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Synthesis and Characterization of Latent Reactive Oligo Oxyethylene Carbosilane and Carbosiloxane Carbosilane Copolymers...

HIDE
 Title Page
 Dedication
 Acknowledgement
 List of Tables
 List of Figures
 Abstract
 Acyclic diene metathesis polymerization...
 Synthetic modification of crosslink...
 Synthesis and characterization...
 Synthesis and characterization...
 Appendix
 References
 Biographical sketch
 

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SYNTHESIS AND CHARACTERIZAT ION OF LATENT REACTIVE OLIGO(OXYETHYLENE)/CARBOSILANE AND CARBOSILOXANE/CARBOSILANE COPOLYMERS VIA ACYCLIC DIENE METATHESIS POLYMERIZATION (ADM ET) FOR THERMOSET MATERIALS By PIOTR PAWE MAT OKA A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2006

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Copyright 2006 by Piotr Pawe Mat oka

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Mojej ukochanej onie Kornelii i moim r odzicom za ich bezgraniczn mi o wyrozumia o i przyja To my lovely wife Kornelia and my pare nts for their eternal love, understanding, and friendship.

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iv ACKNOWLEDGMENTS There are a great number of people who have given me their support, encouragement, and support during my graduate career. First and foremost, I must thank my wife – Kornelia. She has been everything for me during the course of my dissertation work. She has been my rock, my motivation and my friend. Without her I would be incomplete. I would like to thank my parents for their endless love, devotion, support and sacrifices they have made that allowed me to become a person that I am today. They taught me at a young age what was important in life, and showed me how to work hard to achieve my goals. I need to acknowledge the pe ople that molded my career as a student of chemistry before going to collage and finally to gr aduate school. I would like to thank my secondary school chemistry teacher Mrs. Krystyna wi ch and my high school chemistry teacher Mrs. Danuta Boli ska for being wonderful teachers. At Adam Mickiewicz University I would lik e to express my sincere thanks to Dr. Wioleta Patroniak for her friendship and help in making right decision at my undergraduate career. Sincere gratitude al so goes to Prof. Bogdan Marciniec, my undergraduate advisor whose encouragement and support made my undergraduate research career extremely rewa rding experience. I cannot leav e out my best friend that I had pleasure to study with Dr. Piotr Pawlu whose friendship I value very much.

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v During my career at University of Florid a I have had pleasure to meet and work among extraordinary people, such Dr. John Sworen, who I would like to thank for taking the time to teach me good laboratory techniqu es, for introducing me to my project early in my graduate career, and for being a true friend. I extend my thanks to my classmates/friends Dr. Florence Courchay (aka BMB) and Dr. Travis Baughman for all wonderful time we have spend together, especially marvelous time we had during our trip to Europe. I cannot omit my “Polish fello w” Dr. Ryan Walczak who I thank for all scientific and non-scientific discussion that we had. There have been many people that have enriched my life, both inside and outside of the laboratory sincere thanks goes to all of the past and current members of th e Wagener research gr oup for their helpful discussions and friendship including Dr. Jason Smith, Dr Tim Hopkins, Dr. Violeta Petkovska, Dr. Garrett Oakle y, Giovanni Rojas, Erik Be rda, James Leonard, Meghan Greenfield and Zach Kean. I have to thank also other members of the floor who I had pleasure to meet. My experience at the Un iversity of Florida would not have been complete without making the acquaintances of Dr. Carl Gaupp, Dr. C.J. DuBois, Dr. Ben Reeves, Tim Steckler, Bob Brookins, Merv e “Marwa” Ertas, Sophie Bernard, and Victoria Broadstreet. Enough thanks cannot be expressed to Lorra ine Williams and Sara Klossner in the polymer office. Without them, the little thi ngs that make everything run smoothly, but no one wants to think about, would never get done. I also extend my thanks to Lori Clark for her help in the graduate office.

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vi Many thanks are extended to my comm ittee members, Dr. John R. Reynolds, Dr. Michael J. Scott, Dr. Daniel R. Talham, and Dr. Anthony B. Brennan for their help throughout my journey at the University of Florida Finally, I would like to express my sincer e appreciation to my research advisor Professor Ken Wagener. First, I would like to thank him for his encouragement, guidance, patience, and unders tanding during the c ourse of my graduate career. Second, I gratefully value his advice and his confid ence in my abilities as a chemist. Most importantly I would like to thank him for ha ving always time to sit and talk about not only chemistry but simply everyday life. I will forever be thankful for his presence in my life.

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vii TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iv LIST OF TABLES.............................................................................................................xi LIST OF FIGURES..........................................................................................................xii ABSTRACT.....................................................................................................................xv i CHAPTER 1 ACYCLIC DIENE METATHESIS POLYMERIZATION (ADMET) APPROACH TO SILICONCONTAINING MATERIALS........................................1 1.1 Introduction.............................................................................................................1 1.2 Silicon Chemistry...................................................................................................3 1.3 Olefin Metathesis....................................................................................................4 1.3.1 Brief History of Olefin Metathesis...............................................................6 1.3.2 Introduction to ADMET Polymerization......................................................8 1.4 Olefin Metathesis Chemistry of Compounds Containing Silicon........................12 1.4.1 Acyclic Diene Oligomerization and Polymerization of Containing Silicon Dienes..................................................................................................14 1.4.2 ADMET Catalyzed by “Ill-Defined” Catalytic Systems............................15 1.4.3 ADMET Catalyzed by “Well-Defined” Catalytic Systems........................18 1.4.3.1 Polycarbosilanes...............................................................................18 1.4.3.2 Polycarbosiloxanes...........................................................................21 1.4.3.3 Telechelic oligomers........................................................................24 1.4.3.4 Functionalized polycarbosilanes......................................................26 1.4.3.5 Latent reactive elastomers................................................................27 1.5 Silylative Coupling (SC) Polycondensation.........................................................28 1.6 Crosslinking Methods for Silicon-Containing Materials......................................31 1.7 Purpose of Study...................................................................................................33 2 SYNTHETIC MODIFICATION OF CROSSLINK DENSITY AND SOFT SEGMENT IN POLYCARBOSILANE/POLYCARBOSILOXANE ELASTOMERS..........................................................................................................34 2.1 Introduction...........................................................................................................34 2.2 Synthetically Modified Crosslink Density............................................................36

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viii 2.3 Synthetic Soft Segment Modification...................................................................39 2.4 Conclusions...........................................................................................................43 2.5 Experimental Methods..........................................................................................44 2.5.1 General Considerations..............................................................................44 2.5.2 Materials.....................................................................................................45 2.5.3 Monomer Synthesis....................................................................................46 2.5.3.1 Tris(4-pentenyl)methylsilane (80)....................................................46 2.5.3.2 Diundecenyltriethylene glycol (83)..................................................47 2.5.4. General Metathesis Conditions..................................................................47 2.5.4.1 Polymerization of diundecenyltriethylane glycol (83).....................48 2.5.4.2 Terpolymerization of mono mers 75, 76, and 80 to produce terpolymer 81..........................................................................................48 2.5.4.3 Terpolymerization of mono mers 75, 83, and 80 to produce terpolymer 84..........................................................................................49 3 SYNTHESIS AND CHARACTERIZATION OF OLIGO(OXYETHYLENE)/CARBOSI LANE COPOLYMERS AND THERMOSETS..........................................................................................................50 3.1 Introduction...........................................................................................................50 3.2 Synthesis of Monomers........................................................................................51 3.2.1 Monomers for Soft Phase Modification.....................................................51 3.2.2 Monomers for Crosslink Density Modification.........................................53 3.3 ADMET Polymerization.......................................................................................54 3.3.1 Synthesis of Oligo(oxyethylen e)/Oligo(ethylene) Copolymers.................54 3.3.1.1 Structural characterization................................................................56 3.3.1.2 Thermal behavior of unsaturated polymers......................................59 3.3.1.3 Thermal stability of unsaturated polymers.......................................64 3.3.2 Polymerization of “Chain-In ternal” Crosslinker 3sp2OMe.......................65 3.3.3 Synthesis and Characterization of “Latent Reactive” Copolymers............66 3.4 Preparation and Character ization of Thermosets..................................................69 3.4.1 Thermal Behavior and De gradation of Thermosets...................................71 3.4.2 Mechanical Properties................................................................................74 3.5 Conclusions...........................................................................................................79 3.6 Experimental Methods..........................................................................................80 3.6.1 Materials.....................................................................................................80 3.6.2 Instrumentation and Analysis.....................................................................80 3.6.3 Monomer Synthesis....................................................................................82 3.6.3.1 Synthesis of di(oxyethylene) -di-4-pentenyl ether (3sp2gl) (86)..........................................................................................................82 3.6.3.2 Synthesis of tri(oxyethylene) -di-4-pentenyl ether (3sp3gl) (87)..........................................................................................................82 3.6.3.3 Synthesis of tetra(oxyethylene) -di-4-pentenyl ether (3sp4gl) (88)..........................................................................................................83 3.6.3.4 Synthesis of tri(oxyethylene) -di-7-octenyl ether (6sp3gl) (89).83 3.6.3.5 Synthesis of tetra(oxyethylene) -di-7-octenyl ether (6sp4gl) (90)..........................................................................................................83

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ix 3.6.3.6 Synthesis of di(oxyethylene) -di-10-undecenyl ether (9sp2gl) (91)..........................................................................................................84 3.6.3.7 Synthesis of tri(oxyethylene) -di-10-undecenyl ether (9sp3gl) (92)..........................................................................................................85 3.6.3.8 Synthesis of tetra(oxyethylene) -di-10-undecenyl ether (9sp4gl) (93)...........................................................................................85 3.6.3.9 Synthesis of 10-undecenyldimet hoxymethylsilane 9sp2OMe (97).85 3.6.3.10 Synthesis of di(4-pentenyl)dimethoxysilane 3sp2OMe (100).......86 3.6.4 General Metathesis Conditions...................................................................87 3.6.4.1 Synthesis of poly3sp2gl...................................................................88 3.6.4.2 Synthesis of poly3sp3gl...................................................................88 3.6.4.3 Synthesis of poly3sp4gl...................................................................88 3.6.4.4 Synthesis of poly6sp3gl...................................................................89 3.6.4.5 Synthesis of poly6sp4gl...................................................................89 3.6.4.6 Synthesis of poly9sp2gl...................................................................89 3.6.4.7 Synthesis of poly9sp3gl...................................................................90 3.6.4.8 Synthesis of poly9sp4gl...................................................................90 3.6.5 Preparation of Copolymers and Thermosets..............................................91 4 SYNTHESIS AND CHARACTERIZATION OF CARBOSILOXANE/CARBOSILANE CO POLYMERS AND THERMOSETS.....93 4.1 Introduction...........................................................................................................93 4.2 Monomer Synthesis..............................................................................................94 4.3 ADMET Polymerization.......................................................................................97 4.3.1 Synthesis of Oligo(siloxane )/Oligo(ethylene) Copolymers.......................97 4.3.1.1 Structural characterization................................................................98 4.3.1.2 Thermal analysis............................................................................101 4.3.2 Synthesis of “Latent Reactive” Car bosilane/Carbosiloxane Copolymers104 4.4 Preparation and Character ization of Thermosets................................................105 4.5 Conclusions.........................................................................................................108 4.6 Experimental Methods........................................................................................109 4.6.1 Materials...................................................................................................109 4.6.2 Instrumentation and Analysis...................................................................109 4.6.3 Monomer Synthesis..................................................................................109 4.6.3.1 Synthesis of 1,5-bis(hexeny l)-1,1,3,3,5,5-hexamethyltrisiloxane 4sp3Si (192)..........................................................................................109 4.6.3.2 Synthesis of 1,7-bis(hexenyl)-1,1,3,3,5,5,7,7octamethyltetrasiloxane 4sp4Si (193)..................................................110 4.6.3.3 Synthesis of 1,5-bis(octenyl )-1,1,3,3,5,5-hexamethyltrisiloxane 6sp3Si (194)..........................................................................................111 4.6.3.4 Synthesis of 1,7-bis(octenyl)-1,1,3,3,5,5,7,7octaamethyltrisiloxane 6sp4Si (195)...................................................111 4.6.4 General Metathesis Conditions.................................................................111 4.6.4.1 Synthesis of poly4sp3Si.................................................................112 4.6.4.2 Synthesis of poly4sp4Si.................................................................113 4.6.4.3 Synthesis of poly6sp3Si.................................................................113

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x 4.6.4.4 Synthesis of poly6sp4Si.................................................................113 4.6.5 Preparation of Copolymers and Thermosets............................................114 APPENDIX......................................................................................................................1 15 LIST OF REFERENCES.................................................................................................118 BIOGRAPHICAL SKETCH...........................................................................................127

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xi LIST OF TABLES Table page 1-1 Comparison of various silicon and carbon bond lengths and energies......................3 2-1 Mechanical properties of the unsaturated ADMET copolymers and a commercially available elastomer............................................................................35 2-2 Synthetic research objectives...................................................................................36 3-1 GPC data of uns aturated polymers...........................................................................55 3-2 Thermal analysis of the unsaturated polymers.........................................................60 3-3 Physical properties of selected thermosets compositions.........................................77 4-1 GPC data for unsaturat ed polycarbosiloxanes.........................................................97 4-2 Thermal analysis of the unsaturated polymers.......................................................102 4-3 Mechanical properties of carbos iloxane/carbosilane thermosets...........................106 4-4 Thermal degradation data of carbosiloxane thermosets.........................................108 A-1 Results of mechanical tests on dicomponent thermosets xlink 1-8........................115 A-2 Results of mechanical tests on dicomponent thermosets xlink 9-16......................115

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xii LIST OF FIGURES Figure page 1-1 Types of olefin metathesis: a) simple exchange reactions; b, c) metathesis polymerization and ring-closing metath esis; c) metathesis degradation....................5 1-2 Metallacyclobutane mechanism.................................................................................6 1-3 Well-defined metathesis catalysts..............................................................................7 1-4 Acyclic diene metathesis (ADMET) and ring-opening metathesis (ROMP) polymerizations..........................................................................................................8 1-5 Theoretical degree of polymerizatio n vs. conversion in condensation type polymerization..........................................................................................................10 1-6 ADMET polymerization of 1,9-decadiene...............................................................10 1-7 The catalytic cycle of ADMET polymerization.......................................................11 1-8 Ring-opening metathesis polymerization of 1,1-dimethyl-1-silacyclopent -3-ene..13 1-9 ROMP of silylsubstituted norbornens......................................................................13 1-10 ROMP using Casey’s carbene complex...................................................................13 1-11 Polymerization of diallyland allyl-bu tenyl derivatives of disubstituted silanes....15 1-12 Polymerization of dially ltetramethyldisiloxane.......................................................16 1-13 Metathesis of diallyltetramethyldisilane..................................................................17 1-14 Metathesis of dialkenylsilacyclobutane...................................................................17 1-15 Copolymerization of divinyldimethylsilane (32) with 1,9-decadiene (10) ..............18 1-16 Productive and non-productive metathesis..............................................................19 1-17 Polycarbosilanes via ADMET..................................................................................20 1-18 Polycarbosilanes with th e disilacyclobutane rings...................................................21

