A novel thioxanthone-hydroxyalkylphenone bifunctional photoinitiator: Synthesis, characterization and mechanism of photopolymerization

A novel bifunctional photoinitiator (named as TX-EG-IPDI-2959) with thioxanthone and hydroxyalkylphenone moieties was synthesized by the reaction of isophorone diisocyanate with Irgacure 2959 and 2-(2-hydroxyethoxy) thioxanthone. The molecular structure of TX-EG-IPDI-2959 was characterized by 1H NMR, high-resolution mass spectroscopy, UV–vis and FT-IR. The photochemical behavior of TX-EG-IPDI-2959 was investigated through the photolysis and polymerization of butyl acrylate by UV–vis and HRMS. Compared with the combination of Irgacure 2959 and 2-(2-hydroxyethoxy) thioxanthone, the CC bond cleavage of hydroxyalkylphenone to produce free radical fragments was effectively done under the irradiation of visible LED light. The obvious intramolecular synergistic effect between the hydroxyalkylphenone and thioxanthone moieties has been confirmed based on HRMS analysis of photobleach and photopolymerization. In addition, the photopolymerization kinetic of an UV gel and trimethylolpropane triacrylate initiated by TX-EG-IPDI-2959 were also investigated. The plausible photochemical reaction mechanism of TX-EG-IPDI-2959 was proposed.