Phenylene Oxide Research Articles

Anion exchange membranes with excellent monovalent anion perm-selectivity for electrodialysis applications

In recent years, ion exchange membranes with monovalent ion perm-selectivity are highly desirable. Here, two strategies were adopted simultaneously to prepare anion exchange membranes with excellent monovalent anion perm-selectivity. One is to adjust membranes’ hydrophobicity by grafting single long chain tertiary amines of different alkyl chain lengths (N,N-dimethylhexadecylamine (DMA16), N,N-Dimethylhexylamine (DMHA), and trimethylamine (TMA)) onto bromomethylated poly (phenylene oxide) (BPPO) backbones and regulating the molar ratio of the tertiary amine and the bromobenzyl in BPPO. Results show that the obtained membrane C16-0.5, which was grafted with the longest tertiary amine (DMA16) and has the lowest molar ratio of DMA16 and the bromobenzyl in BPPO, exhibits the lowest water uptake (WU) and highest monovalent anion perm-selectivity (PSO4Cl) between Cl− and SO42− (12.84). The other is to regulate membranes’ compactness through post-treatments, including heat treatment and surface modification by forming a polypyrrole layer on the membrane surface. Results show that membrane C16-0.75-H120, which was under the heat treatment of 120 °C, shows a higher PSO4Cl (7.58) than membrane C16-0.75 (5.02) without any heat treatment; moreover, membrane C16-0.75-pr, which was coated with a polypyrrole layer on the surface, has a higher PSO4Cl (9.0) than membrane C16-0.75 (5.02) without any surface modification. In addition, membranes C16-0.5, C16-0.75-H120 and C16-0.75-pr have more excellent PSO4Cl than the commercial membrane ASV (6.52). To sum up, results in this study suggest that both of the two strategies are highly effective to improve membranes’ perm-selectivity.

Azole structures influence fuel cell performance of phosphoric acid-doped poly(phenylene oxide) with azoles on side chains

We synthesized three types of polymer electrolyte membranes (PEMs) by functionalizing poly(phenylene oxide) with triazole, benzimidazole and imidazole groups, respectively on the side chains. The effect of azole structures on the fuel cell performance was investigated by analyzing and comparing the PEM properties at the sufficient PA doping level. We reveal for the first time that PEM performance is influenced by azole structures (pKa and steric hindrance). The higher pKa of imidazole was advantageous to the formation of protonic defects, enhancing the proton conduction. However, the steric hindrance of bulky benzimidazole interrupted acid-base interaction and the formation of protonic defects. The imidazole-containing membrane (XIMPPO) showed the anhydrous proton conductivity 130 mS/cm at 150 °C and the triazole-containing membrane (XTAPPO) and the benzimidazole-containing membrane (XBIPPO) showed 114 mS/cm and 102 mS/cm, respectively. Imidazole was also the most effective for the fuel cell performance, showing the peak power density of 0.20 W/cm2 and XTAPPO and XBIPPO showed 0.16 W/cm2 and 0.17 W/cm2, respectively.

Dielectric Relaxation of Nanocomposites Based on Poly(phenylene oxide) and Endometallofullerene

The molecular mobility of poly(phenylene oxide) nanocomposites with endometallofullerene at a concentration of 0.1, 0.5, and 1.0 wt % is studied by dielectric spectroscopy. Two processes of dipole polarization relaxation in the glassy state (β-process) and in the rubbery state (α-process) are found. It is shown that the molecular mobility of the β-process related to the presence of a nanoadditive does not change with concentration. Molecular mobility in the region of the α-process, which is associated with segmental mobility, shows a downward trend.

Permeation of CO2 and N2 through glassy poly(dimethyl phenylene) oxide under steady‐ and presteady‐state conditions

AbstractGlassy polymers are often used for gas separations because of their high selectivity. Although the dual‐mode permeation model correctly fits their sorption and permeation isotherms, its physical interpretation is disputed, and it does not describe permeation far from steady state, a condition expected when separations involve intermittent renewable energy sources. To develop a more comprehensive permeation model, we combine experiment, molecular dynamics, and multiscale reaction–diffusion modeling to characterize the time‐dependent permeation of N2 and CO2 through a glassy poly(dimethyl phenylene oxide) membrane, a model system. Simulations of experimental time‐dependent permeation data for both gases in the presteady‐state and steady‐state regimes show that both single‐ and dual‐mode reaction–diffusion models reproduce the experimental observations, and that sorbed gas concentrations lag the external pressure rise. The results point to environment‐sensitive diffusion coefficients as a vital characteristic of transport in glassy polymers.

