solutions is unsupported by observation

There is general agreement that the observation of shear banding in well entangled polymer solutions and melts has strong implications for existing models of chain entanglement during large deformation. Understandably, observations of this phenomenon by our group in numerous prior measurements have been controversial because of the challenge that these observations raise for the physical validity of the reptation/tube model. We welcome independent measurements aimed at verifying or refuting our conclusions based on carefully prepared, well-characterized and strongly entangled polymer solutions. It is clear that Li et al.’s measurements were based on solutions that were either only marginally entangled or polydisperse, which understandably did not exhibit shear banding under the weak shearing conditions that they chose. We publicly repeat our prior private offer to provide shear-banding samples for Li et al. to test under the rheological conditions that were explore previously but not employed by Li et al. (2014). Li et al. (2014) stated “we agree that the sample MW is different from that specified by the supplier and has the Z = 22 entanglement number”. But rather than making additional measurements on well entangled relatively monodisperse PB solutions following previous protocols, they continue to maintain that their former measurements were sufficient to demonstrate that shear banding does not exist in highly entangled polymer solutions in absence of artifacts. We find Li, et al.'s position to be unconvincing, and we next discuss in detail why their conclusions cannot stand, including a description of why the prior solutions in Ravindranath et al. (2007) had the correct characterization. We first note Li et al. (2014)'s acknowledgement that the molecular weights Mw and molecular mass distributions (as characterized by the polydispersity index, PDI) reported in thei