Preparation and Characterization of Highly Cross-Linked Polyimide Aerogels Based on Polyimide Containing Trimethoxysilane Side Groups

In this study, highly cross-linked and completelyimidized polyimide aerogels were prepared from polyimide containingtrimethoxysilane side groups, which was obtained as the condensationproduct of polyimide containing acid chloride side groups and3-aminopropyltrimethoxysilane. After adding water and acid catalyst,the trimethoxysilane side groups hydrolyzed and condensed oneanother, and a continuous increase in the complex viscosities of thepolyimide solutions with time was observed. The formed polyimidegels were dried by freeze-drying from tert-butyl alcohol to obtainpolyimide aerogels, which consisted of a three-dimensional network of polyimide fibers tangled together. By varying the solution concentration of the polyimide containing trimethoxysilane side groups, polyimide aerogels with different densities (ranging from 0.19 to 0.42 g/cm3) were obtained. The resulting polyimide aerogels had small pore diameter (ranging from 20.7 to 58.3 nm), high surface area (ranging from 310 to 344 m2/g), high 5% weight loss temperature in air (at about 440 °C), and an excellent mechanical property. In addition, the glass transition temperature (349 °C) of the polyimide aerogels was much higher than that (210 °C) of the corresponding linear polyimide. So, even after being heated at 300 °C for 30 min, the porous structure of the polyimide aerogels was not completely destroyed.