Search results for "ATAL"
showing 10 items of 10591 documents
A supported titanium postmetallocene catalyst: Effect of selected conditions on ethylene polymerization
2011
Ethylene polymerization with a titanium complex [N,N-ethylenebis(3-methoxysalicylideneiminato)titanium dichloride] immobilized on the magnesium support with the formula MgCl2(THF)0.32(Et2AlCl)0.36 was studied. In particular, the effects of polymerization temperature, monomer pressure, and polymerization time on the activity of the catalyst and on the polyethylene properties (molecular weight and its distribution, melting point, crystallinity, and bulk density) were evaluated. The findings of investigations prove that the studied supported titanium catalyst is highly active in ethylene polymerization, and its activity increases with increasing temperature and monomer pressure. Moreover, stab…
Transition metal complexes of tetradentate and bidentate Schiff bases as catalysts for ethylene polymerization: Effect of transition metal and cocata…
2009
This article compares catalytic performance of ethylene polymerization in similar polymerization conditions of transition metal complexes having two ligands [O,N] (phenoxy-imine) and having one tetradentate ligand [O,N,N,O] (salphen or salen). It is shown that the activity of both complex types as well as the product properties depend in the same way on the type of central metal in the complex and on the cocatalyst used. Although the type of ligand has some effect on the catalyst activity, yet it does not control the properties of the obtained products. The vanadium and zirconium complexes, irrespective of the cocatalyst used, yield linear polyethylene with high molecular weight (a few hund…
Effect of sample preparation on gel permeation chromatography results of determination of molecular weight of polyethylene obtained with using of zir…
2003
Molecular weights of polyethylene (PE) obtained with using of zirconocene catalyst activated with large excess of methylaluminoxane (MAO) were determined by gel permeation chromatography (GPC) method. It was found that repeatability of the measurements is strongly influenced by MAO remained in PE samples as well as time of sample keeping in the apparatus (dissolution + measurement time) at temp. 142 °C. A method of MAO removing from PE samples, before GPC measurement, based on additional washing of the sample with HF in methanol solution has been proposed. This modification leads to better both authenticity and repeatability of the results. Studies on the influence of time of sample keeping…
Effect of immobilization of titanocene catalyst in aralkyl imidazolium chloroaluminate media on performance of biphasic ethylene polymerization and p…
2012
1-(2-Phenylethyl)-3-methylimidazolium and 1-benzyl-3-methylimidazolium chloroaluminates, [Ph-C2mim][AlCl4] and [Bzlmim][AlCl4], were applied as media of the Cp2TiCl2 catalyst for biphasic ethylene polymerization. The studied aralkyl ionic liquids ensure greater stability of the catalyst at higher temperatures and more regular morphology of the produced polyethylene than analogous 1-n-alkyl-3-methylimidazolium chloroaluminates. The alkylaluminium compound participates in the termination reaction of the polymer chain. The catalyst is stable and enables recycling of the ionic liquid phase in the consecutive polymerization reactions. The [Ph-C2mim][AlCl4] ionic liquid and AlEt2Cl alkylaluminium…
Ethylene polymerization with FI complexes having novel phenoxy‐imine ligands: Effect of metal type and complex immobilization
2011
A series of bis(phenoxy‐imine) vanadium and zirconium complexes with different types of R3 substituents at the nitrogen atom, where R3 = phenyl, naphthyl, or anthryl, was synthesized and investigated in ethylene polymerization. Moreover, the catalytic performance was verified for three supported catalysts, which had been obtained by immobilization of bis[N‐(salicylidene)‐1‐naphthylaminato]M(IV) dichloride complexes (M = V, Zr, or Ti) on the magnesium carrier MgCl2(THF)2/Et2AlCl. Catalytic performance of both supported and homogeneous catalysts was verified in conjunction with methylaluminoxane (MAO) or with alkylaluminium compounds (EtnAlCl3−n, n = 1–3). The activity of FI vanadium and zirc…
Dichlorovanadium (IV) complexes with salen‐type ligands for ethylene polymerization
2008
Vanadium complexes with tetradentate salen‐type ligands were first time explored in ethylene polymerizations. The effects of the vanadium complex structure, the alkyl aluminum cocatalysts type (EtAlCl2, Et2AlCl, Et3Al, and MAO), and the polymerization conditions (Al/V molar ratio, temperature) on polyethylene yield were explored. It was found that EtAlCl2 in conjunction with investigated vanadium complexes produced the most efficient catalytic systems. It was shown, moreover, that the structural changes of the tetradentate salen ligand (type of bridge which bond donor nitrogen atoms and type of substituent on aryl rings) affected activity of the catalytic system. The complexes containing li…
Ethylene polymerization using vanadium catalyst supported on silica modified by pyridinium ionic liquid
2016
Vanadium catalyst systems (SIL1–3A(B)/V) for ethylene polymerization were obtained by immobilization of the Cp2VCl2precursor (V) in the ionic liquid -[3-(triethoxysilyl)propyl]pyridinium chloride (IL), modified by AlCl3 and AlEtCl2(A) or AlEt2Cl (B), and supported on three types of silica carrier S1–3. The properties of the ionic liquid supports were determined using Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller measurements, scanning electron microscopy and elemental analysis. The best results (above 2 tons PE (mol V)−1(0.5 h)−1) were obtained using the catalyst system SIL3B/V. Addition of ethyl trichloroacetate is possible in the ionic liquid medium and it further increas…
Direct synthesis of fibrous high molecular weight polyethylene using vanadium catalysts supported on an SiO2 ionic liquid system
2015
Polyethylene of fibrous morphology was obtained using Cp2VCl2 and VCl2(salenCl2) catalysts activated by AlEt2Cl and AlEtCl2 and heterogenized on a supported ionic liquid system prepared with SiO2 and 1-(3-triethoxysilyl)propyl-3-methylimidazolium chloroaluminate. The fibre length ranges from 15 to 60 µm, depending on the reaction conditions. The polyethylene is characterized by a high molecular weight ((1.1–2.4) × 106 g mol−1) and a narrow molecular weight distribution (1.4–2.5). It is a linear polymer, properly without branching. The DSC method reveals characteristic changes in melting temperature and crystallinity degree between the first and second scan heating cycles (141 °C and 136 °C,…
Nature of activating effect of two‐step polymerization of propylene
1999
The prepolymerization effect on propylene polymerization in the presence of a TiCl3‐based catalyst, modified by di‐n‐buthyl ether, was studied. The influence of prepolymerization on the electron spin resonance spectra and morphology of the catalyst, as well as the properties and the morphology of both prepolymer and regular polymerization products, was investigated. The polymer morphology was evaluated through scanning electron microscopy, polymer bulk density, and particle size distribution. Some evidence of the enhancement effect of prepolymerization on the catalyst activity and stereospecificity was obtained. No influence from prepolymerization was observed on molecular weight and its di…