Flexible Copolyimide Aerogels with Exceptional Thermo-Mechanical Stability and Near-Zero Shrinkage through a Synergistic Copolymerization Strategy

Polyimide (PI) aerogels show significant promise for aerospace thermal protection owing to their excellent thermal stability. However, their applicability in demanding environments is limited by pronounced thermal shrinkage above 200 °C, coupled with insufficient studies of high-temperature stability. Herein, we develop a strategy synergistically combining 3,3′-dimethylbenzidine (DMBZ) and 4,4′-(9-fluorenylidene)dianiline (FDA) with 4,4′-oxidiphthalic anhydride (ODPA) and the flexible cross-linker 1,3,5-triaminophenoxybenzene (TAB) to fabricate flexible copolyimide aerogels through copolymerization–modification–chemical imidization. The resulting PI aerogels demonstrate excellent mechanical properties (Young’s modulus reaching up to 50 MPa), hydrophobicity (water contact angle of 140.6° and water absorption rate of 0.5%), and notable thermal insulation (thermal conductivity as low as 0.056 W·m^–1·K^–1 at 250 °C). Crucially, they exhibit outstanding high-temperature stability, showing no dimensional change after treatment for 60 min at temperatures ranging from 230 to 270 °C (in 10 °C intervals), good thermal shock resistance, and a 5% weight-loss temperature up to 514 °C. These enhancements originate from the hydrophobic methyl groups in DMBZ and the structural rigidity imparted by FDA. This work successfully addresses the persistent challenge of thermal shrinkage in PI aerogels, significantly enhancing their reliability for aerospace applications requiring prolonged extreme thermal exposure.