Macromolecular [2]Rotaxanes: Effective Synthesis and Characterization.

Macromolecular [2]rotaxanes, which consist of a polymer chain threading into a wheel component, were synthesized in high yield and with high purity. The synthesis was achieved by the ring-opening polymerization (ROP) of δ-valerolactone (VL) using a hydroxyl-terminated pseudorotaxane as an initiator with diphenyl phosphate as a catalyst in dichloromethane at room temperature. The 1H NMR, gel permeation chromatography (GPC), and MALDI-TOF-MS measurements of the resulting poly(δ-valerolactone)s clearly indicate the presence of the rotaxane structure with the polymer chain, confirming that the diphenyl phosphate-catalyzed ROP of VL proceeds without deslippage of the wheel component. The obtained macromolecular [2]rotaxane was acetylated to afford a nonionic macromolecular [2]rotaxane, in which only one wheel component is movable from one end to another along the polymer chain.