Benzoin type photoinitiator for free radical polymerization

Benzoin, a popular photoinitiator for free radical polymerization of vinyl monomers, was improved by introduction of two methyl thioether substituents. This new benzoin derivative showed an about 50 times higher light absorption in the near‐UV spectral region and performed better than the unsubstituted benzoin in polymerization experiments 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 α‐cleavage mechanism (kα = 2.2 × 105 s−1) from the electronic triplet state with a quantum yield of 0.1 is the primary photoreaction to generate the initiating free radicals. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 This new benzoin derivative performed significantly better in photo‐polymerization experiments of bulk solutions or films of acrylate monomers than the unsubstituted benzoin, a popular photoinitiator. Studies suggest that a slow α‐cleavage mechanism from the electronic triplet state with a quantum yield of 0.1 is the primary photoreaction to generate the initiating free radicals.