Molecular-modelling studies of the polypropylene catalyst

Abstract

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 MgCl₂via a ‘triply bound’ model. This results in one of the Cl–Ti–Cl bond angles opening up to 135°, 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.