Unimolecular fragmentation of type I photoinitiators

Benzoin and benzoin etbers /= 0 OH /= Q -r-o R methyl, ethyl, ethyl, isopropyl, n-butyl, isobutyl 

Hydroxyalkylphenones Phenylglyoxylates S-Phenyl thiobenzoates O-Acyl-a-oximo ketones 

In spite of the large number of available photoinitiators [4], the search for new initiators is ongoing. For example, S-(4-benzoyl)phenylthiobenzoate, BpSBz, has been found to be a type I photoinitiator. Upon exposure to light it is cleaved into free radicals (quantum yield 0.45), which initiate the polymerization of methyl methacrylate. In contrast, BpOBz (see Chart 10.1) is not cleaved. It forms a long-lived triplet state rather than free radicals [43]. 

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