A qualitative model for polymerisation of propylene with a MgCl2-supported TiCl4 Ziegler-Natta catalyst

A qualitative model for polymerisation of propylene with a MgCl₂-supported TiCl₄ Ziegler-Natta catalyst is developed. A series of polymerisation with increasing external electron donor/Ti ratio is performed and the polymers are analysed with GPC, ¹³C NMR and DSC. The model explains the trends in isotacticity and isotactic sequence length based on an equilibrium reaction of the electron donor, which is either coordinated next to an active site or extracted to the solution by the cocatalyst AlR₃. Different rates for propagation and termination reactions when the donor is present or absent are used to explain the trends in activity and molar mass. The possibilities for a quantitative model and parameter estimation are discussed.