bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Mechanism Which Restricts Chain Growth in Polymerization with Alkylaluminum-Titanium Tetrachloride Complex Catalysts
Authors: Bresler S. E. , Mosevitskiĭ M. I. , Poddubnyĭ I. Ya , Guan-I Shi 
Published: February 2011

Abstract
In the production of polymers having a highly regular structure of the molecular chains, catalyst complexes of the Ziegler type are currently in wide use. The development of mechanisms for the separate steps in the catalytic process is of primary significance. This report outlines some results on a study of the mechanisms involved in isoprene polymerization with complexes formed through the interaction of Al (iso-C4H9)3 and TiCl4; the data were obtained from the sedimentation of the polymers in the ultracentrifuge, in combination with data on the kinetics of polymerization. We have indicated previously1 that in isoprene polymerization using the specified catalysts, the growth of the macromolecules proceeds quite rapidly, the time interval between the first appearance of active chains and the termination of reaction being only a few minutes; subsequently there follows an immediate stationary condition. However, with use of the ultracentrifuge we have obtained molecular weight distributions of polymers which are substantially different from the equilibrium distribution expected from present-day kinetic theories of polymerization. They were characterized by relatively low dispersion and, in the main, strongly distorted by high-molecular bands; in most cases, there was practically a complete absence of molecules with a molecular weight less than 200–300 thousand.
Synthesis of Isoprene Tagged with C14
Authors: Korotkov A. A. , Rakova G. V. 
Published: February 2011

Abstract
For a study of the mechanism of catalysis of polymerization of diene hydrocarbons and also for investigation of the process of catalysis of copolymerization the following hydrocarbons tagged with C14 were synthesized: benzene, toluene and isoprene. The simplest ordinary methods possible were used for these syntheses to obtain pure active preparations in good yields from starting materials containing radioactive carbon.
Dynamic Vitrification and the Activation Energy of Rubbery Polymers
Authors: Bartenev G. M. , Zaĭtseva V. D. 
Published: February 2011

Abstract
1. The resistance to brittleness of a wide variety of rubbers was studied by the method of periodic deformation. 2. Dynamic glassing, during which transition from the highly elastic into the brittle state is observed, always occurs in the liquid state of aggregation of a polymer, where the activation energy of molecular rearrangement changes with temperature according to an exponential law. 3. In a small temperature interval the change of the activation energy can be approximated by a linear law; consequently, Equations (1) and (4) expressing the dependence of the temperature of transition of the rubber into the brittle state on the frequency of deformations are satisfied approximately. The constants entering into these equations and their relationship to the activation energy are determined. 4. The activation energy of dynamic glassing is directly proportional to the glass temperature of the polymer and is greater than the activation energy of static glassing by approximately 5–10%, consequently the rate of establishment of the equilibrium structure is greater than the rate of stress relaxation or the rate of development of elastomeric deformation. 5. The relatively high activation energy of dynamic in comparison with static glassing is caused, apparently, by the larger size of the segments of the polymer chain during mechanical action compared to the size during free thermal motion.
Ozone Air Velocity Factor in Ozone Cracking
Authors: Cheetham I. C. , Gurney W. A. 
Published: February 2011

Abstract
Investigations based on the stress relaxation of natural rubber in ozonized atmospheres have produced relationships between cracking, ozone concentration and ozone air velocity. It is shown that at low ozone air velocities the rate of cracking is critically dependent upon the air speed value. The occurrence of discrepancies arising between results from testing chambers operating under identical conditions of concentration, temperature and light intensity is demonstrated at the end of the paper. A brief mention of similar work has been published but it is felt that more detail may help in the standardization of ozone testing procedure.
The Biosynthesis of Rubber
Authors: Fournier P. , Tuong-Chi-Cuong  
Published: February 2011

Abstract
The goal seems now well defined, but the means necessary for its attainment have yet to be chosen. Undoubtedly, isotopic methods will be the appropriate approach to gather the required information. They will be used less for investigation of individual transformations than for establishing the balance of transformation of the precursors. Finally, it is very fortunate that latex can be broadly compared to a homogenate of laticiferous cells. Therefore, it is reasonable to believe that, used with precaution, the latex must reflect the ability of the tree to form rubber and that the study of the points that are mentioned will be possible by using this medium. No matter how successfully the mechanisms limiting or controlling the rubber production will be located, it will remain a problem to modify them in the desired way, because the tree (hevea brasiliensis) forms a system in equilibrium. In this system, all reactions are interdependent and a reaction requiring manganese or calcium will interfere with those which are poisoned by these metals. … In short, it is impossible to modify entirely the plant life. Consequently, the action of the researcher will always be limited because drastic modifications of the state of equilibrium would cause undesirable effects. But just as medicine can modify certain metabolisms of a patient if it proceeds without brutality, it may be possible to act in a limited way upon the basic metabolisms of hevea. This does not mean that the productivity of the tree will not be changed considerably, but in any case the methods employed will have to be very mild. Before reaching this goal, many important problems will have to be solved. As in medicine, identification of the basic metabolism will not suggest the therapeutic method for their acceleration. Without this background information, no treatment can be conceived, but no miracle drug results from diagnosis alone. The dual aspect of any studies in this field is striking: the immense possibilities anticipated are tempered by the problems involved in plant life. In view of the scientific progress of the last five years, such a restrictive statement seems to be out of order. The evolution of our knowledge is so fast, that such preconceived ideas may rapidly become obsolete and so obscure our view for new progress. We believe it necessary to conclude this review with such a warning, making the reader aware of the hopes as well as the limitations of the studies on the biosynthesis of cis-polyisoprene.
Oil-Extended Rubbers
Authors: Storey E. B. 
Published: February 2011

Abstract
One hesitates to close this review by adding a paragraph of conclusions. The term “oil-extension principle” introduced a new concept to the manufacturer of synthetic rubbers. The principle (if it may be identified by such a word) and the application of the products it generated do not involve any novel or unfamiliar approaches to the art of rubber compounding. Indeed, it would be rendering a disservice to the progress of their adoption by industry to suggest that it required a revision in the viewpoint of the rubber compounder. The use of softeners in compounding was almost coincidental with the discovery of rubberlike substances by the explorers of the 16th century. The development of carbon blacks having more useful characteristics in rubber came after the compounder had become familiar with the application of innumerable inorganic fillers in rubber and, indeed, soots and lampblacks. The tailor-made synthetic rubbers were developed by the chemical industry in the second-quarter of the 20th century and it is scarcely likely that higher molecular weight types would not be produced nor that any inherent processing problems would not be solved when there existed an economic and raw material incentive to do so. These are the contributions of the polymerization chemists and the synthetic rubber industry. Where it is more economically-attractive and technically-desirable to add softener and filler to the synthetic rubber in the manufacturing process, oil-extended rubbers and filler masterbatches will be provided as raw materials for the rubber industry. If on the other hand, these ingredients may be added quite readily during factory mixing operations, without any detrimental effects on the polymer quality, the synthetic rubber producer would be quite unwise to attempt to usurp the functions of the rubber manufacturer. The income of the rubber manufacturer, depends upon the skill and economy that he applies to the operation of mixing rubber with liquid and solid materials and this is the prime occupation of a rubber compounder. It would avail the synthetic rubber producer nothing to try and convince the compounder that he is doing something novel and unusual by preparing softener-filler masterbatches. However, the compounder will be receptive to a pre-blended product that enables him to produce rubber mixes of better or different quality at an equal, or lower, cost. This is the aim and accomplishment of oil-extended rubbers.
Instrumental Methods for the Analysis of Polymeric Materials
Authors: Mitchell J. , Lord S. S. 
Published: February 2011

Abstract
Advances in our knowledge of the chemical and physical structure of polymeric substances have been due in large measure to new and improved instrumental methods of analysis. From the standpoint of chemical structure all polymers have at least one functional group, often in low concentration, e.g., an end group. Principal progress has been made, first, in identification of these groups, and, more recently, in their quantitative determination and location within the molecule. In some cases conventional chemical methods have been greatly improved to provide the high sensitivity required for these analyses, particularly for groups such as acid, amine, ester and carbonyl. However, most chemical methods depend on reaction in solution. Often the choice of solvent is limiting, since it must be inert toward both the sample and the reagents as well as be capable of dissolving a significant amount of the material to be analyzed. In many cases a suitable solvent is not available. Many of these restrictions do not apply to instrumental techniques. Infrared spectrophotometric methods, for example, may be (a) nondestructive and the sample can be recovered for other studies, (b) rapid, often being completed within several minutes, (c) direct in which films or dispersions can be handled and, therefore, limited solubility is not a problem, (d) capable of providing information on physical as well as chemical structure, and (e) capable of supplying other useful information during the course of an analysis. Examples of techniques used in analyses for chemical and physical structure are: (see PDF for table) This paper reviews primarily recent advances in instrumental techniques which have been shown to be capable of quantitative analysis for chemical structure. Also, reference is made to the use of infrared spectroscopy, nuclear magnetic resonance spectroscopy, and differential thermal analysis in studies of physical structure. Applications to characterizations of elastomers are emphasized, although for illustrative purposes investigations of other polymers often are discussed.
Nuclear Magnetic Resonance Studies of Elastomers
Authors: Slichter W. P. 
Published: February 2011

Abstract
The remarkable property that we associate with rubberlike elasticity, the high degree of elastic deformability, has long been known to arise from molecular motion. In fact, Joule recognized a century ago that the retractive force in stretched rubber stems from thermal motions of molecules rather than from attractive forces between molecules, a conclusion which was all the more remarkable because Joule had no idea of the polymeric nature of rubber. This review tells of the newest technique for studying molecular motion, nuclear magnetic resonance spectroscopy (NMR), and of its application to studies of rubberlike substances. Appropriately, the most important measurements of rubberlike elasticity have been mechanical—creep, stress relaxation, dynamic response. The visco-elastic properties have been studied theoretically and have been measured profusely. They have told us much about the spectra of relaxation processes, which range over many decades of frequency. However, the mechanical experiments occur at the macroscopic level. Conclusions as to behavior at the molecular level depend upon the soundness of models. Plainly it is also valuable to examine motion directly at the molecular level. There are several techniques that accomplish this end. Infrared spectroscopy and dielectric relaxation studies are two kinds of measurement that directly indicate the motion of atoms and molecules. To these techniques is added nuclear magnetic resonance spectroscopy. This method responds to molecular behavior quite differently from other kinds of measurement, and avoids some of the restrictions encountered in these other techniques. For example, the requirement of a permanent electric dipole moment effectively excludes dielectric measurements for the study of pure natural rubber and other hydrocarbons, yet motion in such substances is readily seen by NMR. On the other hand, there are distinct limitations to the use of nuclear resonance, as we shall note. In this paper, we shall review the phenomenon of nuclear magnetic resonance, with emphasis on its use in studies of molecular motion in elastomers. It would be wrong to say that NMR has achieved the importance of the principal physical techniques used to study elastomers. Indeed, the information on elastomers yielded by NMR consists largely of isolated examples. Still, we shall seek to show that the method is powerful and has great potentialities. For a more detailed review of the fundamental physics than is given here, the reader is referred to the excellent paper by Pake. A comprehensive survey of NMR studies of polymers is given by Powles.
Preformed Aluminum Triisobutyl-Titanium Tetrachloride Catalysts for Isoprene Polymerization
Authors: Schoenberg E. , Chalfant D. L. , Mayor R. H. 
Published: February 2011

Abstract
Variables in the preparation of mixed aluminum triisobutyl-titanium tetra-chloride catalysts for isoprene polymerization were studied. All the preformed catalysts were tested unaged in solution polymerizations at 50° C using various catalyst levels. The yields of solid rubber and low-molecular-weight oily material in the polymerization products were determined. The solid rubber was analyzed for cis 1,4 content, inherent viscosity, and per cent gel. The most active catalysts for the synthesis of cis 1,4-polyisoprene were those prepared at low temperatures, below 20° C. Superior catalytic performance and improved polymer properties were obtained with catalysts preformed by either gradually adding the aluminum alkyl to titanium tetrachloride or by mixing the two cocatalysts at a constant Al/Ti ratio in the range of 0.9 to 1.0. By comparison, the gradual addition of titanium halide to the alkyl resulted in catalysts of lower activity and inferior polymer properties; it also required higher Al/Ti ratios for the preparation of all cis 1,4 rubber. An increase in catalyst preparation temperature led to gradually lower activity to where species preformed at 125° C showed little or no activity. High preparation temperatures, further, caused a shift in the Al/Ti ratio—optimum for cis 1,4 synthesis—to lower values when the aluminum to titanium order of addition was employed, and to higher ratios for the reversed type of addition. Al/Ti ratios above and below the optimum produced a cis 1,4 rubber which was increasingly contaminated with by-products of oily and leathery type polymeric material, respectively. Maximum yields of oily polymers were obtained with low temperature catalysts of Al/Ti ratios within 1.5 and 2.0. Catalysts preformed by the aluminum to titanium order of addition at 90° C produced cis 1,4-polyisoprene at Al/Ti ratios of 0.5 to 0.6. Preformed catalysts are preferred over those prepared in situ in the presence of isoprene because they show higher activity, more reproducible polymerizations and improved polymer products.
Structure Effects and Related Polymer Properties in Polybutadiene. I. Preparation and Characterization
Authors: Berger M. , Buckley D. J. 
Published: February 2011

