Sulfonated PEEK

N. Shibuya and R.S. Porter, Kinetics of PEEK sulfonation in concentrated sulfuric acid, Macromolecules, 1992, 25, 6495-6499 F. Wang and J. Rovers, Functionalization of poly(aryl ether ether ketone) (PEEK) Synthesis and properties of aldehyde and carboxylic acid substituted PEEK, Macromolecules, 1993, 26, 5295-5302. 

In blends of PPESK and sulfonated poly (ether ether ketone) (PEEK), both methanol permeability and proton conductivity increase nonlinearly with increasing content of PEEK. Sulfonated PAES copolymers obtained from sulfonated 4,4 -dichlorodiphenyl sulfone, 4,4 -dichlorodiphenyl sulf-one and phenolphthalein have been tested with respect to their use for direct methanol fuel cell application. The proton conductivity increases linearly with the degree of sulfonation, but the methanol permeability increases linearly up to 20 mol-% sulfonated monomer content. Above this level, a sudden increase in permeability is observed. This effect is referred to as percolation threshold. 

Furthermore, the PEEK sulfonation can be realized introducing directly the sulfonic acid group onto the polymer back-bone [5-7] by modification or by polymerizing suUbnated monomers [8,9],... 

Table 1. S-PEEK sulfonation degree dependence by the Monomer M/Monomer K ratio in the nucleophilic aromatic substitution reaction [10]...

However, not depending on which way is realized the PEEK sulfonation, the DS can affect several important parameters, describing the thermo-mechanical and electrochemical behaviour of the S-PEEKs, such as ... 

The lEC of the S-PEEKs depends on the DS and on the reaetion time and, in some case, they can reach values close to 2.4 meq/g with DS equal to 85% after 120 hours of sulfonation, carried out via concentrated sulphuric acid [19]. Also when the PEEK sulfonation proceeds via sulfonated monomer copolymerization without any side reactions, the lEC increases with increasing DS and shows values ranging between 0.7 and 1.5 meq/g, corresponding to DS of 40 and 120%, respectively [11]. 

Generally, the S-PEEK sulfonic concentration, indicated by the DS, plays the main role for what concerns the proton migration through an electrolyte polymer. With increasing DS,... 

Shibuya, N. and R.S. Porter. 1992. Kinetics of PEEK sulfonation in concentrated sulfuric acid. Macromolecules 25 6495-6499. 

Savinell and co-workers, [105-107], who have principally studied phosphoric acid doped polybenzimidazole (PBl). Similar systems have been reported by He and co-workers [108], who in addition report the conductivities of PBl based membranes doped with PTA and zirconium hydrogen phosphate [108], Acid-base interactions in entirely polymeric systems have been reported by Kerres and co-workers [102], who prepared and stndied several membranes prepared by blending polymers with acidic (snlfonated-PEEK, sulfonated polyethersulfone) and basic (polybenzimidazole, poly-vinylpyridine) characteristics. Selected acid-base polymer systems are discnssed in the following. 

For DS <30%, sPEEK polymers are soluble in dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or A-methylpyrrolidone (NMP). For DS >50%, sPEEKs are soluble in A,iV-dimethylacetamide (DMAc) also at room temperature [151], while for DS above 60%, sPEEKs are highly swollen in methanol/water solution at 80-90 °C, and for these reasons, they are not suitable for DMFC applications [155]. For DS >70%, sPEEKs are soluble in methanol, and for DS = 100%, in hot water [182,183]. When PEEK sulfonation is carried out via the concentrated sulfuric acid procedure, it is limited and takes place only on the four chemically equivalent positions of the hydroquinone segment and the DS does not exceed the value of 100% owing to the electron-withdrawing deactivating... 

Daoust, D., Devaux, J., Godard, R, Mechanism and kinetics of poly(ether ether ketone) (PEEK) sulfonation in concentrated sulfuric acid at room temperature. Part 1. Quahtative comparison between polymer and monomer model compound sulfonation, Polym. Int., 2001, 50, 917-924. 

Many nonfluorinated specialty polymers have been functionalized, characterized, and tested for the application in direct alcohol fuel cells but the most promising polymer type is PEEK. Sulfonation of these polymers leads to structures that can nanoseparate similar to Nafion. Sulfonation degree has a significant impact on... 

Polyarylether Ketones. The aromatic polyether ketones are tme thermoplastics. Although several are commercially available, two resins in particular, poly ether ether ketone [31694-16-3] (PEEK) from ICI and poly ether ketone ketone (PEKK) from Du Pont, have received most of the attention. PEEK was first synthesized in 1981 (20) and has been well studied it is the subject of numerous papers because of its potential use in high performance aircraft. Tough, semicrystalline PEEK is prepared by the condensation of bis(4-fiuorophenyl) ketone with the potassium salt of bis(4-hydroxyphenyl) ketone in a diaryl sulfone solvent, such as diphenyl sulfone. The choice of solvent is critical other solvents, such as Hquid HE, promote the reaction but lead to premature low molecular-weight crystals, which do not exhibit sufficient toughness (21). 

