Stereoselective zwitterionic ring-opening polymerization of rac-lactide

Abstract Stereoselective zwitterionic ring-opening polymerization (ZROP) poses a potentially great challenge in polymer chemistry because of its unique ion-pairing catalysis mechanism. Herein, a stereoselective ZROP of rac -lactide ( rac -LA) was explored for synthesis of isotactic cyclic polylactides by using commercially available N -heterocyclic carbene (NHC) catalysts at low temperature in tetrahydrofuran. The epimerization of lactide during ZROP can be inhibited at low temperature. The best isoselectivity can reach to a high value of P m  = 0.91 associated with a high melting point ( T m ) of 193 °C. The resulting polylactides exhibit narrow molecular weight distributions ( M w / M n 1 H NMR and MALDI-TOF MS analyses.