Novel Imido‐Cr/Silica Ethylene Polymerization Catalysts Modified from the Phillips Catalyst

Abstract

In this work, novel imido-Cr/silica catalysts are synthesized by modifying the Phillips catalyst CrO x /silica with isocyanates. The imido-Cr/silica, which has moderate activities of 200-300 kgPE molCr −1 bar −1 , shows lower efficiency than CrO x /silica for C 2 H 4 polymerization. On the other hand, regarding to the modified catalysts, the productivity can be improved almost linearly with increasing C 2 H 4 pressure, and very stable activities are observed during the 1 h run of C 2 H 4 polymerization. When compared with CrO x /silica, the modified catalysts can produce polyethylene (PE) with much higher molecular weight (MW) and broader molecular weight distribution (MWD), which is featured by a distinct ultrahigh MW shoulder. Meanwhile, the MW and MWD of the PE products can be reduced obviously by adding a small amount of H 2 before C 2 H 4 polymerization. In addition, it is found that more 1-hexene can be copolymerized by CrO x /silica, and it is preferentially incorporated into a portion of the PE chains. While such a preference is much less significant for the modified catalysts.