bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermally stimulated discharge currents from polystyrene‐chloranil complex
Authors: Pillai P. K. C. , Rashmi  
Published: April 2003

AbstractTransitions in a polystyrene‐chloranil molecular complex have been analyzed by thermally stimulated discharge (TSD) current measurements. Peaks have been observed in the current spectra at 79 (α), 128 (ρ), and at 36°C (β). These peaks are attributed to the following mechanisms: the α peak to the randomization of dipoles at the glass–rubber transition, the ρ peak to the release of space charges via long‐range molecular motions at the liquid–liquid transition, and the β peak to the torsional vibrations of the phenyl side group. A high‐temperature treatment is found to narrow the distribution of the α relaxation and removes the ρ peak from the TSD spectrum. Repeated TSD runs on the same sample have been found to generate charges which give a small peak at 141°C. Absorbed water is found to shift the β and α relaxations to 39 and 91°C. Activation energy, relaxation time, and relaxation constant have been calculated for the α relaxation by the method of Bucci et al. The calculated values of activation energies have been compared with those reported in the literature for pure polystyrene.
Diffusion with discontinuous swelling. V. Type II diffusion into sheets and spheres
Authors: Peterlin A. 
Published: April 2003

AbstractType II diffusion into uniform spheres (radius R) and sheets (thickness 2l) is calculated under the assumption that the glass‐gel boundary proceeds at a constant velocity v from the surface towards the interior of the sample, that the diffusion coefficient Dg in the glass is constant and that the diffusion coefficient Dr of the rubbery gel is so much higher than vR or vl that practically no sorbate gradient is needed for the transport through the gel of the sorbate. The diffusion process is completed when this boundary reaches the center of the sample. The concentration profile of the sorbate in the glassy matrix in front of the boundary varies with time and velocity v. It does not, however, influence the boundary propagation velocity. Hence the often observed increase of the rate of the weight gain just at the end of the diffusion process is not considered at all. The relative weight gain of the sample W(t)/W∞ as a function of time is the only quantity usually measured. From the ordinate intercept A and the initial slope B of the plot of W(t)/t1/2W∞ vs. t1/2, one can calculate the characteristic transport properties, i.e., the diffusion coefficient Dg of the glass and the velocity v of the glass–gel boundary.
Dielectric properties of oligomers. VII. Low‐molecular‐weight propylene glycols
Authors: Ikada E. , Fukushima H. , Watanabe T. 
Published: April 2003

AbstractThe dielectric properties of low‐molecular‐weight propylene glycols HO[CH(CH3)CH2O]nH (n = 3, 4, 5) were investigated to clarify the effect of chain length on the dielectric properties. The measurement of dielectric constant and dielectric loss was carried out over the frequency range 30 Hz to 30 MHz at temperatures of −20 to −65°C. The static dielectric constants of these glycols are between 10 and 30, slightly smaller than values for the corresponding ethylene glycols of the same degree of polymerization. All of the Cole–Cole arcs, even that for pentapropylene glycol, can be represented by the empirical Davidson–Cole equation. The dielectric properties of homologous propylene glycols are compared with those for the ethylene glycols and are discussed in terms of the effects of chain length and intermolecular hydrogen bonds.
Recoverable compliance of a series of bimodal molecular weight blends of polystyrene
Authors: Orbon Stephen J. , Plazek Donald J. 
Published: April 2003

AbstractA series of bimodal molecular weight polystyrene blends was prepared. One component had a molecular weight greater than Mc and one less. The recoverable compliances were measured, and the retardation spectra determined via direct inversion. The retardation spectra of the blends are interpreted on the basis of the behavior of the spectra of the components, as a function of composition. It was observed that the low molecular weight component acted as a solvent. The effect of blending on the high molecular weight spectrum was to shift the position of the first peak to longer times and that of the second peak to shorter times. The peak separation was found to be proportional to the 3.4 power of the product of the molecular weight and the volume fraction of the high molecular weight component.
Melting and crystallization of IUPAC low‐density polyethylenes—characterization by differential scanning calorimetry
Authors: Magill J. H. , Peddada S. 
Published: April 2003

