bluuebunny/crossref_metadata_2025_split huggingface dataset:
Radiation chemistry of linear low‐density polyethylene. II. Kinetics of alkyl and allyl free‐radical decay reactions
Authors: Basheer Rafil , Dole Malcolm 
Published: April 2003

AbstractQuenched and annealed samples of linear low‐density polyethylene (LLDPE) were γ irradiated in vacuo at 77 K; the kinetics of the alkyl free‐radical decay reactions were studied at room temperature, and of the allyl free‐radical reactions at 60, 70, and 80°C. The ESR signals saturate at a slightly higher microwave power in the LLDPE than in high‐density polyethylene (HDPE), and the alkyl radicals start decaying at a lower temperature in the LLDPE than in the HDPE. As in the HDPE the decay of the alkyl free radicals at room temperature in the LLDPE follows the kinetic equation for two simultaneous first‐order reactions with the fraction of the faster‐decaying component being slightly greater in the quenched than in the annealed samples. In the case of the allyl free radicals the decay at 60°C follows the equation based on one fraction of the radicals decaying according to second‐order kinetics in the presence of other nondecaying radicals. At higher temperatures the data are best understood in terms of a second‐order rate equation with a continuously variable time‐dependent rate constant as suggested by Hamill and Funabashi.
Oxidative destruction of polyolefins under stress. The action of ozone on polyethylene and polypropylene
Authors: Popov A. A. , Blinov N. N. , Krisyuk B. E. , Karpova S. G. , Privalova L. G. , Zaikov G. E. 
Published: April 2003

AbstractTensile stresses accelerate the rate of oxidation by ozone of films of polyolefins, high‐density and low‐density polyethylene, and isotactic polypropylene. Experiments have been performed on thin (up to 20 μm) uniaxially oriented films under constant stress σ, under conditions where the chemical kinetics rather than diffusion dominates. It is found that the oxidation rate is proportional to exp(γ′σ/RT) where γ′ is an empirical constant. The effects of unimolecular chain scission and the change of molecular polymer parameters under stress on this dependence are negligible. An analogy with the kinetics of oxidation of stressed cycloparaffins by ozone is noted. A mechanism is suggested to explain the accelerating effect of tensile deformations on chemical processes involving rehybridization of carbon atoms in the main chain from the sp3 to the sp2 state. An ESR study with a stable nitroxyl radical probe revealed a change in the segmental mobility of polymer chains in the course of loading.
The onset of three‐phase separation in ternary polymer solutions
Authors: Fujita H. , Einaga Y. 
Published: April 2003

AbstractA theoretical study is made of three‐phase separation in a ternary solution consisting of a pure solvent and two homologous monodisperse polymers with relative chain lengths P1 and P2. The Flory—Huggins interaction parameter X is assumed to depend linearly on the volume fraction ϕ of the polymer mixture: χ = χ0(T) + k(T)ϕ. For a given P1 the ratio of P2 to P1 for the onset of three‐phase separation increases with an increase in k, first gradually and then sharply. Loci of critical points for this condition on the χ0 vs. ϕ diagram are determined for a series of fixed values of P1 and their significance is discussed.
Rheological studies of moderately concentrated polystyrene solutions. I. A new method for the extrapolation of the zero‐shear viscosity
Authors: Ballauff M. , Krämer H. , Wolf B. A. 
Published: April 2003

AbstractMeasurements of the viscosity coefficient η of solutions of polystyrene (Mw = 6.0 × 105 and 1.77 × 106) in trans‐decalin (TD, θ solvent) and toluene (TL, good solvent) as function of shear rate (11−104 s−1), concentration (4.24−11.21 wt %), and temperature (10–50°C) are reported. As a new theoretically grounded method for the determination of the zero‐shear viscosity η0 it is proposed to plot η as a function of $\left({\eta \dot \gamma} \right)^3$. The intercepts of the straight lines obtained by this procedure give η0 in good agreement with directly measured values.
Existence of a distribution of hole‐trap activation energies in FEP‐Teflon
Authors: Hagekyriakou J. , Fleming R. J. 
Published: April 2003

