Shear dependence of viscosity–molecular weight transitions. A study of entanglement effects

The flow behavior of concentrated polymer solutions covering molecular weights up to 150,000 were examined at shear rates up to 200,000 sec.−1. The viscosity–molecular weight–shear rate results of previous workers recognizing only single critical molecular weight M*, above which ordinary Bueche entanglements dominated the flow, were compared with our findings in which two distinct critical molecular weights, upper M* and lower M** exist. These results are compared with the theory, and new interpretations are presented.