bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure and properties of thin films of binary rodlike/flexible polyimide mixtures
Authors: Rojstaczer S. , Ree M. , Yoon D. Y. , Volksen W. 
Published: April 2003

AbstractBinary mixtures of a rodlike poly(p‐phenylene pyromellitimide) (PMDA‐PDA) and a flexible 6F‐BDAF polyimide synthesized from hexafluoroisopropylidene diphthalic anhydride and 2,2‐bis(4‐aminophenoxy‐p‐phenylene) hexafluoropropane were prepared by solution‐blending of the meta‐PMDA‐PDA poly(amic ethyl ester) and 6F‐BDAF poly(amic acid) precursors, followed by solvent evaporation and thermal imidization. Mixtures containing different molecular weights of 6F‐BDAF poly(amic acid) were studied. The size scale of the phase separation, as measured by light scattering, is ca. 1 μm or smaller in most cases. The domain size is primarily set by the demixing of the precursor polymers during solvent evaporation, with no significant coarsening observed during the thermal imidization. The observed variation of the domain size with molecular and process parameters such as composition, molecular weight, and film thickness is discussed in terms of the miscibility of the precursor polymers, rate of solvent evaporation, and solidification. Dynamic mechanical thermal analysis and dielectric relaxation measurements indicate that the glass transition temperature of 6F‐BDAF is unaffected in all of the mixtures studied, indicating complete demixing of rodlike and flexible polyimides in agreement with theory. X‐ray photoelectron spectroscopy results show a strong surface segregation of 6F‐BDAF in mixtures containing as low as 10% by weight of the 6F‐BDAF component in the bulk. The mixtures with PMDA‐PDA as the major matrix component therefore exhibit excellent mechanical toughness, dimensional stability up to 500°C, low coefficients of thermal expansion (< ca. 10 ppm/°C), and low dielectric constants (<3.0). On the other hand, the surface properties of the mixtures are dominated by the flexible 6F‐BDAF, resulting in excellent polymer/polymer self‐adhesion (lamination) properties between fully imidized films.
On‐line measurement of the RMS radius of gyration and molecular weight of polyimide precursor fractions eluting from a size‐exclusion chromatograph
Authors: Kim Seong , Cotts Patricia M. , Volksen Willi 
Published: April 2003

AbstractThe recent introduction of multiangle light‐scattering detectors for size‐exclusion chromatography has made possible the measurement of the root mean square radius of gyration (Rg) and molecular weight (M) of polymer fractions eluting from a size‐exclusion chromatography column. The characterization of the dimensions of a polymer may be accomplished with only a few milligrams. The dimensions of a polyimide precursor prepared by the condensation of the meta‐diethyl ester of pyromellitic dianhydride with para‐phenylene diamine have been measured with this technique. The dependence of Rg on M across the distribution is compared with that predicted for a freely rotating chain, and with other similar polymers measured with hydrodynamic techniques.
Dipole moments of poly(p‐chlorostyrene) chains determined in benzene, isopropyl benzene and n‐propyl benzene
Authors: Yilmaz Ferdane , Baysal Bahattin M. 
Published: April 2003

AbstractDipole moments of poly(p‐chlorostyrene) were determined from dielectric and refractive index measurements performed on their dilute benzene, isopropyl benzene and n‐propyl benzene solutions over a wide range of temperatures. Experimental results are expressed in terms of the dimensionless dipole moment ratios, Dx = 〈μ2〉/xμ02. The temperature coefficients of dipole moments, d In 〈μ2〉/dT were calculated. The presence and importance of the specific solvent‐segment interactions are demonstrated by considering the temperature dependence of the dipole moment ratio in the vicinity of the theta temperature. These results are compared with dipole moments and temperature coefficients which were calculated by Bahar et al. using the appropriate rotational isomeric state model to study the local solvent effect for the poly (p‐chlorostyrene)‐benzene system.
Effect of cyclic stress on enthalpy relaxation in polycarbonate
Authors: Liu Liang B. , Yee Albert F. , Gidley David W. 
Published: April 2003

