Use of pyrazoles as ligands greatly enhances the catalytic activity of titanium iso-propoxide for the ring-opening polymerization of l-lactide: a cooperation effect.

Using TiO i Pr 4 with a pyrazole ligand for one-pot LA polymerization improved catalytic activity compared with using TiO i Pr 4 only. At 60 °C, TiO i Pr 4 with fur Pz exhibited a higher catalytic activity (approximately 3-fold) than TiO i Pr 4 . At room temperature, TiO i Pr 4 with Bu Pz exhibited a higher catalytic activity (approximately 17-fold) than TiO i Pr 4 . High molecular mass PLA ( M n GPC = 51 100, and Đ = 1.10) could be produced by using TiO i Pr 4 with fur Pz in melt polymerization ([TiO i Pr 4 ] : [ fur Pz] = 1000 : 1 : 1 at 100 °C, 240 min). The crystal structure of Me Pz 2 Ti 2 O i Pr 7 revealed the cooperative activation between two Ti atoms during LA polymerization.