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

Abstract

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.

INEXPENSIVE CO{sub 2} THICKENING AGENTS FOR IMPROVED MOBILITY CONTROL OF CO{sub 2} FLOODS

“…Poly(lactide) The solubility of PLA in CO 2 , Figure 6, has been determined previously (Conway et al 2001). PVAc is also more soluble in CO 2 than PLA despite the similarity of their compositions.…”

“…Polyethers were also successfully studied for their CO 2 solubility by Drohmann and Beckman (53) . McHugh et al investigated the effects of placing the carbonyl group in the backbone rather than as part of a side chain (54) . Though many functional groups containing a Lewis base have been effective in lowering the cloud point pressure of non-fluorous polymers, incorporating the acetate group as a side chain 42 of a hydrocarbon chain [poly(vinyl acetate)] (see Figure 4) currently yields the most versatile non-fluorous CO 2 -philic polymer as it is miscible with CO 2 at relatively low pressures at high molecular weights and weight percentages (55) .…”

“…Placing the carbonyl group as a Lewis base in the backbone can lower the miscibility pressure of a nonfluorous polymer, though not to the extent seen when placing the group in a side chain 84 (PVAc). At 308 K, poly(lactide) (PLA) at a molecular weight of 128,500 at five weight percent will dissolve in CO 2 at about 140 MPa (54) . Under the same conditions and with the same molecular weight, PVAc exhibits a cloud point pressure of 70 MPa (55) .…”

Inexpensive CO2 Thickening Agents for Improved Mobility Control of CO2 Floods

“…McHugh et al investigated the effects of placing the carbonyl group in the backbone rather than as part of a side chain (54) . Though many functional groups containing a Lewis base have been effective in lowering the cloud point pressure of non-fluorous polymers, incorporating the acetate group as a side chain of a hydrocarbon chain [poly(vinyl acetate)] (see Figure 4) currently yields the most versatile non-fluorous CO 2 -philic polymer as it is miscible with CO 2 at relatively low pressures at high molecular weights and weight percentages (55) .…”

“…Placing the carbonyl group as a Lewis base in the backbone can lower the miscibility pressure of a non-fluorous polymer, though not to the extent seen when placing the group in a side chain (PVAc). At 308 K, poly(lactide) (PLA) at a molecular weight of 128,500 at five weight percent will dissolve in CO 2 at about 140 MPa (54) .…”