bluuebunny/crossref_metadata_2025_split huggingface dataset:
NMR approach to properties of polymeric membranes. Kinetics of membrane formation
Authors: Viallat Annie , Perez Sylvie 
Published: April 2003

AbstractNuclear magnetic resonance (NMR) is used to characterize properties of polyetherimide membranes obtained from a phase inversion process. At the end of the phase inversion and prior to the subsequent thermal treatments, the membrane is made of a porous structure filled of solvent and nonsolvent molecules embedded in a concentrated polymer–solvent matrix in the glassy state. The confinement of the small solvent and non solvent molecules in the porous system leads to a restriction of their mobility. The kinetics of membrane formation is observed from NMR. It is found that the penetration of non‐solvent and the propagation of the glassy phase into the system obey simple diffusion laws. © 1993 John Wiley & Sons, Inc.
Photophysical processes in aromatic polyimides. Studies with model compounds
Authors: Hasegawa Masatoshi , Shindo Yoichi , Sugimura Tokuko , Ohshima Shigeru , Horie Kazuyuki , Kochi Masakatsu , Yokota Rikio , Mita Itaru 
Published: April 2003

AbstractEmission mechanism in an aromatic polyimide, PI(BPDA/PDA), derived from biphenyltetracarboxylic dianhydride and p‐phenylene diamine were studied with ultraviolet visible absorption and fluorescence spectra of a series of the model compounds. The excitation spectrum of the intermolecular charge‐transfer (CT) fluorescence peaking around 550 nm of PI(BPDA/PDA) thin film was completely consistent with the absorption spectrum, indicating that the intermolecular CT fluorescence emission of PI(BPDA/PDA) film is not caused by direct excitation of the CT absorption band, but by light absorption due to structural units in the polymer backbone. The UV‐vis. absorption spectra of the model compounds corresponding to the structural units in PI(BPDA/PDA) showed that the longest wavelength absorption band is due to the biphenylbisimide moiety. The band was assigned as π, π* transition with the polarization spectrum of the model compound. The fluorescence spectra of the model compounds changed sensitively depending on the conformation around N‐phenyl bond. The lifetime measurement for the model compounds suggested that intramolecular CT process occurs very rapidly. © 1993 John Wiley & Sons, Inc.
Analysis of mechanical behavior in cold‐drawing deformation of polymers
Authors: Xixiong Zhu 
Published: April 2003

AbstractWhen stretched under uniaxial stress, ductile polymers usually exhibit unstable plastic deformation, which embodies two phases: (a) yielding with the formation of a neck and (b) cold‐drawing with the propagation of necking shoulders. The mechanical state associated with this deformation behavior is analyzed. The discussion is divided into three parts. The first part is a general treatment of the constitutive function of flow stress in the plastic state, in which a series of relations among various characterizing parameters are formulated. The second part provides three mechanical criteria for necking deformation and propagation of necking shoulders: the condition of unstable plastic deformation requiring \documentclass{article}\pagestyle{empty}\begin{document}$ D_P = - \left( {\partial {{\ln \dot \varepsilon } \mathord{\left/ {\vphantom {{\ln \dot \varepsilon } {\partial \varepsilon }}} \right. \kern-\nulldelimiterspace} {\partial \varepsilon }}} \right)_P < 0 $\end{document} the stabilizing deformation mode, which requires \documentclass{article}\pagestyle{empty}\begin{document}$ \gamma _p = \left( {{{dD_p } \mathord{\left/ {\vphantom {{dD_p } {d\varepsilon }}} \right. \kern-\nulldelimiterspace} {d\varepsilon }}} \right)_P > 0 $\end{document} and the obvious localization of unstable plastic deformation. The third part describes a mathematical model which can be used in calculations to fit the contour of the necking shoulder. This model is developed according to rational considerations for the relation of In \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document} to ε. Experimental data on PE rod specimens are well fitted by this model. © 1993 John Wiley & Sons, Inc.
NMR study of the propagation center in cationic polymerization of N‐benzoyl‐8‐octanelactam. I. The structure of model living oligomers
Authors: Kříž J. , Puffr R. 
Published: April 2003

