High-pressure phase behavior data reported here demonstrate the nuanced impact fluorine exerts on polymer solubility in supercritical fluid solvents. Copolymers are used that contain a perfluorocyclobutyl ether group with varying amounts of bis-aryl isopropylidene (6H) or bis-aryl hexafluoroisopropylidene (6F). Surprisingly, it takes at least 2000 bar and 190 degrees C to dissolve the 6H homopolymer in CO2 even though every repeat group has similar to 15 mol % fluorine and two ether oxygens, both of which enhance polymer solubility in CO2. The copolymer cloud-point curves in CO2 monotonically shift significantly to lower temperatures and pressures as the 6F content is increased from 0 to 100%. This shift is ascribed to the decrease in long-range, chain-chain interactions due to poor packing of the 6F-rich chains, to the increase in solvent accessible surface area of fluorinated groups, and to the increase in the fractional free volume (FFV) of 6F-rich chains. The cloud-point curves in propane also initially shift to lower temperatures and pressures with increasing 6F content, but the 6F homopolymer and 6H homopolymer curves cross one another so that the 6H homopolymers are more soluble at low temperatures while 6F homopolymers are more soluble at high temperatures. The reversal in propane solubility behavior with increasing 6F content and temperature results from a delicate balance between repulsive fluorine-hydrocarbon interactions that do not favor copolymer solubility and reduced long-range, chain-chain interactions and increased copolymer FFV that both favor copolymer solubility. The cloud-point data also show that for both CO2 and propane the impact of 6F content is greater than the impact of weight-average molecular weight in the range 15-93 kg/mol, where molecular weight is expected to have a large impact.