Date of Award

Summer 7-22-2022

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

School

Polymer Science and Engineering

Committee Chair

Derek L. Patton

Committee Chair School

Polymer Science and Engineering

Committee Member 2

Sarah E. Morgan

Committee Member 2 School

Polymer Science and Engineering

Committee Member 3

Yoan C. Simon

Committee Member 3 School

Polymer Science and Engineering

Committee Member 4

Sergei Nazarenko

Committee Member 4 School

Polymer Science and Engineering

Committee Member 5

James W. Rawlins

Committee Member 5 School

Polymer Science and Engineering

Abstract

With plastic production poised to increase in coming years, there arises a need to develop new polymeric materials designed to combat the global pollution crisis. A commonly utilized approach in addressing this challenge is to employ a responsive functional moiety into the polymer architecture. Thiol-X reactions, a commonly utilized class of “click” reactions, have garnered broad implementation in new stimuli-responsive materials. This work specifically focuses on utilizing radical-mediated thiol-ene coupling and base-catalyzed thiol-isocyanate reactions to develop a library of ternary thiol-ene/thiourethane covalent adaptable networks (CANs) and hydrolytically labile poly(thioether ketal) thermoplastics. CANs are a class of network materials capable of undergoing dynamic exchange, rendering the material reprocessable while maintaining the high-performance properties traditionally associated with thermosets. Herein, the thiourethane moiety, formed via the thiol-isocyanate reaction, is employed as the dynamic covalent chemistry (DCC) utilized in our approach to CANs. Additionally, linear thiol-ene photopolymerizations are employed to develop a series of poly(thioether ketal) thermoplastics. The ketal moiety incorporated into the polymer backbone of these materials render the resulting material hydrolytically labile – allowing the material to readily degrade at its end-of-lifetime. The work presented herein should provide a framework by which new environmentally friendly materials can be developed.

Chapter I of this dissertation focuses on the various utility of thiol-X reactions within the realm of polymeric materials – with specific interest on implementation within CANs and thermoplastic synthesis. Chapter II outlines the methods by which the thiol-X based materials, described herein, were developed and studied. Chapter III focuses on understanding the specific structure-property relationship of ternary thiol-ene/thiourethane CANs affecting vitrimeric relaxation behaviors and material property retention throughout reprocessing. Chapter IV elaborates on the stoichiometric effects of ternary thiol-ene/thiourethane on the dynamic exchange equilibrium – ultimately dictating thermal relaxation behaviors. Finally, Chapter V utilizes linear thiol-ene photopolymerizations to develop a library of poly(thioether ketals) capable of undergo hydrolysis within an acidic environment while remaining stable in basic and neutral conditions.

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