Partial pore blockage and polymer chain rigidification phenomena in PEO/ZIF-8 mixed matrix membranes synthesized by in situ polymerization

Nanostructured zeolitic imidazolate frameworks (ZIF-8) was incorporated into the mixture of poly (ethylene glycol) methyl ether acrylate (PEGMEA) and pentaerythritol triacrylate (PETA) to synthesize mixed matrix membranes (MMMs) by in situ polymerization for CO2/CH4 separation. The solvent-free polymerization between PEGMEA and PETA was induced by UV light with 1-hydroxylcyclohexyl phenyl ketone as initiator. The chemical structural characterization was performed by Fourier transform infrared spectroscopy. The morphology was characterized by scanning electron microscope. The average chain-to-chain distance of the polymer chains in MMMs was investigated by X-ray diffraction. The thermal property was evaluated by differential scanning calorimetry. The CH4 and CO2 gas transport properties of MMMs are reported. The relationship between gas permeation-separation performances or physical properties and ZIF-8 loading is also discussed. However, the permeation-separation performance was not improved in Robeson upper bound plot compared with original polymer membrane as predicted. The significant partial pore blockage and polymer rigidification effect around the ZIFs confirmed by the increase in glass temperature and the decrease in the d-spacing, were mainly responsible for the failure in performance improvement, which offset the high diffusion induced by porous ZIF-8.