Type 2 photoinitiators, primary reactions

The primary reaction of Type 2 photoinitiators is a hydrogen abstraction from the tertiary amine by a triplet excited ketone. The amino radical thus formed is sufficiently active to initiate the polymerization of vinyl monomers Scheme 2. 

The initiation process constitutes the first reaction step in free radical polymerization, leading to the generation of (primary) radicals. The kinetics of the initiation process, ie its rate and effectiveness, are of fundamental importance in both theoretical studies and commercial applications. Commercial procedures mainly rely on the formation of primary radicals via thermal decomposition processes using azo- and peroxy-type compounds. Investigative kinetic studies are— to a large extent—carried out using photoinitiators, which decompose upon irradiation with UV or visible light. The main reason for this choice is the possibility to define exact start and end times of the initiation and subsequently the polymerization process. 

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