Side-chain pseudopolyrotaxanes by threading cucurbituril[6] onto quaternized poly-4-vinylpyridine derivative: Synthesis and properties

A novel side-chain pseudopolyrotaxanes 4 is synthesized from cucurbituril (CB6]) and quaternized poly-4-vinylpyridine derivative 3 in water by simple stirring at room temperature. CB6] beads are localized on hexamethylene units in side chains of 3 as found by NMR studies, and the hydrophobic and charge-dipole interactions are the driving force. The degree of threading (q/n, the average number of CB6] beads per repeat recognition unit of 3) can be controlled from 0.2 to 1.0 by controlling the amount of CB6] added. The reduced viscosity of pseudopolyrotaxanes in aqueous solution has smaller change with the change of the concentration or temperature, which is consistent with the hydrodynamic radius and more rigid chain conformation because of the threaded CB6]. DLS results show the average hydrodynamic diameter (D_h) of the pseudopolyrotaxanes in solution increases with the increasing of CB6] threaded. The pseudopolyrotaxanes have higher thermal stability and intensity of absorption band than the parent polymer 3 as found by TGA and UV-vis studies. The decomposition temperature and intensity of absorption increase with increasing amount of CB6] threaded. The effect of NaI to pseudopolyrotaxanes is studied by the transmittance with UV-vis, and the result shows that NaI is the satisfied precipitant to the pseudopolyrotaxanes.