Effect of aluminoxane on molecular weight and molecular weight distribution of polyethylene prepared by an iron-based catalyst

A series of aluminoxanes, tetraethylaluminoxane (TEAO), tetraalkylaluminoxane (TAAO), Et2AlOB(4 - F - C6H4)OAlEt2 (BTEAO) and ethyl-iso-butylaluminoxane modified with p-fluorophenyl-boric acid (BEBAO), were prepared and their effects on molecular weight (MM and molecular weight distribution (MWD) of polyethylene prepared by the iron-based catalyst [(ArN=C(Me))(2)C5H3N]FeCl2 (Ar=2,6-dimethylphenyl) (1) were investigated. It was found that TEAO and BTEAO were highly efficient activators for iron-based catalysts and introducing the branched bulky group (eg iso-Bu) into the aluminoxane activator could improve the MW of the resulting polyethylene. The MW of polyethylene produced by activators modified by p-fluorophenylboric acid was higher than for other aluminoxane activators. The TEAO- and TAAO-based polyethylene exhibited attractive bimodal MWD, and the lower MW fraction of bimodal MWD was shown to be produced in the early stage of polymerization due to chain transfer to the aluminium activator. (C) 2004 Society of Chemical Industry.