bluuebunny/crossref_metadata_2025_split huggingface dataset:
Laser‐Raman study of the longitudinal acoustic mode in polyethylene
Authors: Olf H. G. , Peterlin A. , Peticolas W. L. 
Published: April 2003

AbstractA Raman band of low frequency, arising from an accordionlike vibration of all‐trans \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{&#x02010;&#x02010;} ({\rm CH}_2 \rlap{&#x02010;&#x02010;})_n $\end{document} segments and previously observed in normal paraffins and in polyethylene single crystals, has now also been found in bulk and in cold‐drawn polyethylene, both linear and branched. The accordionlike vibration, or longitudinal acoustic mode (LAM), in polyethylene is compared with the LAM in normal paraffins. Whereas the Raman bands corresponding to the third (LAM‐3) and higher modes are quite intense in a long‐chain paraffin such as n‐C94H190, they are so weak in polyethylene as to be unobservable with the apparatus used. This is attributed to the presence of the chain fold in polyethylene. Of the two extreme structural models of the fold here discussed, namely the models of “tight folds” and of “loose loops,” only the latter seems capable of accounting for the weakness of LAM‐3 and higher modes in polyethylene. A quantity called “nominal Raman length” is defined as the length of that all‐trans n‐paraffin that would have the same LAM‐1 frequency as the polyethylene sample under consideration. The nominal Raman length is always greater than the average long spacing, deduced from discrete x‐ray scattering at small angles after applying a Lorentz correction, and, after allowing for chain tilt, is found equal to the segment length between folds. This can be accounted for by both of the models mentioned. As a test of the theory of surface melting the frequency of the accordion vibration of annealed polyethylene single crystals was measured as a function of temperature up to the melting point; no frequency change with temperature was observable. On the basis of the naive idea that there is complete decoupling of the vibrations in the all‐trans chain segment from the disordered (molten) surface layer, one would predict that upon surface melting and the concomitant shortening of the all‐trans segment, the LAM‐1 frequency should increase. A more careful analysis, taking into account the existence of coupling of the LAM to the surface layer, shows that the outcome of this experiment does not necessarily invalidate the idea of surface melting. Bulk polyethylene samples exposed to 60Co γ‐radiation for doses up to 100 Mrad show a slight shift of the Raman band to lower frequencies, whereas no such shift was observed upon absorption of a swelling agent. A search, without success, was made for a longitudinal acoustic mode in polypropylene, poly(vinylidene fluoride), nylon 66, and polyoxymethylene.
Atomic mechanism of fracture of solid polymers
Authors: Zhurkov S. N. , Korsukov V. E. 
Published: April 2003

AbstractMacromolecular chain scission under mechanical stress has been studied by infrared spectroscopy. The dependence of accumulation of chemical bond scissions on temperature T and uniaxial tensile stress σ has been investigated. The rate constant K for bond dissociation under mechanical stress has been found to obey the modified Arrhenius equation: K = K0 exp{ − (EA − ασ)/RA}. The quantitative connection between the rate constant for bond dissociation and mechanical lifetime τ has been established. Analysis of the experimental data indicates that the strength and mechanical lifetime of polymers is determined by the kinetics of mechanochemical scission of the main chains of polymer molecules.
Excluded‐volume effect for various chain models. I. Application to optical anisotropy and end‐to‐end distance of linear polymers
Authors: Lemaire Bernard , Fourche Georges , Sanchez Edouard 
Published: April 2003

AbstractA study of the effect of excluded volume on the mean‐square optical anisotropy 〈γ2〉 and the mean‐square end‐to‐end distance 〈R2〉 has been carried out for polymer chains of up to 2000 bonds. The calculations have been made for models assuming (a) equiprobability of internal rotations and (b) interdependence of short‐range intramolecular interactions. All the results indicate that 〈γ2〉 is practically insensitive to the excluded‐volume effect. Concomitantly the behavior of 〈R2〉 has been analyzed.
Small‐angle light scattering from hedrites, ovoids, and spiral ovoids. I. Theoretical considerations
Authors: Gałȩski A. , Kryszewski M. 
Published: April 2003