AbstractMelting and crystallization measurements were made on three low‐density polyethylenes claimed to be chemically similar and to have comparable flow behavior, but exhibiting differences in processing and end‐use properties. These IUPAC‐characterized materials were found to possess almost indistinguishable DSC melting curves obtained from the original polymers or for samples isothermally crystallized in this work. However, in isothermal melt crystallization experiments that were made at high sensitivity, readily distinguishable features were found, thus highlighting the DSC procedure as a useful, simple, and valid means of detecting subtle differences in the crystallizability. These differences are more easily revealed in solidification than in melt flow curves and are undoubtedly correlatable with physical processing where crystallization plays a significant role in determining the material end‐product behavior of semicrystalline polymers.
Some remarks on the dynamics of polymer melts
Authors: Daoud M. , De Gennes P. G. 
Published: April 2003

AbstractConsidering one long chain (N monomeric units) in a homodisperse melt of chemically identical, but shorter, “solvent” chains (P monomers per chain), we propose some tentative scaling laws for the self‐diffusion constant D(N) and the relaxation time T(N) of the solute chain. We also discuss the viscosity increment δη due to a small volume fraction Φ of the long chains. We find three regimes of behavior, depending on N and P, and on the distance between entanglement points (assumed smaller than N and P): (A) reptation of the N chain; (B) Stokes–Einstein regime; the solute moves like a usual polymer coil in a viscous fluid of P chains; (C) mixed regime, where D(N) is controlled by reptation, while δη is of type B. Contrary to our earlier belief, we find no significant regime where the process of “tube renewal” could be dominant.
Transport properties in concentrated polymer solutions
Authors: Perico A. , Cuniberti C. 
Published: April 2003

AbstractTransport properties of polymer solutions at finite concentration are derived in the partial draining case by formulating a static version of the theory given by Freed and Edwards (FE) for unentangled concentrated polymer solution. The method follows the Kirkwood—Riseman theory for infinitely dilute solutions: the dynamics of the polymer are ignored apart from the overall rotation or translation of the chain and the solvent velocity is given by the Navier—Stokes equations perturbed by point friction forces. The concentration dependence of viscosity and translational friction coefficient of finite chains obtained by numerical calculations are compared with the results of the FE closed‐form solution. It is shown that the screening of the hydrodynamic interaction approximately follows Debye‐like behavior in the entire range of concentration. The progressive balancing of the increasing intramolecular hydrodynamic interaction with its reduction due to the screening effects, as the molecular weight increases, is well evidenced by comparing results obtained at constant number concentration for different chain lengths.
Statistical thermodynamics of polymer solutions. VIII. Effect of intermolecular correlations on rayleigh scattering
Authors: Casassa Edward F. 
Published: April 2003

AbstractThe effect of intermolecular correlations on the angular dependence of the intensity of Rayleigh scattering from a dilute solution of a flexible‐chain polymer in a good solvent is studied for an approximate model that retains the random‐flight intramolecular segment‐pair correlation while probabilities of multiple intermolecular contacts are simplified as products of probabilities of single contacts, all conditional on a common “initial” contact. This model, unlike one in which a polymer chain is represented as a spherically symmetrical cloud of segments, gives very little deviation from Zimm's “single‐contact” approximation in light scattering: i.e., the initial concentration dependence of the concentration/intensity ratio is almost the same at all scattering angles. This behavior, which appears to underestimate the intermolecular correlations, can be accounted for by the symmetry of the bimolecular cluster as represented by the model.
Raman spectra of styrene‐sodium methacrylate copolymers—evidence for ion clustering
Authors: Neppel A. , Butler I. S. , Eisenberg A. 
Published: April 2003

AbstractRaman spectra of a series of styrene‐sodium methacrylate copolymers of varying sodium methacrylate contents have been investigated in the 425–100 cm−1 region. The bands appearing at 254 and 166 cm−1 have been attributed to ion multiplets and clusters, respectively. From an analysis of the intensities of these bands and a comparison of these intensities with those obtained from an analysis of dielectric data, it seems that Raman spectroscopy is a useful method for determining the concentrations of ions in the two different kinds of sites.
Concentration dependence of the viscoelastic properties of polystyrene‐tricresyl phosphate solutions
Authors: Plazek Donald J. , Riande Evaristo , Markovitz Hershel , Raghupathi N. 
Published: April 2003

