bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tetramethylthiuram Disulfide Vulcanization of Extracted Rubber. III. Short-Path Distillation of TMTD and Its Reaction Products from Rubber
Authors: Craig David , Juve A. E. , Davidson W. L. 
Published: February 2011

Abstract
During the course of this study we have found short-path distillation to be an especially useful procedure for separating volatile substances from macromolecular weight materials. For this reason and because the still which we have used most frequently has some rather novel features, it seems appropriate to devote the third paper of the series to a general description of our technique. Figure 1 is a schematic drawing of the still. Tube A is the heater tube, to the outside of which the samples in sheeted out form are attached by means of copper wire. The heater tube contains about 30 cc. of a liquid whose boiling point is the temperature at which the distillation is to be conducted. The liquid is boiled by an internal heating element regulated by means of a variable transformer. The leads H to the heating element enter through a rubber stopper in the upper end of the heater tube which is open to the atmosphere through flask G. For low-boiling heater liquids such as methanol, a condenser must be attached to the upper end of the heater tube. For the work described in the present series of papers, Cellosolve, b.p. 133° C, was used as the heater liquid. Tube B of Figure 1 is the condenser tube. Ordinarily, air cooling is sufficient to condense such materials as the usual rubber antioxidants, softeners, accelerators, fat acids, sulfur, etc. For special purposes, tube B is cooled by wrapping it with rubber tubing through which tap water was circulated or it is cooled with dry ice. The gap of this still, i.e., the distance from the heater tube to the condenser tube, is about 2 cm. The U-tube C, made of 1.25-inch glass tubing, constitutes a trap. It usually has been cooled with dry ice and acetone in I. That U-tube is connected to a booster pump D through a second dry-Ice trap. The pressure usually used has been less than 0.01 mm. and has been measured by a McCleod gage attached to E below the dry ice trap F. Where higher pressures have been used, the vacuum source has usually not included the booster pump.
Molecular Structure of Styrene-Butadiene Copolymers. Dynamic Mechanical Measurements
Authors: Nielsen L. E. , Buchdahl Rolf , Claver G. C. 
Published: February 2011

Abstract
The dynamic shear modulus, mechanical damping, swelling properties in benzene, and infrared spectra have been determined on a series of styrene-butadiene copolymers which were prepared under a variety of polymerization conditions. Evidence is presented which indicates it may be possible to prepare a poly-butadiene rubber which retains its rubberlike properties down to −120° C. Materials of the same overall composition were often found to differ greatly in structure as determined by these experimental methods. Many of these differences can be explained in terms of various types of heterogeneity found in the copolymers. The temperature of maximum mechanical damping is primarily determined by the composition of the copolymer, whereas the width of the damping peak is related to the heterogeneity of the material. The work reported here is part of an investigation of the differences in physical properaties of polymers of like composition that occur as a result of changes in polymerization conditions.
Butadiene-Styrene Resinous Copolymers
Authors: D'Ianni J. D. , Hess L. D. , Mast W. C. 
Published: February 2011

Abstract
Although high-styrene resins have become of great commercial importance during the past 5 years (approximately 25,000,000 pounds manufactured in 1949), comparatively little information on the polymerization processes or any systematic review of their properties can be found in the technical literature. The object of the present paper is to supply such information. A series of butadiene-styrene copolymers with charging ratios of 50/50, 40/60, 30/70, 20/80, and 10/90 was prepared. Polystyrene, prepared under the same conditions, was included as a control. Properties of the latexes and resins obtained, presented in a systematic manner, were found to be largely dependent on the monomer ratio employed in the polymerization. for the first time a coherent picture is presented of the entire plastic range of the styrene-butadiene resins. This should encourage the further development of this large and expanding field, which includes such applications as natural and synthetic rubber reinforcing, impact resistant compositions, protective coatings, and latex paints.
Polysulfide Polymers
Authors: Fettes E. M. , Jorczak J. S. 
Published: February 2011

Abstract
The chemistry of the condensation polymerization is reviewed briefly. The structures of the polymeric products as well as the effects of copolymerization, cross-linking, end groups, and molecular weight upon polymer properties are discussed. The composition and properties of the commercial crude rubbers, water dispersions, and liquid polymers are presented together with ideas on the mechanism of their vulcanization. The reason for the odor of polysulfide polymers is discussed. Some information is presented on solvent resistance, stress relaxation, and other characteristics of the polymers. Applications for the different types of products are summarized.
The Rubber Hydrocarbon in Freshly Tapped Hevea Latex
Authors: Bloomfield George F. 
Published: February 2011

