Supramolecular metallacyclic hydrogels with tunable strength switched by host guest interactions
Herein, we present the construction of a new type of supramolecular hydrogel with tunable strength switched by host guest interactions via a hierarchical self assembly strategy. Firstly, through coordination driven self assembly, a rhomboidal metallacycle H with two crown ether units and two chain transfer agent (CTA) units was constructed. The successful construction of metallacycle H was confirmed via multiple NMR and MS spectra. Subsequently, two poly(N isopropylacrylamide) (PNIPAM) chains were introduced into the metallacycle through reversible addition fragmentation chain transfer polymerization of N isopropylacrylamide (NIPAM) monomers. The obtained PNIPAM chains can form hydrogels upon being mixed with water. With the addition of the ditopic guest G to the system, a new polymer network was formed via host guest interactions between the crown ether units and the guest. Interestingly, the strength of the hydrogel increased in the presence of the ditopic guest G and decreased with the addition of KPF6 as a competitive guest.