Block Copolymers by Combination of Radical and Promoted Cationic Polymerization Routes

A block copolymer of cyclohexene oxide and styrene was prepared by using afunctional azoben-zoin initiators via a two-step procedure. The functionality of the initiator pertains to thermally degradable azo group and thermally stable photoactive benzoin groups. In the first step, thermal polymerization of styrene using azobenzoin initiators was carried out to yield polymers with photoactive end groups. These prepolymers were used to induce polymerization of cyclohexene oxide through formation of electron donor macroradicals upon photolysis and subsequent oxidation to corresponding carbocations in the presence of l-ethoxy-2-methylpyridinium hexafluorophosphate resulting in the formation of a block copolymer. A different sequence of the same procedure was also employed. Successful blocking has been confirmed by a strong change in the molecular weight of the prepolymer and the block copolymer as well as IR and NMR spectral measurements.