Solubility of carbon dioxide, methane, and propane in silicone polymers. Effect of polymer backbone chains

The solubility of carbon dioxide, methane, and propane in poly(dimethyl silmethylene) [(CH3)2SiCH2]x and poly(tetramethyl silhexylene siloxane) [(CH3)2Si (CH2)6Si (CH3)2O]x was measured in the temperature range from 10.0 to 55.0°C and at elevated pressures. The present results are compared with similar measurements made with other silicone polymers. At a given temperature and pressure, the solubility of the above three gases is highest in poly(dimethyl siloxane) (Me2SiO)x. The gas solubility is decreased by either backbone‐chain or side‐chain substitutions of functional groups in (Me2SiO)x which increase the stiffness of the polymer chains and decrease the specific or fractional free volume of the polymers. It is conjectured that a decrease in the free volume of silicone polymers has a greater effect in decreasing the gas solubility than differences in gas/polymer interactions [with the exception of specific interactions (e.g., between CO2 and polar groups in the polymer)]. © 1993 John Wiley & Sons, Inc.