bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stress Relaxation during the Photoxidation of Peroxide Crosslinked Rubber
Authors: Dunn J. R. , Scanlan J. , Watson W. F. 
Published: February 2011

Abstract
The chemical reactions involved in the thermal and photochemical aging of natural rubber vulcanizates are largely unknown. Experimental difficulties have precluded direct chemical investigation owing to the insolubility of the crosslinked networks and the small extent of reaction required for a great deterioration in physical properties. Accordingly recourse has been made to physical measurement. Tobolsky et al. (e.g. Ref. (1)) have shown that the relaxation in stress on holding a rubber strip at constant extension during aging is a convenient experimental measure capable of interpretation in terms of network breakdown. In photochemical studies the opacity of conventional sulfur vulcanizates provides a further complication. In the present work, the stress relaxation technique has been used in a study of the degradation by 365 mµ radiation of the comparatively transparent and chemically simple rubber networks obtained after crosslinking by organic peroxides.
Electron Paramagnetic Resonance of Radicals Formed during Milling
Authors: Bresler S. E. , Zhurkov S. N. , Kazbekov E. N. , Saminskiĭ E. M. , Tomashevskiĭ E. E. 
Published: February 2011

Abstract
It is well known that during the mechanical degradation of polymers there takes place scission of molecular chains and the formation of macroradicals. It is of considerable interest to study the electron paramagnetic resonance (EPR) spectra of the macroradicals produced by milling, and to compare them with the spectra of the macroradicals formed in the process of polymerization, and also during the irradiation of polymers by gamma rays and neutrons. We may endeavor to compare the amount of macroradicals formed with the extent of mechanical destruction (for instance with the area of the new interface which is formed). In addition, as was found by experience, the macroradicals formed by mechanical scission are good models for the investigation of reactivity since practically all of them are in the newly formed surface layers and are therefore very accessible to various chemical influences. They enter easily into reaction with various agents present in the medium since in this process diffusion from the surface is found in practice not to be a predominating factor. In the present communication we give the first EPR results obtained on mechanically degraded polymers.
The Mechanism of Radiation Damage to Elastomers. II. Crosslinking and Antirad Action
Authors: Bauman Richard G. 
Published: February 2011

Abstract
All of the antirads studied serve to decrease the rate of crosslinking of carbon black loaded natural rubber during irradiation in a vacuum. Oxygen also serves very effectively as an antirad toward crosslinking. In air, some antirads enhance this protective effect of oxygen; others serve actually to increase the rate of crosslinking. Mechanisms sufficient but not necessary to explain these observations are presented. They involve reactions of the antirads with polymer radicals, viz.: R⋅+ARH→RH+AR⋅ (stable) reactions of oxygen with polymer radicals, viz.: R⋅+O2→RO2⋅ and reactions of oxygen with antirads, viz.: ARH+O2→oxidized products The ratio of scissions to crosslinks ranges from 45 to 4.3 in air and 2.3 to 0.92 in vacuum. The sol-gel measurements of other workers show, however, that most (90–99%) of these scissions are only temporary chain breaks which are rapidly reformed.
Measurement of the Aging of Rubber Vulcanizates
Authors: Mandel J. , Roth F. L. , Steel M. N. , Stiehler R. D. 
Published: February 2011

Abstract
Ultimate elongation (strain at failure) can be used to assess the aging of all rubber vulcanizates. For this purpose, it appears that Equation (2) can be used to express the early part of the aging process, corresponding to a period of aging at room temperature of 10 or more years. Prediction of shelf aging from tests at two or more elevated temperatures is only possible if the relationship between aging and temperature is known. For some rubber compounds the Arrhenius equation appears to hold. In these instances, it provides an effective means for estimating shelf aging.
Rapid Identification of Polyisoprene in Cured and Uncured Compounds
Authors: Mano Eloisa B. 
Published: February 2011

Abstract
On account of the industrial development of synthetic elastomers the identification of the different types of rubber in artifacts became a necessity. Several methods have been tried and periodically reviewed by Bekkedhal and by Tyler and Higuchi. As far as the synthetic rubbers are concerned, the types being produced in industrial quantities have characteristic groups which permit their easy detection by chemical means. However, natural rubber, poly-cis-isoprene, presents a more difficult identification, especially if in admixture with other elastomers and compound ingredients, in vulcanizates—and the same is true for the synthetic poly-cis-isoprene, the production of which has just recently started. The use of special techniques as X-ray diffraction, infrared spectroscopy and chromatography permits the identification of the natural rubber hydrocarbon, but equipment for them is not always available for routine work. Simple techniques have been tried. Not mentioning methods which depend on experimenter interpretation, as behavior to burning, which furnishes valuable preliminary information for an experimenter, we verified that two tests in the British literature are of great utility. These consist of determining the swelling ratios in benzene, petroleum ether and aniline and the time of reaction in a mixture of concentrated nitric and sulfuric acids. As chemical reactions, characteristic of natural rubber and its reclaim, the old Weber reaction, the trichloroacetic acid reaction and the well known chromic oxidation to acetic acid are mentioned.
The Stereoregular Polymerization of Isoprene with Lithium and Organo-Lithium Compounds
Authors: Stearns R. S. , Forman L. E. 
Published: February 2011

