High-pressure phase behavior of boltorn hyperbranched polymers in supercritical fluids

Experimental phase behavior data are reported for three hyperbranched polyester polymers, Boltorn H20 (B-H20), Boltorn H2004 (B-H2004), and Boltorn U3000 (B-U3000) in supercritical ethane, propane, propylene, CO2, and dimethyl ether (DME) at temperatures to 450 K and pressures to 200 MPa. B-H20 has 100% hydroxyl terminal groups, B-H2004 has 60% saturated C6 and C8 hydrocarbon terminal groups, and B-U3000 has 90% unsaturated C16 and C18 hydrocarbon terminal groups. Cloud point, liquid–vapor, and liquid–liquid–vapor phase transitions are measured with a high-pressure, variable-volume, view cell for each Boltorn polymer at ∼5 wt% in solution. B-H20, with 100% hydroxyl terminal groups, only dissolves in DME, which is expected to hydrogen bond to the polymer hydroxyl groups. At the other extreme, B-U3000, with long chain, nonpolar hydrocarbon terminal groups, is significantly more soluble in nonpolar ethane and propane compared to propylene, CO2, or DME.