Temperature rising elution fractionation of polypropylene produced by heterogeneous Ziegler-Natta catalysts

Four catalyst systems, MgCl2/TiCl4-AlEt3, MgCl2/di-n-butyl phthalate (DNBP)TliCl(4)-AlEt3, MgCl2/TiCl4-AlEt3/diphenyl dimethoxyl silane (DPDMS) and MgCl2/DNBP/TiCl4-AlEt3/DPDMS, were prepared and the polypropylene samples obtained using them were fractionated with the preparative temperature rising elution fractionation (TREF) technique. It was found that electron donors had an important influence on the tacticity distribution of polypropylene. Some key fractions were characterized by C-13 NMR and the structures of the fractions eluted at different temperatures were analyzed. The results showed that the fractionation was performed mainly according to tacticity and that electron donors increased the percentage of isotactic fractions. It was also observed that electron donors decreased the isotacticity of the first fraction. A possible explanation was proposed. (C) 1998 Elsevier Science Ltd. All rights reserved.