Excluded volume effects in swollen polymeric networks

Abstract Information on the parameters of polymeric networks obtained by crosslinking in solution can be provided by deswelling measurements in polymer solutions of different concentration. However, under these conditions, the existing theories describing the swelling behavior are conflicting and no definite conclusion on the network properties seems as yet justifiable. Moreover, excluded volume and chain connectivity effects are not accounted for in either of the theories. Thirdly, the effect of the presence of crosslinkis and the number of connected polymer segments in the network on the value of the Huggins' interaction parameter to be used in the expressions for the free energy of mixing is not clear. Nevertheless, the available experimental data have shown some preference for Hermans' theory over Flory's theory, whereas James and Guth's expression must be rejected altogether. A dependence of the degree of swelling q 0 , at which the partial molar free energy of elasticity equals zero, on solvent power of the swelling agent has been previously observed and has been further investigated in this study. To this end, methyl methacrylate was copolymerized with small amounts of divinylbenzene in dilute benzene solutions yielding six samples with different crosslink densities and q 0 values. A large dependence of q 0 on the osmotic second virial coefficient in four solvents was observed. The applicability of current theories for polymer–solvent interaction upon intramolecular chain dimensions to the chains in the networks has been investigated. Flory's expression for volume expansion of polymer chains falls short, but two other relations for the same initial effect show that the second virial coefficient dependence of q 0 may be attributed to volume exclusion, similarly as in free chains. The validity of these relations, however, is expected to hold only for a rather limited range of the network parameters.