Dual-responsive crown ether-based supramolecular chain extended polymers

Based on the benzo-21-crown-7 (B21C7)/secondary ammonium salt molecular recognition motif, dual-responsive supramolecular chain extended polymers with a biodegradable poly(ε-caprolactone) (PCL) chain as the scaffold were successfully prepared by self-assembly of a heteroditopic macromonomer which was synthesized by a combination of ring-opening polymerization and click reaction. ¹H NMR spectroscopy, FT-IR, solution viscometry, diffusion NMR and differential scanning calorimetry were employed to characterize these novel supramolecular chain extended polymers. Due to the environmental responsiveness of the recognition of the B21C7 host unit to the secondary ammonium salt guest moiety, the supramolecular chain extended polymers respond to pH and cation stimuli. The crystallization behavior of the PCL segments of the supramolecular chain extended polymers and the neutral counterpart were investigated by polarized optical microscopy. The B21C7/secondary ammonium salt host-guest interactions cause a decrease of the chain mobility of PCL and make the crystallization rate of PCL much slower in comparison with the case of the neutral counterpart.