A porous metal-organic framework composite with flexible anion-exchange polymers threaded within the host cavity demonstrates very fast and reversible ion-exchange activity. Polyvinyl benzyl trimethylammonium hydroxide (PVBTAH) caged in ZIF-8 is synthesized in steps of chloro-monomer impregnation, in situ polymerization, amination, and alkaline ion exchange. The synthesized non-cross-linked PVBTAH similar to ZIF-8 material exhibits superior ion-exchange kinetics compared to conventional ion-exchange resins.