Deciphering the Role of Internal Donors in Shaping Heterogeneous Ziegler-Natta Catalysts Based on Nonempirical Structural Determination

The addition of internal donors (IDs) to the heterogeneous Ziegler-Natta catalyst for propylene polymerization is fundamental to obtain highly isotactic polypropylene, but its role in shaping the stereospecific structure of the catalyst is still not comprehended. In this work, we apply nonempirical structure determination, based on a genetic algorithm and density functional theory calculations, to ternary systems composing MgCl2, TiCl4, and ID. We found that the copresence of TiCl4 and ID led to the preferential formation of specific surface motifs, involving sharp edges and concavities. This was achieved by concerted adsorption of chelating ID and octahedral TiCl4 and significantly promoted TiCl4 situated in stereospecific environments. The multiplicity of adsorption modes of IDs was found to have a direct consequence on the structural diversity, where phthalate exhibited far greater diversity than 1,3-diether. In conclusion, this study revealed the essentiality of ID-driven reconstruction of MgCl2 in understanding the structure and function of this catalyst.