AbstractWhen FEP‐Teflon samples are electron irradiated at room temperature in open circuit and stored in that state for varying times following the end of irradiation, the temperature of the first current peak of the short‐circuit TSC plot increases with increasing storage time. A new model is presented to explain this phenomenon, its main features being (i) a quasicontinuous distribution of hole‐trap activation energies, the “center of mass” of the trapped hole population moving toward the deeper end of the distribution during the storage time, and (ii) an electron/hole recombination coefficient much smaller than that implied in an earlier model. It is shown that the assumption of a single dominant type of hole trap implies an unrealistically large frequency factor.
Nonlinear viscoelasticity and the Cox–Merz relations for polymeric fluids
Authors: Booij H. C. , Leblans P. , Palmen J. , Tiemersma‐Thoone G. 
Published: April 2003

AbstractThis investigation concerns the important class of fluids whose rheological properties are described by a quasilinear viscoelastic constitutive equation of the Boltzmann superposition type. The first Cox–Merz relation is closely approximated by such a fluid if its nonlinearity in shear can be described by the strain measure $ S_{12} (\gamma) = \int_0^\gamma {J_0} (\upsilon)dv $, irrespective of the distribution of its relaxation times and, hence, its linear viscoelastic properties. Here γ equals the shear strain and J0 the zeroth‐order Bessel function. The second Cox–Merz relation is met by materials with a different nonlinearity, namely S12(γ) = Si(γ), where Si is the sine integral. Experimental data on melts of a polystyrene and a low‐density polyethylene sample were utilized to demonstrate that both Cox–Merz relations cannot hold simultaneously.
Rheo‐optical studies on the deformation mechanism of semicrystalline polymers. XIV. Alpha and beta mechanical dispersions of spherulitic high‐density polyethylene and the dynamic orientation distribution function of crystallites
Authors: Fujita Ken‐Ichi , Niwa Hideyuki , Nomura Shunji , Kawai Hiromichi 
Published: April 2003

AbstractThe dynamic tensile deformation mechanism of spherulitic high‐density polyethylene was investigated by dynamic x‐ray diffraction at various temperatures and frequencies in order to assign the α and β mechanical dispersions explicity. The uniaxial orientation distribution function q(ζj,0) of the jth crystal plane and its dynamic response Δq′j(ζj,0) in phase with dynamic strain were observed for the (110), (200), (210) and (020) crystal planes. Then the orientation distribution function w(ζ,0,η) of crystallites (crystal grains) and its dynamic response Δw′(ζ,0,η), also in phase with the dynamic strain, were determined by a mathematical transformation procedure proposed by Roe and Krigbaum on the basis of the Legendre addition theorem. The temperature and frequency dependences of w′(ζ,0,η) were analyzed in terms of the model parameters for dynamic spherulite deformation combining affine orientation of crystal lamellae with several types of preferential reorientation of the crystal grains within the orienting lamellae. The following assignments are made: (i) The α mechanical dispersion must be assigned to the dynamic orientation dispersion of crystal grains within the crystal lamellae, involving two types of preferential rotations of the grains about their own crystal b and a axes. The rotation about the b axis is associated with lamellar detwisting, mostly in the equatorial zone of uniaxially deformed spherulites; the rotation about the a axis is associated with intralamellar shearing, mostly in the polar zone of the spherulites. Thus both rotations are intralamellar grain‐boundary phenomena. (ii) The β mechanical dispersion must be assigned to the dynamic orientation dispersion of the crystal lamellae behaving as rigid bodies. It is not accompanied by reorientation of the crystal grains, but is associated with orientation dispersion of noncrystalline material between the lamellae. Thus it is an interlamellar grain‐boundary phenomena.
In‐plane orientation of polyimide
Authors: Russell T. P. , Gugger H. , Swalen J. D. 
Published: April 2003

AbstractAs a nondestructive method of evaluation, we have used integrated optics to investigate thin films (<8 μm) of polyamic acid and polyimide as a function of molecular weight, initial imidization temperature, method of imidization, and annealing treatment. Polyamic acid films were found to exhibit a large optical anisotropy, indicating preferential alignment of the long axis of the molecule in the plane of the film. Imidization increased the birefringence of the film by a factor of 2.5 and reduced the film thickness. The only parameter that was found to effect the anisotropy of the films was the method of imidization. Chemical imidization was found to increase the birefringence by a factor of 3, indicative of a higher degree of molecular orientation parallel to the film surface. This effect was not observed in thicker (>25‐μm) films using x‐ray diffraction where the orientation function was found to be independent of the method of imidization.
The incipient characteristic tearing energy for an elastomer crosslinked under strain
Authors: Rivlin R. S. , Thomas A. G. 
Published: April 2003

