Masters Theses

Date of Award

8-2025

Degree Type

Thesis

Degree Name

Master of Science

Major

Chemistry

Major Professor

Johnathan N. Brantley

Committee Members

Ampofo Darko, Michael Kilbey, Johnathan Brantley

Abstract

The idea of polymer upcycling revolves around using the functional groups that are already present in a polymer, especially in the backbone, to produce high-value derivatives or encourage controlled degradation. This strategy uses polymers as substrates for functionalization or selective degradation processes. However, the intrinsic stability of C–H and C-X bonds limits advancement in this field. Building a library of polymer modification techniques and widening the scope of applicable chemical transformations are crucial to increasing the chemical space available for creating novel and varied polymeric materials. This research employed both photoredox catalysis and hydrogen bonding catalysis.

Polyolefins and polyvinyl chlorides (PVC), which have fully saturated carbon–carbon backbones, make up most commodity polymers. Nevertheless, the backbones of several widely used polymers, such as polyisoprene, polynorbornene and polybutadiene include alternative topologies with olefinic connections. Despite being produced in lesser quantities than polyolefins, these polymers nonetheless present environmental problems when manufactured on a big scale. Notably, olefin units due to unsaturation, provide a helpful reactive location for chemical modification and reactivity. In previous work, my lab colleagues used generated radical cation intermediates via electrochemistry to achieve electrochemical degradation and functionalization by taking advantage of the olefinic reactivity of polyalkenamers. Slow degradation rates, severe oxidative conditions from constant voltage application, and a restricted functionalization range were some of the disadvantages of this strategy. We used photocatalytic redox techniques to get beyond these obstacles. When exposed to blue light, or even solar source, we were able to efficiently degrade polyalkenamers using triphenylpyrylium tetrafluoroborate(metal free) as the photocatalyst in both ambient and inert atmospheres and also functionalize polyalkenamers via nucleophile trapping.

Motivated by small-molecule organocatalysis' substitution selectivity and C-X bond activation, where urea or thiourea motifs offer exceptional site-specificity through noncovalent interactions, suggested the idea for macromolecular applications. With this method, H-bond donor motifs are used in the substitution reactions of PVC. PVC is a polymer rich in C-Cl bonds and occupies a significant proportion of plastic production due to its high tensile strength and durability. By examining a library of H-bond motifs, the planned interactions activate leaving groups, allowing replacement at otherwise unreactive locations without the need for harsh or metal catalysts. The activation was proposed to occur via the stabilization of the halide leaving group by weakening the carbon-halide bond. This mode of activation enhances nucleophilic substitutions. Under these metal-free circumstances, attempts to functionalize PVC using hydrogen bond donor (HBD) catalysis saw little potential. We proposed that this chemical route would serve a better functionalization tool as compared to the dehydrohalogenation functionalization of PVC with the emission of HCl. Little discernible substitution or alteration was found in spite of evaluating different HBDs, nucleophiles, and reaction configurations. The hydrogen bonding induced substitution reaction was probably hampered by the poor reactivity and restricted accessibility of the C–Cl bonds.

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