bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural models for homogeneous organic‐inorganic hybrid materials: Simulations of small‐angle X‐ray scattering profiles
Authors: Landry Michael R. , Coltrain Bradley K. , Landry Christine J. T. , O'Reilly James M. 
Published: April 2003

AbstractTwo morphological models have been proposed to describe small‐angle x‐ray scattering from organic‐inorganic composite (OIC) materials. The first model invokes the idea of a liquid‐like arrangement among noninterpenetrating fractal clusters, and the second employs an empirical correlation function that would be expected for a bicontinuous two‐phase (B2P) picture with the inorganic portion exhibiting fractal characteristics. Simulated scattering profiles have been generated for direct comparison with experimental data. The samples studied were a triethoxysilane‐endcapped bisphenol A epoxide resin (EAS) reacted in the presence of tetraethoxysilane (TEOS) under slightly basic conditions, and a random trimethoxysilane‐functionalized copolymer of poly(methyl methacrylate) (MMA‐TMS) with added tetramethoxysilane (TMOS), reacted in an acidic medium. Each morphology model qualitatively simulates the broad scattering maximum and limiting high‐angle slope commonly seen in SAXS profiles. It is concluded that the inorganic phase in the EAS hybrid exhibits particle‐like characteristics at length scales less than approximately 250 Å, and the organic and inorganic components are bicontinuous at larger distances. The MMATMS composite is better described by bicontinuous organic and inorganic phases with a periodic fluctuation of about 40 Å. The scattering maximum arises either from the mean separation of particles or a dominant wavelength in a concentration fluctuation, similar to that observed for spinodal decomposition. In either case, the SAXS peak position is related to the distance between junction points of the crosslinked organic polymer. © 1995 John Wiley & Sons, Inc.
Magic angle carbon‐13 NMR study of solid poly(ethylene naphthalene‐2,6‐dicarboxylate)
Authors: Abis Luigi , Merlo Edoardo , Po' Riccardo 
Published: April 2003

AbstractAmorphous (1) and semicrystalline (2) samples of poly(ethylene naphthalene‐2,6‐dicarboxylate) (PEN) have been investigated by cross‐polarization/magic angle spinning (CP/MAS) 13C NMR at 26°C (1 and 2), 100°C (1) and 120°C (2) in order to study the phase structure and the local motion of polymer chain segments at temperatures below and close to Tg (120°C). The lineshape of the ethylene unit 13C signal in sample 2 is consistent with the presence of two components which were assigned to trans and gauche conformations. The first component arises mainly from the crystalline regions and the second one from the amorphous part. Cross‐polarization curves were traced by changing the contact time between carbon and proton reservoirs. TCH (cross relaxation time) and proton T1p (spin‐lattice relaxation time in the rotating frame) values were obtained as best fit parameters by fitting calculated curves to the experimental data. All 13C NMR data are consistent with the presence of highly rigid ethylene units in both semicrystalline and amorphous samples within the temperature range (T) investigated. This result is in disagreement with the 1H NMR wide line spectra which showed a noticeable narrowing of the linewidth with increasing temperature in the same range, hence indicating a great mobility of the chain segments. To account for this discrepancy a qualitative model based on the existence of two distinct dynamic regions, one where motion is highly restricted and the other one where large reorientations of ethylene group torsional angles take place, is suggested. The NMR results led to the conclusion that three structural phases are present in PEN: crystalline, very rigid amorphous, and very mobile amorphous. © 1995 John Wiley & Sons, Inc.
Morphology and electro‐optic responses of poly(methyl methacrylate)/nematic liquid crystal composite films: Effect of the polymer molecular weight
Authors: Kim B. K. , Ok Y. S. , Choi C. H. 
Published: April 2003

AbstractThe director configuration, state of liquid crystal (LC) phase aggregation, and the electooptic properties of thin polymer films of poly(methyl methacrylate) (PMMA) containing nematic liquid crystal have been studied. Measurements included scanning electron micrograph (SEM), polarized optical micrographs (POM), and transmittance response of the film with the applied electric AC voltage and frequency. Two types of PMMA with significantly different molecular weight (Mw) were used, and the effects of polymer molecular weight on morphology and electro‐optic properties of the composite films were examined. © 1995 John Wiley & Sons, Inc.
Calculating poly(ethylene‐co‐acrylic acid)‐solvent phase behavior with the SAFT equation of state
Authors: Hasch Bruce M. , McHugh Mark A. 
Published: April 2003

