bluuebunny/crossref_metadata_2025_split huggingface dataset:
Infrared study of a thianthrenic polymer
Authors: Bertinelli F. , Bizzarri P. Costa , Casa C. Della , Fiorini M. 
Published: April 2003

AbstractWith the aim of finding insights into the as‐yet unclear chemical structure of thianthrenic polymers, a detailed IR analysis on a sample previously prepared by us is reported. The IR spectrum is interpreted mainly by way of two correlated reference units: the unsubstituted thianthrene and the 1,2,4,5‐tetrahalosubstituted benzene. Since a full interpretation of the spectrum of the thianthrene molecule is still lacking, we have tried a first assignment, taking o‐dihalobenzenes as component models. The spectrum of the polymer is found to correlate well with spectra of the reference moieties. Other units, taken into account to get the most reliable picture of the polymeric structure, seem to be present at appreciable concentrations. Our results lead us to propose the existence of regular, fully intramolecularly cyclized thianthrenic segments limited by defective units, mainly 1,2,4‐trithiosubstituted benzene. A narrow peak at 886 cm−1 can be interpreted as a regularity band, supporting the existence of chain segments where the repeat units are correlated by translational symmetry.
A partial phase diagram for a mixture of polystyrene with a low molecular weight styrene‐dimethylsiloxane block copolymer
Authors: Wang Baoyu , Krause Sonja 
Published: April 2003

AbstractDifferential scanning calorimetry (DSC) was used to examine the miscibility of polystyrene (PS), mol. wt. 105, with a phase‐separated styrene‐dimethylsiloxane (S‐DMS) diblock copolymer, Mn = 3800, 86 wt% S. Mixtures whose S content varied from 4 to 96 wt% PS were examined at a 10 K min−1 heating rate following a 200 K min−1 cooling rate from temperatures varying from 403 to 573 K. At some compositions, two glass transition temperatures, Tgs, corresponding to PS transitions were observed; at others only a single Tg was observed. When it was assumed that the 200 K min−1 cooling rate corresponded to quenching from the starting temperature, and when the heat capacity changes at the S glass transitions were used to calculate the percentage of S repeat units undergoing each glass transition, it was possible to calculate an approximate partial phase diagram for this mixture. At 96 wt% PS, there was evidence for a small amount of mixed S phase, possibly block copolymer micelles, in equilibrium with PS; from about 60 to 90 wt% PS, the S repeat units from the block copolymer appeared to be completely mixed with the PS. At lower wt% PS, unmixed block copolymer was in equilibrium with block copolymer whose S segments were mixed with the PS. The phase diagram appeared to vary only slightly with temperature.
Chemical and electrochemical doping in poly(paraphenylene vinylene) blends
Authors: Schlenoff Joseph B. , Machado Joseph M. , Glatkowski P. J. , Karasz Frank E. 
Published: April 2003

AbstractBlends of poly(p‐phenylene vinylene) (PPV), with other polymers were made by film‐casting from an aqueous mixture of the water‐soluble sulfonium salt precursor to PPV and the second polymer. The rates of chemical doping, using As F5, and of electrochemical doping, using perchlorate counter ion, of the PPV component are strongly influenced by the nature of the added macromolecule. In all cases studied the blends appear to be phase separated under all conditions. The most versatile blend was with poly(ethylene oxide) (PEO), which could be heated to 225°C without degradation and which yielded the highest electrical conductivity when doped. The utility of blends was demonstrated using free‐standing PPV/PEO blend samples as rechargeable battery electrodes.
Monoclinic‐to‐orthorhombic transformation in polyethylene
Authors: Takahashi Yasuhiro , Ishida Takeshi , Furusaka Michihiro 
Published: April 2003

AbstractThe monoclinic‐to‐orthorhombic phase transformation induced by heat‐treatment in polyethylene was studied by x‐ray and neutron diffraction. X‐ray diffraction patterns obtained with a position‐sensitive proportional counter system showed overlaps of the several reflections of orthorhombic and monoclinic forms. Therefore, they were resolved into individual peaks by assuming the Gaussian‐Cauchy function. From the intensity distributions in reciprocal space, the geometrical relation between two forms in the transformation was clarified. Furthermore, a mechanism was proposed from the change in half‐widths. In a crystallite, the boundary between the orthorhombic and monoclinic forms, parallel to the orthorhombic (110) and monoclinic (010) planes, moves to the monoclinic side as annealing proceeds, and the transformation takes place.
Studies of self‐diffusion of poly(dimethylsiloxane) chains in PDMS model networks by pulsed field gradient NMR
Authors: Garrido Leoncio , Mark James E. , Ackerman Jerome L. , Kinsey Robert A. 
Published: April 2003

