Synthesis, Characterization and Thermal Decomposition Of

SYNTHESIS, CHARACTERIZATION AND THERMAL DECOMPOSITION OF HYBRID AND REVERSE FLUOROSILICONES by Michael Perry Cyrus Conrad A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Graduate Department of Chemical Engineering and Applied Chemistry University of Toronto © Copyright by Michael Perry Cyrus Conrad, 2009 Synthesis, Characterization and Thermal Decomposition of Hybrid and Reverse Fluorosilicones Doctor of Philosophy, 2009 Michael Perry Cyrus Conrad Department of Chemical Engineering and Applied Chemistry University of Toronto Abstract Traditional fluorosilicones contain a siloxane backbone and pendant fluorinated group leading to low temperature ductility and excellent thermal stability. However, acidic or basic catalysts can reduce the thermal stability from a potential 350 °C to 150 °C. The predominant decomposition mechanism is through chain scission and it is hypothesized that preventing this will result in polymers with higher thermal stability. Three approaches were taken to prevent chain scission. First, a series of hybrid fluorosilicones based on (trifluorovinyl)benzene were synthesized through condensation polymerization with initial decomposition temperatures of approximately 240 °C. These were compared to similar aromatic polyethers and removal of the ether oxygen lowered the initial decomposition temperature by approximately 190 °C demonstrating the importance of this oxygen to the stability of polyethers. Second, reverse fluorosilicone (fluorinated backbone and pendant siloxane) terpolymers of chlorotrifluoroethylene (CTFE), vinyl acetate (VAc) and methacryloxypropyl-terminated polydimethylsiloxane (PDMSMA) were synthesized in supercritical CO2 (scCO2) or by emulsion polymerization. Chain scission was prevented as initial decomposition occurred between 231 and 278 °C. In both the ii emulsion and scCO2 cases, VAc was essential in facilitating cross-propagation between CTFE and PDMSMA and the branching was similar suggesting polymerization media does not affect polymer structure. Emulsion-based polymers had higher molar masses and thermal stability whereas comparable scCO2 polymers had higher yields and incorporated more PDMSMA. Third, a series of homo-, co-, and terpolymers of CTFE, VAc and methacryloxypropyl-terminated silsesquioxane (POSSMA) were synthesized representing the first synthesis of POSSMA containing polymers in scCO2 and demonstrating reverse fluorosilicones can be synthesized without VAc. Chain scission was prevented as initial decomposition occurred from 244 to 296 °C with thermal stability increasing with CTFE content to a limit. Decomposition of the polymers was examined and mechanism elucidated. In air, the copolymers give 40 to 47 wt% char since the silsesquioxane oxidizes to SiO2 while in N2, no residue is seen. In contrast, the terpolymers give a carbonaceous residue of approximately 20 wt% in N2. The flammability and surface properties of the polymers were examined with the terpolymers having flammability similar to p(CTFE) and surface properties comparable to p(POSSMA) giving a low-flammability, hydrophobic polymer. iii Acknowledgements I would like to thank the following people: Patrizia, without whose unwavering support this thesis would have been impossible, Adamo, for being a constant reminder of the need to finish, My family for all their encouragement over the many years, Karyn Ho, Doug Baumann, Catherine Kang, and Ryan Wylie for being a sounding board to many of my ideas both Ph.D. related and otherwise and being my on campus support team during the final year of my thesis, Drs. Bilal Baradie, Jordan Wosnick and Naum Naveh for their assistance and expertise in the various aspects of this thesis, Drs. Peter Brodersen and David McNally at the University of Toronto for their help in obtaining the XPS spectra and solid state 13C NMR, respectively, Dr. SungCheal Moon and Professor Richard Farris at the University of Massachusetts, Amherst for help in obtaining the PCFC data, Profs. Mark Kortschot and Mitchell Winnik for their guidance through an eventful thesis, and Prof. Molly Shoichet for giving me the space to find my own path to the completion of this thesis. iv Table of Contents Abstract .................................................................................................. ii Acknowledgements ............................................................................... iv List of Tables ......................................................................................... ix List of Figures ....................................................................................... xi List of Schemes .................................................................................. xvii 1 Introduction ...................................................................................... 1 1.1 Thermal Stability ......................................................................................... 1 1.1.1 Effect of Polymer Composition ............................................................. 4 1.1.2 Effect of Polymer Structure .................................................................. 5 1.1.3 Effect on Other Polymer Properties ...................................................... 7 1.2 Traditional Fluorosilicones ........................................................................ 8 1.2.1 Structure ............................................................................................... 8 1.2.2 Synthesis ............................................................................................ 10 1.2.3 Properties ........................................................................................... 13 1.2.3.1 Thermal Stability ...................................................................... 13 1.2.3.2 Surface Energy ........................................................................ 16 1.2.4 Potential Improvements ...................................................................... 17 1.3 Hybrid Fluorosilicones ............................................................................. 18 1.3.1 Structure ............................................................................................. 19 1.3.2 Synthesis ............................................................................................ 21 1.3.3 Properties ........................................................................................... 22 1.3.4 Potential Improvements ...................................................................... 26 1.4 Reverse Fluorosilicones .......................................................................... 27 1.4.1 Synthesis ............................................................................................ 28 1.4.2 Properties ........................................................................................... 29 1.4.2.1 Thermal ................................................................................... 29 1.4.2.2 Surface .................................................................................... 31 v 1.4.3 Potential Improvements ...................................................................... 32 1.5 Hypotheses ............................................................................................... 40 1.6 Objectives ................................................................................................. 42 1.7 References ................................................................................................ 44 2 Synthesis and Thermal Stability of a Perfluorocyclobutane based Aromatic Hybrid Fluorosilicone ............................................................. 49 2.1 Abstract ..................................................................................................... 49 2.2 Introduction ............................................................................................... 50 2.3 Experimental ............................................................................................. 53 2.3.1 Modeling ............................................................................................. 53 2.3.2 Materials ............................................................................................. 53 2.3.3 Characterization ................................................................................. 54 2.3.4 Synthesis of Monomers ...................................................................... 55 2.3.5 Synthesis of Polymers ........................................................................ 57 2.4 Results and Discussion ........................................................................... 60 2.4.1 Modeling ............................................................................................. 60 2.4.2 Polymerization .................................................................................... 62 2.4.3 Thermal Properties ............................................................................. 69 2.5 Conclusion ................................................................................................ 78 2.6 References ................................................................................................ 79 3 Synthesis of Fluorosilicone Terpolymers through Emulsion or Supercritical Carbon Dioxide ................................................................ 82 3.1 Abstract ..................................................................................................... 82 3.2 Introduction ..............................................................................................

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