Aromatic Poly(ether ketone)s with Pendant Sulfonic Acid Phenyl Groups Prepared by a Mild Sulfonation Method for Proton Exchange Membranes

Abstract

The sulfonation selectivity of seven poly(ether ether ketone)s (PEEKs) was investigated, and several possessed targeted single-or double-substituted sites per repeated unit on pendant phenyl groups via the postsulfonation approach. The presence of the various pendant groups enabled postsulfonation to occur under mild reaction conditions, in much shorter times than required for the sulfonation of commercial PEEK. A series of poly(ether ketone)s (PEKs) with ion exchange capacity of 2.23-0.84 mequiv/g could be realized by controlling the length of unsulfonated segments of both homopolymers and copolymers. These side-group sulfonation polymers had excellent mechanical properties, good thermal and oxidative stability, and good dimensional stability in hot water. The methanol permeability values of Me-SPEEKK, Me-SPEEKDK, Ph-SPEEKK, and Ph-SPEEKDK at room temperature were in the range 3.31 × 10 -7 -9.55 × 10 -8 cm 2 /s, which is several times lower than that of Nafion 117. Me-SPEEKK and Ph-SPEEKK also exhibited high proton conductivity of 0.15 S/cm at 100°C, which is higher than that of Nafion 117. Transmission electron microscopy analysis was used to observe their microstructure for evidence of microphase separation of ionic and hydrophobic domains. The results showed these side-group-acid materials are possible inexpensive candidate materials for proton exchange membranes in fuel cell applications.

Enhanced thermo-oxidative stability of sulfophenylated poly(ether sulfone)s

“…The results evaluated in Fenton's reagent at 80 C are shown in Table 2. It is generally the case that polymers having lower DS always exhibit better oxidative stability by this test [21].It was interesting to note that the diphenylated series exhibited improved oxidative resistance over the mono-phenylated series, when compared at similar DS. For example, DiPh-SPES-50 (IEC w 1.70 meq/g) maintained film integrity after a 3 h treatment in Fenton's reagent, whereas Ph-SPES-40 (IEC w 1.60 meq/g) had already dissolved into Fenton's reagent after 2.5 h treatment.…”

“…Although the sulfonation conditions for polymers are often more vigorous than those used for simple low-MW compounds, several series of polymers have been be sulfonated under mild sulfonation conditions [20,21]. The monophenylated polymers [7] wherein sulfonated sites occur both on the side chain and main chain may be less desirable in terms of PEM properties such as chemical stability and ability to go some degree of phase separation between hydrophilic and hydrophobic regions.…”

Sulfonated naphthalenic polyimides containing ether and ketone linkages as polymer electrolyte membranes

“…Perfluorosulfonic acid type membranes, such as Nafion (DuPont) series, which possess excellent oxidative and dimensional stabilities and high proton conductivity, are the commercial stateof-the-art PEMs currently utilized in PEMFC and DMFC systems [2]. However, some deficiencies are well-recognized, such as its high cost, high fuel crossover, low operation temperature (≤80 • C) and environmental recycling uncertainty [3][4][5]. In this respect, much research effort is being directed to develop new PEMs with lower cost and good overall performance as alternatives to replace per-fluorosulfonic acid type membranes [6][7][8][9][10][11].…”

Sulphonated Biphenylated Poly(aryl ether ketone)s for Fuel Cell Applications

“…In addition, DS is usually adjusted by the reaction time, which results in the difficulty in its precise control. Recently, we reported some polymers having good site selectivity and which have fully sulphonated substitutions within a short reaction time by post-sulphonation method [18]. This is in strong contrast to the sulphonation of PEEK, which occurs over a long reaction period of hundreds of hours.…”