AbstractStatistical Associating Fluid Theory (SAFT) is used to model the cloud‐point behavior of poly(ethylene‐co‐acrylic acid), with up to 7 mol % acid content, in propane, butane, propylene, butene, and dimethyl ether at temperatures to 250°C and pressure to 2600 bar. The values for the pure component temperature‐independent segment volumes, nonspecific interaction energies, and the numbers of segments per molecule are equal to those used for polyethylene, because these copolymers contain modest amounts of acrylic acid repeat units. Two different approaches are used to determine values of the pure component energy of hydrogen bonding, ϵ/k, and the binary interaction parameter, kij. In one approach, ϵ/k for acid dimerization is obtained from literature spectroscopic data and a constant value of kij is fit to each copolymer‐solvent cloud‐point curve. Increasing the value of kij shifts the predicted cloud‐point curves to higher temperatures and pressures. For the five solvents used in this study, kij decreased steadily in the range of 0.040 to −0.025 as the acid content in the copolymer increased. The predicted cloud‐point curves are in good agreement with experimental data, and the impact of hydrogen bonding on the phase behavior is well represented, even if kij is set equal to zero. For the second approach, ϵ/k is set to ∼ 90% of the value obtained from spectroscopic data as determined from a fit of a single poly(ethylene‐co‐acrylic acid)‐butane cloud‐point curve, while kij is fit to the corresponding polyethylene‐solvent system. This approach requires less mixture data than the previous approach, and the calculated cloud‐point curves are also in good agreement with experimental data, except for the EAA‐DME systems. © 1995 John Wiley & Sons, Inc.
The ionic conductive property of sulfonated polyethylene oxide polyurethane ionomers
Authors: Xu Hai‐Sheng , Yang Chang‐Zheng 
Published: April 2003

AbstractA series of lithium and sodium salts of sulfonated polyethylene oxide (PEO) polyurethane ionomers in different levels of ionization were prepared. It has been found that this material is a new type of ionic conductive polymer, characterized by a single‐ion transport mechanism and good mechanical properties. The ionization level significantly influences the ionic conductivity of the samples. When the mole ratio of the metal ion and ether oxygen atom is about 0.05, the ionomers exhibit maximum cationic conductivity. An optimal cationic conductivity of 1.0 × 10−5 S/cm is obtained at about 70°C without any addition of organic plasticizer. The conductivity increases apparently when propylene carbonate and low MW PEO are added to the polyurethane ionomer. © 1995 John Wiley & Sons, Inc.
Plasticization and crystallization of cis‐1,4 polyisoprene mixed with methyl linolate
Authors: Kawahara Seiichi , Tanaka Yasuyuki 
Published: April 2003

AbstractCrystallization behavior of synthetic cis‐1,4 polyisoprene mixed with methyl linolate was investigated by differential scanning calorimetry and dilatometry. At isothermal crystallization temperature of −25°C, a rate of crystallization decreased with the addition of 1 wt % methyl linolate, whereas it increased with a large amount of methyl linolate, about 30% by weight. Although Avrami constant of cis‐1,4 polyisoprene was 2.82, that of mixtures containing 1 and 30 wt % methyl linolate was found to be approximately 4. This implies the same crystallization mechanism was in operation in the mixtures. Since glass transition temperature, Tg, of cis‐1,4 polyisoprene decreased as the methyl linolate content of mixture increased, methyl linolate was found to be plasticizer for cis‐1,4 polyisoprene. The increase in the rate of crystallization in the mixtures was corresponding to the decrease in Tg. © 1995 John Wiley & Sons, Inc.
Molecular weight distribution by stirring‐induced fractional precipitation
Authors: Habibe Maria Eunice S. , Esperidião Maria Cecilia A. 
Published: April 2003

