Extensional rheology of ring polystyrene melt and linear/ring polystyrene blends

The state‐of‐the‐art understanding of entangled linear polymers is based on the concept of physical network formation from entanglements. The physical network is characterized by aplateau modulus in linear viscoelastic (LVE) measurements. However, linking the two free ends of a linear polymer, thereafter called a ring polymer, has dramatic consequences. For example, non-concatenated rings have much lower zero‐shear‐rate viscosity compared to their linear entangled counterparts. A plateau modulus is not observed in LVE measurements for ring polymers [1].Due to the difficulties in synthesis, which leads to very limited amount of samples, well‐defined ring polymers have never been studied in extensional flow. In this work, we present the first results of extensional rheology of a ring polystyrene (PS) melt with the molecular weight 185k(Ring‐185k). We show that the ring PS is surprisingly strain hardening in extensional flow, and reaches the same extensional steady state viscosity as its linear counterpart (Lin‐185k) when the stretch rate is fast enough. We further present the extensional rheology of blends made of Ring‐185k and Lin‐185k, with weight fraction of 5%, 20%, and 30% of Ring‐185k, respectively. We show that in the transient stress‐strain responses, stress overshoot is observed for the samples containing 20% and 30% Ring‐185k, while the stress overshoot is not observed for the pure Ring‐185k and Lin‐185k.The present results shed light into the fascinating flow properties of polymers without free ends, while they also advance the state‐of‐the‐art in polymer physics. At the same time, they open the route for understanding the response of folded proteins and chromosome territories under strong external fields.