PHOTOSENSITIZER/PHOTOINITIATOR INTERACTIONS IN COPOLYMERIC SYSTEMS BEARING SIDE-CHAIN THIOXANTHONE AND ALPHA-MORPHOLINO ACETOPHENONE MOIETIES

Laser irradiation at 355 nm of copolymers obtained from 1-[(2-acryloyloxy)ethoxycarbonyl]thioxanthone with 1-[4-(2-acryloyloxyethylthio)phenyl]-2-methyl-2-morpholino-propan-1-one in toluene or 1,6-hexanediol diacrylate/n-butyl acrylate (1:1) solution, clearly indicates that the rate constant of excitation transfer from side-chain thioxanthone to alpha-morpholinoketone moieties is two orders of magnitude higher than that observed for the corresponding low-molecular-weight structural models mixture, such as 1-[2-isobutyroyloxy)ethoxycarbonyl]thioxanthone and 1-[4-(2-isobutyroyloxyethylthio)phenyl]-2-methyl-2-morpholino-propan-1-one. Evaluation of the efficiency of the above photosensitization process confirms that it is much higher in the copolymer systems. Photophysical and photoinitiation polymerization data suggest that the sensitization process mainly occurs through an energy transfer rather than an electron transfer mechanism, favoured by the forced close vicinity of the two photosensitive moieties attached to the same macromolecule.