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.

The effect of dissolved carbon dioxide on the glass transition temperature of a polymer, PMMA, has been investigated using molecular probe chromatography. The probe solute was iso‐octane, and the specific retention volumes of this solute in pure PMMA and mixtures of PMMA with CO2 were measured over a temperature range of 0 to 180°C and CO2 pressures from 1 to 75 atm. The amount of CO2 dissolved in the polymer was calculated from a model fit to previously published solubility data determined chromatographically. Classical van't Hoff‐type plots were used to determine the glass transition temperature of CO2‐impregnated PMMA from low pressure up to 46 atm of CO2. Solvent‐induced plasticization was observed with the glass transition temperature decreasing by about 40°C. At some pressures, glass transitions at low temperatures could not be determined from the van't Hoff plots because of the proximity of the polymer glass transition temperature to the gas–liquid transition temperature for CO2. For these pressures, a new method was developed to determine the glass transition composition. The glass transition pressure was then calculated from the measured composition and temperature using an isotherm model. In every case, the glass transition temperature decreased linearly with increasing concentration of CO2 in the polymer. However, at higher compositions, the glass transition pressure decreased with increasing composition and decreasing temperature. The observed retention volume of iso‐octane with PMMA in a glassy state was correlated with an adsorption model developed from a theory for liquid–solid chromatography derived by Martire. This model accurately described the observed decrease in retention of iso‐octane by adsorption on the surface of glassy PMMA with increasing concentration of CO2 dissolved in the polymer. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2537–2549, 1998

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. 96

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