Developing CrOx/VOx/Ind2ZrCl2/Silica/TiBA tri-metallic catalysts for controllable synthesis of trimodal UHMWPE/HDPE in-reactor blends

A series of mono-, bi- and tri-metallic catalysts including Ind 2 ZrCl 2 /silica, CrO x /VO x /silica and CrO x /VO x /Ind 2 ZrCl 2 /silica were synthesized for C 2 H 4 polymerization in this work. The results show that conventional cocatalyst TiBA could hardly activate Ind 2 ZrCl 2 /silica. However, under the assistance of the surface species over CrO x /VO x /silica, traces of TiBA (Al/metal ＜15, molar ratio) endowed the Zr species with moderate activity. The combined results of XPS, FTIR-pyridine-adsorption and DRS Uv–vis show that the Lewis acidic Cr and V sites could interact with Ind 2 ZrCl 2 and improve the electronic deficiency of Zr center, which is possible to promote zirconocene activation, though direct Si-O-Zr linkage was non-negligible, and redox between Cr(VI)/V(V) and zirconocene existed. The Zr species were responsible for ultra-high molecular weight polyethylene (UHMWPE) synthesis, and the relative content of UHMWPE fractions could be controllably regulated by polymerization temperature, partial pressure of hydrogen and the loading amount of Zr. Generally, these tri-metallic catalysts CrO x /VO x /Ind 2 ZrCl 2 /silica could synthesize trimodal HDPE/UHMWPE in-reactor blends with very broad molecular weight distribution. Meanwhile, owing to the excellent copolymerization ability of zirconcene, preferential distribution of the short chain branches along the ultra-high molecular weight (MW) chains for C 2 H 4 /1-hexene trimodal copolymers was achieved. The rheological results show that the fractions with extreme MW difference in the trimodal polyethylene (PE) exhibited excellent miscibility, and its superiority in processing and mechanical properties over the monomodal PE with similar MW was verified by rheological, tensile and impact tests.