Fabrication of Polyimide Aerogels Cross-Linked by a Cost-Effective Amine-Functionalized Hyperbranched Polysiloxane (NH₂–HBPSi)

Polyimide (PI) aerogels were prepared from anhydride end-capped polyamic acid oligomers cross-linked by a low-cost lab-made amine-functionalized hyperbranched polysiloxane macromer (NH₂–HBPSi). NH₂–HBPSi was synthesized via the hydrolysis–condensation reaction between phenyltrimethoxysilane, tetraethoxysilane, and γ-aminopropylmethyldiethoxysilane, which are all cheap commercially available silane-coupling agents. To determine the effects of the NH₂–HBPSi cross-linker on the formation and properties of aerogels, two different PI oligomers, synthesized from relatively flexible 4,4′-oxidianiline and rigid-rod 2,2′-dimethylbenzidine, were investigated. The resulting PI aerogels showed comparable properties with the triamine cross-linked PI aerogels, such as low densities (0.12 to 0.20 g cm^–3), high BET specific surface areas (279 to 460 m² g^–1), low thermal conductivities (29–32 mW m^–1 K^–1), and excellent mechanical and thermal properties across the range of NH₂–HBPSi cross-linker concentrations used (2.5 to 12.5 wt %). Moreover, the thermal insulation, dielectric, and CO₂ uptake performances were also investigated, demonstrating the broad range of potential applications for these multifunctional cross-linked PI aerogels. Considering the low-cost and facile synthesis for this NH₂–HBPSi macromer cross-linking agent, we anticipate that this work can overcome the drawbacks of expensive conventional PI cross-linkers and offer a simple approach to produce low-cost PI aerogels at scale.