bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetic analysis of cis‐trans thermal isomerization of polyacetylene
Authors: Tanabe Yoshikazu , Kyotani Hiroko , Shimomura Masaki , Akagi Kazuo , Suezaki Minoru , Kasai Takanori , Shirakawa Hideki 
Published: April 2003

AbstractA single broad exothermic peak due to cis‐trans isomerization appears near 140°C in the differential scanning calorimetry (DSC) curve of polyacetylene (PA) films, polymerized by a nonsolvent method using a high‐temperature‐aged catalyst. This exothermic peakis described by a two‐state model, in which population probabilities for cis and trans states are assumed to change through the forward and backward reactions. The enthalpy difference between the two states is 1.69 kcal/mol, which was derived from the slope of the plot of heat of isomerization versus cis content. The activation energy was determined experimentally from the heating‐rate dependence of the peak temperature. A single activated process with an activation energy of 28 kcal/mol was observed for the PA film. Other parameters such as the preexponential factor were estimated by comparing theoretical and experimental DSC curves.
Small‐angle neutron and x‐ray scattering study of swollen nylon‐6
Authors: Pleštil Josef , Baldrian Josef , Ostanevich Yurii M. , Bezzabotnov Vadim Yu 
Published: April 2003

AbstractResults of swelling and small‐angle scattering experiments on samples of nylon‐6 swollen with heavy water are discussed on the basis of the lamellar and switchboard models. The small‐angle neutron scattering (SANS) intensity is very sensitive to the distribution of water in swollen samples, while the small‐angle x‐ray scattering (SAXS) data characterize the dry samples. The observed values of the mean‐square fluctuation of scattering‐density can be explained by a model with assumed inhomogeneous swelling of the amorphous phase.
Thermal and dilute‐solution properties of zwitterionic copolymers
Authors: Cardoso Judith , Manero Octavio 
Published: April 2003

AbstractWe report the synthesis, characterization, thermal and dilute‐solution properties of zwitterionic copolymers of the sulfobetaine type, where the proportion of ionic groups is varied over a wide range. Two different structures are considered: poly (2‐vinyl pyridine sulfopropyl betaine) and poly (4‐vinyl pyridine sulfopropyl betaine). Synthesis is carried out to obtain random copolymers which are further characterized and their ionic content determined. At low proportions of ionic groups, the behavior is similar to that observed in ionomers, with substantial differences between the two structures, Increased interaction among the zwitterionic groups at higher charge densities is evidenced, which leads to the formation of clusters and agglomerates. An increase in the intrinsic viscosity with salt content in aqueous solutions is also observed. This behavior is analogous to that of homopolymers with 100% ionic content, but with particular features of interest.
Influence of polydispersity and amine–epoxide ratio on molecular mobility in epoxy networks
Authors: Iannacchione G. , Von Meerwall E. 
Published: April 2003

AbstractUsing nuclear magnetic resonance (NMR) T2 relaxation and pulsed‐gradient spin‐echo diffusion experiments at 175.5°C, molecular motions of the sole and gel of several epoxies of the type diglycidyl ether of bisphenol‐A (DGEBA; Shell Epon 1007F and 1009F) cured with 4,4′‐diaminodiphenyl sulfone (DDS) have been studies as a function of curative content. It was found that the fraction of protons associated with the shorter T2 component cannot be identified as the gel fraction until the substantial bimodal polymer polydispersity is accounted for in the spin relaxation model. The gel fraction and both relaxation rates have maxima near curing stoichiometry, and fall off more rapidly on the curative‐poor side. The diffusion spectrum of the sol fraction was consistent with a light species (Epon 828 remnants) plus a polydisperse (M̄w/M̄n ≅2) heavier species, in agreement with resin and sol gel permeation chromatography (GPC) results. Numerical simulations also show that polymer polydispersity is likely to affect the interpretation of T2 relaxation found in the literature.
Microrheology of high‐polymer solutions
Authors: Montfort J. P. , Tonck A. , Loubet J. L. , Georges J. M. 
Published: April 2003

