Reaction rates of the antioxidants of amine derivatives with benzoyl peroxide (BPO), perbenzoic acid (PBA) and radicals originated from azobisisobutyronitrile (AIBN) in oxygen were investigated to estimate the reaction mechanism of the antioxidants. The observed rates of the reactions were plotted against the oxidation potentials of the amines.
As the results, the reaction rates of the amine derivatives with PBA and BPO had a maximum between 0.2 and 0.3 volt of the oxidation potentials of the amines, while the rates of the amines with AIBN in oxygen had a mximum near to 0.4 volt. The former is much similar to the relation between the effect of antiozonants and their oxidation potentials. The latter resembles the relation of the effect of antioxidants to their oxidation potentials. As reported in the previous papers, the former relation may be regarded as an ionic reaction of the amines. From the latter relation, it is assumed that the antioxidants react with peroxy radical of rubber to inhibit the reaction of the propagation.

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Influences of antioxidants on cure rate are investigated and discussed with respect to the efficiencies as antioxidants. As the results, the following facts are recognized; (1) The influences of phenolic compounds on cure rate are little in a curing system of 2-mercaptobenzothiazole with haxamethylene-tetramine. (2) Cure rate of cis-polyisoprene with dicumyl peroxide is much retarded by addition of phenolic antioxidants. (3) The retarding rate by phenolic compounds in peroxide cure system is correlated with the efficiency as antioxidants for sulfur vulcanizates. (4) The oxidation potentials of the effective phenolic compounds lie in about 0.7 V-SCE.
From these results, the radical reactivity of phenolic compound seems to be used as a measure for the estimation of antioxidant ability towards sulfur vulcanizates. The competitive reaction ratio of dicumyl peroxide with phenolic compound to rubber affords the antioxidant efficiency towards sulfur vulcanizate of cis-polyisoprene.

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