bluuebunny/crossref_metadata_2025 huggingface dataset:
A dual‐mode interpretation of nuclear spin relaxation for 13CO2 sorbed in polystyrene
Authors: Bandis A. , Cauley B. J. , Inglefield C. E. , Wen W.‐Y. , Inglefield P. T. , Jones A. A. , Melc'Uk A.
Published: April 2003

Recently we presented a dual‐mode interpretation of the nuclear spin relaxation for 13CO2 sorbed in polycarbonate [E. J. Cain, W.‐Y. Wen, A. A. Jones, P. T. Inglefield, B. J. Cauley, and J. T. Bendler, Journal of Polymer Science, Part B, Polymer Physics, Vol. 29, p. 1009 (1991)]. We have made similar investigation on spin relaxation for 13CO2 sorbed in polystyrene and are presenting the results in this report. 13C spin‐lattice relaxation, spin‐spin relaxation, and nuclear Overhauser enhancements (NOE) are reported for 13CO2 sorbed in glassy polystyrene. These spin relaxation parameters were determined as a function of temperature and Larmor frequency. A quantitative interpretation is based on a two‐site, rapid exchange model, which is consistent with the NMR result. Gas molecules in the dissolved site have rotational, collisional, and translational dynamics typical of low molecular weight liquids. Sorbed molecules in the Langmuir site have much slower rotational and translational motions. The activation energy for motions in the dissolved site is about 7.5 KJ/mol, while that for the Langmuir site is about 15.5 KJ/mol. The translational diffusion constants derived from the NMR data range from 10−7 to 10−9 cm2/s and are consistent with the apparent diffusion constant from the permeability measurements of 4.9 × 10−8cm2/s at 35°C. A relation between the permeability value and the NMR values is available from a theoretical description of the dual‐mode model in terms of a random walk on a lattice containing two sites. As a modification of our previous lattice model (E. J. Cain et al., Journal of Polymer Science, Part B, Polymer Physics, Vol. 29, p. 1009 (1991)), the temperature dependence of the fraction of Langmuir sites in the lattice is taken into account. Parameter values characterizing the motion of CO2 in polystyrene are found to be similar to the corresponding ones in polycarbonate. © 1993 John Wiley & Sons, Inc.
The response of microstructure to processing in a series of poly(siloxaneimide) copolymers
Authors: Samseth Jon , Spontak Richard J. , Mortensen Kell
Published: April 2003

Poly(siloxaneimide) (PSI) segmented copolymers exhibit organized microdomains if the blocks are sufficiently incompatible. As with neat diblock and triblock copolymers, the processing route employed to prepare films of PSI materials is expected to influence the dimensions and/or morphology of the resultant microstructure. In this work, small‐angle neutron scattering (SANS) is utilized to characterize the disordered microstructure found in films of a series of PSI copolymers which are subjected to solvent casting and various thermal treatments. Microstructural dimensions such as the periodicity and correlation length are deduced from the Teubner‐Strey (TS) model for disordered microemulsions. The scattering intensity of each copolymer up to q = 5.0 nm−1, where q is the scattering vector, is found to scale as q−2.8+−0.1. Results indicate that processing the materials as cast films or as melt‐pressed films allowed to cool slowly has a small, but discernible, effect on microstructural characteristics. SANS profiles of films quenched from elevated temperatures reveal a clear transition in microdomain periodicity, which correlates well with the glass transition temperature of the imide microphase in these and other materials of similar chemical structure. © 1993 John Wiley & Sons, Inc.
Structure and properties of semicrystalline polymers via high‐frequency acoustic and x‐ray measurements. I. Ferroelectric P(VDF/TrFE) copolymer
Authors: Krüger J. K. , Prechtl M. , Wittmann J. C. , Meyer S. , Legrand J. F. , D'Asseza G.
Published: April 2003

Acoustic, opto‐acoustic, and x‐ray investigations have been performed in order to study the influence of irradiation, electrical poling, and mechanical orientation on the morphology of ferroelectric random copolymers of vinylidene fluoride and trifluorethylene {P[VDF/TrFE] (70/30)}. The influences of these different treatments on the molecular orientation distribution of the amorphous and crystalline phases are discussed, as well as their influences on the crystallinity of the material. The elastic stiffness and the related viscosity tensors of P[VDF/TrFE] (70/30), the elastic stiffness modulus of the amorphous matrix, and the hierarchy of stiffness constants of the crystalline state have been determined. © 1993 John Wiley & Sons, Inc.
Segmental orientation in aromatic polyesters by solid‐state nuclear magnetic resonance and modeling
Authors: Rutledge G. C. , Ward I. M.
Published: April 2003

Proton spin‐spin relaxation measurements and the corresponding second moments 〈ΔH2〉 of broad line spectra are reported for powder samples of homopolyesters of hydroxybenzoic acid (HBA) and hydroxynaphthoic acid (HNA) and for oriented tape samples of HIQ‐35, a terpolyester composed of HBA, isophthalic acid, and hydroquinone. These are reviewed in relation to previous results reported for related copolyesters of HBA and HNA. In particular, the values of 〈ΔH2〉 for isotropic samples were predominantly composition dependent and of little practical value for studies of detailed molecular structure. Orientation‐dependent second‐moment anisotropies, on the other hand, provide indirect insight into molecular conformation and orientation through comparison with results from detailed molecular models. The orientations of monomers are well described by the distribution function proposed by Bower; a quantitatively accurate description of the orientation distribution in cylindrically symmetric geometries requires only the Legendre polynomial coefficient 〈P2〉. Modeling results based on rotational isomeric state theory for chain segments of finite length and high degrees of orientation successfully reproduce the degrees of anisotropy observed in 〈ΔH2〉 for both HBA/HNA and HIQ polymers. The model provides a link between measures of orientation obtained at different molecular scales by mechanical analysis, wide‐angle x‐ray diffraction, and nuclear magnetic resonance spectroscopy. © 1993 John Wiley & Sons, Inc.
Poly(N‐n‐butylitaconimide). Preparation and characterization
Authors: Matsumoto Akikazu , Umehara Sachiyo , Watanabe Hiroyuki , Otsu Takayuki
Published: April 2003

