Preparation and characterization of branched and linear sulfonated poly(ether ketone sulfone) proton exchange membranes for fuel cell applications

Branched sulfonated poly(ether ketone sulfone)s (Br‐SPEKS) were prepared with bisphenol A, bis(4‐fluorophenyl)sulfone, 3,3′‐disodiumsulfonyl‐4,4′‐difluorobenzophenone, and THPE (1,1,1‐tris‐p‐hydroxyphenylethane), respectively, at 180 °C using potassium carbonate in NMP (N‐methylpyrrolidinone). THPE, as a branching agent, was used with 0.4 mol % of bisphenol A to synthesize branched copolymers. Copolymers containing 10–50 mol % disulfonated units were cast from dimethylsulfoxide solutions to form films. Linear sulfonated poly(ether ketone sulfone)s (SPEKS) were also synthesized without THPE. The films were converted from the salt to acid forms with dilute hydrochloric acid. A series of copolymers were studied by Fourier transform infrared, ¹H‐NMR spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Sorption experiments were conducted to observe the interaction of sulfonated polymers with water and methanol. The ion‐exchange capacity (IEC), a measure of proton conductivity, was evaluated. The synthesized Br‐SPEKS and SPEKS membranes exhibit conductivities (25 °C) from 1.04 × 10^?3 to 4.32 × 10^?3 S/cm, water swell from 20.18 to 62.35%, IEC from 0.24 to 0.83 mequiv/g, and methanol diffusion coefficients from 3.2 × 10^?7 to 4.7 × 10^?7 cm²/S at 25 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1792–1799, 2008     

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     

Direct copolymerization of sulfonated poly(phthalazinone arylene ether)s for proton‐exchange‐membrane materials

Sulfonated poly(phthalazinone ether ketone) (SPPEK) copolymers and sulfonated poly(phthalazinone ether sulfone) (SPPES) copolymers containing pendant sodium sulfonate groups were prepared by direct copolymerization. The reaction of disodium 3,3′‐disulfonate‐4,4′‐difluorobenzophenone (SDFB‐Na), 4,4′‐difluorobenzophenone (DFB), and 4‐(4‐hydroxyphenyl)‐1(2H)‐phthalazinone (DHPZ) at 170 °C in N‐methyl‐2‐pyrrolidione containing anhydrous potassium carbonate gave SPPEKs. SPPESs were similarly obtained with 3,3′‐disulfonate‐4,4′‐difluorophenyl sulfone, 4‐fluorophenyl sulfone (DFS), and DHPZ as monomers. The sulfonic acid groups, being on deactivated positions of the polymer backbone, were expected to be hydrolytically more stable than postsulfonated polymers. Fourier transform infrared and ¹H NMR were used to characterize the structures and degrees of sulfonation of the sulfonated polymers. Membrane films of SPPEKs with SDFB‐Na/DFB molar feed ratios of up to 60/40 and SPPESs with sulfonated 4‐fluorophenyl sulfone/DFS molar feed ratios of up to 50/50 were cast from N,N‐dimethylacetamide polymer solutions. Membrane films in acid form were then obtained by the treatment of the sodium‐form membrane films in 2 N sulfuric acid at room temperature. An increase in the number of sulfonate groups in the copolymers resulted in an increased glass‐transition temperature and enhanced membrane hydrophilicity. The sodium‐form copolymers were thermally more stable than their acid forms. The proton conductivities of the acid‐form copolymers with sulfonated monomer/unsulfonated monomer molar feed ratios of 0.5 and 0.6 were higher than 10^?2 S/cm and increased with temperature; they were less temperature‐dependent than those of the postsulfonated products. SPPESH‐50 showed higher conductivity than the corresponding postsulfonated poly(phthalazinone ether sulfone). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2731–2742, 2003     

Synthesis and properties of sulfonated polyimides from homologous sulfonated diamines bearing bis(aminophenoxyphenyl)sulfone

