Metal–organic frameworks (MOFs) are inherently crystalline, brittle porous solids. Conversely, polymers are flexible, malleable, and processable solids that are used for a broad range of commonly used technologies. The stark differences between the nature of MOFs and polymers has motivated efforts to hybridize crystalline MOFs and flexible polymers to produce composites that retain the desired properties of these disparate materials. Importantly, studies have shown that MOFs can be used to influence polymer structure, and polymers can be used to modulate MOF growth and characteristics. In this Review, we highlight the development and recent advances in the synthesis of MOF-polymer mixed-matrix membranes (MMMs) and applications of these MMMs in gas and liquid separations and purifications, including aqueous applications such as dye removal, toxic heavy metal sequestration, and desalination. Other elegant ways of synthesizing MOF-polymer hybrid materials, such as grafting polymers to and from MOFs, polymerization of polymers within MOFs, using polymers to template MOFs, and the bottom-up synthesis of polyMOFs and polyMOPs are also discussed. This review highlights recent papers in the advancement of MOF-polymer hybrid materials, as well as seminal reports that significantly advanced the field.

A new self-healing multiphase polymer is developed in which a pervasive network of dynamic metal-ligand (zinc-imidazole) interactions are programmed in the soft matrix of a hard/soft two-phase brush copolymer system. The mechanical and dynamic properties of the materials can be tuned by varying a number of molecular parameters (e.g., backbone/brush degree of polymerization and brush density) as well as the ligand/metal ratio. Following mechanical damage, these thermoplastic elastomers show excellent self-healing ability under ambient conditions without any intervention.

Tunable mechanical response under dynamic and static loading is desirable for many technological applications. Traditionally, mechanical performance of polymeric materials is controlled by modulating structural (i.e., molecular weight, chain packing, or cross-link density) or temporal parameters (such as kinetics of the exchange of dynamic cross-linkers). Metal–ligand interactions are uniquely suited to control both structural and temporal parameters as the thermodynamics and kinetics of mechanically active cross-linkers can be varied by careful selection of metal without significant synthetic modification of the polymer backbone. Here, we have demonstrated that it is possible to engineer desired mechanical properties in a metallopolymer with a high degree of tunability by simply changing the type and amount of added metal. Specifically, we cross-linked an imidazole-containing brush copolymer system with the divalent cations of zinc, copper, and cobalt. Using rheology and tensile experiments, we have correlated the emergent mechanical properties to the stoichiometric ratio of ligand to metal as well as the coordination number and ligand exchange mechanism of the imidazole–metal cross-links. In contrary to the general view that unbound free ligands are normally regarded as mechanically inactive dangling chains in metallopolymer networks, this study clearly shows that they can play a critical role in stress distribution and chain relaxation. Importantly, this work shows for the first time that it is possible to simultaneously control both the structure of networks and the temporal response of bulk materials using dynamic association of weak and monodentate ligands with transition metals.

The first polymer-MOF hybrid material (polyMOF) with a UiO-66 architecture is reported, prepared from polymers with varying alkyl spacers, molecular weights, and dispersities. With appropriate spacing, mesoporous UiO-66 polyMOF can be obtained having an uncommon, interlaced crystal morphology, suggesting that polyMOFs can be used to generate MOF materials with hierarchical architectures.