Impact of the Synthesis Method on the Solid-State Charge Transport of Radical Polymers

Recyclable Organic Radical Electrodes for Metal-Free Batteries

Organic batteries are one of the possible routes for transitioning to sustainable energy storage solutions. However, the recycling of organic batteries, which is a key step toward circularity, is not easily achieved. This work shows the direct recycling of poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl) (PTMA) and poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl acrylamide) (PTAm) based composite electrodes. After charge-discharge cycling, the electrodes are deconstructed using a solubilizing-solvent and then reconstructed using a casting-solvent. The electrochemical properties of the original and recycled electrodes are compared using cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) cycling, from which it is discovered using time-of-flight secondary ion mass spectrometry (ToF-SIMS) that recycling can be challenged by the formation of a cathode electrolyte interphase (CEI). In turn, an additive is proposed to modify the CEI layer and improve the properties after recycling. Last, an anionic rocking chair battery consisting of PTAm electrodes as both positive and negative electrodes is demonstrated, in which the electrodes are recycled to form a new battery. This work demonstrates the recycling of composite electrodes for organic batteries and provides insights into the challenges and possible solutions for recycling the next-generation electrochemical energy storage devices.

Charge Transfer in Spatially Defined Organic Radical Polymers

Charge transfer in nonconjugated redox-active polymers is influenced by redox site proximity and polymer flexibility, but it is challenging to observe these effects independently. In this work, spatially defined radical-containing polymers are synthesized by using acyclic diene metathesis (ADMET) polymerization of α,ω-dienes bearing a central activated ester. Postpolymerization functionalization with 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO) introduces TEMPO radical groups onto the polymer backbone through amide linkages to yield spatially defined polymers with radical units every 9, 11, 15, and 21 carbons. Increased radical spacing leads to reduced spin-spin coupling and increased chain flexibility. The glass transition temperatures (Tg) range from 47.6 to -13.8 °C, depending on the radical spacing. The spatially defined TEMPO-substituted polymer with a spacing length of 15 carbons displays the lowest Tg and the shortest hopping distance, as shown through molecular dynamics simulations. Also, this polymer displays kinetics 1000 times faster than the commonly studied TEMPO-containing polymer poly(2,2,6,6-tetramethylpiperidinyloxy-4-ylacrylamide) (PTAm). Remarkably, comparison of the diffusion and kinetics attributed to the redox reaction reveals that both the apparent diffusion coefficient and the self-exchange reaction rate constant are correlated to the polymer's Tg as log[Dapp] and log[kex,app] ∼ Tg, respectively. Critically, these data demonstrate that controlling the spacing of redox-active groups along a polymer backbone strongly influences backbone flexibility and radical packing, which leads to synergetic improvements in the charge transfer kinetics of nonconjugated redox-active polymers.

Practical Cell Design for PTMA-Based Organic Batteries: an Experimental and Modeling Study

Poly(2,2,6,6-tetramethyl-1-piperidinyloxy methacrylate) (PTMA) is one of the most promising organic cathode materials thanks to its relatively high redox potential, good rate performance, and cycling stability. However, being a p-type material, PTMA-based batteries pose additional challenges compared to conventional lithium-ion systems due to the involvement of anions in the redox process. This study presents a comprehensive approach to optimize such batteries, addressing challenges in electrode design, scalability, and cost. Experimental results at a laboratory scale demonstrate high active mass loadings of PTMA electrodes (up to 9.65 mg cm-2), achieving theoretical areal capacities that exceed 1 mAh cm-2. Detailed physics-based simulations and cost and performance analysis clarify the critical role of the electrolyte and the impact of the anion amount in the PTMA redox process, highlighting the benefits and the drawbacks of using highly concentrated electrolytes. The cost and energy density of lithium metal batteries with such high mass loading PTMA cathodes were simulated, finding that their performance is inferior to batteries based on inorganic cathodes even in the most optimistic conditions. In general, this work emphasizes the importance of considering a broader perspective beyond the lab scale and highlights the challenges in upscaling to realistic battery configurations.

