Copoly(arylene ether nitrile) and copoly(arylene ether sulfone) ionomers with pendant sulfobenzoyl groups for proton conducting fuel cell membranes

Three series of fully aromatic ionomers with naphthalene moieties and pendant sulfobenzoyl side chains were prepared via K₂CO₃ mediated nucleophilic aromatic substitution reactions. The first series consisted of poly(arylene ether)s prepared by polycondensations of 2,6‐difluoro‐2′‐sulfobenzophenone (DFSBP) and 2,6‐dihydroxynaphthalene or 2,7‐dihydroxynaphthalene (2,7‐DHN). In the second series, copoly(arylene ether nitrile)s with different ion‐exchange capacities (IECs) were prepared by polycondensations of DFSBP, 2,6‐difluorobenzonitrile (DFBN), and 2,7‐DHN. In the third series, bis(4‐fluorophenyl)sulfone was used instead of DFBN to prepare copoly(arylene ether sulfone)s. Thus, all the ionomers had sulfonic acid units placed in stable positions close to the electron withdrawing ketone link of the side chains. Mechanically strong proton‐exchange membranes with IECs between 1.1 and 2.3 meq g⁻¹ were cast from dimethylsulfoxide solutions. High thermal stability was indicted by high degradation temperatures between 266 and 287 °C (1 °C min⁻¹ under air) and high glass transition temperatures between 245 and 306 °C, depending on the IEC. The copolymer membranes reached proton conductivities of 0.3 S cm⁻¹ under fully humidified conditions. At IECs above ∼1.6 meq g⁻¹, the copolymer membranes reached higher proton conductivities than Nafion^® in the range between −20 and 120 °C. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and properties of multiblock copoly(arylene ether)s containing superacid groups for fuel cell membranes

A series of block copoly(arylene ether)s containing pendant superacid groups were synthesized, and their properties were investigated for fuel cell applications. Two series of telechelic oligomers, iodo‐substituted oligo(arylene ether ketone)s and oligo(arylene ether sulfone)s, were synthesized. The degree of oligomerization and the end groups were controlled by changing the feed ratio of the monomers. The nucleophilic substitution polymerization of the two oligomers provided iodo‐substituted precursor block copolymers. The iodo groups were converted to perfluorosulfonic acid groups via the Ullmann coupling reaction. The high degree of perfluorosulfonation (up to 83%) was achieved by optimizing the reaction conditions. Tough and bendable membranes were prepared by solution casting. The ionomer membranes exhibited characteristic hydrophilic/hydrophobic phase separation with large hydrophilic clusters (ca. 10 nm), which were different from that of our previous random copolymers with similar molecular structure. The block copolymer structure was found to be effective in improving the proton‐conducting behavior of the superacid‐modified poly(arylene ether) ionomer membranes without increasing the ion exchange capacity (IEC). The highest proton conductivity was 0.13 S/cm at 80 °C, 90% relative humidity, for the block copolymer ionomer membrane with IEC = 1.29 mequiv/g. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and properties of sulfonated multiblock copoly(ether sulfone)s by a chain extender

A new series of sulfonated multiblock copoly(ether sulfone)s applicable to proton exchange membrane fuel cells was synthesized. The multiblock copolymers were synthesized by the nucleophilic aromatic substitution of hydroxyl‐terminated oligomers in the presence of highly reactive decafluorobiphenyl (DFB) as a chain extender. Because of the high reactivity of DFB, the ether–ether interchange reaction, which could lead to a randomized polymer architecture, was prevented, and multiblock copolymers with high molecular weights were easily produced. The multiblock copolymers gave tough, flexible, and transparent membranes by solution casting. The ion exchange capacity values could be easily controlled by changing the sulfonated block ratios in the copolymers. The resulting membranes demonstrated good oxidative and dimensional stability and significantly higher proton conductivity than sulfonated random poly(ether sulfone) copolymers. The morphologies of the membranes were investigated by tapping mode atomic force microscopy, which showed that the multiblock membranes had a clear hydrophilic/hydrophobic separated structure. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3947–3957, 2008     

Synthesis and characterization of multiblock partially fluorinated hydrophobic poly(arylene ether sulfone)‐hydrophilic disulfonated poly(arylene ether sulfone) copolymers for proton exchange membranes

