bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study of the dielectric β‐relaxation in poly(ethylene terephthalate) and ethylene isophthalate terephthalate copolyesters
Authors: Tatsumi Tomiwo , Ito Eiko , Hayakawa Reinosuke 
Published: April 2003

AbstractThe dielectric β‐relaxation in poly(ethylene terephthalate) and ethylene isophthalate terephthalate copolyesters with various ethylene isophthalate contents was investigated over a wide range of frequencies. Isothermal spectra and normalized plots show that the dielectric β‐relaxation is characterized by the molecular structure between the aromatic rings. The equilibrium polarizability of the motional segment, which was estimated from the dielectric increment obtained by the best fit of the Havriliak‐Negami equation to the Cole‐Cole plot, indicates that torsional vibrations of the main chain are correlated over a length corresponding to one monomer.
Relationship between crystallization of the PDMS block and morphology of poly(butadiene‐b‐dimethylsiloxane)
Authors: Li Weidong , Huang Baotong 
Published: April 2003

AbstractStudies using transmission electron microscopy, differential scanning calorimetry, and X‐ray diffraction showed correlations between the crystallization behavior of the polydimethylsiloxane (PDMS) block and the morphology of the block copolymer poly(butadiene‐b‐dimethylsiloxane) (PB‐PDMS). When the PDMS component existed as spheres dispersed in a PB matrix, the crystallization rate of the PDMS block was lower than when the PDMS phase existed in rod or cylinder form.
Small‐angle scattering of polarized light. IV. Isotropic to birefringent transition for spheres
Authors: Peuvrel E. , Siegert D. , Navard P. , Meeten G. H. 
Published: April 2003

AbstractThe Rayleigh‐Gans‐Debye approximation is used to investigate the small‐angle, cross‐polarized light scattering by a sphere of radius a, birefringence Δμ and relative index μ. If θmax is the polar scattering angle of the intensity maxima, the quantity Ûmax = 4πa/λ × sin (θmax/2) behaves in two different ways according to the signs of Δμ and μ − 1. When Δμ > 0, μ > 1 or Δμ < 0, μ < 1, then Ûmax varies from 2.8 to 4.1 as Δμ increases from zero. If Δμ < 0, μ > 1 or Δμ > 0, μ < 1, then Ûmax goes from 2.8 to about 6, thereafter decreasing to 4.1. Another interesting result is that the value of Ûmax for a highly briefringent sphere is 4.1 only for large diameters. It decreases to 4.0 when the diameter decreases.
CO2 permeability and amorphous fractional free‐volume in uniaxially drawn HDPE
Authors: Sha Hongjian , Harrison Ian R. 
Published: April 2003

AbstractThe CO2 permeability of uniaxially drawn high‐density polyethylene (HDPE) was investigated and drastic changes were observed as a function of draw ratio. An estimation of variations in both density and fractional free volume of the amorphous component in the drawn polymers was made on the basis of experimental data. The dramatic variations in permeability resulting from drawing were shown to be the consequence of changes of fractional free volume in the amorphous phase of the drawn polymer. Good correlation exists between measured solubility and diffusion coefficients of drawn samples and the estimated fractional free volume; this correlation agrees with the existing free volume theory for diffusion in polymers.
The temperature window of minimum flow resistance in melt flow of polyethylene. Further studies on the effect of strain rate and branching
Authors: Waddon A. J. , Keller A. 
Published: April 2003

AbstractThe existence of a narrow temperature window (150–153°C) of smooth extrudability coupled with a minimum in flow resistance (extrusion pressure) in high‐molecular weight polyethylene (>4 × 105 g mol−1) was the subject of a previous article where it was associated with strain‐induced formation of the mobile hexagonal mesophase. The new findings of this note show that this minimum in flow resistance only sets in above a critical strain rate; this is interpreted in terms of the requirement of a critical strain rate in order to stretch molecules to their fully extended configuration. Furthermore, this critical strain rate is shown to be higher for lower molecular weight materials, in agreement with a priori considerations. Additionally, the temperature at which the pressure minimum occurs in a polyethylene containing methyl branches shifts to a significantly lower value than that for the linear material. This is interpreted in terms of the CH3 groups raising the crystal free energy, thereby lowering the temperature at which the transition to the hexagonal phase occurs.
Frequency and molecular‐mass‐dependent nonexponential proton NMR relaxation in polymer melts
Authors: Hiller W. G. , Schneider H. , Fedotov V. D. 
Published: April 2003