AbstractModel living oligomers of N‐benzoyl‐8‐octanelactam initiated by the model octanoylium hexachloroantimonate, SbCl5, and by Ph3C+ AsF6−, were studied by 1H and 13C one‐ and two‐dimensional nuclear magnetic resonance using the COSY, S‐INEPT, COLOC, and ROESY methods. If prepared in the more solvating mixture of 1,1,2,2‐tetrachloroethane (TCE) with 1,2‐dichlorobenzene, the oligomers were found to be linear with the acylium ion as a living group on one end; in TCE only, the oligomers are highly branched. In both cases, the propagation center appears to be strongly coordinated to the nearest benzoylamide chain group. © 1993 John Wiley & Sons, Inc.
Liquid crystalline main chain polymers with a poly(p‐phenyleneterephthalate) backbone. 2. Fiber spinning and mechanical properties of polyesters with alkoxy side chains
Authors: Damman S. B. , Mercx F. P. M. 
Published: April 2003

AbstractFiber spinning and mechanical properties of four rigid polyesters with alkoxy substituents of different length and placement were evaluated. Properties of oriented fibers from the polymer with dodecyloxy substituents on the terephthalate moiety, PTA12HQ, were significantly affected by the crystal modification. At room temperature the following properties (tensile modulus E, tensile strength σb, and strain at break εb) could be obtained: E = 9.5 GPa, σb = 85 MPa and εb = 1.1% for phase Lf (the “frozen in layered mesophase”); E = 10.4 GPa, σb = 59 MPa and εb = 0.6% for modification A; E = 17.3 GPa, σb = 158 MPa and εb = 1.2% for modification B. Because of the higher amount of main chains per cross sectional area the polymer with hexyloxy side chains, PTA6HQ, showed better properties at a comparable degree of molecular orientation: E = 24 GPa, σb = 270 MPa, εb = 1.4%. Fibers obtained from the polyester with dodecyloxy substituents on the hydroquinone moiety, PTAHQ12, were too brittle to handle. The polyester with dodecyloxy substituents on both moieties, PTA12HQ12, was spun from the isotropic melt. Because of the obtained low degree of orientation, properties (E = 1 GPa, σb = 40 MPa, and εb = 6.3%) were governed by interactions between the chains (the main chains are not load‐bearing). © 1993 John Wiley & Sons, Inc.
Dynamic rheo‐optical characterization of a low‐density polyethylene/perdeuterated high‐density polyethylene blend by two‐dimensional step‐scan FTIR spectroscopy
Authors: Gregoriou Vasilis G. , Noda Isao , Dowrey Anthony E. , Marcott Curtis , Chao James L. , Palmer Richard A. 
Published: April 2003

AbstractDynamic mechanical analysis coupled with polarized step‐scan FTIR transmission and two‐dimensional correlation analysis (2D FTIR) has been used to monitor the submolecular orientational responses of the components of a semicrystalline 50 : 50 blend of low‐density polyethylene (LDPE) and perdeuterated high‐density polyethylene (d*‐HDPE) to a small amplitude uniaxial 23.47 Hz sinusoidal mechanical strain. Perdeuteration of the HDPE component allowed the distinction of its response from that of the LDPE in the blend samples. The experiments were carried out at room temperature. Analysis of the data indicates that the crystalline parts of the two components reorient at different rates, with the functional groups of the high‐density portion reorienting faster, in general, than those of the LDPE in response to the mechanical strain. © 1993 John Wiley & Sons, Inc.
Higher order hydrodynamic interactions in the calculation of polymer transport properties
Authors: Phillies George D. J. , Kirkitelos Paul C. 
Published: April 2003

AbstractHigher order hydrodynamics interactions are short‐range modifications to the Oseen tensor Tij and its self‐interaction counterpart Tii. They differ from the Oseen tensor in having terms of higher order than the first in a/R, a being a bead radius and R being a bead‐bead distance. Effects of higher order hydrodynamic interactions on whole chain–whole chain hydrodynamic interactions are here computed. Higher order hydrodynamic interactions are shown to lead to a concentration dependence of the diffusion and friction coefficients of a free monomer. However, while higher order interactions make contributions of the same nature to the drag coefficients of a monomer and of a whole chain, the contributions are not simply multiplicative, removing a justification for the common practice of correcting polymer solution transport data for “monomer friction effects” via a normalization with data on friction coefficients of free monomers. © 1993 John Wiley & Sons, Inc.
Structure and electrical conductivity of ion‐implanted rigid‐rod and ladder polymers
Authors: Wang C. S. , Burkett J. , Lee C. Y‐C , Arnold F. E. 
Published: April 2003

