Durable Metal‐Organic Frameworks by Covalent Hybridization with Polyurethane and Polyallophanate

Abstract Metal‐organic frameworks (MOFs) are expected for have a multitude of applications due to their high porosity, crystallinity, and designability. However, the mechanical properties of MOFs are brittle due to the porosity and the weak coordination bond between the metal ions and the organic ligands. A method for enhancing the mechanical properties of MOFs while maintaining high porosity is anticipated to facilitate long‐term, stable utilization. In the present work, single crystals of MOFs are combined with polyurethanes inside pores of crystal using the crystal component‐linking method. Guest molecules of diisocyanates are introduced into the pores of MOFs composed of organic ligands with hydroxy groups, and the organic ligands are linked by the guest molecules via urethane bonds. The excess diisocyanates yielded allophanates, which function as crosslinking points, thereby forming polymer networks within the MOFs. The compressive fracture strength of MOFs combined with polyurethane and allophanate networks is observed to be approximately thirty times greater than that of MOFs without polymer networks. The covalent combination of rigid and fragile MOFs with flexible polymer networks is a promising approach for the improvement of the mechanical properties of MOFs.