bluuebunny/crossref_metadata_2025_split huggingface dataset:
Heat Conduction and Molecular Structure in Rubberlike Polymers
Authors: Rehner John 
Published: February 2011

Abstract
In this paper experimentally determined values are reported for the thermal diffusivity (k) of various rubberlike polymers. Corresponding values of the thermal conductivity (W) can be computed from the well-known relationship, W=kρcP, where ρ and cP denote the density and specific heat at constant pressure of the composition. Measurements were made on (1) pure-gum stocks prepared with natural rubber, Butyl (GR-I), Perbunan-18, Perbunan-26, Perbunan-35, Buna-S (GR-S), polybutadiene, Neoprene-GN, polyisoprene, Silastic-160, and Silastic-180; (2) pure-gum stocks of the first five rubbers listed under (1) containing in addition 20 parts of a hydrocarbon softener (Bardol), based on 100 parts by weight of the polymer; and (3) the Bardol stocks containing in addition 54 parts of carbon black (Kosmobile-66). From measurements of the rate of change of temperature within a rubber sphere suddenly subjected to a change in its surface temperature, it was found possible to determine the dependence of k on temperature. A satisfactory definition of the “mean” temperature of a sphere under these conditions is described. In a discussion of the effect of chemical composition and structure on heat conduction, the bearing of hindered rotation, cross-linking and branching and interatomic bond strength on the results is pointed out. Values are derived for certain other properties of some of the polymers, including their characteristic Debye temperatures, specific heats at constant volume, flexibility of the main valence chains, compressibilities, and sound velocities.
Low Temperature Characteristics of Elastomers
Authors: Gehman S. D. , Woodford D. E. , Wilkinson C. S. 
Published: February 2011

Abstract
The low temperature stiffening of elastomers frequently limits their usefulness. A new laboratory test for measuring their stiffness at low temperatures is described. Strips of the stocks to be tested are mounted around a cylindrical rack in a vertical, cylindrical insulated chamber. The temperature in the chamber is controlled by cooling the base externally with dry ice and by a moderate regulated flow of precooled air through dry ice in the bottom of the chamber. This system gives stable temperatures which are easily controlled. The chamber can be rotated to attach the samples in succession, by means of projecting top grips, to a suitably mounted torsion wire. The stiffness is measured by the angle of twist of the sample when the torsion head is rotated 180°. The relative modulus for any temperature is calculated as the ratio of the modulus at this temperature to that at 25° C. Plots of angle of twist against temperature show a rather sharp break at the low temperature end of the curve. This determines a somewhat subjective “freezing point”. Curves are given to illustrate the wide variety of low temperature stiffening characteristics for elastomers. In unplasticized stocks the chemical composition of the monomers is the dominating factor for these properties for various synthetic rubbers. The stiffness of elastomers which are capable of crystallization on stretching, such as Hevea, Neoprene, and Butyl rubber, depends not only on temperature but also on time of exposure. To study these effects, the foregoing apparatus was used in a cold room. A rather long induction period occurs, during which the stiffness is essentially constant. It then increases and eventually reaches a larger constant value. Several months may be required to complete these changes. x-Ray examination of Hevea and Butyl proved that the increased stiffness on long exposure is due to crystallization. No change was observed in the stiffness of GR-S in the period of 2.5 months at − 30° C. Reduction in the speed of retraction is a critical measure of the deterioration of high elasticity at low temperatures. It gives a wide differeniation at moderately low temperatures between Butyl rubber and Hevea or GR-S, whereas a slow modulus test does not.
Effect of Stretching on the Properties of Rubber
Authors: Mullins L. 
Published: February 2011

