Production and Properties of Polyimide Aerogels Based on 4,4'-Oxydianiline and 3,3',4,4'-Benzophenonetetracarboxylic and Pyromellitic Dianhydrides

Two series of polyimide aerogels (PI AGs) based on 4,4'-oxydianiline (ODA) and one of the two dianhydrides, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA), were synthesized by low-temperature polycondensation of ODA–BTDA and ODA–PMDA monomer pairs in dimethylformamide with the addition of the crosslinking agent 1,2,3-tris(4-aminophenyl)benzene (TAB), followed by chemical imidization in situ in solution and subsequent drying of PI gel with supercritical (SC) CO2. PI AGs with a specific surface area of up to Ssp = 230 m2/g were obtained. The influence of the chemical structure of the anhydride and the TAB content on the shrinkage and specific surface area of the synthesized PI AGs was studied. The morphological structure of PI AE was examined using scanning electron microscopy. A comparison was made of the specific surface area Ssp values for samples obtained by drying the gel with SC CO2 with and without preliminary replacement of the solvent (DMF) with acetone. It was found that drying without replacing the solvent results in higher Ssp values than drying with solvent replacement and significantly reduces the overall duration of the process of obtaining PI AE.