Abstract
Stereoregular polybutadienes, of both high trans and high cis contents, were isomerized to provide polymers of varying cis-trans content. These isomerizates were used to study structural effects on physical properties. The isomerizations were carried out under photosensitized conditions in benzene solution at 25° C. The reaction was controlled to deliver polymers over the range 0–95 per cent trans content. This range was selected to provide crystalline and semicrystalline polymers whose structures could be examined in terms of sequencing or blocking by established x-ray techniques. Isomer contents were measured accurately by infrared traces. Isomerizations reached an equilibrium of 77 per cent trans regardless of whether the reaction started with high trans or high cis polybutadienes. Intrinsic viscosity was found to increase regularly with trans content in conformity with the larger size of the trans unit. ηsp/c versus c relations were observed to give a complicated form and this subject was deferred for further study. Crystallinity decreased regularly with reduced trans content as the equilibrium of 77 per cent trans was approached. Continued isomerization at the point of equilibrium produced a completely amorphous polymer. The melting temperatures of the crystalline polymers were studied in detail by x-ray camera and counting techniques. These polymers exhibited two crystal forms. One form was stable up to 60° C and invariant with cis-trans content in the range 80–95 per cent trans. Below 80 per cent trans the melting point of this form decreased with further reduction in trans content. The melting temperature of the other crystal form was dependent on trans content and decreased with decreased trans content until it coincided with the melting temperature of the other form. The distributions of trans and cis units and sequences of them were calculated through construction of matrices of transition probabilities. Copolymer theory was invoked to calculate pseudo reactivity ratios for the trans and cis forms. The melting temperatures of the two crystals were found to follow the predicted curves for random copolymers, although not simultaneously. This behavior is discussed. The crystallinity of the isomerizates of high trans content was found to be similar to block copolymers in spite of the fact that the method of their preparation would require that they be characterized as random. The importance of a crystal transition in this case is stressed along with the general effects due to the amount and type of the noncrystallizable unit.
Volatility of Antioxidants and Antiozonants. 1. Pure Compounds in Absence of Rubber
Authors: Spacht R. B. , Hollingshead W. S. , Bullard H. L. , Wills D. C. 
Published: February 2011

Abstract
Comparable volatility data are presented for three phenolic and five aromatic amine compounds. Vapor pressure curves for the materials are given along with the vapor pressure equations derived from these curves. The equations are used to calculate temperatures at which the eight compounds would have equal vapor pressure. Vapor pressures of each material are calculated at specified temperatures. Data are given for several methods of determining actual losses of antioxidants at several different temperatures and at several different airflows. Surface effects are also studied. In general, all methods give the same relative rating of the eight materials, but quantitative data vary considerably with the method used.
Solvent Resistance of Silicone Elastomers: Solvent-Polymer Interactions
Authors: Yerrick K. B. , Beck H. N. 
Published: February 2011

Abstract
The solubility parameters, δp, of a number of polymers have been determined by swelling in a series of solvents with various solubility parameter values, δ0. The δp values were obtained for (see PDF for diagram) During the course of this work it was concluded that solvent nature (polarity and association) play an important role in the swelling power of a solvent. These interactions create considerable ambiguity of the data in cases where dipole interaction or association takes place between polymer-solvent pairs or solvent-solvent pairs. For this reason a series of “select” solvents were chosen that did not display these interactions. Included in these “select” solvents were the aliphatic and aromatic hydrocarbons (δ0=6.0–9.2). In addition the aliphatic alcohols which are strongly hydrogen bonded were included to cover the upper range of δ0 values (δ0=10.8–14.2). This study has revealed that the swelling curves of siloxane copolymers yield only the individual δp values of the homopolymers. From these results it appears as though this type of measurement is not sensitive to copolymer structure, i.e., random or block copolymer structure.
Proton Magnetic Resonance in Natural Rubber: Comparison with Dielectric Measurements
Authors: Kusumoto Hazime , Gutowsky H. S. 
Published: February 2011

Abstract
Proton magnetic resonance studies have been made of cured natural rubber containing up to 31 per cent combined sulfur. Line shapes and spin-lattice relaxation times were observed at temperatures between −190° and 180° C. In the line shape studies, the main effect of the combined sulfur was upon the temperature at which the line width is narrowed by the molecular segmental motions. The temperature at the onset of the major line width narrowing increases from −50° C for raw rubber to about 10° C for 31 per cent combined sulfur. A relation was found between the dependence upon sulfur content of the line width changes and the second-order transition temperature. The proton spin-lattice relaxation time T1 was measured for three cured samples in the temperature range above the motional narrowing region. The T1 vs. temperature curves agree qualitatively with the theory of Kubo and Tomita. The general features of the T1 curves are consistent with a distribution of correlation times which broadens with increasing sulfur content. Energies of activation were computed from these results and they are compared with the dielectric relaxation data obtained previously. The effect of a distribution of correlation time is discussed.
Characteristic Viscoelastic Parameters for Amorphous Polymers
Authors: Tobolsky A. V. , Takahashi M. 
Published: February 2011

Abstract
By use of a reference value of modulus equal to 109 dynes/cm2 and a reference value of time equal to 10 sec, characteristic viscoelastic parameters are defined from stress relaxation master curves and from modulus-temperature curves. Values of these parameters are tabulated for several linear amorphous polymers and slightly crosslinked amorphous polymers.