Synthesis of pH-sensitive sulfonamide-based hydrogels with controllable crosslinking density by post thermo-curing

Sulfonamide-containing linear copolymers were synthesized via copolymerization of N-(4-methacrylamido)-N′-(4,6-dimethylpyrimidin-2-yl) benzene-1-sulfonamide (SAM) and N,N′-dimethylacrylamide (DMAAm) via free-radical polymerization at room temperature using redox initiators. The redox-initiated polymerization could undergo nearly complete reaction in which the copolymer composition was almost the same as the feeding monomer ratio. These linear copolymers could be dissolved in water and displayed pH-sensitive properties around the physiological pH value of human body with a very sharp transition window less than 0.1 pH unit. Moreover, by introducing N-methyloyl acrylamide (NMA) monomer into the reaction system, the resulting copolymers could become crosslinked hydrogels when subjected to post thermo-curing through the NMA units. The crosslinking density and pH-sensitivity could be manipulated by changing the curing time and temperature. Therefore, swelling ratio and gel fraction of hydrogels could be accurately tailored. The pH-sensitive windows of these hydrogels were found to maintain in between 6.80 to 7.40, which implied that these hydrogels would be a suitable candidate for biomedical materials.