Cationic latices with excellent cocatalytic properties were designed by emulsion polymerization of styrene using monodisperse amphiphilic polystyrene-ionene diblock copolymers as surfactant. The amphiphilic block copolymers built in during the emulsion polymerization of styrene, with the water-soluble initiator 2,2’-azobis(2-amidinopropane) dihydrochloride, possess electrostatic as well as steric stabilization properties. A major advantage of the preparative procedure used is that no extensive cleaning procedures need to be applied. After immobilization of the tetrasodium cobalt(II) phthalocyaninetetrasulfonate (CoPc(NaSO3)(4)) catalyst onto the latex, reactive latices were obtained which show very high catalytic oxidation rates toward the mercaptoethanol autoxidation. The highest catalytic activity (500 mol of O-2/(mol of Co . s)), 15 times higher as compared with the polymer-free system, was achieved with latices with relatively short ionene blocks with 7 quaternary ammonium groups at their particle surface. Despite relatively low surface charge densities, apparently enough ionene chains of sufficient length are present at the particle surface to stabilize the highly active CoPc(NaSO3)(4) dimers and to achieve substrate enrichment.