Synthesis of Poly(ε-caprolactone) with a Stable Nitroxyl Radical as an End-Functional Group and Its Application to a Counter Radical for Living Radical Polymerization

The quantitative synthesis of poly(ε-caprolactone) (PCL) with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) at one chain end was attained through the anionic polymerization of CL by an aluminum tri(4-oxy-TEMPO), which was prepared by the reaction of triethylaluminum and 4-hydroxy-TEMPO. The TEMPO-supported PCL behaved as a polymeric counter radical for the radical polymerization of styrene, giving poly(CL- block -styrene) in quantitative efficiency. The radical polymerization was found to proceed in accordance with a living mechanism, because the conversion of styrene linearly increased over time, and the molecular weight was directly proportional to the reciprocal of the initial concentration of the PCL. The resulting copolymers had two glass transition temperatures due to the PCL block and polystyrene and one melting endotherm based on the crystalline phases of PCL. The TEM picture of the film obtained from the block copolymer demonstrated microphase segregation.