Elementary Studies On Preparation Of Porous Polyimide Microspheres Using Nano-Silica As Porogen

Organic/inorganic nana-composites have attracted great interest since they frequently exhibit unexpected properties synergistically derived from two components, which combine the advantages of the inorganic materials(rigidity, high thermal stability) and the organic Polymer (flexibility, dielectric, ductility, and process ability). As so far one rank polymer possessing the highest class of heat-resisting on the practical application, polyimide is one of the most ideal choice for synthesis of composite materials, the nana-SiO2 is currently to apply one of the most extensive nana-materials, its special surface effect, the effect of the quantum size and volume effect etc, which has pay attention to researchers at many science materials. Polyimide/silica nana-composite have broad application prospects in the electronics, chemical industry, aviation and many other fields combining the features of both them. At present, the literature reports of polyimide/silica nana-composites has focused on the composite film, there are few reports of polyimide/silica nana-composite microspheres.Polyimide/silica nano-composite spheres were successfully prepared using non-aqueous emulsion polymerization method, which had high heat resistance, good spherical shape and dispersion, porous polyimide microspheres were obtained through etching in hydrofluoric acid Solution. The main contents and conclusions are as follows:(1) The modification of nano-silica using 3-aminopropyltriethoxysilane (KH-550)The surface hydroxyl group of silica nana-particles makes it difficult to be dispersed uniformly in organic matrix and have a strong tendency to agglomerate. So we surface modification of nano-silica was necessary in front of the preparation of nana-composite microspheres. The surface structure and characteristics of modified particles were studied and characterized by FT-IR、 TGA and TEM. The results showed that silane coupling agent could modify SiO2 nana-particles successfully and improve its dispersivity.(2) Preparation of polyimide/silica nana-composite microspheres using non-aqueous emulsion PolymerizationInvestigate the influence of the join way, add time and add quantity of nana-silica to morphology, particle size and thermal performance of nana-composite microspheres. When nano-Si02 was added by the form of glue and after 3-4h polymerization, the composite microspheres with smooth surfaces were homogeneously distributed with uniform size; added amount of nano-silica should not be more than 20%, the thermal stability of the composite microspheres increased with the increase of the amount of silica; the smooth surface of the nano-composite microspheres after the thermal imidization indicated no phase separation occurred.(3) Elementary studies on pore-making of nana-silicaPI porous microspheres were obtained via the composite microspheres etching in hydrofluoric acid Solution, studied and characterized by SEM、specific surface area、TGA and FT-IR. The specific surface area of porous microspheres proportional to the amount of silica; Most of hole distribution inside the microspheres, local hole with 30-50 nm distribution on the surface of microsphere; The thermal properties of porous microspheres decreased by 80℃ than nana-composite microspheres, but still as high as 470℃.