Use of C14 Tagged Cumyl Peroxide to Study Peroxide Vulcanization of Ethylene Propylene Copolymers

Peroxides are used today as crosslinking agents for elastomers in general, and for saturated elastomers in particular. Among peroxides, cumyl peroxide merits special attention because of the small danger in handling since it decomposes appreciably only above 120–130° C. The mechanism of the vulcanization reaction has been considered very simple, leading to the formation of carbon-to-carbon bonds between polymer molecules. The path of the reaction can be followed if one can determine at every instant the amount of crosslinking and of peroxide decomposition products, or the quantity of residual peroxide. From the existing literature, it appears evident that the degree of crosslinking in natural rubber and the recovery of peroxide fragments justify the reactions proposed in the chemical scheme. However, in the case of ethylene propylene rubber these lead to the conclusion that the peroxide is only partly used. This different fate of cumyl peroxide, depending on whether the decomposition occurs in natural rubber or in an ethylene propylene copolymer, demonstrates that other reactions occur, which involve primary peroxide radicals or the secondary polymeric radicals, or both, in a manner different from the proposed scheme.