bluuebunny/crossref_metadata_2025_split huggingface dataset:
Equilibrium Molecular Weight Distribution of Cyclic and Linear Methylsiloxanes
Authors: Carmichael Jack B. , Heffel James 
Published: February 2011

Abstract
Data are reported for the equilibrium molecular size distributions of cyclic and linear methylsiloxanes in five polymers with number average molecular weights ranging from 459 to 1348. The distributions of linear species agree with the earlier work of Scott and agree reasonably well with the Flory theory of random reorganization. The amounts of cyclic molecules are sharply dependent on molecular weight. However, the equilibrium constants for cyclic formation for cyclic species with four to eight units are shown to be virtually identical with the equilibrium constants for cyclic formation in high molecular weight polymers reported in a previous publication. For octamethylcyclotetrasiloxane, Kav in moles of siloxane units per liter was found to be 0.72 in this study. For high polymers, Kav was previously reported to be 0.74.
Swelling of Rubber in Liquid and Vapor (Schroeder's Paradox)
Authors: Musty J. W. G. , Pattle R. E. , Smith P. J. A. 
Published: February 2011

Abstract
Polymeric substances usually swell less when placed in the vapor of a liquid in a closed vessel than they do in the liquid itself. This is known as “Schroeder's Paradox”, and many attempts have been made to explain it. With lightly vulcanized rubber and carbon tetrachloride the paradoxical behavior is caused by small differences in temperature (of order 0.1° C) which exist under normal conditions between a liquid and its vapor in a closed vessel; the vapor is normally the warmer of the two. Strict temperature control abolishes the paradox.
Solvents for Synthetic Rubbers
Authors: King L. F. 
Published: February 2011

Abstract
The effects of solvent characteristics on viscosities of several synthetic rubber hydrocarbon solutions was determined. Normal and isoparaffins (Ce and C7) yielded lower viscosity solutions than naphthenes and aromatics at 10 weight per cent of solvent and 8 grams of rubber per 100 cm3 of solvent, concentrations of interest to rubber cement and adhesive manufacturers. Solubility varied markedly with elastomer and solvent. Butadiene acrylonitrile copolymer and ethylene propylcnc tcrpolymer were the least soluble; cis-polyisoprene, butyl rubbers, and ethylene propylene copolymer were soluble in all thinners. No general correlation was found on a solvent volume basis between solution viscosity and solvent viscosity or between relative viscosity and hydrocarbon type.
Properties of Random and Block Copolymers of Butadiene and Styrene. III. Three Sequence Styrene-Butadiene-Styrene Block Polymers
Authors: Childers C. W. , Kraus G. 
Published: February 2011

Abstract
In butadiene styrene copolymers containing long block sequences chain segments associate with like segments to form a two phase structure. Properties of such polymers are dependent not only on composition and molecular weight but also on block sequence along the chain. Polymers containing two or more polystyrene blocks per molecule form networks and exhibit elastomeric properties in the uncured state resembling those of filler reinforced vulcanizates. This behavior is shown both by linear styrene-butadiene-styrene elastomers and multichain block copolymers branched in the polybutadiene blocks. A prominent loss tangent peak was observed around —40° C for the multichain polymers. Stress strain following prestretching and stress relaxation measurements indicate some shifting of polystyrene associations during stretching. Tensile strength is reduced by increasing temperature and addition of plasticizers. Reinforcement by polystyrene domains in vulcanized block copolymers is evident from tensile strength, dynamic modulus, and swelling measurements, but decreases with increased crosslinking. The number of styrene sequences in the primary molecules is less important after vulcanization as crosslinking destroys the individuality of the original polymer chains.
NMR Composition Analysis of Copolymers
Authors: Mochel Virgil D. 
Published: February 2011

