Fe3O4/Polystyrene（PSt） magnetic particles with core/shell structure have been prepared in thepresence of Fe3O4 magnetic fluid in ethanol/water medium by dispersion polymeriation of styrene. A Fe3O4particle formation mechanism was proposed. According to this mechanism, the size of particle nuclei isdetermined by the extent of aggregation of Fe3O4 /oligomer. Magnetic particles with diameter ranging from 5to 200 μm were prepared under different reaction conditions. Some polymerization parameters such as theconcentration of monomer, stabilizer, initiator, and ethanol which affect particle size and size distribution arediscussed and their effect on particle formation are explained by the proposed mechanism.
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