Polyrotaxane (PR) is a supramolecular assembly composed of multiple ring molecules and one axial polymer chain, in which ring molecules can slide on the axial chain. Although the sliding motion was utilized for various kinds of PR-based devices, the internal molecular dynamics in PR has not been cleared yet. In this study, we investigated internal molecular dynamics of PR, composed of a-cyclodextrins (CDs) and a poly(ethylene glycol) (PEG) axial chain, in solution by means of quasi-elastic neutron scattering (QENS) measurements and full-atomistic molecular dynamics (MD) simulations. From MD simulations, we estimated the diffusion coefficients of CD and PEG monomer in PR, showing good agreement with QENS results. From MD trajectories, the sliding motion of CD along a PEG chain has been observed and quantified for the first time. The dynamics of CD along the chain have found to be diffusive, and diffusion coefficient for the sliding motion is much smaller than that of the translational diffusion of CD in PR at 300K. The retardation of the sliding motion is caused by the potential barrier on PEG for CD. By adding the jump diffusion term to the Einstein-Stokes diffusion model, we propose a simple equation describing the diffusion coefficient of the sliding dynamics in PR, (Fig. 1) which is valid for designing rotaxanes and polyrotaxanes with any switching or sliding speed.

Molecular dynamics of polyrotaxane investigated by neutron scattering experiments and MD simulations

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.