AbstractIn a previous paper a two‐network model for an elastomer in which crosslinks have been introduced in the strained state, similar to that proposed by Green and Tobolsky, was used to calculate the dependence of the incipient characteristic tearing energy on the number of chain segments in each of the two networks, the number of links in these chain segments, and the deformation at which the crosslinking takes place. The tearing energies were calculated for tearing on planes perpendicular to the principal directions of this deformation. Here the calculations are extended to cover tearing on a plane with arbitrary orientation.
Concentration effects and thermodynamic nonideality in gel chromatography
Authors: Bleha T. , Spychaj T. , Vondra R. , Berek D. 
Published: April 2003

AbstractThe dependence of the elution volume Ve on the concentration of injected polymer c in gel chromatography is presented for several systems including poly(styrene) and poly(methyl methacrylate) in a number of pure solvents with SiO2‐based gels. The linear dependence of Ve on c and Kav on c (where Kav is the distribution coefficient) is confirmed in the region of very low concentration. The slopes k of the straight lines increase with increasing relative molecular masses M of the polymer injected and with increasing thermodynamic nonideality of the system (as expressed by the second virial coefficient A2). The significance of the slope of the GPC calibration curve for meaningful comparison of the concentration effects in various chromatographic systems is pointed out. A recently found correlation between k and (A2M)γ is confirmed with a γ value of about 0.8. A possible theoretical explanation for the deviation of γ from unity is discussed. Finally, the influence of both the polymer concentration and the thermodynamic quality of the eluent on the resolution index of the chromatographic system is evaluated with the conclusion that thermodynamically poor solvents should be preferred for preparative GPC separations with very high loads.
Theoretical models for diffusion in glassy polymers
Authors: Cohen Donald S. 
Published: April 2003

AbstractA model is derived which incorporates and unifies many of the diverse observations occurring in diffusion in glassy polymers. This unification is made possible by explicitly formulating the common property of a glassy polymer in all its various modes, namely the finite relaxation time due to its slow response to changing conditions. The application and use of the model in various situations is discussed.
Glass transition in poly(propylene glycol) networks
Authors: Andrady A. L. , Sefcik M. D. 
Published: April 2003

AbstractDifficulty in controlling and determining the structural parameters of polymer networks has hindered experimental studies on the glass transition in crosslinked polymers. A series of wellcharacterized networks of poly(propylene glycol) having narrow network chain‐length distributions and average molecular weight between crosslinksMcin the range of 425–3000 has been prepared. The glass transition temperaturesTgof these networks were found to vary linearly withM, consistent with several theoretical treatments. Both the physical crosslinking and the incorporation of crosslinking agent into the system (a “copolymer” effect) are shown to be responsible for increase inTgupon crosslinking in this system.Varying the network chain‐length distribution without changingMcdid not affect theTgof the system. The chemical nature of the crosslinking agent, however, does affect theTgof the network, particularly at high crosslink densities.
Morphology of conducting organic polymers: Polythiophene and poly(3‐methyl thiophene)
Authors: Tourillon G. , Garnier F. 
Published: April 2003

AbstractPolythiophene and substituted polythiophene can be electrochemically generated as very adhesive thin films or as thick powdery deposits. The homogeneity of the thin films is very high, but it decreases when the film thickness is increased. Scanning electron microscopy shows that the nature of the dopant strongly influences the film morphology. Transmission electron microscopy reveals mainly a fibrillar structure, with a fibril diameter of 200 Å in the undoped state, and 800 Å in the doped conducting state.
Silicone networks with junctions of high functionality and the theory of rubber elasticity
Authors: Flory Paul J. , Erman Burak 
Published: April 2003

