bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cis-Trans Isomerization in Polybutadiene
Authors: Golub M. A. 
Published: February 2011

Abstract
About twenty years ago, in an effort to transform natural rubber into gutta-percha, Meyer and Ferri irradiated a solution of Hevea in cyclohexane with ultraviolet light, but were unable to detect any cis-trans isomerization in polyisoprene. Later, Ferri showed that treatment of both Hevea and Gutta with certain chemicals, such as chlorostannic acid and titanium tetrachloride, gave rise to closely resembling products which were considered at the time to have structures intermediate between the two geometric forms of naturally-occurring polyisoprene. These resulting polymers were, however, crosslinked in the course of chemical treatment and probably also cyclized, so that in the light of present knowledge about the cyclizing tendencies of the materials employed, this change cannot be regarded as a genuine interconversion of cis and trans double bonds. No true instance of cis-trans isomerization unaccompanied by other structural changes has been reported heretofore for a high polymer, except for the polyenes which are conjugated structures of relatively very low molecular weight. This communication reports the successful transformation of the cis-1,4 units in polybutadiene into corresponding trans units by means of ultraviolet irradiation in the presence of a suitable sensitizer, which may be any one of a wide variety of organic bromine or sulfur compounds. Surprisingly, this isomerization could not be induced in natural rubber.
The Mechanism of the Deactivating Effect
Authors: Bras Jeanle , Danjard Jean Claude 
Published: February 2011

Abstract
It was shown by one of us that certain substances, called deactivates, can protect vulcanized rubber against aging by a process which is different from that of antioxidants. The proposed mechanism involved a deactivation of the primary peroxides by transforming them into oxides of rubber without causing any chain scission. This hypothesis, however, did not appear to be completely satisfactory. In fact, deactivators do not protect raw rubber against oxidation, but actually accelerate its degradation in solution, especially in the presence of a peroxide which enhances this deterioration. Moreover, if was shown that the deactivators possess a chemical structure which is very similar to that of certain vulcanization accelerators, and also that they have an effect on the vulcanization. This had led to the suggestion that their effect could be attributed to the initial structure of the vulcanized rubber. We have considered the possibility of obtaining some useful information on this subject by means of stress relaxation measurements which involve the decrease in tensile strength with time of a stretched test piece. The measurements were carried out either by maintaining the test piece at constant elongation (continuous relaxation), or by stretching the relaxed sample to a constant elongation from time to time (discontinuous relaxation). It has been established that the continuous relaxation method accounts solely for the chain scissions which are produced in the vulcanized rubber network, whereas the intermolecular linkages formed during the tests contribute to the discontinuous relaxation picture. The results of some preliminary experiments we have carried out are given in Figure 1. Two rubber compounds, accelerated with diphenylguanidine and mercaptobenzothiazole, respectively, and known to have quite different aging properties, were employed. Vulcanizates containing either an antioxidant A (phenyl-2-naphthylamine) or a deactivator D (zinc mercaptobenzimidazolate) were compared with the control vulcanizates T.
Quantitative Determination of Antioxidants, after a Chromatographic Separation on Completely Acetylated Filter Paper. II. Determination of Some p-Phenylenediamine Derivatives
Authors: Zijp J. W. H. 
Published: February 2011

Abstract
In this paper methods are given for the quantitative determination of three antioxidants, viz., N,N′-diphenyl-p-phenylenediamine, N,N′-di-2-naphthyl-p-phenylenediamine and N-phenyl-N′-cyclohexyl-p-phenylenediamine. According to these methods the antioxidants are extracted from the rubber compound, separated by partition chromatography on completely acetylated filter paper and oxidized to the corresponding p-quinonediimines, after which these oxidation products are determined colorimetrically.
Some Factors Which Determine the Flight of Aerological Sounding Balloons
Authors: Angioletti A. , Felice J. 
Published: February 2011

Abstract
Examination of Equations (8), which connect the external pressure and thus the altitude to the dilation of the balloon, shows that the most important factor with regard to the “limited” bursting height is the elongation at break of the envelope at temperatures of the order of −40° C and −60° C. The elasticity modulus of the material and the thickness of the envelope are therefore of little importance with respect to the bursting height. It must be remembered, however, that the thickness has an indirect influence because it increases the weight of the balloon proportionally, and possible irregularities in the envelope will be all the more harmful as the thickness decreases. As for the lift force, this remains practically constant during the ascent of the balloon. On the basis of experimental determinations, the elevated concentrations of ozone will not have a particularly harmful influence on the rubber envelope, even if it is of natural rubber, due to temperatures at high altitudes of less than −40° C, the high state of tension of the rubber, and the brief duration of the flight.
Dynamic Properties of Elastomers
Authors: Gehman S. D. 
Published: February 2011

