bluuebunny/crossref_metadata_2025_split huggingface dataset:
NMR studies of the structural development of high‐speed melt‐spun poly (ethylene terephthalate) fibers
Authors: Tzou D. L. , Desai P. , Abhiraman A. S. , Huang T.‐H 
Published: April 2003

AbstractLineshape simulation of 13C nuclear magnetic resonances was employed to characterize the structural development of poly (ethylene terephthalate) (PET) during fiber formation and subsequent processing. In all spectra the carbonyl (CA) and glycoethylene (GE) resonances can be simulated with two components. The intensity variation of these components has been interpreted quantitatively on the basis of four morphological components in the solid‐state structure, with clearly defined differences in order between them. The four components are, in decreasing structural order, (i) crystalline (C), (ii) noncrystalline with order in both CA and GE environments (NC1), (iii) noncrystalline with order only in the GE environment (NC2), and (iv) amorphous (NCA). The crystalline component has been taken here to correspond to the high‐density component which has been estimated from flotation and optical density measurements. Such an analysis reveals a smooth pattern of evolution of order within a range of conditions in melt spinning and subsequent thermomechanical processing of PET fibers. Cold drawing at room temperature was seen to induce substantial ordering only in the GE environment. In contrast, annealing at a temperature significantly above glass transition temperature (Tg) for 2 h appears to cause the conversion of amorphous component to crystalline from with little accumulation of the intermediate components.
Conformations and 13C NMR chemical shifts of some polyamides in the solid state as studied by high‐resolution 13C NMR spectroscopy
Authors: Kubo Kimihiro , Ando Isao , Shiibashi Toru , Yamanobe Takeshi , Komoto Tadashi 
Published: April 2003

AbstractHigh‐resolution 13Carbon nuclear magnetic resonance (NMR) spectra of Nylons 4, 6, and 66 in the solid state were measured over a wide range of temperature. From the results, it was found that resonance lines of crystalline and noncrystalline components were separable and their chemical shifts were determined. The 13C chemical shift behavior is closely related to their conformation. The origin of the conformational effects on the chemical shifts is discussed.
Investigation of ethylene‐vinyl alcohol copolymers for surface modification of contact lenses
Authors: Ou S. H. , Ishida H. , Lando J. B. 
Published: April 2003

AbstractEthylene‐vinyl alcohol copolymers from 0 to 57 mol % of vinyl alcohol were investigated for potential contact lens surface modification. Films of the ethylene‐vinyl alcohol copolymers made by solution casting, showed that the copolymers with a high percentage of vinyl alcohol groups possessed excellent surface properties such as good wettability, low protein (albumin) and lipid adsorption, and no conformational change of the adsorbed protein. Utilizing the Langmuir‐Blodgett dipping technique, an ultrathin layer of ethylene‐vinyl alcohol copolymer was deposited on a silicone rubber substrate. This initial results confirm that wettability was improved and the amount of protein adsorbed was reduced significantly after only one deposition trip.
Solubility of water in polyimides: Quartz crystal microbalance measurements
Authors: Moylan Christopher R. , Best Margaret Evans , Ree Moonhor 
Published: April 2003

AbstractThe solubility of water vapor in four different polyimides at 100% relative humidity and 22°C was measured by means of a quartz crystal microbalance system. The results confirm earlier conclusions that diffusion in these polymers is Fickian, and are sufficiently precise that the order of solubilities is unambiguous. The differences between the values are interpreted in terms of morphological variations rather than variations in chemical affinity for water. Diffusion coefficients are also reported.
Effects of orientation on the mechanical and dielectric relaxation behavior of cycloaliphatic polyester networks
Authors: Díaz‐Calleja Ricardo , Riande Evaristo , Guzmán Julio 
Published: April 2003