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xiii 1-19 Non-productive ADMET polymerization................................................................21 1-20 ADMET polymerization of s iloxane containing dienes...........................................22 1-21 Controlled diene insertion via ADMET...................................................................23 1-22 ADMET copolymerization of di vinyltetraethoxydisiloxane....................................24 1-23 Telechelic polymers via ADMET............................................................................25 1-24 ADMET polymerization of -telechelic diene macromonomer..........................25 1-25 Chloroand dichloro-functiona lized polycarbosilanes via ADMET.......................26 1-26 Two routes to pol ymer modification........................................................................26 1-27 Latent reactive carbosilo xane/carbosilane copolymer.............................................27 1-28 The latent reactivity co ncept to attain diverse behavior of materials.......................28 1-29 Catalytic cycle of silylative coupling.......................................................................29 1-30 SC polycondensation of divinyl substituted silicon monomers................................30 1-31 Starburst oligomer via SC........................................................................................31 2-1 Atmospherically cros slinked ADMET copolymers.................................................34 2-2 Chain-end crosslinking molecules...........................................................................37 2-3 Chain-end crosslinking in the polycarbosilanes via ADMET..................................38 2-4 1H NMR spectra of monomer 83. .............................................................................40 2-5 Glass transition temperatures fo r various lengths of polyoxyethylene....................41 2-6 High elastic material cont aining increased soft phase and chain-end crosslinker...43 3-1 Glycol-based monomers...........................................................................................52 3-2 Synthesis of 9sp4gl (93) ...........................................................................................52 3-3 Synthesis of end9sp2OMe and 3sp2OMe ..............................................................54 3-4 1H NMR spectra of monomer 6sp3gl and polymer poly6sp3gl. .............................56 3-5 13C NMR spectra of monomer 6sp3gl and polymer poly6sp3gl .............................57 3-6 FT-IR spectra of 6sp3gl and poly6sp3gl .................................................................58

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xiv 3-7 DSC traces of unsaturated 3sp microblock copolymers...........................................62 3-8 DSC traces of unsaturated 6sp microblock copolymers...........................................62 3-9 DSC traces of unsaturated 9sp microblock copolymers...........................................63 3-10 TGA traces of poly6sp4gl ........................................................................................64 3-11 1H NMR spectra of 3sp2OMe and poly3sp2OMe ..................................................65 3-12 Compositions of “latent reactive” unsaturated copolymers.....................................67 3-13 1H (A) and 13C (B) NMR spectra of copolymer 38 ( 147 ).......................................68 3-14 Composition and structure of crosslinked materials................................................70 3-15 Moisture cured xlink 39 at room temperature.........................................................71 3-16 DSC curves of poly6sp4gl copolymer 29 and xlink 29 .........................................72 3-17 TGA traces in an oxidative atmosphere...................................................................73 3-18 TGA traces in an inert atmosphere...........................................................................74 3-19a Stress/strain curves...................................................................................................75 3-19b Stress/strain curves...................................................................................................75 3-19c Stress/strain curves...................................................................................................76 3-20 Stress/strain curves a nd picture of thermosets wi th good elastic properties............79 4-1 Synthesis of siloxane-based dienes via hydrosilylation...................................95 4-2 Siloxane-based diene monomers......................................................................96 4-3 1H NMR spectra of 6sp4Si (top) and poly6sp4Si (bottom).....................................98 4-4 13C NMR spectra of 6sp4Si (top) and poly6sp4Si (bottom)....................................99 4-5 FT-IR spectra of 6sp4Si (blue) and poly6sp4Si (red)............................................100 4-6 DSC traces of polycarbosiloxanes..........................................................................102 4-7 Thermogravimetric analysis of polymer (198) in nitrogen and air........................103 4-8 “Latent reactive” carbosilan e/carbosiloxane copolymers......................................104 4-9 1H (top) and 13C (bottom) NMR spectra for copolymer 48 (208) .........................105

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xv 4-10 Siloxane-based thermosets.....................................................................................106 4-11 Stress/strain curves of car bosiloxane/carbosilane thermosets................................108 A-1 Stress/strain curves of dico mponent thermosets xlink 1-8.....................................116 A-2 Stress/strain curves of dico mponent thermosets xlink 9-16...................................117

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xvi Abstract of Dissertation Pres ented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy SYNTHESIS AND CHARACTERIZAT ION OF LATENT REACTIVE OLIGO(OXYETHYLENE)/CARBOSILANE AND CARBOSILOXANE/CARBOSILANE COPOLYMERS VIA ACYCLIC DIENE METATHESIS POLYMERIZATION (ADM ET) FOR THERMOSET MATERIALS By Piotr Pawe Mat oka May 2006 Chair: Kenneth B. Wagener Major Department: Chemistry Elastomeric materials can be found in many as pects of our life and the spectrum of their use is broad. From shoe soles, cable insulators, and automotiv e parts to advanced medical equipment, these polymeric material s are based on natural or synthetic rubbers such as butyl rubber or silicones. Although many of these products have been used for years, the development of novel synthetic me thods for the improvement and creation of new classes of elastomers are continuously being sought. Acyclic diene metathesis (ADMET) has been proven to be an effective tool in the synthesis of latent reactive carbosilane/c arbosiloxane copolymers bearing a methoxyfunctional group on each repeat unit. The polymer ization results in a linear thermoplastic polymer. The latent reactive methoxy groups remain inert during polymerization; however, exposure to moisture triggers hydrol ysis and the formation of a chemically

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xvii crosslinked thermoset. The thermoset’s prop erties can be modified by varying the ratio of carbosilane and carbosiloxane repeat units in the final material. Synthetic modification of the crosslink dens ity and run length in the soft phase in polycarbosilane/polycarbosiloxane elastomers is discussed. The incorporation of “chainend” crosslinks has improved mechanical performance by limiting the formation of dangling chains. In addition, increasing the run length of th e soft phase, to achieve a better balance between soft phase concentr ation and crosslink density, generates a material showing significantly im proved mechanical performance. Various oligo(oxyethylene) and carbosiloxane -dienes with different lengths of oxyethylene or siloxane units and alkenyl chains have been synthesized to investigate their influence on the properties of the resultant materials. Consequently, numerous thermoset materi als that show physical properties from elastic to flexible plastic beha vior were prepared and analy zed. The results obtained from mechanical testing and thermal analysis can be directly related to the structure of the thermoset.

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1 CHAPTER 1 ACYCLIC DIENE METATHESIS POLYME RIZATION (ADMET) APPROACH TO SILICON-CONTAINING MATERIALS 1.1 Introduction As an inherent part of organometallic ch emistry, organosilicon chemistry is one of the rapidly developing fields of science. Throughout nature, ma ny well-known inorganic and polymeric compounds contain silicon; however, there are no naturally occurring organosilanes. Organosilicon chemistry has blossomed since Kippi ng’s pioneering work at the beginning of the 20th century. Numerous applications1-4 have been reported in the manufacture of synthetic reag ents and intermediates, bioactive molecules, biomedical materials, electronic devices, specialty plas tics, elastomers, coatings, and fibers. Throughout the years, researchers have focused on silicon-carbon hybrids compounds rather than purely inorganic structures. Silicon/carbon hybrid polymeric materials have garnered considerable attention for their enhanced properties (som e that cannot be attained by using polymers based only on carbon). The uniqueness of the silicon-carbon copolymers comes from their high thermal stability, good electrical resistance, lo w surface tension, release and lubrication properties, high hydrophobicity, low glass transition, and low toxicity for the natural environment.4 The siloxane unit or the silicon at om can be incorporated into carbonbased polymer backbone to tailor desired properties of the resultant material.2,5 Several synthetic methods involving anioni c ring-opening polymerization, thermal

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2 cyclopolymerization, condensation, and coup ling reactions have been applied to synthesize such hybrids.1,4 The simplest and most widely known organosilicon polymers are based on silicones or polysiloxanes. This general class, well known for over 100 years, has many valuable and unique properties. Silicones in particular, like polydimethylsiloxanes (PDMS), exhibit hydrophobicity, thermal and oxidative stability, el ectrical resistance, low glass-transition temperature, low envi ronmental toxicity, gas permeability, and antiadhesive properties. However, silicone elastomers based on polydimethylsiloxane (PDMS) alone have relatively weak mechanical properties.2,4,6,7 To improve their mechanical performance (thereby extending their commercial use), researchers have modified these silicon-based materials. Th e most economically viable method has been to incorporate silica-based fillers in the polymer’s matrix. For example, fillers have been shown to impart elongation and overall mechanic al properties of the resultant material.8 These silicon-based materials (PDMS) can al so be enhanced by incorporating carbon segments resulting in silicon/carbon copolym ers, which can be achieved via block or grafted copolymers. There are numerous exam ples of these hybrid materials based on PDMSblock -polysulfone,9 PDMSblock -poly(methyl methacrylate),10 PDMSblock polyamide-6,11 PDMSblock -poly( -methylstyrene),12 PDMSblock -(bisphenol A polycarbonate),13,14 PDMSblock -polystyrene,15 poly(vinyl alcohol)graft -PDMS,16 and segmented polyurethanegraft -PDMS.17 Silicon-based hybrids are not the only example of organosilicon copolymers. Progress in organometallic chemistry and in the chemistry of novel materials led to production of new silicon-containing mate rials such as polycarbosilanes and

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3 polycarbosiloxanes. These saturated or uns aturated materials offer many potential industry applications, and produ ce new challenges for organosilicon chemists. Recently, these materials have found uses in gas-separa tion membranes or as ce ramics precursors. 1.2 Silicon Chemistry Silicon is a second-row element, directly under carbon in the periodic table, suggesting similar chemistry and reactivity to that of carbon. Silanes when compared to their analogous carbon compounds (particularl y in nucleophilic s ubstitution) show enhanced reactivity and relative rates. This tr end relates to silicon’s larger size and lower electronegativity, and the atom ’s availability to impart lo w-energy orbital bonding (Table 1-1).18 Table 1-1. Comparison of various silic on and carbon bond lengths and energies Bond Bond Length () Bond Energy (kJ/mol) Si-C 1.90 318 C-C 1.54 334 Si-O 1.63 531 C-O 1.44 340 Si-Cl 2.11 471 C-Cl 1.81 335 Correlations to silicon’s reactivity or st ability can be made and explained using Table 1-1. For example, silicon-halogen bonds are easily cleaved by nucleophiles while resistant to homolytic fission. Thes e observation are realized by the large electronegativity differences and high polar izability of both atoms producing highly ionic bond in character.19 Also, silicon-oxygen bonds (s iloxanes and silanols) are not analogous to carbon-oxygen sigma bonds (ether s and alcohols). The lone pairs on oxygen can overlap with an empty d-orbital on silicon, resulting in a highly polarized

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4 bond. Recently, it was shown that orbitals can participate in back-bonding because of their lower energy versus empty d-orbitals.1 This interaction justifies the fact that silanols are stronger proton donors than aliphati c alcohols and that th e decreased basicity of oxygen is observed in the following or der: C-O-C > Si-O-C > Si-O-Si. 1.3 Olefin Metathesis Olefin metathesis has been investigated for over 50 years as one of the most motivating discoveries in organometallic chem istry, widely used in both academic and industrial settings.20-22 In 2005, professors Yves Ch auvin, Robert H. Grubbs, and Richard R. Schrock were awarded the Nobel Pr ize in Chemistry “for the development of the metathesis method in organic synthesi s.” The name, proposed by Calderon, Chen, and Scott23 in 1967, originates from the Greek wo rd “metathesis” meaning changing or exchanging positions. The metathesis pro cess involves reaction of two carbon-carbon double bonds that yields two new olefins (F igure 1-1) and is described as an intramolecular and intermolecular exchange of substituents on 1, 2 di-, tri-, or tetrafunctional double bonds and “can be compared to a dance in which the couples change partners.” 24 This process can be divi ded into four categories: Simple exchange reactions Metathesis reaction involving two equal olefins Cross-metathesis (CM) reaction involving two different olefins Metathesis polymerizations Ring-opening metathesis polymerization (ROMP) Acyclic diene metathesis polymerization (ADMET) Ring-closing metathesis (RCM) Metathesis degradation of unsaturated polymers

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5 RCMA D M E TR O M P+ + R R R' + + R' R' R' Degradative Metathesis of Unsaturated Polymers + CM n a) d) b, c) Figure 1-1. Types of olefin metathesis: a) si mple exchange reactions; b, c) metathesis polymerization and ring-closing metath esis; c) metathesis degradation. Many applications benefit from olefin metathesis, making this mild method for creating a new carbon-carbon double bond a conve nient tool for synthesis of small molecules and for macromolecular synthesis. While the pharmaceutical industry has embraced ring-closing metathesis to synthesize complex cyclic structures, acyclic diene metathesis and ring-opening polymerizations are widely used by polymer chemists to produce a vast number of functionalized hydrocarbon polymers and silicon-carbon based hybrids. In the next sections some background information on the ADMET approach to silicon-containing polymers and copolymers cat alyzed by “well-defined” catalyst systems is described. Complementary method to ADMET polymerization such as silylative

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6 coupling (SC) polycondensation of divinyl organosilicon deri vatives (which shows low metathesis activity) is also discussed. 1.3.1 Brief History of Olefin Metathesis The first research on olefin metathesis a nd its industrial appl ication that led to publication was by Banks and Bailey25 from Philips Petroleum in 1964. The observed reaction was called olefin disp roportionate and was performed in the presence of the heterogeneous catalyst. The publication, however, was foreshadowed by Eleuterio’s26 and Peters’27 patent disclosures few years earlier. Several mechanisms were initially proposed to account for all observed exchange reaction products. The process consisten tly involves subseque ntial bond breaking and reformation after a transition metal 2+2 cycloaddition/retroaddition mechanism. The Chauvin mechanism (Figure 1-2) was initially ignored, only to become the most widely accepted mechanism with both metalla-cycle and metalla-carbene intermediates.28 [M] R'' R' R + [M] R R' R'' [M] R R' R'' + Figure 1-2. Metallacyclobutane mechanism. Olefin metathesis is a catalytically ini tiated reaction with num erous active catalytic systems. These catalysts, either homogene ous or heterogeneous, contain transition metals such as molybdenum, tungsten, rhenium, tantalum, ruthenium, rhodium, or titanium.20 Common to industrial applications the catalyst systems are typically heterogeneous versions of either Mo, W, or Rh oxides or carbonyls supported on highly developed Al2O3 or SiO2. The presence of co-catalyst is often required in these systems, usually a Lewis acid (a main group trior tetravalent metal). On the other hand,

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7 homogeneous systems (coordination complexe s) can be active with or without the presence of the co-catalyst. In the early days of olefin metathesis, organometallic ch emists raced to synthesize metal carbene complexes that might improve understanding of the metathesis process.2933 Further investigations during the mi d-1980s led Schrock and coworkers to the development of neutral carbene complexes based on tungsten34-36 and molybdenum37-39 (Figure 1-3). These catalysts were active in metathesis transformations and were called “well-defined” because the catalytically active species were easy too identify by spectroscopic methods. Because of the oxophyllic nature and low-tolerance to polar-functional groups, there were some limitati ons in the utility of these catalysts. Efforts were made to develop catalyst syst ems based on late transition metals that in complexes form catalysts more tolerant to air, moisture and functional groups. N W O O CHR' CF3 CF3 F3C F3C CH3 H3C R'= t -Bu; N Mo O O CHR'' CF3 CF3 F3C F3C CH3 H3C Ru PCy3 Ph PCy3 Cl Cl Ru Ph PCy3 Cl Cl N N R''= -C(Me)2Ph [Ru]** Ru PCy3 PCy3 Cl Cl Ph Ph [Ru]* [W] [Mo] [Ru] (1) (2) (3) (4) (5) Figure 1-3. Well-defined metathesis catalysts. In 1992 Grubbs and coworkers40 introduced the first well-defined ruthenium based catalyst [Ru] (3) (Figure 1-3), where their increased stability allowed for manipulations

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8 outside an inert atmosphere. The ligation sp here of the first-generation ruthenium-based catalyst [Ru]* (4) was soon modified by substitution of one phosphine ligand with a N-heterocyclic carbene ligand.41,42 In some cases this change achieved catalytic activity comparable to one of the molybdenum Schrock’s catalyst41 [Mo] (2) and a higher tolerance of functional groups was observed than in the first-ge neration Grubbs’ catalyst [Ru]* (4) .42 Structural isomerization 43,44 of the olefin can accompany olefin metathesis, an event that influences the synthesis of the exact structures through RCM and ADMET. Despite of vast number of “well-defined” ca talysts that have been synthesized, none of them have proven to be applicable fo r all substrates or transformations. 1.3.2 Introduction to ADMET Polymerization The discoveries and developments in the field of olefin metathesis and organometallic chemistry have made olefin meta thesis a convenient synthetic tool for the synthesis of functionalized a nd non-functionalized polyolefins.21 As previously mentioned there are two modes of olefin metathesis polymerization: ring-opening metathesis polymerization (ROMP)21 and acyclic diene metathesis polymerization (ADMET)21 (Figure 1-4). n n C2H4cat. cat. ADMET ROMP (7) (6) (8) (9) Figure 1-4. Acyclic diene metathesis (ADM ET) and ring-opening metathesis (ROMP) polymerizations.

