Equilibrium Swelling of Highly Cross-Linked Polymeric Resins

A modified expression for the change in chemical potential of a solvent, in a polymer network, due to isotropic swelling was obtained by substituting a non-Gaussian chain length probability distribution in Flory's statistical analysis of rubber elasticity. The affine non-Gaussian expression for the free energy change due to elastic deformation was compared to both the traditional Flory and the James-Guth phantom network expressions for the free energy change due to elastic deformation using available experimental data for the swelling of highly cross-linked polymeric resins. Among the different models for the elastic contribution to the free energy change resulting from isotropic swelling, the non-Gaussian elasticity expression was found to be as good as, or slightly better than the Flory expression, and clearly superior to the James-Guth phantom network expression. Both of the two different expressions used to represent the free energy of mixing, the Flory-Huggins expression and a modified version of the quasi-chemical mixing expression, were found to be equally successful when describing the isotropic swelling of cross-linked polymeric resins