bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sorption of water and organic solutes in polyimide films and its effects on dielectric properties
Authors: Lim B. S. , Nowick A. S. , Lee Kang‐Wook , Viehbeck Alfred 
Published: April 2003

AbstractThe effect of structure on the sorption kinetics of water and of various organic solutes into polyimide (PMDA‐ODA) thin films was studied. The major techniques employed include measurements of sorption kinetics, density, and dielectric relaxation. More solute uptake, lower densities and higher diffusivities were observed for films cured at lower temperatures. By measuring both changes of mass and of density, the volume expansion of the polymer due to each solute was obtained; this was found to be proportional to the molar volume of the solute. The two dielectric relaxation peaks (denoted by γ1 and γ2) due to water (and other solutes) were studied in detail to obtain the relevant activation energies and the separate dipole moments. While water and methylene chloride appear in both γ1 and γ2 configurations, methyl and ethyl alcohol appear mainly as γ2, while acetic acid is primarily γ1. It was concluded that the γ1 configurations are relatively homogeneously distributed throughout the polymer, involving loose bonding to the polymer structure, while the γ2 configurations involve small clusters, probably chains of molecules. © 1993 John Wiley & Sons, Inc.
Physical transitions and crystallization phenomena in poly(ethylene terephthalate) studied by microhardness
Authors: Calleja F. J. Baltá , Cruz C. Santa , Asano T. 
Published: April 2003

AbstractThe crystallization behavior of poly(ethylene terephthalate) both with and without sodium montanate, a crystal nucleating agent, has been studied using the microhardness technique. The kinetics of crystallization from the glassy state were investigated in real time by measuring the microhardness H at different crystallization temperatures. Results are discussed in terms of the Avrami equation. Values of the Avrami exponent n of about 3 are observed for samples irrespective of nucleating agent. For samples with nucleant two crystallization ranges are observed: a first range which corresponds to a fast crystallization from nucleating agent particles and a second range which is associated with a slow self‐crystallization mode. New transitions evidenced by the presence of a small maximum in H as a function of annealing time and temperature are detected at temperatures above Tg for physically aged samples. The kinetics of this transition have also been examined. It is further shown that the presence of nucleating agent induces a hardening at room temperature which is similar to the effect produced by the physical aging of the samples below Tg. Finally, it is found that aging reduces the rate of creep of the material under the indenter. © 1993 John Wiley & Sons, Inc.
Thermal flexibility of aromatic polymide chains in solution from viscometric analysis
Authors: Lavrenko Peter N. , Okatova Olga V. 
Published: April 2003

AbstractIntrinsic viscosities of poly(p‐phenylene terephthalamide) (PPTA) and poly(m‐phenylene isophthalamide) (PMIA) samples of the same molecular weight are determined in 90%, 96% and 100% sulfuric acid at temperatures from 0 to 130°C. Conditions are established under which the degree of coiling of PPTA molecule is close to that for PMIA. Experimental data are compared with the results of theoretical calculations of the Kuhn segment length. In the light of this comparison, some quantitative characteristics of the deformational flexibility mechanism for aromatic polyamide chains and the hindrance to intramolecular rotation are discussed. © 1993 John Wiley & Sons, Inc.
Solid polymers doped with rare earth metal salts. II. Thermal behavior and morphology of the neodymium acetate–poly(ethylene oxide) system
Authors: Twomey Conor J. , Chen Shaw H. , Blanton Tom , Schmid Ansgar , Marshall Kenneth L. 
Published: April 2003

AbstractSamples of poly(ethylene oxide), PEO, doped with neodymium acetate, Nd (Act)3, were prepared and found to be microphase separated. At an EO/Nd (Act)3 molar ratio no less than 4, wide‐angle x‐ray diffraction (WAXD) patterns and small‐angle x‐ray scattering (SAXS) data suggest that bulk Nd (Act)3 and ionic clusters are both absent. It is inferred from differential scanning calorimetry (DSC) thermograms that in the presence of PEO, Nd (Act)3 forms an amorphous phase which is different from the amorphous phase formed by Nd (Act)3 alone. The tighter binding of CH3COO‐ to Nd3+, in comparison to Cl‐, appears to be responsible for the lack of true dissolution of Nd (Act)3 in PEO, a behavior clearly distinct from a number of polymer‐metal salt complexes reported in the literature. © 1993 John Wiley & Sons, Inc.
Multifractal analysis. A new method for the characterization of the morphology of multicomponent polymer systems
Authors: Blacher S. , Brouers F. , Fayt R. , Teyssié P. 
Published: April 2003

