Preparation Of Magnetic Polymer Microspheres

Magnetic polymer microsphere is a kind of hybrid microsphere with magnetic property, which is composed of polymer and inorganic magnetic particles. They can be classified into three kinds according to their structures. One is composed of polymeric core and magnetic shell; the other is composed of magnetic core and polymeric shell; the third is composed of polymeric core and shell, and the magnetic material located in the middle layer. The main advantage of magnetic polymeric microspheres over conventional polymeric microspheres is that, because of their superparamagnetic properties, they can be rapidly separated from solution under magnetic field. In the past decades, a great number of scientists have dedicated their efforts to preparation of different kinds of magnetic polymer microspheres and many strategies have been performed to producing magnetic polymer microspheres. Up to now, there are three ways to prepare magnetic polymer microspheres: (1) Encapsulation of magnetic particles with preformed natural or synthetic polymers is the simple and classical method to prepare magnetic polymer microspheres; (2) Another method is developed by Ugelstad through direct precipitation of iron salt inside the porous polystyrene particles; (3) The third method is to suspend magnetic particles in the dispersed phase and then polymerize the monomer in the presence of the magnetic particles to form magnetic polymer microspheres. In this article, miniemulsion polymerization and soap-free emulsion polymerization were adopted to prepare magnetic polymer microspheres with different structures. The magnetic polymer microspheres were characterized by X-ray diffraction (XRD), dynamic light scattering (DLS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM) and thermogravimetric analysis (TGA). Some results have been obtained as follows:1. The Fe3O4 magnetic particles were prepared by the coprecipitation of FeCl3.6H2O and NH3.H2O. Polymethacrylic acid or oleic acid was used to modify the iron oxide nanoparticles in synthetic process. The Fe3O4 particles are somewhat irregularly shaped from oval to sphere and the particle size was around 10 nm. The Fe3O4 particles are superparamagnetic. Stable water-based and oil-based magnetic fluid can be achieved. The magnetic fluid was used in collecting leaked oil and used as contrast agent in magnetic resonance imaging.2. The magnetic polystyrene microspheres were prepared by miniemulsion polymerization. The monomer is styrene and the initiator is benzoyl peroxide. The nanosized iron oxide particles can be well encapsulated in polystyrene microspheres and they are superparamagnetic. Fe3(VPSt-DVB-tBMA microspheres were also prepared and the size of these microspheres was about 120nm. Stable water-based magnetic fluid could be achieved when Fe3(VPSt-DVB-tBMA microspheres containing 30% tBMA in monomers were hydrolyzed.3. The magnetic polyacrylamide microspheres were prepared by one-step inverse miniemulsion polymerization using Span 80 as the emulsifier and isobutyronitrile as the initiator. The magnetic polymer microspheres are spherical and their size was about 80 nm. The nanosized iron oxide particles can be well encapsulated in polyacrylamide particles and the magnetic polymer microspheres are superparamagnetic. Crosslinked magnetic polyacrylamide microspheres can been transfered to aqueous solution .4. Fe3O4/SiO2 composite particles were prepared via sol-gel process based on inverse miniemulsion. The composite particles are superparamagnetic and each composite particle contains many magnetic nanoparticles. X-ray diffraction patterns show silica shell is amorphous, and the crystallinity of the magnetic nanoparticulate core is retained after the coating's procedure. Fe3O4/SiO2 nanosized composite particles can be...