bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemical modification of poly(substituted‐acetylene): II. Pervaporation of ethanol / water mixture through poly(1‐trimethylsilyl‐1‐propyne) / poly(dimethylsiloxane) graft copolymer membrane
Authors: Nagase Yu , Ishihara Kazuhiko , Matsui Kiyohide 
Published: April 2003

AbstractPoly(1‐trimethylsilyl‐1‐propyne)/poly(dimethylsiloxane) (PTMSP/PDMS) graft copolymer was prepared to evaluate the permeation characteristic at pervaporation of aqueous ethanol solution through the graft copolymer membrane. For the preparation of PTMSP/PDMS graft copolymer, an improved synthetic procedure was released in this paper, which comprised a one‐pot reaction of PTMSP in lithium bis(trimethylsilyl)amide followed by treatment with hexamethylcyclotrisiloxane and trimethylchlorosilane. PDMS content of the graft copolymer was controlled in the range 5–74 mol%. Very tough and thin membranes could be prepared from these copolymers having various PDMS content by the solvent casting method. The permselectivity of the membranes was investigated by pervaporation of ethanol/water mixture at 30°C. Preferential permeation of ethanol was observed for the membranes. It was also found that the selectivity of every copolymer membrane was higher than that of the PTMSP membrane. Moreover, the selectivity depended on the PDMS content of the graft copolymer. The separation factor and permeation rate assumed the maximum values at 12 mol% PDMS content. At the maximum point, 7 wt% aqueous ethanol solution was concentrated to about 70 wt% ethanol solution, and the separation factor and permeation rate were 28.3 and 2.45 × 10−3g · m/m2 · h, respectively. Such a high permselectivity for ethanol might be due to a delicate alteration of membrane structure, which was induced by the introduction of a short PDMS side chain into a PTMSP backbone.
Rate of physical aging of polycarbonate at a constant tensile strain
Authors: Ricco T. , Smith Thor L. 
Published: April 2003

AbstractA study was made of the physical aging of an annealed polycarbonate film at a constant extension of 2.6% at 5 temperatures from 30 to 110°C. During stress relaxation at the constant extension, the storage modulus in tension, E′, was determined by imposing a sinusoidal strain of small amplitude at frequencies up to 25 Hz during an aging period, commonly of 5 h. Plots of log E′ against log f, where f is the frequency, gave parallel straight lines, each at a different aging (elapsed) time te. These lines were superposed by shifts along the abscissa. The obtained shift factors log a varied linearly with log te, the slope being the aging rate μ, a quantity introduced by Struik. The results show that μ is about 1.37 at 30°C and that it increases progressively with the temperature and becomes approximately 2.13 at 110°C. Another measure of the aging rate is the rate of increase of E′ with te, expressed as the percent increase per decade of the aging time. This quantity also increases progressively with the temperature from about 2.6% at 30°C to nearly 3.5% per decade of time at 110°C.
Structure‐property relationships of copolyamides. II. crystal structure of drawn copolyamide films
Authors: Baik Doo Hyun , Jo Won Ho 
Published: April 2003

AbstractThe crystal structures of drawn copolyamides 6/6.6, 6/6.T, 6/6.1, 6/PXD.6, 6/MXD.6, and 6/MXD.I were examined by wide‐angle x‐ray diffraction. Copolyamide 6/6.6, which follows the inclusion model, shows only α‐characteristics at all the comonomer compositions examined (0–33.3 mol%). However, the other copolyamides, which follow either the partial‐inclusion or complete‐exclusion model, show γ‐characteristics more predominantly as the comonomer content increases. The interplanar spacing of the (200) planes, which corresponds to the hydrogen bond distance between antiparallel chains, remain constant, whereas the spacing of the (020) planes corresponding to the distance between hydrogen bonded sheets increases monotonically with increasing the comonomer content. It is also observed that both the crystal perfection index and the crystal thickness decrease as the comonomer content increases.
Ethylene‐propylene copolymerization initiated with solubilized ziegler‐natta macromolecular complexes. II. Characterization of [styrene]‐b‐[ethylene‐co‐propylene] copolymers
Authors: Cansell François , Siove Alain , Belorgey Georges 
Published: April 2003