AbstractThe mechanical and dielectric relaxation behavior of strained and unstrained networks, prepared from hydroxyl‐terminated poly(diethylene glycol‐trans‐1,4‐cyclohexane dicarboxylate) (PDGC), is studied over a wide interval of frequencies and temperatures. The mechanical relaxation spectrum exhibits a glass‐rubber absorption, designated β, located in the vicinity of 0°C at 0.1 Hz, followed by a β relaxation which appears to be the result of two overlapping peaks centered at −80°C (β1) and −110°C(β2). These two peaks coalesce into a single peak in the case of strained networks. The dielectric relaxation spectrum also exhibits an α absorption followed by a subglass β relaxation whose width decreases as the elongation ratio λ increases. The activation energy associated with the mechanical β1 appears to increase as λ increases. However, the activation energy of the dielectric β process does not show a clear dependence on the elongation ratio. The analysis of the conformational characteristics of PDGC chains indicates that rotational transitions through the CcyC* bonds of the acid residue would give rise to high dielectric activity. Conformational changes about the CH2CH2 bonds of the glycol residue would produce significant mechanical activity but, comparatively, low dielectric activity. The glass‐rubber absorption is slightly displaced toward the high‐temperature side as the elongation ration increases, suggesting that the entropic effects overcome the volume effects. The glass‐rubber transition is interpreted in terms of the free volume theory.
Molecular deformation of high‐modulus polyethylene fibers studied by micro‐raman spectroscopy
Authors: Kip Bert J. , Van Eijk Marcel C. P. , Meier Robert J. 
Published: April 2003

AbstractRaman spectra of the CC stretching region of strained gel‐spun ultradrawn ultrahighmolecular weight polyethylene fibers were recorded. On the low‐wavenumber side of both the asymmetric and symmetric band, an additional broad band appeared during straining of the fiber, indicating the presence of CC bonds exhibiting high strain. The fraction of such CC bonds was estimated to be 40%. At 4% strain, the shifts of the CC stretching bands were found to increase linearly with the initial Young's modulus. From Raman spectra, information about strain distribution can be obtained. Considering the observed differences in strain distribution between fibers produced in a different way, it can be understood why one sample can be drawn to a higher extent without rupture of CC bonds. The results were discussed in conjunction with results of X‐ray measurements reported by Prasad and Grubb. It is suggested that the fibers can be described by two crystalline fractions mixed on the molecular level and an additional small amount of a third fraction with a low Young's modulus.
Light scattering and size exclusion chromatography of semi‐flexible polyimide precursors
Authors: Kim Seong H. , Cotts Patricia M. 
Published: April 2003

AbstractMeasurement of the molecular weight, radius, and molecular weight distribution of polyimide precursors (amic acids and easters) is quite difficult due to strong polymer–solvent interactions, electrostatic interactions, and the possibility of partial imidization in solution. The large quantities of solvent and high dilutions necessary in liquid chromatography make this technique the most sensitive to these effects. The distortions in the chromatogram from these effects can make assessment of the molecular weight distribution from a polystyrene calibration very tenuous. Use of a light‐scattering detector permits direct measurement of the scattering intensity (and thus the molecular weight), as the sample elutes from the column. For the esters, anomalous peaks and unexpectedly large apparent values for both the molecular weight and molecular weight distribution are shown to be due primarily to partial imidization in solution catalyzed by basic solvent impurities. Chromatographic results obtained in neutralized solvent are in agreement with light‐scattering results obtained at higher concentrations.
Phase behavior of polystyrene–polyisoprene–toluene systems in the temperature range 15–45°c
Authors: Tseng Hsiao‐show , Lloyd Douglas R. , Ward Thomas C. 
Published: April 2003

AbstractThe phase behavior of narrow molecular weight distribution samples of polystyrene and polyisoprene in the presence of toluene was investigated by means of gel permeation chromatography. Equilibrium phase diagrams, tie lines, and critical points for a number of partially miscible polystyrene‐polyisoprene‐toluene systems were generated at 15 and 30°C and 1 atm pressure. The data were combined with previously reported results at 45°C. Using the experimentally determined phase compositions along with literature values of the polymer–solvent interaction parameters, the polymer–polymer interaction parameters were evaluated using the Flory–Huggins theory. The influence of temperature, polymer molecular weight, and polymer–solvant interaction parameters on the size, shape, and location of the equilibrium phase curve, the location of the critical point, and the polymer–polymer interaction parameter was studied.
Chemical modification of poly(substituted‐acetylene). I. Synthesis and gas permeability of poly(1‐trimethylsilyl‐1‐propyne)/poly (dimethylsiloxane) graft copolymer
Authors: Nagase Yu , Ueda Tomoko , Matsui Kiyohide , Uchikura Masaki 
Published: April 2003