Abstract
The results of tensile stress-strain, stress relaxation, swelling, electric conductivity, and power factor tests show that the properties of pure vulcanizates are only slightly affected by previous stretching or flexing; on the other hand, the properties of vulcanizates containing reinforcing agents, or fillers which stiffen the rubber, may be considerably changed by previous stretching. The increases of stiffness, electric conductivity, and power factor produced by the incorporation of the fillers are destroyed by flexing or stretching. From most practical points of view these changes are of a permanent nature, as at normal temperatures the recovery towards the initial properties is slow. These effects are attributed to the breakdown of both agglomerates and chains of filler particles, and the adsorption of the filler particles on the rubber.
Tensile Strengths of Pure Gum Natural Rubber Compounds
Authors: Gee Geoffrey 
Published: February 2011

Abstract
The tensile properties of a range of pure-gum natural rubbers have been reviewed, and it has been shown that their principal features can be understood on the assumption that the tensile strength measured in a given test depends directly on the amount of crystallization at break. The most important single factor in determining tensile strength is the degree of cross-linking. Cross-linking is only needed in order to prevent plastic flow, thus making it possible for the molecules to align themselves by stretching, and hence to crystallize. A very highly cross-linked rubber is weak because the load required to stretch it is so high that the rubber is broken before the elongation becomes large enough to produce crystallization. In general, vulcanization also involves reactions, e.g., the combination of sulfur with the rubber, which inhibit crystallization by producing structural modifications of the rubber. These reduce the tensile strength, especially when the degree of cross-linking is large. These ideas readily explain the effects of swelling and of the temperature of test. They are also used in a brief discussion of the phenomena of overcure, reversion, and aging.
The Thermoelastic Properties of Rubber
Authors: Meyer Kurt H. , Van der Wyk A. J. A. 
Published: February 2011

Abstract
In an earlier communication it was shown that, within a certain range of elongations, viz., 100 to 300 per cent, and at constant elongation, the stress in stretched rubber is directly proportional to the absolute temperature. Within this range, therefore, the stress is analogous to the pressure of an ideal gas, which at constant volume is likewise proportional to the temperature. This behavior of rubber and of other rubberlike substances is said to be ideal. However, a sample of rubber the behavior of which is ideal at elongations of 100 per cent and higher deviates from this behavior when its elongation is less than 100 per cent or greater than 500 per cent. One of the reasons for these deviations from ideal behavior at high deformations has already been discussed in a previous publication; as a result of stretching, rubber begins to crystallize. The crystallites do not contribute to the elastic force, but if the temperature is raised, they fuse and thereby increase the stress, which then increases more rapidly than that of an ideal rubber. The deviations from ideal behavior at small deformations have not in any way been studied thoroughly, so the first part of the present work is concerned with these deviations from ideal behavior. First of all it is well to discuss some experimental facts. The thermal coefficient of the force F at constant elongation Δl, (∂F/∂T)Δl, is negative for low elongations (up to about 10 per cent), i.e., the force decreases with rise in temperature, and the coefficient of linear expansion in the direction of traction remains positive, like that of an ordinary material. At elongations of approximately 10 per cent, the stress is independent of the temperature; at this point the coefficient of linear expansion in the direction of stretching is, therefore, equal to zero. At higher deformations, the stress increases with rise in temperature, a phenomenon which indicates a negative coefficient of linear expansion.
Mechanism and Theory of Vulcanization
Authors: Stiehler Robert D. , Wakelin James H. 
Published: February 2011

Abstract
x-Ray and stress-strain data have been obtained which indicate that accelerators and divalent metallic compounds, as well as sulfur, react with rubber molecules during vulcanization and become a part of the rubber vulcanizate. The vulcanization reaction was found to behave like a normal chemical reaction in solution, which is influenced by the temperature, solubilities of the reacting ingredients, relative strengths and concentrations of the acids present, pH, and chemical nature of the vulcanizing agent. On the basis of these results and the known characteristics of vulcanized rubber, the original hypothesis of Goodyear and the more recent conclusions of Midgley, Henne, and Shepard were developed into a theory of vulcanization which postulates that vulcanization is a process by which the intermolecular forces are increased through the introduction of polar groups, generally acidic in nature, into the rubber molecules. This is accomplished by the reaction of certain types of oxidizing agents with the alpha-methylene carbon atoms or double bonds. These intermolecular forces are further increased with soluble divalent metallic compounds by the formation of ionic valences between divalent metallic ions and polar acidic groups of the rubber vulcanizate. These divalent metallic ions may bridge the rubber molecules through ionic valences in the form of a salt. Intermolecular forces established during vulcanization give rigidity to the molecular structure, which retards plastic flow and crystallization of rubber molecules. They also are responsible for other characteristics of vulcanized rubber. The molecules in vulcanized rubber are presumably not joined by primary-valence bonds through sulfur or oxygen bridges, but retain their individual existence.
The Combined Action of Maleic N-Methylimide and p-Bromobenzoyl Peroxide on Natural Rubber
Authors: Delalande André 
Published: February 2011

