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.