Cross-linking-chain scission problems

The main problem is related to exposure of these materials to high temperatures in the presence of oxygen. These conditions favor the oxidative degradation of the elastomer, which leads to opposing changes in its structure. On the one hand, chain scission can occur, and on the other hand, cross-links can be generated. If chain scission dominates, the hardness and modulus of the elastomer will decrease. If, however, cross-links are generated, both the hardness and the modulus increase and the strain at fracture will decrease. Other mechanical properties are altered by an increase in... 

The reaction cycle discussed so far consumes oxygen and converts it to hydroperoxides on the polymer chain. If this were the only set of reactions, it would not cause much trouble, except in applications involving high frequency electrical fields, where the introduction of polar groups has deleterious effects on dielectric losses. The real problem is that side reactions of radicals can cause chain scission and cross-linking. 

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