PHOTO-CROSS-LINKING STUDIES OF S-ACRYLOYL O-ETHYL XANTHATE COPOLYMERS

S-Acryloyl O-ethyl xanthate was copolymerized with styrene and methyl methacrylate, giving rise to copolymers containing the photoactive acyl xanthate chromophore. Thin films of these copolymers, on irradiation, undergo phototransformations leading to crosslinked polymers. The photocrosslinking yield of the copolymers depends mainly on their molecular weight and not on the composition of the copolymer. The mechanism of photocrosslinking was investigated through nanosecond laser flash photolysis studies. The 308 nm laser pulse excitation of the copolymers in benzene produces radical intermediates, arising through a C(=O)-S bond fission. The assignment of the photogenerated (ethoxycarbonylthiocarbonyl)thiyl radical is based on its characteristic long wavelength absorption maximum (lambda(max) approximately 660 nm in benzene), ready quenching by nitroxy radicals and similarity in spectra and kinetics with those of the radical transient, photogenerated from the model substrate, S-isobutyryl O-ethyl xanthate.