Benzoin Type Photoinitiator for Free Radical Polymerization

ABSTRACT: Benzoin, a popular photoinitiator for free radical polymerization of vinyl monomers, was improved by intro-duction of two methyl thioether substituents. This new ben-zoin derivative showed an about 50 times higher light absorption in the near-UV spectral region and performed bet-ter than the unsubstituted benzoin in polymerization experi-ments in bulk solutions or films of acrylate monomers when low initiator concentrations are used. Laser flash photolysis, low temperature luminescence experiments and photoproduct studies by mass spectrometry suggest that a slow a-cleavage mechanism (ka 2.2 105 s1) from the electronic triplet state with a quantum yield of 0.1 is the primary photoreac-tion to generate the initiating free radicals. VC 2013 Wile