Poly(N‐n‐butylitaconimide) was prepared by radical polymerization in benzene and in bulk at 60°C and was subsequently fractionated at 30°C with benzene and methanol as solvent and nonsolvent, respectively. Relationships between molecular weight and intrinsic viscosity (Mark‐Houwink‐Sakurada equations) in tetrahydrofuran, benzene, and toluene at 30°C are established. From the Burchard‐Stockmayer‐Fixman plot, the characteristic ratio of this polymer is determined, and local chain conformation is discussed in relation to the termination process in radical polymerization. © 1993 John Wiley & Sons, Inc.
Gas sorption and diffusion in hydrogen‐bonded polymers. I. Vinyl alcohol/vinyl butyral copolymers
Authors: Reimers M. J. , Cibulsky M. J. , Barbari T. A.
Published: April 2003

A series of vinyl alcohol/vinyl butyral copolymers was examined to assess the effect of internal hydrogen bonding on gas sorption and diffusion. Sorption and permeation measurements for carbon dioxide and methane were performed on four vinyl alcohol/vinyl butyral copolymers. Upon comparing the various data, it was found that hydrogen‐bonded copolymers exhibit a much wider variation in diffusion coefficient than non‐hydrogen‐bonded copolymers. The fractional free volumes of the studied copolymers were considerably lower than expected based on values of the diffusion coefficient. This may be due to the fact that predicted occupied volumes are too large and that the effect of internal hydrogen bonding is not accounted for properly. Using a relationship between infrared spectral shift and hydrogen‐bond length, fractional free volumes in the hydrogen bonded copolymers were correlated with the interatomic spacing associated with the hydrogen bond. This implies that the average length of a hydrogen bond can be used as a measure of chain packing in hydrogen‐bonded polymers. © 1993 John Wiley & Sons, Inc.
The effect of N2O4 on the crystalline structure of cellulose
Authors: Gert E. V. , Torgashov V. I. , Shishonok M. V. , Sinyak S. I. , Kaputskii F. N.
Published: April 2003

Depending on reaction conditions, the system cellulose–N2O4 may give two different unstable crystalline compounds, one being an ester (cellulose trinitrite), the second, an adduct of cellulose and HNO3 (the Knecht compound). For these compounds, mechanisms of the formation of the crystalline phase as a result of topochemical reaction and self‐organization are discussed. The different characteristics of structural transformations of the fiber under nitrosation and nitration are noted. The existence of polymorphic forms of the Knecht compound is suggested. These labile nitrogen‐containing compounds make possible the regeneration of cellulose in its various modifications (cellulose I, II, IV, or amorphous cellulose) from the cellulose–N2O4 system. The formation of unstable compounds and their ability to crystallize in the reaction medium allows the passage from amorphous cellulose to its crystalline modifications II or IV under mild conditions. The causes of decrystallization of cellulose by N2O4 are established. © 1993 John Wiley & Sons, Inc.
Anomalous freezing point depression of solvents in a swollen homogeneous rubber network
Authors: Grobler J. H. A. , McGill W. J.
Published: April 2003

The freezing point depression of a solvent, imbibed by crosslinked polyisoprene networks, was studied. It is argued that in a swollen vulcanizate, polymer chains subdivide the solvent, creating zones too small for nucleation on cooling to occur at the normal freezing point of the solvent. The freezing point of the solvent is identified with the temperature at which nuclei can form in the swollen network. A linear relationship between freezing point and the volume fraction of rubber in the swollen gel is predicted for a uniformly crosslinked network. Such a relationship is shown to hold for gamma‐irradiated polyisoprene, but not for peroxide‐cured samples, where deviations from linearity are interpreted as indicative of nonuniformity in the network. © 1993 John Wiley & Sons, Inc.
Scattering properties, stability analysis, and phase separation of polyelectrolyte mixtures
Authors: Benmouna M. , Aziz S. , Vilgis T. A.
Published: April 2003

The conditions of stability for weakly charged polyelectrolyte mixtures are analyzed from a scattering theory developed previously. In the thermodynamic limit of zero wave vector q = 0, it is found that electrostatic interaction induces a compatibility enhancement which is discussed for various cases of charge distributions. The condition of microphase separation transition at the wave vector for which the scattering is a maximum is also discussed. © 1993 John Wiley & Sons, Inc.
Correlation between chain segment and ion mobility in an epoxy resin system. A free volume analysis
Authors: Simpson Joycelyn O. , Bidstrup Sue Ann
Published: April 2003