Three homologous sulfonated diamines bearing a bis(aminophenoxyphenyl)sulfone structure, namely, bis[4‐(4‐aminophenoxy)phenyl]sulfone‐3,3′‐disulfonic acid (pBAPPS‐3DS), bis[4‐(4‐aminophenoxy)phenyl]sulfone‐2,2′‐disulfonic acid (pBAPPS‐2DS), and bis[4‐(4‐aminophenoxy)‐2‐(3‐sulfobenzoyl)phenyl]sulfone (pBAPPS‐2DSB), were synthesized. A series of sulfonated polyimides (SPIs) were synthesized from 1,4,5,8‐naphthalene tetracarboxylic dianhydride, these sulfonated diamines, and nonsulfonated diamines, and their properties were investigated in comparison with those reported for the SPIs from another homologous diamine or bis[4‐(3‐aminophenoxy)phenyl]sulfone‐3,3′‐disulfonic acid (mBAPPS‐3DS). These SPIs were soluble in common aprotic solvents and showed reasonably high proton conductivity, except for pBAPPS‐2DS‐based SPIs, the conductivity of which was slightly lower because of the lower water uptake. The water stability of these SPIs considerably depended on the structure of the sulfonated diamines and was in the order of pBAPPS‐2DSB ≈ pBAPPS‐2DS > pBAPPS‐3DS ? mBAPPS‐3DS. Their water stability was much lower than that of the SPIs from 4,4′‐bis(4‐aminophenoxy)biphenyl‐3,3′‐disulfonic acid. The reason was discussed on the basis of the basicity of the sulfonated diamine and the solubility property of the SPIs. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2797–2811, 2007     

Membranes from poly(aryl ether)‐based ionomers containing multiblock segments of randomly distributed nanoclusters of 18 sulfonic acid groups

Multiblock copolymers 1a (M_n = 31,500–47,400) of sulfonated poly(aryl ether)s were synthesized by polycondensation of 4,4′‐difluorobenzophenone (DFBP), bis(4‐hydroxyphenyl)sulfone (BHPS), and an hydroxy‐terminated sulfonated oligomer, which was synthesized from DFBP and 2,2′,3,3′,5,5′‐hexaphenyl‐4,4′‐dihydroxybiphenyl a . The copolymerization of trimeric monomer b with DFBP and BHPS gave a series of copolymers 1b (M_n = 26,200–45,900). The copolymers were then sulfonated with chlorosulfonic acid to give ionomers 3a with hydrophilic multiblock segments and ionomers 3b with segments containing clusters of 18 sulfonic acid groups. The proton exchange membranes cast from ionomers 3a and 3b were characterized with regard to thermal stability, water uptake, proton conductivity, and morphology. Transmission electron microscopy images of 3a‐1 and 3b‐1 revealed a phase separation similar to that of Nafion that may explain their higher proton conductivities compared with randomly sulfonated copolymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4762–4773, 2009     

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 properties of novel benzimidazole‐containing sulfonated polyethersulfones for fuel cell applications

A novel series of benzimidazole‐containing sulfonated poly(arylene sulfones)s with controllable amount of basic 2,6‐bis(benzimidazol‐2‐yl)pyridine (BIP) and sulfonic acid groups have been prepared by the copolycondensation of a new BIP‐containing arylene difluoride monomer (DFSBIP) with a sulfonated arylene difluoride (DSDFS) and 4,4′‐biphenol (BP). All the resulting polymers have high molecular weights, good thermal stability, and can form uniform and tough membranes by simple solution casting. Because of the strong acid–base interaction between BIP and sulfonic acid groups, ionic crosslinking networks forms that resulted in polymer membranes with good dimensional stability in water even at high temperature (e.g., 100 °C). The ion exchange capacity (IEC) of the polymer membranes was investigated through a new simple pH‐determination method. A comparison between the experimental IEC values with the calculated ones based on the polymer structures indicated that each BIP unit interacted with one sulfonic acid group. Thus, by controlling the relative content of BIP units and sulfonate groups in the polymers, the intra‐ and intermolecular acid–base interactions could be readily optimized so as to achieve polymers with high IEC values, high proton conductivities as well as low swelling ratios, demonstrating good potential for proton exchange membrane applications. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1920–1929, 2009     

Synthesis of sulfonated aromatic poly(ether amide)s and their application to proton exchange membrane fuel cells

