Abstract: The insufficient interfacial adhesion between carbon fibers and the PEEK matrix remains a key obstacle to realizing the full mechanical and thermal performance of CF/PEEK composites. This work proposes a biphenyl-containing branched poly(aryl-ether-nitrile) (BPEN) with controlled branching degree as an interfacial compatibilizer and subsequently processed with PEEK via a powder-impregnation assisted hot-pressing method to fabricate CF@BPEN/PEEK laminated composites. When the BPEN branching degree is 10 %, the CF@BPEN/PEEK laminated composites exhibit interlaminar shear strength of 39.7 MPa and a flexural strength of 506.5 MPa, which are 66.1 % and 39.2 % higher than pristine CF/PEEK laminated composites (23.9 and 363.9 MPa), respectively. In addition, the modified laminated composites show enhanced thermal conductivity (1.45 W m^‒1 K^‒1), an elevated glass transition temperature by approximately 4 °C, and a remarkable X-band electromagnetic interference shielding effectiveness of 41.0 dB. These multifunctional enhancements originate from a robust, diffusion-driven interphase, constructed through π-π stacking interactions between BPEN biphenyl units and PEEK chains, as well as hydrogen bonding between cyano groups and oxygen-containing sites on the fiber surface. Furthermore, the polarization induced by the strong polar BPEN structure contributes to effective EMI performance.

Key words: Carbon fiber, PEEK, Branched poly(aryl-ether-nitrile), Interfacial adhesion, Mechanical properties