The cloud‐point behaviors of poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride‐co‐22 mol % hexafluoropropylene) (VDF–HFP22) are reported at temperatures up to 250 °C and pressures up to 3000 bar in supercritical CO2, CHF3, CH2F2, CHClF2, CClF3, CH3CHF2, CH2FCF3, CHF2CF3, and CH3CClF2. The molecular weight of PVDF has a smaller effect on the cloud point than the solvent quality. Cloud‐point pressures for both fluoropolymers decrease as the solvent polarizability, polar moment per molar volume, and density increases. However, it is extremely difficult to dissolve either fluoropolymer in CClF3, which has a large polarizability and a small dipole moment. CO2 is an effective solvent because it complexes with the CF dipole at low temperatures where energetic interactions fix the phase behavior. In addition, polymer architecture has a strong impact on the cloud‐point pressure. VDF–HFP22 has lower cloud‐point pressures than PVDF in all solvents because it has a larger free volume that promotes facile interactions between the solvent and the polymer segments. Cloud‐point data are also reported for amorphous poly(tetrafluoroethylene‐co‐x mol % 2,2‐bistrifluoromethyl‐4,5‐difluoro‐1,3‐dioxole) (TFE–PDDx ; x = 65 and 85) in CO2. These data provide an interesting comparison to the PVDF–CO2 and VDF–HFP22–CO2 systems because TFE–PDD65 and TFE–PDD87 have very high glass‐transition temperatures of 160 and 240 °C, respectively. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2832–2840, 2000
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.
Cloud-point data between 40 and 240°C and pressures to 2750 bar are presented for a low molecular weight, semicrystalline polyester resin of 53.4 mol % adipic acid and 46.6 mol % 1,4-cyclohexanedimethanol in supercritical CO 2 , dimethyl ether (DME), and chlorodifluoromethane (CDFM), and in mixtures of CO 2 with DME, CDFM, methanol, ethanol, butanol, octanol, hexafluoroisopropanol, acetone, and cyclohexane. Carbon dioxide, by itself, is an extremely weak supercritical fluid (SCF) solvent because this polyester only dissolves at pressures in excess of 2000 bar and at temperatures over 180°C. However, DME and CDFM are excellent solvents for this polyester, which dissolves at 16 bar and 40°C in CDFM and at 167 bar and 55°C in DME. The melting point of this polyester is reduced from 105 to 40°C in CDFM and to 55°C in DME, which makes the polyester amenable to high intensity mixing for the efficient dispersion of inorganics or crosslinking agents and other hard to deposit materials.
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