POSS@TiCl4 nanoparticles:A minimalism styled Ziegler-Natta catalytic system

Li, Wei and Dong, Chuanding and Wang, Xiaodong and Wang, Jingdai and Yang, Yongrong (2023) POSS@TiCl4 nanoparticles:A minimalism styled Ziegler-Natta catalytic system. Journal of Catalysis, 421. pp. 384-392. ISSN 0021-9517

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Abstract

Heterogeneous catalysis plays a crucial role in industrial olefin polymerization. Mechanistic understanding and optimization of Ziegler-Natta (ZN) catalyst are limited by the considerable complexity resulting from the multiple ingredients and complicated structures. Re-designing ZN catalytic systems with reduced complexity and adequate performance is of great interest. Here, we show that self-assembled polyhedral oligomeric silsesquioxane (POSS)@TiCl4 nanoparticles can effectively immobilize TiCl4 molecules in n-heptane solution, achieving the exceptional utilization of active centres. This uncomplicated system exhibits heterogeneous-like catalytic performance in ethylene polymerization, featured by high activities, fouling-free polymerization and a series of desirable properties of the nascent polymers such as reduced entanglement and spherical morphology. In addition, these catalytic nanoparticles show robust resistance to H2, and enhanced incorporation of comonomer towards ethylene/1-hexene copolymerization. By using DFT calculations the possible structures of the Ti active centres are proposed, of which a flexible double-Ti structure coordinated to Si-O-Si shows the most reduced energy barrier for ethylene insertion.