Reaction of ozone with natural hevea and acrylonitrile‐butadiene rubbers

The physical changes that occur when ozone reacts with unvulcanized rubber or unstretched vulcanizates have been studied. The speed of reaction is controlled by diffusion of gas into the rubber; as a consequence, initial products formed near the surface are subjected to further action by ozone. To minimize this possibility experiments have been carried out with thin films of Hevea rubber and monolayers of Hycar OR‐15, and the products have been characterized by infrared spectroscopy. The results are considered in relation to observations on the ozonization of simpler compounds recorded in the literature. It is concluded that, during ozonization there is a spontaneous scission at the carbon‐carbon double band with the production of aldehyde and/or ketone and a peroxy biradical. The measurements show the presence of a reaction which is inhibited by 1% phenyl‐β‐naphthalamine and which is presumably a chain reaction. The nature of this chain reaction is discussed and it is shown that suppression of this reaction does not prevent the cracking of stretched vulcanizates. The suggestion is made that the characteristic feature of cracking is a reaction which takes place in a thin layer at the surface of the rubber.