AbstractIn order to improve the selectivity and the stability and the stability for gas permeation of poly (1‐trimethylsilyl‐1‐propyne) (PTMSP) membrane, it was chemically modified by grafting polydimethylsiloxane (PDMS) chains. The graft copolymers were synthesized by four different methods via metallation of PTMSP with n‐butyllithium. PDMS content of the graft co‐polymers was controlled in the range of 4–92 mol %. Very tough, thin membranes could be prepared from these graft copolymers using a solvent casting method. Thermal property and gas permeability of the copolymer membranes thus obtained were evaluated. These membranes were relatively thermally stable, and the softening points were over about 150°C. Oxygen permeability coefficients Po2 and selectivity Po2/PN2 of PTMSP/PDMS graft copolymers depended on the PDMS content, the former was in the range of 1 X 10−8 to 2 × 10−7 cm3 (STP)· cm/(cm2· s · cm. Hg) and the latter was 2.0–3.1. Minimum values of PO2 and PN2 occured at PDMS content of about 55 mol %. The introduction of more than 60 mol % of PDMS resulted in oxygen permeability coefficient which was maintained for more than one moth (PO2 = 2 − 6 × 10 −8 cm 3 (STP)· cm/(cm2·s·cm Hg), PO2/PN2 = 2.3–2.7).
A model of fibril deformation in crazes
Authors: Leonov A. I. , Brown H. R. 
Published: April 2003

AbstractA theoretical model is proposed to describe quantitatively the steady‐state deformations of fibrils in crazes. In the model, the total force is represented as the sum of high elastic, plastic (actually, nonlinear viscous), and surface tension forces; the first two being modeled by using elongational rheology and the third represented in exact form. The model description is reduced to a boundary value problem for a second‐order ordinary differential equation describing the profile of fibrils. This problem results in an energy balance which, in turn, leads readily to a thermodynamic description of the equilibrium conditions for the deformations of homogeneous fibrils far from the interface (z → ∞). Two possible regimes of fibril deformation were found, depending on the periodicity of the fibrils in the craze. The first is Paredes and Fischer's regime of static deformations of fibrils under action of elastic forces and surface tension where the periodicity is determined by the condition for the static regime to exist. The second is Kramer's drawing regime where the fibril periodicity is found from the Fields and Achby maximization of craze tip advance speed. The choice between these two regimes is made to minimize the complete Gibbs' free energy including surface tension for the equilibrium state of fibrils at z → ∞. The model predicts that the static regime usually appears under moderate stresses and changes for the drawing regime when stresses increase. Hence, this model solves the contradictions between the static and drawing approaches proposed in literature. Examples of both the static and drawing regimes of fibril deformations are demonstrated and some comparisons with data are represented.
Ferroelectric polarization switching in nylon‐11
Authors: Lee J. W. , Takase Y. , Newman B. A. , Scheinbeim J. I. 
Published: April 2003

AbstractCold‐drawn Nylon‐11 films, which were prepared by stretching the melt‐quenched films to a draw ratio of 2.8: 1 at room temperature, were found to exhibit an electric displacement versus electric field hysteresis loop. The results confirmed that the Nylon‐11 film exhibited ferroelectric behavior at or below room temperature. The coercive fields were 65, 98, 125, 160, and 215 MV/m at 20, 0, −20, −40, and −60°C and the remanent polarization at −20°C (where there was considerably less dc conduction) was 56 mC/m2. Switching of the polarization was almost completed within 20 ms.
Effect of annealing on the ferroelectric behavior of nylon ‐ 11 and nylon ‐ 7
Authors: Lee J. W. , Takase Y. , Newman B. A. , Scheinbeim J. I. 
Published: April 2003

