Enhanced Mechanical Performance of Biphenyl Phthalonitrile Composites Through Regulation of Molecular Structure via Aromatic Diamines

Biphenyl phthalonitrile (BIPN) resin exhibits considerable potential for high‐performance fiber‐reinforced composites. High curing temperature and limited interfacial adhesion remain critical challenges for practical application. Two aromatic diamines, 1,3‐bis(3‐aminophenoxy) benzene (m‐APB) and 4,4′‐diaminobenzanilide (DABA), were employed as curing promoters to regulate the curing behavior and interfacial characteristics of BIPN. A melt prepolymerization strategy was adopted to obtain stable B‐staged prepolymers with tunable reactivity. The introduced amino functionalities were found to promote nitrile activation and cyclization toward triazine‐rich network structures. The incorporation of amide‐containing DABA increased the matrix polarity and promoted the formation of a more stable interfacial microstructure with reduced interfacial defects. The enhanced polarity strengthened the interaction between the resin matrix and the surface silanol groups of quartz fibers, thereby improving interfacial adhesion and mechanical performance. X‐ray photoelectron spectroscopy reveals pronounced modification of the O 1s chemical environment in composites, indicative of strengthened interfacial interactions. The DABA‐modified composites exhibit improved flexural properties and interlaminar shear strength while the resins maintaining good thermal stability under both nitrogen and air atmospheres. This work provides structural insight into the regulation of nitrile reactivity and interfacial behavior through aromatic diamine modification in biphenyl phthalonitrile composite systems.