Tough Supramolecular Elastomer via Entropy-Driven Hydrogen Bonds between Vicinal Diols
Chaehoon Kim, Shintaro Nakagawa, Masataka Seshimo, Hirotaka Ejima, Hirohiko Houjou, Naoko Yoshie
Abstract
Multidentate hydrogen bonds (H-bonds) play a pivotal role in determining the structure, dynamicity, and function of biological macromolecules, motivating many researchers to design artificial H-bonded functional polymers. However, it is still challenging to achieve mechanical robustness without sacrificing dynamicity because of the rigid and aggregating nature of conventional strong H-bonding motifs. Here, we show that extremely simple aliphatic vicinal diols (VDs) form an unexpectedly strong yet flexible dimer, yielding a mechanically robust and highly dynamic, recyclable, and self-healable elastomer simply by embedding VDs into polymer backbones. Density functional theory calculation revealed that the VDs could dimerize into multiple stable forms through multidentate H-bonds, and the dimerization was favored not only enthalpically but also entropically because of the wide variety of dimer modes. These entropy-driven strong H-bonds endowed the VD-functionalized polymer with mechanical robustness similar to that of covalently cross-linked elastomers while retaining functionalities based on the dynamicity of the H-bonds. The flexible nature of VD dimers also suppressed their aggregation. This study demonstrates the new concept of entropy-driven H-bonds in polymeric materials that realizes both mechanical robustness and dynamicity.