(22b) Polyimides and Their Derivatives for Gas Separation Applications

High performance polymers are of interest for high temperature gas separations, especially for the sequestration of carbon dioxide. A new family of high performance imide polymers has been identified as a successful membrane separation material. VTEC polyimides possess the desired thermal properties (up to 500 °C) along with being robust and flexible even after multiple thermal cycles (up to 400 °C). Polyimides are excellent materials for high selectivity for smaller kinetic diameter gases such as H₂ and CO₂; however, they have very low fluxes. We have blended small amounts of different compounds with VTEC polyimide, and these blends have very different flux properties than the starting polymeric films. A notable problem when using glassy polymers is their moisture content, especially when making blends with other compounds. It has been found that water entrapped within the polymer matrix (left over from the solvent, or physisorbed) can also cause the polymer's fluxes and selectivities to change dramatically. Additionally, the presence of molecular water in the polymer's void volume has been validated through Positron Annihilation Lifetime (PAL) spectroscopy. In this presentation, polymer characterization and gas-separation testing results will be discussed.