AbstractBased on creep and creep‐recovery measurements, the viscoelastic functions [J(t), Jr(t), J′(ω), J″(ω), G′(ω), G″(ω), and L(lnτ)] are presented for solutions of a narrow molecular‐weight‐distribution polystyrene in tri‐m‐tolyl phosphate in the concentration range of 1% to 100% polymer. For concentrations of 25% polymer and above, two maxima are exhibited by the retardation spectrum, L(lnτ). In the neighborhood of each of the maxima the retardation spectra of the more concentrated solutions can be superimposed by translations along both the logL and logτ axes. Reflecting the increasing width of the rubbery plateau with increasing polymer concentration, the dependence of the concentration time‐scale shift factors is greater for the terminal region of response. The response of the solvent is seen at the lower concentrations and it is a less sensitive function of the concentration than that of the polystyrene. This behavior is associated with the previously reported observation of two glass‐transition temperatures in the middle concentration range. For the higher concentrations, both the steady‐state and rubbery‐plateau compliances are inversely proportional to the square of the concentration.
Method for viscosity measurements at high pressure
Authors: Birnboim Meyer H. , Weiss H. 
Published: April 2003

AbstractThe technique of quasielastic light scattering is utilized to determine the viscosity of fluids subjected to large hydrostatic pressures. In this method, a small concentration of insoluble polystyrene spheres of known diameter, 0.109 μm, is added to the fluid. The high‐pressure cell in which the fluid is contained has three optical windows. The laser light scattered from the suspended spheres is analyzed to determine the diffusion coefficient of the spheres. Since, by the Stokes law, the viscosity of the fluid is determined from the measured diffusion coefficient and known particle radius r. A small correction is required for the contraction of the spheres and for refractive‐index change of the water under pressure. Results on the viscosity of water at 25°C up to pressures of 2.5 kbar are reported and compared with published results. This method is applicable to lubricants and polymer solutions where the viscosity is many orders of magnitude greater than that of water.
Unperturbed dimensions of cyclochain polymers
Authors: Pavlova S. A. , Timofeeva G. I. , Ronova I. A. , Pancratova L. A. 
Published: April 2003

AbstractThe conformational parameters of three polyoxadiazoles were calculated by a direct computer simulation assuming free rotation about virtual bonds. The results obtained proved to be close to those derived from viscosity and sedimentation experiments.
Crystallization of polydioxolan. III. Microscopy and dilatometric analysis of the crystallization kinetics
Authors: Archambault Pierre , Prud'Homme Robert E. 
Published: April 2003

AbstractCrystallization kinetics has been studied for a polydioxolan (PDOL) sample, over a wide temperature range, by dilatometry and microscopy. The dilatometry results can be analyzed using the Avrami equation. At temperatures higher than 22°C, the crystallization data must be analyzed in two steps: the first part of the curve corresponds to PDOL with a very disordered morphology (Phase I) while the second part of the crystallization curve is related to a spherulitic morphology (Phase II). The passage from the low to the high crystallization temperature region is associated with a change in the Avrami exponent from 3 to 4. The crystal surface free‐energy product σσe was found to be 18 × 102 erg2/cm4, very close to that of polyoxymethylene. The crystallization kinetics was studied by microscopy over the temperature range−18 to 35°C. Growth and nucleation rates were recorded. Two phases are found only at temperatures higher than 22°C. The appearance of Phase II is related to a decrease in the growth rate of the sample. From the growth rates, the crystal surface free‐energy product σσe was found equal to 17 × 102 erg2/cm4. The detailed analysis of the crystallization of the two phases reveals a complicated process which can be divided into four different steps: (a) growth of a disordered phase, Phase I; (b) nucleation of a higher birefringence structure; (c) propagation of a high birefringence phase; and (d) spherulitic growth, Phase II. The analysis of PDOL crystallization strongly suggests the presence of a hedrite → oval → spherulite transition: the hedrite formation corresponds to step (a), the oval formation to steps (b) and (c), and the spherulite formation to step (d).
Melt crystallization of polypropylene: Effect of contact with fiber substrates
Authors: Campbell D. , Qayyum M. M. 
Published: April 2003

