Mononuclear complexes with heterocyclic ligands as ethylene polymerization catalysts for single-reactor bimodal polyethylene technology

Abstract

27 complexes of titanium, zirconium and vanadium with 1,2-bis(benzimidazolyl)benzene, 1,2-bis(benzimidazolyl)ethane and 1,1-bis(benzimidazolyl)methane ligands have been synthesized and characterized. After activation with methylalumoxane (MAO) these complexes proved as good catalysts for ethylene polymerization inspite of the hetero atoms in the ligands and the oxophilicity of the metals. Nearly all produced polyethylenes showed bimodal or multimodal molecular weight distributions indicating more than one active site of the catalysts in the various polymerization steps. Obviously, after activation with MAO, a mononuclear catalyst molecule can interact differently with the cocatalyst. This is an easy and elegant approach to single-reactor bimodal/multimodal polyethylene technology. The polymerization activity of the catalyst system 1,2-bis(benzimidazolyl) benzene zirconium tetrachloride (29/MAO) was investigated at different polymerization temperatures and structure–property-relationships were studied. The effect of the polymerization temperature on both molecular weights and polydispersities of the polymers produced with catalyst 29/MAO was investigated at 20, 40, and 60°C. The molecular weights Mw were 1.3⋅106, 1.2⋅106 and 9.7⋅105g/mol and the polydispersity indices PDI 693, 248 and 223 respectively.