Synthesis And Characterization Of Magnetic Polymer Microspheres

Magnetic polymer microsphere is a kind of microsphere with magnetism and special structure, which is composed of polymer and inorganic magnetic materials. It can not only be endowed with functional groups on surface by copolymerization or surface modification, but also be separated quickly and easily from mixtures by exterior magnetic field. Therefore, since 1970's, as a new type of functional material it has gained broad applications in biomedicine, magnetic materials, cytology, bioengineerings, separating engineerings and stealth technologies.One focus of this thesis was to prepare nano-Fe3O4 by microemulsion method and chemical co-precipitation method. The feature of nano-Fe3O4 was characterized by TEM. The results were that the particles prepared by microemulsion method were monodispersion and the diameter was in the 10nm. But their crystalline and magnetic responsibility was weak. The nanoparticles prepared by chemical co-precipitation method had the better characters.One of the main difficulties in synthesis core-shell magnetic polymers is the monodispersion of the magnetic nanoparticles in organic monomer. In this paper, on the basis of summarizing the research fruits of magnetic and magnetic polymer microspheres worldwide, oleic acid was adopted as the surface modifier.The other focus of this paper was on the preparation of Styrene(St) by emulsifier-free polymerization. Some influencing factors,such as ultrasonic dispersion,organic medium,polymerization temperature , initiator concentration and surfactant in ferrofluid on emulsifier-free polymerization,were discussed respectively. At last, the mechanism of emulsifier-free polymerization containing ferrofluids was proposed.As one of the important properties of magnetic polymer microspheres, average number diameter could be controlled by ultrasonic dispersing time, KPS feeding, acetone concentration and surfactant concentration. Of all these influencing factors, the changing of surfactant concentration could get broader rang of average number diameter. And the average number diameter of magnetic polymer microspheres was inversely proportion to surfactant concentration under critical micellar concentration(CMC). However, the increasing of surfactant concentration led to the decreasing of monodispersity of magnetic polymer microspheres.At the same time, water/acetone mixing medium was used and adjusted in order to obtain composite particles with better monodispersity and less organic impurities. The effect of these parameters on the variation of final particle size and size distribution, the morphology, magnetic content and magnetic response were investigated in detail. From the experiment, we can see the excessive acetone led to the decreasing of monodispersity of magnetic polymer microspheres.All the results of research on magnetic polymer microspheres mentioned above, the improved emulsifier-free polymerization method is one better and promising method because it can prepare magnetic composite microspheres with high magnetic content, good magnetic response, clean surface, high efficiency of encapsulation.