Stereoselective ring-opening polymerization of rac-lactide by bulky chiral and achiral N-heterocyclic carbenes

Despite the extraordinary success has been achieved in metal catalyst-promoted stereoselective ring-opening polymerization (ROP) of rac-lactide (rac-LA), well-controlled stereoselective rac-LA ROP by organic catalyst still remains a scientific challenge. Here we report our investigations into organocatalytic stereoselective ROP of rac-LA by utilizing novel bulky chiral and achiral N-heterocyclic carbenes (NHC), 1,3-bis-(1'-naphthylethyl)imidazolin-2-ylidene. The effect of polymerization conditions (e.g. solvent, temperature, alcohol initiator) on ROP behavior by these bulky NHCs has been fully studied, leading to the formation of isotactic-rich stereoblock polylactide (P (i) = 0.81) under optimized conditions with high activity (Conv. = 98% in 30 min) and narrow molecular weight dispersity (AEe = 1.05).