Enhanced conductivity and stability of anion exchange membranes depending on chain lengths with crosslinking based on poly(phenylene oxide)

Quaternized polymer electrolytes (QPXs) with various lengths of side chains terminating in quaternary ammonium groups are synthesized, with the aim of enhancing anion conductivity. When chain lengths are equal, the crosslinked membranes have better alkaline stabilities than non-crosslinked membranes. cQPH, which has a hexyl acyl chain and a crosslinked structure shows the best anion conductivity (105 mS/cm at 80 °C) owing to a good phase separation. In addition, it has superior alkaline stability, retaining up to 88% of its conductivity after immersion in 1 M NaOH at 80 °C for 16 days. Moreover, QPXs and cQPXs show enough thermal stability over 200 °C to operate in alkaline fuel cell systems. The dimensional stabilities of the membranes are measured, showing that water is absorbed while the strength is maintained. These results imply that cQPXs can be promising materials for use in alkaline fuel cells.

Supersoft, Stretchable, Tough, and Adhesive Elastomers with Dual Metal‐Ionic Crosslinked Double‐Network Structure

AbstractSoft, stretchable, tough, and adhesive elastomers are developed based on the metal‐ionic crosslinked double network structure, where the metal ion coordination of sulfonated poly(phenylene oxide) (SPPO) is used for the first network and the soft chemical crosslinked poly(ethyl acrylate) (PEA) is used for the second network. The influence of SPPO content on the tensile, cyclic tensile, adhesive, and rheological behavior of the elastomers is systematically investigated. It is observed that the elastomers are immensely soft and stretchable with tunable modulus from 0.038 to 0.086 MPa, fracture strain of ≈1400%, fracture stress in the range 0.20–1.2 MPa, work of extension of 0.72–5.6 MJ m−3, fast self‐recovery of 5 s after experiencing 200% strain, and robust adhesive behavior on glass substrates with interface debonding energy ≈35.2 J m−2. The mechanical behavior of the double‐network elastomers at the macroscopic scale is related to the dynamic breaking and reforming of the metal‐ion coordination at the molecular scale in the first network. This study provides a facile approach for the synthesis of elastomers with multidimensional mechanical behavior and broadens the applications of the elastomers in the field of flexible electronic devices, soft robotics, among others.

Highly conductive and stable anion‐exchange membranes based on crosslinked poly(arylene ether sulfone)‐block‐poly(phenylene oxide) Networks

ABSTRACTIn the field of the developments of next‐generation polymer electrolyte membranes, high conductivity is often regarded as the first important performance requirement. There is still a huge challenge to face, which is hard to achieve the balance between high ion conductivity (mainly related to ion‐exchange capacity [IEC]) and good mechanical‐dimensional stability (represented by swelling ratio [SR]). Here, a family of crosslinked block polyelectrolytes consisting of hydrophobic rigid poly(arylene ether sulfone) segments to ensure enough dimensional stability and hydrophilic poly(phenylene oxide) segments bearing long‐flexible chains with high‐density multications to serve as crosslinker and carrier for ion transport are prepared. The polyelectrolyte with an IEC of 3.04 mmol g−1 exhibits a high hydroxide conductivity of 126 mS cm−1 and a low SR of 8.6% at 80 °C. No obvious degradation below 200 °C is observed, and maximum tensile strength reaches 28.4 MPa. As a conclusion, these crosslinked membranes based on well‐designed block polyelectrolytes exhibit an excellent combination of high ion conductivity and good mechanical‐dimensional stability to meet the performance requirements for the application of anion‐exchange membranes. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020, 58, 391–401

Fuel cell evaluation of anion exchange membranes based on poly(phenylene oxide) with different cationic group placement

Comparison of four poly(phenylene oxide) membranes in an AEMFC and the correlation between performance, ionic conductivity and water flux properties.

Effect of quasi-stationary electric field on charge transfer in poly(phenylene oxide) based composites

The article explores the processes of charge transfer in the samples of polymeric composites based on poly(phenylene oxide) with fullerene and endometalfullerene in the electric field of low frequencies (f = 10−1Hz). The article identifies transfer processes connected with intramolecular and intermolecular conductivity. It is found that conductive channels are formed in a polymeric matrix at high concentrations of fullerene, thus, the type of conductivity changes from semiconductor to metallic. The embedding of iron into the fullerene frame molecule leads to the appearance of metallic conductivity of the composite in some temperature range.

