Quaternary Poly Research Articles

Morphology engineering of nanofibrous poly(acrylonitrile)-based strong anion exchange membranes for enhanced protein adsorption and recovery

The (bio)pharmaceutical and food industries are transitioning towards circular economy to minimise waste and foster sustainability in the supply chain of biomolecule-based drugs and supplements. Membrane chromatography is expected to play a crucial role in this transition, with the potential to maximize recovery and reduce operating costs. The development of chromatographical membranes is however impeded by the lack of understanding on the membrane structure – chemistry – performance relationship. Here a one-pot synthesis of anion exchange membranes with engineered nanofibrous morphology was studied by electrospinning the blend of polyacrylonitrile (PAN) and tailored quaternized poly(acrylonitrile)-co-poly(2-(dimethylamino)ethyl acrylate) copolymer containing 15 mol% of functional groups, namely PAN-pAQ membranes. Comprehensive evaluations were conducted on the influence of the electrospinning parameters on the nanofibre morphology, surface properties and binding capacity of model protein bovine serum albumin (BSA). The fibre alignment was shown to play a significant role, i.e., membrane with anisotropic fibres obtained by increasing the drum rotational speed to 2000 rpm allowed a high BSA binding capacity of 166 mg∙g−1, i.e., 45–66 % higher than other membranes with randomly-oriented nanofibres. This study is expected to contribute towards the design of future membranes for effective purification and recovery of biomolecules from natural and waste streams, promoting circular bio-economy.

Polydopamine Adhesion: Catechol, Amine, Dihydroxyindole, and Aggregation Dynamics.

While polydopamine (PDA) possesses the surface-independent adhesion property of mussel-binding proteins, significant differences exist between them. Particularly, PDA's short and rigid backbone differs from the long and flexible protein sequence of mussel-binding proteins. Given that adhesion relies on achieving a conformal contact with large surface coverage, PDA has drawbacks as an adhesive. In our study, we investigated the roles of each building block of PDA to build a better understanding of their binding mechanisms. Initially, we anticipated that catecholamine oligomers form specific binding with substrates. However, our study showed that the universal adhesion of PDA is initiated by the solubility limit of growing oligomers by forming agglomerates, complemented by multiple binding modes of catechol. Notably, in the absence of amines, poly(catechol) either remained in solution or formed minor suspensions without any surface coating, underscoring the essential role of amines in the adhesion process by facilitating insoluble aggregate formation. To substantiate our findings, we induced poly(catechol) aggregation using quaternized poly(4-vinylpyridine) (qPVP), leading to subsequent surface adhesion upon agglomerate formation.

1,2,3-Triazolium vs 1,2,4-triazolium quaternized poly (2, 6-dimethyl-1, 4-phenylene oxide) (PPO) anion exchange membranes (AEMs): A molecular dynamics (MD) study

This work investigates AEMs prepared from Poly (2, 6-dimethyl-1, 4-Phenylene Oxide) (PPO) quaternized with 1,2,3-triazolium and 1,2,4-triazolium, using molecular dynamics (MD) simulations to compare and evaluate their hydroxide transport and their stability against hydroxide degradation at different hydration levels. Hydroxide diffusivity (DOH) at λ = 6 is 0.69 × 10−10 m2/s, and 0.23 × 10−10 m2/s, at λ = 9 is 0.97 × 10−10 m2/s, and 0.67 × 10−10 m2/s and at λ = 12 is 1.85 × 10−10 m2/s, and 1.69 × 10−10 m2/s for 1,2,3-triPPO and 1,2,4-triPPO, respectively. At lower hydration levels (λ = 6 and λ = 9), 1,2,4-triPPO is stable against hydroxide degradation. However, at higher hydration levels, 1,2,3-triPPO has fewer hydroxide ions around the cationic group due to the hydroxide ions being solvated by the water, making it harder for the hydroxide ions to approach the cationic group at higher hydration levels, which means 1,2,3-triPPO is stable against hydroxide degradation.

