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SUMMARYA very simple theory of swelling and collapse of weakly charged polyelectrolyte networks in the solution of an oppositely charged surfactant has been developed. The following contributions to the free energy were taken into account: free energy of volume interaction and of elastic deformation of the network chains, free energy connected with micelle formation and free energy of translational motion of all mobile ions in the system (translational entropy). Both the cases of a solution of charged surfactant and that of a mixed solution of charged and neutral surfactant components have been taken into account. It has been shown that the behaviour of the network depends on the total surfactant concentration in the system and corresponds to one of the three following regimes: At low concentration, micelles inside the network are not formed and the behaviour of the polymer network is similar to that of a network swelling in the solution of a lowmolecular-weight salt (regime 1). In the second regime, surfactant concentration inside the network exceeds the critical micelle concentration and micelles are formed; in this regime the network collapses because surfactant molecules, aggregated in micelles, cease to create "exerting" osmotic pressure in the network sample. In the third regime, at very high surfactant concentration, formation of additional micelles inside the network ceases, and the network dimensions coincide with those of the corresponding neutral network.

Conformational transitions of hydrogels of poly(methacrylic acid) induced by complexation with poly(ethy1ene glycol) were investigated. The degree of swelling of the interpolymer complex depends strongly on the pH of the solution and on the concentration of poly(ethy1ene glycol). It was shown that the addition of polytethylene glycol) results in sharp conformational transitions of neutral poly(methacry1ic acid) gels in the collapsed state due to complex formation between the network and the linear polymer. The addition of the excess of poly(ethy1ene glycol) leads to reentrant swelling of the gel. A phase transition of the complex PMAA gel-PEG in the collapsed state determined by the concentration of low molecular weight acid in the solution was observed. IntroductionPolymer networks can form complexes with linear macromolecules via hydrogen bonding. The complexation significantly influences the conformational state of the swollen networks.The formation of intermacromolecular complexes (IMCs) between the linear polymers poly(methacry1ic acid) (PMAA) and poly(ethy1ene glycol) (PEG) was thoroughly investigated.' It has been shown that complex formation results in the transition of polymer coils in the globular state. The IMCs are formed by hydrogen bonding between the carboxy groups of PMAA and the ether oxygen atoms of PEG. These IMCs are also stabilized by hydrophobic interactions.The complexation phenomena in the swollen PMAA networks can be quite different from those in linear polymers due to the elasticity of the network. The conformational changes of the hydrogels of cross-linked PMAA induced by interactions with linear PEG were observed in refs 2-9. The detail analysis of the degree of swelling and of the composition of the complexes formed by PMAA gels and PEG in neutral aqueous medium was performed in refs 7 and 8. In particular, it has been shown that the increase of the chain length of the linear component results in a strong decrease of the effective dissociation constant of the IMC.The conformational changes of the PMAA network caused by IMC formation can be of pronounced practical interest. Osada has proposed the use of such complexes to control the contraction of the PMAA The complexes of the PMAA network with PEG can be used as carriers of enzymes and drugs for their controlled release.

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