Transport of Neutral and Charged Solutes in Imidazolium-Functionalized Poly(phenylene oxide) Membranes for Artificial Photosynthesis

Anion exchange membranes (AEMs) play an essential role in artificial photosynthesis devices, which photoelectrochemically convert CO2 and water into useful products. AEMs allow the transport of cha...

Influences of non-ionic branches on the properties of the anion exchange membranes based on imidazolium functionalized poly (2, 6-dimethyl-1, 4-phenylene oxide)

Different nonionic groups were, respectively, grafted onto the backbone of 1,2,4,5-tetramethylimidazolium functionalized poly(2,6-dimethyl-1,4-phenyleneoxide) to fabricate anion exchange membranes (AEMs). The presence of the nonionic branches significantly decreased the water swelling of the AEMs by 145% compared to that of the original imidazolium functionalized PPO (Im-PPO) with a comparable hydration level (λ) of around 20. The membrane possessing side chains of the 2-ethoxyethanamine exhibited a hydroxide conductivity of 64 mS cm−1 at 80 °C, while that Im-PPO only showed a conductivity of 48 mS cm−1 under the same conditions. It is found that the presence of ether-containing side chains facilitated formation of more obvious hydrophilic-hydrophobic nanoscopic domains according to the images of atomic force microscope (AFM), and the results of small angle X-ray scattering (SAXS) of the membranes. As a result, the AEM grafted with 2-ethoxyethanamine or 3-methoxypropylamine exhibited higher tensile stress at break and lower methanol permeability than that the pristine Im-PPO membrane. In addition, the ether-containing branches allowed the AEMs to exhibit high alkaline stability. A conductivity of about 54 and 47 mS cm−1 was retained after immersed this kind of AEMs in 1 M KOH at 60 °C for 300 and 750 h, respectively.

Facile Preparation of Electromagnetic Interference Shielding Materials Enabled by Constructing Interconnected Network of Multi-walled Carbon Nanotubes in a Miscible Polymeric Blend

Electromagnetic interference (EMI) shielding materials are in great demand in electronic equipment and our surrounding environment to resist the increasing serious radiation pollution. Compared with their metal counterparts, conductive polymer composites (CPCs) have unique advantages of lightweight, corrosive resistance, low cost, and excellent processability, and are therefore an ideal choice for developing high-performance EMI shielding materials. However, CPCs based EMI shielding materials are limited to high filler loading, which caused poor mechanical properties and processability. Here, we demonstrate a facile and highly scalable approach to develop high-performance EMI shielding materials with low filler loading by using miscible poly(phenylene oxide)/polystyrene (PPO/PS) blend as the matrix. In contrast to PS/carbon nanotubes (CNTs) composites, PPO/PS/CNTs composites show much higher EMI shielding effectiveness caused by good dispersion of CNTs and highly interconnected conductive network. An excellent EMI shieling effectiveness of 23–25 dB is achieved for PPO/PS/10%CNTs composites with a thickness of only 375 µm, which is superior to most of reported polymer/CNTs composites prepared by melt-compounding. In addition, the results show that although absorption is the major shielding mechanism, the contribution of reflection is also important and closely related to the connectivity of conductive network, as well as the electrical conductivity of the CPCs.

The trade-off between membrane permselectivity and conductivity: A percolation simulation of mass transport

Ion exchange membranes (IEMs) have been widely applied in water desalination, separation and sustainable energy generation. In these applications, ionic conductivity and permselectivity draw the most attention from researchers. However, theoretical guidance is still lacking on where to find the optimized membrane properties in applications that are sensitive to both conductance and permselectivity. In this study, we have proposed a novel model by combining the simplified three-phases of an IEM and the percolation theory. Using open and closed sites to represent the polymeric and interstitial electrolyte phases of the membrane matrix on a 3D lattice, membrane permselectivity and conductivity can be successfully modeled and simulated on a set of sulfonated poly(2,6,-dimethyl-1, 4-phenylene oxide) (SPPO) membranes prepared using different organic solvents (N-Methyl-2-pyrrolidone, dimethylformamide and dimethyl sulfoxide), and commercial Fumatech FKS membranes. The resulting simulation provides good agreement with experimental observations. Notably, the decrease in permselectivity upon decreasing membrane thickness is well explained by the model considering the membrane void ratio and the percolative states of the lattice structure. When the membrane void ratio is larger than the critical threshold of 0.31, it renders the membrane low permselectivity while high conductance. This work potentially provides fundamental guidance in developing high-performance IEMs.

