Model for the formation of active titanium complexes on MgCl2-ethyl benzoate-TiCl4catalysts for propylene polymerization

Abstract

Carbonyl (C-O) bonds of ethyl benzoate (EB) in the support and the catalysts were investigated by infrared (IR) spectroscopy, and a model for the MgCl2-EB-TiCl4 complex was proposed. The characteristic carbonyl peaks at 1690 cm-1 and 1636 cm-1 can be attributed to the carbonyl vibrations in linear EB-MgCl2 and bridged EB-MgCl2 complex, respectively. With small amounts of EB added to MgCl2, both linear and bridged EB/MgCl2 complexes are formed. A further increase in the amount of EB converts all of the complexes to the linear form. The active site for propylene polymerization seems to be the TiCl4-MgCl2 complex, generated by activation with TiCl4 of the bridged EB-MgCl2 complex, some of which is converted to the linear EB-MgCl2 complex. The linear EB-MgCl2 complex tends to inactivate the (EB-TiCl4)2 complex. The catalytic activity for propylene polymerization was consistent with the proposed model and the IR investigation.