bluuebunny/crossref_metadata_2025 huggingface dataset:
2H NMR characterization of phenylene ring flip motion in poly(p‐phenylene vinylene) films
Authors: Simpson Jeffrey H. , Rice David M. , Karasz Frank E.
Published: April 2003

Solid‐state 2H quadrupole echo nuclear magnetic resonance (NMR) spectra and measurements of 2H spin lattice relaxation times have been obtained for films of poly(p‐phenylene vinylene) deuterated in phenylene ring positions (PPV‐d4). NMR line shapes show that all the phenylene rings of PPV undergo 180° rotational jumps about the 1,4 ring axis (“ring flips”) at 225°C. The temperature dependence of the 2H line shapes show that the jump motion is thermally activated, with a median activation energy, Ea = 15 kcal/mol, and a distribution of activation energies of less than ±2 kcal/mol. The jump rate was also determined from the magnitude of the anisotropic T2 relaxation associated with 2H line shapes and from the curvature of inversion recovery intensity data. The experimental activation energy for jumps is comparable to the intramolecular potential barrier for rotation about phenylene vinylene bonds. 2H NMR provides a method for determining the phenylene‐vinylene rotational barrier in pristine PPV, and may potentially be used to study conjugation in conducting films.
The application of ultrasonic waves to the electrochemical polymerization of thiophene
Authors: Osawa Satoshi , Ito Masayoshi , Tanaka K. , Kuwano J.
Published: April 2003

The electrochemical polymerization of thiophene was carried out both in the presence and absence of ultrasonic waves. Without irradiation, the anode potential increased with increasing current density. Polymerization at high potential gave a low polymer yield and produced macroscopically heterogeneous films. Ultrasonic irradiation resulted in an improvement of polymer yield and in a lowering of the anode potential during polymerization. The effects were especially marked when the polymerizations were carried out at low temperature, low monomer concentration, and high current density. These results are explained by the formation of diffusion layer in the vicinity of the electrode during electrochemical reactions.
Crystallite morphology in thermotropic random copolymers: Application of transmission electron microscopy
Authors: Spontak Richard J. , Windle Alan H.
Published: April 2003

The morphology of nonperiodic layer (NPL) crystallites appearing in three thermotropic random copolyesters composed of 30/70, 58/42, and 75/25 monomer ratios of p‐oxybenzoate (B) and 2,6‐oxynaphthoate (N) is investigated with transmission electron microscopy. Copolymer films, produced by shearing the materials above their melting points and subsequently annealing them above their glass transition temperature, exhibit ordered entities averaging no more than 20 nm thick and 40–60 nm long, as observed with dark‐field imaging. Selected‐area electron diffractograms exhibit sharp equatorial reflections, indicating ordered packing of random intramolecular sequences of the molecules. Microdensitometry of these diffraction patterns reveal that both the equatorial and first meridional reflections are radiation sensitive, decaying exponentially with dose. Saturation doses (v) for the crystallites depend on the copolymer composition and degree of polymerization (DP) and are estimated to be approximately 130–150C/m2 for the high‐molecular‐weight copolymers (DP ≈ 150), with the N‐rich copolymer possessing greater radiation resistance, and about 430 C/m2 for a low‐molecular‐weight copolymer (DP ≈ 25).
Measurement of the density distributions in quenched polycarbonate specimens by a quantitative schlieren optical technique
Authors: Wimberger‐Friedl R. , Prast G. , Kurstjens A. V. , De Bruin J. G.
Published: April 2003

A new technique for the determination of spatial density distributions is described. The density is derived from the refractive index gradient as determined with a quantitative Schlieren optical technique. The advantages of this technique are a high spatial resolution and sensitivity. Gapwise profiles can be measured without slicing the sample so that more reliable data are obtained quickly. This is demonstrated for the gapwise density distributions in quenched polycarbonate specimens. It is shown that the density distribution is determined by a competition between the local cooling rate variation and the cooling stress distribution. The residual density is predominantly determined by the coolant temperature. The density in the core is higher than at the surface for high coolant temperatures, whereas for low coolant temperatures the density in the core is lower than at the surface. The observed effects are explained semiquantitatively by a simple model using calculated cooling stresses and cooling rates.
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

