Cloud-point behavior of binary and ternary mixtures of PHPMA and PHPA in supercritical fluid solvents

Three different supercritical fluids, CO2, dimethyl ether (DME), and chlorodifluoromethane (CHClF2), were investigated as potential solvents for processing two (meth)acrylate polymers. High pressure phase behavior data to 505 K and 265.7 MPa were reported for poly(hydroxypropyl methacrylate) [PHPMA] and poly(hydroxypropyl acrylate) [PHPA] in the supercritical fluid solvents + cosolvent system. Cloud-point curves for the PHPA and PHPMA in the supercritical DME show about a 40.0 MPa pressure difference of constant temperature at ∼373 K. The phase behavior for the PHPMA + DME + 2-hydroxypropyl methacrylate (2-HPMA) and PHPA + DME + 2-hydroxypropyl acrylate (2-HPA) systems were measured from changes of the pressure–temperature curve slope, and with cosolvent concentrations of w3 = 0–0.463 (2-HPMA) and w3 = 0–0.453 (2-HPA), respectively. The PHPMA + DME + w3 = 0.0–0.238 CO2 and PHPA + DME + w3 = 0.0–0.210 CO2 mixture show UCST-type behavior with a negative slope, and then the pressure increases smoothly for temperatures in the range of 323–492 K. PHPMA and PHPA do not dissolve in pure CO2 at a temperature of 518 K and pressure of 280.0 MPa. The location of the PHPMA + CO2 cloud-point curve shifts to lower temperatures and pressures when w3 = 0.40–0.66 2-HPMA was added to the PHPMA + CO2 solution. The phase behavior for the PHPA + CO2 + w3 = 0.35–0.68 2-HPA system changes the pressure–temperature curve from an upper critical solution temperature (UCST) region to a lower critical solution temperature (LCST) region as the 2-HPA concentration increases. The PHPMA + CO2 + w3 = 0.689 2-HPMA phase behavior curve intersects a fluid → liquid + vapor (LV) curve at ∼393 K and ∼16.0 MPa.