Marzena Białek

Oxovanadium(IV) complexes with (ONNO)-chelating ligands as catalysts for ethylene homo- and copolymerization

Oxovanadium(IV) complexes with [ONNO]-type tetradentate Schiff base ligands: salen, acacen, aceten, acetph (H2salen = N,N′-ethylenebis(salicylideneimine), H2aceten = N,N′-ethylenebis(2-hydroxyacetophenoneimine), H2acacen = N,N′-ethylenebis(acetylacetonimine), H2acetph = N,N′-phenylene-1,2-bis(2-hydroxyacetophenoneimine)), were the first time investigated in ethylene polymerization and ethylene/1-octene copolymerization processes. In general, all these complexes are moderately active precatalyst for ethylene polymerization upon activation with EtAlCl2 and they give high molecular weight linear polyethylenes. Their activity in copolymerization was found relatively low. However, they yielded copolymers with high 1-octene incorporation even at low comonomer concentrations in the feed. The catalytic performance in homo- and copolymerization was influenced by both the ligand structure and polymerization parameters (Al/V molar ratio, polymerization temperature, comonomer feed concentration). In addition, the [VO(acacen)] was supported onto magnesium supports, and in the presence of various cocatalyst and at different reaction conditions it was screened as the catalyst of choice for ethylene homo- and copolymerization.

Studies of Intermolecular Heterogeneity Distribution in Ethylene/1-hexene Copolymers Using DSC Method

The investigation of the intermolecular composition distribution of an ethylene/1-hexene copolymers using DSC method has been carried out. The known methods: step crystallization (SC) and successive self-nucleation/annealing (SSA) have been adapted for this purpose, and particularly, the optimal condition of the process have been chosen to enable the best fractional crystallization of the copolymer. The method has been applied for fractionation of two ethylene/1-hexenecopolymers synthesized with supported vanadium and zirconocene catalysts and having similar concentrations of 1-hexene. Although metallocene catalysts are known from their more homogeneous structure of active sites in comparison to multi-site Ziegler–Natta catalysts, the copolymers obtained over both catalytic systems gave DSC curves resolved into several peaks but with different melting points. Using the Thomson–Gibbs equation, comparable average lamellar thickness of the separated peaks has been calculated. The amounts of copolymer fraction with defined lamellar thickness have been determined. It was obtained that the copolymer produced from the metallocene system contains a thinner and more homogeneous lamella thickness than that obtained with Ziegler–Natta vanadium catalyst supported on the same carrier.

Effect of hydrogen on the ethylene polymerization process over Ziegler–Natta catalysts supported on MgCl2(THF)2. I. Studies of the chain-transfer reaction

The effect of hydrogen on the molecular weight of polyethylene obtained over vanadium catalysts (based on VCl4 and VOCl3) supported on MgCl2(THF)2 was studied and the results were compared to those obtained for similar titanium catalysts. It was confirmed that the dependencies of the transfer reaction on the hydrogen concentration are a half-order in all investigated systems. However, the transition metal of the catalytic site affects the ratio of the transfer rate with hydrogen to the propagation rate (ktr,H/kp) and the results showed that hydrogen is a more effective agent of polyethylene molecular weight control in vanadium-based systems as compared to the titanium catalyst.

Ethylene/1-olefin copolymerization behaviour of vanadium and titanium complexes bearing salen-type ligand

Ethylene/1-olefin copolymerization using vanadium and titanium complexes bearing tetradentate [O,N,N,O]-type ligand and EtAlCl2 or MAO as a cocatalyst is carried out. In the presence of the vanadium complex activated with EtAlCl2 is observed (a) negative “comonomer effect”, (b) high comonomer incorporation and narrow chemical composition distribution (CCD), (c) unexpected copolymer microstructure, and (d) increased molecular weight of copolymers when compared with the homopolymer. In contrast, titanium catalyst gives copolymers with lower 1-olefin content and broad CCD. Supported complexes show higher activity, lower 1-olefins incorporation and give copolymers with ultra high molecular weights.

