MIXED COCATALYST SYSTEMS IN METALLOCENE ETHYLENE POLYMERIZATION

The effect of the cocatalysts resulting from mixing AlR(3) (R = Me (TEA), Et (TEA) and (i)Bu (TIBA)), and B(C6F5)(3) with MAO at different molar ratios on ethylene polymerization activities and on the molecular weight and microstructures of the resulting polymers using the catalyst Cp(2)ZrCl(2) was explored. It has been observed that activities increase at low TMA concentrations with increasing TMA/MAO ratios, reaching a maximum at the TMA/MAO ratio of 0.3-0.5. A decrease of the polymerization activities was observed at higher TMA/MAO ratios. Addition of TEA or TIBA to the MAO brings about a decrease in the polymerization activities, being the effect stronger for TEA. The use of B(C6F5)(3) in the mixed cocatalyst systems leads to higher activities stabilizing also the active centers. The molecular weights of the polyethylenes follow the same trend, i.e. they decrease with increasing AlR(3)/MAO ratios (TIBA, with bulky R, gives the highest molecular weight because of the reduction of chain transfer reactions to the aluminium compound) but they are little affected by the presence of B(C6F5)(3).