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

Abstract

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 Tg. Trends in the Tg depression were the same as those reported for the solubility of these gases in PMMA; the higher the solubility the larger the depression in Tg. 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 (dTg/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.