STUDIES ON THE POLYMERIZATION OF ETHYLENE USING A HIGH-YIELD MGCL2-SUPPORTED TITANIUM CATALYST .4. STRUCTURAL INVESTIGATION BY X-RAY-DIFFRACTION AND ELECTRON-SPIN-RESONANCE MEASUREMENTS ON THE STATE OF TITANIUM IONS I THE STANDARD SYSTEM AND ITS MODIFICATIONS

The MgCl2-supported titanium catalyst MTK(ST) was characterized by X-r ay diffraction measurement and electron spin resonance (ESR) spectrosc opy. To obtain a better understanding of the nature of active sites th e process of catalyst formation was interrupted at several stages to o btain samples for ESR measurements. Likewise some systematic modificat ions of the standard system were performed and the results were studie d by ESR technique. The structural data were correlated with the activ ity pattern in the polymerization of ethylene. It is suggested that th e precursor of an active site is a clustered titanium species containi ng titanium ions of mixed valence state which is complexed and alkylat ed by AlR3 giving a polymerization active species of high efficiency. A comparison with the polymerization data suggests that the active spe cies or its immediate precursor is characterized by an ESR signal with rhombic anisotropy with g1 = 1,94, g2 = 1,89, g3 = 1,76.