bluuebunny/crossref_metadata_2025_split huggingface dataset:
A relationship between network chain concentration and time dependence of rupture for SBR vulcanizates
Authors: Fedors R. F. , Landel R. F. 
Published: April 2003

AbstractThe failure properties of crosslinked elastomers are influenced by variables such as the test rate, test temperature, chemical nature of the elastomers, degree of crosslinking, etc. For an elastomer with a fixed degree of crosslinkingthe time dependence of both the stress‐ and strain‐at‐break, when determined as a function of the test rate and test speed, can be correlated using a time–temperature shift such as the WLF aT shift factor. When a similar study is carried out with a sample having a different degree of crosslinking, the time dependence of both the stress‐ and strain‐at‐break is shifted along the time scale. It is demonstrated here that the time dependence of failure obtained as a function of the degree of crosslinking can be superposed on a master curve by the use of a time shift factor whose value depends directly on the degree of crosslinking.
Unperturbed dimensions of poly(9‐vinyladenine)
Authors: Kaye H. , Chou H. J. 
Published: April 2003

AbstractThe effect of base stacking interactions on the conformation of poly(9‐vinyladenine) (PVAd) was investigated by osmometry, intrinsic viscosity, and light‐scattering measurements. At neutral pH, ideal solution behavior (θ conditions) for this polymer was observed at 26 and 40°C. Intrinsic viscosity measurements revealed a conformational transition on heating from 26 to 40°C, while the ultraviolet absorbance of the solution was insensitive to the change. The transition was accompanied by an inversion in sign of the entropy parameter from negative to positive and an increase in the partial specific volume. At 40°, the variation of intrinsic viscosity with molecular weight corresponded to a random coil conformation, but the characteristic ratio, r̄02/nl2 = 8.6 ± 0.2 indicated that the unperturbed dimensions were smaller than usually observed for comparable vinyl polymers. At 26°, a rare macromolecular phenomenon was found, the intrinsic viscosity–molecular weight relation and the estimated r̄02/nl2 of 6.0–6.8 suggested that the PVAd was in a very highly compacted coil conformation, approaching a semirigid sphere. It is proposed that this effect be named the introversion phenomenon. Unlike polyadenylic acid, whose unperturbed dimensions increase with decreasing temperature due to nearest‐neighbor base stacking, the results reported here suggest that both nearest‐neighbor and long‐range intramolecular base stacking occur in PVAd. The different stereochemical arrangements of bases in PVAd and Poly A are probably responsible for the opposite behavior observed.
Transient and steady‐state water vapor permeation through polymer films
Authors: Hubbell W. H. , Brandt H. , Munir Z. A. 
Published: April 2003

AbstractWater vapor transport properties for the polymers Kapton HReference to a company or product name does not imply approval or recommendation of the product by the University of California or the U.S. Atomic Energy Commission to the exclusion of others that may be suitable.
and Parylene C were determined over a temperature range of 20 to 55°C. Activation energies and entropies for permeation as well as partial molar free energies, heats, and entropies of dilution were calculated for water vapor concentrations ranging from 3 × 10−6 to 1 × 10−3 mole H2O per cm3 of polymer. Mylar A was tested to extend the available data for partial molar heats and entropies of dilution and to compare permeation and diffusion results with the corresponding values in the literature. Diffusion coefficients were measured using the time‐lag technique of Barrer but employing a modified test apparatus. Equilibrium sorption isotherms at 30°C were obtained for Mylar A and Kapton H with a Cahn microbalance. The ratios of the permeability to diffusion coefficients as measured from time‐lag experiments agreed with solubility coefficients within 3% for Mylar A and within 12% for Kapton H. Both polymers obeyed Henry's law. The results were interpreted in light of polymer polarity and morphology.
The growth of shear bands in polystyrene
Authors: Kramer Edward J. 
Published: April 2003