Steady shear viscosity and ionic conductivity have been measured for nine commercial diglycidyl ether of bisphenol‐A (DGEBA) epoxy resins with molecular weights ranging from 340 to 14,200. The temperature dependence of viscosity and ionic conductivity was modeled using free volume viscosity and ionic conductivity relationships, which correlate the fractional free volume required for polymer chain segment motion (B) and the fractional free volume required for ion motion (B′) with polymer structure. The fractional free volume required for polymer chain segment mobility was observed to increase systematically with the molecular weight of the resins. The fractional free volume required for ion mobility did not vary for the resin series. A stoichiometric mixture of a low molecular weight DGEBA resin and a 4,4′‐diaminodiphenyl sulfone cross‐linker was partially polymerized to extents of reaction ranging from 0% to 49%. The fractional free volume required for polymer segment mobility for these partially polymerized samples was consistent with results for the neat resins. © 1993 John Wiley & Sons, Inc.
Reactive rubbers as toughening agents for thermoset polyester resins. Molecular analysis by FTIR and fracture behavior of the resulting blends
Authors: Martuscelli E. , Musto P. , Ragosta G. , Scarinzi G. , Bertotti E.
Published: April 2003

A reactive rubber obtained by isocyanation of hydroxyl‐terminated polybutadiene was used as toughening agent for an unsaturated polyester resin. Both the isocyanation and the successive reaction between the modified rubber and the polyester were investigated by Fourier‐transform infrared spectroscopy (FTIR). Fracture measurements at high and low strain rate were carried out on the cured materials to test their toughness. The failure mechanisms were established by morphological analysis of fractured surfaces, performed by scanning electron microscopy. © 1993 John Wiley & Sons, Inc.
Haze and extinction for a composite medium with quasitransparent optically stratified particles
Authors: Alexander‐Katz Roberto
Published: April 2003

Haze and extinction are studied for coreshell particles in a matrix near transparency. It is shown that, close to transparency, a core‐shell particle behaves optically differently from a nonstructured particle due to the presence of a minimum in the scattering pattern for any particle size. For small particles or domains (<λ/2), this difference is more pronounced. In particular, compositional effects on haze and extinction are studied. It is found that under certain conditions, for the same global composition, strongly optically stratified par‐ticles give lower haze than the homogeneously distributed one by one to two orders of magnitude. The same occurs with the extinction coefficient, however the global composition at which this becomes important differs from that corresponding to a minimum haze. The origin of this difference is discussed in the light of the structure of the scattering pattern in each case. This implies that, for a transparent polymer blend with stratified domains, the minimum haze, maximum transmission and the theoretically perfect matching com‐positions, are all different. Finally, it is shown that, for small highly optically inhomogeneous core‐shell particles, haze goes through an inflection point with increasing particle size, in contrast with the usual monotonically increasing, singly concave, behavior. © 1993 John Wiley & Sons, Inc.
Permeation of high‐pressure gases in poly(ethylene‐co‐vinyl acetate)
Authors: Naito Yasutoshi , Bourbon Dominique , Terada Katsuhiko , Kamiya Yoshinori
Published: April 2003

A previously proposed theoretical treatment to elucidate the pressure dependence of gas permeability is improved in order to apply it to polymer‐gas systems in which gas dissolution follows the Flory‐Huggins equation. Permeation rates of N2, CH4, and CO2 in poly(ethylene‐co‐vinyl acetate) are measured in the pressure range below 90 atm at 10–40°C, and the effect of pressure on permeability is found for each gas. The data are analyzed using the improved method to estimate the contributions of concentration and hydrostatic pressure to the pressure dependence of permeability. The concentration effect decreases with increasing temperature, whereas the hydrostatic‐pressure effect is almost independent of temperature. Crystallinity dependence of the concentration effect is discussed in connection with high‐pressure permeation data of other semicrystalline polymers reported elsewhere. © 1993 John Wiley & Sons, Inc.
NMR study of the structure of poly(N‐benzoyl‐8‐octanelactam)
Authors: Kříž Jaroslav , Puffr Rudolf
Published: April 2003

The structure of a polymer prepared by the polymerization of N‐benzoyl‐8‐octanelactam initiated with benzoic acid was studied by 1H and 13C NMR, using S‐INEPT, COSY, COLOC, and ROSEY methods, with the aid of model oligomers. Beside the expected N‐benzoylated segments, the polymer also contained deacylated segments and about 50% of branching units. The polymer can be characterized as a statistical, highly branched copolymer of N‐benzoyl‐8‐octanelactam and 8‐octanelactam. © 1993 John Wiley & Sons, Inc.
Radiation‐induced crosslinking of polyethylene in the presence of acetylene: A gel fraction, UV‐visible, and ESR spectroscopy study
Authors: Jones R. A. , Salmon G. A. , Ward I. M.
Published: April 2003

Electron‐spin resonance (ESR) and altraviolet (UV) visible spectroscopic evidence has been found for the formation of diene, triene and tetraene, following the irradiation of polyethylene in the presence of acetylene. The polyenes are formed by a mechanism which is different from that observed under vacuum or with inert gas saturation. The sum of the G (polyene) values obtained by UV spectroscopy is almost half that of initial radical formation. It is concluded that polyene bridges, predominantly diene, form crosslinks between radical pairs. G (X) values determined from gel fraction data, using Saito‐Kang‐Dole theory, are found to be greatly in error and misrepresentative of crosslink changes. © 1993 John Wiley & Sons, Inc.
Electrical, thermal, and photo properties of poly(phenylene vinylene) precursors: I. Laser‐induced elimination reactions in precursor polymer films
Authors: Torres‐Filho Afranio , Lenz Robert W.
Published: April 2003

