The present article offers a new approach to create a multifunctional material based on magnetic nanoparticles, which can be dispersed in aqueous and organic media. The preparation of this material was performed by binding covalently polymer chains based on a reactive diblock-copolymer of the polystyrene-SiCl2-poly(2-vinylpyridine) type, with average molecular weight per number (M-n) equal to 14,700 g/mol and a polydispersity index (PDI) less than 1.1, onto the surface of gamma-Fe2O3 magnetic nanoparticles. The dichlorosilane moiety of the diblock-copolymer reacted with the OH groups of the magnetic nanoparticles immobilizing the polymer chain onto its surface. This reaction was monitored by FTIR and the polymer grafting density was determined by TGA and BET. Dynamic light scattering revealed that the hydrodynamic diameter of the nanoparticles increased after immobilizing the polymer. Contact angle measurements demonstrated the ability of the hybrid material to interact with organic and aqueous media allowing its dispersion in solvents with different polarities. This property was used to prepare a magnetically active emulsion. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1668-1675, 2010