Constructing ABA- and ABCBA-Type Multiblock Copolyesters with Structural Diversity by Organocatalytic Self-Switchable Copolymerization

Self-switchable ring-opening copolymerization of epoxides, cyclic anhydrides, and cyclic esters catalyzed by an organocatalyst has been proved to be a promising approach to sequence-controlled (multi)block copolymers. However, the scope of the cyclic esters is only limited to lactide, and selection of some anhydrides usually produced random copolymers with an ill-defined sequence. To overcome these challenges, we investigated the one-pot selective polymerization of O-carboxyanhydrides (OCAs)/cyclic anhydrides/epoxides and established an alternative pathway for well-defined multiblock copolyesters with structural diversity and functionality. A potential organocatalyst for self-switchable copolymerization was optimized using ring-opening polymerization of OCA and ring-opening alternating copolymerization of cyclic anhydrides/epoxides as model reactions. Subsequently, the chemoselectivity in terpolymerization was investigated by kinetic studies, and the formation of the sequence-defined triblock copolymer was identified by NMR and GPC analysis. Density functional theory (DFT) calculations for model reactions were also conducted to illustrate the excellent chemoselectivity in terpolymerization. The newly established self-switchable pathway exhibited broad monomer adaptability, and the structures of the monomer (including some challenging anhydrides) have no effect on the chemoselectivity. Finally, one-step synthesis of ABCBA-type pentablock copolyester without external monomer addition was explored from a self-switchable quadri-polymerization of OCAs, cyclic anhydries, epoxides, and lactide.

Automated summary

The self-switchable pathway for the copolymerization of epoxides, cyclic anhydrides, and cyclic esters has been shown to be effective in producing well-defined copolymers with structural diversity and functionality. Through optimization of the organocatalyst and kinetic studies, a sequence-defined triblock copolymer was successfully synthesized, demonstrating excellent chemoselectivity in terpolymerization. The newly established pathway showed broad monomer adaptability and allowed for the one-step synthesis of complex pentablock copolyesters.