Riboflavin triethanolamine as photoinitiator system of vinyl polymerization. A mechanistic study by laser flash photolysis

The polymerization of 2-hydroxyethyl methacrylate photoinitiated by riboflavin in the presence of triethanolamine was investigated. The polymerization was also studied using as photoinitiator lumichrome, the major product obtained in the anaerobic photoreduction of riboflavin. Photopolymerization rates were measured as a function of amine concentration in the UV (366 nm) and visible (>450 nm) regions. The quenching of the excited states of the dyes by triethanolamine was investigated by fluorescence lifetime and laser flash photolysis experiments. Quenching rate constants were determined in the absence and the presence of monomer. These rate constants and singlet and triplet lifetimes were used to fit the polymerization rate vs amine concentration curves. From the fitting it was concluded that the interaction of both singlet and triplet excited states with the amine led to the 2-hydroxyethyl methacrylate polymerization.