Nearly “zero” shrinkage polyimide aerogel enabled by thiazine/imidazole in-situ co-catalyzed low-temperature imidization strategy for thermal insulation and electromagnetic transparency

Addressing the structural shrinkage during high-temperature imidization (>300 °C) of polyimide (PI) aerogels is a critical challenge for enhancing their thermal insulation and electromagnetic wave-transparent performance in aerospace applications. Herein, a thiazine/imidazole in-situ co-catalyzed low-temperature imidization strategy is developed for the first time, by which PI aerogel with nearly “zero” shrinkage is successfully prepared. This method works by introducing 2,4-diamino-6-[2-(2-methyl-1-imidazolyl) ethyl]-1,3,5-triazine (2MZ-AZINE), whose dual amino groups not only construct a crosslinked network with polyamic acid chains but also precisely anchor catalytic groups onto the side chains, thereby enabling highly efficient low-temperature cyclization. Experimental results indicate that cyclization temperature is reduced from conventionally over 300 °C to 200 °C, consequently reducing shrinkage of PI aerogel significantly from 30.6% to 3.1%. Correspondingly, the 2MZ-AZINE-PI aerogel achieves low density (4.74 mg cm −3 ), super-hydrophobicity (152.7° water contact angle) and low thermal conductivity (25.3 mW m −1  K −1 ). Thermal insulation tests show that the 2 cm-thick 2MZ-AZINE-PI controls the surface temperature to be less than 62.3 °C after 20 min on a 200 °C hot stage (versus 72.8 °C for common PI aerogel), demonstrating superior thermal protection. Moreover, 2MZ-AZINE-PI exhibits record-low dielectric constant in the X-band (8–12 GHz), remarkably close to that of air, with permittivity of 1.004 and loss tangent of 8 × 10 −4 , confirming its exceptional electromagnetic wave-transparent properties. This work establishes a practically useful new paradigm for designing integrated thermal protection/electromagnetic wave-transparent PI aerogel materials for potential aerospace applications.