The differential reactivity of methylmethacrylate (MMA) and vinylpyrrolidone (VP) in free radical copolymerization, with stirring in methanol, renders an emulsified two phase system. The dispersed and continuous liquid phases contain copolymers rich in MMA and VP, respectively. When Fe3O4 magnetic nanoparticles (mNPs) stabilized with tetramethylammonium hydroxide are added to this emulsion, the mNPs are located in the continuous phase. Very small chemical changes in the methacrylic or vinylic chains are able to guide the mNP toward the interface or to the inside of the dispersed phase since quite a selective functionalization of each phase may be achieved separately. Thus, a small addition of methacrylic acid as comonomer (0.5% molar) guides all of the mNPs to the interface while a 0.5% molar of sulfopropyl methacrylate induces the migration of all mNPs to the dispersed phase. When 0.5% molar of a VP derivative bearing sulfonate functionality is added, the mNPs are found both in the interface and in the continuous phase. The addition of water allows solid MMA-based microspheres to be obtained incorporating the mNPs selectively either at the surface or in the core.