Copolymer of propylene with a small amount of butene was prepared with supported Ziegler Natta catalyst MgCl2/TiCl4 AlEt3/DPDMS and was fractionated with preparative temperature rising elution fractionation technique.The composition and tacticity distribution of copolymer were studied.It is found that the copolymer has a broad tacticity distribution and fractionation is mainly conducted according to tacticity.Compositional heterogeneity also exists to some extent.Isotacticity of fractions increases with elution temperature

but butene content shows a maximum in the fraction eluted at 70℃.With combination of previous work

this phenomenon is explained to be the result of the presence of electron donor in aspecific active site.