Synthesis and characterization of ionic liquid incorporated quaternized poly(2,6-dimethyl-1,4-phenylene oxide) and NiO/IrO2 electrocatalyst for anion exchange membrane fuel cell applications

Incorporating an ionic liquid into QPPO enhances ionic conductivity and single cell performance. Additionally, a homemade NIF ORR electrocatalyst was utilized in the cathode chamber of the fuel cell system to develop low-cost MEA for AEMFCs.

Enantioselective Molecularly Imprinted Polymer for Tyrosine, Tryptophan, and Phenylalanine, and the Possibility of the Crop-Circle-Like Imprinting.

Molecularly imprinted polymer (L-MIP) for L-tyrosine (L-Tyr) is prepared by the complexation between quaternized poly(4-vinylpyridine/divinylbenzene) (QVP) and poly(acrylamide-co-acrylic acid) (PAmA) in alkaline solution. The L-MIP shows higher enantioselectivity for L-isomers of tyrosine, together with tryptophan (Trp) and phenylalanine (Phe) compared to the D-isomers of them. The sorption isotherms of the three D-enantiomers are converged to one isotherm. It can reflect that the sorption of D-enantiomers can be relied mainly on the common segment, -CH2 -CH(NH2 )-COOH, neglecting any effect of bulkier aromatic groups. The imprinted common segment can be opened on the surface of MIP from the D-enantiomers. For the L-enantiomers, the sorption discrepancies are depended on the size of the aromatic group implying that the phenolic moiety of L-Tyr can be also opened. Thus, the imprinted sites are proposed to be opened on the surface of L-MIP similar to the crop-circle-like. The enantioselectivity factors, αef = QL /QD , for Tyr, Trp, and Phe are 1.52, 1.30, and 1.52 for L- to D-isomers, respectively. And the uptake differences between D- and L-enantiomers of Tyr, Trp, and Phe are 31.8, 20.7, and 29mg per 1g MIP, respectively.

Covalent bonding of quaternary ammonium compounds and zwitterionic polymer functional layers on polydimethylsiloxane against Escherichia Coli adhesion.

Quaternary ammonium compounds (QACs) are recognized by the World Health Organization as a useful disinfectant against microbes. The synergistic effect of zwitterionic polymers with QACs as antimicrobial agents rather than QACs alone is yet to be investigated. A potential strategy is the use of covalent bonding to halt the release of minute antibacterials and a hierarchy of functional layers to detain and annihilate microbes. The strategy was tested on a polydimethylsiloxane (PDMS) surface on which quaternized poly(2-dimethylaminoethyl methacrylate) (qDMA+) and sulfobetaine (SBMA) were hierarchically functionalized. Attenuated total reflectance Fourier transform infrared analysis confirmed the quaternization of DMA to qDMA+, grafting of qDMA + on PDMS (PDMS-qDMA+), and grafting of the SBMA overlayer on PDMS-qDMA+ (PDMS-qDMA+-SB). Contact angle measurement showed that PDMS-qDMA + exhibited the lowest contact angle (26.2 ± 2.9°) compared with the hydrophobic PDMS (115.2 ± 1.6°), but that of PDMSqDMA+-SB increased to 56.3 ± 1.3°. The Escherichia coli survival count revealed that PDMS-qDMA+ and PDMS-qDMA+-SB exhibited significantly greater bactericidal ability than PDMS. Confocal laser scanning microscopy revealed fewer dead bacteria on PDMS-qDMA+-SB than on PDMS-qDMA+. Scanning electron microscopy demonstrated that E. coli was disintegrated on the functionalized surface via dual-end cell lysis. To the best of our knowledge, this is the first observation of this type of process. The results confirmed the potent antibacterial and cell disruption activities of the qDMA+ and SBMA modified PDMS surface.

Multi-Functional Polymer Membranes Enable Integrated CO2 Capture and Conversion in a Single, Continuous-Flow Membrane Reactor under Mild Conditions.

