Toward high-performance stereo- and sequence-defined block copolymers via site-monomer specific recognition of chiral three-site organocatalyst

The development of high-performance 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 organocatalyst incorporating boron and chiral thiourea and tertiary amine groups is 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 P8 with an ultimate tensile strength of 54 ± 3 MPa and an elongation at break of 270 ± 10%. Our strategy provides distinctive insights into designing robust organocatalysts and promising sustainable polymers.