bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stereochemistry of Rubber Biosynthesis
Authors: Archer B. L. , Barnard D. , Cockbain E. G. , Cornforth J. W. , Cornforth Rita H. , Popják G. 
Published: February 2011

Abstract
The stereochemistry of the formation of natural rubber and trans-trans-farnesyl pyrophosphate in latex has been studied in vitro using [2−14C−(4R)−3H1] and [2−14C−(4S)−4−3H1]mevalonates as substrates. The proton eliminated from C-2 of isopentenyl pyrophosphate during the formation of farnesyl pyrophosphate in latex has the same steric position as that released in the liver system, and is epimeric with that eliminated during the biosynthesis of rubber. Complete stereospecificity is exhibited by the enzymes in the two cases. In rubber biosynthesis isoprene residues are incorporated directly in all-cis configuration without the intervention of trans structures.
Road Surface Characteristics and Skidding Resistance
Authors: Sabey Barbara E. 
Published: February 2011

Abstract
When roads are wet their skidding resistance is reduced by the lubricating action of the film of water on the road. Under some circumstances this reduction may be substantial and the extent of it is largely dependent on the characteristics of the road surface. The first requirement for a good skidding resistance on wet roads is to facilitate break through of the water film in order to establish areas of dry contact between the road and the tire. Drainage channels, provided by the large scale texture of the road or by a pattern on the tire, assist in getting rid of the main bulk of water and are of increasing importance the higher the speed. The penetration of the remaining water film can be achieved only if there are sufficient fine scale sharp edges in the road on which high pressures (about 1000 lb/in2) are built up. The existence of such fine scale sharpness gives the surfaces a harsh feel. When vehicles are travelling at speeds of about 30 mph the fine scale texture of the road is the dominant factor determining skidding resistance. However, as they travel faster, it becomes increasingly difficult to penetrate the water film in the time available, however harsh the surface. At high speeds the requirements for a good skidding resistance are therefore different. The resistance to skidding arises to a larger extent from energy losses in the rubber of the tire as the surface of the tread is deformed by projections in the road surface and, although the physical properties of the tread rubber are important in this respect, it is essential to have sufficiently large and angular projections in the road surface to deform the tread, even though a water film may still be present on the surface. At higher speeds the coarseness of texture becomes as important as its harshness.
Elastic Properties and Network Structure in Silicone Gum Vulcanizates
Authors: Bobear W. J. 
Published: February 2011

Abstract
A model of a rubber network formed from finite, linear polymer chains is treated, using expressions from accepted elastic theory as well as relations that have been less generally used or only implied. The resultant empirical mathematical expressions conform very closely to the predictions of the simple kinetic theory of rubber elasticity and are mathematically consistent, in that the major properties and measurements are interrelated, and apparent inconsistencies in the literature are reconciled. As a consequence, an empirical equation is developed for the relationship between elastic properties and network structure in silicone gum vulcanizates. This equation is then applied to the estimation of peroxide crosslinking efficiencies.
Steady State Melt Viscosity of Plasticized Hydrocarbon Elastomers
Authors: Kraus G. , Gruver J. T. 
Published: February 2011

Abstract
The steady state melt viscosity of several plasticized hydrocarbon elastomers is described by a reduced variable treatment which allows superposition of the viscosity and shear rate curve for any polymer containing a diluent on the viscosity curve of the pure polymer. The shift factors which accomplish this superposition may in turn be broken up into two factors: (1) a function of the volume concentration of the diluent alone, which represents the loosening of the entanglement network, and (2) a factor representing the effect of the diluent on segmental friction and chain configuration. The latter is shown to be related to the temperature of measurement and the glass transition temperatures of both polymer and diluent. The relationships developed permit predictions of plasticizer efficacy for any diluent and polymer combination from glass transition and density data alone.
Entropy Elasticity in High Polymers
Authors: Linhardt Friedrich 
Published: February 2011

