Surface acidic sites on supported titanium-magnesium catalyst for propylene polymerization: ESR study via adsorption of stable nitroxyl radicals

ESR was used for studying the interaction between the stable nitroxyl radical TEMPO (2,2,6,6‐tetramethylpyperidin‐1‐oxyl) and the titanium‐magnesium catalysts TiCl4/MgCl2 and TiCl4/MgCl2 · nD (D is either diisobutyl phthalate or 2,2‐diisobutyl‐1,3‐dimethoxypropane), as well as TiCl4/MgCl2 · nD treated with triethylaluminium. In all cases, only part of the surface titanium complexes (18–53 mol‐%) exhibit Lewis acid properties and can interact with TEMPO. The portion of titanium complexes with acidic properties depends on the composition and preparation of the catalysts, and it decreases upon treatment with triethylaluminium.