Preparation And Formation Mechanism Of Magnetic Functional Polymer-based Nanocomposite Particles Through Miniemulsion Polymerization

As a new functional nanocomposite material,polymer/Fe₃O₄ nanocomposite particles?polymer/Fe₃O₄ NCPs?are widely applied in magnetic resonance imaging,drug delivery and protein separation.Miniemulsion polymerization is one of the best technique to prepare this material because of the unique droplet nucleation mechanism.However,some plain polymer particles will form during the miniemulsion polymerization,and which decrease the composite efficiency between polymer and inorganic particles.For solving above problem,this paper researched the formation mechanism of particles during the polymerization in Fe₃O₄ nanoparticles-containing miniemulsion system and proposed the improved method to increase the fraction of nanocomposite particles effectively.Ultimately,the emulsion with high composite particles fraction was prepared.Firstly,this paper prepared the Fe₃O₄ nanoparticles with average size of 18 nm via coprecipitation method.And then,the Fe₃O₄ nanoparticles were modified by 3-?isobutenyloxy?propyl trimethoxysilane?MPS?and the prepared MPS-modified Fe₃O₄nanoparticles?MPS-Fe₃O₄?were well dispersed in hydrophobic monomer.The dispersion of MPS-Fe₃O₄ in monomer methyl methacrylate?MMA?with different degree of MPS modification or solid content was researched by dynamic light scattering?DLS??thermogravimetric analysis?TGA?and vibration sample magnetometer?VSM?.The best recipe for hydrophobic modification was proposed.On this basis,MPS-Fe₃O₄as the inorganic particles,styrene?St??MMA and methacrylic acid?MAA?as the comonomers,Tween-20 and post-added SDS as the emulsifiers,the emulsion containing polymer/Fe₃O₄ NCPs was prepared through miniemulsion polymerization.The morphological evolution of latexes during the polymerization and the particle characteristics of nanocomposite particles were characterized by transmission electron microscope?TEM?and DLS.The effects of the amount of MAA?post-added SDS and the content of MPS-Fe₃O₄ on the formation of nanocomposite particles were researched.And the formation mechanism of polymer/Fe₃O₄ NCPs in the process of MAA-containing miniemulsion polymerization was proposed.It was found that the MPS molecules were coupled on the surface of Fe₃O₄nanoparticles after hydrophobic modification and the coupling density of MPS was adjustable.The dispersion ability of MPS-Fe₃O₄ in monomer increased with the increase of the amount of MPS.The hydrophobic modification on the Fe₃O₄ surface had little effect on magnetism and MPS-Fe₃O₄ also had good magnetic intensity and superparamagnetism.The fraction of polymer/Fe₃O₄ NCPs in emulsion was very low when SDS was the emulsifier.However,when Tween-20 was the emulsifier to prepare the monomer miniemulsion and trace SDS was post-added,the fraction of polymer/Fe₃O₄ NCPs increased to 50%.The addition of MAA could improve the dispersity of Fe₃O₄ between monomer droplets and enhance the interaction between Fe₃O₄ and polymer.Thus,the of polymer/Fe₃O₄ NCPs was further increased to 84%when MAA was added to polymerization system.It should be pointed out that the amount of MAA must be controlled strictly.The amount of post-added SDS also had an important influence on the fraction of polymer/Fe₃O₄ NCPs.The fraction decreased with the increase of SDS dosage.However,the content of MPS-Fe₃O₄ had little effect on the fraction of polymer/Fe₃O₄ NCPs within the scope of the experiment.Based on the above miniemulsion polymerization,the emulsion with high fraction of polymer/Fe₃O₄ NCPs and high fluorescence intensity was prepared when the hydrophobic fluorescent molecules tetraphenylethylene?TPE?were added in the polymerization system.The test curves of fluorescence spectrophotometer showed that the maximum fluorescence intensity of emulsion could be controlled by TPE dosage.The TEM images showed that the addition of TPE had little effect on the fraction of polymer/Fe₃O₄ NCPs and latexes average size in emulsion.In this paper,a miniemulsion polymerization to prepared high polymer/Fe₃O₄NCPs fraction emulsion was proposed,and the formation mechanism of polymer/Fe₃O₄NCPs was also proposed.The regulation of polymer/Fe₃O₄ NCPs fraction in emulsion was achieved at mechanism level.On this basis,the nanocomposite particles were functionalized by carboxyl groups and the fluorescent molecules were added into this system.Ultimately,the emulsion with high polymer/Fe₃O₄ NCPs fraction and high fluorescence intensity was prepared effectively.The results of this paper have important reference significance on the production and application of magnetic polymer-based nanocomposite particles.