  Blends of multicyclic and linear polymers under biaxial elongational flow
were analyzed using coarse-grained molecular dynamics simulations. The
multicyclic/linear blends displayed overshoot in the normal stress difference
at the start-up of biaxial elongational flow. This overshoot was steeper for
multicyclic/linear blends than for our previously reported monocyclic/linear
blends [T. Murashima, K. Hagita, and T. Kawakatsu, Macromolecules, 2021, 54,
7210]. Investigation of the origin of the overshoot in the multicyclic/linear
blends revealed a different mechanism than that previously observed in our
monocyclic/linear blends. Specifically, a "topological transition" mechanism
comprising a morphological change from the open- to closed-ring state was
observed in the multicyclic chains, but not in the monocyclic chains. This
topological transition drastically changes the stress of the rings. Although
the topological transition was also observed in asymmetric-multicyclic/linear
blends, no stress overshoot appeared, owing to the asymmetry in the multicyclic
chains. Therefore, we hypothesized that the structural symmetry in multicyclic
chains is indispensable for overshoot behavior to occur. We determined that the
topological transition in multicyclic chains with structural symmetry induces
stress-overshoot behavior in multicyclic/linear blends under biaxial
elongational flow.
