Polybenzimidazole pyridine

Xiao, L. et al.. Synthesis and characterization of pyridine-based polybenzimidazoles for high temperature polymer electrolyte membrane fuel cell applications. Fuel Cells, 5, 287, 2005. 

Lixiang, X. Zhang, H. Choe, E.-W. Scanlon, E. Ramanathan, L.S. Benicewicz, B.C. Synthesis and characterization of pyridine-based polybenzimidazoles as novel fuel cell membrane materials. Fuel Chem. Div. Prepr. 2003, 48, 447. 

Besides pyridine-containing polystyrene and pol)q5ropylene resins, polybenzimidazole has been employed as support for nickel(II) acetylacetonate [94]. The nickel-loaded polymer was shown to be an efficient catalyst for the epoxidation of (S)-(—)-limonene, a-pinene, and 1-octene using isobutyraldehyde/02 as coreac-tant/oxidant. However, significant metal leaching from the support associated with a loss of activity upon recycling was reported. It was shown that the reaction is heterogeneously catalyzed, and leached metal species did not contribute to the catal)d ic activity. 

The acid-base Nafion composite membranes include blends of Nafion with polypyrrole (PPy) [98-104], polybenzimidazole (PBI) [105-107], poly (propyleneoxide) (PPO) [108, 109], polyfurfuryl alcohol (PFA) [110], poly(vinyl alcohol) (PVA) [111-115], sulfonated phenol-formaldehyde (sPF) [116], polyvinylidene fluoride (PVdF) [117-122], poly(p-phenylene vinylene) (PPV) [123], poly(vinyl pyrrolidone) (PVP) [124] polyanifine (PANI) [125-128], polyethylene (PE) [129], poly(ethylene-terephtalate) [130], sulfated p-cyclodextrin (sCD) [131], sulfonated poly(ether ether ketone) (sPEEK) [132-135], sulfonated poly(aryl ether ketone) (sPAEK) [136], poly(arylene ether sulfone) (PAES) [137], poly(vinylimidazole) (PVl) [138], poly(vinyl pyridine) (PVPy) [139], poly (tetrafluoroethylene) (PTFE) [140-142], poly(fluorinated ethylene-propylene) [143], sulfonated polyhedral oligomeric silsesquioxane (sPOSS) [144], poly (3,4-ethylenedioxythiophene) (PEDT) [145, 146], polyrotaxanes (PR) [147], purple membrane [148], sulfonated polystyrene (PSSA) [149, 150], polystyrene-b-poly(ethylene-ran-butylene)-bpolystyrene (SEES) [151], poly(2-acrylamido-2-methyl-l-propanesulphonic acid-co-l,6-hexanediol propoxylate diacrylate-co-ethyl methacrylate) (AMPS) [152], and chitosan [31]. A binary PVA/chitosan [153] and a ternary Nafion composite with PVA, polyimide (PI) and 8-trimethoxy silylpropyl glycerin ether-1,3,6-pyrenetrisulfonic acid (TSPS) has also been reported [154]. 

In order to modify the state-of-the-art PBI stmcture and consequently its properties, significant effort has been focused on the synthesis of pyridine-based polybenzimidazoles. A systematic synthesis with different stractures was initiated to study the effect of the polymer molecular stmcture on the final film properties. The substitution of pyridine dicarboxylic acids (PDA) for the iso-/terephthalic acids is particularly interesting, because it increases the number of basic groups in the polymer backbones. The general stmcture of the series of pyridine-based polybenzimidazole (PPBI) homopolymers from 3,3 -4,4 -tetraaminobiphenyl (TAB) and 2,4-, 2,6-, 2,5- or 3,5-pyridine dicarboxylic acids using the PPA synthetic process is shown in Fig. 6. Monomer purity and accurate stoichiometry are cmcial to obtain high molecular weight polymers. 

