Predicting the effect of dissolved carbon dioxide on the glass transition temperature of poly(acrylic acid)

The morphology and size of poly(acrylic acid) (PAA) particles produced by precipitation polymerization in supercritical CO₂ (scCO₂) depends on the glass transition temperature (Tg) 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 Tg 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 (ψ) of 1, the solubility of CO₂ in PAA was underestimated and Tg was overestimated, although the trend of Tg with CO₂ pressure was captured. When was determined by fitting the SL-EOS to the measured sorption of scCO₂ in PAA, the calculated Tg's agreed very well with measured values.