(699f) Effect of Chain-End Group in Higly Polar Yet Amorphous Poly(1,3-dioxolane)-Based Polymers on Gas Separation Properties

Poly(ethylene oxide) (PEO) based polymers are leading membrane materials for CO₂/N₂ separation with a balanced high CO₂ permeability and CO₂/N₂ selectivity because the ether oxygen groups show affinity towards CO₂. Herein, we report polymers based on 1,3-dioxolane with higher ether oxygen content than PEO, achieving superior CO₂/N₂ separation performance. Specifically, macromonomers of poly(1,3-dioxolane) acrylate (PDXLA) with short PDXL branches (n = 4 – 8) were synthesized via ring-opening polymerization of 1,3-dioxolane, and solid polymers were obtained by photopolymerization of PDXLA. The chain-end group in PDXL was converted from OH- to acetyl- (CH₃C=O, Ac-) and propionyl- (CH₃CH₂C=O, Pr-) to disrupt H-bonding. The chemical structure of the macromonomers was confirmed using NMR, and the amorphous nature of the polymers was validated using DSC and WAXD. Pure- and mixed-gas CO₂/N₂ separation properties were determined as a function of feed pressure, composition, and temperature, and the effect of chain-end group in PDXLA on the gas separation performance was also investigated. The polymer derived from PDXLA8 (with 8 repeating units of dioxolane) exhibits the best separation performance with CO₂ permeability of 220 Barrer and CO₂/N₂ selectivity of 56 at 35 ^oC, above the 2008 Robeson’s upper bound. The CO₂ permeability increases to 270 Barrer when the OH-group was converted to Ac-chain-end group and further increases to 410 Barrer for Pr-chain-end group. This is due to the increase in chain flexibility, indicating by decreasing in T_g from -60°C to -70°C. The structure/property relationship in this series of amorphous, highly polar polymers with exciting separation performance will be discussed.