Novel SiO2-supported chromium catalyst bearing new organo-siloxane ligand for ethylene polymerization

Nowadays, SiO2-supported Cr-based catalysts mainly including oxo chromium (Phillips catalyst) and silyl chromate (UCC catalyst) systems are still important industrial catalysts for ethylene polymerization. It was found that the addition of triphenylsilanol could transform Phillips catalyst into silyl chromate catalyst. In this work, a new chiral organo-silanol was synthesized and subsequently introduced to modify the Phillips catalysts in order to develop a new SiO2-support Cr-based catalyst with a chiral organo-siloxane ligand for ethylene polymerization. The new catalyst was characterized by X-ray photoelectron spectroscopy (XPS) and solid-state NMR methods. The new Cr-based catalysts with chiral organo-siloxane ligand presented as an active catalyst for ethylene polymerization, and their kinetic characteristic is found to be similar with that of calcined Phillips catalyst combined with TEA cocatalyst. It was very interesting to find the existence of short chain branches (SCBs) in these ethylene homo-polymers. The introduction of the new chiral organo-siloxane ligand was also found to produce polyethylene with bimodal molecular weight distribution and to enhance the amount of SCBs, which might be due to the steric and/or electronic effect of such chiral ligand, indicating a new method to improve the performance of Cr-based catalyst for polyethylene production.

Graphical abstractA novel Cr-based catalyst bearing new organo-siloxane ligand was developed successfully through chemical modification of traditional Phillips CrOx/SiO2 catalyst using a chiral organo-silanol namely (R)-methyl-(1-naphthyl)-phenylsilanol. The catalyst combined with triethylaluminium (TEA) was found to produce polyethylene with bimodal molecular weight distribution, as well as to promote short chain branching. Figure optionsDownload full-size imageDownload as PowerPoint slide