The research presented in this thesis focuses on application of olefin metathesis to the construction of hyperbranched and cyclic macromolecules.  The olefin metathesis reaction is briefly reviewed in Chapter 1, along with its applications in polymer synthesis.  A very mild, simple, and modular, olefin metathesis-based hyperbranched polymerization route is presented in Chapter 2.  This method utilizes the cross metathesis selectivity of the functional group tolerant N-heterocyclic carbene ruthenium catalyst towards different types of alkenes, and it can be applied to the polymerization of many easily prepared ABn monomers.  Moreover, the same method can be used to post-synthetically functionalize such polymers for realization of their substrate carrying potential.  Chapter 3 describes one such functionalization example—a pyrene analyte is attached to a metathesis derived hyperbranched polymer.  This modification of the polymer provides insight into its solution structure relative to a linear analog.  In addition, molecular weight control of the metathesis hyperbranched polymerization is discussed in detail in Chapter 4.  The careful choice of the catalysts loading and the use of a multifunctional core are found to be important parameters in preparation of polymers which span a range of molecular weights.



Even well-established materials, such as polyethylene, can benefit from olefin metathesis and the unusual polymeric architectures it can efficiently create.  For example, a cyclic polymer which lacks end groups, as opposed to having many end groups like a hyperbranched polymer, is expected to possess unique physical properties.  The preparation of cyclic and linear polyethylenes and the study of their relative rheological properties are described in Chapter 5.  The polymerization methodology outlined in this chapter takes advantage of ring-expansion metathesis polymerization—a facile method for the synthesis of cyclic macromolecules.  Some efforts directed at molecular weight control of this cyclic polymerization are also discussed.</p

Gorodetskaya, Irina A.