AbstractCopolymerization of ethylene (E) with propylene (P) initiated with soluble (polystyrene)100‐butadiene3‐Li/TiCl4 complexes leads to [St]‐b‐[E‐co‐P] diblock copolymers with a random [E‐P] block. GPC and 13C‐NMR analyses of copolymers with various compositions and block lengths disclose well‐defined linear structures. From DSC measurements of such materials, three different endothermal transition regions are observed: two glass transition regions corresponding, respectively, to the Tg of styrenic and olefinic blocks, and one [E‐P] block melting region in which propylene units play a primary role. Furthermore, an additional endotherm is observed, depending on the thermal history of the sample.
Permeability of pure and mixed gases in silicone rubber at elevated pressures
Authors: Jordan S. M. , Koros W. J. 
Published: April 2003

AbstractThe transport properties of silicone rubber are reported at 35°C for a series of pure gases (He, N2, CH4, CO2, and C2H4) and gas mixtures (CO2/CH4 and N2/CO2) for pressures up to 60 atm. The effects of pressure and concentration on the permeability of various gases have been analyzed to consider plasticization and hydrostatic compression effects. Over an extended pressure and concentration range, both compression of free volume and eventual plasticization phenomena were observed for the various penetrants. In pure component studies, plasticization effects tended to dominate hydrostatic compression effects for the more condensible penetrants (C2H4 and CO2) while the reverse was true for the low sorbing N2 and He. These issues are discussed in terms of penetrant diffusion coefficients versus pressure to clarify the interplay between the opposing effects for the penetrants of markedly different solubilities. Additional insight into the somewhat complex interplay of the plasticization and hydrostatic compression effects are given by mixed gas permeation results. It was found that the permeability of nitrogen in a 10/90 CO2/N2 and a 50/50 CO2/N2 mixture was increased by the presence of CO2 because the plasticizing nature of CO2 is able to overcome nitrogen's compression effect.
A study of wet PVC gels by raman spectroscopy
Authors: Jackson R. S. , Bower D. I. , Maddams W. F. 
Published: April 2003

AbstractRaman spectroscopy has been used to study PVC gels made in cyclohexanone in the wet state at concentrations from 21 to 93% by weight of PVC. Parallel and perpendicular spectra were obtained in the C‐Cl stretching region, and after subtraction of the solvent spectrum they were analyzed into a set of overlapping peaks due to various structural components. The positions of the peaks found were in good agreement with those found earlier for PVC samples in the solid state. The fractional contribution of the areas of peaks assigned to crystalline material to the total area under the C‐Cl stretching region was used to estimate the crystallinity of the gels, and changes in their depolarization ratios and relative intensities were interpretated as providing further evidence for the presence of two types of crystallites in PVC gels. From a determination of the crystallinity at the gel transition point and reasonable assumptions, the contributions of the two types of crystallites to the total crystallinity were estimated.
Temperature dependence of swelling of crosslinked poly(N,N′‐alkyl substituted acrylamides) in water
Authors: Bae You Han , Okano Teruo , Kim Sung Wan 
Published: April 2003

AbstractThe swelling of crosslinked poiy(N,N′‐alkyl substituted acrylamides) in water was studied in relation to temperature changes. Conventional swelling theory and separation of the polymer solvent interaction parameter into enthalpic and entropic contributions were used to characterize the temperature dependence of swelling in water. The thermosensitivity of swelling can be attributed to the delicate hydrophilic/hydrophobic balance of polymer chains and is affected by the size, configuration, and mobility of alkyl side groups. A sharp swelling transition may occur at an optimum hydrophilic/hydrophobic balance but was found only in the N‐isopropylacrylamide network among the networks tested. This swelling transition pattern was also reflected by the endothermic peak of the DSC thermogram of the swollen sample.
Structure and properties of propylene‐ethylene block copolymers and the corresponding blends
Authors: Wang Lixiao , Huang Baotong 
Published: April 2003

AbstractStructure and properties of presumed polypropylene(PP)‐b‐polyethylene(PE) block copolymers (PPPE) and the corresponding blends (PP/PE) have been investigated by wide‐angle x‐ray scattering (WAXS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), torsional pendulum apparatus, and other techniques measuring mechanical properties. Crystallinity, morphological structure, and mechanical properties of the block copolymers and blends vary with the PP and PE compositions. Compared with PP homopolymers and PP/PE blends, PP and PE segments in PP‐PE block copolymers have a reduced crystallinity, especially PE segments. An additional peak at about −40°C is observed in dynamic relaxation spectra; substantially different morphology is revealed; and mechanical properties are greatly improved for the sequentially copolymerized PP‐PE block copolymers, indicating the existence of PP‐PE block structure.
Transport of hexane vapor in polystyrene at 25°C I. Analysis of integral sorption data
Authors: Kang Yong Soo , Meldon Jerry H. , Sung Nakho 
Published: April 2003

