We investigated the folding and crosslinking of diblock copolymers with interblock-crosslinkable units in dilute solution. We used a bead-spring model for the polymer and Monte Carlo simulations for the crosslinking. At no and small interblock attractive interaction, the observed zipping between spatially proximate crosslinkers results in single-chain nanoparticles resembling expanded ladder-type polymers. Stronger attractive interactions between the different blocks lead to an enhanced internal confinement resulting in more compact, randomly crosslinked structures. The structural outcome of the "reactive" Monte Carlo (MC) simulations was also qualitatively recovered by applying "reactive" molecular dynamics (MD) simulations.

Charged colloid systems pose challenges and offer unexpected chances in their dispersion/solution behaviour because of the interdependence of structural reorganizations, electrostatics and molecular ion binding. Here, strong polyelectrolytic P(NIPAM-co-MAPTAC) microgels/nanogels consisting of N-isopropylacrylamide (NIPAM) and [3-(methacryloylamino)propyl]trimethylammonium chloride (MAPTAC, quaternized from N-(3-dimethylaminopropyl)methacrylamide, DMAPMA) with ultrasmall hydrodynamic radius (41 nm, 20 degrees C, 0.1 m KCl; minimum: 25 nm) are prepared and investigated with varying concentrations of multivalent counterions as ionic cargo (i.e. hexacyanoferrate(III)). We combine paramagnetic relaxation enhancement NMR (PRE-NMR), dynamic light scattering DLS, and small angle X-ray scattering SAXS (fuzzy-sphere extended model) with quantum chemical calculations (r(2)SCAN-3c) to probe binding geometries and structural transitions across varying salt concentrations and temperatures under flooding (/nondialyzed) versus dialyzed conditions. PRE-NMR reveals selective [Fe(CN)(6)](3-) binding to MAPTAC, assisted with secondary amide-hexacyanoferrate coordination according to quantum chemical calculations. SAXS quantifies ion-induced reorganizations: core contraction, fuzzy shell expansion, and changes in the correlation length upon hexacyanoferrate addition, accompanied by a reentrant swelling based on the preferential interaction of hexacyanoferrate with the charged microgel domains. This multiscale approach demonstrates that peripheral charge localization enables reversible switching between intra- and interparticle crosslinking, where the thermal history above 55 degrees C can be recorded. Our results could have implications on applications like sensing, controlled release and nanoparticle-templated catalysis.

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.

Poly(arylene piperidinium) (PAP) polymers have emerged as promising candidates for applications as anion exchange membranes (AEMs) and have seen some commercial use in the form of PiperION by Versogen; however, PiperION contains fluorinated units to balance its ionic content. Fluorine-free variants are environmentally more friendly alternatives as recycling is facilitated. Herein, we report a series of four fluorine-free PAP membranes that are mechanically robust and feature moderate water uptake yet high ionic conductivity. p-Quaterphenyl (pQP) is copolymerized with either m- or p-terphenyl (m/pTP) and N-methyl-4-piperidone under superacid-catalyzed polyhydroxyalkylation conditions. The molar ratios of the reactants are adjusted to maintain a balance of solubility and flexibility of the polymers and to reach ion exchange capacities between 2.53 and 2.66 mequiv g-1. The polymers exhibit thermal stability of Td,95 > 260 °C, Young's moduli between 0.7 and 1.0 GPa, and ultimate tensile stresses of 50-60 MPa in the dry state. Additionally, under submersion tensile deformation, the Young's moduli and ultimate tensile stresses are in the range 200-320 MPa and 15-22 MPa, respectively. The sample with an equimolar ratio of pQP and mTP was found to exhibit a robust nature with elongation up to 170% when subjected to submersion tensile deformation, thus showing attractive mechanical properties under relevant working conditions. Wet membranes show an ionomer SAXS peak in the range of 5 nm, suggesting clustering of water and ionic parts of the chain. High hydroxide conductivity of up to 197 mS cm-1 at 80 °C is observed. Such behavior is promising considering their water uptake of 85% at 80 °C as an upper limit, resulting in moderate areal and through-plane swellings of 100% and 55%, respectively. The results demonstrate that fluorine-free PAPs can be tuned to match important criteria of AEMs, including low water uptake, high dimensional and alkaline stability, and high hydroxide conductivity.

