dihydroxyperoxide u03b1 u03b1 39 bis tert butylperoxy p diisopro pylbenzene 2 5 dimethyl 2 5 di benzoylperoxy hexane tert butyl peroxyisopropyl carbonate etc in the peroxide vulcanization using the organic peroxide a polyfunctional unsaturated compound such as tri meth allyl isocyanurate tri meth allyl cyanurate triallyl trimellitate n n 39 m phenylene bismaleimide diallyl phthalate tris diallylamine s triazine triallyl phosphite 1 2 polybutadiene ethylene glycol diacrylate diethylene glycol diacrylate etc can be usually used as a crosslinking agent to obtain more distinguished vulcanization characteristics mechanical strength compression set characteristics etc a divalent metal oxide or hydroxide such as oxides or hydroxides of calcium magnesium lead zinc etc can be also used as a crosslinking aid if desired these compounds can also act as an acid acceptor the foregoing respective components for the peroxide vulcanization system are usually used in the following proportions to 100 parts by weight of the fluorine containing block copolymer about 0 1 to about 10 parts by weight preferably about 0 5 to about 5 parts by weight of an organic peroxide about 0 1 to about 10 parts by weight preferably about 0 5 to about 5 parts by weight of a crosslinking agent and not more than about 15 parts by weight of a crosslinking aid the foregoing respective components for the vulcanization system can be mixed and kneaded directly with the fluorine containing block copolymer or diluted with carbon black silica clay talc diatomaceous earth barium sulfate etc or used as a master.