Research On MgCl₂/SiO₂ Complex Support Catalyst Used In Propylene Polymerization And Multistage Polymerization

It is well known that support and donor have much important impact on Ziegler-Natta catalyst systems for olefin polymerization. Now the research aim on Ziegler-Natta catalyst for olefin polymerization is not only high activity, but also high performance and texture structure of Ziegler-Natta catalyst. In this paper, we assembled SiO₂/MgCl₂ by spray drying technology and obtained complex support. The complex support reacted with TiCl₄ and internal donor gave the catalyst for propylene polymerization. The catalyst was characterized by SEM, BET, XRD, XPS and EDX. The analysis results showed that the SiO₂ function as an inertia support, there is no chemistry inter-action between the element of silica and magnesium or titanium. The complex support catalyst is porous spherical and well distributed. The behavior of the catalyst for polymerization and multistage polymerization of propylene were investigated using propylene bulk polymerization and bulk-gas series polymerization, respectively. The results showed that it is accord to the case of conventional Ziegler-Natta Catalyst, polymerization reaction conditions and external donor have much effects on catalyst performance. The polypropylene grains were also spherical and well size-distributed because of duplicating the morphology of the catalyst. The catalyst had high activity, high stereospecificity and sensitive hydrogen responsibility. The multistage polymerization of propylene for high performance polypropylene was studied using this catalyst system. It was found that the final high impact polypropylene after two stages of reaction is still freeflowing, spherical granules. Homopolymer obtained from the first stage has the pore diameter between 100nm and 10000nm which are suitable for EPR insertion during ethylene-propylene copolymerization.