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Ferrocene-Functionalized Hydrophobically Modified Ethoxylated Urethane: Redox-Responsive Controlled Self-Assembly and Rheological Behavior in Aqueous Solution

Chang, Xueyi, Du, Zhukang, Hu, Feiyan, Cheng, Zhiyu, Ren, Biye, Fu, Shiyu, Tong, Zhen
Langmuir 2016 v.32 no.46 pp. 12137-12145
aqueous solutions, catalysts, drug delivery systems, hydrophobicity, liquids, micelles, models, oxidation, polymers, urethane, viscoelasticity
In this work, we present a novel redox-responsive ferrocene-functionalized hydrophobically modified ethoxylated urethane (Fc-HEUR) model polymer. The effects of a redox-induced hydrophobicity change of ferrocenyl hydrophobes on the self-assembly and rheological properties of Fc-HEUR in aqueous solution were investigated. In view of the redox-induced change in the hydrophilic–lipophilic balance of polymers, the Fc-HEUR polymer in aqueous solution can reversibly self-assemble into spherical micelles and larger micellar aggregates of different nanoscales and also disassemble by redox reactions immediately. Moreover, we have demonstrated that a rearrangement of micellar junctions takes place through a bridge–loop or loop–bridge transition in the concentrated polymer solution followed by redox reactions, which induces a great change in the rheological properties of the polymer solution: a viscoelastic liquid for the reduction state Fc-HEUR and a viscous liquid for the oxidation state Fc⁺-HEUR, owing to their different relaxation behaviors. Particularly, the associative structures and rheological properties of the Fc-HEUR aqueous solution can be reversibly controlled by redox reactions. This work will be useful not only for understanding of the thickening mechanism of stimuli-responsive HEURs but also for the development of reversible self-assembly and controlled rheological fluids, which may have some special application in drug delivery systems, catalyst supports, sensors, and microfluidic devices.