Full (Electro-)Chemical Control over the Aggregation State of Diblock Copolymer Mixtures Including Nonequilibrium Micelles

Abstract

Stimuli-responsive polymers have endowed soft matter research with numerous applications. Moving beyond classical stimuli like temperature or pH, we introduce an electrochemical approach to control block copolymer aggregation by shifting between bishydrophilic and amphiphilic states. The aqueous solutions of the nonionic-cationic block copolymers poly[N-(3-aminopropyl)methacrylamide]₃₀-b-poly(N,N-dimethylacrylamide)₁₂₀ (PAPMA₃₀-b-PDMAA₁₂₀), synthesized via RAFT polymerization, and poly(ethylene oxide)₁₁₄-b-poly{[2-(methacryloyloxy)ethyl]diisopropylmethylammonium chloride}₁₇₁ (i.e., PEO₁₁₄-b-PDPAEMA₁₇₁ with a quaternized poly(diisopropylaminoethyl methacrylate) block, abbreviated as qPDPAEMA), were investigated for micellization via Dynamic Light Scattering (DLS), Small Angle X-ray Scattering (SAXS), and Cryogenic Transmission Electron Microscopy (cryo-TEM). Both polymers exhibit selective aggregation with hexacyanoferrate species: PAPMA-b-PDMAA forms aggregates specifically in the presence of ferrocyanide ions ([Fe(CN)₆]^4–), while PEO-b-qPDPAEMA forms micelles with ferricyanide ions ([Fe(CN)₆]^3–). These polymer systems demonstrate both chemical and electrochemical reversibility, with the combined polymer system allowing selective control over the type of polymer that aggregates by modulating the ferricyanide/ferrocyanide ratio. Furthermore, the pH sensitivity of PAPMA-b-PDMAA allows the disintegration of the micellar state by increasing the pH (electro-)chemically. In total, these results demonstrate full control over the assembly state of complex polymer mixtures by electrochemical means. In addition, it is shown for PEO-b-qPDPAEMA that electrochemical switching as a soft trigger leads to the thermodynamically preferred micelle morphology, while rapid chemical redox leads to kinetically trapped, nonequilibrium micelles. Here, electrochemistry can act as a trigger to transform the trapped micelles toward the thermodynamically stable ones, which can be recycled back to the nonequilibrium micelles. The principle of this electrochemically triggered micellization could represent a significant step toward developing stimuli-sensitive materials for autonomous drug delivery, sensing, or even smart materials within a systems chemistry approach.