Modification of a Ziegler‐Natta catalyst with a metallocene catalyst and its olefin polymerization behavior

Abstract

AbstractA Ziegler‐Natta catalyst was modified with a metallocene catalyst and its polymerization behavior was examined. In the modification of the TiCl4 catalyst supported on MgCl2 (MgCl2‐Ti) with a rac‐ethylenebis(indenyl)zirconium dichloride (rac‐Et(Ind)2ZrCl2, EIZ) catalyst, the obtained catalyst showed relatively low activity but produced high isotactic polypropylene. These results suggest that the EIZ catalyst might block a non‐isospecific site and modify a Ti‐active site to form highly isospecific sites. To combine two catalysts in olefin polymerization by catalyst transitioning methods, the sequential addition of catalysts and a co‐catalyst was tried. It was found that an alkylaluminum like triethylaluminum (TEA) can act as a deactivation agent for a metallocene catalyst. In ethylene polymerization, catalyst transitioning was accomplished with the sequential addition of bis(cyclopentadienyl)zirconium dichloride (Cp2ZrCl2)/methylaluminoxane (MAO), TEA, and a titanium tetrachloride/vanadium oxytrichloride (TiCl4/VOCl3, Ti‐V) catalyst. Using this method, it was possible to control the molecular weight distribution (MWD) of polyethylene in a bimodal pattern. In the presence of hydrogen, polyethylene with a very broad MWD was obtained due to a different hydrogen effect on the Cp2ZrCl2 and Ti‐V catalyst. The obtained polyethylene with a broader MWD exhibited more apparent shear thinning.