AbstractDepending on the coagulation conditions, poly(p‐phenylene‐1,3,4‐oxadiazole) in the solid state forms two modifications, as can be evidenced by FTIR spectroscopy and by wide‐angle X‐ray scattering curves (WAXS). In both cases each modification is detectable by characteristic peaks. Processing of fibers or films from solutions in concentrated sulfuric acid by coagulation in water results in the formation of a thermodynamically non‐equilibrium form, defined as β‐modification. Under special conditions it is possible to obtain the three‐dimensionally ordered equilibrium α‐structure that leads to processing products with markedl