Studies of the Vulcanization of Elastic High Polymers. VI. The Vulcanization of Natural Rubber with Benzoyl Peroxide. Part 1

Abstract The vulcanization of natural rubber by benzoyl peroxide between 110° and 50° C has been investigated. The analysis of the kinetics has led to the following results: 1. The benzoyl peroxide concentration decreases at all temperatures according to a reaction of the first order. The velocity constants have been given. 2. Benzoic acid is formed in a slower reaction, but also according to a first order rate. The limiting value of benzoic acid formation depends on the temperature. It decreases with increasing temperature. The velocity constants for benzoic acid formation have been calculated. 3. With larger additions of peroxide to the rubber, both reactions are of the zero order as long as the solubility limit of the peroxide is exceeded. 4. The temperature dependence of the velocity constants of both reactions has been discussed, and it has been shown that at lower temperatures the formation of benzoic acid and the decrease of peroxide become equally rapid. 5. The analogy between thiuram vulcanization and peroxide vulcanization with respect to their kinetics has been pointed out. 6. It has been made apparent that, in both peroxide vulcanization and thiuram vulcanization, one is obliged to assume the formation of an intermediate compound. But, at the same time, it is not possible to make this consistent with the reaction mechanism which Farmer has developed for peroxide vulcanization, nor to apply to peroxide vulcanization the relationships found by Bartlett for the polymerization of allyl acetate by benzoyl peroxide.