A Study of the Mechanism of Phenol and Amine thiols as Antifatigue Agents by ESR

Abstract

The reaction of 4-mercaptoacetami dodiphenylamine (MADA) with natural rubber latex in the presence of a free radical redox system consisting of tert-butyl hydroperoxide /tetraethylenepentamine has been investigated. A colormetric method has been used to estimate the concentration of the bound MADA. Oxygen absorption and stress relaxation measurements have been used to evaluate the antioxidant activity of bound MADA both before and after extraction with an organic azeotropic mixture. The antiozonant and antifatigue activity of bound MADA have also been determined and it is found that fully extracted rubbers containing this entity are quite resistant to ozone cracking. Mechanistic investigations have been carried out on the nature of the chemical bonds in cross-linked rubber that break under the influence of mechanical stress, and on the way in which a commercial antifatigue agent, 4-iso-propy1-4-pheny1--p-phenylenediamine (IPPD), inhibits the mechanodegradation of natural rubber vulcanisates. A diarylnitroxyl radical derived from IPPD has been shown to be formed during fatigue and to be regenerated continuously during fatiguing by a cyclic mechanism involving the corresponding hydroxylamine. The antifatigue activity of hindered phenols particularly those containing sulphur and the mechanism involved in their antifatigue activity in natural rubber vulcanisates has also been studied.