Titanium and vanadium ethylene polymerization catalysts containing tris(pyrazolyl)borate ligand: Effects of polymerization parameters on activity and polymer properties

Abstract

Pr 2 -C 6 H 3 ) was investigated in toluene or hexane using MAO or TiBA/MAO (1:1) as activators, and varying the polymerization temperature. The polymerization results showed that independently of the catalysts precursors used in the polymerization run, higher activities were found using TiBA/MAO/hexane system. For titanium species, the maximum catalytic activities were reached at 60 ºC while for vanadium ones the highest activities were attained at 30 ºC. .

Metal salen complexes as ethylene polymerization catalysts - effect of catalytic system composition on its activity and properties of polymerization products

“…725 000. The effect of the transition metal type on the molecular weight value of the product is similar to that observed for other post-metallocene catalysts, namely for the systems which contain complexes with tris(pyrazolyl)borate ligands [33].…”

Dichlorovanadium (IV) complexes with salen‐type ligands for ethylene polymerization

“…The vanadium complex V3a was subjected to activation in succession with: Et 3 Al, Et 2 AlCl, and EtAlCl 2 , and the obtained catalysts were tested in the ethylene polymerization reaction. The presented results (Table 1) show that the investigated complexes exhibit modest to moderate activity (from 14.9 to 350 kg/(mol v ·0.5 h)), which is more or less comparable to some other vanadium systems described in literature 3, 6, 7(a–c), 22, 23. It should be highlighted, however, that the polymerization process was conducted over 5 to 15 min only in most of those studies, and the activity was then recalculated to 1 h, with the stable nature of active sites in the polymerization process assumed.…”

“…The literature reports6, 7(b,c), 23 and our earlier studies2(b) demonstrate that vanadium complexes are pretty sensitive to the catalyst synthesis reaction conditions (type and share of a cocatalyst) as well as polymerization conditions (predominantly temperature); that sensitivity is most probably caused by poor resistance of vanadium complexes to changes in metal oxidation states. Therefore, the studies on those systems require that the optimum conditions for the catalyst synthesis and for polymerization itself must be precisely selected beforehand.…”

“…It should be noticed that variety of postmetallocene catalysts is available which results not only from the type of metal center but also from unlimited in practice variety of applicable ligands 1. Some previous studies on postmetallocene catalysts in olefin polymerization and copolymerization involved vanadium complexes having bis(phenoxy)amine3 and bis(phenoxy‐imine)4 ligands, tridentate bis(imino)pyridyl ligands,5 and tris(pyrazolyl)borate ligands 6. Nomura and coworkers7 employed (arylimido)(aryloxo)vanadium complexes in ethylene homo and copolymerization, while Takaoki and Miyatake synthesized polypropylene with the use of vanadyl complexes with 2,2′‐thiobis(4‐methyl‐6‐ tert ‐butylphenoxy) ligand 8.…”

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“…That adverse temperature effect for the vanadium system seems to result from the lower stability of the system: vanadium is reduced to lower oxidation states, which are inactive under such conditions. That relation was observed also for other postmetallocene vanadium catalysts 22, 35–37. Hence, when a weaker reducer is used instead of MAO, for example, Et 2 AlCl, the increasing temperature should enhance the reaction rate, and indeed, for the vanadium catalyst activated by Et 2 AlCl, its activity grows to follow the temperature increase over the whole scope, that is, from 20 to 60 °C, for which the activity climbs up from 168 to nearly 4000 kg/mol.…”