Grafted Polyrotaxanes: Scaling Theory and Molecular Dynamics Simulations

We analyze the scaling properties of grafted polyrotaxanes and compare the resulting scaling laws with molecular dynamics simulations. These molecules display a resemblance to bottle brushes, but the mobility of the rotors yields a backbone tension that is uniform along its contour. Properties like brush extension, backbone tension, and rotor mobility as functions of rotor density and degree of polymerization of grafted chains are well covered by a simple scaling model. The dynamics of rotor release after a breakup of the polyrotaxane a process recently observed in laboratory experiments is studied in detail. It consists of three stages: a rapid backbone retraction, a driven rotor expulsion, and a diffusive transport. The complexity of this process, which may be exploited for drug delivery systems, is asking for further in-depth simulation studies.