AbstractA theoretical treatment of the nonexponential relaxation behavior of the different proton nuclear magnetic resonance (NMR) relaxation processes in polymer melts is presented. Formulas are derived for a three‐component model given by two versions and a homogeneous distribution of correlation times. The theoretical results were tested with measurements of T1, T2e, and T2 as functions of frequency and molecular mass in linear fractionated polyethylene samples. While the T1 relaxation always yields exponential magnetization decays, the T2e and T2 measurements show biexponential relaxation behavior. From the calculations it was found that the correlation time of the local motion is independent of the molecular mass, whereas the correlation time of the slowest motional process increases with M2.8w for the three‐component model and with M2.2w for the distribution of correlation times, respectively. © 1992 John Wiley & Sons, Inc.
Fickian diffusion in glassy polymer‐solvent systems
Authors: Vrentas J. S. , Vrentas C. M. 
Published: April 2003

AbstractA free‐volume theory is developed for the analysis of Fickian diffusion processes in glassy polymers. Equations are presented for the prediction of mutual diffusion coefficients in concentrated glassy polymer‐penetrant systems. The concentration dependence of the mutual diffusion coefficient is dependent on how much free volume the solvent contributes to the system and on how the addition of solvent affects the densification of the polymer matrix. © 1992 John Wiley & Sons, Inc.
The relation between the microphase separation transition and the glass transition in diblock copolymers
Authors: Stühn B. 
Published: April 2003

AbstractThe microphase separation transition (MST) has been studied for short chain diblock copolymers poly(styrene‐b‐isoprene) and poly(styrene‐b‐mma). A detailed analysis of small‐angle x‐ray scattering (SAXS) profiles in the homogeneous phase allows determination of the interaction parameter and the spinodal temperature Ts of the MST. Ts for the PS/PI diblocks is found to be lower than the glass transition temperature of their hard blocks. This results in a coupling of the MST and the glass transition. Using both structural (SAXS) and thermal differential scanning calorimetry (DSC) methods it is shown that an endothermal peak found in the DSC diagrams is related to the combined effect of the MST and the glass transition. © 1992 John Wiley & Sons, Inc.
Characterization of inhomogeneous polyacrylamide hydrogels
Authors: Cohen Y. , Ramon O. , Kopelman I. J. , Mizrahi S. 
Published: April 2003

AbstractThe physical and structural properties of acrylamide gels have been characterized by osmotic deswelling, mechanical compression, and x‐ray scattering. These properties vary considerably with the concentration of the crosslinking agent bisacrylamide, at fixed total monomers concentration (10% wt/wt water). In particular, changes in the properties appear more prominent at a crosslinking level of about 5‐6% (wt bisacrylamide/wt monomers). The compression modulus of as‐prepared and swollen gels passes through a maximum at this level of crosslinking. The swelling pressure curves can be separated into osmotic and elastic contributions of the gel network. The elastic part exhibits similar behavior to the compression modulus. The scaling of the osmotic part with the gel concentration varies with the degree of crosslinking, changing from 2.33 to 3.09. This indicates that the solvent power of water decreases with increasing crosslinking level, towards Φ conditions. The scattering patterns from the gels have been analyzed as arising from additive contributions from a homogeneous gel matrix, and embedded heterogeneities having a higher crosslinking density. These heterogeneities become much more prominent at the same level of crosslinking about 5‐6%. Hysteresis observed in the sorption/desorption behavior of polyacrylamide gel suggests that further irreversible structural changes may occur at water activities lower than probed by osmotic deswelling. © 1992 John Wiley & Sons, Inc.
Fermi resonance in the infrared spectra of Nylon‐11
Authors: Fina Leslie J. , Yu Hsin Her 
Published: April 2003

AbstractNylon‐11 is prepared by casting from the solvents trifluoroacetic acid and m‐cresol and by melt‐crystallization. Room‐temperature infrared spectra are compared in terms of possible crystal structures. The spectra are examined for the presence of Fermi resonance which occurs between the N‐H stretching fundamental mode and the overtone and combination modes of the amide I and II vibrations. An analysis of peak frequencies and intensities is used to provide support for the assignment of the amide II overtone and the amide I + II combination modes. A newly observed peak in the spectra is assigned to the amide I overtone. Symmetry considerations are discussed which predict the resonance of the overtone and combination modes with the N‐H stretching fundamental. © 1992 John Wiley & Sons, Inc.
Chain scission in polystyrene by impact fracture
Authors: Yang Arnold C.‐M. , Lee C. K. , Ferline Susan L. 
Published: April 2003

