The porous magnetic polymer microspheres containing carboxyl group were prepared by modified suspension polymerization by using stryene (St)

divinylbenzene (DVB) and methacrylic acid (MAA) as monomers in the presence of magnetic γ-Fe2O3 which was coated with oleic acid (OA).In this experiment

three modification measures were adopted.First

the surface of the magnetic particles was treated by anionic surfactant OA to improve the hydrophobicity of mciro-size magnetic γ-Fe2O3 Second

the monomer phase containing surface modified magnetic particles and porogens was sonicated for some time to improve the dispersibility of magnetic γ-Fe2O3 in the monomer phase and strengthen absorbence of the monomer and initiator on the γ-Fe2O3 surface.Third

the aqueous phase was added to the monomer phase

and the mixture was sonicated for some time before polymerization to make sure all the magnetic particles can be dispersed in the monomer phase to form stable and uniform droplets which is diffrent from the conventional suspension polymerization with the monomer phase added to the aqueous phase.The pretreatment and polymerization process are as follows:Firstly

10~20 g sample of magnetic particles was added to 200 mL ethanol/water solution (volume ratio=1)

and sonicated in a 250 mL beaker for 0.5 h to eliminate impurities on its surface.Then

the purified magnetic powder and 120 g deionized water were mixed together in a 250 mL

three-necked flask equipped with a stirrer

a condenser and a thermometer.As the mixture heated to 85℃

the OA (2/3 (wt/wt) to magnetic particles) was added dropwise within 15 min and the reaction was kept at pH=5.5 for 1 h with vigorous stirring.Afterwards

the resulting materials were isolated by magnetic decantation and washed with deionized water for several times to remove the excess OA.The treated magnetic particles were dried at 50℃ for 12 h.Magnetic porous microspheres were prepared by modified suspension polymerization in a 250 mL fourneck

roundbottomed flask fitted with a mechanical stirrer

a thermometer

a reflux condenser and a nitrogen gas inlet tube.The monomer phase which consisted of 15 mL monomers (St/MAA/DVB＝9/3/3(mL))

0.2 g AIBN as initiator

15 mL diluent system(toluene/n-heptane=2/1 (V/V)) and surface treated magnetic particles was sonicated for 15min.The aqueous phase (AP) was prepared by addition of 0.48 g HEC

0.5 g NaCl and 90 mL deionized water.Then the aqueous phase was added to the organic phase and sonicated for 15 min.Hence

the suspension system was kept at 70℃ for 24 h.The polymer produced beads were filtrated and washed with hot distilled water

ethanol and acetone several times to remove water-soluble impurities

followed by soak in 1 mol/L HCl for 48 h and extraction with solvent in a Soxhlet extractor for 24 h to remove the porogens and organic impurities.The purified beads were washed with methanol and distilled water and then dried under vacuum for 24 h.FTIR

SEM

optical microscopy and TG were used to characterize the chemical composition

morphology

size and magnetic particle distribution and magnetic characteristics of magnetic polymer microsphere.FTIR analysis demonstrated that the hydrophobicity of magnetic γ-Fe2O3 was improved significantly by chemisorption and esterification after the surface modified by oleic acid.The results of FTIR and optical microscopy analysis demonstrated that the desired polymer was bonded to the surface of γ-Fe2O3 particles

and the polymer microspheres contained carboxyl groups.But the magnetic particles were not uniformly incorporated in the magnetic microspheres because of the magnetic agglomerating force.The morphology analysis by SEM and optical microscopy confirmed that the composite magnetic γ-Fe2O3/P(St-DVB-MAA) microsphere had a good sphericity with porous structure and a relatively uniform diameter of about 0.4~0.9 mm.The results of TG analysis indicated the content of magnetite in microspheres was 12.12%.