AbstractShear‐band growth velocities have been determined as a function of stress and temperature in polystyrene. The results demonstrate that shear bands can propagate under isothermal conditions; an adiabatic temperature rise at the shear band tip is not necessary for continued localization and growth of the band. The velocity is stress activated with a shear activation volume of 4600 Å3 and thermally activated with an activation enthalpy of 2.8 eV. Comparison of these values of the activation parameters with those for bulk shear flow in polystyrene indicates that the shear band propagation is controlled by the plastic strain rate of the glassy polymer immediately ahead of the tip of the band. Argon's molecular kink model of the elemental deformation process is consistent with measured values of the activation parameters whereas Bowden and Raha's dislocation model is not. The shear bands grow at an angle of ca. 38° to the axis of compression, and if the direction of compression is altered, the shear bands will change direction so as to maintain the 38° angle. Current explanations can not quantitatively account for the large deviation of the shear bands from the 45° plane of maximum shear stress.
ESR study of primary radical formation during mechanical degradation of poly(2,6‐dimethyl‐p‐phenylene oxide) solid
Authors: Nagamura Toshihiko , Takayanagi Motowo 
Published: April 2003

AbstractRadical formation during mechanical degradation of solid poly(2,6‐dimethyl‐p‐phenylene oxide) (PPO) was investigated by electron spin resonance (ESR). The ESR spectrum of PPO fractured at room temperature in air consisted of eight lines with a separation of about 5.5 gauss with g = 2.0043, indicating a small asymmetry. For PPO fractured in liquid nitrogen, a similar spectrum was observed at −196°C in air or in vacuo. These spectra have been identified as belonging to a 2,6‐dimethyl‐substituted phenoxy radical and thus indicate the occurrence of main‐chain rupture. The phenyl radical which was expected to be formed together with a 2,6‐dimethyl‐substituted phenoxy radical could not be detected, but at temperatures below −46°C a small hump was observed at g = 2.034. By subtracting the spectrum observed after decay of this hump from the original one, the resulting curve was the characteristic asymmetric spectrum of a peroxy radical, which was presumably formed by the reaction between a phenyl radical and oxygen. The radical decay curve showed two stepwise‐decaying regions; one located in the temperature region between about −120°C and −80°C where only a small number of radicals decayed, another located in the temperature region from about −30°C to 100°C where almost all mechanically formed radicals decayed. The latter radical decay, which occurred considerably below the glass‐transition temperature of PPO, was attributed to the molecular motions associated with the mechanical β* relaxation on the basis of the activation energy and the temperature region.
Mechanical behavior of SBR–glass bead composites
Authors: Fedors R. F. , Landel R. F. 
Published: April 2003

AbstractThe mechanical properties of crosslinked SBR containing varying amounts of a glass bead filler have been studied. It is shown that the stress–strain response at a given test rate and temperature can be rationalized provided dewetting around the glass bead filler is taken into account. Direct measurements of the volume dilatation as a function of both strain and filler content have been obtained. This information in conjunction with the model proposed herein has been used to satisfactorily reproduce the stress–strain curves to strains up to about 200%. It is also shown that at the break point complete dewetting has occurred so that the rupture properties of the filled are the same as that of the unfilled gum. This was found to be true for all temperatures and rates studied.
Crystallization of polystyrene–poly(ethylene oxide) multiblock copolymers
Authors: Shimura Yukio , Hatakeyama Tatsuko 
Published: April 2003

AbstractThe heat of fusion of poly(ethylene oxide) blocks has been measured by DSC on twelve polystyrene–poly(ethylene oxide) multiblock (AB)n copolymers and two ABA triblock copolymers after conditioning at various times and temperatures. Regardless of the length of polystyrene blocks, copolymers with poly(ethylene oxide) blocks with M̄n = 404 showed no heat of fusion, those with M̄n = 900 almost no peaks, those with M̄n = 1960 small broad peaks, and those with M̄n = 5650 clearly observable peaks. the greatest heat of fusion measured for block copolymers was 60–70% of the value for hompolymer. Small‐angle x‐ray patterns are given. The relation between crystal growth and block length is discussed.
Dynamics of macromolecular chains. I. Theory of motions on a tetrahedral lattice
Authors: Valeur Bernard , Jarry Jean‐Pierre , Geny François , Monnerie Lucien 
Published: April 2003

AbstractThe bond correlation function for a macromolecular model chain on a tetrahedral lattice is derived by considering elementary three‐bond and four‐bond motions. The method of calculation allows the conformational structure of the chain to be involved in the final equations. Moreover, when the three‐bond motions are considered alone, no linearization assumption is required; hence, the theory is valid at short times.
The elastic free energy and the elastic equation of state: Elongation and swelling of polydimethylsiloxane networks
Authors: Flory Paul J. , Tatara Yoh‐Ichi 
Published: April 2003