A variety of high-temperature-resistant PBIs were synthesized and reported in the Uterature. The most widely used PBI is poly[2,2 -(l,3-phenylene)-5,5-benzimidazole] (known as m-PBI) [22]. The other variations are poly[2,2 -( 1,4- phenylene)-5,5 -benzimidazole] (known as p-PBI) [13], poly(4,4 -diphenylether-5,5 -bibenzimidazole) (OPBI) [23], poly(2,5-benzimidazole) (AB-PBI) [24], pyridine-based PBI [25], sulfonated PBI [26], hyperbranched polybenzimidazole (HPBI) [27], naphthalene-based PBI [28], fluorinated PBI [29], PBI block copolymer [30], sulfonated PBI copolymer with sulfone or sulfonic acid groups in the backbone [31,32], PBFnano-composite [33], cross-linked PBI [34], and many others. Different approaches have been taken by the researchers to modify the structure and properties of the fluorinated PBI. A detailed summary of these works is discussed below. 

Jana et al. prepared alternative tetraamine monomer, 2,6-bis(3, 4 -diaminophenyl)-4-phenylpyridine (Py-TAB), for synthesizing pyridine bridge polybenzimidazole (Py-PBI) (Figure 5.15) [42]. 

Pyridine polybenzimidazoles (py-PBIs, Fig. 5d) have been investigated for their use in fuel cells because of their high concentration of basic sites (amine and imine groups). Similar to AB-PBI, the high concentration of basic sites allow these polymers to have a high affinity to acids. The pyridine moiety is commonly combined with the traditional PBI stmcture by including it as part of the backbone structure. 

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]. 

Molleo MA, Chen X, Ploehn HJ et al (2014) High polymer content 3,5-pyridine-polybenzimidazole copolymer membranes with improved compressive properties. Fuel Cells 14 16-25... 

Yang JS, Xu YX, Zhou L et al (2013) Hydroxyl pyridine containing polybenzimidazole membranes for proton exchange membrane fuel cells. J Membr Sci 446 318-325... 

Fig. 10.12 Chemical structure of repeat units for pyridine-based polybenzimidazoles...

Fig. 10.13 Conductivities of phosphoric acid doped pyridine polybenzimidazoles. Reproduced from [22] with permission of John Wiley and Sons...

Su PH, Cheng J, Li JF et al (2014) High temperature polybenzimidazole membrane electrode assemblies using pyridine-polybenzimizazole as catalyst layer binder. J Power Sources 260 131-139... 

Cleemann et al. [83] showed strong dependence of the fuel cell performance degradation on the catalyst supports. Graphitized carbon black and multi-walled carbon nanotubes as catalyst supports showed improvement in the catalyst and fuel cell durability. Further wrapping the carbon nanombes by a polymer, e.g., PBl [87] or pyridine-containing polybenzimidazole (PyPBl) was found to improve the utilization efficiency and durability. The... 

Fujigaya T, Okamoto M, Nakashima N (2009) Design of an assembly of pyridine-containing polybenzimidazole, carbon nanotubes and Pt nanoparticles for a fuel cell electrocatalyst with a high electrochemically active surface area. Carbon 47 3227-3232... 

Fig. 7.14 Temperature dependence of proton conductivity of a 2,5-PPBI membrane with 20.4 mol H3PO4 doping. Reprinted with permission from Ref. [54] L. Xiao, et al.. Synthesis and characterization of pyridine-based polybenzimidazole for high temperature polymer electrolyte membrane fuel cell application. Fuel Cell, 5, 287-295 (2005). Copyright Wiley-VCH...

Xiao, L., H. Zhang, T. Jana, E. Scanlon, R. Chen, E. W. Choe, L. S. Ramanathan, S. Yu, and B. C. Benicewicz, Synthesis and characterization of pyridine-based of polybenzimidazoles for high temperature polymer electrolyte membrane fuel cell applications . Fuel Cells 5(2) (2005) 287-295. 

Besides the covalent crosslinking, Kerres et al. investigated the properties of fuel cell membranes of ionicaUy crosslinked polysulfonic adds. This type of crosslinking was achieved by blending sulfonated poly(arylene ether sul-fone)s and poly(arylene ether ketone)s with basic polymers, such as polybenzimidazole, poly(ethylene imine), poly(vinyl pyridine), or amino functional-... 

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