A novel pH-responsive supramolecular polymer constructed by pillar[5]arene-based host-guest interactions

Abstract

A novel pH-responsive supramolecular polymer based on the pillar[5]arene/imidazolium cation recognition motif was successfully prepared. It was demonstrated that the binding strength between the monomer molecules in solution could be reduced by adding base, thereby leading to a decrease in the polymerization degree, while a reverse switch could be achieved by the addition of acid to change the monomer back to the cationic state. These processes were confirmed by 1H NMR, DOSY experiments, viscosity measurements and theoretical calculations. Moreover, a rod-like fiber was drawn from a high concentration solution of the monomer and characterized by SEM, providing direct evidence of the formation of a supramolecular polymer with high molecular weight and high degree of the linear chain extension. In this study, a reversible transition between the high-molecular-weight supramolecular polymer and the relatively low-molecular-weight one, that is, a control of the polymerization degree, was realized by simply altering the solution pH. These results are helpful for the future fabrication of adaptive and smart supramolecular materials with stimuli-responsiveness and special functions. © The Royal Society of Chemistry 2013.