Herein, we present a membrane-based system designed to capture CO2 from dilute mixtures and convert the captured CO2 into value-added products in a single integrated process operated continuously under mild conditions. Specifically, we demonstrate that quaternized poly(4-vinylpyridine) (P4VP) membranes are selective CO2 separation membranes that are also catalytically active for cyclic carbonate synthesis from the cycloaddition of CO2 to epichlorohydrin. We further demonstrate that quaternized P4VP membranes can integrate CO2 capture, including from dilute mixtures down to 0.1 kPa of CO2, with CO2 conversion to cyclic carbonates at 57 °C and atmospheric pressure. The catalytic membrane acts as both the CO2 capture and conversion medium, providing an energy-efficient alternative to sorbent-based capture, compression, transport, and storage. The membrane is also potentially tunable for the conversion of CO2 to a variety of products, including chemicals and fuels not limited to cyclic carbonates, which would be a transformative shift in carbon capture and utilization technology.

Alkali-resistant poly (vinyl benzyl chloride) based anion exchange membranes with outstanding flexibility and high hydroxide ion conductivity

Preparing AEMs with robust mechanical properties, high ionic conductivity and excellent chemical stability is challenging. Here, cross-linked/aggregated AEMs are prepared by incorporating hydrophilic Jeffamine cross-linkers and hydrophobic side chains into the rigid quaternized poly (vinyl benzyl chloride). Jeffamine's flexibility ensures high elongation at break of the cross-linked/aggregated membranes (125.0–199.8%). The hydrophobic side chain limits excessive water absorption and facilitates self-aggregation of hydrophilic and hydrophobic domains, enhancing tensile strength (5.08–7.40 Mpa in wet state) and improving ionic conductivity of the AEMs (73.8–110.4 mS cm−1 at 80 °C). Alkali-resistant PVB, restricted dimensionality, and ordered micro-phase separation morphology contribute to outstanding chemical stability of the AEMs. Degradation of both backbones and cations is <20% after treatment in 1 M NaOH solution at 80 °C for 30 days. Based on the membrane, a peak power density of 354.4 mW cm−2 at 60 °C is yielded.

Poly(4-vinylpyridine)iodonium triiodide: A new efficient catalyst for the synthesis of 3,3-diheteroaromatic oxindole analogues

The synthesis of a series of 3,3-diheteroaromatic oxindoles has been effectively produced through treatment of indole-2,3-dione (isatin) with various indoles and pyrroles using quaternized poly(4-vinylpyridine)iodinium iodide , under solvent-free condition and neutral medium. The reaction proceeds rapidly with excellent yields. This catalyst has been shown to be stable and highly recyclable.

Microstructural orientation of anion exchange membrane through mechanical stretching for improved ion transport

Synthesis of anion exchange membranes (AEMs) with orientated nano/micro-structure and with tunable ion-channels is of great interest for applications in fuel cells, water electrolyzers, and redox flow batteries. However, there is still a dearth of work in the detailed understanding of anion conductivity from a polymer structure‒property perspective. Herein, we demonstrate an easy and versatile strategy to fabricate highly conductive AEMs. By stretching the AEMs, an improvement in OH− conductivities of AEMs is achieved. The effect of elongation at different water contents on polymer structures and OH− conductivities was investigated by a combination of molecular dynamics (MD) simulation and experimental study, giving insights into macromolecular orientation at the atomic level. The morphological changes, which consist of oriented polymer chains and elongated water clusters, are quantified by a combination of two dimensional small angle X-ray scattering (SAXS), scanning electron microscopy (SEM) and radial distribution functions. Detailed analyses of interatomic distances reveal morphological variations of hydrophilic domains and their interactions with water and OH− under elongation at different hydration levels. Furthermore, the OH− conductivities of our synthesized quaternized poly(2,6-dimethyl-1,4-phenylene oxide) (QPPO) AEMs increased significantly after stretching to 20% elongation at all water contents. Specifically, OH− conductivity of stretched QPPO was 2.24 times more than the original AEM at 60% RH. The higher relative increase in OH− conductivity at lower water content may be caused by the lower flexibility of side chains at lower hydrated level. This work verifies the significance of porous and/or oriented AEM structure in the improvement on anion conductivity and water transport efficiency.