AbstractIsotropic and oriented thin films of rigid‐rod, rigid‐rod pseudo‐ladder, and ladder polymers were ion‐bombarded with 84Kr+ to a dose of 4 × 1016 ions/cm2. The bombardment was conducted at two conditions: one at 190 keV energy with 0.12 μA/cm2 current density and the other at 200 keV energy with 2.0 μA/cm2 current density. With the low current density, the polymers developed a uniform ion‐bombarded layer of about 0.35 μm at the surface. This layer showed an electrical conductivity on the order of 10−3s/cm at ambient conditions, an enhancement of 6 to 9 orders of magnitude from the pristine polymers. The enhanced conductivity was found to decrease to 10−6s/cm after the implanted krypton was removed by heating under reduced pressure. It suggests that the enhanced conductivity was due to a synergistic effect of structural change of the polymers and chemical doping by the im‐planted ions. With the high current density, most polymer films, except that of rigid‐rod pseudo‐ladder poly(p‐(2,5‐dihydroxy) phenylene benzobisthiazole) (DPBT), developed an additional fibrous network structure over the uniform ion‐bombarded layer. The comparable conductivity, 53 to 157 s/cm, measured for the various ion‐bombarded films in‐dicated that neither the molecular structure, rigid‐rod or ladder, nor the molecular packing order, isotropic or oriented, constituted significant effect on the conductivity of ion‐bombarded polymers. Since krypton could not be detected in the polymers ion‐bombarded with high current density, the enhanced conductivity was attributed to the structural change of the polymers. The DPBT films ion‐bombarded with high current density showed holes of micron size, probably due to the decomposition of hydroxy pendents from the rigid‐rod backbone. © 1993 John Wiley & Sons, Inc.
Thermally stimulated current and DSC studies of the broadened glass transition in liquid crystalline polymers
Authors: Sauer Bryan B. , Beckerbauer Richard , Wang Lixiao 
Published: April 2003

AbstractThe high sensitivity of the thermally stimulated current, thermal sampling (TS) method is emphasized in a study of the breadth of the glass transition in several liquid‐crystalline polymers (LCPs). Differential scanning calorimetry (DSC) was performed on all samples to further quantify the glass transition regions. For “random” copolyester LCPs with widely varying degrees of crystallinity, including highly amorphous samples, very broad glass tran‐sition regions were observed. One semicrystalline alternating copolyester and a series of semicrystalline azomethine LCPs were studied as examples of structurally regular polymers. These exhibited relatively sharp glass transitions more comparable to ordinary isotropic amorphous or semicrystalline polymers. The broad glass transitions in the random copolyesters are attributed to structural heterogeneity of the chains. In one example of a moderate‐crystallinity random copolyester LCP (Vectra), glass transitions ranging up to ca. 150°C in breadth were determined by the thermal sampling (TS) method and DSC. In other lower crystallinity copolyester LCPs, the main glass transition temperature as determined by DSC was comparable to that determined by TSC although cooperative relaxations of a minor fraction of the overall relaxing species were detected well below the main Tg, by the TS method and not by DSC. Rapid quenches from the isotropic melt to an isotropic glass were possible with one LCP. The anisotropic and isotropic glassy states for this LCP were found to have the same breadth of the glass transition as was determined by the TS method, although TSC and DSC show that Tg is shifted downward by ca. 15°C in the anisotropic glass as compared to the isotropic glass. © 1993 John Wiley & Sons, Inc.
Tracer diffusion of star‐branched polystyrenes in poly(vinyl methyl ether) gels
Authors: Won J. , Lodge T. P. 
Published: April 2003

AbstractThe tracer diffusion of 3‐, 4‐, and 12‐arm polystyrene (PS) stars in poly(vinyl methyl ether) (PVME) gels has been measured by dynamic light scattering (DLS). The intensity correlation functions were analyzed by two methods. One was that employed previously in a DLS study of linear PS diffusion in PVME gels [N. A. Rotstein and T. P. Lodge, Macromolecules, Vol. 24. p. 1316 (1992)], and the other was based on consideration of possible nonergodicity effects [P. N. Pusey and W. van Megen, Physica A, Vol. 157, p. 705 (1990)]. Both methods gave equivalent results, suggesting that nonergodicity plays a small role in this system. This conclusion is not unreasonable, given that the PVME gels are almost isorefractive with the solvent (toluene), and that the signal is dominated by scattering from the PS chains. The resulting star diffusivities are consistently less than or equal to those for linear probes of comparable size, with the difference increasing with molecular weight. The diffusivities are also less than or equal to those obtained for the same stars in PVME solutions. A weak dependence on the number of arms is also observed. Finally, the mobility of a given star in a gel is much more sensitive to variations in the average molecular weight between cross‐links than is the mobility of a linear chain. All of these features in the data are broadly consistent with the reptation hypothesis. © 1993 John Wiley & Sons, Inc.
Scattering experiments on polymer solutions
Authors: Chu Benjamin 
Published: April 2003

