Carboxylic acid capped gamma-Fe2O3 nanoparticles were prepared by the standard decomposition of Fe(CO)5 in di-n-octyl ether and oleic acid. Two methods were employed to introduce surface functionality to the nanoparticles. First, a thermally stable, tert-butyldiphenylsilyl-protected hydroxyl group was incorporated into the carboxylic acid surfactant used during the synthesis. Subsequent deprotection and transformation installed a 2-bromopropionyl ester group on the particle surface (the functional-group-interchange method). The resulting nanoparticles were 4.53 nm in average diameter and were characterized with IR spectroscopy, transmission electron microscopy (TEM), selected area electron diffraction, and elemental analysis. Second, a 2-bromopropionyl ester group was installed on the particle surface after synthesis via the exchange of the surface oleic acid with a carboxylic acid containing the desired 2-bromopropionyl ester unit (the ligand-exchange method). The resulting nanoparticles were 4.30 nm in average diameter and were characterized with IR spectroscopy, TEM, and elemental analysis. Monitoring the percentage of bromine incorporated into the nanoparticle sample versus the ligand-exchange reaction time indicated that the number of initiator-containing carboxylic acids that could be exchanged onto the surface was limited, presumably by the steric size of the 2-bromopropionyl ester group. Styrene was then polymerized directly off gamma-Fe2O3 nanoparticles, and this yielded hybrid core-shell structures. The measurements of the magnetic properties of the samples demonstrated that the magnetism of the core gamma-Fe2O3 nanoparticle did not change during the performance of the chemical transformations. (c) 2005 Wiley Periodicals, Inc.