Abstract
The large volume uses of rubber involve its cushioning, quieting, vibration-energy absorbing and isolating characteristics. Applications such as tires, belts, and engine mounts employ rubber under conditions of rapidly repeated deformations which are relatively small compared to ultimate breaking values. Although ultimate values and fatigue tests are important as criteria of quality, they are of no assistance to the engineer, designer or technologist for anticipating the response of his product to the forces experienced in service. To fill this need, there has grown up a body of technical and scientific methods, data, and principles usually referred to as the field of dynamic properties. The term dynamic properties as applied to elastomers usually means vibration properties which are displayed in response to sinusoidal forces. But restriction to sinusoidal forces is unduly narrow. In principle, both theory and experiment can be extended to more complex force patterns, such as square or saw tooth waves, if there is occasion to do so. The distinctive feature of the field of dynamic properties lies, perhaps, more in the amplitudes of the deformations, which are relatively small, than in the force diagram or the frequency. Results at quite low frequencies are sometimes included in work regarded to be on dynamic properties but the amplitudes are always rather small. In polymer science, the field of dynamic properties has tended to be restricted to amplitudes so low that the properties are essentially linear. This would provide a convenient definition but it is an unacceptable limitation from a technological standpoint where it is highly desirable to extend the work into the nonlinear region. On the other hand, fatigue and failure phenomena are definitely excluded from consideration here. Ordinary tensile stress-strain tests have a dynamic aspect but such results are not included in the catagory of dynamic properties. The field to be known as the dynamic properties of elastomers logically comprises the properties exhibited in response to periodic or transient forces for all types of deformation small enough not to induce appreciable fatigue or failure during the investigation. There is no good reason for limiting the frequency on either the low or high side. Temperature is, of course, a most important variable.
The Vulcanization of Rubber with Sulfur
Authors: Craig David 
Published: February 2011

Abstract
E. H. Farmer compiled a review of vulcanization which was published in 1946 as an important chapter in Volume II of “Advances in Colloid Science”. About two years later, Normann Bergem published a review under the same title. These authors dealt with the subject from rather fundamental points of view, but, because of more recent work from many laboratories and the increasing importance of elastomers, a fresh survey seems warranted. Accordingly, the present review aims to bring a part of the subject up-to-date. The viewpoint taken differs from those of Farmer and Bergem in some respects which seem rather important. For example, emphasis will be placed on the various rates of reactions including those of the scorch and reversion periods and on the importance of possible intermediates such as hydrogen sulfide and suitably terminated sulfur chains. The kinetic theory of elastomeric behavior constitutes the background against which any current treatment of vulcanization should be developed. Actually, vulcanization is a part of this background. Thus, Busse considered the following conditions necessary for the existence of rubberlike elasticity: (1) the presence of long chain molecules with freely rotating links, (2) the presence of weak secondary forces between molecules, and (3) the crosslinking of molecules into a three dimensional network. The three conditions taken together, at least in present day thinking, imply that long range elasticity results from the kinetic activity of segments which resembles yet differs from the kinetic activity of gas molecules. A segment is composed at most of only a few monomer units and is terminated at either end with another segment, a crosslink or an endgroup. When terminated with an endgroup, its kinetic activity may even detract from network behavior and then it is a defect. When terminated by a crosslink or another segment it is an integral part of the network and as such can contribute to the overall elasticity. It is more or less obvious that segments terminated by crosslinks and the crosslinks themselves should display an activity different from that of segments distant from crosslinks. Crosslinks, though relatively massive, are expected to move in a limited way (microBrownian) as a result of the kinetic activity of nearby segments. Crosslinks are necessary but are thus a sort of network defect. Those of lower functionality probably can contribute beneficially to the overall kinetic activity.
Carboxylic Elastomers
Authors: Brown H. P. 
Published: February 2011

Abstract
The degree to which a polymer is rubbery is influenced by the detailed shape and chemical composition of the macromolecules. Polymers which are rubbery possess relatively weak interchain forces and may lack linear symmetry and orderly arrangement of the molecule. As stronger interchain forces are added and symmetry and regularity are increased, the rubbery characteristics are gradually supplanted by those of fiber forming materials. Copolymerization with hydrocarbon chains may be used to reduce polymer to polymer interaction, destroy regularity and symmetry and favor rubbery characteristics. On the other hand it may be employed to introduce polar groups into hydrocarbon polymers and thereby increase interchain and intrachain forces. With increasing amounts of these polar groups polymer strength increases at the expense of elasticity with respect to both speed and range of extension and recovery. The polar groups also alter the solvent resistance of the polymer. In copolymerizations, carboxylic monomers tend to destroy regularity and symmetry thereby favoring rubbery properties over crystallinity. The strong polar nature of the carboxyl groups however increases interchain and intrachain forces imparting increased strength to the polymer at the expense of elasticity. Carboxyl groups were first introduced into rubbers for the purpose of altering polymer properties. When carboxyl groups are so employed, the resultant carboxylic rubbers are best regarded as polar elastomers. Carboxyl groups have also been introduced into rubbers in order that reactions characteristic of the carboxylic functional group might be employed to crosslink the polymer chains or attach them to other molecules or surfaces. When the carboxyl group is present in order that its functional reactivities may be employed, the carboxylic rubbers are best regarded as functional elastomers. This review is concerned with the preparation, properties and evaluation of carboxylic rubbers both as polar and as functional elastomers.
Rubbers from Basic Monomers. Vinylpyridine Polymers
Authors: Haws J. R. 
Published: February 2011