AbstractWe have measured the diffusion of poly(dimethylsiloxane) (PDMS) chains in PDMS model networks by using a pulsed field gradient NMR technique. The model networks have been prepared by tetrafunctional endliking of linear PDMS chains having molecular weights Mn of 3,700 and 7,400 g mol−1. The diffusants have been incorporated in the networks by immersing pieces of them in PDMS linear chains with molecular weights Mn between 3,000 and 12,000 g mol−1 and molecular weight distributions Mw/Mn between 1.1 and 1.7. Although spin‐echo attenuation results were fitted to a model which takes into account polydispersity of the diffusant, these results did not exhibit any dependency upon the molecular weight distribution. The self‐diffusion coefficients of PDMS chains in the PDMS model networks were found to be smaller than in the melt, and the exponents for the diffusion coefficient dependence on Mn in the networks were found to be about‐1.3. Free diffusion will give an exponent equal to‐1, whereas free volume contributions or behavior intermediate between free and entangled diffusion will increase the magnitude of the exponent.
Layer‐lattices in Ziegler–Natta catalysts
Authors: Zannetti R. , Marega C. , Marigo A. , Martorana A. 
Published: April 2003

AbstractSome layered inorganic compounds of interest in old and new polymerization processes by Ziegler‐Natta stereospecific catalysis have been studied. The results are reported of an investigation concerning the crystallographic disorder phenomena in α‐TiCl3, VCl3, FeCl3, ball‐milled α‐MgCl2, β‐MgCl2, and in a new catalytic system produced according to some recent trends in the field. Best fits are reported of the experimental x‐ray diffraction patterns with patterns calculated for a theoretical model that accounts for structural disorder; the different fits indicate that disorder phenomena due to stacking faults are rather frequent in the examined compounds. The catalytic systems are more and more dispersed, and the maximum of dispersion in heterogeneous systems is reached for the recently proposed formulations.
A nucleation theory for the anomalous freezing point depression of solvents in swollen rubber gels
Authors: Honiball D. , Huson M. G. , McGill W. J. 
Published: April 2003

AbstractIt is shown that, on cooling, solvent present at the surface of swollen vulcanizates freezes before the onset of freezing in the gel solvent, causing gel solvent to diffuse to the sample surface where it adds to existing crystalline areas. At the freezing point of the gel solvent a liquid‐solid equilibrium does not exist, and a theory is postulated to account for the freezing point depression observed in swollen gels in terms of the conditions required for the formation of crystalline nuclei within the gel solvent. The theory is shown to apply to the freezing of cyclohexane and benzene in vulcanized and unvulcanized natural rubber. In line with the theory the presence of carbon black does not alter the solvent freezing point, but vacuole formation around nonreinforcing fillers leads to lower freezing point depressions.
Electroinitiated polymerization of halophenols: Electroinitiation potential‐lumo relations
Authors: Türker L. , Kisakürek D. , Şen Ş. , Toppare L. , Akbulut U. 
Published: April 2003

AbstractElectroinitiated polymerizations can be carried out by direct electron transfer via constant potential electrolysis.1–3 In doing so, the anodic (Ep, a) and the cathodic (Ep, c) potentials of the monomers must be measured by cyclic voltammetry. The cathodic peak potentials of halophenols were measured on Pt0 electrode versus Ag0/Ag+ in acetonitrile.Electroinitiated polymerization of bis(pyridine), bis(4‐chloro‐2,6‐dibromophenoxide) copper (II) complex was studied in dimethylformamide‐tetrabutylammonium fluoroborate by direct electron transfer from the cathode. Poly(phenylene oxides) obtained from the anolyte revealed that the monomer undergoes 1,2 as well as 1,4 addition reactions.Lowest unoccupied molecular orbital energies of the monomers were calculated by Hückel molecular orbital theory. The experimental Ep, c values were correlated to theoretical LUMO energies and electron densities using a multivariable linear regression model.
Uniaxial drawing of poly(ethyleneoxide)/poly(methyl methacrylate) blends by solid‐state extrusion
Authors: Kim Bong Shik , Porter Roger S. 
Published: April 2003

