Sulfonated Poly(arylene Ether Sulfone)s Research Articles

Proton exchange membranes from double-filler of sulfonated titanium dioxide nanotubes and graphitic carbon nitride nanosheets integrated into sulfonated poly(aryl ether sulfone)s

Inorganic-organic composite proton exchange membranes (PEMs) are promising substitutes in proton exchange membrane fuel cells. To improve the compatibility between inorganic fillers and polyelectrolytes, along with alleviating filler aggregation, a series of composite PEMs incorporating both sulfonated titanium dioxide nanotubes (sTiNT) and graphitic carbon nitride nanosheets (g-C3N4) into sulfonated poly (aryl ether sulfone) s (SPAES) have been prepared. The distinct morphology of sTiNT and g-C3N4, coupled with their respective sulfonic acids and amine/imine functionalities, endow the fillers with exceptional compatibility and dispersivity within SPAES. The obtained SPAES/sTiNT/g-C3N4 membranes exhibit superior thermal, size and mechanical stability, robust oxidative resistance, together with high proton conductivity. The SPAES/sTiNT/g-C3N4(1/3) membrane particularly exhibits proton conductivity of 202 mS/cm and swelling below 10% (90 °C), a hydrogen fuel cell output of 512 mW/cm2 (80 °C), which is 1.6 times of the SPAES membrane. The results suggest the great potential of multi-filler compositing strategy for alternative PEMs exploration.

Role of Doping Agent Degree of Sulfonation and Casting Solvent on the Electrical Conductivity and Morphology of PEDOT:SPAES Thin Films.

Poly(3,4-ethylenedioxythiophene) (PEDOT) plays a key role in the field of electrically conducting materials, despite its poor solubility and processability. Various molecules and polymers carrying sulfonic groups can be used to enhance PEDOT’s electrical conductivity. Among all, sulfonated polyarylether sulfone (SPAES), prepared via homogenous synthesis with controlled degree of sulfonation (DS), is a very promising PEDOT doping agent. In this work, PEDOT was synthesized via high-concentration solvent-based emulsion polymerization using 1% w/w of SPAES with different DS as dopant. It was found that the PEDOT:SPAESs obtained have improved solubility in the chosen reaction solvents, i.e., N, N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and N-methyl-2-pyrrolidone and, for the first time, the role of doping agent, DS and polymerization solvents were investigated analyzing the electrical properties of SPAESs and PEDOT:SPAES samples and studying the different morphology of PEDOT-based thin films. High DS of SPAES, i.e., 2.4 meq R-SO3− g−1 of polymer, proved crucial in enhancing PEDOT’s electrical conductivity. Furthermore, the DMSO capability to favor PEDOT and SPAES chains rearrangement and interaction results in the formation of a polymer film with more homogenous morphology and higher conductivity than the ones prepared from DMAc, DMF, and NMP.

Titanium oxide/graphitic carbon nitride nanocomposites as fillers for enhancing the performance of SPAES membranes for fuel cells

Our work deals with the fabrication of nanocomposite membranes by reinforcing sulfonated poly(aryl ether sulfone)s (SPAES) properties through incorporating various titanium oxide/graphitic carbon nitride (TiO2/g-C3N4) nanocomposite contents. They reveal promising results for applications in proton exchange membrane fuel cells. The nanocomposites introduction provides the membranes with noticeable proton conductivity, mechanical and dimensional stability improvements in comparison with the control SPAES membrane. The SPAES-TiO2/g-C3N4-1.0 nanocomposite membrane demonstrates the prominent proton conductivity of 325.3mScm−1 at 80°C and 258.4mScm−1 at 94.1% RH, as well as outstanding oxidative stability of only weight loss of 4.6% after the Fenton’s accelerating aging at 80°C for 1h. For the single fuel cell performance, it reaches the highest power density of 525.6mWcm-2 at 1150.8mAcm-2. These results suggest the good prospect of the dual compositing strategy for membrane modification in the fuel cell applications.