Smart bactericidal surfaces with thermoresponsive switchability and pH[sbnd]controlled regenerability

We developed smart bactericidal surfaces with thermoresponsive switchability and pH-controlled regenerability, which was prepared by the reversible formation of dynamic Schiff base bonds between amino-functionalized surfaces (surfaces modified by polydopamine, Sub-PDA) and aldehyde-terminated polymers consist of thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) and bactericidal quaternized poly(dimethylaminoethylmethacrylate) (QPDMAEMA). At room temperature below the lower critical solution temperature (LCST), the PNIPAM chains were stretchable, leading to the burial of the bactericidal QPDMAEMA chains and the loss of bactericidatity. At physiological temperature above the LCST, the PNIPAM chains collapsed, leading to the exposure of the bactericidal QPDMAEMA chains and facilitating the contact killing of bacteria. The dead bacteria could be detached by the extended PNIPAM chains when the temperature returned to the room temperature below the LCST. Meanwhile, the long-lasting and regenerable bactericidal surfaces could be achieved by the reversible destruction at pH 2 and formation at pH 8.5 of Schiff base bonds between amino-functionalized surfaces and aldehyde-terminated polymers. The study thus presents a promising approach to the realization of smart, multifunctional bactericidal surfaces, and may find applications in diverse biomedical materials and devices.

Assembly of polyelectrolyte star block copolymers at the oil-water interface.

To understand and resolve adsorption, reconfiguration, and equilibrium conformations of charged star copolymers, we carried out an integrated experimental and coarse-grained molecular dynamics simulation study of the assembly process at the oil-water interface. This is important to guide development of novel surfactants or amphiphiles for chemical transformations and separations. The star block copolymer consisted of arms that are comprised of hydrophilic-hydrophobic block copolymers that are covalently tethered via the hydrophobic blocks to one point. The hydrophobic core represents polystyrene (PS) chains, while the hydrophilic corona represents quaternized poly(2-vinylpyridine) (P2VP) chains. The P2VP is modeled to become protonated when in contact with an acidic aqueous phase, thereby massively increasing the hydrophilicity of this block, and changing the nature of the star at the oil-water interface. This results in a configurational change whereby the chains comprising the hydrophilic corona are significantly stretched into the aqueous phase, while the hydrophobic core remains solubilized in the oil phase. In the simulations, we followed the kinetics of the anchoring and assembly of the star block copolymer at the interface, monitoring the lateral assembly, and the subsequent reconfiguration of the star via changes in the interfacial tension that varies as the degree-of-protonation increases. At low fractions of protonation, the arm cannot fully partition into the aqueous side of the interface and instead interacts with other arms in the oil phase forming a network near the interface. These insights were used to interpret the non-monotonic dependence of pH with the asymptotic interfacial tension from pendant drop tensiometry experiments and spectral signatures of aromatic stretches seen in vibrational sum frequency generation (SFG) spectroscopy. We describe the relationship of interfacial tension to the star assembly via the Frumkin isotherm, which phenomenologically describes anti-cooperativity in adsorbing stars to the interface due to crowding. Although our model explicitly considers long-range electrostatics, the contribution of electrostatics to interfacial tension is small and brought about by strong counterion condensation at the interface. These results provide key insights into resolving the adsorption, reconfiguration, and equilibrium conformations of charged star block copolymers as surfactants.

Poly(aspartic acid)-based self-healing hydrogel with precise antibacterial ability for rapid infected-wound repairing

The development of wound dressings with antibacterial activities and simultaneous pro-healing functions are always urgent in treating bacterial wound infection. Herein, a novel multifunctional self-healing hydrogel was designed and prepared by crosslinking quaternary ammonium/boronic acid modified poly(aspartic acid) and poly (vinyl alcohol) polymers with targeted peptide MP196- conjugated polydopamine. The formation of this hydrogel not only improves the biocompatibility of quaternary poly(aspartic acid), but also enhances antibacterial efficacy by pH-triggering dissociation under the low pH bacterial microenvironment. Moreover, precise photothermal treatment can be achieved. In vitro study suggested high synergistic antibacterial efficiency(∼100 %) under near-infrared light, significantly higher than a single antibacterial strategy (66.0–82.6 %). In vivo study suggested infected wounds treated with the hydrogel showed an optimal healing rate(92.0 %) after 7 days. The survival rate of the bacteria in the epidermal tissues was reduced to 2.3 %. Besides, the suitable self-healing property of this hydrogel facilitated its application in the diversity of wound shapes. Thus, the novel poly(aspartic acid) hydrogel might be a promising candidate for precise therapy of bacteria-infected wounds.

