Poly(lactide‐co‐glycolide) solution behavior in supercritical CO 2 , CHF 3 , and CHClF 2

Cloud point and solution density data between 20 and 100°C 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 CO 2 , CHClF 2 , and CHF 3 . PLA dissolves in CO 2 at pressures near 1400 bar, in CHF 3 at pressures of 500 to 750 bar, and in CHClF 2 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 CO 2 , 25 bar/(mol GA) in CHF 3 , and by only 2.5 bar/(mol GA) in CHClF 2 . PLGA 50 does not dissolve in CO 2 to pressures of 3000 bar whereas it is readily soluble in CHClF 2 at pressures as low as 100 bar at 50°C. 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 CO 2 . 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°C range used to obtain cloud point data. More than likely, the ability of the acidic hydrogen in CHF 3 and CHClF 2 to complex with the ester linkage in PLGA makes these better solvents than CO 2 especially since any change in favorable energetic interactions is magnified due to the liquid‐like densities exhibited by these SCF solvents. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1155–1161, 2001