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|Title:||Post-Synthetic Modification of Polymeric Structures using the Strain-Promoted Azide-Alkyne Cycloaddition|
|Department:||Chemistry and Chemical Biology|
|Abstract:||The discovery of functional materials and compounds is a goal shared across multiple fields of chemistry. This can be achieved by preparing multiple derivatives from independent syntheses, or by the post-synthetic modification (PSM) of a reactive material. This distinction is important in the realm of polymer chemistry, as it significantly reduces the synthetic workload, while maintaining a constant degree of polymerization (DP) between the derivatized series. The criteria for a suitable reaction are complicated by the need for efficient and quantitative chemistry. In the world of small molecule synthesis, impure products can be easily removed from the target substrate. However, for a polymer to undergo a successful PSM, every reactive unit must be converted without fail, as defects are covalently bound to the scaffold. This issue is further amplified by the low solubility (and at times, insolubility) of polymeric materials in a narrow selection of solvents. In my Thesis, I address this issue by introducing a reactive dibenzocyclooctyne (DIBO) repeat unit into polymeric and macromolecule structures, such as linear conjugated polymers and covalent organic frameworks (COFs). The strained-alkyne present in DIBO undergoes the strain-promoted azide-alkyne cycloaddition (SPAAC) to readily produce triazoles with a variety of organic azides. I initially explore the utility of the SPAAC reaction to produce a library of conjugated polymers, differing only in their side-chain in Chapter 2. By using PSM to accomplish this, the DP of all the polymers remained identical. This is vital, as the objective of this polymer library was to reveal the effect of varying the side-chain on the supramolecular complexes formed between the produced conjugated polymers, and single-walled carbon nanotubes (SWNTs). We showed that the polymers retained the same DP among the series and established a new understanding of polymer-SWNT interactions. Although we had a viable scaffold for PSM with SPAAC, the imine-backbone of the polymer compromised the long-term stability of the structure. Imines are prone to hydrolysis and are especially unstable in acidic environments. A compromised polymer backbone would diminish the importance of a uniform DP among our polymer library. To remedy this, in Chapter 3, I prepared a novel bisaldehyde DIBO monomer, and polymerized it with Wittig chemistry. I show that this new polymer system possessed the same reactivity with azides, with the benefit of long-term stability, and interesting photophysical properties that the previous polymer lacked. To demonstrate this, the new polymer was ultimately cross-linked to form a photoluminescent hydrogel. Lastly in Chapter 4, I attempt the synthesis of a COF bearing a DIBO repeat unit. COFs are a fascinating class of polymer materials, and the PSM and exfoliation of these materials are of scientific interest. I demonstrate the synthesis, and thoroughly characterize a DIBO bearing COF. The COF undergoes PSM with SPAAC, and I leverage this reactivity to prepare a stable colloidal dispersion of the 2D polymeric sheets.|
|Appears in Collections:||Open Access Dissertations and Theses|
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