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Polyimides that contained thianthrene and dibenzo‐p‐dioxins units were synthesized. The tricyclic fused rings were successfully incorporated by polymerizing the diamines of the units with aromatic tetracarboxylic dianhydrides. The resulting polyamic acids were converted to polyimides by thermal cyclodehydration. The influence of the tricyclic units on the properties of the polyimides has been investigated. Polyimides that contained dibenzo‐p‐dioxins (ODP) exhibited sufficient thermal stability but were insoluble even in concentrated sulfuric acid. The introduction of a methyl group did not produce an appreciable increase in solubility. Thianthrene polyimides were considerably less stable than the equivalent polymers derived from open‐chain diamine, 4,4′‐diaminodiphenyl sulfide but were partly soluble in acid solvents. The results are discussed in terms of packing the polymer molecules.

The condensation of isatin with o-phenylenediamine has been studied in various kinds of solvents. The reaction gave pure indolo[2,3-b]quinoxaline (1) in acidic solvents, while it gave a mixture containing at least two out three compounds, 1, an anil and a spiro compound, in neutral or basic organic solvents. The anil and spiro compounds were converted to 1 in the presence of acid or by heating them above their melting points. The mechanism of the formation of these compounds and the conversion could be explained by the presence of the intermediate of the adduct formed between the amino groups of o-phenylenediamine and the β-carbonyl of isatin.

2‐Sulfoterephthalic acid (STA) and disulfoisophthalic acid (DSIA) were synthesized through the sulfonation and the oxidation of m‐ and p‐xylene. The polycondensation reactions of STA and DSIA with aromatic tetraamines gave polybenzimidazoles which contained one or two sulfonic acid groups for each repeating unit. The polymer obtained was soluble in sulfuric acid, some organic solvents, and aqueous strong alkaline solution. The polymers were stable up to 400°C, but they gave polybenzimidazoles above 400°C by eliminating sulfonic acid groups, instead of ring closure.