Photopolymerization of free radical curing has the advantage over the heat curing as it allows continuous systems that are solvent-free, low temperature cure, and energy saving. The cure rate of coatings is a function of surface thickness, monomer reactivity and radiation intensity. When irradiated, the photocatalyst undergoes pi electron transition to the singlet state. This may stabilize at the triplet state, for a lifetime of >10-6 seconds. Free radical formation from the triplet state could occur by H-abstraction or by intramolecular splitting.
The majority of photocatalysts are energized by ultraviolet light. Camphorquinone is unique in that it creates free radicals by blue-light irradiation. It is best used with electron transfer accelerators such as animes or animes containing monomers, for example.