003

Amorphous poly(ethylene naphthalene‐2,6‐dicarboxylate) (PEN) films (∼ 220 μm thick), stored in ambient atmosphere for different periods of time and after annealing at different temperatures below Tg = 123°C, for different times, have been investigated by infrared spectroscopy (FTIR), microhardness, and differential scanning calorimetry (DSC). FTIR spectroscopy and weight measurements reveal the presence of water which is easily removed by annealing of the films. Films again recover their initial weight and absorption bands after 1‐2 days storage in ambient atmosphere. Samples annealed at different temperatures Ta for different times ta show an increasing microhardness for relatively short times of ta. The microhardness passes through a maximum at an annealing time depending on Ta, and it decreases toward values somewhat larger than the initial ones. The changes observed in the microhardness and in the values of the excess enthalpy with storage time of the samples at room temperature depend on the physical aging as well as on the content of water of PEN films. © 1995 John Wiley & Sons, Inc.
Blends of glycidyl methacrylate/methyl methacrylate copolymers with poly(vinylidene fluoride)
Authors: Gan P. P. , Paul D. R.
Published: April 2003

Blends of glycidyl methacrylate (GMA)/methyl methacrylate (MMA) copolymers with poly (vinylidene fluoride) (PVDF) were found to be miscible when the GMA content of the copolymer is 35.7 wt % or less. The miscible blends did not phase separate upon heating prior to thermal decomposition. The melting point depression method, based on both the Flory‐Huggins theory and the equation of state theory of Sanchez‐Lacombe, was used to evaluate interaction parameters for each pair. The magnitude of these parameters appears to be much larger than interaction energies evaluated by other methods. Possible reasons for this are discussed. © 1995 John Wiley & Sons, Inc.
An XRD characterization of the thermal degradation of polyacrylonitrile
Authors: Chatterjee Nandini , Basu Sudhapada , Palit S. K. , Maiti Mrinal M.
Published: April 2003

Thermal degradation of polyacrylonitrile (PAN) has been studied by combined differential thermal analysis, thermogravimetry, and XRD analysis. On the basis of the experimental observations, it has been suggested that the intramolecular polymerization of nitrile groups to a conjugated polyimine structure is initially limited to only the amorphous zone of PAN, which involves little evolution of off‐gases. Polymerization of nitrile group in the crystalline zone starts with the melting of crystallites with the evolution of off‐gases from the amorphous‐crystalline zone interface. ©1995 John Wiley & Sons, Inc.
Microdeformation in thin films of 3FDA/PMDA polyimide and polyimide nanofoams
Authors: Plummer C. J. G. , Hedrick J. L. , Kausch H.‐H. , Hilborn J. G.
Published: April 2003

Transmission electron microscopy has been used to investigate the microdeformation behavior of thermally imidized thermoplastic pyromellitic dianhydride/1,1‐bis(4‐amino‐phenyl)‐1‐phenyl‐2,2,2 trifluoroethylene (3FDA/PMDA) polyimide films with a Tg of ∼ 440°C, prepared by solution casting of a polyamic ester precursor. Failure of the films at room temperature was by unstable cracking at about 5% strain, accompanied by homogeneous shear deformation at the crack tips. As the temperature was raised to above 100°C, zones of mixed shear and crazing were observed, and a stick‐slip mode of cracking. Above about 300°C shear was once again the dominant deformation mechanism and the films became fully ductile. In films containing porosity on a scale of a few nanometers, prepared by thermal degradation/imidization of a 3FDA/PMDA/poly α‐methyl styrene graft copolymer, film failure at room temperature was also by unstable cracking, but a zone of multiple craze‐like features was observed at crack tips, rather than a single shear deformation zone. The increase in extent of this zone of craze‐like features as the temperature was raised was again associated with an increase in crack stability. ©1995 John Wiley & Sons, Inc.
Solution properties of exocellular polysaccharides of rhizobium leguminosarum. Static and dynamic light‐scattering: Characterization in dilute solution
Authors: Coviello T. , Burchard W. , Dentini M. , Crescenzi V. , Morris V. J.
Published: April 2003