The elimination reaction of polyelectrolyte films of poly(phenylene vinylene) precursor polymers into the fully conjugated chain was induced by irradiation with an Ar+ laser emitting at 514.5 nm. The experiments were conducted using as cast precursor polyelec‐trolyte films of both the unsubstituted poly(phenylene vinylene), H‐PPV, and its 2,5‐dimethoxyphenylene derivative, DMEO‐PPV. Precursor polymer films impregnated with an azosulfonic dye, which had a strong absorption at the laser emission wavelength, were also irradiated. The elimination reaction was followed by comparing the elemental analysis and the infrared and visibleultraviolet spectra of the irradiated and nonirradiated areas. With the unsubstituted PPV film no elimination was detected even at power fluence levels up to approximately 350 W/cm‐2, but elimination and conversion to the conjugated polymer could be observed at 10 W/cm‐2 when the dye was present. For DMEO‐PPV the elimination reaction occurred with or without dye impregnation, and similar marking threshold values were measured in both cases. The molecular mechanism used to explain such observations and the possible application in the area of microelectronics are also discussed. © 1993 John Wiley & Sons, Inc.
Gas transport properties of poly(2,2,4,4‐tetramethyl cyclobutane carbonate)
Authors: Aguilar‐Vega M. , Paul D. R.
Published: April 2003

Gas transport properties of semicrystalline films of poly(2,2,4,4‐tetramethyl cyclobutane carbonate) (TMCBPC) were studied. Permeability coefficients for He, O2, N2, CH4, and CO2 at 35°C for pressures between 1 and 20 atm are reported as well as sorption isotherms for N2, CH4, and CO2 at the same conditions. The permeability coefficients for TMCBPC are larger than corresponding values for the aromatic bisphenol‐A polycarbonate (PC) and tetramethyl bisphenol‐A polycarbonate (TMPC), even though the TMCBPC films are semicrystalline. These results are explained on the basis of the larger free volume available for permeation in this polymer. Significant TMCBPC plasticization by CO2 was also observed and this causes typical time‐dependent behavior. The plasticization process starts at very low pressures compared with the behavior of aromatic polycarbonates PC and TMPC. This early onset of plasticization seems to be related also to the larger free volume in the amorphous phase of TMCBPC which favors high gas sorption. The diffusion coefficients for TMCBPC are also larger than those reported for the aromatic polycarbonates PC and TMPC. Ideal gas separation factors were found to follow the usual trend; that is, as permeability increases, the ideal separation factor decreases. © 1993 John Wiley & Sons, Inc.
Anisotropic effects in thermogravimetry of polymeric composites
Authors: Salin I. M. , Seferis J. C.
Published: April 2003

The weight loss of carbon fiber‐reinforced polymeric composites in air has been found to depend on the sample surface characteristics such as fiber orientation with respect to the exposed surfaces. This phenomenon can be attributed to the diffusion of oxygen through the sample and the dependence of diffusion rate on fiber orientation. Recently, an anisotropic degradation methodolgy was proposed, based on the unreactedcore principle, commonly used in catalysis, as extended to account for the anisotropic effects. In this work, these anisotropic diffusion effects were also identified for small thermogravimetric (TGA) samples. Isothermal TGA experiments were performed in air at 310°C using samples weighing 10–163mg. Weight loss was found to be a strong function of fiber orientation. The anisotropic degradation methodology successfully predicted the weight loss of all samples, although some deviation attributed to the sample edge effects was observed. When samples were examined by optical microscopy, a degraded zone was observed on the sample surfaces. The thickness of this layer depended on the type of exposed surface, validating the anisotropic degradation methodology. © 1993 John Wiley & Sons, Inc.
Diffusion as a probe to assess stretching‐induced morphological changes in polyurethane
Authors: Sreenivasan K.
Published: April 2003

An analysis of the diffusion of toluene through polyurethane based on bis (p‐cyclohexyl diisocyanate), poly(tetramethylene glycol) 1000, and 1,4‐butane diol, subjected to varied degrees of elongation by stretching, is presented. The diffusion coefficient is increased by 60% in polymers drawn to 200% and above. Beyond 400% elongation, the diffusion coefficient attained a constant value. Associated changes are observed in the wide‐angle x‐ray diffraction pattern. These diffusion and x‐ray changes are correlated with restructuring of the polymer induced by stretching. © 1993 John Wiley & Sons, Inc.
Melting behavior of drawn polypropylene
Authors: Yan Rong Jiang , Jiang Bingzheng
Published: April 2003

The melting behavior of drawn, compression‐molded isotactic polypropylene has been ex‐amined in terms of the infuence of drawing conditions on the observed properties. Two endothermic peaks were observed on differential scanning calorimetry (DSC) for samples when high draw ratios and high heating rates were used during DSC tests. The peak at lower temperature is influenced by draw ratio, temperature, and rate, and exhibits a strong superheating effect. The species associated with this peak can partially recrystallize into another species associated with the peak at higher temprature during DSC measurements. The position of the peak at higher temperature depends only on draw ratio. It is proposed that the doubel‐melting peaks at lower and higher temperature result from extremely thin quasi‐amorphous or crystalline layers between microfibrils and the lamellar crystals within microfibrils, repectively. © 1993 John Wiley & Sons, Inc.
Thermal expansion of irradiated polyethylene from 10 to 340 K
Authors: Jayanna H. S. , Subramanyam S. V.
Published: April 2003

The coefficient of thermal expansion of γ‐irradiated polyethylene has been measured from 10 to 340 K by using the three‐terminal capacitance technique. The samples are irradiated to 500 Mrad in steps of 100 Mrad in air at room temperature with γ‐rays from a Co60 source at a dose rate of 0.3 Mrad/h. The crystallinity of the sample is measured by x‐ray diffraction. The crystallinity is found to decrease with radiation dose. The thermal expansion coefficient is found to be constant with radiation doses from 10 to 110 K and decreases with doses from 110 to 340 K. © Wiley & Sons, Inc.
Sorption of carbon dioxide in fluorinated poyimides
Authors: Tanaka Kazuhiro , Kita Hidetoshi , Okamoto Ken‐Ichi
Published: April 2003

