High molecular weight polybenzimidazoles and polybenzoxazoles having cyclohexane, cyclopropane, and spiro [3:3]heptane rings in the main chain were prepared by solution polycondensation of 3,3′‐diaminobenzidine tetrahydrochloride dihydrate, or 3,3′ ‐dihydroxybenzidine dihydrochloride with the corresponding dicarboxylic acids in polyphosphoric acid. Their preparation and physical properties, such as thermal stability, solubility, and crystallinity are described.
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Inoue et al. (1966) studied this question.
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