bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetic Studies in the Chemistry of Rubber and Related Materials. III. Thermochemistry and Mechanisms of Olefin Oxidation
Authors: Bolland J. L. , Gee Geoffrey 
Published: February 2011

Abstract
A new estimate of the O—O bond strength in hydroperoxides is reported, based on a determination of the heats of oxidation of ethyl linoleate and linolenate. This value is employed, together with other known bond strengths and resonance energies, to estimate the heats of a number of alternative oxidation reactions of olefins. By considering the effects of the olefin structure on these heats of reaction, it is possible to see how structural differences can lead to the formation of different oxidation products. The discussion is confined to primary products of the oxidation chain, but, even so, a considerable diversity of behavior is shown to be possible. The final material may include simple monomeric hydroperoxides, polymers with varying amounts of oxygen incorporated in the chain, cyclic peroxides, and scission products. The very limited experimental evidence available falls generally into line with expectation.
Accelerated Aging of Vulcanized Rubber. Factors Determining the Relation between Oven and Bomb Aging
Authors: Newton R. G. , Scott J. R. 
Published: February 2011

Abstract
A study has been made of the influence of the following factors on the relative rates of tensile deterioration of natural rubber vulcanizates in the Geer oven and oxygen bomb, both at 70° C : period of vulcanization, sulfur ratio, nature of accelerator. Expressing this relation as the oven/bomb ratio, i.e., the ratio between oven and bomb aging periods that give the same deterioration, the following conclusions are drawn. (1) Varying the period of vulcanization of a given mix over a moderate range (2:3) around the optimum does not noticeably alter the oven/bomb ratio, except in unaccelerated mixes, where overvulcanization gave an abnormally low ratio, owing to the rubber perishing very rapidly in the oven. (2) The effect of varying the sulfur ratio within the usual limits for soft rubbers is small, and appears to result from the quicker vulcanization of the mixes richer in sulfur. (3) The nature of the accelerator profoundly affects the ratio, values ranging from 3 to 27 being found among the present mixes ; this effect is believed to be exerted through the influence of the accelerator both on rate of vulcanization and on the oxidizability of the vulcanizate. Theoretical considerations indicate that a rubber which vulcanizes quickly and (or) oxidizes slowly should give a low oven/bomb ratio, whereas one that vulcanizes slowly and(or) oxidizes quickly should give a higher ratio. The experimental data are generally in accord with this, and there is evidence that both rate of vulcanization and oxidizability can have an important effect, but the data do not enable the separate effect of each to be assessed exactly. The bearing of the results on the use of the oven and bomb tests is briefly discussed. It is shown that they demonstrate the fallacy of using a single factor for converting oven to bomb aging periods or vice versa, and that the relative natural aging resistances of widely different vulcanizates cannot be reliably assessed by either test, a limitation arising from the fact that the relative importance of oxidative decay and aftervulcanization varies from one type of mix to another, and that the temperature coefficients of these processes are not necessarily the same. These facts are very important in relation to the choice and application of accelerated aging tests for specification purposes, since these usually have to be applied to rubbers of unknown compositions, which are likely to vary widely in their relative response to different aging conditions.
Stress-Optical Properties of Rubber
Authors: Treloar L. R. G. 
Published: February 2011

Abstract
Considerable progress in the quantitative description of the mechanical properties of rubber has taken place in recent years by the consideration of a rubber as a network of statistically kinked long-chain molecules. A treatment of the optical properties of strained rubber on this basis, with the assumption that the links of the molecular chain are themselves optically anisotropic, has been developed by Kuhn and Grün for the special case of simple elongation, and by me for general homogeneous strain. In the latter case, the rubber has three principal refractive indices, n1, n2, and n3, corresponding to the three principal axes of the strain ellipsoid.
Two Methods of Protection against Oxygen and the Improvement Which Results from Their Combined Use. I. Observations on the Mechanism of Protection
Authors: Le Bras Jean 
Published: February 2011

