Cross-Linked and Rigid Polyimide Composite Foams with Prominent Fire Resistant, Thermal Insulating, and Wave-Transparent Properties

High-performance and light-weight polymer foams with ultralow dielectric constant, good thermal stability, and high mechanical strength are greatly needed in aviation and aerospace fields. In this work, cross-linked and rigid polyimide (PI) composite foams were fabricated based on norbornene terminated polyamide ester oligomer precursor powders via thermal foaming method. The obtained PI composite foams exhibit outstanding characteristics of light weight (90–130 kg·m–3) and high mechanical strength. When the glass fiber (GF) loading was 10 wt %, the compressive strength and modulus of PI/GF composite foams reached 1.7 and 49.6 MPa, respectively. Moreover, the PI foams exhibit remarkable thermal stability and fire-resistant property (LOI > 42%). The thermal conductivity of the prepared PI foams was measured to be in the range of 0.039–0.052 W·m–1·K–1 at room temperature. In addition, the PI composite foams present ultralow dielectric characteristic (tan δ = 0.006–0.008 at 10 GHz) and prominent wave-transparent performance (>95%) in the X band (8.2–12.4 GHz). These beneficial integrated properties enable the resultant PI composite foams to be attractive candidates for applications in aviation and aerospace fields.