Segmented sulfonated poly(arylene ether sulfone)‐b‐polyimide copolymers for proton exchange membrane fuel cells. I. Copolymer synthesis and fundamental properties

Segmented disulfonated poly(arylene ether sulfone)‐b‐polyimide copolymers based on hydrophilic and hydrophobic oligomers were synthesized and evaluated for use as proton exchange membranes (PEMs). Amine terminated sulfonated poly (arylene ether sulfone) hydrophilic oligomers and anhydride terminated naphthalene based polyimide hydrophobic oligomers were synthesized via step growth polymerization including high temperature one‐pot imidization. Synthesis of the multiblock copolymers was achieved by an imidization coupling reaction of hydrophilic and hydrophobic oligomers oligomers in a m‐cresol/NMP mixed solvent system, producing high molecular weight tough and ductile membranes. Proton conductivities and water uptake increased with increasing ion exchange capacities (IECs) of the copolymers as expected. The morphologies of the multiblock copolymers were investigated by tapping mode atomic force microscopy (TM‐AFM) and their measurements revealed that the multiblock copolymers had well‐defined nano‐phase separated morphologies which were clearly a function of block lengths. Hydrolytic stability test at 80 °C water for 1000 h showed that multiblock copolymer membranes retained intrinsic viscosities of about 80% of the original values and maintained flexibility which was much improved over polyimide random copolymers. The synthesis and fundamental properties of the multiblock copolymers are reported here and the systematic fuel cell properties will be provided in a separate article. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4879–4890, 2007     

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     

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     

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     

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 characterization of poly(arylene ether ketone)s bearing pendant sulfonic acid groups for proton exchange membrane materials

A bisphenol monomer (2,5‐dimethoxy)phenylhydroquinone was prepared and further polymerized to obtain poly(arylene ether ketone) copolymers containing methoxy groups. After demethylation and sulfobutylation, a series of novel poly(arylene ether ketone)s bearing pendant sulfonic acid group (SPAEKs) with different sulfonation content were obtained. The chemical structures of all the copolymers were analyzed by ¹H NMR and ¹³C NMR spectra. Flexible and tough membranes with reasonably good mechanical properties were prepared. The resulting side‐chain‐type SPAEK membranes showed good dimensional stability, and their water uptake and swelling ratio were lower than those of conventional main‐chain‐type SPAEK membranes with similar ion exchange capacity. Proton conductivities of these side‐chain‐type sulfonated copolymers were higher than 0.01 S/cm and increased gradually with increasing temperature. Their methanol permeability values were in the range of 1.97 × 10^?7–5.81 × 10^?7 cm²/s, which were much lower than that of Nafion 117. A combination of suitable proton conductivities, low water uptake, low swelling ratio, and high methanol resistance for these side‐chain‐type SPAEK films indicated that they may be good candidate material for proton exchange membrane in fuel cell applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis and characterization of poly(aryl ether ketone) ionomers with sulfonic acid groups on pendant aliphatic chains for proton-exchange membrane fuel cells

A series of parent poly(aryl ether ketone)s bearing different content of unsaturated pendant propenyl groups were synthesized via nucleophilic substitution polymerization from 3,3′-diallyl-4,4′-dihydroxybiphenyl, 9,9′-bis(4-hydroxyphenyl) fluorene and 4,4′-difluorobenzophenone. The polymers with pendant aliphatic sulfonic acid groups were further synthesized by free radical thiol-ene coupling reactions between 3-mercapto-1-propanesulfonic sodium and the parent propenyl functional copolymers. The resulting sulfonated polymers with high inherent viscosity (1.83-4.69 dL/g) were soluble in polar organic solvents and can form flexible and transparent membranes by casting from their solutions. The copolymers with different ion exchange capacity could be conveniently synthesized by varying the monomers ratios. Transmission electron microscopy (TEM) was used to examine the microstructures of the membrane and the results revealed that significant hydrophilic/hydrophobic microphase separation with spherical, uniform-sized (5-10 nm) and well-dispersed hydrophilic domains was afforded. The proton conductivities of the as-prepared membranes and the state-of-the-art Nafion 117 membrane in fully hydrated state were investigated. The results revealed that the proton conductivity of the synthesized membranes increased more remarkably than that of Nafion 117 membrane with increasing temperature. The membrane with 1.69 mequiv/g of IEC had a conductivity of 2.5 × 10⁻² Scm⁻¹ at 100 °C. The membranes also possessed excellent mechanical properties, good thermal, oxidative, hydrolytic and dimensional stabilities.     