Three polysaccharides, Rhizobium leguminosarum 8002 EPS(I), Rhizobium trifolii TA1‐EPS (II), Rhizobium leguminosarum 127K87 EPS (III), produced by bacteria of Rhizobium genus have been investigated by static and dynamic light scattering combined with chirooptical measurements. All three polymers have the same backbone but differ in the length of the side chains and in the content of minor substituents. An isothermal conformational transition coil → helix was observed with I and II by adding salt (NaCl). The molecular parameters of the polysaccharides in the ordered state were determined by light‐scattering data. Increasing the ionic strength a shrinking of the helix was observed accompanied by a corresponding decrease in the radius of gyration. An extraordinary chain stiffness in terms of Kuhn segment lengths was found in both cases, similar to that already observed for other microbial polysaccharides. In the case of III no disorder → order transition was induced by the salt, and the scattering behavior corresponds to that of a rather flexible polymer with a characteristic ratio C∞ = 24. The incapability of III to form a helical structure is attributed to the effect of the very long side chain. The analysis of the time correlation functions revealed typical flexible chain behavior for all three polysaccharides. This behavior for the two ordered polymers is in agreement with a recent theory by Maggs and is due to bending modes of the rods. ©1995 John Wiley & Sons, Inc.
Polymer decoration study in chain folding behavior of solution‐grown poly(ethylene oxide) crystals
Authors: Chen Jianhua , Cheng Stephen Z. D. , Wu Scott S. , Lotz Bernard , Wittmann Jean‐Claude
Published: April 2003

The polymer decoration method based on the vaporization and condensation‐crystallization of polyethylene (PE) upon the fold surface of polymer crystals has been widely used to study the chain folding behavior of the crystals. When this method was utilized to study solution‐grown high molecular weight poly (ethylene oxide) (PEO) lamellar crystals, the highly anisotropic, low molecular weight fragment PE decorated become oriented parallel to the fold direction and form rods, which can be observed by transmission electron microscopy (TEM) and electron diffraction (ED). The growth sectors were clearly observed. From the ED patterns the {200} planes of the orthorhombic low molecular weight PE rod crystals can be observed, and the c‐axis of these crystals is aligned parallel to the {120} growth planes of the PEO crystals. The decoration results indicate that the major fold orientation of high molecular weight PEO single crystals grown from dilute solution is along the {120} planes. © 1995 John Wiley & Sons, Inc.
Interrelation between crystallization and liquid crystal formation: A calorimetric and polarizing microscopical study on a monotropic polymer system
Authors: Heberer D. , Keller A. , Percec V.
Published: April 2003

The crystallization of the monotropic liquid crystal forming polyether, poly‐n‐nonyl‐4 4′‐biphenyl‐2‐chloroethane, was investigated using DSC calorimetry and polarizing optical microscopy. The principal theme was the nature of crystallization from the nematic liquid crystalline state, which in the monotropic system could be directly compared with the more familiar crystallization from the isotropic melt using one and the same compound. Novel, polarizing optical structures were observed that combine features of both the usual LCPs (fine “grains”) and those of the conventional crystallizeable polymers (spherulites) with differing degrees of prominence of each according to crystallization conditions. The considerations of such structural observations, combined with the calorimetric results and the newly gained information on the kinetics of the crystallization process, reveal an acceleration of the overall crystallization rate at the stage where liquid crystal formation sets in as assessed by calorimetry but not as registered with the polarizing microscope, leading to wider issues regarding the conception of “amorphous crystalline ratio” and its extension to the liquid crystal state. Beyond polymers, the new findings lead to the more general considerations on metastable phases, specifically to their emergence and competition with the phases of ultimate stability. In this respect the present study on a monotropic LCP provides an illustrative example of a more general treatment presented previously. © 1995 John Wiley & Sons, Inc.
Molecular weight segregation induced by interfacial melt reactivity in polyamide 6/reactive rubber blends
Authors: Maréchal Philippe , Legras Roger , Dekoninck Jean‐Marc
Published: April 2003

