Supramolecular polymeric materials
have received much attention
in recent years due to the fabrication of supramolecular materials
with mechanical properties and stimuli-responsive properties in response
to polymeric designs based on noncovalent cross-linkers. Host–guest
interactions are useful noncovalent interactions that can be employed
to realize supramolecular materials. To understand the relationship
between the mechanical properties of supramolecular polymeric materials
based on host–guest interactions and the molecular structure
of guest molecules on the polymer side chain, we prepared supramolecular
hydrogels cross-linked by inclusion complexes between cyclodextrin
(CD) and cationic alkyl guests on the polymer side chain. The mechanical
properties were influenced by an electric barrier due to the cationic
group, CD cavity size, length of the guest unit, charge number of
the electric barrier, and reduction responsiveness.
Although the introduction of an electric barrier to the end of the
alkyl guest moiety increased the rupture stress, the rupture strain
decreased due to the electric repulsion of the CD unit and the cationic
group. The rupture stress of the αCD-cationic alkyl hydrogel
was higher than that of the βCD-cationic alkyl hydrogel because
electric repulsion between the αCD unit and the cationic group
is higher than that of the βCD unit due to the relatively small
cavity size of αCD. The fracture energy increased as the alkyl
chain length or charge number of the cationic guest group increased.
We demonstrated the change in the mechanical properties by reduction
stimulus.
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