TEMPERATURE RISING ELUTION FRACTIONATION OF POLYPROPYLENE PRODUCED BYHETEROGENEOUS ZIEGLER-NATTA CATALYSTS

Four catalyst systems, MgCl2/TiCl4-AlEt3, MgCl2/di-n-butyl phthalate ( DNBP)TliCl(4)-AlEt3, MgCl2/TiCl4-AlEt3/diphenyl dimethoxyl silane (DPD MS) and MgCl2/DNBP/TiCl4-AlEt3/DPDMS, were prepared and the polypropyl ene samples obtained using them were fractionated with the preparative temperature rising elution fractionation (TREF) technique. It was fou nd that electron donors had an important influence on the tacticity di stribution of polypropylene. Some key fractions were characterized by C-13 NMR and the structures of the fractions eluted at different tempe ratures were analyzed. The results showed that the fractionation was p erformed mainly according to tacticity and that electron donors increa sed the percentage of isotactic fractions. It was also observed that e lectron donors decreased the isotacticity of the first fraction. A pos sible explanation was proposed. (C) 1998 Elsevier Science Ltd. All rig hts reserved.