Polymer Electrolyte Membranes Derived from New Sulfone Monomers with Pendent Sulfonic Acid Groups

Abstract

New monomers containing two or four pendent phenyl groups were synthesized by bromination of bis(4-fluorophenyl) sulfone, followed by Suzuki coupling with benzeneboronic acid. The resulting monomers were converted to the corresponding sulfonated monomers having two or four pendent sulfonic acid groups, predominately at the p-phenyl position. Aromatic nucleophilic substitution (SNAr) polycondensation using the di- and tetrasulfonated monomers provided sulfonated poly(arylene ether sulfone) copolymers S2-PAES-xx and S4-PAES-xx, respectively, where xx refers to the molar ratio of the sulfonated to non-sulfonated pendent phenyl monomer. Copoly(arylene ether sulfone)s based on the corresponding non-sulfonated monomers were also synthesized for a parallel study on postpolymerization sulfonation of these copolymers. Postsulfonation occurred predominately at the para-pendent phenyl site, and the reactions were complete within a short time (about 30 min), without evidence of chain degradation. Flexible and tough membranes having high mechanical strength were obtained by solution casting of all four series of copolymers. The copolymers with two or four pendent sulfonic acid groups had high proton conductivities in the range of 44−142 mS/cm for S2-PAES-xx and 51−158 mS/cm for S4-PAES-xx at room temperature, respectively. The methanol permeabilities of these copolymers were in the range of 0.8 × 10−8−15.0 × 10−7 cm2/s, which is lower than Nafion (16.7 × 10−7 cm2/s). The S4-PAES-xx membranes displayed better properties (lower water uptake and higher proton conductivities) than the S2-PAES-xx membranes, which can be attributed to the more blocky architecture of the sulfonic acid groups in the S4 membranes. A combination of high proton conductivities, low water uptake, and low methanol permeabilities for some of the obtained copolymers indicated that they are good candidate materials for proton exchange membrane in fuel cell applications.

Sulfonated fluorinated-aromatic polymers as proton exchange membranes

“…This finding was in accordance with the previous findings by Li et al (56), where two or four pendent phenyl sulfonic acid groups were introduced as side chains. However, the proton conductivity values of the sulfonated copolymers obtained by Li et al (56) were somewhat higher, lying in the range between 82 and 298 mS/cm for 2-SPAEs-xx and between 106 and 311 mS/cm for 2-SPAEsxx at 80°C.…”

A new class of highly-conducting polymer electrolyte membranes: Aromatic ABA triblock copolymers

“…[19][20][21][22] However, unlike the previously reported random or multiblock copolymers, [3] in which higher temperature induced excessive swelling, the temperature had less of an influence on the water uptake and dimensional swelling of 3 membranes, as shown in especially when compared with other copolymer systems at this temperature difference. [3,48,49] Although each sulfonic acid group was solvated by about 26 water molecules, at reduced relative humidity and elevated temperature, a similar but higher water uptake tendency compared with Nafion 112 was observed (Figure 7a). These overall results demonstrate that triblock copolymer structures, while containing a high amount of water, were effective in preventing excessive water swelling, even at elevated temperatures (> 80 o C).…”

“…[49,50] the properties are adequate, and reasonable when taking into account the higher water uptake of the triblock membranes. We attribute this to the hydrophilic water-containing domains formed by the proton-conducting blocks that segregate the hydrophobic main chain, resulting in weaker physical interactions between hydrophobic blocks and lower mechanical strength of the membranes.…”

Sulfonated hydrocarbon membranes for medium-temperature and low-humidity proton exchange membrane fuel cells (PEMFCs)

“…Li et al utilized this concept to synthesize SPAES copolymers having two or four sulfonated pendant phenyl rings using monomer sulfonation method as well as postpolymerization sulfonation method, as shown in Fig. 39 [145]. Monomer sulfonation led to sulfonated monomers having two or four pendent sulfonic acid groups at the pphenyl position.…”