Climate change requires enhanced autonomous temperature monitoring during logistics/transport. A cheap approach comprises the use of temperature-sensitive copolymers that undergo temperature-induced irreversible coagulation. The synthesis/characterization of pentablock copolymers (PBCP) starting from poloxamer PEO130-b-PPO44-b-PEO130 (poly(ethylene oxide)130-b-poly(propylene oxide)44-b-poly(ethylene oxide)130) and adding two terminal qPDMAEMA85 (quaternized poly[(2-dimethylamino)ethyl methacrylate]85) blocks is presented. Mixing of PBCP solutions with hexacyanoferrate(III)/ferricyanide solutions leads to a reduction of the decane/water interfacial tension accompanied by a co/self-assembly toward flower-like micelles in cold water because of the formation of an insoluble/hydrophobic qPDMAEMA/ferricyanide complex. In cold water, the PEO/PPO blocks provide colloidal stability over months. In hot water, the temperature-responsive PPO block is dehydrated, leading to a pronounced temperature dependence of the oil-water interfacial tension. In solution, the sticky PPO segments exposed at the micellar corona cause a colloidal clustering above a certain threshold temperature, which follows Smoluchowski-type kinetics. This coagulation remains for months even after cooling, indicating the presence of a kinetically trapped nonequilibrium state for at least one of the observed micellar structures. Therefore, the system memorizes a previous suffering of heat. This phenomenon is linked to an exchange of qPDMAEMA-blocks bridging the micellar cores after PPO-induced clustering. The addition of ferrous ions hampers the exchange, leading to the reversible coagulation of Prussian blue loaded micelles. Hence, the Fe2+ addition causes a shift from history monitoring to the sensing of the present temperature. Presumably, the system can be adapted for different temperatures in order to monitor transport and storage in a simple way. Hence, these polymeric "flowers" could contribute to preventing waste and sustaining the quality of goods (e.g., food) by temperature-induced bouquet formation, where an irreversible exchange of "tentacles" between the flowers stabilizes the bouquet at other temperatures as well.

The controlled growth of surface-modifying polymer films by electrodeposition often fails because of the lack of redox activity of these compounds. Here, electroactive complexants help to electrodeposit non-electroactive polymers. Hence, we investigate the counterion-induced electrodeposition of polyelectrolytes: three quaternized poly(N,N-dialkylaminoethyl methacrylate)s (qPDAAEMA), in particular their methyl, ethyl, and isopropyl derivatives (i. e. qPDMAEMA, qPDEAEMA, and qPDPAEMA), provide transparent solutions in the presence of hexacyanoferrate(II) (ferrocyanide) at specific concentration windows of the KCl supporting electrolyte. Below a certain KCl concentration, insolubility dominates irrespective of the hexacyanoferrate valency, whilst above an upper threshold, full solubility is observed. Between these limits, oxidation reversibly electrodeposits polymer/hexacyanoferrate(III) (ferricyanide) complexes. Hydrodynamic voltammetry (and data analysis using in-house software) provides access to the deposition efficiency (DE). qPDEAEMA with ethyl substituents shows highest DEs; larger or smaller substituents fall short because of a balance between "hydrophobicity" and charge separation, shifting the window toward smaller salt concentrations with increasing alkyl size. We always observe a DE maximum close to the minimum salt concentration, whilst electrochemical quartz crystal microbalance (EQCM) measurements indicate a change in film water content close to the maximum. These effects, being also discussed in terms of polymer conformation, can direct the future engineering of electroassisted coatings.

“Layer-by-layer” deposits of coordination polymers show a rich morphology spectrum and display unusual structural transformations as a function of the deposition cycle number.

