Modification and Synthesis of Polymers by Inverse Electron Demand Diels Alder (IEDDA) Reaction Of 1,2,4,5-Tetrazines

Abstract

The applications of 1,2,4,5-Tetrazines in polymer post-functionalization and Diels Alder cycloaddition polymerization are presented in the five chapters of this dissertation. In the last two decades, tetrazine click chemistry has been used extensively in biochemical research due to its fast kinetics as well as many other appealing features, such as being catalyst-free, high yielding, etc. Meanwhile, the click reaction of tetrazines has been used for polymer and material modification but not as frequently as in biochemical research. Further, given the fact that tetrazines react through Diels Alder cycloaddition mechanism, it is also worthwhile to explore the Diels Alder cycloaddition polymerization of tetrazine monomers. In this dissertation, the first chapter provides an overview of polymer functionalization with tetrazines and the Diels Alder polymerization. It highlights the tetrazine click modification of polymers and organic frameworks while briefly summarizing the progress of Diels Alder polymerization. In the second chapter, a novel application of 1,2,4,5-tetrazine click chemistry in the polymer post functionalization will be presented and explained in detail. The tetrazine click chemistry of polymers advances to a new stage under solvent-free conditions. Additionally, the modification immediately crosslinks the linear polymers due to the trimerization of the dihydropyridazine intermediates. The structure of the crosslink was determined by a small molecule model study with 2D NMR experiments and X-ray crystal structure analysis. Lastly, the modification created a flexible polymeric foam material. The third chapter is focused on the dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate post functionalization of polybutadienes to make UV absorbing materials with a built-in antioxidant. It includes the synthesis of the tetrazine, post functionalization of the polymer, sample preparation and characterization of the materials. The anti-oxidative property of the polymer was studied by NMR experiments after its exposure to sunlight. A gelation delay study of the model compound is also included in order to show the anti-oxidative property. The fourth chapter records the attempted polymerization of tetrazines through Diels Alder cycloaddition polymerization. Three sets of tetrazines and diacetylenes were tested; the results convinced us that tetrazine species could be polymerized directly through Diels Alder cycloaddition polymerization. However, more studies need to be done to figure out the best conditions and type of diacetylenes that can produce soluble and high molecular weight polyarylenes from the Diels Alder cycloaddition polymerization of the 1,2,4,5-tetrazines. Finally, the last chapter concludes and summarizes my work on the post functionalization of polymers through tetrazine click chemistry and the Diels Alder cycloaddition polymerization of tetrazines. Additionally, I propose future studies for the modification and synthesis of polymers by iEDDA of 1,2,4,5-tetrazines.