Framework-Imprint Synthesis of Faceted Hierarchical Porous Organic Polymer Colloidal Particles

Amorphous porous organic polymers (POPs) are promising filler materials for mixed matrix membranes (MMMs). However, it is challenging to synthesize nanosized, monodispersed POP colloidal particles (CPs) suitable for membrane fabrication. Here, well-defined octahedral POP CPs with imine, ketone, or amine linkages were synthesized using octahedral MOF particles as sacrificial templates. In addition to shape replication, the MOF template also played a substantial role in spatially organizing polymer chains, resulting in highly porous POPs that are unattainable through bulk polymerization. For the first time, the mechanical properties of a single POP CP was examined by quantitative in situ compression testing under a scanning electron microscope. Introducing imine-linked POP CPs into a polyimide matrix led to a series of pure-organic defect-free MMMs exhibiting excellent homogeneity and flexibility. As a result, increasing the loading of POP in MMMs led to a stepwise increase in CO₂ permeability with largely unchanged CO₂/N₂ and CO₂/CH₄ selectivity.