Propene Polymerization on Titanium-Magnesium Catalysts, 4. ESR Study of Ti3+ Ions
Makromolekulare Chemie up to 1993, continued as Macromolecular Chemistry and Physics
Sergeev Sergei A.
Poluboyarov Vladimir A.
Zakharov Vladimir A.
Anufrienko Vladimir F.
Bukatov Gennadii D.
The role of Ti3+ ions in titanium-magnesium catalysts of various composition, TiCl4/MgCl2 + AlR3, TiCl4/MgCl2 + Al(i-Bu)3 + EB, TiCl4/EB/MgCl2 + Al(i-Bu)3 and TiCl4/EB/MgCl2 + 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 Ti3+ 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 Ti3+ ions produce no signals in the ESR spectra, Ti3+ 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 TiCl3, formed on the MgCl2 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.