Sol-Gel Fabrication of Polyimide-Silica Hybrid Film and its Characterization through TGA and FTIR

Polyimide-Silica hybrid films with nanostructure were successfully prepared using the sol-gel technique by hydrolysis-polycondensation of tetraethoxysilane (TEOS) in the polyamicacid solution. At the first step polyamic acid was prepared from 4,4 ((Hexafluoroisopropylidene) bis (phthalic anhydride) and Bis (4-aminophenyl) ether (ODA) in methanol/water (1:1 by volume) solution and a amber-colored product for the use in the polyimide synthesis was obtained. The sol-gel reaction requires water to hydrolyze tetraethoxysilane (TEOS), however the existence of water might induce the hydrolyze of polyamic acid , so a solution of polyamic acid in DMAc was stirred in the presence of 1ml of water to avoid the hydrolysis degradation of polyamic acid during the reaction. By heating at 270 oC flexible hybrid films were obtained containing up to 70% silica content. The films with less than 22% silica content were yellow and transparent, whereas the films with higher silica content were yellow and opaque. Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) were used to study hybrids containing various proportions of TEOS. Silica particles with diameter of around 60-105 nm were observed in hybrids films by scanning electron microscopy. The particale size increased with increasing the silica content. Thermogravimetric analysis (TGA) were done under N2 atmosphere at a rate of 20oC/min.  

Keywords:

sol-gel process , Polyimide , Silica , Nanocomposite , Organicinorganic Hybrid Materials , Tetraethoxysilane