Redox: Organic Robust Radicals and Their Polymers for Energy Conversion/Storage Devices

Persistent radicals can hold their unpaired electrons even under conditions where they accumulate, leading to the unique characteristics of radical ensembles with open-shell structures and their molecular properties, such as magneticity, radical trapping, catalysis, charge storage, and electrical conductivity. The molecules also display fast, reversible redox reactions, which have attracted particular attention for energy conversion and storage devices. This paper reviews the electrochemical aspects of persistent radicals and the corresponding macromolecules, radical polymers. Radical structures and their redox reactions are introduced, focusing on redox potentials, bistability, and kinetic constants for electrode reactions and electron self-exchange reactions. Unique charge transport and storage properties are also observed with the accumulated form of redox sites in radical polymers. The radical molecules have potential electrochemical applications, including in rechargeable batteries, redox flow cells, photovoltaics, diodes, and transistors, and in catalysts, which are reviewed in the last part of this paper.

Influence of Backbone on the Performance of Pendant Polymer Electrode Materials in Li-ion Batteries

Pendant polymers are a promising class of electrode materials due to their synthetic simplicity, derivation from sustainable feedstocks, and potentially benign synthesis. These materials consist of a redox-active pendant tethered to a polymer backbone, which mitigates dissolution during electrode cycling. To date, an extensive number of pendant groups have been studied within the context of metal-ion batteries. However, the choice of the polymer backbone and its impact on the electrode performance have been relatively understudied. In this work, we use a postpolymerization modification approach to synthesize a series of viologen-bearing redox-active pendant polymers with similar molecular weights but three distinct chemical backbones, namely, polyacrylamide, polymethacrylamide, and polystyryl. By evaluating the polymers in lithium-ion batteries, we show that the polymer backbone has a significant influence on electrode performance and behavior. Specifically, the polymethacrylamide displays slower kinetics than the other two polymers, resulting in lower capacities, particularly at high cycling rates. Furthermore, the charge storage mechanism is dependent on the nature of the backbone: the polyacrylamide shows a significant capacitive contribution to charge storage, while the polystyryl does not. The difference in performance between the polymer electrode materials is ascribed to a difference in chain mobility and packing within the electrode films. Overall, this work shows that the fundamental properties of the polymer backbone are critical to the design of high-performance polymer electrodes.

Multimodal investigation of electronic transport in PTMA and its impact on organic radical battery performance

Organic radical batteries (ORBs) represent a viable pathway to a more sustainable energy storage technology compared to conventional Li-ion batteries. For further materials and cell development towards competitive energy and power densities, a deeper understanding of electron transport and conductivity in organic radical polymer cathodes is required. Such electron transport is characterised by electron hopping processes, which depend on the presence of closely spaced hopping sites. Using a combination of electrochemical, electron paramagnetic resonance (EPR) spectroscopic, and theoretical molecular dynamics as well as density functional theory modelling techniques, we explored how compositional characteristics of cross-linked poly(2,2,6,6-tetramethyl-1-piperidinyloxy-4-yl methacrylate) (PTMA) polymers govern electron hopping and rationalise their impact on ORB performance. Electrochemistry and EPR spectroscopy not only show a correlation between capacity and the total number of radicals in an ORB using a PTMA cathode, but also indicates that the state-of-health degrades about twice as fast if the amount of radical is reduced by 15%. The presence of up to 3% free monomer radicals did not improve fast charging capabilities. Pulsed EPR indicated that these radicals readily dissolve into the electrolyte but a direct effect on battery degradation could not be shown. However, a qualitative impact cannot be excluded either. The work further illustrates that nitroxide units have a high affinity to the carbon black conductive additive, indicating the possibility of its participation in electron hopping. At the same time, the polymers attempt to adopt a compact conformation to increase radical-radical contact. Hence, a kinetic competition exists, which might gradually be altered towards a thermodynamically more stable configuration by repeated cycling, yet further investigations are required for its characterisation.