AbstractUltradrawn ribbons of solution‐cast blends of poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) have been prepared by a solid‐state coextrusion in a capillary rheometer. An increase of noncrystallizable PMMA in the blends drastically decreased the drawability from a draw ratio of 36 for pure PEO to 5 for a mixture of PEO/PMMA 40/60% by weight. A low crystallinity and depression of melting temperature for PEO were observed with increasing draw. The Flory‐Huggins theory for melting temperature depression has been used to derive the binary interaction parameter for these blends.
Effect of drawing on the α relaxation of poly(vinyl alcohol)
Authors: Garrett Paul D. , Grubb David T. 
Published: April 2003

AbstractThe α relaxation of isotropic and drawn poly(vinyl alcohol) dried gel films was studied using dynamic mechanical analysis. The temperature of the relaxation Tα increased from 160°C in the isotropic gel to 220°C in a fiber drawn 19 ×. The relaxation, which is associated with the crystalline regions of the material, also decreased continuously in magnitude as drawing proceeded, although crystallinity increased. At draw ratios over 12 ×, the relaxation became difficult to resolve, and no relaxation was observed in fibers drawn over 19 ×. The melting points of the fibers increased with draw ratio, but not enough to account for the large change in Tα. Crystal thickness in the fiber direction also increased with draw ratio. An analogy is drawn to the case of polyethylene where crystal thickness has been found to control Tα. The absence of a resolvable α relaxation is one reason why it is difficult to draw poly(vinyl alcohol) gels to extremely high ratios.
Preferential solvation in polymer cosolvent systems: Polystyrene + cyclohexane + ethanol and poly(vinyl‐2‐pyridine) + nitromethane + carbon tetrachloride
Authors: Viras Fotini , Viras Kyriakos 
Published: April 2003

AbstractTwo cosolvent systems are studied by light scattering and viscosity measurements. The cosolvency mechanism is discussed in relation to the preferential adsorption, solubility parameter, and excess free energy of mixing of the two liquid components. The cosolvency effects are attributed to a “true” and an “apparent” cosolvency.
Pressure dependence of the dielectric properties and phase transitions of polyvinylidene fluoride (PVDF) and a copolymer with trifluoroethylene
Authors: Samara George A. 
Published: April 2003

AbstractThe frequency, temperature, and hydrostatic pressure dependences of the dielectric properties, molecular relaxations, and phase transitions in PVDF and a copolymer with a 30 mol% trifluoroethylene were investigated. The β‐relaxation peak temperature Tβ and the melting temperature Tm of both polymers, and the ferroelectric transition temperature Tc of the copolymer, are strong increasing functions of pressure. The magnitudes of the pressure derivatives of Tβ, Tc, and Tm increase in the order of the “transition” temperatures, i.e., Tβ(P) < Tc(P) < Tm(P). These results can be qualitatively understood in terms of the nature of the molecular motion and/or reorientation processes involved. The results on the copolymer suggest that pressure should induce a ferroelectric‐paraelectric transition in PVDF below Tm, but such a transition was not observed over the limited pressure range of the present experiments. The relaxational dynamic (not static) nature of the melting process in these materials is indicated by the observed dependence of Tm on probe frequency. The frequency (or rate) and strong pressure dependences of Tm of PVDF provide a rational explanation for why it is possible to use this polymer as a piezoelectric shock‐wave gauge to relatively high shock pressures and the accompanying high temperatures.
Rate‐dependent nonlinear constitutive equation of polypropylene
Authors: Kitagawa Masayoshi , Mori Tatsuya , Matsutani Tomohiko 
Published: April 2003

AbstractIn order to investigate the viscoelastic‐plastic properties of polymer solids and construct a constitutive equation for them, torsional tests were performed on polypropylene (PP) hollow cylinders. Testing was conducted under constant strain rate, abrupt change of strain rate, stress relaxation, creep, and cyclic loading conditions. The experimental data were compared with the numerical results derived from an overstress model. It is shown that the overstress theory explains the viscoelastic‐plastic properties of PP well, provided that the current strain is not below the maximum previous strain.
14CO2 and CO2 Transport in polycarbonate: Measurement of the time lag and permeability
Authors: Alger Montgomery M. , Ward William J. , Stanley Thomas J. 
Published: April 2003

