Solution cross-linked poly(isobutylene) gels: Synthesis and swelling behavior

We prepared several series of PIE gels starting from butyl rubber in dilute toluene solutions using sulfur monochloride as a cross-linking agent. By u sing 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 g els in toluene increased with decreasing concentration of sulfur monochlori de or butyl rubber in the organic phase. The solubility parameter of the so lution 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 mi xtures, PIE gels with 4% cross-linker content exhibited an abrupt deswellin g when the toluene content of the external solution was decreased from 97 t o 90%. By using the theory of equilibrium swelling, it was shown that the g el passes through critical conditions as the quality of the solvent becomes poorer.