Mercaptoalkoxy-thioxanthones as a novel photoinitiator for free radical polymerization

The series of mercaptoalkoxy-thioxanthones, new group of photoinitiators for free radical polymerization, are synthesized and characterized. The kinetics of free radical polymerization was studied using a polymerization solution composed of either monomer (2-ethyl-2-(hydroxymethyl)-1,3-propanediol triacrylate (TMPTA)) and initiator (synthesized thioxanthone derivatives) for one-component photoinitiating system or monomer, initiator and co-initiator ( N -phenyl-glycine (NPG)) for two-component photoinitiating system. These compounds effectively initiate a acrylate polymerization. Based on the mechanism on the electron-transfer process and nanosecond laser flash photolysis experiments, we proposed sequence of reactions leading to the formation of radical species capable of initiating the chain reaction.