AbstractA series of measurements of integral n‐hexane vapor sorption at 25°C and moderate activity, in polystyrene microspheres of varying radii, exhibits typical non‐Fickian behavior: nonoverlap of curves of fractional uptake versus (square root of time)/radius. The data are examined in light of a sorption isotherm indicating hexane solubility in excess of that predicted by the Flory–Huggins equation, up to the hexane activity at which the glass transition apparently occurs. A transport analysis is developed based on the assumption that below the transition temperature Tg the rate of sorption is limited by the rate of polymer chain relaxations induced by the penetrant, which facilitate hexane entry into, and immobilization in, glassy microvoids.
Epitaxial crystallization of polyoxymethylene on NaCl single crystal in dilute solution
Authors: Sato Yukihiko 
Published: April 2003

AbstractThe epitaxial crystallization of polyoxymethylene (POM) is observed from 0.01% cyclohexanol solution on the (001) cleavage face of NaCl. High‐resolution electron microscopy reveals that the crystals are definitely triangular, rather than rectangular prisms, although the crystals have previously been interpreted as “edge‐on” arrangements of lamellar crystals. An electron diffraction pattern obtained from films, which were piled up with a maximum of nine sheets per grid, shows that plane spacing of the epitaxial crystals is 3.87 Å and almost the same as the
\[
\left\{ {10\bar 10} \right\}
\] spacing (3.86 Å) of hexagonal single crystal of POM: the axes of POM fold chains in the crystals are parallel to the (001) plane. A possible mechanism for the epitaxial crystallization of POM is proposed.
Sorption and partial molar volume of gases in poly (dimethyl siloxane)
Authors: Kamiya Yoshinori , Naito Yasutoshi , Hirose Takuji , Mizoguchi Keishin 
Published: April 2003

AbstractSorption of N2, O2, Ar, CH4, CO2, C2H4, and C2H6 in poly (dimethyl siloxane) liquid and rubber and the dilation of the polymers due to sorption of the gases are studied at 25°C under pressures up to 50 atm. In the liquid, the sorption isotherms for low‐solubility and high‐solubility gases are described by Henry's law and the Flory–Huggins equation, respectively. Gas sorption in the rubber, which contains a 29 wt % silica filler, follows the dual‐mode sorption model, though marked hysteresis is observed in the sorption of O2 and CH4. The dilation isotherms increase linearly or exponentially in both polymers with increasing pressure. Considering that gas molecules adsorbed into micropores of the filler particles do not participate in the dilation, partial molar volumes of the dissolved gases in the rubber are determined from data of sorption and dilation. The values are nearly equal to the partial molar volumes in the liquid (48–60 cm3/mol).
Polyurethane cationomers. II. Phase inversion and its effect on physical properties
Authors: Chen Show‐An , Chan Wu‐Chung 
Published: April 2003

AbstractThe three series of polyether polyurethane cationomers based on MDI, HDI, and TDI that are the subject of Part I, undergo emulsification (or phase inversion) on addition of water to solutions in MEK. The phase inversion mechanism depends on the structure of hard segment, ionic content, and dispersion temperature. The dispersion process can be divided into three stages involving a separation of hard segment aggregates due to adsorption of water on their surface, water entering into disordered and then ordered hard domains, and finally a rearrangement of agglomerates to form microspheres. The extent of penetration of water into the disordered hard domains decreases with increasing glass transition temperature; while in ordered hard domains, penetration depends on the dissociation temperature of urethane–urethane hydrogen bonds. Thus the penetration of water into the hard domains is strongly dependent on the dispersion temperature. Films cast from the emulsions have both ordered and disordered hard segment regions, this is also true of films cast directly from solution. The dispersion can disrupt the order in hard domains, leading to an increased phase separation for the MDI system and to a slightly increased phase mixing for the HDI and TDI systems. Films cast from solutions have a morphology with soft domains as a continuous phase and hard domains as a fibrillar network dispersed in the continuous phase. After dispersion, the hard segments originally distributed in the dispersed phase can be inverted to become a hard domain network or a continuous phase.
Relaxation dynamics of carbon dioxide sorbed in poly (dimethyl siloxane) rubber
Authors: Cain Edward J. , Jones Alan A. , Inglefield Paul T. , Jost Robert D. , Liu Xiangzhe , Wen Wen‐yang 
Published: April 2003