AbstractThe number of chain scissions ns per unit fracture area by impact in high‐molecular weight polystyrene is determined to be approximately 3.3 × 1014/cm2 at room temperature. This is almost 20 times larger than would be expected if chain scissions took place only at, or very close to, fracture surfaces. This result was obtained by measuring the molecular weight decrease and the total fracture area of the impact fragments by using size exclusion chromatography and statistical particle size measurements, respectively. The large ns strongly indicates that significant chain breakage occurs during crazing before the propagation of cracks. An average craze thickness before breakdown under impact is estimated from ns to be around 2 μm. In a diluted polymer, ns is found to be significantly lower than the extrapolated value, assuming a linear dilution of entangled chain crossings at the fracture surface. This low chain scission density, however, can be explained by taking into account the reduction of craze breakdown strain in the diluted polymers. Finally, the broken chain ends of polystyrene appear to be stable under ambient conditions. © 1992 John Wiley & Sons, Inc.
A computer simulation of trapping electrophoresis
Authors: Slater Gary W. , Villeneuve Christine 
Published: April 2003

AbstractThe gel electrophoretic migration of streptavidin‐DNA complexes is severely altered by the phenomenon known as “trapping electrophoresis.” We present a first computer simulation study of this process. Our simulations use the very efficient biased reptation algorithm. The steady state is characterized by a large increase in band broadening and interband separation. However, we also find that for a narrow range of molecular sizes, the separation power of gel electrophoresis is greatly increased. We discuss the implications of our findings for the possible improvement of DNA sequencing technologies. © 1992 John Wiley & Sons, Inc.
Aggregation in conducting copolymer solutions
Authors: Dai Liming , White John W. 
Published: April 2003

AbstractThe structure of polyacetylene–polyisoprene block copolymer solutions prepared by a modified anionic to Zeigler‐Natta method is reprted. Small‐angle x‐ray scattering results are consistent with formation of wormlike micelles, which arise mainly from interactions between the polyacetylene blocks of the copolymer in solution at room temperature. Aggrgation of the wormlike micelle can be described in terms of fractal geometry. I2‐doping produces marked changes in the optical spectrum of the acetylenic block and the small‐angle scattering indicates a change in polymer aggregation to a lamellar form. It is concluded that micellar structure is the natural morphology for solutions and gels of conducting polyacetylene–polyisoprene copolymers and that this persists into the solid state. Thus, conduction mechanisms for these polymers may bear re‐examination using micelles as the structural basis. © 1993 John Wiley & Sons, Inc.
Diffusion of nonionic azo dyes in nylon‐6
Authors: Shibusawa Takao 
Published: April 2003

AbstractDiffusion of 2,4‐dinitroaniline and three nonionic azo dyes in Nylon‐6 film was studied by analysis of the concentration‐distance curves (profiles) of penetrants in the polymer. Actual diffusivities D(c) of penetrants in polymer, diffusion coefficients as a function of the concentration Cf of penetrant in polymer, were calculated from the profile. It was found that D(c) is almost constant or decreases gradually with decreasing Cf in the range of high‐medium Cf but decreases appreciably with decreasing Cf at low Cf. The change in D(c) with Cf was explained in terms of the dual‐mode sorption‐diffusion model. The penetrants diffuse in the polymer as two distinct species, i.e., a dissolved species and an adsorbed species. The former is the penetrant taken up by the polymer by a partition mechanism (dissolved species) and the latter is that taken up by Langmuir sorption (adsorbed species). The actual diffusivity DP(c) of the dissolved species decreases with decreasing Cf. While the actual diffusivity DL(c) of the adsorbed species normally increases gradually with decreasing Cf. DP(c) is usually larger than DL(c). © 1993 John Wiley & Sons, Inc.
Polymer crystallization and reorganization during heating: Simulation with the sadler/gilmer model
Authors: Goldbeck‐Wood G. 
Published: April 2003

