AbstractThe phase diagrams of the ternary system poly(ethenyl‐1,3,4‐oxadiazole‐2,5‐diyl‐1,4 phenylene), sulfuric acid, and water indicated that the increase of the ethenyl residue in the copolymers increased the solubility in the acid. The critical point of separation in sulfuric acid was determined, and it decreased from 74 to 60.5 as the ethenyl ratio of copolymers was increased. The electrical properties in the temperature range of 0–90°C at a fixed frequency of 1592 Hz were also investigated. The tan δ values increased with increase in temperature and passed through a maximum. The temperature of this maximum varied with the nature of the copolymer. The observed increase in the dielectric constant with temperature may be due to increased segmental motion in the amorphous region of
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