bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetic Analysis of Organic Halides. II. Analysis of Macromolecules Built up of Monohalide Units
Authors: Salomon G. , Koningsberger C. 
Published: February 2011

Abstract
A number of hydrochlorides of natural and synthetic rubbers and allied polymers have been prepared and subjected to kinetic analysis with organic bases. The hydrochlorides of natural rubber react at 100° C at a rate identical to that of low-molecular tertiary chlorides. At 50° C the reactivity of the polymer is, however, reduced by physical factors. The hydrochloride of GR-S (a synthetic rubber made from butadiene and styrene) has been prepared for the first time by heating the swollen polymer with HC1 under pressure. Kinetic analysis of this product revealed two fractions: the expected secondary chloride, and a small fraction of a very reactive (tertiary?) chloride. After elimination of experimental difficulties, we succeeded in the preparation and kinetic identification of the pure tertiary hydrobromide of natural rubber. Attempts to prepare the secondary bromide under peroxide conditions failed. Kinetic analysis of two types of Neoprene revealed the presence of a small quantity of allylic groups in the polymer, while 95 per cent of the chlorine in Neoprene has the expected stability of a vinyl chloride. This stability can be used for the identification of Neoprene.
A Rapid Determination of the Average Molecular Weight of Rubber in Hevea Latex
Authors: van Essen W. J. 
Published: February 2011

Abstract
A method is described for determining viscometrically the molecular weight of rubber in freshly tapped latex. For this purpose the latex is dissolved in a toluene-pyridine mixture. From the intrinsic viscosity of this solution the molecular weight of the rubber can be determined by the Staudinger equation and a known viscosity constant. Molecular weights varying between 238,000 and 480,000 have been found, depending on the kind of clone. Rubber in fresh latex does not have a lower molecular weight than in old preserved latex.
Stability of Compounded Latex
Authors: Hayes K. W. 
Published: February 2011

Abstract
Thickening experiments with compounded latex are described showing the maximum thickening effect of zinc oxide when at a concentration of less than 1 per cent on the dry rubber content of a 60 per cent latex compound. Gelation tests with sodium fluorsilicate indicate that the curve relating the pH of gelation to the zinc oxide concentration is closely related to the curve showing the effect on the viscosity of the zinc oxide concentration. A theory is proposed to account for the maximum thickening effect.
Abrasion Resistance and Its Measurement
Authors: Buist J. M. 
Published: February 2011

Abstract
Abrasion resistance is not a specific property of rubber, but depends both on the method of measurement and the machine used. The relation between abrasion resistance and the simpler physical properties, and the use of the regression technique whereby equations relating abrasion resistance, tensile strength, and hardness have been developed, are discussed. Twenty-one existing abrasion machines are reviewed and classified in one of four categories, and, wherever possible, an indication is given of the types of compound where good correlation with service is claimed. Most of the machines have been used for compound development work, but correlation with actual wear trials must be improved before the service life can be forecast accurately. Until the mechanism of abrasion is better understood the I.S.O. decision to adopt a simple method, e.g., du Pont, as a basis for standardization is sound. Work with eight sole and heel compounds and twelve tire treads shows that the order of merit obtained in the normal du Pont test is almost completely the reverse of service. With tire tread compounds, extraction of the test-pieces in ethanol-toluene-azeotrope improved the correlation with service. Further work with compounds of known service wear is required, and the extraction method in its present form does not improve the accuracy of any comparison of two compounds from different polymers, e.g., natural rubber and GR-S. The use of zinc as a standard material for checking the cutting power of the abrasive has been investigated and its use is not recommended for the du Pont type of machine.
Dynamic Shear Properties of Rubberlike Polymers
Authors: Hopkins I. L. 
Published: February 2011

