Solubility of non-ionic poly(fluorooxetane)-block-(ethylene oxide)-block-(fluorooxetane) surfactants in carbon dioxide

The impact of side chain and midblock length on the solubility of ABA triblock copolymers of fluorooxetane-(ethylene oxide)-fluorooxetane in carbon dioxide is examined. The use of short fluorinated side chains instead of long fluorinated chains prevents issues with bioaccumulation of the degradation products of the surfactant. At 40 °C for the same degree of polymerization, increasing the number of perfluoro-units from one to four results in a non-monotonic change in the cloud point pressure; the cloud point pressure decreases as the side chain is increased from perfluoromethyl to perfluoroethyl. However, further increasing the fluorinated side chain to perfluorobutyl results in a significant increase in the cloud point. However when the temperature is increased to 60 °C, the cloud point pressure for the surfactants with perfluoroethyl and perfluorobutyl side chains is statistically similar, while the perfluoromethyloxetane based surfactant requires a substantially larger pressure to obtain comparable solubility. An increase in cloud point pressure is observed when increasing the hydrophilic ethylene oxide segment. These results illustrate that commercially available fluorooxetane-(ethylene oxide)-fluorooxetane surfactants are highly soluble in CO₂.