Sulfonated polyimides

In addition to Nafion-based catalyst layers, additional types have been developed, including CLs with different ion exchange capacities (lECs) [57,58] or with other hydrocarbon-type ionomers such as sulfonated poly(ether ether ketone) [58-60], sulfonated polysulfone [61,62], sulfonated polyether ionomers [63], and borosiloxane electrolytes [64], as well as sulfonated polyimide [65]. These nonfluorinated polymer materials have been targeted to reduce cost and/or increase operating temperature. Unfortunately, such CLs still encounter problems with low Pt utilization, flooding, and inferior performance compared wifh convenfional Nafion-based CLs. 

Higuchi, E., Okamoto, K., Miyatake, K., Uchida, H., and Watanabe, M. Gas diffusion electrodes for polymer electrolyte fuel cell using sulfonated polyimide. Research on Chemical Intermediates 2006 32 533-542. 

Little characterization of 17 and 18 is available in the open literature. In the case of 19 and 20, both pol5dmides displayed microphase separation in contrast to statistically, main-chain sulfonated polyimides for which little, if any, microphase separation is observed. Eor 19, hydrophilic domains were seen to be on the order of 5 nm in size. Similarly, 20 (where x = 3, y = 10, n = 50) with a... 

Miyatake, K., Asano, N. and Watanabe, M. 2003. Synthesis and properties of novel sulfonated polyimides containing 1,5-naphthylene moieties. Journal of Polymer Science Part A Polymer Chemistry 41 3901-3907. 

Fang, J., Guo, X., Harada, S., Watari, T., Tanaka, K., Kita, H. and Okamoto, K. 2002. Novel sulfonated polyimides as polyelectrolytes for fuel cell applications. 1. Synthesis, proton conductivity, and water stability of polyimides from 4,4 -diaminophenyl ether-2,2 -disulfonic acid. Macromolecules 35 9022-9028. 

Okamoto, K. 2003. Sulfonated polyimides for polymer electrolyte membrane fuel cell. Journal of Photopolymer Science and Technolgy 16 247-254. 

Faure, S., Pineri, M., Aldebert, R, Mercier, R. and Sillion, S. 1999. Sulfonated polyimides, membranes and fuel cells. E. Patent 897 407 Al. 

Zhou, W, Watari, T., Kita, H. and Okamoto, K. 2002. Gas permeation properties of flexible pyrolytic membranes from sulfonated polyimides. Chemistry Letters 5 534-535. 

Figure 23. Sulfonated diamines for direct synthesis of sulfonated polyimides.

Principally, one commercially available sulfonated diamine (4,4 -diamino-2,2 -biphenyl disulfonic acid) has been used to synthesize sulfonated polyimides. In addition to the commercially available diamine, several novel sulfonated diamines incorporating flexible or kinked structures have been prepared in Okamoto s lab. " The chemical structures and names of all five diamines are shown in Figure 23. 

Figure 24. Synthesis of a five-membered ring sulfonated polyimide containing phosphine oxide.

Benzimidazole-containing sulfonated polyimides, (IV), prepared by Bmnelle [4] were effective as proton exchange membranes for fuel cells. 

The crossover of methanol has caused problems in finding a suitable membrane material. On the positive electrode side, methanol combines with oxygen to form CO2. Among the alternatives to pure Nafion are Nafion filled with zirconium phosphate or grafted with styrene to inhibit methanol transport (Bauer and Willert-Porada, 2003 Sauk et al., 2004), as well as non-Nafion membrane materials such as sulfonated polyimide (Woo et al., 2003). None have achieved performance as good as the one shown in Fig. 3.53, which, however, has a substantial methanol crossover rate. 

We examine in this chapter the hydration mechanisms of two completely different types of macromolecules a natural biopolymer, HA and a synthetic polymer, a sulfonated polyimide that may be used in the industry. These two types of macromolecules are completely different types of macromolecules. 

Figure 10.5 Development of the H-bond network in a sulfonated polyimide (homo)polymer made of chains of aromatic and polyaromatic substituted cycles. Three repeat units of a chain are represented. Structure of the dried membrane in the upper drawing, of the membrane in equilibrium with an atmosphere with hygrometry 15% (middle page drawing) and 65% (lower drawing).

