Morphological and physical property effects for solvent cast films of poly‐2, 5(6) benzimidazole

A polybenzimidazole having the structural repeat unit magnified image 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.