Investigation of termination reactions in free radical photopolymerization of UV powder formulations

The termination mechanisms occurring in a UV powder coating system during photopolymerization process are investigated and compared to a conventional acrylate monomer system. The influence of the photoinitiator concentration, viscosity and conversion percentage of the monomer are assessed leading to the study of curing kinetics of a UV powder urethane diacrylate based system. It is shown that termination occurs mainly by bimolecular termination (PRT). This mechanism is related to low reactive double bonds concentration and high photoinitiator concentration in the UV powder system. Moreover, the effect of surrounding atmosphere points out the role of the oxygen on polymerization mechanisms.