Densely Sulfophenylated Segmented Copoly(arylene ether sulfone) Proton Exchange Membranes

Abstract

Segmented copoly(arylene ether sulfone) membranes having densely sulfonated pendent phenyl blocks were synthesized by the coupling reaction of phenoxide-terminated oligomers with bis(4-hydroxyphenyl) sulfone and decafluorobiphenyl (DFBP), followed by postpolymerization sulfonation of the blocks containing pendent phenyl substituents. The coupling reaction was conducted at relatively low temperature by utilizing highly reactive DFBP to prevent any possible trans-etherification that would randomize the hydrophilic–hydrophobic sequences. Segmented copolymer molecular weights were reasonably high, as determined by viscosity measurements. Postsulfonation occurred selectively on the pendent phenyl substituent to yield hydrophilic blocks that were highly sulfonated in regular sequence on the linked phenyl rings. The resulting polymers gave transparent, flexible, and tough membranes by solution casting. Morphological observation by transmission electron microscopy (TEM) and atomic force microscopy (AFM) showed that the high local concentration and regular sequence of pendent sulfonic acid groups within the hydrophilic blocks enhanced nanophase separation between the hydrophobic and hydrophilic blocks. A comparison of copolymers with similar ion exchange capacities (IECs) indicated that proton conductivity and water uptake were strongly influenced by the hydrophilic block sequence lengths. Proton conductivity and water uptake increased with increasing block length, even at low relative humidity (RH). The ionomer membrane with X20Y20 (X and Y refer to the number of hydrophilic and hydrophobic repeat units, respectively) and 1.82 mequiv/g of IEC had a proton conductivity of 3.6 × 10–2 S/cm at 80 °C and 50% RH, which is comparable to that of perfluorinated ionomer (Nafion) membrane (4.0 × 10–2 S/cm).

Multiblock copolymers based on poly(p-phenylene)-co-poly(arylene ether sulfone ketone) with sulfonated multiphenyl pendant groups for polymer electrolyte fuel cell (PEMFC) application

“…Sulfone and ketone groups were introduced in hydrophobic block in order to ward off electrophilic substitution attack of sulfonic acid group by improving electron deficient property of hydrophobic chain. Moreover, sulfonated multiphenyl pendant side groups were introduced in order to improve the solubility and nanophase separation between the hydrophilic sulfonic acid-containing regions and the hydrophobic polymer main chain [21,22]. The physical properties, morphology, and PEMFC performance of these polymers is presented herein.…”

Fluorene-Based Poly(arylene ether sulfone)s Containing Clustered Flexible Pendant Sulfonic Acids as Proton Exchange Membranes

“…Densely sulfonated segmented poly(arylene ether sulfone)s showed nanophase separation of hydrophilic and hydrophobic blocks. 42 Over the past few years, much research focus has been on fluorene-based sulfonated poly(arylene ether)s. 43À49 It has been demonstrated that fluorene-based PEMs show some attractive properties, not only for chemical, thermal, and mechanical stability, but also good proton conductivities and fuel cell performance over several thousand hours. 46 Herein, we introduce a new fluorene-based bisphenol monomer and derived sulfonated poly(arylene ether sulfone) copolymers containing clusters of four butylsulfonic acid units per repeat unit along the main chain.…”

Poly(arlyene ether sulfone) based semi-interpenetrating polymer network membranes containing cross-linked poly(vinyl phosphonic acid) chains for fuel cell applications at high temperature and low humidity conditions

“…Among these hydrocarbon polymers, SPAES has been widely studied for high-temperature PEMs due to its high thermal stability, excellent mechanical strength, and its relatively low cost [18]. Still the direct application of pure SPAES has been limited because the SPAES having these advantages normally has lower proton conductivity than the perfluorosulfonic acid polymers [19,20]. The proton conductivity of SPAES could be increased by increasing the degree of sulfonation (DS), while the SPAES with high DS do not have high enough physical and chemical stability for PEMFC operation.…”