An effective strategy to enhance the performance of the proton exchange membranes based on sulfonated poly(ether ether ketone)s

We report an effective and facile approach to enhance the dimensional and chemical stability of sulfonated poly(ether ether ketone) (SPEEK) type proton exchange membranes through simple polymer blending for fuel cell applications, using commercial available materials. The polymeric blends with sulfonated poly(aryl ether sulfone)s (SPAES) were simply fabricated by a three-component system, which contained SPEEK (10–50 wt%, 1.83 mmol/g), and SPAES-40 (1.72 mmol/g)/SPAES-50 (2.04 mmol/g) at 1:1 in weight. The SPAES-40 was selected for mechanical and dimensional stability reinforcing, while SPAES-50 for the good polymer compatibility. The obtained SPEEK/SPAES blend membranes showed depressed water uptake, better dimensional and oxidative stability, together with higher proton conductivity beyond 70 °C than the pristine SPEEK membrane. The apparent improvements in membrane properties were associated with the homogeneous dispersion of SPEEK and both SPAES copolymers inside the membranes as well as the rearrangements of the polymeric chains. The SPEEK content should be properly controlled in the range of 10–40% (B10 to B40). In a H2/O2 fuel cell test, B30 showed a maximum power density of 700 mW/cm2, which was 1.6 times as high as that of B40 at 80 °C under 100% RH. The further cross-linking treatment produced more ductile and enduring blend membranes, indicating an appreciable prospective for fuel cell applications.

Four-polymer blend proton exchange membranes derived from sulfonated poly(aryl ether sulfone)s with various sulfonation degrees for application in fuel cells

Our objective was to prepare a novel series of four-polymer blend proton exchange membranes (PEMs) which could be used in PEM fuel cells (PEMFCs). They were fabricated by the blending of four sulfonated poly(aryl ether sulfone)s (SPAES) copolymers, SPAES-20, SPAES-30, SPAES-40 and SPAES-50 with sulfonation degree (DS) of 20%, 30%, 40% and 50%, respectively. Because of the step by step changes in DS of polymers in the four-polymer blend membranes, single-phase solutions were formed and converted into transparent and flexible membranes readily. The blend modification endowed the obtained membranes considerably improved dimensional, thermal, hydrolytic and oxidative stabilities, together with good methanol resistance at similar ion exchange capacity (IEC) level while comparing with the control membranes. Among the blend membranes, the B4 (0.5:1:2:2) membrane showed the highest proton conductivity (203.1 mS cm−1 at 90 °C and 169.2 mS cm−1 at 94.1% RH) with excellent oxidative (5.1% mass loss in Fenton's reagent at 80 °C for 1 h) and dimensional stability (<15% at 80 °C). In the H2/O2 fuel cell operation, its maximum power output achieved 467.98 mW cm−2 at 1050 mA cm−2. The SPAES blend membranes are promising for application in the PEMFCs.

Post-synthetic MIL-53(Al)-SO3H incorporated sulfonated polyarylethersulfone with cardo (SPES-C) membranes for separating methanol and methyl tert-butyl ether mixture

The post-synthetic MIL-53(Al)-SO3H was prepared and incorporated into sulfonated polyarylethersulfone with cardo (SPES-C) polymer matrix to form mixed matrix membranes (MMMs). The as-prepared MIL-53(Al)-SO3H was characterized by wide angle X-ray diffraction (WAXRD), fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), intelligent gravimetric analysis (IGA), scanning electron microscope (SEM) and elemental analysis. Positron annihilation lifetime spectroscopy (PALS), thermo gravimetric analysis (TGA), SEM, FTIR and water contact angle measurements were performed to investigate the properties and structure of MMMs. The results showed that MIL-53(Al)-SO3H was successfully synthesized without crystal structure collapse. The particle sizes were in nanometer scale. MIL-53(Al)-SO3H preferentially adsorbed methanol (MeOH) over methyl tert-butyl ether (MTBE). MIL-53(Al)-SO3H dispersed in SPES-C phase uniformly and no obvious interfacial defects could be observed. The membrane hydrophilicity, swelling behavior as well as free volume parameters could be effectively tuned by changing filler loading. The as-prepared MMMs demonstrated excellent separation performance and encouraging long-term stability for MeOH (15 wt%)/MTBE mixture. With increasing the filler loading, the permeation flux increased and the separation factor showed an up and down trend. When MIL-53(Al)-SO3H loading was below 15 wt%, an antitrade-off phenomenon was obtained. M-15 with 15 wt% loading exhibited the optimal separation performance (permeation flux of 0.368 kg·m−2·h−1 and separation factor of 1990).