Abstract
High resolution NMR spectroscopy has been shown to be a most useful tool for elucidation of compositions and structures of polymers. It is a rapid, accurate method of analysis and requires no external calibration. This technique of composition analysis can be applied to any copolymer, terpolymer, or homopolymer with various structural isomers, provided a suitable number of resonance peaks can be unambiguously assigned to at least one proton of each of the structures present. Accuracy depends upon the relative isolation of these selected peaks. The method was applied to butadiene styrene and butadiene isoprene copolymers. Equations developed previously for both systems were extended and modified to give better accuracy. In the former copolymer the NMR analysis for block styrene agreed very well with the chemical oxidative degradation method over the range 0-20 per cent. It is believed that sequence lengths smaller than five styrene units can be observed as block styrene by NMR. It was also shown that there is a sequence distribution effect in the 1,2 addition butadiene olefinic resonance region of the spectrum. This effect is also observed in polybutadienes and in the butadiene isoprene copolymers. Further study of this might be fruitful. Accuracy of the NMR method was demonstrated in the butadiene isoprene case by study of four high conversion, emulsion copolymers and six blends of butadiene and isoprene homopolymers. In all samples except one the total isoprene content found by either the detailed NMR analysis or the much more simplified NMR analysis agreed within 2 per cent of that known to be present. Accuracy is greatest for those copolymers or blends which have relatively low 1,2 addition butadiene contents, such as with butyllithium-catalyzed polymers. Accuracy is poor when the copolymer or blend has an isoprene content less than 10 per cent along with a high 1,2 addition butadiene content. Composition analysis of copolymers by NMR will become increasingly important since it often provides a direct, simple fingerprint of the various structures. However, NMR will probably make its most significant contributions in stereochemical studies of tacticities, sequence distributions, and orientation, such as head-to-head or tail-to-tail linkages. In these problems deuteration techniques, double resonance techniques, and higher field strengths play an indispensable role.
Mechanism of Thermal Degradation of Certain Polyether Polyurethans
Authors: Ingham J. D. , Rapp N. S. 
Published: February 2011

Abstract
Relatively few publications have appeared that describe basic studies of thermal degradative processes that can occur in polyether polyurethans. This article is an account of some studies of the mechanism of degradation of uncrosslinked polyurethan prepared from poly(propylene oxide) (PPO) and 2,4-tolylene diisocyanate (TDI) at temperatures up to 320° C in a vacuum or inert atmosphere. These are referred to as PT polymers.
Application of dn/dc Data for Determination of Partial Specific Volumes of Dissolved Macromolecules
Authors: Heller Wilfried 
Published: February 2011

Abstract
The principles of a method are outlined whereby one can determine the partia specific volume of a solute, V, by means of measurements of dn/dc using a suitable pair of equations and a simple graphical interpolation procedure. The method yields V data which compare well with densitometrically obtained V data if the polarizability of both solvent and solute molecules is unaffected by the solution process. It is tested successfully on solutions of polystyrene in various solvents. The method appears to be particularly attractive for measurements of the change of V with temperature and also for conveniently following the time rate of changes in V such as during the coil → helix transition.
Principle of Strength Reinforcement in Filled Rubbers
Authors: Oberth A. E. 
Published: February 2011

Abstract
Effects of filler on mechanical properties of composites result from stress concentrations developed in the matrix and filler particles. Stress concentrations in filler particles relieve stress in the matrix which, under a given load, deforms less than it would in absence of filler. This accounts for high modulus as well as strength reinforcement in filled materials. Stress concentration in the matrix, decreasing with increasing content of filler, is responsible for internal tearing of composites. Magnitude of this internal tearing, which can be measured by volume increase of a specimen under strain, depends on many factors such as: shape of filler, orientation of filler particles, particle size, particle size distribution, nature of boundary layer between filler and matrix, crosslink density and tear properties of the matrix, as well as environmental pressure in the test. High dilatation results in low tensile strength of the composite and conversely if dilatation is suppressed maximum strength reinforcement is obtained.
Effect of Strain on Rate of Crystallization of Natural Rubber
Authors: Dunning D. J. , Pennells P. J. 
Published: February 2011

