Photo- and thermo-responsive supramolecular polymer networks via in situ polymerization using homoternary macrocyclic host with coumarin monomers in water

A water-soluble coumarin monomer comprising quaternary ammonium ionic moiety can bind with a gamma-cyclodextrin (gamma-CD) macrocyclic host in a 2 : 1 ratio to form a homoternary complex in water. The coumarin monomer-based supramolecular crosslinker produces host-guest complexes with double bonds at both termini, and can be co-polymerized with water-soluble dimethylaminoethyl methacrylate (DMAEMA) by in situ redox or thermal polymerization. The resulting hydrogel, which consists of non-covalent supramolecular polymer networks, is tough, has a high viscoelastic modulus, and is capable of rapid self-healing. The covalent polymer networks that are formed via [2 + 2] coumarin dimerization by UV photo-irradiation within the gamma-CD cavity can increase the viscoelasticity of a system. Furthermore, at temperatures above the lower critical solution temperature (i.e. 50 degrees C), the viscoelastic moduli of a covalent hydrogel comprising DMAEMA units are at least one order of magnitude greater than those of the same gel at 25 degrees C owing to the associative non-covalent hydrophobic interactions. The material can confer on-demand viscoelastic properties through the host-guest-mediated supramolecular system. It has potential for use in printable, injectable, and adhesive materials because it responds to external photo and thermal stimuli.

Automated summary

This study demonstrates the synthesis of a water-soluble coumarin monomer and its supramolecular complex with gamma-cyclodextrin (gamma-CD) macrocyclic host, resulting in a hydrogel material with high strength, high viscoelastic modulus, and rapid self-healing ability. The material's viscoelasticity is enhanced through UV-induced covalent polymer networks formation within the gamma-CD cavity. Furthermore, the material shows responsiveness to visible light and thermal stimuli, making it potentially useful for printable, injectable, and adhesive materials.