ROMP Synthesis of Side‐Chain Ferrocene‐Containing Polyelectrolyte and Its Redox‐Responsive Hydrogels Showing Dramatically Improved Swelling with β‐Cyclodextrin

A new side‐chain ferrocene (Fc)‐containing polyelectrolyte has been synthesized by controlled ring‐opening metathesis polymerization of a water‐soluble Fc‐containing norbornene‐based quaternary ammonium salt, as well as the corresponding covalently cross‐linked polyelectrolyte hydrogel. In order to provide Fc‐containing supramolecular polyelectrolyte hydrogels whose swelling property is largely improved by host−guest interaction, a covalently cross‐linked polyelectrolyte hydrogel is soaked into the β‐CD aqueous solution to form β‐CD@Fc supramolecular polyelectrolyte hydrogel, or alternatively the quaternary ammonium salt supramolecular monomer is first formed, then copolymerized with a crosslinking agent to fabricate the supramolecular hydrogel with better water absorption ability. All the Fc‐containing hydrogels exhibited good redox‐responsiveness with swelling–shrinking behaviors by chemically reversibly adjusting the disassembly/assembly of β‐CD@Fc inclusion complexes. This is the first example of side‐chain Fc‐containing polycationic supramolecular hydrogels possessing swelling–shrinking properties based on the splitting/combining of β‐CD and Fc units, and potential applications are expected as controlled drug delivery and actuators.