Design, Synthesis and Gas Adsorption Study of Porous Organic Polymers (POPs) and Covalent Organic Frameworks (COFs) Through Dynamic Covalent Chemistry

Porous organic polymers (POPs) as a new class of porous materials have received tremendous research interest in the past decade. POPs are constructed from lightweight elements through strong covalent bonds; as a result, they possess high specific surface area, porosity, high physiochemical stability, and tunable pore structure, etc. POPs have great potential for application in many different fields, such as gas adsorption, separation, heterogeneous catalysis, energy storage, chemical sensing, optoelectronics, etc. This thesis is mainly focused on the design, synthesis, and property study of POPs through different types of dynamic covalent chemical reactions, with a particular focus on investigating their application in gas adsorption and separation. In chapter 1, the current development of POPs is reviewed. The classification of POPs, synthetic strategies, and their various potential applications will be discussed. In chapter 2, the synthesis of a series of imine-linked porous polymer frameworks (PPFs) through dynamic imine condensation is reported. The resulting PPFs exhibit high specific surface area and high physical stability. Gas adsorption studies revealed that these types of materials have high H2, CH4, C2H2, and CO2 adsorption capacity and high CO2/N2 adsorption selectivity, which can be used as potential gas storage and separation materials. In chapter 3, porous poly (aryleneethynylene) networks (PAEs) were prepared through both reversible alkyne metathesis and irreversible Sonogashira cross coupling reactions. The PAEs prepared through dynamic alkyne metathesis consistently show higher surface area than those prepared through Sonogashira cross coupling, thus indicating the advantage of dynamic alkyne metathesis in the porous organic polymer synthesis. In chapter 4, the photoresponsive azobenzene moiety was incorporated into POPs, and a series of photoresponsive POPs were synthesized. These photoresponsive POPs exhibit permanent porosity. Gas adsorption studies revealed that their pore size distribution and CO2 adsorption behavior is responsive to the ultraviolet visible light (UV) irradiation, and the process is highly reversible even after a few cycles. In chapter 5, the desymmetrized vertex design strategy was employed in the synthesis of covalent organic frameworks (COFs), which show an alternative heterogeneous hexagonal pore structure as expected. Both experimental data and theoretical models confirm the heterogeneous pore structure COFs. This new synthetic method will provide a new possibility for the synthesis of complicated COFs containing heterogeneous pore structures. Chapter 6 describes the perspective and near future work based on the current research progress. The construction of COFs with heterogeneous pore structures from other aromatic building blocks is explored. Given the geometry of the building blocks used, COFs with up to three different pore sizes or alternating tetragonal and octagonal pores are expected. The synthesis and characterization of these COFs with new topology are currently being pursued