bluuebunny/crossref_metadata_2025_split huggingface dataset:
Alternating‐current ionic conduction and dielectric relaxation of poly(vinylidene fluoride) at high temperatures
Authors: Yano Shinichi , Tadano Kenji , Aoki Koichiro , Koizumi Naokazu 
Published: April 2003

AbstractDielectric properties of poly(vinylidene fluoride) have been studied in the frequency range 20 Hz to 1 MHz and between 100 and 220°C, during heating and cooling. The dielectric constant and loss change abruptly at the temperature Tm corresponding to the melting point. At lower frequencies, two types of ionic conductin are observed. One appears below Tm and is attributed to interfacial polarization. The other occurs above Tm and is related to electrode polarization. These results suggest that a crystalline polymer is a heterogeneous medium for ionic transport, while the melt is a homogeneous medium. From these results, the nature of ac ionic conduction in crystalline polymers is discussed. At high frequency, the α relaxation is observed below Tm. It is due to the molecular motion in the crystalline region and disappears at Tm.
Optical studies of the deformation of model filled rubbers
Authors: Ong C. S. M. , Stein R. S. 
Published: April 2003

AbstractThe strain pattern about a spherical glass bead imbedded in a stretched rubber has been calculated and used to predict the birefringence and light scattering. This is compared with experimental measurements of the retardation pattern observed using a polarization microscope and deduced from the low‐angle laser Hv light scattering pattern. The agreement with theory is favorable. The light scattering is suggestive of similar origins of light scattering from crystallizing rubbers and from inhomogeneously crosslinked rubbers.
Relaxations in the transition region of crosslinked polyesters. II. The glass transition
Authors: Cook W. D. , Delatycki O. 
Published: April 2003

AbstractThe glass‐transition region of crosslinked polymers prepared from poly(1,2‐propylene phthalate fumarate) and styrene was studied using a torsion pendulum. The glass‐transition temperature and the modulus in the rubbery region of these polymers were analyzed in terms of the crosslink density. The styrene concentration at which the maximum crosslink density occurs, as estimated from the viscoelastic data, is found to be in agreement with estimates made by other workers using chemical methods.
Scattering of light from thin polymer films. I. Multiple scattering
Authors: Prud'homme Robert E. , Bourland Larry , Natarajan Raj T. , Stein Richard S. 
Published: April 2003

AbstractA general method is described to take into account the multiple scattering effect in a small‐angle light scattering from thin polymer films. It is seen that multiple scattering tends to make the scattering envelope more diffuse, reducing the intensity in the high intensity regions and increasing it in the low intensity regions. The method is applied here to a spherulitic system, but it is valid for any other system where the principal scattering is in the forward direction.
Crystallization during polymerization of diazomethane. I. The boron trifluoride catalyzed reaction
Authors: Mucha Maria , Wunderlich Bernhard 
Published: April 2003

AbstractThe polymerization and crystallization of diazomethane was analyzed starting with various monomer and catalyst concentrations by following the monomer concentration and analysis of the solid polymethylene produced. Electron microscopy, thermal analysis, x‐ray diffraction, and viscometry and density determinations were used to characterize the crystals as produced and after etching with nitric acid. The crystals have a fibrillar and a lamellar component and show no regular chain folding of the molecules. The overall process follows only very approximately the path expected for an ideal living‐polymer system capable of reaction in solution and in the solid state. For more detailed correspondence, it was necessary to assume two reaction paths and two crystallization paths.
ESR study of radicals formed during tensile deformation of poly[p‐(2‐hydroxyethoxy) benzoic acid] fibers
Authors: Nagamura Toshihiko , Takayanagi Motowo 
Published: April 2003