Nonconjugated Redox-Active Polymers: Electron Transfer Mechanisms, Energy Storage, and Chemical Versatility

The storage of electric energy in a safe and environmentally friendly way is of ever-growing importance for a modern, technology-based society. With future pressures predicted for batteries that contain strategic metals, there is increasing interest in metal-free electrode materials. Among candidate materials, nonconjugated redox-active polymers (NC-RAPs) have advantages in terms of cost-effectiveness, good processability, unique electrochemical properties, and precise tuning for different battery chemistries. Here, we review the current state of the art regarding the mechanisms of redox kinetics, molecular design, synthesis, and application of NC-RAPs in electrochemical energy storage and conversion. Different redox chemistries are compared, including polyquinones, polyimides, polyketones, sulfur-containing polymers, radical-containing polymers, polyphenylamines, polyphenazines, polyphenothiazines, polyphenoxazines, and polyviologens. We close with cell design principles considering electrolyte optimization and cell configuration. Finally, we point to fundamental and applied areas of future promise for designer NC-RAPs.

Chameleon Multienvironment Nanoreactors

Nanoreactors consisting of hydrophilic porous SiO₂ shells and amphiphilic copolymer cores have been prepared, which can easily self-tune their hydrophilic/hydrophobic balance depending on the environment and exhibit chameleon-like behavior. The accordingly obtained nanoparticles show excellent colloidal stability in a variety of solvents with different polarity. Most importantly, thanks to the assistance of the nitroxide radicals attached to the amphiphilic copolymers, the synthesized nanoreactors show high catalytic activity for model reactions in both polar and nonpolar environments and, more particularly, realize a high selectivity for the products resulting from the oxidation of benzyl alcohol in toluene.

Thianthrene polymers as 4 V-class organic mediators for redox targeting reaction with LiMn2O4 in flow batteries

Redox targeting reaction is an emerging idea for boosting the energy density of redox-flow batteries: mobile redox mediators transport electrical charges in the cells, whereas large-density electrode-active materials are fixed in tanks. This study reports 4 V-class organic polymer mediators using thianthrene derivatives as redox units. The higher potentials than conventional organic mediators (up to 3.8 V) enable charging LiMn₂O₄ as an inorganic cathode offering a large theoretical volumetric capacity of 500 Ah/L. Soluble or nanoparticle polymer design is beneficial for suppressing crossover reactions (ca. 3% after 300 h), simultaneously contributing to mediation reactions. The successful mediation cycles observed by repeated charging/discharging steps indicate the future capability of designing particle-based redox targeting systems with porous separators, benefiting from higher energy density and lower cost.

Nitroxide-Containing Amphiphilic Random Terpolymers for Marine Antifouling and Fouling-Release Coatings

Two types of amphiphilic random terpolymers, poly(ethylene glycol methyl ether methacrylate)-ran-poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate)-ran-poly(polydimethyl siloxane methacrylate) (PEGMEMA-r-PTMA-r-PDMSMA), were synthesized and evaluated for antifouling (AF) and fouling-release (FR) properties using diverse marine fouling organisms. In the first stage of production, the two respective precursor amine terpolymers containing (2,2,6,6-tetramethyl-4-piperidyl methacrylate) units (PEGMEMA-r-PTMPM-r-PDMSMA) were synthesized by atom transfer radical polymerization using various comonomer ratios and two initiators: alkyl halide and fluoroalkyl halide. In the second stage, these were selectively oxidized to introduce nitroxide radical functionalities. Finally, the terpolymers were incorporated into a PDMS host matrix to create coatings. AF and FR properties were examined using the alga Ulva linza, the barnacle Balanus improvisus, and the tubeworm Ficopomatus enigmaticus. The effects of comonomer ratios on surface properties and fouling assay results for each set of coatings are discussed in detail. There were marked differences in the effectiveness of these systems against the different fouling organisms. The terpolymers had distinct advantages over monopolymeric systems across the different organisms, and the nonfluorinated PEG and nitroxide combination was identified as the most effective formulation against B. improvisus and F. enigmaticus.

