G. D. Bukatov

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.

Homogeneous and supported catalysts based on bis(imino)pyridyl Iron(II) complexes for ethylene polymerization

Data on ethylene polymerization on homogeneous and supported catalysts based on 2,6-bis(imino)pyridyl Fe(II) complexes activated by trialkylaluminums are considered (activity, the molecular-weight characteristics of polymers, the number of active sites, and the propagation rate constants). Unlike homogeneous systems, the supported catalysts prepared with the use of various carriers (SiO2, Al2O3, and MgCl2) exhibited high stability and activity at 70–80°C and produced high-molecular-weight polyethylene with a broad molecular-weight distribution (MWD). The molecular weights and MWDs of polymers and the propagation rate constant depended on the nature of the carrier only slightly. The reasons for an unusual effect of an increase in the activity of the supported catalysts in ethylene polymerization in the presence of hydrogen are discussed.

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.

State of titanium in supported titanium-magnesium catalysts for propylene polymerization

The oxidation state of titanium and the coordination state of Ti3+ ions in TiCl4/D1/MgCl2 (D1 is a phthalate) supported titanium-magnesium catalysts (TMCs) after the interaction with an AlEt3/D2 cocatalyst (D2 is propyltrimethoxysilane or dicyclopentyldimethoxysilane) were studied by chemical analysis and EPR spectroscopy. Different oxidation state distributions of titanium ions were observed in the activated catalyst and mother liquor: Ti3+ and Ti2+ ions were predominant in the activated catalyst and mother liquor, respectively. The effects of interaction conditions (reaction temperature and time and Al/Ti and D2/Ti molar ratios) of TMCs with the cocatalyst on the state of titanium in activated samples were studied. The interaction of TMCs with the cocatalyst decreased the titanium content and caused the appearance of aluminum in the activated sample, which was most clearly pronounced at a temperature of 25°C and occurred within the first 10 min of treatment. An increase in the temperature to 70°C and an increase in the interaction time to 60 min only slightly affected the concentrations of titanium and aluminum. The presence of D2 as a cocatalyst constituent facilitated the removal of titanium compounds and restricted the adsorption of aluminum compounds on the catalyst surface. The main fraction of titanium consisted of Ti3+ ions (62–89%), and the rest was Ti4+ ions (22–35%) under mild interaction conditions (25°C; Si/Ti = 25) or Ti4+ (0–21%) and Ti2+ (9–21%) ions under more severe conditions (50 or 70°C; Si/Ti from 0 to 5). According to EPR-spectroscopic data, at D2/Ti from 1 to 5, Ti3+ ions mainly occurred as associates, whereas they occurred as isolated ions at D2/Ti = 25. The initial and activated catalysts were similar in activity in the reaction of propylene polymerization, and titanium compounds, which were removed from the catalyst upon interaction with AlEt3/D2, were inactive in this process.

Effect of titanium–magnesium catalyst morphology on the properties of polypropylene upon propylene polymerization in a liquid monomer

The effect of the particle size of an IK-8-21 domestic titanium-magnesium catalyst on the properties of polypropylene (PP) produced during the polymerization of propylene in a liquid monomer is studied. Catalysts with particle sizes of 20 to 64 μm are shown to have high activity and identical sensitivity to hydrogen and allow PP to be obtained with a narrow distribution of particles over size, high isotacticity, and close values of crystallinity, melting temperature, and physicomechanical properties. A slight decrease in the activity and bulk density of PP powder is observed when the average size of catalyst particles is increased from 20 to 43 μm. A more notable reduction in the activity and bulk density of PP powder is observed for catalyst with particle sizes of 62 to 64 μm. IK-8-21 catalyst is not inferior to its foreign analogues with respect to the properties of the resulting PP.

Polymerization of propylene in liquid monomer using state-of-the-art high-performance titanium-magnesium catalysts

A comparative study of propylene polymerization in liquid monomer is performed under laboratory conditions using the IK-8-21 Ti-Mg catalyst designed at the Boreskov Institute of Catalysis and imported industrial catalysts (conditionally labeled TMC-1, -2, and -3). The activity and stereospecificity of the catalysts are estimated along with properties of the resulting polypropylene (granular composition and physicomechanical characteristics). It is shown that the IK-8-21 catalyst is not inferior to imported counterparts in terms of catalytic properties in the synthesis of polypropylene. The polypropylene powder formed on IK-8-21 is homogeneous and has good morphology. The physicomechanical characteristics of polypropylene synthesized on the domestic IK-8-21 catalyst are similar to those for polypropylene prepared with the imported TMK-1 catalyst.

Titanium-magnesium catalysts for propylene polymerization: The effect of donors

The chain transfer reaction with hydrogen at propylene polymerization over Ti-Mg catalysts (TMCs) of composition TiCl4/D1/MgCl2-AlEt3/D2 is studied in a wide hydrogen concentration range. A two-step mechanism of this reaction is suggested. This mechanism accounts for the fractional order of the reaction with respect to hydrogen concentration. Constants of chain transfer reaction with hydrogen are determined for TMC with different donors: 1,3-diether or dibutyl phthalate as D1 and tetraethoxysilane or dicyclopentyldimethoxysilane as D2. In propylene polymerization over the TMCs, the length of the polymer chain is mainly determined by the ratio of the propylene and hydrogen concentrations because the propagation and chain transfer rate constants are comparable. The rate constant of chain transfer with hydrogen at ethylene polymerization is significantly (more than one order of magnitude) less, and higher hydrogen concentrations are required for attaining the same degree of polymerization. The results of this study might be helpful in simulation of industrial polymerization processes and in control of the polymer molar mass.