Cloud points of biodegradable polymers in compressed liquid and supercritical chlorodifluoromethane

Experimental cloud point curves were measured using a variable-volume view cell apparatus for poly(L-lactide) (L-PLA), poly(D,L-lactide) (D,L-PLA), and poly(D,L-lactide-co-glycolide) (D,L-PLG) in high-pressure chlorodifluoromethane (HCFC-22) solvent. All the biodegradable polymers studied in this work exhibited a lower critical solution temperature (LCST) phase behavior in HCFC-22. The L-PLA (MW = 2000 g.mol(-1)) was soluble in HCFC-22 over the temperature range of 343.15 to 393.15 K and at pressures of less than 16 MPa. The P-x isotherms and T-x isobars showed a very broad critical region. The L-PLA was observed to become less soluble in HCFC-22 as its molecular weight increased. No differences in the cloud points were observed between the L-PLA and D,L-PLA polymers. When the D,L-lactide content in the D,L-PLG copolymers was decreased, the single-phase region shrunk in size.