Ziegler-Natta catalysts for propylene polymerization –Interaction of an external donor with the catalyst

The interaction of the external donor (propyltrimethoxysilane - PTMS) with titanium-magnesium catalysts (TMCs) containing dibutylphthalate (DBP) as internal donor, which were prepared in different ways, wasstudied by chemical analysis and infrared diffuse reflectance spectroscopy (DRIFTS). The chemical compositionof the catalysts after their interaction with heptane solutions of PTMS, PTMS/AlEt3 or AlEt3 during 1h at 70°Cshowed that this interaction led to removal of both TiCl4 and DBP from the catalysts. The fractions of DBP and Tiextracted, as well as the amounts of PTMS and AlEt3 bound, depended on the method of synthesizing the catalysts.DRIFT spectroscopy data concerning the state of DBP in the catalysts, before and after treatment with heptanesolutions of PTMS or PTMS/AlEt3 during 1h at 70°C, showed that PTMS could substitute both TiCl4 and DBP,while adsorbing on coordinatively unsaturated Ti and Mg ions in the catalyst. The presence of AlEt3 played a keyrole in the interaction of PTMS with the catalyst. Activity data for propylene polymerization showed that treatmentof TMC catalysts with PTMS before polymerization led to a sharp activity decrease due to deactivation of activesites, while the interaction of the catalyst with PTMS in the presence of AlEt3 led only to a slight decrease ofactivity, probably due to deactivation of non-stereospecifc active centers. Polyolefns J (2017) 4: 87-97

Keywords:

Titanium-magnesium catalyst , propylene polymerization , dibutylphthalate , propyltrimethoxysilane , DRIFTS