Abstract
A simple apparatus for determining the dynamic properties of elastomers in shear at audio frequencies is appraised. Typical values of shear modulus and viscosity for several elastomers are given, both at room conditions and at 150° F. The frequencies of test range from 100 to 5250 cycles per second, the shear moduli from 0.5×106 to 480×106 dynes per sq. cm. and the viscosities from 20 to 75,000 poises.
Rheometric Tests and Extrusion
Authors: Eccher Silvio 
Published: February 2011

Abstract
A cylindrical rheometer of the Couette type, suitable for the experimental determination of the rheological properties of extruded materials, was designed to provide data which could not be obtained with existing plastometers. The purpose of this study was strictly practical, as the work was performed in connection with a study of extruders. The results obtained on twenty-five different materials—natural and synthetic rubbers and compounds of both with various fillers—are reported; measurements fall within shear rate limits from 1 to 100 seconds−1. In this interval the relationship between logD (rate of shear) and logτ (shear stress) is nearly a straight line. It may, therefore, be analytically interpreted by the power law : D=−(τ/c)n, where n and c are parameters characteristic of the material. As the power law is known to be of limited validity, attempts were made to ascertain the limits of its application in laminar flow through a cylindrical hole. The results of measurements carried out on a 2-inch extruder and employing the same materials as were tested by the rheometer are reported. Measurements of pressure and flow were made, using discharge holes of various diameters and operating the screw at various speeds. Reasonable agreement was found between values of flow and pressure determined with an extruder and those calculated from parameters n and c determined with the cylindrical rheometer.
X-Ray Study of the Crystallization of Vulcanized Rubber during Stretching. II.
Authors: Kasotochkin V. I. , Lukin B. V. 
Published: February 2011

Abstract
1. The relation between the crystal content of stretched vulcanizates to the time of vulcanization for different mixtures of natural rubber was studied by the x-ray method. 2. It was shown that the tensile strength is a function of the crystal content of the stretched vulcanizate and of the total time of vulcanization. 3. The nature of crystal formation depends on the following factors: changes of density of the network of sulfur bridges, their distribution, the degree of oxidative destruction, and the quantity of bound sulfur which has not formed bridges between the molecular chains.
Crystallization in Unstretched Rubber. Microscopic Study in Polarized Light
Authors: Campbell H. N. , Allen M. D. 
Published: February 2011

Abstract
Since many elastomers indicate by their physical properties that crystallization occurs even when such crystallization is not detectable by x-ray diffraction, a direct microscopic study in polarized light was undertaken. This study confirms the presence of such crystallinity not only in rubber but also in polybutadiene and some low-temperature copolymers. Furthermore, the same crystal pattern is reproduced on melting and refreezing provided the intermediate melting temperature is not too high. This indicates that x-ray diffraction is not a very sensitive method for detecting small amounts of crystallinity in high polymers. The reproduction of the crystal pattern on refreezing shows that the molecular segments have limited mobility even at room temperature; this may require revision of current theories of the origin of retractive forces in elastomers.
Vulcanization of Synthetic Rubbers
Authors: Pisarenko A. P. , Rebinder P. A. 
Published: February 2011

Abstract
Although for a century since the discovery of the vulcanization of rubber by sulfur many investigators have worked in this field, the problem of vulcanization can still not be considered to be well understood, either from the theoretical or the practical point of view. The basis of the most widely accepted theory of vulcanization of rubber is the concept of bridges, according to which the vulcanizing agent, sulfur, unites the macromolecules of rubber into spatial chains by primary valences. The concept that such spatial structures are formed during the vulcanization process explains well the decrease in the degree of saturation of the rubber and the changes in its physical properties, e.g., decreases in solubility and plastic flow, and considerable increases in strength, modulus, and resilience. A number of experimentally established facts, however, can never be reconciled with the bridge theory of vulcanization, especially when the vulcanization of synthetic rubbers is investigated. As a consequence of this, a number of investigators in this country have pointed out the shortcomings of the bridge theory and the necessity of finding a better explanation of the physico-chemical and colloidal reactions which take place during the vulcanization of rubber. More recently Dogadkin and his associates have shown that even when an accelerator is added, which leads to an increase of the bridge sulfur content of the vulcanizate, the total amount remains insignificant, e.g., in the case of natural rubber it amounts to only 7–10 per cent and, in the case of synthetic rubber, to 2–6 per cent of the total bound sulfur.
Refractometric Determination of Second-Order Transition Temperatures in Polymers. V. Determination of the Refractive Indexes of Elastomers at Temperatures from 25 to −120° C
Authors: Wiley Richard H. , Brauer G. M. , Bennett A. R. 
Published: February 2011