AbstractTaking into consideration results of our microscopy studies and data given in the literature on the structure of hedrites, ovoids, and spiral ovoids, we have developed optical models for these morphological entities. These models are applied to calculations of small‐angle scattered light intensity distributions for these structural elements. Analytic formulae computed for the Vv and Hv scattering patterns contain terms dependent only on azimuthal angle μ and vertical angle θ. For hedrites and ovoids, equations are derived relating the characteristic points of scattered light intensity patterns to structural parameters. The corresponding diagrams of light intensity distributions are given.
Gas sorption in polymer membranes containing adsorptive fillers
Authors: Kemp D. R. , Paul D. R. 
Published: April 2003

AbstractThe equilibrium and kinetics of gas sorption by a silicone rubber filled with highly adsorptive molecular sieves was studied. Sorption in this system is by two mechanisms: gas is simply dissolved in the polymer matrix according to Henry's law, while it is adsorbed by the dispersed sieve phase in accordance with a Langmuir's isotherm. The latter effectively immobilizes the gas molecules preventing their further diffusion. All equilibrium parameters were determined experimentally. Immobilization greatly affects sorption kinetics and renders conventional analyses invalid. A theory to account for this process was adapted from a previous analysis by Vieth and Sladek which assumes that the kinetics of adsorption is very fast compared to diffusion. For this situation the kinetics always assume a Fickean form. The experimental data agreed very well with the predictions of this theory in a comparison where all parameters were defined by independent experiments. It was found that a single effective diffusion coefficient describes sorption kinetics, steady‐state permeation, and time‐lag results once the effects of immobilization are properly accounted for.
Rheology of poly(vinyl chloride) melts. II. Shear rate‐dependent properties
Authors: Utracki L. A. 
Published: April 2003

AbstractFour samples containing 40, 60, 80, and 97 wt‐% of poly(vinyl chloride), the rest being plasticizer and stabilizer, were tested by using the Weissenberg Rheogoniometer in the steady‐shearing mode at temperatures between 155 and 235°C and rates of shear \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma = 0.01 - 400 $\end{document} sec−1. The viscosity η versus \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} follows Graessley's theoretical dependence for infinitely entangled system. The primary normal‐stress difference coefficient ψ versus \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} is well described by the same theoretical function, used with the square of its argument. The temperature dependence of η0 and ψ0 shows discontinuities at T = Tb. The numerical values of Tb can be calculated from the theory of the melting point depression due to diluent. The activation energy of viscous flow Eη below Tb is 5–9 times as large as above this temperature. The activation energy of normal stress is found to be Eψ ≈ 5Eη. The characteristic relaxation times τo, ψp, calculated from superposition of η versus \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} and ψ versus \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} data, respectively, onto Graessley's master curves, and τN, computed from zero shear parameters η0 and ψ0, differ in their sensitivity to the melting of microcrystalline regions. It is postulated that in the systems investigated, aggregates with long lifetimes are being formed, increasing the effective molecular weight and introducing changes in the effective polydispersity.
NMR spectrum of poly(vinyl chloride)
Authors: Hassan A. M. 
Published: April 2003

AbstractThe 100‐MHz proton NMR spectra of commercial and laboratory‐prepared poly(vinyl chloride) (PVC) have been measured in various solvents at high temperature (80–150°C). Tacticity in PVC was determined by the analysis of the β‐proton spectrum. The spectrum was calculated assuming that the PVC chain consists of tetrad sequences of monomer units and that their distribution in the chain is described by a simple Bernoulli‐sequence statistics with a Pm (the probability of isotactic placement) of 0.45 for commercial PVC polymerized at 50°C. Tacticity calibration curves based on measurements made for the polymer in pentachloroethane and β‐dichlorobenzene were established, and they provide a simple method for the measurement of tacticity in PVC directly from the observed spectra. Excluding samples prepared in butyraldehyde solution, the formation of syndiotactic structures in PVC (prepared by free‐radical polymerization) was found to be favored by lowering the polymerization temperature. This preference is due to an increase in the activation enthalpy of 510 cal/mole which is required for forming an isotactic placement in the chain during the propagation step.
A lattice theory of light scattering from disordered spherulites
Authors: Yoon Do Yeung , Stein Richard S. 
Published: April 2003