Abstract
The observations which are recorded in the present paper represent an extension of the single case of litharge which has already been described. They show that, when small percentages of certain substances are added to rubber with a view to protecting the rubber from deterioration by oxygen, these substances are capable of directing the combination of oxygen with the rubber in different ways. This is shown by the fact that, as a result, a given percentage of combined oxygen does not lead to the same deterioration in physical properties. This difference in behavior can be explained logically on the basis of the antioxygenic theory by assuming that some agents act, not by retarding the rate of oxidation, but by deactivating the peroxides as soon as they are formed. By what term are these agents to be designated? First of all it should be recalled how an antioxygenic substance is defined. Every substance is an antioxygenic agent when it has the power, in small percentages, of retarding the rate of absorption of free oxygen by an autoxidizable substance. This definition obviously does not apply to a perfect deactivating agent, since the latter has no effect on the rate of absorption of oxygen, in spite of it too protecting rubber against deterioration by oxygen, and therefore being equally worthy, from the practical point of view, of being called an antioxygenic agent. However, this would only lead to confusion between the phenomenon itself and its effects. Furthermore, since commercial antioxygenic substances appear to show, to a greater or less degree, a combination of the two actions, one might consider designating them by some term which would embody both mechanisms. The word “antiaging agent” is not suitable, for it is too general and applies to cases where, in addition to oxygen, other influences such as light and repeated flexing play a part. There is, then, a problem in terminology to be settled, but this will have to be left unanswered provisionally until sufficient facts which have a more direct bearing on the case are available. Finally attention should be called to the useful effect which may be pictured as a possibility when the two types of protective agents which have been described act jointly. In other words, if the two mechanisms in question were to be superimposed, it would appear to be possible to improve considerably the resistance of rubber to deterioration by oxygen, since any oxygen which escapes the protective action of the true antioxygenic agent has its harmful effect reduced by the deactivating agent. To express it figuratively, it might be said that oxygen which has succeeded in overcoming the first obstacle opposing its action finds itself confronted with a new defense which puts the oxygen partially out of action. As shown by experiments carried out on this subject, which are described in the following paper of this series, this theoretical conclusion is actually borne out by the results of the experiments.
The Autoxidation of Rubber and Mechanisms of Protection against Oxygen
Authors: Le Bras Jean 
Published: February 2011

Abstract
The autoxidation of ethylenic hydrocarbons has been the object of various investigations, and various authors, among whom Engler and Stephens in particular might be mentioned, have studied the part played by peroxides. Up to 1936 it was generally believed that structurally these peroxides represent the fixation of one molecule of oxygen on the double bond. About this time, however, Criegee on the one hand, and Hock and Sehrader on the other, published papers almost simultaneously on the preparation and constitution of cyclohexene peroxide, in which they demonstrated that the latter can exist in the form of a hydroperoxide.Later these investigators offered further proof in favor of this view by extending the reaction to other hydrocarbons. These studies led to the important conclusion that ethylenic hydrocarbons have two sensitive points: the double bond itself, and the carbon in α-position to this double bond; hence there are two forms of the peroxide, the first of which retains its unsaturated character.
Effect of Temperature on Resilience
Authors: Mullins L. 
Published: February 2011

