Magnetite (Fe3O4) nanoparticles were prepared by in situ precipitation and oxidation of ferrous ions in the presence of omega-functionalized polystyrenes having carboxylate, sulfonate, thiol, and thiolated groups. Based on the results, for the orthogonal experimental design, both the ratio of the concentration of iron precursor to polymer and the reaction temperature were the, major factors controlling the particle size and its shape morphology. By adjusting the reaction conditions, the iron oxide particle size can be effectively controlled in the range between 2 and 20 nm. The magnetite-based polymer composite was characterized by UV-vis spectroscopy, thermogravimetric analysis, transmission electron microscopy, and X-ray diffraction. Magnetization measurements revealed that the nanocomposite materials exhibit superparamagnetic behavior at room temperature. (c) 2006 Elsevier B.V. All rights reserved.