AbstractA lattice theory of orientational disorder in two‐dimensional spherulites is developed in which the orientation direction of the optic axis in lattice cells is allowed statistically to deviate from its mean value in a manner correlated with the orientation in neighboring cells. The Hv light scattering patterns arising from such disordered spherulites deviate from the patterns for perfect spherulites in that there is excess intensity at both small and large scattering angles and the intensity at the maximum is lower. A comparison of the calculated scattering angular dependence with that which is experimentally measured permits assignment of values of correlation parameters. A consequence of this disorder is that the spherulite birefringence is reduced below that calculated on the basis of perfect crystalline orientation in agreement with experiment.
Solution properties of high molecular weight polystyrene
Authors: Fukuda Mitsutoshi , Fukutomi Makoto , Kato Yoshio , Hashimoto Tsutomu 
Published: April 2003

AbstractA series of polystyrenes with weight‐average molecular weight M̄w up to 1.3 × 107 was prepared by anionic polymerization in tetrahydrofuran (THF). Each sample was characterized by gel‐permeation chromatography, light scattering, and viscometry. It was found that each sample had an almost symmetrical and very narrow molecular weight distribution (M̄w/M̄n < 1.07). The mean‐square unperturbed radius of gyration 〈S2〉0 was determined in trans‐decalin at 20.4°C as 〈S2〉0 = 7.86 × 10−18M̄w (cm2). The particle scattering factor was well represented by the Debye equation irrespective of solvent in the range of M̄w < 4 × 106, and only a small deviation was observed in benzene at higher molecular weights. The penetration function Ψ ≡ A2M2/4π3/2NA〈S〉23/2 was found to approach a relatively low asymptotic value of 0.21–0.23 at molecular weights above 2 × 106 in benzene at 30°C, where A2 is the second virial coefficient and NA is Avogrado's number. It was also found that the theta temperature in trans‐decalin was affected by the nature of polymer samples. A difference of about 3°C in the theta temperature was observed between two series of anionic polystyrenes, one prepared in THF and the other in benzene, but there was practically no difference in unperturbed chain dimension.
Electronic conduction and polarization in polyphthalocyanines
Authors: Norrell Charles J. , Pohl Herbert A. , Thomas Mani , Berlin K. Darrell 
Published: April 2003

AbstractThe polymeric hydrogen form of phthalocyanine is found to be more conductive than the metallic derivatives, in contrast to the behavior of the monomers. In addition, the polymers were found to be much more conductive than the corresponding monomers with the resistivity of the polymers ranging from 7 ohm‐cm to about 3 × 106 ohm‐cm. The polymers were found to have moderately high dielectric constants ranging from 16 to 1300 at room temperature, depending upon the applied pressure. Based on the dependences of the conductivity and permittivity upon the electric field strength, the average molecular length of the conductive paths within the polymer molecule has been estimated to be 100–1000 Å. In view of these estimated lengths, together with the exponential dependence of the permittivity and conductivity upon the pressure and temperature, the dispersion of the dielectric constants in the range of 10–100 KHz, and the chemical architecture of these ribbonlike polymers, the electronic behavior of these polymers is concluded to be consonant with the model of essentially one‐dimensional conduction within and along the chains by freed charges. Much as in a number of previously studied highly conjugated polymers, the present polyphthalocyanines are semiconducting and exhibit nomadic polarization, with dielectric constants ranging from 70 to 1300.
Properties of cellulose acetate in solution. I. Light scattering, osmometry, and viscometry on dilute solutions
Authors: Tanner D. W. , Berry G. C. 
Published: April 2003

AbstractLight‐scattering, osmotic pressure, and viscometric studies on fractions of cellulose acetate (degree of substitution 2.45) in three solvents are described. The data yield the dependence of the mean‐square radius of gyration 〈s2〉, the second virial coefficient Γ2, and the intrinsic viscosity [η] on molecular weight M and temperature. The results are interpreted to show that excluded volume effects on 〈s2〉 are negligible, even though Γ2 is large and dΓ2/dT is positive. The large experimental value of d In [η]/d In M is interpreted in terms of partial draining effects. Data on 〈s2〉 and [η] for other cellulose esters in the literature are similarly interpreted. Significant aggregation found in solutions of cellulose acetate in many solvents is discussed.
Vibrational spectra of thiuram sulfides: Normal coordinate analysis of tetramethylthiuram mono‐, di‐, and tetrasulfides
Authors: Coleman M. M. , Koenig J. L. , Shelton J. R. 
Published: April 2003