AbstractWe have discovered recently that melt‐quenched and cold‐drawn Nylon ‐ 11 films exhibit very clear ferroelectric hysteresis behavior. In the present study, a remanent polarization as high as 86 mC/m2 has been found in Nylon ‐ 7 samples; this is significantly higher than that usually observed in poly (vinylidene fluoride) films. The effect of annealing on the electric displacement versus electric field characteristics of both Nylon ‐ 11 and Nylon ‐ 7 films have been studied and show an increased coercive field (62 to 115 MV/m for Nylon ‐ 11 and 79 to 97 MV/m for Nylon ‐ 7) and a decreased remanent polarization (51 to 17.3 mC/m2 for Nylon ‐ 11 and 86 to 70.5 mC/m2 for Nylon ‐ 7) with increasing annealing temperature from 25 to 145°C.
Nonintegral and integral folding crystal growth in low‐molecular mass poly(ethylene oxide) fractions. I. Isothermal lamellar thickening and thinning
Authors: Cheng Stephen Z. D. , Zhang Anqiu , Chen Jianhua , Heberer Daniel P. 
Published: April 2003

AbstractThe overall crystallization and crystal melting of one low‐molecular mass poly(ethylene oxide) (PEO) fraction (MW 3000) have been investigated by differential scanning calorimetry (DSC) and in situ small‐angle x‐ray scattering (SAXS). The salient new results indicate that initial transient crystals with nonintegral folding (NIF) chain lengths form over a wide range of crystallization temperatures. This NIF structure subsequently transforms into crystal forms with integral folding (IF). The PEO IF crystals consist of the extended chain (n = 0) crystal and the once‐folded chain (n = 1) crystal, while the NIF has an intermediate fold length. The NIF → IF transformation occurs either by lamellar thickening or thinning. The NIF crystal is less stable than the IF(n = 1) crystal, but its growth is more rapid. Crystallization of the PEO (MW 3000) fraction is thus recognized as a compromise between the direction of the thermodynamic driving force and the kinetic pathway. Some potential consequences of these observations are also addressed.
Gas transport properties of liquid crystalline poly (ethylene terephthalate‐co‐p‐oxybenzoate)
Authors: Weinkauf D. H. , Paul D. R. 
Published: April 2003

AbstractGas transport properties are reported for a series of films prepared from thermotropic poly (ethylene terephthalate‐co‐p‐oxybenzoate), or PET/PHB, having compositions of 60 and 80 mol % PHB. The mesomorphic and crystalline morphology of the copolyester films was examined by cross‐polarized light microscopy, differential scanning calorimetry (DSC), and x‐ray diffraction. Melt‐processed films of both compositions appeared to exhibit an entirely anisotropic morphology with low levels of conventional crystallinity. Solution‐cast films prepared from the 60 mol % material were found to contain a large fraction of isotropic regions, which become ordered upon annealing above the glass transition. Permeability measurements were made for He, H2, O2, N2, and CO2 at 35°C and the diffusivities were computed from time‐lag data. The largely anisotropic films exhibit good barrier properties resulting from very low solubility coefficients. The partially isotropic 60 mol % films show much higher permeability coefficients driven primarily by increased solubility coefficients, while diffusivity is affected to a lesser extent. These results appear to contrast with what is observed in semicrystalline systems where increased crystalline order results in more dramatic reductions in penetrant mobility.
X‐ray scattering studies of the structure of aqueous hydroxy‐propylcellulose solutions
Authors: Wignall G. D. , Annis B. K. , Triolo R. 
Published: April 2003

AbstractX‐ray diffraction studies have been undertaken on aqueous solutions of hydroxy propylcellulose (HPC) over a wide range of the scattering vector Q. The experiments revealed only modest differences in local structure on a distance scale ca. 5–300 Å despite the fact that they covered concentrations generally interpreted as ranging from the isotropic (35.1 wt %) to the anisotropic liquid crystalline (LC) phase (53.5 wt %). Several models were used to interpret the small‐angle scattering data, and each gave similar structural parameters and extrapolated intensities (Q → 0) for both solutions. Peaks were observed with d‐spacings ca. 12–17 Å in both materials. Wide‐angle x‐ray scattering (WAXS) showed slightly increased local order over a size range ca. 5–20 Å for the anisotropic solution, and this is consistent with a greater intensity of the 13 Å peak in this material. It is difficult to reconcile these findings with an interpretation of the LC state involving major differences with the isotropic phase and a high degree of orientational order extending over long length scales.
Gas permeability of a new silicone ring polymer: Isotactic poly(phenyl silsesquioxane)
Authors: Mi Y. , Stern S. A. 
Published: April 2003