Nanoscale Selective Passivation of Electrodes Contacting a 2D Semiconductor

Abstract2D semiconducting materials have become the central component of various nanoelectronic devices and sensors. For sensors operating in liquid, it is crucial to efficiently block the electron transfer that occurs between the electrodes contacting the 2D material and the interfering redox species. This reduces current leakages and preserves a good signal‐to‐noise ratio. Here, a simple electrochemical method is presented for passivating the electrodes contacting a monolayer of MoS2, a representative of transition metal dichalcogenide semiconductors. The method is based on blocking the electrode surface by a thin and compact layer of electronically nonconductive poly(phenylene oxide), PPO, formed by electrochemical polymerization of phenol. Since the phenol polymerization occurs in the potential window where MoS2 is electrochemically inactive, the PPO deposition is area‐selective, limited to the electrode surface. The deposited PPO film is characterized by electrochemical, X‐ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy techniques. The applicability of this method is demonstrated by coating the electrodes of a MoS2‐based field‐effect transistor coupled with a nanopore. The highly selective deposition, the simple approach, and the compatibility with MoS2 makes this method a good strategy for efficient insulation of micro‐ and nanoelectrodes contacting 2D semiconductor‐based devices.

Anion exchange composite membranes composed of poly(phenylene oxide) containing quaternary ammonium and polyethylene support for alkaline anion exchange membrane fuel cell applications

Novel anion exchange composite membranes with controlled thicknesses have been developed by a simple pore-filling method using poly(phenylene oxide) containing a quaternary ammonium group as an anion conducting polymer electrolyte and a polyethylene porous substrate support for alkaline anion exchange membrane fuel cell applications. The thickness optimization could be done by controlling the viscosity of the polymer electrolyte solution. The resulting composite membrane prepared using 5 centipoise (cP) viscous polymer electrolyte solution composed of the co-solvent system such as dimethylacetamide (DMAc) and ethanol showed a uniformly thin structure of about 40 μm thickness. Among the composite membranes developed here, the membrane with the optimized thickness exhibited high tensile strength (45.6 MPa), and a low contact angle (13.19°) indicative of a hydrophilic surface, as well as high hydroxide conductivity (38.9 mS/cm) due to the combined effect of the reinforcement of the robust PE substrate and the sound impregnation of aminated poly(phenylene oxide). Membrane electrode assembly using A-PPO30E200 revealed excellent cell performance (peak power density:153 mW/cm2 at 0.43 V) than those of commercial FAA-3-50 Fumatech anion exchange membrane (peak power density:114 mW/cm2 at 0.43 V) under the operating condition of 60 °C and 100% RH.

Interpolyelectrolyte Complexes of Polyaniline and Sulfonated Poly(phenylene oxide)

The oxidative polymerization of aniline is studied for the first time in the presence of sulfonated poly(2,6-dimethyl-1,4-phenylene oxide). The polymerization leads to the formation of polyaniline-sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) interpolyelectrolyte complexes in which polyaniline is in the protonated form (as emeraldine salt). It is shown that the polyaniline–sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) complexes, depending on their composition, have either only proton conductivity from 0.015 to 0.1 S/cm, or mixed electronic-proton conductivity (10–6 S/cm electronic conductivity and 0.015 S/cm proton conductivity), or only electronic conductivity (up to 10–2 S/cm).

SPPO-based cation exchange membranes with a positively charged layer for cation fractionation

The synthesis of monovalent cation perm-selective membranes (MCPMs) to efficiently discriminate amongst cations from seawater is of great importance for several industrial applications. However, a technical approach is highly desired to construct MCPMs to obtain a high ionic flux and sustain perm-selectivity, simultaneously. In the present work, the thickness of the quaternized poly (2, 6-dimethyl-1, 4-phenylene oxide) (QPPO) layer on the surface of SPPO-PVA (SPVA) composite membrane was adjusted using a facile procedure to achieve high perm-selectivity without scarifying the ionic flux. The thickness of the selective layer was precisely controlled using various concentrations of the QPPO solution. By the introduction of the cationic layer on the SPVA membrane, the monovalent cation can be separated from the divalent cation by their difference in charge density. The influence of the selective barrier (thickness) endows MCPMs with high perm-selectivity up to 12.7 for 0.1 mol L−1 Li+/Mg2+ system, which is very satisfactory for polymeric membranes. The fabricated membranes have low electrical resistance and high limiting current density (ilim). Keeping in view the ED results, the prepared membranes with selective surface layer could be a viable candidate for Li+ selective separation from divalent cation Mg2+.

