Studies On Preparation Of Porous PI Microspheres Using Nano-silica As Porogen

In the last decades, owing to several special added-value applications in the area of catalysts, separation, chromatographic carriers, adsorbents, low-dielectric fillers, storage and deliver carriers for drugs, phonics crystals, nano-electronics, or biotechnology, porous polymer materials, especially spherical ones, have been the hotspot of active study area in the development of new materials and some of the resulting porous particles have been shown to be of practical use. Polyimide (PI) is considered as the most promising candidates that could satisfy the above requirements with a high thermal stability, good mechanical properties, excellent adhesion properties and outstanding dimensional stability, satisfing a variety of requirements, such as desirable thermal stability, chemical resistance, and high modulus to support the void structure.In this paper, we employed silica nanoparticles as the inorganic phase to introduce into the composite system by in situ polymerization, the silica component was subsequently etched away by hydrofluoric acid, leaving the pores whose size and shape were tuned by the silica particles. Both composites and porous spheres were subjected to a variety of characterizations including by Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray Diffraction, Particle Size Analysis and Thermo-gravimetric Analysis (TGA). Herein, we also discussed the mechanism for the fabrication of the porous PI spheres with well-developed porosity that could be applied as surface-related applications.The main contents and conclusions are as follows:1. The introduction of silica did not yield negative effects on the preparation process of PI spheres. There supplied many physical and chemical cross-linking points between the two phases and formed a considerable fine interconnected network system.2. The composites with the bumpy surface and uneven size distribution were fractal in aqueous system compared to the ones which were spherical perfectly with a smooth and dense surface and a narrow size distribution with non-aqueous system.3. At higher silica contents, a considerable fine interconnected network system had formed again between the two phases, arising the saturation effects due to the SiO2-SiO2interactions, which improved the local order structure of PI molecular chains in some ways and enhanced the thermal stability of polymer.4. The HF etching have little influence on the structure of PI domains. The obtained porous PI spheres with interconnected porous structure were almost spherical and the average size of the pores employed about the range size of70-120nm.5. The porous microspheres were fractal with the bumpy surface and the porous structure existed inside and outside the spheres in aqueous system, while the ones with porous structure only inside the spheres were spherical perfectly with a smooth and dense surface in non-aqueous system.6. The PI spheres with obvious continuous porous structures are prepared by using the100nm of nano-SiO2. While the final nanopore structures of the ones prepared by nano-SiO2of20nm are still superficial and lack of connectivity.