Polyimide Microwave Absorption Foam Reinforced With Epoxy Resin and Integrated With Multifunctionality

ABSTRACT Polyimide (PI) microwave absorption (MA) foam is favored in the aerospace field due to its lightweight and chemical stability. However, the poor mechanical properties of PI foam matrix restrict its broader application. While monomer design and component optimization can enhance the mechanical property of PI MA foam, the inherent high melt temperature and viscosity still limit in‐depth structure design. Consequently, improving the intrinsic mechanical property of PI MA foam remains a significant challenge. Here, we employ the in situ foaming process, grafting epoxy groups onto PI main chain and incorporating rigid segments to create a cross‐linked, interpenetrated, and entangled network system dominated by epoxy‐PI molecular chains. The enhanced polarity and stiffness of the PI main chain through molecular design, and the optimized skeletal structure through component regulation, jointly improve the mechanical strength of the PI MA foam. The obtained PI MA foam maintains structural stability even under the dual impact of high temperature (200°C) and load (10 000 times of self‐weight). Due to the superior impedance matching and multiple reflection paths, the foam offers the optimal effective absorption bandwidth (EAB) of 10.5 GHz at low CNT content (1.5 wt.%) and thin thickness (2.5 mm). This research provides a straightforward and industrial‐scale strategy to prepare multifunctional PI MA foam suitable for electromagnetic/infrared stealth in harsh environments.