Effect of external donor in polymerization of propylene by a MgCl2 supported titanium catalyst

Polypropylene (PP) prepared with a MgCl₂/TiCl₄-Et₃Al/Ph₂Si(OMe)₂ catalyst system was fractionated by temperature rising elution fractionation method in order to investigate the effect of Ph₂Si(OMe)₂ as an external donor (ED). This PP had a broad and continuous distribution of tacticity. In comparison to the system without donor, however, ED brought a decrease of lower isotactic portions and an increase of higher isotactic ones simultaneously to the resulting polymer. The latter portions were eluted at higher temperature than the corresponding component obtained without donor, showing that the higher isotactic PP was newly produced by ED.