Magnesium complexes bearing N,N-bidentate phenanthrene derivatives for the stereoselective ring-opening polymerization of rac-lactides

Abstract

Three unreported magnesium complexes (1: R = C₆H₅, 2: R = 2,6-Et₂C₆H₃, 3: R = 2-^tBuC₆H₄) bearing N,N-bidentate phenanthrene derivatives derived from Schiff bases were synthesized. These complexes were characterized using ¹H and ¹³C NMR spectroscopy and elemental analyses and employed for rac-lactide and L-lactide polymerization. Complex 1 showed the highest activity among these Mg complexes for the ring-opening polymerization (ROP) of L-lactide, and complex 3 showed the highest stereoselectivity for the ROP of rac-lactide, achieving partially heterotactic polylactide (PLA) with a P_r of 0.76. The polymerization kinetics utilizing 2 as a catalyst were researched in detail. The kinetics of the polymerization data revealed that the rate of polymerization was first-order with respect to monomer, and had an order of 0.97 with respect to catalyst. There was a linear relationship between the L-lactide conversion and the number-average molecular weight of PLA.