The promoting effects of 2,4-ionene on the cobalt(II) phthalocyaninetetracarboxylic acid-[CoPc(COOH)(4)] and cobalt(II) phthalocyanineoctacarboxylic acid-[CoPc(COOH)(8)] catalyzed autoxidation of 2-mercaptoethanol were studied. Dimerization of the CoPc(COOH)(4) catalyst, combined with the disappearance of the catalytically inactive mu-peroxo complex and the appearance of substrate enrichment in the presence of 2,4-ionene, results in a 40-fold enhancement of the oxidation rate as compared with the polymer-free system. UV-VIS spectroscopy indicates that CoPc(COOH)(8) is incapable of forming mu-peroxo complexes or 2,4-ionene-induced dimeric catalyst species under normal reaction conditions. Thus, it was possible to study exclusively the ionene-induced effect of substrate enrichment. Addition of 2,4-ionene to an aqueous CoPc(COOH)(8) solution results in an activity enhancement by a factor of 2-3, which can be ascribed to substrate enrichment. Additionally, using monodisperse ionene oligomers showed a molecular weight dependence of 2,4-ionene on the catalytic activity of CoPc(COOH)(8), as was observed for the conventional 2,4-ionene/cobalt phthalocyaninetetrasodiumsulfonate system. The optimal polycation/catalyst ratios of both systems decrease with increasing chain length of 2,4-ionene, until a constant value is reached. This leads to the conclusion that the optimal polymer/catalyst ratios are predominantly determined by substrate enrichment.