Cloud points of poly(L-lactide) in HCFC-22, HFC-23, HFC-32, HFC-125, HFC-143a, HFC-152a, HFC-227ea, dimethyl ether (DME), and HCFC-22+CO2 in the supercritical state

Abstract

Cloud points were measured using the high-pressure variable-volume cell apparatus for poly(L-lactide) in chlorodifluoromethane (HCFC-22), trifluoromethane (HFC-23), difluoroethane (HFC-32), pentafluoroethane (HFC-125), 1,1,1-trifluoroethane (HFC-143a), 1,1-difluoroethane (HFC-152a), 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea), and dimethyl ether (DME), respectively. The cloud points were characterized as functions of pressure, temperature, and polymer molecular weight. Cloud point pressures of poly(L-lactide) were studied at temperature ranging up to 413.2 K for polymer concentrations of about 3 mass %. The phase behavior of poly(L-lactide) in DME, HCFC-22, and HFC-23 exhibited LCST (lower critical solution temperature) behavior, and that of poly(L-lactide) in HFC-32 and HFC-152a exhibited UCST (upper critical solution temperature) behavior. However, poly(L-lactide) had a low solubility in HFC-125, HFC-143a, and HFC-227ea even at 413.2 K and 150 MPa. In addition, the phase behavior of poly(L-lactide) was investigated as a function of CO2 in a HCFC-22 + CO2 mixture.