IN-SITU MEASUREMENT OF THE GLASS-TRANSITION TEMPERATURE OF POLYMERS WITH COMPRESSED FLUID DILUENTS

In situ measurement of the creep compliance of poly (methyl methacryla te) (PMMA) and poly (ethyl methacrylate) (PEMA), equilibrated with a p ressurized CO2 phase, is used to determine the glass transition temper ature. Corrections due to dilation of the polymer by CO2 as well as th e buoyancy are assessed. Both polymer systems exhibit a recently disco vered phenomenon, retrograde vitrification, in which a liquid polymer becomes a glass with an increase in temperature. The experimental resu lts are predicted semi-quantitatively in terms of the temperature and pressure effects on the solubility of the compressed fluid in the poly mer. (C) 1994 John Wiley & Sons, Inc.