Caltech Theses and Dissertations

NONLINEAR POLYMERIC ARCHITECTURES VIA OLEFIN METATHESIS   Thesis by Irina A. Gorodetskaya  In Partial Fulfillment of the Requirements for the degree of Doctor of Philosophy   CALIFORNIA INSTITUTE OF TECHNOLOGY Pasadena, California 2009 (Defended November 25, 2008) ii                2009 Irina A. Gorodetskaya All Rights Reserved iii       To my grandmother Yadviga             iv ACKNOWLEDGEMENTS First, I would like to thank my research advisor, Professor Grubbs, for accepting me into his group.  Being a part of the Grubbs groups was everything I sought in a graduate school experience.  I am very grateful to Bob for his seemingly infinite patience, which allowed me the time and resources to pursue the projects that were interesting to me at my own pace.  Bob’s guidance, combined with the consistently diverse and stimulating environment of the group, provided an invaluable learning experience on both scientific and personal levels, and it has made me a smarter, better, stronger person. I am grateful to Dr. Tae-Lim Choi for believing in me and for being so persistently “annoying” with his suggestions on the potential of olefin metathesis chemistry for hyperbranched polymerization.  This thesis would not be quite the same without the research that evolved from the TLC’s nagging—thank you so much! Next, I thank my most immediate collaborators over the years at Caltech.  Lucia Fernandez-Ballister from the Kornfield group at Caltech and Jian Wang from the McKenna group at Texas Tech taught me everything I know about the rheology of polymer melts.  They greatly contributed to the cyclic polymers research presented in Chapter 5 of this thesis (while making me secretly happy I did not choose chemical engineering as my major).  Alon Gorodetsky provided his invaluable expertise in the study of pyrene-functionalized polymers described in Chapter 3.  Finally, Katya Vinogradova worked very long hours on the hyperbranched project over the summer of 2007 as a summer undergraduate research fellow.  Thank you all!  I greatly benefited from your skill, knowledge, and time, and it has been a pleasure to know you and work with you. I would also like to thank Alon again, Dr. Rose Conrad, and Dr. Ian Stewart for their time and help in proof-reading this thesis.  I am sorry, but despite all of the language coaching you provided, I don’t have enough fancy English words in my vocabulary to express my gratitude to you for reading it all (including the experimentals!) and providing numerous helpful suggestions.  I also enjoyed sharing the lab with Rose and Ian, and our non-thesis- and even non-science-related(!) conversations.  v I am very grateful to Professor Tobias Ritter, the most brilliant synthetic chemist I have ever met, for a number of key research suggestions, but also, and more importantly, for teaching me one of the most valuable skills I gained while in graduate school—driving.  Having a car not only greatly enriched my life in Southern California, but also, finally, made me feel truly American.  On this note, I would also like to thank Dr. Donde Anderson for risking her life as my diving buddy and navigator in my early driving days. I am at loss of words, again, to describe the depth of my gratitude to my family, whether relatively close (within the US borders) or far abroad (Russia and Ukraine).  Your unconditional love and support (moral and financial) made all the difference and got me through the grad school: mom, dad, grandma Lyuba, Natasha, tyetushka, Bobochka—I love you all.  Special thanks go to cousin Pitrovich, who is currently the farthest away relative, but used to be the closest in San Francisco, where he was always happy to see me, even if for a few minutes of a practically unannounced, 3 am on a week-night visit of a camping gear emergency.  Thank you for all your help, advice, and genuine interest in my well-being; and also for introducing me to Mitya, Olya, Fedor, Sasha, who became my adoptive Pasadena family. I want to thank my thesis committee: Professor Tirrell, Professor Heath, and Professor Barton. Finally, I wish to thank all of the friends and acquaintances, who are not singled out on this undeservingly short list, but whose friendships, love, care and kindness have touched my life over the past few years, making my not-so-short stay in Pasadena special and memorable.   vi ABSTRACT The research presented in this thesis focuses on application of different forms of olefin metathesis, in conjunction with judicious choices of catalysts and monomers, to the construction of hyperbranched and cyclic macromolecules.  This multifaceted reaction is briefly reviewed in Chapter 1, along with ruthenium-based metathesis catalysts and applications of olefin metathesis in polymer synthesis. Hyperbranched polymers are curious materials which feature multiple end groups and possess a host of desirable physical properties; potential applications stemming from the unique properties of these macromolecules include their use as viscosity lowering additives and analyte carriers.  In general, the major drawbacks faced by the classical, ABn monomer-based hyperbranched polymers are the limited availability of specially designed monomers, harsh synthetic conditions, and poor control of the required step-growth polymerization methods.  A very mild, simple, and modular, olefin metathesis-based hyperbranched polymerization route, which addresses some of these challenges, is presented in Chapter 2.  This method utilizes the cross metathesis selectivity of the functional group tolerant N-heterocyclic carbene ruthenium catalyst towards different types of alkenes, and it can be applied to the polymerization of many easily prepared ABn monomers.  Moreover, the same method can be used to post-synthetically functionalize such polymers for realization of their substrate carrying potential.  Chapter 3 describes one functionalization example—a pyrene analyte is attached to a metathesis derived hyperbranched polymer.  This modification of the polymer provides insight into its solution structure relative to a linear analog.  In addition, molecular weight control of the metathesis hyperbranched polymerization is discussed in detail in Chapter 4.  The careful choice of the catalysts loading and the use of a multifunctional core are found to be important parameters in preparation of polymers which span a range of molecular weights. Even well-established materials, such as polyethylene, can benefit from olefin metathesis and the unusual polymeric architectures it can efficiently create.  