Enhanced cationic photocuring of epoxides with styrene oxide as a reactive diluent

Styrene oxide [StO] has been investigated as a reactive diluent for cationic photocurable formulations to provide key requirements such as low viscosity and negligible odor, in addition to high photoreactivity. The formulations were composed of commercial cyclic ethers including epoxides and oxetanes in StO using diarylioclonium salt as a photoinitiator, and they gave enhanced photocuring by analyzing with differential photocalorimetry. In particular, the cationic formulations composed of StO, bisphenol A diglycidyl ether, (3-glycidoxypropyl)trimethoxysilane and others rendered improved mechanical and thermal properties when their photocured coatings were examined. The gel content and pencil hardness values of photocured films were determined to evaluate the formulations. For the mechanistic explanation of the enhanced photoreactivity, the polymer-bound benzyl cations formed by a chain process in the polymer chains comprising StO moieties were postulated to serve as additional sites for the initiation of cationic photopolymerization of StO and cyclic ether monomers. (C) 2011 Elsevier B.V. All rights reserved.