Responses of 6FDA-based polyimide thin membranes to CO2 exposure and physical aging as monitored by gas permeability

Membranes made from glassy polymers have been of great interest in the past decade for CO2 removal from natural gas streams; however, strongly soluble gases, such as CO2, can cause “plasticization” of polymer membranes, which greatly reduces the separation efficiency. This work examines the response of several 6FDA-based polyimides thin film membranes with thicknesses around 200 nm to CO2 exposure and physical aging. DABA units are incorporated to create crosslinkable sites for such materials. Introducing DABA units to the 6FDA-DAM and 6FDA-mPDA polymers seems to result in materials even more prone to CO2 plasticization. A unique thermal annealing approach is used to crosslink the polyimides via decarboxylation of the DABA units; the resulting crosslinked polymers appear to be much more plasticization resistant at high CO2 pressures compared to their DABA containing counterparts prior to crosslinking. Prior thermal history plays a significant role in both the physical aging of the thin film membranes and their CO2 plasticization resistance particularly for chemical structures that tend to lead to high free volume and permeability.