AbstractA new surface force apparatus is used for investigating the viscoelastic properties of high‐polymer solutions or polymer melts confined between two solid surfaces. We describe the experimental setup and discuss how to obtain the rheological behavior of the liquid from the transfer function given by two capacitance displacement transducers. In particular, we point out that for a distance between the surfaces enclosing a thin film below some thousands of Angströms, the elastic deformation of the solids is no longer negligible. Experiments conducted on a semidilute solution of polybutadiene show the applicability of the device for study of the dynamic properties of thin‐film polymers.
Epitaxial growth of isotactic polypropylene on oriented polyethylene from solution
Authors: Kawaguchi Akiyoshi , Okihara Takumi , Murakami Syozo , Ohara Masayoshi , Katayama Ken‐Ichi , Petermann Jürgen 
Published: April 2003

AbstractOriented polyethylene (PE) films with surfaces bounded by the (100) plane were prepared. On the film surfaces, isotactic polypropylene (iPP) was crystallized epitaxially from solution as quadrits with their sides parallel and perpendicular to the polyethylene chain axis. In the through wide‐angle x‐ray diffraction pattern (taken with incident x‐rays normal to the polyethylene film surface), the 111 iPP reflections was observed on the meridian (Parallel to the polyethylene chain axis). In the edge patterns (taken with x‐rays incident on the edge of the polyethylene film), 040 and 060 reflections were observed on the equator. From the diffraction patterns, the following lattice coincidence was observed between polyethylene and isotactic polypropylene: (010)iPP//(100) PE, [101]iPP//[001] PE. The Small‐angle x‐ray scattering patterns showed that edge‐on isotactic polypropylene lamellae 9 nm thick were arranged with their long axes inclined at an angle of 40° from the polyethylene axis. Molecular chains were oriented within the lamellae normal to the surfaces.
Gas transport in poly [bis(trifluoroethoxy) phosphazene] above the T(1) transition
Authors: Mizoguchi Keishin , Kamiya Yoshinori , Hirose Takuji 
Published: April 2003

AbstractGas permeation measurements were performed by the time‐lag method for 13 gases in poly [bis(trifluoroethoxy) phosphazene] above the mesophase transition, T (1) transition, of the crystals. Hysteresis was found in the temperature dependence of the permeability coefficients for CO2, O2, and N2 in the transition region as observed by dilatometry and differential scanning calorimetry. Independently the solubility of CO2 was determined gravimetrically above and below T(1). Noticeable change and hysteresis were also observed in the temperature dependence of the solubility coefficients. Diffusion of CO2 in the measophase is suggested from the permeation and sorption measurements. Gas transport parameters of CO2 in the mesophase are estimated, and the contributions of the mesophase and the crystalline phase to gas transport are considered.
Effect of isopropylidene replacement on gas transport properties of polycarbonates
Authors: McHattie J. S. , Koros W. J. , Paul D. R. 
Published: April 2003

AbstractThe gas sorption and transport properties of a series of polycarbonates in which the isopropylidene unit of bisphenol A polycarbonate has been replaced with another molecular group are presented. Two new materials, bisphenol of norbornane polycarbonate (NBPC) and bisphenol Z polycarbonate (PCZ), are compared with several polymers which have been studied previously in this laboratory, including bisphenol A polycarbonate (PC), hexafluorobisphenol A polycarbonate (HFPC), and bisphenol of chloral polycarbonate (BCPC). The effect of molecular structure on chain mobility and chain packing is related to the gas transport properties. Dynamic mechanical thermal analysis and differential scanning calorimetry are used to judge chain mobility, while x‐ray diffraction and free volume calculations give information about chain packing. Permeability measurements were made for He, H2, O2, N2, CH4, and CO2 at 35°C over a range of pressures up to 20 atm. Sorption experiments were also done for N2, CH4, and CO2 under the same conditions. The permeability coefficients of these polymers rank in the order HFPC ≫ NBPC>PC>BCPC ≫ PCZ for all of the gases. With the exception of BCPC, this order correlates well with fractional free volume. The low gas permeability of BCPC is attributed to a polarity effect. In general, bulky and relatively immobile substituents, as in HFPC and NBPC, can yield improved separation characteristics. The polar group of BCPC and the flexible cyclohexyl substituent of PCZ result in relatively low gas permeability.
Application of the bendler–shlesinger generalization of the vogel equation to ion‐conducting polymers
Authors: Fontanella J. J. , Wintersgill M. C. , Coughlin C. S. , Mazaud P. , Greenbaum S. G. 
Published: April 2003

