Abstract

The polymerization of methyl methacrylate photoinitiated by 2-chlorothio-xanthone in the presence of amines of different structures has been investigated. The photoinitiation efficiency of these systems is highly dependent on the structure of the amine. The polymerization rate increases with the amine concentration, reaching a constant value in an amine concentration range of 10-30 mM. At these amine concentrations, aliphatic hydroxyalkyl amines are more efficient photoinitiators than the corresponding alkyl-substituted compounds. Dimethylanilines with electron-acceptor substituents in the 4-position give higher polymerization rates than electron-donorsubstituted anilines. The photophysics of these photoinitiation systems has been studied in the polymerization medium. These data show that the singlet and triplet excited states of thioxanthones are efficiently deactivated by the amine. Rate constants are well correlated to the oxidation potential of the amine. These studies have allowed us to simulate the dependence of the photoinitiation efficiency with the amine concentration and indicate that the active radicals are produced from the interaction of the ketone triplet with the amine. Also, photochemical studies have allowed us to establish that the dependence of the polymerization rate on structural features of amines is mainly due to differences in the fraction of produced active radicals that add to the monomer. © 2002 Wiley Periodicals, Inc. J. Polym. Sci. Part A: Polym. Chem.