Abstract
Vulcanized rubber has an unusual property, known early in the 19th century, but not understood until 1935: it increases in stiffness with rise in operating temperature. A strip of rubber loaded with a weight and heated does not stretch; on the contrary, it contracts to some extent. Theoretical interpretations of this effect showed deformation of rubber, as well as its softness and high extensibility, to be determined by entropy, among other things. “Entropy elasticity” was looked upon as a peculiarity of rubber. It was thus only logical, when materials were classified as “rubbers” that they should be distinguished from all other materials by using the expression “entropy elastic behavior”. To be sure, one is inclined today to consider entropy elasticity a characteristic of all high polymers, including those not crosslinked. The present article reports an experimental approach to this problem.
Simple Theory of Stress Strain Properties of Filled Polymers
Authors: Nielsen Lawrence E. 
Published: February 2011

Abstract
By the use of simple models of filled plastics, approximate equations are derived for elongation to break in the case of perfect adhesion between the phases and for the tensile strength in the case of no adhesion between the polymer and filler phases. By combining these equations with equations for the modulus (assuming Hookean behavior) all the stress strain properties can be derived, including rough estimates of the impact strength, as a function of filler concentration. The theory predicts a very rapid decrease in elongation to break as filler concentration increases, especially with good adhesion; it is also predicted that the tensile strength of a filled polymer can be greater than that of an unfilled polymer.
Forms of Combination of Sulfur in Vulcanization of Rubber
Authors: Scheele Walter 
Published: February 2011

Abstract
A certain portion of the sulfur used appears as polysulfide sulfur in all vulcanization processes. The polysulfide concentration passes through a maximum with time, so that it must be considered to be an intermediate product which disappears to form final products. It is shown that the dependence of polysulfide sulfur concentration on time may be described by an empirical equation with three constants, of which one is related to the system, the other two depending in a characteristic way on concentration or temperature. The application of this equation permits recognition of a close relation between the kinetics of sulfur decrease and that of polysulfide formation. This leads to a kinetic theory of formation and decrease of polysulfide sulfur which is developed in detail. Applying the experimentally determined first order velocity constants of sulfur decrease and conditions obtaining for polysulfide maximum, velocity constants for polysulfide decrease can be calculated. With these, equations for the functional relation between polysulfide sulfur and time as well as for the increase of final products may be set up. Good correspondence between theory and experiment is found for the dependence of polysulfide sulfur in the vulcanizate on time. Comparisons were examined which indicate the validity and applicability of the kinetics developed.
Reactions of Carbenes with Unsaturated Polymers
Authors: Lishanskii M. S. , Tsitokhtsev V. A. , Vinogradova N. D. 
Published: February 2011

Abstract
The literature has a limited amount of data on chain reactions of unsaturated polymers, in particular diene polymers. The appearance of a paper dealing with addition of dichlorocarbene to polyisoprene and to polybutadiene has impelled us to publish results of studies we made on reactions of unsaturated polymers with carbenes, which have made it possible for the first time to obtain polymers containing in the main chain, or in the side chains, cyclopropane groups with polar substituents. Addition of carbenes to cis-1, 4-polyisoprene, trans-1, 4-polyisoprene, 1, 4-polybutadiene, and 1, 2-polybutadiene was accomplished through decomposition reactions of diazoacetic esters catalyzed by copper salts (for carbethoxycarbene and carbomethoxycarbene) and the reaction of the ethyl ester of trichloroacetic acid with sodium methylate (for dichlorocarbene).
Determination of Double Bonds in Ethylene Propylene Terpolymer Rubbers
Authors: Hank R. 
Published: February 2011

