Moisture-resistance, mechanical and thermal properties of polyimide aerogels

Cross-linked polyimide aerogel has excellent mechanical properties, heat insulation and flame retardancy, but it is easy to absorb water in a humid environment, causing its structure to collapse and deformation, which greatly limits the application of the materials. In this study, a flexible monomer 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FAPB) is introduced into the 4,4′-oxydianiline(ODA)/3,3′,4,4′-biphenyltetracarboxylic dianhydride(BPDA) framework structure, which greatly improve the moisture resistance of the aerogel. The polyimide aerogel obtained by replacing 37.5 mol% of 6FAPB with ODA has water absorption rate as low as 9.5% and water contact angle of 112°. It is found that the aerogel containing 37.5 mol% of 6FAPB do not change significantly after water absorption. In addition, the mechanical properties of polyimide aerogels are also improved, the elongation at break increased from 39.7 to 64.7%. At the same time, the prepared aerogel has good dielectric properties, which greatly improves the range of applications for the aerogels.