Solvent-Free Dehydrohalogenative Polycondensation toward Robust Covalent Organic Frameworks

The scalable synthesis of high-crystalline covalent organic frameworks with irreversible bond linkages remains a significant challenge, especially those constructed via dehydrohalogenative condensation. Here, we report a green and scalable solvent-free synthesis method for the COFs from dehydrohalogenative polycondensation via "metal salt eutectic melt." In this approach, hydroxyl monomers form a self-generating eutectic melt with benzoic acid upon alkali metal treatment, enabling direct melt polymerization of high-melting-point monomers at significantly reduced temperatures. This solvent-free synthesis strategy exhibits broad generality and operational simplicity, affording not only polyether (dioxin- and cyanurate-linked) COFs but also polyester COFs with enhanced crystallinity and porosity, and enabling ease of scale-up synthesis (e.g., hundred-gram-scale), surpassing conventional solvothermal and solvent-free methods. Furthermore, the resulting COFs can directly form monoliths with exceptional mechanical properties that rival those of commercial polymers prepared from nucleophilic substitution. When used as an anode for lithium batteries, the COFs exhibit an outstanding stability over 10,000 cycles at 20 A g^-1, surpassing state-of-the-art COFs and organic materials. This work thus bridges molecular design and synthesis, green chemistry, and energy technology, pointing toward a future where advanced materials are both performance-optimized and sustainably manufactured.