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© 2015 Nicholas a Johnson All Rights Reserved © 2015 NICHOLAS A JOHNSON ALL RIGHTS RESERVED PHOSPHAZENES: FROM POLYMER TO SUPERBASE A Dissertation Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Nicholas A. Johnson August, 2015 PHOSPHAZENES: FROM POLYMER TO SUPERBASE Nicholas A Johnson Dissertation Approved: Accepted: Advisor Department Chair Dr. Claire A. Tessier Dr. Kim C. Calvo Committee Member Interim Dean of the College Dr. Wiley J. Youngs Dr. Chand K. Midha Committee Member Dean of the Graduate School Dr. Peter L. Rinaldi Dr. Rex D. Ramsier Committee Member Date Dr. Chrys Wesdemiotis Committee Member Dr. Coleen Pugh ii ABSTRACT Polyphosphazenes represent the largest class of inorganic backbone polymers and a wide array of applications exists and continues to accumulate. Although many useful phosphazene polymer systems exist, commercial use has been limited due to irreproducibilities and high cost of the parent polymer, polydichlorophosphazene, from which most other polyphosphazenes are derived. Although the ring-opening polymerization of [PCl2N]3 has been extensively studied since the mid-1960s, the mechanism is still under much debate and the search for novel initiators to the process is ongoing. The majority of phosphazenes are derived from the chlorophosphazenes; however, the properties of the P-N backbone of phosphazenes can be greatly tuned with the addition of different side groups attached to the phosphorus atom. A large variety of applications for substituted phosphazene compounds have been developed ranging from biological materials that are water-degradable to phosphazene superbases that have been used as initiators for several organic polymerizations. The main focus of this dissertation is fundamental phosphazene chemistry ranging from investigations of the initiating steps of the ring-opening polymerization of [PCl2N]3 to interactions of phosphazene superbases with classic Lewis acids. This dissertation is divided into six chapters: introduction, interactions of phosphazene superbases with group 1 and group 12 Lewis acids, interactions of phosphazene superbases with group 13 Lewis acids, reaction of phosphazene superbases with [PCl2N]3, phosphazenes for biological applications, and conclusion. Chapter I provides iii an overall review of polyphosphazene synthesis including initiators and mechanistic discussions as well as use of phosphazene superbases as frustrated Lewis pairs and initiators in anionic ring-opening polymerizations. Chapter II contains explorations of phosphazene superbases and their interactions with group 1 and group 12 Lewis acids. Chapter III is an investigation of phosphazene superbases with Group 13 Lewis acids and a brief investigation into these complexes frustrated Lewis pair (FLP) capabilities. Chapter IV explores the interactions of phosphazene superbases with cyclic chlorophosphazene trimer ([PCl2N]3) and the investigation of a tadpole-like structure that is formed, similar to the complex that is implicated as the initiating species to ring- opening polymerization. Chapter V investigates the utility of ethylene glycol substituted [PCl2N]3 as a phosphazene-based drug delivery system including synthesis and purification of stereoisomers. Chapter VI contains the conclusions of this dissertation. iv DEDICATION This dissertation is dedicated to my grandma, Darlene Johnson. In life the two things she held in the highest regard were faith and family. Not only was she a shining example of how to live my life but also showed me the priorities of life and living that I still maintain to this day. She taught me to love life and be thankful for all that God has given me. Thank you grandma for being one of the most amazing women I have ever known. v ACKNOWLEDGEMENTS First and foremost I would like to express my deepest gratitude to my research advisor Dr. Claire A. Tessier. She have always been supportive and loving throughout my entire time at The University of Akron and a constant source of inspiration and admiration. She taught me how to be a better scientist, researcher, teacher, educator, and person. She will forever be my chemistry mom. To my co-advisor Dr. Wiley J. Youngs. Through bottles of scotch and long talks about chemistry he has always been more than willing to hear all of my ridiculous ideas with only minimal amounts of ridicule. I would not have made it as far as I have without him. I would like to thank all of my other committee members, Dr. Peter Rinaldi, Dr. Chrys Wesdemiotis and Dr. Coleen Pugh. I would also like to thank Dr. Mathew J. Panzner. Each and every day I aspirer to be more like the chemist you have become. I would like to thank of the Tessier-Youngs’ research group members including Zin-Min Tun, Dave Bowers, Joanna, Beres, Tammy Donohue, Nikki Robishaw, Pat Wagers, Mike DeBord, Marie Southerland, Kerri Shelton, Mike Stromyer and many others. A special thanks to Ben Thome and Jaosn Stiel. I would never have made it through graduate school without the two of you and I cannot begin to expresses what you both have meant to me over the past 4 years. To all of the friends I made who have supported me through my time at the University of Akron, especially Dan Jackson, Colin Wright, and Nikki Swanson. vi Finally I would like to thank my family. My amazing parents, Jeff and Terri Johnson. You have always been supportive of me through all of my ups and downs. My oldest brother Luke and his wife Krista, thank you for keeping me going through the past five years as well as letting me play and spend time with my two amazing nieces, Rory and Ellie Bellie. Thank you Noah for being there to hear me complain and vent about grad school. I look forward to the amazing chemist that you are going to become. Thank you Aaron for being there for whatever I needed from you. Whether it was someone to go to the bar with or just hang out and talk about life. You remain one of the smartest people I have ever met, never forget that. vii TABLE OF CONTENTS Page LIST OF TABLES ......................................................................................................... xiiii LIST OF FIGURES ..................................................................................................... xivv LIST OF SCHEMES .................................................................................................... xviii LIST OF EQUATIONS ................................................................................................. xviii CHAPTER I. INTRODUCTION .......................................................................................................... 1 1.1 Polyphosphsazenes, applications and importance .................................................... 1 1.2 Polydichlorophosphazene ......................................................................................... 3 1.2.1 Synthesis of [PCl2N]n ................................................................................... 3 1.2.2 Initiators of the ring-opening polymerization of [PCl2N]3............................... 6 1.2.3 Mechanism of the ring-opening polymerization of [PCl2N]3 .......................... 7 1.3 Acid-base chemistry of phosphazenes ....................................................................11 1.3.1 Brønsted-Lowry acid base chemistry of phosphazenes ............................. 11 1.3.2 Lewis acid-base chemistry of phosphazenes ............................................ 12 1.4 Phosphazene superbases .......................................................................................13 1.4.1 Phosphazene superbases as frustraed Lewis pairs ................................... 14 1.5 Phosphazenes for biological applications ................................................................15 1.6 References ..............................................................................................................17 II. GROUP 1 AND 12 LEWIS ACID ADDUCTS OF PHOSPHAZENE SUPERBASES 2.1 Introduction ..............................................................................................................23 viii 2.2 Experimental ...........................................................................................................24 2.2.1 General Procedures .................................................................................. 24 2.2.2 Materials ................................................................................................... 25 2.2.3 NMR Spectroscopy ................................................................................... 25 2.2.4 X-ray Crystallography ............................................................................... 26 2.2.4 Preparations of [LiX(P2Et)]2 (X=Cl or Br) .............................................. 27 2.2.6 Preparations of [LiX(P2tBu)]2 (X = Cl or Br) .......................................... 29 2.2.7 Preparations of [ZnCl2(P2Et)]2 .............................................................. 30 2.2.8 Preparations of [ZnCl2(P2tBu)] ............................................................... 31 2.3 Results and Discussion ...........................................................................................32 2.3.1 Crystal Strutures ....................................................................................... 33 2.3.2 NMR Specroscopy .................................................................................... 44 2.4 Conclusions .............................................................................................................52
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