Swelling behaviour of poly(?-hydroxyacrylic acid) gel

Abstract

Poly(α-hydroxy acrylic acid) (PHA) and poly(acrylicacid) (PAA) gels were prepared by irradiating the respective 15 wt% aqueous solutions with γ-rays. Swelling ratios for PHA gel were measured as a function of pH and divalent cation (Mg2+, Ca2+, Mn2+, Co2+, Ni2+, Cu2+) concentration C2 in the external solution to provide a comparison with the results for PAA gels. It 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 corresponding steep swelling of PAA gel was observed at pH 3–6. Cation specificity in the equilibrium swelling ratio at a lower C2 value (1.0 × 10−3 M) was approximately consistent with the binding selectivity in the solution system. Typically, the swelling ratio of PHA gel in the presence of Ca2+ was significantly lower than in the Mg2+ system, while the difference was slight for PAA gel. The response of the swelling ratio to changes in pH and C2 was analysed as a first order relaxation to estimate the time constants. The (de)swelling kinetics measured by both the pH and C2 jump were qualitatively interpreted in terms of main-chain stiffness and intermolecular hydrogen bonding in the respective polymers. © 2000 Society of Chemical Industry