Novel chemical-bonded polymerizable sulfur-containing photoinitiators comprising the structure of planar N-phenylmaleimide and benzophenone for photopolymerization

As a continuation of the research on chemical-bonded photoinitiators comprising the structure of planar N-phenylmaleimide (NPMI) and benzophenone (BP), three novel polymerizable sulfur-containing photoinitiator MTPBP, CMTPBP and BMTPBP were synthesized by introducing NPMI group into benzophenone (BP). BP was selected as the reference to evaluate their photoefficiency. These novel photoinitiators possess greatly red-shifted UV maximal absorption, and their fluorescence emission varies. Three representative types of different functionality monomers, methyl methacrylate (MMA), 1,6-hexanediol diacrylate (HDDA) and trimethylolpropane triacrylate (TMPTA), initiated by the three novel photoinitiators were studied through dilatometer and photo-DSC using unsaturated tertiary amine N,N-dimethylaminoethyl methacrylate (DMAEMA) as the coinitiator. The results show surprising high efficiency of these chemical-bonded photoinitiators towards different monomers in contrast to BP, and they can initiate photopolymerization without the coinitiator because of the photolysis at C–S bond. The results also verify that the higher viscosity of monomers and the larger molecular size of the photoinitiators may restrict the bimolecular H-abstraction reaction.