AbstractPossible effects of cyclic stress on physical aging in polycarbonate were investigated using differential scanning calorimetry (DSC) measurements. When the enthalpy overshoot by DSC of specimens of different previous thermophysical aging histories is measured as a function of the cyclic stress amplitudes, two characteristic regimes are observed. By correlating with optical microscopic observations, these regimes are identified as the incubation and crazing stages (denoted regimes I and II, respectively). The enthalpy relaxation behavior in Regime I is similar to thermophysical aging, indicating that the glassy structure as a whole is initially shifted to one where molecular mobility is retarded by relatively low amplitude cyclic stress. A strong interaction is also seen between the enthalpy overshoot and previous physical aging. That is, the more the material is previously aged, and the shorter the incubation period, the longer the crazing region is. As a result, brittle failure occurs over a wider load range compared with less aged specimens.
Lyotropic mesophases of cellulose in the ammonia/ammonium thiocyanate solvent system: Phase relationships
Authors: Yang Kap‐Seung , Cuculo John A. , Theil Michael H. 
Published: April 2003

AbstractMesophase formation of the cellulose/NH3/NH4SCN system has been studied as a function of system composition at 25°C. Compositions for incipience of mesophase formation and for wholly anisotropic phase formation have been determined and relevant phase diagrams constructed. The biphasic gap narrowed when the solvent composition approached 75.5 weight percent NH4SCN and as the cellulose concentration decreased. As solvent composition was changed, the minimum cellulose volume fraction for mesophase formation ranged between 0.02 to 0.045.
A Raman microscopy study of stress transfer in high‐performance epoxy composites reinforced with polyethylene fibers
Authors: Boogh Louis C. N. , Meier Robert J. , Kausch Henning‐H. , Kip Bert J. 
Published: April 2003

AbstractRaman spectroscopy is shown to be a very powerful method for the study of stress transfer in epoxy composite materials reinforced with high‐performance polyethylene (PE) fibers. We found that the stress transfer length as determined by Raman spectroscopy is substantially shorter for a plasma‐treated fiber than for an untreated one. A shorter stress transfer length indicates stronger interactions between fiber and matrix. Furthermore, the stress transfer length was higher for a PE fiber/epoxy matrix cured at a higher temperature.
Temperature dependence of the conformational relaxation time of polymer molecules in elongational flow: Invariance of the molecular weight exponent
Authors: Narh K. A. , Odell J. A. , Keller A. 
Published: April 2003

AbstractUsing an elongational flow technique, we have investigated the relationship between the molecular conformational relaxation time and the molecular weight for a solvent whose quality was altered thermally from near θ to a good solvent state. The materials used were closely monodisperse samples of atactic polystyrene. The results show that the relaxation time τ varies with the molecular weight M as τ ∝ M1.5, independent of the solvent quality, a result which apparently is at variance with the observed molecular weight dependence of intrinsic viscosity. Despite this invariance of the molecular weight exponent with solvent quality, our results also show that the coils do expand when the solvent quality was increased in agreement with the mean‐field theory of Flory.
Dried gels from linear low‐density polyethylene: Morphology, thermal behavior, and mechanical properties
Authors: Darras O. , Seguela R. , Rietsch F. 
Published: April 2003

AbstractDried gels of a linear low‐density polyethylene cast from decalin solutions are investigated with particular attention toward structural, thermal, and mechanical properties. The number‐average and weight‐average molecular weights are Mn= 32,000 and Mw= 160,000. In the concentration range 1.00–0.20, the swollen gels exhibit nearly isotropic shrinkage upon drying, which is relevant to an ideal crosslinked network behavior. For the concentrations below 0.20, a strong departure from the isotropic shrinkage indicates that the chains begin to disengage from the macromolecular network owing to the dilution effect. The melting behavior of the dried gels shows that crystallization from solution improves the crystal perfection notably as concerns the more defective crystals. The concomitant decrease of the crystal thickness judged from small‐angle X‐ray scattering is ascribed to a reduction of the surface free energy which is consistent with the build up of regular chain‐folded macroconformations. The drawability of the dried gels is considerably improved with increasing dilution as a result of the gradual disentanglement of the coils prior to the crystallization in solution. But beyond concentration 0.20, the drawability drops because of the loss of intermolecular cohesion when the chains begin to disengage from the network. The drastic change of yield behavior between the melt‐crystallized and solution‐crystallized samples reveals a ductile‐to‐brittle transition in the mechanism of failure of the crystallites at low strain. This phenomenon is related to the improvement of regular chain‐folding.
Equilibration of mixtures of polyamic acids studied using size‐exclusion chromatography and light scattering
Authors: Cotts Patricia M. , Volksen Willi , Ferline Susan 
Published: April 2003

