A new type of epoxy monomer 1,5-bis(4-fluorobenzoyl)-2,6-diglycidyl ether naphthalene (DGENF) was obtained through a three-step procedure involving Friedel–Crafts acylation, demethylation, and followed by nucleophilic reaction. The chemical structures were confirmed by 1HNMR, 19FNMR and FT-IR. After curing with methylhexahydrophthalic anhydride (MeHHPA), the properties of DGENF epoxy resin were measured and compared with three other kinds of commercial epoxy resins. As a result, DGENF exhibited excellent thermal stability, hydrophobic and dielectric properties. For example, DGENF had a higher glass transition temperature of 170 °C than the other three commercial epoxy resins. DGENF showed a higher contact angle of 116°, which could satisfy the standard of hydrophobic materials. In addition, DGENF showed significantly lower dielectric constant (2.97 at 1 MHz) and dielectric loss (0.0188 at 1 MHz) than those of the other commercial epoxy resins because of the introduction of fluorine on the side chains, which improved the electronegativity of the epoxy resin and reduced the polarizability of molecules efficiently. Herein, we believe the novel naphthyl epoxy resin (DGENF) has demonstrated potential application in electronic industries.

•SPEEKs were successfully synthesized by a direct aromatic nucleophilic substitution polymerization of sulfonated monomers.•The sensor showed wide operating work range and excellent humidity-sensing properties.•The sensor is capable of detecting the small hysteresis (less than 3% RH).•Protons and ions contribution contributed to the conductance of the SPEEK polymer in low and high relative humidity according to the complex impedance spectra.Sulfonated poly (ether ether ketone)s (SPEEKs) with different values of sulfonation degree were successfully synthesized by a direct aromatic nucleophilic substitution polymerization of sulfonated monomers. By the direct-synthesis method, the number of sulfonic acid groups can be precisely controlled. They were then fabricated by spin coating on a ceramic substrate to be used as a novel polymeric humidity sensor. The morphology of the ionic polymers especially the microstructure of ionic clusters, water sorption and the complex impedance spectra of the sensors were investigated to explain the humidity sensing characteristics and the sensing mechanism under different relative humidity. In addition, SPEEK-6 polymer with sulfonation degree (Ds = 1.18) was chosen as the optimal humidity sensing materials, which possessed high sensitivity and satisfactory linearity ranging from 11% RH to 97% RH. Furthermore, it exhibited a small hysteresis (less than 3% RH) during the sorption processes, an acceptable response/recovery time (100 s response and 105 s of recovery time) and an excellent repeatability. These results indicated SPEEKs could be promising for applications in humidity sensor.

•CaCl2 was employed not only as dopant to significantly improve the sensitivity, but also as cross-linker to reduce the sorption hysteresis.•The sensor showed wide operating work range and excellent humidity-sensing properties.•The sensor is capable of detecting little hysteresis (1.14%), fast response (2 s).•Based on the complex impedance spectra of humidity sensors, the process of conductivity is a combination of intrinsic charge transport (charge doping by water molecules), ion transport and diffusion processes over the whole RH range.This study presented a novel polymeric humidity sensor based on CaCl2-doped sulfonated poly (ether ether ketone) (SPEEK). For the first time, we developed a crosslinking procedure to modify SPEEK for humidity sensors application. SPEEKs with fixed value of sulfonation degree were synthesized by a direct aromatic nucleophilic substitution polymerization of sulfonated monomers. The obtained polymer was used to prepare humidity sensitive composites by doping CaCl2, and then they were fabricated by spin coating on a ceramic substrate to use as a novel polymeric humidity sensor. Humidity-sensing performances were investigated by varying both CaCl2 concentration and relative humidity. Comparing with the pristine polymer, CaCl2-doped SPEEK showed improved humidity sensing properties and the 10 wt%- CaCl2/SPEEK sensor showed the best sensing properties for high sensitivity, little hysteresis (1.14%), fast response (2 s)/recovery time (65 s) and outstanding stability. Additionally, the morphology and thermal properties of composites and the humidity sensing mechanism of the sensors were discussed in detail. Most importantly, CaCl2 was employed not only as dopant to significantly improve the sensitivity, but also as cross-linker to reduce the sorption hysteresis. This study demonstrated that these humidity sensors could offer a great potential for applications.In the case of doped SPEEK membranes, the process of conductivity is a combination of intrinsic charge transport (charge doping by water molecules), ion transport and diffusion processes over the whole RH range.Download high-res image (93KB)Download full-size image