Nanoconfined anti-oxidizing RAFT nitroxide radical polymer for reduction of low-density lipoprotein oxidation and foam cell formation

Atherosclerosis is a leading cause of death worldwide. Antioxidant therapy has been considered a promising treatment modality for atherosclerosis, since reactive oxygen species (ROS) play a major role in the pathogenesis of atherosclerosis. We developed ROS-scavenging antioxidant nanoparticles (NPs) that can serve as an effective therapy for atherosclerosis. The newly developed novel antioxidant ROS-eliminating NPs were synthesized via reversible addition-fragmentation chain-transfer (RAFT) polymerization and act as a superoxide dismutase (SOD) mimetic agent. SOD is an anti-ROS enzyme which is difficult to use for passive delivery due to its low half-life and stability. Copolymers were synthesized using different feed ratios of 2,2,6,6-tetramethyl-4-piperidyl methacrylate (PMA) and glycidyl methacrylate (GMA) monomers and an anti-ROS nitroxyl radical polymer was prepared via oxidation. The copolymer was further conjugated with a 6-aminofluorescein via a oxirane ring opening reaction for intracellular delivery in RAW 264.7 cells. The synthesized copolymers were blended to create NPs (∼150 nm size) in aqueous medium and highly stable up to three weeks. The NPs were shown to be taken up by macrophages and to be cytocompatible even at high dose levels (500 μg mL-1). Finally, the nitroxide NPs has been shown to inhibit foam cell formation in macrophages by decreasing internalization of oxidized low-density lipoproteins.

Electronic and Magnetic Properties of a Three-Arm Nonconjugated Open-Shell Macromolecule

Nonconjugated radical polymers (i.e., macromolecules with aliphatic backbones that have stable open-shell sites along their pendant groups) have arisen as an intriguing complement to π-conjugated polymers in organic electronic devices and may prove to have superior properties in magneto-responsive applications. To date, however, the design of nonconjugated radical polymers has primarily focused on linear homopolymer, copolymer, and block polymer motifs even though conjugated dendritic macromolecules (i.e., polyradicals) have shown significant promise in terms of their response under applied magnetic fields. Here, we address this gap in creating a nonconjugated, three-arm radical macromolecule with nitroxide open-shell sites using a straightforward, single-step reaction, and we evaluated the electronic and magnetic properties of this material using a combined computational and experimental approach. The synthetic approach employed resulted in a high-purity macromolecule with a well-defined molecular weight and narrow molecular weight distribution. Moreover, epoxide-based units were implemented in the three-arm radical macromolecule design, and this resulted in a nonlinear radical macromolecule with a low (i.e., below room temperature) glass transition temperature and one that was an amorphous material in the solid state. These properties allowed thin films of the three-arm radical macromolecule to have electrical conductivity values on par with many linear radical polymers previously reported, and our computational efforts suggest the potential of higher generation open-shell dendrimers to achieve advanced electronic and magnetic properties. Importantly, the three-arm radical macromolecule also demonstrated antiferromagnetic exchange coupling between spins at temperatures < 10 K. In this way, this effort puts forward key structure-property relationships in nonlinear radical macromolecules and presents a clear path for the creation of next-generation macromolecules of this type.

Amphiphilic Nitroxide-Bearing Siloxane-Based Block Copolymer Coatings for Enhanced Marine Fouling Release

The buildup of organic matter and organisms on surfaces exposed to marine environments, known as biofouling, is a disruptive and costly process affecting maritime operations. Previous research has identified some of the surface characteristics particularly suited to the creation of antifouling and fouling-release surfaces, but there remains room for improvement against both macrofouling and microfouling organisms. Characterization of their adhesives has shown that many rely on oxidative chemistries. In this work, we explore the incorporation of the stable radical 2,2,6,6-tetramethylpipiderin-1-oxyl (TEMPO) as a component in an amphiphilic block copolymer system to act as an inhibitor for marine cements, disrupting adhesion of macrofouling organisms. Using polystyrene-b-poly(dimethylsiloxane-r-vinylmethysiloxane) block copolymers, pendent vinyl groups were functionalized with TEMPO and poly(ethylene glycol) to construct an amphiphilic material with redox active character. The antifouling and fouling-release performance of these materials was investigated through settlement and removal assays of three model fouling organisms and correlated to surface structure and chemistry. Surfaces showed significant antifouling character and fouling-release performance was increased substantially toward barnacles by the incorporation of stable radicals, indicating their potential for marine antifouling applications.

