MODEL FOR THE FORMATION OF ACTIVE TITANIUM COMPLEXES ON MGCL2-ETHYL BENZOATE-TICL4 CATALYSTS FOR PROPYLENE POLYMERIZATION

Carbonyl (C-O) bonds of ethyl benzoate (EB) in the support and the cat alysts were investigated by infrared (IR) spectroscopy, and a model fo r 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 vi brations 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 con verts all of the complexes to the linear form. The active site for pro pylene polymerization seems to be the TiCl4-MgCl2 complex, generated b y activation with TiCl4 of the bridged EB-MgCl2 complex, some of which is converted to the linear EB-MgCl2 complex. The linear EB-MgCl2 comp lex tends to inactivate the (EB-TiCl4)2 complex. The catalytic activit y for propylene polymerization was consistent with the proposed model and the IR investigation.