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 + cosolvent mixtures was studied using a high-pressure, variable-volume view cell. 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 different polymer concentrations (ranging from 0.5 to 4 mass %). Cloud point-pressures for PPG (M-w = 830, 4%) in ethane + cosolvent mixtures were measured for several different cosolvent concentrations (ranging from 9 to 42 solvent mass %). The phase behavior of the PPG + ethane system transitioned from lower critical solution temperature (LCST)-like to a merged U-LCST-like behavior as the polymer concentration or the polymer molecular weight was increased. In general, the addition of the cosolvents reduced the cloud point pressure. The addition of chloroform cosolvent reduced the cloud point pressure more than carbon tetrachloride due to hydrogen bonding between PPG and chloroform. The Lattice Fluid Hydrogen Bonding equation of state was used to model the experimental data.