One-Pot Synthesis of Oxygenated Block Copolymers by Polymerization of Epoxides and Lactide Using Cationic Indium Complexes

Cationic indium complexes were used as catalysts for the copolymerization of epoxides and racemic lactide (rac-LA) via sequential addition to form high-molecular weight block copolymers. Mechanistic studies and control experiments indicate that the epoxide is polymerized by a cationic mechanism to yield a neutral alkoxide indium species that subsequently polymerizes the lactide by a coordination-insertion mechanism with no significant interference of the two mechanisms under polymerization conditions. The thermal and tensile properties of different block copolymers were studied, revealing mostly amorphous materials. We were able to control the ductility and stiffness of the copolymers by tuning the nature and chain length of the blocks.