Ethylene polymerization with homogeneous Ziegler-Natta catalysts: theoretical study on the role of ion pairs in the polymerization mechanism

The thermodynamics of the reaction of an ethylene molecule with the Cp₂TiCH₃Cl/Al(CH₃)₂Cl system (Cp = η₅-C₅H₅), as a model for olefin polymerization with homogeneous Ziegler-Natta catalysts, was investigated via quantum mechanical DFT calculations. The comparison of the calculated energies for three possible titanium-olefin coordinated intermediates, the ionic complex Cp₂TiCH₃(C₂H₄)⁺/Al(CH₃)₂Cl, the bimetallic complex Cp₂TiCH₃(C₂H₄)^δ+ · Al(CH₃)₂Cl and the olefin-separated ion pair Cp₂TiCH/C₂H₄/Al(CH₃)₂Cl, shows that the most feasible polymerization mechanism occurs via olefin-separated ion pair.