AbstractWe have probed the dynamics of 13CO2 molecules sorbed in poly (dimethyl siloxane) rubber by nuclear magnetic resonance (NMR) relaxation. The spin‐lattice and spin‐spin relaxation times as well as nuclear Overhauser enhancements were determined as functions of temperature at three magnetic field strengths. The relaxation mechanisms found to be important are intermolecular dipole‐dipole relaxation and spin rotation relaxation with a minor contribution from chemical shift anisotropy relaxation. Our analysis shows that the assumption of a single correlation time for each motional mechanism is inconsistent with the NOE data and spin‐spin relaxation times. However, if a distribution of correlation times is assumed, one can interpret all of the experimental data in a reasonable manner. We have quantitatively elucidated the spin relaxation mechanisms and determined the parameters which characterize the distribution times for 13CO2 Collisional motions, rotational motions, and translational motions in the silicone rubber. A fractional exponential correlation function of the Williams‐Watts type with a fractional exponent of 0.58 is used in our description of the 13CO2 dynamics. This exponent is typical of the distribution of time scales associated with segmental motion in polymeric rubbers. The broad distribution needed to describe the data has implications for the coupling of diffusion to segmental motion and for the relationship between macroscopic permeability and the molecular level character of diffusion.
NMR and dynamic mechanical studies of miscibility enhancement via ionic interactions in polystyrene/poly (ethyl acrylate) blends
Authors: Zhang Xinsheng , Eisenberg Adi 
Published: April 2003

AbstractDirect ion‐ion interactions in ionomer blends are achieved through microion elimination by mixing the two ionomers, poly (styrene ‐co‐tetraalkylammonium methacrylate) and poly (ethyl acrylate‐co‐Nmethyl‐4‐vinyl pyridinium. iodide), in a benzene/ methanol mixture. The pyridiniumcarboxylate ionion interactions are compared with pyridinium‐sulfonate interactions which were described before. It is shown that carboxylate ions are much less effective than sulfonate ions in enhancing miscibility in the polystyrene/ poly (ethyl acrylate) system. Complete miscibility is not attained for this polymer pair even with up to 10 mol % ions. In another system, ion pair‐ion pair blends were prepared by mixing poly (styrene‐co‐sodium styrenesulfonate) with poly (ethyl acrylateco‐N‐methyl‐4‐vinyl pyridinium iodide), also in a benzene/ methanol mixture. The results show that ion pair‐ion pair associations are also a much weaker driving force for miscibility enhancement in this polymer pair than the corresponding direct pyridinium‐sulfonate ion‐ion interactions. A ranking is presented of the relative strengths of the various ionic interactions in their effect on miscibility enhancement, which also includes ion‐dipole interactions (sodium sulfonate‐pyridine).
Solid‐state 13C NMR characterization of annealed poly (p‐phenylene vinylene) PPV Films
Authors: Simpson Jeffrey H. , Egger Norbert , Masse Michael A. , Rice David M. , Karasz Frank E. 
Published: April 2003

AbstractSolid‐state 13C cross‐polarization magic‐angle spinning (CPMAS) nuclear magnetic resonance (NMR) spectra have been obtained for annealed films of poly (p‐phenylene vinylene) (PPV), prepared through the precursor route and for a deuterated PPV‐d4, poly (p‐2,3,5,6 tetradeuterophenylene vinylene). 13C CPMAS spectra of PPV are of high resolution, typically characteristic of a nearly fully crystalline structure. All four phenylene and vinylene resonances have been assigned, and for stretched films the 13C CPMAS linewidth and the quality of crystallinity are independent of the draw ratio. 13C CPMAS resolution and crystallite size (as determined by transmission electron microscopy, TEM) depend upon final annealing temperature. The greatest NMR resolution and largest crystallite size are obtained for films annealed at 300°C. The 13C CPMAS NMR spectra show the presence of phenylene ring 180° rotational jumps, and 13C CPMAS resolution is affected by rotational disorder about phenylene‐vinylene bonds. NMR data show that PPV films possess molecular motion at elevated temperatures. Enhancement of this motion during annealing may provide a means for improving the quality of PPV crystallinity.
Synthesis and unperturbed dimensions of poly(diphenylmethyl methacrylate)
Authors: Mays Jimmy W. , Hadjichristidis Nikos , Lindner J. S. 
Published: April 2003

