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The steady state shear rheological properties of solutions of a rodlike polyamide, poly‐p‐phenyleneterephthalamide (PPT), in 100% sulfuric acid have been compared with those of solutions of a flexible chain polyamide, nylon 6,6 in the same solvent. For solutions of similar concentration (c) and molecular weight (M), it was found that the primary normal stress difference (N1) and the viscosity (η), compared at the same shear rate (γ), were an order of magnitude greater for solutions of PPT. It was believed that this behavior could be accounted for through the formation of an enhanced entanglement network in the PPT solutions. Plots of the zero shear viscosity (η0) versus cMw, where Mw is the weight average molecular weight, for both systems revealed that “bends” occurred in the data corresponding to a critical entanglement molecular weight (Mc) of 1180 for PPT (this corresponds to 30 main chain atoms (z)) and to 5260 (z=330) for nylon 6,6. More significantly, η0 was found to be proportional to (cMu)6.8...

Comparison of the Rheological Properties of Concentrated Solutions of a Rodlike and a Flexible Chain Polyamide