Abstract
It has been shown that lithium metal and organolithium compounds, when used as catalysts for the polymerization of isoprene, yield a polymer containing 93–95% cis-1,4 configuration and 5–7% 3,4-addition product. The catalytic mechanism in the case of lithium and its compounds, irrespective of their solubility, appears to be homogeneous. It is suggested that the formation of a stereoregular polymer from isoprene and lithium is the result of the C—Li bond forming a coordination complex with the monomer in the cis configuration followed by rearrangement of this coordination complex to form a six-membered, cyclic, activated complex. The stability of the complex is a result of the ability of the lithium atom to undergo partial hybridization and thus assume a valency greater than one. Lewis bases, such as ethers, change the stereospecific aspects of the lithium-catalyzed polymerization of isoprene by the formation of a stable complex between the base and the carbon-bound lithium. This complex between the ether and the C—Li bond increases the ionic character of the C—Li bond to the extent that it becomes equivalent to that of the C—Na bond.
Infrared Analysis of Butadiene Polymers
Authors: Kimmer W. , Schmalz E. O. 
Published: February 2011

Abstract
Whereas older methods for the determination of 1,2-, cis-1,4 and trans-1,4 units in high polymers require pure olefins as calibration substances, this is no longer necessary with the newly developed method which is described in this paper. From 3 different polymer samples 3 dilution series are prepared and the infrared spectra are recorded. The extinction coefficients are extrapolated to c=0 by a modified base line procedure and the resulting operational extinction coefficients are coupled mathematically (determinants) to yield the actual extinction coefficients of the pure isomers. These may be expressed as mole per cent of the isomeric units for the individual polymer samples. The procedure described may also be applied to other chemical mixtures without the need for pure calibration substances.
General Considerations on the Structure of Crystalline Hydrocarbon Polymers
Authors: Natta G. , Corradini P. 
Published: February 2011

Abstract
Owing to the discovery of stereospecific polymerization processes effected in our Institute, we were able to determine, in the last few years, the crystal structure of a great number of new polymers. In this work we will discuss the general principles leading to the determination of the shape and mode of packing of macromolecules in the crystals.
The Crystal Structure of Cis-1,4 Polybutadiene
Authors: Natta G. , Corradini P. 
Published: February 2011

Abstract
In previous works, we announced the identification and discussed the structure of three of the four possible pure stereoisomers of polybutadiene ; two with 1,2 enchainment (isotactic and syndiotactic respectively) and the third with trans-1,4 enchainment. In a letter to the Editor of Angewandte Chemie we have given preliminary data concerning the crystal structure of the polymer with cis-1,4 configuration, of which we succeeded in preparing sufficiently long and crystallizable macro-molecular chains formed by cis-1, 4 units. All the various stereoisomeric polymers we examined were prepared with different catalysts, all obtained by reaction of metalalkyls on suitable compounds of transition elements. For all these catalysts the mechanism of the polymerization reaction is of the co-ordinated anionic type. The different behavior can be ascribed to the mode of co-ordination of the olefin with the metallorganic complex of the transition metal.
Effect of Crystallization of Polymers on Dielectric Loss
Authors: Mikhaĭlov G. P. , Sazhin B. I. 
Published: February 2011

Abstract
The values of ε′ and tan 5 in the range of dielectric losses of relaxation character decrease on crystallization of polymers. In the case of medium frequency relaxation losses tan δ sometimes decreases 2 to 4 fold and ε′ by 20 to 30%. This is mainly connected with transition of polar portions of macromoleules into crystallites, on the one hand, and on the other hand with an increase in the breadth of the relaxation spectrum for the polar groups remaining in the amorphous phase. The relaxation time for the medium frequency relaxation dielectric losses, connected with the thermal motion of segments of maeromolecules, in the amorphous phase, increases on crystallization, while for high frequency relaxation losses, reflecting the thermal motion of separate groups or links, does not change or indeed even decreases. The dielectric method may be used for the investigation of the kinetics of crystallization and melting of polymers and, in the case of polar polymers, also for the determination of the degree of crystallinity.
Adhesion Phenomena in the Bonding of Rubber to Metal by Means of Lei˘konat Bonding Agent. 2. Unfilled Vulcanized Rubber
Authors: Deryagin B. V. , Zherebkov S. K. , Medvedeva A. M. 
Published: February 2011