Abstract
The recent use of rubber components in extremes of climate and under a variety of service conditions has drawn attention to the importance of the knowledge of the physical properties of rubber vulcanizates at temperatures other than normal; the dearth of such knowledge has been emphasized by the enforced replacement of natural rubber by synthetic rubbers having reduced resistance to cold. When designing mechanical parts, the engineer must know first the conditions under which the part will be required to operate and, second, the physical properties under these conditions of the materials to be used. In a recent review Riesing has given illustrations of the importance of such knowledge; in particular he has shown that rubber mountings in an automobile may well be subjected to temperatures as high as 80 to 100° C, and although rubber mountings normally warm up during their operation, they may commence to function at extremely low temperatures, while there is a limiting temperature below which they fail even to warm up. The first part of this paper gives the results of the measurement of rebound resilience on a number of vulcanizates over a wide range of temperatures. Resilience is one of the important physical properties of a rubber vulcanizate, and in designing parts for shock or energy absorption, data on the resilience of the material are essential; for such applications a material with a low resilience is required, but as the energy absorbed manifests itself in the form of heat, the temperature rise of the absorber may control the permissible value of the resilience. In many other applications it is necessary that the material should have a high resilience and so absorb little energy. The resilience is normally determined by measuring the rebound of a ball or pendulum after impact on a sample of rubber; various other methods have been used, involving, either measurement of the decay in amplitude of the damped free vibration which results when a sample is deformed and then released, or measurement of the energy loss during sustained forced vibrations. Unhappily, the results from one test do not always show great similarity to the results from another test and, as a result, the engineer has to relay on empirical correlations with resilience tests conducted in a particular way, or on service behavior. The second part of this paper gives the lines along which an investigation is being conducted to illuminate the significance of these dissimilarities. The measurement of resilience over a range of temperatures has an added importance, since it throws some light on the structure of the rubber and on the processes taking place during deformation. Recent papers which have just become available in this country show that there has been interest and activity in this field in Germany during the war years.
Composition of Butadiene-Styrene Copolymers Prepared by Emulsion Polymerization
Authors: Meehan E. J. 
Published: February 2011

Abstract
The formation of a high-polymer molecule occurs by the successive additions of monomer molecules to a growing chain (chain propagation), the growing chain itself being made up of a number of monomer molecules with a radical derived from a monomer molecule on the end of the chain at which addition occurs. It was pointed out by Norrish and Brookman that chain propagation in the formation of a copolymer from two polymerizing monomers involves four different reactions; the growing chain may have a radical unit derived from either of two monomers at the end of the chain, to which either of two monomer molecules may add. In general it may be expected that the four growth processes will involve four different reaction-rate constants. This situation has been studied thoroughly from the theoretical point of view by Alfrey and Goldfinger, by Mayo and Lewis, by Wall, and by Simha and Branson. The theoretical treatment has been extended by Walling and Briggs to the copolymerization of an arbitrary number of monomers. A considerable amount of experimental data on copolymerizations of various pairs of monomers in homogeneous solution and the quantitative interpretation in terms of the concept given above have been presented. Prior to the comprehensive treatments of the composition of copolymers referred to above, Wall had shown that a relatively simple treatment could be given to the problem, on the assumption that only two rate constants are involved in the chain propagation, corresponding to the addition of either of two monomers to the growing chain This would mean that both radical types on the end of the growing chain would have the same relative reactivity with monomers. Wall has pointed out that such a copolymerization would be “ideal” in the same sense as a pair of liquids which follows Raoult's law. Mayo and Lewis, however, have stated that this “ideal” copolymerization behavior does not correspond to the experimental facts in the case of the bulk copolymerization of styrene and methyl methacrylate, or in the case of the copolymerization of maleic anhydride with certain ethylene derivatives.
Alkaline Materials as Accelerators for GR-S
Authors: Breckley Joseph 
Published: February 2011

Abstract
During the development of the national synthetic rubber program it was decided to utilize the research and development facilities of compounding material suppliers in an investigation to determine the best methods of formulating GR-S and other synthetic rubbers. This investigation was directed by the Compounding Research Branch of the Office of the Rubber Director, which then collected and distributed to the participating laboratories the large amount of data gained from the many tests carried on with different accelerators, fillers, and softeners in GR-S. Included in this information were indications that the curing rate of GR-S was affected to a considerable degree by inorganic oxides and alkaline materials. Consequently this phase of the problem was investigated still further in this laboratory, and some data were released through the same agency regarding the efficacy of magnesia, litharge, and red lead as activators for some organic accelerators. The results obtained encouraged further work to determine the effect of more strongly alkaline materials. It was discovered that ethanolamines were very effective activators for some organic accelerators; in fact, triethanolamine activates tetramethylthiuram monosulfide so strongly that a combination of the two materials promotes vulcanization of GR-S at room temperature.
Determination of Rubber Hydrocarbon by a Gravimetric Rubber Bromide Method
Authors: Willits C. O. , Swain M. L. , Ogg C. L. 
Published: February 2011

