Transparent and tough poly (2-hydroxyethyl methacrylate) hydrogels prepared in water/IL mixtures
Poly (2-hydroxyethyl methacrylate) (PHEMA) hydrogels with high transparence and excellent mechanical properties are fabricated via in situ free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) in the mixtures of water and 1-butyl-3-methylimidazolium chloride (BmimCl) followed by exchanging the BmimCl with water. Compared with the PHEMA hydrogels prepared without BmimCl, the obtained hydrogels display denser and more homogeneous microstructure, which contribute to their highly transparent appearance and outstanding mechanical properties. The hydrogels could achieve elongation at break and tensile strength up to 705% and 173 kPa, respectively at swollen equilibrium states. Furthermore, the hydrogels also reveal fast recovery in water after circle elongation, showing anti-fatigue properties owing to their quick reformation of hydrogen bonds between polymer chains. More importantly, the hydrogels are able to retain considerable mechanical strength in water over a wide pH range (1 to 13) due to their stable cross-linking structures. It is believed that this novel type of transparent PHEMA hydrogels combined with outstanding mechanical properties, superior stability and anti-fatigue property would find extensive applications in biomedical and industrial fields.