Curing of Fluoroelastomers by Peroxides

Abstract Peroxide-curable fluoroelastomers offer advantages in acid and steam resistance over their conventional counterparts. The peroxide-curability is provided by incorporating a bromine-based cure site in the vinylidene fluoride copolymers or terpolymers. The peroxide cure system comprises an aliphatic peroxide, an appropriate coagent, and an acid acceptor. The preferred coagent is triallylisocyanurate but other compounds having two or three olefinic groups attached to hetero atoms such as N, Si, or O are also effective. The concentration of the curesite monomer affects the rate, state, and stability of the cure. A cure mechanism is proposed in which the initiation step involves radical formation from peroxide decomposition and addition of the radicals to the coagent. Propagation involves the abstraction of bromine atoms from polymer molecules by coagent radicals to give fluorocarbon polymer radicals, which, in turn, add to coagent molecules to generate new radicals. This type of mechanism is supported by the cure characteristics, by the nature of the coagents, by analysis of the volatile by-products emitted during the cure, and by ESR data on model compounds.