Advances in Modification of Phthalonitrile‐Based Fiber‐Reinforced Composites: A Review

ABSTRACT Phthalonitrile (PN)‐based fiber‐reinforced polymer composites (FRPs) have long been celebrated for exceptional thermal and mechanical performance, yet their practical deployment is hindered by persistent challenges in interfacial adhesion. Present research remains fragmented into disparate, case‐specific studies, leaving the modification‐strategy landscape and its intrinsic interconnections largely unexplored. This review therefore dissects the latest modification paradigms of FRPs, mapping how PN monomer design, matrix additives and fiber surface engineering translate from molecular‐scale innovations to macroscopic property gains. It first summarizes the effects of different PN monomers on the thermal and mechanical behavior of FRPs. A systematic taxonomy is then provided, contrasting matrix‐centric approaches—which elucidate modifier mechanisms and their impact on composite properties—with fiber‐centric techniques that enhance interfacial adhesion and interactions through specific surface treatments. Finally, the review outlines future research avenues that promise to push PN‐based FRPs beyond current performance ceilings, offering a roadmap for researchers and industries seeking next‐generation high‐performance materials.