PH-SENSITIVE HYDROGELS BASED ON NONIONIC ACRYLIC COPOLYMERS

Hydrogels based on ethoxytriethyleneglycol monomethacrylate/methyl met hacrylate copolymers were prepared by free radical polymerization at 7 0 degrees C in bulk with 2,2'-azobisisobutyronitrile as initiator. The swelling behaviour of the hydrogels was studied by immersion of the f ilms in water and in buffered solutions at various pHs. The hydration process was followed gravimetrically measuring the water uptake of the films with the time of treatment. The kinetics fit adequately a Ficki an law for reduced sorption coefficients, M(t)/M(infinity), lower than 0.6. The values of the diffusion coefficient were lower at neutral pH than at acidic or alkaline pHs, and they seemed to be independent of the copolymer composition. The results obtained were consistent with t he stress relaxation model of polymer chains predicted for a relativel y fast hydration process. The swelling process is reversible and the p olymeric films are stable after repeating cycles of hydration and deso rption promoted by the change of pH in appropriate buffered solutions. (C) 1997 Elsevier Science Limited.