AbstractThe normal coordinate analyses of tetramethylthiuram mono‐, di‐, and tetrasulfides have been carried out by utilizing vibrational energies obtained from infrared and Raman spectroscopic data reported here. The CS vibration is demonstrated to be highly coupled and to contribute to frequencies in the 850–1000 cm−1 region, but can be identified based on the strong Raman intensity. The results are useful in interpreting the spectra of these complex vulcanizing agents.
Molecular weight–mechanical property interrelationships. V. Poly(vinyl chloride) fracture surfaces: The effect of molecular weight and vapor environment
Authors: Martin John R. , Johnson Julian F. 
Published: April 2003

AbstractThe fracture and craze surfaces of four PVC fractions (M̄w = 51000 to 228000) and two bimodal blends were examined with a scanning electron microscope. The fraction with the lowest molecular weight gave brittle fractures when fatigued in nitrogen and ethanol vapor. Walls of crazed ductile matter formed at the surface of higher molecular weight samples. Thickness of this ductile material increased with molecular weight. There appeared to be a balance between craze propagation into the sample and brittle fracture due to dilitational and tensile stresses in the interior regions of the test films.
Excluded volume effect for various chain models. II. Application to optical anisotropy and end‐to‐end distance of branched polymers
Authors: Lemaire Bernard , Fourche Georges 
Published: April 2003

AbstractMonte Carlo simulation has been used to investigate the excluded volume problem for branched polymers. The mean‐square optical anisotropy and mean‐square end‐to‐end distance were examined for two models including short‐range intramolecular interactions. Molecules of regular‐comb and random‐comb type were studied. The various effects found are discussed.
An etching technique to reveal the supermolecular structure of crystalline polymers
Authors: Bartosiewicz L. , Mencik Z. 
Published: April 2003

AbstractHighly polished surfaces of nylon 6, nylon 66, polychlorotrifluoroethylene and polypropylene were etched by aromatic and chlorinated hydrocarbons at temperatures between 25 and 75°C to reveal surface morphology. Comparison with micrographs obtained with microtomed sections shows the absence of etching artifacts which are known to accompany the use of oxidizing etching agents.
Statistical mechanics of two‐dimensional wormlike chains
Authors: Fujii Motoharu , Shimada Jiro , Yamakawa Hiromi 
Published: April 2003

AbstractThe bivariate distribution function and the ring closure probability for a continuous wormlike chain derived by Gobush et al. and by Yamakawa and Stockmayer are translated into the two‐dimensional case. The results may be written in terms of Fourier series instead of spherical harmonics. Evaluation is carried out to terms of order t−3, where t is the ratio of the total contour length to the persistence length.
High‐speed gel‐permeation chromatography
Authors: Kato Yoshio , Kido Shiro , Yamamoto Manabu , Hashimoto Tsutomu 
Published: April 2003

AbstractTo establish optimum operating conditions for high‐speed gel‐permeation chromatography (GPC), the effects of column packing particle size, solvent flow rate, and column length on the separation efficiency have been investigated by using monodisperse polystyrene samples and polystyrene gel columns (TSK‐GEL column, Type‐H). Decreasing the particle size of the column packing reduces the time required to obtain a given resolution. Monodisperse polystyrene standards were measured under the optimum operating conditions established (gel particle size 5 μ, column length 2 ft, flow rate 2.5 ml/min). The molecular weight distribution of a polymer mixture was determined in less than 10 min with the same accuracy as by the conventional GPC. Such short analysis time enables one to use GPC for in‐plant quality control.
Stress relaxation in carbon‐black‐filled styrene–butadiene rubber
Authors: Oono Ryo 
Published: April 2003

