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 (N d and the viscosity (1J), compared at the same shear rate (1'), 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 (1Jo) versus cM w , where M w is the weight average molecular weight, for both systems revealed that "bends" occurred in the data corresponding to a critical entanglement molecular weight (Me) of 1180 for PPT (this corresponds to 30 main chain atoms (a) and to 5260 (z = 330) for nylon 6,6. More significantly, 1Jo was found to be proportional to (CM w ) 6.S for solutions ofPPT and to (cM w )3.4for nylon 6,6 solutions. 1J versus l' curves were similar in shape for both systems and could be reduced to the same master curve with the only difference being that the relaxation times or shifting factors were considerably greater for the PPT solutions. This suggested that the process of destroying entanglements may be similar for both polymers.
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Baird et al. (1979) studied this question.
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