Stereoselective ring-opening polymerization of rac-lactides catalyzed by titanium complexes containing N,N-bidentate phenanthrene derivatives

Three titanium complexes with N,N-bidentate phenanthrene derivatives (1: R = Pr-i, 2: R = C6H5, 3: R = 2,6-(Pr2C6H3)-Pr-i) were synthesized. These complexes were characterized using H-1/C-13 NMR spectroscopy and elemental analysis and employed in the ring-opening polymerization (ROP) of L-lactide and rac-lactide. Complex 1 displayed the highest activity among these complexes for ROP of L-lactide, and complex 3 showed the highest stereoselectivity for the ROP of rac-lactide attaining a partially heterotactic polylactide (PLA) with a P-r of 0.63. The polymerization kinetics employing 3 as the catalyst were researched. The kinetic studies revealed that the polymerization rate was first-order with respect to the monomer.