CONFORMATIONAL TRANSITIONS IN POLY(METHACRYLIC ACID) GEL POLY(ETHYLENE GLYCOL) COMPLEXES - EFFECT OF THE GEL CROSS-LINKING DENSITY/

We present results on the effect of the cross-linking density on the c ollapse of poly(methacrylic acid) gels induced by the interaction with linear poly(ethylene glycol) and on their subsequent reswelling (reen trant transition). The abruptness and the amplitude of both transition s increase with decreasing cross-linking density of the gel. A special feature of the reswelling transition for the PMAA gel/PEG system is t he existence of a wide range of PEG concentrations where both collapse d and swollen states of the gel are stable. The conditions for the exi stence of such a region are easier realized for slightly cross-linked gels. The corresponding theoretical explanation is given. The swelling degree of the collapsed gels increases with increasing cross-linking density, which is explained by the presence of a certain amount of hyd rophilic PEG loops in highly cross-linked gels.