Though amphiphiles are ubiquitously used for altering interfaces, interfacial reorganization processes are in many cases obscure. For example, adsorption of micelles to liquid-liquid interfaces is often accompanied by rapid reorganizations toward monolayers. Then, the involved time scales are too short to be followed accurately. A block copolymer system, which comprises poly(ethylene oxide)(110)-b-poly{[2-(methacryloyloxy)ethyl]diisopropylmethylammonium chloride}(170) (i.e., PEO110-b-qPDPAEMA(170) with quaternized poly(diisopropylaminoethyl methacrylate)) is presented. Its reorganization kinetics at the water/n-decane interface is slowed down by electrostatic interactions with ferricyanide ([Fe(CN)(6)](3-)). This deceleration allows an observation of the restructuring of the adsorbed micelles not only by tracing the interfacial pressure, but also by analyzing the interfacial rheology and structure with help of atomic force microscopy. The observed micellar flattening and subsequent merging toward a physically interconnected monolayer lead to a viscoelastic interface well detectable by interfacial shear rheology (ISR). Furthermore, the "gelled" interface is redox-active, enabling a return to purely viscous interfaces and hence a manipulation of the rheological properties by redox reactions. Additionally, interfacial Prussian blue formation stiffens the interface. Such manipulation and in-depth knowledge of the rheology of complex interfaces can be beneficial for the development of emulsion formulations in industry or medicine, where colloidal stability or adapted permeability is crucial.

Variable interfacial tension could be desirable for many applications. Beyond classical stimuli like temperature, we introduce an electrochemical approach employing polymers. Hence, aqueous solutions of the nonionic-cationic block copolymer poly(ethylene oxide)114-b-poly{[2-(methacryloyloxy)ethyl]diisopropylmethylammonium chloride}171 (i.e., PEO114-b-PDPAEMA171 with a quaternized poly(diisopropylaminoethyl methacrylate) block) were investigated by emerging drop measurements and dynamic light scattering, analyzing the PEO114-b-qPDPAEMA171 impact on the interfacial tension between water and n-decane and its micellar formation in the aqueous bulk phase. Potassium hexacyanoferrates (HCFs) were used as electroactive complexants for the charged block, which convert the bishydrophilic copolymer into amphiphilic species. Interestingly, ferricyanides ([Fe(CN)6]3-) act as stronger complexants than ferrocyanides ([Fe(CN)6]4-), leading to an insoluble qPDPAEMA block in the presence of ferricyanides. Hence, bulk micellization was demonstrated by light scattering. Due to their addressability, in situ redox experiments were performed to trace the interfacial tension under electrochemical control, directly utilizing a drop shape analyzer. Here, the open-circuit potential (OCP) was changed by electrolysis to vary the ratio between ferricyanides and ferrocyanides in the aqueous solution. While a chemical oxidation/reduction is feasible, also an electrochemical oxidation leads to a significant change in the interfacial tension properties. In contrast, a corresponding electrochemical reduction showed only a slight response after converting ferricyanides to ferrocyanides. Atomic force microscopy (AFM) images of the liquid/liquid interface transferred to a solid substrate showed particles that are in accordance with the diameter from light scattering experiments of the bulk phase. In conclusion, the present results could be an important step toward economic switching of interfaces suitable, e.g., for emulsion breakage.

We demonstrate a novel method to synthesize aqueous microgels with supramolecular redox-cleavable crosslinks. The redox-cleavable crosslinker was synthesized on the basis of host–guest interactions...

Thermosensitive N-isopropylacrylamide based cationic microgels (mu G) were synthesized and complexed with anionic liposomes containing encapsulated antitumor antibiotic Doxorubicin (Dox). Compositions of the resulting complexes, in terms of a liposome-to-mu G number ratio N, varied from N = 0.5 to a saturated complex with N = 30 where the surface of mu G particles is fully covered with liposomes. The microgels collapse when heated from 25 up to 50 degrees C and the surface area of a microgel particle decreases. The thermo-induced contraction is accompanied with release of Dox from the mu G-bound liposomes while a significant fraction of DOX is released for both the unsaturated and saturated complexes. Therefore, two mechanisms are hypothesized for the thermoinduced Dox release. The first one is due to temperature-induced conformational changes of polymer chains, subsequent rearrangements at liposome-microgel interface via liposome-microgel interaction. This mechanism can work for the complexes of any composition. The second process, namely a squeezing of liposomes via liposome-liposome interaction followed by Dox release can become significant for the saturated complex. The results we have obtained are of great interest for constructing multi-liposomal drug carriers, diagnostic systems and catalysts.

Modelling and synthesis go hand in hand to efficiently engineer copolymer microgels with various architectures: core–shell structures (with ferrocene mainly in the core or in the shell) and also microgels with homogeneous comonomer distribution.

