High-and Low-Temperature Solution Polymerizations

Numerous communications describe the use of high-temperature solution polymerization techniques. Of the solvents used, poly(pbosphoric acid), introduced in 1964 into polybenzimidazole chemistry by Iwakura et al.30), doubtlessly occupies the first position, and a great many syntheses employing the poly(phosphoric add) solution technique have since been reported from various polymer laboratories31-39). 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-sensitive free bases. In addi- 

As D Alelio s patent embodies conditions of low condensation temperatures and so, just like some of the aforementioned solution polymerizations44,4, teaches conditions beneficial to reactant and product 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 such monomers being te-trahaloterephthalaldehydes or the crosslinkable 3-vinylisophthalaldehyde. It does not, however, provide for the isolation and application of prepolymers and, thus, for utilization of die two-stage approach so beneficial from a processing and application standpoint. 

Spectroscopic information, supported by the results of a non-polymeric model reaction study50, indicates the prepolymers to possess a predominantly open-chain structure of 

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