DFT Study On The Role Of Electron Donor In Propylene Polymerization Over Ziegler-Natta Catalysts

As a kind of versatile resin, polypropylene shows superior performances in a very wide range of applications with low cost. In present, the MgCl2-supported Ziegler-Natta catalyst still plays a dominate role in the industrial production of the most widely used polypropylene. Since the discovery of the first generation of Ziegler-Natta catalyst, the researchers have been conducted tremendous works to understand the reaction mechanisms and to further improve the catalytic activities, the stereoselectivity and regioselectivity of propylene polymerization. In the literature, most of the mechanistic studies were based on idealistic crystalline surface models of the supported active site, in which a flawless plane of MgCl2is always employed. However, the MgCl2support in industrial Ziegler-Natta catalyst has many surface defects, which may play a key factor in understanding the real mechanism of propylene polymerization catalyzed by the Ziegler-Natta catalyst.In our previous study, we established10models with different kinds of defects on the MgCl2(110) and (104) surfaces, In this work, we employed the previously determined active center model and futher inverstigated the adsorption of four kinds of electron donors on the adjacent vacancy of the Ti-active species including ethyl benzoate (EB), di-n-butyl phthalate (DNBP), cyclohexyl methyl dimethoxy silane (CHMMS), and dimethoxy dicyclopentyl silane (DCPMS). Futhermore, the stereo-and regioselective behaviors of this active site model were also investigated. It was found that EB and DCPMS can greatly enhance the stereoselectivity of the active center. On the basis of the DFT calculations, the role of electron donors in propylene polymerization over Ziegler-Natta catalysts has been elucided. The conclusion of this work could guide the further development of new electron donors for development of new generation Ziegler-Natta catalysts.