Recently, Dutta and Maiti [21] reported nitro displacement polymerization of the bisphenol dianion with the sulfone activated dinitro aromatic compounds. In addition, there have been recent reports of the development of functionalized PEEK [22] and polyether sulfone ketone (PESK) [23] that are comparable to commercially available high performance polymers. 

Epoxy Polyimide PEEK Polyamideimide Polyetherimidc Polysulfone sulfone Polyphenylene Phenolics... 

Aprotic polar solvents have to be used for several reasons. They are often good solvents for both monomers (including phenolates) and amorphous polymers. In addition, they can also stabilize the Meisenheimer intermediates. Common aprotic polar solvents, such as DMSO, /V,/V-dimcthyl acetamide (DMAc), DMF, N-methyl pyrrolidone (NMP), and cyclohexylpyrrolidone (CHP) can be used. Under some circumstances, very high reaction temperature and boiling point solvents such as sulfolane and diphenyl sulfone (DPS) have to be used due to the poor reactivity of the monomers or poor solubility of the resulting, possibly semicrystalline polymers, as in the PEEK systems. 

Polyetheretherketone (PEEK) fibers electrical properties of, 23 718 properties of, 20 199t sulfonation of, 23 717 PEEK-based composites, 26 764 Peel-apart color films, 19 286 Peel-apart film(s), 19 274, 281, 282, 299, 314... 

Wholly aromatic polymers are thought to be one of the more promising routes to high performance PEMs because of their availability, processability, wide variety of chemical compositions, and anticipated stability in the fuel cell environment. Specifically, poly(arylene ether) materials such as poly-(arylene ether ether ketone) (PEEK), poly(arylene ether sulfone), and their derivatives are the focus of many investigations, and the synthesis of these materials has been widely reported.This family of copolymers is attractive for use in PEMs because of their well-known oxidative and hydrolytic stability under harsh conditions and because many different chemical structures, including partially fluorinated materials, are possible, as shown in Figure 8. Introduction of active proton exchange sites to poly-(arylene ether) s has been accomplished by both a polymer postmodification approach and direct co-... 

Poly(ether ether ketone) (PEEK) is an aromatic, high performance, semicrystalline polymer with extremely good thermal stability, chemical resistance, and electrical and mechanical properties. This polymer shows little solubility in organic solvents due to the crystallinity. One of the first ways to characterize PEEK was by sulfonating the polymer. By adding sulfonic acid groups to the backbone, the crystallinity decreased and solubility increased.Commercially available Victrex appears to be one of the more interesting poly(arylene ether) s used for postmodification. 

Figure 10. Chemical structures of unsulfonated and sulfonated PEEK.

Kobayashi et al. reported sulfonation of poly(4-phenoxybenzoyl-1,4-phenylene) (PPBP) with sulfuric acid and compared the data with those of sulfonated PEEK. As reported, the authors employed sulfuric acid for the sulfonation reaction to avoid or at least minimize degradation of the polymer by chlorosulfonic acid or fuming sulfuric acid (Figure 27). 

Nylon, polyacetal, polycarbonates, poly(2,6-dimethyl)phenylene oxide (PPO), polyimides, polyphenylene sulfide (PPS), polyphenylene sulfones, polyaryl sulfones, polyalkylene phthalates, and polyarylether ketones (PEEK) are stiff high-melting polymers which are classified as engineering plastics. The formulas for the repeating units of some of these engineering plastics are shown in Figure 1.15. 

Stiff polymers, such as polyphenylene, nylon 66, polyphenylene sulfone, and polyarylether ketone (PEEK), have relatively high Tg values because of the presence of phenylene and sulfone or carbonyl stiffening groups in the chain. 

Sulfonation is very useful chemical modification of polymer, as it induces high polarity in the polymer changing its chemical as well as physical properties. Sulfonated polymers are also important precursors for ionomer formation [75]. There are reports of sulfonation of ethylene-propylene diene terpolymer (EPDM) [76, 77], polyarylene-ether-sulfone [78], polyaromatic ether ketone [79], polyether ether ketone (PEEK) [80], styrene-ethylene-butylene-styrene block copolymer, (SEBS) [81]. Poly [bis(3-methyl phenoxy) phosphozene] [82], Sulfonated polymers show a distinct peak at 1176 cm"1 due to stretching vibration of 0=S=0 in the -S03H group. Another peak appears at 881 cm 1 due to stretching vibration of S-OH bond. However, the position of different vibrational bands due to sulfonation depends on the nature of the cations as well as types of solvents [75, 76]. 

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