Control of Ziegler-Natta Catalyst Activity by Structural Design of Alkoxysilanes-based External Donors
Herein, the evaluation of four commercial alkoxysilanes and two laboratories synthesized novel diethoxysilacycloalkanes as external donors towards propylene polymerization has been investigated. Propylene polymerizations were carried out using fourth generation Ziegler-Natta (ZN) catalyst containing diisobutylphthalate (DIBP) as an internal donor in conjunction with triethylaluminium (TEAL) as co-catalyst. The performance of the six external donors studied herein has been described by correlating the experimental results with the predictions from first principle density functional theory calculations. The theoretical binding energies of the complex formed between the external donors and the co-catalyst were found to have a reasonable correlation with the experimentally measured productivity of polypropylene. The comparative results confirmed that certain essential structural characteristics of the external donors are prerequisites to achieve an enhanced activity of the catalyst and stereospecificity of polypropylene.