High interfacial performance ultra‐low <i>k</i><scp>PBO</scp> wave‐transparent composite derived from in situ entangled chain and ion‐crosslinking

Abstract Poly‐p‐phenylene benzobisoxazole (PBO) fiber‐reinforced polymer composites exhibit outstanding mechanical properties, dielectric performance, and design flexibility, offering significant potential for applications in areas such as 5G communication, aerospace, and radome. However, achieving a balance between the mechanical properties and interfacial performance of PBO fibers remains a significant challenge. Herein, a non‐destructive interfacial modification of PBO fibers is designed. By constructing an entangled polymer network coating on the surface, the interfacial shear strength (IFSS) of the PBO fibers increases by 131% (from 6.51 to 15.03 MPa). Additionally, the tensile strength of the modified PBO fibers is 4.42 GPa, which represents a decrease of only 4.95% compared to the 4.65 GPa of UNPBO. Furthermore, the PBO fibers are combined with cyanate ester (CE) resin to fabricate laminated composites. The interlaminar shear strength (ILSS) increases from 16.12 to 30.59 MPa, representing an improvement of 89.76%, and the modified PBO composite exhibits better dielectric properties. The entangled polymer network on the surface of PBO fibers is formed by the interpenetration of PBO with the copolymer chain and the coupling of calcium ion‐crosslinking. Overall, this work provides an excellent surface functionalization method that further expands the application prospects of PBO composites. Highlights A novel method for non‐damage surface modification of PBO fibers. The mechanism of interfacial strengthening was investigated. PBO/CE wave‐transparent composite with high mechanical properties and low dielectric characteristics.