Preparation And Characterization Of Fe₃O₄/P?St-PU? Magnetic Microspheres

Magnetic microspheres have properties of common polymer microspheres, a variety of functional groups?such as amine group, carboxyl group, sulfonic group, etc? can be introduced onto the surface of magnetic microspheres by chemical methods, these functional groups can be combined with heavy metal ions, dyes, enzymes, drugs by methods of chemical bonding, electrostatic interaction, etc. Meanwhile, magnetic microspheres have magnetic responsiveness, they can be quickly separated from the surrounding medium under the effect of external magnetic field, simplifying the separation steps. As a kind of functional polymer material, magnetic microspheres have been widely used in fields such as biomedicine?targeted drugs, clinical diagnosis?, wastewater treatment, magnetic materials, cytology?cell labeling, cell separation?, etc. In this work, the magnetic microspheres containing Fe₃O₄ and copolymer of styrene and hydrophilic monomer were prepared by dispersion polymerization,and different polymerization conditions that affected the preparation of magnetic microspheres were systematically studied in the thesis.This thesis consists of three parts associated with each other:Part?: Fe₃O₄ nanoparticles were modified by oleic acid, and the modified Fe₃O₄ nanoparticles were characterized by EDS energy spectrum, infrared spectrum and visible spectrophotometer, etc. In addition, how pH affected the mass fraction of oleic acid of the modified Fe₃O₄ was studied in this part of the thesis. The experimental results showed that the surface of Fe₃O₄ nanoparticles changed from hydrophilic to hydrophobic after modification by oleic acid, alkaline and strong acidic conditions adversed to the modification of Fe₃O₄ nanoparticles by oleic acid, the optimum pH of the modification of Fe₃O₄ nanoparticles by oleic acid was about 5.8.Part?: Without using catalyst, a block polyurethane?PU? macromonomer with hydrophilic segment and double bond was prepared by using poly?ethylene glycol??PEG?,2,4-toluene-diisocyanate?TDI? and ?-hydroxyethyl methacrylate?HEMA? under normal conditions, and the synthetic PU macromonomer was characterized by infrared spectrum. It was concluded by experiments that the reaction conditions?such as reagent dosage, reaction temperature, reaction time, gas-tightness of device, etc? should be well controlled in the process of the synthesis of PU macromonomer. Because of the bad gas-tightness of device itself and impure reagents, part of TDI could react with water and other impurities. For this reason, TDI should be over used in the experiments, the molar ratio of TDI to PEG was 1.3.Part?: Fe₃O₄/P?St-PU? magnetic microspheres were prepared by dispersion copolymerization of styrene with PU macromonomer in the presence of Fe₃O₄ nanoparticlesin ethanol/water medium, PEG was used as dispersant in the process of the preparation of magnetic microspheres and the polymerization reaction was initiated by potassium persulfate?KPS?. Then, Fe₃O₄/P?St-PU? magnetic microspheres were characterized by different means such as EDS energy spectrum, scanning electron microscope, infrared spectrum, transmission electron microscope, vibrating sample magnetometer, etc. In addition, different polymerization conditions including the dosage of Fe₃O₄, styrene, dispersant, initiator and PU macromonomer, the mass fraction of oleic acid of the modified Fe₃O₄, the volume fraction of ethanol in dispersion medium, average molecular weight of dispersant, molecular weight of PU macromonomer, which affected the preparation of magnetic microspheres were studied in this part of the thesis. The experimental results showed that Fe₃O₄ nanoparticles were coated by polymers successfully, the prepared microspheres were approximate superparamagnetic,magnetic microspheres had good magnetic responsiveness and they can be quickly separated from the surrounding medium under the effect of external magnetic field, the average particle size of magnetic microspheres was 269 nm, particle size distribution of magnetic microspheres was wide and the particle sizes of most of the magnetic microspheres were between 200 nm and 400 nm, different polymerization conditions had significant impacts on the component content, magnetic responsiveness, acid resistance, amphipathy, average particle size and particle size distribution of magnetic microspheres. It was concluded by experiments that the optimum condition for the polymerization reaction: the dosage of Fe₃O₄ was 2.3g, the volume fraction of ethanol in the dispersion medium was 10%, the dosage of PEG 2000 was 3g, the dosage of initiator was one point five percent of that of monomers. Moreover, it was observed by experiments that under the condition of fixed molar ratio of PU to St, the structure of magnetic microspheres was related to the molecular mass of PU macromonomer, inner dense microspheres and inner loose porous microspheres could be prepared by adjusting the molecular mass of PU macromonomer.