AbstractLaser light‐scattering characterization of poly(tetrafluoroethylene) (PTFE) in a perfluoroalkane (perfluorotetracosane) or oligomers of poly(chlorotrifluoroethylene) at temperatures near the crystalline melting point of PTFE and studies of the coil‐to‐globule transition for polystyrene in cyclohexane are reviewed. Discussions on approach to solving some experimental problems are emphasized. © 1993 John Wiley & Sons, Inc.
Ion‐Exchange equilibria in cationic polyelectrolytes
Authors: Ríos Hernán E. , Ternero Gerardo A. , Barraza Raúl G. , Gamboa Irma C. 
Published: April 2003

AbstractA method which allows the evaluation of phenomenological ion exchange constants Kex is proposed and tested in a cationic polyelectrolyte system. Results for nitrate/chloride exchange are nearly constant over the entire concentration range studied. However, for nitrate/bromide exchange, the results depend on the polyelectrolyte concentration, with Kex following the same trend as the mean activity coefficient for the polyion bromide. For polyion fluoride, a conformational change is probably induced as nitrate is added to the solution and the result deviates from the linear relationship predicted by the method. Benzene sulfonate behaves like a hydrophilic anion, whereas tosylate and ethylbenzene sulfonate also induce conformational changes by hydrophobic interactions. These results are supported by viscosity measurements and agree well with those recently reported by Satoh, who considered changes in apparent molar volume. © 1994 John Wiley & Sons, Inc.
Study of the miscibility of poly(vinyl pyridines) with poly(vinyl acetate), poly(vinyl alcohol) and their copolymers
Authors: Cesteros L. C. , Isasi J. R. , Katime Issa 
Published: April 2003

AbstractMiscibility of poly(4‐vinyl pyridine) (P4VP) and poly(2‐vinyl pyridine) (P2VP) with poly(viny acetate) (PVAc), poly(vinyl alcohol) PVA and poly(vinyl acetate‐co‐alcohol) (ACA copolymers) has been investigated over a wide composition range. Differentiaal scanning calorimetry (DSC) results indicate that P2VP is immiscible with PVAC, PVA, and their copolymers over the whole composition range. In turn, P4VP appears to be immiscible with PVAC and PVA, but miscible with some ACA copolymers in certain range of composition. The P4VP‐ACA phase diagram for different copolymer compositions has been determined. The variation of the glass transition temperature with composition for miscible mixtures was found to follow the Gordon‐Taylor equation, with the parameter κ dependent upon copolymer composition. FTIR analysis of blends reveal the existence of specific interactions via hydrogen bonding between hydroxyl groups and the nitrogen of the pyridinic ring, which appear to be decisive for miscibility. © 1994 John Wiley & Sons, Inc.
Effects of methylene chloride sorption on the properties of poly(ether ether ketone)
Authors: Arzak A. , Eguiazábal J. I. , Nazábal J. 
Published: April 2003

AbstractSorption of methylene chloride by poly(ether ether ketone) (PEEK) has been studied for both amorphous and highly crystalline polymer. After the determination of sorption and desorption curves, the crystallinity of the two materials after desorption was determined both by density and X‐ray measurements. The experimental results indicate the existence of solvent‐induced crystallization in initially amorphous PEEK and a virtual lack of this process in highly crystalline PEEK. In the latter case, the observed density increase is attributed to solvent compression and a decrease in free volume. The mechanical behavior of both PEEKs is consistent with their crystallinity levels. The mechanical behavior of both PEEKs before and after sorption allows us to discern the separate effects of the two processes to which the presence of methylene chloride in PEEK gives rise, i.e., plasticization and solvent‐induced crystallization. © 1994 John Wiley & Sons, Inc.
Deformation effects on ionic transport in polymeric films
Authors: Sakamoto W. K. , Gonzalez E. R. , Zimmerman R. L. , Rúvolo‐Filho A. 
Published: April 2003

AbstractWhen a periodical deformation is applied to a cellophane film through which an ion flux is established by a concentration gradient, an electrical signal, synchronous with the deformation, can be detected on electrodes placed on both sides of the membrane. This signal was studied as a function of the amplitude and frequency of the deformation and the ionic concentration. Ionic resistance, permeability, water content and ionic concentration measurements were carried out in order to explain the particular dependence of the signal with the ionic concentration. © 1994 John Wiley & Sons, Inc.
Small‐Angle light scattering from an anisotropic sphere: Anisotropy and size effects
Authors: Holoubek J. 
Published: April 2003

