Block copolymers obtained by free-radical mechanism. I. Methyl methacrylate and styrene



Block copolymers were synthesized using styrene and methyl methacrylate as the monomers and a multifunctional initiator, di-t-butyl 4,4′-azobis(4-cyanoperoxyvalerate). The unique feature of this sequential initiator is the fact that the formation of the free radicals can be achieved thermally and/or by a redox system at different stages. The polymerizations for the formation of the block copolymer were carried out in two stages. First, a polymeric initiator was synthesized, which was then used in the second stage to initiate the polymerization of the second monomer. Styrene and methyl methacrylate were used as the comonomers. Selective solvent fractionation was used for the separation of the block from the homopolymers. The separation technique was found to be efficient, giving pure block copolymers which could subsequently be characterized by GPC, NMR, IR, and EM techniques.