A novel synthesis approach to partially fluorinated sulfonimide based poly (arylene ether sulfone) s for proton exchange membrane

Innovation of novel low cost proton conductive materials with super acidity has been the ever-increasing thirst for PEMFCs. Sulfonimide groups have the strongest gas-phase super-acidity with excellent thermal and chemical stability. Therefore, a series of partially fluorinated sulfonimide functionalized poly(arylene ether sulfone)s (SIPAES-xx) were successfully synthesized by chemical modification of sulfonated polyarylethersulfone (SPAES). The SPAESs were synthesized first by the direct polymerization of 4,4′ -dichlorodiphenylsulfone (DCDPS), 3,3′-disulfonate-4,4′-dichlorodiphenylsulfone (SDCDPS), and bisphenol. Thereafter, all arylsulfonic acid groups were converted into more acidic sulfonimide acid groups using partial fluorinated fluorosulfonyl imide monomer. The effect of the conversion of arylsulfonic acid function into sulfonimide was evaluated through thermal and chemical analysis. 1H-NMR, FTIR, TGA, FE SEM, and AFM were used to illustrate the structure, thermal and chemical properties of (SIPAES-xx) membranes. The membranes showed IEC values of 0.78–1.41 mequiv./g with 6.7–40.6% water uptake for 20–40% ionic groups. The synthesized SIPAES-40 membranes showed comparable proton conductivity to Nafion® 117 at same conditions. Nevertheless, the aromatic sulfonimide remained stable up to 370 °C. Furthermore, the presence of fluorine within the sulfonimide polymer provided high dimensional stability and oxidative durability by protecting the polymer chain from oxidizing radical species. Therefore, the synthesized SIPAES-xx membranes have the potential features as a proton exchange membrane (PEM) materials in the fuel cell.

A Combined XRD, Solvatochromic, and Cyclic Voltammetric Study of Poly (3,4-Ethylenedioxythiophene) Doped with Sulfonated Polyarylethersulfones: Towards New Conducting Polymers.

Despite the poor solubility in organic solvents, poly (3,4-ethylenedioxythiophene) (PEDOT) is one of the most successful conducting polymers. To improve PEDOT conductivity, the dopants commonly used are molecules/polymers carrying sulfonic functionalities. In addition to these species, sulfonated polyarylethersulfone (SPAES), obtained via homogeneous synthesis with different degrees of sulfonation (DS), can be used thanks to both the tight control over the DS and the charge separation present in SPAES structure. Here, PEDOTs having enhanced solubility in the chosen reaction solvents (N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and N-methyl-2-pyrrolidone) were synthesized via a high-concentration solvent-based emulsion polymerization with very low amounts of SPAES as dopant (1% w/w with respect to EDOT monomer), characterized by different DS. The influence of solvents and of the adopted doping agent was studied on PEDOT_SPAESs analyzing (i) the chemical structure, comparing via X-ray diffraction (XRD) the crystalline structures of undoped and commercial PEDOTs with PEDOT_SPAES’ amorphous structure; (ii) solvatochromic behavior, observing UV absorption wavelength variation as solvents and SPAES’ DS change; and (iii) electrochemical properties: voltammetric peak heights of PEDOT_SPAES cast onto glassy carbon electrodes differ for each solvent and in general are better than the ones obtained for neat SPAES, PEDOTs, and glassy carbon.