Effect of hydrogen on the ethylene polymerization process over Ziegler–Natta catalysts supported on MgCl2(THF)2. II. Kinetic studies

This article reports on a study of the effects of hydrogen on the activity of vanadium and titanium catalysts supported on MgCl 2 (THF) 2 in ethylene polymerization. It was found that hydrogen did not change the stable nature of the active sites and the polydispersity index of the polyethylene obtained. The propagation rate, expressed as k p , was found to be independent of the presence and concentration of hydrogen, indicating that this reacting agent does not modify the reactivity of the active sites. However, the presence of hydrogen in the polymerization medium is responsible for partial deactivation of the active sites just before polymerization is initiated.

Titanium-biphenoxide catalysts for ethylene polymerization

Titanium (IV) complexes containing sterically bulky ligands such as 2, 2′- methylenebis (4-methyl-6-tert butyl phenol) (MBTP) were synthesized by stoichiometric reaction between Ti(IV)alkoxide or halide and the biphenol. These catalyst precursors formulated as [Ti(O^O)RR′] were characterized by physicochemical and spectroscopic methods. The newly prepared Titanium biphenoxides were found to be active in polymerization of ethylene at high temperatures and pressures in combination with ethylaluminum sesquichloride (Et3Al2Cl3) as co-catalyst. The linear polyethylene obtained by this route exhibit low-molecular weights, are highly crystalline and display narrow polydispersities. The physical properties of polymers thus obtained closely resemble specialty PE waxes that are industrially important for surface coating, ink formulations and mar resistance applications.

Effect of AlR 3 (R = Me, Et, i Bu) addition on the composition and microstructure of ethylene/1-olefin copolymers made with post-metallocene complexes of group 4 elements

AbstractThe effect of trialkylaluminum compound (AlR3, where R = Me, Et, iBu) addition on the performance of the [LigZrCl]2(μ-O)/AliBu3/Ph3CB(C6F5)4 and LigTiCl2/AliBu3/Ph3CB(C6F5)4 (Lig = Me2N(CH2)2N(CH2-2-O-3,5-tBu2-C6H2)2) catalysts in ethylene/1-olefin copolymerization was investigated. The presence of AlMe3 in the feed during the copolymerization process catalyzed by the diamine-bis(phenolate) zirconium catalyst greatly increases the amount of incorporated comonomer and leads to microstructural changes, e.g., the formation of blocky and alternating sequences of 1-olefin units. Moreover, the use of AlMe3 limits the reaction yield and decreases the molecular weight of the produced copolymers. The catalytic properties of the diamine-bis(phenolate) titanium catalyst were much less affected by trimethylaluminum; its use slightly decreased the catalyst activity and copolymer molecular weight. A lower molecular weight was also detected for the copolymers produced by catalysts in the presence of both AlEt3 and AliBu3, whereas they did not cause any important changes in the catalytic activity, overall composition or microstructure of the produced copolymers. Copolymerization tests with other catalytic systems, (LigFI)2ZrCl2/AliBu3/Ph3CB(C6F5)4 (LigFI = (C6H5)N = CH(2-O-3,5-tBu2-C6H2)) and Et(Ind)2ZrCl2/MMAO, in the presence of AlMe3, were also carried out for the purpose of comparison.The effect of trialkylaluminium compound (AlR3, where R = Me, Et, iBu) addition on the performance of the transition metal complex/AliBu3/Ph3CB(C6F5)4 catalysts in ethylene/1-olefin copolymerization was investigated. It was shown that AlR3 may affect the catalytic properties of the system (activity, comonomer incorporation, and copolymer microstructure). This influence is dependent on the type of organoaluminum compound and on the structure of the complex, i.e., on the structure of the ligand and on the type of transition metal.

2,4-Di-tert-butyl-6-({[2-(di-methyl-amino)-eth-yl](2-hy-droxy-benz-yl)amino}-meth-yl)phenol.

The title compound, C26H40N2O2, has both its N atoms in trigonal-pyramidal geometries. The molecular structure is stabilized by O—H⋯N and C—H⋯O hydrogen bonds. In the crystal, C—H⋯π interactions lead to the formation of a supramolecular helical chain along the b-axis direction.