Abstract
It is already known that natural rubber is capable of combining, under certain conditions, with various unsaturated compounds. Bacon and Farmer, for example, have fixed maleic anhydride on rubber in solution in the presence of benzoyl peroxide. This reaction has been applied likewise to acrylic acid, to acrylonitrile and to methacrylonitrile. Bacon and Farmer carried out the reaction with solutions of rubber which were refluxed for 18 hours, without, however, attempting to avoid the extraneous effect of atmospheric oxygen. The present author was, therefore, prompted to carry out the reaction protected from air in sealed tubes into which the solvent was introduced by distillation in a vacuum according to a technique based on that employed by Moureu and Dufraisse in their studies of autoxidation. In an effort to explain the mechanism of the reactions, maleic N-methylimide was chosen as the unsaturated reagent in the reaction and p-bromobenzoyl peroxide as the catalyst. These two compounds, in virtue of the nitrogen atoms and bromine atom in their respective molecules, made it possible to determine by analysis what became of them as a result of the reaction.
The Photoelastic Properties of Rubber. I. Theory of the Optical Properties of Strained Rubber
Authors: Treloar L. R. G. 
Published: February 2011

Abstract
From the consideration of vulcanized rubber as a network of randomly kinked molecular chains, the optical constants corresponding to the most general type of homogeneous strain are derived. Under such a strain the rubber is shown to acquire the properties of an optically biaxial crystal, characterized by three principal refractive indices in the directions of the principal axes of strain. For directions of light propagation parallel to one of the principal axes, the birefringence is shown to be a simple function of the principal extensions and is, moreover, proportional to the difference between the two corresponding principal stresses. If the rubber is swollen with a liquid having the same refractive index as itself, the birefringence for a given state of strain varies inversely as the cube root of the swelling ratio, as do also the principal stresses.
The Photoelastic Properties of Rubber. II. Double Refraction and Crystallization in Stretched Vulcanized Rubber
Authors: Treloar L. R. G. 
Published: February 2011

Abstract
From an investigation of the variation of birefringence, with elongation in vulcanized rubber extended at temperatures ranging from −50° to +100° C, it is possible to distinguish the effects of crystallization from the true strain-birefringence. The latter agrees closely with theoretical expectations in its dependence on stress and on elongation. The data do not permit of a quantitative estimation of the relative amounts of crystalline material present under various conditions. Experiments with stretched swollen rubber further confirm the theory and yield further evidence on the effects of crystallization.
Equilibrium Properties of High Polymer Solutions and Gels
Authors: Gee Geoffrey 
Published: February 2011

Abstract
The equilibrium between a polymer and a liquid is of fundamental importance in a number of problems of considerable practical as well as theoretical interest. As examples may be mentioned: (1) the choice of a solvent or plasticizer for a given polymer; (2) choice of a suitable polymer for use, e.g., as a gasket in contact with specified liquids; (3) the combined solvent or swelling action of a mixture of liquids; (4) the effect of mechanical deformation, e.g., compression, on the solvent resistance of a polymer; and (5) the separation of a polymer into fractions by the use of solvent-precipitant mixtures. It must be emphasized at the outset that in some of them other factors are involved, but these are not considered in the present paper. The basic assumption is made here that, given enough time, a system comprising polymer and liquid will reach a steady state, and that if two condensed phases are then present, they must be in true thermodynamic equilibrium. The disturbing influence of such time-dependent processes as degradation and plastic flow may, in certain practical cases, prevent the attainment of a steady state, but these possibilities require separate discussion. Within the limited space available, all that can be attempted is a brief outline of the general methods which have been used, illustrated by applying them to the first two of the above problems.
Preparation and Properties of Rubberlike High Polymers. IV. Correlation between Structure and Properties of Elastomers Derived from Dienes
Authors: Salomon G. , Koningsberger C. 
Published: February 2011