Abstract
Interest in vinylpyridine and vinylpyridine derivatives as monomers for production of synthetic rubber was evidenced immediately prior to World War II. In 1939 and 1940, European patents were issued on polymerization of vinylpyridines and their copolymerization with other monomers. Research in the United States on vinylpyridines and their derivatives as comonomers began in the early 1940's. Much of the early work was conducted under the Government synthetic rubber program with work carried out by several of the participating universities and rubber companies. At that time, vinylpyridine rubbers created a considerable amount of interest in the rubber industry. Compared to the 122° F butadiene/styrene copolymer then in use, butadiene/vinylpyridine copolymers displayed a superiority in several properties, notably tensile strength, tear resistance and resistance to cut growth. A number of terpolymers containing vinylpyridine type monomers were also investigated and these, with some exceptions, exhibited the same general advantages and disadvantages as the two-component copolymers. Some difficulty was encountered in early polymerization of vinylpyridine copolymers on a large scale, chiefly in preflocculation and lack of proper control over polymer viscosity and conversion rates. These problems were lessened somewhat in the polymerization of three-monomer systems. Processing difficulties were also encountered arising from incompatibility of vinylpyridine copolymers with other rubbers and a high rate of cure resulting in scorching tendencies. Treadwear results of tires made with these rubbers were encouraging but again complications appeared in the form of tread separations and an excessive increase in hardness after use. Because of the above-mentioned problems, together with the introduction of improved 41° F butadiene/styrene rubber, interest in these rubbers waned somewhat after World War II. More recently, however, interest in vinylpyridine rubbers has risen due to commercial availability of new monomers and the possibility of utilizing the reactivity of vinylpyridine polymers through new compounding techniques.
Changes in Elastomers Due to Radiation from Cobalt
Authors: Gehman S. D. , Hobbs L. M. 
Published: February 2011

Abstract
A survey has been made of the effects of intense gamma radiation on the physical properties of elastomers and plastics. Such information is required to determine the types of elastomers which are most resistant to radiation, to estimate the service life of elastomers exposed to radiation, and to show favorable trends in compounding for radiation resistance. Intense radiation may affect the physical properties of elastomers benficially or adversely, depending on the type of elastomer and the exposure dose, although hardening and embrittlement are most commonly observed. The possibility is apparent of developing elastomer compounds with improved radiation resistance, especially by the use of chemical agents which affect free-radical reactions. The nature of the elastomer, however, will probably severely limit what can be accomplished by compounding.
Heat Build-Up and Destruction of Vulcanizates under Dynamic Stress
Authors: Kainradl P. , Händler F. 
Published: February 2011

Abstract
The classification of various mixtures of natural rubber and of synthetic rubber and of synthetic rubbers with respect to heat build-up under dynamic stress depends on the experimental conditions under which the vulcanizates are tested. In many cases a reversal of the order of the mixtures is found when the latter are compared at constant deformation instead of at constant periodic stress. This is true also of flexing to the point of destruction of various types of vulcanizates. The dependence of the dynamic properties on the temperature and on the stress is characteristic of the type of vulcanizate. Hence, any classification of various mixtures depends not only on the character, but also on the magnitude of the stress. These differences were found within the temperature range encountered in practice, as in tires. Consequently, no definite conclusions about the temperature rise in the range of heat build-up extending to the point of destruction can be drawn from measurements of the dynamic properties at room temperature. Changes of the dynamic properties can also take place during dynamic stressing without any considerable rise of temperature. In general, the temperature rise in the static state and the flex life are related in the sense that the higher the temperature, the shorter is the flex life, if the preceding facts are taken into consideration. However, the experiments on the temperatures of destruction show that the flex life of different vulcanizates differs even when the rise of temperature is the same. For a flex life of 100 minutes, natural-rubber vulcanizates containing active carbon blacks were destroyed at higher temperatures (170°–185° C) than was the base mixture containing no filler (about 160° C). The synthetic-rubber mixtures showed greater heat build-up (190°–220° C). These differences are found with different, as well as with equal, mechanical stress on the vulcanizate. The nature of the destruction for a given stress depends to a considerable degree on the structure of the vulcanizate. When flexed to the point of destruction, natural-rubber vulcanizates containing zinc oxide or SRF carbon blacks, and all synthetic-rubber vulcanizates, crack from the core outward, without showing any extensive thermal decomposition. On the other hand, natural-rubber vulcanizates containing active carbon blacks or Aerosil showed definite evidence of heat decomposition in the center, i.e., stickiness and porosity. This distinction in the destruction patterns gives the impression that the cause of destruction in the first case is chiefly a mechanical attack, whereas in the latter, it is chiefly thermal decomposition. It must be concluded from all the experimental results that several chemical reactions of destruction, having different temperature coefficients, proceed simultaneously, and that direct mechanical attack by the external forces is, to a greater or less extent, added to the heat effect.
The Solubility of N-Phenyl-2-Naphthylamine in Elastomers
Authors: Reitlinger S. A. , Kuzminskii˘ A. S. 
Published: February 2011