AbstractThe transamidation reaction in a polyamic acid solution has been investigated using size‐exclusion chromatography and low‐angle light scattering. Mixtures of a high‐molecular weight (DP = 150) and a low‐molecular weight (DP = 10) polymer and of the high‐molecular weight polymer with monomer were studied. Mixtures were made at high and low concentrations. The polyamic acid studied is the product of the polycondensation of 3,3′,4,4′‐biphenyltetracarboxylic acid dianhydride (BPDA) with oxydianiline (ODA). In all cases the molecular weight distribution equilibrated with time to a most‐probable distribution with a DP consistent with the stoichiometry of the mixture. Equilibration required about 2 weeks for mixtures of 10% by weight at ambient temperatures. The effect of addition of a small amount (5%) of low‐molecular weight material to sample of high‐molecular weight is dramatic; for DP = 150 the molecular weight is decreased by more than one‐half. In an entangled solution or melt, this would reduce the viscosity by an order of magnitude.
Plasticization of a poly(ethyl acrylate) ionomer by an alkyl aniline
Authors: Tong Xia , Bazuin C. Geraldine 
Published: April 2003

AbstractThe plasticization by 4‐decylaniline (4DA) of a microphase‐separated poly(ethyl acrylate) ionomer containing sodium carboxylate groups is examined. Dynamic mechanical thermal analysis, supplemented by differential scanning calorimetry, shows that the matrix and cluster glass transitions (Tg's) in the ionomer are both depressed by ca. 1°C/wt % 4DA; this, in turn, is similar to the Tg depression in the blend of the parent poly(ethyl acrylate) (PEA) with 4DA. There is no evidence of 4DA crystallinity in the blend. Small‐angle x‐ray scattering (SAXS) measurements show that the ionomer peak increases in intensity and decreases in scattering angle with increasing concentration of 4DA in the blend; the corresponding Bragg spacing, initially at 2.3 nm, increases by ca. 0.04 nm/wt % 4DA. These results, supported by preliminary spectroscopic measurements, are attributed to hydrogen bonding interactions between the amine groups of 4DA and the ester groups in PEA and the ionomer, rendering the blend miscible. It is argued that the uniform distribution of 4DA throughout the material plasticizes both phases of the ionomer by adding free volume; this also accounts for the increase in the characteristic spacing detected by SAXS.
Local order and shape of a polymer chain in an external electric field
Authors: Walasek Janusz 
Published: April 2003

AbstractA solution of polymer chains in the presence of an external electric field is considered. Dipole‐like interactions between polymer chain segment‐vectors and the electric field are assumed to be proportional to the cosine of the angle between the segment‐vector and the direction of the electric field. Parameters characterizing the shape of the chain (i.e., the chain end‐to‐end distance and cross‐section per chain), and parameters describing the local order at the segmental and chain level (i.e., moments of the first and second Legendre polynomials 〈P1〉 and 〈P2〉 are calculated. The optical anisotropy and the molecular shape change induced by the external electric field are discussed.
Space available to small diffusants in polymeric glasses: Analysis of unoccupied space and its connectivity
Authors: Arizzi S. , Mott P. H. , Suter U. W. 
Published: April 2003

AbstractGiven a diffusant, modeled as a hard sphere, and a microstructure representative of a glassy polymer, represented as a rigid matrix of hard sphere atoms, a quantitative determination of the unoccupied space in the polymer was achieved by applying a Delaunay tessellation of space to available glassy microstructures of atactic polypropylene and bisphenol‐A‐polycarbonate. A description is also given of how local portions of unoccupied space are distributed and interconnected across a polymeric matrix. The shape and dimensions of clustered portions of unoccupied space were analyzed. A visualization of these clusters indicated significant differences, depending on the nature of the diffusant.
Relaxations in thermosets. XIII. Effects of post‐cure and aging on the sub‐Tg relaxations of nonstoichiometric epoxide‐based thermosets
Authors: Mangion M. B. M. , Wang Manli , Johari G. P. 
Published: April 2003

AbstractThe dielectric permittivity and loss of diglycidyl ether of bisphenol‐A (DGEBA) cured with greater than and less than the stoichiometric amounts of diaminodiphenyl methane (DDM) have been measured over a temperature range 77–350 K prior to curing and gelation, after curing at about 340 K and further aging for a predetermined period. The height of the γ‐relaxation peak monotonically decreases during the post‐cure period and becomes masked by the contributions from the β‐relaxation peak, whose height, in turn, first increases on postcuring to a same maximum value for both nonstoichiometric thermosets and then decreases. This decrease is attributed to physical aging effects. The β‐relaxation peak shifts towards higher temperature on postcuring. Comparison between the changes in the dielectric properties of the saturated and starved thermosets show that while the γ‐relaxation process may be attributed to the motion of the epoxide dipolar groups of the unreacted DGEBA, the β‐relaxation process is not attributable entirely to the motion of OH groups and of the unreacted amines in the thermoset. Explanations involving the chain and network packing in the structure of a thermoset are necessary for the observed behavior of the β‐relaxation process in amine saturated and starved thermosets.
FTIR separation of nylon‐6 chain conformations: Clarification of the mesomorphous and γ‐crystalline phases
Authors: Rotter G. , Ishida H. 
Published: April 2003

AbstractSpecific infrared absorptions for each form of Nylon‐6 have been indentified. Quenched films were prepared by melt casting and converted in turn to the α‐crystalline and γ‐crystalline structures. The films were examined using Fourier transform infrared spectroscopy (FTIR) with the attenuated total reflection configuration and by X‐ray diffractometry. The FTIR spectrum of the pure mesomorphous component of the quenched film was calculated by subtracting away the contribution of α‐crystalline peaks present due to incomplete quenching. A curve‐fitting procedure was applied to the pure mesomorphous and gamma crystalline spectra. Several peaks in the mesomorphous spectrum are observed to develop a shoulder upon conversion to the γ‐crystalline form. This is due to the extra gauche character imparted to the CN bond between the methylene unit and the amide group. These and other band assignments were confirmed by analysis of model compounds.
Free energy of an inhomogeneous polymer–polymer–solvent system. II
Authors: Ariyapadi Murali V. , Nauman E. Bruce 
Published: April 2003

AbstractA complete expression for the enthalpy of mixing of inhomogeneous polymer–polymer–solvent systems applicable for small as well as large concentration fluctuations has been developed. This is used to express the free energy of inhomogeneous polymer–polymer–solvent systems in an extended form of the Landau‐Ginzburg functional. The gradient energy parameters obtained here are consistent with the published results. The free energy functional has been applied to develop a generalized continuity equation for spinodal decomposition in polymer–polymer systems. A linearized version of this continuity equation has been used to study the effect of the gradient terms on the dominant wavelength during spinodal decomposition.
Gas transport in poly(vinyl methylbenzoates)
Authors: Terada Katsuhiko , Mizoguchi Keishin , Hirose Takuji 
Published: April 2003

AbstractPermeation of eight gases (He, Ne, Ar, Kr, O2, N2, CO2, and CH4) in three isomeric poly(vinyl methylbenzoates) was measured by the time‐lag method, and the effects of the shape of side groups on gas transport in the polymers were investigated. The p‐methylphenyl side group of poly(vinyl p‐methylbenzoate), which increases both interchain and intrachain distances, caused an increase in gas diffusivity. The diffusivity and density data were consistent with free volume theory. Two other isomeric polymers, poly(vinyl o‐methylbenzoate) and poly(vinyl m‐methylbenzoate), had lower gas diffusivities than poly(vinyl p‐methylbenzoate) and poly(vinyl benzoate). The o‐methyl and m‐methyl groups on the phenyl ring were found to hinder gas diffusion, i.e., decrease the free volume. In contrast, the solubility of the gases in all these polymers was similar because of their similar chemical structures. The effects of hydroxyl groups also were investigated by the use of poly(vinyl m‐methylbenzoate) containing a small number of vinyl alcohol units. The decrease in gas diffusivity was attributed to the decrease of free volume due to hydrogen bonding, but the change of gas solubility was still negligible.
A study of stress distribution in model composites by finite‐element analysis. II. Fiber/matrix interfacial effects
Authors: Fan Cun F. , Hsu Shaw L. 
Published: April 2003