AbstractThe synthesis, fractionation, and characterization of poly(diphenylmethyl methacrylate) (PDPMM) are described. Analysis of tacticity by 13C nuclear magnetic resonance (NMR) revealed a high (25%) isotactic content. Results of low‐angle light scattering and intrinsic viscosity measurements in toluene indicate that PDPMM chains behave as random coils and that toluene is a thermodynamically good solvent. The characteristic ratio C∞ of the chains was determined from viscosity measurements in a near‐theta solvent, 3‐heptanone at 45°C. The corresponding value of C∞ = 14.0 is consistent with previous work on poly(triphenylmethyl methacrylate), C∞ = 20.3, and poly(benzyl methacrylate), C∞ = 10.0, and reflects the bulkiness of the side group and the increase in isotactic content of the chains with increasing substitution.
On the melting behavior of a thermotropic rigid random copolyester based on terephthalic acid and substituted hydroquinones
Authors: Ghanem Antoine M. , Dickinson L. C. , Porter Roger S. , Zachariades Anagnostis E. 
Published: April 2003

AbstractThermotropic liquid crystalline random copolyesters, based on terephthalic acid and substituted hydroquinones, display an unusually large heat for the crystal‐nematic transition; this phenomenon is related to their highly ordered structures. To modify the structures, annealing was carried out in the solid state at different temperatures over different times. As the annealing time or temperature is increased, the melting peaks shift to higher temperatures, whereas the heat of fusion shows no significant change or is lowered, respectively. An explanation is offered in terms of crystal perfection and a molecular weight increase. No evidence for a random‐to‐block conversion on annealing is found.
Thermal expansion of poly(ether‐ether‐ketone) (PEEK)
Authors: Choy C. L. , Leung W. P. , Nakafuku C. 
Published: April 2003

AbstractThermal expansivities along the a, b, and c axes of the orthorhombic unit cell of poly (ether‐ether‐ketone (PEEK) crystals have been determined from 160 to 470 K by wide‐angle x‐ray diffraction. The expansivities along the a and b axes are positive while the expansivity along the c (chain) direction is negative, with values of
\[
\alpha _a^c = 11.3 \times 10^{ ‐ 5} {\rm K}^{ ‐ {\rm 1}} ,{\rm }\alpha _b^c = 4.6 \times 10^{ ‐ 5} {\rm K}^{ ‐ {\rm 1}} ,
\] and
\[
\alpha _\parallel ^c = ‐ 1.4 \times 10^{ ‐ 5} {\rm K}^{ ‐ {\rm 1}}
\] at 300 K. The negative α arises from the effective shortening along the chain axis caused by the torsional and bending motions of the chain, whereas the large and positive α and α reflect the weak interactions across the chains. Using a dilatometric technique we have also studied the expansion behavior of isotropic PEEK as a function of crystallinity (X = 0−0.34) and have measured thermal expansivities of oriented PEEK (draw ratio 1–4) parallel and perpendicular to the draw direction. The effects of crystallinity and orientation can be understood by treating semicrystalline PEEK as a composite consisting of crystallites embedded in an amorphous matrix.
Effect of a methylmethacrylate–butadiene–styrene modifier on the dynamics of the viscoelastic beta process in poly(vinyl chloride)
Authors: Havriliak S. , Shortridge T. J. 
Published: April 2003

AbstractThe viscoelastic properties of a methylmethacrylate–butadiene–styrene (MBS) modifier over the temperature range −140 to 20°C and frequency range 0.01592 (0.1 Rad/s) to 79.62 Hz (500 Rad/s) is represented in terms of a relaxation function proposed by Havriliak and Shortridge to represent the viscoelastic beta process of MBS‐modified and unmodified poly(vinyl chloride) (PVC). The parameters of the expression as well as their temperature dependence were determined from the multiresponse methods developed by Havriliak and Watts. The complex modulus of PVC/MBS modifier blends at 8.26, 10.71, and 13.04 wt % modifier, over a temperature range −140–20°C, and at a frequency of 1 Hz can be represented, nearly within experimental error, in terms of the complex modulus of the neat components, the volume fraction of the modifier, and the blend equations of Uemura and Takayanagi. The small but persistent deviations that are observed are discussed in terms of hydrostatic stresses due to differential coefficients of expansion.