Thioxanthone photoinitiator containing polymerizable N-aromatic maleimide for photopolymerization

A novel polymerizable free radical photoinitiator, 2-maleimidethioxanthone (MTX), was synthesized by introducing directly maleimide (MI) group into the molecule of thioxanthone (TX). N-methyldiethanolamine (MDEA) was chosen as coinitiator for TX, TX/N-phenylmaleimide (NPMI) and MTX. FT-IR and 1H NMR confirm the structure of MTX. UV–vis spectra of the three photoinitiators are similar and both exhibit the maximal absorption about 390 nm. Fluorescence spectra show MTX/MDEA has lower fluorescence intensity than the other two systems. The photopolymerization of trimethylolpropane triacrylate (TMPTA), initiated by TX/MDEA, TX/NPMI/MDEA, and MTX/MDEA systems, was studied by differential scanning photocalorimetry (photo-DSC). The results show that MTX/MDEA is much more efficient than TX/NPMI/MDEA and TX/MDEA, and TX/NPMI/MDEA is more efficient than TX/MDEA, due to the synergistic effect between TX moiety and maleimide group. Meanwhile, MTX also enjoys the unique advantage of being consumed during polymerization, which will certainly reduce the migration of the species.