NONIONIZABLE POLYACRYLIC HYDROGELS SENSITIVE TO PH FOR BIOMEDICAL APPLICATIONS

Hydrogels based on ethoxytriethyleneglycol monomethacrylate/methyl met hacrylate (T/M) copolymers were prepared by free radical polymerizatio n at 70 degrees C in bulk with azobisisobutyronitrile as initiator. Th e reactivity ratios were calculated by Fineman-Ross (FR) and Kelen-Tud os (KT) linearization methods and by the non-linear least square metho d suggested by Tidwell and Mortimer (TM). The reactivity ratios obtain ed were r(T) = 0.17 +/- 0.03, r(M) = 0.70 +/- 0.01 (FR method); r(T) = 0.19 +/- 0.02, r(M) = 0.76 +/- 0.03 (KT method) and r(T) = 0.18; r(M) = 0.75 (TM method). Microstructure was obtained in terms of the distr ibution of T- and M-centred triads. The swelling behaviour of the hydr ogels was studied by immersion of the films in water and in buffered s olutions at various pH values and it was analysed by comparison with t hat of poly(ethoxytriethyleneglycol monomethacrylate). It was observed that not only the average copolymer composition but also the distribu tion of monomeric sequences play an important role in the swelling beh aviour.