Metal-size influence of alkali metal complexes for polymerization of rac-lactide

Abstract A series of alkali metal complexes with 2,2′-ethylidenebis(4,6-di-tert-butylphenol) (EDBP-H 2 ) as a ligand have been synthesized. In the presence of benzyl alcohol as an initiator, all complexes exhibit good catalytic behaviors for the ring-opening polymerization (ROP) of rac -lactide, giving desirable molecular weights and narrow molecular weight distributions. The relative order of activities for this series of complexes is Li > Na > K > Rb, which is related to metallic ion radius; and Lewis acidity of these metal ions is also an important factor for the kinetics of the ROP. The relative order of stereoselectivities for this series of complexes is Rb ≈ K > Na ≫ Li in this system. The first example of Rb complex in the ROP of rac -lactide in this paper was also described, showing a modest activity and a nice polymerization control, even with a certain isoselectivity.