Binary 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

The 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

Dipole 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

Possible 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

Mesophase 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

Raman 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

Using 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

Dried 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

The 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

The 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

A 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

Given 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

The 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

Specific 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

A 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

Permeation 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

Finite‐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

Several 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

An 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

Gas 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.
Sorption and diffusion of water vapor in polyimide films
Authors: Okamoto Ken‐Ichi , Tanihara Nozomu , Watanabe Hitoshi , Tanaka Kazuhiro , Kita Hidetoshi , Nakamura Asumaru , Kusuki Yoshihiro , Nakagawa Kanji
Published: April 2003

Sorption and diffusion of water vapor are investigated gravimetrically for polyimide films. The activity dependence of the solubility and diffusion coefficients, S and D, respectively, is classified under four types: (1) constant S and D type, (2) dual‐mode sorption and transport type, (3) dual‐mode type followed by a deviation due to a plasticization effect at high vapor activity, and (4) constant S and D type followed by a deviation due to water cluster formation at high activity. For the dual‐mode type, the Henry's law component is much larger than the Langmuir component except at low activity, and therefore deviation in behavior from the first type is small. S is larger for polyimides with higher content of polar groups such as carbonyl, carboxyl, and sulfonyl. D is larger for polyimides with a higher fraction of free space, with some exceptions. The polyimide from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride and dimethyl‐3,7‐diaminodibenzothiophene‐5, 5‐dioxide belongs to the third type and displays both large S and large D. The polyimide from 2,2‐bis(3,4‐dicarboxyphenyl) hexafluoropropane dianhydride and 4,4′‐oxydianiline belongs to the fourth type, and has the largest D but rather small S because of the hydrophobic C(CF3)2 groups. © 1992 John Wiley & Sons, Inc.
Persistence of regions with high segment density in polyethylene melts
Authors: Bremner Tim , Rudin Alfred
Published: April 2003

Proton nuclear magnetic resonance (NMR) spin‐spin relaxation measurements were made on three commercial‐grade polyethylenes in the melt state, free of solvent. All samples exhibit a three‐component relaxation behavior, with components being assigned to amorphous low‐molecular weight material (non‐network fraction), amorphous entangled network fraction, and an ordered or high‐segmental‐density fraction, in order of decreasing relaxation times. Sample thermal history is shown to have a considerable effect on the overall relaxation behavior, and therefore on the relative amounts of each of the three components in the melt. An adequate thermal treatment of samples produces an equilibrium melt with invariant composition of the three fractions. The effects of thermal history on the relative amount of high‐segment‐density regions in the melt parallels its effect on the fraction of crystalline material in the solid polymer. These results are evidence for the persistence of ordered regions in polyethylene at temperatures well above the crystalline melting point of the polymer. We further comment on the nature of the two slower relaxing components and present examples of how the components manifest themselves in other polymer characterization techniques. © 1992 John Wiley & Sons, Inc.
On the nature of order in wholly aromatic liquid crystalline random copolymers
Authors: Biswas A.
Published: April 2003

Two different models of order in the solid state of wholly aromatic liquid crystalline copolymers (ALCPs), namely the nonperiodic layer (NPL) model of Windle et al. and the paracrystalline lattice (PCL) model of Biswas and Blackwell, have been analyzed with respect to experimental and theoretical observations. The NPL model proposes the formation of ordered domains by matching random sequences between adjacent chains while the PCL model relies on the presence of conformational correlations between adjacent monomers, without explicit sequence matching, to form ordered domains. The presence of three‐dimensional order in the quenched state of ALCPs has been reported previously. The initial stages of crystallization are very likely to be assisted by the presence of small sequence matched domains. However, the probabilities for the formation of NPL domains having sizes comparable to those observed experimentally in the quenched state are extremely small. The PCL model, on the other hand, is not hampered by probability statistics and also provides a better fit to the experimental wide‐angle x‐ray scattering data along the fiber (Z) axis. The reported calorimetric data on ALCPs are also inconsistent with the presence of significant motion between chains, which is required for the NPL crystal to grow during the process of annealing. In contrast, the observation of a slow crystallization process, which converts the quenched hexagonal phase to the ordered orthorhombic phase, is adequately described by the PCL model as occurring via local conformational changes and small axial shifts between adjacent monomers. The observations from dielectric relaxation, nuclear magnetic resonance and dynamical mechanical spectroscopy studies also favor the PCL model over the NPL model of order in the solid state of ALCPs. © 1992 John Wiley & Sons, Inc.
Polymer miscibility in capillaries
Authors: Cifra P. , Karasz F. E. , Macknight W. J.
Published: April 2003

