In situ measurement of the glass transition temperature of polymers with compressed fluid diluents

In situ measurement of the creep compliance of poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA), equilibrated with a pressurized CO2 phase, is used to determine the glass transition temperature. Corrections due to dilation of the polymer by CO2 as well as the buoyancy are assessed. Both polymer systems exhibit a recently discovered phenomenon, retrograde vitrification, in which a liquid polymer becomes a glass with an increase in temperature. The experimental results are predicted semi‐quantitatively in terms of the temperature and pressure effects on the solubility of the compressed fluid in the polymer. © 1994 John Wiley & Sons, Inc.