AbstractPolymer crystallization and melting under nonisothermal conditions are investigated by means of an extended version of the two‐dimensional Sadler / Gilmer pinning model. In particular, the case of a constant heating rate is simulated. Lamellar thickening and eventual melting are studied for a range of heating rates and initial temperatures. An approach to equilibrium (i.e. infinite thickness at Tom) by slowing down the heating rate is found to be more than exponentially suppressed. Similarities with heating experiments on polyethylene and PEEK are demonstrated. © 1993 John Wiley & Sons, Inc.
Elastic modulus and atomic displacements of skeleton and side groups in stretching of a polymer chain
Authors: Enomoto Satoru , Chuman Hiroshi , Kurihara Azusa 
Published: April 2003

AbstractWe propose a new method of calculating elastic modulus and atomic displacements of a stretched polymer chain. We use a stretched Cartesian coordinate system and a stretched B matrix defined by the Cartesian displacement components of the bonds to express the potential energy matrix Fx for stretching. The method is used to calculate elastic moduli of planar‐zigzag‐chain vinyl polymers and helical‐chain isotactic polypropylene and the atomic displacements of their skeleton and side groups. The skeletal displacements of planar‐zigzag‐chain polymers are about ten times larger than those of the side groups and reverse displacements of the two adjacent skeletal units occur in the direction perpendicular to the stretching direction along the fiber axis. In the case of isotactic polypropylene, the methyl group has more effect than the torsional change around the CC bond on the skeletal deformation. © 1993 John Wiley & Sons, Inc.
Synthesis and electrical conductivity of poly(1,4‐phenylenevinylene‐co‐2‐nitro‐1,4‐phenylenevinylene)
Authors: Jin Jung‐Il , Yu Sang‐Hyeun , Shim Hong‐Ku 
Published: April 2003

AbstractA series of PPV copolymers containing 2‐nitro‐1,4‐phenylenevinylene (NO2‐PV) units were prepared via the water‐soluble precursor route. They were obtained in film form and were doped with I2 and FeCl3. Doping increased the electrical conductivities to maximum values of about 3×10−2 and 3×10−1 s cm−1, respectively, for the two dopants. Conductivity depended strongly on the composition of the copolymers; it reached a maximum value at ca. 1–2 mol % of NO2‐PV units in the copolymers and then dropped rapidly with further increase in NO2‐PV content. Electronic effects of the substituent and morphological changes induced by copolymerization appear to interplay intricately, resulting in the occurrence of a maximum conducting composition. © 1993 John Wiley & Sons, Inc.
Transition regions and surface melting in partially crystalline polyethylene: A raman spectroscopic study
Authors: Mutter R. , Stille W. , Strobl G. 
Published: April 2003

AbstractStructures of semi crystalline high‐molecular weight polyethylene and their changes with temperature were studied by analysis of Raman spectra. Decomposition of spectra into contributions of an orthorhombic crystalline phase, a meltlike phase, and two kinds of transition regions yields the respective mass fractions. The results of temperature dependent measurements is indicative of a largely reversible surface melting process, the transition regions being located at the crystal surfaces. As‐polymerized samples show a large fraction of the intermediate phase. Annealing leads to a reduction of this phase. © 1993 John Wiley & Sons, Inc.
Morphology and properties of polycaprolactone‐poly(dimethyl siloxane)‐polycaprolactone triblock copolymers
Authors: Lovinger Andrew J. , Han B. J. , Padden Frank J. , Mirau Peter A. 
Published: April 2003

AbstractThe molecular structure, crystallization, solid‐state morphology, thermal properties, and phase behavior of two copolymers consisting of a poly(dimethylsiloxane) (PDMS) mid‐block coupled to polycaprolactone (PCL) end‐blocks were investigated. Both copolymers (which differ only in the molecular lengths of the PCL end‐blocks) were found to be lamellar systems, whose core consists of PCL chains having the same crystal structure as PCL homopolymer, and whose amorphous interlayers contain the PDMS blocks and the PCL noncrystalline segments. From x‐ray and electron‐microscopy results, it is expected that the PCL blocks may be folded once in the longer copolymer and not at all in the shorter. As a result of their differing PCL lengths, the former crystallizes as regular PCL spherulites (at a growth rate reduced with respect to PCL homopolymer), whereas the latter yields only defective, immature axialites of low overall crystallinity. Electron diffraction showed that these spherulites grow preferentially along b crystallographic axis and that the PCL crystalline stems are arranged perpendicularly to their lamellae. © 1993 John Wiley & Sons, Inc.
Unusual pressure‐induced phase behavior in crystalline poly‐4‐methyl‐pentene‐1
Authors: Rastogi S. , Newman M. , Keller A. 
Published: April 2003