A thermodynamic analysis predicts an increase in miscibility, relative to that in the bulk state, for a polymer mixture confined in a capillary with a diameter of the order of the size of the polymer coils. This is derived by using both the concepts of growing domains and a consideration of the thickness of polymer–polymer interfaces. The analysis is combined with a Monte Carlo lattice simulation that provides results on such confined systems. Intermixing, described in terms of the number of heterocontacts and the dimensions of the polymer chains in the capillary parallel and perpendicular to the tubular axis, is investigated. The results confirm that demixing in homogeneous mixtures is hindered, whereas intermixing is enhanced, in the capillary relative to that in the unconfined mixture. © 1992 John Wiley & Sons, Inc.
Real‐time X‐ray scattering study of thermal expansion of poly(butylene terephthalate)
Authors: Huo Peter Pengtao , Cebe Peggy , Capel Malcolm
Published: April 2003

Real‐time x‐ray scattering at elevated temperatures has been used to investigate the thermal expansion characteristics of poly(butylene terephthalate), PBT. Changes in the six lattice parameters of the α‐form of PBT were obtained from wide‐angle x‐ray scattering over the temperature range from 35 to 215°C. The linear thermal expansion coefficients relating the unit cell parameters at temperature T to their values at 0°C are found to be

The temperature dependence of both the long period and the lamellar thickness of semicrystalline PBT were determined from real‐time small‐angle x‐ray scattering analysis of the one‐dimensional electron density correlation function. The long period, lamellar thickness, and degree of crystallinity increase as the temperature increases. We find an average linear thermal expansion coefficient of the bulk material to be αave = 5.0 × 10−4°C−1. © 1992 John Wiley & Sons, Inc.
Folded chain crystallization of random terpolymer liquid crystal polymers from the nematic state
Authors: Kent S. L. , Geil P. H.
Published: April 2003

The morphology of ca. equimolar random terpolymer liquid crystal polymers of an aliphatic segment of 4–7 carbon atoms, oxybenzoate, and dioxyphenyl crystallized from the nematic state in the form of thin films on glycerine by slow cooling and quenching has been characterized by electron microscopy (TEM) and diffraction (ED). In all cases a folded chain, lamellar structure is found. The ED studies suggest adjacent reentry, and despite a large ΔH, indicate no change in lateral molecular packing at the crystal‐“liquid crystal” transition with a transformation to the nematic state at a higher temperature “liquid crystal”‐liquid crystal transition. The results are interpreted as suggesting similar folded chain, lamellar morphology in the nematic state. © 1992 John Wiley & Sons, Inc.
Surface tension of random copolymer melts
Authors: Donley J. P. , Fredrickson G. H.
Published: April 2003

A mean‐field theory is presented to describe the surface tension and interfacial profile of random A‐B multiblock copolymer melts in contact with air or a solid substrate. The copolymer model accounts for variations in average composition and block sequence distribution, and reduces to a model for statistical copolymers as the block size approaches that of a monomer. Ideal copolymers lacking chemical correlations between successive segments are predicted to have a larger surface tension than “blocky” copolymers with a tendency for repeated segments of A or B. © 1992 John Wiley & Sons, Inc.
NMR free induction decay in crosslinked polydimethylsiloxane networks. Theoretical analysis
Authors: Kulagina T. P. , Litvinov V. M. , Summanen K. T.
Published: April 2003

A theory of nuclear magnetic resonance free induction decay (FID) in crosslinked poly‐dimethysiloxane networks is proposed. The anomalously small amplitude of the FID asymptotes at high temperatures is explained as due to crosslink motions. The Anderson‐Weiss theory is generalized to account for the non‐Gaussian distribution of local dipolar fields. © 1993 John Wiley & Sons, Inc.
Heat capacities of solid copoly(amino acid)s
Authors: Roles K. A. , Wunderlich Bernhard
Published: April 2003

