Effects of Mechanically Interlocked Structure on Ionic Conductivity in Polyrotaxane-Based Polymer Electrolytes

The mobility of threaded host molecules in mechanically interlocked polymers (MIPs) has been demonstrated as an important factor for the enhanced ionic conductivity of solid polymer electrolytes (SPEs). A polyrotaxane (PR)-based MIP electrolyte with a necklace-like structure showed high ionic conductivity (σ = 5.93 × 10⁻³ S cm⁻¹ at 25 °C and 1.44 × 10⁻² S cm⁻¹ at 60 °C) and high Li⁺ ion transference number (t₊ = 0.71). To understand the effect of the molecular mobility on the ion transport behavior, various types of PRs-based MIP electrolytes containing different number of threaded host molecules were designed. As a result, the PR-based MIP electrolyte with the lowest inclusion ratio which is expected to show highest molecular mobility exhibits highest ion transportation ability. The dynamic nature of the threaded host molecules in different PRs were characterized by measuring T₂ relaxation time using ¹H-NMR. As a result, PRs containing lowest host molecules showed the largest T₂ relaxation time (0.215 s) and this tendency was very well corelated with ionic conductivity of the PRs-based electrolytes. This highlights the importance of the molecular mobility of MIPs electrolytes in designing solid state polymer electrolytes to enhance the ionic conductivity.