Toward Stereo- and Sequence-Defined Block Copolymers via a Three-Site Organocatalyst

Abstract

The development of sustainable polymers as candidates to replace petroleum-based plastics is a priority, but still a grand challenge. Here, we report a series of stereo- and sequence-defined copolymers with isotactic polylactide and alternating/regioregular polythiocarbonate blocks from one-pot, metal-free, and switchable copolymerization of rac-lactide, COS, and epoxides. The highly active organocatalysts incorporating boron and chiral thiourea and tertiary amine groups are developed based on the site-monomer specific recognition mechanism; in short, the boron site selectively activates epoxides through B–O bonds and the thiourea site selectively activates lactide through hydrogen bonds. Such block copolymers manifest impressive toughness and ductility owing to their isotactic polylactide fragments and high molecular weights, such as P10 with a molecular weight of 92.3 kDa, an ultimate tensile strength of 59 ± 3 MPa, and an elongation at break of 222 ± 25%. Our strategy provides distinctive insights into designing robust organocatalysts and promising sustainable polymers.