Abstract
1. The bond strength of vulcanized rubber to metal brought about by means of a bonding agent film is regulated by the ratio of the intensities of interaction of the bonding agent film with the contacting surfaces at the bonding agent- rubber and bonding agent-metal interfaces. Where these are approximately equal the bond strength is greatest. Where they differ sharply the bond strength decreases. 2. One of the factors influencing the intensity of interaction of a bonding agent film with vulcanized rubber is a reduction in the thickness of the bonding agent film ; with reduction in the thickness of the bonding agent film the intensity of interaction of the bonding agent with the vulcanized rubber falls; this is expressed in varying ways in the bond strength to metal of vulcanizates of various rubbers, causing a fall-off in some cases, and in some other cases a certain increase in the bond strength of the vulcanized rubber to the metal. 3. By means of the Lei˘konat bonding agent it is possible to bond unfilled vulcanizates based on the majority of existing polymers, whether polar or non-polar, to metal sufficiently strongly. 4. It is established that on increasing the number of polar groups in the polymer there is an increase in the intensity of interaction of the bonding agent film with the vulcanizate containing that rubber.
Vulcanization of Elastomers. 26. Vulcanization of Natural and Synthetic Rubbers by Sulfur in the Presence of Organic Bases
Authors: Scheele Walter , Redetzky Wolfgang 
Published: February 2011

Abstract
In connection with earlier research work, we have carefully studied the decrease of sulfur during the vulcanization of Perbunan N 2818 in the presence of DPG, at various temperatures and with varied molar concentrations of sulfur and accelerator. We found : 1. The sulfur concentration decreases at all temperatures according to a time law of order 0.8. An activation energy of about 28 kcal/mole is derived from the temperature dependence of the rate constant. 2. The reaction order is independent of the initial concentration of reactants. 3. A discrepancy is found in the order of the reaction with respect to time and with respect to concentration, and it is clearly shown that the dependence of the initial rate on the initial concentration can not be expressed by a single power law. 4. The attempt is made to explain the discrepancy by postulating catalysis by an intermediate compound. The consequences from this consideration are compared with the experimental results, and, on the whole, agreement is found between theory and experiment.
A Method of Screening Antiozonants
Authors: Sullivan F. A. V. , Davis A. R. 
Published: February 2011

Abstract
A method has been developed for screening compounds for potential antiozonant use based upon the ability of the compound to suppress the reaction of ozone with cyclohexene when a mixture of the two is subjected to the action of a stream of ozonized air. The method is satisfactory as a tool for selecting compounds for testing in rubber. In a rubber formulation, however, there are many factors concerned with the functioning of a compound as an antiozonant in addition to its ability to react preferentially with ozone at a faster rate than the unsaturated linkages in the rubber. Testing the most promising compounds in a rubber formulation is required to establish their commercial value as antiozonants.
Vulcanization of Elastomers. 28. Vulcanization of Natural and Synthetic Rubbers with Sulfur in the Absence of Accelerators. I
Authors: Echte Elisabeth , Scheele Walter , Sonnenberg Sigrun 
Published: February 2011

Abstract
The decrease of sulfur concentration in the reaction of sulfur with natural rubber was studied. The following was found : 1. Sulfur decrease follows the 0.6th order law independent of temperature as long as the sulfur is dissolved in the gum (temperature!). From the rate-temperature relation, an activation energy of 35 kcal/mole is calculated. 2. In an investigation of the kinetics of sulfur concentration at constant temperature but increasing starting concentration, the following two cases can be differentiated : a) As long as the sulfur is soluble in the gum, sulfur decrease still follows the 0.6th order, possibly due to autocatalysis ; the linear relationship between starting rate and starting concentration shows that the process is 1st order with respect to the concentration; this may be the consequence of a thermal, rate determining cleavage of the S8 ring. b) As the sulfur at higher concentration is only incompletely soluble in the gum, conversion curves with points of inflection are found ; this becomes more pronounced at higher concentration. At the start of the reaction one finds an autocatalytic sulfur decrease basically of zero order; in the latter part of the reaction after passing the point of inflection a 0.6th order is observed, as in the range of complete sulfur solubility. 3. A discrepancy between the time law and the concentration-rate relationship is found in pure as well as accelerated sulfur vulcanization ; these conditions are compared and discussed.
Radical and Ionic Reactions of Tetraethylthiuram Disulfide
Authors: Klebanskiĭ A. L. , Fomina L. P. 
Published: February 2011

Abstract
1. Investigation of the process of radical dissociation of TETD in carbon tetrachloride indicates that at 145° thiuram radicals are formed which react with the carbon tetrachloride to form (C2H5)2N—C‖S—SCl and CS2. 2. A quantitative determination of the products of the base-influenced dissociation of TETD was carried out. A kinetic investigation of this reaction, in which initiator (K2S2O3) and inhibitor (PBNA) were shown to have no velocity effect whatever, indicates that the process is an ionic one. 3. It is shown that in the reaction of TETD with diethylamine, one of the reaction products appears to be diethylammonium diethyldithiocarbamate.
Vulcanization of SBR in a Thermal Neutron Field
Authors: Anderson Herbert R. 
Published: February 2011

