SWELLING OF POLYACRYLAMIDE GELS IN AQUEOUS-SOLUTIONS OF ETHYLENE-GLYCOL OLIGOMERS

Addition of a small amount of ethylene glycol oligomers (OEG), with th e number of repeat units y = 2-4, in an aqueous solution leads to the contraction of both linear and cross-linked poly(acrylamide-co-acrylic acid) chains. The results present clear evidence for the screening Ef fect of OEG on the ionic groups of the polymer chains. Measurements in dicate that the pre-swollen poly(acrylamide-co-acrylic acid) gels imme rsed in aqueous OEG solutions are at equilibrium. However, as the mole cular weight of OEG increases, these gels cannot attain their equilibr ium swelling ratio due to the appearance of non-equilibrium structures . The stability of these structures increases as the initial swelling degree of the gels increases. (C) 1997 Elsevier Science Ltd.