(606a) Systematic Design of Fluorinated Poly(ether imide)s to Elucidate Polymer-Penetrant Interactions for Fluorinated and Highly Condensable Penetrants

Recovery and reclamation of fluorinated gases is becoming increasingly urgent as the US moves to phase down high global warming potential (GWP) fluorinated refrigerants through the American Innovation and Manufacturing (AIM) Act. Unfortunately, these separations are accomplished primarily via distillation today, and studies in the open literature on separating fluorinated gases are exceedingly rare. To address this critical knowledge gap, we present a study on sorption-diffusion behavior of fluorinated refrigerants, hydrocarbon gases, and plasticization-inducing CO₂ in poly(ether imide)s (PEIs) using a methodical approach to systematically investigate the role of fluorine composition of the polymer and of the gas penetrant on separation performance. In order to identify the key structure-property relationships governed by backbone fluorination, the PEIs were systematically designed by modifying fluorine content in the monomers, leading to analogous backbone structures with varying degrees of fluorination. Using these PEIs, we combined pure- and mixed-gas permeation experiments with pure-gas pressure-decay sorption experiments to analyze changes in permeability, diffusivity, and sorption, as well as parameters governing dual-mode sorption behavior. Furthermore, we focus our study on the transport behavior of representative gases, including R-14 (CF₄) and R-32 (CH₂F₂), as well as CO₂ and light hydrocarbons in order to compare the effect of controlling penetrant fluorination against varying fluorine content. We also present our work using Grand Canonical Monte Carlo (GCMC) simulations to validate experimental trends in sorption between hydrocarbon and fluorocarbon polymers and penetrants. The impact of fluorine on penetrant-induced plasticization is evaluated by performing permeation experiments with CO₂ swept to high pressure and analyzed via the partial-immobilization framework as discussed by Paul and Koros [1] and expanded to include plasticization behavior by Stern and Saxena [2]. Lastly, mixed-gas results are compared between CH₄/CO₂ and CH₄/C₂H₆ systems. CO₂ and C₂H₆ in particular were chosen due to their similar condensabilities as represented by their almost identical critical temperatures. With these data, we discuss potential of fluorinated polymer membranes (both perfluorinated and partially fluorinated) as an exceptional materials design choice for refrigerant and plasticization-inducing separations.

[1] Paul DR, Koros WJ. Effect of partially immobilizing sorption on permeability and the diffusion time lag. J. Polym. Sci., Polym. Phys. Ed. 1976; 14(4): 675-685.

[2] Stern SA, Saxena V. Concentration-dependent transport of gases and vapors in glassy polymers. J. Membr. Sci. 1980; 7(1): 47-59.