Multiple hydrogen bonds as tools to enhance the mechanical and mechanoresponsive properties of polymers

Abstract Polymers incorporating hydrogen bonding (H-bonding) units have attracted significant attention for their ability to enhance mechanical properties, including elastic modulus, toughness, and stretchability, owing to the reversible nature of H-bonds. These interactions can act as apparent crosslinks under small strains and facilitate energy dissipation and network restoration under large strains or upon stress release. A critical aspect influencing the macroscopic behavior of such materials is the structural flexibility of the H-bonding motifs. This review categorizes H-bonds into two groups: “rigid” multiple H-bonds, often characterized by π-conjugated units and structural complementarity (e.g., UPy and nucleobases), which impart directionality and strong association, and “flexible” multiple H-bonds (e.g., aliphatic vicinal diols), which exhibit various bonding modes due to conformational freedom and the absence of strong π-conjugation. We discuss how these differences in structural flexibility profoundly affect the mechanoresponsive behavior of the polymers. This review is specifically focused on H-bonds within polymers without solvents, thereby elucidating the intrinsic effects of H-bond architecture on material properties, independent of solvent or small-molecule interactions.