Effect of Vulcanization on Rubber Structure. A Problem in Probabilities

Abstract

Abstract In Goodyear's day, the problem of understanding the process of vulcanization could be expressed by the question: “Why does heating rubber with sulfur keep it from getting soft and tacky on a hot summer day, and hard and boardy in cold winter weather?” The deceptive simplicity of this question probably inspired the hope, which has come down almost to the present day, that the secrets of vulcanization and even of the elasticity of rubber could be explained in terms of the properties and reactions of simple organic molecules, such as the reactions of sulfur with simple olefins. The vast increase in the knowledge of giant molecules during the past decade has shattered any basis there may have been for such a hope, but occasional articles show that this desire for simplicity continues to live and to color our thinking on this problem. This paper discusses some of the inherent limitations of the old, simpler pictures of vulcanization and the structure of rubber, and some of the implications of the present view that crude rubber is built up of giant molecules. Probably there are not merely one or two or half a dozen reactions, but rather there are literally millions of possible vulcanization reactions, each of which may influence the physical properties of the rubber. The study of these reactions will require new and far more sensitive methods of physical and chemical analysis than have been available heretofore, as well as new points of view in interpreting the data.