| In recent years, as a novel functional material, polymer microspheres have attracted much attention from both fields of science and industry, due to their widely applications in nanotechnology, biotechnology, electronics, and clean energy. Therefore, various kinds of polymer microspheres have been synthesized, and some of the products have been commercialized. Furthermore, as the study extends, the traditional isotropic spherical microspheres can no longer meet the requirements of practical applications. Under the impulse of dual factors of theoretical research and application demand, novel polymer microspheres, which have special chemical composition and morphology, are springing up. Among them, Janus (anisotropic) and porous microspheres are the most attractive ones. Janus microspheres, with asymmetric structure and/or composition, can be used as amphiphilic surfactants, magnetic bifunctional materials, optical materials, and catalyst. Meanwhile, porous microspheres, which have a higher specific surface area and lower density to the original hollow microspheres, have been widely applied to the field of surface science. Certain progress has been made in the research of Janus and porous microspheres, but there is still little relation between the two useful morphologies. How to design a new synthetic route, which can combine Janus morphology with porous structure, has become a pressing issue.In this thesis, we not only focus on the preparation of novel porous or Janus microspheres, but also combine them together to fabricate Janus microspheres with porous structure. The amphiphilic sulfonated polystyrene (SPS) microspheres are used as the clue. Firstly, radiation seeded polymerization method is employed to fill the scientific gap in the preparation of porous microspheres. Secondly, this method is extended to the synthesis of the Janus microspheres with complex structure. Finally, a novel kind of polymerization method:radiation freezing emulsion polymerization is designed to synthesize porous and Janus polymer microspheres at the temperature of subzero. This thesis can be divided into the following four parts:(1) The fabrication of sponge-like porous materials based on swollen crosslinked sulfonated polystyrene (CSPS) microspheres through radiation polymerization. In this chapter, we discovered that submicro-sized CSPS microspheres (200nm) can be swollen into a gel-like structure. Based on this feature, CSPS microspheres are first swollen in methyl methacrylate(MMA)/water system, and then the polymerization of MMA is initiated by y-ray. As a result, a novel kind of sponge-like material, with the porous structure fixed by interlinked PMMA nanoparticles and micron-sized CSPS-PMMA microspheres, is one-step fabricated. The nitrogen adsorption isotherm discloses that the material has a high specific surface area of29m2/g and a narrow pore size distribution of60-120nm. The formation mechanism discloses that the soluble CSPS segments, which contain in the original microspheres, are essential to the sponge-like structure. Subsequently, the final morphology of sponge-like materials can be controlled by the weight ratio of CSPS microspheres, monomer, and crosslinking agent. Finally, the rich sulfonic groups in the CSPS microspheres can be used to adsorb Ag ions. So that after the radiation polymerization and reduction, Ag-loaded sponge-like materials can be one-step fabricated.(2) Synthesis of polymer/inorganic Janus microspheres via asymmetric swelling-dissolving process. In this chapter, at first, decentered sulfonated polystyrene/SiO2(SPS/SiO2) microspheres are synthesized by the seeded dispersion polymerization and the sulfonated modification. Then two kinds of new anisotropic SPS/SiO2composite microspheres, i.e., actinia-like and porous snowman-like particles are easily fabricated by taking advantages of the asymmetric swelling-dissolving property of the original SPS/SiO2microspheres in a ternary mixing solvent (water/ethanol/heptane). Actinia-like microspheres, with a silica core embedded in a "blooming" SPS matrix, are obtained when the composition of the mixed solvent is5:5:0.1. If the amount of heptane in the mixed solvent is doubled, porous snowman-like microspheres are produced. Moreover, during this process, heptane can swell and dissolve these particles; water can react with the sulfonic groups existing on the surfaces of the SPS/SiO2microspheres; ethanol can reduce the surface tension between water and heptane, and promote the swelling-dissolving process. Finally, we discover that the composition of the ternary mixing solvent, the size and sulfonated degree of the original SPS/SiO2microspheres, will strongly impact on the final morphology of the product.(3) The fabrication of anisotropic porous composite (APC) microspheres and application as scaffolds of CdS nanoparticles. In this chapter, based on the above research, SPS/SiO2microspheres with large diameter and low sulfonated degree are used as the template to fabricate APC microspheres, via a swelling-osmosis process in a ternary mixing solvent (water/ethanol/heptane) at70℃. Electron microscope images and nitrogen adsorption results disclose that the specific surface area and pore size distribution of the APC microspheres are11.2m2/g and20-110nm respectively, which indicates that the microsphere has hierarchically porous structure. In addition, by tracking the swelling-osmosis process, we find that the mechanism consists of two stages:firstly, the SPS part is quickly swollen and dissolved by heptane, and the mesopores structure is formed; secondly, water and ethanol slowly osmosis into these microspheres, and the macropores structure is obtained. Finally, the prepared APC microspheres are utilized as scaffolds to load fluoresce CdS nanoparticles through y-ray reduction, and the loading rate is up to57.6%.(4) Synthesis of porous and Janus microspheres via radiation freezing polymerization. In this chapter, we design two new polymerization methods:radiation emulsion freezing polymerization and radiation seeded freezing polymerization. The basic idea is to freeze the aqueous phase of traditional O/W system to the ice, so that the monomer droplets change into micro reactor vessel with "hard wall". Then, y-ray is utilized here to initiate the polymerization at subzero temperature. Micron-sized porous polymer microspheres can be obtained through radiation miniemulsion freezing polymerization. The mechanism is similar to the interfacial polymerization, and the morphology can be controlled by varying the total adsorbed dose and the addition of chemical initiator. Meanwhile, waterdrop-like and walnut-like Janus microspheres can be obtained through radiation seeded freezing polymerization, while the monomer is St and MMA respectively. In addition, if we raise the concentration of SPS microspheres,"bamboo-like" self-assembly can be formed. |
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