Exploration and Application of Mechanoresponsive Polymers: Polymer Architecture, Amplified Response, and Additive Manufacturing

Thesis (Ph.D.)--University of Washington, 2015My graduate work has been primarily dedicated to basic and applied research in the field of polymer mechanochemistry, or more specifically, the exploration and application of polymers that undergo targeted chemical transformations in response to mechanical force. In chapter one, I begin by discussing our work on exploring how polymer architecture affects the kinetics of mechanochemical reactivity. We compared linear and star polymer degradation kinetics both with and without mechanoresponsive moieties in the polymer backbone. We determined that the molecular weight of the arms, regardless of architecture, was the defining kinetic parameter. In the next chapter, I describe the development of a computational model that predicts the evolving molecular weight distribution of star polymers undergoing mechanochemical degradation. We demonstrate the model for three- and four-arm star polymers and describe how it can be expanded for a n-arm star polymer. In chapter three, I discuss our work on studying the kinetics and mechanism of mechanochemical activation, and subsequent depolymerization, of a low ceiling temperature polymer. In addition to our demonstrating that complete deppolymerization of a polymer to its monomer units is possible (mechanochemically), we also are able to experimentally support a heterolytic degradation mechanism, which is rare in polymer mechanochemistry. I conclude my work on mechanochemisty by describing our work on 3D printing of mechanochromic polymers. We printed complex architectures that would be difficult if not impossible to prepare with other manufacturing techniques, as well as developed a prototype force sensor. I conclude this dissertation by describing some of the work that I have done that is not related to polymer mechanochemisty. I discuss our work on developing a thermal trigger for the depolymerization of a polyurethane into its monomer units. We explored the temperature-dependent depolymerization kinetics and confirmed the mechanism of the trigger activation with chain-end trapping experiments