Toward the Development of “CO₂-philic” Hydrocarbons. 1. Use of Side-Chain Functionalization to Lower the Miscibility Pressure of Polydimethylsiloxanes in CO₂

Previous fundamental work on the solvent properties of carbon dioxide by the research groups of McHugh, DeSimone, Johnston, and Eckert has been used as a road map for the design of materials that will be miscible with CO 2 at relatively moderate pressures. In this initial work, judicious side chain functionalization of an oligomeric silicone has been shown to produce a material whose phase behavior in CO 2 resembles that of a fluorinated polyether. The phase behavior results are quite dramatic in that addition of only five ester-functional side chains to the silicone polymer lowers the cloud point curve at 22 °C by 2500 psi. It was also observed that addition of simple alkyl side chains raises the cloud point pressures of the silicone in CO 2 . This latter observation is consistent with results on the phase behavior of poly( n -alkyl acrylates) in CO 2 that showed that increasing alkyl content (i.e., increasing alkyl chain length) also raises cloud point pressures .