Controlled Synthesis of High-Molecular-Weight and Isotactic Cyclic Polylactides from rac-Lactide Using Aminophenolate Zinc Chlorides

No-end topology provides cyclic polyesters with potential abstracting applications, but more efficient and selective routes still need to be explored to access cyclic polyesters with high molecular weights and tacticity control. We report here that a series of aminophenolate zinc chlorides display hyperstability and hyper productivity toward the ring-opening polymerization of technical grade rac-lactide (rac-LA) in cyclohexene oxide, capable of converting up to 20,000 equiv of rac-LA (TONs up to 18,600) to cyclic polymers with high molecular weights and narrow to moderate distributions (M-n up to 58.0 kg/mol, (D) over bar = 1.19-1.60). At ambient temperature, highly isotactic cyclic poly(rac-LA)s could be obtained (e.g., complex 6, P-m = 0.87, M-n = 23.5 kg/mol, 25 degrees C; with P-m further improved to 0.93 at -45 degrees C), which show to possess stereoblocky microstructures. Selective end-to-end cyclization proved to be thoroughly involved in the polymerization, leading to cyclic polylactides with only even-numbered lactyl units.