Crosslinking of Linear Polyimines Into Aminal‐Linked Porous Organic Polymers for C ₂ Hydrocarbon/Methane Separation

ABSTRACT

Hypercrosslinked polymers, a class of porous organic polymers (POPs), are constructed by crosslinking linear polymers or knitting small aromatic molecules with a molecular crosslinker, typically via Friedel–Crafts alkylation. In this study, we report a new approach for the synthesis of POPs via the crosslinking of linear polyimines with m ‑phenylenediamine through nucleophilic addition of amines to imines, forming aminal linkages. The resulting aminal‐linked POPs, with an estimated low cost of 16 USD/kg, exhibited high surface areas up to 650 m ² /g and abundant microporosity, in contrast to the ∼100 m ² /g observed for the linear polyimine. This method demonstrated good generality: four linear polyimines with different structures were successfully crosslinked into POPs with high porosity. Both experimental results and theoretical calculations indicate that the use of diamines at the meta‐position is critical for efficient crosslinking, whereas para‐diamines did not initiate crosslinking. With their high surface area and rich microporosity, these POPs displayed high adsorption capacities for C ₂ hydrocarbons and CO ₂ , but significantly lower capacity for CH ₄ . Dynamic breakthrough experiments confirmed excellent separation performance for C ₂ hydrocarbons/CH ₄ mixtures, highlighting their potential for hydrocarbon separation. This study provides a new strategy for the synthesis of cost‐effective POPs and demonstrates their promising applications in gas separation.