Theoretical study of heterogeneous Ziegler-Natta catalysts: A comparison between TiCl3 catalysts and MgCl2 supported catalysts by using paired interacting orbitals (PIO) analysis

Two types of industrial heterogeneous Ziegler-Natta propylene polymerization catalysts, TiCl3 type and MgCl2 supported TiCl4 type, were examined by paired interacting orbitals (PIO) analysis proposed by Fujimoto et al.. The ligand located trans to propylene was found to obstruct the insertion but was essential for the stereospecific insertion of propylene. The ligand located trans to the alkyl group of the active site was found to be necessary for activating the alkyl-Ti bond. The regioselectivity and stereoselectivity of the iso-specific polymerization site on the heterogeneous Ziegler-Natta catalyst system were confirmed. The polymerization activity of MgCl2 supported TiCl4 catalyst was larger than that of the TiCl3 catalyst.