Polybenzimidazole synthesis solubility

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. 

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... 

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

Wang G, Xiao G, Yan D (2011) Synthesis and properties of soluble sulfonated polybenzimidazoles derived from asymmetric dicarboxylic acid monomers with sulfonate group as proton exchange membrane. J Membr Sci 369 388-396... 

In the 1960s, Marvel and coworkers reported the synthesis of polybenzimidazole and polybenzborimidazoline. These polymers possessed low solubility in organic solvents. Polybenzimidazole containing ferrocenyl units in its backbone (109) (Scheme 27) was prepared by the 1 2 polycondensation of l,r-ferrocenedimethanol (107) with 3,3, 4,4 -biphenyl-tetw-amine (108) in the presence of [RuCl2(PPh3)3]. Mossbauer spectroscopy showed that approximately 20% of the iron centers were... 

In some special cases, Ueda s approach is more useful for PBI synthesis. For example, the authors found that the copolymerization of disodium 4,6-fcis(4-carboxyphenoxy) benzene-l,3-disulfonate (BCPOBDS-Na), 4,4 -dicarboxydiphenyl ether (DCDPE), and 3,3 -diaminobenzidine (DABz) in Eaton s reagent at IdO C yielded organo soluble linear sulfonated polybenzimidazoles (SOPBIs) [7], whereas insoluble gel was obtained when the polymerization was conducted in PPA probably because of the occurrence of cross-linking reactions between sulfonate groups and activated benzene rings. 

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