Initiation of cationic polymerization via oxidation of free radicals using pyridinium salts

Pyridinium ions of appropriate reduction potential E^red _{1 2} are capable of oxidizing carbon-centred free radicals to carbocations that can initiate the polymerization of various compounds. 1-Ethoxy-2-methyl pyridinium ions of E^red _{1 2} = -0.7 V were found to react with free radicals generated by (a) photolysis or (b) thermolysis of various compounds. Radical generation was achieved in case (a) with benzoinmethylether, diphenyl-2,4,6-trimethylbenzoylphosphine oxide or benzophenone/tetrahydrofuran (BP/THF) and in case (b) with phenylazotriphenylmethane, BP/THF, benzoylperoxide/THF or 2,2-azobisisobutyronitrile/THF. The following monomers were polymerized: 1,2-epoxycyclohexane (cyclohexene oxide) and n-butylvinyl ether.