A chromatographic method, namely, mass spectrometric tracer pulse
chromatography, MSTPC, was used to
measure the solubility of carbon dioxide in PMMA, poly(methyl
methacrylate), over a wide range of
temperatures (−10 to 180 °C) and pressures (<90 atm). In this
range of experimental conditions, CO2 was
present as a gas or supercritical fluid and the polymer was either in a
glassy or rubbery state (T
g =
100-110
°C). Three lattice theories were evaluated for correlation with
the experimental solubility data. The Sanchez−Lacombe, Panayiotou−Vera, and Martire−Boehm models were used to
calculate the densities of the pure
gas and binary liquid phases from an equation of state and the chemical
potential of CO2 in both the pure gas
and polymer mixtures. The solubility of CO2 in PMMA as
a function of temperature and pressure was
calculated from these three lattice theory models and compared with the
experimental data. Only one
temperature-dependent adjustable parameter was used in these
calculations to fit the theoretical models to the
experimental data.
Mass spectrometric tracer pulse chromatography was used to measure the solubility of carbon dioxide in poly(dimethylsiloxane) over a wide range of pressures (15-100 atm) and temperatures from 35 to 120 °C. The data were compared with previously published results obtained with a wide variety of experimental methods including piezoelectric, gravimetric, dilatometric, and chromatographic procedures. The results are in agreement for pressures below the critical pressure of C0 2 but differ considerably for higher pressures. The lattice fluid model proposed by Sanchez and Lacombe, and later applied specifically to chromatographic systems by Martire and Boehm, was used to model the experimental solubility data using both measured characteristic parameters (ρ*, T* and P*) and critical constants as reduction parameters for the model. The models were used to calculate the interaction parameter, χ, from the experimental data. The results showed that the interaction parameter varied inversely with temperature as expected; however, the measured parameter also changed with the composition of the C0 2 -polymer mixture. This composition dependence is not predicted from the model and indicates that the models as currently structured are not strictly applicable to the C0 2 -PDMS system at temperatures and pressures close to critical.With the advent of supercritical fluid chromatography, SFC, the apparent gap between gas and liquid chromatography was finally occupied by a new chromatographic technique in which the mobile phase could vary continuously from a gas at low pressure Corresponding author.
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