Pores and Polymers: Metal–Organic Framework and Polymer Composite Materials

Conspectus Porous materials, most notably metal–organic frameworks (MOFs), covalent organic frameworks (COFs), hydrogen-bonded frameworks (HOFs), and related materials have gained increasing attention for their unique properties and characteristics, which was crowned with the 2025 Nobel Prize in Chemistry (in recognition of the discovery of MOFs). The high internal surface areas, porosity, pore variety, chemical tunability, and high crystallinity have made these next-generation porous solids the subject of intense interest for ∼25 years. The propensity of these solids to form as crystalline materials (which has been highly prized by researchers in the field) provides great benefits with respect to definitive structural characterization and rational design of these compounds. However, crystallinity comes with a cost, which is a lack of processability and malleability. Like most crystalline, microcrystalline, or powdered solids, these next-generation porous solids have a limited ability to be formed into films, fibers, coatings, monoliths, or flexible materials because of their crystalline structure. As these materials become increasingly deployed into potential technological applications, their limited processability will similarly limit their utility and ability to integrate into fully functioning technologies. As such, efforts to integrate MOFs (and related materials) with flexible polymers has become of substantial interest. This Account highlights the research journey of the author to combine MOFs with polymers in various constructs that seek to retain the unique physicochemical properties of MOFs (e.g., crystallinity, functional tunability, porosity), while exhibiting macroscopic processability more like that of organic polymers. Simple mixing of MOFs and polymers to generate mixed-matrix membranes (MMMs) provides a relatively straightforward solution to this challenge. However, selection of appropriate polymers for forming MMMs is required to avoid pore filling and loss of MOF porosity. Thinner membranes and films can be achieved by polymer grafting onto MOF particles to generate self-assembled MOF monolayers (SAMMs). SAMMs achieve ultrathin form factors but are mechanically fragile relative to MMMs. Finally, a true integration of MOFs and polymers is achieved with polyMOFs, where 1-dimensional, organic, noncrystalline polymers are used as the organic building component of the MOF. In polyMOFs, the two components of the composite─the MOF and the polymer─become truly integrated and indistinguishable, whereby the MOF is the polymer and the polymer is the MOF. That stated, the utility and materials characteristics of polyMOFs are presently rather underwhelming compared to MMMs or SAMMs. Taken together, this Account seeks to describe a range of approaches to integrating MOFs and polymers, highlight success, illuminate future challenges, and inspire more creative efforts in the field.