Aerogels are low density solids having low thermal conductivity, low dielectric constant, and high surface area, among other properties, due to their fine pore structure. Aerogels consist on a solid network structure, and are made, for example, by extracting a liquid portion of a gel through supercritical fluid extraction while allowing the gel to maintain a solid structure. Polyimide aerogels combine low thermal conductivity and low dielectric constant with excellent mechanical properties in comparison with silica and polymer-silica hybrid aerogels.
Polyimides are polymers of imide monomers. Polyimides have the general chemical structure shown immediately below.

Polyimide aerogels are excellent insulators due to their high porosity, low thermal conductivity, flexibility, and low density. Accordingly, polyimide aerogels are useful for various applications ranging from lightweight substrates for high performance antennae, to flexible insulation for space suits and spacecraft decelerators such as inflatable structures for spacecraft entry, descent, and landing (EDL) on planets, among other applications. Finding cost efficient precursors, however, to synthesize polyimide aerogels is crucial to large scale manufacturing and commercialization.
Certain polyamines, organic compounds with plural primary amino groups, namely, 1,3,5-triaminophenoxybenzene (TAB), 2,4,6-tris(4-aminophenyl)pyridine (TAPP), octa-(aminophenoxy)silsesquioxane (OAPS), or 1,3,5-tris-(aminophenyl)benzene (TAPB), have been used to cross-link anhydride end-capped polyimide oligomers for synthesizing polyimide aerogels. Moreover, polyamine cross-linkers known to be suitable for synthesizing polyimide aerogels have been found to be commercially unavailable at times, and somewhat expensive, thus inhibiting scale up of manufacturing and production of polyimide aerogels for widespread use.
Another alternative process for obtaining cross-linked polyimide aerogels includes reacting dianhydrides with triisocyanates, and applying a room temperature cure. Thermogravimetric analysis (TGA) of aerogels produced at room temperature and 90° C. using this alternative process revealed weight loss of 5% to 7% with an onset of about 200° C., which is indicative of incomplete imidization.
Polyimide aerogels made without using any cross-linker tend to shrink undesirably during fabrication, and suitable products are believed to derive substantially only from syntheses using pyromellitic dianhydride. Linear polyamide-polyimide clay aerogel composites have also been fabricated for alternative processes for making polyimide aerogels. Polyamide-imides are thermosetting or thermoplastic, amorphous polymers. Freeze-drying instead of supercritical fluid extraction is used during such processes to remove the liquid. The clay acts as a template for the formation of the porous aerogel structure. The mechanical properties of the resulting gel, however, are weaker than desired, and the thermal conductivities are higher than those associated with polyimide aerogels formed using supercritical fluid extraction.
Thus, an alternative polyimide aerogel and process of manufacture is needed. In particular, a low cost alternative for mechanically strong polymer aerogels would be beneficial.
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