Abstract
The determination of the solubility of N-phenyl-2-naphthylamine in elastomers is of great importance in determining the correct percentage of this substance to add to an elastomer to protect it from oxidation. Kuzminskii˘ and Lezhnev have shown that the duration of the induction of the oxidation of rubber depends on the concentration of N-phenyl-2-naphthylamine inhibitor in the rubber.
The Cross-Linking of Rubber by Pile Radiation
Authors: Charlesby Arthur 
Published: February 2011

Abstract
The degree of cross-linking produced in a rubber by high-energy radiation is proportional to the radiation dose. Unit radiation, as defined in the text, links 1.1 per cent of the isoprene units. The distribution of molecular weight prior to cross-linking agrees with a Poisson distribution. Gel formation begins for γ=0.5. From the radiation dose required to initiate gel formation, the initial average molecular weight can be deduced. The increase of gel fraction with radiation dose follows the relationship deduced theoretically in the first part of the article. Measurement of gel fraction gives an alternative method of calculating the initial average molecular weight. Where some cross-linking is present in the rubber prior to cross-linking, this may be evaluated. In accordance with the theory presented in the article, the viscosity of the sol fraction rises initially, then decreases as the radiation dose increases. This provides a third method of measuring molecular weight, or of relating viscosity to molecular weight, which can be deduced from measurement of gel fraction. The swelling of very lightly cross-linked gel has been compared with the Flory-Huggins relationship, which is found to hold down to very lightly cross-linked gels for which the cross-linking index is only 0.2. To obtain this agreement, it is necessary to consider the swelling of the dry gel, rather than the whole specimen, and to ignore the cross-links required to form the gel itself.
Reinforced Rubber Stocks under the Electron Microscope
Authors: Chappuis M. M. , Polley M. H. , Schulz R. A. 
Published: February 2011

Abstract
A transfer technique and a microtome technique have been developed for preparing standard rubber stocks for electron-microscope examination. The transfer technique is rapid and simple, and is adequate for the identification of unknown carbon black in an unvulcanized stock. The microtome technique is more satisfactory in that it reveals clearly the discrete particles of a reinforcing pigment as they are dispersed in the rubber matrix.
Kinetics and Mechanism of Hydrochlorination of Synthetic and Natural Polyisoprene Latex
Authors: Crampsey Edward , Gordon Manfred , Taylor James S. 
Published: February 2011

Abstract
The kinetics of hydrochlorination of synthetic polyisoprene emulsions, prepared by new and simple methods, are studied for comparison with the same reaction of natural latex. Nearly identical zero-order rate constants apply to both substrates at 300° K and 1 or 2 atmospheres of hydrogen chloride, despite differences in the detailed structure of the polymers. The conclusion that the substrates are not concerned in the rate control follows, since the rates of chain reactions which might give zero-order constants are very sensitive to the detailed structure of the polymers. Two initial rate abnormalities are observed. The first is shown to be due to a fast surface reaction, the second probably reflects the presence of a basic retarder in natural rubber particles only. Similar abnormalities of the cyclization reaction, reported earlier, are explained similarly. The effects of energetic factors and concentration on the hydrochlorination rate support visualization of the simple rate-determining step as: H+ + Cl− → (H+, Cl−) (ion pair), where the proton is probably solvated as H2C+. The critical transition state must be uncharged, because the reaction rate is unaffected by a change of dielectric constant due to the conversion of rubber hydrocarbon into rubber hydrochloride. Existence of the ion pair as reactive intermediate confirms Gordon and Taylor's recent stereochemical theories on hydrochlorination of natural rubber. The rapid surface reaction is ascribed to the ready formation of ion pairs or similar species in the aqueous phase, and the limited range (about 15 A) or the surface reaction to the slow rate of diffusion of unchanged rubber units to the surface.