The modification of Mg(OEt)2-based Ziegler-Natta catalysts with various metal chlorides were examined on ethylene homopolymerization and copolymerization with 1-hexene. One of the selected metal chlorides (FeCl2, ZnCl2 and MnCl2) was added together with SiCl4 in the chlorination stage of Mg(OEt)2. It was found that the introduction of metal chlorides affect the exposure of Ti on the surface as well as the catalyst surface area. The homopolymerization activity correlated well with the surface Ti, in the order ZN-Fe > ZN-Si > ZN-Zn > ZN-Mn > ZN-none, while the copolymerization activity was independent of the surface Ti/Mg atomic ratio and increased in the following order; ZN-Fe > ZN-Zn > ZN-Mn > ZN-Si > ZN-none. The results showed that among various metal chlorides, the addition of FeCl2 could enhance both the Brenauer-Emmett-Teller (BET) specific surface area and the surface atomic ratio of Ti/Mg, leading to the highest activity in both ethylene homo- and copolymerization. The exposure of Ti species on outer surfaces could be thought as a sign of easier mass transfer phenomena leading to the improvement of catalyst performances.
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