A series of wholly aromatic sulfonated poly(ether amide)s (SPEAs) containing a sulfonic acid group on the dicarbonyl aromatic ring were prepared via a polycondensation reaction of sulfonated terephthalic acid (STA), terephthalic acid (TA), and aromatic diamine monomers. The degree of sulfonation was readily controlled by adjusting the monomer feed ratio of STA and TA in the polymerization process, and randomly sulfonated polymers with an ion exchange capacity (IEC) of 1.0–1.8 mequiv/g were prepared using this protocol. The chemical structures of randomly sulfonated polymers were characterized using NMR and FT‐IR spectroscopies. Gel permeation chromatography analysis of SPEAs indicated the formation of high‐molecular‐weight sulfonated polymer. Tough and flexible SPEA membranes were obtained from solution of N,N‐dimethylacetamide, and thermogravimetric analysis of these membranes showed a high degree of thermal stability. Compared with previously reported sulfonated aromatic polyamides, these new SPEAs showed a significantly lower water uptake of 10–30%. In proton conductivity measurements, ODA‐SPEA‐70 (IEC = 1.80 mequiv/g), which was obtained from polycondensation of 4,4′‐oxydianiline and 70 mol % STA, showed a comparable proton conductivity (105 mS/cm) to that of Nafion 117 at 80 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 485–496, 2009     

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 multiblock sulfonated poly(arylene ether sulfone) membranes with different hydrophilic moieties for application in polymer electrolyte membrane fuel cell

Multiblock sulfonated poly(arylene ether sulfone)s were synthesized to investigate the structural effects on their membrane properties. Three different types of sulfonated hydrophilic blocks were used; their structures possessed different acidity and local concentration of sulfonic acid groups. For the comparison between the block copolymers, a hydrophobic block with the same chemical structure and block length was used. The different acidities and local concentration were achieved using different sulfonation methods, such as postsulfonation and direct condensation with sulfonated monomers, and different monomers for preparing the hydrophilic block. The higher acidity and concentration of sulfonic acid groups resulted in higher proton conductivity under certain relative humidity conditions and phase separation as shown in the transmission electron microscopy analysis. The synthesized oligomers and polymers were well characterized, and the other physical properties were also investigated. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2947–2957     

Polybenzimidazole block sulfonated poly(arylene ether sulfone) ionomers

Novel ionomers based on polybenzimidazole block sulfonated poly(arylene ether sulfone) show excellent thermal properties. The ionic aggregation of sulfonic acid groups leads to well-developed phase separated morphology and thus high proton conductivity at wide humidity range, up to 65 mS cm(-1) at 90% relative humidity.     

Synthesis and characterization of sulfonated poly(phthalazinone ether phosphine oxide)s by direct polycondensation for proton exchange membranes

A series of sulfonated poly(phthalazinone ether phosphine oxide)s (sPPEPO) were prepared via aromatic nucleophilic substitution polycondensation of 4‐(4‐hydroxyphenyl) phthalazinone (HPPZ) with sulfonated bis(4‐fluorophenyl)phenyl phosphine oxide (sBFPPO) and bis(4‐fluorophenyl)phenyl phosphine oxide (BFPPO) at various ratios. The properties such as molecular weight, ion exchange capacity (IEC), swelling, thermal stability, proton conductivity, and morphology were investigated. sPPEPO with high IEC exhibited high proton conductivity while they still showed low swelling. Typically, sPPEPO with IEC of 1.54 and 1.69 meq/g exhibited high conductivity of 0.091 and 0.19 S/cm, and low swelling ratios of 14.3% and 19.5% at 80 °C, respectively. The low swelling was attributed to the strong intermolecular interaction including the electrostatic force and hydrogen bond. sPPEPO would be promising candidates used as polyelectrolyte membranes for fuel cells. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1758–1769, 2008     

Investigation of sulfonated poly(ether ether ketone sulfone)/heteropolyacid composite membranes for high temperature fuel cell applications