Structural design of pyrene-functionalized TEMPO-containing polymers for enhanced electrochemical storage performance

We demonstrate the importance of rational structural design of pyrene-functionalized radical (i.e. 2,2,6,6-tetramethyl-1-piperidinyloxy, TEMPO) copolymers for enhanced electrochemical performance by providing insightful guidance for designing high-performance polymer-based electrodes for energy storage applications.

Design of an n-type low glass transition temperature radical polymer

We document the design, synthesis, and characterization of the first low glass transition temperature, n-type (i.e., preferentially-reduced) radical polymer.

Quantifying internal charge transfer and mixed ion-electron transfer in conjugated radical polymers

Macromolecular radicals are receiving growing interest as functional materials in energy storage devices and in electronics. With the need for enhanced conductivity, researchers have turned to macromolecular radicals bearing conjugated backbones, but results thus far have yielded conjugated radical polymers that are inferior in comparison to their non-conjugated partners. The emerging explanation is that the radical unit and the conjugated backbone (both being redox active) transfer electrons between each other, essentially "quenching" conductivity or capacity. Here, the internal charge transfer process is quantified using a polythiophene loaded with 0, 25, or 100% nitroxide radicals (2,2,6,6-tetramethyl-1-piperidinyloxy [TEMPO]). Importantly, deconvolution of the cyclic voltammograms shows mixed faradaic and non-faradaic contributions that contribute to the internal charge transfer process. Further, mixed ion-electron transfer is determined for the 100% TEMPO-loaded conjugated radical polymer, from which it is estimated that one triflate anion and one propylene carbone molecule are exchanged for every electron. Although these findings indicate the reason behind their poor conductivity and capacity, they point to how these materials might be used as voltage regulators in the future.

Solution-Processable Thermally Crosslinked Organic Radical Polymer Battery Cathodes

Organic radical polymers are promising cathode materials for next-generation batteries because of their rapid charge transfer and high cycling stability. However, these organic polymer electrodes gradually dissolve in the electrolyte, resulting in capacity fade. Several crosslinking methods have been developed to improve the performance of these electrodes, but they are either not compatible with carbon additives or compromise the solution processability of the electrodes. A one-step post-synthetic, carbon-compatible crosslinking method was developed to effectively crosslink an organic polymer electrode and allow for easy solution processing. The highest electrode capacity of 104 mAh g^-1 (vs. a theoretical capacity of 111 mAh g^-1 ) is achieved by introducing 1 mol % of the crosslinker, whereas the highest capacity retention (99.6 %) is obtained with 3 mol % crosslinker. In addition, mass transfer was observed in situ by using electrochemical quartz crystal microbalance with dissipation monitoring. These results may guide future electrode design toward fast-charging and high-capacity organic electrodes.

100th Anniversary of Macromolecular Science Viewpoint: Fundamentals for the Future of Macromolecular Nitroxide Radicals

Macromolecular radicals, radical polymers, and polyradicals bear unique functionalities derived from their pendant radical groups. The increasing need for organic functional materials is driving the growth in research interest in macromolecular radicals for batteries, electronics, memory, and imaging. This Viewpoint summarizes the current state-of-knowledge regarding the macromolecular nitroxide radicals' redox mechanism, conductivity, chain conformation, controlled polymerization, network structure, conjugated forms, and applications. The nitroxide radical group is the focus because it is the most widely studied. Although most literature focuses upon applications, an emerging body of work is highlighting the fundamental physicochemical properties of macromolecular radicals. To this end, this Viewpoint recommends areas of opportunity in fundamental studies and best practices in reporting.