Novel sulfonated poly(arylene ether ketones) (SDN-PAEK-x), consisting of dual naphthalene and flexible sulfoalkyl groups, were prepared via polycondensation, demethylation, and sulfobutylation grafting reaction. Among them, SDN-PAEK-1.94 membrane with the highest ion exchange capacity (IEC = 2.46 mequiv·g–1) exhibited the highest proton conductivity, which was 0.147 S· cm–1 at 25 °C and 0.271 S·cm–1 at 80 °C, respectively. The introduction of dual naphthalene moieties is expected to achieve much enhanced properties compared to those of sulfonated poly(arylene ether ketones) (SNPAEK-x), consisting of single naphthalene and flexible sulfoalkyl groups. Compared with SNPAEK-1.60 with a similar IEC, SDN-PAEK-1.74 membrane showed higher proton conductivity, higher IEC normalized conductivity, and higher effective proton mobility, although it had lower analytical acid concentration. The SDN-PAEK-x membranes with IECs higher than 1.96 mequiv·g–1 also exhibited higher proton conductivity than that of recast Nafion membrane. Furthermore, SDN-PAEK-1.94 displayed a better single cell performance with a maximum power density of 60 mW·cm–2 at 80 °C. Considering its high proton conductivity, excellent single cell performance, good mechanical stabilities, low membrane swelling, and methanol permeability, SDN-PAEK-x membranes are promising candidates as alternative polymer electrolyte membranes to Nafion for direct methanol fuel cell applications.Keywords: fuel cell; naphathalene moieties; poly(arylene ether ketone); polymer electrolyte membranes; proton conductivity; sulfoalkyl groups

•Novel side-chain type sulfonated poly (arylene ether ketone)s were prepared, and the Ds can be controlled precisely.•The water sorption behaviour of the polymers has been discussed from the mechanism.•The effect of the structure on the humidity sensitivity properties has been discussed in detail.•High Ds materials show excellent sensitivity and stability in a wide humidity range.A series of novel side-chain-type sulfonated polymer aromatic electrolytes (PAEK-SO3Na-x) with different sulfonation degrees (Ds) were synthesized through a polycondensation of 1,5-bis(4-fluorobenzoyl)-2,6-dimethoxynaphthalene and hydroquinone, followed by a demethylation and sulfobutylation reaction. The structures and Ds of the polymers were confirmed by their 1H NMR spectra and the hydrophilic nature of the membranes was characterized by water uptake and contact angle test. A dual-mode sorption model was applied to analyze the water vapor sorption of the polymers. Humidity sensors were prepared from PAEK-SO3Na-x. Then the sensitivity and responsibility of the sensors were characterized in detail. The variation range of the impedance of the sensors was from 107 Ω to 102 Ω between 11% RH and 97% RH, which was wider than many other polymeric humidity sensors reported and indicated a good sensitivity. The response time of PAEK-SO3Na-80 was 90 s and 100 s for desorption and adsorption, respectively. It is for the first time to apply side-chain-type sulfonated polymer electrolyte to humidity sensors and this new kind of sensitivity material showed a good application prospect.

