Merging of cationic RAFT and radical RAFT polymerizations with ring-opening polymerizations for the synthesis of asymmetric ABCD type tetrablock copolymers in one pot

Abstract

Olefin monomers are divided into cationically polymerizable ones (monomer A, such as vinyl ethers) and radically polymerizable ones (monomer B, such as acrylates); in parallel, cyclic ester monomers are polymerizable either electrophilically (monomer C, such as lactones) or nucleophilically (monomer D, such as lactides). To address the challenge of polymerizing the distinctive four types of monomers in one pot into ABCD type tetrablock copolymers, we proposed a bifunctional reversible addition–fragmentation chain transfer (RAFT) agent bearing both the RAFT polymerization site and ring-opening polymerization (ROP) site. The RAFT site was able to copolymerize A and B via switching the cationic RAFT polymerization (cRAFT) to radical RAFT polymerization (rRAFT). Subsequently, the ROP site copolymerized C and D by switching the electrophilic ROP to nucleophilic ROP. A general dual-switch strategy of both RAFT and ROP mechanism transitions successfully produced ABCD-type tetrablock quaterpolymers in one pot by sequential monomer feeding. Poly(isobutyl vinyl ether)-b-poly(methyl methacrylate)-b-poly(δ-valerolactone)-b-polylactide (PIBVE-b-PMMA-b-PVL-b-PLA) was synthesized. All synthesized homopolymers and multi-block copolymers exhibited predicted molecular weights and relatively narrow dispersities (Đ ≤ 1.45). The copolymerization strategy paved a new avenue to combine cRAFT, rRAFT and ROPs to copolymerize vinyl and cyclic ester monomers for rational design and precise synthesis of multiblock copolymers with advanced architectures and functionalities.