AbstractIt has been demonstrated that use of polymeric emulsifiers under usual processing conditions in the melt state is a powerful technique for preparing polymer alloys. Digitized representation of optical micrographs of thin sections of blends of a low‐density polyethylene and polystyrene (20 wt % PE‐80 wt % PS) containing 2 and 5 wt % of two hydrogenated polybutadiene‐polystyrene block copolymers exhibit different degrees of homogeneity as well as different morphological structures which can be studied by a multifractal analysis. We show how these differences are reflected in the f(α) spectrum of singularities which can be obtained by a box counting method in the canonical approximation. We have found a correlation between the f(α) curves and the mechanical properties of the corresponding samples: the samples which area the less multifractals have the best mechanical properties. © 1993 John Wiley & Sons, Inc.
FT‐Raman investigation of the thermal curing of PMDA/ODA polyamic acids
Authors: Johnson C. , Wunder S. L. 
Published: April 2003

AbstractThe effect of solvent on the curing reactions of PMDA/ODA polyamic acids has been investigated using Fourier transform (FT)‐Raman spectroscopy. Films of different thicknesses were cured by: (1) doctor blading 15% solids solutions onto glass slides, (2) removing all but the bound NMP, and (3) removing all the N‐methypyrrolidinone (NMP). The rate of cure and final degree of conversion of the PMDA/ODA polyamic acid to polyimide increased substantially in the presence of NMP, and this effect was attributed to the plasticizing effect of the solvent. Below a critical solvent concentration, which was estimated to be approximately 40% of the NMP concentration in the bound‐solvent limit, the rate of imidization slowed down considerably. Comparison of FT‐Raman data for PMDA/ODA polyamic acid: (1) in solution in NMP, (2) complexed with NMP in the solid state, and (3) in the solid state after all the NMP had been removed with water, indicated that intermolecular interactions were greatest in the latter case and weakest in solution. Spectra of PMDA/ODA in NMP solution provide strong evidence for binding of NMP to the amide carbonyl in solution. © 1993 John Wiley & Sons, Inc.
A hole‐filling theory of anomalous diffusion in glassy polymers. Effects of microvoids
Authors: Neogi P. 
Published: April 2003

AbstractNon‐Fickian diffusion is often observed at low concentrations and without any obvious irreversible changes. This contradicts some of the predictions of the existing theories, which in general work quite well. For these cases, it is suggested that the filling of microvoids give rise to such effects. The effective diffusivity and a memory‐dependent source/sink term are obtained for describing the overall transport in heterogeneous media under local volume averaging. Some comparisons with experiments are shown. This mechanism is confined to low concentrations and supplements the existing theories which are effective at higher concentrations. © John Wiley & Sons, Inc.
A study of phase separation of crystalline and miscible polymer blends. Poly(ε‐caprolactone)/poly(styrene‐co‐acrylonitrile)
Authors: Li Wenguang , Prud'Homme Robert E. 
Published: April 2003

AbstractThe phase separation of a crystalline and miscible polymer blend, poly(ε‐caprolactone) /poly(styrene‐co‐acrylonitrile) (PCL/SAN), has been studied by differential scanning calorimetry (DSC), using a SAN containing 28.3% of acrylonitrile units. Several phenomena can be associated with the occurrence of phase separation depending upon the composition of the mixture. Following annealing at high temperatures, below and above the phase separation temperature Tc, three cases can be distinguished. In Case I, there is no sign of crystallization during quenching and DSC scanning, but a melting peak is observed at Tc, and above. In Case II, there is no crystallization on quenching but it does occur during the DSC run; the shift of the crystallization peak can then be related to Tc. In Case III, there is crystallization on quenching, and additional crystallization during the DSC run; the change of area of the crystallization peak is indicative of Tc. From these observations, the phase diagram of the system was determined. © 1993 John Wiley & Sons, Inc.
Determination of density changes with expansion polymerization
Authors: Millich F. , Eick J. D. , Chen G. P. , Byerley T. J. , Hellmuth E. W. 
Published: April 2003

