Poly(lactide-co-glycolide) solution behavior in supercritical CO2, CHF3, and CHClF2

Cloud point and solution density data between 20 and 100 degreesC and pressures to 3000 bar are presented for poly(lactide) (PLA) and poly(lactide-co-glycolide) (PLGA(x), where the molar concentration of glycolide in the backbone x ranges from 0 to 50 mol %) in supercritical CO2, CHClF2, and CHF3. PLA dissolves in CO2 at pressures near 1400 bar, in CHF, at pressures of 500 to 750 bar, and in CHClF2 at pressures of 20-100 bar. As glycolide (GA) is added to the backbone of PLGA, the cloud point pressure increases by 50 bar/(mol GA) in CO2, 25 bar/(mol GA) in CHF3, and by only 2.5 bar/(mol GA) in CHClF2. PLGA(50) does not dissolve in CO2 to pressures of 3000 bar whereas it is readily soluble in CHClF2 at pressures as low as 100 bar at 50 degreesC. In comparison, the increases in cloud point pressure with increasing weight average molecular weight (M-w) are only approximately 2.3 bar/(1000 M-w) for PLGA copolymers in CO2. The solution densities with all three SCF solvents range from 1.1 to 1.5 g/cm(3) and they vary only by a small amount over the 80 degreesC range used to obtain cloud point data. More than likely, the ability of the acidic hydrogen in CHF3 and CHClF2 to complex with the ester linkage in PLGA makes these better solvents than CO2 especially since any change in favorable energetic interactions is magnified due to the liquid-like densities exhibited by these SCF solvents. (C) 2001 John Wiley & Sons, Inc.