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Design and Implementation of Multi-Responsive Azobenzene Triggers in Self-Immolative and Degradable Polymers

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Design and Implementation of Multi-Responsive Azobenzene Triggers in Self-Immolative and Degradable Polymers Western University Scholarship@Western Electronic Thesis and Dissertation Repository 3-22-2016 12:00 AM Design and Implementation of Multi-Responsive Azobenzene Triggers in Self-Immolative and Degradable Polymers Andrew D. Wong The University of Western Ontario Supervisor Elizabeth R. Gillies The University of Western Ontario Graduate Program in Chemical and Biochemical Engineering A thesis submitted in partial fulfillment of the equirr ements for the degree in Doctor of Philosophy © Andrew D. Wong 2016 Follow this and additional works at: https://ir.lib.uwo.ca/etd Part of the Polymer Science Commons Recommended Citation Wong, Andrew D., "Design and Implementation of Multi-Responsive Azobenzene Triggers in Self- Immolative and Degradable Polymers" (2016). Electronic Thesis and Dissertation Repository. 3629. https://ir.lib.uwo.ca/etd/3629 This Dissertation/Thesis is brought to you for free and open access by Scholarship@Western. It has been accepted for inclusion in Electronic Thesis and Dissertation Repository by an authorized administrator of Scholarship@Western. For more information, please contact [email protected]. Abstract Self-immolative polymers are a recently developed class of degradable polymers capable of undergoing end-to-end depolymerization following the reaction of their endcaps with appropriate stimuli. Self-immolative materials originated in the field of prodrug chemistry, and evolved into self-immolative oligomers, dendrimers, and most recently, linear polymers. Many stimuli-responsive endcaps have been developed, but typically can only respond to one stimulus. Azobenzenes are a well-known class of stimuli-responsive molecules most commonly used as photoswitches, due to their facile trans-cis isomerization. In addition to their photochemistry, azobenzenes have recently been found to be selectively reduction- sensitive, and are therefore of interest as endcaps in self-immolative polymers. The two fields of azobenzenes and self-immolative polymers have not previously been combined, and it is the work described herein that is the first to do so. This thesis demonstrates that azobenzenes can be useful as multistimuli-responsive units in self-immolative polymers. First, the reduction-sensitivity of azobenzene was demonstrated in the context of two self-immolative polymer backbones. The synthesis and depolymerization of these materials showed that azobenzene endcaps could be successfully incorporated into – and used to trigger – self-immolative polymers. In the next study, a library of reduction-sensitive azobenzenes was prepared to determine which azobenzene compounds were most suited for use as reduction-sensitive endcaps. A 2-Cl azobenzene derivative was reduced most quickly, and this compound was incorporated as pendant units in an amphiphilic chain-shattering graft copolymer based on a poly(ester amide) backbone. It was found that these azobenzenes imparted both photo- and reduction-sensitivity to aqueous polymer assemblies, and could respond synergistically to both stimuli. In the final study, two distinct linear self-immolative polymer backbones, a polycarbamate and a polyglyoxylate, were synthesized with an azobenzene linker, and conjugated to poly(ethylene oxide) using click chemistry. The synthesized amphiphilic block copolymers were reduction-sensitive, and their aqueous assemblies were shown to encapsulate and release a hydrophobic cargo under reducing conditions. The multifaceted applicability of azobenzene was highlighted in these studies, first as a reduction-sensitive endcap, then as a dual-responsive trigger for chain-shattering poly(ester amide)s, and finally as a reduction-sensitive linker in diblock copolymers. Keywords Azobenzene, self-immolative, polymer, stimuli-responsive, reduction, reduction-sensitive, isomerization, photoisomerization, chain-shattering polymer, block copolymer, amphiphilic, nanoassembly, degradation, glyoxylate, carbamate. ii Co-Authorship Statement The work described in this thesis contains contributions from the author as well as coworkers Thomas M. Güngör, Alexander L. Prinzen, Bo Fan, and supervisor Dr. Elizabeth Gillies. The contributions of each are described below. Chapter 1 was written by the author and edited by Dr. Elizabeth Gillies. Chapter 2 describes a project proposed by the author, supervised by Dr. Elizabeth Gillies, and for which the experimental work was carried out in part by the author, and in part by the Masters student Thomas M. Güngör. The synthesis and degradation of small molecules was carried out by the author. The design, synthesis, and degradation of the elimination-based polymer and its controls was