Polybenzimidazole high temperature applications

Much attention has been paid to the synthesis of fluorine-containing condensation polymers because of their unique properties (43) and different classes of polymers including polyethers, polyesters, polycarbonates, polyamides, polyurethanes, polyimides, polybenzimidazoles, and epoxy prepolymers containing pendent or backbone-incorporated bis-trifluoromethyl groups have been developed. These polymers exhibit promise as film formers, gas separation membranes, seals, soluble polymers, coatings, adhesives, and in other high temperature applications (103,104). Such polymers show increased solubility, glass-transition temperature, flame resistance, thermal stability, oxidation and environmental stability, decreased color, crystallinity, dielectric constant, and water absorption. 

Polybenzimidazoles Mainly polymers of 3,3, 4,4 -tetraminonbiphenyl (diaminobenzidine) and diphenyl isophthalate. Has good heat, fire, and chemical resistance. Used as coatings and fibers in aerospace and other high-temperature applications. Also called PBI. 

Qian W, Shang Y, Fang M et al (2012) Sulfonated polybenzimidazole/zirconium phosphate composite membranes for high temperature applications. Int J Hydrogen Energy 37 12919-12924... 

Abstract This chapter discusses polybenzimidazole (PBI), PBI blends, and some of their high temperature applications. The chapter first reviews the PBI polymer, including its history, structure, properties, synthesis, advantages and limitations. It then focuses on various PBI blends and their properties. The chapter also summarizes current commercial PBI and PBI blend products and provides examples of PBI and PBI blends in high temperature apphcations. 

Key words polybenzimidazole, high performance polymer blend, high temperature applications. 

Staudt, R. and J. Boyer, Development of polybenzimidazole-based, high temperature membrane and electrode assemblies for stationary and automotive applications, U.S. DOE 2004 Annual Program Review Proceedings, Philadelphia, PA, May 2004. 

Many heterocyclic polymers have been produced in an attempt to develop high-temperature-resistant polymers for aerospace applications. Among these are the polybenzimidazoles (PBIs), which are prepared from aromatic tetramines and esters of dicarboxylic acids (structure 4.63). In standardized procedures, the reactants are heated to below 300°C forming soluble prepolymer, which is converted to the final insoluble polymer by further heating ... 

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. 

Electro-insulation materials. The retention of dielectric properties in a high-temperature environment, coupled with good corrosion resistance in contact with certain reactive chemicals, suggests excellent possibilities of polybenzimidazole use in electrical insulation and other dielectric applications at high operating temperatures and/or in aggressive chemical environments. Typical applications, hence, can be foimd in special cable and wire insulation, in the manufacture of circuit boards and radomes for supersonic aircraft, as battery and electrolytic cell separators, and as fuel cell frame structural materials. Some recent publications in the patent and technical report literature may serve to illustrate such applications. 

In 1983 Celanese began the production of polybenzimidazole (PBI) by using diphenyl isophthalate and 3,3 -diaminobenzidine, DAB. PBI is a high-temperature and flame-resistant fiber, used in the production of safety gloves and various items of protective clothing as well as for the production of PBI-based membranes for reverse osmosis and ultrafiltration applications. 

Structural engineering materials Use as structural materials, especially under conditions of ablation or in high-temperature environments, has been one of the prime objectives of polybenzimidazole development ever since Marvel s first publication.This holds to a small extent for molded products and to a predominant extent for laminates. Almost all the polymers evaluated and used in these technical applications are of the type 1. 

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. 

These new types and forms of fiber provided the industry with more freedom to select the most appropriate type of fiber reinforcement for a given application. Newly developed, high modulus plastics, such as cycloaliphatic epoxies and new-generation high-temperature plastics, such as polybenzimidazole and nylon plastics, offer another degree of fi-eedom in terms of material matrix selection. 

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]. 

Chuang SW, Hsu SL (2006) Synthesis and properties of a new fluorine-containing polybenzimidazole for high-temperature fuel cells applications. J Polym Sci Pol Chem 44 4508-4513... 

Kim SK, Kim TH, Jung JW, Lee JC (2009) Polybenzimidazole containing benzimidazole side groups for high-temperature fuel cells applications. Polymer 50 3495-3502... 

Coordination polymers containing rotaxane linkers 12CSR5896. Design and synthesis of cross-Hnked poly(benzoxazine)- and polybenzimidazole-based copolymer membranes and their application to an electrolyte membrane for a high-temperature PEM fuel cell 13P77. 

The most important resins available for use as adhesives in high-temperature structural applications are polyimides (Pis) and polybenzimidazoles (PBIs), both of which are described later (see Sections 5.35 and 5.33). These resins are supplied as prepolymers containing open heterocyclic rings, which are soluble and fusible. At elevated temperatures, the prepolymers undergo condensation reactions leading to ring closure and the formation of insoluble and infusible cured resins. 

Initially developed in the late 1950s and early 1960s, polybenzimidazoles are prepared by reaction of tetrafunctional aromatic amines with aromatic esters (Fig. 1). They find application as High-temperature adhesives. 

Materials that come close to the ideal ladder structure are thermosetting polyimides and polybenzimidazoles. These are used primarily in high-temperature aerospace applications as composites and adhesives. 

Aromatic polybenzimidazoles were synthesized by H. Vogel and C. S. Marvel in 1951 with anticipation, later justified, that the polymers would have exceptional thermal and oxidative stability. Subsequently, NASA and the Air Force Materials Laboratory (AFML) sponsored considerable work with polybenzimidazoles for aerospace and defense applications as a non-flammable and thermally stable textile fiber and as high temperature matrix resins, adhesives and foams. The route to fiber used solutions of high molecular weight polymer. Structural applications used low temperature melting pre-polymers that were cured (polymerized) in place. Applications of polybenzimidazoles were not implemented in the 60 s and 70 s since the polymers tetraamine precursors were not commercially available. 

Polybenzimidazoles first appeared in US Patent 2,895,948 in 1959. In 1961, Vogel and Marvel opened the field of high temperature polymers [1] with their studies of the thermal stability of aromatic polybenzimidazoles [3]. Subsequently, AFML and NASA funded programs for basic studies and for structural and textile applications of polybenzimidazoles to meet new aircraft and aerospace material needs. Several reviews were published [4-7]. Structural applications of polybenzimidazoles are still in developmental stages which is discussed below. One polybenzimidazole polymer (PBI) which was developed for fiber applications is now commercial. Details of the polymer synthesis and fiber process are described in the next section. 

Seel DC, Benicewicz BC, Xiao L, Schmidt TJ (2009) High-temperature polybenzimidazole-based membranes. In Vielstich W, Yokokawa H, Gasteiger HA (eds) Handbook of Fuel Cells-Fundamentals, Technology and Applications, vol 5. John Wiley Sons, Chichester, pp 300-312... 

Xiao L (2003) Novel polybenzimidazole derivatives for high temperature polymta- electrolyte membrane fuel cell application. PhD Thesis, Rensselaer Polytechnic Institute, Troy, NY... 

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