Study On Properties And Preparation Of PMMA-PAA Magnetic Microspheres With Crosslinking Structures

Magnetic nanoparticles were synthesized by precipitation method through dropwise adding aqueous solution of ammonia to mixed solution of Fe (II) and Fe (III) salts. The surfaces of Fe₃O₄ nanoparticles were modified by using a certain amount of sodium oleate under in-situ processing, to obtain hydrophobic surface of Fe₃O₄ nanoparticles. The properties of the hydrophybic Fe₃O₄ nanoparticles, such as structures, morphologies, diameter and diameter distribution were characterized by Fourier transformation infrared (FTIR),transmission electron microscopy (TEM) and X-ray diffraction(XRD) separately. The effect of the reaction medium pH value to the hydrophybic Fe₃O₄ nanoparticles was ananysised by ZETA electric potential.It showed that the amount of the sodium oleate has the important influence on the performance,particle size and size distribution of the Fe₃O₄ nanoparticles.Crosslinked magnetic composite microspheres with poly(crylic acid)-co-poly(methyl methacrylate) (PAA-PMMA) as shell and Fe₃O₄ as core were obtained by dispersion copolymerization initiated with 2,2'-azobisisobutyronitrile (AIBN) in ethanol/water mixed solvent containing poly(vinylpyrrolidone) (PVP) as stabilizer in the presence of Fe₃O₄ nanoparticles and divinylbenzene (DVB). The organic functional groups of magnetic composite microspheres were characterized by FTIR. The morphologies,diameter and diameter distribution of the microspheres were characterized by Transmission Electron Microscopy. The magnetism content and the thermostability of the microspheres were characterized by thermogravimetric analysis (TGA). The acid resistance of hydrophybic Fe₃O₄ nanoparticles and magnetic composite microspheres were characterized by Ultra-violet (UV) spectroscopy. The crosslinked microspheres contained 40-70 wt % of Fe₃O₄ through TGA analysis. The average size of the microspheres can be controlled in the 100 nm to 2μm range by changing the polymerization conditions. It was found that the surface properties of Fe₃O₄ nanoparticles, ratio of ethanol to water, amount of AIBN, DVB and PVP can affect size and polydispersity of the composite microspheres.Polymer microspheres with carboxyl group on the surface were prepared by dispersion copolymerization with three monomers. The structures of polymer microspheres were characterized by Fourier transform infrared (FTIR) .The morphologies, diameter and diameter distribution of the microspheres were characterized by Scanning Electron Microscopy (SEM) and Dynamic Laser Light Scattering (DLS).It was found that when the ratio of ethanol to water was 7:3, the concentration of stabilizer were kept at 4.1wt%, the morphologies and polydispersity of the obtained polymer microspheres were the best.Under the protection of nitrogen, a certain amount of polymer microspheres was dispersed into the water. Then Fe2+ and Fe3+ salt solution (molar ratio was 1:2) was added to the dispersed liquid, control the speed of dropping while instilling the NH4OH. To form Fe₃O₄ nanoparticles which would load on the surface of the polymer microspheres by the method of co-precipitation, just adjust pH to 13.Thus the core-shell composite magnetic microspheres were formed. The structures of magnetic microspheres were characterized by FTIR. The morphologies of magnetic microspheres were characterized by Transmission Electron Microscopy (TEM). The stability of magnetic microspheres and magnetism content were characterized by thermogravimetric analysis (TGA).