Abstract
In previous papers a refractometric method was described for determining second-order transition temperatures of polymers whose transitions occur between 75 and −60° C. In the present study, an Abbé refractometer was insulated and used to determine the refractive indexes of polymers down to − 120° C and the transition points of natural rubber and a number of synthetic rubbers.
Study of Bonded Units
Authors: Buist J. M. , Lindsey C. H. , Naunton W. J. S. , Stafford R. L. , Williams G. E. 
Published: February 2011

Abstract
The work was undertaken because no satisfactory and discriminating test is available for evaluating rubber-to-metal bonding agents. In former tests the testing of the bonding agent was confused with the testing of the test unit as a unit. A method was evolved which discriminated between bonding agents which had previously been regarded as equivalent. In the course of the work new facts such as the importance of the volume of the rubber rather than the shape factor (which must, of course be considered from the stability angle) came to light. The significance of the work lies in two directions—better testing of metal-to-rubber bonding agents and a better understanding of the facts underlying the design of rubber-metal spring units. A tentative method for measuring the tear strength of the rubber used in the unit was put forward.
Volume Changes in the Stretching of Vulcanized Natural Rubber
Authors: Gee Geoffrey , Stern Jan , Treloar L. R. G. 
Published: February 2011

Abstract
Measurements are presented of the volume changes accompanying small (≯100%) elongations of vulcanized natural rubber completely free from undissolved particles. The small expansions found agree with those calculated from the known compressibility of rubber and the hydrostatic component of the stretching force. It is pointed out that this volume change mechanism applies generally to any isotropic material, and does not contribute significantly (in rubber) to the tensile stress.
Dynamic Study of Reinforcement
Authors: Waring J. R. S. 
Published: February 2011

Abstract
The measurements were undertaken to obtain a better understanding of the mechanism of the reinforcement of rubber by carbon black. Results are given for the dynamic compression modulus and its temperature and amplitude coefficients, in the temperature range 30° to 70° C and at amplitudes of vibration around 0.0036 cm., for natural rubber, Neoprene Type GN, GR-S, and Perbunan. Data are also given on the effect of vibration and temperature on electrical conductivity. The results are discussed in relation to the general level of reinforcement. Evidence is given for the rupture of more than one type of cohesive bond in repeated cycles of vibration. A tentative system of analysis is proposed. The different effects of temperature and continuous vibration on dynamic modulus are attributed to a thixotropic breakdown in the case of vibration. The significance of such a “structure” dynamically hard at small amplitudes of vibration, is related to abrasion of tires in service.
Relation of Peroxide Decomposition to Rubber Degradation
Authors: Kendall C. E. 
Published: February 2011

Abstract
It appeared that an investigation of the reactions between peroxides and deactivators of rubber degradation, such as mercaptobenzimidazole, would help to explain the action of these sulfur compounds. Le Bras, who proposed the use of these compounds, considered that they function by deactivating the peroxides formed by autoxidation. It was found that mercaptobenzimidazole and simpler related compounds such as thiourea reacted with alkyl hydroperoxides with the formation of hydroxyl or alkoxy radicals and this led to attack on the solvent or on other molecules present, in a manner resembling the action of ferrous salt-hydrogen peroxide. This suggested that rubber would also be attacked and probably degraded. It was found that mercaptobenzimidazole with excess of peroxide gave rapid degradation of rubber in solution if access of oxygen was permitted. Thiourea, thioacetamide, some dithiocarbonates, and aromatic thiols were also effective, but aliphatic thiols and ethylmercaptobenzimidazole were ineffective. Softened or “depolymerized” rubber was prepared by addition of the reagents to rubber solutions or to latex. The use of these sulfur compounds in the presence of peroxides provides a means of obtaining a controlled amount of breakdown of rubber, and products ranging from normal plasticized rubber to a viscous liquid can be prepared. Under different conditions, mercaptobenzimidazole may either promote degradation (as shown in this paper) or retard it (as stated by Le Bras), and a possible explanation for this reversal of behavior is suggested.
Rubber Oxidation and Antioxidant Actions
Authors: Baxter S. , Morgan W. Mc G. , Roebuck D. S. P. 
Published: February 2011

