We prepared several series of PIE gels starting from butyl rubber in dilute toluene solutions using sulfur monochloride as a cross-linking agent. By using solution and suspension cross-linking techniques, PIE gels in the form of rods or beads in the size range of 0.1-2 mm were prepared and subjected to swelling in solvent-nonsolvent mixtures. The swelling capacity of the gels in toluene increased with decreasing concentration of sulfur monochloride or butyl rubber in the organic phase. The solubility parameter of the solution cross-linked PIE gels was found to be 16.8 +/- 0.8 MPa0.5, in accord with the reported value for bulk cross-linked gels. In toluene-methanol mixtures, PIE gels with 4% cross-linker content exhibited an abrupt deswelling when the toluene content of the external solution was decreased from 97 to 90%. By using the theory of equilibrium swelling, it was shown that the gel passes through critical conditions as the quality of the solvent becomes poorer.