Highly reinforced pore-filling membranes based on sulfonated poly(arylene ether sulfone)s for high-temperature/low-humidity polymer electrolyte membrane fuel cells

A series of pore-filling membranes are prepared by impregnating porous cross-linked benzoxazine-benzimidazole copolymer P(pBUa-co-BI) substrates with sulfonated poly(arylene ether sulfone)s (SPAES)s having different degree of sulfonation for polymer electrolyte membrane fuel cells operating at high-temperatures (>100°C) and low-humidity (<50% RH) conditions. The SPAESs are synthesized by reacting 4,4’-dihydroxybiphenyl with the mixtures of disulfonate-4,4’-difluorodiphenylsulfone and 4,4’-difluorodiphenylsulfone in different ratios. The porous P(pBUa-co-BI) substrates are prepared by extracting dibutyl phthalate (DBP) included in P(pBUa-co-BI) films using methanol. The P(pBUa-co-BI) films are prepared by stepwise heating the casted N,N-dimethylacetamide solution containing the mixtures of poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole] (PBI), 3-phenyl-3,4- dihydro-6-tert-butyl-2H-1,3-benzoxazine (pBUa), and DBP to 220°C. The pore-filling membranes are found to have much improved dimensional stability and mechanical strength compared with the SPAES membranes. Although the proton conductivity values of the pore-filling membranes are slightly smaller than those of the SPAES membrane, their cell performance is superior to that of the SPAES membrane at 120°C and 40% RH conditions because ultrathin pore-filling membranes (15–20µm) having high mechanical strength can be prepared and they can contain a larger content of chemically-bound water.

Combining control of branching and sulfonation in one-pot synthesis of random sulfonated polyarylethersulfones: effects on thermal stability and water retention

In functional polymers with tunable hydrophilic behaviour like sulfonated polyarylethersulfone (SPES) high ionic conductance can be obtained directly by increasing the concentration of sulfonic moieties along the macromolecular chain. This, however, often comes to the cost of excessive water sorption, which can lead to membrane rupture and consequent device failure. To overcome this drawback, and to reconcile high hydrophilicity with the high mechanical properties of aromatic polymers, we propose the use of SPES copolymers with a low degree of branching. A series of branched SPES was synthesized using homogeneous (one-pot) copolymerization by replacing an amount up to 0.9% mol of the difunctional monomer 4,4′-dihydroxydiphenyl with the trifunctional 1,3,5-trihydroxybenzene (THB). The polymers were characterized by 1H-NMR spectroscopy, intrinsic viscosity, water sorption measurements, thermogravimetric analysis and differential scanning calorimetry. Like linear SPES, branched SPES is totally amorphous and soluble in polar aprotic solvents, lending itself to easy fabrication of membranes and coatings. Besides reducing the water sorption and in-plane swelling of SPES membranes upon equilibration in liquid, branching also improves the retention of water in swollen membranes.

Conductive inks based on methacrylate end‐capped poly(3,4‐ethylenedioxythiophene) for printed and flexible electronics

A new synthesis of methacrylate end‐capped poly(3,4‐ethylenedioxythiophene) (PEDOT) was performed: the polymer is soluble in common organic solvents, thus overcoming the well‐known technical problems related to the use of commercial PEDOT in different printing technologies, such as screen printing, due to its poor processability and compatibility in formulations with other resins and polymers. The new synthetic method developed is based on the direct oxidative polycondensation of 3,4‐ethylenedioxythiophene (EDOT) in the presence of an oxidant species and a crosslinkable end‐capper, i.e., methacrylate end‐capped EDOT (mEDOT), prepared via Friedel Crafts acylation with methacryloyl chloride. The oxidative polycondensation between EDOT and mEDOT monomers in the presence of a new kind of doping agent, Sulfonated Polyarylethersulfone (SPES)—characterized by different degree of sulfonation (DS)—was conducted, leading to functional end‐capped conducting PEDOT (mPEDOT_SPES), with conductivity of 210 S/cm, 50 S/cm higher than the one of commercial PEDOT. Thanks to the enhancement of solubility, leading to better processability, end‐capped PEDOTs were formulated with a thermoplastic ink, Plastisol®, and electronic circuits were successfully screen printed on flexible cotton substrates, to obtain printed crosslinkable electronic circuits. The conductive features of mPEDOT_SPESs were successfully compared with the ones of PEDOT and of not‐doped end‐capped PEDOTs. POLYM. ENG. SCI., 57:491–501, 2017. © 2017 Society of Plastics Engineers