Amino-substituted poly(ether ether ketone) (APEEK) and sulfonated poly(ether ether ketone) (SPEEK, IEC = 2.07 mequiv. g−1) have been synthesized via nucleophilic aromatic substitution reaction. The structures of APEEK and SPEEK were characterized by 1H NMR spectra. The composite membranes based on APEEK and SPEEK were confirmed by their FTIR spectra, indicating the formation of intermolecular ionic cross-linking networks between amino and sulfonic groups. The water uptake, proton and methanol transport properties of composite membranes were also determined for fuel cell applications. The results showed that the composite membranes exhibit high selectivity, appropriate proton conductivities as well as reduced water uptake and methanol permeability when compared with the pristine SPEEK membrane. Furthermore, it should be noted that the intermolecular ionic cross-linking effectively improved the tensile strength, breaking elongation, and thermal stabilities of the membranes. In particular, the SPEEK-10 membrane (the weight ratio of APEEK is 10%) showed a tensile strength of 121.2 MPa and breaking elongation of 93.5%, which were 1.5 times and 2.5 times higher than those of pristine SPEEK, respectively. The high selectivity, thermal and mechanical properties indicate that the composite membranes are promising to be used as proton exchange membranes for direct methanol fuel cells.

•Quaternized polymer membranes and three model compounds were prepared.•The alkaline stability was detailed compared.•Benzyltrimethylammonium based membranes had the better alkaline stability.The alkaline stability of benzyltrimethylammonium, benzylmethylimidazolium and benzyldimethylimidazolium functionalized poly(arylene ether ketone) anion exchange membranes (AEMs) were investigated by conductivity change and NMR experiments. The corresponding small molecular model compounds were synthesized and used to determine the degradation degree of benzyltrimethylammonium, benzylmethylimidazolium and benzyldimethylimidazolium cations. The results showed only 7% of benzyltrimethylammonium model compound degraded in 1 M NaOH at 60 °C; whereas, benzylmethylimidazolium and benzyldimethylimidazolium model compounds had a degradation of 55% and 46% at the same condition, respectively. The alkaline stability of three cations follows the order: benzyltrimethylammonium > benzyldimethylimidazolium > benzylmethylimidazolium. The NMR spectra and hydroxide conductivity change with immersing time in 1 M NaOH at 60 °C also confirmed that benzyltrimethylammonium functionalized polymer had a relative better alkaline stability than benzylmethylimidazolium and benzyldimethylimidazolium functionalized polymers in alkaline environment at elevated temperature. This research enriches the investigation on the alkaline stability of anion exchange membranes with quaternary ammonium, imidazolium and C2-substituted imidazolium.

•SPEEK and SPEEK with metal salts-ion substitution is successfully synthesized.•The sensor showed highly sensitive and excellent humidity-sensing properties.•The sensor is capable of detecting the small hysteresis (less than 2% RH).•Ionic conductivities contributed to the transmission in low and high relative humidity according to the complex impedance spectra.Sulfonated poly (ether ether ketone) (SPEEK) was successfully synthesized by post-sulfonation. A novel humidity sensor was made of SPEEK and SPEEK with metal salts-ion (Ca2+, Cu2+) substitution and fabricated by spin coating on a ceramic substrate. The effect of different counter-ion forms on the electrical and humidity-sensing properties of SPEEK membranes was investigated. The chemical structure of SPEEK was confirmed using its 1H NMR spectrum. The polymeric materials were detailed characterized, including FTIR spectra, thermogravimetric analysis (TGA), and contact angle measurement. These results indicated there were significant differences in their chemical structure, thermal and transport properties for SPEEK when exchanged with the different metal salts-ions. In addition, comparing with SPEEK, the humidity-sensing properties of SPEEK-Ca2+ exhibited high sensitivity from 33% RH to 97% RH, satisfactory linearity, small hysteresis during the sorption processes, short response/recovery time, excellent repeatability and complex impedance in low and high relative humidity. This means that the water molecules in the SPEEK-Ca2+ membranes interact with the Ca2+ cations more strongly when exchanged with the different metal salts-ions, and in result the diffusion of the water molecules is reduced. These results inditated this novel polymer electrolyte with metal salts-ion would be a promising candidate for humidity sensor applications.

We have developed basic ionic liquid-based hybrid membranes with ionic liquid modified zeolitic imidazolate frameworks (ZIFs) as fillers, aiming to enhance the electrochemical and physical properties of the membrane.