Sorption isotherms of CO2 for ten fluorinated polyimides measured at 35°C and up to about 25 atm are analyzed according to the dual‐mode sorption model. Sorption properties for these polyimides are compared with those for other glassy Polymers including unfluorinated polyimides. The glassy polymers with higher glass transition temperatures Tg tend to show greater CO2 sorption. Introduction of a C (CF3)2 linkage into the repeat unit of the main chain increases the sorption by 20–80%. For glassy polymers, including the fluorinated and unfluorinated polyimides, the Langmuir affinity constant b and Henry's law solubility constant kD are correlated with the content of functional (carbonyl or sulfonyl) groups [FG], and composite parameter reflecting the magnitude of both [FG] and free‐space fraction VF, respectively, with some exceptions. The Langmuir capacity constant C′H is correlated with Tg, but there are two correlation lines; one for unfluorinated polyimides and a different one for other glassy polymers including fluorinated polyimides. The slope of the former group is smaller probably because of smaller differences in thermal probably because of smaller differences in thermal expansion coefficients in rubbery and glassy states. Most fluorinated polyimides show greater solubility of CO2 than unfluorinated polyimides and other glassy polymers, because of their larger C′H and kD. © 1993 John Wiley & Sons, Inc.
Crystal structure of poly(p‐benzamide)
Authors: Takahashi Yasuhiro , Ozaki Yusuke , Takase Minoru , Krigbaum W. R.
Published: April 2003

Redetermination of the crystal structure of poly(p‐benzamide) was made by using newly collected intensity data. The molecular conformation is TCTC, where the internal rotation angles about the NC bond of the amide group and about the virtual bond of N‐phenyl‐C are T (trans) and C (cis) conformations, respectively. Two molecular chains pass through a rectangular unit cell with dimension, a = 7.75 Å, b = 5.30 Å, c (fiber axis) = 12.87 Å, and the space group, P212121‐D. The reflection observed at the spacing of 010 may be attributed to the reflection due to another crystal polymorph or the diffuse scattering due to disorder. © 1993 John Wiley & Sons, Inc.
Cellulose‐based fibers from liquid–crystalline solutions. II. Processing and morphology of acetate/butyrate esters
Authors: Davé Vipul , Glasser Wolfgang G. , Wilkes Garth L.
Published: April 2003

Fibers were spun from isotropic and anisotropic dimethylacetamide solutions of cellulose esters. Take‐up speeds of the dry jet/wet spinning process varied. Water served as the coagulant. The mechanical properties of the fibers increased as spinning progressed from the isotropic to the anisotropic state of the solution. A trade‐off in solubility and fiber properties was noted as the butyryl acetyl ratio decreased. Whereas high butyryl content enhances both overall solubility and the formation of liquid–crystalline solutions at lower concentration, it results in lower fiber modulus and strength. Morphology of the fibers depended on the coagulation rate which was influenced by the concentration of the sppinning solution. The level of orientation and crystallinity of the fibers increased somewhat when they were spun from liquid‐crystalline solutions. © 1993 John Wiley & Sons, Inc.
Fluorescence study of thermotropic liquid‐crystalline polyesters
Authors: Hashimoto Hideyuki , Hasegawa Masatoshi , Horie Kazuyuki , Yamashita Takashi , Ushiki Hideharu , Mita Itaru
Published: April 2003

Photoluminescence behavior (polarization, lifetime) related to liquid‐crystal (LC) formation was examined for the thermotropic liquid‐crystalline polyesters poly [(ethylene terephthalate)‐co‐(p‐oxybenzoate)] (PET40/OBA60) (OBA content: 60 mol %) and poly [(ethylene 2,6‐naphthalene dicarboxylate)‐co‐(p‐oxybenzoate)] (PEN50/OBA50) (OBA:50 mol %). The Growth of liquid‐crystalline (LC) phases of PET40/OBA60 proceeded during annealing. even at low temperature (e.g., 138°C) and were promoted by an increase in annealing temperatures Ta in the experimental temperature range 138–260°C. The concentration dependence of fluorescence spectra of PET40/OBA60 in solution suggested that the fluorescences at 325 and 395 nm can be attributed to monomer and ground‐state dimer, respectively. The increase in dimer fluorescence intensity and the decrease in the fluorescence anisotropy ratio r from 0.06 to –0.14 were observed with growth of LC phases. These effects are explained by an increase in the ground‐state dimer population and a slight change in the dimer configuration, respectively.