AbstractUltrahigh molecular weight polyethylenes GUR, UTEC 2540, and UTEC 3540 were fractionated by precipitation from cooling of solutions with stirring [stirring‐induced fractional precipitation (SIFP)]. The samples were dissolved in decalin and precipitated over the temperature range of 100‐78°C. Three types of procedures were investigated. From fractionation data, the integral and differential molecular weight distribution (MWD) of the polymer were calculated. The MWD and average molecular weights, $\bar M_w$ and $\bar M_n$, by size exclusion chromatography (SEC) and the limiting viscosity number of the fractions and whole polymer were determined. From these data, the Mark‐Houwink constants were calculated. The ‘K’ and ‘aη’ values obtained were 6.70 × 10−4 and 0.69, respectively. The MWD curves calculated from SIFP technique by using these constants are in accordance with the MWD by SEC. Fractionation depended on the chemical nature of the stirrer and the cooling rate of the solution during precipitation. The methodology is reproducible. Faster fractionation was observed compared with other methods. © 1995 John Wiley & Sons, Inc.
Thin films of nylon 13,13 casted on water: Morphology and properties
Authors: Wang Li Hui , Porter Roger S. 
Published: April 2003

AbstractSubstrate‐free thin film of Nylon 13,13 has been prepared continuously by casting the polymer on a water surface from m‐cresol solution. The uniform thickness of film is ca. 500 A, as measured with a Profilometer. Film morphology and properties have been characterized by transmission electronic microscopy (TEM), x‐ray photoelectron spectroscopy, wide‐angle x‐ray scattering, differential scanning calorimetry and by contact angle measurements. Results show that there is no preferential accumulation of the amide group toward the water surface. A spherulite structure exists in this film with a crystallinity of 26% by DSC. Fibers were drawn from the films which had a tensile modulus of 5 GPa, stiffer than reported for this nylon as prepared by other means. Other members of the nylon series, such as Nylon 6, Nylon 12, have also been prepared in films by the same casting method under modified conditions. © 1995 John Wiley & Sons, Inc.
Ionic conduction in LiSCN/dimethylformamide/poly(propylene oxide) system I. Dissociation equilibria of LiSCN
Authors: Mitani Kazuishi , Adachi Keiichiro 
Published: April 2003

AbstractDissociation equilibria of lithiumthiocyanate (LiSCN) in N,N‐dimethylformamide (DMF) solutions of poly (propylene oxide) (PPO) were investigated by using infrared spectroscopy. The stretching bands due to the thiocyanate ions SCN−1 and the LiSCN ion pair were found at 2058 and 2072 cm−1, respectively. At high LiSCN concentration C of ca. 20 wt %, another weak band due to the dimer (LiSCN)2 was observed. From the ratio of the areas of the absorption bands, the dissociation constant K1 for the equilibrium LiSCN ↔ Li+ + SCN−1 and that K2 for (LiSCN)2 ↔ 2LiSCN have been determined. With increasing DMF content, K1 increases from 1 × 10−4 for bulk PPO to 4.8 × 10−1 for pure DMF at 299 K. Log K1 is not linear against inverse of the dielectric constant ϵ of the medium and decreases with increasing temperature. The enthalpy (ΔH) and entropy (ΔS) changes for the dissociation of LiSCN are both negative. ©1995 John Wiley & Sons, Inc.
Solubility and transport of water vapor in some 6FDA‐based polyimides
Authors: Lokhandwala K. A. , Nadakatti S. M. , Stern S. A. 
Published: April 2003

AbstractPermeability, diffusion, and solubility coefficients for H2O vapor in four different 6FDA‐based polyimides were determined at temperatures between 25 and 45°C and over a wide range of relative humidities. The solubility of H2O vapor in some of the polyimides studied can be described by the “dual‐mode sorption” model whereas in other polyimides it is represented by the Flory‐Huggins equation, which suggests that the latter polymers are plasticized by H2O. The solubility of H2O vapor in the polyimides decreases as the temperature is raised and increases with increasing polarity of the polymer. The diffusion coefficients for H2O in the polyimides studied either increase or pass through a weak maximum with increasing H2O activity, or concentration in the polymers. The latter behavior is probably due to a clustering of H2O molecules in the polyimides at higher H2O activities or concentrations. The diffusion coefficients for H2O decrease as the chain‐packing density of the polyimides increases. The permeability coefficients for H2O vapor in 6FDA‐based polyimide membranes either increase slightly or are constant as the H2O activity is increased. The experimental values of the permeability coefficients are consistent with the values determined from diffusion and solubility coefficients. The permeability of the polyimides to H2O vapor appears to be controlled by the solubility of H2O in the polymers. The polyimides studied exhibit a very high selectivity for H2O vapor relative to CH4, and therefore are potentially useful membrane materials for the dehydration of natural gas. ©1995 John Wiley & Sons, Inc.
Ultrasonic properties of PVC (S‐27/R63) in the glassy region
Authors: Guney H. Yüksel , Oskay Taner , Özkan H. Sinan 
Published: April 2003

