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Prehnjr Mines 0052E 11152.Pdf USE OF CHAIN GROWTH POLYCONDENSATION VIA SUBSTITUENT EFFECTS FOR THE DEVELOPMENT OF NEW POLYMER BRUSH SYSTEMS by Frederick C. Prehn Jr. A thesis submitted to the Faculty and the Board of Trustees of Colorado School of Mines in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Materials Science). Golden, Colorado Date Signed: Frederick C. Prehn Jr. Signed: Dr. Stephen G. Boyes Thesis Advisor Golden, Colorado Date Signed: Dr. Ryan O’Hayre Professor and Head Department of Materials Science ii ABSTRACT Polymers are extensively used as the main component of many coating technologies. Attachment strategies to produce polymer films with advanced functionalities have evolved from a top down technique to embody more of a bottom up approach, where thin films are actually grown from the substrate of interest. This grafting from technique has allowed for the development of polymer films with advanced architectures and improved functionality through the use of controlled/living radical polymerization (LRP) techniques that produce random coil polymers. These polymers, however, are unable to exhibit properties that polymers with more rigid character possess. The ability to produce brush films with polymers that are more elongated and have the ability to order with one another in a more of a crystalline arrangement offers the opportunity to create polymer brush films with impressive new performance properties. In order to prepare brushes from rigid polymers, it is imperative to employ a chain growth condensation (CGC) polymerization technique in place of the more conventional step growth method. The two procedures employed to achieve CGC are the activation/deactivation method through the use of substituent effects and the catalyst transfer technique used in cross coupling reactions. To date, only conjugated polymer brushes employing catalyst transfer reactions have been produced. There remains a wide variety of high performance polymers that have yet to be used in polymer brushes that can be made via the CGC process. One particular type of condensation polymer, poly(aromatic amides) or aramids, has the potential to expand the role of polymer brushes into new and exciting areas. The main goal of this dissertation is to achieve the first examples of aramid brushes using substituent effect CGC. To this effect, the synthesis of well-defined, surface-initiated poly(N-octyl-p-benzamide) brushes was demonstrated using a novel grafting from surface initiated CGC technique. Issues with the thickness and solubility of these brushes sparked interest to further understand the factors that influence the preparation of poly(benzamides) using substituent effect CGC. Studies were conducted to investigate the role iii of the monomer ester substituents and initiator structure in the CGC polymerization. It was found that the monomer ester substituents play a major role in maintaining control over the polymerization, determine the overall reaction kinetics, and improving solubility of the reaction system. Experimental results and computational studies demonstrate that the overall effect of the monomer ester substituent is more dependent on the stability of the leaving group than the electrophilicity of the reacting carbonyl. Improvements upon the preliminary aramid brushes were realized by using the expanded understanding of the CGC technique through the use of substituent effects and has allowed for the creation of thicker brushes in a shorter time period. While, this thesis work documents the synthesis of the first aramid polymer brushes and provides a more comprehensive understanding of the substituent effect CGC process, there remains a great amount of work to further understand the structure and properties of the demonstrated brushes, in addition to expanding the work to new monomer structures. iv TABLE OF CONTENTS ABSTRACT .............................................................................................................................. iii LIST OF FIGURES .................................................................................................................. xi LIST OF TABLES ..................................................................................................................... xv LIST OF SCHEMES ................................................................................................................. xvi ACKNOWLEDGEMENTS ........................................................................................................ xix DEDICATION ........................................................................................................................... xx CHAPTER 1 INTRODUCTION ................................................................................................. 1 CHAPTER 2 RESEARCH BACKGROUND AND MOTIVATION............................................... 9 2.1 Surface Coatings .......................................................................................................... 9 2.1.1 Importance & Significance of Surface Coatings ................................................... 9 2.2 Polymer Coatings ......................................................................................................... 11 2.2.1 Polymeric Film Preparation and Applications ....................................................... 11 2.2.2 Chemical Attachment of Organic Molecules to Inorganic Surfaces ...................... 13 2.3 Polymer Brushes .......................................................................................................... 17 2.3.1 Polymer Brush Preparation .................................................................................. 19 2.3.2 Controlled-Living Polymerization Techniques and Subsequent Brushes .............. 21 2.3.3 Random Coil Polymer Brushes: Governing Structure and Properties .................. 25 2.3.4 Limitations of Conventional Random Coil Brushes .............................................. 28 2.4 Chain Growth vs. Step Growth Polymerization Techniques .......................................... 29 v 2.4.1 Condensation Polymers: Potential to Produce Different Backbones .................... 30 2.5 Chain Growth Polycondensation: Revolutionizing Condensation Polymer Synthesis .... 33 2.5.1 Chain Growth Polymerization via the Activation/Deactivation Method .................. 34 2.5.2 Chain Growth Condensation via Catalyst Transfer Method .................................. 42 2.6 Rigid-Rod Polymer Brushes ......................................................................................... 45 2.6.1 Early Work Investigating Semi-Flexible, Rigid Rod Polymer Brushes .................. 46 2.6.2 Conjugated Polymer Brushes .............................................................................. 48 2.6.3 Surface-Initiated Chain Growth Condensation Polymerization ............................. 50 2.7 Background Summary .................................................................................................. 58 2.7.1 Thesis Hypothesis ............................................................................................... 59 CHAPTER 3 SURFACE-INITIATED CHAIN GROWTH POLYARAMID BRUSHES ................. 60 3.1 Introduction .................................................................................................................. 60 3.2 Experimental Section ................................................................................................... 64 3.2.1 Materials .............................................................................................................. 64 3.2.2 Characterization .................................................................................................. 64 3.2.3 Synthesis Methods .............................................................................................. 65 3.2.3.1 Synthesis of Monomers and Initiators ......................................................... 65 3.2.3.2 Polymerization Methods .............................................................................. 67 3.3 Results and Discussion ................................................................................................ 69 3.3.1 Design of Functional Initiator and Solution Polymerizations ................................. 70 vi 3.3.2 Synthesis of Silane Based CGC Initiator (TMS-Amide) ........................................ 72 3.3.3 Deposition of TMS-Amide on to SiO2/Si Wafers ................................................... 73 3.3.4 Growth of Aramid Brushes Using CGC from Surface-Immobilized Initiators on Flat Silicon Substrates ....................................................................................... 76 3.3.5 Living Character of the Aramid Brushes............................................................... 80 3.3.6 Growth of Aramid Brushes sing CGC from Surface-Immobilized Initiators on High Surface Area Silica ..................................................................................... 83 3.4 Conclusions ................................................................................................................. 87 CHAPTER 4 INVESTIGATION OF THE SUBSTITUENT ESTER LEAVING GROUP EFFECT ON SYNTHESIS OF POLY(N-OCTYL-BENZAMIDE) VIA CHAIN GROWTH POLYCONDENSATION ....................................................... 88 4.1 Introduction .................................................................................................................. 88 4.2 Experimental Section ..................................................................................................
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