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9 ROMP falls into chain-addition type polymer ization category. It is an exothermic reaction, thermodynamically driven by the rel ease of ring strain in a cyclic olefin monomer. ADMET is step-growth condensat ion type polymerization and thermally neutral. It is important to understand requirements and consequences for these classifications. Acyclic diene metathesis is a step-growt h condensation type polymerization that normally employs an -diene in conjunction with a meta thesis catalyst to produce high molecular unsaturated polymer. The reaction is driven by removal of a small condensate, usually ethylene. ADMET follows the sa me rules as any other polycondensation reaction, meaning that high conversions (>99%) with no side reactions are necessary to produce high molecular weight polymers.45 This reaction, as in the case any condensation polymerization, is an equilibrium process, which proceeds in a stepwise fashion to form dimer, trimer, tetramer, and so on to obtain high molecular polymer. The size of the polymer increases continuously with time (conversion) at relatively slow rate. Growth of molecular weight is described the Carother’s eq uation that relates the numberaverage degree of polymerization nX (also known as the degree of polymerization, DP ) to the extent of reaction p or conversion of the diene monomer. p Xn 1 1 Figure 1-5 shows a typical plot of theoretical nX versus conversion of the monomer in any condensation type polymeri zation. High molecular weight polymer is obtained at the end of polymerization when the conversion of monomer is larger than that of 99%. Thus, a highly active catalytic system is required throughout the polymerization; most catalysts however, show hi gher activity towards terminal olefins for steric hindrance

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10 reasons, and so –diene monomers are often used in acyclic diene metathesis polymerization. 0 50 100 150 200 020406080100 % ConversionDegree of Polymerizatio n Figure 1-5. Theoretical degree of polymeriza tion vs. conversion in condensation type polymerization. Early investigations of polymerization of 1,5-hexadine (6) and 1,9-decadine (10) (Figure 6), by Wagener and co-workers in the mid-1980s, demonstrat ed that “classical” catalysts such as WCl6/EtAlCl2 can lead to both cationic vinyl addition chemistry and in addition to polycondensation chemistry,20,46 thereby defining the need for active and well-defined catalyst for metathes is. Fortunately, in 1986, Schrock34 and co-workers successfully prepared the firs t well-defined, single site cat alyst, a breakthrough in this field. This breakthrough led to more stable ruthenium based catalytic systems discovered by Grubbs. (11) (10) 6 6 n cat. C2H4 Figure 1-6. ADMET polymerization of 1,9-decadiene.

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11 Like many other polycondensation reac tions, ADMET polymerization is best performed in the bulk (neat) to maximize the molar concentration of monomer (terminal olefins) and to promote a shif t in the equilibrium of the reaction from monomer towards unsaturated polymer formation. Bulk polymerization also minimizes undesired cyclization, a well known concurrent r eaction in polycondensation chemistry.45 Moreover, high vacuum is applied to rem ove the condensate ethylene, which further shifts reaction towards polymer formation. R LnM R' LnM R LnM R R LnMCH2 LnM R R H2CCH2 + R R R LnM R R' LnM R' R R' Figure 1-7. The catalytic cy cle of ADMET polymerization. The mechanism of the ADMET polymerizati on cycle, Figure 1-7, has been well documented.46,47 Each step in this mechanism is in true chemical e quilibrium, and the ultimate driving force for the reaction is removal of ethylene. The catalytic cycle starts with coordination of an olefin, followe d by formation of a metallacyclobutane intermediate and productive cleavage that leads to the formation of the metathesis active alkylidene complex. These subsequent reactions produce a methylidene complex

PAGE 29

12 followed by the coordination of another m onomer. Productive cleavage of another metallacyclobutane results in release of one et hylene molecule per each catalytic cycle. The developments in the field of welldefined catalysts along with the clean mechanism of ADMET have become instrume ntal in the synthesis of novel polymers with controlled architectures. The de sign starts with the preparation of –diene bearing desired type of functionality or specific type of branching. The resultant polymer retains this functionality and a specific backbone sequence. ADMET has produced unsaturated polymers where the functiona lities have been ethers,48 esters,49 carbonates,50 sulfides,51 and many more functionalities.52,53 Consequently, ADMET bypass typical synthetic obstacles in the synthesis of polymers a nd copolymers, and allows creating polymer structures that cannot be pr epared via other routes. 1.4 Olefin Metathesis Chemistry of Compounds Containing Silicon In the early seventies, research on me tathesis was predominantly focused on producing materials from simple silicon f unctionalized olefins. In 1971, Friedman described the first example of these materials by the metathes is of monoalkenylsilanes in the presence of MoO3/Al2O3.54 In addition to these simp le materials, a variety of organosilicon compounds can be produced using metathesis and can be divided into three categories based on choice of polymeriza tion method and structure of monomer: ROMP of unsaturated silacycloalkenes ROMP of silylsubstituted cycloalkenes ADMET of –dienes containing silicon First, the ROMP of the unsaturated sila cycloalkenes leads to polymers containing silicon atoms incorporated in the carbon b ackbone, as exemplified in Figure 8. The

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13 metathesis of 1,1dimethyl1-silacyclopent3-ene (12) proceeds in the presence of tungsten55 or alumina-rhenium56 and offers a broad scope for all silacycloalkenes, except for the thermodynamically stable silacyclohexene derivatives. (13) Si CH3 H3C Si cat. n n CH3 CH3 (12) Figure 1-8. Ring-opening metathesis polymer ization of 1,1-dimethyl-1-silacyclopent -3-ene. Second, the ROMP of silylsubstituted ol efins leads to unsaturated polymers (Figure 1-9) containing penda nt silyl groups used to m odify the properties of the polymer’s backbone. One such example is th e ROMP of silylsubst ituted norbornenes in the presence of either a homogeneous t ungsten catalyst or a heterogeneous aluminarhenium catalyst.57 (13) (12) R R n n cat. R = SiMe3, SiMe2CH2SiMe3, SiCl3, Si(OEt)3 Figure 1-9. ROMP of sily lsubstituted norbornens. An interesting example of ROMP is the re action of 1-(trimethyl silyl)cyclobut-1-ene (16) in the presence of Casey’s carbene complex (Figure 1-10).58 (17) (16) SiMe3 cat. n n cat. = (CO)5W=CPh2 SiMe3 Figure 1-10. ROMP using Casey’s carbene complex. The resultant polymer shows a repeating h ead-to-tail structur e containing only the cis double bond configuration. Moreov er, this trimethylsilyl groups can be easily converted

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14 into different functionality making them a surrogate for the functional group before metathesis. Third, the ADMET polymerization of –dienes containing silicon leads to formation of unsaturated polymers which, de pending on the structur e of monomer, can either include silicon functiona lity incorporated into polymer backbone or as a pendant groups along the polymer chain. Contrary to ROMP which can be limited to the use of strained cyclic monomers, ADMET offers wide spectrum of polymer structures. Thus, utility of ADMET polymerization will be discussed in the next section. 1.4.1 Acyclic Diene Oligomerization and Polymerization Acyclic diene metathesis polymerization of silicon-containi ng compounds is the most universal method amenable for the synt hesis of unsaturated organosilicon oligomers and polymers. The clean and efficient chemistry of ADMET combine desired material properties of both carbon and silicon based polymers in the rando m linear copolymer. Moreover, the high selectivity of olefin metathesis facilita tes an introduction of a wider range of possible “functional ha ndles” to manipulate the overa ll material properties. Metathesis of dialkenylsilicon deriva tives can be achieved either by an intramolecular or an intermolecular appr oach. The intermolecular ADMET reaction between -dienes (with exceptions of divinyl derivatives) produces linear, unsaturated polycarbosilane or polycarbosiloxane oligomers or polymers. Unsaturated heterocyclic organosilicons can also be produced by an intramolecular reaction if preferred. The mechanism of reaction is strictly depe ndent on the structure of the initial -diene and substituents on silicon; note that in so me cases a six membered ring compound will be preferentially formed as the most thermodyna mically stable product. Since all possible

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15 pathways are in equilibrium, both the seven a nd five membered rings are rarely observed. Product formation can be influenced to some ex tent by the presence or absence of solvent in the reaction environment. As mentioned, the divinyl derivati ves of silicon compounds do not undergo homometathesis, mainly due to the steric and electronic effects of two silyl groups present on the adjacent carbon atoms in the intermediate metallacyclobutane.35 However, while studying the hydrosilative activity of simple Ru(II) and Ru(III) complexes, Marciniec and coworkers59-62 have shown that catalytic me tathesis of alkoxyvinylsilanes is a competing reaction. However, soon af ter was found that th is process does not operate through metallacyclobutan e mechanism. Thus, appli cation of this silylative coupling (SC) polycondensation in the fo rmation of macromolecular structures containing silicon will be described in the later in separate section. 1.4.2 ADMET Catalyzed by “Ill-Defined” Catalytic Systems. Ill-defined catalyst systems do not easily lend themselves to metathesis polymerization chemistry, thus the practical ut ility and the scope of olefin metathesis have been limited toward functional gr oups, such the ones based on silicon. (18) Si R1R2 Si Si R1 R2 R1 R2 n n n x Si Si R1 R2 R1 R2 n n x Si R1 R2 n [Re] -C2H4, 35 oC + + [Re] = Re2O7/Al2O3 + Sn(or Pb)R4R1 = R2 = Me, Et or R1 = Me, R2 = Ph where: n = 1; R1 = R2 = Me where n = 2; x = 1-4 (19)(20) (21) Figure 1-11. Polymerization of diallyland allyl-butenyl derivativ es of disubstituted silanes.

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16 The first information regarding metathesis and co-metathesis reactions in the presence of these aforementione d catalytic systems were publis hed in early eighties. The reactions reported by Vdovin et al .63 utilized the heterogeneous Re2O7/Al2O3 catalyst along with a tetraalkyltin or tetraalkyllead cocatalysts. Vdovin’s and Finkelshtein’s63-66 research interests were focused on polymer ization of diallyl an d the allyl-butenyl derivatives of methyl, ethyl, and phenyl subst ituted silanes, as presented in Figure 1-11. Predominantly, cyclic products (20) were formed along with so me traces of oligomeric compounds. The attempted polymerization of diallyltetramethyldisiloxane (22)67, Figure 1-12, performed in the presence of Re2O7/Al2O3+Sn(Pb)R4, was accompanied by partial cleavage of the Si-Callyl and Si-O bonds, resulting in di ssproportionation of the Si-O bonds and formation of polysiloxane chains. (22) Si O Si Si O Si Me Me Me Me Me Me Me Me Si O Si Me Me Me Me m n Si O Si Me Me Me Me cat. + + C2H4(23) (24) (25) Figure 1-12. Polymerization of diallyltetramethyldisiloxane. Similarly to what is observed during atte mpted polymerization of diallyl and the allyl-butenyl derivatives of disubstituted sila nes, polymerization of diallyltetramethyldisilane (26) resulted in formation of bot h linear and cyclic products, where the former predominates (Figure 1-13). In this case, cyclized product is formed

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17 over the linear structure, what one can be attr ibuted to the higher stability of the six membered disilane product. (26)(27) Si Me Me Si Me Me cat. C2H4Si Si Me Me Me Me n Si Si Me Me Me Me + (28) Figure 1-13. Metathesis of diallyltetramethyldisilane. Many attempts have been taken to intr oduce a secondary func tionality (“latent reactive sites”) to silicon-based monomer other than those used by ADMET. An interesting example shows ADMET polymeri zation of dialkenysilanes containing the highly reactive silacyclobutane 68,69 (Figure 1-14). Hence, Finkelshtein observed that ADMET chemistry occurs in the same manner as for any other dialkenylsilanes, while maintaining the highly reactiv e silacyclobutane in every re peat unit. The resultant oligomer’s expansion, when heated, cleavag e of Si-C bonds in the four-membered ring yielding a crosslinked, waxy material. (29) (30) (31) Si Si n m Si n + cat. C2H4n = 1, 2 n m = 13 Figure 1-14. Metathesis of dialkenylsilacyclobutane. In spite of the lack of metathetical co nversion for divinyl organosilicon derivatives, Kawai and coworkers70,71 have recently reported successful synthesis of conjugated oligo(silylene-vinylene)s from tetravinylsilanes and divi nylsilanes in the presence of Re2O3/Al2O3 promoted with SnBu4. These polymers are important class of partly conjugated optical materi als, which based on the ab initio molecular calculation, should exhibit high transparency and relatively high second and third hyperpol arizability. It was

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18 found that the addition of tetrabutyltin is e ssential for ADMET to occur. The reactivity of Schrock’s and Grubbs’ catalysts was also examined; however th e catalysts did not succeeded, for reasons described previously. All products were linear oligomers, and cyclic products were not detected. 1.4.3 ADMET Catalyzed by “Well-Defined” Catalytic Systems In the early 90’s Wagener and co-workers72-75 opened a new chapter in the synthesis of unsaturated polymers and c opolymers containing silicon by preparing polycarbosilanes and polycarbosiloxanes with acyclic diene metathesis polymerization using well-defined ADMET cat alysts (Figure 1-2). 1.4.3.1 Polycarbosilanes Polycarbosilanes are an interesting cla ss of polymers due to the presence of covalent bond between silicon and carbon atom s in the backbone. Po tential applications of these materials in the broad range of fields have triggered considerable interest in their preparation.2 (32)(33) (10) Si CH3 CH3 [W] -C2H4n 6 + 6 Si CH3 CH3 m Figure 1-15. Copolymerization of divinyldimethylsilane (32) with 1,9-decadiene (10) The first silane diene, dimethyldivinylsilane (32) ,72 subjected to ADMET polymerization did not polymerize in the pr esence of the tungsten based Schrock’s catalyst [W] (1) where the lack of productive metathes is was attributed to the steric influence of the trisubstituted silicon atom adjacent to the double bond. Similar results were obtained by Schrock and coworkers36 in the attempted metathesis of vinyltrimethylsilane. The ster ic influence was further dem onstrated via copolymerization

