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

Abstract

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 ligands with cyclohexylene bridges were more active than those with ethylene bridges. Furthermore, the presence of electron‐withdrawing groups at the para position and electron‐donating substituents at the ortho position on the aryl rings of the ligands resulted in improved activity in relation to the systems with no substituents (with the exception of bulky t‐Bu group). The results presented also revealed that all vanadium complexes activated by common organoaluminum compounds gave linear polyethylenes with high melting points (134.8–137.6 °C), high molecular weights, and broad molecular weight distribution. The polymer produced in the presence of MAO possesses clearly lower melting point (131.4 °C) and some side groups (around 9/1000 C). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6940–6949, 2008

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

“…The increase in the 1-octene concentration reduced that activity even further. The activity of vanadium catalysts, when used in copolymerization at Al/V = 129 mol/mol and at the comonomer concentration of 0.40 mol/dm 3 (Table 2, entry 33, 31 and 26), was dependent on the ligand structure and that relation was the same as for ethylene homopolymerization 26,22). It is seen that the comonomer incorporation is evidently lower at a higher cocatalyst/complex molar ratio than at a lower Al/V ratio.…”

“…The temperature effect on the catalytic activity was evaluated for the same complex at the Al/V molar ratio equal to 514 (Table 1, entry 6 and 7). As can be seen, the catalytic system based on the oxovanadium complex bearing a salen ligand did not offer a good thermal stability, just alike salen complexes of vanadium(IV) dichloride reported by us earlier [22].…”

“…Another method is based on the use of an activator with a lower reduction potential. Earlier reports [18,22] indicate that salen complexes of vanadium dichloride and vanadium complexes with diamino-bis(phenolate) ligands give higher polymerization activities in conjunction with chloroalkylaluminium compounds, especially with EtAlCl 2 . It was also shown that active species in the catalysts which contain oxovanadium complexes are formed only after their activation with a chlorine atom-containing alkylaluminium compound and vanadium is in an oxidation state of +4 in them [19,20].…”

“…We recently reported that salen-type complexes of vanadium(IV) dichloride were efficient ethylene polymerization catalysts, especially after immobilization on the magnesium support [22,23]. In this paper we present the catalytic properties of oxovanadium(IV) complexes bearing salen-type and other tetradentate Schiff base ligands.…”

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

“…Ethylenebis(5-chlorosalicylideneiminato)vanadium dichloride, VCl 2 (salenCl 2 ), and ethylenebis(5-chlorosalicylideneiminato)titanium dichloride, TiCl 2 (salenCl 2 ), were synthesised as reported in [22]. The magnesium support, MgCl 2 (THF) 2 /Et 2 AlCl, was prepared according to the procedure presented in [23].…”