Effect of the alkoxyl ligands on ethylene polymerization by TpTiCl2(OR) complexes

Abstract The TpTiCl 2 (OR) (where Tp = hydrotris(pyrazolyl)borate; R = Me, Et, i -Pr, n -Bu) and TpTiCl 3 complexes activated with very low concentration of MAO (≥200 Al/Ti) showed very high activity in the ethylene polymerization. The substitution of one chlorine ligand in the TpTiCl 3 for one alkoxyl ligand increases the catalytic activity up to 76 times and 3.4 times respect to Cp 2 ZrCl 2 at the same reaction conditions. The TpTiCl 2 (OR) precatalysts activity decreases in the following order: TpTiCl 2 (OEt) > TpTiCl 2 (O n -Bu) ≈ TpTiCl 2 (O i -Pr) ≫ TpTiCl 2 (OMe) > TpTiCl 3 . The alkyl chain size of the alkoxyl ligands strongly affects the catalytic activity and the molecular weights of the polymers, prevailing the steric effect over the electronic effect. The resulting polymers can be classified as ultra-high molecular weight polyethylenes with basically linear structure.