Polyamide 6 (PA) and ethylene‐propylene rubber with maleic functionality (EPMA) were blended in a batch mixer. EPMA anhydride groups react with amine chain ends of polyamide and form a grafted copolymer at the interface. The molecular weights of the grafted PA and of the free PA were measured. The molecular weight of the free PA decreases during the processing. This effect is due to the hydrolysis of the PA consecutively to its reaction with anhydride groups. The molecular weight of both grafted and free polyamide decreases during the processing. Moreover, the molecular weight of the grafted PA is lower than that of the free PA. At constant mixing time, a high conversion level produces grafted PA with a higher molecular weight. This is the result of molecular weight segregation for interfacial reaction. Small molecules react faster at the interface than larger ones. If we compare experimental results with model predictions, two segregation regimes are observed. For high shear and low EPMA concentrations, dispersion is very fast; the segregation only depends on molecular elasticity. In this case, the best correlation between model and experiment is obtained for low interfacial thicknesses. For low shear, or for EPMA concentrations close to the phase inversion composition, the segregation is more noticeable, which is mainly due to the diffusion of macromolecules through the brush of already grafted molecules. In this case, there is a clear competition between the compatibilization and the grafting reaction. Molecular weight segregation gives low ratio of the grafted PA molecular weight to the free PA molecular weight. This is detrimental to interfacial properties of the grafted copolymer formed by melt reactivity. Strategies are developed to improve this ratio in order to investigate its influence on the mechanical properties. © 1995 John Wiley & Sons, Inc.
Gas permeability and permselectivity of polyimides with large aromatic rings
Authors: Tanaka Kazuhiro , Osada Yasuharu , Kita Hidetoshi , Okamoto Ken‐ichi
Published: April 2003

Polyimides with large aromatic rings were prepared from 3,6‐diaminocarbazole (CDA), N‐ethyl‐3,6‐diaminocarbazole (ECDA), 2,7‐diaminofluorene (DAF), 2,7‐diaminofluorenon (DAFO), and dimethyl‐3,7‐diaminodibenzothiophene‐5,5‐dioxide (DDBT) with 2‐bis(2,4‐dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA). Their physical properties, including gas permeability and permselectivity, were investigated in comparison with those of the related polyimides from 1,3‐phenylenediamine (mPD). Glass transition temperatures of the polyimides with large aromatic rings were much higher than those of the mPD‐based polyimides as a result of increased rigidity of the former polymer chains. With changing diamine from mPD to the large aromatic diamines, charge transfer (CT) interaction between the moieties of acid anhydride and diamine seems to be enhanced, judging from the red shift of absorption edge of the polyimide films and the red shift of CT excitation band of the 6FDA‐based polyimides in solution. Fraction of free space (VF) was a little smaller for the polyimides with large aromatic rings except DDBT than for the mPD‐based polyimides, probably because of enhancement in polymer chain‐chain interactions as a result of the increased CT interaction. The DDBT‐based polyimides had large VF than the mPD‐based polyimides because of the nonplanar structure of neighboring dibenzothiophene‐5,5‐dioxide and imide rings. For the 6FDA‐based polyimides, permeability coefficients to H2, O2, N2, CO2, and CH4 were in the order, DAFO < mPD ∼ DAF < CDA < ECDA < DDBT. As for the membrane performance for H2/CH4, CO2/CH4, and O2/N2 systems, it is significant to change diamine from mPD to DDBT or CDA, but not to DAF or DAFO. The DDBT‐based polyimides were excellent for H2/CH4 and CO2/CH4 separations. © 1995 John Wiley & Sons, Inc.