(392f) Physical Aging and CO2 Sorption in “High Free-Volume” Glassy Polymers

Thin film glassy polymers are mostly used as gas separation membranes due to their excellent permeability-selectivity properties; however, accelerated physical aging in free-standing thin films reduces permeability over time and limits membrane performance [1, 2]. Recently, “high free-volume” glassy polymers have gained significant interest in membrane applications mainly due to their high gas permeability [3]. Poly(1-trimethylsilyl-1-propyne) (PTMSP) is a “high free-volume” polymer with very high gas permeability; however, its high physical aging rate and solubility in many of the organic compounds in process streams of interest limit its practical utility. On the other hand, amorphous Teflon AF 2400 from DuPont has high gas permeability and good chemical stability, making it an interesting candidate as a gas separation membrane for some applications. The physical aging behavior and CO₂ sorption in thin films < 1 µm have been studied. These thin films show lower permeability than thick films but they do not seem to show the accelerated physical aging rates observed for other glassy polymers such as PSF, PI, and PPO. The selectivity did not change with physical aging. Results on physical aging rate and CO₂ sorption in thin Teflon AF 2400 films are compared with other commercially available amorphous Teflon materials having relatively lower free volume. The CO₂ sorption in thin films as measured by ellipsometry is compared with bulk films. The results are also compared with a polymer with intrinsic microporosity (PIM-1), which showed a faster physical aging compared to amorphous Teflon.