Recently heat capacities Cp of poly(amino acid)s of all naturally occurring amino acids have been determined. In a second step the heat capacities of four copoly(amino acid) s are studied in this research. Poly(L‐lysine · HBr‐alanine), poly(L‐Lysine · HBr‐phenylalanine), poly(sodium‐L‐glutamate‐tyrosine), and poly(L‐proline‐glycine‐proline) heat capacities are measured by differential scanning calorimetry in the temperature range 230–390 K. This is followed by an analysis using approximate group vibrations and fitting the Cp contributions of the skeletal vibrations of the corresponding homopolymers to a two‐parameter Tarasov function. Good agreement is found between experiment and calculation. Predictions of heat capacities based on homopoly(amino acid)s are thus expected to be possible for all polypeptides, and enthalpies, entropies, and Gibbs functions for the solid state can be derived.
Relaxations in thermosets. XIX. Dielectric effects during curing of diglycidyl ether of bisphenol‐A with a catalyst and the properties of the thermoset
Authors: Alig I. , Johari G. P.
Published: April 2003

Changes in the dielectric permittivity ε′ and loss epsiv;″ during the curing of DGEBA catalyzed by 10 mole % dimethylbenzylamine have been studied from sol to gel to glass formation regions at different temperatures from 323 to 390 K. The ε′ monotonically decreases with time of cure, and ε″ initially decreases by several orders of magnitude and then increases to reach a peak value before finally decreasing to a low value characteristic of the glassy state. The features shift to shorter times and the peak vanishes as the curing temperature is increased. The decrease of ε″ at the initial stage of cure has been analyzed in terms of dc conductivity σ0, which follows a power law, σ0 ∝︁ (tg–t)x, as well as a new singularity equation, σ0 ∝︁ exp[–B/(t0–t)] where tg, x, B, and t0 are empirical constants that vary with the curing temperature; tg is close to the time for gelation; and t0 ≥ time for vitrification. The dielectric properties of the thermoset formed after different periods of cure have been studied from 77 to 325 K. Similar studies of the thermosets formed at different temperatures have been made. Increase in the curing period decreases the heights of both the γ‐and α‐relaxation peaks and increases their separation, while a β‐relaxation peak emerges. Isothermal curing at high temperatures decreases the height of the γ peak to a vanishingly small value and increases that of the β peak from a vanishingly small value. In both the uncured and fully cured states, there is only one sub‐Tg relaxation process named γ for the uncured and β for the cured state. These results are discussed in terms of our general physical concepts of local mode motions in an amorphous matrix. © 1993 John Wiley & Sons, Inc.
Solubility of carbon dioxide, methane, and propane in silicone polymers. Effect of polymer backbone chains
Authors: Shah V. M. , Hardy B. J. , Stern S. A.
Published: April 2003

The solubility of carbon dioxide, methane, and propane in poly(dimethyl silmethylene) [(CH3)2SiCH2]x and poly(tetramethyl silhexylene siloxane) [(CH3)2Si (CH2)6Si (CH3)2O]x was measured in the temperature range from 10.0 to 55.0°C and at elevated pressures. The present results are compared with similar measurements made with other silicone polymers. At a given temperature and pressure, the solubility of the above three gases is highest in poly(dimethyl siloxane) (Me2SiO)x. The gas solubility is decreased by either backbone‐chain or side‐chain substitutions of functional groups in (Me2SiO)x which increase the stiffness of the polymer chains and decrease the specific or fractional free volume of the polymers. It is conjectured that a decrease in the free volume of silicone polymers has a greater effect in decreasing the gas solubility than differences in gas/polymer interactions [with the exception of specific interactions (e.g., between CO2 and polar groups in the polymer)]. © 1993 John Wiley & Sons, Inc.
Ellipsometric study of the glass transition and thermal expansion coefficients of thin polymer films
Authors: Beaucage G. , Composto R. , Stein R. S.
Published: April 2003

The glass transition (Tg) of thin polystyrene films (ca. 3000 A˚) cast on silicon wafers was determined by a new technique. An ellipsometer was used to determine the refractive index and thickness of the polystyrene films. Tg was determined by measuring the temperature dependence of the refractive index. The change in thickness with temperature was used to calculate the linear and bulk thermal expansion coefficients of the material. A significant shift in Tg, possibly due to strains induced in the cooled films, was observed between heating and cooling for polystyrene films. © 1993 John Wiley & Sons, Inc.
Spectroscopic evidence for radiation‐induced crosslinking of poly(tetrafluoroethylene)
Authors: Rye Robert
Published: April 2003

