Abstract
Gels of poly(α-hydroxyacrylic acid) (PHA) and poly(acrylic acid) (PAA) were prepared by gamma irradiation of 15 wt% aqueous solutions. Gelation of the two polymers occurred only in the lower pH range (1–4). Ab initio energy calculations for radical formation on the PHA main chain suggested that the hydrogen atom of the hydroxyl group is easily attacked by hydroxyl radicals when a lactone ring is formed between adjacent OH and COOH groups. The swelling ratios (SR) of PHA and PAA gels were measured in water as a function of state of dissociation of the COOH group. For PHA gel, SR gradually increased above pH 1 and steeply above pH 6. The steep increase for PHA is ascribed to lactone ring-opening in the gel, as suggested by i.r. peak displacement.
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