AbstractMaterials that polymerize without substantial volume contraction have numerous valuable applications in dentistry and other fields. Two new symmetrical aliphatic spiro‐orthocar‐bonates, formulated from cis‐ and trans‐2‐hydroxymethyl‐cyclohexanol to give 2,3,8,9‐di(tetramethylene)‐1,5,7,11‐tetraoxaspiro [5,5] undecanes, showed, by density determinations in dilute solution, that expansion occurs with polymerization. The cis / cis‐spiroorthocarbonate racemic mixture showed a 3.9% expansion upon polymerization, and the trans/trans racemic mixture showed a 3.5% expansion. The densities were determined by pycnometry, with a precision reliable to at least four figures. This method is thus recommended for cases of soluble monomer/polymer pairs for which the density difference will be small and where the partial specific volumes are independent of concentration, thereby avoiding the complexities of variable physical states of monomer and/or polymer. © 1993 John Wiley & Sons, Inc.
Whiskers of poly(3‐alkylthiophene)s
Authors: Ihn Kyo Jin , Moulton Jeff , Smith Paul 
Published: April 2003

AbstractIt is shown that poly(3‐alkylthiophene)s may readily crystallize from poor solvents in the form of whiskers. The experimental conditions required for the formation of whiskers were found to depend upon the alkyl side‐chain length, solvent quality, and temperature. In all cases studied for alkyl side‐chain lengths of 3‐12 carbon atoms, the widths of the whiskers were of the order of 15nm, while their lengths often exceeded tens of microns. The thickness of the whiskers formed under the experimental conditions employed was found to scale with side‐chain length, and was approximately 2 or 3 times the a/2 lattice dimension of the polymer unit cell. Packing of the macromolecules within the whiskers was such that the polymer backbones were normal to the whisker length; that is, the b‐axis was oriented parallel to the long axis of the whiskers. These results are thought to be relevant to known thermochromism phenomena associated with poly(3‐alkylthiophene)s. © 1993 John Wiley & Sons, Inc.
The effect of drawing on the transport of gases through polyethylene
Authors: Webb J. A. , Bower D. I. , Ward I. M. , Cardew P. T. 
Published: April 2003

AbstractA study has been made of the gas transport properties of polyethylene films of two different grades, Hizex 7000F and Rigidex 002‐55, one‐way drawn at 115°C to draw ratios in the range 1–20. Measurements of the permeability and diffusion coefficients of helium, oxygen, carbon dioxide and nitrogen have been made with a dynamic flow rate technique, utilizing a mass spectrometer detection system, and of oxygen using a commercial OXTRAN system. The samples were characterized by the measurement of density, birefringence and modulus and by wide‐angle x‐ray diffraction and differential scanning calorimetry. There is a large decrease in both the permeability and diffusion coefficients for all gases with increasing polymer draw ratio, with up to an 80‐fold decrease in permeability for the larger permeants compared with the 10‐fold decrease observed for helium. The solubilities of all the gases decrease only by a factor of ∼ 2. The diffusion results are discussed in terms of geometric impedance and chain immobilization factors. The solubilities, on the other hand, appear to relate primarily to the amorphous volume fraction of the polymer. © 1993 John Wiley & Sons, Inc.
Tensile yield of polyethylene in relation to crystal thickness
Authors: Darras O. , Séguéla R. 
Published: April 2003

AbstractTensile yield stress measurements have been performed on a serie of four ethylene/1‐butene copolymers covering the crystallinity range 0.33–0.74. Samples have been prepared from melt‐crystallization and from solution‐crystallization at various concentrations in decalin in order to span a wide range of crystal thickness. It is shown that tensile yield stress depends on crystal thickness rather than on crystallinity. This result is perfectly consistent with a plasticity model based on the nucleation of dislocations. Besides, it in‐dicates that the main role of the amorphous phase is only to transmit the load upon the crystals, irrespective of its proportion. The yield stress dependence on crystallinity reported previously relies on the direct correlation of crystal thickness and crystallinity, in the case of melt‐crystallized samples only. Discrepancies with the model are amply discussed. © 1993 John Wiley & Sons, Inc.
An investigation of the smectic‐isotropic transition in a side‐chain liquid crystal polymer by synchrotron radiation x‐ray diffraction
Authors: Galli G. , Mcnamee S. G. , Ober C. K. 
Published: April 2003

