Organic peroxides (PO) are used as crosslinking (vulcanizing) agents. Free radicals generated from PO can abstract hydrogens from saturated rubbers such as polyethylene, ethylene-propylene-diene terpolymer and highly hydrogenated acrylonitrile-butadiene rubber to form intermolecular C-C bonds. The crosslinking using PO is effective for the improvement of heat resistance of rubber, and therefore, the technique becomes much important especially in automotive applications. The thermal decomposition rates, mechanisms and products for several kinds of PO are reviewed. Dicumyl peroxide (DCP) is a most typical and widely used crosslinking agent. However, acetophenone derived from DCP as a decomposition product sometimes causes a smell problem of rubber. α, α'-Bis (t-butylperoxy)-1, 3-diisopropylbenene is used as the substitute for DCP, because it has almost same activity as DCP and generates less smell products. The radical generation efficiency of 2, 5-dimethyl-2, 5-di (t-butylperoxy) hexane (HXA) is lower than that of 2, 5-dimethyl-2, 5-di (t-butylperoxy) hexyne-3 because of less hydrogen abstracting ability of the alkyl radical generated from β-scission of the intermediate t-alkoxy radical of HXA. t-Butylperoxy-2-ethylhexyl monocarbonate is low temperature active and has high hydrogen abstracting ability, and then it is used as the substitute for 1, 1-di (t-butylperoxy) cyclohexane.