Homogeneous synthesis and characterization of sulfonated polyarylethersulfones having low degree of sulfonation and highly hydrophilic behavior

In the present paper, the wettability of polyarylethersulfones (PESs) was promoted through the controlled introduction of sulfonic groups in PES polymeric chain. Homogeneous synthesis using a sulfonated comonomer introduced sulfonic groups while exerting a tight control over the degree of sulfonation (DS) and avoiding the undesired side reactions brought about by heterogeneous sulfonation reactions. A series of sulfonated polyarylethersulfones (SPESs) with very low amounts of sulfonic groups - 0.5, 0.75, and 1 meq SO 3 -* g-1 of polymer - was synthesized via polycondensation using 4,4’-difluorodiphenylsulfone, 4,4’-dihydroxydiphenyl and a sulfonated comonomer, 2,5-dihydroxybenzene-1-sulfonate potassium salt. The presence of sulfonic groups was confirmed by Fourier transform infrared (FTIR) spectra; the macromolecular structure and the real DS of SPESs were determined by 1H NMR; the molecular weights were investigated by size exclusion chromatography (SEC); ion exchange capacity (IEC) values, measured by potentiometric titration, are in good agreement with the experimental DS. The polyelectrolyte effect was studied on intrinsic viscosity (IV) measurements. The effect of DS on the thermal properties of SPES membranes was studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC); wetting properties were characterized by static water contact angle (SWCA) measurements on membranes obtained via solution casting. The results showed that an increased DS results in higher glass transition temperatures (T g ) and lower water contact angles, the latter dropping from $$\overline {91} ^\circ $$ to $$\overline {43} ^\circ $$ as DS was raised from 0 to 1.0 meq SO 3 -* g-1. This work demonstrates that homogeneous synthesis of SPES is an efficient way to prepare SPES membranes with tightly controlled DS and enhanced hydrophilic properties, in particular, an excellent hydrophilic SWCA even at very low amounts of sulfonic moieties.

Synthesis and characterization of multi-block poly(arylene ether sulfone) membranes with highly sulfonated blocks for use in polymer electrolyte membrane fuel cells

We synthesized novel sulfonated poly(arylene ether sulfone)s (SPAESs) multi-block copolymer membranes containing highly sulfonated hydrophilic blocks. Two different kinds of multi-block SPAESs sharing the same structure of hydrophobic blocks were proposed to investigate the membrane properties based on the effects of the hydrophilic blocks bearing sulfonic acids. The higher local concentration and acidity of the sulfonic acid groups in the hydrophilic block induced higher proton conductivity. The block SPAESs showed comparable proton conductivities to those of the state-of-the-art perfluorinated sulfonic acid (PFSA) membranes, and their transmission electron microscopy (TEM) images revealed a well-developed phase separation. In particular, the SPAES 4 X10Y10 membrane showed excellent proton conductivity, which was higher than that of the PFSA over the entire relative humidity (RH) range at 80°C. Moreover, the multi-block SPAES membranes showed a comparable fuel cell performance to the Nafion membranes, even at 50% and 30% RH.

Preparation and Characterization of Proton Exchange Membrane Based on Sulfonated Poly(arylene ether sulfone)/Polyacrylonitrile (SPAES/PAN)

Sulfonated poly (arylene ether sulfone) s (SPAESs) exhibit good proton conductivity, thermal and mechanical properties, could act as candidates of proton exchange membranes for fuel cells. At the same time, the poor oxidative stability and excessive swelling ratio of SPAESs bring limitations for its further use. In this article, PAN was employed to mix with SPAES, and then SPAES/PAN blend membranes were prepared from the blend solution by casting. The water uptake, dimensional and oxidative stability, proton conductivity were measured with respect to the addition content of PAN, the phase morphology of the resultant SPAES/PAN were also observed by SEM. The results explained that the corporation of PAN into SPAES could reduce the water uptake and improve the oxidative stability of the obtained membranes compared with the pristine SPAES membrane. That the PAN phase distributed as separated domains in SPAES matrix was found, the interaction between SPAES and PAN may be present, which is responsible for the improvement of dimensional and oxidative stability. Although the proton conductivity of the blend membranes became reduced with increase of PAN content in the SPAES/PAN blend, the conductivity of 0.0265S/cm at 30°C could still be reached, satisfying the requirement for proton exchange membrane Fuel Cell

