Crosslinking of natural rubber by dicumyl peroxide in the presence of oxidation inhibitors

A number of phenols, simple and N‐substituted aromatic amines, thioamides, and thioanilides which are known to inhibit free radical reactions have been introduced into dicumyl peroxide–natural rubber cures, and their influence upon the degree of crosslinking has been determined. A simple kinetic scheme allows a calculation of the relative reactivities of these additives and the values obtained are compared with those of other workers for the same additives but in different systems. It is concluded that the additives interfere with the crosslinking reaction by exchanging a hydrogen atom with the free radicals involved, and the sequence of reactivities is readily explained in terms of current theories for the effect of substituents upon the reactivity of organic compounds. Types of materials likely to be useful as antioxidants in dicumyl cures are discussed.