Hydrophobic‐hydrophilic sequence multiblock copolymers, based on alternating segments of phenoxide terminated fully disulfonated poly(arylene ether sulfone) (BPS100) and fluorine‐terminated poly(arylene ether sulfone) (6FBPS0) were synthesized and evaluated for application as proton exchange membranes. By utilizing mild reaction conditions the ether–ether interchange reactions were minimized, preventing the randomization of the multiblock copolymers. Tough, ductile, transparent membranes were solution cast from the block copolymers and were characterized with regard to intrinsic viscosity, morphology, water uptake, and proton conductivity. The conductivity values of the 6FBPS0‐BPSH100 membranes were compared to Nafion 212 and a partially fluorinated sulfonated poly(arylene ether sulfone) random copolymer (6F40BP60). The nanophase separated morphology was confirmed by transmission electron microscopy and small angle X‐ray scattering, and enhanced proton conductivity at reduced relative humidity was observed with longer block lengths. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Highly sulfonated multiblock copoly(ether sulfone)s for fuel cell membranes

Highly sulfonated multiblock copoly(ether sulfone)s applicable to proton electrolyte fuel cells (PEFCs) were synthesized by the coupling reaction of corresponding hydroxyl‐ terminated oligomers in the presence of highly reactive decafluorobiphenyl (DFB) as a chain extender, followed by postsulfonation with concentrated sulfuric acid. Their molecular weights were reasonably high as determined by viscosity measurement (η_inh = 0.72–1.58 dL/g). It was also confirmed that postsulfonation selectively took place in hydrophilic segments to yield highly sulfonated multiblock copolymers (IEC = 1.90–2.75 mequiv/g). The resulting polymers gave transparent, flexible, and tough membranes by solution casting. The 4b membrane, as a representative sample, demonstrated good mechanical strength in the dry state regardless of high IEC value (2.75 mequiv/g). The 4a–c membranes with higher IEC values (IEC = 2.75–2.79 mequiv/g) maintained high water uptake (13.7–17.7 wt %) at 50% RH and it was still high (7.4–8.5 wt %) at 30% RH. Proton conductivity of all membranes at 80 °C and 95% RH was higher than that of Nafion 117. Furthermore, the 4a membrane showed high proton conductivity, comparable with Nafion 117 in the range of 50–95% RH, and maintained high proton conductivity (2.3 × 10^?3 S/cm) even at 30% RH. Finally, the surface morphology of the membrane was investigated by tapping mode atomic force microscopy, which showed well‐connected hydrophilic domains that could work as proton transportation channel. This phase separation and the high water uptake behavior probably contributed to high and effective proton conduction in a wide range of relative humidity. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2757–2764, 2010     

Synthesis and characterization of partially disulfonated hydroquinone‐based poly(arylene ether sulfone)s random copolymers for application as proton exchange membranes

Partially disulfonated hydroquinone (HQ)‐based poly(arylene ether sulfone) random copolymers were synthesized and characterized for application as proton exchange membranes. The copolymer composition was varied in the degree of disulfonation. The copolymers were characterized by ¹H NMR, Differential Scanning Calorimetry (DSC), and other analytical techniques. The copolymer with a 25% degree of disulfonation showed the best balance between water uptake and proton conductivity. The copolymers showed substantially reduced methanol permeability compared with Nafion® and satisfactory direct methanol fuel cell performance. The methanol selectivity improved significantly in comparison to Nafion® 117. At a given ionic composition, the HQ‐based system showed higher water uptake and proton conductivity than the biphenol‐based (BPSH‐xx) poly(arylene ether sulfone)s copolymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 384–391, 2009     

Thermal decomposition products of copoly(arylene ether sulfone)s characterized by direct pyrolysis mass spectrometry

Pyrolysis products with mass of up to 850 Da were detected by direct pyrolysis mass spectrometric (DPMS) analysis of a series of copoly(arylene ether sulfone)s (PES-PPO) synthesized by nucleophilic condensation of either 4,4′-dichlorodiphenylsulfone (CDPS) or 4,4′-bis-(4-chlorophenyl sulfonyl) biphenyl (long chain dichloride, LCDC) with different molar ratios of hydroquinone (HQ) or dihydroxydiphenylsulfone (HDPS). Pyrolysis products retaining the repeating units of the initial copolymers were formed at temperatures ranging from 420 °C to 470 °C (near the initial decomposition temperature). At temperatures higher than 450 °C were observed products containing biphenyl units, formed by the elimination process of SO₂ from diphenyl sulfone bridges. Products having biphenyl and dibenzofuran moieties were detected in the mass spectra recorded at temperatures above 550 °C. These units were formed by loss of hydrogen atom from diphenyl ether bridges. Although the EI (18 eV) mass spectra of the pyrolysis products of the samples investigated were very similar, it was found that the relative intensity of some ions reflects the molar composition of the copolymers analysed. Cyclic and linear oligomers with very low molecular mass, present in the crude copolymers, were also detected by DPMS. Thermogravimetric analysis also showed their excellent thermal stability below 400 °C. It indicates that the copolymers yield a char residue of 40-45% at 800 °C, which increases with the PPO mole fraction in the samples.     

