Synthesis of graft copolymers by the combination of ATRP and enzymatic ROP in scCO2

A simple strategy is reported for the synthesis of well-defined graft copolymers of poly(methyl methacrylate-co-2-hydroxyethyl methacrylate) P(MMA-co-HEMA) with poly(epsilon-caprolactone) (PCL) grafted chains. Using scCO(2) as the only solvent, a one-step synthetic approach is adopted to prepare copolymer backbones via atom transfer radical polymerization (ATRP), and grafted chains are added via enzymatic ring-opening polymerization (eROP). Exhaustive study of the enzymatic grafting efficiency showed that only the hydroxyl groups in the backbone initiated the polymerization of epsilon-CL, resulting in an exceptional polymer architecture which is not accessible by conventional chemical polymerization methodology. The lower grafting density obtained (ca. 30-40%) with the enzymatic polymerization of epsilon-CL indicates that the system is likely limited by steric hindrance.