Methylaluminum sesquichloride (Al2Cl3Me3, MAS), in the presence of ethyl trichloroacetate (ETAC), is found to be an effective catalyst for the production of polyethylene. Optimal catalyst productivities are obtained for a MAS:ETAC ratio of 1:1 at a reaction temperature of 75 degrees C. The polymerization is first order in both ethylene and MAS/ETAC concentration. NMR studies indicate that a 1:1 adduct is formed between binuclear MAS and ETAC, which is postulated to be a direct precursor to the active species. The productivity at elevated temperatures is limited by a radical decomposition process. Screening of various additives revealed that many halogenated organic reagents can act as activators, including carbon tetrachloride and p-toluene sulfonyl chloride. Improved productivities are obtained using sulfonyl chloride activators due to circumvention of radical decomposition pathways.