PEN50/OBA50 showed monomer fluorescence at 395 nm due to naphthalenedicarboxylate segments and excimer fluorescence at 430 nm. The r value for the excimer fluorescence decreased from zero to about −0.14 with growth of the LC phase. Such an extraordinary phenomena, in comparison with the usual excimer fluorescences which occurs through energy migration, could be interpreted as the result of formation of high‐concentration excimer sites induced by chain orientation in LC domains. © 1993 John Wiley & Sons, Inc.
A small‐angle x‐ray scattering study of starch gelatinization in excess and limiting water
Authors: Cameron Ruth E. , Donald Athene M.
Published: April 2003

The architecture of the starch granule, and its subsequent disruption due to the application of heat and water, known as gelatinization, is of wide interest. Small‐angle x‐ray scattering (SAXS) techniques have been used to study gelatinization in limiting and excess water. SAXS allows the absorption of water into the differing regions of the starch granule to be monitored. In excess water, a process of cooperative melting can be seen. In limiting water, the crystalline order melts at a higher temperature. These features have been studied, and observed features of the gelatinization related to those known from other techniques. © 1993 John Wiley & Sons, Inc.
Nuclear spin relaxation dynamics of 13CO2 sorbed in polyisobutene rubber
Authors: Dong Z. P. , Cauley B. J. , Bandis A. , Mou C. W. , Inglefield C. E. , Jones A. A. , Inglefield P. T. , Wen W.‐Y.
Published: April 2003

Recently we presented the dynamics of 13CO2 molecules sorbed in silicone rubber (PDMS) ascertained from spin relaxation experiments. Results of a similar investigation for 13CO2 sorbed in polyisobutene (PIB) are presented in this report. The spin‐lattice and spin‐spin relaxation times as well as nuclear Overhauser enhancements (NOE) were determined as a function of temperature and Larmor frequency. The relaxation mechanisms found to be important for 13CO2/PIB system are intermolecular dipole‐dipole relaxation and chemical shift anisotropy with a minor contribution from spin rotation relaxation. We have determined the parameters which characterize correlation times for 13CO2 collisional motion, rotational motion, and translational motions in the PIB. The self‐diffusion coefficient of 5.15 × 10−8 cm2/s obtained from the nuclear magnetic resonance (NMR) data is close to the literature value of the mutual diffusion coefficient of CO2 in PIB at 300 K obtained from permeability measurements. In contrast to the case of CO2/PDMS in which a broad distribution (characterized by a fractional exponential correlation function of the Williams‐Watts type with α = 0.58) is observed, a sharp distribution with a fractional exponent, α, of 0.99 is found for the CO2/PIB system. Instead of assuming an Arrhenius type temperature dependence, we used a Williams‐Landel‐Ferry type temperature dependence and found it to be better suited to describe the behavior of this system. PIB is a densely packed “strong” chain polymer which responds gradually to the temperature variation and gas sorption. In contrast PDMS is a relatively loosely packed “fragile” polymer with a propensity to exhibit rapid dynamic responses to the temperature change and gas sorption. © 1993 John Wiley & Sons, Inc.
Electron and photon emission accompanying deformation and fracture of polycarbonate
Authors: Zimmerman K. A. , Langford S. C. , Dickinson J. T. , Dion R. P.
Published: April 2003

Electron and photon emission accompanying tensile loading and failure of polycarbonate show weak emissions during the onset of neck formation and intense emissions during the fracture event itself. These results are interpreted in terms of formation of active species by bond breaking followed by emission driven by energy released by recombination. Fast time scale measurements during fracture show that intense electron and photon emission typically begins about 50 μs prior to the completion of fracture and is most intense at the completion of fracture. The gradual onset reflects the final stages of growth of the failure‐initiating defect. Defect growth was monitored by measuring the intensity of a light beam transmitted through the gauge length of the sample; the transmission is sensitive to scattering by surface and bulk defects. A marked decrease in transmission begins some tens of ms prior to fracture due to scattering from the fracture‐initiating defect. These measurements allow accurate correlations of defect growth with the onset of the electron and photon signals. © 1993 John Wiley & Sons, Inc.
Theoretical prediction of maxima in association constants for complex formation between flavin mononucleotide and indoleacetate in the presence of polyelectrolytes
Authors: Ishiwatari Tsutomu , Itoh Fumiko , Ohbayashi Mie , Mitsuishi Masaru
Published: April 2003

The effects of ionene polymers (6,3‐ionene, 6,6‐ionene, 6,8‐ionene, and 6,12‐ionene) with various charge densities upon association constants K for the complexation between flavin mononucleotide and indoleacetate have been studied. Except for 6,12‐ionene, K increases with increasing polymer concentration then passes through a maximum, and declines at high polymer concentrations. The value of the maximum K increases in the order 6,8‐ionene > 6,3‐ionene > 6,6‐ionene. In contrast, 6,12‐ionene gives only a monotone increasing curve with increasing polymer concentration. These curves are analyzed using the theory of the partition coefficient proposed in the previous paper. The types of the curves that the theory predicts are classified in greater detail than in the previous paper, and examples are given. © 1993 John Wiley & Sons, Inc.
Coionomeric mixtures of polyhydroxyethers and ethylene methacrylic acid copolymers. II. Compatibilizers for blends of polybutylene terephthalate and ethylene butyl acrylate copolymers
Authors: Mascia L. , Moggi A.
Published: April 2003

Blends of polybutylene terephthalate and ethylene butyl acrylate copolymers were studied at two extreme concentration levels so that each polymer would form, in turn, a particulate dispersed phase. The blends contained 5% by weight of a coionomeric compatibilizer, which was produced from 1 : 1 mixtures of a polyhydroxy ether of bisphenol A and the sodium ionomer of an ethylene methacrylic acid copolymer, using sodium ethoxide to enhance the formation of ionomeric clusters together with an A‐B‐A block oligomer to assist the solubilization of the two ionomeric polymers. In all cases the addition of the coionomeric compatibilizer mixture to the blend was found to decrease the size of the dispersed particles with a concomitant reduction in the interphase gap. It was also observed that the dispersed polymer exhibited a lower level of crystallinity and a slightly lower melting point than when it was present as a matrix, particularly for the case of the ethylene butylacrylate copolymer. The inability of the compatibilizer to completely prevent the formation of an interfacial gap which did not allow the blends to achieve more substantial improvements in mechanical properties, was attributed to the vast difference in crystallization temperature between the two polymers. © 1993 John Wiley & Sons, Inc.
Partial molar volume of small molecules in glassy polymers
Authors: Kirchheim R.
Published: April 2003

