Effects of high-concentration salt solutions and pH on swelling behavior of physically and chemically cross-linked hybrid hydrophobic association hydrogels with good mechanical strength

New physically and chemically cross-linked hybrid hydrophobic association hydrogels (Hybrid HA-gels) were prepared by radical copolymerization. The effect of salinity on the swelling behavior of Hybrid HA-gels was studied. Hybrid HA-gels, like ampholytic hydrogels, displayed antipolyelectrolyte behavior in high-concentration NaCl and MgCl2 solutions. According to the analysis of experimental data, the antipolyeletrolyte behavior of Hybrid HA-gels should be attributed to the rapid hydrolysis of amide groups on polymer, and the hydrolysis reaction can be promoted by high concentrations of salt solutions. Also, the results of swelling tests verified also the reversibility of complexing action of Ca2+ with carboxylate groups within the Hybrid HA-gels. In addition, the effect of pH values on the swelling behavior of the Hybrid HA-gels was also studied in detail.