Viscosity and temperature transitions in dimethylacetamide solutions of polyamidobenzimidazole and its blends with polysulfone

The rheological properties of 5% solutions of a fiber-forming polyamidobenzimidazole in DMAA containing LiCl additives and polyamidobenzimidazole-polysulfone blends in the same solvent have been studied. The total concentration of polymer blends with various component ratios is 5 wt %. At temperatures below ∼110°C, the systems under study behave as non-Newtonian fluids and their viscosity decreases with temperature. At T > 110°C, the temperature dependence of viscosity passes through a minimum. The position of the minimum on the temperature scale decreases with the concentration of polyamidobenzimidazole. This character of a change in viscosity is associated with the phase separation of polyamidobenzimidazole solution that leads to its gelation. The temperature corresponding to the minimum viscosity coincides with the onset temperature of a sharp turbidity of solution during heating. It is suggested that solutions containing up to 5% polyamidobenzimidazole possess an LCST. The addition of up to 50% polysulfone has almost no effect on the temperature of transition but brings about a marked decline in the viscosity of the system.