Ethylene-Propylene Rubber Vulcanization with Aralkyl Peroxide and Coagents

Abstract Ethylene-propylene rubber (EPR) has been described in terms of its performance characteristics both by Prof. Natta and by the authors, who concur basically on its merits. Before such evaluations were possible, however, a difficult vulcanization problem was faced. The same paraffin inertness which is advantageous in the vulcanized product ruled out most of the conventional vulcanization technology. Work on the vulcanization problem at Hercules indicates that, with few promising alternatives, aralkyl and alkyl peroxides provide the best practical solution. This paper presents some conclusions and interpretations based on the exploratory work at Hercules on the EPR vulcanization process with dicumyl peroxide. The supporting evidence is derived mainly from crosslink density analysis by the solvent swelling method of Kraus. Special use was made of a “per cent gel” factor and of analysis of the sol fraction of incompletely cured vulcanizates. The copolymers described were prepared in Hercules laboratories.