Synthesis and proton conductivity of sulfonated,multi‐phenylated poly(arylene ether)s

A series of sterically‐encumbered, sulfonated, poly(arylene ether) copolymers were synthesized and their proton conductivity examined. The series was prepared by copolymerizing a novel monomer, 2″,3″,5″,6″‐tetraphenyl‐[1,1′:4',1″:4″,1″':4″',1″″‐quinquephenyl]‐4,4″″‐diol, with 4,4'‐difluorobenzophenone and bisphenol A. Subsequent sulfonation and solution casting provided membranes possessing ion exchange capacities of 1.9 to 2.7 mmol/g and excellent mechanical properties (Young's modulus, 0.2–1.2 GPa; tensile strength, 35–70 MPa; elongation at break, 62–231%). Water uptake ranged from 34 to 98 wt% at 80 °C/100% RH. Proton conductivities ranged between 0.24 to 16 mS/cm at 80 °C/60% RH, and 3 to 167 mS/cm at 80 °C/95% RH. TEM analysis of the polymers, in the dehydrated state, revealed isolated spherical aggregates of ions, which presumably coalesce when hydrated to provide highly conductive pathways. The strategy of using highly‐encumbered polymer frameworks for the design of mechanically‐robust and dimensionally‐stable proton conducting membranes is demonstrated. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2579‐2587     

Sulfonated poly(ether sulfone)s with binaphthyl units as proton exchange membranes for fuel cell application

Sulfonated poly(ether sulfone)s containing binaphthyl units (BNSHs) were successfully prepared for fuel cell application. BNSHs, which have very simple structures, were easily synthesized by postsulfonation of poly(1,1′‐dinaphthyl ether phenyl sulfone)s and gave tough, flexible, and transparent membranes by solvent casting. The BNSH membranes showed low water uptake compared to a typical sulfonated poly(ether ether sulfone) (BPSH‐40) membrane with a similar ion exchange capacity (IEC) value and water insolubility, even with a high IEC values of 3.19 mequiv/g because of their rigid and bulky structures. The BNSH‐100 membrane (IEC = 3.19 mequiv/g) exhibited excellent proton conductivity, which was comparable to or even higher than that of Nafion 117, over a range of 30–95% relative humidity (RH). The excellent proton conductivity, especially under low RH conditions, suggests that the BNSH‐100 membrane has excellent proton paths because of its high IEC value, and water insolubility due to the high hydrophobicity of the binaphthyl structure. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5827–5834, 2009     

Highly proton conducting proton‐exchange membranes based on fluorinated poly(arylene ether ketone)s with octasulfonated segments

A new bisphenol monomer containing a pair of electron‐rich tetra‐arylmethane units was designed and synthesized. Based on this monomer, along with commercial 4,4′‐(hexafluoroisopropylidene)diphenol A and 4,4′‐difluorobenzophenone, a series of novel poly(arylene ether ketone)s containing octasulfonated segments of varying molar percentage (x) (6F‐SPAEK‐x) were successfully synthesized by polycondensation reactions, followed by sulfonation. Tough, flexible, and transparent membranes, exhibiting excellent thermal stabilities and mechanical properties were obtained by casting. 6F‐SPAEK‐x samples exhibited appropriate water uptake and swelling ratios at moderate ion exchange capacities (IECs) and excellent proton conductivities. The highest proton conductivity (215 mS cm⁻¹) is observed for hydrated 6F‐SPAEK‐15 (IEC = 1.68 meq g⁻¹) at 100 °C, which is more than 1.5 times that of Nafion 117. Furthermore, the 6F‐SPAEK‐10 membrane exhibited comparable proton conductivity (102 mS cm⁻¹) to that of Nafion 117 at 80 °C, with a relatively low IEC value (1.26 meq g⁻¹). Even under 30% relative humidity, the 6F‐SPAEK‐20 membrane (2.06 meq g⁻¹) showed adequate conductivity (2.1 mS cm⁻¹) compared with Nafion 117 (3.4 mS cm⁻¹). The excellent comprehensive properties of these membranes are attributed to well‐defined nanophase‐separated structures promoted by strong polarity differences between highly ionized and fluorinated hydrophobic segments. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 25–37     

