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

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.

Automated summary

In this study, self-assembled polyhedral oligomeric silsesquioxane (POSS)@TiCl4 nanoparticles were used to effectively immobilize TiCl4 molecules in n-heptane solution, resulting in the utilization of active centres. This uncomplicated system exhibited heterogeneous-like catalytic performance in ethylene polymerization, with high activities, fouling-free polymerization, and desirable properties of the nascent polymers. Moreover, these catalytic nanoparticles showed resistance to H2 and enhanced incorporation of comonomer in ethylene/1-hexene copolymerization. The proposed Ti active centres structures provided insights into the reduction of the energy barrier for ethylene insertion.