Synthesis, characterization and rheological properties of acrylamide/ acidic monomer/ N-(4-ethylphenyl) acrylamide Terpolymers as pH- responsive hydrogels and nanogels

Novel pH-responsive superabsorbent hydrogels (HGs) and nanogels (NGs) with high water uptake and adjustable viscoelastic behavior were synthesized by free radical polymerization of acrylamide (AM) and a small amount of N-(4-ethylphenyl)acrylamide (EΦAM) hydrophobic comonomer in the presence of three different acidic monomers. Structure of the synthesized linear terpolymers was investigated by 1H-NMR spectroscopy. The solution viscosity of the linear terpolymers was measured at different pH and temperatures, where AM-EΦAM-AMPS terpolymer showed higher viscosity in different conditions. Equilibrium swelling ratio (ESR) of hydrogels was studied using response surface methodology and empirically modeled as a function of pH and temperature as stimuli.