Abstract
Developments in the field of sulfur vulcanized unsaturated ethylene propylene terpolymer rubbers, also known as EPT rubbers, have progressed rapidly in recent years. Considerable success has been achieved in producing EPT rubbers from ethylene, propylene, and various dienes. Initial difficulties, involving introduction of double bonds into already known ethylene propylene copolymers, were soon overcome when it became clear that it was not the then commonly conjugated dienes such as butadiene and isoprene, but rather nonconjugated dienes, which were required for successful terpolymerization with ethylene and propylene, according to the Ziegler process. As with butyl rubber, it is sufficient, for vulcanization purposes, to incorporate one or two mole per cent of such dienes into the terpolymer. It is especially important, not only for polymerization, but also for rubber processing, to know the type and amount of unsaturation. In this article we wish first of all to report on double bond determinations in general and then, in particular, on qualitative and quantitative dicyclopentadiene determinations in ethylene propylene terpolymers. It is especially important, not only for polymerization, but also for rubber processing, to know the type and amount of unsaturation. In this article we wish first of all to report on double bond determinations in general and then, in particular, on qualitative and quantitative dicyclopentadiene determinations in ethylene propylene terpolymers.
Fracture of Amorphous Polymers
Authors: Landel R. F. , Fedors R. F. 
Published: February 2011

Abstract
At sufficiently high temperatures compared to the glass temperature, both experimental evidence (Figure 7) and Equation (10) predict that failure envelopes obtained from samples differing in νe will superpose to a common response curve f(ε) independent of chemical structure of the polymer when σb is normalized to unit νeT. At lower temperatures, experiment and Equation (8) indicate that in such a normalized plot, individual failure envelopes will diverge from the common response curve, f(ε), due primarily to the effect of the chain flexibility parameter n. As the temperature is lowered still further, Equation (6) shows that the shapes of individual envelopes may vary if the time dependences of E and g differ. This effect is presumably the factor which produces the difference in shapes between the Viton elastomers and the others shown in Figure 7. In addition, Equation (4) relates the maximum value which λb can attain to other readily measured parameters, notably νe. Thus knowledge of these two parameters, νe and n, is sufficient to predict to a good approximation the shape and location of the failure envelope up to the region of (λb)max.
Crystallization in Stretched Polymer Networks. I. trans-Polychloroprene
Authors: Gent A. N. 
Published: February 2011

Abstract
Changes in tensile stress afford a simple means of studying the rates of crystallization and the melting temperatures in crosslinked polymers subjected to simple extension. The form and magnitude of the stress changes in networks of trans-polychloroprene are closely similar to those observed for cis-1:4-polyisoprene and cis-l:4-polybutadiene networks. They are in accord with the formation of oriented crystallites and incompatible with folded chain crystallization at extensions as low as 15 per cent. It seems likely that the present networks do not crystallize by chain folding even in the unstretched state. The large increases in rate of crystallization with extension are approximately accounted for by corresponding increases in the equilibrium melting temperature. Direct measurements of the melting temperature show similar rises with extension. The rise in melting temperature is in good agreement with Flory's theoretical treatment of oriented crystallization at extension ratios of three and higher (when the crystallite orientation is complete) for three networks having different degrees of crosslinking. When referred to a constant segmental mobility, namely, that obtaining at Tg+50° C, the rates of crystallization at various extensions obey a common dependence upon the degree of supercooling. This relation is in fair accord with theories of nucleation kinetics, except at the lowest temperatures where there is some indication of the appearance of a new crystal form.
Preparation and Properties of Polymer Mixtures
Authors: Pazonyi T. , Dimitrov M. 
Published: February 2011

Abstract
A useful and generally accepted method of increasing the available selection of plastics is the manufacture, by blending existing polymers, of mixed materials with new properties. Properties of the blend can be expected to correspond to the additive properties of the plastics making up the mixture, in accordance with their proportions. This is very often the sole purpose of the process, e.g., when plasticizing a brittle polymer with a more plastic one. It can however also be expected that some properties of the blend may be better than what would be given by pure additivity, as is observed with some mixed solvents or alloys. Polymers are mixed industrially on processing machinery similar to that used for processing plastics, or mixing in additives, i.e., on mills, in internal mixers, mixing extruders, Ko-Kneaders, etc. Adequate mixing is often only possible at the processing temperature of the material which requires the highest temperature. Experience has shown that in the usual processing conditions only certain polymers are miscible. Nonmiscible polymers separate in the course of or at the end of the mixing process. Such material disintegrates into thin layers or fibers on cooling. The practical compatibility of polymers is not easy to explain theoretically. We shall see that in some systems the mixtures are mutual solutions of their components, while in others the possibility of forming a true mixture must be excluded, yet blends with valuable properties are easily obtained in practice.
Vapor Pressure of a Swollen Crosslinked Elastomer
Authors: Gee G. , Herbert J. B. M. , Roberts R. C. 
Published: February 2011