completed by the author, while the synthesis and degradation of the alternating cyclization and elimination-based polymer was completed by Thomas M. Güngör. Data analysis was carried out by the author, and the manuscript was prepared as a collaboration between the author and Dr. Elizabeth Gillies. Chapter 3 describes a project conceived of and designed by the author and Dr. Elizabeth Gillies, and its experimental component was shared between the author and Alexander L. Prinzen, a fourth-year undergraduate student supervised directly by the author. The majority of azobenzene compounds were synthesized and tested by Alexander L. Prinzen, using a synthetic route and methodology developed by the author. Design of the polymers for use in the study was a collaboration between all parties, while synthesis of the polymers was completed by Alexander L. Prinzen. Testing and degradation of the polymers and their controls was shared between the author and Alexander L. Prinzen. Analysis of relevant data was carried out by the author, and assisted by Alexander L. Prinzen. The manuscript was prepared by the author and Dr. Elizabeth Gillies. Chapter 4 details a project designed by the author and Dr. Elizabeth Gillies, and for which the experimental component was completed in part by the author, and in part by the Ph.D. candidate Bo Fan. The azobenzene endcap was prepared by the author, in addition to the polycarbamates. Modification of the azobenzene endcap to a chloroformate, and subsequent synthesis of polyglyoxylates, their controls, and their amphiphilic block copolymers was iii completed by Bo Fan. All degradation experiments and data analysis were completed by the author. The manuscript was drafted by the author and Dr. Elizabeth Gillies. iv Acknowledgments I would like to thank my supervisor, Dr. Elizabeth Gillies, without whom none of this work would have been possible. Her years of patient mentoring and encouragement have been greatly appreciated. I’m especially grateful for the freedom to pursue so many of my own harebrained ideas, of which this thesis is mainly composed. Over my many years in the Gillies Group, I had the pleasure of working with many talented and wonderful people, who kept me entertained and in good company. For their contributions to my thesis, I want to thank Thomas Güngör, Alex Prinzen, and Bo Fan. Dr. Matthew DeWit put up with years of questions, and helped to mold me into the scientist I am today. Brooke Raycraft helped me keep my spirits up in some of my most challenging times. I would like to thank my examination committee, Dr. Wankei Wan, Dr. James Wisner, Dr. Yue Zhao, and Dr. Argyrios Margaritis, for taking the time to read and evaluate my thesis. I also want to thank the friends I’ve made outside the lab in the last few years for keeping me sane. My time here would not have been the same without Dr. Stacey Hallman, Dr. Laura Kang, Dr. Asha Parekh, and Harley Smith, who were my pillars of support. They always made time for me, whether it was over Scotch, coffee, or Skype. Finally, I want to thank my family: my mother, Carrie-Faye; my father, Frank; and my sister, Melanie, for their love and support over the years. They are always with me, despite the distance. Words cannot express the impact they have had and continue to have on my life. v Table of Contents Abstract ................................................................................................................................ i Co-Authorship Statement................................................................................................... iii Acknowledgments............................................................................................................... v Table of Contents ............................................................................................................... vi List of Tables .................................................................................................................... xii List of Figures .................................................................................................................. xiii List of Abbreviations ..................................................................................................... xxiii Chapter 1 ............................................................................................................................. 1 1 Azobenzenes and Self-Immolative Polymers: Two Worlds Collide ............................. 1 Azobenzene ............................................................................................................. 1 1.1.1 Overview ..................................................................................................... 1 1.1.2 Applications of Azobenzene ....................................................................... 1 1.1.3 Synthesis of Azobenzene Derivatives ........................................................
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