Abstract
The nonlinear rheology of entangled polymers is strongly influenced by molecular architecture, yet architectural complexity does not necessarily translate into superior processing performance. Here, we investigate the transient shear and uniaxial elongation responses of symmetric star-branched and linear polystyrene chains of similar span length, using recent experimental data of Liu et al. (2025). Predictions are performed with the clustered fixed slip-link model (CFSM), a coarse-grained implementation of the discrete slip-link model, recently revised to accurately describe the mean-field constraint dynamics in star-branched polymers (Katzarova et al. Macromolecules, 59(1):564–574 2026). The model quantitatively reproduces the transient shear response for both architectures at moderately large Rouse-Weissenberg numbers ( \(Wi_\textrm{R}\lesssim 2\) ) and captures elongational stress growth up to Hencky strains of approximately two, achieving a level of agreement with experiment that is unprecedented for coarse-grained models in these nonlinear regimes. Consistent with prior experimental interpretations, we confirm theoretically that the Rouse-stretch time of symmetric star polymers can be estimated in the same manner as for linear chains, provided the span length is taken as twice the arm molecular weight. The results further suggest that, far-from-equilibrium, branch-point diffusion in star polymers plays a diminished role in the nonlinear response, highlighting an architectural effect relevant to polymer processing flows.
Graphical abstract
