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1. By using a redox system consisting of iron salts plus dimethylphenyl-paracresol, the rate of breakdown was considerably increased and structure-formation suppressed. This enables thermal oxidative plasticization to be used in industry for butadiene-acrylonitrile rubbers. 2. As the number of nitrile groups in the polymer increases, the rate of breakdown during thermal oxidative plasticization decreases and structure- formation occurs more rapidly. Butadiene-acrylonitrile (82:18) rubber has the greatest rate of breakdown, and the (60:40) copolymer the highest rate of structure-formation. 3. Vulcanizates of stocks based on thermally softened experimental butadiene-acrylonitrile rubbers are slightly inferior as regards strength and elasticity to similar vulcanizates of mechanically softened rubber. Their properties are, however, sufficiently high to enable thermal oxidative plasticization to be applied industrially.

1. The authors investigate the inhibited oxidation of SKN-18, SKN-26 and SKN-40 butadiene-acrylonitrile rubbers in a micro-oxidation apparatus at various temperatures. 2. It is established that the rate of inhibited oxidation of butadiene-acrylonitrile rubbers is determined by their nitrile group content. On increasing the amount of acrylonitrile in the polymer the rate of oxidation decreases. 3. The energy of activation of inhibited oxidation of butadiene-acrylonitrile rubbers (29 to 30 kcal/mole) is calculated according to the Arrhenius equation. The energy of activation of inhibited oxidation of SKN rubbers is 5 kcal/mole higher than the energy of activation of inhibited oxidation of SKS-30 rubber and 10 kcal/mole higher than that of SKB rubber. 4. The structural changes in SKN rubbers in inhibited oxidation are determined by their nitrile groups. For SKN-26 and SKN-40 the predominant process in all stages of oxidation is the process of crosslinking. In the case of SKN-18 the process of degradation predominates at the beginning, and in the later stages the process of crosslinking. 5. A correlation is demonstrated between the behavior of SKN rubbers in oxidation and in thermal oxidative plasticization.