AbstractPreviously published audio frequency electrical conductivity results for ion‐conducting polymers have been reanalyzed in terms of the Bendler‐Shlesinger (BENSH) generalization of the Vogel equation. The materials studied include poly (propylene oxide) (PPO), amorphous poly (ethylene oxide) (PEO), poly (dimethylsiloxane‐ethylene oxide) (PDMS‐EO), and polyphosphazene (MEEP) ‐based material. The BENSH equation provides a better fit of both vacuum and high‐pressure data for PPO and PDMS‐EO than does the Vogel equation. For MEEP, for which the data are of a lower accuracy, and PEO, for which the data are over a narrower range of temperatures, the Vogel equation provides a better fit. However, for the most reliable data, a systematic difference between the VTF equation and the data is found, while the BENSH equation fits all portions of the data equally well. It is concluded that the BENSH equation, and hence the defect‐diffusion model, provides an excellent description of the electrical conductivity for ion‐conducting polymers.
Phase behavior of poly(ethylene oxide) and sulfonated polystyrene blends with and without solvent
Authors: Lee Sang Cheol , Lee Moo Sung , Jo Won Ho 
Published: April 2003

AbstractThe phase behavior of poly (ethylene oxide) (PEO) and poly(styrene‐co‐sodium sulfonated styrene) (SPS) blends has been examined as a function of copolymer composition. The mixtures show complex coacervation in dilute benzene/methanol (9/1, v/v) solution. The presence of intermolecular interactions between PEO and SPS in solution is verified by viscometry. Interaction between PEO and SPS in the solid state was supported by small‐angle x‐ray scattering; however, binary blends containing low PEO content show high miscibility, whereas the blends with high PEO content show phase separation.
Studies of structure formation in grafting of polyacrylonitrile to polycaproamide fibers
Authors: Bogoeva‐Catseva G. , Pimonenko N. Yu. , Gabrielyan G. A. , Fazlyev F. A. , Gal'Braikh L. S. 
Published: April 2003

AbstractThe relationship between the basic structure parameters of a polycaproamide (PCA) substrate and the structure of grafted polyacrylonitrile (PAN) was studied. The influence of the total degree of crystallinity of the PCA fiber, its crystal modification, and the orientation of crystallites on the PAN structure in the copolymer were analyzed. The structure of PCA‐PAN graft copolymers was studied by infrared spectroscopy (dichroism and ATR), X‐ray structure analysis, nuclear magnetic resonance, and scanning electron microscopy. The development of an oriented isotactic structure was found in PAN grafted to a PCA substrate having a bigh degree of orientation. The type of crystal modification of PCA does not affect the structure formation process in PAN. The oriented structures in PAN arise directly in the course of synthesis rather than on the subsequent rearrangement of the molecular chains under the action of orientation drawing. In contrast to earlier findings, our studies indicate that synthesis under the conditions specified increases the degree of crystallinity of PCA and crystallite size. The grafted PAN chains are presumed to grow epitaxially under the influence of PCA crystallites.
Effect of diblock copolymers on dynamic mechanical properties of polyethylene/polystyrene blends
Authors: Brahimi B. , Ait‐Kadi A. , Ajji A. , Fayt R. 
Published: April 2003

AbstractA systematic investigation of the dynamic mechanical properties of high‐density polyethylene (HDPE)/high‐impact polystyrene (HIPS)/copolymer blends was carried out. Blends of 80/20 weight percent of HDPE/HIPS were prepared in the melt state at 180°C in a batch mixer. Synthesized pure diblock (H77) and tapered diblock (H35) copolymers of hydrogenated polybutadiene (HPB) and polystyrene (PS) were added at different concentrations (1, 3, and 5 wt %), and the dynamic mechanical properties were investigated. The results show that: (1) both the tapered and the pure diblock copolymers enhance the phase dispersion and the interphase interactions; (2) structure and molecular weight are both important parameters in the molecular design of copolymers; (3) important effects occur when only small amounts of copolymer are added (up to the interface saturation concentration SC); (4) a micellar structure formation is possible when the copolymer is in excess in the blend; (5) the effect of the copolymer structure on the SC and the critical micellar concentration (CMC) is more pronounced than the effect of molecular weight. These concentrations are found to be lower for the tapered diblock copolymer. The analysis of the dynamic mechanical thermal analysis (DMTA) results obtained for the 20/80 HDPE/HIPS blend leads to the conclusion that the copolymers also enhance the interactions between heterogeneous phases. Similar conclusions based on electron microscopy were reported in the literature. DMTA shows great potential to relate macroscopic observations to the state of a copolymer in an immiscible blend.
Interaction of CO2 gas with silicone elastomer at high ambient pressures
Authors: Briscoe B. J. , Zakaria S. 
Published: April 2003

