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| - High-Pressure CO2-Expanded Solvents: Simultaneous Measurement of CO2 Sorption andSwelling of Liquid Polymers with in-Situ Near-IR Spectroscopy
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| - In-situ near-infrared (NIR) spectroscopy was used to simultaneously measure the sorption of high-pressureCO2 and the swelling of poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG). NIR spectroscopyin transmission mode allowed us to measure the sorption of CO2 using its combination bands and follow theswelling of liquid polymer via the decrease in absorbance of the overtone bands of polymer. The concentrationof CO2 dissolved in polymer was determined from the absorbance of the ν1 + 2ν2 + ν3 band of CO2 at 4950cm-1. Overtone bands of PEG (at 4855 cm-1) and PPG (at 5778 cm-1) were used to measure polymer densityand calculate the extent of polymer swelling. The data obtained at different pressures in the range of 20−116bar and temperatures of 25−40 °C compare well with literature values for both polymers. In particular, acomparison is made with the use of in-situ ATR-IR spectroscopy, where a change in the refractive index ofthe polymer occurs when it is subjected to CO2. The results obtained show that NIR transmission spectroscopyis a reliable method for studying the phase behavior of liquid solvents subjected to high-pressure or supercriticalCO2. Implications of this method range from studies of CO2-induced viscosity reduction to the use of CO2-expanded solvents for catalysis and materials processing.
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