The supramolecular assembly through host-guest complexation between cyclodextrin (CD) hosts and hydrophobic guests is a powerful method of constructing tunable and switchable polymeric networks. Recently, another interesting way to form polymeric networks by using CD-dimers to crosslink guest substituted polymers was reported. In this work, we demonstrate that α,α-CD Dimer and viologen polymer form polymeric hydrogels. α-Cyclodextrin (α-CD) was bound to a terephthalic moiety by the reaction of 6-amino-α-CD with terephthalic acid in DMF to give the α,α-CD Dimer. Viologen polymer were prepared by treatment of 4,4'-dipyridyl with 1,10-dibromodecane in DMSO by heating for 2 d. Viologen polymer was chosen since viologen polymer is known to be included and held strongly in α-CD. The ¹H NMR spectrum of the mixture of the α,α-CD Dimer and VP showed that the signals of VP protons shifted to the lower field. This result indicated the formation of the inclusion complex between CD and VP. To get more insight on the interaction of host-guest complex, we determined the viscosity of the mixture of VP with α,α-CD Dimer. High viscosity enhancements were observed when α,α-CD Dimer was added to VP solutions as a result of the polymer inclusion association. The hydrogel was prepared by mixing VP and α,α-CD Dimer in aqueous solutions at 100 ℃ for 24 h followed by evaporating the solvent, then adding a little water to give a brown gel. When the VP concentration was 30 mmol/L, increasing the concentration of α,α-CD Dimer, a hydrogel was formed with a phase transition at 30 mmol/L. Additionally, the influences of α,α-CD Dimer concentration, temperature and type of Dimers on the hydrogel formation were also studied. Adding a competitive guest molecule into the hydrogel induced a phase transition into the sol state. The hydrogel also has good thermal stability.

Key words: cyclodextrin dimer, host-guest interaction, supramolecular gel, viologen polymer