Abstract
The nuclear reactions B10(n,α)Li7* and Li6(n,α)H3 can be used to generate highly ionizing particles in a pure thermal neutron field to vulcanize an otherwise transparent rubber compound. Vulcanizates have satisfactory physical properties comparable with those produced by other means of vulcanization, e.g., gamma rays and peroxides. Such vulcanizates possessed negligible residual radioactivity. The somewhat analogous initiating systems gave vastly different vulcanizates with the same parent rubber compound in a helium atmosphere, and a possible explanation is presented. The G values for lithium methoxide promotion (ca. 3) are comparable with those obtained with gamma-ray vulcanizates. Promotion is less efficient with boron nitride, the average values of G being approximately 0.9. The irradiation atmosphere has a pronounced influence on the type of vulcanizate produced and on the energy utilization. Substitution of air for helium as the irradiation atmosphere increases net crosslinking of cold rubber with boron nitride promotion, while it decreases it when lithium methoxide is used as the promoter.
The Attack of Ozone on Stretched Rubber Vulcanizates. I. The Rate of Cut Growth
Authors: Braden M. , Gent A. N. 
Published: February 2011

Abstract
The growth of cracks in the surface of stretched components of vulcanized rubber on exposure to the atmosphere is a serious deficiency. It detracts from the appearance, serviceability, and strength, and may lead to early failure. A comprehensive review of the process and the evidence for attributing it to the action of ozone in the atmosphere has been given by Newton, the following features being established. (1) The action of ozone on unstretched rubber is slight, no cracks being formed. (2) At small extensions of the order of 10%, cracks appear and grow to form large incisions in the exposed surface. (3) At higher extensions, the number of cracks is larger, but their final size is smaller due to mutual interference. The deterioration of the rubber may be considered less serious, therefore, since the component possesses a finely etched surface rather than one containing a few large cuts. The basic process appears to consist of the initiation and propagation of a single incision in a deformed rubber under the action of an atmosphere containing ozone. However, the experimental studies that have been reported previously have been concerned with the gross deterioration of an exposed surface when many cracks form simultaneously. It is difficult to deduce from such observations the behavior of a growing incision for the following reasons. Firstly, the presence of a crack will alter the surface deformations in its neighborhood, and hence may seriously affect the growth of nearby cracks. Secondly, cracks formed on the surface grow simultaneously in length and in depth, the deformation in the region of the growing edges presumably varying with the crack shape as well as with its size. Thirdly, the cracks may propagate by ozone attack at the growing tips and also by attack at points on the surface in close proximity to them. Finally, it is likely that surface irregularities will affect the local deformation, while foreign materials such as dust, decomposition products, or “bloomed” ingredients of the rubber compound may affect the access of ozone.
Energy Requirements of Mechanical Shear Degradation in Concentrated Polymer Solutions
Authors: Bestul A. B. 
Published: February 2011

Abstract
Molecular weight decrease by mechanical shearing results when solutions of around 10% of polyisobutene having average molecular weights above 500,000 are forced through a capillary at nominal rates of shear above 10,000 sec−1. Comparison of observed plots of shear load vs. duration of shearing at fixed rates of shear during this degradation process with the corresponding estimated plots which would be expected to obtain if degradation did not occur provide a means of evaluating the amount of applied shearing energy which is dissipated by the degradation process. The result is several hundred thousand kilo-calories per mole of broken bonds, which is several thousand times the bond energy of carbon-carbon bonds. This finding is consistent with the hypothesis that whenever a bond breaks the system loses much of the free energy temporarily stored in bonds and macromolecular chains located in a comparatively large volume surrounding the broken bond, these bonds and chains having been involved in concentrating the required activation energy into the ruptured bond.
Mechanochemical Reactions Leading to Reinforcement in Rubbers
Authors: Ceresa R. J. 
Published: February 2011

Abstract
The development of the single rotor internal mixer (at the British Rubber Producers' Research Association) has facilitated the research into mechanochemical reactions of a wide range of high polymers. The term “mechanochemical” has been applied to reactions such as mastication, the mechanism of which involves the primary step of mechanical scission of a polymer chain into polymeric free radicals at a carbon to carbon or other covalent bond. The processes which have been studied previously include the cold mastication of rubberlike polymers, the formation of carbon gel, the interpolymerization of two elastomers during blending, and block copolymerization by the cold mastication of polymers plasticized by vinyl monomers. The evidence for the polymeric free radical nature of these reactions has recently been reviewed.