The ethylene polymerization behavior of a series of titanium(IV) and vanadium(V) complexes, [Tp'MXCl2] (1, M= Ti, Tp'= TpMs*, X = Cl; 2, M = Ti, Tp'= TpMs, X = Cl; 3, M = V, Tp'= TpMs*, X = NtBu; 4, M = V, Tp'= TpMs*, X = NAr) (TpMs*= HB(3-mesityl-pyrazolyl)2(5-mesityl-pyrazolyl)_, TpMs = HB(3-mesityl-pyrazolyl)3_, Ar = 2,6-iPr2-C6 H3) 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. Studies related to the influence of the [Al]/[M] molar ratio (M = Ti, V) have shown that these catalyst precursors presented highest activities using Al concentrations as low as 50:1. DSC curves showed the production of linear polyethylene with melting temperature in the range of 123-140 °C. The viscosity average molecular weights of the polyethylenes are in the range of 7 x 10³-16.4 x 10(6) g mol-1.
titanium (IV); vanadium (V); tris(pyrazolyl)borate; ethylene polymerization; HDPE; UHMWPE
