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

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 (D = 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 D 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.