Study of the state of titanium ions and the composition of the active component in titanium-magnesium catalysts for ethylene polymerization

The state of Ti³⁺ ions formed at various steps of preparation and activation of highly active titanium-magnesium catalysts of various composition (dry milling of TiCl₃ with MgCl₂; reduction of TiCl₄ by nonsolvated magnesium dialkyl; interaction of the TiCl₄/MgCl₂ system with an organoaluminium compound) was studied by the ESR method. It was found that in all systems studied the same three types of Ti³⁺ ions in the chlorine environment are formed, differing in coordination and localization sites in MgCl₂. The content of these ions depends on the composition and preparation conditions of the catalysts, and does not exceed 20% of the total content of titanium. Most of the Ti³⁺ ions formed in all systems enter the composition of particles or surface aggregates of TiCl₃ and appear in the ESR spectra only after dissolution of the sample in pyridine. The active centers of titanium-magnesium catalysts are supposed to be constituents of these particles or of surface aggregates.