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19 of divinylsilane (32) with 1,9-decadiene (10) 72, where the divinyl repeat unit was found to insert in a singular ma nner along the backbone, Figure 15. (34) LnW Si CH3 CH3 Si H3C H3C Si CH3 CH3 Si Si CH3 CH3 CH3 CH3 LnW=CH2+ + LnW Si CH3 CH3 LnW Si CH3 CH3 R LnW Si CH3 CH3 Si R CH3 CH3 LnW=CH2+ + R Metathesis Co-Metathesis (35) (36) (37) (32) (38) (39) (40) (41) (32) Figure 1-16. Productive and non-productive metathesis. Finkelshtein 66 provides a different explanati on for the lack of reactivity of divinyldimethylsubstituted s ilanes in the ADMET polymerizat ion. His rationalization is based on the formation of the highly stable silylated carbene complex, Figure 1-16, and its reactivity under copolymerization conditi ons. During the homopolymerization of divinylsilanes, formation of the me tathesis active methylidene complex (35) competes with an inactive silylated carbene (37) The reaction goes through the thermodynamically more favorable process th at leads to formation of the stronger stabilized silylated carbene and thus the metathesis product is not observed. In the case

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20 of copolymerization, the stability of both car bene complexes does not differ significantly and two pathways are possible. The producti ve copolymer formation is realized along with the unproductive formation of the starting divinylsilanes. Further investigations have shown that monomers with the methylene spacers incorporated between the silicon atom and the olefin are able to undergo productive metathesis polymerization (Figure 1-17) 72. Successful ADMET polymerization produces unsaturated polymers containing predominately (80%) trans double bonds. Exceptions are observed while polymerizing stiffer carbon segments; for example, the polymerization of 1,4-bis-(dimethylally lsilyl)benzene results in a 47% cis configuration along the unsaturated backbone.72 (46) (42) (43) (47) (45) (44) Si CH3 CH3 Si CH3 CH3 Si Si CH3 CH3 CH3 CH3 Si Si CH3 CH3 CH3 CH3 [W] n [W] -C2H4-C2H4 Si Si CH3 CH3 CH3 CH3 Si Si CH3 CH3 CH3 CH3 n n [W] -C2H4 Figure 1-17. Polycarbosilanes via ADMET. As shown in Figure 1-14 Finkelshtein68,69 has successfully polymerized -diene bearing highly reactive silacyclobutane using ADMET methodology. Similar study using “well-defined” catalytic system was conducted by Interrante and coworkers.76 The carbosilane polymers and copolymers were synt hesized with the disilacyclobutane rings imbedded into the copolymer’s backbone (Figure 1-18).

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21 (48) (49) (50) n Si Si 2 2 Me Me Si Si 2 2 Me Me n Si Si 6 Me Me [Ru]** CH2CH2TPA TSH TPA: tripropylamine TSH: p-toluenesulfonydrizide Figure 1-18. Polycarbosilanes with the disilacyclobutane rings. Unsaturated materials were hydrogenate d using methodology developed by Hahn77, which does not require the use of high-pressure H2, and the disilacyclobutane rings were thermally induced to open resulting in a tr ansparent, crosslinked solid material. 1.4.3.2 Polycarbosiloxanes A similar to carbosilanes, investigation of ADMET has shown that siloxanes are also polymerizable with the Schrock’s molybdenum catalyst [Mo] (2) (Figure 1-19 and Figure 1-20). Polymerization leads to fo rmation of unsaturated polycarbosiloxanes.73,74 (52) (53) (51) Si O Si CH3 CH3 CH3 CH3 Si O Si CH3 CH3 CH3 CH3 Si O Si CH3 CH3 H3C H3C [Mo] no metathesis [Mo] -C2H4 Figure 1-19. Non-productive ADMET polymerization. As in the case of divinyldimethylsilane, st erics has a predominant effect on both the productive and non-productive metathes is rates of vinylcarbosiloxane (51) (Figure 1-19). On the other hand, the reaction of 1,3 -diallyl-1,1,3,3-tetramethyldisiloxane (52) where siloxane group is “spaced out” by one methylene unit, leads to the ring formation (53)78 and essentially quantitative c onversion for cyclization of diallyldisiloxane was observed. This exclusive and fast cyclization w ith no oligomerization indicates great

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22 thermodynamic stability of this seven membered ring (Figure 1-19). Thus, an increased flexibility of siloxanes require s longer distances between the ol efin and silicon to produce ADMET linear polymers, as shown in Figure 1-20. Si O Si O Si CH3 CH3 CH3 CH3 CH3 CH3 [Mo] -C2H4Si O Si O Si CH3 CH3 CH3 CH3 CH3 CH3 n Si O Si O Si CH3 CH3 CH3 CH3 CH3 CH3 Si O Si O Si CH3 CH3 CH3 CH3 CH3 CH3 n 3 3 [Mo] -C2H4 Si CH3 CH3 O Si CH3 CH3 Si CH3 CH3 O Si CH3 CH3 Si CH3 CH3 O Si CH3 CH3 Si CH3 CH3 O Si CH3 CH3 n [Mo] -C2H4(54) (55) (56) (57) (58) (59) Figure 1-20. ADMET polymerization of siloxane containing dienes. Another noteworthy example of ADMET copol ymerization is an insertion of an aromatic diene repeat unit into an unsaturated polycarbosiloxane.74 Smith et al have shown that slow addition of small diene m onomer to unsaturated oligomer offers more than statistical control of copolymer by ki netically inhibiting homometathesis of the added diene (Figure 1-21). As previously shown in Figure 1-19 divinyl siloxane derivatives are reluctant to homometathesis; however, like divinyl silane they undergo copolymerization. The first successful copolymerization of divinyltetraethoxydisiloxane (63) with 1,9-decadiene (10) in the presence of the Grubbs’ catalyst [Ru]** (5) was reported by Malecka et al. Figure

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23 1-22.79 No consecutive linkage of divi nyltetraethoxydisiloxane was observed. Surprisingly, in the similar experime nt where divinyltetraethoxydisiloxane (63) was substituted with divinyltetramethyldisiloxane (51) copolymerization failed and no polymeric or oligomeric products were detect ed. The lack of metathetical activity of divinyltetramethyldisiloxane (51) in copolymerization wa s attributed to the decomposition of the Grubbs’ catalyst [Ru]** (5) due to the -transfer of silyl group to ruthenium in the metallacyclobutane, previously observed by Pietraszuk et al.80 (60) (62) (61) Si O Si O Si Si O Si O Si n Toluene [W] Si O Si O Si Si O Si O Si n y CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 Figure 1-21. Controlled di ene insertion via ADMET. Marciniec and Majchrzak81 have subjected divinyltetradisiloxane to ADMET copolymerization conditions in th e presence of 1, 4-divinylbenzene (65) (Figure 1-22). Analysis of this copolymer showed th e structure to be perfectly linear and trans (stereo)regular.

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24 (63) (64) (10) Si O Si OEt OEt OEt OEt Si O Si OEt OEt OEt OEt 6 6 6 n y + [Ru]* CH2CH2 Si O Si OEt OEt OEt OEt + Si O Si OEt OEt OEt OEt n [Ru]* CH2CH2 (63) (66) (65) Figure 1-22. ADMET copolymerization of divinyltetraethoxydisiloxane. 1.4.3.3 Telechelic oligomers Telechelic polymers are macromolecules wh ich contain one or more functional end groups that can form bonds with another mol ecule. They offer potential use e.g. in the formulation of model networks82 or in the preparation of thermoplastic elastomers.83 Preparation of this type of macromolecule is not trivial, especially those possessing functionality of 2.0 essentia l for the stoichiometric ba lance in the polycondensation reactions.84 ADMET polymerization is a convenient route to prepare an -telechelic polyoctenamers with the functionality close to 2.0.85,86 1,9-decadiene (10) was polymerized in the presence of the Schrock’s catalyst [Mo] (2) using dimers (71) of 5-hexenyl-methoxydimethylsilane or 5-hexenyl-chlorodimethylsi lane as chain limiters Figure 1-23. As expected, the number averag e molecular weights for these telechelic oligomers were proportional to the ratio of the monomer to the chain limiter. Further, these highly reactive macromonomers were exploited to synthesize ABA block copolymer of polydimethylsiloxanepolyoctenamer-polydimethylsiloxane.

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25 (71) (72) (10) 6 + CH2CH2Si Si CH3 CH3 CH3 CH3 3 3 X X Si Si CH3 CH3 CH3 CH3 X X 3 3 6 n where: X = -Cl, -OCH3[Ru]* or [Mo] Figure 1-23. Telechelic polymers via ADMET. Smith and Wagener73 synthesized -oligodiene via hydrosilation of 1,4-pentadiene (68) with 1,1,3,3-tetramethyldisiloxane (67) which then was exposed to ADMET conditions as shown in Figure 1-24. Th is nonvolatile, quick flowing liquid is an ideal monomer for ADMET polymerization due to the fact that continuous high vacuum can be applied during polymerization. (67) (70) (69) (68) HSi O Si H CH3 CH3 CH3 CH3 + [Pt] Si O Si Si O Si CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 x Si O Si Si O Si CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 x n [Mo] CH2CH2[Pt] = Karstedt's catalyst Figure 1-24. ADMET polymerization of -telechelic diene macromonomer.

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26 1.4.3.4 Functionalized polycarbosilanes The polycarbosilanes presented in Section 1.3.1.2.1 possess a simple silicon-carbon backbone. In order to introduce functionality along the polymer’s backbone, Cummings et al.87,88 synthesized chloroand dichlorosilane -dienes (73) that undergo successful ADMET polymerization (Figure 1-25) in th e presence of the Schrock’s catalyst [Mo] (2) (73)(74) CH2CH2Si Cl R x Si Cl R x x n where: R = Cl, CH3 x [Mo] Figure 1-25. Chloroand dichloro-func tionalized polycarbosilanes via ADMET. These chlorofunctionalized thermoplastic materials were exposed to different nucleophilic organolithium salts yielding pol ymers with various physical properties depending on the bulkiness of the nucleophiles. This concept was previously used by Allcock4 to tailor desired properties of polyphosph azanes. Allcock has also showed that cyclolinear phosphazane containing polymers that can be obtained via ADMET polymerization.89,90 Si Cl Cl x x nN u cSi Cl Cl x x x nSi Nuc Nuc x Si Nuc Nuc x x N u cA D M E T A D M E T Figure 1-26. Two routes to polymer modification.

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27 Subsequently, Church et al.91,92 demonstrated the utility and flexibility of ADMET in the one-pot synthesis of alkoxy-functionalized carbosilanes. They demonstrated that functionalization can be facili tated either via macromolecula r substitution or substitution on the -diene monomer (Figure 1-26). As no ted above both pendant groups on the carbosilane polymer backbone ha ve a significant effect on the physical properties of resultant polymer. These alkoxy-functionalized polymers can be further crosslinked to yield a polymer network. 1.4.3.5 Latent reactive elastomers The functionalized polycar bosilanes via ADMET descri bed above offer a new approach to the synthesis of materials exhi biting variable physica l properties. This research has led to a new type of synthesis involving “latent reactive” carbosilane/carbosiloxane copolymers by Brzezinska75 (Figure 1-27), illustrating the random incorporation of “laten t reactivity” throughout polyc arbosiloxane backbone in the form of the alkoxy-substituted carbosilane. (77) (76) (75) Si Si Si O Si OCH3 OCH3 OCH3 OCH3 CH3 CH3 CH3 CH3 y x Si Si Si O Si OCH3 OCH3 OCH3 OCH3 CH3 CH3 CH3 CH3 + [Mo] + Carbosiloxane SOFT Latent Reactive Carbosilane HARD Figure 1-27. Latent reactive car bosiloxane/carbosilane copolymer. It is well known that the methyl silyl ether bond, which inert during ADMET chemistry, easily hydrolyzes in the presence of moisture and condenses to form stable siloxane linkage.7 Consequently, the phys ical properties of ADMET

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28 polycarbosilane/polycarbosiloxane copolymers can be tuned by selecting the appropriate molar concentrations of each monomer. Fi gure 1-28 illustrates this modular approach and shows its extensive application in th e generation a large nu mber of materials exhibiting physical properties from elastic materials to plastics. Hard Soft Hard Soft Hard SoftOCH3 OCH3 Latent Reactive Carbosilane Hard Soft + ElastomerIntermediate Properties Plastic Low (10%) Hard Segment Content High (> 90%) Hard Segment Content Equal Ratios (50/50) Figure 1-28. The latent reactivity concept to attain diverse behavior of materials. 1.5 Silylative Coupling (SC) Polycondensation Previously mentioned, ADMET polymerizat ion is a universal method to obtain unsaturated organosilicon pol ymers. A vast number of -dienes containing silicon functionality tend to be active in this pro cess, when catalyzed by well-defined carbene complexes. On the other hand divinyl orga nosilicon compounds are an exception, since they remain inert under conditions of acycl ic diene metathesis polymerization. It happens that the sterics of silyl gr oups stimulate a nonproductive cleavage of disilylmetallacyclobutane.35 The Marciniec research group has found an important way to so lve this problem. Divergent to well-defined olef in metathesis catalysts, num erous ruthenium and rhodium complexes that contain or generate in situ metal-hydrogen or metal-silicon bonds catalyze intermolecular polycondensation of di vinyldiorganosilicon derivatives.