A new bisphenol monomer, 3,3′,5,5′-tetramethoxy-4,4′-dihydroxybiphenyl, was synthesized and copolymerized to prepare diphenyl-based poly(arylene ether sulfone) copolymers containing tetra-methoxy groups (MOPAES). After converting the methoxy group to the reactive hydroxyl group, the resulting side-chain-type sulfonated copolymers (SOPAES) with a hydrogen bonded network were obtained by a sulfobutylation reaction. The copolymers were characterized and confirmed by 1H NMR, FT-IR, thermogravimetric analysis (TGA) and small-angle X-ray scattering. The water uptake, proton and methanol transport properties of the resulting membranes were also determined for fuel cell applications. These SOPAES series membranes showed high proton conductivity in the range of 0.032–0.054 and 0.084–0.142 S cm−1 at 25 and 80 °C under hydrated conditions, respectively. SOPAES-40 (IEC = 1.38 mequiv. g−1) showed comparable proton conductivity with Nafion 117 in the hydrated state. The methanol permeability of these membranes was in the range of 1.58–4.29 × 10−7 cm2 s−1, which is much lower than Nafion (1.55 × 10−6 cm2 s−1). It should be noted that the intra/inter hydrogen bonds formed between sulfonic acid and hydroxyl groups or between hydroxyl and hydroxyl groups improved the mechanical properties and reduced the methanol permeability of the membranes effectively. A combination of suitable proton conductivity, low water uptake, and low methanol crossover for selected SOPAES indicates that they are good candidates as proton exchange membrane materials for fuel cells.

A novel in situ-foaming material was successfully prepared by a naphthalene-based hydroxyl-containing poly(arylene ether ketone) (PAEK) modified with thermally labile tert-butyloxycarbonyl which can decompose and in situ generate CO2 and isobutene as the foaming agents. The structure and thermal properties of the polymers were characterized by using 1H NMR spectra and thermogravimetry coupled time-resolved mass spectrogram (TG/MS). The resulting polymers exhibited relatively high Tg because of the existence of a rigid naphthalene moiety. Then closed microcellular porous membranes with a wide range of expansion ratio (ER) were obtained by a simple thermal treatment from 140 °C to 280 °C for 60 seconds, without using any other physical or chemical foaming agents. The highest ER was 53.98%. This method has never been reported before on high-performance poly(aryl ether) materials. Furthermore, we investigated the relationship between the foaming temperature and the morphology of membranes in detail by using density measurement and scanning electron microscopy (SEM).

A novel cross-linking strategy for imidazolium-functionalized poly(arylene ether ketone) containing tetramethyl groups, used as anion exchange membranes, is presented in this paper. The preparation of anion exchange membranes comprised of converting benzylic methyl to bromomethyl groups by a radical reaction, quaternization of the bromometylated poly(arylene ether ketone) with 1-vinylimidazole and subsequent anion exchange reaction. The photo-crosslinking reaction, induced by UV-light under the activation of a photo-initiator, was simple and controllable compared to the conventional cross-linking process via a multifunctional cross-linking agent. All the vinylimidazolium-founctionalized poly(arylene ether ketone) membranes showed good mechanical and thermal stabilities. Moreover, the cross-linked membranes exhibited better dimensional stabilities. The ionic conductivity of cross-linked membranes was still acceptable although that property decreased with UV irradiation time due to the compact cross-linked structure. For example, the VImPAEK-15 min-HCO3 membrane with irradiation time of 15 min showed a moderate bicarbonate anion conductivity of 0.021 S cm−1 and a low swelling ratio of 10.74% at 70 °C. The alkaline stability test under both high and relatively low alkaline conditions was carried out. Although the vinylimidazolium cation is unstable in strong alkaline solution, the cross-linked vinylimidazolium-based membranes are chemically stable in the bicarbonate anion form under relatively low alkaline conditions. The results showed that the cross-linked membrane induced by UV irradiation could be used for electrochemical devices that were operated at less extreme pHs.

