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Abstract
Quinone methides (QM) are analogs of quinones with a benzylic methylene group in place of one of the carbonyl oxygens. Isomeric ortho- and para-quinone methides, while possessing similar electronic structures, show very different properties. o-Quinone methides (oQM) are more reactive towards nucleophiles and undergo efficient inverse electron-demand-Diels-Alder (IEDDA) reaction with electron-rich alkenes. p-Quinone methide (pQM), while also acting as Michael acceptors, is not reactive in IEDDA. Chapter One is an overview of reactions, generation methods, types of QMs, their applications, and the goals of the research projects. Our research group is interested in exploring applications of o-naphthoquinone methides (o-NQMs) that are photochemically generated from (3-hydroxynaphthalen-2-yl)methanol (o-NQMP) derivatives using UV-A light. Chapter two describes the photochemistry of a novel QM system that can produce both o-NQM and p-QM upon irradiation with UV-A light. These photogenerated QMs are conjugated to an aromatic system at the methide position, and the reactivity of such conjugated QMs has not been explored previously. Herein, a detailed study of the photophysical properties and photoreactivity of novel Quinone methide precursor (QMP), as well as their comparison with two structural analogs is reported. Additionally, chapter two discusses the potential applications of the novel QMP and its structural analogs as fluorophores for imaging techniques.
Polyethylene terephthalate (PET) is one of the world's most widely used plastics. While PET is thermoplastic, and therefore, is potentially recyclable, the recycling rate is low. Huge quantities of this non-biodegradable polymer end up in the environment casing significant damage. Chapter three elaborates on our effort to develop a photodegradable analog of PET by incorporating a suitable o-NQMP-based photocleavable linker into the macromolecule. This “end-of-life” engineered PET analog can be depolymerized using powerful UV lamps for subsequent re-use and has faster rates of degradation in the environment under sunlight than PET.
The most preferred method for PET recycling is chemical depolymerization, where the polymer is cleaved back into original monomers. However, the process requires a catalyst for efficient and complete depolymerization. Chapters four and five describe the feasibility studies of using thiols and bases as inexpensive catalysts for PET recycling.