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29 R3Si SiR3 SiR3 SiR3 [Ru] SiR3 [Ru]H [Ru] H H SiR3H H [Ru] R3Si H H H SiR3 [Ru] H H SiR3 H SiR3 SiR3 SiR3 +[Ru] = RuHCl(CO)(PPh3)n Figure 1-29. Catalytic cycle of silylative coupling. At first, Marciniec et al.60 proposed a mechanism in which carbene is formed by rearrangement of a metal hydride complex. Soon after it was found that catalysis operates via non-metallacarbene mechanism;93,94 where series of -complexes are formed via insertion-elimination, as depicted in Fi gure 1-29. These transformations were termed silylative coupling polycondensation (S C) (or as referred by Finkelshtein66 may as well be called Marciniec’s metathesis). Complexa tion of the olefin to electrophilic metal center is followed by metal in sertion into the C-H bond. Elim ination of ethylene yields metal-silyl complex that coordinates another vinylsilane, which in serts into M-Si bond followed by reductive elimination of homome tathesis product while regenerating hydride complex. Formation of the 1,1-bis(silyl) ethene as product along with cis/trans 1,2bis(silyl)ethenes distinguish this reaction from olefin metathesis where only former two are formed. Early attempts at polymer synthesis via SC polycondensation of divinylsilanes and bisvinylsiloxanes (Figure 1-30) catalyzed by RuCl2(PPh3)3 and RuHCl(CO)(PPh3)3

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30 yielded polymers in moderate conversions,95,96 too low for step-growth polymer chemistry. CH2CH2Si Si mwhere: Si = silane, siloxane cat.= RuCl2(PPh3)3 or RuHCl(CO)(PPh3)3 cat. Si n Figure 1-30. SC polycondensation of divinylsubstituted silicon monomers. While rhodium-based catalysts were used two monomers of divinyltetramethyldisiloxane have undergone ring closure which subjected to X-ray spectroscopy revealed a boat conformation.97 Further studies in the synthesis of po lycarbosilanes and pol ycarbosiloxanes from divinyl organosilicon derivativ es were conducted by Malecka et al.98-100 who demonstrated the dependence of catalyst identity on polymer’s morphology. SC polycondensation of divinyl organosilicon compounds catalyzed by ruthenium-phosphine complexes, such as shown in Figure 1-30, yielded linear polycarbosilanes or polycarbosiloxanes. Both trans -1,2and gem -1,1fragments were present in the polymer’s backbone, while highly stereoselective trans -tactic structures were formed when [RuCl2(CO)3]2 was used. Moderate molecular weights of polymers were obtained as well. Majchrzak et al.81,101-103 have successfully synthesized numerous phenylenesilylene-vinylene and siloxylene-vinylene-p henylene polymers and copolymers via SC polycondensation, producing highly stereoand regioselective stru ctures with values of Mw from 13,100 to 34,800 g/mol.103 Alternate ruthenium complexes were screened in order to find a catalyst that promotes these regular structures. Furthermore, they have

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31 extended the utility of SC polycondensation to the synthesis of or ganosilicon starburst materials that contains the silicon-bridged -conjugated structure,104,105 as shown in Figure 1-31. Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si m n p Figure 1-31. Starburst oligomer via SC. 1.6 Crosslinking Methods for Silicon-Containing Materials. Elastomers are described as „materials that can be stretched ma ny times its original length without breaking, and will snap back to its original size when it is released.”106 To prevent polymer chains from slipping past each other during elongation, either physical or chemical crosslinks have to be present. Elastomers containing physical cros slinks e.g. glassy polymer (with Tg above room temperature) or semi-crystalline polymer (with Tm above room temperature) are termed thermoplastic elastomers, because they can be reshaped upon heating above Tg or Tm. On

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32 the other hand, elastomers that contain ch emical crosslinks are called thermoset elastomers, and polymer chains are hold together through covalent bonds forming a single networked molecule. The degree of cr osslinking is very important for the final properties of materials. Too many crosslinks make material stronger, but brittle, and only lightly crosslinked materials are effective elastomers. Applications of silicon-based materials in elastomers, coatings, and resins require that the materials do not flow; therefore cros slinking of these materi als is necessary. In general, crosslinking requires presence of trior tetrafunctional silanes that can react under ionic conditions, or organic groups that are pendan t or are on the end of the silicone polymer. Most silicone elastomers are prepared via one of the three crosslinking routes: moisture cure, heat-activat ed radical cure, or addition cure.1,4 First, moisture cure crosslinking, very often referred to as room-temperature vulcanization (RTV), takes a dvantage of the susceptibility of the silicon atom to nucleophilic substitution. Very often hydroxyterminated polysiloxanes are crosslinked by reacting with trior tetrafuncti onal silanes at room temperatur e. The rate of the cure is strictly dependent on the rate of hydrolysis of the leaving groups, thus very often these reactions are catalyzed by acids, bases, and by tin or titanium alkoxy/acyloxy derivatives. Second, heat-activated radical cure (high-temperature vulcanization HTV) involves formation of free radicals from peroxides e.g. m -chlorobenzoyl peroxide or dit -butyl peroxide. Two main reactions are observed while using these systems: the hydrogen radical abstraction from the methyl gr oup attached to the silicon and the radical addition to vinyl groups. The reactivity of th e latter reaction is hi gher than the hydrogen radical abstraction; therefore lower temper atures can be used to crosslink vinyl-

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33 substituted silicones. Th e distribution of vinyl groups along polymer backbone plays important role in the characteristics of the cu red materials. The formation of the polymer network is more efficient in the syst ems where vinyl groups are distributed homogenously, rather than the blocky systems where vinyl groups tend to react with each other. In the latter case this reactions do not contribute to formation of the network. Third, addition cure requires presence of the vinyl-terminated and hydrogenterminated polymers in the system. The addition reaction occurs under mild conditions and in most cases is catalyzed by platinum based catalysts. Since this is an addition reaction no by products are forme d, however the residual cataly st remains trapped in the network. 1.7 Purpose of Study. This document reports the progress in th e investigation of ADMET application in production of solvent resistant elastomeric materials and plas tics. The objective is to create a “common denominator” in materials (shown in Figure 1-27), wherein mechanical performance can be varied from highly elasto meric to flexible plastic, depending on the molar ratio of monomers used during polym erization. Improvements of processability, durability, and elastic ity are sought. The study has focused on the improvement of previously synthesized materials through variation of the length of the soft pha se, and introduction of the labile siliconalkoxy end group. In result numerous new siloxa ne or oxyethylene based materials have been synthesized a nd characterized.

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34 CHAPTER 2 SYNTHETIC MODIFICATION OF CROSSL INK DENSITY AND SOFT SEGMENT IN POLYCARBOSILANE/POLY CARBOSILOXANE ELASTOMERS 2.1 Introduction The clean and efficient chemistry afford ed by ADMET, mentioned in the previous chapter, allows for the comb ination of the best material properties of both carbon and silicon into a precise random linear copolymer. Moreover, th e high selectivity of olefin metathesis allows for a wide r range of possible functiona l handles to manipulate the overall material properties. The be havior of ADMET carbosilane/carbosiloxane copolymers can be achieved by selecting the appropriate molar concentrations of each monomer, as demonstrated in Figure 1-27, to generate a large number of materials. Si Si Si O Si OCH3 OCH3 OCH3 OCH3 CH3 CH3 CH3 CH3 y x x = 10.1% H2O Si Si Si O Si CH3 CH3 CH3 CH3 y x Si Si Si O Si CH3 CH3 CH3 CH3 y xO O O O Chain-Internal Crosslinks Chain-Internal Crosslinks Single Elastic Link in Backbone Single Elastic Link in BackboneO O Si Si Si O Si OCH3 OCH3 OCH3 OCH3 CH3 CH3 CH3 CH3 + [Ru]or[Mo]+ Carbosiloxane SOFT Latent Reactive Carbosilane HARD+n CH3OH(75) (76) (77) (78) Figure 2-1. Atmospherically cr osslinked ADMET copolymers.

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35 The production of these previously obtained hybrid systems using ADMET chemistry is described in Figure 2-1.75,107 These carbon/silicon copolymers contain “chain-internal” crosslinks only, where the ratio of 75 to 76 co-monomers determines its fundamental mechanical performance, varyi ng from a rigid to an elastic behavior. However co-monomer identity, functionality, and ratio are predominant factors in controlling the elastic propertie s of the material. While our initial silicon thermoset copolymers of this type are freestanding film s, they are relatively weak (low tensile strength) (Table 2-1). Table 2-1. Mechanical properties of the unsaturated ADMET copolymers and a commercially available elastomer. a) Filler free Fast Cure pure silicon-based elastomer purchased from Gelest Since the goal of the research is to produ ce solvent resistant and durable thermosets based on polycarbosilanes, we focused on the factors influencing tensile strength and other properties in order to improve our initial material (Figure 2-1). The successful production of silicon hybrid polymers vi a ADMET requires that our methodology conform to certain thermoplastic material cr iteria. First, cross link density in such materials is important and must be tailored precisely to balance m echanical strength and brittleness while maintaining chemical and so lvent resistance. Second, the soft phase should be amorphous and sufficient in length to observe elastomeric behavior; moreover, the run length of the soft phase between cr osslink sites plays an important role in Materials Modulus (MPa) Tensile Strength (MPa) Elongation (%) Polymer 78 0.16 0.2 20 Polymer 82 0.7 0.4 84 Polymer 85 6.0 0.6 400 Gelest Zipcone f Seriesa 2.0 0.7 150

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36 elasticity allowing for low crosslink density, ye t still enabling solvent resistance. While our initial materials are interesting (Figure 2-1, material 78 ) they lack sufficient tensile strength, most likely from an imbalance in crosslink density and soft phase morphology generated from the presence of dangling-ch ains in the three dimensional network.108 Thus, in Table 2-2 we have outlined synthetic modification to our ini tial materials that in our opinion should improve th eir overall performance Table 2-2. Synthetic research objectives. Research Objectives Schematic Representation Benefit Synthetically modified crosslink density H3COSi H3CO H3COxChain-end latent crosslinking Will enhance tensile strength and mechanical durability. Synthetic soft segment modification SiOSi CH3CH3CH3CH3x yIncreased run length in soft segment (y>1) Will significantly improve degree of elasticity, degree of elastic recovery, and the propensity for phase separation. 2.2 Synthetically Modified Crosslink Density The architecture of our initial hybrid c opolymers are composed of a carbosiloxane soft phase containing a siloxane bond (Si-O-Si ), giving flexibility and mobility, while the carbosilane hard monomer lacks this motional free dom since the Si-O-Si link is pendant to and therefore not part of the linear polymer backbone. Thus, as illustrated in Figure 2-1, these crosslinks, which we term “ch ain-internal”, are found exclusively in the hard phase of the copolymer, where their pres ence is critical since placing them in the soft segment would limit elasticity. As a result the latent reactive sites are placed in the hybrid material by the carbosilane monomer alone, in which its content does not exceed 10% by weight. These low monomer concentrat ions are necessary to produce flexible

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37 materials. As was shown by Brzezinska75 this chain-internal crosslinker is randomly incorporated into polymer backbone, theref ore crosslinking will occur at random points to the neighboring chains. This will re sult in formation of uncapped chain-ends (dangling-chains). Dangling chains are desc ribed as chains that are connected to the junction at only one end point. These mobile chains, which are elastically ineffective, represent network imperfec tions diluting the ultimate properties of the ADMET elastomer. In fact Andrady et al. has shown that both th e ultimate strength and maximum extensibility of a material ar e lower for networks containing danglingchains.109 In an effort to circumvent this pr oblem, we have introduced the concept of “chain-end” crosslinking to complement “ch ain-internal” crosslinking in attempt to produce more perfect networks. Figure 2-2 s hows two different molecules that can be used as chain-end crosslinkers. Si OCH3 OCH3 OCH3 x Si x x x CH3(80) (79) Figure 2-2. Chain-end cr osslinking molecules. This approach to increase the crosslink de nsity comprises two distinct concepts. First, note that a polymer synthesized using compound 79 (Figure 2-2) would produce a latent reactive, end-capped linear polymer. The mention of compound 61 is only for comparison and introduction of our new latent concept and its use will be discussed in Chapter 3. On the other hand, compound 80 synthesized by a Grignard reaction of 5bromo-1-pentene with trichloromethylsila ne, contains three ADMET active terminal olefins (ƒ = 3), therefore, using chain-end crosslinker 80 will result in a crosslinked

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38 network via the ADMET polymerization mechanism. Initially, we focused on proving the chain-end crosslinking concept using monomer 80 by combining it with our previously reported75 the hard and soft carbosiloxane and carbosilane monomers described in Figure 2-1. As men tioned above, introduction of monomer 80 should produce better-defined networks in material 82 and an observable improvement in its mechanical response when compared to material 78 .. ADMET polymerization is a step-growth type of polycondensation, where the initial monomer molar ratios are directly tran sferred to the polymer produced. Also, due to the nature of the substrates polymerize d, all monomers are incorporated randomly in the polymer. Si O Si CH3 CH3 CH3 CH3 y y Si Si OCH3 OCH3 OCH3 OCH3 z z+ Si x x x CH3+ Si Si Si O Si OCH3 OCH3 OCH3CH3 CH3 CH3 CH3 Si CH3 m n xy y z OCH3 z cat. Si CH3 Si CH3 z zChain-End Crosslinks Chain-End Crosslinks Si Si Si O Si CH3 CH3 CH3 CH3 y x Si Si Si O Si CH3 CH3 CH3 CH3 y xO O O O Chain-Internal Crosslinks Chain-Internal Crosslinks Single Elastic Link in Backbone Single Elastic Link in BackboneO O H2O(75) (76) (80) (81) (82) Figure 2-3. Chain-end cr osslinking in the polycarbosilanes via ADMET.

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39 Figure 2-3 illustrates the synthesis of a copolymer possessing both types of crosslinks using an initial soft/hard/chainend crosslinker molar ratio of 20:1:1 ratio, respectively. The use of metathesis (ADMET) generates polymers in which all monomers are randomly incorporated. Also, the high conversions n eeded in metathesis chemistry allows for a direct transfer of monomer feed ratios to the growing polymer chains. Both Schrock’s molybdenum catalyst [Mo] (2) (at room temperature) and 2nd generation Grubbs’ catalyst [Ru]** (5) (at 67-70 C) were examined in this study. Polymerizations were initiated using a 250:1 monomer: catalyst ratio regardless of catalyst chosen. Following initiation the reaction mixture was poured onto a Teflon plate and placed either in a room temperature vacuum desiccator (Schrock’s catalyst), or in a high temperature vacuum oven for secondgeneration Grubbs’ catalyst. Both catalyst systems produce free standing films, where so lvent resistance is rendered by the chainend crosslinker 82 These freestanding films were then exposed to atmospheric moisture to activate the “chain-internal” latent crosslinks. The resultant material ( 82 ) containing chain-end crosslinks shows signi ficant improvement in tensile strength (Table 2-1), when compared with our initial material ( 78 ) without chain-end crosslinks. Preliminary mechanical data recorded a modulus of 0.7 MPa and 84% extensibility for material 82. When compared to material 78 (modulus 0.16 MPa, 20% exte nsion) the importance of chain-end crosslinking concept is evident. 2.3 Synthetic Soft Segment Modification The minimization of network defects by using “chain-end” crosslinks has a profound enhancement over the material’s bulk pr operties. In an atte mpt to obtain better elongation, further modification was investigated by the incorporation of a different soft phase monomer. Throughout our initial study, we have solely employed the carbosilane

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40 monomer 76 a monomer possessing an inherently low Tg reflective of the Si-O-Si base unit. The homopolymer of monomer 76 has an observed glass transition onset of –91 C making it a desirable soft phase.75 However, when this monomer is employed in a random copolymer (material 82 ) array with the hard phase monomer 75 overall elongations are limited to approximately 80%. The most efficient way to enhance elasticity would be to increase the run length of the siloxane soft phase. However, due to obstacles encountered dur ing the synthesis and purification of such monomers, we initially focu sed on an easily synthesizable soft phase. Diene versions of polyoxyethyl ene are well known and have found wide application as soft phase segments,110-117 while this soft phase is not siloxane based the synthesis of these dienes are trivial and can be produ ced in large quantities. Treatment of a representative bromoalkene with a glycolic alkoxide yields analytically pure monomer 83 after purification.118 Other method used in the synthesis of family of glycol-based dienes will be discussed in Chapter 3. Figure 2-4. 1H NMR spectra of monomer 83.