AbstractThe isothermal crystallization of isotactic polypropylene at different temperatures in the presence of fibrous substrates has been investigated. It is shown that preferential transcrystalline growth occurs at the fiber surface and that changes in nucleation density in the bulk material adjacent to the fibers also occur, the extent of which is dependent on temperature and fiber volume fraction. The effects are discussed in terms of the diffusion of heterogeneities in the bulk due to interaction and the adsorption on the fibers.
Further studies of the preferred chain conformation of crystalline poly(vinylidene chloride)
Authors: Wu M. S. , Painter P. C. , Coleman M. M. 
Published: April 2003

AbstractThe polymer chain conformation of crystalline poly(vinylidene chloride) (PVDC) has been the subject of controversy for the past three decades. In this study, a combination of techniques has been employed in an attempt to elucidate the preferred conformation of PVDC. Conformational models containing two monomers per translational repeat distance have been considered. Calculations of the translational repeat distance and the nonbonded Cl ⃛Cl contact distance between two adjacent CCl2 groups have been performed for each of the models. By comparing these results with those derived from x‐ray analysis and a theoretical estimation of the minimum nonbonded Cl ⃛Cl contact distance, an initial judgment of the structural feasibility of the models has been gained. A symmetry analysis has been performed for each conformational model and theoretical estimations of the polarization and intensity of the CCl and CH stretching vibrations have been obtained. These results have been compared with experimental infrared and Raman spectra. It is concluded that a TXTX′ (where X and X′ are torsional angles of equal value but opposite sign) chain‐conformational model for PVDC is favored.
Normal vibrational analysis of poly(vinylidene chloride)
Authors: Wu M. S. , Painter P. C. , Coleman M. M. 
Published: April 2003

AbstractNormal coordinate calculations have been performed for poly(vinylidene chloride) employing a TXTX′ conformational model (X and X′ denote torsional angles of equal value but opposite sign). A valence force field previously determined from the model compounds 2,2‐dichloropropane and 2,2‐dichlorobutane was directly transferred to the chain conformation of the polymer. The results are in excellent agreement with the observed vibrational spectra and we have been able to satisfactorily assign all the major normal modes.
Partial molal volumes of polymers in aqueous solutions from partial molal volume group contributions
Authors: Zana R. 
Published: April 2003

AbstractIt is shown that the partial molal volumes (pmv) of the repeat units of nonionic polymers in aqueous solutions calculated from pmv group contributions, obtained from pmv data for small molecules and salts in aqueous solutions, agree in most instances to within ± 1 cm3/mole with the experimental values. The pmv of ionic polymers calculated from pmv group contributions have been found to be always larger than the experimental values. The difference gives a lower bound of the cooperative electrostrictive effect of neighboring charged sites of the polymer chain on surrounding water molecules.
Isotope effect in the diffusion of hydrogen and deuterium in polymers
Authors: Toi Keio , Takeuchi Kazutoshi , Tokuda Taneki 
Published: April 2003

AbstractTemperature dependences of diffusion and permeation coefficients of hydrogen and deuterium in glassy and rubbery polymer films have been measured. The size of the free volume element in rubbery polymers has been calculated according to the theory of Frisch and Rogers for the quantum isotope effect, but the free volume is too large for precise calculation below the glass‐transition temperature. The cooperative movement of segments is also discussed using the ratio of preexponential factors for diffusion mechanisms above and below the glass‐transition temperature.
Lamellar morphology of polyethylene: Electron microscopy of a melt‐crystallized sharp fraction
Authors: Grubb D. T. , Keller A. 
Published: April 2003