AbstractTransport of CO2 across polycarbonate films has been studied using a diffusion cell technique employing a radioactively labelled tracer (14CO2). Because the 14CO2 driving force could be established independently of the unlabelled CO2 driving force, several classes of experiments not possible with conventional techniques were performed. These different classes of experiments showed measurably different time lags. Formally, these experiments all are limiting cases of the more general mixed‐gas permeation problem; however, simplifying assumptions in the dual sorption theory are possible because the tracer concentration approaches zero and because the two species in this special mixed‐gas problem exhibit the same dual sorption parameters. These simplifications allow derivation of analytical expressions for the time lag for both the unlabelled and labelled gas species. The experimental measurements are in good agreement with the dual sorption model formulated for the mixed‐gas tracer diffusion problem.
Fit of a nonreptative model of polymer melt dynamics to experimental melt diffusion constant measurements
Authors: Yeates Alan T. , Skolnick Jeffrey , Yaris Robert 
Published: April 2003

AbstractA model of polymer melt diffusion recently proposed by Skolnick, Yaris, and Kolinski and which does not invoke reptation as the dominant mechanism of polymer melt motion is used to fit polymer self‐diffusion constant data measured by Antonietti, Fölsch, and Sillescu for a homopolymeric melt as well as for a probe in a larger molecular weight matrix. The quality of fit of the data indicates that reptation theory cannot be verified by simple comparison to diffusion constant measurements.
Solution behavior of sulfonate ionomer interpolymer complexes
Authors: Lundberg R. D. , Phillips R. R. , Peiffer D. G. 
Published: April 2003

AbstractThe interaction of metal sulfonate ionomers with polymers containing low levels of amines has been investigated in solution. For example, zinc sulfo EPDM and a styrene/vinyl pyridine copolymer form such complexes over broad concentration ranges. The resultant solutions offer enhanced viscosities at dilute polymer concentrations. At high polymer levels solutions based on these complexes are lower in viscosity than the ionomer alone. These interpolymer complexes have been shown to exhibit an improved property/rheology balance in bulk systems. In solution, polymer complexes provide control of hydrocarbon solution viscosity not available with conventional polymers. Reduced viscosity‐concentration studies suggest that these polymer complexes are a result of the amine‐containing polymer interacting with intramolecular‐associated ionomer coils, which at higher concentrations form a pseudonetwork.
Rotational diffusivity of rodlike molecules in amorphous polymeric matrices
Authors: Hill Davide A. , Soane David S. 
Published: April 2003

AbstractIn this note, scaling laws for rotational diffusivity of dilute monodisperse rigid‐rod molecules (guest rods) in semidilute amorphous polymer solutions (host molecules) are derived. The coillike matrix molecules are modeled as a collection of flexibly connected rigid subunits. This allows an analogy with the Doi‐Edwards theory for monodisperse rigid rods in semidilute solutions to be used in the analysis. Very strong dependencies are predicted for the rotational diffusivity of the rods on host polymer volume fraction and rod length. In semidilute polymer solutions the coils dramatically hinder the rotational freedom of the rods for r2 ≫ ψp−1, r being the rod aspect ratio and ψp the polymer volume fraction.
Birefringence of polyethylene melt in transient elongational flow at constant strain rate
Authors: Koyama K. , Ishizuka O. 
Published: April 2003

AbstractSimultaneous birefringence and elongational viscosity measurements were carried out on molten commercial grade, low‐density polyethylenes during simple elongational flow at constant strain rate and constant temperature. The birefringence increased with time during constant strain rate elongation. The increase in birefringence was a linear function of elongational stress throughout whole elongation, but the elongational viscosity increased in two stages. The increase in elongational viscosity can be divided into linear viscoelastic and nonlnear viscoelastic regions. The linear region appeared at small strain and the nonlinear region appeared at strain greater than 0.7. The elongational viscosity in the nonlinear region increased much more rapidly than that in the linear region. The Gaussian approximation, which is commonly used in molecular models, could be used for the transient elongational flow. A constant stress‐optical coefficient C = 1.3 × 10−10 cm2/dyn was obtained for all the elongational experiments, independent of strain rate (0.002‐0.2s−1). The stress‐optical coefficients were weakly dependent on temperature, as predicted by the theory of rubber elasticity.
The physical properties of bisphenol‐a‐based epoxy resins during and after curing. II. Creep behavior above and below the glass transition temperature
Authors: Plazek D. J. , Choy I. C. 
Published: April 2003