AbstractInteraction of high‐pressure CO2 gas with a silicone elastomer, and to a lesser extent, with a nitrile rubber and a PTFE have been investigated. Sorptive dilations of the polymers were measured with the help of custom‐made piezoelectric ultrasonic transducers under gas pressures of up to ca. 22 MPa at 42°C. The gas mass sorption was determined by a vibrating reed probe. For the silicone elastomer system the dilation isotherm mimics the sorption isotherm. The partial molar volume (PMV) of the absorbed CO2 gas in the silicone elastomer has been computed. A significant drop in the PMV value is observed when the CO2 gas becomes supercritical. In the transition region, the transmission of ultrasonic signals through the specimen indicated the formation of discrete small (estimated as about 60 μm in diameter) high density zones of CO2 in the rubber matrix. The plasticization effects of the absorbed high pressure CO2 gas have been identified from the interpretation of the changes in the acoustic longitudinal modulus obtained from ultrasonic transmission measurements. The effects of rapid gas decompression on the structural integrity of the various polymers have also been determined. Significant inflation of certain specimens occur toward the latter stages of the decompression cycle. The initiation and development of internal cracks or bubbles was followed by monitoring the ultrasonic signal attenuation.
The gas permeability and packing density of copolymers of methacryloxypropyltris (trimethylsiloxy) silane and methylmethacrylate
Authors: Gu W. , Chern R. T. , Chen R. Y. S. 
Published: April 2003

AbstractA series of random copolymers of methylmethacrylate and methacryloxypropyltris (trimethylsiloxy) silane were synthesized by free radical polymerization under ultraviolet light. The permeabilities of these copolymers to carbon dioxide, oxygen, and nitrogen were determined and correlated with the packing densities of the polymers. Correlation between the permeability and permselectivity of these copolymers is also addressed.
An NMR study of the electron beam‐induced polymerization of trimethylolpropane triacrylate and trimethylolpropane trimethacrylate
Authors: Harrell J. W. , Choudhury Mubinur , Ahuja Sanjay , Walker William 
Published: April 2003

AbstractElectron beam‐induced polymerization of trimethylolpropane triacrylate (TMPTA) and its methacrylate analog (TMPTMA) was studied using nuclear magnetic resonance (NMR) relaxation time measurements. Free induction decays (FID) of partially polymerized samples consist of a short Gaussian component and a longer component comprised of a distribution of simple exponentials. The relative intensity of the Gaussian component increases with radiation dose. T1 and T1ρ values were measured as a function of temperature and radiation dose. The relaxation is due primarily to methyl group reorientation at low temperatures, ethyl group reorientation at intermediate temperatures, and whole‐molecule reorientation at high temperatures. In both compounds, the T1 and T1ρ values at the high temperature minima increase with increasing dose, and the minima values can be used to estimate the degree of polymerization. The temperature at which the T1ρ minimum occurs increases with dose, suggesting an increase in the glass transition temperature, Tg, with polymerization. The polymerization appears to have very little effect on the low temperature CH3 reorientation in TMPTA. In TMPTMA the polymerization appears to reduce the mobility of the methacrylate methyl groups.
An analytical technique for measuring relative tie‐molecule concentration in polyethylene
Authors: Lustiger A. , Ishikawa N. 
Published: April 2003

AbstractWhile consideration of the crystalline domains have long dominated research in understanding the properties of semicrystalline polymers, a satisfactory understanding of crack growth in these materials can only be realized by developing corresponding analytical tools to characterize the amorphous region. Since slow stable cracks in these materials preferentially form between crystalline lamellae, the role of tie molecules—the amorphous chains that bridge crystalline lamellae—are particularly important in this regard. Unfortunately, there is no method readily available for quantitative assessment of tie molecules. Through deformation and subsequent chlorination of polyethylene films, it is demonstrated that infrared dichroism can be used to determine relative tie‐molecule concentration. Using this technique, one can a priori predict which resin in a series having comparable densities but widely varying molecular weights or comonomer distributions exhibits better crack resistance.
Thermoacoustic measurements during cure of epoxy resin at room temperature
Authors: Yoon Hyoung No , Yoon Chang No , Kim Ho Chul 
Published: April 2003

