This paper presents the results of a thoroughly unorthodox approach to the synthetic rubber problem. In developing their new butyl rubber, the Esso Laboratories have turned to simple olefins rather than diolefins or more complicated chemical derivatives as the main raw material.
The present distinction between the thoughts expressed by the terms synthetic rubber and rubber synthesis is indicative of the changes in viewpoint on which current progress in the duplication of rubberlike properties is based. For almost fifty years after the discovery by Williams that isoprene is the fundamental structural unit of rubber, research was directed toward rubber synthesis. Bouchardat, Tilden, Wallach, Hoffman, Mathews, and Harries all made valuable contributions to the chemistry of rubberlike products from isoprene. That none of them accomplished the purpose of synthesizing rubber is an accepted fact. In the preparation of a rubberlike material from dimethylbutadiene, Kondakow departed from classical attempts at rubber synthesis, and laid the foundation for the first commercial “synthetic rubber”, the German wartime “methyl rubber”. The tradition that rubber properties were related to high unsaturation persisted, and has led to numerous theories of elastic behavior based on geometric structures resulting from unsaturated linkages. Whitby and Staudinger questioned the importance of unsaturation in determining rubberlike behavior, but encountered some difficulty in finding adequate support for this view, owing to the poor elastic properties of the practical examples available to them. Our studies on polymers of the simple monoölefins, which have been in progress for the past ten years, have led to some interesting conclusions in regard to this point. It was shown that high-molecular-weight linear polymers derived from simple olefins, such as the butylenes, possess a majority of the properties characteristic of rubber. Only the susceptibility to chemical action can definitely be attributed to the unsaturation of the natural rubber molecule. Physical properties which appear not to be intrinsically dependent on the carbon-double bond-carbon configuration are: tensile strength, elasticity, rebound, elastic memory, x-ray structure, mechanical orientation, electrical properties, and fractional solubility. It was, however, conclusively demonstrated that the saturated polymers are not capable of vulcanization in conventional manner.
INFLUENCE ON TIRE LIFETHE first scientific paper on Butyl rubber was presented at the 100th meeting of the American Chemical Society in September 1940 by Frolich. Since that time numerous publications (1-18) have described the properties and compounding technique of this polymer.Although Butyl has been referred to as a specialty rubber, it can also be used to replace natural rubber in many applications.Butyl was found to be a remarkable barrier to the passage of gases (10), in-
Until the last decade the explanation of those properties for which rubber is unique was confined largely to the study of rubber itself. Duplication of these properties involved the synthesis of polymers from isoprene and its immediate homologs. The discovery that chloroprene could be polymerized to a rubberlike substance altered the character of the study and represented a distinct departure in the type of diolefin used. The production of Thiokol, phosphonitrile, and the various vinyl polymers has resulted in the duplication of certain rubberlike physical properties by chemical structures wholly unrelated to rubber. Observation of the behavior of these newer elastics must lead to the conclusion that many physical characteristics of rubber are not inherent in the conformation of the rubber molecule alone. Whitby suggested that any general view of the structure of rubber can be regarded as acceptable only if it is applicable to other elastic colloids. Conversely, those properties of rubber which are not shared by other elastics must be explained by structural features not common to them all. A logical product to consider for the segregation of properties relating to the rubber structure per se and those capable of being shared by other molecules is hydrorubber. This substance has been observed to have certain “rubbery” properties, but unfortunately for comparison it has been prepared only in a degraded or low molecular weight form and therefore (from the standpoint of physical state) is not directly comparable with rubber.
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