Synthesis and characterization of poly(1‐benzoylthiosemicarbazide) and poly(1,3,4‐thiadiazole amine) from 2‐( p ‐aminophenyl)‐1,3,4‐oxadiazoline‐5‐thione via ring‐opening process

A novel thermally stable and semiconducting polyheterocycle, poly(1,3,4‐thiadiazole amine), was synthesized from 2‐( p ‐aminophenyl)‐1,3,4‐oxadiazoline‐5‐thione via ring‐opening. The polymer is a new class of ordered alternating copoly(aniline) containing 1,3,4‐thiadiazole heterocyclic units. An investigation of the reaction of 2‐phenyl‐1,3,4‐oxadiazoline‐5‐thione with aniline was conducted as a model reaction for the polymerization, and poly(phosphoric acid) (PPA) and phosphorus pentoxide/methanesulfonic acid (PPMA) were found to be favorable both as condensing agent and solvent for the formation of 2‐anilino‐5‐phenyl‐1,3,4‐thiadiazole as a model compound. The polymerization was carried out both by two‐step procedure that included ring‐opening self‐polyaddition giving poly(1‐benzoylthiosemicarbazide), followed by cyclodehydration to poly(1,3,4‐thiadiazole amine), and by a one‐step procedure including cyclodehydration in situ. The poly(1‐benzoylthiosemicarbazide) which was formed in the first step in m ‐cresol had reduced viscosities up to 0,42 dL·g −1 , and it was converted to poly(1,3,4‐thiadiazole amine) by treating in PPA or PPMA. Poly(1,3,4‐thiadiazole amine) having reduced viscosities up to 0,25 dL·g −1 was also synthesized by the direct one‐step polymerization in PPA or PPMA. The polymer is highly thermally stable and exhibited no weight loss up to 350°C under nitrogen. Its electric conductivity was less than 10 −10 S·cm −1 at ambient temperature, but markedly increased to 2,9·10 −7 S·cm −1 upon doping with iodine.