Improvement in titanium complexes supported by Schiff bases in ring-opening polymerization of cyclic esters: ONO-tridentate Schiff bases

Abstract A series of titanium (Ti) complexes bearing ONO-tridentate Schiff bases were synthesized and their application to the ring-opening polymerization of L-lactide and e-caprolactone was studied. Ti complexes bearing ONO-tridentate Schiff bases revealed a greater catalytic activity compared to other previously synthesized Ti complexes bearing multi-dentate phenolate ligands. We hypothesize that using ONO-tridentate Schiff bases as ligands reduces the occupied space and increases the monomer coordination around the Ti center, thereby increasing catalytic activity. The electronic effect of the phenolate group on the polymerization rate was also studied, showing that electron-donating substituents on the ligands could drastically increase polymerization activity.