A series of sulfonated naphthalene-based poly (arylene ether ketone)s (SNPAEK-xx) with pendant sulfoalkyl groups were prepared by polycondensation of 1,5-bis(4-fluorobenzoyl)-2,6-dimethoxynaphthalene and o-methylhydroquinone, followed by a demethylation and sulfobutylation reaction. The sulfonate degree of SNPAEK-xx could be controlled easily by adjusting the ratio of 1,4-butane sultone to the hydroxyl content in the demethylated polymers. Flexible and tough membranes with reasonably high mechanical strength were prepared. SNPAEK-xx membranes showed a high ionic exchange capacity (IEC) in the range of 1.13 to 2.27 mequiv. g−1, and the highest proton conductivity of 0.191 S cm−1 at 80 °C. They exhibited low methanol permeability in the range of 1.25–10.22 × 10−7 cm2 s−1, which was much lower than that of Nafion 117. Transmission electron microscopy analysis of SNPAEK-xx revealed that they had a more obvious phase separated structure between the hydrophilic side chain and hydrophobic fully aromatic domains at a higher IEC. Combining their high thermal and mechanical stability, high selectivity, lower water swelling ratio, SNPAEK-xx membranes could be promising materials as alternative to Nafion membranes for direct methanol fuel cell applications.

Quaternized poly(ether ether ketone)s (QPEEKs), which were aminated by trimethylamine (TMeA), triethylamine (TEtA), tripropylamine (TPrA) and 1-methylimidazole (MeIm), were prepared and used as phosphoric acid (PA)-doped high-temperature proton exchange membranes. These QPEEK membranes showed high glass transition temperature (Tg was higher than 483 K) and high thermal stability (T5% was higher than 486 K). The tensile strengths of these QPEEK membranes were higher than 60 MPa. The PA-doped im-QPEEK, which was aminated by MeIm, had the highest Wdoping (159 wt%) and proton conductivity (0.05 S cm−1 at 473 K). For the other three PA-doped QPEEK membranes, the Wdoping and proton conductivity decreased with the increase of the length of trialkyl side chains on quaternary ammonium groups. According to our study, the PA absorbing ability was subjected to the structures of quaternary ammonium groups instead of the basicities of quaternary aminating reagents. All PA-doped membranes had great oxidative stability and could last for more than 5 h in 3 wt% H2O2, 4 ppm Fe2+ Fenton solution at 353 K.

Functionalized graphene oxide (FGO) reinforced quaternized poly(ether ether ketone) membranes were prepared for high temperature proton exchange membrane applications. The introduction of FGO significantly improved the mechanical strength and oxidative stability of these membranes at a high doping level. These reinforced membranes showed high tensile strength up to 40 MPa and high proton conductivity up to 58 mS cm−1 at 200 °C.

The liquid nature of ionic liquids (ILs) limits their use in potential electrolytes due to the problem of leakage. Herein, we design a new strategy to immobilize an ionic liquid by incorporating it within ZIF-8 (ZIF = zeolitic imidazolate framework) by the ionothermal method.

A series of cross-linked sulfonated poly (arylene ether ketones) containing tri-side-chain pendent sulfonic groups (SQNPAEK) were prepared by the Friedel–Crafts acylation reaction in order to solve the problem of high methanol crossover and maintain high proton conductivity for direct methanol fuel cells. For this purpose, sulfonated poly(arylene ether ketones) with pendent carboxylic acid groups were synthesized based on phenolphthalein carboxylic monomers to be used as a macro-crosslinker. The cross-linked membranes showed improved mechanical properties, chemical resistance and oxidative stability. The water uptake and swelling ratio of cross-linked membranes decreased from 57.3% to 18.7%, and from 12.2% to 3.03%, respectively. And the methanol permeability decreased from 0.94 × 10−7 cm2 s−1 to 0.37 × 10−7 cm2 s−1. Regarding the high proton conductivity, it showed enhanced performance over the pristine membrane, up to 0.29 S cm−1. Thus, the cross-linked membranes possessed the better performance implying their potential for practical application in high-energy-density devices.

