A polybenzimidazole having the structural repeat unit

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and designated AB-PBI was formed into films by casting or precipitating from dilute solutions. Selected films were swollen in a plasticizing medium arid drawn about 2X. All films were dried in a vacuum oven to aid in the removal of residual solvent and moisture. Wide angle X-ray scattering (WAXS) was used to show the type of ordering found in this material and to indicate the extent of molecular orientation. Neither a glass transition nor a crystalline melting point has been observed for this polymer, A Perkin-Elmer DSC was used to scan the temperature range from −150 to H-400°C in search of secondary transitions. The rheovibron proved more sensitive and a transition was located in the vicinity of −60°C. An activation energy-was determined. The morphology of this polymer is subject to speculation. The ability of the chain to adopt a linear conformation leads to the possibility of a liquid-crystalline nature in solution. A model based on the data in hand is suggested. Stress-strain data was used to compare the mechanical properties of films prepared by several methods as well as to demonstrate the effect of orientation on strength.