Abstract
The correlation between structure and properties of elastomers prepared from dienes, natural rubber, gutta-percha, as well as those of some significant derivatives of natural rubber, are discussed. The similar influence exerted by methyl groups on the brittle point, elastic recovery, and permeability to gases is demonstrated and separated from the effect caused by insertion of —CH2— CHR— groups in straight-chain polybutadiene, which takes place during co-polymerization or 1,2 addition. The preponderant influence of an unbranched-chain structure on tensile strength at elevated temperatures and in the swollen state is illustrated. Complex compounds with silver nitrate provide further evidence for the particular symmetry of the natural rubber chain: They are reinforcing agents for synthetic elastomers. The brittle points of hydrochlorides from natural rubber, gutta-percha, and polyisoprene are compared with those of polyvinyl compounds. Correlation between the structure of molecular units in a polymeric paraffin derivative and its elasticity is pointed out.
Some Structural and Chemical Aspects of Aging and Degradation of Vinyl and Diene Polymers
Authors: Mesrobian Robert B. , Tobolsky Arthur V. 
Published: February 2011

Abstract
The chemical reactivity of vinyl and diene polymers manifested during aging and degradation is similar to the reactivity manifested during polymerization. The activated intermediates are radicals, and the reaction proceeds by a chain mechanism. A discussion of the possible types of aggregative and disaggregative processes involved in aging is presented. On the basis that polymerization and degradation occur by means of the same radical mechanism, experimental evidence is given to indicate that under certain conditions both reactions may occur simultaneously. Viscosity changes of solutions of mono- and polystyrene and methyl methacrylate were studied under varying conditions of heat, oxygen, catalysts, light, and photosensitizers. An analysis of the concurrent aggregative and disaggregative reactions involved in aging may be obtained by isolating one reaction from the other, either by various physical methods, such as intermittent and continuous stress relaxation, or by such classical methods as sol—gel determinations and aging in solution. A comparative study of the rate of oxygen absorption of a large number of polymer types was undertaken to evaluate the factors affecting oxidation. Evidence is presented to show that these factors may be specified by the following: (1) chemical structure of the polymeric material, (2) presence of antioxidants, and (3) compounding and vulcanization. The oxidizability of polymeric materials was also studied in a circulating oxygen absorption apparatus to determine the effect of evolved, gaseous oxidation products. A preliminary study of the effect of light on the aging of Butyl and GR-S, measured by oxygen absorption and stress relaxation, is presented.
Properties of Polychloroprene Molecules in Solution
Authors: Svedberg Ingrid , Kinell Per-Olof 
Published: February 2011

Abstract
Polychloroprenes from emulsion and bulk polymerization were investigated in the ultracentrifuge and by means of diffusion experiments. It was found that the sedimentation constants for B-polymers are independent of the polymerization conditions. This is not to the same degree the case for A-polymers. The diffusion coefficients of both types of polymers are more sensitive to differences in size of the molecules formed. A linear relationship between diffusion coefficient and the inverse value of the molecular weight has been established for B-polymers, and an inverse square root dependence for A-polymers. In the terminology of Kuhn and Kuhn, the molecules of the B-polymers should be completely drained and the molecules of the A-polymers incompletely drained. The shape of the molecules and the polydispersity of the substances are discussed. The difficulties of obtaining true and accurate values of molecular constants for such an inhomogeneous material are pointed out. This investigation is a part of fundamental research work on synthetic rubber carried out at the request of the Government Commission on Industry in Sweden and under the direction of Professor The Svedberg. The authors wish to express their sincere thanks to Professor The Svedberg for his very kind interest and for the main facilities put at their disposal.
Evaluation of Sodium-Catalyzed Copolymers of 1,3-Butadiene and Styrene
Authors: Juve A. E. , Goff M. M. , Schroeder C. H. , Meyer A. W. , Brooks M. C. 
Published: February 2011

