Polymer physics and flow dynamics of thermodynamically pure ring polymers

Ring polymers have fascinated polymer chemists and physicists for decades, yet achieving a complete understanding of the dynamics of pure ring polymer systems has remained elusive due to major challenges in residual linear polymer contamination. Despite recent advances in purification methods, trace amounts of linear polymers are thought to remain in existing ring polymer samples, greatly affecting the mechanical properties of these materials. Here, we study the equilibrium and non-equilibrium flow properties of synthetic rings based on cyclic poly(phtalaldehyde) (cPPA), a low-ceiling temperature polymer whose linear chain analogues are thermodynamically unstable at room temperature due to depolymerization at free ends. The polymerization reaction yields high molecular weight cyclic polymers with no free ends, thereby providing highly pure and thermodynamically stable ring polymers. Using this approach, we study the linear viscoelastic properties, zero-shear viscosity, and nonlinear flow response of cPPA samples as a function of polymer molecular weight and weight fraction. Overall, these results give insight into the dynamics of ring polymer systems with unprecedented purity.