Magnetic Polymer Microspheres

Magnetic polymer microsphere is a kind of microsphere with magnetism and special structure, which composed of polymer and inorganic magnetic materials. It not only can be endowed with functional groups on surface by copolymerization or surface modification, but also can be separated conveniently from mixtures under enforced magnetic field. Therefore it has gained broad applications in biomedicine, bioengineering, cytology and separating engineering.It needs magnetic polymer microspheres with large particle size(>1μm ) and monodispersity in area such as biological separation. Dispersion polymerization is the most convenient way to synthesize polymer beads with large particle size and monodispersity and to graft functional groups in the beads' surface, so we use dispersion polymerization to synthesize magnetic polymer beads with large particle size and monodispersity.Fe3O4 was used to be the core material of the microspheres, which was prepared by co-precipitation method. Magnetic polymer microspheres were prepared through polymer encapsulation of small Fe3O4 particles, using dispersion polymerization of styrene or styrene/MAA in aqueous ethanol medium. Poly(N-vinylpyrrolidone)(PVP) and 2,2'azo-isobutyrodinitrile(AIBN) were utilized as steric stabilizer and initiator, respectively. The effect of reaction temperature, dispersion medium, stabilizer, initiator, monomer and ferrofluid on the particle size and size distribution were investigated. Scanning electron microscope(SEM), transmission electron microscope(TEM), magnetic balance and Fourier inverse transformation infrared spectrum were used to characterize the magnetic polymer microspheres. Mechanism of dispersion polymerization in the presence of ferrofluid was also discussed and the microspheres were used to extract rare metal for the first time.Study shows that the average particle size of the microsheres increaseswith increasing reaction temperature, initiator concentration, monomer concentration and with decreasing stabilizer concentration. Particle size increase first, then decrease with increasing ferrofluid. Stabilizer concentration, initiator concentration and dispersion medium have great effect on the particle size distribution.The original works we have done are as follows. Fistly, microspheres with particle size from 0.5 to 4μm and standard deviation down to 2 percent were synthesized, which contain more than 10 percent magnetic material. Secondly, A critical point was found during the particle size increasing with increasing initiator concentration for the first time. The third, it is found that there exist the minimum concentration of initiator and stabilizer to obtain the best uniform microspheres. Finally, the microspheres were used to extract rare metal for the first time.Study shows that the mechanism of dispersion polymerization in the presence of ferrofluid is similarity to that of pure dispersion polymerization. A mechanism of small ferrofluid particles as the core of the polymerization was proposed.