An End-Bifunctionalized Hydrophobically Modified Ethoxylated Urethane Model Polymer: Multiple Stimuli-Responsive Aggregation and Rheology in Aqueous Solution

Hydrophobically modified ethoxylated urethanes (HEURs) belong to an important class of telechelic associative polymers for improving solution rheological properties in many industrial fields. In this work, we describe the synthesis and solution behavior of a novel hydrophobically modified ethoxylated urethane model polymer (AzoFcHEUR) end-bifunctionalized by Percec-type mini-dendron 3-(6-ferro c enyhexyl oxyl)-5-(6-azobenzenehexyloxy)benzyl alcohol. The telechelic polymer containing both azobenzene and ferrocene moieties in aqueous solution performs multiple stimuli-responsive aggregation and rheological properties dependent on the magnitude of amphiphicity change of functional end groups upon exposure to different external stimuli such as light irradiation and/or redox reaction. It has been demonstrated that the stimuli-responsive hydrophobicity change of end groups induces a reversible micellar transition or rearrangement of micellar aggregates in dilute AzoFc-HEUR aqueous solution and a rearrangement of physical network from a dense network to a sparse network in dense AzoFc-HEUR aqueous solution and vice versa. This work is the first report of such multiple stimuli-responsive rheological properties of telechelic polymers in dense solution induced by photo-and/or redox-stimuli. The results are therefore of interest not only for the fundamental science in the controlled self-assembly of telechelic polymer in aqueous solution but also for specific applications of HEURs in the control of viscoelasticity of polymer solution, fabrication, and transmission of soft materials, medicines and cosmetics, ink for inkjet printers, and flow rate controlling systems, where careful viscosity control is necessary.