Polybenzimidazoles phosphonated

Figure 23.10 Proton conductivity of a few prototypical proton conducting separator materials Nafion as a representative of hydrated acid ionomers (see also Fig. 23.2(a) [43, 78], a complex of PBI (polybenzimidazole) and phosphoric acid as a representative of adducts of basic polymers and oxo-acids (see also Fig. 23.2(b)) [16], phosphonic acid covalently immobilized via an alkane spacer at a siloxane backbone (see also Fig. 23.2(c)) [127], the acid salt CsHSO, [125] and an Y-doped BaZrOj [126].

To prepare new and inexpensive membranes, various trials have been made 196 sulfonated aromatic polyether membrane such as polyether ketones (PEEK),197 sulfonated polysulfone198 and membranes from sulfonated polyphenylene sulfide,199 phosphoric acid-doped polybenzimidazole, (PBI),200 polybenzimidazole having sulfonic acid groups,201 polybenzimidazole with phosphonic acid groups,202 a blend membrane of polybenzimidazole and sulfonated polysulfone,203 sulfonated phosphazene polymer.204... 

Sakaguchi Y, Kitamura K, Nakao J, Hamamoto S, Tachimori H, Takase S (2001) Preparation and properties of sulfonated or phosphonated polybenzimidazoles and polybenzoxazoles. 

Kerres et al., among others, developed the acid-base blend membranes from sulfonated polymers and aminated or other basic polymers [98] and concluded that the protonation of the basic groups is incomplete if the base is too weak [99]. Very recently, Frutsaert et al. [70] synthesized novel polymers for the development of high temperature PEMFC membranes comprising a blend of s-PEEK and a fluorinated copolymer bearing imidazole functions as pendant groups. The extensive work on intermediate temperature fuel cell membranes are well reviewed in Chap. 4 of this book including polybenzimidazole as the basic component and sulfonated and phosphonated ionomers of either nonfluorinated or partially fluorinated backbones as the acidic component. 

The scope of the reviewed R D work is limited to intermediate-T acid-base blend membranes prepared by mixing polybenzimidazoles and sulfonated or phosphonated acidic polymers. Other membrane types, where the acid-base concept was used to improve their relevant... 

Polybenzimidazoles with pendent acidic groups sulfopropylated polybenzimidazole [31], sulfonated polybenzimidazole by the grafting of (4-bromomethyl)benzenesulfonate onto PBI [32], phosphonated fuUy aromatic polyethers containing pyridine building blocks [33], sidfraiated aromatic polyethers containing pyridine units [34], sulfonated polybenzimidazoles from sulfonated dicar-boxylic acid monomers [35-37]. 

In the following, those publications dealing with synthesis and characterization of intermediate-T blend membranes from PBI basic polymers and sulfonated or phosphonated polymers utilized as acidic macromolecular cross-linkers in the blends are discussed. In Fig. 4.4, those polybenzimidazoles along... 

Sll, Fig. 4.5) are depicted along with B2. Again, all TGAs indicate excellent and similar thermal stabilities of all membranes up to 300 °C. Therefore, it can be concluded that both sulfonated and phosphonated polymers can be selected as acidic cross-linkers for polybenzimidazole membranes. 

Atanasov V, Gudat D, Ruffmann B et al (2013) Highly phosphonated polypentafluoro-styrene characterization and blends with polybenzimidazole. Eur Polym J 49 3977-3985... 

Kannan R, Kagalwala HN, Chaudhaii HD et al (2011) Improved performance of phosphonated carbon nanotube-polybenzimidazole composite membranes in proton exchange mtanbrane fuel cells. J Mater Chem 21 7223-7231... 

Phosphonated polybenzimidazoles were prepared by the interaction of 3,3, 4,4 -tetraaminodiphenylsulfone with 3,5-dicarboxylbenzenephosphonic add (DCP) (Scheme 8) [55]. 

The proton conductivity of such polymers was close to 10 Scm , and it was higher than that of suhbnated polymers. Although the phosphonated structure has advantage of increasing the proton conductivity in ion-containing polybenzimidazole, incorporation of DCP in these polymers decreases the solubihty in N-methyl-2-pyrrolidone (N-MP). 

The copolymer with STA DCP = 50 50 showed good solubihty in N-MP, but only similar level of conductivity to the sulfonated polymer. When the content of DCP was increased to STA/DCP = 30 70, the conductivity jumped to similar level of phosphonated polymer, while maintaining the solubihty in N-MP. Further increase of DCP content to STA/DCP = 15 85 induced the decrease in solubihty. There is a narrow region where good conductivity and solubihty coexist in these copolymers. Ion-containing polybenzimidazoles showed exceUent stabihty against hydrolysis, radical attack and dimensional change in wet/dry cycles. 

AT-substituted polybenzimidazoles, containing phosphonic acid groups which are linked to benzimidazole cycles by means of ethylenic groups, were prepared by treatment of different polybenzimidazoles with diethylvinylphos-phonate [78] in accordance with Scheme 21. 

Current research activities are focused on the identification of membrane materials and structures with high proton conductivity and low methanol permeability. Ultimately, one would tike membranes that work well in a DMFC at 10-20 M methanol, but the focus of most research is on much lower methanol feed concentrations (0.5 and 1.0 M). Since DMFCs are designed primarily for the portable power/electronics market, operating temperatures in the 25-80°C range are usually considered. Extensive data is available in the literature on new membrane materials with reduced methanol permeability, including sulfonated or phosphonated copolymers, phosphoric-acid-doped polybenzimidazole, and various blends and composites (see Table 29.6 for a listing of DMFC properties). 

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