Abstract
The crystallization of vulcanized natural rubber under strain gives this polymer a strength which is not present in a noncrystallizing rubber. However, if the rubber is stretched very rapidly the strength falls suggesting that a finite time is necessary for the crystallization to build up. An apparatus was constructed to enable changes in crystallinity to be detected over a time range down to hundredths of a second after the rubber had been stretched. The method consisted in extending the rubber very rapidly by passing a long strip between two sets of rolls, the second of which was rotating at a greater speed than the first. At any chosen point between the rolls there was a sample of rubber which had been stretched for a fixed time. By moving between the sets of rolls one moved along the time scale after stretching. The crystallinity of the rubber was detected by an x-ray technique. The results showed an initial period (which varied from one twentieth sec for an extension ratio of 5 to 20 sec for an extension ratio of 3.6) in which no crystallization was observed. This was followed by a gradual rise in crystallinity. The level of crystallinity was still increasing after periods of a week after stretching.
Nonnewtonian Flow of Poly(Dimethyl Siloxane)
Authors: Ito Yoshio 
Published: February 2011

Abstract
Nonnewtonian flow of poly(dimethyl siloxanes) of various molecular weights has been studied with a short capillary viscosimeter. The experiment covered a wide range of shear rate, from 10−1 to 3×106sec−1. Results were as follows: (1) Flow behavior of the sample changes with the degree of polymerization. For siloxanes with degrees of polymerization less than 1.55×102, flow of the fluid is newtonian throughout the whole range of shear rates; for siloxanes with degrees of polymerization from 3.22×102 to 2.63×103, flow is nonnewtonian at moderate shear rates; it again becomes newtonian at high shear rates. With degrees of polymerization more than 3.31×103, the spiral flow rises to a high shear rate. (2) Plow behavior of the samples is expressed by modifying Shishido's equation proposed for nonnewtonian polymer solutions. (3) When the observed flow curve contains its inflection point, the upper newtonian viscosity can be estimated by a new method proposed here. (4) The relations among the end correction of capillary, the pressure loss, and the shear stress proposed by Shishido for polymer solutions are applicable to poly(dimethy! siloxane) also.
Ordered Structures of Styrene Butadiene Block Copolymers
Authors: Vanzo Ed 
Published: February 2011

Abstract
Anionically prepared block copolymers of butadiene and styrene exhibit solution properties which result from a two dimensional ordering of the polymer molecules. The most notable of these properties is the iridescent colors of toluene solutions which are dependent on concentration and abruptly change on mechanical deformation. Electron micrographs of the surface of cast films indicate that the ordered structure is retained to some degree in the solid state.
Polymer Fractionation at a Lower Critical Solution Temperature Phase Boundary
Authors: Baker C. H. , Clemson C. S. , Allen G. 
Published: February 2011

Abstract
The influence of pressure on a lower critical solution temperature is much more pronounced than on an upper critical solution temperature. Accordingly it is possible to control phase separation at a LCST phase boundary under isothermal conditions by merely adjusting the pressure on the system. An apparatus has been constructed to investigate the isothermal fractionation of polyisobutene in which precipitation is controlled by pressure. Two samples of polyisobutene of Mv=1.76×106 and 9.0×104 have been fractionated in isopentane solution so as to yield up to six and nine fractions respectively. The integral molecular weight distribution curves thus obtained are compared with those obtained from conventional fractionations at an UCST. The sensitivity of the method is poor with regard to the separation of low molecular weight fractions and degradation occurs at the higher temperatures to an appreciable extent.
Recent Advances in Knowledge of Rubber Friction and Tire Wear
Authors: Schallamach A. 
Published: February 2011

Abstract
Progress in the last few years in understanding rubber friction and tire wear justifies a survey of developments since a review of the subject in 1958. Work on fundamental of friction and abrasion has mainly evolved from conceptions formed in the earlier investigations; it had, however, not been realized that wear of tires and, indeed, abrasion on certain laboratory machines brings into play gross properties of the tire or testpiece which affect rate of wear just as much as the actual abrasion resistance of the tread compound. This new field of research has led to rationalization of road testing, and has helped to bridge the gap between laboratory and road. A report on these developments is given. Much of the work is concerned with the viscoelastic nature of rubber friction and abrasion, which has come to light through the experimentally established validity of the rate-temperature equivalence principle for these processes. This principle, which holds good for all viscoelastic processes, is briefly described in the next section in order not to interrupt the subsequent argument.
Role of Computers in Elastomer Research
Authors: Claxton W. E. , Pearson Dale , Clarke R. E. , Conant F. S. 
Published: February 2011

