Network polymers derived from the integration of flexible organic polymers and rigid metal-organic frameworks

Polymer gels, a representative state of network polymers, are a valuable and well-known class of materials with various functional and attractive properties and are thus commonly used in daily life. The properties of a polymer gel depend not only on the chemical structure of the network but also on the physical structure, including crosslinking points, polymer chains or network compositions, as demonstrated by recent studies on polymer gels with elaborate physical structures. By using a new type of porous crystal, a metal-organic framework (MOF) consisting of organic ligands and metal ions, as the key material, several research groups have developed a synthetic procedure for the formation of network polymers with highly controlled structures. This review focuses on the integration of MOFs and organic network polymers to form shaped network polymers or organic-inorganic hybrid networks through the following three methods: (1) polymerization of the organic ligands in a MOF using the guest molecules, (2) polymerization of homopolymerizable organic ligands in a MOF in the absence of guest molecules, and (3) formation of MOFs from polymeric organic ligands.