An ATR−IR Study of Poly (Dimethylsiloxane) under High-Pressure Carbon Dioxide: Simultaneous Measurement of Sorption and Swelling

The CO 2 sorption and the consequent swelling of un-cross-linked poly (dimethylsiloxane) (PDMS) have been measured simultaneously at high pressure using in-situ ATR (Attenuated Total Reflectance)−IR spectroscopy. The absorbance of the ν 3 (2335 cm -1 ) band of CO 2 dissolved in PDMS was used to determine quantitative sorption data. The absorbance of the IR band of PDMS was used to calculate the polymer swelling. Data at 25 °C and 50 °C for pressures up to 12 MPa are reported and compared to literature values. A shift of the δ(CH 3 ) band of PDMS (at 1259 cm -1 ) was observed with the increase of sorbed CO 2 and was related to the swelling of the polymer. This is a novel use for high-pressure in-situ ATR−IR spectroscopy, which allows the simultaneous measurement of gas sorption and polymer swelling and provides molecular-level insight into the behavior of polymers under high-pressure or supercritical CO 2 .