Abstract
Direct determination of rubber hydrocarbon in crude rubbers and in latices has been generally considered so inaccurate and unreliable that determination of rubber hydrocarbon by difference has been a common practice. The difference method usually suffices in the analysis of products derived from Hevea rubber, in which the nonrubber components have been well characterized or occur in low concentration. In the analysis of natural rubber products obtained from sources other than Hevea, such as guayule, kok-saghyz, and Cryptostegia, the situation is different. The chemical and physical properties of the nonrubber components of such products are largely unknown, and in many cases the nonrubber contaminants are present in excessive amounts, sometimes more than 50 per cent of the total. Since the rubber hydrocarbon analysis usually affords the most reliable means for estimating the rubber content of plants and for following the concentration and purification of rubber by mechanical and chemical processes, it appeared desirable to devise or adapt a method which would permit direct determination of this constituent in the presence of relatively large amounts of natural and added contaminants.
Variation in the Specific Heat of Rubber as a Function of Elongation
Authors: Mayor Andre 
Published: February 2011

Abstract
The changes in specific heat of several samples of rubber when stretched were measured. Unvulcanized rubber showed no change in specific heat when it was stretched up to 300 per cent. The specific heat of vulcanized rubber increased very slightly and in proportion to the elongation. With some of the samples, a bend in the curve appeared at about 200 per cent elongation at room temperature, in which case the linear increase in specific heat was about ten times at higher elongations. Supposedly this sudden increase in specific heat is related to the heat of crystallization.
Methods of Averaging Physical Test Results. Use of Median
Authors: Buist J. M. , Davies O. L. 
Published: February 2011

Abstract
Different testing laboratories use different methods of averaging test results, and it would facilitate comparison of results between different establishments if a uniform procedure could be agreed upon. To facilitate the correct choice the following methods have been compared: (1) Averaging all results within 10 per cent of the highest. (2) Averaging all results until the average is within 10 per cent of the highest. (3) Averaging the highest four results out of six, the highest three out of four. (4) Taking the median. (5) Method of Horrobin and Davies. Methods (1) and (2) are unacceptable on logical grounds, but there is little to choose between methods (3) and (4). The choice for routine use rests on simplicity of method and freedom from bias. Method (3) introduces a slight bias by always rejecting the low result and, therefore, it is recommended that the median be used either by averaging the middle two out of four results or by averaging the middle four out of six results. For five rings we take the average of the middle three and for four rings the average of the middle two. When we are interested in estimating the variations arising at each source in rubber testing, it is preferable to use the more elaborate method (5). This is considered the most logical of all methods, but it is not suitable for routine use.
Device for Evaluating Surface Cracking of GR-S
Authors: Throdahl M. C. 
Published: February 2011