The sulfonated poly(ether ether ketone sulfone) (SPEEKS)/heteropolyacid (HPA) composite membranes with different HPA content in SPEEKS copolymers matrix with different degree of sulfonation (DS) were investigated for high temperature proton exchange membrane fuel cells. Composite membranes were characterized by Fourier transfer infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). FTIR band shifts suggested that the sulfonic acid groups on the copolymer backbone strongly interact with HPA particles. SEM pictures showed that the HPA particles were uniformly distributed throughout the SPEEKS membranes matrix and particle sizes decreased with the increment of copolymers' DS. The holes were not found in SPEEKS‐4/HPA30 (consisting of 70% SPEEKS copolymers with DS = 0.8 and 30% HPA) composite membrane after composite membranes were treated with boiling water for 24 h. Thermal stabilities of the composite membranes were better than those of pure sulfonated copolymers membranes. Although the composite membranes possessed lower water uptake, it exhibited higher proton conductivity for SPEEKS‐4/HPA30 especially at high temperature (above 100 °C). Its proton conductivity linearly increased from 0.068 S/cm at 25 °C to 0.095 S/cm at 120 °C, which was higher than 0.06 S/cm of Nafion 117. In contrast, proton conductivity of pure SPEEKS‐4 membrane only increased from 0.062 S/cm at 25 °C to 0.078 S/cm at 80 °C. At 120 °C, proton conductivity decreased to poor 0.073 S/cm. The result indicated that composite membranes exhibited high proton conductivity at high temperature. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1967–1978, 2006     

Effect of acidification treatment and morphological stability of sulfonated poly(arylene ether sulfone) copolymer proton‐exchange membranes for fuel‐cell use above 100 °C

Directly copolymerized wholly aromatic sulfonated poly(arylene ether sulfone) copolymers derived from 4,4′‐biphenol, 4,4′‐dichlorodiphenyl sulfone, 3,3′‐disulfonated, and 4,4′‐dichlorodiphenyl sulfone (BPSH) were evaluated as proton‐exchange membranes for elevated temperature operation (100–140 °C). Acidification of the copolymer from the sulfonated form after the nucleophilic step (condensation) copolymerization involved either immersing the solvent‐cast membrane in sulfuric acid at 30 °C for 24 h and washing with water at 30 °C for 24 h (method 1) or immersion in sulfuric acid at 100 °C for 2 h followed by similar water treatment at 100 °C for 2 h (method 2). The fully hydrated BPSH membranes treated by method 2 exhibited higher proton conductivity, greater water absorption, and less temperature dependence on proton conductivity as compared with the membranes acidified at 30 °C. In contrast, the conductivity and water absorption of a control perfluorosulfonic acid copolymer (Nafion 1135) were invariant with treatment temperature; however, the conductivity of the Nafion membranes at elevated temperature was strongly dependent on heating rate or temperature. Tapping‐mode atomic force microscope results demonstrated that all of the membranes exposed to high‐temperature conditions underwent an irreversible change of the ionic domain microstructure, the extent of which depended on the concentration of sulfonic acid sites in the BPSH system. The effect of aging membranes based on BPSH and Nafion at elevated temperature on proton conductivity is also discussed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2816–2828, 2003     

Sulfonated poly(aryl ether ether ketone ketone)s containing fluorinated moieties as proton exchange membrane materials

A series of sulfonated poly(aryl ether ether ketone ketone)s statistical copolymers with high molecular weights were synthesized via an aromatic nucleophilic substitution polymerization. The sulfonation content (SC), defined as the number of sulfonic acid groups contained in an average repeat unit, could be controlled by the feed ratios of monomers. Flexible and strong membranes in sodium sulfonate form could be prepared by the solution casting method, and readily transformed to their proton forms by treating them in 2 N sulfuric acid. The polymers showed high T_gs, which increased with an increase in SC. Membranes prepared from the present sulfonated poly(ether ether ketone ketone) copolymers containing the hexafluoroisopropylidene moiety (SPEEKK‐6F) and copolymers containing the pendant 3,5‐ditrifluoromethylphenyl moiety (SPEEKK‐6FP) had lower water uptakes and lower swelling ratios in comparison with previously prepared copolymers containing 6F units. All of the polymers possessed proton conductivities higher than 1 × 10^?2 S/cm at room temperature, and proton conductivity values of several polymers were comparable to that of Nafion at high relative humidity. Their thermal stability, oxidative stability, and mechanical properties were also evaluated. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2299–2310, 2006     

