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

Abstract

A water-soluble coumarin monomer comprising quaternary ammonium ionic moiety can bind with a γ-cyclodextrin (γ-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 γ-CD cavity can increase the viscoelasticity of a system. Furthermore, at temperatures above the lower critical solution temperature (i.e. 50 °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 °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.