Preparation Of Polymer Microspheres By A Nonhydrolytic Sol-Gel Route And Pickering Emulsion Polymerization

Polymer microspheres and polymer/inorganic composite particles have special size,morphology and function, which have potential applications in electronics,photoelectricity,medicine and architecture etc. Up to now, various preparation methods have been developed to get the polymer and polymer nanocomposite particles with uniform dimension. In order to obtain a stable emulsion from two immiscible phases, it is often necessary to add some surface active compounds like surfactants or organic solvents, which is disadvantageous for the further applications in industry. Recently, instead of the surfactant, inorganic particles such as silica, clay, zinc oxide and titania have been employed to stabilize Pickering emulsions by self-assembly at the oil-water interfaces. Inorganic solid particles have special advantages like recycle,ontoxicity,low cost and reducing foam problem. There have been increasingly interests in the synthesis of stable colloidal particles with different kinds of surface structures and morphologies via inorganic-stabilized polymerization. Titania nanoparticles as one of the most studied semiconductors have attracted amount of attention for exhibiting various properties such as a high refractive index, UV light absorption, and photocatalysis etc. Titania has been widely used in the photoinduced decomposition of organic pollutants in water and in air and for photoelectrochemical solar cells. In addition, there are certain research development on the initiation of polymerization and extending activity of titania into the visible light region.In this thesis, a novel, convenient and controlled nonhydrolytic sol-gel method was used to prepare nanosized anatase titania particles. The obtained particles can be well dispersed in water to form a stable titania hydrosol, which exhibits strong UV absorption and high photocatalytic activity. We synthesized PS microspheres with narrow size distribution using the self-made titania hydrosol. In this process, the titania nanoparticles were utilized to stabilize the emulsion droplets, and initiated the polymerization of styrene. Extensive investigation were done about the effect of monomer,cross-linking agent,co-monomer and acidity/basicity on the morphology and size distribution of the resulting polymer microspheres. It was found the cross-linking agent could obviously improve the particle size distribution. Adding partially soluble monomer MMA could reduce the microsphere size and finally nanosized latex was obtained. Adding basic ammonia to the titania hydrosol led to lower surface charge density, bigger particle size and weakly flocculation, which greatly improved the emulsion stability. As a result, polystyrene microspheres with narrow size distribution were prepared.The surface structure of the titania nanoparticles plays an important role on the stability of the Pickering emulsion and the morphology of the final microspheres. Herein, bifunctional molecule acrylic acid and sodium styrene sulfonate were used to modify the titania hydrosol. Through the modified titania-stabilized photocatalytic emulsion polymerization, nanosized polystyere/titania composite particles were obtained. It was demonstrated the carboxyl group of acrylic acid induced a strong bridging bidentate coordination with the titania nanoparticles, which improved titania hydrosol organophilic. SEM,TEM and TGA results showed that the functionalized titania hydrosol via adding a very small amount of AA provided the emulsion system with better stability, which revealed smaller polymer particle of about 100nm. The nanoparticles absorbed a large amount of titania nanoparticles to form well-structured titania armored polystyrene nanospheres, which exhibited high thermal stability and high glass transition temperature. Adding negatively charged NaSS could induce an electrostatic interaction with positively charged titania nanoparticles, and reduced the surface charge density. Consequently, the nanocomposite spheres with the diameter of around 120 nm were prepared. Several tests indicated latex particles with titania-rich surfaces. The well-defined core-shell structure of the obtained polystyrene/titania composite particles was confirmed by the formation of fragile hollow titania nanospheres after thermogravimetric analysis tests. Titania photoinduced Pickering emulsion polymerization provides a novel route to prepare polymer microspheres with special morphology and function.Different from the traditional sol-gel method (SG), nonhydrolytic sol-gel route (NHSG) shows special reaction mechanism, which may endow the prepared inorganic particles with considerable organic groups on the surface. This provides an improved compatibility between the polymer matrices and the inorganic particles. Hererin, PMMA/titania hybrid thin films were prepared by combining PMMA with the titania nanoparticles via NHSG route. It was found the titania nanoparticles were well dispersed in the polymer matrices, and remained small size without obvious aggregation. The hybrid films showed good optical transparency and high thermal stability. In order to identify the universality for inorganic particles with organophilicity via NHSG, PMMA/silica hybrid thin films were obtained by inducing the silica hydrosol into the PMMA. The results supported that at the similar silica content, PMMA/silica hybrid thin films synthesized by NHSG route had improved thermal and other properties compared to the samples prepared by the SG route.NHSG endows the obtained titania nanoparticles with both good dispersion in water and organic groups-rich surfaces, which offers a possibility to get carbon-doped titania with response to visible light. As observed, the titania nanoparticles after calcinations exhibited excellent crystallinity of anatase and strong absorption in visible light region. As followed, microspheres were synthesized via carbon-doped titania stabilized emulsion polymerization under visible light irradiation. After removing the free polymer components, the titania were suface-grafted by some amounts of polymer chains, which led to stable dispersion in THE...