AbstractThe permeability of isotactic poly(phenyl silsesquioxane) (PPSQ) to O2 and N2 at 25.0°C and to CO2 and CH4 at 35.0°C was measured at low pressures by the “time‐lag” method. PPSQ is a glassy silicone polymer with an 8‐atom ring structure of alternating Si and O atoms. The CO2/CH4 selectivity of PPSQ is markedly higher than that of other silicone polymers, whereas its O2/N2 selectivity appears to be only slightly higher. PPSQ is not as effective a “molecular sieve” as would be expected from its ring structure, possibly because its relatively large mean interchain distance suggests that this polymer has a large mean free volume.
Relaxations in thermosets. VI. Effects of crosslinking on sub‐Tg relaxations during the curing and aging of epoxide‐based thermosets
Authors: Mangion M. B. M. , Johari G. P. 
Published: April 2003

AbstractThe dielectric permittivity and loss of diglycidyl ether of bisphenol‐A‐based thermosets cured with diaminodiphenyl methane and diaminodiphenyl sulfone have been measured over a temperature range 77–400 K after curing or aging for a predetermined duration. Of the two sub‐Tg relaxations, the height of the γ relaxation peak monotonically decreases during both the cure and postcure periods, and the height of the β relaxation peak first increases to a maximum value and then decreases. This decrease is attributed to physical aging effects. The height of the α‐relaxation peak decreases. The γ‐ and β‐relaxation peaks become increasingly separated in temperature. A concept of accumulated equivalent curing time which is based upon known chemical kinetics has been introduced for use in both theoretical and practical aspects of the study of thermosets. It is shown that substantial curing of the sample occurs during its slow heating to the curing temperature. The use of this concept in the curing of thermosets is illustrated. A procedure for the analysis of the distribution of relaxation times from a set of results limited in both frequency and temperature range is described. The distribution parameter is 0.20 and 0.16 for the γ and β process, respectively, and remains constant with postcuring and physical aging. The distribution parameter for the α process decreases from 0.60 to 0.36 on curing.
The effect of pressure on gas permeation through semicrystalline polymers above the glass transition temperature
Authors: Naito Yasutoshi , Mizoguchi Keishin , Terada Katsuhiko , Kamiya Yoshinori 
Published: April 2003

AbstractA method is proposed to analyze the effect of pressure on permeation of gases through semicrystalline polymers above the glass transition temperature. The method utilizes similarities in molecular diameters of the gases and differences in their solubilities. Two polymers, polyethylene and polypropylene, and a series of gases are chosen for an application of the method, and the effect of pressure on the permeabilities for 10 gases is measured in the pressure range 1–130 atm at 25°C. For polymers, the logarithm of the permeability coefficient is linear in the pressure for each gas, with negative slope for slightly soluble gases (He, Ne, H2, N2, O2, and Ar) and positive slope for highly soluble gases (CH4, Kr, CO2, and N2O). Analyzing these slopes by the method proposed permits contributions of hydrostatic pressure and concentration to the pressure dependence of permeation to be evaluated. On the basis of the results, the mechanism of gas permeation in rubbery films under high pressures is discussed.
Mathematical modeling of seeded miniemulsion copolymerization for oil‐soluble initiator
Authors: Rodriguez Valmore S. , Asua Jose M. , El‐Aasser Mohamed S. , Silebi Cesar A. 
Published: April 2003

AbstractA mathematical model of seeded miniemulsion copolymerization of styrene‐methyl methacrylate for oil‐soluble initiator is presented. The mathematical model includes the mass transfer, from the miniemulsion droplets to the polymer particles, by both molecular diffusion and collision between miniemulsion droplets and the polymer particles. The mathematical model also includes the calculation of both the distribution of partices with i radicals and the average number of radicals per particle in the miniemulsion copolymerization using oil‐soluble initator. Studies were carried out on the mass transfer coefficients of monomers across the interface between the miniemulsion droplet and the aqueous phase, hexadecane concentration in the miniemulsion droplets, the miniemulsion droplet sizes, and the collision between miniemulsion droplets. The results indicated that the copolymerization of styrene‐methyl methacrylate was not a mass transfer controlled process. The mass transfer by collision between miniemulsion droplets and polymer particles plays an important role and was included in the model in order to predict the experimental data of seeded miniemulsion copolymerization.