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41 For example, the NMR spectrum for monomer 83 is shown in Figure 2-4. The characteristic integration of the polyoxyet hylene segment at 3.6 ppm, as well as, the observed resonances for the diene can be seen at 5.8 and 5.0 ppm. While polyoxyethylene are excellent soft segments; their glass transition is dependent on the number of repeating et hylene oxide units. An increase in Tg is observed with larger numbers of ethylene oxide, Figure 2-5.119 For example, the small molecule ethylene glycol (n=1) exhibits a Tg = 93C while an increase to -50C is observed when n=9. Initially, monomer 83 was chosen as the model soft phase due to its low glass transition (-75C) relative to monomer 76 (-91C). Hopefully, the close proximity of the two Tgs would reduce the effects cause d by the monomers’ molecular differences. The goal in the future is to pr oduce soft phases based solely on siloxane, in effect utilizing the purely amorphous nature of silicon; in fact, the best-known elastomers, polydimethylsiloxane (PDMS), exhibit Tgs as low as -123C. H O OHn n Tg (C) 1 -93 2 -83 3 -75 4 -70 9 -50 Figure 2-5. Glass transition temperatures for various lengths of polyoxyethylene The homopolymer synthesized with monomer 83 under standard bulk ADMET polycondensation conditions genera ted a linear polymer having an Mn = 28,000 g/mol. Thermal analysis of this oxyethylenebased ADMET homopolymer yielded a melting temperature of 35.7 C and a recrystallization temperature of 16.6 C revealing semi-

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42 crystalline properties typical for pristine polyoxyethylene. Repeated DSC scans led to identical enthalpies of melting and re crystallization for this macromolecule. Given the viability of this oxyethylenebased monomer in homometathesis, it was employed in the ADMET terpolymerization sc heme describing earlier (Figure 2-3), substituting the new oxyethylene diene for th e carbosiloxane monomer (Figure 2-6). Identical monomer ratios (20:1:1) and catalyst loadings (250:1) were employed comparable to the siloxane based terpolymer. A 10 fold increase in elongation-to-break was observed, from less than 80% to 400% (Figur e 2-6). It is appare nt that 4 ethylene oxide units are sufficient to ge nerate highly elastic materials, and this data suggests that fewer ethylene oxide units (perhaps 2 or 3) may prove of value. The data in Table 2-1 also illustrates a cl ear enhancement in modulus and tenacity for polymer 85 as compared with polymer 78 and 82 The modulus, tenacity, and elongation increase along with presence of chai n-end crosslinking and with a longer soft phase, as expected. Moreover, the tenacity matches that of commercial silicone elastomers, combined with a significantly hi gher modulus and elongation. It is evident that “chain-end” crosslinking combined with the soft phase modifi cation offer enhanced elasticity and performance over ou r initial materials. In order to produce materials that are more UV stable and offer the lowest possible Tgs, investigations to generate allsiloxane copolymers possessing fully latent ch ain-internal and chain-end crosslink sites, including the use of siloxane ch ain-end crosslinkers such as 79 (Figure 2-2), are described in following chapters.

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43 Si Si O O OCH3 OCH3 OCH3 OCH3 Si 9CH3 3 Si Si O O O O Si 9CH3 3 Si Si O O O O Si 9CH3 3 H2O xy z x x z z y y AtmosphericO O Longer Length Soft Phase Chain-End Crosslinks Chain-End Crosslinks Si Si O O OCH3 OCH3 OCH3 OCH3 9 3 9 + + + +CH3OH [Ru](83) (75) (84) (85) Chain-Internal Crosslinks Chain-Internal Crosslinks Si x x x CH3(80) Apply Tension Release Tension Figure 2-6. High elastic mate rial containing increased soft phase and chain-end crosslinker. 2.4 Conclusions ADMET polymerization of carbosilane/car bosiloxane copolymers bearing “latent reactive sites" offers a new approach to th e synthesis of materials exhibiting variable physical properties. Latent reactive met hoxy groups remain inert during metathesis polymerization; exposure of the copolymer to moisture triggers hydrolysis (latent crosslinking). The incorpor ation of “chain-end” crosslinks has improved mechanical performance by limiting the formation of danglin g chains. In addition increasing the run

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44 length of the soft phase, in order to ac hieve a better balance between soft phase concentration and crosslink density, gene rates a material exhibiting significant mechanical performance. The material wh ere the soft phase was changed from the siloxane unit to the polyoxyethylene glycol leads to formation of crosslinked film 70 that exhibits good material properties (modulus 6 MPa, elongation 500%). We are pursuing this research with the goal of generating all-siloxane copolymers possessing fully latent chain-internal and chai n-end crosslink sites. 2.5 Experimental Methods 2.5.1 General Considerations 1H NMR (300 MHz) and 13C NMR (75 Hz) spectra of the ADMET polymers and monomers were recorded in CDCl3 or C6D6 on either a Mercury series or Varian VXR300 NMR super-conducting spectrometer. Chemical shifts were referenced to residual CHCl3 (7.25 for 1H and 77.23 for 13C) and to residual C6D6 (7.15 for 1H and 128.39 for 13C). High-resolution mass spec tral (HRMS) data were obt ained on a Finnegan 4500 gas chromatograph/mass spectrometer using ei ther the chemical ionization (CI) or electrospray ionization (ESI) mode. Elemental analysis was carried out by Atlantic Microlab Inc. (Norcross, GA). Gel permeation chromatography (GPC) of the unsaturated ADMET polymer was performed using two 300 mm Polymer Labor atories gel 5m mixed-C columns. The instrument consisted of a Rainin SD-300 pump, Hewlett-Packar d 1047-A RI detector (254 nm), TC-45 Eppendorf column heater set to 35 C, and Waters U6K injector. The polymer samples were dissolved in HPLC gr ade THF (approximately 0.1% w/v), filtered before injection, and collected at a flow rate of 1.0 mL/min. Retention times were

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45 calibrated to polystyrene standards purcha sed from Polymer La boratories (Amherst, MA). Differential scanning calorimetry (DSC) wa s performed using a Perkin-Elmer DSC 7 at a heating rate of 10 C/min. Thermal calibrations we re made using indium and freshly distilled n -octane as references. Heats of fusi on were referenced against indium. All samples were prepared in hermetically sealed pans (4-7 mg/sample) and were run using an empty pan as a reference. The samples were scanned for multiple cycles to remove recrystallization differences between samples, and the results reported from the second scan cycle. Mechanical tests were performed at the Univ ersity of Florida facility by courtesy of Dr. Brenan’s research group, using an Inst ron model 1122 load frame upgraded with an MTS ReNew system running MTS TestWorks 4 software and a 500 g load cell for the experiments. Tensile specimens were cut from the cured freestanding films using an ASTM D1822-68 type L dogbone die. Each specimen was individually measured to account for thickness variability in calcula tions. The grip separation for the samples was set at 25.4 mm and the width of the testing portion was se t at 3.1 mm. Tensile measurements were made according to ASTM D412-97 at rate of 2 inch/min. 2.5.2 Materials. All reagent grade solv ents were freshly distilled over a Na/K alloy, except for THF which was dried using K-benzophenone kety l. 5-bromo-1-pentene and 11-bromo-1undecene were purchased from Aldrich and dried over activated 4 sieves. Magnesium turnings (Aldrich) were activated by vacuum drying at 100 C prior to use. Triethylene

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46 glycol (Aldrich) was dried by azeotr opic distillation using toluene and bis(trimethoxysilyl)ethane (Gel est) was distilled over CaH2. Any necessary chlorosilanes were purchased from Gelest and used as re ceived. Deuterated solvents (Cambridge Isotope Laboratories) were stored over activated 4 sieves. Filler Free fast Cure pure Silicon based elastomer was purchased from Gelest. The metathesis catalysts Cl2Ru(IMes)(PCy3)[=CHPh]42 and [Mo=CHCMe2Ph(=N-C6H3-2,6i -Pr2-) (OCMe(CF3)2)2]38,120 were synthesized according to li terature procedure. All other compounds were used as received. 2.5.3 Monomer Synthesis Monomer 75 and 76 were synthesized according to a literature procedure.75 2.5.3.1 Tris(4-pentenyl)methylsilane (80) A 250 mL three-necked round bottom flask equipped with an additional funnel, condenser, and stir bar was flame-dried unde r vacuum, and then flushed with argon. Magnesium turnings (2.1 g, 0.087 mol) and dr y diethyl ether (50 mL) were added. A solution of 5-bromo-1-pentene (11.8 g, 0.0800 mol) and 50 mL of diethyl ether was added drop-wise to maintain a constant reflux. The solution was refluxed for an additional hour, cooled to room temperature, and a mixture of trichloromethylsilane (3.32 g, 0.0221 mol) in Et2O (10 mL) was slowly added. Upon addition, the solution was refluxed (2 hours), cooled and the product was diluted with 50 mL of dry pentane and separated via cannula. The organics were ev aporated under reduced pressure yielding 6.5 g of a clear, colorless liquid. The crude product was purified by column chromatography using straight hexanes. Monomer 80 was collected in 80% and the following spectral properties were observed: 1H NMR (CDCl3): = –0.05 (s, H3), 0.5 (m, br, H6), 1.4 (m, br, H6), 2.05 (m, br, H6), 5.0 (m, br, H6), 5.8 (m, br, H3). 13C NMR (CDCl3): = –5.25,

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47 13.36, 23.40, 37.79, 114.43, 138.99. MS (70 eV): m/z = 181.1412 (M+-C5H9). (C16H30Si) (250.49): Calcd. C 76.72, H 12.07; Found C 76.69, H 12.18. 2.5.3.2 Diundecenyltriethylene glycol (83). The synthetic procedure was modi fied from published procedure.118 Sodium hydride (6.5 g, 0.27 mol, 60% dispersion) was placed in a flame-dried, Ar-purged, threenecked 1000 mL round-bottom flask equipped with a stir bar, condenser, and an additional funnel. Dried tr iethylene glycol (8.1 g, 0.068 mo l) and 260 mL of dry THF were combined in a flame-dried 500 mL Schl enk flask. The solution was transferred to the additional funnel and the mixture was adde d drop-wise under cons tant stirring. After 24 h, 11-bromo-1-undecene (40 g, 0.17 mol) in 240 mL of THF was added and stirred for an additional 72 h at reflux. Upon cooling, 50 mL of water was added, stirred for 15 minutes, and extracted using ether. The combin ed organic extracts were washed with a saturated NaCl solution, dried over MgSO4, filtered, and evaporated under reduced pressure. The crude product was then purified by column chromatography using hexanes/diethyl ether (80:20%). The frac tions were concentrated yielding 15 g of monomer 83 The following spectral pr operties were observed: 1H NMR (CDCl3): = 1.25 (m, br, H24), 1.60 (m, br, H4), 2.10 (m, br, H4), 3.53 (m, br, H4), 3.60 (m, br, H12), 4.95 (m, br, H4), 5.85 (m, br, H2). 13C NMR (CDCl3): = 26.10, 28.94, 29.14, 29.45, 29.49, 29.51, 29.55, 29.62, 29.66, 33.81, 70.04, 70.64, 71.53, 114.06, 139.18. MS (70 eV): m/z = 455.4121 (M+). (C28H55O4) (454.72): Calcd. C 73.96, H 11.97; Found C 73.91, H 12.18. 2.5.4. General Metathesis Conditions All monomers used in polymerization were purified and degassed prior to polymerization. All glassware was thoroughl y cleaned and dried under vacuum before

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48 use. The polymerizations were initiated in an argon-filled glove box by placing the appropriate amount of monomer followed by either metathesis catalyst and slowly stirred for 2 minutes. In all cases the m onomer: catalyst ratios were 250:1. 2.5.4.1 Polymerization of diundecenylt riethylane glycol (83) The monomer was polymerized using the above procedure. Monomer 83 (0.51 g, 0.0021 mol) was added to the reactio n tube charged with Grubbs’ 2nd generation catalyst (7.30 mg, 8.58x10-6 mol). The reaction tube was seal ed using a Kontes Teflon valve and placed under an intermediate vacuum until the mixture became viscous. The reaction flask was then placed in a 40 C oil bath a nd high vacuum (<0.01 mm Hg) was applied. The temperature was gradually raised to 70 C over 72 hours. After three days, the polymerization was quenched via dissolution in toluene followed by precipitation in acetone. The following properties were observed: 1H NMR (CDCl3): = 1.25 (m, br, H24), 1.60 (m, br, H4), 2.10 (m, br, H4), 3.53 (m, br, H4), 3.60 (m, br, H12), 5.56 (br, H2); 13C NMR (CDCl3): = 25.91, 26.06, 27.17, 28.96, 29.10, 29.16, 29.31, 29.43, 29.46, 29.60, 29.73, 32.49, 32.57, 70.01, 70.57, 70.58, 71.50, 130.30. GPC data (THF vs. polystyrene standards): Mn = 27 770 g/mol; PDI ( Mw/Mn) = 1.55. DSC Results: Tm (melting peak) = 35.7 C, hm = 86.8 J/g; Recrystallization Tc (recrystallization peak) = 20.1 C, hc = -88.8 J/g 2.5.4.2 Terpolymerization of monomers 75, 76, and 80 to produce terpolymer 81 Terpolymer 81 was prepared at 1: 20: 1 monomeric ratio using monomer 75 (0.17 g, 5.0 x 10-4 mol), monomer 76 (3.0 g, 0.010 mol) and monomer 80 (0.13 g, 5.2 x 10-4 mol). The monomers were stirred for 5 minut es to ensure a homogeneous mixture before the addition of either 2nd generation Grubbs’ cat alyst (0.0372 g, 4.41 x 10-5 mol), or Schrock’s catalyst (0.0341 g, 4.41 x 10-4 mol). The reaction mixture was sealed,

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49 removed from the glove box, and stirre d under vacuum for 10 minutes. The polymerization mixture was th en poured out on a Teflon plate and placed in a vacuum oven at 70 C for 72 h. In the case of Schroc k’s catalyst, the reacti on mixture was cast in the glove box and placed inside a vacuum de siccator. The desiccator was removed from the glove box, and placed on a high vacuum lin e at room temperature for 72 h. Vigorous bubbling of the ethylene gas byproduct was observed, followed by formation of a thin film. After 72 h the Teflon plate was removed from a vacuum oven and exposed to 80% moist atmosphere having a pH 6.5-7.0, for a period of 3 weeks. 2.5.4.3 Terpolymerization of monomers 75, 83, and 80 to produce terpolymer 84 Terpolymer 84 was prepared by mixing monomer 75 (0.11 g, 3.3 x 10-4 mol), monomer 83 (3.1 g, 6.6 x 10-3 mol), and monomer 80 (0.0862 g, 3.46 x 10-4 mol) resulting in a 1: 20: 1 monomer ratio. Follo wing the same procedure as for terpolymer 81 all monomers were mixed and stirred prior to the addition of the catalyst. In this case, 2nd generation Grubbs’ catalyst (0.035 g, 4.1 x 10-5 mol) was added and the reaction mixture was stirred, sealed, removed from the glove box, and placed for 10 minutes on a high vacuum line. The mixture wa s then transferred to the Teflon plate and placed in a vacuum oven at 70 C. After 72 h, the Teflon plate was removed and the thin film was exposed to 80% moist atmosphere having pH 6.5-7.0 for a period of 3 weeks.

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51 CHAPTER 3 SYNTHESIS AND CHARACTERIZATION OF OLIGO(OXYETHYLENE)/CARBOSILANE COPOLYMERS AND THERMOSETS 3.1 Introduction Encouraged by results obtained fr om the previous investigation,121 we synthesized fully latent reactive processable and durable materials. Although our ultimate goal is to produce carbosiloxane/carbosilane based material s, our focus shifted to materials based on the oxyethylene segments. The previous study121 has proven that th e incorporation of these segments can result in a thermoset that exhibits good physical properties. As mentioned in the previous chapte r, polyethylene glycol has found wide application as a soft phase segment.110,112,122 This hydrophilic polyether received considerable attention for use in biomaterials due to its low interfacial energy with water, relative structural stability, lack of binding sites for reac tive proteins, and high chain mobility.123 It has been used extensively in th e preparation of polymer electrolytes,124-126 crosslinked hydrogels,127-129 membranes130-132 and amphiphilic copolymers.118,133,134 In the preparation of membranes for biol ogical applications, control over the pore size and good mechanical properties are a necessity in order to enhance the transport of hydrophilic entities. Thus the preparat ion of such membranes requires highly monodisperse polyethylene glycol chains, which are further te rminated with allyl groups susceptible to hydrosilylation. The synthesi s involves the random cohydrosilylation of -diallyl-PEG and -diallyl-PIB segments with pentamethylcyclopentasiloxane131 resulting in the formation of a network that restrains post reaction shaping.

