CO₂-based amphiphilic block copolymers: Facile one-step synthesis and aqueous self-assembly

Construction of CO2-based amphiphilic block copolymers (ABCs) is an efficient method for providing CO2-based polycarbonates with self-assembly properties in aqueous media. It is challenging to construct CO2-based ABCs by one-step strategies from mixed monomers because hydrophilic blocks, usually composed of polar monomers, have negative effects on the synthesis of polycarbonates. In this work, we report a one-step method to construct CO2-based ABCs obtained by simultaneous ring-opening copolymerization (ROCOP) of CO2/epoxides and reversible addition-fragmentation chain transfer (RAFT) polymerization of N-isopropyl acrylamide (NIPAM). A trithiocarbonate/carboxy compound was used as the bifunctional chain transfer agent, and an aluminum porphyrin complex was used as the catalyst for ROCOP, which proved to be efficient in CO2 copolymerization even in the presence of NIPAM with strong polarity. This strategy allows flexible control over the molecular weight (5-16 kg/mol) and the hydrophilic-hydrophobic balance (HLB 9-18) of the ABCs, and ensures narrow polydispersity D (1.1-1.3) of the polymers. The ABCs can further self-assemble into micelles in water with controllable diameters and reversible phase transformation behavior with temperature changes from 25 to 40 degrees C. This simple route to CO2-based ABCs with multiple functions has large potential in biomedical applications.