Indium-Catalyzed Block Copolymerization of Lactide and Methyl Methacrylate by Sequential Addition

We report a metal-mediated sequential addition synthetic route for copolymerization of lactide (or ε-caprolactone) and methyl methacrylate. We synthesized a series of neutral and cationic indium complexes supported by tridentate Schiff base ligands and investigated their reactivities for the homo- and copolymerization of lactide or ε-caprolactone and methyl methacrylate. We showed that the neutral indium complex (±)-(NNiOtBu)­In­(CH2SiMe3)2 (2) catalyzes the sequential block copolymerization of lactide/ε-caprolactone and methyl methacrylate without any additional reagents or synthetic steps. The block copolymers were stringently characterized by size exclusion chromatography (SEC), diffusion ordered NMR spectroscopy (DOSY), differential scanning calorimetry (DSC), and fractional precipitation techniques.