The synthesis of branched polyethylene from single ethylene feed has been achieved by using a methylaluminoxane-activated titanium complex bearing a tetradentate bis(phenolate) ligand with a 1,4-dithiabutanediyl bridge 1. This catalyst produces polyethylene with activities up to 6200 kg polymer/mol h bar. As evidenced by C-13 NMR analyses, the polyethylenes contain ethyl, n-butyl, and long-chain (n-hexyl or longer) branches in a range variable from 0.2 to 2.0%, depending on the experimental parameters. NMR and gas chromatography/mass spectrometry analyses suggest that such polymer microstructure arises from the in situ production of oligomers and their subsequent incorporation into the growing polyethylene chain. The broad molecular weight distribution of these polyethylenes indicates the presence of different catalytic species. The related catalyst system 2 bearing a longer 1,5-dithiapentanediyl bridge produces linear polyethylene with moderate activity. (C) 2004 Wiley Periodicals, Inc.