The Reaction of Molecular Oxygen with Rubber

It is nearly a century since Hofmann and Spiller made the first recorded experimental observations linking oxygen with substantial changes in polyisoprenoid hydrocarbons. In the first sixty-odd years following this work technological progress was slow, but certain characteristic features of the oxidation reaction were observed. It was firmly established that oxygen played an important role in the deterioration of rubber and rubber products with the passage of time, and the accelerating effects of exposure to light or to elevated temperatures were realized. Within a short additional period a very nearly complete solution to the problems of oxygen aging was obtained with the discovery of efficient vulcanization methods and of effective antioxidants. These discoveries made possible the transition of rubber from a relatively expensive, short-lived material of commerce to its present position of a high-volume, low-cost, essential ingredient of our everyday life. Since that period technological progress has consisted in steady refinements of these important discoveries. During these years many observations necessary for understanding the chemistry of the oxidation process were accumulated, but it was necessary to wait for two fundamental developments in order to obtain a complete explanation of the reactions occurring during the reaction of rubber with oxygen. These were, first, a clear realization of the high molecular character of the rubber hydrocarbon and the effect of this on its macroscopic properties, and-second, the work on oxidation of low molecular weight olefins which forms the basis for inferring the nature of steps in the oxidation of rubber inaccessible because of experimental difficulties. Since both of these developments have been made it is quite probable that we shall know in complete detail the reaction sequence in rubber oxidation before the centennial of Hofmann's paper is reached.