AbstractFinite‐element analysis, in conjunction with a spectroscopic mechanical method, has been applied in a study of stress distribution in fiber reinforced model composites. In this study, special emphasis was devoted to an understanding of variation of stress distribution with changing fiber/matrix interfacial properties. Experimental studies were focused on the effects of coating properties of an anisotropic polydiacetylene fiber in an epoxy matrix. Stress transfer efficiency and stress distribution curves were shown to be clearly dependent on the nature and thickness of the interface, although the effects of a thin coating are limited. Lower stress transfer efficiency, even failure, was observed for thicker coatings. Calculated results, utilizing the finite element method for model composites, agree qualitatively well with experimental data. A detailed description of possible failure modes for the discontinuous fiber composites has been developed from these finite‐element calculations.
On the measurement of the χ‐parameter under the zero average contrast condition
Authors: Benmouna M. , Fischer E. W. , Ewen B. , Duval M. 
Published: April 2003

AbstractSeveral methods for measuring directly the interaction parameter X as a function of polymer concentration are presented. These methods are applied to symmetric ternary mixtures of homopolymers and copolymers in solution under the zero average contrast condition. They can be used for an arbitrary concentration from dilute solution to the bulk and at any value of the scattering wavenumber q. Possible combinations of static and dynamic measurements are presented. © 1992 John Wiley & Sons, Inc.
Infrared method for measuring orientation in polyethylene films
Authors: Kissin Y. V. 
Published: April 2003

AbstractAn infrared method is described for measuring crystalline phase orientation in polyethylene films. The method uses the absorbances of the 730 and 719 cm−1 bands in the polarized spectra of an oriented film and in the spectra of an unoriented film made from the same polymer to estimate the orientation parameters of the orthorhombic crystal cell axes. © 1992 John Wiley & Sons, Inc.
Gas permeability and permselectivity of fluorinated polybenzoxazoles
Authors: Okamoto Ken‐Ichi , Tanaka Kazuhiro , Muraoka Michiaki , Kita Hidetoshi , Maruyama Yutaka 
Published: April 2003

AbstractGas permeability and permselectivity are investigated for polybenzoxazoles from bis(3‐amino‐4‐hydroxyphenyl)‐1,1,1,3,3,3‐hexafluoropropane (BAHHP) and aromatic diacid chlorides. Effects of thermal cyclization on the permeation properties are also investigated. The polybenzoxazole from BAHHP and 4,4′‐(1,1,1,3,3,3‐hexafluoroisopropylidene)dibenzoyl chloride (HFDB) displays high performance for CO2/CH4 separation (
\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm P}_{{\rm CO}_2 } $\end{document}
= 6.1 × 10−9 cm3 (STP) cm−1 s−1 cm‐Hg−1, and
\documentclass{article}\pagestyle{empty}\begin{document}$ {{{\rm P}_{{\rm CO}_2 } } \mathord{\left/ {\vphantom {{{\rm P}_{{\rm CO}_2 } } {{\rm P}_{{\rm CH}_4 } }}} \right. \kern-\nulldelimiterspace} {{\rm P}_{{\rm CH}_4 } }} $\end{document}
= 38 at 35°C). The polybenzoxazole from BAHHP and 2,6‐naphthalene dicarbonyl chloride displays high performance for H2/CO or H2/CH4 separation (
\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm P}_{{\rm H}_2 } $\end{document}
= 2.4 × 10−9 cm3 (STP) cm−1 s−1 cm‐Hg−1,
\documentclass{article}\pagestyle{empty}\begin{document}$ {{{\rm P}_{{\rm H}_2 } } \mathord{\left/ {\vphantom {{{\rm P}_{{\rm H}_2 } } {{\rm P}_{{\rm CO}} }}} \right. \kern-\nulldelimiterspace} {{\rm P}_{{\rm CO}} }} $\end{document}
= 71, and
\documentclass{article}\pagestyle{empty}\begin{document}$ {{{\rm P}_{{\rm H}_2 } } \mathord{\left/ {\vphantom {{{\rm P}_{{\rm H}_2 } } {{\rm P}_{{\rm CH}_{\rm 4} } }}} \right. \kern-\nulldelimiterspace} {{\rm P}_{{\rm CH}_{\rm 4} } }} $\end{document}
= 250). Permeation properties for the polybenzoxazole from BAHHP and HFDB are close to those for a polyimide of similar chemical structure. The permeation properties are discussed in connection with packing density and local segmental mobility. © 1992 John Wiley & Sons, Inc.