AbstractThe ultrasonic properties of PVC (S‐27/R63) in the glassy region have been investigated as a function of temperature. The propagation velocities and absorption of the longitudinal and transverse ultrasonic waves have been measured at constant frequency of 2 MHz and at temperatures varying between −5°C and 75°C, using the ultrasonic immersion technique. The variation of the elastic moduli with temperature has been derived from these measurements. The results thus obtained have been compared to those previously published in the literature for different PVC and other polymer samples. ©1995 John Wiley & Sons, Inc.
Rationalization of the ratio of excimer‐to‐monomer fluorescence emission intensity in bichromophoric diesters of 1‐pyrenoic acid and mono‐, di‐, tri‐, and tetraethylene glycols
Authors: Martin Olga , Mendicuti Francisco , Saiz Enrique , Mattice Wayne L. 
Published: April 2003

AbstractThe ratio of excimer to monomer emission intensities, denoted by ID/IM, was measured for Py–COO(CH2CH2O)mCO  Py, where Py denotes the 1‐pyrenyl group and m = 1–4, in solvents of different viscosity, η. Three different systems were used to change the viscosity of the medium: (a) Mixtures of methanol and ethylene glycol at 25°C, (b) linear aliphatic alcohols, H(CH2)nOH, where n =1–6, also at 25°C, and (c) ethylene glycol over the range 6.6–35°C. The ratio ID/IM decreases sharply as η increases, and the rate of the decrease in ID/IM is a function of m. Quantitatively, the dependence of ID/IM on η at high viscosity, i.e., the slope [d(ID/IM)/d(1/η)]∞, is larger in the present work than in another series of 1‐pyrenyl diesters in which the flexible spacer is an oligomer of polyethylene, instead of an oligomer of polyoxyethylene. In the limit where η → ∞, the ratio ID/IM assumes its largest value in the bichromophoric compound with m = 2. However, as η decreases the compound with m = 3 becomes the one with the largest ID/IM. A complete rotational isomeric state analysis (for the compounds with m = 1–3) and a Monte Carlo simulation (for the compound m = 4) of the conformations of the diesters can rationalize the behavior of ID/IM in the high viscosity limit. ©1995 John Wiley & Sons, Inc.
Surfactant exudation in the presence of a coalescing aid in latex films studied by atomic force microscopy1
Authors: Juhué Didier , Wang Yongcai , Lang Jacques , Leung On‐Man , Goh M. Cynthia , Winnik Mitchell A. 
Published: April 2003

AbstractWe report atomic force microscopy images of surfactant (SDS) exudation in PBMA latex films, in the presence and the absence of a coalescing aid (Texanol™, TPM). The exudates appear as hilly islets, and at times as mountains, at the film surface. Their size and number increase upon annealing above the glass‐transition temperature of the latex polymer. TPM was found to be a strong promoter of surfactant exudation at the air‐polymer interface. In the absence of TPM, annealing the films for several hours at 70°C led to very little migration of surfactant to the surface at most sites in the film. When the films with structures of SDS on their surface were immersed in water, these structures disappeared. Pores, ranging in size from tens to hundreds of nm in diameter, were clearly visible in the surface of the films. These films dry from the edges of the film inward, with a propagation front concentrating the water‐soluble species into a turbid, moist region in the center. At this site, the rate at which the surfactant comes to the surface is enormously enhanced over that at other sites in the film. This is likely due to the high concentration of surfactant in this region, transported there by the drying process. © 1995 John Wiley & Sons, Inc.
Gas transport properties of polyarylates part I: Connector and pendant group effects
Authors: Pixton M. R. , Paul D. R. 
Published: April 2003