Prospects of organic electrode materials for practical lithium batteries

Organic materials have attracted much attention for their utility as lithium-battery electrodes because their tunable structures can be sustainably prepared from abundant precursors in an environmentally friendly manner. Most research into organic electrodes has focused on the material level instead of evaluating performance in practical batteries. This Review addresses this by first providing an overview of the history and redox of organic electrode materials and then evaluating the prospects and remaining challenges of organic electrode materials for practical lithium batteries. Our evaluations are made according to energy density, power density, cycle life, gravimetric density, electronic conductivity and other relevant parameters, such as energy efficiency, cost and resource availability. We posit that research in this field must focus more on the intrinsic electronic conductivity and density of organic electrode materials, after which a comprehensive optimization of full batteries should be performed under practically relevant conditions. We hope to stimulate high-quality applied research that might see the future commercialization of organic electrode materials.

Asymmetric Redox-Polymer Interfaces for Electrochemical Reactive Separations: Synergistic Capture and Conversion of Arsenic

Advanced redox-polymer materials offer a powerful platform for integrating electroseparations and electrocatalysis, especially for water purification and environmental remediation applications. The selective capture and remediation of trivalent arsenic (As(III)) is a central challenge for water purification due to its high toxicity and difficulty to remove at ultra-dilute concentrations. Current methods present low ion selectivity, and require multistep processes to transform arsenic to the less harmful As(V) state. The tandem selective capture and conversion of As(III) to As(V) is achieved using an asymmetric design of two redox-active polymers, poly(vinyl)ferrocene (PVF) and poly-TEMPO-methacrylate (PTMA). During capture, PVF selectively removes As(III) with exceptional uptake (>100 mg As/g adsorbent), and during release, synergistic electrocatalytic oxidation of As(III) to As(V) with >90% efficiency can be achieved by PTMA, a radical-based redox polymer. The system demonstrates >90% removal efficiencies with real wastewater and concentrations of arsenic as low as 10 ppb. By integrating electron-transfer through the judicious design of asymmetric redox-materials, an order-of-magnitude energy efficiency increase can be achieved compared to non-faradaic, carbon-based materials. The study demonstrates for the first time the effectiveness of asymmetric redox-active polymers for integrated reactive separations and electrochemically mediated process intensification for environmental remediation.

Photopatterning and Electrochemical Energy Storage Properties of an On-Chip Organic Radical Microbattery

One potential way to fabricate battery-on-chip is photopatterning electrochemical energy storage materials directly on electronics through lithography, but applicable materials are primarily limited to transparent photocurable resins. The transparency of the photoresist would be sacrificed after extra addition of insoluble inorganic battery materials and conductors. Given the importance of radical polymers for their appropriate solubility, optical transparency, and radical robustness, they may have potential application in on-chip energy storage, transport, and conversion devices. Herein, an anodic photoresist is proposed by modifying the MicroChem SU8 resist with a radical polymer poly(2,2,6,6-tetramethyl-4-piperidinyl-N-oxyl methacrylate) and an ionic conductor lithium perchlorate. It can be photopatterned on silicon wafer with 10 μm scale resolution, and it exhibits charge/discharge potentials at ca. 0.68 V versus silver chloride electrode; the coulomb efficiency is regarded as nearly equaling 100%. Although the specific capacity of the photopatterned film electrode is found to be modest, 1 × 10^-5 mA h·cm^-2, it presents 1/8 of its theoretical electron storage ability. All-solid-state half-cells with circular features 30 μm in diameter are prepared by means of overlay exposure using the as-prepared photoresist and lithium perchlorate-modified SU8 as the anodic electrode and solid electrolyte, respectively. These results suggest a promising way of using radical polymers for the integration of electrochemical energy in microelectronics.

