A series of cross-linked copolymer films based on 1-vinyl-2-pyrrolidone and methyl methacrylate were produced using different poly(ethylene glycol) dimethacrylates as cross-linking agents. The average molecular mass of the cross-linking agent was varied, then allowing the foaming process using supercritical CO2 (ScCO2), obtaining microcellular films with different cellular structures as a function of the molecular mass of the cross-linking agent. The chemical structure, swelling behavior, CO2 uptake and cellular morphology of the materials were studied. Finally, the influence of the different cross-linking agents in the mechanical properties was also evaluated by measuring the tensile properties of the microcellular films.