In Figure 11.6, the two elementary hydration spectra / and W of a sulfonated polyimide membrane, together with the spectrum of the dried membrane, are displayed. The same analysis as described above for HA provides sufficient information to establish the hydration mechanism of this membrane, detailed in Ch. 10 and shown in Figure 10.5. It may be noted that these hydration spectra do not correspond to successive hydration mechanisms, as for HA, but correspond to the ionization of SO3H groups into SO3 HjO by addition of a single H2O molecule (Z ), and to hydration of these 803 H3O+ complexes by HjO molecules (// ). 

The above described results, obtained after a quantitative analysis of IR spectra, are quite precise. Up to now they have been obtained for a small number only of macromolecules. Let us nevertheless mention that in the case of a much simpler system, glycine, hydration mechanisms could also be determined from IR spectra in solid matrices (56) and, as can be seen in Figure 6.3, resulted in the formation of a zwitterion. These precise results may be extended to many other macromolecules besides HA or the sulfonated polyimide membranes discussed in Ch. 10. The quantitative analysis performed above on these spectra conveys a lot of information on the structures of the H-bond networks that HjO... 

Figure 11.6 IR spectrum of a dried sulfonated polyimide membrane (homopolymer) 10 pm thick and the two corresponding elementary hydration spectra / and Dashed vertical lines show corresponding bands.

The main developments in the field of sulfonated polyimide membranes are... 

As well as 4,4 -diaminobiphenyl-2,2 -disulfonic acid [46-57], diamines such as sulfonated bis-(3-aminophenyl)phenyl phosphine oxide (Figure 1.9) were used for the preparation of sulfonated polyimides [58] ... 

G. Meyer, G. Gebel, L. Gonon, P. Capron, D. Marscaq, C. Marestin, and R. Mercier. Degradation of sulfonated polyimide membranes in fuel cell conditions. J. Power Sources, 157 293-301, June 2006. 

SPSs), sulfonated polyimides (SPIs), sulfonated polyfphenylene) s (SPPs), sulfonated poly(arylene)-type polymers (SPAs), and sulfonated poly(phosphazene)s (SPPtis). " They contain hydro-phobic blocks (hydrocarbon backbone) and hydrophilic blocks (containing sulfonic acid groups). Sulfonic acid groups, which are commonly employed as hydrophilic functional groups, form well-defined nanosized channels for proton conduction. 

Y. Yin, O. Yamada, K. Tanaka, K.-I. Okamoto, On the development of naphthalene-based sulfonated polyimide membranes for fuel cell applications. Polymer Journal 2006,38(3), 197-219. 

Sulfonated aromatic polymers have been widely studied as alternatives to Nafion due to potentially attractive mechanical properties, thermal and chemical stability, and commercial availability of the base aromatic polymers. Aromatic polymers studied in fuel cell apphcations include sulfonated poly(p-phenylene)s, sulfonated polysulfones, sulfonated poly(ether ether ke-tone)s (SPEEKs), sulfonated polyimides (SPIs), sulfonated polyphosphazenes, and sulfonated polybenzimidazoles. Representative chemical structures of sulfonated aromatic polymers are shown in Scheme 3. Aromatic polymers are readily sulfonated using concentrated sulfuric acid, fuming sulfuric acid, chlorosulfonic acid, or sulfur trioxide. Post-sulfonation reactions suffer from a lack of control over the degree and location of functionalization, and the... 

Fig. 8 SANS spectra of water-swollen x/y = 30 70 sulfonated polyimides possessing varying ionic block length [143]...

E. Vallejo, G. Pourcelly, C. Gavach, R. Mercier, M. Pineri, Sulfonated polyimides as proton conductor exchange membranes. Physicochemical properties and separation H /Mz by electrodialysis comparison with a per-fluorosulfonic membrane. Journal of Membrane Science 160 (1999). 

W. Essafi, G. Gebel, R. Mercier, Sulfonated Polyimide lonomers A Structural Study. Macromolecules 37 (2004) 1431-1440. 

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