Synthesis of novel pH-sensitive poly(methacrylic acid-co-acrylamide) hydrogels and their swelling behavior

A kind of novel hydrogels, poly(methacrylic acid-co-acrylamide) [poly(MAA-co-AM)], were prepared by radical aqueous copolymerization of acrylamide and methacrylic acid in the presence of crosslinker N-N-methylenebisacrylamide (BIS). The swelling dynamics of the prepared dry hydrogels were investaged. The results show that the swelling behaviors of the prepared hydrogels are different with the different contents of methacrylic acid (MAA) in the hydrogels, and the swelling ratio of the hydrogels prepared increases with the increase of pH value of the solution. When the prepared hydrogels were shifted between solutions with pH=2 and pH=12, the hydrogels exhibit rapid reversible swelling-deswelling property, and their responsive rates are affected significantly by stirring. The hydrogels with absorbed water in equilibrium can be deswelled in both acid and alkaline solutions, they shrink more than 90% in solution of pH=2 within 10 min, and the shrinking rates decrease with the increase of pH value of the solution. The swelling properties of prepared hydrogels in NaCl and CaCl2 solutions were investigated; the results show that the influences of the ionic strength and the charge of counter ion in the solution are obvious, and that the hydrogels display the reversible swelling-deswelling property in water and NaCl solution.