AbstractDynamic thermoacoustic measurements were used to observe the curing of epoxy resin. Measurements were made at the modulation frequency (20 Hz) as a function of time. A two‐step increase of the thermoacoustic signal output was notable and could be explained in terms of the transitions liquid → rubber → glass.
The reaction of phenylpropylsilsesquioxane in the fiber spinning regime
Authors: Ishida H. , Shick R. , Hurwitz F. 
Published: April 2003

AbstractA potential ceramic precursor, a phenylpropylsilsesquioxane co‐oligomer from Petrarch Systems (Petpps), was studied under conditions where fiber spinning is performed. The reaction kinetics of residual silanols of Petpps are studied using Fourier transform infrared spectroscopy in the temperature range 100–150°C. The activation energy and the reaction order of the silanol condensation reaction in the molten Petpps are determined. A combination of gel permeation chromatography, liquid chromatography, and nuclear magnetic resonance spectroscopy is used to study the possibility of copolymerization between the phenyl and propyl silane moieties.
Miscibility behavior and reequilibration of binary poly(amic acid) mixtures
Authors: Ree M. , Yoon D. Y. , Volksen W. 
Published: April 2003

AbstractFive poly (amic acid) solutions based on PMDA‐PDA, PMDA‐ODA, PMDA‐6F, ODPA‐ODA, and 6FDA‐ODA were prepared in N‐methylpyrrolidone at a polymer concentration of ca. 10 wt %. From these five poly (amic acid) solutions, six different binary blends were prepared: PMDA‐PDA/PMDA‐ODA, PMDA‐PDA/PMDA‐6F, PMDA‐ODA/6FDA‐ODA, PMDA‐ODA/ODPA‐ODA, PMDA‐PDA/ODPA‐ODA, and PMDA‐PDA/6FDA‐ODA. These blends were then characterized with respect to miscibility in the ternary state (polyamic acid‐1/polyamic acid‐2/N‐methylpyrrolidone), the condensed state (ca. 70 wt % polymer), and the fully imidized state. All blends except for PMDA‐PDA/PMDA‐6F yielded homogeneous mixtures in the ternary solution of 10 wt % polymer concentration. The PMDA‐PDA/PMDA‐6F mixture eventually became homogeneous after 10 days of mixing at room temperature. Upon solvent evaporation (condensed state) and full cure (imidized state) two blends incorporating ODPA‐ODA as one of the components exhibited apparent miscibility as evidenced by optical microscopy. The remaining blends exhibited large‐scale phase separation upon solvent evaporation with no significant differences in the overall morphology between the condensed and imidized state. However, as in the case of the PMDA‐PDA/PMDA‐6F ternary system, the morphology in the condensed and imidized state was strongly dependent on the mixing time of the precursor poly(amic acid) components; the phase‐separated domain size decreased with increasing mixing time, eventually leading to complete miscibility. These results are discussed with respect to the proposed “polymer‐monomer” reequilibration reaction as well as its implications with respect to the preparation of polyimide molecular composites.
Surface orientation of a liquid‐crystalline polymer studied by polarized reflection spectroscopy
Authors: Kaito Akira , Nakayama Kazuo , Kyotani Mutsumasa 
Published: April 2003

AbstractThe polarized reflection spectrum was used to evaluate the surface orientation of extruded sheets of liquid‐crystalline copolyester consisting of 73 mol % 4‐hydroxybenzoic acid units and 27 mol % 2‐hydroxy‐6‐naphthoic acid units. The anisotropy of absorption index was evaluated from the specular reflectance using the Fresnel equation and the Kramers‐Kronig relation. An intense absorption and observed in the ultraviolet region was assigned to the π* ←π transitions of the constituent monomeric units. The observed spectra of the liquidcrystalline polymer were successfully interpreted by use of the spectroscopic data on the monomers. The transition moment directions of the monomeric units were calculated by molecular orbital calculations within the framework of the CNDO/S‐Cl approximation. The Surface orientation functions obtained from polarized reflection spectra were compared with the crystal orientation functions in the bulk, which were obtained from the azimuthal intensity distribution of wide‐angle x‐ray diffraction. The orientation behaviour at the surface of the liquid‐crystalline polymer was shown to be equivalent to the orientation behaviour in the bulk at higher draw‐down ratio.