Synthesis and properties of poly(arylene ether)s bearing sulfonic acid groups on pendant phenyl rings

Two kinds of new aromatic poly(arylene ether)s containing sulfonic acid groups were synthesized. Polymer 1 composed of tetraphenylphenylene ether and perfluorobiphenylene units was sulfonated with chlorosulfonic acid. Sulfonation took place only at the para position of the pendant phenyl rings. The average degree of sulfonation per repeating unit (m) was controlled from 1 to 4. Sulfonated polymer 2 with m = 3 was soluble in methanol and dimethyl sulfoxide and swelled in water. Incorporating bis(3,5‐dimethylphenyl)sulfone moieties into the sulfonated polymer imparts less methanol affinity. Polymers 4 with 30–65 mol % tetrakis(sulfophenyl)phenylene ether units has high decomposition temperatures above 300 °C, hydrophilicity, and good hydrolytic stability. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3211–3217, 2001     

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     

Selectively sulfonated poly(aryl ether sulfone)‐b‐polybutadiene for proton exchange membrane

A series of selectively sulfonated poly(arylene ether sulfone)‐b‐polybutadiene copolymers (SPAES‐b‐PB) were prepared based on carboxyl terminated polybutadiene (CTPB) and sulfonated poly(arylene ether sulfone) (SPAES) that was directly prepared by polycondensation of 4,4′‐isopropylidenediphenol with different molar ratios of disodium 3,3′‐disulfonate‐4,4′‐dichlorodiphenyl sulfone (SDCDPS) to 4,4′‐dichlorodiphenylsulfone (DCDPS), and subsequent selective postsulfonation of flexible PB block was carried out. Epoxidized modification of membranes was conducted by an in situ‐generated peracid method. The content of sulfonic acid groups attaching to aromatic rings in SPAES was determined by ¹H NMR and was in good aggrement with the controlled ratios. The effect of sulfonated rigid blocks on the postsulfonation of PB blocks was studied by Fourier transform infrared spectroscopy. The glass transition temperature (T_g) and the temperature of the melting peak (T) of membranes in acid form were studied by differential scanning calorimetry. Fenton's reagent test revealed that the selectively sulfonated SPAES‐b‐PB membranes had good stability to oxidation. The microstructure of rod‐like rigid SPAES blocks and interpenetrating network of ions were observed by transmission electron microscopy. Complex impedance measurement showed that an epoxidized membrane with SPAES‐40 exhibited the highest proton conductivity (1.08 × 10^?1 S/cm, 90 °C), which was due to the formation of obvious ionic networks. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 665–672, 2006     

Fluorinated Poly(aryl ether) Containing a 4‐Bromophenyl Pendant Group and its Phosphonated Derivative

Summary: A high‐molecular‐weight fluorinated poly(aryl ether) with a 4‐bromophenyl pendant group has been synthesized based on a bromo‐bisphenol. A phosphonic acid derivative is readily prepared from this in high conversion yield. The phosphonated polymer possesses excellent thermal, oxidative, and dimensional stability, low methanol permeability, and reasonable proton conductivity, and may be a candidate polymeric electrolyte membrane for fuel cell applications.

Synthesis of a poly(aryl ether) with a phosphonic acid group.     

Sulfophenylation of Polysulfones for Proton‐Conducting Fuel Cell Membranes

Polysulfone has been sulfophenylated by lithiation and anionic reaction with 2‐sulfobenzoic acid cyclic anhydride. This provides a new convenient method to modify polysulfones by attaching pendant sulfonated phenyl groups via ketone links. Membranes of the sulfophenylated polysulfones show promise for use in proton‐exchange‐membrane fuel cells. For example, a membrane with 0.9 sulfophenyl units per repeating polysulfone unit and 30 wt.‐% water was found to have a proton conductivity of 32 mS/cm at 60°C.     

Effect of ammonium groups on the properties and alkaline stability of poly(arylene ether)‐based anion exchange membranes

Five kinds of ammonium groups functionalized partially fluorinated poly(arylene ether) block copolymer membranes were prepared for investigating the structure–property relationship as anion exchange membranes (AEMs). Consequently, the pyridine (PYR)‐modified membrane showed the highest alkaline and hydrazine stability in terms of the conductivity, water uptake, and dry weight. The chloromethylated precursor block copolymers were reacted with amines, such as trimethylamine, N‐butyldimethylamine, 1‐methylimidazole, 1,2‐dimethylimidazole, and PYR to provide the target quaternized poly(arylene ether)s. The structures of the polymers, as well as model compounds and oligomers were well characterized by ¹H NMR spectra. The obtained AEMs were subjected to water uptake and hydroxide ion conductivity measurements and stabilities in aqueous alkaline and hydrazine media. The pyridinium‐functionalized quaternized polymers membrane showed the highest alkaline and hydrazine stability with minor losses in the conductivity, water uptake, and dry weight. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 383–389     

Synthesis of partially fluorinated poly(arylene ether sulfone) multiblock copolymers bearing perfluorosulfonic functions

