FTIR spectroscopic study of supported titanium–magnesium catalysts for propylene polymerization containing diether and succinate as internal donors

Abstract

The data on the interaction of internal stereoregulating donors (IDs) diethyl 2,4-diisobutyl succinate (DIBS), 2-isopropyl-2-isopentyl-1,3-dimethoxypropane (IPIPDMP) and a mixture of these IDs with the δ-MgCl₂ support, and the data on the transformations occurring upon interaction between surface structures of these donors and TiCl₄ in model MgCl₂/ID/TiCl₄ samples were obtained by the chemical analysis and IR spectroscopy. It was found that DIBS interacts with penta- and tetracoordinated Mg ions yielding three types of surface species, while IPIPDMP forms surface species with tetracoordinated Mg ions. In the mixed-donor sample MgCl₂/(DIBS+IPIPDMP) donors IPIPDMP and DIBS are anchored to different sites of the MgCl₂ surface and do not compete with each other. The interaction of the MgCl₂/DIBS sample with TiCl₄ leads to the replacing of one third of DIBS anchored to tetracoordinated magnesium ions by TiCl₄, while two thirds of TiCl₄ are anchored to the vacant sites on MgCl₂. In the case of MgCl₂/IPIPDMP, TiCl₄ is mostly anchored to the vacant sites of MgCl₂. Treatment of the mixed-donor MgCl₂/(DIBS+IPIPDMP) sample with TiCl₄ results in partial removal of DIBS and IPIPDMP and TiCl₄ fixation at both vacant and freed surface sites. The data obtained for real highly-active titanium–magnesium catalysts for propylene polymerization containing IPIPDMP, DIBS, and the DIBS+IPIPDMP mixture donors are close to those for the respective MgCl₂/ID/TiCl₄ model samples. The key difference is that the contents of ID and TiCl₄ increase abruptly and the ID/TiCl₄ molar ratio changes in real TMCs.