Aggregation and Rheology of an Azobenzene-Functionalized Hydrophobically Modified Ethoxylated Urethane in Aqueous Solution

Abstract

Hydrophobically modified ethoxylated urethanes (HEURs) belong to an important class of telechelic associative polymers for improving solution rheological properties. We designed and prepared a novel azobenzene end-functionalized HEUR polymer (AzoHEUR), which was used to investigate the effects of hydrophobicity change of end hydrophobes induced by photoisomerization of azobenzene on the solution aggregation and rheological properties. The concentrated AzoHEUR solutions show a reversible rheological property change upon alternative exposure to UV and visible light. We have demonstrated that a reversible change in hydrophilic–lipophilic balance of polymer followed by photoisomerization of azobenzene induces a reversible rearrangement of micellar junctions through loop–bridge or bridge–loop transitions, which reversibly changes not only the network connectivity but also the solution relaxation behavior. Moreover, a structural model is proposed to describe the rearrangement of micellar junctions induced by ph...