Due to a demand by the aerospace industry, NASA has begun developing the next generation of polyimide foams which could be utilized to reduce vehicle weight for the X-33 and Reusable Launch Vehicle (RLV) programmes. The activity at NASA Langley Research Center focuses on developing polyimide foam and foam structures which are made using monomeric solutions or salt solutions formed from the reaction of a dianhydride and diamine dissolved in a mixture of foaming agents and alkyl alcohols. This process can produce polyimide foams with varying properties from a large number of monomers and monomer blends. The specific densities of these foams can range from 0.008 g cc−1 to 0.32 g cc−1. Polyimide foams at densities of 0.032 g cc−1 and 0.08 g cc−1 were tested for a wide range of physical properties. The foams demonstrated excellent thermal stability at 321°C, a good thermal conductivity at 25°C of 0.03 W m−1 K−1, compressive strengths as high as 0.84 MPa at 10% deflection and a limiting oxygen index of 51%. Thermomechanical cyclic testing was also performed on these materials for 50 cycles at temperatures from −253°C to 204°C. The foams survived the cyclic testing without debonding or cracking. Thermal forming of the 0.032 g cc−1 foam was performed and a minimum radius curvature of 0.0711 m was achieved. The foams exhibited excellent properties overall and are shown to be viable for use as cryogenic insulation on the next generation RLV.

Thermal curing of poly(4,4'-oxybis(phenylenepyromellitamic acid)) (PAA) films prepared from PAA solutions using a novel solvent system composed of tetrahydrofuran (THF) and methanol (MeOH) has been investigated. In the drying process of casted PAA films, MeOH was entirely evaporated, while a significant amount of THF remained in the dried film. The progress of thermal imidization was observed during the process of drying at 80 °C. NMR measurements for the dried film revealed that the thermal imidization of trans-amidized PAA predominated over that of cis-amidized PAA. Dynamic mechanical thermal analyses (DMTA) pointed out that the dried PAA film containing THF showed no significant plasticization during the thermal cure. This indicates the mobility of polymer chain would be low during the thermal cure so that the resulting polyimide film has a higher in-plane orientation. The coefficient of thermal expansion (CTE) of the polyimide film was found to be low compared with a film obtained from a PAA solution using NMP.

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