| Abstract: | Poly(p-phenylene benzbisoxazole) and poly(p-phenylene benzbisthiazole) belong to the class of extended-chain, rigid-rod polymers possessing high modulus, high strength, and good thermal and oxidative resistance. Fibers and films of these polymers are processed from anisotropic solutions in strong acids such as methane sulfonic acid or polyphosphoric acid. The electronic absorption and vibrational spectra of the model compounds have been investigated in order to characterize the structures in the solid state and in nonprotonic solvents. The dramatic intensity differences in the spectra obtained have been interpreted by variations in the dihedral angle between the plane of the phenyl group and the plane of the central heterocyclic ring which affect the resonance configuration between the two rings. |
