Molecular engineering of cyano-functionalized heterocyclic sizings: balancing rigidity-flexibility and structural congruence for high-temperature interfacial performance in CF/PBPESK composites

Enhancing the interfacial heat resistance between carbon fibers (CF) and high-performance thermoplastics is critical for their high-temperature forming and applications. This study designed and synthesized three heterocyclic poly(aryl ether nitrile sulfone) (PAENS) sizing agents—poly(phthalazinone ether nitrile sulfone), poly(bisphthalazinone ether nitrile sulfone) (PBPENS), and poly(sulfone-type bisphthalazinone nitrile sulfone)—all incorporating strongly polar cyano groups. These agents were applied to CF via a simple impregnation method to improve interfacial properties of CF reinforced poly(bisphthalazinone ether sulfone ketone) (CF/PBPESK) composites. The PAENS sizing agents, containing sulfone groups and heterocyclic structures, showed good compatibility with the PBPESK matrix, and their different heterocyclic structures imparted varying molecular chain flexibility and glass transition temperatures ( T g ). At room temperature, the PBPENS sizing modified CF/PBPESK (PBPENS@CF/PBPESK) composite demonstrated the most significant improvement, exhibiting a 43% increase in interfacial shear strength and a 32% increase in interlaminar shear strength compared with the desized CF/PBPESK composite. At elevated temperatures, the PBPENS@CF/PBPESK also exhibited the highest flexural strength and retention rate. The PBPENS, balancing molecular rigidity (via heterocyclic units) with flexibility (via ether bonds), and matching the matrix in structural similarity and T g , achieved excellent interface strengthening effects. This work provides crucial guidance for designing high-temperature-resistant thermoplastic sizing agents demanding applications.