Wave‐Transparent Composites Based on Phthalonitrile‐Cyanate Ester Blends With Optimized Crosslinking Network Through a Feasible Chemical Design

ABSTRACT Aircraft wave‐transparent radome composites require high‐temperature resistance to ensure structural integrity and wave‐transparent performance at high flight speeds. Herein, aminophthalonitrile (4‐APN) was innovatively integrated into the bismaleimide (BMI)‐cyanate ester (CE) system, and a nitrogen‐rich crosslinking network was meticulously engineered to confer both superior heat resistance and dielectric properties, utilizing a stepwise reaction strategy. At low temperatures, 4‐APN directionally triggered the Michael addition reaction of the BMI double bonds to pre‐consume the highly reactive primary amine. Subsequently, the secondary amine catalyzed the orderly trimerization of CE at elevated temperatures, which synergistically inhibited the autocatalytic generation of the polar by‐products. Ultimately, the structural‐functional integration design of high‐temperature‐resistant and radar‐transparent composites was achieved by combining with aramid continuous fibers. The resulting aramid fiber‐reinforced composites demonstrated remarkable dielectric properties (dielectric constant of 3.2 and dielectric loss of 0.007), high heat resistance ( T _g > 280°C), and high flexural strength (578 MPa). Wave‐transparent properties in the X‐band (8–12 GHz) remain stable with a transmittance of approximately 91%. The simple and efficient preparation process lays a solid foundation for the large‐scale production of composites, offering broad potential for industrial applications.