Mechanistic investigation of cyclic ketene acetal radical ring-opening homo- and co-polymerization and preparation of PEO graft copolymers with tunable composition†
Radical ring-opening polymerization (rROP) of cyclic ketene acetals (CKAs) provides a chain-growth polymerization pathway for polyester synthesis. The radical polymerizations of 2-methylene-1,3,6-trioxocane (MTC) and 5,6-benzo-2-methylene-1,3-dioxepane (BMDO) were investigated, where different radical initiation, termination and transfer pathways were observed. The semi-batch copolymerization of these CKAs with N-vinyl pyrrolidone (NVP) employing slow dosing strategies provides a route to prepare linear copolymers with a uniform ester distribution. The semi-batch polymerization of MTC and NVP using polyethylene oxide (PEO) as the solvent leads to radical transfer onto oxyethylene, enabling the preparation of graft copolymers with a PEO backbone and MTC-co-NVP containing side chains. Differential scanning calorimetry (DSC) characterization of CKA copolymers demonstrates the effects of polymer chemical structures and architectures on their thermal properties.