Chromatographic investigation of the effect of dissolved carbon dioxide on the glass transition temperature of a polymer and the solubility of a third component (additive)

Abstract

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

Raman spectroscopic study of CO2 sorption process in poly methyl methacrylate

“…At the normal T g , rubber is transformed into glass with decreasing temperature. Another transition occurs at a temperature below the normal T g 11. At the second transition temperature T gl , a transition from glass to rubber occurs on cooling.…”

Ductile‐to‐brittle transition behavior of low molecular weight polycarbonate under carbon dioxide

“…The molecular motion of polymers can be also accelerated by the plasticization effect of compressed gas . Compressed gas is absorbed into the free volume between polymer chains, so that molecular motion is accelerated , glass transition temperature is depressed , deformation is enhanced with an increase in the amount of absorbed gas in the polymers associated with the increased gas pressure. Our recent study on the stress–strain behavior of PMMA under compressed gas revealed that molecular orientation is enhanced with increased pressure of carbon dioxide (CO 2 ) due to the plasticization effect when the amount of gas absorbed into the polymers is large at high CO 2 pressure, while it is suppressed by the hydrostatic pressure effect when the amount of absorbed gas is small at low CO 2 pressure .…”

Determination of thermodynamic properties by supercritical fluid chromatography

“…Even at subcritical pressures, CO 2 can cause T g depressions of several tens of • C. The glass transition temperature of the stationary polymer at a particular pressure of the fluid can be obtained from isobaric temperature dependence of the specific retention volume of a solute ("molecular probe"). Employing iso-octane as the probe solute, Edwards et al [179] studied plasticisation of PMMA by CO 2 at temperatures within 0-180 • C and pressures within 0.1-7.6 MPa, and noted T g depressions of up to 40 • C. The observed retention volume of the solute on glassy PMMA could be correlated with an adsorption model based on theory of fluid-solid chromatography [180]. Edwards et al [181] also investigated the PMMA-CO 2 interaction by MSTPC with isotopically labelled CO 2 ( 13 C 18 O 16 O) at temperatures within −10 to 180 • C and pressures up to 9.1 MPa.…”