(618b) Polyoxymethylene-Based Amorphous Polymers with Superior CO2/N2 Separation Performance

Poly(ethylene oxide) (PEO) containing polymers are leading membrane materials for CO₂/N₂ separation with a balanced high CO₂ permeability and CO₂/N₂ selectivity because of the affinity of ether oxygen towards CO₂. Herein, we design polymers based on polyoxymethylene (POM) with higher ether oxygen content than PEO and thus more superior separation properties. The challenge is to disrupt the crystallization of these highly polar polymers and achieve high gas permeability. We first synthesize macromonomers of polyoxymethylene acrylate (POMA) by ring-opening polymerization of 1,3,5-trioxane (TX) following by capping with acetic anhydride. The POMA with short chain length can then be polymerized to obtain amorphous polymers (polyPOMA). The macromonomers were characterized using NMR, FTIR, and GPC for the chemical structure and chain length, and the polymers were characterized using DSC and XRD to confirm the amorphous nature. Pure- and mixed-gas CO₂/N₂ separation properties were determined, and the effect of POMA chain length on the gas separation performance was investigated. When the number of the repeating units of POM segments is 9, the membranes show the best performance with CO₂ permeability of ~200 Barrer and CO₂/N₂ selectivity of ~70 at 35 ^oC, above the 2008 Robeson’s upper bound. When tested with simulated flue gas containing 15% CO₂ and 85% N₂, the POM-based membranes exhibit stable CO₂/N₂ separation performance in the presence of water vapor at temperatures up to 60 ℃. We will also elucidate the structure/property relationship in this series of polymers with exciting separation performance.