Alkaline stability of model anion exchange membranes based on poly(phenylene oxide) (PPO) with grafted quaternary ammonium groups: Influence of the functionalization route

We study the effect of pendent methyl groups on the alkaline stability of model anion exchange polymers based on poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) with grafted trimethylammonium groups. The polymer backbone is modified varying the synthesis procedure: by the bromination route, the ionomeric ammonium groups are inserted on the structural methyl group of PPO (Br-PPO-TMA), while by the chloromethylation route the ammonium groups are attached in the ortho-position to the methyl group of PPO (Cl-PPO-TMA). The properties of the membranes are studied by NMR and FTIR spectroscopy, thermogravimetry, water uptake, mechanical tensile tests, small-angle X-ray scattering (SAXS) and impedance spectroscopy. SAXS analysis indicates a better nanophase separation for Cl-PPO-TMA, which is consistent with a slightly larger water uptake and ionic conductivity. The properties of the two polymers are also compared before and after the aging in 2 M NaOH at 80 °C for different times. The thermogravimetric analysis shows the loss of the ammonium groups and the backbone ether cleavage after alkali treatments. The samples prepared by the bromination route show a higher stability of ionic conductivity, presumably due to a reduced alkaline attack of the ammonium groups, although DFT calculations do not show major differences of thermodynamic and kinetic reaction parameters. After alkaline treatment, the mechanical properties are more degraded for the Br-PPO-TMA compound. The decreased mechanical properties can be attributed to a reduction of the average chain length of PPO by alkaline scission of the ether links. Both synthesis routes have advantages and disadvantages, but the higher reproducibility and the better mechanical properties of samples prepared by chloromethylation are considered preponderant benefits.

Novel electrodialysis membranes with hydrophobic alkyl spacers and zwitterion structure enable high monovalent/divalent cation selectivity

Development of monovalent cations perm-selective membranes (MCPMs) for electrodialysis with the ability to improve cation flux, selectivity and reduce membrane swelling are the major concerns in different industrial applications, such as seawater desalination and wastewater purification. We designed and fabricated the novel MCPMs of quaternized poly(2,6-dimethyl phenylene oxide)s containing different lengths of alkyl spacers which were grafted directly to the nitrogen-centered cations connected to hydrophilic carboxylic and sulfonic acids groups. Pendant chains were in charge of tuning the membrane hydrophobicity and promoting the microphase separation. We observed that during changing the hydrophobicity of MCPMs, higher cation flux, greater perm-selectivity and more dimensional stability of monovalent cations perm-selective membrane can be achieved. The cations selectivity of prepared MCPMs was measured from electrodialysis in a Na+/Mg2+ system and compared with the commercial monovalent cation selective NeoseptaTM CIMS membrane. Highest perm-selectivity (PMg+2Na+) that reached up to 25.26 was observed for the MCPMs with the longest hydrophobic pendant chain which demonstrated that enhancement of membranes hydrophobicity considerably improved the monovalent cation perm-selectivity. These observations are quite interesting to expedite the improvement of monovalent cations perm-selective membranes for electrodialysis.

Humidity-Dependent Surface Structure and Hydroxide Conductance of a Model Quaternary Ammonium Anion Exchange Membrane

Anion exchange membrane (AEM) fuel cells (AEMFCs) are a promising cost-effective alternative energy conversion technology because of the potential implementation of earth-abundant catalysts, obviating the need for precious metals. AEMs, however, have low conductivity and suffer from poor stability. The conductivity of the AEM is inherently tied to the complex phase-separated morphology, as its dependence on the hydration level is not well understood. In this report, we employ phase-contrast tapping mode and conductive-probe atomic force microscopy (cp-AFM) to study the nanoscale surface morphology and hydroxide conductance of a commercially available quaternary ammonium (QA) AEM by FuMA-Tech GmbH (Fumapem FAA-3). The chemical structure of FAA-3 consists of a poly(phenylene oxide) backbone with QA functionality. The morphology of FAA-3 was observed in the bromide (FAA-3-Br-) and hydroxide form (FAA-3-OH-) in dehydrated and hydrated conditions. Under dehydrated conditions, both membranes showed no phase contrast, indicating the absence of phase-separated hydrophilic domains at the surface. At hydrated conditions, FAA-3-Br- shows randomly dispersed isolated clusters, while FAA-3-OH- shows elongated fibrillar structures extending microns in length. cp-AFM of hydrated FAA-3-OH- showed that these elongated regions were insulating. These results provide morphological evidence for the conduction of hydroxide at the surface and its dependence on the hydration level.