Synthesis Of SiO₂/Polymer Composite Materials And Cross-linked Polymer

During the last decades, there has been increasing interest in the nanosizedmaterials that can be synthesized due to its potential in developing novelmaterials with unique functions. As the novel core-shell materials withfunctional groups, inorganic-organic polymer core-shell particles all throughhave been the focus. These kind of core-shell particles realize the molecularscale fabrication, which not only have both advantages of inorganic and organicmaterials, but also have the properties in the fields of electrics, optics,magnetics, mechanics, energetics and catalyzer. The organic core can enhancethe properties in mechanical strength and scratch resistance, and the polymershell can exhibit elasticity and film formation ability, make the organic corecompete with the organic phase, enhance the thermal stability in theenvironment and insulate the organic core from environment, and all of theseextent its applications. The latex particles with polymer shell have improvingphysical and chemical and mechanical properties, creating synergistic effects.In recent years, considerable effort has been devoted the development of themethods for the synthesis of composite particles consisting of organic corecovered with polymer shell. That can be summarized following kinds: 1)employing cross-linkers made the organic core and the monomers compatible,then the polymerization carries on the surface of the organic core. 2) emulsifier,monomer or initiator can be absorbed to the surface of the organic core, then themonomer polymerize and the core-shell particles formed.In many organic materials, the silica have many advantages:1)chemicalstability and optical transparence,2)the hydroxyl on the silica surface can bereact with the other molecules for surface modification,3)the silica canintermingle with dies. And it has been apply in many fields, such as medicine,coating and filling ect.In our work, we mainly studied the synthesis of the composite particles ofsilica covered with polystyrene. First, we synthesized the monodisperse silicawith different diameter, which is hydrophilic and not compete with themonomer. For the following coating, the silica must be treated with cross-linkerto change the hydrophilic to the hydrophobic. Here we employed1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane (Vi-D4) as themodification agent to treat the silica spheres for the first time. Then theemulsion polymerization of styrene was conducted in a water-rich medium inthe presence of emulsifier, an initiator, a buffer and modified nanosized silicaspheres. Monodisperse silica/polystyrene nanocomposite particles withcore-shell structure were obtained, and these particles have uniform size andgood dispersibility. The effects of the surfactant concentration and compositionof the reaction medium on the particles was studied, moreover the modifyingmechanism of silica spheres was discussed. This method we used is feasible andavailable, by which can prepare many composite nanoparticles with specialproperties such as optical, electric, magnetic etc. In addition, Vi-D4 could bepossibility modified other inorganic cores such as ZnS, CaCO3, TiO2, Fe3O4 etc.Owning to the peculiar structure of nanosized polymer network, theapplication of it would be more widely and the synthesis of it becomes thefocus, and it is very difficult to prepare this fine structure. So far, little workrelated to this field has been reported. In this article, the cross-linked latexparticles of polystyrene were obtained by emulsion polymerization, and thecross-link is between latex particles, which are different from the commoncross-link in the inner of the latex particles. And the effect of the monomer,emulsifier and cross-linker on the products was studied in detail. By controllingthe effect parameter, different cross-linked polymer can be obtained, whichwould be the rudiment of the nanosized polymer network potentially. Theproducts were characterized by FTIR, TEM, XPS and DLS.