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 collapse of poly‐(methacrylic acid) gels induced by the interaction with linear poly(ethylene glycol) and on their subsequent reswelling (reentrant transition). The abruptness and the amplitude of both transitions increase with decreasing cross‐linking density of the gel. A special feature of the reswelling transition for the PMAA gel/PEG system is the existence of a wide range of PEG concentrations where both collapsed and swollen states of the gel are stable. The conditions for the existence 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 hydrophilic PEG loops in highly cross‐linked gels.