Role of electron donor in the polymerization of propylene with MgCl2-supported catalysts

MgCl2-supported Ziegler-Natta (Z-N) catalysts containing three different Lewis bases (diisobutyl phthalate, 9,9-bis(methoxymethyl)fluorine and 1,1-bis(methoxymethyl)cyclobutane) as internal donors were prepared for propylene polymerization. The relationship between the structure of donors and the performance of catalysts were investigated. The Z-N catalyst containing 9,9-bis(methoxymethyl)fluorine as internal donor and the related compounds were characterized by FTIR spectroscopy. It was found that the internal donor in the MgCl2/TiCl2/Donor catalyst system was directly coordinated to MgCl2. The introduction of internal donors decreased the Ti content in the catalyst system, increased the catalytic activity and narrowed the molecular mass distribution of polymers obtained. The stereospecificity of Z-N catalysts greatly depended on the structure of electron donors. A model of multi-active sites on heterogeneous Z-N catalyst was proposed to explain the experimental results.