Assessing the Range of Validity of Current Tube Models through Analysis of a Comprehensive Set of Star-Linear 1,4-Polybutadiene Polymer Blends

We blend newly synthesized nearly monodisperse four-arm star 1,4-polybutadienes with various well-entangled linear polymers, confirming the conclusions in Desai et al. [ Macromolecules201649 (13)49644977 ] that advanced tube models, namely, the hierarchical 3.0 and branch-on-branch models [ Wang, Z.; et al. J. Rheol.201054 (2)223260 ], fail to predict the linear rheological data when the pure linear polymers have shorter relaxation times, but within 3-4 orders of magnitude of the star polymer. However, when the linear polymer has a longer relaxation time than the star, our new work, surprisingly, finds that non-monotonic dependence of terminal relaxation behavior on composition is both observed experimentally and captured by the models. Combined with previous data from the literature, we present results from over 50 1,4-polybutadiene star-linear blends, suitable for thorough testing of rheological models of entangled polymers.