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51 Silylated polyethers have found applications in the sealant industry. For example MS Polymer developed by Kaneka Corporat ion in Japan, composed of high molecular weight polypropylene oxide endcapped with sily l groups, has been used in formulation of sealants and caulks.135 The synthesis of silyl terminat ed polyethers involves reaction of polypropylene glycol with allyl chloride in the presence of alkali metals which produces allyl terminated polyether, followed by hydr osilylation with methyldimethoxysilane in the presence of the platinum ch loride catalyst. The resultant silyl terminated polyether is subsequently mixed with fillers, plasticizers, and a curing catalyst to obtain a room temperature curing composition. This chapter describes the design and synt hesis of unsaturated “latent reactive” oligo(oxyethylene)/carbosilane copolymers prepared via acyclic diene metathesis polymerization. Methoxy groups attached to silicon atoms have been chosen as the “latent reactive” sites that have prev iously been proven to be inert during metathesis.75,85,121,136 Exposure to moisture triggers the hydrolysis of methoxy groups, which undergo condensation reaction to yield cr osslinked materials. The synthesis and characterization of monomers, polymers, a nd both linear and crosslinked copolymers is reported. 3.2 Synthesis of Monomers 3.2.1 Monomers for Soft Phase Modification A family of monomers (Figure 3-1), with different lengths of oligo(oxyethylene) and methylene spacers between the carbon-carbon double bond and the oligo(oxyethylene) unit, has been synthesized in order to investigate the influence of the structural modifications on th e properties of the resulting materials. For clarity, the nomenclature shown in Figure 3-1 is used in stead of the full name s of the monomers.

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52 The first number corresponds to th e number of methylene units (“ sp ”) between oxygen and the vinyl group; the second num ber corresponds to a glycol (“ gl ”) used in the monomer synthesis (e.g. 2 for di ethylene glycol). Consequent ly, abbreviations used for the polymers are “ poly ” followed by the monomer abbreviation. O O 3 3 23sp2gl O O 3 3 33sp3gl O O 3 3 43sp4gl O O 6 6 36sp3gl O O 6 6 46sp4gl O O 9 9 29sp2gl O O 9 9 39sp3gl O O 9 9 49sp4gl (86) (87) (88) (89) (90) (91) (92) (93) Figure 3-1. Glycol-based monomers. Williamson’s ether synthesis, described in Chapter 2, was used to prepare the 3sp and 6sp monomers. The 9sp monomers were synthesized vi a another synthetic route that involves reaction of 1-undecene-11-ol and an appropriate ditosylated oligo(oxyethylene) glycol in the presence of sodium hydride (example presented in Figure 3-2). The 1undecene-11-ol used in this reaction was synt hesized according to literature procedure.137 OH 9Ts O O Ts 4 O O 9 9 4+ NaH DMF, 0 oC(94) (95) (93) Figure 3-2. Synthesis of 9sp4gl (93) The synthesis, workup, and product purifi cation via column chromatography was followed by vacuum distillation over calci um hydride to yield analytically pure monomers, which were stored in an in ert atmosphere of a glove box. Common

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53 spectroscopic methods such as 1H NMR, 13C NMR, and FT-IR were used to characterize all monomers. 3.2.2 Monomers for Crosslink Density Modification As described in Chapter 2 our initial ma terials were composed of two monomers: the “soft phase” monomer 76 and the latent reactive “chain-internal” crosslinker 75 From previous studies75,121 we have learned that the rati o of used monomers dictates properties of the final thermoset. Moreover, we have found that the crosslink density modification via an incorporation of the “chai n-end” crosslinker as the third component enhances properties of our materials by limiting the formation of dangling chains.121 However, due to the nature of this “chain-end” crosslinker 80 used in this study, a thermoset is formed already during the polym erization restraining further processing of the polymer. Since the ultimate goal of this research is the synthesis of fully “latent reactive”, linear processable materials for thermoset elas tomers, we have decided to synthesize a latent reactive “chain-end” crosslinker. Th e synthesis of such monomer shown in Figure 3-3, involves the Grignard coupli ng of 11-chloro-1-undecene with trimethoxymethylsilane (96) The use of this monofunctional metathesis active monomer 97 in the synthesis of latent reactive materials has a dual purpos e. First, the placement of 97 on the end of chains will ensure linearity of the resultant polymer and facilitate further processing. Second, presence of labile methoxy groups on the silicon atom that participate in the crosslinking process will lim it the formation of dangling chains in the final thermoset. The crosslink density of our materials can be further modified using “chaininternal” crosslinker 100 (Figure 3-3) bearing only two methoxy groups on the silicon

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54 atom instead of four as used in previous studies.121 Using the same synthetic methodology as in the case of 97 the Grignard coupling of 5-magnesiumbromo-1pentene (98) and tetramethylorthosilicate (99) was applied. (95) Si OCH3 OCH3 MgBr MgCl Si CH3 OCH3 OCH3 H3COSi OCH3 OCH3 CH3 H3COSi OCH3 OCH3 OCH3 + Et2O + Et2O end9sp2OMe 3sp2OMe (96) (97) (98)(99)(100) Figure 3-3. Synthesis of end9sp2OMe and 3sp2OMe In both cases after workup and distillation an analytically pure monomer was obtained as proven by 1H NMR, 13C NMR, and FT-IR. Once again short names were assigned for cl arity, as shown in Figure 3-3. The first part of the name depicts number of methyl ene groups between silicon atom and the vinyl group, whereas the second part describes numbe r of the latent reactive methoxy groups present in the monomer. Conseque ntly, the short name for monomer 75 described in Chapter 2, will be 3sp4OMe In order to distinguish the -diene monomers from a monofunctional “chain-end” monomer, th e word “end” was placed before an abbreviation. 3.3 ADMET Polymerization 3.3.1 Synthesis of Oligo(oxyethylen e)/Oligo(ethylene) Copolymers Polymers were synthesized from monomers presented in Figure 3-1 under standard bulk ADMET polycondensation conditions using the 1st generation Grubbs’ catalyst [Ru] (4) Although our initial pol ymerization of monomer 9sp3gl was catalyzed by 2nd

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55 generation Grubbs’ catalyst [Ru]** (5) the [Ru] (4) was used to conduct metathesis in mild conditions and to prevent olefin isomerization during polymerization.43,138 Resulting linear unsaturated polymers can be described as alternating (AB)n microblock copolymers of oligo(oxyethylene) and oligo(ethylene). All polymers are viscous liquids except for ones made from 9sp monomers. Table 3-1. GPC data of unsaturated polymers. GPC (g/mol)a Polymer Mn Mw PDI poly3sp2gl (101) 35,766 63,306 1.77 poly3sp3gl (102) 34,565 65,328 1.89 poly3sp4gl (103) 34,890 66,634 1.91 poly6sp3gl (104) 36,193 62,976 1.74 poly6sp4gl (105) 30,734 49,174 1.60 poly9sp2gl (106) 51,750 106,605 2.06 poly9sp3gl (107) 40,103 72,185 1.80 poly9sp4gl (108) 46,840 96,490 2.06 a) referenced to PS standards in THF at 40C; The standard spectroscopic methods (1H NMR, 13C NMR, FT-IR), the gelpermeation chromatography (GPC) and the ther mal analysis (DSC, TGA) were used for the structural characterization and verifi cation of the monomers’ conversion to high molecular weight polymers. Table 3-1 summ arizes the results obtained from the gelpermeation chromatography analysis on unsaturated polymers, while a more detailed discussion regarding 1H NMR, 13C NMR, FT-IR and the thermal analysis is described in the following sections.

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56 3.3.1.1 Structural characterization The spectra of monomers with the same alkenyl group length or the same number of oligo(oxyethylene) units are homologous. T hus the spectra of polymers obtained from these monomers are very similar as well. Figure 3-4. 1H NMR spectra of monomer 6sp3gl and polymer poly6sp3gl. In Figure 3-4, a representative 1H NMR spectra of monomer 6sp3gl (89) and polymer poly6sp3gl (104) is presented. The top of the figure shows 1H NMR spectra with characteristic peaks between 3.53-3.63 ppm that co rrespond to protons on the oxyethylene segment. As shown in Figure 34, the chemical shifts for the monomer and the unsaturated polymer remain the same, but the intensity of signals depends on the length of the oxyethylene segment. The 1H NMR spectra clearly illustrates quan titative conversion of the monomer to the high molecular weight unsaturated polymer This can be observed by the complete disappearance of the vinyl groups in the m onomer, (peaks at 4.9 and 5.7 ppm in the top

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57 spectra), and by the newly formed peak at 5.3 ppm of the internal olefin that appears in the spectrum of polymer (bottom). Figure 3-5. 13C NMR spectra of monomer 6sp3gl and polymer poly6sp3gl The chemical structures of the monome r and the polymer were characterized by 13C NMR and are shown in Figure 3-5. The spect ra of the monomer and the polymer show characteristic carbon signals of oxyethylene segments present at 71.3 and 70.8 ppm. As in the olefinic region of 6sp3gl (89) and poly6sp3gl (104) of the 1H NMR spectra, the 13C NMR spectral changes are also observed. Two signals of vinyl carbons at 114.1 and 139.8 ppm present in the monomer disappear while two new peaks at 130.3 ppm (major) and 129.5ppm (minor) are formed in the polym er. These two new signals correspond to

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58 trans and cis isomers of the 1,2-disubstituted double bonds along the polymer backbone, further confirming high conversion of a monome r to the unsaturated polymer. Moreover, the resonance of the allylic carbon in the monomer spectrum at 33.6 ppm splits into two new signals (32.5 and 27.1 ppm) in the spectrum of polymer due to the trans and cis geometries around this carbon. The relative proportion of cis and trans carbons by 13C NMR show approximately 80% content of the later, which is in an agreement with previous reports on ADMET polymerization.52,53 The high content of the trans olefin in AMDET products is attributed to the most st able conformation of the metallacyclobutane intermediate.53 Figure 3-6. FT-IR spectra of 6sp3gl and poly6sp3gl Chemical structures of the monomer and th e polymer were also verified by FT-IR spectroscopy. For exam ple FT-IR spectra of 6sp3gl and poly6sp3gl shown in Figure 3-6 contain a strong band at 1121 cm-1 that corresponds to the as ymmetric stretch of the C-O-

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59 C ether bonds from the oxyethylene segment a nd is present in both the monomer and the polymer. Characteristic wavenumber bands that correspond to the vinyl group in the monomer are observed at 3080, 1642, 994 and 914 cm-1. These peaks were not observed in the poly6sp3gl instead a new sharp absorbance assigned to the trans carbon-carbon double bond appeared at 968 cm-1. Due to the low concentration of the cis conformation in the polymer, the expected band at 730-665 cm-1 was not detected. These results further demonstrate high conversion of monomer to corresponding polymer. 3.3.1.2 Thermal behavior of unsaturated polymers Thermal analysis of the family of alternating (AB)n microblock copolymers was performed by differential scanning calorime try (DSC). Detailed characteristics of thermal transitions for unsaturated polymers are summarized in Table 3-2. Values of glass transition temperatures (Tg) were taken at the mid-point of the transition and the melting transition temperatures (Tm) were taken as the temper ature at the peak of the melting transition in the second heating scan. Similarly, the crystallization temperature (Tc) was taken as the temperature at the peak of crystallization transition in the second cooling scans. The data was collected by scanning samples from -150 to 80 C at 10 C/min and reported from second heating a nd cooling scans. All polymers described below exhibit unique thermal properties. Th e combination of melti ng, crystallization, and glass transition, three phenom ena that are important with respect to the design and processing of polymeric materials, have been observed for this family of unsaturated (AB)n microblock copolymers.

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60 Table 3-2. Thermal analysis of the unsaturated polymers. DSC TGA (C)e Polymer Tg (C)a Cp (J/(g C) Tm (C)b Tc (C)c H (J/g) Tg/Tm d TN2 Tair poly3sp2gl -79.0 -0.78 242 250 poly3sp3gl -76.2 -0.83 245 245 poly3sp4gl -74.1 -0.88 -35.4 4.8 0.80 252 251 poly6sp3gl -75.0 -0.29 12.9 -12.4 53.7 0.69 231 235 poly6sp4gl -76.0 -0.33 13.3 -16.2 46.6 0.68 239 227 poly9sp2gl -50.4 -0.39 57.1 35.8 82.4 0.67 314 295 poly9sp3gl -55.2 -044 45.9 26.1 70.6 0.68 282 248 poly9sp4gl -56.4 -0.34 42.5 19.4 55.8 0.68 276 258 a) values taken from the mid-point; b) valu es assign to the top of the melt; c) values assign to the bottom of the recrystallization; d) calculated from obsolete temperatures; e) recorded at 5% total mass loss unde r nitrogen gas or air, 20 C/min The glass transition temperatures reported in Table 3-2 for poly3sp2gl poly3sp3gl and poly3sp4gl polymers were essentially identica l with the values published by Baker et al .124 for the same polymers obtained from ADMET polycondensation catalyzed by [Mo] (2) The actual DSC thermograms of unsaturat ed polymers are presented in Figures 3-7 – 3-9 and are grouped into three graphs base d on the number of methylene units in the polymer. Thermograms of poly3sp2gl and poly3sp3gl display glass transition temperatures at -79 and -76 C respectivel y, revealing the purely amorphous character of these polymers. In the case of poly3sp4gl after relaxation at -74 C a cold crystallization at -50 C is observed, followed by melti ng peak at -35 C. Comparison of Tg’s in the series of 3sp polymers shows their dependence on the length of the ethylene oxide segment. The glass transition values incr ease as the content of the ethylene oxide increases, a trend observe d previously by Faucher119 in a series of ethylene oxide polymers.

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61 The thermal behavior of polymers poly6sp3gl and poly6sp4gl (Figure 3-8) is basically the same. In the heating scan a low relaxation temperatur e can be seen at-75 and -76 C for poly6sp3gl and poly6sp4gl respectively, followed by a sharp melt at -13 C with the heats of fusion of 53.7 J/g for poly6sp3gl and of 46.6 J/g for poly6sp4gl Upon cooling both thermograms display sharp cr ystallization peaks at -12 and -16 C and both the enthalpy of melting and the enthalpy of recrystallization exhibit the same energy for both polymers. Moreover, similar H values for the melt and recrystallization suggest a similar crystal packing of these polymers. Analysis of thermograms for poly9sp3gl and poly9sp4gl exhibit similar trends as described above for the 6sp polymers. Heating scans reve al very weak glass transition temperatures at -55 and -56 C for poly9sp3gl and poly9sp4gl correspondingly, presumably due to the semicrystalline nature of these materials. Sharp melting peaks are present in both thermograms at 46 C for poly9sp3gl and 42 C for poly9sp4gl After repeated scanning, both the heat of fusion of the melt and the enthal py of recrystallization exhibit the same energy. Thermal analysis performed on poly9sp2gl showed relaxation at -50 C followed by a melt, cold crystalliz ation and another melt at 57 C and a single sharp recrystallization peak upon cooling scan at 35 C. Overall heats of fusion for the heating run and the cooling run are virtually identical varying only by 0.08 J/g. Similar to the series of 3sp polymers, dependence of Tg and Tm values on the number of ethylene oxide segments present in the repeat unit is evident.

