Monte Carlo simulations have been performed to examine the volumetric behavior of model nonionic gel systems where the solvent is at subcritical and supercritical conditions. It is found that the degree of swelling correlates well with the density changes of the solvent: swelling decreases as the solvent becomes less dense. As the temperature is increased at constant pressure, gel swelling exhibits a monotonic decreasing trend whose onset approximately agrees with the solvent’s boiling point for subcritical pressures and, for supercritical pressure, with the location of the lower critical solution temperature (LCST) of the solvent–uncrosslinked polymer system. Evidence of an incipient first-order volume phase transition has been detected for polymeric networks with long strand lengths in contact with a supercritical solvent.

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