Abstract
Many experimental investigations into the oxidation or aging characteristics of rubbers have been carried out during the last 30 years. Some have studied changes in physical properties during artificial aging and have linked these with culcanizate composition and with changes occurring during natural aging. Others have studied the kinetics and mechanisms of the chemical reactions involved. Both approaches have contributed much to the general body of knowledge on this subject. In more recent years, serious attempts have been made to correlate rate and extent of oxygen absorption with changes in physical properties, and conclusions drawn from this work have proved to be of considerable interest. In most of the work reported, however, oxygen absorption experiments were carried out on one sample of rubber, using a laboratory absorption apparatus, and deterioration of the physical properties of different samples were determined after aging for appropriate periods in an aging oven. Alternatively, direct measurement of the oxygen absorption of a tensile specimen during a given period of aging was made, and the properties of different specimens related. To obtain significant results it has proved desirable to carry out a considerable number of repeat experiments and to subject the data to careful statistical analysis. In an attempt to overcome some of the difficulties inherent in such an approach, a method was developed whereby simultaneous measurement of oxygen absorption characteristics and the change in elastic properties of a single specimen of rubber during aging can be made under closely controlled conditions. It is believed that direct correlations of this nature can lead not only to a much deeper insight into the mechanism of aging, but also to more practical use of present knowledge of the chemistry and kinetics of polymer aging. The investigation reported here is part of a larger investigation designed to lead ultimately to new means of improving age resistance of natural and synthetic rubbers.
Butadiene and Its Polymers. V. Formation of Spongy Butadiene Polymer
Authors: Piotrovskii˘ K. I. 
Published: February 2011

Abstract
1. It is shown that the formation of spongy butadiene polymer is accelerated by the addition to the butadiene of most metals and certain crystalline substances. This spongy polymer is not formed on lead or copper. 2. It is shown that the formation of spongy polymer on iron takes place at practically any polymerization temperature. 3. It is proved that in the absence, both in the butadiene and in the apparatus, of oxygen and peroxides, no spongy polymer is formed, and also that peroxides accelerate the formation of spongy polymer. 4. It is proved that the activation of the formation of spongy polymer by iron is of an adsorptive nature, and the formation of spongy polymer on iron can prevent the formation of a unimolecular layer of a polar substance on the surface of the iron. 5. An outline scheme of the process of thermopolymerization of butadiene is given, with experimental data on the formation of its cyclic dimer, of a rubber-like polymer, and of the spongy polymer.
The Sulfonation of Natural Rubber
Authors: van Amerongen G. J. 
Published: February 2011

Abstract
Like many olefins, natural rubber is capable of reacting with sulfur dioxide, with formation of a sulfone. The reaction is a chain reaction which is started by certain catalysts. The structure of the rubber sulfone is: (see PDF for diagram) and the theoretical proportion of sulfur is 24.2 per cent. Table I gives some experimental results obtained in the reaction of rubber with sulfur dioxide.
Kinetics of Cyclization of Hevea Latex
Authors: Gordon Manfred 
Published: February 2011