Abstract
1. Dynamic flex-cracking may be studied indoors under conditions which yield results closely comparable to outdoor atmospheric exposure. 2. Although the photographs are not sufficient to show the depth of cracking, it was observed that the stocks of several compounds which showed the tendency to bloom and migrate to the surface cracked badly and to a depth equivalent to control stocks. By comparison, however, these same stocks when statistically exposed showed only slight tendency to crack in the usual exposure time of 100 hours. 3. Minimum concentration of additives for retarding the rate of surface cracking was found to be 0.25 per cent, but best results were obtained with 1 per cent. 4. Cracking always occurred at right angles to the direction of strain. Preliminary studies with this apparatus indicated that none of the specimens cracked when exposed in the looped but unstretched position (this was done by removal of the pin and stirrup) up to 50 hours of exposure, but some cracked slightly at 100 hours. Flexing in the laboratory without the source of ultraviolet light did not produce cracking of the specimen in 100 hours. The nature and severity of cracking were made the same for natural sunlight outdoor exposure in July as they were for artificially generated conditions of the laboratory except that approximately 3 weeks (roughly 60 exposure hours) were required. (This overall time was due to excessive rain, which necessitated coverage of the entire flexing mechanism during much of the time.) This may not be a fair comparison because of the rather contaminated atmospheric conditions in Nitro, W. Va. However, stocks of the same composition flexed on a revolving belt in Florida atmosphere cracked in the same manner as those shown here. Variation of degree of strain from 10 to 35 per cent did not produce significant differences in results. This is in agreement with the observations of Powell and Gough, who pointed out that the so-called critical stretch does not exist. Change in height of the light source—that is, the radiation intensity—over the short range did not produce significant changes in rate of cracking. In order that the surface temperature of the stock remains at 30–35° C, the minimum height was fixed at 50 cm. above the turntable.
Copolymers of Butadiene with Halogenated Styrenes
Authors: Marvel C. S. , Inskeep G. Esler , Deanin Rudolph , Juve A. E. , Schroeder C. H. , Goff M. M. 
Published: February 2011

Abstract
Butadiene has been copolymerized in a typical emulsion polymerization recipe with each of the monochloro-, monobromo-, monofluoro-, and dichlorostyrenes, with the mixed mono-, di-, tri-, tetra-, and pentachlorostyrenes, and with p-cyanostyrene and several of its derivatives. While 2,5- and 3,4-dichlorostyrene copolymerized with butadiene more rapidly than does styrene itself, 2,6-dichlorostyrene and the mixed tri-, tetra-, and pentachlorostyrenes copolymerized at a slower rate than did the control. 2,5-Dichlorostyrene entered the copolymer much more rapidly, and 2,6-dichlorostyrene and pentachlorostyrene much more slowly, then does styrene itself. The mono- and dihalogenated styrenes in general gave copolymers whose quality indexes were about equal to that of GR-S; o-chlorostyrene, 2,5- and 3,4-dichlorostyrenes, and p-cyanostyrene all gave copolymers with quality indexes higher than that of GR-S. The mixed tri- and tetrachlorostyrenes gave copolymers of inferior quality.
Physical Properties of Diene Polymers. Effects of Side Vinyl Groups and Other Structural Features
Authors: D'Ianni James D. 
Published: February 2011

Abstract
The detailed molecular structures of natural rubber, emulsion polyisoprene, polyisoprene prepared with an organometallic catalyst, and sodium polyisoprene were studied by comparison of data available from infrared absorption spectra, perbenzoic acid titration, refractive index, density, iodine number, chromic acid oxidation, and hydrochlorination. These polymers showed decreasing amounts of 1,4-addition content in the order listed. Similar data were collected where possible for emulsion polybutadiene, polybutadiene prepared with an organometallic catalyst, and potassium polybutadiene (Buna-85), as well as for GR-S and corresponding butadiene-styrene copolymers prepared with an organometallic catalyst and with sodium. These two groups also showed decreasing 1,4-addition content in the order listed. Correlation of structure inferred from the above data with physical properties of corresponding tread stock vulcanizates indicated that for diene polymers with decreasing amount of 1,4-addition content the brittle point rose, the rebound value decreased, and the tensile strength increased, provided comparison was restricted to polymers of approximately the same molecular weight range made with the same monomer. Natural rubber occupied a unique position because it was substantially a linear high polymer with the cis-configuration around all the double bonds. For the butadiene-styrene 75/25 copolymers the brittle point rose with decreasing amount of 1,4-addition content, but no satisfactory correlation could be obtained for the tensile strength and the rebound value, probably because of the predominant effect of the phenyl side groups.