Highly Flowable Nano TiO₂/Porous Organic Polymer (POP) Supports for Efficient Metallocene Catalysts

Porous organic polymers (POPs) have proven to be an efficient support in the olefin polymerization catalyst field. In this paper, nano TiO₂ beads were used to modulate the pore structure, bulk density, and surface morphology and flowability of the prepared POPs. With the incorporation of the hydrophilic nano TiO₂ beads, the prepared TiO₂/POP supports obtained reasonable specific surface area (100-300 m²/g) and higher bulk density (0.26-0.35 g/mL) and flowability than the pure POP supports. The results show that bulk density of the prepared TiO₂/POP particles increased when adding an increased amount of TiO₂, and when 37.5% TiO₂ (weight percent to the total comonomers divinylbenzene (DVB) and 2-hydroxyethyl methacrylate (HEMA)) and 3:1 DVB/HEMA (molar ratio) were added, highly flowable TiO₂/POP composites (POP-6 and POP-7) were obtained. With the modulation of the nano TiO₂ template during the support synthesis, the prepared POP-7 particles successfully achieved a normal distribution with a narrow particle size distribution (PSD) of 0.717 and average particle size of 24.1 m, a specific surface area (SSA) of 279 m²/g, and relatively high bulk density of 0.30 g/mL. Furthermore, all the prepared TiO₂/POP supports obtained higher ethylene polymerization activity than silica gel-supported commercial metallocene catalyst. The immobilized (n-BuCp)₂ZrCl₂/MAO@POP-7 catalyst exhibited the highest ethylene polymerization activity of 4794 kg PE/mol Zr.bar.h and productivity of 389 g PE/g cat, more than twice that of the commercial counterpart. Even higher catalyst productivity (3197 g PE/g cat) and bulk density of the produced PE (0.36 g/mL) could be obtained in higher ethylene partial pressure at 80 ∘C for 2 h, and the prepared TiO₂/POP catalyst shows no obvious Zr⁺ active sites decay during the ethylene polymerization.