Date of Award
Master of Science in Chemical Sciences (MSCB)
Graham S. Collier
Janet L. Shaw
Thomas C. Leeper
Conjugated polymers have been studied for various applications such as electrochromics, organic photovoltaics, organic light-emitting diodes, thin film transistors, biosensors, and energy storage materials. They have received significant attention from many researchers because they are relatively inexpensive and possess a high degree of synthetic tailorability that enables tuning of optical, electrochemical, and physical properties. However, many state-of-the-art polymers require synthetic protocols that use multiple arduous synthetic steps, harmful chemical reagents, and produce toxic byproducts. Additionally, the synthesized polymers are not typically designed to be degradable and will accumulate during waste disposal without end-of-life management strategies. Therefore, there is a need to incorporate simplified and benign synthesis into the design of degradable polymers. In this vein, degradable azomethine-containing polymers were synthesized using “simple” monomer synthesis and polymerization protocols in an effort to reduce environmental impact for the development of conjugated polymers. First, monomer synthesis was simplified through the one-step multicomponent reaction to make dihydro[3,2-b]pyrrolopyrrole (DHPPs), as well as solvent-free mechanochemistry to synthesize dibrominated monomers amenable to robust Suzuki polycondensations. Monomer preparation through mechanochemistry has the added benefit of reducing the need for non-renewable and energy-intensive solvents as well as the amount of waste generated through organic synthesis. Additionally, the DHPP comonomers were vi polymerized via benign acid-catalyzed polycondensations, where the only byproduct is water. The dynamic equilibrium of the azomethine bond was exploited to show that the synthesized polymers were degradable in the presence of acid, and the degradation of said polymers was monitored via nuclear magnetic resonance, UV-visible, and fluorescence spectroscopies. The results from this work introduce a new design motif for DHPP copolymers which allows for the ability to incorporate environmentally conscious synthesis at multiple steps of the polymer production process while also creating polymers that address growing concerns about waste management of polymeric materials. Additionally, the incorporation of mechanochemistry into azomethine-containing monomers motivates further study into solvent-free synthesis as a way to mitigate the reliance on solvents and reduce the energy required to produce solvents and dispose of solvent waste. In sum, the efforts described in this thesis represent a “cradle-to-grave” initiative to improve sustainable considerations for the development of next-generation conjugated polymers.
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