Strengthening the weak link: A covalent organic framework-based coupling agent for high-performance epoxy nanocomposites

The development of high-performance nanocomposites critically depends on effective interfacial coupling agents, with multifunctional variants offering particular promise. Herein, we propose the rational design and synthesis of a multifunctional silane coupling agent via covalent organic framework (COF) self-assembly. This agent (COF-APTES) integrates a high density of amino groups and ethoxy silane terminals within a porous, thermally stable architecture. We demonstrate its application in grafting onto nano-SiO₂ to fabricate a modified filler (SiO₂-COF-APTES) for reinforcing epoxy composites. Comprehensive characterization reveals that the COF-APTES enhances the epoxy-filler interface through a synergistic mechanism: its abundant amino groups enable robust covalent bonding with the epoxy matrix, while its porous structure provides physical interlocking and promotes the formation of an interpenetrating network. Consequently, composites reinforced with SiO₂-COF-APTES exhibit a 71% increase in tensile strength and a 42% increase in shear strength compared to those with unmodified SiO₂. This work demonstrates that the COF self-assembly strategy can serve as a feasible approach for designing multifunctional coupling agents, providing a potential pathway to improve the interfacial properties and mechanical performance of polymer nanocomposites.