A review on self-initiated and photoinitiator-free system for photopolymerization

Photopolymerization is a polymerization reaction where a light source provides energy for the formation of active species and further follows the conventional polymerization process. This polymerization technique has recently gained interest because of its high curing rate, lower energy consumption, low volatile organic component and relatively low cost. In such a system, the photoinitiator is a vital component as it governs the curing rate. It is a chemical substance that absorbs the radiation and forms reactive species that further attacks the monomer and leads to the photopolymerization reaction. The photoinitiators employed are expensive, oxygen-sensitive, possess pungent odour and migrate to the film surface, resulting in yellowing and degradation of the polymeric system. Thus, it is a requisite to decrease the concentration of a photoinitiator in a particular system. The paper briefly discusses alternate methods for conventionally photoinitiator-based photopolymerization, such as short-wavelength sources, unique monomers such as electron acceptor/donor system, thiol-ene system and specific particles.