Block copolymers containing stable radical and fluorinated blocks with long-range ordered morphologies prepared by anionic polymerization

We report a facile synthetic approach to create stable radical block copolymers containing a secondary fluorinated block via anionic polymerization using a bulky, sterically hindered countercation composed of a sodium ion and di-benzo-18-crown-6 complex. The synthetic conditions described in this report allowed for controlled molecular weights and dispersity (<1.3) of both homopolymers: poly(2,2,6,6-tetramethyl-1-piperidinyloxy-methacrylate) (PTMA) and poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) as well as their block copolymers (PTMA-b-PTFEMA). The stable radical concentration of the polymers was determined by electron spin resonance (ESR) and showed radical content above 70%. An analysis of the microphase morphologies in PTMA-b-PTFEMA thin films via atomic force microscopy (AFM) and grazing incidence small angle X-ray scattering (GISAXS) showed clear evidence of long-range ordering of lamellar and cylindrical morphologies with 32 and 36 nm spacing, respectively. The long-range ordering of the morphologies was developed with the aid of two separate neutral layers: PTMA-ran-PTFEMA-ran-poly(hydroxyl ethyl methacrylate) (PHEMA) and poly(isobutyl methacrylate) (PiBMA)-ran-PTFEMA-ran-PHEMA, which helped us corroborate, along with the Zisman method, the surface energy estimation of PTMA to be 30.1 mJ/m2.

Real-time insight into the doping mechanism of redox-active organic radical polymers

Organic radical polymers for batteries represent some of the fastest-charging redox active materials available. Electron transport and charge storage must be accompanied by ion transport and doping for charge neutrality, but the nature of this process in organic radical polymers is not well understood. This is difficult to intuitively predict because the pendant radical group distinguishes organic radical polymers from conjugated, charged or polar polymers. Here we show for the first time a quantitative view of in situ ion transport and doping in organic radical polymers during the redox process. Two modes dominate: doping by lithium ion expulsion and doping by anion uptake. The dominance of one mode over the other is controlled by anion type, electrolyte concentration and timescale. These results apply in any scenario in which electrolyte is in contact with a non-conjugated redox active polymer and present a means of quantifying doping effects.

Aqueous one-pot synthesis of epoxy-functional diblock copolymer worms from a single monomer: new anisotropic scaffolds for potential charge storage applications

The one-pot synthesis of highly anisotropic epoxy-functional diblock copolymer worms is achieved directly in water using a single monomer (glycidyl methacrylate).

How to Install TEMPO in Dielectric Polymers-Their Rational Design toward Energy-Storable Materials

Polar groups and the charge-transport capability play significant roles in the dielectric properties of organic polymers, and thus influence the electric energy density upon application as a capacitor material. Here, the dielectric properties and electric conductivity of a series of polymers containing 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radicals are investigated. The neat radical polymer poly(TEMPO methacrylate) (PTMA) has a high dielectric constant but poor breakdown strength. Poly(methyl methacrylate) (PMMA) is introduced as an insulating polymer with high resistivity on breakdown, along with molecular design of PTMA. Copolymers of TEMPO methacrylate and methyl methacrylate, P(TMA-r-MMA), exhibit high breakdown strengths but low dielectric constants. PMMA blended with TEMPO exhibits the highest electric energy density of 7.4 J cm^-3 (that of PTMA is 0.48 J cm^-3 as a control), with both a high dielectric constant (≈6.8) and a high breakdown strength (≈500 MV m^-1 ). It benefits from long-range but not bulk charge transport in the blends, which is different from the bulk charge transport in PTMA and the short-range charge transport in P(TMA-r-MMA). These results indicate that the TEMPO moiety located in the high breakdown matrix leads to a high energy-storage density in the capacitor.

A nonconjugated radical polymer glass with high electrical conductivity

Solid-state conducting polymers usually have highly conjugated macromolecular backbones and require intentional doping in order to achieve high electrical conductivities. Conversely, single-component, charge-neutral macromolecules could be synthetically simpler and have improved processibility and ambient stability. We show that poly(4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl), a nonconjugated radical polymer with a subambient glass transition temperature, underwent rapid solid-state charge transfer reactions and had an electrical conductivity of up to 28 siemens per meter over channel lengths up to 0.6 micrometers. The charge transport through the radical polymer film was enabled with thermal annealing at 80°C, which allowed for the formation of a percolating network of open-shell sites in electronic communication with one another. The electrical conductivity was not enhanced by intentional doping, and thin films of this material showed high optical transparency.

Polynitroxide copolymers to reduce biofilm fouling on surfaces

Polynitroxide films – the first example of surface tethered nitroxides reducing biofilm fouling.