Modification of a Ziegler-Natta catalyst with a metallocene catalyst and its olefin polymerization behavior (original) (raw)

1999, Polymer Engineering & Science

A Ziegler-Natta catalyst was modified with a metallocene catalyst and its polymerization behavior was examined. In the modification of the TiCl, catalyst supported on MgCb (MgCb-Ti) with a rac-ethylenebis(indeny1)zirconium dichloride (rac-Et(Ind)&Cb. 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 mod@ 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(cyclopentadieny1)zirconium dichloride (Cp&rClJ/methylaluminoxane (MAO), TEA, and a titanium tetrachloride/vanadium oxytrichloride (TiC14/VOCl,, 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 Cp,ZrCl, and Ti-V catalyst. The obtained polyethylene with a broader MWD exhibited more apparent shear thinning.