AbstractWe report some highly unusual phase behavior, of general implication for condensed matter, on the polymer poly(4‐methyl‐pentene‐1) (P4MP1) induced by changes in pressure and temperature, as observed in situ by x‐ray diffraction. Upon increasing pressure beyond a threhold, the polymer, crystalline under ambient conditions, loses its crystalline order isothermally, passing through a continuously varying sequence of mesomorphic states, the process being reversible. This behavior is observed in two widely separated temperature regions, suggesting, for the first time in a single component system, the possibility of reentrant liquid‐crystal and amorphous phases. At the upper temperature region (ca. 250°C) there is a consecutive increase and decrease of melting point with pressure. In the lower temperature region (room temperature) the pressure converts the crystal into an amorphous‐like glass obviating the need for going through the melt first, and this in a reversible manner. The latter pressure‐induced disordered phase converts into crystal on raising the temperature, and reverts to the glassy, disordered phase on lowering the temperature. Some aspects of this behavior have been found quite recently in water‐ice and silica but the process of “melting on cooling” has no precedent in any known system. Other unexpected findings include a new pressure‐induced modification of P4MP1 with a one‐way only entry with temperature, but full reversibility with pressure leading to a triple point in the PT phase diagram. The above highly uncommon results are putting several prevailing preconceptions to test which are being scrutinized. In the course of it some early expectations on general phase behavior, allowing among others for reentrant phases in one component systems, are being invoked as potentially appropriate for certain polymeric systems, if not for condensed matter in general. © 1993 John Wiley & Sons, Inc.
Langmuir‐Blodgett films of polymethacrylates with side chains containing functionalized aromatic schiff's bases
Authors: Takahashi T. , Miller P. , Chen Y. M. , Samuelson L. , Galotti D. , Mandal B. K. , Kumar J. , Tripathy S. K. 
Published: April 2003

AbstractLangmuir‐Blodgett (LB) film formation has been investigated for polymers in which non‐linear optical (NLO) moieties are attached to the side chain of a polymethacrylate (PMA) backbone. Polymer monolayers were successfully transferred onto hydrophilic glass substrates using a moving‐wall type LB trough. The LB films were characterized by pressure‐area isotherms, polarized ultraviolet visible spectra, ellipsometry, and second harmonic generation measurements. The characterization shows that NLO moieties in the side chain are inclined at a shallow angle to the plane of the substrate. The second‐order nonlinear optical coefficient and molecular hyperpolarizability were also calculated. © 1993 John Wiley & Sons, Inc.
Improvement to the lattice‐fluid prediction of gas solubilities in polymer liquids
Authors: Rodgers Patrick A. , Sanchez Isaac C. 
Published: April 2003

AbstractPreviously we have shown that the Lattice Fluid (LF) model can quantitatively predict, without adjustable parameters, gas solubilities for hydrocarbon and chlorinated hydrocarbon vapors in nonpolar polymers. For polar polymers, the model can also predict, with reasonable success, the solubilities of polar and aromatic vapors. However, the solubilities in polar/nonpolar combinations of gas and polymer are systematically overestimated. These are cases in which the geometric mean approximation for the interaction parameter is not expected to be valid. This paper demonstrates that with the addition of a simple empirical correlation for the interaction parameter based on Hansen's three‐dimensional solubility parameters, the LF model is then able to quantitatively predict solubilities in all types of gas/polymer systems (excluding strongly self‐associating systems, such as alcohols). No adjustable parameters are used; only the pure component equation‐of‐state and solubility parameters are required. © 1993 John Wiley & Sons, Inc.
Configuration‐Dependent properties of the poly(dimethylsilmethylene) chain in the third‐order interaction approximation
Authors: Wu Xiaoyi , Jin Jinsheng , Zhang Linxi , Xu Jianmin 
Published: April 2003

AbstractOn the basis of rotational isomeric state theory, first‐order, second‐order, and third‐order conformation energies Eσ, Eω and Eφi respecively, are calculated for poly(dimethylsilmethylene) (CH2—Si(CH3)2)x using the Lennard–Jones potential function. With the third‐order interaction included, the characteristic ratios and temperature coefficients 〈R2〉0 and 〈μ2〉0 are obtained:

These results are in satisfactory agreement with the experimental data previously reported. © 1993 John Wiley & Sons, Inc.