In situ polymerization induced supramolecular hydrogels of chitosan and poly(acrylic acid-acrylamide) with high toughness

Abstract

A novel type of supramolecular hydrogel was developed by in situ polymerization of acrylic acid (AA) and acrylamide (AM) monomers in the aqueous solution of chitosan (CS), in which nanofiber-structured CS and polyelectrolyte chains of poly(acrylic acid-acrylamide) P(AA-r-AM) form the dynamic cross-linked network through the electrostatic interaction of ions. ¹H NMR, WAXD, SEM and TEM were used to trace the formation of this supramolecular hydrogel, and revealed that CS chains aggregate into a nanofiber when the copolymerization of AA and AM proceeded. The obtained hydrogels exhibited good comprehensive mechanical properties. With the excellent fatigue resistance and a high toughness of ∼500 J m⁻³, the tensile strength and elongation of hydrogel-5 are 120 kPa and 1600%, respectively. The obtained supramolecular hydrogel can self-heal and exhibited no residual strain after continuous deformation-resting processes and loading–unloading tests. Furthermore, the obtained hydrogels can be used to adsorb metal ions in water, interestingly their tensile modulus enhanced several times after adsorption of metal ions.