The morphology and size of poly(acrylic acid) (PAA) particles produced by precipitation polymerization in supercritical CO2 (scCO(2)) depends on the glass transition temperature (T-g) of the polymer at reaction conditions. In this study, the use of the Sanchez-Lacombe equation of state (SL-EOS), in conjunction with Chow's equation, to predict the effect Of CO2 pressure on the T-g of PAA was evaluated. Characteristic parameters for PAA were determined by fitting density data. Characteristic parameters for CO2 were determined by fitting density data in the supercritical region. When the SL-EOS was used in a purely predictive mode, with a binary interaction parameter (psi) of 1, the solubility of CO2 in PAA was underestimated and T-g was overestimated, although the trend of T-g with CO2 pressure was captured. When was determined by fitting the SL-EOS to the measured sorption Of SCCO2 in PAA, the calculated T-g's agreed very well with measured values. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 2136-2143, 2010