Fibers of thermally stable ordered heterocycle–amide copolymers

Thermostable fibers were spun from several ordered heterocycle‐amide copolymers. Tenacities up to 8 g./den. at standard conditions were obtained. The polymers were prepared by condensation of arylene diacid chlorides with aromatic diamines containing preformed heterocyclic units of types known to be thermally stable (oxadiazole, thiazole, and bithiazole). Fiber tensile properties were determined at temperatures up to that at which the fiber failed. Each fiber had a zero strength temperature of over 515°C. in nitrogen, and each had appreciable strength at 400°C. In general, the fiber showed excellent retention of tenacity after heat aging for long periods of time at 300°C. in air. An oxadiazole‐amide fiber retained three‐fourths of its original tenacity after 168 hr. under these conditions.