RAFT/ROP binary polymerization towards well-defined graft copolymers

Graft copolymers have been extensively applied in fields including photonics, biomaterials and rheological modifiers, but their simple and efficient synthesis remains challenging. Herein, well-defined graft copolymers of poly(N-hydroxyethyl acrylamide)-g-poly(epsilon-caprolactone) (PHEAA-g-PCL) were successfully synthesized using a binary polymerization approach. Specifically, the simultaneous reversible addition-fragmentation chain transfer (RAFT) polymerization and ring-opening polymerization (ROP) were possible in binary polymerization as compared to traditional "grafting-through" and "grafting-from" approaches. The resulting PHEAA-g-PCL copolymers prepared by three routes were characterized and exhibited comparable physical and chemical properties. More importantly, the binary polymerization was extensively investigated based on kinetic modelling. Both experiments and theoretical investigations on the binary polymerization revealed that RAFT polymerization and ROP occurred almost orthogonally. Therefore, such binary polymerization offered a feasible way towards structurally precise and controllable graft copolymers. The kinetic model proposed also provided a method to thoroughly evaluate the binary polymerization. The RAFT/ROP binary polymerization enables the efficient synthesis of controlled and well-defined poly(N-hydroxyethyl acrylamide)-poly(epsilon-caprolactone) (PHEAA-g-PCL) as compared to the conventional "two-step" method.