Cloud Points of Poly((epsilon)-caprolactone), Poly(l-lactide), and Polystyrene in Supercritical Fluids

Cloud points were measured, using a high-pressure variable volume cell apparatus for poly((epsilon)-caprolactone) (PCL), poly(L-lactide) (PLA), and polystyrene (PS) in chlorodifluoromethane (HCFC-22), trifluoromethane (HFC-23), difluoroethane (HFC-32), 1,1-difluoroethane (HFC-152a), dimethyl ether (DME), and HCFC-22 + CO2. The cloud points were characterized as functions of pressure, temperature, and polymer molecular weight. The cloud points of these polymers were studied at temperatures ranging up to 413.2 K with various polymer concentrations and the solubility of the above-mentioned three polymers in DME was compared. Among all systems, the cloud point data for PCL + HCFC-22, PCL + DME, PLA + HCFC-22, PLA + HFC-23, PLA + DME, PS + DME, PCL + HCFC-22 + CO2, and PLA + HCFC-22 + CO2 exhibited lower critical solution temperature (LCST) behavior, whereas those for PLA + HFC-152a and PLA + HFC-32 showed upper critical solution temperature (UCST) behavior. The cloud point pressure of PLA and PCL in the HCFC-22 + CO2 system increased as the amount of CO2 increased. This suggests that the nonpolar CO2 could not solubilize the polar polymer. Thus, the cloud point of PLA and PCL can be controlled by the amount of adding CO2 as an antisolvent, and this can be applied to nanoparticle formation processes.