Synthesis and characterization of pH and temperature responsive poly(2-hydroxyethyl methacrylate-co-acrylamide) hydrogels

Acrylamide/2-hydroxyethyl methacrylate hydrogels were prepared by simultaneous radiation-induced cross-linking copolymerization of acrylamide (AAm), 2-hydroxyethyl methacrylate (HEMA) and water mixtures at a radiation dose of 10 kGy. Hydrogels were characterized by infrared spectroscopy. Dynamic and equilibrium swelling of hydrogels in water and in buffer solutions were investigated. They were sensitive to pH and temperature. Swelling was non-Fickean and increased with increasing the acrylamide content. Temperature dependence of the equilibrium water uptake of copolymers exhibited a discontinuity around 35 °C resulting from the weakening of the hydrogen bonds between the hydroxyl groups of HEMA and the amide groups of AAm. The thermodynamic and network parameters derived from swelling and mechanical measurements are compared and discussed. They exhibit a strong dependence on the AAm content in the hydrogel. These hydrogels can be considered for applications in fields requiring environmentally responsive hydrogels such as medicine, pharmacy and bioengeneering.