Molecular design and multiscale interpretation of the structure-property relationship of phthalonitrile resins containing polyimide skeletons

This study establishes a systematic mechanistic framework for phthalonitrile resins containing polyimide skeletons (PIPN) to address their narrow processing window and unclear thermo-mechanical regulation. Six PIPN model compound with varied dianhydride structures PM (PMDA), BP(BPDA), F (6FDA), ABP(ABPDA), K(BTDA), E (BPADA) were designed and synthesized. Through integrated multiscale simulations and experimental characterization, a comprehensive “structure–weak interactions–packing order–molecular mobility–energetics–macroscopic properties” correlation model was constructed for the first time. Molecular backbone rigidity, symmetry and planarity govern the performance: fully rigid PM-PIPN exhibited strongest π-π stacking and electrostatic interactions, yielding the highest melting point (390°C) and superior predicted modulus. Conversely, flexible segments (E-PIPN) or sterically hindered groups (F-PIPN) systematically weakened intermolecular interactions, reducing both melting point and modulus while increasing Poisson’s ratio. Electrostatic potential analysis, weak interaction visualization (IRI), mean square displacement (MSD) and cohesive energy density calculations synergistically revealed the regulation mechanisms from electronic, spatial, dynamic and energetic perspectives. This mechanistic framework provides theoretical foundations for rational molecular design of high-performance PIPN resins.