Volume dependence of the elastic equation of state

The elastic component of the solvent chemical potential in isotropically swollen polymer networks is investigated as a function of the degree of dilation. The experimental method is similar to one employed by Gee, Herbert, and Roberts; the differential solvent vapor sorption by crosslinked and uncrosslinked polymers is measured as a function of solvent activity. Three systems have been investigated: poly(dimethylsiloxane) + benzene, poly(styrene‐co‐butadiene) + benzene, and poly(styrene‐co‐butadiene) + n ‐heptane. The same vulcanizate was used for the latter two series of measurements. The qualitative behavior found for all three systems is in general agreement with the results of Gee et al. on natural rubber + benzene. The data suggest that the elastic and mixing free energies are not separable.