Colorless and Transparent Polyimide Aerogels via Molecular Engineering toward Energy-Efficient Windows.

Energy loss through windows significantly contributes to building energy consumption, highlighting the demand for transparent thermal-insulating materials. Colorless, transparent polyimide (PI) aerogels are a promising class of candidate materials, but their development has been hindered by the challenging balance among optical transparency, color quality, and thermomechanical properties. Herein, we report a colorless and transparent PI aerogel through molecular engineering of the polymer network. Optimized aerogel (PI-2) with exceptional combined properties has been fabricated via copolymerization of 4,4'-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA), 4,4'-oxydianiline (ODA), and p-phenylenediamine (p-PDA), cross-linked with 1,3,5-tris-(4-aminophenoxy)-benzene (TAB) and processed via supercritical drying. The introduction of p-PDA enhances molecular chain rigidity and optimizes the nanoporous structure (peak pore size of 19.1 nm), simultaneously reducing light scattering and suppressing heat transfer. Compared to control samples without p-PDA (PI-1) or with 2,2'-dimethyl-4,4'-diaminobiphenyl (DMBZ, PI-3), PI-2 achieves colorlessness and high optical transmittance (57.1% at 800 nm) while maintaining superior thermal and mechanical performance. This work provides a strategy for developing colorless, transparent PI aerogels with potential applications for energy-efficient windows and optoelectronic devices.