MOLECULAR-MODELING STUDIES OF THE POLYPROPYLENE CATALYST

Polypropylene is formed using a catalyst typically consisting of TiCl4 supported on a MgCl2 substrate. A combination of molecular-modelling methods has been used to investigate the catalyst at the atomic level. Molecular graphics and static lattice calculations show that MgCl2 exhibits stable surfaces in which surface Mg ions are four, five and six coordinated. Density functional theory calculations show that TiCl4 binds to MgCl2 via a 'triply bound' model. This results in one of the Cl-Ti-Cl bond angles opening up to 135-degrees, an event that clearly facilitates cis insertion of the monomer unit at this position. These calculations also demonstrate the stability of this TiCl4/MgCl2 cluster with a propene monomer unit.