Properties of PEMs based on cross-linked sulfonated poly(ether ether ketone)

Abstract

PEMs prepared from sulfonated poly(ether ether ketone) and cross-linked with simple polyols (ethylene glycol and glycerol), exhibited enhanced strength, stability in hot water and high proton conductivity. The properties and chemical structure of the cross-linked membranes were studied using TGA, 1 H NMR and FTIR. These data suggest that ethylene glycol and glycerol molecules do not link neighbouring main chains via sulfonic acid functions, but rather form alcohol-ether oligomers, bonded to -SO 3 -group and generating an interpenetrating network which interacts with the main chains. The thermal stability of cross-linked membranes is inferior to that of non-cross-linked ones. It is shown that splitting off of the sulfonic acid groups occurring above 200• C is accompanied by main chain degradation in both initial and cross-linked membranes. The fact that the degradation temperature exceeds 200• C suggests that this could be a promising and effective approach to cross-linking sulfonated membranes for FC application.

Thermal Stability of Sulfonated Poly(Ether Ether Ketone) Films: on the Role of Protodesulfonation

“…In addition, differences between SO 2 and SO 3 [30] Mikhailenko et al have suggested that the release of CO 2 prior to the SO 2 release could indicate the formation of an electrophile (RSO 2 þ ) available for cross-linking via ipso or H-substitution, under the release of a hydroxyl radical that can directly react with the main chain. [27] However, as no further evidence for these degradation reactions is seen, and CO 2 that has been sorbed in the proton-rich watery environment present in the material cannot be excluded as alternative CO 2 sources, we consider this reaction unlikely in our system.…”

“…Previous studies on SPEEK decomposition only reported SO 2 release in a unimodal peak between 200 and 400 8C (a temperature shift of some tens of degrees could be the result of differences in heating rate), although not all studies include an evolved-gas analysis up to a temperature of 500 8C. [13,15,17,27] Scheme 1 summarizes the two possible routes for SO x loss from the material: protodesulfonation or ipso substitution. If a sulfone (R-SO 2 -R) bridge is formed by ipso substitution, this sulfone bridge can in turn decompose at higher temperatures, yielding the release of a second SO x species.…”

Influence of ionic liquids on the properties of sulfonated polymer membranes

“…The precipitated polymer (SPEEK) was washed several times until the pH of the wash water was 5. The polymer was subsequently dried in air at room temperature for 48 h and then dried in an oven at 60 C for 48 h, which resulted in clear, nonporous films [20,21].…”

Crosslinking of sulphonated poly (ether ether ketone) using aromatic bis(hydroxymethyl) compound

“…Further, in aqueous environment at relatively high temperature (fuel cell operating temperature) SPEEK membrane swells extensively and as a result the mechanical property is not adequate enough to be useful for long-term application in fuel cells. Many research efforts have been undertaken to prepare more stable and mechanically strong membranes through crosslinking [9][10][11][12][13][14][15][16]. Crosslinking of sulphonated aromatic hydrocarbons can be achieved through bridging the reactive sulphonic acid group available in the polymer.…”

“…Crosslinking of SPEEK has also been obtained by aliphatic/aromatic amines [12] and imide containing amines [13]. Advantages and disadvantages of such efforts have recently been elaborated [14,15]. Kaliaguine and co-workers carried out detailed study on crosslinking of SPEEK using glycol, glycerol and erythritol in different solvent/solvent pair [14].…”