AbstractIn this work we have used synchrotron x‐radiation diffraction to follow in real‐time the isotropic‐smoetic phase transition of a side‐chain liquid crystalline polymer. The analysis of the x‐ray data indicated that the transition occurs within a very narrow biphasic region. As the transition takes place, the size of the smectic regions, as indicated by the width of the diffraction peaks, changed only very slightly before impingement, suggesting a two‐dimensional growth pattern. A thermal investigation of the polymer paralleling the x‐ray experiments was undertaken and a kinetic analysis applied to the resulting data. Qualitative agreement with a disk‐like growth of the smectic regions was found. We have shown that the overall kinetics of the isotropic‐smectic transition of a side‐chain polymer can be studied by x‐ray diffraction permitting the evaluation of several structural parameters. © 1993 John Wiley & Sons, Inc.
An experimental and theoretical study of the PVT equation of state of butadiene and isoprene elastomers to 200°C and 200 MPa
Authors: Yi Y. X. , Zoller P. 
Published: April 2003

AbstractWe have performed and analyzed extensive pressure‐volume‐temperature (PVT) measurements on uncrosslinked polybutadiene and polyisoprene elastomers from ambient temperature to about 200°C and 200 MPa. In the polybutadiene series, 1,2 content varied from 8 to 87%, the remainder being similar amounts of cis‐1,4 and trans‐1,4. In the polyisoprene series the 3,4 content varied from 8 to 64%, the trans‐1,4 content was 12–16%, and the remainder was cis‐1,4, with < 4% 1,2 content. We report parameters describing the experimental data in terms of the empirical Tait equation, the cell model, the Simha‐Som‐cynsky equation, the Sanchez‐Lacombe, and the Flory‐Orwoll‐Vrij models. In general the parameters show systematic changes with the microstructure content. The agreement between theory and experiment is excellent for the Tait equation, and also for the Simha‐Somcynsky model and the cell model. The maximum deviation between theory and experiment was less than 0.004 cm3/g for the Simha‐Somcynsky theory, and less than 0.005 cm3/g for the cell model. Average absolute deviations are three to four times less. For the Sanchez‐Lacombe and the Flory‐Orwoll‐Vrij models, the maximum deviations are 5–8 times as large, and very systematic. Parameter derived from the Simha‐Somcynsky theory are discussed with respect to the microstructure, and with respect to the glass transition of these two series of materials. © 1993 John Wiley & Sons, Inc.
Orientational–deformational nature of flow birefringence in solutions of rigid‐chain polymers
Authors: Pogodina N. V. 
Published: April 2003

AbstractThe orientational–deformational nature of flow birefringence (FB) in solutions of rigid‐chain polymers is confirmed experimentally. The possibility of a direct determination of the internal viscosity parameter by the dependence of the FB relaxation time on the solvent viscosity is demonstrated. Indirect manifestation of internal viscosity in the FB relaxation time is confirmed by the dependence of the form factor on the degree of coiling. © 1993 John Wiley & Sons, Inc.
Increase in dynamic modulus of nylon 6 fiber in repeated heating and cooling cycles under sinusoidal deformation
Authors: Kunugi Toshio , Suzuki Akihiro , Chida Kimitaka 
Published: April 2003

AbstractThe repeated heating and cooling cycles under sinusoidal deformation have been investigated on nylon 6 fibers. The fibers zone‐drawn twice at high temperatures were used, which have a crystallinity of 52.2% and a birefringence of 59.4×10−3. The heating and cooling cycle was performed twice at a frequency of 110 Hz over a temperature range from 0°C to 180°C and 190°C. The crystallinity and birefringence of the treated fiber were 51.7% and 60.7×10−3, respectively, indicating almost no changes in molecular orientation and crystallinity. However, the dynamic modulus, E′, increased steadily over whole temperature range measured. Finally, the E′ value reached 21 GPa at room temperature and 10 GPa ever at 180°C. The elongation of fiber after two cycles was only about 5%. © 1993 John Wiley & Sons, Inc.
Electron paramagnetic resonance spectroscopic studies of thermally generated free radicals in PMR‐15 polyimide resins
Authors: Ahn Myong K. , Stringfellow Thomas C. , Fasano Matthew , Bowles Kenneth J. , Meador Michael A. 
Published: April 2003