AbstractThe elastic free energy for a tetrafunctional network is here expressed as

where λ1, etc., are the principal extension ratios relative to the state of reference (wherein 〈r2〉 = 〈r2〉0), and C1, C2, and m are arbitrary parameters. The free energy of a swollen system is taken to be the sum G = Gmix + Gel of Gel and the free energy of mixing \documentclass{article}\pagestyle{empty}\begin{document}$ G_{{\rm mix}} = RT\left[ {n_1 \ln v_1 + n_2 \ln v_2 + \bar \chi n_1 v_2 } \right] $\end{document}. Stress‐strain relations and the chemical potential μ1 are derived from G as functions of the elasticity parameters C1, C2, and m, and of the thermodynamic interaction parameter χ or of \documentclass{article}\pagestyle{empty}\begin{document}$\chi = \bar \chi + n_1 v_2^{ - 1} \partial \bar \chi /\partial n_1 $\end{document}. The dilation of the semi‐open system subject to deformation when exposed to diluent at fixed activity is derived as the sum of the dilation at fixed composition and the dilation due to absorption of diluent. Experiments are reported on the dependence of the equilibrium retractive force on elongation for cross‐linked polydimethylsiloxanes (PDMS) exposed to benzene or hexamethyldisiloxane vapor at regulated activities. Volume fractions of samples covered the range v2 = 1.00 to v2 ≈ 0.30. With the choice of m = ½ the elastic behavior of a given polymer is well represented by one combination of values for C1 and C2 at all dilutions by either diluent. The dependence of the Mooney‐Rivlin (C2) term on volume is thus established, at least for PDMS, and the scope of the semi‐empirical free energy expression and its consequents is greatly enlarged. Values of χ deduced from the equilibrium swelling of the unstrained networks exposed to benzene at various activities are in excellent agreement with those obtained previously from vapor pressures and osmotic pressures on linear PDMS. The results of Allen, Kirkham, Padget, and Price on the elastic behavior of natural rubber are discussed, with particular reference to the coefficients of dilation with elongation which they determined at fixed composition. The present results lend strong support to the principle of additivity of the free energies attributable to the network and to the bulk liquid system, respectively. This principle is fundamental to the analysis of rubber elasticity.
Viscoelastic behavior of glass‐bead filled crosslinked polymers in the dry and swollen states
Authors: Acierno D. , Nicolais L. , Vojta V. , Janáček J. 
Published: April 2003

AbstractStress relaxation and moduli of elasticity of the composite system crosslinked poly(2‐hydroxyethyl methacrylate) (PHEMA)–glass beads were studied dry and swollen in water to equilibrium state over the temperature range 5–170°C. The moduli of the composites in the dry state increased with increasing filler concentration, while those of the composites measured in the swollen state up to the volume concentration of the filler v ≅ 0.15 decreased. In this respect the composites behaved as porous systems, i.e., as polymers with macroscopic defects. This effect was explained as a consequence of weak filler–matrix interaction. The results were compared with the existing theories of moduli of the composite materials.
Determination of the coefficients of selective sorption in the system polymer–ternary solvent by the density and refractive index increments method
Authors: Stejskal Jaroslav , Kratochvíl Pavel 
Published: April 2003

AbstractThe method of density and refractive index increments was used for the determination of the coefficients of selective sorption of acetophenone and bromoform on polymer in the system poly(methyl methacrylate)–isopropanol–acetophenone–bromoform as a function of the composition of the ternary solvent. In systems containing more than 80% by volume of bromoform the precipitant—isopropanol—is selectively sorbed. The conditions under which the method gives satisfactory results and some methodological problems of densitometry have been discussed.
Relaxation spectra of concentrated polystyrene solutions
Authors: Osaki Kunihiro , Fukuda Mitsutoshi , Kurata Michio 
Published: April 2003

