The cocatalytic properties of monodisperse 2,4-ionene oligomers were tested in the cobalt(II) phthalocaninetetrakis(sodium sulfonate) (CoPc(NaSO3)(4))-catalyzed autoxidation of 1-dodecanethiol. A tremendous rate increase in the dodecanethiol oxidation by a factor of 100, as compared with the polymer-free system, was observed for monodisperse ionene oligomers, with four quaternary ammonium groups and with 4-bromobutyl end groups. By contrast, the same oligomers terminated with the more hydrophilic dimethylamino end groups showed no enhancement in the catalytic activity. These differences can be ascribed to very effective interactions between the hydrophobic 4-bromobutyl end groups with the hydrophobic thiol, resulting in an enormous increase of the thiol-water interface, due to a decrease in dodecanethiol droplet size. The effects of the end groups decrease with increasing number of N+. 2,4-Ionenes with at least eight quaternary ammonium groups showed similar cocatalytic properties as the high molecular weight 2,4-ionenes. Moreover, the effect of end-capping of polymeric 2,4- and 3,3-ionenes even with long n-alkyl bromides is limited.