Abstract
This investigation was undertaken with the aim of using vapor pressure measurements to study the configurational free energy changes involved in the isotropic dilation of a network. The main conclusion is that the assumptions implicit in this approach require further study. These same assumptions are involved in conventional determinations of crosslinking from swelling. There is reason to suspect that such measurements overestimate crosslinking.
Radiation Induced cis and trans Isomerization of Polyisoprenes and Temperature Dependence of the Equilibria
Authors: Tsurugi Jitsuo , Fukumoto Tsugio , Yamagami Masayuki , Itatani Hiroshi 
Published: February 2011

Abstract
The cis and trans interconversion of polyisoprenes in solutions induced by γ-radiation in the presence of a sensitizer, which is any one of organic bromides or n-butyl mercaptan, was studied by using hevea and gutta percha as starting substances. The percentage cis remaining or converted after irradiation was determined by the infrared absorption. The equilibrium constants for the interconversion at 22, 60, and 100° C were found to be 3.00, 5.25, and 7.33, respectively. The firstorder rate constants for as cis → trans and trans → cis isomerizations at 22° C were calculated to be 9.05 and 2.91, respectively. The results were interpreted by the mechanism proposed by Golub, according to which the double bonds from π complexes with radiolytic fragments from sensitizers give a radical transition state capable of interconversion. However, our results showing that heating shifts the equilibrium toward trans isomer are not in accord with the mechanisms of the radiation-induced isomerization of polybutadiene of Golub and those for photoisom-erization of aromatic azo compounds.
Kinetics of Urethan Cleavage in Crosslinked Polyurethans
Authors: Singh Ajaib , Weissbein Leonard 
Published: February 2011

Abstract
A series of clean, well defined polyurethan networks was synthesized from polyester glycols, 2, 4-tolylene diisocyanate, and 1, 1′, 1″-trimethylolpropane by means that afforded precise control over the content of urethan groups per network chain. The thermal cleavage of these networks was studied using the technique of stress relaxation. Analysis of the stress relaxation data on each network structure revealed two exponential decay processes differing in rate by about an order of magnitude. The rate of the slower process, which dominates the overall stress decay, was shown to be directly dependent on the content of urethan groups per network chain. Positive identification of this process with urethan cleavage was thereby established. The kinetic and thermodynamic constants associated with urethan cleavage were then calculated from data on this process at different temperatures. The more transient stress decay process was not uniquely definable, but probably originated from the cleavage of one or more types of weak linkages found in small but variable proportions in the different polyurethan networks. The nature and origin of these weak linkages was discussed.
Application of the Hydrodynamic-Structural Theory of Non-Newtonian Flow to Suspensions which Exhibit Moderate Shear Thickening with Particular Reference to “Dilatant” Vinyl Plastisols
Authors: Gillespie T. 
Published: February 2011

Abstract
A general equation, derived in previous work, fits flow data for moderately shear thickening dispersions of poly (vinyl chloride) particles in an oil. The theory on which the equation is based predicts that the number of structural links in a disperse system can increase with increasing shear rate without shear thickening, provided n∞/n0&lt;2, where n∞ and n0 are the number of links per cubic centimeter at infinite shear rate and zero shear rate, respectively. This could account for the unexplained occurrence of “volume dilatancy” without “rheological dilatancy” previously reported in the literature. When n∞/n0&lt;2, viscosity increases with increasing shear rate to a maximum value and then the viscosity decreases with further increase in shear rate. This effect is explained as a competition between increase in the number of links with increasing shear rate and decrease in link lifetime with increasing shear rate. Aging of vinyl plastisols is examined and found to involve changes in both hydrodynamic and structural viscosity which can be explained by absorption of oil into the porous poly (vinyl chloride) particles.
Rapid Treadwear Ratings with Radioactive Isotopes
Authors: Gehman S. D. , Reilly P. J. , Larsen G. M. 
Published: February 2011

