Swelling behaviour of poly(alpha-hydroxyacrylic acid) gel

Poly(alpha-hydroxy acrylic acid) (PHA) and poly(acrylicacid) (PAA) gels wer e prepared by irradiating the respective 15wt% aqueous solutions with gamma -rays. Swelling ratios for PHA gel were measured as a function of pH and di valent cation (Mg2+, Ca2+, Mn2+, Co2+, Ni2+, Cu2+) concentration C-2 in the external solution to provide a comparison with the results for PAA gels. I t was found that the swelling ratio of PHA gel steeply increases between pH 2 and 4, followed by a gradual swelling in the higher pH region. The corre sponding steep swelling of PAA gel was observed at pH 3-6. Cation specifici ty in the equilibrium swelling ratio at a lower C-2 value (1.0 x 10(-3) M) was approximately consistent with the binding selectivity in the solution s ystem. Typically, the swelling ratio of PHA gel in the presence of Ca2+ was significantly lower than in the Mg2+ system, while the difference was slig ht for PAA gel. The response of the swelling ratio to changes in pH and C-2 was analysed as a first order relaxation to estimate the time constants. T he (de)swelling kinetics measured by both the pH and C-2 jump were qualitat ively interpreted in terms of main-chain stiffness and intermolecular hydro gen bonding in the respective polymers. (C) 2000 Society of Chemical Indust ry.