Organochromium Complexes with Nitrogen-Containing Ligands for Ethylene Polymerization

7 Organochromium Complexes with Nitrogen-Containing Ligands for Ethylene Polymerization 

Esteruelas et al. [40] reported very high activity, single-site, ethylene polymerization catalysts prepared with tridentate (N,N,N) ligands based on Bis(imino)pyridyl chromium (III) complexes that were activated with tri-isobutyl aluminum (TIBA) or alkylaluminoxane (-Al(R)-O), where R is methyl or isobutyl. 

Most of the complexes examined as ethylene polymerization catalysts also produced a large amount of a low molecular weight polymer component (waxes), but if this polymer fraction was removed from the product, the remaining polyethylene exhibited a narrow MWD, indicating a single-site catalyst. Obviously, elimination of the species producing the low molecular weight polymer component would be necessary to develop a commercial catalyst. 

However, data points 10 and 12 in Table 3.10 are particularly important. Data Point 10, in which complex 22 was tested with tri-isobutylalmninox-ane (TIBAO) as cocatalyst, provided polyethylene without extractables (waxes) with commercially important molecular weight for certain apph-cations such as high-density polyethylene for injection molding. Data Point 12 showed that complex 24 exhibited extremely high activity of 4.14 X 10 g/PE/mol Cr/bar/hr, which corresponds to a residual chromium content in the polyethylene of about 0.2 ppm, which most likely exceeds the activity of any other Cr-based catalyst. 

In a copolymerization experiment carried out under the same polymerization conditions as Data Point 14, except in the presence of 15 ml of 1-hexene, the data show that complex 24 reacts with 1-hexene in an 

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