For example, a cyclic polymer which lacks end groups, as opposed to having many end groups like a  vii hyperbranched polymer, is expected to possess unique physical properties.  The preparation of cyclic and linear polyethylenes and the study of their relative rheological properties are described in Chapter 5.  The polymerization methodology outlined in this Chapter takes advantage of ring-expansion metathesis polymerization—a facile method for the synthesis of cyclic macromolecules.  Some efforts directed at molecular weight control of this cyclic polymerization are also discussed. Taken together, the findings presented in this thesis emphasize the utility of olefin metathesis for the preparation of nonlinear polymers.  The unusual polymeric architectures available through this chemical transformation may lead to a host of new materials with unique properties.    viii TABLE OF CONTENTS CHAPTER 1:  Introduction to Olefin Metathesis and Its Applications in Polymer Synthesis ................................................................................................ 1 Olefin Metathesis........................................................................................... 2 Polymer Synthesis Applications of Olefin Metathesis................................. 6 ADMET .................................................................................................... 6 ROMP ...................................................................................................... 7 Summary and Thesis Research ..................................................................... 8 References.................................................................................................... 11  CHAPTER 2: Hyperbranched Polymers via Acyclic Diene Metathesis Polymerization ................................................................................................... 14 Abstract ........................................................................................................ 15 Introduction.................................................................................................. 16 Results and Discussion................................................................................ 17 Conclusion ................................................................................................... 23 Experimental Procedures............................................................................. 24 Representative Polymerization Procedure............................................ 31 References.................................................................................................... 33     ix CHAPTER 3: An Olefin Metathesis Route to the Preparation of Functionalized Hyperbranched Polymers .................................................................................. 35 Abstract ........................................................................................................ 36 Introduction.................................................................................................. 37 Results and Discussion................................................................................ 38 Functionalization of the Hyperbranched Polymer................................ 38 Preparation of the Pyrene Modified Linear Analog ............................. 43 Fluorescence Properties of Pyrene-Functionalized Hyperbranched and Linear Polymers.............................................................................. 45 Conclusion ................................................................................................... 46 Experimental Procedures............................................................................. 48 References.................................................................................................... 52  CHAPTER 4: Towards Molecular Weight Control of the Hyperbranched ADMET Polymerization .................................................................................... 54 Abstract ........................................................................................................ 55 Introduction.................................................................................................. 56 Results and Discussion................................................................................ 58 Catalyst Loading.................................................................................... 58 Reaction Time ....................................................................................... 62 Addition of a Multifunctional Core ...................................................... 64 Conclusion ................................................................................................... 66 Experimental Procedures............................................................................. 67   x References.................................................................................................... 68  CHAPTER 5: The Importance of Molecular Weight Control for Cyclic Polymers Prepared via Ring-Expansion Metathesis Polymerization .............. 69 Abstract ........................................................................................................ 70 Introduction.................................................................................................. 71 Results and Discussion................................................................................ 72 Part 1: Studies of shear-induced crystallization processes in polyethylene and the need for large cyclic polymers. .......................... 72 Part 2: Studies of the viscoelastic properties of cyclic polyethylene and the need for small cyclic polymers ................................................ 77 Conclusion ................................................................................................... 82 Polymerization Experimental Procedures................................................... 84 References.................................................................................................... 86  Appendix A: Towards ABn-Based Hyperbranched Polyethylene .................... 88 Experimental Procedures............................................................................. 91 Notes and References .................................................................................. 93    xi LIST OF FIGURES, SCHEMES AND TABLES CHAPTER 1  Figures Figure 1.1.  Ruthenium-based olefin metathesis catalysts ........................... 5  Schemes Scheme 1.1.  