AbstractRadical formation during tensile deformation of highly oriented poly[p‐(2‐hydroxyethoxy)benzoic acid] fibers was investigated by electron spin resonance. Stretching of fibers in vacuo and in a stream of nitrogen gas at room temperature generated a large number of radicals which increased rapidly with macroscopic strain, while stretching in air generated only a small number of radicals. The radicals formed in vacuo or in nitrogen decayed rather rapidly after introduction of air. The observed spectrum was apparently a triplet with a line separation of about 7.5 gauss and a small asymmetry. The inspection of the hyperfine structure, line separation, and total width of the spectrum and the comparison between the observed and the calculated spectrum based on a model substance proved that the observed species is a phenoxy type radical generated by rupture of main chains. A small asymmetry of observed spectrum was explained by anisotropy of the g‐tensor. The alkyl end‐radical generated together with one of the phenoxy type could not be detected, perhaps owing to its high reactivity.
Small‐angle x‐ray study of deformed bulk polyethylene
Authors: Gerasimov V. I. , Genin Ya V. , Tsvankin D. Ya. 
Published: April 2003

AbstractScattering by extruded polyethylene films has been used to analyze in detail the small‐angle scattering of x‐rays by strained spherulitic samples. It is shown that the basic small‐angle patterns in spherulitic specimens can be obtained by summing small‐angle reflections from films drawn both parallel and normal to the direction of extrusion. The representation of a complex pattern by superposition of simpler reflection makes it possible to calculate local strains in various regions of spherulites in bulk specimens.
Determination of the Flory–Huggins χ parameter, the heat of dilution, and the excess heat capacity of some alkanes in polydimethylsiloxane by gas chromatography
Authors: Hammers W. E. , De Ligny C. L. 
Published: April 2003

AbstractThe change in standard chemical potential of a number of alkanes on PDMS going from dilute solution to the perfect vapor ΔḠ was measured by gas chromatography over a large range of temperatures. The change in standard chemical potential of the alkane going from the pure liquid to the perfect vapor ΔḠ was calculated from fugacity data. These data were fitted separately to three Taylor's series expansions wherein the (partial) heat capacity of vaporization is zero, constant, and linearly dependent on temperature, respectively. On the basis of statistical and physical arguments it was concluded that the partial excess functions determined by gas chromatography should be described with a temperature‐independent partial excess heat capacity.
Convergence of the distribution functions for wormlike chains
Authors: Shimada Jiro , Fujii Motoharu , Yamakawa Hiromi 
Published: April 2003

AbstractThe Daniels‐type distribution functions of the end‐to‐end distance of three‐dimensional and two‐dimensional wormlike chains are obtained to terms of order t−10, by an operational method with use of a digital computer, where t is the ratio of the total chain contour length to the Kuhn segment length in three‐dimensional cases and of the contour length to the persistence length in two‐dimensional cases. The convergence of the ring‐closure probability and the mean reciprocal distance is examined on the basis of these distribution functions. A similar study of the moment‐based distribution functions is also made.
Time‐dependent photocurrents in polyethylene
Authors: Wintle H. J. 
Published: April 2003

AbstractA detailed study of the photocurrents in low‐density polyethylene at wavelengths of 350 nm, 300 nm, and 240 nm has confirmed that the current is a linear function of intensity and has established that the observed decrease of current depends on the integrated flux of quanta at the metal–polymer interface, and is independent of intensity and pulse repetition rate. Comparison with electron excitation experiments shows that in the present case, optical ionization occurs within a few angstroms of the interface.Connections between the present results and known photodegradation data are explored, but no firm correlation can be obtained either for the initial “fast transient” or for the “slow transient” which occurs only in the shorter wavelength region. Possible models for hole injection are presented.
Crazing and fracture in crystalline, isotactic polypropylene and the effect of morphology, gaseous environments, and temperature
Authors: Olf H. G. , Peterlin A. 
Published: April 2003

