105: Mechanochemical annealing route to crystalline covalent frameworks from amorphous polymers

Abstract: Amorphous-to-crystalline transformation in covalent organic frameworks (COFs) presents an intriguing phenomenon, yet its potential through solid-state mechanochemistry has remained hitherto unexplored. Herein, we develop a mechanochemical annealing strategy for the rapid synthesis of highly crystalline COFs from their amorphous analogs under ambient conditions. Utilizing ball milling, a total of 8 Schiff-based COFs with varying linkages, core structures, and dimensions were synthesized from their amorphous forms in as little as one hour under air at room temperature. Furthermore, this strategy was also successfully scaled up to the gram scale for efficient COF production. Notably, the COFs obtained via mechanochemical annealing exhibit higher crystallinity than those synthesized directly through the de novo mechanochemical route. The inherent dynamic nature of the imine linkage in the solid state was unequivocally demonstrated through a scrambling experiment using imine-based molecular compounds. This strategy not only highlights the dynamic self-healing capabilities of amorphous polymers under mechanical forces but also offers a facile pathway for COF synthesis through mechanochemical transformation