Partially fluorinated sulfonated poly(arylene sulfone)s blended with polybenzimidazole

A partially fluorinated and sulfonated poly(arylene sulfone) (SPSO) was successfully synthesized via nucleophilic polycondensation of 2,2‐bis(4‐fluorophenyl)hexafluoro‐propane with 4,4′‐thiobisbenzenethiol (TBBT). In a second step, the prepared poly(arylene sulfide) was oxidized to SPSO. The polymer was blended with the polybenzimidazole PBIOO^® to obtain a mechanically stable membrane. This film was compared with other polymer blends, which were synthesized in our group in the last years. We were especially interested in the influence of different bridging groups such as ether, ketone, and sulfone groups. The affect on properties such as water uptake (WU), thermal stability, proton conductivity, and oxidative stability were analyzed in this work. Additionally, the blend membranes were characterized by gel permeation chromatography. The novel SPSO blend shows a high molecular weight, and its blend membrane with PBIOO has an excellent onset of ? SO₃H group splitting‐off temperature (T_onset) of 334 °C. The proton conductivity amounts to 0.11 S cm^?1, and the water uptake reaches 30%. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of novel crosslinked sulfonated poly(ether sulfone)s using bisazide and their properties for fuel cell application

Novel crosslinked sulfonated poly(ether sulfone)s (PESs) were prepared by thermal irradiation of the allyl-terminated telechelic sulfone polymers using a bisazide. The sulfonated polymers in different comonomer compositions were fully characterized by ¹H NMR, and the crosslinked structure was also verified by FT-IR spectroscopic analyses. Having both the uniform distribution of the hydrophilic conductive sites and controlled hydrophobic nature by minimized crosslinking over the rigid rod poly(ether sulfone) backbone, the crosslinked polymer membrane (PES-60) offered excellent proton conductivity of 0.79 S cm⁻¹ at 100 °C together with hydrolytic and oxidative stability. In addition, only 17% of methanol permeability of the Nafion^® was observed for the crosslinked PES-60.     

Sulfonated carbon nanotubes/sulfonated poly(ether sulfone ether ketone ketone) composites for polymer electrolyte membranes

A series of composite membranes consisting of sulfonated carbon nanotubes (sCNTs) and sulfonated poly(ether sulfone ether ketone ketone) were successfully fabricated via the solution casting method. The chemical structure, as well as the long‐term stability of the sCNTs in different solvents, was investigated by Fourier transform infrared (FTIR) analysis and solubility experiment, respectively. The morphology, tensile strength, proton conductivity, and methanol permeability of the composite membranes were also investigated. The scanning electron microscope (SEM) observation indicated the good dispersion of the carbon nanotubes in polymer matrix as well as the strong interfacial bonding between the sulfonated poly(ether sulfone ether ketone ketone) (SPESEKK) matrix and sCNTs. The addition of either pristine carbon nanotubes or modified carbon nanotubes significantly enhanced the tensile strength of the SPESEKK membrane. The proton conductivity of the SPESEKK membrane increased while the methanol permeability decreased as the sCNTs content increased, showing a strong interaction between the modified nanotubes and SPESEKK. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis of highly sulfonated polybenzimidazoles by direct copolymerization and grafting

A series of highly sulfonated, ether‐containing polybenzimidazoles (SOPBI) with controlled sulfonation degrees were synthesized from various stoichiometric ratio mixtures of sodium 6,6'‐oxybis(3‐carboxybenzenesulfonate) (SODBA), 4,4'‐oxydibenzoic acid (ODBA), and 3,3'‐diaminobenzidine (DAB) by solution copolycondensation in poly(phosphoric acid). The resulting sulfonated polymers were further sulfonated by grafting of pendant sulfonic acid chains via a reaction of 1,3‐propane sultone with lithiated‐N of the imidazole rings in the polymer backbone, yielding materials with high, absolute IEC values (3.42–4.15 meq g^?1). Due to self‐neutralization, the solid state polymers possessed “free” acid content of 1.40 to 2.15 meq g^?1, were soluble in organic solvents yet insoluble in aqueous solution, while displaying proton conductivites (11–47 mS cm^?1) at elevated temperatures (80 °C, 95% RH). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3654–3666