Reactions of cumyl peroxide with polyisoprenes and polybutadienes are compared. Hydrogen abstraction from polyisoprenes and recombination of polymer radicals yield a network with crosslink concentration equal to that of decomposed peroxide. The concentration of crosslinks in polybutadiene networks is much greater than that of decomposed peroxide. Values of the ratio of these two concentrations as high as 50 have been calculated from swelling measurements of the vulcanizates. The polybutadienyl radical attacks double bonds in the polymer; thus crosslinks are formed by propagation. Infrared analysis shows that propagation proceeds via unsaturation in the main chain as well as via double bonds of vinyl side groups. The experimental relation between crosslink concentration and antioxidant concentration is consistent with a reaction scheme based on termination of polymer radicals by antioxidant only.

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