Polybenzimidazole chemical structures

Fig. 7 Chemical structures of some sulfonated polymers and a polyimide (A) sulfonated polyetheretherketone, PEEK, PSE (B) sulfonated polyphenylenesulfide, PPS (C) sulfonated polysulfone (D) poly(4,4 -biphenol) (4,4 -dichlorodiphenyl sulfone), BPSH-XX (XX is mol% of disulfdonated units) (E) sulfonated polybenzimidazole, PBI (F) polyimide.

Figure 10.8 Chemical structure of (a) polybenzimidazole (PBI) and (b) phosphoric acid-doped PBI.

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... 

A third class of material that have been used are the polybenzimidazoles, polybenzimidazolones, polyamidehydrazide and polyimides. The chemical structures of these materials have been given in chapter H. 

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

Polybenzimidazole (PBI) is a unique and highly stable linear heterocyclic polymer. The chemic structure is shown in Fig. 12.42. PBI exhibits excellent thermal stability, resistance to chemicals, acid and base hydrolysis, and temperature resistance. PBI can withstand temperatures as high as 430°C, and, in short bursts, to 760°C. It does not burn and maintains its properties as low as -196°C. 

Chemical structure of (a) aromatic polyimides, (b) aromatic polyamides, and (c) aromatic polybenzimidazoles. 

FIGURE 8.39 Chemical structures of four kinds of polybenzimidazoles. (Reprinted from Chang, Z. et al., Polym. Degrad. Stabil., 95, 2648, 2010. With permission.)... 

These plastics, also known as pyrrones, are experimental materials prepared from aromatic dianhydrides and aromatic tetraamines. The polymer syntheses provide soluble prepolymers that are converted to the pyrrone structures by thermal or chemical dehydration. The precursors can be used to cast films or coatings, or can be molded under very high pressures into filled or unfilled forms. The pyrrones combine some of the best properties of the polybenzimidazoles and polyimides. The pyrrone films are exceptionally radiation resistant and retain their strength properties after 10,000 megarads of 1-MeV electrons. 

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. 

The most important resins available for use as adhesives in high temperature structural applications are 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 [8]. Table 5.5 provides examples of performance properties of a poly-etherimide adhesive (Ultem is trademark of SABIC Corp). IP-600 stands for Thermid IP-600 for which the chemical formula is shown in Rgure 5.1. 

The polyaromatic resins, polyimide and polybenzimidazole (PBI), offer greater thermal resistance than any other commercially available adhesive. The rigidity of their molecular chains decreases the possibiUty of chain scission caused by thermally agitated chemical bonds. The aromaticity of the structure provides high bond dissociation energy and acts as an energy sink to the thermal environments [1]. 

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