Design and synthesis of sustainable porous organic polymers through SNAr chemistry for adsorption and catalysis

Abstract

Porous materials with permanent pores introduced by structural design are widely used for adsorptions such as gas capture and separation, water purification, and for catalysis. A sub class, porous organic polymers, which are synthesized from only organic monomers, have advantages of chemical stability, cost efficiency, light weight, structural tunability, and versatility. Strategies to construct multifunctional network structures often entail using rare catalysts, inaccessible monomers and extreme conditions. A sustainable guided design and synthesis is needed. In this thesis, nucleophilic aromatic substitution ($S_NAr$) reactions were employed to build complex superstructures from sustainable building blocks by using common reagents or trace amounts of catalysts. The permanently porous network polymers were then used for gas capture and separation, size dependent separations and catalysis. Processability was also studied to attain widespread use in industry. Chapter 2 introduces the synthesis of highly porous organic polymers from a food coloring dye, erythrosine B by Sonogashira coupling reaction. To recover and repurpose the catalysts used in the synthesis, residual palladium, copper, and triphenylphosphine were quantified for the first time for these kinds of materials. The polymers were then applied as heterogeneous catalysts for Suzuki coupling reaction and saved costly addition of new Pd based catalysts. In addition, substrate size dependence due to pore effect was observed, which is not possible with commercial catalysts. In Chapter 3, metal-free synthesis of C-C bonded porous organic polymers is suggested. Perfluorinated arene cores allowed fluoride substitution to take place easily. Silylated alkynes were activated with trace fluoride ions and the $S_NAr$ coupling resulted in microporous networks. Superhydrophobicity of the porous polymers due to the fluorine covered pores was used for organic solvent adsorption in both liquid and vapor state. Furthermore, by utilizing both superhydrophobicity and microporosity, the polymer was used to separate two small molecules with the same boiling point. In Chapter 4, sulfone containing polymers of intrinsic microporosity are discussed. A new reaction for seven-membered sulfone ring synthesis was serendipitously developed, only using sulfuric acid as a solvent and catalyst. The resulting new chemical structures were reported based on instrumental analyses. Polymers from this sulfone monomer have high stability against heat and chemicals. The structures are processable and microporous, proving their promise in especially membrane applications. In conclusion, this thesis shows three different classes of porous organic polymers with varying degree of sustainability and applications. The polymers are highly porous, stable and scalable, and could be easily implemented in industrial applications. The discovery and use of new chemistries described here will open new paths for materials design and synthesis.