Unveiling Viscoelasticity of Polyethylene Glycol/α-Cyclodextrin Polyrotaxane Solutions: Flexible Chain Dynamics and Hierarchical Structural Adaptation Processes

As representative mechanically interlocked polymers, polyrotaxanes (PRs) present unique challenges in understanding their viscoelasticity due to the dynamic coupling between rings’ sliding and intrinsic backbone chain relaxation. Although substantial progress has been made in characterizing the static architecture of PRs in solution, their dynamic nature remains poorly explored, and existing research mainly reveals the chain motion on short-time scales. Furthermore, the influence of the noncovalent interaction between threaded rings on the macroscopic mechanical response of PR solution has rarely been evaluated. Herein, linear and nonlinear rheological characterizations were performed on polyethylene glycol/α-cyclodextrin (PEG/α-CD) polyrotaxane solutions across various concentration regimes. Scaling and hydrodynamic analyses of specific viscosity indicated the flexible chain behavior of PRs in dimethyl sulfoxide. In the concentrated regime, nonlinear rheological tests with progressively increasing shear strength were employed to elucidate the complex dynamic processes arising from ring sliding and intermolecular hydrogen-bond dissociation. It elucidates that ring sliding can be triggered under moderate shear prior to extensive hydrogen-bond disruption. The characteristic stresses related to the sliding transition, the onset of association network breakdown, and the high-stress limit are quantitatively estimated. The comprehensive understanding of the nonequilibrium, multiscale dynamics of PR solutions highlights the profound influence of hydrogen-bond association on the macroscopic mechanical response of PEG/α-CD PRs in the solution state.