Membranes of sulfonated poly (arylene ether ketone) containing carboxyl groups (SPAEK-C) are modified by alternating deposition of oppositely charged polyelectrolytes [carboxyl-functionalized multiwalled carbon nanotubes (C-MWCNTs) and chitosan (CS)] in order to reduce methanol crossover and maintain high proton conductivity in a direct methanol fuel cell (DMFC). Fourier transform infrared spectroscopy confirms that C-MWCNTs and CS are assembled in the multilayers. The morphology of membranes is studied by scanning electron microscopy. The results confirm the presence of thin C-MWCNTs/CS multilayers coated on the SPAEK-C membrane. The SPAEK-C-(C-MWCNTs/CS)n membranes maintain high proton conductivity values up to 0.058 Scm−1 at 25 °C and 0.24 Scm−1 at 80 °C, which are superior to previous layer-by-layer assembled polyelectrolyte systems. Meanwhile, the methanol permeability of these modified membranes is effectively reduced. The selectivity of SPAEK-C-(C-MWCNTs/CS)n is two orders of magnitude greater than that of Nafion® 117, making these modified membranes a good alternative to be used in DMFCs. The thermal stability, water uptake, swelling ratio and proton conductivity of SPAEK-C and SPAEK-C-(C-MWCNTs/CS)n membranes are also investigated.

•Novel TFC RO membranes were obtained by coating SPAES-C on a microporous polysulfone support.•A secondary cross-linked PVA layer was coated on the top of SPAES-C layer to improve the NaCl rejection.•After cross-linking, the NaCl rejection increased from 91.2% to 96.8%.•The multilayer RO membranes showed good chlorine-tolerance.Sulfonated cardo poly(arylene ether sulfone) copolymers (SPAES-C) were synthesized via post-sulfonation of the parent polymer. A series of reverse osmosis composite membranes were obtained by coating SPAES-C on porous polysulfone support membranes, with varying the concentration of coating solutions. The SEM results indicated that the obtained reverse osmosis membranes had smooth surface, and no defect was observed. Meanwhile, the functional layer thickness obtained from the SEM results was in the range from 300 to 400 nm. All the resulting membranes showed good water flux and appropriate NaCl rejection. In order to improve the NaCl rejection, a secondary layer of formaldehyde-cross-linked polyvinyl alcohol was coated on the surface of SPAES-C membrane, and this layer could improve NaCl rejection from 91.2% to 96.8% without a serious loss of water permeability. Compared with commercial PA reverse osmosis membrane, the composite membranes based on SPAES-C showed excellent chlorine-tolerance in reverse osmosis operation.

We have developed basic ionic liquid-based hybrid membranes with ionic liquid modified zeolitic imidazolate frameworks (ZIFs) as fillers, aiming to enhance the electrochemical and physical properties of the membrane.

The liquid nature of ionic liquids (ILs) limits their use in potential electrolytes due to the problem of leakage. Herein, we design a new strategy to immobilize an ionic liquid by incorporating it within ZIF-8 (ZIF = zeolitic imidazolate framework) by the ionothermal method.

Functionalized graphene oxide (FGO) reinforced quaternized poly(ether ether ketone) membranes were prepared for high temperature proton exchange membrane applications. The introduction of FGO significantly improved the mechanical strength and oxidative stability of these membranes at a high doping level. These reinforced membranes showed high tensile strength up to 40 MPa and high proton conductivity up to 58 mS cm−1 at 200 °C.

Quaternized poly(ether ether ketone)s (QPEEKs), which were aminated by trimethylamine (TMeA), triethylamine (TEtA), tripropylamine (TPrA) and 1-methylimidazole (MeIm), were prepared and used as phosphoric acid (PA)-doped high-temperature proton exchange membranes. These QPEEK membranes showed high glass transition temperature (Tg was higher than 483 K) and high thermal stability (T5% was higher than 486 K). The tensile strengths of these QPEEK membranes were higher than 60 MPa. The PA-doped im-QPEEK, which was aminated by MeIm, had the highest Wdoping (159 wt%) and proton conductivity (0.05 S cm−1 at 473 K). For the other three PA-doped QPEEK membranes, the Wdoping and proton conductivity decreased with the increase of the length of trialkyl side chains on quaternary ammonium groups. According to our study, the PA absorbing ability was subjected to the structures of quaternary ammonium groups instead of the basicities of quaternary aminating reagents. All PA-doped membranes had great oxidative stability and could last for more than 5 h in 3 wt% H2O2, 4 ppm Fe2+ Fenton solution at 353 K.