Direct spectroscopic evidence for radiation‐induced crosslinking of poly(tetrafluoroethylene) (PTFE) is presented for all x‐ray and electron dose levels above which it is possible to distinguish between deliberately introduced radiation damage and the x‐ray damage inherent in obtaining an x‐ray photoelectron spectrum (XPS). The C (1s) spectrum obtained after irradiation with 2 keV electrons for all doses greater than 1 μA‐min/cm2 consists of a four‐peak spectrum identical to that previously obtained for plasma‐polymerized tetrafluoroethylene and assigned to carbon atoms with variable numbers of bound F atoms (CF3, CF2, CF1, and CF0). X‐ray irradiated PTFE can be fitted with the same four‐peak spectrum. At or below an electron dose level of 1 μA‐min/cm2, the radiation damage is comparable to that produced by the x‐ray dose necessary to obtain an XPS spectrum. The CF1 and CF0 components increase with increasing electron dose, and at high electron doses dominate the spectrum. With increasing dose the CF3 component approaches a constant value while both the CF2 component and the total F : C ratio decreases. These four components are those expected to result from radiation‐induced crosslinking reactions of the polymer and are consistent with previous suggestions that crosslinking is the basis of radiation patterned adhesion to PTFE. © 1993 John Wiley & Sons, Inc.
Thermal conductivity of gel‐spun polyethylene fibers
Authors: Choy C. L. , Fei Y. , Xi T. G.
Published: April 2003

The thermal conductivities of unidirectional gel‐spun polyethylene fiber‐reinforced composites have been measured parallel (K∥︁) and perpendicular (K⊥) to the fiber axis from 15 to 300K. The axial thermal conductivity K∥︁ varies linearly with volume fraction vf of fiber, while the transverse thermal conductivity K⊥ follows the Halpin‐Tsai equation. Extrapolation to vf = 1 gives the thermal conductivity of gel‐spun polyethylene fiber which, at 300K, has values of 380 and 3.3 mW cm−1K−1 along and perpendicular to the fiber axis, respectively. The axial thermal conductivity is exceptionally high for polymers, and is more than twice the thermal conductivity of stainless steel. This high value arises from the presence of a large fraction of long (> 50 nm) extended chain crystals in the fiber. Further improvement of up to a factor of 10 is possible if the length and volume fraction of the extended chain crystals can be increased. © 1993 John Wiley & Sons, Inc.
On‐line small‐angle and wide‐angle x‐ray scattering studies on melt‐spinning poly(vinylidene fluoride) tape using synchrotron radiation
Authors: Cakmak M. , Teitge A. , Zachmann H. G. , White J. L.
Published: April 2003

On‐line small‐angle and wide‐angle x‐ray scattering experiments were performed during the melt spinning of polyvinylidene fluoride using the DESY synchrotron light source. In these studies, the melt‐spinning apparatus consisting of a screw extruder, a metering pump, and a take‐up motor system were assembled on two separate stepper‐motor‐driven platforms. To investigate the structure development during crystallization, the tape location at the desired distance from the die could be positioned at the beam level with synchronous vertical movement of extruder and take‐up platforms. Small‐angle and wide‐angle x‐ray patterns were taken simultaneously with a two‐dimensional wire detector and one‐dimensional wire detector. In a separate study, two‐dimensional WAXS data were also taken under identical processing conditions to observe the off‐equator diffraction behavior during the crystallization. The data obtained for a variety of take‐up speeds generally indicate that SAXS d‐spacings first appear large in the early stages of crystallization and gradually decrease along the spin‐line (as the crystallization progresses). As the take‐up speed increases, the crystallization onset position moves away from the die and d‐spacings observed at the onset increase. In addition, the shape of the discrete scattering pattern starts as a meridional streak and converts to a teardrop shape with the tip of the pattern pointing toward the beam stop at the early stages of crystallization for high take‐up speeds. This does not occur at low take‐up speeds and is attributed to the differences in crystallization behavior which is spherulitic or sheaflike to row nucleated crystallites. Our studies also showed that SAXS patterns appear earlier than the wide‐angle crystalline diffraction peaks indicating the SAXS technique to be more sensitive to the structural changes at these stages. An idealized model is developed to explain the observed patterns at high take‐up speeds. This consists of two regimes. In regime 1, the periodic fluctuations due to the alternating crystalline and amorphous regions form along the regions where eventually the “shish” structures develop. In the second stage, a volume filling crystallization takes place between the existing crystallites along the shish structure and simultaneously radial overgrowth of crystallites (i.e., the “kebabs”) takes place. This causes the observed reduction in the average d‐spacing. © 1993 John Wiley & Sons, Inc.