Photoinduced Thermal Polymerization Reactions

The combination of thermally induced and photoinduced free radical polymerization of (meth)acrylic monomers has only been scarcely presented in the literature. In this study, a two-component system with a near-infrared (NIR) dye combined with a thermal initiator is presented. The dye acts as a very efficient heat generator (heater) upon irradiation with NIR light. Several thermal initiators are presented such as an alkoxyamine (e.g., BlocBuilder-MA), azo derivatives, and (hydro)peroxides. The heat delivered by the dye dissociates the thermal initiator, which initiates the free radical polymerization of (meth)acrylates. Several types of heat generators are presented such as borate-based dyes and a silicon phthalocyanine derivative. For the first time, the effects of the NIR heater concentration, light intensity, and monomer structure on the heat released are studied using thermal imaging studies. NIR light curing is challenging but offers significant advantages: it is safer than shorter wavelength, and it allows a deeper penetration of the light and therefore a better curing of filled samples for a unique access to composites. Systems using a cyanine borate as a dye give high conversion rate of C═C for methacrylate monomer under air. Two wavelengths of irradiation are studied: 785 and 850 nm. The presence of additives (phosphines or iodonium salts) can also improve the polymerization profiles.