Photoinitiators and photoinitiation - Part 15. The photodecomposition of some [Z] O-sulphonyl 2-oximinoketones and some [Z] O-sulphamoyl 2-oximinoketones

The photodecomposition of some [Z]-O-sulphonyl 2-oximinoketones is studied by ESR spectroscopy At low temperatures (T < -70 degrees C), alpha-ketoiminyl radicals are observed, indicative of initial N-O bond cleavage, implying that O-sulphonyl land O-sulphamoyl) fragments are split off as sulphonyloxy land sulphamoyloxy) radicals in much the same way as acyloxy radicals in the case of O-acyl 2-oximinoketones studied before. At room temperature in the presence of a spin-trap, the trapped benzoyl radical is observed, which must have been formed by fragmentation of the alpha-ketoiminyl radical. The title compounds are shown to photoinitiate the polymerization of acrylates and to photoinduce the acid-catalyzed crosslinking of a melamine resin.