Abstract
Sodium-catalyzed butadiene-styrene copolymers (S-BS), of composition 75 weight-per cent butadiene: 25 weight-per cent styrene, have been compounded in tread type recipes. Evaluation tests showed properties significantly different from those of GR-S, the emulsion-phase free radical—catalyzed copolymers of identical monomer composition. 1. The processing characteristics of S-BS are considerably superior to those of GR-S, although one experience with a high temperature internal mix may indicate some limitation. Objective laboratory processing tests show that S-BS resembles high-styrene emulsion copolymers in that it can be satisfactorily fabricated from stocks containing less filler than is required in GR-S stocks for similar uses. 2. Stress-strain properties based on limited compounding studies are similar to those of GR-S. 3. The flex crack growth—hysteresis balance for S-BS vulcanizates is much superior to that of GR-S vulcanizates. Vulcanizates of emulsion polymers of high styrene content also had a flex crack growth—hysteresis balance superior to that of GR-S vulcanizates. 4. The low temperature properties of S-BS vulcanizates are inferior to those of GR-S vulcanizates. Brittle points and low temperature Young's modulus of S-BS vulcanizates are much higher than those of GR-S vulcanizates.
Effects of Cross-Linking and Branching on the Molecular Constitution of Diene Polymers
Authors: Flory Paul J. 
Published: February 2011

Abstract
Reaction mechanisms whereby cross-linked and branched polymer structures may be formed during the polymerization of dienes are discussed. A kinetic treatment of the formation of cross-linkages via the occasional addition of a free radical to the unsaturated carbon of a structural unit of a previously polymerized molecule is presented. It is pointed out that the rate of this addition step relative to monomer addition can be deduced from the average chain length and the conversion at which gelation occurs. Cross-linkages introduced by the mechanism under consideration are not distributed at random, but the deviations from a random distribution are unimportant except at high conversions. Conditions are examined under which the cross-linking reaction decreases the total number of molecules more rapidly than they are formed. Physical properties of polymers (with particular emphasis on vulcanized rubbers) are most conveniently interpreted in terms of (1) the primary molecular weight (i.e., molecular weight in the absence of cross-linkages) and its distribution, and (2) the concentration of cross-linkages. The actual molecular-weight distribution, which may be severely distorted by the presence of cross-linkages, is inappropriate for direct correlation with the more important physical properties. The modifiers or regulators commonly employed in diene polymerizations suppress gel formation by reducing the primary molecular weight; they do not actually reduce cross-linking. This reduction in molecular weight is not without other undesired consequences, however.
The Addition of Thio Compounds to Olefins. II. Reactions of Thiolacetic and Mono-, Di-, and Trichlorothiolacetic Acids
Authors: Cunneen J. I. 
Published: February 2011

Abstract
Cyclohexene, 1-methylcyclohexene, dihydromyrcene, squalene, and rubber combine additively with the above named thio acids, the reactions proceeding similarly to, but more easily than, those reported earlier for thiols. The parallelism noted previously between the ease of thiol addition and the facility of proton removal from the S—H bond, as measured by acidity, not only extends to thiol acids generally, but also accords with the fact that among the latter themselves the more acid chloro-substituted compounds are the more active addenda. A reactivity order, cyclohexenes &gt; dihydromyrcene &gt; squalene &gt; rubber, is again evident, but whereas this serves to make the last olefin inert towards thiols, yet thio acid adducts are readily prepared, and these are of considerable technological interest as oil- and gasoline-resistant rubbers.