Direct polybenzimidazoles

In summary, the polybenzimidazole story reviewed in the foregoing sections reflects a vast research effort indeed, accomplished over the years in numerous polymer laboratories. A wide ran of direct and two-stage synthetic approaches is now available to the polymer chemist, and an equally wide scope of challenging possibilities of application has opened up to the technologist. It should also be clear from the presented material, however, that tte stage of commercial maturity has not as yet been attained, and intriguing new developments both on the preparative side and in the application s[Aere can, therefore, with confidence be expected in the years to come. 

Polybenzimidazole films doped with phosphoric acid have also been investigated for direct methanol fuel cells. These membranes, however, only display the requisite conductivities at high temperatures and have only been demonstrated in vapor feed systems operated at 150-200 C. Thus, although these novel membrane applications have been demonstrated to have decreased methanol permeability in fuel cells, none of the systems have been successful in being applied to low temperature liquid-feed direct methanol fuel cells. 

Fibers spun from polyvinyl alcohol, polybenzimidazoles, polyamides, and aromatic polyamides have been used as carbon fiber precursors. However, at present, the most attractive precursors are made from acrylonitrile copolymers and pitch, and a small amount from rayon. Today more than 95% of the carbon fibers produced for advanced composite applications are based on acrylic precursors. Pitch-based precursors are generally the least expensive, but do not yield carbon fibers with an attractive combination of tenacity (breaking strength, modulus, and elongation as those made from a acrylic precursor fiber). The acrylic precursors provide a much higher carbon yield where compared to rayon, typically 55% versus 20% for rayon, and this translates directly into increased productivity. 

Polybenzimidazole (PBI) (initially manufactured by Hoechst-Celanese, now PE ME A) is one of the few polymers under consideration for high-temperature operation. The application of PBI [206, 207] and the noncommercial AB-PBI [208] in fuel cells was introduced by Savinell and coworkers. For that, the membrane was immersed in concentrated phosphoric acid to reach the needed proton conductivity. Operation up to 200 °C is reported [209]. A disadvantage of this class of membranes is the acid leaching out during operation, particularly problematic for cells directly fed with liquid fuels. Additionally, the phosphoric acid may adsorb on the platinum surface. A review on membranes for fuel cells operating above 100 °C has been recently published [209]. 

Many polybenzimidazoles are prepared by direct condensation. They are colored polymers that mostly melt above 400 One such material is formed from 3,3 -diaminobenzidine and dipheyl isophthalate by heating the two together at 350-400 °C in an inert atmosphere ... 

What are direct condensation polymers How are polybenzimidazoles, polybenzoxazoles, polybenzthiazoles, polyoxidiazoles, polybenzotriazoles, and polysulfodiazoles prepared Illustrate with chemical equations. 

Hou H, Sun G, He R, Wu Z, Sun B (2008) Alkali doped polybenzimidazole membrane for high performance alkaline direct methanol fuel cell. J Power Sources 182 95-99... 

The vast catalogue of polymeric materials reviewed here included Nafion composite with inorganic and organic fillers, and non-fluorinated proton conducting membranes such as sulfonated polyimides, poly(arylene ether)s, polysulfones, poly (vinyl alcohol), polystyrenes, and acid-doped polybenzimidazoles. Anion-exchange membranes are also discussed because of the facile electro-oxidation of alcohols in alkaline media and because of the minimizatirHi of alcohol crossover in alkaline direct alcohol fuel cells. 

Wycisk R, Chisholm J, Lee J, Lin J, Pintauro PN (2006) Direct methanol fuel cell membranes from Nafion-polybenzimidazole blends. J Power Sources 163 9-17... 

Gubler L, Kramer D, Belack J, Unsal O, Schmidt TJ, Scherer GG (2007) Celtec-V. A polybenzimidazole-based membrane for the direct methanol fuel cell. J Electrochem Soc... 

Hou H, Wang S, Jiang Q, Jin W, Jiang L, Sun G (2011) Durability study of KOH doped polybenzimidazole membrane for air-breathing alkaline direct ethanol fuel cell. J Power Sources 196 3244-3248... 

Wang J-T, Wainright JS, Savinell RF, Lilt M (1996) A direct methanol fuel cell using acid-doped polybenzimidazole as polymCT electrolyte. J Appl Electrochem 26 751-756... 

Chuang SW, Hsu LC, Hsu CL (2007) Synthesis and proptuties of fluorine-containing polybenzimidazole/montmmillonite nanocomposite membranes for direct methanol fuel cell applications. J Power Sources 168 172-177... 

Lobato J, Canizares P, Rodrigo MA, Linares JJ (2009) Study of different bimetallic anodic catalysts supported on carbon for a high temperature polybenzimidazole-based direct ethanol fuel cell. Appl Catal B-Environ 91 269-274... 

Linares JJ, Rocha TA, Zignani S, Paganin VA, Gonzalez ER (2013) Different anode catalyst for high temperature polybenzimidazole-based direct ethanol fuel cells. Int J Hydrogen Energ 38 620-630... 

Because the thermal stability of polystyrenes and polymethacrylates is limited to 200°C, continuous use of a polymer-supported reactive species tends to be limited to significantly lower temperatures than this (see polymeric sulphonic acids). There is considerable interest in supporting, in particular, alkene oxidation catalysts on polymers and to operate reactions at temperatures above 200°C. To achieve this, novel thermo-oxidatively stable supports are required and some progress has been made in this direction. More details of specific applications will be given later, but supports based on, for example, polyacrylonitrile [50-52], polyamides [53-56], polysulphone [57, 58], polyaniline [59] and polybenzimidazole... 

A. Sannigrahi, S. Ghosh, S. Maity, T. Jana, Structurally isomeric monomers directed copolymerization of polybenzimidazoles and their properties. Polymer 51 (25) (2010) 5929-5941. 

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