Oxygen mediated and wavelength tunable cationic photopolymerization reactions under air and low intensity: A new concept

A new concept which allows efficient cationic photopolymerization reactions under air, at any excitation wavelength in the UV-visible range and under low light intensities (conventional Xe lamp and/or laser diodes) is presented. It is based on the use of a versatile free radical promoted cationic process for the photoinitiation step which only requires a radical source, a silane and an usual iodonium salt and takes advantage of the presence of oxygen. The tunable character of the absorption is connected with the choice of the radical source. The oxygen enhancement is due to the particular role played by the silane. In every case, the silylium cation is the most efficient structure for the cationic ring opening reaction. Examples of the performance achieved (e.g. a conversion close to 100%) with such systems over the 390-580 nm range using various irradiation devices is shown and discussed.