Crown ether complexes of potassium quinolin-8-olates: synthesis, characterization and catalysis toward the ring-opening polymerization of rac-lactide

Abstract

A series of crown ether complexes of potassium quinolin-8-olates were synthesized and characterized. Catalysis of these complexes towards the ring-opening polymerization of rac-lactide was evaluated. The crown ether complexes of potassium quinolin-8-olate and potassium 2-methylquinolin-8-olate exhibited high catalytic activity and good molecular weight control. The 18-crown-6 complex of potassium 5-chloroquinolin-8-olate showed lower catalytic activity and poor molecular weight control; whereas the 18-crown-6 complex of potassium 5,7-dichloroquinolin-8-olate was inactive. Among the complexes, 18-crown-6 complex of potassium quinolin-8-olate showed the best selectivity of isotacticity, the P_m value achieving 0.75 when the polymerization was performed in toluene at 0 °C.