Synthesis of cyclic polymers and block copolymers by monomer insertion into cyclic initiator by a radical mechanism

Cyclic poly(methyl acrylate) with controlled ring size and narrow ring size distribution was successfully prepared by the Co-60 gamma-ray-induced polymerization of methyl acrylate at -30 degreesC in the presence of cyclic initiator 3. GPC, H-1 NMR, and MALDI-TOF confirmed the cyclic structure of the obtained polymers. With the same method and using cyclic PMA as macroinitiator instead of cyclic initiator 3, amphiphilic cyclic block copolymers poly(N-isopropylacrylamide-b-methylacrylate-b-N-isopropylacrylamide)s were obtained. The structures and compositions of the block copolymers obtained were investigated by GPC and NMR measurements. The living nature of the polymerization was supported by the linear evolution of molecular weight with conversion, constant concentration of chain radicals, and narrow molecular weight distribution. Thus, ring sizes and narrow distribution of cyclic polymers and cyclic block copolymers can be controlled.