AbstractStress crazing is studied in three forms of crystalline, isotactic polypropylene (PP): (1) smectic/nonspherulitic, (2) monoclinic/nonspherulitic, and (3) monoclinic/spherulitic PP. Optical and scanning electron microscopy as well as stress—strain measurements are used to characterize crazing behavior in these three forms as a function of temperature (−210 to 60°C) and of the gaseous environment (vacuum, He, N2, Ar, O2, and CO2). Forms 1 and 2 are found to craze much like an amorphous, glassy polymer in the temperature range between −210 and −20°C, irrespective of environment. The plastic crazing strain is large close to the glass‐transition range (ca. −20°C) of amorphous PP and in the neighborhood of the condensation temperature of the environmental gas. Near condensation, the gas acts as a crazing agent inasmuch as the stress necessary to promote crazing is lower in its presence than in vacuum. A gas is the more efficient as a crazing agent, the greater is its thermodynamic activity.Spherulitic PP (form 3) crazes in an entirely different manner from an amorphous, glassy polymer, showing that the presence of spherulites influences crazing behavior much more profoundly than the mere presence of a smectic or monoclinic crystal lattice. Below room temperature, crazes are generally restricted in length to a single spherulite, emanating from the center and going along radii perpendicular, within about 15°, to the direction of stress. They never go along spherulite boundaries. Gases near their condensation temperature act as crazing agents much as in nonspherulitic PP. Above room temperature the crazes are no longer related to the spherulite structure, being extremely long and perfectly perpendicular to the stress direction. Apparently the crystals are softened enough by thermally activated segmental motion to permit easy propagation of the craze. The morphology of the fracture surfaces and its dependence on temperature and environment is described and discussed. Concerning the action of gases as crazing agents it is argued that the gas is strongly absorbed at the craze tip, where stress concentration increases both the equilibrium gas solubility and the diffusion constant. Hence, a plasticized zone is formed having a decreased yield stress for plastic flow. This is considered to be the main mechanism by which the gas acts as a crazing agent. In addition, reduction of the surface energy of the polymer by the adsorbed gas eases the hole formation involved in crazing.
Solvent effects in flow birefringence of polymer solutions. General theory and discussion of form effects
Authors: Fortelný I. 
Published: April 2003

AbstractA new, more realistic optical model of a dilute polymer solution is used to calculate the intrinsic birefringence. A general formula is derived valid for an arbitrary equilibrium distribution function of particles in the system. Besides the contributions due to the polymer and solvent, the resulting relation for intrinsic birefringence also contains terms reflecting the effect of orientation of solvent surrounding the polymer chain and the contribution of optical interactions between polymer segments and molecules of solvent. A detailed discussion of the optical interactions in an isotropic solvent reveals that the problem may be transformed in the first approximation into that of interactions between excess dipoles; however, any separation of the macroform and microform effects has no theoretical justification. It is shown that the microform effect depends on a detailed optical model of the statistical segment, and this effect is calculated for two simple models. The expression suggested by Tsvetkov cannot be applied to a segment consisting of anisotropic monomers.
Mechanism of dc electrical conductivity in poly(vinyl chloride)
Authors: Lupu A. , Giurgea M. , Baltog I. , Gluck P. 
Published: April 2003

AbstractDc conductivity measurements were performed as a function of temperature on unplasticized poly(vinyl chloride) and on PVC plasticized with various amounts of dioctylphthalate. The conductivity curves consist of two or three straight‐line segments denoted I, II, and III with increasing of temperature. The intersection of segments I and II occurs at the glass‐transition temperature Tg. The slope in region I is independent of the DOP concentration, while the slope in region II decreases slowly with an increase in the amount of DOP. No dependence of the conductivity on the molecular weight was found. From the conductivity curves, activation energies were evaluated below and above Tg. These satisfactorily coincide with those determined by dielectric loss or by electrical transient phenomena. A dc conduction mechanism is proposed based on electronic hopping favored by the micro‐Brownian motions responsible for dielectric losses. These motions involve smaller chain lengths below than above Tg. The experimental results are discussed and interpreted in terms of the proposed mechanism.
Viscoelastic study of the conformational transition of poly(methacrylic acid) in dilute aqueous solution
Authors: Okamoto Hideho , Wada Yasaku 
Published: April 2003