The sorption of atoms or molecules in glassy polymers is assumed to occur within a variety of sites belonging to the intermolecular volume and providing different space for the dissolved molecules. If the size of the small molecule is larger than the size of the site, the glassy polymer is elastically distorted during sorption of the solute molecules. Minimizing the total free energy yields the result that large sites are occupied first, giving rise to small volume changes only. By increasing the solute concentration, smaller sites have to be occupied as well and the corresponding volume changes are larger. Thus the molecules can be considered to act as probes for the intermolecular space. A quantitative analysis and comparison with experimental results provides information on the intermolecular space in a glassy polymer. Compared to the dual‐sorption model, the model of this study is able to explain the nonlinear relationship between volume change of the polymer and the partial pressure of the solute. At large solute concentrations, swelling of the glassy polymer or its transformation into the rubbery state occurs, which gives rise to structural changes after desorption. © 1993 John Wiley & Sons, Inc.
Self‐nucleation and enhanced nucleation of polymers. Definition of a convenient calorimetric “efficiency scale” and evaluation of nucleating additives in isotactic polypropylene (α phase)
Authors: Fillon B. , Lotz B. , Thierry A. , Wittmann J. C.
Published: April 2003

A simple, convenient and reliable calorimetric efficiency scale is proposed for the evaluation of nucleating additives for polymers. The scale is based on conventional differential scanning calorimetry cooling runs and makes use of a crystallization range determined in self‐nucleation experiments. It can be correlated with spherulite sizes, and indicates the potential range of improvement of nucleating additives. Typical nucleating agents for isotactic polypropylene are evaluated; at best they rate at 60 to ca. 70% on this efficiency scale. © 1993 John Wiley & Sons, Inc.
Self‐nucleation and recrystallization of polymers. Isotactic polypropylene, β phase: β‐α conversion and β‐α growth transitions
Authors: Fillon B. , Thierry A. , Wittmann J. C. , Lotz B.
Published: April 2003

The mechanisms which, in isotactic polypropylene, create α phase nuclei on partial melting of β phase spherulites are investigated by thermal analysis and optical and electron microscopy. Nuclei concentrations are determined from recrystallization characteristics. α phase nuclei are formed within β spherulites via two different mechanisms: (1) a low temperature formation of latent α phase nuclei (αβ* nuclei) linked with a hitherto unsuspected β to α growth transition at T = T* ∼ 105°C, and (2) a high temperature α phase nucleation process (αβ nuclei), also linked with a similar β to α growth transition at 140°C first reported by Varga et al. The low temperature nucleation mechanism is the more efficient one: it significantly affects the melting of β phase, and results in samples with over 1013 α nuclei · cm−3. © 1993 John Wiley & Sons, Inc.
Electronic transport properties of polyaniline/PVC blends
Authors: Subramaniam C. K. , Kaiser A. B. , Gilberd P. W. , Wessling B.
Published: April 2003

The electrical conductivity and thermoelectric power of polyaniline/PVC blends was measured. Surprisingly, the conductivity of the blends is greater at low temperatures than that of the pure polyaniline sample. The conductivity follows approximately an exp (−T−1/2) law over a considerable range of temperature, with deviations from this law observed at high temperature increases (with positive sign) except at very low temperatures, where negative peaks are observed. Possible models to interpret these observations are mentioned. © 1993 John Wiley & Sons, Inc.
Interaction of slightly cross‐linked gels of poly(diallyldimethylammonium bromide) with sodium dodecyl sulfate. Diffusion of surfactant ions in gel
Authors: Philippova O. E. , Starodoubtzev S. G.
Published: April 2003

The dynamics of the changing microenvironment of the fluorescent probe pyrene in slightly cross‐linked networks of poly(diallyldimethylmmonium bromide) during diffusion of sodium dodecyl sulfate (SDS) in the gel phase has been investigated by fluorescence spectroscopy. Values of the spectral ratio I3/I1 for pyrene monomer included in SDS micelles in the swollen networks fall between the corresponding values for pyrene in water and for pyrene dissolved in SDS micelles in aqueous solution. In the narrow interval of the surfactant concentrations in the gel phase, the formation of pyrene excimers is observed. The values of the critical micelle concentration in the gel phase (ca. 5 × 10−4 to 8 × 10−4 mol/L) are tenfold lower than in aqueous solutions of the surfactant. The effective micellar diffusion coeffecient D in the gel phase increases with increasing swelling of the network. © 1993 John Wiley & Sons, Inc.
Study of free volume and crystallinity in polybithiophene and poly(3‐methylthiophene)
Authors: Nicolau Y. F. , Moser P.
Published: April 2003

