New pyridinium salts as versatile compounds for dye sensitized photopolymerization

A series of pyridinium salts were synthesized and investigated as new dyes for photoinitiating systems of polymerization. They exhibit a strong absorption at about 550 nm well matching with the visible light emission of different convenient visible light sources. Interestingly, very soft irradiation (halogen lamp) as well as laser diode exposure (457 and 532 nm) can be used. When employed in the presence of a silane and an iodonium salt, they efficiently initiate the free radical polymerization of acrylates and free radical promoted cationic polymerization of epoxides. An acrylate/epoxide blend is also easily polymerized i.e. for the synthesis of interpenetrating polymer networks. In combination with amine, the proposed dyes can also initiate free radical polymerizations. The mechanisms analyzed by ESR and photolysis experiments are discussed for the different multi-component initiating systems.