AbstractThe creep behavior of a series of fully cured epoxy resins with different crosslink densities was determined from the glassy compliance level to the equilibrium compliance Je at temperatures above Tg and at the glassy level below Tg during spontaneous densification at four aging temperatures, 4,4‐diamino diphenyl sulfone DDS was used to crosslink the epoxy resins. The shear creep compliance curves J(t) obtained with materials at equilibrium densities near and above Tg were compared at their respective Tgs. Tgs from 101 to 205°C were observed for the epoxies which were based on the diglycidyl ether of bisphenol A. Creep rates were found to be the same at short times, and equilibrium compliances Je were close to the predictions of the kinetic theory of rubberlike elasticity. Time scale shift factors determined during physical aging were reduced to Tg. At compliances below 2 × 10−10 cm2/dyn, Andrade creep, where J(t) is a linear function of the cube root of creep time, was observed. The time to reach an equilibrium volume at Tg was found to be longer for the epoxy resin with lower crosslink densities. The increase of density during curing is illustrated for the epoxy resin with the highest crosslink density.
The deformation behavior of polyethersulfone and polycarbonate
Authors: Plummer C. J. G. , Donald A. M. 
Published: April 2003

AbstractIn thin films of polyethersulfone and polycarbonate it is shown that crazing becomes increasingly likely to occur as the temperature is raised. The transition temperature depends on strain rate and molecular weight. Three regimes of behavior can be identified. In both the low‐temperature (shear deformation) and high‐temperature (crazing) regimes the strain to craze is independent of molecular weight. However, in the intermediate crazing regime chain length is important, indicating the importance of disentanglement over this temperature range. It is thought that at the highest temperatures disentanglement is still occurring, but the rate‐determining step is now general plastic flow into the craze fibrils.
Spectroscopic study of a model composite: Compressive behavior of the reinforcement fiber and the buildup of thermal residual stress
Authors: Fan C. F. , Hsu S. L. 
Published: April 2003

AbstractThe compressive behavior of polydiacetylene (PDA) single‐crystal fiber and the buildup of thermal residual stress in PDA/epoxy model composite systems have been studied by Raman‐mechanical spectroscopy. The compressive failure of the PDA fiber has been directly observed when the macroscopic compressive stress, applied during a bending experiment, exceeds a critical value. Fiber failure in model composites caused by thermal residual stress can also be observed by Raman measurements as well as optical microscopy. In fact, the most clear indication of fiber failure was the observation of kink bands formed. The thermal residual stress buildup which resulted from significant temperature changes in this model composite have also been studied. Contrary to most accepted views, our analysis showed the adhesion between the reinforcement fiber to the epoxy matrix to be strong.
Annealing of polymers in the solid‐melt region. I. A new approach to estimate the equilibrium melting temperature of polymer crystals
Authors: Khanna Yash P. , Kumar Rakesh 
Published: April 2003

AbstractAn annealing scheme for semicrystalline polymers is presented whereby a polymer is annealed in its solid‐melt region, leading to crystals approaching the equilibrium crystals in terms of melting temperature. The annealing data is mathematically treated to estimate the equilibrium melting temperature (T0m) of polymer crystals. As is the case with any extrapolation procedure, there are minor shortcomings with our approach, but these are far outweighed by the advantages; the latter are exemplified by a comparison with the widely used Hoffman‐Weeks method for estimating (T0m). The validity of our annealing scheme for the estimation of (T0m) is demonstrated by analysis of well‐studied polymers such as nylon 6, polyethylene terephthalate (PET), polyethylene (PE), polypivalolactone (PPL), and polytetrafluoroethylene (PTFE); other polymers studied include polyether ether ketone (PEEK) and nylon 4,6.