High-temperature insulating polyimide aerogels with a hierarchical porous hyper-cross-linked structure derived from aqueous polymerization of mesostructured silica-grafted Poly(amic acid) salt

Abstract

Polyimide (PI) aerogels have garnered significant interest in thermal protection applications because of their excellent high-temperature resistance and broad operational range. Nevertheless, there are still research challenges, such as the extensive use of organic solvents, shrinkage during drying, and the need for improved thermal/electrical insulation and mechanical properties. Addressing these challenges is crucial for enhancing the practical application of PI aerogels in demanding environments. Herein, we propose a facile, green, and scalable method for fabricating freeze-dried PI aerogels via the aqueous polymerization of amino-functionalized mesoporous silica-grafted poly(amic acid) salts (PAAS-g-AMS). Our findings demonstrate that water-borne PI (W-PI)-g-AMS aerogels have a three-dimensional covalent network with a macroporous/mesoporous architecture, which minimizes molecular chain slippage and shrinkage during thermal imidization. The W-PI-g-AMS aerogels possess excellent properties, such as high porosity (>91 %), a low bulk density (122.4 mg cm⁻³), minimal shrinkage (8.1 %), good compressive strength (6.15 MPa) and modulus (1.86 MPa), a high degradation temperature (T_{d5 %} = 599.4 °C), a low fire growth rate index (0.075 W g⁻¹ s⁻¹), low thermal conductivity (0.08241 W m⁻¹ K⁻¹), and a remarkably low dielectric constant (D_k = 1.25 at 1 MHz) and dissipation factor (D_f = 0.001 at 1 MHz), indicating their potential for use as substitute materials for thermal and electrical superinsulation in the aerospace and transportation industries in extreme environments.