Abstract
Incorporation of radioactive isotopes in small surface areas of tire treads permits wear measurements by counting before and after wear. The isotope is limited to a depth of about ten mils so that the fraction of activity worn off is appreciable in a hundred miles or so. Such experiments were made with S35, Zn65O, and I125. The first two were applied to uncured tires in thin sheets chemically identical to the tread compounds. Zn65 was counted with a shielded Geiger—Müller tube. For S35, miniature specimens were cored from the tire treads, dissolved in hot xylene, and counted in an automatic, liquid scintillation counter. Filter paper was laminated to aluminum foil and dipped in a solution of iodine and Iodine-125 in toluene. Small disks or strips were applied to tire treads, usually after a break-in run of several hundred miles. The iodine diffuses rapidly into the rubber, combining stably in some compounds and otherwise being fixed by subsequent application of a solution of silver perchlorate in toluene. Counting was preferable with a scintillation probe about ninety times more sensitive than a Geiger-Müller tube. Wear calibration curves were secured by controlled grinding and counting of a similarly tagged specimen of each tread compound. Physical properties were not affected appreciably by these iodine concentrations. Radioactivity in a tire tagged by strips across the tread at five places was about two microcuries. Results correlated well with conventional techniques. Road contamination from such tests is insignificant. The I125 method has advantages in versatility, acceleration of tire wear tests, fast recognition of localized wear and wear patterns, better “control” of weather, road, and vehicle conditions by shortening the tests, and should reduce compound interaction for test tires made with sectors of different tread compounds.
Coefficient of Wet Friction of Tire Treads
Authors: Kern W. F. 
Published: February 2011

Abstract
The schematic presentation in Figure 1 is an attempt to demonstrate the importance of friction coefficient in matters of driving safety and abrasion resistance, which are of interest to both tire manufacturers and users. References 1 to 3 present the viewpoint of road engineers, designers of motor vehicles, tire producers, rubber compounding experts, and various suppliers of different raw products. The numerous factors involved in producing skid resistant tires are summarized in Figure 2. From among such factors, we take up, here, only the tire element within the contact surface of the tire. The coefficient of friction for this element was investigated with test specimens, preferably under wet conditions, as a function of speed, temperature, and load, and against friction bases that exhibited a variety of grip characteristics. This coefficient of friction is affected by a number of other variables, Tables I and Ia, some of which will be discussed in this article.
Carbon Black Surface Areas by the Harkins and Jura Absolute Method
Authors: Kraus G. , Rollmann K. W. 
Published: February 2011

Abstract
The Harkins and Jura (HJ) absolute method of surface area determination (Harkins and Jura, J. Am. Chem. Soc. 66, 919, 1944) has been applied to a large number of carbon blacks. Surface area is calculated from the heat of immersion of the solid powder covered by a preadsorbed multilayer of the immersion liquid. For non-porous carbon blacks good agreement with nitrogen adsorption surface areas is obtained, but with porous blacks the HJ method gives smaller values since micropores are filled and bridged over by the pre-adsorbed film. Thus the HJ areas are more nearly representative of particle size and may be used to calibrate indirect methods of particle size determination. An example of this is shown using light reflectance values on dry carbon black and possible complications due to particle size distribution in the use of the reflectance test are discussed.
Effect of Carbon Black Densification on Structure Measurements
Authors: Dollinger R. E. , Kallenberger R. H. , Studebaker M. L. 
Published: February 2011

Abstract
A simple method of pretreating carbon black has been developed which permits measurements to be made on the dry carbon black which reflect on the basic property called “structure.” Correlation between these measurements and extrusion shrinkage of raw stocks is demonstrated. With a small surface area adjustment, this correlation is believed to be as reliable as extrusion shrinkage values.