General mechanism of olefin metathesis................................ 2 Scheme 1.2.  Types of olefin metathesis reactions....................................... 3 Scheme 1.3.  Selectivity of 1st and 2nd generation ruthenium catalysts. ...... 6 Scheme 1.4.  Olefin metathesis routes to polyethylene of different                        architectures............................................................................. 9 Tables Table 1.1.  Functional group tolerance of olefin metathesis catalysts. ........ 4  CHAPTER 2  Figures Figure 2.1.  Acyclic diene metathesis polymerization catalyst. ................. 18 Figure 2.2.  Monomers for hyperbranched ADMET polymerization........ 18 Figure 2.3.  1H NMR spectra of monomer 4                     and hyperbranched polymer 4a............................................... 19 Figure 2.4.  Mark-Houwink-Sakurada plots for polymers 2a–7a.............. 21 Figure 2.5.  Representative MALS-SEC traces for polymerization of 4                     with consecutive batch catalyst addition. ............................... 32  Schemes Scheme 2.1.  Synthesis of dendritic polymers...................................... 16 Scheme 2.2.  Synthesis of AB2 monomer 4                       and its hyperbranched ADMET polymerization. ........... 18   xii Scheme 2.3.  AB2 monomers which were found to be challenging                       for ADMET. .................................................................... 22 Scheme 2.4.  Synthesis of AB4 monomer for hyperbranched                       ADMET polymerization. ................................................ 23 Scheme 2.5.  Synthesis of monomer 2.................................................. 24 Scheme 2.6.  Synthesis of monomers 3 and 5. ..................................... 25 Scheme 2.7.  Synthesis of monomer 6.................................................. 27 Scheme 2.8.  Synthesis of monomer 7.................................................. 28 Scheme 2.9.  Synthesis of monomer 8.................................................. 30 Scheme 2.10.  Synthesis of monomer 9................................................ 30  Tables Table 2.1.  Results for polymerization of 2–7. ........................................... 20  CHAPTER 3  Figures Figure 3.1.  Imidazolinylidene-based ruthenium olefin metathesis                     catalyst 1. ................................................................................. 38 Figure 3.2.  SEC traces for 3 before and after functionalization                     with 0.5 equivalents of 10-bromo-1-decene. .......................... 40 Figure 3.3.  1H NMR spectra with integration values for 2, 3, and 5. ....... 42 Figure 3.4.  SEC traces for crude 3, crude and purified 5. ......................... 43 Figure 3.5.  1H NMR spectra with integration values for 6, 7, and 8. ....... 44 Figure 3.6.  (A) UV-visible absorbance and fluorescence emission                           spectra for 4, 5, and 8.                     (B) A plot of the monomer to excimer intensity emission                           ratio at various concentrations. ......................................... 46  Schemes Scheme 3.1.  Hyperbranched ADMET polymerization   xiii                       and subsequent end group functionalization. ....................... 39 Scheme 3.2.  Hyperbranched polymer 3 functionalization with pyrene.... 41 Scheme 3.3.  Synthesis of the pyrene-functionalized                       linear polymeric analog......................................................... 44 Scheme 3.4.  Synthesis of the monomers for linear ROMP....................... 49  CHAPTER 4  Figures Figure 4.1.  ADMET catalyst 1 ................................................................... 57 Figure 4.2.  SEC traces for 3 made with different amounts of 1................ 58 Figure 4.3.  SEC traces for 5 made with different amounts of 1................ 60 Figure 4.4.  Molecular weight and PDI timeline of 3 at 0.5 mol % of 1. .. 62 Figure 4.5.  Proposed polymerization “error” correction mechanism. ...... 63 Figure 4.6.  The dependence of the observed Mw at 0.5 mol % of 1                     on the addition time of 8-bromo-1-octene. ............................. 64 Figure 4.7.  SEC traces for 3 made with a fixed amount of 1 but different                     amounts of 4. ........................................................................... 65  Schemes Scheme 4.1.  Hyperbranched ADMET polymerization. ............................ 57 Scheme 4.2.  Linear ADMET polymerization............................................ 59 Scheme 4.3.  The “chain-walking” mechanism for hyperbranched                       ADMET polymerization at low loading of 1. ...................... 61  CHAPTER 5  Figures Figure 5.1.  The effect of shear stress on polymer chain orientation. ........ 73 Figure 5.2.  Catalysts required for the preparation of linear and cyclic                     polyalkenamers........................................................................ 74 Figure 5.3.  Polarized optical microscopy of selected samples.................. 77   xiv Figure 5.4.  The results of the viscoelastic properties investigation                     of cyclic PE prepared by REMP. ............................................ 79 Figure 5.5.  Proposed 2nd generation REMP catalysts................................ 80 Figure 5.6.  First accomplished 2nd generation REMP catalyst. ................ 83  Schemes Scheme 5.1.  Ring-expansion polymerization. ........................................... 72 Scheme 5.2.  Synthesis of long and short linear PE chains........................ 75 Scheme 5.3.  Synthesis of large PE rings.................................................... 76 Scheme 5.4.  Synthetic route towards 2nd generation REMP catalyst 4. ... 81 Scheme 5.5.  Synthetic route towards 2nd generation REMP catalyst 5. ... 82  Tables Table 5.1.  Results for REMP of cyclic alkenes with 3.............................. 76  Appendix A  Figures Figure A1.  Hyperbranched ADMET catalysts .......................................... 90 Figure A2.  H NMR evidence for polymerization of 3 to 4. ...................... 90  Schemes Scheme A1.  Synthetic route towards the hyperbranched polyethylene via                      ADMET. ................................................................................. 90    1  

Nonlinear Polymeric Architectures via Olefin Metathesis

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Nonlinear Polymeric Architectures via Olefin Metathesis

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