Energy material - the role of silicotungstic acid and fly ash in sulfonated poly (ether sulfone) composites for PEMFC applications

The composite polymer electrolyte membranes were prepared from sulfonated poly (ether sulfone) (SPES), silicotungstic acid (STA) and fly ash (FA). Post sulfonation process was adopted to synthesize SPES using sulphuric and chlorosulfonic acid. The prepared electrolyte membranes were examined by water uptake capacity, swelling ratio, ion-exchange ability, proton conductivity, thermal stability and electrochemical performance for evaluating the pertinence of these membranes in fuel cell applications. As such the pristine membrane restricts with the proton conductivity of 0.042?S cm^?1 at 30?°C and 0.060?S cm^?1 at 90?°C while the polymer composite membrane, SP-STA-FA-10 reveals the maximum conductivity of 0.054?S cm^?1 at 30?°C and 0.073?S cm^?1 at 90?°C. It also exhibits good thermal stability than that of the pure membrane. The membrane electrode assemblies (MEAs) have been successfully developed from SPES as well as SP-STA-FA-10 membranes and their electrochemical performance were studied the wide range of current density. Herein, the composite membranes derived from SPES, STA and FA can be viable candidates for fuel cell applications.     

Locally sulfonated poly(ether sulfone)s with highly sulfonated units as proton exchange membrane

Novel locally sulfonated poly(ether sulfone)s with highly sulfonated units were successfully synthesized for fuel cell applications. Poly(ether sulfone)s were prepared by the nucleophilic substitution of bis(4‐fluorophenyl) sulfone with 1,2,4,5‐tetrakis([1,1′‐biphenyl]‐2‐oxy)‐3,6‐bis(4‐hydroxyphenoxy)benzene and bis(4‐hydroxyphenyl) sulfide, followed by oxidation using m‐chloroperoxybenzoic acid. The desired highly sulfonated units were easily introduced by postsulfonation and each one had ten sulfonic acid groups. The sulfonated polymers gave tough, flexible, and transparent membranes by solvent casting. The high contrast in polarity between highly sulfonated units and hydrophobic poly(ether sulfone) units enabled the formation of defined phase‐separated structures and well‐connected proton paths. The sulfonated polymers exhibited excellent proton conductivity over a wide range of relative humidities. The proton conductivity of the sulfonated polymer with an ion exchange capacity value of 2.38 mequiv/g was comparable to that of Nafion 117 even at 30% relative humidity. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3444–3453, 2009     

Synthesis of highly sulfonated poly(arylene ether sulfone) random (statistical) copolymers via direct polymerization

Novel biphenol‐based wholly aromatic poly (arylene ether sulfones) containing pendant sulfonate groups were prepared by direct aromatic nucleophilic substitution polycondensation of disodium 3,3′‐disulfonate‐4,4′‐dichlorodiphenyl sulfone (SDCDPS), 4,4′‐dichlorodiphenylsulfone (DCDPS) and biphenol. Copolymerization proceeded quantitatively to high molecular weight in N‐methyl‐2‐pyrrolidinone at 190°C in the presence of anhydrous potassium carbonate. Tough membranes were successfully cast from the control and the copolymers, which had a SDCDPS/DCDPS mole ratio of either 40:60 or 60:40 using N,N‐dimethylactamide; the 100% SDCDPS homopolymer was water soluble. Short‐term aging (30 min) indicates that the desired acid form membranes are stable to 220°C in air and conductivity values at 25°C of 0.110 (40%) and 0.170 S/cm (60%) were measured, which are comparable to or higher than the state‐of‐the art fluorinated copolymer Nafion 1135 control. The new copolymers, which contain ion conductivity sites on deactivated rings, are candidates as new polymeric electrolyte materials for proton exchange membrane (PEM) fuel cells. Further research comparing their membrane behavior to post‐sulfonated systems is in progress.     

