On the mechanism of acylphosphine oxide promoted cationic polymerization

Abstract

Abstract The light-induced initiation of the cationic polymerization of the diepoxide (3,4-epoxycyclohexylmethyl)-3′,4′-epoxy-cyclohexane carboxylate (EEC) and of n-butylvinyl ether in the presence of Ph2I+PF6− and 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TMDPO) or 2,6-dimethoxybenzoyldimethoxy-phosphine oxide (DMPME) was investigated. It turned out that 2,4,6-trimethylbenzoyl radicals and diphenylphosphonyl radicals do not react with Ph2I+ ions but abstract hydrogens from appropriate donors such as tetrahydrofuran. The resulting carbon-centered radicals are converted into carbocations by reaction with Ph2I+ ions. These carbocations initiate the polymerization of EEC. Radicals formed in the photolysis of DMPME seem to react with Ph2I+ ions. The species generated in these reactions were capable of initiating the polymerization of EEC. n-Butylvinyl ether was readily polymerized in the presence of TMDPO and Ph2I+ ions. Phosphorus was incorporated into the polymer as evidenced by P-31 NMR measurements. The proposed initiation mechanism assumes the addition of the Ph 2 P O radical to CH2CH(OR). The radical resulting from this addition is capable of reacting with Ph2I+.