Polymer Additives to Personal Protective Equipment can Inactivate Pathogens.

Face masks have been proven to be medicine’s best public health tool for preventing transmission of airborne pathogens. However, in situations with continuous exposure, lower quality and “do-it-yourself” face masks cannot provide adequate protection against pathogens, especially when mishandled. In addition, the use of multiple face masks each day places a strain on personal protective equipment (PPE) supply and is not environmentally sustainable. Therefore, there is a significant clinical and commercial need for a reusable, pathogen-inactivating face mask. Herein, we propose adding quaternary poly(dimethylaminohexadecyl methacrylate), q(PDMAHDM), abbreviated to q(PDM), to existing fabric networks to generate “contact-killing” face masks—effectively turning cotton, polypropylene, and polyester into pathogen resistant materials. It was found that q(PDM)-integrated face masks were able to inactivate both Gram-positive and Gram-negative bacteria in liquid culture and aerosolized droplets. Furthermore, q(PDM) was electrospun into homogeneous polymer fibers, which makes the polymer practical for low-cost, scaled-up production.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10439-022-03100-1.

(Invited) Bipolar Membranes with a 3D Junction of Interlocking Electrospun Fibers

Bipolar membranes (BPMs), typically laminated layers of anion-exchange and cation-exchange polymers, have the unique capability of splitting water at a potential near 0.83 V. Such membranes are used in electrodialysis membrane separation processes. They also have applications in water electrolyzers, CO2 electrolysis cells, and self-humidifying fuel cells. We report here on recent developments regarding BPMs with a high interfacial area, 3D nanofiber junction.Membranes were prepared by first creating a bipolar junction layer, by the simultaneous electrospinning of anion-exchange and cation-exchange polymers, with the addition of catalyst nanoparticles to facilitate water splitting. Solvent vapor exposure and hot-pressing closed all interfiber pores, to create a dense film of interpenetrating and interlocking nanofibers of positively and negatively charged polymers. In one fabrication method, dense films of solution cast anion and cation-exchange polymers were hot-pressed onto the opposing surfaces of the junction layer to create a tri-layer BPM. Membranes were also fabricated by electrospinning all three layers of the BPM: first spinning anion-exchange fibers, followed by dual fiber spinning with catalyst spraying, and then spinning only cation-exchange fibers. Solvent exposure and hot-pressing closed all interfiber voids.BPMs were made with a junction layer 12-15 mm thick, where the total membrane thickness was 50-80 mm. Membranes were prepared with both hydrocarbon and fluoropolymer ionomers, e.g., sulfonated poly(ether ether ketone) or perfluorosulfonic acid as the cation-exchange polymer and either quaternized poly(phenylene oxide), AEMIONä (an imidazolium-based polymer sold by Ionomr Innovations, Inc.), or PiperION (a poly(aryl piperidinium) from Versogen) as the anion-exchange polymer. A variety of different junction layer catalysts powders were examined, including Al(OH)3 and graphene oxide. Membranes were evaluated in an H-cell for the collection of steady-state current-voltage data and in a flow cell for long-term constant current water splitting (electrolysis) operation, typically with an aqueous Na2SO4 electrolyte. The 3D junction membranes performed exceptionally well: (i) the water splitting potential was low (near the expected value of 0.83 V), (ii) the transmembrane voltage drop was small at high currents (e.g., a voltage drop of 1.1 V up to 1.1 A/cm2), and (iii) the extended bipolar reaction zone for water splitting with interlocking fibers allowed for high current density operation with no evidence of membrane degradation.In this talk, the effect of membrane composition (the type/amount of anion and cation exchange polymers and choice of catalyst) and structure (the thickness of the layers) on short-term and long-term membrane performance will be discussed. Results will be presented for operating the bipolar membrane in water splitting and water generation modes.