AbstractThe dynamic viscosity of dilute aqueous solution of poly(methacrylic acid) (PMA) was measured over the frequency range 2–500 kHz for various degrees of ionization. The relaxation spectrum calculated from the viscosity exhibits a conformational relaxation spectrum in the short‐time region and a rotational one in the long‐time region. The former is fitted by the Zimm theory over the entire range of ionization, including the transition from a compact structure to an open one. The conformational relaxation time begins to increase at the midpoint of the transition region, but the rotational relaxation time increases very markedly in the initial stage of the transition.The present and previously reported experimental findings are interpreted in terms of the assumption that the compact structure is stabilized by short‐range methyl–methyl bonding as well as “long‐range” methyl–methyl bonding (bonding between methyl groups spatially close but remotely connected along the chain contour). In the initial stage of the transition, the latter primarily break up, resulting in expansion of overall chain dimensions, and subsequently the former are destroyed, resulting in the change in local chain conformation.
The alpha–beta transformation in polypivalolactone. II. A simple mechanical model
Authors: Prud'Homme Robert E. 
Published: April 2003

AbstractA simple mechanical model based on the equilibrium rate theory of Burte and Halsey is presented in order to explain the stress–strain curve of polypivalolactone (PPL) fibers. A semiquantitative application of this model indicates that the PPL alpha–beta transformation implies the cooperative deformation of at least thrity chain units and that the free energy difference between the alpha and beta states is of the order of 2 kcal/mole of monomer.
Thermal analysis and dilatometry of glasses formed under elevated pressure
Authors: Weitz Alexander , Wunderlich Bernhard 
Published: April 2003

AbstractDensified glasses, formed from the liquid state by cooling at 5°C/hr under elevated pressures of up to 517 MN/m2, were studied by thermal analysis and dilatometry at ambient pressure. The materials studied were polystyrene, poly(methyl methacrylate), phenolphthalein, sucrose, and a 1 : 1 mixture by weight of potassium and calcium nitrate. Enthalpies of the densified glasses were found to be up to 2–6 J/g greater than the enthalpies of the glasses formed at atmospheric pressure. The major enthalpy and volume relaxation on heating the densified glasses was found to be not correlated The upper temperature limit of the glass‐transition region remained constant for all glasses cooled at various pressures, while the lower temperature limit of the polymeric glasses decreased up to 55°C with increasing pressure. The interpretation of the data suggests that an additional, significant volume relaxation occurred on depressurization at room temperature for all glasses analyzed.
Synthesis and solution properties of linear, four‐branched, and six‐branched star polyisoprenes
Authors: Hadjichristidis N. , Roovers J. E. L. 
Published: April 2003

AbstractA number of linear, four‐ and six‐branched regular star polyisoprenes were synthesized by anionic polymerization techniques in benzene using lithium as the counterion and polyfunctional silicon chloride compounds as the coupling agents. Light‐scattering measurements in dioxane were performed in order to establish Θ solvent conditions. Determinations of the radius of gyration of the polymers of different structure indicate that g = 〈S2〉0,br/〈S2〉0,lin agree closely with random flight calculations for the ratios. Intrinsic viscosities determined in a Θ solvent establish g′ = [η]br/[η]lin to be 0.773 and 0.625 for the four‐ and six‐branched polyisoprenes, respectively. In a good solvent g′ values are slightly lower. These values are compared with theoretical estimates. Viscosities of 19.29% (w/w) solutions of the polyisoprenes in n‐decane at 25°C are correlated with the intrinsic viscosities of the polymers under Θ conditions.
Crystallization and melting of polyethylene under high pressure. I. Crystallization by slow cooling from the melt
Authors: Maeda Yoji , Kanetsuna Hisaaki 
Published: April 2003

