A.G. Potapov

A DFT quantum‐chemical study on the structures and active sites of polymethylaluminoxane

DFT quantum-chemical calculations have been performed to elucidate the geometrical and electronic structure of methylalumoxanes (-Al(Me)0-)n with different size (n=6,8,12). The three-dimensional oxo-bridged (cage) structures of methylalumoxane (MAO) have been analyzed.

27Al NMR MAS study of the surface Al complexes formed in reaction of organoaluminium compounds with supported TiCl4/MgCl2 catalyst

Abstract 27 Al NMR MAS method has been used to study the surface aluminium compounds forming during the treatment of supported TiCl4/MgCl2 catalyst with organoaluminium compounds (OAC) of various composition (AlEt3, AlOct3, AlEt2Cl). Dialkylaluminium chloride has been found to be the main surface compound in the case of trialkylaliminium. Three surface species of dialkylaluminium chloride have been identified: one of them corresponds to 5-coordinated aluminium; the other two correspond to 6-coordinated aluminium with different alkyl-to-chlorine ratio. The relative amounts of surface species depend on the conditions of OAC reaction with catalysts and OAC composition. After polymerization of ethylene or propylene on trioctylaluminium-treated catalysts (polymer yield ca. 1 g/1 g catalyst), the signals of 5-coordinated aluminium disappear from the 27 Al NMR spectra of the catalysts.

27Al NMR MAS study of AlEt3 − nClnMgCl2 systems

Abstract The 27 Al NMR MAS spectra of surface species of aluminum-containing compounds AlEt 3 − n Cl n ( n = 0–3) on MgCl 2 have been measured. The data obtained indicate that 5- and 6-coordinated aluminum compounds form on the MgCl 2 surface. The majority of the AlCl 3 supported in small amounts on MgCl 2 was found to be 4-coordinated.

Supported titanium-magnesium catalysts for propylene polymerization

The results of studies of the synthesis and properties of supported titanium-magnesium catalysts for propylene polymerization performed at the Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, are considered. The composition of the catalysts is TiCl4/D1/MgCl2-AlEt3/D2, where D1 and D2 are stereoregulating donors. With the use of the procedure proposed for the synthesis of titanium-magnesium catalysts, the morphology of catalyst particles depends on the stage of the preparation of a Mg-containing support. The titanium-magnesium catalysts developed afforded polypropylene (PP) in a high yield; this PP was characterized by high isotacticity and excellent morphology. The controllable fragmentation of the catalyst by the polymer is of crucial importance for the retention of the morphology of titanium-magnesium catalyst particles in PP. The fragmentation of catalyst particles to microparticles occurred in the formation of more than 100 g of PP per gram of the catalyst. The surface complexes were studied by DRIFT and MAS NMR spectroscopy and chemical analysis. It was shown that the role of internal donors is to regulate the distribution of TiCl4 on different MgCl2 faces and, thereby, to influence the properties of PP. It was found that chlorine-containing complexes of aluminum compounds were formed on the catalyst surface by the interaction of the catalyst with AlEt3; these complexes can block the major portion of titanium chloride. Data on the number of active sites and the rate constants of polymer chain propagation (kp) at various sites indicate that donor D1 increases the stereospecificity of the catalyst because of an increase in the fraction of highly stereospecific active sites, at which kp is much higher than that at low-stereospecificity active sites. Donor D2 enhances the role of D1. Similar values of kp at sites with the same stereospecificity in titanium-magnesium catalysts and TiCl3 suggest that the role of the support mainly consists in an increase in the dispersity of titanium chloride.

27Al MAS NMR study of the interaction of supported Ziegler–Natta catalysts with organoaluminium co-catalyst in the presence of donors

Abstract 27 Al MAS NMR spectroscopy has been used to study the surface aluminium compounds formed upon interaction of the supported TiCl 4 /donor/MgCl 2 catalyst with AlEt 3 in the presence or absence of the external donor. Similarly with the catalyst without any donors [A.G. Potapov, V.V. Terskikh, V.A. Zakharov, G.D. Bukatov, J. Mol. Catal. A: Chem., 145 (1999) 147], the AlEt 2 Cl formed adsorbs on the catalyst surface. It was found that there is no influence of internal and/or external donors on the state of aluminium in adsorbed AlEt 2 Cl in spite of a decrease of the aluminium content in the presence of external donor.

State of various stereoregulating electron-donating compounds in titanium-magnesium catalysts for propylene polymerization: A diffuse reflectance IR spectroscopic study

Propylene polymerization on TiCl4/donor/MgCl2 (donor = ethyl benzoate, dibutyl phthalate, diisobutyl phthalate, diethyl 2,3-diisopropylsuccinate) supported catalysts is considered. The states of the donors in the catalysts have been investigated by diffuse reflectance IR spectroscopy. Data characterizing the distribution of the donors and the active component (TiCl4) on the support surface have been obtained. Molecular weight distribution data for polypropylene are presented. The molecular weight distribution of polypropylene depends on the location of the donor and TiCl4 molecules.