AbstractResults of Krik, Bidstrup, Merrill, and Meyers on polydimethylsiloxane networks of high functionality ϕ yield values of the reduced force [f*] in the high‐extension limit that are directly proportional to (vs/V) (1 − 2/ϕ) where vs/V is the number of effective chains in volume V. The contention that trapped entanglements contribute significantly to the modulus is refuted by adherence of the results to this proportionality down to the lowest degrees of interlinking. Features of the relationship of stress to strain that appear to be in conflict with current theory are attributable to crowding of chains about the junctions of high functionality and of large linear dimension in the networks investigated by these authors.
Estimation of crystallization temperatures in quenched polyethylene
Authors: Keith H. D. , Loomis T. C. 
Published: April 2003

AbstractA numerical method has been employed to calculate crystallization temperature as a function of position in slabs or films of polyethylene quenched to various temperatures. The method is iterative, and combines a recent theoretical fit to empirical data for rate of crystal growth as a function of temperature with a solution to the thermal diffusion equation which takes latent heat into account. Results apply strictly only to transcrystalline regions near external surfaces but also provide lower limits to crystallization temperatures throughout the interiors of samples where spherulites nucleate ahead of the general crystallization front. Emphasis is given to assessing the relative importance of various physical parameters in determining crystallization temperatures.
Properties of crystallized trans 1,4‐polyisoprene
Authors: Mukherji S. , Woodward A. E. 
Published: April 2003

AbstractStirrer crystallization of a trans‐1,4‐polyisoprene fraction(M̄n = 3 × 105) was carried out from n‐butyl acetate and from n‐heptane solutions (2% w/v). Fibrous crystals in the ß form were obtained at temperatures of 46‐48°C in the two solvents, respectively. At 36‐46°C from n‐butyl acetate and 25‐35°C from n‐heptane lamellar crystallization took place leading predominantly to the α form. Melting endotherms and densities for various samples were obtained. The maximum TENDO for α was 74°C and for ß 79°C and the maximum weight fraction crystallinity for ß was 0.78. The stability of performed α nuclei in n‐butyl acetate and n‐heptane using a fraction with M̄n = 2.5 × 105 was monitored as a function of temperature. The dissolution temperature of fibrous ß‐TPI with the maximum TENDO was measured in 13 liquids and the results analyzed in terms of the Flory‐Huggins parameter. The heats of fusion for the α and ß forms, obtained by extrapolation of heat of fusion versus change in specific volume, were found to be 8.0 and 10 kJ mol−1, respectively. The pressure coefficients of the melting temperature were calculated to be 38 and 43 K kbar−1 and the fold‐surface free energies recalculated to be 42 ± 1 and 53 ± 1 erg cm−2 for the α and ß forms, respectively. The number of monomer units per average noncrystalline chain traverse for the most crystalline fibrous ß‐TPI was estimated at 36.
PCILO conformational energy calculation of model poly(vinyl chloride) molecules
Authors: Alig Ingo , Lochmann Rainer , Wartewig Siegfried 
Published: April 2003

AbstractThe quantum‐chemical PCILO method is applied to models for poly(vinyl chloride) molecules. Calculations of conformational energies were carried out on 2,4‐dichloropentanes. The values and the positions of the energy minima are determined and compared with results of other authors.
Dependence of maximum recoverable deformation of linear flexible‐chain polymers on limiting extension of the chains
Authors: Dreval V. E. , Vinogradov G. V. , Radushkevich B. V. 
Published: April 2003

AbstractUniaxial stretching and orientation of some linear flexible‐chain polymers have been investigated. A functional relation has been found between the maximum recoverable deformation and the limiting extension of the macromolecules. These deformations are found to increase in direct proportion to the square root of the degree of polymerization and to decrease with increasing stiffness of the polymer chain.
An estimation of the number of tie molecules in semicrystalline polymers by means of neutron scattering
Authors: Fischer E. W. , Hahn K. , Kugler J. , Struth U. , Born R. , Stamm M. 
Published: April 2003

AbstractA new method for the evalution of neutron scattering data from semicrystalline polymers is proposed for small and intermiediate q [q = (4π/λ)sinθ/2]. It is based on the assumption that, in general, a molecule cryustallizes in various lamellae. Within one lamella the crystalline stems connected by loop or folds from intramolecular “clusters,” which are connected by tie molecules. Without further assumptions the method yields in a straightforward manner the following quantities: (i) the average number of clusters per molecule, from which the number of tie molecules can be estimated; (ii) the radius of gyration <R> of the centers of the stems belonging to one cluster; and (iii) the radius of gyration <R> of the cluster centers with respect to the center of the molecule the method was successfully tested using experimental data obtained from poly(ethylene oxide), polyethylene, and isotactic polypropylene.
The structure of copolymer crystals formed from dilute solution and in bulk
Authors: Domszy R. C. , Alamo R. , Mathieu P. J. M. , Mandelkern L. 
Published: April 2003

