Preparation of Hydrogels of Methacrylamide with Mono and Dicarboxylic Acids: Investigation of Their Swelling Behavior

Methacrylamide (MAAm) hydrogels were synthesized with mono- (crotonic acid, CrA) and dicarboxylic (maleic acid, MAA) acids via radical copolymerization, utilizing potassium persulfate (KPS) as the initiator and methylenebisacrylamide (MBAAm) as the crosslinker. The swelling behavior of the resulting hydrogels was systematically investigated, with particular focus on the effects of monomer ratio, initiator and crosslinker concentrations, as well as polymerization temperature. These parameters were optimized to maximize the swelling ratio. For poly(MAAm/CrA) hydrogels, the formulation containing 85/15 MAAm/CrA (mol/mol), 2 mol% KPS, 1 mol% MBAAm, and synthesized at 55 °C exhibited the highest swelling capacity (480%) in distilled water. In contrast, for poly(MAAm/MAA) hydrogels, the composition of 75/25 MAAm/MAA (mol/mol) with 1 mol% KPS, 1 mol% MBAAm, and polymerized at 55 °C showed a maximum swelling of 1100%. Further investigations explored the influence of pH, temperature, and electrolyte concentration and type on the swelling properties of the hydrogels prepared under optimized conditions. Both hydrogels demonstrated peak swelling behavior at pH 7, with their swelling profiles varying in response to changes in temperature, electrolyte concentration, and electrolyte type. Swelling kinetics studies revealed that the MAAm/CrA hydrogel exhibited Fickian diffusion in distilled water at room temperature, while the MAAm/MAA hydrogel followed a non-Fickian diffusion mechanism. Scanning electron microscopy (SEM) analysis indicated that the hydrogels synthesized under optimal conditions possessed a porous and well-organized network structure.