Cationic-anionic synchronous ring-opening polymerization

Chemical reactions with incompatible mechanisms (such as nucleophilic reactions and electrophilic reactions, cationic polymerization and anionic polymerization) are usually difficult to perform simultaneously in one-pot. In particular, synchronous cationic-anionic polymerization has been an important challenge in the field of polymer synthesis due to possible coupling termination of both chain ends. We recently found that such terminal couplings can be significantly inhibited by a bismuth salt with a strong nucleophilic anion (e.g., BiCl₃) and disclosed the mechanism. Accordingly, we propose a cationic-anionic polymerization (CAP) method where cationic ring-opening polymerization (CROP) of 2-oxazolines (Ox) and anionic ring-opening polymerization (AROP) of cyclic esters (CE) can be initiated sequentially and propagated simultaneously in one-pot, using bismuth salts as the initial initiators, to afford a multifunctional copolymer polyoxazoline-block-polyester (POx-b-PCE). Furthermore, a block copolymer PAPOZ₂₀-b-PCL₅ synthesized by CAP can self-assemble into micellar aggregates, which exhibit excellent intrinsic antibacterial activities without loading any extra antibiotic components. Overall, such a CAP method opens new avenues for synthesizing multi-component copolymers and biomaterials.