AbstractThe tensile stress relaxation of carbon‐black‐filled SBR was studied in the linear viscoelasticity region as a function of temperature and volume fraction of fillers. Time—temperature superposition was valid, and master relaxation curves were obtained. Carbon black increases the modulus of the compound, especially in the rubbery region, and the time range over which the glass‐rubber transition occurred. The shift factor is divided into three regions; an Arrhenius dependence in rubbery and glassy states, and Williams‐Landel‐Ferry (WLF) dependence in the transition region. The apparent activation energy in the rubbery state increases with the volume fraction of carbon black (or silica) and is unaffected by the structure of the filler. The increase in activation energy is caused by the attachment of rubber chains to the carbon surface. At 30% elongation, the activation energy for carbon‐black‐filled rubber has a value of 32 kcal/mole, independent of structure and concentration of the filler.
Form birefringence of crystalline polymers
Authors: Chang C. , Peiffer D. , Stein Richard S. 
Published: April 2003

AbstractThe theory of Franklin et al. is employed for the calculation of the maximum form birefringence of a polymer having lamellar morphology. The results confirm the experimental conclusion that for low‐density polyethylene, the form birefringence approaches 3% of the total birefringence. The theory also predicts the parabolic dependence of the form birefringence on the refractive index of the amorphous phase. It may be applied to estimate the dynamic form birefringence and leads to a value of the dynamic strain‐optical coefficient which is of the order of 2–15% of the total.
Studies of the amorphous region of polymers. I. Relationship between the change of structure and glass‐transition temperature in drawn poly(ethylene terephthalate)
Authors: Ito Eiko , Hatakeyama Tatsuko 
Published: April 2003

AbstractThe effect of drawing on the glass‐transition temperature of amorphous poly(ethylene terephthalate) has been studied. The Tg decreases to a minimum at a draw ratio of 1.5, then increases to a maximum at a draw ratio of about 2.0, and again decreases with increasing draw ratio. The relationship between the change of structure and Tg is discussed in terms of the configurational entropy and the rate of molecular motion in local‐mode relaxation. On the basis of configurational entropy, the decrease of Tg at the beginning of drawing depends on the increase of configurational entropy, while at draw ratios above 2.0 it depends on the increase of entropy associated with intermolecular interaction. From the point of view of molecular motion, it is concluded that the change of Tg is determined by local oscillations in the amorphous region.
Light scattering studies of narrow fractions of polyethylene
Authors: Go Santos , Mandelkern Leo , Prud'Homme Robert , Stein Richard 
Published: April 2003

AbstractSmall‐angle light scattering experiments were conducted on thin films of linear polyethylene fractions over a very wide range of molecular weights. Spherulitic structures were found in all samples with molecular weight 9 × 105 or less. A rodlike morphology predominates for molecular weights between 1 × 106 and 2 × 106. Still higher fractions yield a very disordered superstructure. These results can be correlated with previous studies of the overall crystallization rates and the resulting properties.
Dilute solution properties and phase separation of branched low‐density polyethylene
Authors: Nakano Seikou 
Published: April 2003

AbstractViscosity, light scattering, and precipitation temperature measurements on dilute solutions of high‐density and low‐density polyethylene fractions have been carried out and a theory by Flory for phase equilibrium of linear polymers has been extended to branched polymer. From the results, it is shown that the entropy parameter ψ, depends on branching; a method for the determination of long‐chain branching in polymer fractions is proposed combining precipitation temperature and molecular weight measurements. The method has been applied to the evaluation of long‐chain branching in low‐density polyethylene.
Dynamic mechanical properties of glass‐filled epoxy resin
Authors: Ebdon Michael P. , Delatycki O. , Williams John G. 
Published: April 2003

AbstractComposite specimens were prepared using soda glass beads and a purified epoxy resin cured with 1,3‐propylene diamine. Some beads were treated with a silane coupling agent. The dynamic mechanical properties of these specimens were measured in the temperature range −190 to +180°C using a free‐oscillation torsion pendulum. The dynamic mechanical relaxation spectrum showed no feature that could be attributed to the formation of a new interfacial phase and the torsional moduli were unaffected by the use of the coupling agent. Increasing the glass content of the specimens decreased the damping and increased the modulus. An attempt was made to predict the composite modulus using the Kerner equation. When the specimens were immersed in boiling water, two effects were noted. First, water was absorbed in the epoxy resin matrix and changes in the dynamic spectrum were observed. Second, in samples filled with untreated glass debonding occurred and the presence of free water at the interface was indicated by the appearance of a new peak near 0°C.