Abstract
The rubber hydrocarbon in latex as it leaves the tree is already a high polymer, with a broad distribution of molecular weight ranging from several millions to below 100,000, with the major part of the hydrocarbon in the higher molecular weight ranges. Changes in the hydrocarbon subsequent to its leaving the tree tend to be degradative, but may also involve cross-linking reactions leading to changes in plasticity. Structural changes in rubber attributed to restricted cross-linking have a greater influence on plasticity than on solution viscosity. A gel component (probably microgel) present in the freshly tapped hydrocarbon is of considerable importance in determining the hardness of raw rubber, but greatly complicates the interpretation of viscometric data, of which evaluation by the equation: [η]=5.02×10−4 M0.67 only appears to be valid for gel-free rubber fractions. Plasticity and intrinsic viscosity cannot, therefore, be generally correlated, although the plasticity is influenced by the spread of the molecular-weight distribution into lower molecular weight regions. The presence of a high proportion of microgel in latex of untapped trees and of branches remote from the tapping panel of trees in regular tapping, and the presence of combined oxygen in the low-molecular fractions of rubber hydrocarbon obtained from both normal and microgel latexes may be of interest in connection with questions of biosynthesis and metabolism of the rubber hydrocarbon of Hevea brasiliensis.
The Application of Rubber in the Quantitative Determination of Ozone
Authors: Bradley C. E. , Haagen-Smit A. J. 
Published: February 2011

Abstract
A convenient rubber cracking test for ozone is described. This method serves not only as a rapid, positive means of identifying ozone in complex gas mixtures but also gives close approximation to the quantity present. Application of the method in determining ozone in heavy smog atmosphere is shown. The high ozone concentration in these tests is attributed to ozone formation under the catalytic action of nitrogen oxides and sunlight.
Radical Mechanisms in Saturated and Olefinic Systems. II. Disubstitutive Carbon-Carbon Cross-Linking by Tertiary Alkoxy Radicals in Isoprenic Olefins and Rubber
Authors: Farmer E. H. , Moore C. G. 
Published: February 2011

Abstract
The high degree of dehydrogenation effected by tert.-butoxy radicals at the α-methylenic groups of olefins enables these radicals to be used for the carbon-to-carbon cross-linking of unsaturated carbon chains, and especially of the polyisoprenic chains of natural rubber. Such cross-linking amounts to a vulcanization process in which the connecting links between chain molecules are just C—C bonds, which may be expected to have appropriate attributes. An examination has first been made of the cross-linking produced by tert.- butoxy radicals (from di-tert.-butyl peroxide) at 140° between the short iso-prenic chains in 1-methylcyclohexene, 4-methylhept-3-ene, 2,6-dimethylocta-2, 6-diene, and digeranyl. Cross-linking proceeds efficiently in each case, and the points of union in these isoprene units which become directly joined are not confined to original α-methylenic carbon atoms. Where the reagent radicals are in considerable deficit, e.g., one per two or three of the isoprene units present, those olefin molecules which are attacked become linked together mostly by single unions to form aggregates containing two, three or four molecules; but in the tetraisoprenic olefins the extent to which more than one union is formed between some of the directly linked molecules becomes appreciable. In natural rubber, cross-linking occurs smoothly and to nearly the full extent corresponding to the (in practice restricted) proportion of peroxidic reagent employed. Good vulcanizates can be so obtained in which the tensile stength is found to increase towards a maximum and then to decline rapidly as the degree of cross-linking steadily increases. Thus to obtain vulcanizates of the optimum physical characteristics, the degree of cross-linking must be suitably chosen. The role of the peroxidic reagent is almost entirely non-additive and non-degradative.
The Effect of Sulfur on the Oxidation of Sodium-Butadiene Rubbers
Authors: Kuzminskii˘ A. S. , Degteva T. G. , Lapteva K. A. , Lezhnev N. N. 
Published: February 2011

Abstract
In the vulcanization of rubber and in the service performance of vulcanized rubber products, oxygen and free sulfur are always present. Consequently it is important to know the effect of sulfur on the oxidation of rubber. The present work is devoted to an investigation of the oxidation of a sodium-butadiene polymer in the presence of sulfur. Dogadkin and his associates established the fact that oxygen has an influence on the nature of the structural changes of rubber during vulcanization. The present authors have shown that any sulfur which is chemically combined with rubber does not appreciably affect the kinetics of its oxidation, and that free sulfur, in solution in rubber, interferes with autocatalytic oxidation. The higher the concentration of sulfur, the greater is this interference (see Figure 1). Introduction of sulfur into rubber during autocatalysis does not prevent the autocatalytic process, but hinders it noticeably (see Figure 2). The introduction of a secondary aromatic amine has been observed to arrest the process altogether. This behavior of sulfur can be explained by its ability to react with intermediate oxidation products, since the rate of combination of sulfur is practically constant (see Figure 3).
Elastic Modulus and Swelling of Butyl Vulcanizates. Influence of Fillers
Authors: Zapp R. L. , Guth Eugene 
Published: February 2011