Compressed pellets of partly crystalline, chemically synthesized, doped (Cl−and FeCl) polybithiophene (PBTd), poly(3‐methylthiophene) (P3MTd), and their neutral (dedoped) forms (PBTn and P3MTn) were studied by wide‐angle x‐ray diffraction and positron annihilation lifetime spectroscopy. As synthesized, PBTd and P3MTd polymers have a helicalsynconformation they crystallize in the hexagonal system. On dedoping, PBT macromolecules change their helicalsynconformation in a rodlikeanticonformation and crystallize in the orthorhombic or monoclinic system, whereas P3MT macromolecules retain their helicalsynconformation. Chemical doping–dedoping cycles lead to amorphous PBT and P3MT in either doped or dedoped states. The P3MT helical macromolecule behaves like a spiral spring; by doping, it becomes axially compressed. The unit‐cell volume of P3MTd is smaller than that of P3MTn. The positron lifetime spectra for all polymers were resolved, without constraint, into three components. The τ1lifetime is attributed to free‐positron annihilation events, the τ2lifetime to positrons annihilating trapped in voids, and the τ3lifetime to positrons annihilating as o‐Ps trapped in cavities located inside the polymer grains for P3MTn and at the surface of the grains for PBTd, PBTn, and P3MTd. Most positrons annihilate when trapped in voids, both in doped and dedoped PBT and P3MT. The doping apparently increases the concentration of the voids and their mean diameter in P3MT, and probably also in PBT. Cavities anchored in the bulk are produced by dedoping. © 1993 John Wiley & Sons, Inc.
Gas transport properties of polyphenylene ethers
Authors: Aguilar‐Vega M. , Paul D. R.
Published: April 2003

Gas transport properties of the polyphenylene ethers poly(2,6‐dimethyl‐1,4‐phenylene oxide)PDMPO, and poly(2,6‐diphenyl‐1,4‐phenylene oxide), PDPPO, and the thioether poly(1,4‐phenylene sulfide), PPS, have been measured as a function of pressure and temperature. The PPS material and free volume correlations were used to estimate the behavior of the unavailable poly(1,4‐phenylene oxide), PPO. The results show that symmetrical substitution of phenyl groups on the backbone of polyphenylene ether, PDPPO, increases the gas transport properties by one order of magnitude relative to the unsubstituted material, PPO. Symmetrical methyl substitution, PDMPO, however, increase the permeability, apparent diffusion and sorption coefficients even further. The gas transport coefficients correlate with the fractional free volume of the polymers. PDMPO has the largest fractional free volume and gas transport coefficients followed by PDPPO and the PPS. The results show that substitution of phenyl groups, which leads to polymers that have better thermal and oxidative stability than methyl substituted ones, can be a useful means for increasing free volume and gas permeability coefficients. While methyl groups appear to be more effective for the latter, the enhanced chemical stability of phenyl rings may be useful when gas separation membranes are to be used in harsh environments. © 1993 John Wiley & Sons, Inc.
Gas transport properties of polycarbonates and polysulfones with aromatic substitutions on the bisphenol connector group
Authors: Aguilar‐Vega M. , Paul D. R.
Published: April 2003

The effect that substitution of aromatic groups on the bisphenol connector unit of bisphenol‐A based polycarbonate and polysulfone materials has on their gas transport properties was assessed. Replacement of a methyl group by a phenyl ring (bisphenol acetophenone polycarbonate, PC‐AP, and bisphenol acetophenone polysulfone, PSF‐AP) gives a small increase in permeability coefficients with similar or slightly higher selectivity for all gases compared to bisphenol‐A polycarbonate, PC, or polysulfone, PSF. Substitution of two locked phenyl rings (fluorene bisophenol polycarbonate, FBPC, and fluorene bisphenol polysulfone, FBPSF) in place of the methyl groups in the connector unit leads to permeability and solubility coeffcients that are about twice those observed for PC or PSF. Increases in permeability for the polycarbonate and polycarbonate and polysulfone materials with aromatic substitutions are related to their larger fractional free volume. FBPC and FBPSF have the largest fractional free volume and the largest permeability coefficients. Thermal measurements show that the fluorene based polycarbonate and polysulfone materials have the highest thermal and oxidative stability. Such aromatic substitutions can be useful for developing gas separation membranes to be used in harsh thermal or oxidative environments. © 1993 John Wiley & Sons, Inc.
Statistical approach to light scattering from deformed textured heterogeneous polymer materials
Authors: Patlazhan S. A.
Published: April 2003

A statistical theory of light scattering from deformed isotropic and textured heterogeneous polymer materials is formulated. Two types of textured structures are analyzed: assemblies of optically isotropic and anisotropic rods and a spatially anisotropic distribution of isotropic spherical inclusion centers. The small‐angle Hv light‐scattering patterns are calculated. The appearance of scattering from isotropic rods and spheres in deformed materials has been demonstrated. The changes of the Hv scattering patterns as a function of elongation and strucuture parameters are discussed. © 1993 John Wiley & Sons, Inc.
Computer simulation of crystallization kinetics and morphology in fiber‐reinforced thermoplastic composites. I. Two‐dimensional case
Authors: Mehl Nathan A. , Rebenfeld Ludwig
Published: April 2003

A body of experimental evidence suggests that reinforcing fibers influence both the crystallization kinetics and morphology of those composite materials that are based on crystallizable thermoplastics. The absence of an analytical model to predict the effect of fibers on crystallization has hindered data analysis. A new approach, using computer simulation of polymer crystallization, makes it possible to study the influence that reinforcing fibers have on the crystallization kinetics and morphology of semicrystalline polymers. Fibers depress the crystallization rate relative to an unreinforced polymer since they constrain spherulitic growth by an impingement mechanism. On the other hand, reinforcing fibers can also enhance crystallization rate by providing added surface nucleation sites. This work describes a two‐dimensional simplification of the crystallization process that occurs in bulk materials. It is demonstrated that the relative bulk and fiber nucleation densities, in addition to the fiber fraction, fiber diameter, and spherulitic growth rate control the crystallization kinetics and also the spherulitic and transcrystalline morphologies that develop in reinforced thermoplastic composites. © 1993 John Wiley & Sons, Inc.