Synthesis and sulfonation of poly(arylene ether)s containing tetraphenyl methane moieties

Novel poly(arylene ether)s with sulfonic acid containing pendent groups were successfully synthesized by the nucleophilic displacement of aromatic dihalides with bisphenols in an aprotic solvent in the presence of excess potassium carbonate followed by sulfonation with chlorosulfonic acid. The sulfonation took place only at the controlled positions on the phenyl rings due to the novel bisphenol structures designed. The sulfonic acid group containing polymers were very soluble in common organic solvents, such as dimethyl sulfoxide, N,N′‐dimethylacetamide, and dimethylformamide, but swelled only slightly in water. These sulfonic acid group containing polymers were readily cast into tough and smooth films from organic solvents. The synthesized polymers had high glass‐transition temperatures of 171.0–240.7 °C and high molecular weights of 15,600–33,000 Da. These films could potentially be used as proton‐exchange membranes for fuel cells. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1779–1788, 2004     

Tensile behavior of Nafion and sulfonated poly(arylene ether sulfone) copolymer membranes and its morphological correlations

The tensile stress–strain behavior of Nafion 117 and sulfonated poly(arylene ether sulfone) copolymer (BPSH35) membranes were explored with respect to the effects of the strain rate, counterion type, molecular weight, and presence of inorganic fillers. The yielding properties of the two films were most affected by the change in the strain rate. The stress–strain curves of Nafion films in acid and salt forms exhibited larger deviations at strains above the yield strain. As the molecular weight of the BPSH35 samples increased, the elongation at break improved significantly. Enhanced mechanical properties were observed for the composite membrane of BPSH35 and zirconium phenylphosphonate (2% w/w) in comparison with its matrix BPSH35 film. The stress‐relaxation behavior of Nafion and BPSH35 membranes was measured at different strain levels and different strain rates. Master curves were constructed in terms of plots of the stress‐relaxation modulus and time on a double‐logarithm scale. A three‐dimensional bundle‐cluster model was proposed to interpret these observations, combining the concepts of elongated polymer aggregates, proton‐conduction channels, and states of water. The rationale focused on the polymer bundle rotation/interphase chain readjustment before yielding and polymer aggregate disentanglements and reorientation after yielding. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1453–1465, 2006     

Sulfonated multiblock copoly(ether sulfone)s as membrane materials for fuel cell applications

Arylene ether multiblock copolymers of the (AB)_n-type with various degrees of sulfonation have been prepared by a two-step polycondensation procedure. Multiblock copolymers in high yields and of high molecular weights were obtained. For comparison random copolymers with the same overall composition were synthesized. The theoretical ion-exchange capacities (IEC) of the materials were ranging from 0.50 mmol/g to 1.25 mmol/g. The water-uptake of the multiblock copolymers showed a linear dependency from the IEC and was increasing with increasing IEC. No differences were observed between random and block copolymers. Furthermore, the hydrolytic stability of aromatic sulfonic acid groups was investigated in this study. Aromatic sulfonic acids, having additional electron donating groups, especially in ortho- or para-position to the sulfonic acid group are sensitive to hydrolytic desulfonation. On the other hand electron-withdrawing groups in meta-position showed a stabilizing effect.     

Ionomers for proton exchange membrane fuel cells by sulfonation of novel dendritic multiblock copoly(ether‐sulfone)s

The synthesis and properties of the first examples of dendritic multiblock co PES s, bearing sulfonated dendritic clusters, that form strong membranes are described. End‐capped dendritic multiblock co PES s with various average block lengths (n = 50–80) were synthesized by two‐step reactions. The synthesis of dendritic blocks consisting of difunctional dendritic block and monofunctional dendritic end‐group was accomplished by an aromatic nucleophilic substitution reaction of hexakis(4‐(4‐fluorophenylsulfonyl)phenyl)benzene with varying amounts of 1‐(4‐hydroxyphenyl)‐2,3,4,5,6‐pentaphenylbenzene, which provides a number of pendant phenyl rings as postsulfonation sites. Polycondensation of a controlled molar ratio between 4,4′‐dihydroxybenzophenone and bis(4‐fluorophenyl)sulfone monomers was carried out in the presence of the difunctional and monofunctional dendritic blocks in sulfolane at 215 °C for 3.5 h. Essentially six sulfonic acid groups were introduced into each hexaphenylbenzene moiety on the dendritic blocks by reaction with a large excess of chlorosulfonic acid, followed by hydrolysis with KOH aqueous solution. The introduction of longer average blocks (n = 60–80) into the dendritic PES s improved the mechanical properties of the resulting sulfonated dendritic PES membranes. At a level of IEC (0.92–1.26 meq/g) similar to Nafion (0.91 meq/g), PES membranes showed proton conductivities (58–67 mS/cm) comparable with that of Nafion (99 mS/cm). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5461–5473, 2009