Abstract
The reinforcing of elastomeric vulcanizates by filler particles has been studied with Butyl rubber, a polymer of limited unsaturation. This limited unsaturation enables a comparison to be made of filler reinforcement in materials having a constant concentration of chemical cross-links, because excess curing agents can be added without increasing the state of cure byond a certain limit. Under such conditions differences in the adsorptive powers of fillers do not result in variations in the ultimate state of vulcanization. Reinforcement in this paper was defined as the ability of a pigment to enhance the elastic or equilibrium stress (at constant elongation) of a vulcanized specimen. Equilibrium stress at 50 per cent elongation was determined on a triple-beam balance, and the internal energy and entropy components of stress were determined. The entropy component of stress was found to conform more closely to the classical viscosity analog equation for reinforcement, where only the volume concentration of filler and not the surface area is the controlling factor. It was observed that carbon blacks, especially those of finer particle size, produced a greater internal energy contribution to stress than did mineral fillers, which appeared as a function of the total pigment surface added. The increase in stress observed with mineral fillers was due largely to entropy contributions. Another manifestation of reinforcement was shown to be the restriction of volume swelling of a network (in a good solvent) in the presence of pigments. Carbon blacks showed the greatest restriction of swelling capacity, and in distinction to stress behavior, this restriction was solely a function of the total surface area of carbon black present, regardless of type. With mineral fillers, far less restriction was observed, and in one case an increase in swelling was noted. This can be attributed to poor bonding, which results in voids. The photomicrograph of clay particles in a thin stretched section of Butyl shows this effect in Figure 21. The role of surface forces in the case of carbon blacks has been further demonstrated through measurements of the elastic properties of swollen rubber. The reinforcing nature of carbon black is maintained in a swollen network, while the weak bonds between the polymer and a mineral filler are destroyed when the chains are separated by the imbibed solvent, and the stress then approaches that of an unloaded compound.
Statistical Kinetics of Hevea Rubber Cyclization
Authors: Gordon M. 
Published: February 2011

Abstract
Rubber cyclization provides a useful illustration of statistical effects intervening in the reactions of long-chain polymers. Analogously to known cyclizations of simple diisoprenic terpenes, each individual cyclization act links two adjacent isoprene units in the rubber chain into a six-membered ring. However, some of the units remain stranded between neighboring rings and escape cyclization for want of a partner. Thus the final polymer has a copolymer structure of 86.5 per cent of diisoprenic rings and 13.5 per cent of uncyclized monisoprenic units. This result is derived from a statistical theory of Flory, and has previously found accurate experimental verification. The bearing of this statistical effect on the reaction kinetics has now been studied for the first time. Dilatometric experiments on rubber emulsions in sulfuric acid have shown that the cyclization reaction conforms in the main with a statistical cyclization law much better than with a first-order equation uncorrected for the survival of stranded units. High accuracy was required for this experimental distinction, whose importance lies in the implicit proof that the polymer units participate in the rate-determining transition complex, in accordance with the accepted proton transfer mechanism. A kinetic proof has incidentally been furnished for the fact that the rubber polymer contains long chains of identical units. When handled by an emulsion technique, this polymer can provide a useful “model compound” for its simpler terpene analogs. Certain rate abnormalities have been observed, including an induction period of reduced rate, probably connected with diffusion effects. A small volume change subsequent to the cyclization reaction may reflect a prototropic double-bond shift. The activation energy and entropy are found to be lower than in previous work, an effect traced in part to a curvature of the Arrhenius plot. The known dependence of cyclization rate on Hammett's acidity function H0 is quantitatively confirmed.
Modern Views on the Chemistry of Vulcanization Changes. I. Nature of the Reaction between Sulfur and Olefins
Authors: Farmer E. Harold , Shipley F. W. 
Published: February 2011

Abstract
At the present time it is taken for granted that in all kinds of linear high polymers, natural or artificial, true polymers or polycondensation products, the establishment of cross-links between adjacent thread molecules is in itself sufficient to transform the physical properties of the material, producing a state which can be collated with the vulcanized state in rubber. Yet in most of these instances—and particularly in the case of vulcanization of natural and synthetic rubbers by sulfur, by peroxides, and by other reagents—the idea that the vulcanized products with their characteristic toughness, swelling capacity, elasticity, etc., derive their special qualities from the mere formation (by one means or another) of connecting links between the original linear molecules still remains a matter of hypothesis. The sulfur-vulcanization process as applied to rubber presents many interesting and very elaborate features, especially those connected with its capacity for being accelerated by a host of similar and dissimilar organic substances, and for being retarded, reversed, delicately controlled, etc. Hence, it is of considerable interest to find out by experiment exactly what sulfur does to the rubber when the two are heated together (either alone or in the presence of different types of accessory reagents) and, thence, to discover whether the production of good vulcanized properties actually depends on the production of chemical cross-links, or on certain kinds of chemical cross-links, or on a judicious combination of cross-linking and mere sulfuration (the latter possibly assisting the establishment of van der Waals forces between molecules as an auxiliary factor) ; or whether, as some physical chemists have been inclined to allege, it results from a state of physical association between molecules which has little or nothing to do with cross-linking. The present series of communications describes recent experimental advances in this subject; it is necessary to explain at the outset that the method of experimental approach adopted has of necessity, owing to the formidable molecular magnitude of even unvulcanized rubber, been by way of the response to vulcanization treatment of comparatively simple olefinic compounds. This approach has thus involved in the first place a study of the chemistry of simple sulfur-olefin reactivity, which was previously never carried far.
Modern Views on the Chemistry of Vulcanization Changes. II. Role of Hydrogen Sulfide
Authors: Naylor Ralph F. 
Published: February 2011