Abstract
Computer usage has spread so rapidly in recent years that these instruments are almost considered to be common tools. Publications may make only casual reference to the computer's role in the investigation or they may omit such reference altogether, if the use was routine in nature. Consequently the literature on elastomer research and technology does not fully represent the growing importance of this extension to human capabilities. Enough references are available, however, to show that computers have penetrated into many areas of rubber science. The aims of this article are, therefore, to review some computer applications that have been made and to indicate potential uses. Perhaps both of these aims can be served by first considering the nature of computers and the type of problem solving for which they are uniquely adapted.
Effect of a Dispersion of Gelled Polymer Particles on Viscoelastic Properties of a Linear Polymer
Authors: Rigbi Zvi 
Published: February 2011

Abstract
In the rubber industry, it has often been observed that dispersion of a relatively small volume fraction of a crosslinked polymer into a linear high polymer improves processability of the latter markedly. Thus, S. P. rubbers of exceptional processability are produced by coagulation of untreated latex mixed with a minor proportion of prevulcanized latex, the latter remaining in the form of discrete particles during subsequent processing operations. Similar effects are produced in the synthetic rubber industry when SBR crosslinked by means of divinyl benzene (SBR 1009 and similar grades) is mill-mixed with “straight” styrene-butadiene copolymer. In another case, a highly gelled butadiene-acrylonitrile polymer is used to enhance processing properties of oil-resistant rubbers.
Thermoelastic Measurements on Some Elastomers
Authors: Barbie J. A. , Standen J. 
Published: February 2011

Abstract
Length versus temperature curves at a series of constant loads have been obtained for cis-polyisoprene, polydimethylsiloxane and ethylene propylene elastomers in the temperature range 25° to 100° C. Thermoelastic coefficients for these networks are evaluated and compared with values obtained by more direct procedures. The deviation of the stress strain data from the simple gaussian theory is discussed briefly in terms of the C2 constant of the Mooney equation.
Hysteresis in Polymers and its Relation to Strength
Authors: Grosch K. A. , Harwood J. A. C. , Payne A. R. 
Published: February 2011

Abstract
Energy density to break measurements on a number of polymers, either partly swollen or dry, reveal that there is a simple relationship between the energy density to break and the hysteresis obtained in the first stress strain cycle taken very near to break. The hysteresis at break was varied by changing the temperature of test or by swelling the polymer.
Glass Transition in Carbon Black Reinforced Rubber
Authors: Smit P. P. A. 
Published: February 2011

Abstract
It can be stated that the effect of carbon black in a rubber vulcanizate with regard to dynamic properties can be explained by assuming physical adsorption of rubber on the black surface. The effect can be represented by assuming an adsorbed layer having different properties from the bulk rubber taking the layer thickness to be at least 20 A. Adsorption-desorption from this layer causes non-linearity and may contribute to losses observed in the glass transition. This adsorption is analogous to adsorption of simple liquids in microporous systems such as silica gel and activated carbon.
Large Deformation Tensile Properties of Elastomers. I. Temperature Dependence of C1 and C2 in the Mooney-Rivlin Equation
Authors: Smith Thor L. 
Published: February 2011

Abstract
Tensile stress strain data were determined at various extension rates and temperatures on unfilled butyl and silicone vulcanizates and on six hydrofluorocarbon (Viton A-HV) vulcanizates that contain between 0.90 and 12.2×10−5 mole of effective network chains per unit volume of gel rubber. From one min isochronal data, values of C1 and C2 in the Mooney-Rivlin equation were derived. For the butyl and silicone vulcanizates from, respectively, −20 to 150° C and —45 to 200° C, C1 increases with temperature at a rate which is in reasonable agreement with published data from force-temperature measurements. Because C2 is sensibly temperature independent over these extended temperature ranges, it is concluded that C2 is a finite quantity under equilibrium conditions. Time dependent behavior was observed on the Viton A-HV vulcanizates between —5 and 230° C. For each vulcanizate between about 25 and 230° C, C1273/T is temperature independent, but it increases with decreasing temperature below about 25° C. Except at the lowest temperatures, C2273/T decreases with increasing-temperature, the rate of decrease becoming progressively less with an increase in crosslink density. Above 25° C the ratio C2/C1, which ranges from about 90 to 0.6, decreases with an increase in either temperature or crosslink density. The time-dependent behavior of C2273/T appears to arise primarily from molecular processes whose relaxation times are considerably longer than the terminal relaxation time of individual chains.
Reinforcement of Polymers. II. Effect of Vulcanization on Tear Strength of Filler Rubber Mixes and on Elastomer to Filler Adhesion
Authors: Yagnyatinskaya S. M. , Raevskii A. G. , Frumkin L. S. , Voyutskii S. S. 
Published: February 2011

Abstract
It has been shown that an increase in the adhesion of elastomer and filler always led to a corresponding increase in tear strength. It was of interest to clarify whether this applies to vulcanizates. We have now studied the change in adhesion strength of the elastomer to filler bond and of the tear strength of filled systems in vulcanization.
Comparison of Viscoelastic and Dielectric Properties of Natural Rubber and Sulfur Systems
Authors: Havranek A. , Bakule R. 
Published: February 2011

Abstract
This paper presents a comparison of viscoelastic and dielectric retardation time spectra of a rubber-sulfur system with a sulfur concentration ranging from 1.75 to 16.4%. The viscoelastic spectra were obtained from creep measurements which were carried out in the time interval 3×10−2 to 5×10+1 sec and a temperature range from −40° C to +70° C. The dielectric spectra were derived from measurements of the frequency dependence of the real and imaginary part of the complex dielectric constant in the frequency range 3×101 to 3×104 cps or temperatures between − 50° and +35° C. The temperature-time superposition principle was used in the derivation of the spectra. The following conclusions may be deduced from the comparison: (1) The retardation times corresponding to the spectral maxima for mechanical measurements are displaced by several orders toward longer times with respect to those for dielectric measurements. (2) The reference temperatures T8, determined from the WLF equation are higher for viscoelastic measurements than for dielectric measurements, especially for samples with a higher sulfur content. (3) The viscoelastic spectra become narrower, while the dielectric spectra broaden with increasing sulfur content. Further, it was ascertained that the results of dielectric measurements correspond to the presumption that the logarithmic retardation time spectrum has the Gaussian form in logarithmic time scale.
Effect of Temperature on Ozone Cracking of Butyl Rubbers
Authors: Gent A. N. , Hirakawa H. 
Published: February 2011

Abstract
Rates of growth of single ozone cracks have been measured for vulcanizates of two butyl rubbers over the temperature range of 20-160° C. Over most of this range the rates are quantitatively related to the segmental mobility of the polymer and depend upon temperature in accord with the appropriate form of the WLF relation. The rates are also proportional to the concentration of ozone. It is therefore concluded that diffusion of ozone into the polymer before reaction is the rate-controlling step. This is contrasted with the behavior of butadiene styrene copolymers, for which rates of crack growth are also quantitatively related to the segmental mobility, but the rates are somewhat larger at equivalent mobilities and the dependence upon ozone concentration is smaller. The difference is attributed to different penetration distances before reaction in polymers containing low and high densities of reactive sites.
The Chemistry of Sulfur Curing. IV. Effects of Organic Accelerators on the Reaction of Cyclohexene with Sulfur
Authors: Wolfe James R. 
Published: February 2011

Abstract
Cyclohexene reacts with sulfur at 140° in the presence of zinc dimethyldithio-carbamate, tetramethylthiuram monosulfide, or tetramethylthiuram disulfide, to produce 2-cyclohexene-1-thiol as the major product after lithium aluminum hydride reduction of the polysulfide compounds. Secondary products are cis- and trans-1, 2-eyclohexanedithiol and cyclohexanethiol. Zinc dimethyldithiocarbamate is postulated to promote the reaction via an ionic mechanism as it causes more trans than cis-1, 2-cyclohexanedithiol to be formed. Tetramethylthiuram monosulfide and disulfide are postulated to promote the reaction via a free radical mechanism as they cause more cis- than trans-1, 2-cyclohexanedithiol to be formed.