AbstractThe morphology of linear polyethylene of Mw/Mn 1.19 crystallized isothermally from the melt has been investigated. Electron microscopy (EM) of stained thin sections gave exceptionally well‐defined images. There were no qualitative differences between Regime I and Regime II crystallization, but the lamellae grown at lower supercooling were thicker, larger, and had fewer spiral growths per unit area of fold surface. Small‐angle x‐ray scattering indicated a much sharper distribution of lamellar thicknesses than EM and Raman LAM did. This is evidence of the complementary nature of the techniques and not a contradiction. EM also revealed nonrepresentative features in detail. There were extremely thin lamellae formed on cooling, indicating molecular weight segregation even in this fractionated material, and there were extremely thick lamellae, attributed to isothermal thickening. As the representative lamellae are also supposed to have thickened isothermally, this raises the issue of when and how the lamellae which are the primary products of crystallization can be identified.
Thermal expansion of epoxy‐resin/particle composites—a size effect
Authors: De F. F. Pinheiro M. , Rosenberg H. M. 
Published: April 2003

AbstractThe thermal expansion of epoxy‐resin (Epikote 828)/particle composites has been measured in the range 77 to 450 K. The fillers used were Cu spheres (seven sizes from 5 to 150 μm diameter) and glass ballotini spheres (three sizes from 3.5 to 200 μm diameter). The volume concentrations used were 0.3 and 0.5 for Cu and 0.3 for glass. The experiments show that the addition of filler raises the glass transition temperature Tg, especially for fine particles. Below the normal value of Tg the thermal expansion is independent of particle size while above Tg the expansion is considerably smaller for samples containing the smaller particles. The effect is more pronounced for Cu than for glass filler. In addition a rapid heating rate reduces the expansion for specimens containing smaller particles but it does not effect the expansion for those containing large particles. The results, which are discussed in the light of the work of other authors, suggest that the addition of particles increases Tg by changing the nature of the polymer not only immediately at the particle surface but also for a considerable distance into the polymer itself. This probably occurs because the epoxy bonds strongly to the particles and this inhibits segmental rotations of the polymer even at considerable distances from the particle surface.
Effect of hydrolysis and drying on the siloxane bonds of a silane coupling agent deposited on E‐glass fibers
Authors: Ishida Hatsuo , Koenig Jack L. 
Published: April 2003

AbstractMolecular structural changes of a vinyl functional silane coupling agent on E‐glass fibers, induced during the immersion test in hot water, have been studied using Fourier transform infrared spectroscopy. The amount of the coupling agent on the glass fibers is reduced by hydrolytic degradation. Silanol groups formed by the hydrolysis of the siloxane groups have been detected in the FT‐IR difference spectrum in the range 930–840 cm−1 due to the SiO stretching mode of the SiOH groups. Heat treatment produces partial reformation of the siloxane bonds.
Effects of pressure on the compressibility and crystallization of poly(ethylene terephthalate)
Authors: Wei K. Y. , Cuculo J. A. 
Published: April 2003

AbstractThe effects of pressure on the compressibility and crystallization of poly(ethylene terephthalate) (PET) have been investigated. The Instron capillary rheometer was adapted as a high‐pressure dilatometer to perform experiments up to 40,000 psi. Compressibilities of solid and molten PET were measured. The increases in compressibility with increase in temperature for the solid state are discussed in terms of free‐volume theory. Results obtained for the melt are explained by invoking the second law of thermodynamics and the effect of pressure on the Gibbs free energy. The effects of temperature and compression rate on the pressure of crystallization (Pc) were also studied. As the crystallization temperature was increased from 240 to 286°C, Pc increased by about 16,000 psi. As the compression rate was raised from 1%/min to 8%/min, Pc increased 10,000 psi. At some undetermined compression rate above 8%/min it seemed impossible to induce crystallization in the melt, even with pressures up to 40,000 psi. Analysis of data on the kinetics of crystallization of PET melt under high pressures revealed low Avrami exponents, for which no unequivocal explanation is offered. It is possible, however, that crystallization at high pressure promotes the formation of a morphology made up of a certain percentage of “extended chains.” The alteration in the attendant spatial geometry involved in the crystallization might explain the lower Avrami exponents found. In another set of experiments, crystallization temperatures (Tc) were measured by slowly cooling PET melt under high pressures. As the pressure was raised from 3000 to 15,000 psi, Tc increased from about 246 to 282.5°C. These results are consistent with thermodynamic theory.