New highly proton-conducting membrane based on sulfonated poly(arylene ether sulfone)s containing fluorophenyl pendant groups, for low-temperature polymer electrolyte membrane fuel cells

A novel series of sulfonated poly(arylene ether sulfone)s (SPAESs) containing fluorophenyl pendant groups are successfully developed and their membranes are evaluated in low-temperature proton exchange membrane fuel cells. The SPAESs are synthesized from 4,4′-dichlorodiphenylsulfone (DCDPS), 3,3′-disulfonate-4,4′-dichlorodiphenylsulfone (SDCDPS), and (4-fluorophenyl)hydroquinone by nucleophilic aromatic substitution polycondensation. The structure and properties of SPAESs membranes are characterized using 1H-NMR, EA, FT-IR, TG, and DSC, along with the proton conductivity, water uptake, ion exchange capacity and chemical stability. A maximum proton conductivity of 0.35 S cm−1 at 90 °C is achieved for SPAES membrane with 50% SDCDPS. These SPAES membranes display high dimensional stability and oxidative durability, due to the introduction of fluorophenyl pendant groups on the polymer backbone. The fuel cell performances of the MEAs with SPAES reaches an initial power density of 120.6 mW cm−2 at 30 °C, and greatly increases to 224.3 mW cm−2 at 80 °C using H2 and O2 gases.

A capillary water retention effect to improve medium-temperature fuel cell performance

We demonstrate that small and narrow hydrophilic conducting domain morphology in sulfonated aromatic membranes leads to much better fuel cell performance at medium temperature and low humidity conditions than those with larger hydrophilic domains. A comparison of three types of sulfonated poly(arylene ether sulfone)s (SPAES) with random, block, and graft architecture indicates that small hydrophilic domain sizes (<5nm) appear to be important in supporting water retention under low relative humidity (RH) conditions intended for medium temperature (>100°C) fuel cell applications. The graft copolymer outperformed both a random copolymer and multiblock copolymer at 120°C and 35% RH fuel cell operating conditions due to capillary condensation of water within the 3–5nm hydrophilic domains.

Preparation and Characterizations of Novel Ultrafiltration Membranes from Sulfonated Poly (Arylene Ether Sulfone)s

Sulfonated poly(arylene ether sulfone)s (SPAES) with different sulfonation degree (DS) were synthesized through aromatic nucleophilic substitution polymerization, and subsequently used to prepare ultrafiltration membranes by the phase inversion method. The performance and morphological structures of the prepared SPAES membranes were investigated and evaluated for ultrafiltration applications. With DS of 3%, the prepared ultrafiltration membrane showed the largest water permeability with bovine serum albumin rejection over 99%.

Covalent‐ionically crosslinked sulfonated poly(arylene ether sulfone)s bearing quinoxaline crosslinkages as proton exchange membranes

AbstractCrosslinkable sulfonated poly(arylene ether sulfone)s (SPAESs) were synthesized by copolymerization of 4,4′‐biphenol with 2,6‐difluorobenzil, 4,4′‐difluorodiphenyl sulfone, and 3,3′‐disulfonated‐4,4′‐difluorodiphenyl sulfone disodium salt. The corresponding covalent‐ionically crosslinked SPAESs were prepared via the cyclocondensation reaction of benzil moieties in polymer chain with 3,3′‐diaminobenzidine. The crosslinking significantly improved the membrane performance, that is, the crosslinked membranes had the lower membrane dimensional swelling, lower methanol permeability, and higher oxidative stability than the corresponding precursor membranes, with keeping the reasonably high proton conductivity. The crosslinked membrane (CS5) with measured ion exchange capacity of 1.47 meq g−1 showed a reasonably high proton conductivity of 112 mS cm−1 with water uptake of 42 wt % at 80°C, and exhibited a low methanol permeability of 2.1 × 10−7 cm2 s−1 for 32 wt % methanol solution at 25°C. The crosslinked SPAES membranes have potential for PEFC and DMFCs. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Properties and degradation of hydrocarbon fuel cell membranes: a comparative study of sulfonated poly(arylene ether sulfone)s with different positions of the acid groups

