Polymer Threaded MOF As an Effective Ion Exchange Material

We extend the concept of “in situ polymerization in MOF” from Kitigawa and co-workers [1], to synthesize ion-exchange polymers into MOFs . We report a porous metal−organic framework composite with flexible anion-exchange polymers threaded within the host cavity.[2] Polyvinyl benzyl trimethylammonium hydroxide (PVBTAH) threaded in ZIF-8 (PVBTAH~ZIF-8) is synthesized in steps of chloro-monomer impregnation, in situ polymerization, amination, and alkaline ion exchange. The synthesized non-cross-linked PVBTAH~ZIF-8 material exhibits superior ion-exchange kinetics compared to conventional ion-exchange resins. The open porous structure of MOF allows the physically trapped polymers to contact solvent freely and exchange ions efficiently, as oppose to the conventional ion-exchange resins in which the binding sites are hidden within the polymeric beads, preventing full utilization of ion exchange sites. It has good potential to be applied as a hybrid polymeric electrolyte in advanced fuel cells and flow batteries which demands high ionic selectivity.

[1] T.Uemura, K.Kitagawa, S. Horike, T. Kawamura, S. Kitagawa, M. Mizuno, and K. Endo, “Radical polymerisation of styrene in porous coordination polymers”, Chem. Commun., 48 (2005) 5968-70.
[2] L. Gao, C.Y. V. Li, K.Y. Chan, and Z.N. Chen, "Metal-Organic Framework Threaded with Aminated Polymer Formed in Situ for Fast and Reversible Ion Exchange”,  J. Am. Chem. Soc., 136 (2014) 7209-7212.