Poly(phenylene oxide)-Based Anion Exchange Membranes Having Linear Cross-Linkers or Star Cross-Linkers

Linear cross-linked and star cross-linked anion exchange membranes (AEMs) are reported in this work, namely, lcQPPO (linear cross-linked quaternized poly(2,4-dimethyl-1,4-phenylene oxide) (PPO)) and scDQPPO (star cross-linked quaternized PPO) . Compared with original quarternized PPO (QPPO), cross-linked AEMs show a restrained swelling degree. But, due to the hindrance of a cross-linking polymer matrix, lcQPPO membranes show decreased ionic conductivity. For scDQPPO, its wide and connective ion channels are beneficial to the conduction of OH–, exhibiting increased ionic conductivity. Besides, the aggregated and cross-linked polymer networks in scDQPPO enhance the chemical stability and mechanical properties of the AEMs. Specifically, for scDQPPO-40, a high OH– conductivity of 100.7 mS cm–1 and a low swelling degree of 20.7% are achieved at 80 °C. The tensile strength and elongation at break of wet scDQPPO-40 at 25 °C are 16.7 MPa and 18.0%. After immersing in 1 M NaOH at 80 °C for 30 days, the loss of ionic conductivity and weight for scDQPPO-40 is 24.2 and 14.8%, with the degradation of tensile strength and elongation at break of 22.2% and 26.7%, respectively. On the basis of the membrane, a fuel cell performance of 0.577 W cm–2 is demonstrated at 60 °C, while, for QPPO-40 and lcQPPO-60, their fuel cell peak power densities are only 0.250 and 0.215 W cm–2.

Structural Model of the Human BTG2–PABPC1 Complex by Combining Mutagenesis, NMR Chemical Shift Perturbation Data and Molecular Docking

Degradation of cytoplasmic mRNA in eukaryotes involves the shortening and removal of the mRNA poly(A) tail by poly(A)-selective ribonuclease (deadenylase) enzymes. In human cells, BTG2 can stimulate deadenylation of poly(A) bound by cytoplasmic poly(A)-binding protein PABPC1. This involves the concurrent binding by BTG2 of PABPC1 and the Caf1/CNOT7 nuclease subunit of the Ccr4-Not deadenylase complex. To understand in molecular detail how PABPC1 and BTG2 interact, we set out to identify amino acid residues of PABPC1 and BTG2 contributing to the interaction. To this end, we first used algorithms to predict PABPC1 interaction surfaces. Comparison of the predicted interaction surface with known residues involved in the binding to poly(A) resulted in the identification of a putative interaction surface for BTG2. Subsequently, we used pulldown assays to confirm the requirement of PABPC1 residues for the interaction with BTG2. Analysis of RNA-binding by PABPC1 variants indicated that PABPC1 residues required for interaction with BTG2 do not interfere with poly(A) binding. After further defining residues of BTG2 that are required for the interaction with PABPC1, we used information from published NMR chemical shift perturbation experiments to guide docking and generate a structural model of the BTG2-PABPC1 complex. A quaternary poly(A)-PABPC1-BTG2-Caf1/CNOT7 model showed that the 3′ end of poly(A) RNA is directed towards the catalytic centre of Caf1/CNOT7, thereby providing a rationale for enhanced deadenylation by Caf1/CNOT7 in the presence of BTG2 and PABPC1.

Crosslinked PAEK-based nanofiber reinforced Nafion membrane with ion-paired interfaces towards high-concentration DMFC

