Diffusion and flow birefringence of poly(naphthoyleneimide benzimidazole) in concentrated sulfuric acid

The effect of changes in chemical structure on the equilibrium and kinetic behavior is examined for fully cyclic poly(naphthoyleneimide benzimidazole) (PNI) molecules in dilute solution in 96% sulfuric acid. With this aim, hy drodynamic and dynamo-optical properties were analyzed over a wide range of molecular weight from 6.7 x 10(3) to 2.5 x 10.(5) The M dependence of the translational diffusion coefficient, D, the shear optical coefficient, Delt a n/Delta tau, the intrinsic orientation of the macromolecules in the flow, [chi/g], and the intrinsic viscosity, [eta], were established as well as t he macromolecule conformation. Results thus obtained indicate the rigid-cha in behavior of the PNI molecules. From their comparison with similar data o btained earlier for poly(amide benzimidazole) the conclusion was made that the exclusion of physical mechanisms of the chain flexibility due to the am ide group leads to a significantly higher equilibrium rigidity of the macro molecule. At the same time, the comparison of the flow birefringence relaxa tion time with the viscometric data indicates the intramolecular motions th at include a large-scale deformation of the PNI chain increasing with the m olecular weight.