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 diaryliodonium 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.

► For cationic photocuring, low viscosity styrene oxide [StO] was used as a reactive diluents. ► Cationic photocuring tendency comprising epoxides was much improved by using StO. ► One step organic–inorganic hybridization by cationic photocuring in StO was achieved.