Laser Raman spectroscopy, in conjunction with an optical high-pressure cell, was used to investigate the poly(methyl methacrylate)-carbon dioxide system. The Raman shifts associated with carbon dioxide molecules in the gas phase and those dissolved in the polymer were used to derive sorption kinetics of carbon dioxide and the carbon dioxide-induced phase changes in the polymer. Measurements were made in the temperature and pressure ranges in which this system is known to exhibit retrograde vitrification behavior. The Raman results on the sorption kinetics and on the onset of plasticization were in agreement with those obtained by gravimetric and calorimetric techniques, respectively. This technique provides a versatile and rapid way of characterizing polymer-gas systems and information that so far has been obtainable only through painstaking and time-consuming techniques. (C) 2003 Wiley Periodicals, Inc.