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

Abstract

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 CO2 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 CO2 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 CO2. This latter observation is consistent with results on the phase behavior of poly(n-alkyl acrylates) in CO2 that showed that increasing alkyl content (i.e., increasing alkyl chain length) also raises cloud point pressures.