Physical Aging and CO2 Exposure Effects for Thin Films of Amorphous Teflon

Polymers with high permeability provide a route to high flux gas separation membranes; however, excellent thermal and chemical stability are usually desired.  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 organic compounds in process streams of interest limit its practical utility. On the other hand, amorphous Teflon AF 2400 (obtained by copolymerization of tetrafluoroethylene and perfluoro-2,2-dimethyl-1,3-dioxole), commercially available from DuPont, also has a high free volume and gas permeability while also having high chemical stability makes it an interesting candidate as a gas separation membrane for some applications. The physical aging behavior, effect of CO₂ exposure 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 (PSF, PI, PPO) in thin film form. The selectivity did not change with physical aging. Short-time CO₂ exposure did not show any significant plasticization effect. Results are also compared with Teflon AF 1600 having lower dioxole comonomer and Hyflon polymers (TFE and 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole (TTD)). The CO₂ sorption in thin films as measured by ellipsometery is compared with bulk films. The physical aging of this polymer as tracked by ellipsometry along with some preliminary results on physical aging, CO₂ exposure and sorption results on polymer with intrinsic microporosity (PIM) will be also presented.