Abstract
In searching for new vulcanizing systems for ethylene-propylene elastomers, we have found several more classes of active agents, heretofore undisclosed. They are: (a) perhaloalkanes and some polyhaloalkanes; (b) polyhalocycloalkenes; and (c) poly-N-halobenzoguanamines. Specific examples are: hexachloroethane, octachloropropane, octachlorocyclopentene, perchlorofulvalene, and N,N,N′,N′-tetrachlorobenzoguanamine. These agents are all effective in ethylene-propylene rubber, and some are capable of vulcanizing polyethylene, polypropylene, polyisobutylene, butyl, and highly unsaturated rubbers and their blends. The agents are most effective in the presence of sulfur. All are active in carbon black stocks, and at least some are active in mineral-filled and oil-extended stocks. Some of the vulcanizing agents can be accelerated by certain oxides and salts of metals widely distributed over the periodic system. Among the most active accelerators are iron compounds, such as iron tallate, stearate, naphthenate, octoate, and oxalate, and corresponding combinations of iron oxide and the free acids. These accelerators are antagonized by the presence of zinc oxide. The chemical diversity of these classes of vulcanizing agents and the complex behavior of the accelerators mentioned preclude an explanation of the vulcanization chemistry at this time.
