bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractSorption 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

AbstractProton 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

AbstractTwo 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

AbstractA 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

AbstractReal‐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

AbstractThe 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

AbstractA 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

AbstractA 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

AbstractRecently 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

AbstractChanges 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

AbstractThe 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

AbstractThe 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

AbstractDirect 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

AbstractThe 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

AbstractOn‐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.
Solid‐State 13C‐NMR detection of the isotropic carbonyl line shape in blends of poly(vinylphenol) with main‐chain polyesters
Authors: Belfiore Laurence A. , Qin Chuan , Ueda Eiji , Pires Alfredo T. N. 
Published: April 2003

AbstractThe solid‐state NMR isotropic line shape of the carbonyl 13C resonance is useful as a qualitative diagnostic probe of the polyester component′s morphology and molecular mobility in partially miscible blends with poly(vinylphenol), PVPh. The main‐chain polyesters chosen for investigation in this study are poly(ethylene succinate), poly(ethylene adipate), poly(butylene adipate), and poly(caprolactone). A crystalline phase exists for polyester‐rich mixtures in all cases. Verification of this claim is provided by DSC endothermic tran‐sitions that map out melting point depression in the temperature‐composition phase dia‐grams. The carbonyl 13C‐NMR signal in the crystalline domains exhibits a full width at half height of 1–2 ppm when the glass transition temperature of the blends is below the temperature of the NMR experiment. In all cases, a single concentration‐dependent glass‐transition temperature is measured by DSC, which increases monotonically from below ambient for polyester‐rich blends to well above ambient for blends that are rich in poly(vinylphenol). When the concentration of the amorphous proton donor PVPh is suf‐ficient to thwart crystallization of the polyester and increase the glass transition temperature of the blends above the temperature of the NMR experiment, the line width of the carbonyl resonance increases three‐ to fourfold to ca. 5–6 ppm. When the blends are completely amorphous and Tg is above ambient, the polyester carbonyl 13C line shape reveals at least two morphologically inequivalent microenvironments. A partially resolved carbonyl signal in rigid amorphous blends is (a) identified at higher chemical shift relative to the crystalline component, and (b) attributed to hydrogen bonding in the amorphous phase. This inter‐action‐sensitive hydrogen‐bonded carbonyl signal accounts for an increasing fraction of the overall NMR absorption envelope of the carbonyl carbon site when the polyester is saturated with PVPh. The main‐chain polyesters were chosen to probe the effect of chemical structure of the proton acceptor on the potential for hydrogen‐bond formation. Aliphatic CH2 spacers between the carbonyl groups dilute the concentration of interacting sites, and the dependence of the carbonyl 13C‐NMR line shape on blend concentration reveals unique spectroscopic behavior in each of the four blend systems investigated. © 1993 John Wiley & Sons, Inc.
A qualitative skin layer formation mechanism for membranes made by dry/wet phase inversion
Authors: Pinnau Ingo , Koros William J. 
Published: April 2003

AbstractOptimized membranes made by a dry/wet phase inversion process using forced‐convective evaporation consist of an ultrathin and pore‐free skin layer supported by a nodular transition layer underlying open‐cell, sponge‐like substructure. It is suggested that the out‐ermost region of such case membranes undergo phase separation by spinodal decomposition in the initial stages of the evaporation process. As a result of the small scale of phase separation present in polymer‒solvent systems, an appreciable capillary pressure occurs in the interstitial space filled with the polymer‐poor phase in contact with air. The resulting force acts normal to the membrane–air interface, which tends to consolidate the polymer‐rich phase to form a nonporous surface layer. © 1993 John Wiley & Sons, Inc.
Moduli of model elastomeric networks prepared from polymer chains having a high plateau modulus, and their interpretation in terms of the constrained‐chain model
Authors: Hsu Y.‐H. , Mark J. E. , Erman B. 
Published: April 2003

AbstractHigh‐molecular weight polybutadiene chains having approximately 47% cis‐1,4 units and 45% trans‐1,4 units were crosslinked through their carbon‐carbon double bonds using p‐bis(dimethylsilyl) benzene as crosslinking agent and chloroplatinic acid as catalyst. This particular polymer was chosen because the high plateau modulus it exhibits in the un‐crosslinked state is taken to indicate large numbers of chain entanglements, and stress–strain measurements on such networks have frequently been interpreted with the assumption that the trapping of such entanglements during crosslinking should contribute significantly to their modull. It is shown in the present investigation that such results are equally well interpreted in terms of the new constrained‐chain theory of rubbery elasticity. © 1993 John Wiley & Sons, Inc.