Mechanism of the Action of Inhibitors of the Oxidation of Elastomers

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Abstract
A number of works have been published in the recent scientific literature concerning the action of antioxidants in elastomers. Most of these works are of an empirical nature and are of purely practical value. In certain foreign works, unsuccessful attempts were made to relate the effectiveness of action of antioxidants with one of their specific properties, for example, with their oxidation-reduction potential. The mechanism of inhibited and of free oxidation of elastomers was studied in detail by one of the present authors. Based on a theory of chain reactions, Semenov concluded that the oxidation of rubber involves a chain degradation process, and he showed that the inhibitor, phenyl-β-naphthylamine, breaks the oxidation chains, reacting with the peroxidic radicals which are formed in the rubber molecules during oxidation. The inhibitor is consumed by union with the hydrocarbon molecule. Consumption of inhibitor during heat treatment of rubber is observed only in the presence of oxygen. In the light of our theories of the oxidation of rubber, and also on the basis of contemporary theories of the activity of radicals, according to which the more active molecules in the radical reactions form less active radicals, and vice versa, the mechanism of the action of inhibitors can be described as follows. The peroxide radicals of the rubber detach the more active or mobile hydrogen from the inhibitor molecule, and the radical formed as a result of this reacts with the rubber radicals, breaking the oxidation chains.

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