Polybenzimidazole solutions

Polybenzimidazole (PBI) Fibers. Poly(2,2 -(y -phenylene)-5,5 -bisbenzimidazole) [25734-65-0] is a textile fiber marketed by Hoechst-Celanese (11) which does not form Hquid crystalline solutions due to its bent meta backbone monomeric component. PBI has exceUent resistance to high temperature and chemicals. 

PA-4,6 synthesis from, 171-172 PA-6,6 polymerization from, 169-170 PA-6,1 synthesis from, 181 PA salt solution, polymerization from, 164 Pawlow, James H., 431 PBIs. See Polybenzimidazoles (PBIs)... 

The resulting polybenzimidazole is amorphous and shows a very high glass transition temperature of 425 °C. It is highly flame resistant. Therefore, FBI fibers that are spun from solution, are used for the production of fireproof protection clothes and also for fabrics of airplane seats. 

Numerous communications describe the use of hi -temperature solution polymerization techniques. Of the solvents used, poly(phosphoric acid), introduced in 1964 into polybenzimidazole chemistry by Iwakura et al. doubtlessly occupies the first position, and a great many syntheses employing the poly(phosphoric add) solution technique have since been reported from various polymer laboratories " Iwakura s technique offers an advantage insofar as the tetraamine monomers may be employed as the stable and easy-to-handle hydrochlorides in place of the extremely air-sendtive free bases. In addi-... 

As D Alelio s patent embodies conditions of low omdensation temperatures and so, just like some of the aforementioned solution polymerizations , teaches a>nditions beneficial to reactant and nx>duct integrity, it permits the preparation of polybenzimidazoles from monomers too unstable thermally or chemically for use in the melt or poly(phosphoric acid) solution processes, examples of sudi monomers being te-trahaloterephthalaldehydes or the crosslinkable 3-vin)fisophthalaldehyde. It does not, however, provide for the isolaticm and application of prepolymers and, thus, for utilization of die two-stage approadi so beneficial from a processing and application standpoint. 

The molecular size of polybenzimidazoles has in the pertinent literature been expressed in terms of inherent (j7i h) or intrinsic ([ ]) viscosities, determined on sulfuric acid solutions or, less frequently, on solutions in formic acid or aprotic solvents. The effect of structure on viscosity behavior appears to be less pronounced than that of the polymerization methods used and of the monomer sensitivity to the employed reaction conditions. In general, melt polymerizations by Marvel s method give products with higher molecular mass than obtained in solution condensations, which may partly be due to increased end group reactivity and interaction at the much higher reaction temperatures encountered in the former process (Cf. Table 1). Furthermore, monomers like bis(phenoxycar-bonyl)ferrocene, diphenyl tetrafluoroterephthalate, or l,7-bis(phenoxycarbonyl)car-... 

Reverse osmosis memhraaes. The exceptionally high moisture regain observed with polybenzimidazole fibers prompted a team at Celanese Research Co to investigate the utility of polybenzimidazole films as semipermeable membranes for reverse osmosis processes, such as sea water desalination66,94). A continuous process was devised in which films were cast from solution into a water precipitation bath. The films were tested for reverse osmosis performance with a saline solution (0.5% Nad) as feed stream at a pressure of 4.14 MN m-2 and a flow rate of 19.8 m min-1. Salt rejection was ca. 95% throughout. A cellulose acetate film of the type commonly used as a reverse osmosis standard was tested under the same conditions for comparison. Table 8 shows the results. 

Sulfonated polybenzimidazoles have been prepared by polycondensation of sulfoterephthalic acid and disulfoisophthalic acid with 3,3 -diaminoben-zidine using high temperature solution polycondensation in PPA [150-153]. 

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. 

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