AbstractThe relaxation modulus G(t) and the stress decay after cessation of steady shear flow were measured on concentrated solutions of polystyrenes in diethyl phthalate. Ranges of concentration c and molecular weight M of the polymer were from 0.112 to 0.329 g/ml and from 1.23 × 106 to 7.62 × 106, respectively. The relaxation spectrum H(τ) as calculated from G(t) for the solution of very high M was found to be composed of two parts. One, at relatively short times, was a broad distribution (plateau zone) with height proportional to c2. The second, at the long‐time end, was very sensitive to concentration and gave rise to a maximum in H(τ) for very high concentrations. The behavior of H(τ) at long times was examined quantitatively by evaluating the longest relaxation time τ10 and the corresponding relaxation strength G10 from G(t) and from the stress decay function, on the assumption of a discrete distribution of relaxation times at long times. The longest relaxation time was approximately proportional to M3.5, even at relatively low concentrations where the zero‐shear viscosity was not proportional to M3.5. The strengths of relaxation modes with the longest few relaxation times are proportional to the third power of concentration.
Fourier transform infrared study of the effects of irradiation on polyethylene
Authors: Tabb D. L. , Sevcik J. J. , Koenig J. L. 
Published: April 2003

AbstractFourier transform infrared spectra have been obtained for polyethylene irradiated in oxygen and nitrogen atmospheres. The spectra before and after irradiation have been compared by digital subtraction. The difference spectra are indicative of changes caused by irradiation. Crosslinking and chain scission reactions produce the observed changes.
Persistent polarization in poly(vinylidene fluoride). I. Surface charges and piezoelectricity of poly(vinylidene fluoride) thermoelectrets
Authors: Murayama Naohiro 
Published: April 2003

AbstractPersistent polarization in poly(vinylidene fluoride) (PVDF) thermoelectrets prepared under high electric field strengths has been studied by measurements of surface charge and piezoelectricity. An anomalous heterocharge appears after the normal homocharge disappears. A model is proposed to explain the surface charge phenomena; the anomalous heterocharge is expressed as a sum of a hidden homocharge and a hidden heterocharge. It is concluded that the anomalous heterocharge as well as the apparent homocharge are not responsible for the piezoelectricity of PVDF electrets. The piezoelectricity is shown to depend on the structure of the original PVDF films or the amount of β‐form crystals. However, the piezoelectricity is not attributed to stress dependence of the spontaneous polarization in the β‐form crystal of PVDF, but to the hidden polarization which bring about the anomalous heterocharge. The hidden polarizations are attributed to trapped charges.
Degrees of order from X‐ray diffraction in highly crystalline poly(vinyl chloride)
Authors: Gouinlock E. V. 
Published: April 2003

AbstractConvenient x‐ray diffraction instrumentation for assessing PVC order is described. A reflectance diffractometer, copper radiation, a monochromator, and a proportional detector are used to make measurements on low molecular weight, highly crystalline PVC prepared using chain‐transfer agents. Interpretation includes a correction for air scattering, employment of a trimodal noncrystalline pattern, and the calculation of crystallinity from the ratio of the crystalline to the total integrated intensity. The results are reasonably insensitive to the assumptions made. The noncrystalline pattern used is taken to indicate a single, partially ordered mesomorphous phase. A whole polymer prepared in the presence of butyraldehyde, a fraction therefrom prepared by precipitation, and a similar fraction terminated by butyl mercaptan have similar molecular weights (M̄n ca. 1600) and crystallinities of 30, 44, and 44%, respectively. Fractionation apparently effects a separation with respect to syndiotactic content, and the resultant crystallinity appears to be the highest valid x‐ray value reported to date for a PVC polymer, irrespective of polymerization variables, fractionation procedure, or molecular weight. The order in these polymers is due in part to their greater syndiotacticity (about 64% for the fractions by 13C NMR spectroscopy), although a more favorable tactic placement distribution may be involved in addition to a possible effect of molecular weight itself.
Dielectric study of relaxations and polymorphism in poly(diethyl siloxane)
Authors: Pochan J. M. , Beatty C. L. , Hinman D. D. , Karasz F. E. 
Published: April 2003