AbstractPMR‐15 is a high‐performance thermoset polyimide resin that is used in many high‐temperature applications. Postcured PMR‐15 produces room‐temperature electron paramagnetic resonance (EPR) spectra from stable freeradical species that are formed during the postcuring stages. The variable‐temperature EPR spectral intensities show a minimum at Tmin in the range −60 to −40°C, and a maximum at Tmax in the range 80–120°C. The EPR intensities follow the inverse temperature dependence of Curie's law below Tmin and are due to a stable free radical. The intensities then increase with increasing temperature between Tmin and Tmax. The free radical with such temperature dependence is not present below Tmin and is undetectable by EPR at temperatures above Tmax. These free radicals are generated during the postcuring process at elevated temperature above 310°C. The thermo‐oxidative degradation involves free radicals generated during the postcuring process in the presence of oxygen gas. © 1993 John Wiley & Sons, Inc.
A bimodal structure of solution‐grown isotactic polypropylene with orthogonally crossed lamellae
Authors: Masada Isao , Okihara Takumi , Murakami Shozo , Ohara Masayoshi , Kawaguchi Akiyoshi , Katayama Ken‐Ichi 
Published: April 2003

AbstractIsotactic polypropylene (iPP) was crystallized from solution on a uniaxially‐oriented iPP film. Small‐angle x‐ray scattering patterns obtained from the sample showed two perpendicularly crossed lameliae 9.3 nm thick that overgrew flat‐on and edge‐on on the substrate. In the through wide‐angel x‐ray diffraction pattern (taken with incident x‐rays normal to the iPP film surface), strong hkO reflections were arranged in an hkO net pattern indicating that the a‐axis of the monoclinic α unit cell was oriented parallel to the chain direction of the substrate. From this, it was concluded that the flat‐on lamellae grew with the a‐axis parallel to the chain axis of the substrate and with the b‐axis parallel to its surface. In the edge wide‐angle x‐ray diffraction pattern (X‐rays incident on the edge of the film), arced, strong 110 and 220 reflections from overgrown crystals were observed on the equator of the fiber pattern of the substrate. This indicated that the edge‐on lamellae epitaxially grew with the c‐axis aligned parallel to the chain axis of the substrate. The homoepitaxy explains the correlated growth mode between the orthogonally crossed lamellae: they grew epitaxially, the a‐axis of one lamella coinciding with the c‐axis of the other and the {010} planes in contact. © 1993 John Wiley & Sons, Inc.
Multiphase structure of segmented polyurethanes: Its relation with spherulite structure
Authors: Li Yingjie , Liu Jian , Yang Huichang , Ma Dezhu , Chu Benjamin 
Published: April 2003

AbstractSmall‐angle light‐scattering (SALS), Polarized light microscopy (PLM), differntial scanning calorimetry (DSC), and small‐angle x‐ray scattering (SAXS) were used to study morphological changes in segmented polyurethanes with 4,4′‐diphenylmethane diisocyanate (MDI) and 1,4‐butanediol (BD) as the hard segment. It was found. for the first time, that spherulites could form from the melt by quenching the polyurethanes in the melt state to annealing temperatures between 120°C and Th, the highest annealing temperature for spherulite formation. Th ranged from 140°C to ca. 170°C and depended upon the hard‐and soft‐segment compatibility. Within the range 120°C to Th, the radius of the spherulite increased with increasing hard‐segment content at each fixed annealing temperature. Annealing at 135–140°C gave rise to the largest spherulites. SAXS was used to investigate the phase‐separated structures corresponding to the spherulite formation. The interdomain spacing increased with increasing hard‐segment content and with increasing annealing temperature.The degree of phase separation first increased with increasing annealing temperature from room temperatures (ca. 25°C), reached a maximum at ca. 107°C, and then decreased with further increase in the annealing temperature. On the basis of these observations, the mechanisms of phase separation, crystallization, and spherulite formation are discussed. © 1993 John Wiley & Sons, Inc.
Optimization of asymmetric permeation in heterogeneous composite membranes
Authors: Yamanaka Tadae 
Published: April 2003

AbstractAsymmetric permeation in two‐phase composite membranes with heterogeneous structures represented by a one‐dimensional distribution of composition is treated theoretically on the basis of an irreversible thermodynamic transport equation. It is assumed that the permeability of one of the component phases is a monotone function of the activity of permeant while that of the other phase is constant, and that the permeability of the composite membrane is given by the volume average of the resistance coefficient, which is the inverse of permeability. Under these assumptions, it is shown that the optimal membrane which maximizes the degree of asymmetric permeation reduces to a binary laminate membrane. The condition for constructing the optimal laminate membrane is obtained explicitly. Conversely a condition on a desirable membrane component which realizes an arbitrary degree of asymmetric permeation is presented. These results can be applied to the optimal design of a membrane valve which is a chemical analog of a diode. © 1993 John Wiley & Sons, Inc.