Tailored Postsynthetic Nitration of a Hypercrosslinked Polymer for Single-Step Ethylene Purification from a Ternary C₂ Gas Mixture

Purifying C₂H₄ from a ternary C₂H₂/C₂H₄/C₂H₆ mixture poses a substantial industrial challenge due to their close physical and chemical properties. In this study, we introduce an innovative design approach to regulate and optimize the nitration degree of a hypercrosslinked polymer to achieve targeted separation performance. We synthesized a porous organic polymer (HCP) using the solvent knitting method and carried out its postsynthetic nitration, resulting in HCP-NO₂-1 and HCP-NO₂-2 with different nitration degrees. Notably, the adsorption capacity shifted from C₂H₆ > C₂H₄ ≈ C₂H₂ for HCP to C₂H₂ > C₂H₆ > C₂H₄ for HCP-NO₂-1 and to C₂H₂ > C₂H₄ ≈ C₂H₆ for HCP-NO₂-2, demonstrating the controllable nature of the separation process via the polar nitro group insertion. Remarkably, HCP-NO₂-1 exhibited a desirable, selective separation of C₂H₄ from the C₂H₆/C₂H₄/C₂H₂ mixture thanks to an exquisite combination of the acidic proton-polar nitro group and nonpolar C−H⋅⋅⋅π interactions. Separation capability was further corroborated by computational simulations and breakthrough tests. This work marks a significant advancement as the first successful postsynthetic functionalization strategy for C₂H₄ purification from a ternary gas mixture among porous organic polymers.