Partially fluorinated poly(arylene ether sulfone) multiblock copolymers bearing perfluorosulfonic functions (ps‐PES‐FPES), with ionic exchange capacity (IEC) ranging between 0.9 and 1.5 meq H⁺/g, are synthesized by regioselective bromination of partially fluorinated poly(arylene ether sulfone) multiblock copolymers (PES‐FPES), followed by Ullman coupling reaction with lithium 1,1,2,2‐tetrafluoro‐2‐(1,1,2,2‐tetrafluoro‐2‐iodoethoxy)ethanesulfonate. The PES‐FPES are prepared by aromatic nucleophilic substitution reaction by an original approach, that is, “one pot two reactions synthesis.” The chemical structures of polymers are analyzed by ¹H and ¹⁹F NMR spectroscopy. The resulted ionomers present two distinct glass transitions and α relaxations revealing phase separation between the hydrophilic and the hydrophobic domains. The phase separation is observed at much lower block lengths of ps‐PES‐FPES as compared with the literature. AFM and SANS observations supported the phase separation, the hydrophilic domains are well dispersed but the connectivity to each other depends on the ps‐PES block lengths. The thermomechanical behavior, the water up‐take, and the conductivity of the ps‐PES‐FPES membranes are compared with those of Nafion 117^® and randomly functionalized polysulfone (ps‐PES). Conductivities close or higher to those of Nafion 117^® are obtained. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1941–1956     

Sulfonated poly(aryl ether ketone)s containing naphthalene moieties obtained by direct copolymerization as novel polymers for proton exchange membranes

A series of sulfonated poly(aryl ether ketone)s (SPAEKs) were prepared by aromatic nucleophilic polycondensation of 2,6‐dihydroxynaphthalene with 5,5′‐carbonyl‐bis(2‐fluorobenzenesulfonate) and 4,4′‐difluorobenzophenone. The structure and degree of sulfonation (DS) of the SPAEKs were characterized using ¹H NMR spectroscopy. The experimentally observed DS values were close to the expected values derived from the starting material ratios. The thermal stabilities of the SPAEKs were characterized by thermogravimetric analysis, which showed that in acid and sodium salt forms they were thermally stable in air up to about 240 and 380 °C, respectively. Transparent membranes cast from the directly polymerized SPAEKs exhibited good mechanical properties in both dry and hydrated states. The dependence of water uptake and of membrane swelling on the DS at different temperatures was studied. SPAEK membranes with a DS from 0.72 to 1.60 maintained adequate mechanical properties after immersion in water at 80 °C for 24 h. The proton conductivity of SPAEK membranes with different degrees of sulfonation was measured as a function of temperature. The proton conductivity of the SPAEK films increased with increased DS, and the highest room temperature conductivity (4.2 × 10^?2 S/cm) was recorded for a SPAEK membrane with a DS of 1.60, which further increased to 1.1 × 10^?1 S/cm at 80 °C. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2866–2876, 2004     

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     

Synthesis of poly(arylene ether sulfone)‐block‐sulfonated polybutadiene: the selective post‐sulfonation of block copolymers as proton exchange membranes

A series of poly(arylene ether sulfone)‐block‐sulfonated polybutadiene (PAES‐b‐sPB) with different ion exchange capacities (IECs) were synthesized and evaluated as proton exchange membranes (PEMs) for possible applications in fuel cells. These sulfonated block copolymers were synthesized via condensation reaction between modified PAES and PB prepolymers, followed by selective post‐sulfonation of PB blocks using acetyl sulfate as the sulfonating reagent. The sulfonic groups were only attached onto PB blocks due to the high reactivity of double bonds to acetyl sulfate. The success of synthesis and selective post‐sulfonation were all confirmed by the Fourier transform infrared (FT‐IR) and nuclear magnetic resonance (NMR) spectra. PAES‐b‐sPB had good film‐forming ability and thermal stability. Mechanical properties of membranes varied with the sulfonation. The presence of sulfonic groups increased the tensile strength and Young's modulus but decreased the elongation at break. Transmission electron microscopy (TEM) images showed large ionic aggregates in membranes. Phase separation as well as the interconnected sulfonate groups which only localized on flexible PB blocks led to these ionic domains. The proton conductivity increased with the increasing IEC and temperature. With relatively low IEC, most membranes still exhibited sufficient proton conductivity. The above results indicated this strategy could be a prospective choice to prepare novel PEMs. Copyright © 2010 John Wiley & Sons, Ltd.     

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     

Ionic organic/inorganic materials. II. New linear and crosslinked poly(ethylene oxide)‐based ionomers by quaternization with chloroalkyl‐functionalized siloxanes

Siloxane‐modified cationic polyelectrolytes were synthesized through the quaternization reaction of a poly(ethylene glycol)‐based polymer containing tertiary amine groups in the chain with chloroalkyl‐functionalized siloxanes. Linear or crosslinked structures were obtained, depending on the functionality of the siloxane: a chloroalkyl‐monofunctionalized or ‐polyfunctionalized siloxane was used. The reaction occurred in solution with n‐propanol as a solvent and NaI as a catalyst. All products were characterized with elemental analysis and IR and ¹H NMR spectrometry. Viscometric measurements of the linear polymer in dilute aqueous solutions revealed typical polyelectrolyte behavior. The swelling capacities in various solvents of the crosslinked structures were determined. The thermal stability of the crosslinked cationic structures obtained with a polyfunctional siloxane as a quaternization agent was much higher than that of the parent polymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3720–3728, 2004