Mechanistic studies of thioxanthone-carbazole as a one-component type II photoinitiator

A mechanistic study concerning photoinitiated free radical polymerization using Thioxanthone-Carbazole (TX-Cz) as a one-component Type II photoinitiator was performed. TX-Cz presented visible initiator characteristics with absorptions at 434 and 414 nm where the molar absorption coefficients were 2014 and 1754 L mol−1 cm−1, respectively. Fluorescence and phosphorescence spectroscopy, as well as laser flash photolysis was employed to study the photophysical properties of TX-Cz. In addition, photopolymerization of methyl methacrylate (MMA) showed that TX-Cz is efficient photoinitiator. To explain the initiation mechanism of TX-Cz, fluorescence and phosphorescence emission spectra of poly (methyl methacrylate) (PMMA) were also taken to see whether the initiator covalently bonded to the polymer. The postulated mechanism is based on inter- molecular reaction of the triplet, 3(TX-Cz)⁎ with the carbazole moiety at ground state, TX-Cz. The photoinitiation efficiency of TX-Cz during gelation of multifunctional acrylates was also investigated by Photo-Differential Scanning Calorimetry (Photo-DSC) technique and high polymerization rates were obtained.