Preparation of magnetite-polystyrene core-shell hybrid nanoparticles, initiated by a covalently bonded azo compound
Magnetite nanoparticles (MNP), onto which the radical initiator 4,4′ azobis (4-cyanovaleric acid) (ACV) was grafted, were used as a macro-initiators in the polymerization of styrene. Bulk and emulsion polymerizations were performed. Core-shell nanoparticles with a magnetite core and a polystyrene (PS) shell were obtained by emulsion polymerizations. A simple geometrical model was proposed to correlate the size of the final PS shell to the styrene/MNP ratio. The diameter of the shell of the prepared core-shell nanoparticles was found to be greater than expected. This was due to the fact that most of the PS shell contained several MNP cores. This feature was confirmed by transmission electron microscopy (TEM) imaging of the stable latexes obtained. Particles of nearly mono-disperse size were obtained by emulsion polymerization, and their diameters decreased as the ratio of MNP/styrene increased. Films were cast from the core-shell nanoparticles dissolved in chloroform. Due to the superparamagnetic properties of the MNP, a change in their organization in the polymer matrix was obtained by applying a magnetic field at a temperature above the Tg of the PS shell. Copyright © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.