NON-SULFUR CURE SYSTEMS
Elastomers with chemically saturated backbones cannot be crosslinked with sulfur and so require alternate curing agents. The most widely used are the peroxides, which are also used with unsaturated elastomers. Metal oxides or difunctional compounds are used in special cases.
Peroxides
Peroxides cure by thermal decomposition into oxy radicals, which abstract a hydrogen from the elastomer to generate polymer radicals. These then react to form carbon-carbon crosslinks. With unsaturated elastomers, this occurs preferentially at the site of allylic hydrogens. The rate of crosslinking is directly proportional to the rate of decomposition of the peroxide. Cure rates and curing temperatures therefore depend on the stability of the peroxide.
Although carbon-carbon crosslinks are more thermally stable than sulfur crosslinks, they provide generally poorer tensile and tear strength. Peroxides are also incompatible with many of the antioxidants used in rubber, since the antioxidants are designed to scavenge and destroy oxy and peroxy free radicals. Peroxides cannot be used with butyl rubber because they cause chain scission and depolymerization.
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