High-pressure calorimetric study of plasticization of poly(methyl methacrylate) by methane,ethylene, and carbon dioxide

Glass transition in the system poly(methyl methacrylate)/compressed gas was studied as a function of the gas pressure p using a high-pressure Tian-Calvet heat flow calorimeter. Measurements were made on PMMA-CH₄-C₂H₄, and ;-CO₂ at pressures to 200 atm. All three gases plasticize the polymer leading to depression of the glass transition temperature T_g. Trends in the T_g depression were the same as those reported for the solubility of these gases in PMMA; the higher the solubility the larger the depression in T_g. CO₂ was found to be the most effective plasticizer producing a depression of about 40°C at a pressure of about 37 atm. In the low-pressure limit, the pressure coefficient of the glass transition temperature (dT_g/dp) was found to be about −0.2°C atm^-1 for PMMA-CH₄, the same as that observed for polystyrene-CH₄. For PMMA-C₂H₄, the pressure coefficient was −0.7°C atm^-1, which is lower than the value of −0.9°C atm^-1 observed for PS-C₂H₄. The pressure coefficient for PMMA-CO₂ was found to be about −1.2°C atm^-1, which is larger than the value of −0.9°C atm^-1 observed for PS-CO₂. © 1996 John Wiley & Sons, Inc.