Key words: polyimides, aerogels, polycondensation, chemical imidization, cyclizing agent, polymer gels supercritical fluids, supercritical drying
Two series of polyimide aerogels (PI AEs) based on 4,4'-oxidianiline (ODA) and two dianhydrides were synthesized: 3,3',4,4'-benzophenone tetracarboxylic acid (BTDA) and pyromellitic acid (PMDA) by low-temperature polycondensation in dimethylformamide monomers pairs (ODA—BTDA) and (ODA—PMDA) with the addition of a crosslinking agent — 1,2,3-tris-(4-aminophenyl)benzene (TAB), chemical in situ imidization in solution, and subsequent drying of the PI gel with a supercritical (SC) fluid — SC-CO2. PI AEs with a specific surface area up to Ss = 230 m2/g were obtained. The effect of the chemical structure of anhydride and the content of TAFB on the amount of shrinkage and Ss of synthesized PI AEs has been studied. The morphological structure of PI AEs has been studied by scanning electron microscopy. The Ss values for PI AEs obtained by drying with preliminary solvent replacement (DMFA) with acetone and without solvent replacement are compared. It has been shown that SK-drying without solvent replacement shows Ss higher values. Carrying out the SC drying stage without first replacing the solvent significantly reduces the total duration of the PI AEs production process.