We report on the synthesis of snowman-like magnetic/nonmagnetic nanocomposite asymmetric particles (SMNAPs) via seeded emulsion polymerization initiated by ?-ray radiation. In situ formation of magnetite in the presence of the emulsified poly(styrene-divinylbenzene-acrylic acid) microspheres affords raspberry-like magnetic nanocomposite particles, which are used as seeds for further seeded emulsion polymerization induced by ?-ray radiation. We study the effect of the kind of surfactant, the kind and content of second monomer, and the content of swelling agent on the morphologies of the final nanocomposite particles. It is found that SMNAPs can be fabricated in high yield using 12-acryloxy-9-octadecenoic acid as the surfactant and styrene as the second monomer with the addition of 2-butanone (a swelling agent). The as-synthesized SMNAPs may serve as magnetically controllable solid surfactants to stabilize O/W immiscible mixtures, which preferentially orientated at the interface. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012