Vinyl polyperoxides degrade through two competing reactions, they pyrolyze unimolecularly through a chain unzipping process but they photolyze mainly through a disproportionation mechanism involving hydrogen transfer process. Surprisingly, in dilute solutions, we have observed that vinyl polyperoxides such as poly(styreneperoxide), poly(methylmethaclate peroxide), poly(alpha-methylstyreneperoxide) and poly(alpha-phenylstyrene peroxide) photolyze to give the same products which are obtained through the chain unzipping process. Still, the photodegradation mechanism seems to be different than the thermal degradation. While thermal degradation is controlled by the dissociation of the O-O bonds, the photodegradation depends upon the stability of the bialkoxy radicals. The poly(alpha-phenylstyrene peroxide), however, shows unusual thermal and photostability which has been explained from stable crystalline structure and retarding effect of the degradation product, respectively.