Abstract
1. The normal addition of hydrogen sulfide to olefins is catalyzed by very small proportions of sulfur, but the rate of addition is too slow to provide a satisfactory basis for the hydrogen sulfide-actuated mechanism of vulcanization. 2. The main products of the sulfur-catalyzed (polar) reaction of hydrogen sulfide with polyisoprenes are substituted pentamethylene sulfides, derived by intramolecular normal addition of the initially formed monothiols. 3. The main products of the ultraviolet light-catalyzed (radical) reaction of hydrogen sulfide with polyisoprenes are monothiols and substituted pentamethylene sulfides, the latter derived by intramolecular abnormal addition. 4. The resemblance of the cyclic sulfides obtained by reaction of free sulfur with polyisoprenes to the products of polar hydrogen sulfide addition (as opposed to the products of the radical-type addition) supports the hypothesis that, in the sulfur-olefin reaction, the radical reaction chain is terminated by the capture of a hydrogen atom by an RS* radical, the thiol so formed adding intramolecularly in a polar reaction catalyzed by sulfur.
Peroxidation in Relation to Olefinic Structure
Authors: Farmer E. Harold 
Published: February 2011

Abstract
The process of autoxidation among olefinic substances comprises two major phenomena, that of the incorporation of molecules of oxygen (peroxidation), and that of secondary change (peroxide breakdown) during which the peroxide groups formed by this incorporation act as oxidizing agents for adjacent unsaturated centers. Interest may, accordingly, be directed towards two quite distinct but composite themes, viz. : (1) the nature of the mechanism by which the oxygen molecules are incorporated, the positions they take up in different kinds of organic molecules, and the effect of their introduction in causing (or not causing) specific types of molecule-linking, and (2) the inherent stability or instability of the peroxide groups in different molecules and its structural cause, the mechanism of breakdown of the peroxidic groups and the way this is influenced by light, heat, or catalytic influences, and finally the manner of utilization of the “active” oxygen given up by the decomposing peroxide groups in forming (by inter- or intramolecular reaction) new oxygeno-groups or, alternatively, in bringing about some small or large degree of scission of the carbon chains. Wherever the peroxido-olefins have a moderately high degree of stability, and they are consequently isolable in tolerably pure condition, no serious difficulty attends the systematic study of their thermal, photo-, or catalyzed decomposition, although as yet but little systematic work has been done in this field : but where their degree of unstability is very high, deductions concerning the character of the peroxido-olefinic structures produced and of their breakdown mechanisms have to be made (at any rate in the first place) from the nature of the secondary autoxidation products actually isolated in practice, and there is then grave danger of erroneous conclusions being drawn. Of course, many autoxidation products are extremely complex in character, and where this is the case the difficulty of correlating breakdown products with their peroxidic precursors is greatly increased. Therefore in prosecuting autoxidation studies, especially those directed towards determining the mechanism of reaction, it is very desirable to have as general guide a detailed knowledge of the structure and breakdown behavior of all the various distinctive types of organic peroxide which are capable of existence, and the following survey represents in the main a contribution in this direction.
Friedel-Crafts Catalysts and Polymerization
Authors: Evans A. G. , Meadows G. W. , Polanyi M. 
Published: February 2011

Abstract
In an earlier communication, evidence was given on which the following conclusion was based. In the dimerization of diisobutene and the polymerization of isobutene, it is essential that a trace of some third component, X, shall be present in addition to the monomer and the Friedel-Crafts catalyst, in order that the reaction shall proceed at an appreciable rate. It was suggested then that this third component was probably water. We have continued this line of investigation by studying the boron trifluoride-catalyzed polymerization of isobutene in the gas phase, using high-vacuum technique. The polymerization reaction was followed by mixing the boron trifluoride and the isobutene in the gas phase and measuring the fall in pressure with time. We may summarize the results as follows: