PLASTICIZATION OF POLY(METHYL METHACRYLATE) (PMMA) NETWORKS BY SUPERCRITICAL CARBON-DIOXIDE

It has been shown by a number of authors that supercritical carbon dioxide is an extremely efficient plasticizer for amorphous, carbonyl-containing polymers. In this paper, we have examined the plasticization of poly(methyl methacrylate) (PMMA) networks by CO2 as a function of pressure using dielectric measurements. Results show that the degree of plasticization increases rapidly at pressures up to approximately 1200 psig (8.274 M Pa), levelling off (and possibly decreasing) at higher pressures. This phenomenon is possibly due to the counteracting effects of pressure on free volume and CO2 sorption. The experimental trends are consistent with predictions of free volume in CO2/PMMA mixtures derived from a modified lattice model.