Phase‐Equilibrium Measurements of the Polystyrene/Styrene/Carbon Dioxide Ternary System at Elevated Pressures Using ATR‐FTIR Spectroscopy

Summary: In this paper a novel ATR‐IR spectroscopic setup for phase‐equilibrium studies of polymer systems in supercritical carbon dioxide is presented. A calibration procedure for the spectroscopic investigations has been developed and verified. The results of isothermal phase‐equilibrium measurements of the polystyrene/styrene/carbon dioxide ternary system are presented and compared to results of well‐established cloud‐point measurements. The phase behaviour was determined at 338.15 K, at two pressures (10 MPa and 15 MPa), and for two polystyrene samples having different molecular weights (6 kg/mol, 105 kg/mol) and narrow molecular‐weight distributions.