An organomagnesium complex containing an imino-phosphanamidinate ligand was found to be a competent catalyst for the ROP of rac-LA and ε-CL as well as their copolymerization via sequential addition of monomers, resulting in the formation of PCL-b-PLA diblock copolymer. The polymers obtained were characterized by 1H, 13C, DOSY NMR, DSC, TGA, POM, and SEM.