(157d) Metal Ions-Coordinated Supramolecular Polymers for Membrane Gas Separations

Metal ions can be used to coordinate with polymer chains, forming supramolecular polymer networks (SPNs), which emerge as an interesting platform for designing high-performance membranes for gas separation. Two examples will be illustrated in this talk. First, cross-linked poly(ethylene oxide) (XLPEO) is used to dissolve Co salts due to the complexation between polar ethylene oxide and Co ions. The polymer networks were thoroughly evaluated using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and differential scanning calorimetry (DSC). Adding the salts generally increases glass transition temperature and decreases gas permeability, which can be described using the VFT equation. Incorporating Co²⁺ ions dramatically increases O2 solubility but decreases O2 diffusivity, resulting in a reduced O2 permeability. For example, adding 6.4 mass% Co(BF₄)₂ in XLPEO increases O₂ solubility by 35 times from 0.18 to 6.4 cm³(STP) cm^−3 atm^−1, and O₂/CO₂ solubility selectivity from 0.12 to 4.8, but it decreases O₂/CO₂ diffusivity selectivity from 0.43 to 0.0056. The SPNs exhibit CO₂/O₂ separation properties above Robeson’s upper bound and superior to state-of-the-art membrane materials. Second, nickel trifluoroacetate can be dissolved in polybenzimidazole (PBI). With metal ions coordinating imidazole rings on PBI chains and trifluoroacetate anions plasticizing the PBI chains, the SPNs achieve higher fractional free volumes yet lower d-spacing than PBI, simultaneously increasing H₂ permeability and H₂/CO₂ selectivity. Structure and property relationships will be presented to guide the design of SPNs for improved gas separation properties.