Dual catalyst system composed by nickel and vanadium complexes containing nitrogen ligands for ethylene polymerization

Branched polyethylene/high-density polyethylene blends (BPE/HDPE) were prepared using the combined [NiCl2(alpha-diimine)] (1) (alpha-diimine = 1,4-bis(2,6-diisopropylphenyl)-acenaphthenediimine) and [Tp(Ms)* VCl2((NBu)-Bu-t)] (2) (Tp(Ms)* = hydridobis (3-mesitylpyrazol-1-yl)(5-mesitylpyrazol-1-yl)) catalysts. The polymerization reactions were performed in hexane or toluene at three different polymerization temperatures (0, 30 and 50 degrees C) and several nickel molar fractions (x(Ni)), using MAO as cocatalyst. At all temperatures, the activities show an approximate linear correlation with x(Ni), indicating a non-synergistic effect between the nickel and the vanadium species. Higher activities were found in toluene at 0 degrees C. The melting temperatures for the polyethylene blends produced at 0 degrees C decrease as x(Ni) increases in the medium indicating good miscibility between the polyethylene phases made by both catalysts. The surface morphology of the BPE/HDPE blends studied by scanning electron microscopy (SEM) revealed low miscibility between the PE phases mainly in the case of the polymer blends produced at high temperature (50 degrees C).