AbstractGas transport of helium, hydrogen, oxygen, nitrogen, methane, and carbon dioxide gases in a series of polyarylates based on isophthalic acid has been examined. These polyarylates were prepared from bisphenol A, hexafluorobisphenol A, phenolphthalein, and fluorene bisphenol monomers to study the effects of varying the bisphenol connector group size and shape. Substitution of a tertiary butyl group at position five on the isophthalate ring increases polymer permeability. The incorporation of a large, bulky connector group increases gas permeability and maintains permselectivity while the substitution of t‐butyl groups increases gas permeability by two‐ to fourfold but lowers permselectivity. Most of the increases in permeability can be related to increases in the diffusion coefficients of all the gases. All the polyarylates have high glass transition temperatures and may be suitable for high temperature gas separation applications. ©1995 John Wiley & Sons, Inc.
1H NMR studies of molecular relaxations of poly‐1‐butene
Authors: Maring D. , Meurer B. , Weill G. 
Published: April 2003

AbstractThe temperature dependance of the proton NMR line shape, T1 and T1ρ of isotactic poly‐1‐butene forms I, I′, II, and III have been studied between 100 and 400 K (up to melting). The usual line shape decompositions concerning rigid vs. crystalline and mobile vs. amorphous phases are discussed. The rigid‐lattice second moments were calculated introducing a fast rotation of the methyl group.Complex spin‐lattice decays were analyzed as a continuous distribution of rates. Relaxation behavior was analyzed in terms of a Williams‐Watt correlation function. Motions in the crystalline parts of samples in forms II and III very similar to the amorphous one were revealed, leading us to compare form II to a condis crystal during the crystal form transformation. © 1995 John Wiley & Sons, Inc.
Relaxations in liquid crystalline poly(tetraethylene oxide terephthaloyl‐bis‐4‐oxybenzoate)
Authors: Gómez M. A. , Marco C. , Fatou J. M. G. , Suarez N. , Laredo E. , Bello A. 
Published: April 2003

AbstractThe relaxation behavior of poly(tetra ethylene oxide terephthaloyl‐bis‐4‐oxybenzoate), PTETOB, was analyzed by thermally stimulated depolarization currents, TSDC, and dynamic mechanical techniques, DMTA, and the results compared with those obtained by differential scanning calcrimetry, thermo‐optical analysis, and x‐ray diffraction. In the low temperature region, −173–30°C, three main transitions were observed and assigned to the γ relaxation, the glass transition of the mesophase and the glass transition temperature of the amorphous material. The complex behavior observed in the range 110–160°C was as signed to a crystal‐crystal transition which competed with the formation of a mesophase and afterward the formation of a smectic A mesophase. At higher temperatures, was observed the transition from the smectic A mesophase to a nematic one, prior to the isotropization temperature. In the TSDC experiments the formation of a permanent electret was detected and the charges trapped in the mesophase were canceled only at the isotropization temperature. © 1995 John Wiley & Sons, Inc.
Gas transport through ethylene‐acrylic acid ionomers
Authors: Nobile M. A. Del , Mensitieri G. , Nicolais L. , Weiss R. A. 
Published: April 2003

AbstractTransport properties of several gases in two ethylene‐acrylic acid ionomers characterized by a different amount of acrylic acid groups and percentage of neutralization have been investigated. Sorption and permeation experiments have been performed with N2, O2, CO2, CH4, C2 H6, and SF6 in the 25–65°C range and with C3H8 only at 25°C. Gas permeabilities, diffusivities, and solubilities were evaluated along with activation energies and heats of solution. Data obtained in the present investigation were compared to analogous results reported in literature for polyethylene to better highlight the effect of ionic aggregates on the gas transport mechanism. © 1995 John Wiley & Sons, Inc.
Scattering properties of branched polymers in the high wave vector region and good solvent conditions
Authors: Benmouna M. , Borsali R. , Khaldi S. 
Published: April 2003

AbstractStatic and dynamic scattering properties of branched polymers in the high‐wave vector region and in good solvent conditions are derived. The treatment of Benoít et al. is extended to good solvent conditions by calculating explicitly the static intensity, including numerical factors. The dynamical properties are also examined and, in particular, the first cumulant of the intermediate scattering function is derived using the preaveraged Oseen tensor. The results are presented in terms of the critical exponent v to account for the effect of swelling due to excluded volume interactions. These interactions are introduced assuming that v is the same everywhere along the chain but ignoring all the refinements introduced by the renormalization group theories in the case of linear chains. © 1995 John Wiley & Sons, Inc.