Water plays important roles in various functions on the surface of polymers and peptides. In this work, host-guest hydrogels with different weight percentages of water were prepared via copolymerization of an acrylamide-modified cyclodextrin host monomer, an acrylamide-modified adamantane guest monomer, and acrylamide. The host-guest hydrogels showed high toughness and readhesion properties, in which the reversible host-guest cross-linking between the poly(acrylamide) chains is important. The mechanical properties of the host-guest hydrogels depend on their water contents. The host-guest hydrogels showed maximum mechanical strength at different water contents. The maximum mechanical strength also varied depending on the type of poly(acrylamide) in the backbone and the amounts of host and guest cross-linking units. The readhesion strength of the host-guest hydrogels varied with water content, indicating that the water in the host-guest hydrogels affects their mechanical strength and readhesion behavior. Tensile tests, contact angle measurements, and differential scanning calorimetry (DSC) revealed that water exists in three states (nonfreezing bound water, intermediate water, and free water) in the hydrogels, and the nonfreezing bound water and the intermediate water affect the mechanical properties, such as toughness and readhesion force. These results indicate that the host-guest interactions, which affect the mechanical properties of the host-guest hydrogels, depend on the nonfreezing bound water and the intermediate water hydrating the host-guest polymer network.
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