PREPARATION OF POLY(ALPHA-HYDROXYACRYLIC ACID) GEL BY GAMMA-IRRADIATION AND ITS SWELLING BEHAVIOR

Gels of poly(alpha-hydroxyacrylic acid) (PHA) and poly(acrylic acid) ( PAA) were prepared by gamma irradiation of 15 wt% aqueous solutions. G elation of the two polymers occurred only in the lower pH range (1-4). Ab initio energy calculations for radical formation on the PHA main c hain suggested that the hydrogen atom of the hydroxyl group is easily attacked by hydroxyl radicals when a lactone ring is formed between ad jacent OH and COOH groups. The swelling ratios (SR) of PHA and PAA gel s 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 steepl y above pH 6. The steep increase for PHA is ascribed to lactone ring-o pening in the gel, as suggested by i.r. peak displacement. (C) 1997 El sevier Science Ltd. All rights reserved.