Measurements and modeling of cloud point behavior for poly(propylene glycol) in ethane and in ethane plus cosolvent mixtures at high pressure

The phase behavior of poly(propylene glycol) (PPG) in ethane and ethane + c osolvent mixtures was studied using a high-pressure, variable-volume view c ell. The cosolvents studied were chloroform and carbon tetrachloride. Cloud point pressures for PPG in ethane were measured for three different weight -average molecular weight (M-w) PPG samples (450; 830; 2160) at several dif ferent polymer concentrations (ranging from 0.5 to 4 mass %). Cloud point-p ressures for PPG (M-w = 830, 4%) in ethane + cosolvent mixtures were measur ed for several different cosolvent concentrations (ranging from 9 to 42 sol vent mass %). The phase behavior of the PPG + ethane system transitioned fr om lower critical solution temperature (LCST)-like to a merged U-LCST-like behavior as the polymer concentration or the polymer molecular weight was i ncreased. In general, the addition of the cosolvents reduced the cloud poin t pressure. The addition of chloroform cosolvent reduced the cloud point pr essure more than carbon tetrachloride due to hydrogen bonding between PPG a nd chloroform. The Lattice Fluid Hydrogen Bonding equation of state was use d to model the experimental data.