AbstractThe thermodynamic and structural properties of a series of hydrogenated polybutadienes, crystalized in the bulk and from dilute solution, have been investigated. These polymers are ethyl‐branched ethylene copolymers with narrow molecular weight and composition distributions. Despite the fact that for both modes of crystallization these random‐sequence copolymers display a lamellar crystalline habit, all of the independent physical chemical measurements are quantitatively consistent in indicating a relatively thin crystallite with a large amorphous disordered overlayer. This is seen to be a very general phenomenon for copolymer crystallization. The core thicknesses, determined from Raman LAM and from small‐angle x‐ray scattering, are in good agreement. Quantitatively consistent values of the degree of crystallinity are obtained from the density, enthalpy of fusion, Raman internal modes, Raman LAM, and small‐angle x‐ray scattering. It is significant that independent thermodynamic and structural methods give the same result.
Electron crystallography of epitaxially grown paraffin
Authors: Moss Barbara , Dorset Douglas L. , Wittmann J. C. , Lotz B. 
Published: April 2003

AbstractThree‐dimensional electron diffraction data from the epitaxially crystallized paraffin n‐C36H74 are investigated in a structure analysis and are found to give a reasonable image of the structure, in agreement with the earlier x‐ray determination. An inconsistency in the refined isotropic temperature factors from different zonal projections, however, indicates the necessity for a more accurate physical model for epitaxially grown crystals which will account for a large spread of diffraction peaks along reciprocal lattice lines parallel to the projection axis.
Crystallinity and thermal properties of polyamides containing cis‐ and trans‐1,3‐cyclohexane rings
Authors: Inoue Kazuo , Hoshino Sadao 
Published: April 2003

AbstractThe cyclohexane ring‐containing polyamide 1,3‐CBMA‐6 was synthesized from 1,3‐cyclohexane‐bismethylamine (1,3‐CBMA) and adipic acid (6), and effects of cis/trans isomers of the ring on crystallinity and thermal properties were studied. Polymers with high cis and high trans contents, respectively, were made by polymerizing the 1,3‐CBMA‐6 salts of 98% cis and 93% trans derived from the salt of 75/25 (cis/trans) by fractional crystallization. A polymer with 97% cis content was highly crystalline, with a melting temperature of 253°C, while one with 93% trans contents was amorphous. In contrast to this, little difference was found in the glass transition temperature of 97 and 84°C. These results indicate that the isomers affect the conformation of the molecular chains, which determines the crystallinity and melting temperature, but they do not much affect the mobility of the chains as manifested by the glass transition.
Heterogeneous nucleation of poly(ethylene terephthalate)
Authors: Garcia Dana 
Published: April 2003

AbstractThe effect of various metal salts as nucleating additives for poly(ethylene terephthalate) (PET) has been investigated. In the case of sodium benzoate and probably for all other effective nucleating additives, the nucleation process can be divided into a “heterogeneous particle nucleation” performed by the unreacted salt and a “homogeneous nucleation” due to the polymer–sodium (metal) salt formed during the extrusion. This polymer–sodium (metal) salt is the major nucleating agent in these systems. We have also shown the fundamental difference between the concept of a nucleating additive and that of a nucleating agent.
Anomalous viscosity behavior of some poly(methyl methacrylate)s prepared by anionic polymerization
Authors: Corner T. , Peaker F. W. 
Published: April 2003

AbstractA series of poly(methyl methacrylate)s with molecular weights in the range 3.0 × 104–1.03 × 106 have been prepared by anionic polymerization and their limiting viscosity numbers determined in a variety of solvents. It was found that whereas the higher‐molecular‐weight polymers behaved normally, the lower‐molecular‐weight polymers showed anomalous behavior. First, the limiting viscosity numbers of the lower‐molecular‐weight polymers were much higher than expected, and, second, their number‐average molecular weights as measured by gel permeation chromatography were considerably smaller than those determined by membrane osmometry.