Propene polymerization on titanium‐magnesium catalysts, 4. ESR study of TI³⁺ ions

Abstract

Abstract The role of Ti 3+ ions in titanium‐magnesium catalysts of various composition, TiCl 4 /MgCl 2 + AlR 3 , TiCl 4 /MgCl 2 + Al(i‐Bu) 3 + EB, TiCl 4 /EB/MgCl 2 + Al(i‐Bu) 3 and TiCl 4 /EB/MgCl 2 + Al(i‐Bu) 3 + EB, was studied by means of ESR. The ESR data and the catalytic properties were compared. It could be shown that the introduction of ethyl benzoate (EB) leads to an increase of stereospecificity, to a considerable increase of the portion of Ti 3+ ions which can be observed by ESR, to the appearance of several new signals in the ESR spectra and to an increase of the portion of titanium in solution, removed from the solid catalyst during the interaction with the organoaluminium cocatalyst. Titanium ions are found mainly in the particles or surface associates whose Ti 3+ ions produce no signals in the ESR spectra, Ti 3+ ions observed by ESR are found to be inactive centers of polymerization. The active centers appear to be localized in highly dispersed particles or surface associates of TiCl 3 , formed on the MgCl 2 surface and are not revealed in the ESR spectra. Increasing stereospecificity in the presence of EB is assumed to be caused by deactivation of non‐stereospecific active centers with ethyl benzoate.