| Magnetic polymer microspheres present enormous application potential in many fields such as Pharmaceutics, materials science, chemistry, biology, owning to its unique magnetic responsive property, small size effect and the functionality introduced by the polymer segment, especially when applied in the research subjects of targeted drug, enzyme immobilization, cell separation, protein separation, nucleic acid separation, carrier for catalyst, magnetic fluid for sealing, magnetic recording materials and magnetic resonance imaging. Controllable living radical polymerization can be a facile and reliable approach for fabricating magnetic polymer microspheres, because the molecular weight of polymer yielded is mono-dispersed and block copolymer can be produced by it. Hence, in the dissertation atom transfer radical polymerization(ATRP) was adopted for preparation of Fe3O4/SiO2/PMMA magnetic polymer microspheres. Two part compose of the main content of this dissertation:1. Nano Fe3O4microspheres with diameters of150nm and variable coefficient of0.129were prepared by precipitation oxidation process in aqueous reaction system, followed by fabricating Fe3O4/SiO2microspheres, of which the average diameter and variable coefficient are180nm and0.131. Both of them are magnetic responsive and stable. The increase of TEOS dosage leads to larger particle sizes and monodisperisty, while higher concentration of Fe3O4microspheres produced smaller microspheres with much better monodisperisty. It’s proved that the magnetic responsive property was retained by Fe3O4/SiO2microspheres, the SiO2layer of which provide protection for the Fe3O4magnetic core from oxidizing and decomposing by oxygen and acid. During the immobilization process of initiator for ATRP, the SiO2layer isolated the magnetic core from acid by-product and provided stability.2. Organic bromide was immobilized on the surface of the Fe3O4/SiO2microspheres as initiator group, followed by ATRP with the presence of CuBr complex as catalyst and monomer methyl methacrylate, to fabricate Fe3O4/SiO2/PMMA magnetic polymer microspheres. TG, SEM, TEM, FTIR, DLS were utilized to characterized the magnetic polymer microspheres. Verified by TG,1.7wt%of the microspheres after the immobilization process was attributed to the organic initiator functional groups. Fe3O4/SiO2/PMMA magnetic polymer microspheres with different thickness and quantity of the PMMA layer can be prepared by varying ATRP reaction time. After4h,8h,12h and16h of ATRP under70℃, the weight fraction of the polymer layer was6.4%,9.7%,28.9%and45.1%respectively. This result tested by TG is in accordance with that tested by weighing method. Hence it’s proved that the thickness and weight fraction of magnetic polymer microspheres can be controlled by varying the reaction time. The TEM images indicated that uniform PMMA layer was formed on the surface of the microspheres even the reaction time varied, typically20nm PMMA layer was formed after4h ATRP and it increased to30nm when ATRP time was8h. The magnetic polymer microspheres prepared can be dispersed in organic solvent and the magnetic responsive property was well retained, therefore it can be rapidly separated by applying external magnetic field. Due to the monodispersity, excellent stability against oxidizing and decomposing by acid, superior magnetic property, and its controllable synthetic process of the polymer layer, the magnetic polymer microspheres prepared here possess great potential for targeted drugs, immobilized enzyme, magnetic separation, catalyst carrier and so on. |
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