PHOTOPOLYMERIZATION OF MULTIFUNCTIONAL MONOMERS .6. INFLUENCE OF PHOTOSTABILIZERS

Time-resolved i.r. spectroscopy was used to investigate the kinetics of the light-induced polymerization of a polyurethane-diacrylate in the presence of u.v. stabilizers and HALS (radical scavengers containing sterically hindered piperidine groups). Oxanilide and 2-hydroxy-phenylbenzotriazole u.v. absorbers were shown to retard the polymerization and to decrease the hardness of the polymer formed. The dependences of the induction period and the polymerization rate on the photostabilizer concentration were examined in the 0.5-2% range for the two types of u.v. absorbers. HALS radical scavengers show no inhibition effect on these radical-induced reactions. This failure is probably due to the fact that the polymerization can only develop in an essentially O2-free medium, which will prevent the formation of the highly reactive nitroxy radical.