Magnetic Fe3O4/P(MMA/DVB)(core)-P(St/GMA/DVB)(shell) composite microspheres with coreshell structure were prepared by a twostep method.(1) Preparation of the magnetic cores:First

the magnetic miniemulsion composed of organic ferrofluid droplets dispersed in water was obtained by rapid addition of an oilbased magnetite ferrofluid

with a solid content 60 wt%

into the aqueous solution using DNS-86 (polymerizable surfactant) as surfactant in the condition of ultrasonic emulsification.Then

the copolymerization monomers of methyl mathacrylate (MMA) and divinyl benzene (DVB) were injected directly into the magnetic miniemulsion.Because of their hydrophobic character

once the monomers were added into the emulsion

the methyl mathacrylate (MMA) and divinyl benzene (DVB) would have a high tendency to diffuse inside the organic phase of the ferrofluid droplets to form monomer swelling magnetic miniemulsion

which were supposed to be the main locus for copolymerization.In succession

the temperature was rapidly increased to 70℃ and starting the miniemulsion copolymerization to form uniform magnetic latexes.(2) Preparation of the core/shell hybrid polymeric microspheres:Through varying the feeding amount of styrene (St)

glycidyl methacrylate (GMA) and DVB

the core-shell structured microspheres were rationally fabricated by the seed emulsion copolymerization using the above magnetic latex as the core emulsion.This preparation process is convenient and effective.Extensive characterization by X-ray diffraction (XRD)

high resolution transmission electron microscopy (HR-TEM)

thermogravimetric analysis (TGA) and vibrating sample magnetometer (VSM) showed that the magnetite content of Fe3O4/P(MMA/DVB) composite microspheres was 84 wt%.The magnetite content of the magnetic composite microspheres with core-shell structure is varied from 20 wt% to 76 wt% by feeding different amounts of monomers.The average diameter of the magnetic seeded microspheres and the core-shell composite microspheres is 150 nm and 350 nm

respectively.The functional epoxy groups on the surface of the core-shell composite microspheres can be further modified to load biomolecules.