Synthesis and characterization of novel redox-active percec-type dendrons

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

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.

Novel ferrocenyl-terminated linear-dendritic amphiphilic block copolymers: synthesis, redox-controlled reversible self-assembly, and oxidation-controlled release

Novel linear-dendritic amphiphilic block copolymers with hydrophilic poly(ethylene glycol) (PEG) block and hydrophobic Percec-type dendrons containing ferrocenyl terminals were synthesized by the esterification reaction of poly(ethylene glycol) methyl ether with ferrocenyl-terminated alkyl-substituted benzoic acid dendrons. On the basis of the results that the critical aggregation concentration (CACox) of the oxidation state polymer is much higher than CACred of the corresponding reduction state, these polymers can reversibly self-assemble into various aggregates, such as spherical, wormlike micelles, and vesicles, and also disassemble into irregular fragments in aqueous solution by redox reaction when changing the polymer concentrations. Copolymer PEG45-b-Fc3 (3) with 3,4,5-tris(11-ferrocenylundecyloxy) benzoic acid (2) can self-assemble into nanoscale wormlike micelles when the polymer concentration in aqueous solution is above its CACox. These wormlike micelles can be transformed into nanosized vesicles by Fe2(SO4)3 and regained by vitamin C. Interestingly, copolymer PEG45-b-Fc2 (5) with 3,5-bis(11-ferrocenylundecyloxy) benzoic acid (4) can reversibly self-assemble into spherical micelles with two different sizes by redox reaction above the CACox, indicating that the terminal hydrophobic tail number of dendrons plays a key role in determining the self-assembled structures. Furthermore, rhodamine 6G (R6G)-loaded polymer aggregates have been successfully used for the oxidation-controlled release of loaded molecules, and the release rate can be mediated by the concentrations of oxidant and copolymers. The results provide an effective approach to the reversible self-assembly of linear-dendritic amphiphilic block copolymers and also promise the potential of these novel redox-responsive amphiphilic block copolymers in drug delivery systems, catalyst supports, and other research fields.