Solution-processable amorphous microporous polymers for membrane applications

The adsorption and transport of molecules or ions in the confined space of microporous materials often reveal properties not seen in either dense bulk or microporous materials. The unexpected behavior of confined polymers motivates their application in advanced technologies. While the majority of microporous materials consist of network/framework-type strong intermolecular connections, making the processing and roll-to-roll fabrication of these materials particularly challenging, there exists a special category of microporous polymers that are amorphous and can be solution-processed. They feature relatively weak intermolecular bond strength, low long-range order, and large free-volume elements due to frustrated polymer chain motion. However, it remains elusive to design and synthesize solution-processable amorphous microporous organic polymers for those working in the field of membrane separations and electrochemistry. The application of membranes derived from these polymers in processes beyond gas separations is also overlooked. Thus, we review the synthetic strategies toward solution-processable amorphous microporous organic polymers (SAMOPs), with a particular focus on the characteristics and the monomer/polymer structural features of each reaction. Computation-based materials design, including computational tools are introduced that can reveal the monomer/polymer rigidity, polymer chain packing, thereby the generation of free volume elements, and the pore architecture, to facilitate the design and identification of desirable polymers. On-polymer modification methodology that can afford standing-alone membranes with functional groups for applications beyond gas separation, especially targeting membrane-based electrochemical devices are subsequently covered. The molecular transport/ion in the sub-1-nm space provided by solution-processable amorphous microporous organic polymers are presented and the wide range application of membranes derived from these polymers is demonstrated. Finally, challenges, perspectives, and future research directions are discussed.