Stereosequence- and topology-controlled synthesis of cyclic polyesters.

Stereoselective control in cyclic polyester synthesis, particularly stereosequence-defined cyclic copolyesters, has not yet been achieved in a single catalytic platform. Achieving this combination is challenging because stereocontrol requires precise chain-end discrimination, whereas ring-expansion growth that generates cyclic topology can be readily perturbed in monomer mixtures. Herein, we report lanthanum catalysts for isoselective ring-expansion polymerization of amino acid-derived O-carboxyanhydrides, affording high-molecular-weight (>100 kDa) cyclic stereoblock poly(α-hydroxy acids) with diverse pendant functional groups, narrow molecular-weight distributions (Ɖ < 1.1), and high isotacticities (Pm > 0.9, where Pm is the probability of meso linkage). Copolymerization of comonomers with opposite chiralities further enables one-pot scalable synthesis of high-molecular-weight (>90 kDa) cyclic gradient copolyesters (Ɖ ~ 1.1). The cyclic gradient copolymers exhibit simultaneously enhanced fracture strength and toughness relative to cyclic and linear block analogs, while maintaining oxygen barrier performance comparable to poly(lactic acid). These findings establish simultaneous stereosequence and topology control as a powerful strategy for accessing superior material properties, moving beyond conventional approaches that rely on changing monomer identity.