For the reasonable comparison of chemical and enzymatic polymerization, manganese(III) acetate and manganese peroxidase (MnP)-catalyzed synthesis of polystyrenes were chosen and studied with respect to the yield and the polydispersity of polymer particles. MnP allowed the production of polystyrene in a higher yield and higher polydispersity (82.34% and 2.61) than manganese(III) acetate (77.90% and 1.75). This is believed to be due to a gradual supply of initiator radicals via a catalytic cycle in MnP-catalyzed polymerization, whereas radicals are generated all at once in Mn(III)-mediated polymerization. NMR spectroscopy revealed that atactic polystyrene was produced by emulsion polymerization using Mn(III) or MnP. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 2935-2941, 2009