AbstractThe dielectric behavior of poly(diethyl siloxane) supports the adiabatic calorimetric findings of Beatty and Karasz. In particular, a sub‐Tg transition is observed near −180°C at 100 Hz, the glass transition near −135°C at 100 Hz, and a first‐order transition near −70°C (crystal–crystal transformation). This glass‐transition temperature is the lowest reported polymeric glass transition for polymers.
Polymerization mechanisms and molecular weight distribution. I. Mathematical treatment
Authors: Braks Jorma G. , Huang Robert Y. M. 
Published: April 2003

AbstractA novel method for determining the polymerization mechanism and the kinetic rate constants from the molecular weight distribution is proposed. The particular criterion function used as basis for parameter adjustment is

where θ is the vector of dependent variables, y(r, θ) is the theoretical molecular weight distribution for the assumed polymerization mechanism, and yE(r) is the experimental molecular weight distribution which is a function of the chain length r. A form of the gradient method of optimization was used to solve the criterion function. The proposed method is particularly powerful since the whole molecular weight distribution is utilized.
Effects of annealing and isothermal crystallization upon crystalline forms of poly(vinylidene fluoride)
Authors: Osaki Shigeyoshi , Ishida Yoichi 
Published: April 2003

AbstractPoly(vinylidene fluoride) exists in three crystalline forms. Optimum conditions for preparing form III were established by infrared spectroscopy, differential scanning calorimetry, and x‐ray diffraction measurements. Form III is easily obtained by annealing mats of solution‐grown crystals of form II at 175–185°C and is also preferentially formed by isothermal crystallization from the melt between 165 and 175°C. Below 165° crystallization of form II is favored. The melting point of form III is higher than that of form II.
Rheology of dispersions of swollen gel particles
Authors: Taylor N. W. , Bagley E. B. 
Published: April 2003

AbstractA centrifugal technique was used to determine the swelling, Q (g swollen gel/g dry polymer), of crosslinked polyacrylate gel particles in water. Both centrifugal force and time of centrifugation affected the magnitude of Q but under constant centrifuge conditions it was found that Q−1 was proportional to μ1/2, μ being the ionic strength. The viscoelastic properties of water dispersions of these gel particles were measured as functions of concentration and ionic strength. Viscosity data were reducible to a normalized master curve by plotting (ηsp/cr) versus cr, where cr is a reduced concentration defined as cQ. Values of shear modulus, G, computed from the first normal stress difference measured at various concentrations and ionic strengths also fell on a single curve when plotted against the reduced concentration, cQ. Comparison of these results with those obtained earlier on a similar polyacrylate dispersion, but one in which as much as 20% of the polyacrylate is in a soluble, uncrosslinked form, shows that the soluble fraction has little effect on the magnitude of the viscosity and, moreover, that the presence or absence of the soluble fraction does not affect the transient stress overshoot phenomenon. As in the earlier work, high absolute values of viscosity occur when cQ ≧ 1, that is when the dispersion consists of close‐packed deformable gel particles in intimate contact with little or no interstitial solvent present.
A normal coordinate analysis of trans‐1,4‐polychloroprene
Authors: Tabb D. L. , Koenig J. L. 
Published: April 2003

AbstractThe fundamental vibrational frequencies of an isolated chain of trans‐1,4‐polychloroprene have been calculated. The agreement between the calculated and experimentally observed crystalline frequencies supports the molecular model for the structure of trans‐1,4‐polychloroprene and the force field employed in the calculations. The results of the normal coordinate analysis indicate that there is essentially no coupling between adjacent translational repeat units of trans‐1,4‐polychloroprene.
Photoconduction in polyolefins and in poly(ethylene–carbon monoxide)
Authors: Chan G. Y. C. , Wintle H. J. 
Published: April 2003

AbstractThe ultraviolet photoconductivity of high‐density polyethylene, polypropylene, and poly(ethylene–carbon monoxide) has been studied in the range 360–180 nm. The response of the polyolefins is similar to that found in low‐density polyethylene both in spectral distribution and in time behavior, with hole injection setting in at 3.7 eV. There is evidence also of electron injection in polypropylene at 4.5 eV and higher energies. A copolymer containing 0.5% CO is similar except that the hole threshold is at 4.2 eV, but a 1% CO copolymer shows marked differences, with electron injection being dominant. It is suggested that the change is due to a shift in the Fermi level rather than direct excitation of electrons from carbonyl groups, but some inconsistencies remain in this model.