Advancing biomedicine by tunable e-transfer into/from microgels.

The multi-liposomal conjugate with encapsulated enzyme laccase is described, capable of releasing the payload when changing the temperature. For this, thermosensitive cationic microgels were synthesized, differing in the molar content of cross-linker from 2 to 8 mol%. The microgels collapsed when heated beyond the volume phase transition temperature (VPTT) of 38-40 degrees C, while the degree of the surface area contraction (phi) decreased with increasing the cross-linker content. At lower temperature, each swollen microgel particle, ca. 320 nm in diameter, adsorbed about 200 intact 50 nm anionic liposomes. Over VPTT, the liposomes disrupted and released their payload that was visually detected via a color "development" of a loaded into liposomes laccase substrate in the surrounding solution: the higher phi the more released enzyme and the higher colored product concentration. So, the correlation between the microgel cross-linking degree and the amount of released liposome payload was demonstrated for the first time. The results we have obtained are of interest for constructing drug carriers, catalysts and diagnostic systems.

We propose a strategy to counteract the salt-driven disassembly of multiliposomal complexes made by electrostatic co-assembly of anionic small unilamellar liposomes and cationic star-shaped polyelectrolytes (made of quaternized poly(dimethylaminoethyl methacrylate) (qPDMAEMA100)3.1). The combined action of (qPDMAEMA100)3.1 and a nonionic star-shaped polymer (PEO12-b-PPO45)4, which comprises diblock copolymer arms uniting a poly(ethylene oxide) PEO inner block and a poly(propylene oxide) PPO terminal block, leads to a stabilization of these complexes against disintegration in saline solutions. Hereby, the anchoring of the PPO terminal blocks to the lipid bilayer and the bridging between several liposomes are at the origin of the promoted structural stability. Two-focus fluorescence correlation spectroscopy verifies the formation of multiliposomal complexes with (PEO12-b-PPO45)4. The polyelectrolyte and the amphiphilic polymer work synergistically, as the joint action still assures some membrane integrity, which is not seen for the mere (PEO12-b-PPO45)4-liposome interaction alone.

In this work, we synthesized electroactive and degradable microgels based on biomacromolecular building blocks, which enable the controlled release of therapeutic drugs. Functional chitosan-poly(hydroquinone) (Ch:PHQ) microgels exhibiting redox-active and pH-sensitive properties were synthesized by an oxidative polymerization in an inverse miniemulsion system. Physically crosslinked microgels were formed by polymerization of hydroquinone in the presence of chitosan through the formation of hydrogen bonds between PHQ and Ch. A series of microgel samples with variable Ch : PHQ ratios were synthesized. These obtained microgels exhibit pH-responsive properties due to the protonation/deprotonation of amino-groups of chitosan in the microgel system. Poly(hydroquinone) is a redox-active polymer exhibiting a two-electron/proton-transfer behavior and conveys this property to the microgels as confirmed by cyclic voltammetry. In addition, the microgels can be switched by electrochemical means: they swell in the oxidized state or shrink in the reduced state. In the presence of urea or lysozyme, the microgels undergo a fast degradation due to the disruption of hydrogen bonds acting as physical crosslinks in the microgel networks or due to the cleavage of glucosidic linkages of the incorporated chitosan scaffold, respectively. Doxorubicin (DOX), an anticancer drug, could be effectively encapsulated into the microgels and released in the presence of an enzyme, indicating that these biodegradable microgels could be used as drug delivery vehicles for tumor cells.

Institute of Physical Chemistry, RWTH Aa Aachen, Germany Department of Biomedical Engineering-FB4 Medical Center Groningen, A. Deusinglaan 1 DWI – Leibniz Institute for Interactive Forckenbeckstraße 50, 52056 Aachen, Germ Groningen Biomolecular Sciences and Biotec Chemistry, University of Groningen, Nijenborgh Ernst-Berl-Institute for Chemical Enginee Technische Universität Darmstadt, Alarich-Weis Chair for Laser Technology LLT, RWTH Aac Aachen, Germany Institute of Inorganic Chemistry, JARA-SOFT 1, 52056 Aachen, Germany GFE Central Facility for Electron Mic Ahornstraße 55, D-52074 Aachen, Germany Cite this: Chem. Sci., 2019, 10, 1844