Supramolecular Materials Cross-Linked by Host–Guest Inclusion Complexes: The Effect of Side Chain Molecules on Mechanical Properties

Functional polymeric materials constructed by noncovalent bonds have attracted considerable attention due to their beneficial stretching and self-healing properties. We chose host–guest interactions using cyclodextrins (CDs) as host molecules to realize supramolecular materials with stretching and self-healing properties. Notably, an inclusion complex of a CD and a guest molecule functions as a reversible bond in a material. Herein, we studied the relationship between the mechanical properties of the materials and host–guest interactions based on the association constants of CDs with guest molecules and molecular structures of the guest molecules. A chemically cross-linked poly(acrylamide) gel showed high rupture stress, although the rupture strain was noticeably low. However, the host–guest hydrogels (CDAAmMe-R hydrogels) exhibited a higher rupture stress and strain of approximately 1000%. These rupture stress and strain values were related to the association constants of the CDs with guest units on the polymer side chain and the structure of the guest molecules. In particular, the αCDAAmMe-Dod hydrogel with a dodecyl group with a long, rod-like structure showed better rupture stress and strain (1250%). The βCDAAmMe-AdAAm hydrogel with a spherical adamantyl acrylamide (AdAAm) group showed better self-healing properties. To realize a practical self-healing process under dry conditions, a poly(methyl triethylene glycol acrylate) xerogels with βCDAAmMe and AdAAm (βCDAAmMe-AdAAm TEGA xerogel) was prepared. The βCDAAmMe-AdAAm TEGA xerogel exhibited self-healing properties, regaining 61% of its initial material strength at 100 °C.