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Download File A ‘Toolkit’ of Small Molecules for Polymer Assembly and Post-Synthetic Modification Using ‘Click’ and Photoactive Chemistries Jeffrey R. Lancaster Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Graduate School of Arts and Sciences COLUMBIA UNIVERSITY 2011 © 2011 Jeffrey R. Lancaster All rights reserved Abstract A ‘Toolkit’ of Small Molecules for Polymer Assembly and Post-Synthetic Modification Using ‘Click’ and Photoactive Chemistries Jeffrey R. Lancaster Small molecules have been synthesized toward the goals of constructing and modifying polymeric materials according to simple, generalizeable, and universal processes. The prepared compounds rely upon a combination of photochemistry and the ‘click’ philosophy to alter the architecture, bulk properties, or surface chemistry of polymers. In Chapter 1, a review is presented that details the many implementations of the ‘click’ philosophy to polymer chemistry. The influence of ‘click’ and photochemistry upon macromolecules is discussed using a topological approach to polymer architecture. Chapter 2 details the synthesis of several second-generation homobifunctional exogenous photocrosslinkers that extend upon previous work from our group. Additionally, a first- generation crosslinker is used to core-crosslink micellar aggregates of block copolymers. Chapter 3 describes the design, synthesis, and implementation of a photoactive ‘click’ activator for polymer surfaces. This chapter extends the notion of a material-specific anchor from hard substrates to a range of soft polymer substrates. Chapter 4 is an inquiry into the nature of the photoreaction of a standard photoactive moiety – benzophenone – with model compounds that represent polymers in which the crosslinkers of Chapter 2 are embedded. Comparison of competitive rates of abstraction gives insight into the reactive preferences of the crosslinkers and anchors of the previous chapters. In Chapter 5 small molecules and macromonomers are described that build upon the compounds described in previous chapters which collectively form the basis of a ‘toolkit’ approach to polymer assembly and modification. Variations and extensions upon the ‘toolkit’ are detailed in order to give a sense of the future possibilities of this approach. Table of Contents List of Figures .............................................................................................................. iii List of Tables............................................................................................................... vii Acknowledgements ...................................................................................................... ix 1. Introduction ........................................................................................................... 1 1.1. Introduction...........................................................................................................................1 1.2. Click Chemistries..................................................................................................................3 1.2.1. Azide-Alkyne Cycloaddition ........................................................................................................4 1.2.2. Other Cycloaddition Reactions Including Diels-Alder Chemistry.............................................9 1.2.3. Thiol-ene, Thiol-yne, Michael Addition ....................................................................................13 1.2.4. Other Click Chemistries ..............................................................................................................16 1.2.5. Applications of ‘Click’ Chemistry ................................................................................19 1.3. Polymers...............................................................................................................................20 1.3.1. Polymer Architecture...................................................................................................................22 1.3.2. Functionalization of polymers ....................................................................................................25 1.3.3. Heterobifunctional Monomers and Polymers ............................................................................34 1.3.4. Macroscopic Polymer Modification – Bulk and Surfaces ........................................................37 1.4. Photochemistry for Polymers ...........................................................................................39 1.4.1. Polymer Crosslinking by Photochemistry..................................................................................40 1.4.2. Photodegradable Linkages in Polymers .....................................................................................42 1.4.3. Patterning .....................................................................................................................................45 1.5. Summary..............................................................................................................................46 1.6. References ............................................................................................................................47 2. Homobifunctional Crosslinkers............................................................................54 2.1. Introduction, Motivation...................................................................................................55 2.2. Candidates for New ‘Universal’ Crosslinkers................................................................59 2.3. Preparation of Homobifunctional Crosslinkers ............................................................64 2.4. Core-Crosslinked Micelles and Crosslinked Thin Films..............................................66 2.4.1. Introduction to Core-Crosslinked Micelles................................................................................66 2.4.2. Preparation of PS-b-PEG Micelles .............................................................................................68 2.4.3. Analysis........................................................................................................................................69 2.4.3.1. Surface Tension ...................................................................................................................69 2.4.3.2. Pyrene Fluorescence............................................................................................................71 2.4.4. Core-Crosslinking of PS-b-PEO Micelles .................................................................................72 2.4.5. Application of Micelles in Drug Delivery .................................................................................74 2.5. Summary..............................................................................................................................75 2.6. References ............................................................................................................................77 3. ‘Click’ Functional Polymer Surfaces ...................................................................85 3.1. Introduction, Motivation...................................................................................................85 3.1.1. Click Functionalization of ‘Hard’ Substrates.............................................................................87 3.1.2. Click Functionalization of ‘Soft’ Substrates..............................................................................92 3.1.3. Patterning of Surface Click Functionality..................................................................................97 i 3.2. Design of Universal ‘Photoclickers’.................................................................................99 3.3. Preparation of Surface Functionalizing Compounds .................................................102 3.4. Surface Preparation .........................................................................................................104 3.5. Surface Analysis................................................................................................................105 3.5.1. Water Contact Angle Analysis..................................................................................................106 3.5.2. Infrared Spectroscopy................................................................................................................109 3.5.3. Fluorogenic Coumarin Azide....................................................................................................113 3.5.4. Surface Functionalization with Nanoparticles .........................................................................114 3.6. Outlook...............................................................................................................................115 3.7. Summary............................................................................................................................117 3.8. References ..........................................................................................................................118 4. 1H NMR Study of Hydrogen Abstraction in Polymers......................................126 4.1. Introduction, Motivation.................................................................................................126 4.2. Analysis ..............................................................................................................................130 4.3. Discussion...........................................................................................................................133
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