Physical Chemical Properties of Complex Aromatic-Heterocyclic Polymers. Part 2

Physical chemical methods have been used to characterize poly1-4, phenylene bisoxazole, PBO, and poly1-4, phenylene bisthiazole, PBT, by studies on dilute solutions. Experimental methods include absolute intensity and intensity fluctuation light scattering, viscometry, and absorption and fluorescence spectroscopy. Both PBO and PBT are soluble only in strong, protic acids, in which the solvated chains are strongly protonated. Consequently, the measured properties depend markedly on the ionic strength of the solvent. The data show that PBO and PBT are rodlike chains, but the analysis is complicated by the tendency of both to undergo interchain association. The latter effect is more pronounced with PBO and than with PBT. The association is not an equilibrium process. It is necessary to combine the results of several kinds of experiments to assess the effects of the metastable association, and to elucidate the molecular structure.