Hierarchical Cellular Poly(m‐phenylene isophthalamide) with High Flame Retardancy, Mechanical Robustness, and Heat Resistance at Extreme Situation.

High‐performance cellular foams with superior mechanical properties and heat resistance are urgently needed to fulfill the applications in extreme environments. However, they are difficult to be prepared because of low gas diffusion rate in high‐performance polymers. In this work, a facile solution‐foaming strategy to prepare multifunctional foams based on poly(m‐phenylene isophthalamide) (PMIA) is reported. The achieved PMIA foams show a hierarchically cellular structure containing macropores and mesopores. Due to their high porosity, the PMIA foams exhibit low thermal conductivity (0.0447–0.0498 W m−1 K−1) and high sound absorption coefficient at different frequency. A bimodal distribution on acoustic absorption is observed. With a bulk density range of 0.089–0.122 g cm−3, PMIA foams possess compressive moduli of 3.2–14.2 MPa and bending strength of 1.1–2.1 MPa, respectively. Moreover, they exhibit a recoverable deformation of 55.4% after 10 cycling 10% strain compressions and maintain a dimensional stability under harsh environment (–196 to 250 °C). Despite generated byproducts like polyurea, they still show a limiting oxygen index (25.2–26.3%) and relatively low heat release rate (178.3 kW m−2). This work provides a facile strategy to efficiently prepare high‐performance PMIA foams for broad application prospects. [ABSTRACT FROM AUTHOR]