CO ₂ Dilation and Transport Characterization of Incrementally Fluorinated Poly(ether imide) Membranes

Penetrant-induced plasticization remains a significant limitation in membrane-based separation technologies, particularly in applications involving condensable species such as CO2 and heavy hydrocarbons. Traditional glassy polymer membranes often suffer performance losses under such conditions, while fluoropolymers have shown promise due to their high permselectivity, sorption characteristics, and potential resistance to plasticization and physical aging. In this study, a series of structurally analogous poly(ether imide)s with systematically varied fluorine contents were evaluated for CO2 transport properties. Sorption and permeability measurements of CO2 were conducted at pressures up to 51 atm at 35 °C and 10 atm at 260 °C. No plasticization pressures were observed at lower temperatures. However, diffusivity data suggest that the absence of fluorine moieties slightly increased the susceptibility to plasticization. This effect is suspected to be an indirect consequence of the increased glassiness in the fluoropolymer material. A review of relevant literature data suggests that increasing glass transition temperature was found to significantly reduce plasticization susceptibility across multiple families of polymers. The hydrocarbon polymer exhibited a higher temperature dependence on permeability, which is reflected in its elevated activation energy of permeation. Additionally, dilatometry studies revealed that the perfluoropolymer had a significantly lower CO2 partial molar volume compared to its hydrocarbon counterpart.