AbstractCrystallization and melting behavior of linear polyethylene under high pressures up to 6000 kg/cm2 has been investigated with a high‐pressure dilatometer. Crystallization was carried out at a cooling rate of 1°C/min from the melt at each pressure. The samples were characterized by differential scanning calorimetry, density, and electron microscopy. Folded‐chain crystals are formed in the low‐pressure region below 2000 kg/cm2. Crystallization in the intermediate‐pressure region between 2000 and 3500 kg/cm2 gives a mixture of folded‐chain and extended‐chain crystals. The extendedchain crystals are the more stable and predominate at increasing pressure. At high pressures above 4700 kg/cm2, two stages of crystallization and of melting can be observed. The phenomenon suggests that the two kinds of extended‐chain crystals with different thermal stability, i.e., the ordinary extended‐chain crystals and “highly extended‐chain” crystals form through individual crystallization processes from the melt at high pressure.
The statistics of chain sectioning experiments on cellulose fibers
Authors: Holt C. , Sellen D. B. 
Published: April 2003

AbstractIt has been suggested that transverse sectioning of natural cellulose fibers can be used to test ideas about microfibril structure. This proposal has been examined theoretically and numerical calculations of the weight‐distribution curve of sectioned chains are given for several different models. These calculations illustrate the effects that different types of chain folding have on the sectioned size distribution. The difficulties involved in the practical execution of this type of experiment are discussed and it is concluded that fiber‐sectioning experiments described in the literature do not disprove the folded‐chain hypothesis.
Shear‐induced crystallization of polymers. I. The four‐roller apparatus
Authors: Torza S. 
Published: April 2003

AbstractWe describe a new technique for producing fibrous crystals from shear‐induced crystallization of polymer solutions and polymer melts. Our technique makes use of a modified version of the 4‐Roller apparatus originally developed by G. I. Taylor to study the formation of emulsions. This apparatus generates a planar extensional flow field in which macromolecules are extended more easily than in flow fields with transverse velocity gradients.
Characterization of macromolecules in liquid solutions by thermal diffusion. I. Dependence of the soret coefficient on the nature of the dispersing medium
Authors: Gaeta F. S. , Scala G. , Brescia G. , Di Chiara A. 
Published: April 2003

AbstractExperiments have been carried out on thermal diffusion of macromolecular particles dispersed in various liquids, with the object of checking some predictions of the radiation‐pressure theory of Soret effect in liquids and of establishing a method of physical characterization of macromolecules in liquid solutions. The experimental results confirm the importance of the ratio G between thermal conductivity K and (phase) velocity v of high‐frequency elastic waves of the materials composing the mixture in determining the thermodiffusive behavior of a liquid solution. We have shown that the migration of the macromolecular component takes place in the same direction in which thermal energy is flowing or opposite to it, depending on whether G of the dispersed particles is smaller or larger relative to the G of the liquid.Another aspect of the same phenomenon may be observed when macroscopic pieces of nonmetallic materials are suspended in a liquid, and heat is made to flow through this solid plunger and the surrounding liquid. The experiments performed with molecular solutions and with macroscopic plungers mutually complement and confirm each other.Anomalous results obtained in the case of solutions of polyvinylpyrrolidone in methanol are also discussed, and the possibility that this might be the consequence of the existence of a marked velocity dispersion in the high‐frequency region of the spectrum of thermal waves in both water and methyl alcohol is indicated.Finally the possibility is hinted that thermal diffusion might have been responsible for the phenomena of molecular selection and evolution which ultimately led to the origin of life on our planet.
Pressure dependence of the thermal conductivity, thermal diffusivity, and specific heat of some polymers
Authors: Andersson Per , Sundqvist Bertil 
Published: April 2003

AbstractThe pressure dependence of the specific heat of poly(methyl methacrylate), polystyrene, and atactic and isotactic polypropylene was determined from simultaneous measurements of thermal conductivity and diffusivity in a cylindrical geometry at 300°K and in the pressure range 0–37 kbar. The thermal conductivity and the diffusivity both increase strongly with pressure, while the specific heat decreases. The pressure dependencies are most pronounced at low pressures. The results are compared with other experimental results and with theoretical calculations.