Effect of the thermodynamic quality of solvent on the viscosity properties of concentrated solutions of poly(4,4′-oxydiphenylene)pyromellitamic acid

Molecular characteristics and rheological behaviour of solutions of poly(4,4′-oxydiphenyl)pyromellitamic acid in a mixture of DMFA (thermodynamically good solvent) with toluene (precipitant) were studied, at various solvent compositions up to that corresponding to a θ-solvent. It was shown that when the initial solutions are diluted by the precipitant, the viscosity of the solutions is independent of the thermodynamic quality of the solvent, and their intrinsic viscosity consequently decreases. A comparison of the rheological behaviour of polyamic acids synthesized in solvents of various thermodynamic quality has shown that the molecular mass of the formed polymer is the higher, the poorer the quality of the solvent.