AbstractThe recently developed theory of light scattering from an anisotropic sphere (taken as a model for a spherulite) summarizes all information obtainable from such scattering system when the Rayleigh‐Gans‐Debye approximation is appropriate. The commonly used procedure of size determination from the maximum of the Hv intensity is tested for a number of models differing in radius size, inherent anisotropy δn and mean refractive index ¯n. It has been confirmed, that the parameter (¯n ‐ 1)/δn plays the decisive role in the angular dependence of the Hv intensity and the influence of that parameter on the size determination and resulting accuracy is specified. The results differ for positive and negative spherulites and the stabilizing role of increasing spherulite size in accuracy of procedure is demonstrated. It has been shown that the RGD approximation is appropriate especially for the case of homogeneous spherulite texture (thus implying, that the refractive index of the surrounding is close to the average refractive index of a single spherulite). The results extrapolated outside of the RGD approximation display invariable Umax position for isotropic contribution with increasing sphere size in contrast to the oscillatory character of Umax predicted by the LM solution. It is proposed to construct the anisotropic solution under an approximation recently suggested for thin anisotropic shell. © 1994 John Wiley & Sons, Inc.
Effect of shear history on the steady shear flow behavior of a thermotropic liquid‐crystalline polymer
Authors: Kim Seung Su , Han Chang Dae 
Published: April 2003

AbstractThe steady shear stress (σ) and first normal stress difference (N1) of a thermotropic liquid‐crystalline polyester, poly[(phenylsulfonyl)‐p‐phenylene 1,10‐decamethylene‐bis(4‐oxybenzoate)] (PSHQ10), in both the isotropic and nematic regions were measured as a function of shear rate (γ), using a cone‐and‐plate rheometer. For the study, PSHQ10 was synthesized via solution polymerization in our laboratory. The PSHQ10 was found to have (a) the weight‐average molecular weight of 45,000 relative to polystyrene standards and a polydispersity index of 2, (b) a glass transition temperature of 88°C, (c) a melting point of 115°C, and (d) a nematic‐to‐isotropic transition temperature of 175°C. For the measurements of σ and N1 in the nematic region of PSHQ10, its initial conditions for the startup of shear flow was controlled by (a) first heating an as‐cast specimen to 190°C, (b) shearing there at γ = 0.085 s−1 for about 5 min, and then (c) cooling slowly down to a predetermined temperature (130, 140, 150, 160, or 171°C) in the nematic region. For each γ chosen, after start‐up of shear flow, we waited for a sufficiently long time until both the shear stress and first normal stress difference leveled off, giving rise to steady‐state values of σ and N1. Emphasis was placed on investigating the effect of shear history on σ and N1 of PSHQ10 in the nematic region. For this, the following experiments were conducted: (a) a fresh specimen was sheared continuously by increasing the γ stepwise, and (b) a presheared specimen was further sheared continuously by increasing the γ stepwise. We have found that fresh specimens exhibited ‘shear‐thinning’ behavior over the entire range of γ (0.008−0.27 s−1) tested, whereas the presheared specimens exhibited both zero‐shear viscosities and shear‐thinning behavior. When using fresh specimens, we found that N1 was positive over the entire range of γ (0.008–0.27 s−1) tested. However, when using presheared specimens we found that (a) at very low γ, N1 initially was negative and then became positive as shearing continued, and (b) at higher γ, N1 was positive over the entire duration of shearing. © 1994 John Wiley & Sons, Inc.
Toughening of highly crosslinked epoxy resins by reactive blending with bisphenol A polycarbonate. II. Yield and fracture behavior
Authors: Di Liello V. , Martuscelli E. , Musto P. , Ragosta G. , Scarinzi G. 
Published: April 2003

AbstractThe yield and fracture behavior of highly crosslinked epoxy resin modified by a reactive blending process carried out in the presence of bisphenol A polycarbonate has been studied. It was found that the fracture toughness of this blend system increases markedly with increasing PC content in the blend. Scanning electron microscopy of the fractured surfaces indicated a crack blunting mechanism as the main source of energy dissipation in the various investigated blend compositions. No evidence of phase separation of the minor component during the curing and postcuring steps was observed. The yield data were correlated with the fracture toughness data to evaluate the extent of crack‐tip blunting. © 1994 John Wiley & Sons, Inc.