Photoinitiation of cationic polymerization by visible light activated titanocene in the presence of onium salts

Abstract

A visible light photoinitiating system for cationic polymerization of cyclic ethers such as cyclohexene oxide (CHO) and vinyl monomers such as n-butyl vinyl ether (BVE) and N-vinyl carbazole (NVC) has been developed, using a fluorinated titanocene free radical photoinitiator, Irgacure 784, together with an onium salt, such as diphenyl iodonium hexafluoro antimonate and N-ethoxy-2-methyl-pyridinium hexafluoro-antimonate. Based on the reported photochemistry of fluorinated titanocenes, a mechanism for generating cationic species is proposed based on electron transfer between photoproducts of titanocene and onium salt. Evidence against the incorporation of an aromatic titanocene moiety in the resulting polymers is presented. Inhibition by a specific proton scavenger suggests that protons may initiate the polymerization.