Tripodal hydrogen bond donor binding with sulfonic acid enables ring-opening polymerization

Abstract

H-bond donor (HBD) and Brønsted acid (BA) co-catalysis (HBD–BA) performed ring-opening polymerization (ROP) of cyclic esters in solution at room temperature. The HBD–BA strategy using thiophosphoric triamide (TPTA) binding with methanesulfonic acid (MSA) enabled the ROP of L-lactide (LA) to polylactide (PLA) with predicted molecular weights (M_n = 2.9–13.8 kDa) and low dispersities (Đ = 1.18–1.22). Associations of TPTA with MSA through triple hydrogen bonds stabilized the sulfonate anion and enhanced the catalytic performance of TPTA–MSA. Homopolymers of LA, trimethylene carbonate (TMC), δ-valerolactone, and ε-caprolactone (CL), and diblock copolymers PLA-b-PTMC and PLA-b-PCL with predicted M_n and narrow Đ were synthesized. NMR measurements, kinetics investigations, and chain extension experiments indicated that the TPTA–MSA catalyzed ROPs were controlled/living in nature. This is the first Brønsted acidic catalysis platform workable in all of the three major types of cyclic ester monomers including lactides, cyclic carbonates, and lactones.