Swelling and collapse of polymer networks

Abstract

The swelling of a polymer network in a good solvent and of the collapse of this sample in a poor solvent is discussed theoretically for networks prepared in the presence of a large amount of diluent. The notation used is convenient for comparison with the theory of the swelling and collapse of a single macromolecule. The reference state for the networks under consideration must be chosen near the θ temperature for the corresponding linear macromolecule. For a free network and a network with fixed dimensions along one or two axes we obtain asymptotic results for the swelling of the network in a good solvent; these do not coincide with the classical Flory results. Results for the collapse of the network, which takes place upon cooling below the θ-point are also obtained. The collapse can occur either as a discrete first order phase transition (if the network chains are stiff or if it is stretched along one or two axes), or as a continuous non-phase transition (located in a narrow temperature range).