To increase the energy density of DMFC system, increasing the methanol concentration is an excellent solution. However, the severe methanol crossover problem limits the application of Nafion in DMFCs with a highly concentrated methanol solution. Here, we proposed a feasible approach to overcome this challenge where Nafion membrane was reinforced with a covalently crosslinked quaternized poly (arylene ether ketone) (PAEK) nanofiber mat for establishing acid-base ion-paired interfaces between them. Firstly, the bromomethylated PAEK precursor was prepared into a three-dimensional fibrous support material using electrospinning. The nanofibers were then quaternized and covalently crosslinked to embed in the Nafion matrix while maintaining their fiber morphology. During the membrane fabrication, the ion-paired interfaces were established between the –N(CH3)3+ on the nanofibers and –SO3- groups of Nafion matrix. The strong ion-paired interaction resulted in low membrane swelling and methanol permeability. TEM confirmed that the hydrophilic ionic clusters were aggregated with controllably distribution along the nanofibers to create long-range and efficient proton transport channels. Therefore, the hybrid membrane F-CQPAEK@Nafion-1.0 showed a high proton conductivity of 0.21 S cm−1 at 80 °C. In 2 M DMFC, the maximum power density (PDmax) of this membrane reached 119.38 mW cm−2, 2.78 times higher than that of recast Nafion. In 10 M DMFC, the PDmax of this hybrid membrane reached 65.31 mW cm−2, which was 3.54 times higher than that of recast Nafion. The results illustrate the possibility of running Nafion-based hybrid membranes in DMFCs with a broad operational flexibility from low concentration to high concentration methanol solutions.

A strategy to design quaternized poly(2,6-dimethyl-1,4-phenylene oxide) anion exchange membranes by atom transfer radical coupling

Sterically crowded organic cations are widely incorporated into aromatic polymers as anion exchange membranes (AEMs) materials to improve the chemical stability. However, due to the reduced entanglement between polymers, these AEMs suffer from poor mechanical properties, low conductivity, and insufficient water uptake, impeding their further application in alkaline fuel cells. To address these limitations, we demonstrate a strategy for designing a stable and conductive AEM material by atom transfer radical coupling reaction between bromomethylated poly (2,6-dimethyl-1,4-phenylene oxide) (BPPO) and quaternized 2,2,6,6-tetramethylpiperidinooxys (T-QA). These quaternized copolymers produced mechanical robust and transparent membranes with less water uptake and swelling ratio. The resulting TQPPO membrane possessing IEC value of 2.13 mmol/g had considerably higher OH − conductivity of 52.4 mS/cm (20 °C) and 103 mS/cm (80 °C) compared with AEMs containing BTMA cations or sterically-protected imidazoliums on PPO matrix, due to the well-developed microphase separation. Since these polymers were free of benzyl-containing quaternary ammoniums, higher alkaline stability over BTMA-based ones was observed when equilibrated in 1 M sodium hydroxide solution at 60 or 80 °C. In addition, a peak power density of 287.5 mW/cm 2 was observed at 80 °C for TQPPO membrane in the practical application of a single hydrogen/oxygen alkaline fuel cell. This work provided an effective strategy to synthesize conductive and stable AEMs from bromomethylated or chloromethylated polymers for alkaline fuel cell applications. • Conductive AEMs with improved alkaline stability were designed by ATRC reaction. • Pendant TEMPO-based cations induced the formation of hydrophilic-hydrophobic microphase separation in AEMs. • AEMs with TEMPO-based cations showed a PPD of 287.5 mW/cm 2 in fuel cells.

Alkali-free quaternized polybenzimidazole membranes with high phosphoric acid retention ability for high temperature proton exchange membrane fuel cells

Although phosphoric acid doped polybenzimidazole has been proposed as promising high-temperature proton exchange membrane, the poor absorption and immobilization ability of phosphoric acid in the membrane hinders its long-term stability. In this work, high-temperature proton exchange membranes with high phosphoric acid uptake and retention ability are fabricated thorough solvent casting of an alkali-free quaternized poly(4,4’-diphenylether-5,5’-bibenzimidazole) (OPBI), followed by doping of phosphoric acid. The optimized membrane with quaternization degree of 50% possesses a high acid-doping-level of 18.8 and an anhydrous conductivity of 85 mS cm−1 at 160 °C. Stability tests reveal that anhydrous proton conductivity remains unchanged during continuous 100 h treatment at 160 °C and it remains 91.7% of its initial value after 100 h treatment at 80 °C under 40% RH. The thus-assembled single cell exhibits the maximum power density values of 0.355, 0.495, and 0.584 Wcm−2 at 160 °C under back pressure of 0, 100, and 200 kPa using hydrogen as fuel and air as oxidant gas.