Abstract
Kinetic measurements on rubber cyclization now are possible by a latex technique; these were undertaken to elucidate the mechanism of the reaction. According to a patented process, dispersions of Hevea latex particles in 70 to 80 per cent sulfuric acid are reproducibly isomerized to a high molecular weight cyclized rubber. A diffusion gradient technique was adopted for measuring the density of the polymer after exposing it to cyclization for varying times. Unimolecular constants, k, spreading over four decades, were obtained and found enormously sensitive to the percentage, c, of sulfuric acid and absolute temperature, T; thus log10k=6+0.17c−7105/T. The constants, k, correlate satisfactorily with Hammett's acidity function, H0. A statistical theory by Flory shows that 13.5 per cent of the isoprene units originally present in rubber are left uncyclized by the reaction. This is in striking agreement with unsaturation measurements made by Fisher in 1927. The kinetic parameters deduced support a nonchain proton transfer mechanism, deprotonation being rate-determining. The proton affinity of rubber is estimated, and a comparison of the cyclization of rubber and other terpenes is presented. The structure proposed for cyclized rubber rings by D'Ianni and co-workers is supported by mechanistic analysis and physical properties. The method of kinetic measurements on stable emulsions in sulfuric acid is of general promise, and the cyclization of rubber polymer presents a useful model reaction for the smaller terpenes.
The Structure of Cyclized Rubber
Authors: van Veersen G. J. 
Published: February 2011

Abstract
The history of cyclized rubber, including a series of structural formulas previously proposed for this polymer, is reviewed briefly. A new formula for cyclized rubber is suggested by applying electronic interpretations of reactions between electrophilic agents and tertiary alkyl olefins and tertiary halides, respectively, to the corresponding reactions with rubber and rubber halides. It is shown that hydrochlorination can be used for the determination of the unsaturation of cyclized rubber. By varying the conditions of hydrochlorination, two types of double bonds can be detected in cyclized rubber, a fact which is in agreement with the structure suggested. By using our method for the determination of the unsaturation, the rate of cyclization at different temperatures and the influence of solvents on the rate of reaction have been determined.
Rubber Oxidation and Aging Studies Safe Limits of Sample Thickness
Authors: Blum George W. , Shelton J. Reid , Winn Hugh 
Published: February 2011

Abstract
Safe limits of sample thickness for rubber oxidation and aging studies, such that the chemical reaction rather than the rate of diffusion will be rate-controlling have been investigated for natural-rubber vulcanizates and for four synthetic-rubber types. For studies involving the entire range of oxidation, including the autocatalytic stage of rapid oxygen absorption, the conventional 0.075-inch thickness is frequently not satisfactory for accelerated aging and oxidation studies if it is desired to avoid limitation by diffusion. Only in the GR-S black stock was this thickness found to be satisfactory up to a temperature of 100° C. The other stocks, including natural rubber, Butaprene-NXM, and Neoprene black and gum stocks all require thinner samples to ensure that the observed rate of oxygen absorption is free of limitation by diffusion. A method of calculating the probable limiting value of sample thickness, above which the rate of oxidation in the autocatalytic stage is limited by diffusion, has been developed on the basis of volumetric oxygen absorption data obtained with GR-S. The method has also been applied to natural-rubber vulcanizates and to other synthetic-rubber types to locate the approximate limiting values at various temperatures for oxidation and aging studies which extend into the autocatalytic stage of rapid reaction. The constant-rate period of oxidation is more important from a practical point of view than the autocatalytic stage, since properties are so seriously degraded as to make the rubber of little value before it reaches the final stage of rapid oxidation. Somewhat thicker samples may be used for studies that are confined to the earlier stages of oxidation. A 0.075-inch sample is free of limitation by diffusion in the constant-rate stage in the following cases: GR-S black and gum stocks at 110° C; Hevea black with added antioxidant at 100° C; and uninhibited Hevea black and gum stocks at 60° C. A 0.040-inch sample is satisfactory in this range for: uninhibited Hevea black at 100° and gum at 80° C; Butaprene-NXM black at 100° and gum at 90° C; and Neoprene black and gum stocks at 100° C.