OLEFIN POLYMERIZATION WITH MODIFIED SPHERICAL ZIRCONIA-SUPPORTED METALLOCENE CATALYSTS

Abstract

In this research, ethylene/1-hexene copolymerizations were conducted with rac-Et(Ind)2ZrCl2 in order to compare effect of MAO supported on spherical zirconia modified with different modifiers; BCl3, SiCl4 and glycerol. All kind of modifiers can enhance the catalytic activity of this heterogeneous catalyst system compared to unmodified-ZrO2 system, but did not affect the copolymers microstructure. The modification of ZrO2 with SiCl4 before supporting MAO showed the highest catalytic activity. However, the reason of the activity improvement by SiCl4-modification has not been clear. In the event of living polymerization accomplished with the modified cocatalyst system, it becomes obvious whether the modification affects the number of active centers (C*) or the propagation rate constant (kp). Considering the living nature of Me2Si(3-C13H8)(1-NtBu)TiMe2-based catalytic systems, ZrO2-supported MAO cocatalyst suggest the living behavior of propylene polymerization with this catalyst. Thus, this catalyst was used with MAO supported on unmodified and SiCl4-modified ZrO2 for clarifying the modification effect of SiCl4 on cocatalyst abilities. The Mn values of polypropylenes increased linearly against the polymerization time regardless the cocatalyst used to give polymers with narrow molecular weight distribution, indicating the living nature of the catalytic systems. Thus, the kp and C* values were evaluated from Mn and the number of polymer chains. When the ZrO2 was modified with SiCl4, the kp value decreased and the C* increased. The latter effect was more significant to enhance the catalytic activity.