Covalent organic frameworks: Polymer chemistry and functional design

Covalent organic frameworks (COF) are a class of crystalline porous polymer that enables the covalent integration of organic units into periodically ordered skeletons and aligned polygonal pores. This structural feature sets a new polymer platform that enables the design of not only structures but also functions. Especially, primary- and high-order structures of COFs are fully pre-designable and synthetically controllable, offering a new diagram of chemistry in designing functional materials. Progress in chemistry and materials science over the past 15 years has greatly enhanced our capability of molecular design and functional exploration to develop a fascinating picture of this new class of polymers. In this review, we survey recent advances of polymer chemistry that enable covalent organic frameworks with unique structural design, synthetic control, and functional development. We summarize the most recent advances in the design of polygonal topologies, outline polymerization reactions to synthesize diverse types of polymers, and scrutinize unique functions to illuminate the structural origins of the most promising applications including catalysis, adsorption, molecular separation, mass transport, and energy storage. Moreover, we propose the key fundamental issues to be addressed and show future directions from the perspectives of chemistry and polymer science.