The properties of conventionally and microwave synthesized poly(acrylamide-co-acrylic acid) hydrogels

The focus of this work was to compare the properties of poly(acrylamide-co-acrylic acid) (poly(Aam-co-Aac)) hydrogels synthesized by conventional and microwave heating, via free-radical polymerization. Conventional synthesis of hydrogels was carried out at a temperature of 60 °C for 90 min, while microwave synthesis lasted only 2 min, providing energy, time and reaction components saving. The effect of formulation synthesis parameters such as feed composition (monomers ratio and crosslinking agent content) and initiator types on the hydrogels properties was investigated. Molecular structure of obtained hydrogels was confirmed by Fourier transform infrared spectroscopy (FTIR). The results of hydrogel swelling measurements indicated the differences between synthesis methods, monomers ratio, amount of crosslinking agent and type of applied initiator. Dynamic rheological measurements have shown that the mechanical strength of hydrogels increases with increase in the acrylic acid amount in hydrogels structure, which was manifested in increased storage modulus values. Also, frequency sweep tests have shown that conventionally synthesized hydrogels have higher storage modulus values than corresponding hydrogels synthesized by microwave method, which implies their higher mechanical strength. The results of differential scanning calorimetry (DSC) measurements have shown that microwave synthesized hydrogels have higher glass transition temperature values which implied their higher degree of crosslinking. X-ray diffraction (XRD) patterns have demonstrated the amorphous nature of hydrogels, which is consistent with the results of swelling and DSC measurements. Conducted investigation emphasizes the possibility of wider application of microwave irradiation in the synthesis of acrylate-based hydrogels with applicable properties.