Phthalonitrile-Terminated Polyimide Adhesives with Benzimidazole-Promoted Curing for High-Temperature Bonding

Abstract

A heat-resistant phthalonitrile-terminated polyimide (PN–PI) adhesive was developed by blending long and short poly(amic acid) chains. The short chains contain benzimidazole units that promote phthalonitrile (PN) end-group curing, while amide units in the long chains provide polar sites for intermolecular and interfacial interactions. Isoquinoline lowers the imidization temperature, allowing ring closure to finish before extensive PN curing. Within the examined composition range, PI3 exhibits a glass transition temperature (Tg) of 347.2 °C, with lap-shear strengths of 18.35 MPa at room temperature and 10.02 MPa during short-term testing at 300 °C. Molecular dynamics (MD) simulations show stronger bulk cohesion in short-chain-rich systems, whereas PI3 gives the most negative interaction energy with Al(111). Density functional theory (DFT) calculations reveal an electron-rich benzimidazole nitrogen, supporting its possible role in PN curing. The combined regulation of chain composition and benzimidazole-promoted PN curing provides a PN–PI adhesive with strong bonding performance at 300 °C.