Non-fluorous polymers with very high solubility in supercritical CO2 down to low pressures

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Abstract
Liquid and supercritical carbon dioxide have attracted much interest as environmentally benign solvents1, but their practical use has been limited by the need for high CO2 pressures to dissolve even small amounts of polar, amphiphilic, organometallic, or high-molecular-mass compounds2,3,4. So-called ‘CO2-philes’ efficiently transport insoluble or poorly soluble materials into CO2 solvent, resulting in the development of a broad range of CO2 -based processes, including homogeneous and heterogeneous polymerization, extraction of proteins and metals, and homogeneous catalysis5,6,7,8,9,10,11. But as the most effective CO2-philes are expensive fluorocarbons, such as poly(perfluoroether), the commercialization of otherwise promising CO2-based processes has met with only limited success. Here we show that copolymers can act as efficient, non-fluorous CO2-philes if their constituent monomers are chosen to optimize the balance between the enthalpy and entropy of solute–copolymer and copolymer–copolymer interactions. Guided by heuristic rules regarding these interactions, we have used inexpensive propylene and CO2 to synthesize a series of poly(ether-carbonate) copolymers that readily dissolve in CO2 at low pressures. Even though non-fluorous polymers are generally assumed to be CO2-phobic, we expect that our design principles can be used to create a wide range of non-fluorous CO2-philes from low-cost raw materials, thus rendering a variety of CO2-based processes economically favourable, particularly in cases where recycling of CO2-philes is difficult.