Ziegler-Natta (Z-N) catalysts for propylene polymerization were prepared in situ using dibutyl phthalate (DNBP) or 9,9-bis(methoxymethyl)fluorene (BMMF) as internal electron donors (IDs) by treating the support precursors (Mg(OEt)2 or MgCl2·2.5EtOH) or MgCl2 complex solutions with TiCl4 respectively. In this study, eight Z-N catalysts containing two types of IDs were prepared via different preparation routes and systematically characterized with modern analytical techniques. The results indicated that, even with the same IDs, the catalysts prepared by different methods exhibited significant differences in chemical composition, particle size distribution, catalytic activity and stereoselectivity. The properties of polypropylene (PP) were largely influenced by the preparation route of the catalysts. Particularly, the catalysts obtained by the reprecipitation method showed the highest catalytic activity and the smallest MgCl2 particle size. The distribution of stereoselective active centers in the catalysts was simultaneously affected by the preparation method and the type of IDs. In addition, the melting point (Tm) of PP could be used as an effective indicator to evaluate the relative content of the highly isotactic active centers in the catalysts. This study provides valuable insights into the rational design of Z-N catalysts for propylene polymerization, highlighting the critical role of the preparation methodology in tailoring the catalyst properties and active center distribution.
Li et al. (Sat,) studied this question.