Cationic polymerization photochemically and thermally induced by phenothiazine cation radical salts

Cation radicals of phenothiazine, N-ethyl-phenothiazine and N-ethyl-2-ethyl-phenothiazine having the counterfoil SbF^-₆ were synthesized, characterized and used as a cationic initiators for the polymerization of N-vinyl carbazole, cyclohexene oxide and tetrahydrofuran. The dication of N-ethyl-phenothiazine and the cation radical of N-ethyl-phenothiazine were found to be less stable and less soluble than the N-ethyl-2-ethyl-phenothiazine cation radical in dichloromethane. Photolysis of the more readily soluble N-ethyl-2-ethylphenothiazine with light of wavelengths 320, 445 and 525 nm in dichloromethane and cyclohexene oxide was studied at room temperature. The magnitude of the quantum yield (0.177) for photobleaching at 525 nm is indicative of an efficient photoactivated initiation of cyclohexene oxide polymerization.