Sulfonated fully aromatic polymers with different positions of the acid groups, but with an identical polymer backbone, have been investigated and compared with respect to their properties as proton-exchange membranes. Three different series of sulfonated poly(arylene ether sulfone)s (SPAES) having the same backbone structure were prepared from 4,4′-dichlorodiphenyl sulfone (DCDPS) and 4,4′-dihydroxybiphenyl (BP), each series comprising three levels of the ion exchange capacity (IEC). The first series of SPAES had the sulfonic acid groups placed in ortho positions to the ether bridges (oeSPAES) and were prepared through post-polymerization sulfonation. The second and third series of SPAES carried the sulfonic acid groups in meta (msSPAES) and ortho (osSPAES) positions to the sulfone bridges, respectively, and were prepared by polycondensations of mixtures of BP, DCDPS and either 3,3′-disulfonated or 2,2′-disulfonated DCDPS, respectively. The latter monomer was synthesized via lithiation–sulfination–oxidation of DCDPS. Analysis of solvent cast membranes showed that the osSPAES copolymers had a high dimensional stability in water up to 100 °C, even at high ionic contents. Moreover, the osSPAES and the msSPAES membranes were better at retaining conductivity at reduced relative humidity than the oeSPAES membranes. Thermogravimetry of the membranes in the acid form under air indicated no significant differences based on the placement of the sulfonic acid groups. The resistance towards radical attack was analyzed by 1H NMR spectroscopy after immersing the membranes in Fenton's reagent at 60 °C, and the ability to retain IEC was found to increase in the order oeSPAES < msSPAES < osSPAES. Membrane stability was also studied in an accelerated hydrolysis test by immersing the membranes in 0.1 M aq. HCl at 200 °C in a sealed vessel. The results showed a dramatic loss of sulfonic acid in the oeSPAES membranes, presumably activated by the proximity of the ether bridges. Careful 1H NMR analysis also suggested that the osSPAES polymers degraded by scission of the sulfone bridges. The position of the sulfonic acid groups ortho to the sulfone bridges seemingly destabilized the latter under the severe conditions employed in the test.

Quinoxaline-based crosslinked membranes of sulfonated poly(arylene ether sulfone)s for fuel cell applications

A series of crosslinkable sulfonated poly(arylene ether sulfone)s (SPAESs) were synthesized by copolymerization of 4,4′-biphenol with 2,6-difluorobenzil and 3,3′-disulfonated-4,4′-difluorodiphenyl sulfone disodium salt. Quinoxaline-based crosslinked SPAESs were prepared via the cyclocondensation reaction of benzil moieties in polymer chain with 3,3′-diaminobenzidine to form quinoxaline groups acting as covalent and acid-base ionic crosslinking. The uncrosslinked and crosslinked SPAES membranes showed high mechanical properties and the isotropic membrane swelling, while the later became insoluble in tested polar aprotic solvents. The crosslinking significantly improved the membrane performance, i.e., the crosslinked membranes had the lower membrane dimensional change, lower methanol permeability and higher oxidative stability than the corresponding precursor membranes, with keeping the reasonably high proton conductivity. The crosslinked membrane ( CS1-2) with measured ion exchange capacity of 1.53 mequiv. g −1 showed a reasonably high proton conductivity of 107 mS/cm with water uptake of 48 wt.% at 80 °C, and exhibited a low methanol permeability of 2.3 × 10 −7 cm 2 s −1 for 32 wt.% methanol solution at 25 °C. The crosslinked SPAES membranes have potential for PEFC and DMFCs.