Polybenzimidazole solubility

Gieselman, M. B. and Reynolds, J. R. 1992. Water-soluble polybenzimidazole-based polyelectrolytes. Macromolecules 25 4832-4834. 

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 ... 

Considerable efforts have centered on carrying out the synthesis of polybenzimidazoles at more moderate temperatures. Polymerization of the isophthalic acid or its diphenyl ester have been successfully carried out in polyphosphoric acid or methanesulfonic acid-phosphorous pentoxide at 140-180°C, but the reaction is limited by the very low solubilities (<5%) of the reactants in that solvent. The lower reaction temperature is a consequence of activation of the carboxyl reactant via phosphorylation. Lower reaction temperatures are also achieved in hot molten nonsolvents such as sulfolane and diphenyl sulfone, but the need to remove such solvents by a filtration or solvent extraction is a disadvantage. 

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. 

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. 

Several years ago, encouraged by the proven intermediacy of polyimidazolines in Gray s imidazole polymer synthesis we set out to demonstrate experimentally an analogous intermediary stage in the polycondensation of Scheme 13 and develop a preparative approach that would enable us to isolate soluble polyimidazoline intermediates. Clearly, if such polymeric imidazolines could be isolated and their further smc th conversion to polybenzimidazoles be accomplished, the door would be opened for the development of two-stage processing techniques involving prepolymer-type materials. Initial... 

B. Gieselman, J.R. Reynolds, Water-soluble polybenzimidazole-based polyelectrolytes, Macmmolecules, 1992, 25, 4832. 

In order to improve the solubility of aromatic polymers silicon-containing polymers have also been synthesized, by introduction of siloxane or silarylene linkages into polymer backbones such as polyamides, polybenzimidazoles and polyimides [50]. The resultant polymers show fair solubility in organic solvents but most of them have poorer thermal stability then their analogues without siloxane or silarylene linkages. 

This polymer in its tautomeric form b soluble in caustic alkali and can be qnm in normal rayon spin-baths. The most interesting fact is that salts of bivalent metals (Za, etc.) added to the sjHn-bath react rapidly with the polymer, framii chelates. Such fibers are highly flame proof, their LOI value being greater than 0.50, i.e., even higher than the corresponding value of the Nonwx fib and of polybenzimidazoles, which are used particularly in aeronautic construction. 

The polymers obtained were soluble in sulfuric acid, some organic solvents, and aqueous strong alkaline solutions. The polymers were stable up to 400 °C, but they yielded polybenzimidazoles by eliminating sulfonic acid groups, instead of ring closure. 

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. 

Polybenzimidazoles (PBIs) are high-temperature-resistant polymers. They are prepared from aromatic tetramines (for example, tetra amino-biphenol) and aromatic dicarboxylic acids (diphenylisophthalate). The reactants are heated to form a soluble prepolymer that is converted to the insoluble polymer by heating at temperatures above 300°C. The general structure of PBI is shown in Fig. 2.12. 

W. Huanga, S.B. Qinga, J.T. Yang, D.Y. Yan, Preparation and characterization of soluble sulfonated polybenzimidazole for proton exchange membrane materials. Chin. J. Polym. Sci. 26 (2) (2008) 121-129. 

S. Qing, W. Huang, D. Yan, Synthesis and properties of soluble sulfonated polybenzimidazoles, React. Funct. Polym. 66 (2) (2006) 219-227. 

S. Maity, T. Jana, Soluble polybenzimidazoles for PEM synthesized from efficient, inexpensive, readily accessible alternative tet-raamine monomer. Macromolecules 46 (17) (2013)6814-6823. 

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