Flow birefringence and the conformational characteristics of the polyimide molecule based on the dianhydride of diphenyltetracarboxylic acid and 2,5-di(p-aminophenyl)pyrimidine☆

Abstract The flow BR method has been employed to investigate a polyimide belonging to a molecularly homologous series and obtained by polycondensation of the dianhydride of 3,3′,4,4′-diphenyltetracarboxylic acid and 2,5-di( p -aminophenyl)pyrimidine in solution in sulphuric acid with an excess (1%) of sulphur trioxide. The method used and the Tsvetkov theory for kinetically rigid chains have been used to determine the lengths of the Kuhn segment A = (24±2.5) nm and the optical anisotropy of the unit length of the chain β L = (21±2) × 10 −17 cm 3 . A theoretical analysis has been made of the mechanisms of chain flexibility.