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62 Figure 3-7. DSC traces of unsaturat ed 3sp microblock copolymers. Figure 3-8. DSC traces of unsaturat ed 6sp microblock copolymers.

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63 Figure 3-9. DSC traces of unsaturat ed 9sp microblock copolymers. However, reverse trends are obs erved when compared to the 3sp polymers, as the number of oxyethylene units increase the values of melting temperature and glass transition temperature decrease. The oxygen at oms of the ethylene oxide segment can be considered as irregularities in the carbon chai n of polyolefins. Thus short ethylene oxide segments and long hydrocarbon segments will contribute to higher melting points and higher relaxation temperat ures as observed for poly9sp2gl where there are only three oxygen atoms per repeat unit in the polymer. Hence, by increasing the content of the oxygen atoms in the polymers’ repeat unit (five oxygen atoms present in the poly9sp4gl ) decreases glass transition and me lting temperatures accordingly. As suggested by the Boyer-Beaman rule for nonsymmetrical crystalline polymers the ratio of Tg/Tm should be close to 2/3. Ta ble 3-2 shows the calculated Tg/Tm ratio

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64 values for the unsaturated polymers fa ll between 0.67 and 0.80, which is in close agreement with the Boyer-Beaman rule. 3.3.1.3 Thermal stability of unsaturated polymers The thermal-degradation behavior of unsat urated polymers has been investigated using thermo-gravimetric analysis (TGA). The analysis was performed for each polymer both in inert (nitrogen) and oxidative (air) atmospheres. The TGA experiments were conducted at a scan rate of 20 C/min fr om 50 to 800 C and summarized results are presented in Table 3-2. Figure 3-10. TGA traces of poly6sp4gl Figure 3-10 illustrates typical TGA curves for unsaturated polymers plotted as weight-loss versus temperature for poly6sp4gl (105) in both atmospheres. The polymer exhibits good thermal stability up to 250 C after which rapid decomposition follows. As shown in Figure 3-8 there is no signifi cant difference in thermal stability for poly6sp4gl in nitrogen and in air. Essentially complete volatilization of the sample is achieved at 460 C under both mediums. This ra pid and complete elimination of mass is

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65 indicative of the structural purity exhibited by these regular polymers. Moreover, due to the fact that these polymers completely decompose thermally in a linear fashion over a narrow temperature range implies that onl y one mechanism of decomposition, more likely ether breakdown, is responsible for their decomposition. 3.3.2 Polymerization of “Chain-Internal” Crosslinker 3sp2OMe To ensure metathesis compatibility th e monomer was homopolymerized in the presence of 1st generation Grubbs’ catalyst (4) The 1H NMR spectra for the monomer and resulting ADMET polymer ( poly3sp2OMe (109) ) are shown in Figure 3-11. Indeed, metathesis does occur and can be easily observed by the disappearance of both the internal and external olefin protons at 5.8 and 5.0 ppm, respectively. This unsaturated carbosilane has been previously synthesized by Church91 et al. during investigation of nucleophilic substitution on silicon-containing -dienes; however, 2nd generation Grubbs’ ruthenium complex (5) was used to promote ADMET polymerization. Figure 3-11. 1H NMR spectra of 3sp2OMe and poly3sp2OMe

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66 The presence of reactive groups in each repeat unit of the polymer makes the characterization and handling of polymer chal lenging. Hydrolytic sensitivity makes GPC analysis unavailable, instead 1H NMR end-group analysis wa s performed indicating a Mn of 45,000 g/mol, four times higher than previously reported.91 Differential scanning calorimetry was performed yielding in the same glass transition (Tg= -80C) as observed by Church et al 3.3.3 Synthesis and Characterization of “Latent Reactive” Copolymers Given the compatibility of monomers me ntioned in previous section and ADMET viability to produce high molecular weight uns aturated polymers, their copolymerization under bulk reaction conditions at mild temperatur es is relatively trivial. Our previous studies of carbosilane or carbosiloxane-based monomers75 have shown that their copolymerization yields completely random copolymers. Copolymerization of the glycol-based monomers with the “chain-int ernal” crosslinkers and/or “chain-end” crosslinker produced random linear copolymers as well. Three general formulations have been made where glycol-based monomers ha ve been copolymerized with 10% by weight of either “chain-internal” crosslinker (75) or (100) or with only “chain-end” crosslinker to yield endcapped oligomers with approximate degree of polymerization equal to five (DP~5), or with both “chain-internal” (5 % by weight) and “chain -end” (2.5% by mol) crosslinkers. Figure 3-12 shows gene ral structures of each composition. Figure 3-13 displays an example of the 1H NMR and 13C NMR spectra for copolymer 38 (147) Characteristic presence of the internal olefin signal at 5.34 ppm for all the polymers prepared by ADMET pol ymerization is visible in the 1H NMR spectrum. Three additional peaks are present in the 1H NMR spectrum of copolymer (147) when compared to the 1H NMR spectrum of poly9sp2gl i.e. at 0.1, 0.6, 3.5 ppm that

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67 corresponds to proton signals of Si-CH3, Si-CH2-, Si-OCH3 groups respectively. The comonomers feed ratio dictates the ratio of monomers present in the copolymer and can be verified by 1H NMR spectroscopy by relating signals of Si-CH3 groups either to SiCH2or CH2-CH2-Ogroups. O O Si Si OMe OMe OMe OMe Si Me OMe OMe Si Me MeO MeO 9 x x 3 3 9 nmO O Si Si Me MeO MeO Me OMe OMe 9 x x x 9n g g O O Si Si OMe OMe Me OMe OMe Si Me MeO MeO x 9 x x 3 3 9 n m g O O Si Si OMe OMe OMe OMe x 3 3g n m O O Si OMe OMe 3 x 3g n mcopolymer 1 (110) : g = 2; x = 3; 2 (111) : g = 3; x = 3; 3 (112) : g = 4; x = 3; 4 (113) : g = 3; x = 6; 5 (114) : g = 4; x = 6; 6 (115) : g = 2; x = 9; 7 (116) : g = 3; x = 9; 8 (117) : g = 4; x = 9;10% wt content 10% wt content n~5copolymer 9 (118) : g = 2; x = 3; 10 (119) : g = 3; x = 3; 11 (120) : g = 4; x = 3; 12 (121) : g = 3; x = 6; 13 (122) : g = 4; x = 6; 14 (123) : g = 2; x = 9; 15 (124) : g = 3; x = 9; 16 (125) : g = 4; x = 9;5% wt content 5% wt contentcopolymer 25 (134) : g = 2; x = 3; 26 (135) : g = 3; x = 3; 27 (136) : g = 4; x = 3; 28 (137) : g = 3; x = 6; 29 (138) : g = 4; x = 6; 30 (139) : g = 2; x = 9; 31 (140) : g = 3; x = 9; 32 (141) : g = 4; x = 9; copolymer 17 (126) : g = 2; x = 3; 18 (127) : g = 3; x = 3; 19 (128) : g = 4; x = 3; 20 (129) : g = 3; x = 6; 21 (130) : g = 4; x = 6; 22 (131) : g = 2; x = 9; 23 (132) : g = 3; x = 9; 24 (133) : g = 4; x = 9; copolymer 33 (142) : g = 2; x = 3; 34 (143) : g = 3; x = 3; 35 (144) : g = 4; x = 3; 36 (145) : g = 3; x = 6; 37 (146) : g = 4; x = 6; 38 (147) : g = 2; x = 9; 39 (148) : g = 3; x = 9; 40 (149) : g = 4; x = 9; Figure 3-12. Compositions of “latent reactive” unsaturated copolymers. 13C NMR spectroscopy further confirms form ation of copolymer by presence of the internal olefin carbons at 129.5-131.2 ppm. Howe ver, multiple signals are present in this

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68 region rather than only two signals ( trans and cis ) that are observed in the 13C NMR spectrum of homopolymers. Th ese multiple signals correspond to presence of additional linkages between different repeat units in the copolymer. Signals from Si-CH3 at -5.8 ppm, Si-CH2at 2.5 ppm, and Si-OCH3 at 50.3 ppm groups are also observed; however, the intensity of these peaks is low due to the low content of both “chain-internal” and “chain-end” crosslinkers in the copolymer. Figure 3-13. 1H (A) and 13C (B) NMR spectra of copolymer 38 ( 147 ).

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69 3.4 Preparation and Characterization of Thermosets It is well known fact that siliconalkoxy bonds as silicon-halide bonds are susceptible to hydrolysis leading to forma tion of silanol groups (Si-OH), which can undergo condensation at appropr iate conditions. In result a thermodynamically stable silicon-oxygen-silicon bond is formed and a bypr oduct such as alcohol or HX is released. Although good efficiency and availability of compounds containing the silicon-halide bond, due to formation of acids during cr osslinking process the alkoxy groups are preferred over the later. Th e process just described is well known as room-temperature vulcanization (RTV) and has b een used in sealant industry for over 30 years. This opportunity exists for copolymers shown in Fi gure 3-12 that contain chain-internal and chain-end crosslink sites. Consequently, wh en these copolymers are exposed to moisture the latent reactivity is triggered yielding in thermoset materials. The composition and short name assigned for simplicity are presented in Figure 3-14. The first attempt to produce thermoset was performed on xlink 39 whose composition with exception of la tent reactive chain-end cros slinker showed good material properties in previous study, as described in Chapter 2. An attempt was made to cast a film of copolymer 39 The polymer was dissolved in to luene, poured into a Teflon mold, and placed on the lab bench to trigger crosslinking. Unfortunately after one day the resultant film started to crack yielding after two days a very brittle material as shown in Figure 3-15.

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70 O O Si Si O O O O Si Me O O Si Me O O 9 x x 3 3 9 nm O O Si Si Me O O Me O O 9 x x x 9n g g O O Si Si O O Me O O Si Me O O x 9 x x 3 3 9 n m g O O Si Si O O O O x 3 3g n m O O Si O O 3 x 3g n mxlink 1 (150) : g = 2; x = 3; 2 (151) : g = 3; x = 3; 3 (152) : g = 4; x = 3; 4 (153) : g = 3; x = 6; 5 (154) : g = 4; x = 6; 6 (155) : g = 2; x = 9; 7 (156) : g = 3; x = 9; 8 (157) : g = 4; x = 9;10% wt content 10% wt content n~5xlink 9 (158) : g = 2; x = 3; 10 (159) : g = 3; x = 3; 11 (160) : g = 4; x = 3; 12 (161) : g = 3; x = 6; 13 (162) : g = 4; x = 6; 14 (163) : g = 2; x = 9; 15 (164) : g = 3; x = 9; 16 (165) : g = 4; x = 9;5% wt content 5% wt contentxlink 25 (174) : g = 2; x = 3; 26 (175) : g = 3; x = 3; 27 (176) : g = 4; x = 3; 28 (177) : g = 3; x = 6; 29 (178) : g = 4; x = 6; 30 (179) : g = 2; x = 9; 31 (180) : g = 3; x = 9; 32 (181) : g = 4; x = 9; xlink 17 (166) : g = 2; x = 3; 18 (167) : g = 3; x = 3; 19 (168) : g = 4; x = 3; 20 (169) : g = 3; x = 6; 21 (170) : g = 4; x = 6; 22 (171) : g = 2; x = 9; 23 (172) : g = 3; x = 9; 24 (173) : g = 4; x = 9; xlink 33 (182) : g = 2; x = 3; 34 (183) : g = 3; x = 3; 35 (184) : g = 4; x = 3; 36 (185) : g = 3; x = 6; 37 (186) : g = 4; x = 6; 38 (187) : g = 2; x = 9; 39 (188) : g = 3; x = 9; 40 (189) : g = 4; x = 9; Figure 3-14. Composition and structure of crosslinked materials. The formation of this brittle material can be justify by information obtained from DSC analysis of poly9sp3gl that showed semi-crystalline nature (Tm=46 C) of this polymer. This kinetic phenomenon, namely cr ystallization takes pl ace before chemical crosslinking occurs yielding in physical crosslinks. It is we ll known fact that crystallinity makes material strong, but it also makes it bri ttle. Thus we have decided to increase

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71 curing temperature to 55-65 C the temp erature above the melting point of 9sp homopolymers to allow latent crosslinking to take place before crystallization. To ensure the same curing conditions during crosslinking al l thermosets have been cast in the oven at the temperature mentioned above. Figure 3-15. Moisture cured xlink 39 at room temperature. 3.4.1 Thermal Behavior and De gradation of Thermosets The morphology of crosslinked materials was investigated by differential scanning calorimetry. Because of the incorporation of “chain-internal” crosslinkers the thermosets were expected to exhibit different mor phology than the corresponding homopolymers or copolymers. Figure 3-16 shows thermal transi tions of select thermoset together with corresponding homopolymer and copolymer. The expected changes in thermal beha vior of this series of homopolymer, copolymer and thermoset are observed, as illust rated in Figure 3-16. Presence of “chaininternal” crosslinker in the composition breaks sequence of poly6sp4gl repeat units making its structure irregular, therefore s uppressing the extent of crystallization. Previously observed melt at 13.3 C for poly6sp4gl drops down to -3 C for copolymer

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72 29 and to -6 C for xlink 29 In the case of xlink 29 the presence of chemical crosslinks limits mobility of the polymer chains to form highly ordered arrangements; as a result the extent of crystallization is suppressed even more. But not only decreasing changes in melting temperatures are observed. An incr ease in values of th e glass temperature transition is evident in the series of poly6sp4gl (Tg= -77 C), copolymer 29 (Tg= -76 C) and xlink 29 (Tg= -73 C); however, the changes are by far more discrete than for the melts. Figure 3-16. DSC curves of poly6sp4gl copolymer 29 and xlink 29 The thermal degradation behavior of thermo sets has been also investigated. Figure 3-17 and 3-18 shows traces of a few selected crosslinked materials in both an oxidative and inert atmosphere respectively as percenta ge weight loss versus temperature in the 50-

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73 800 C range. Good thermal stability for the se ries of thermosets presented in Figure 317 and 3-18 is observed where e ssentially zero percent weight is lost upon heating from 50-300 C, except for those based on 3sp glyc ols. The linear decomposition of these materials implies that only one mechanis m is responsible for their decomposition. Thermal stability of these selected ther mosets has been improved in both medium when compared with the TGA results fo r homopolymers, which is expected for crosslinked materials. Thermal analysis results for the remaini ng thermosets are collected in Appendix. Figure 3-17. TGA traces in an oxidative atmosphere.

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74 Figure 3-18. TGA traces in an inert atmosphere. 3.4.2 Mechanical Properties The mechanical properties of moisture cure d thermosets were examined. As shown in Figure 3-14 couple series of different co mposition networks were prepared and their stress/strain profiles were analyzed in regard of their composition; Table 3-3 summarizes data for these compositions. In order to gain insight into the effect of the relative chain-internal/chain-end/soft phase composition on mechanical properties a series of bicomponent (chain-internal/soft phase) thermosets were prepared and their pr operties investigated. Results from these tests and stress/strain curves for these bi component thermosets have been placed in appendix. A decrease in modulus (E) and tensil e strength (TS) is observed as the length of ethylene glycol increases in the series of thermosets with the same number of

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75 methylene groups. Figure 3-19a. Stress/strain curves. Figure 3-19b. Stress/strain curves.

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76 Figure 3-19c. Stress/strain curves.

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77Table 3-3. Physical properties of selected thermosets compositions. Tensile Strength (MPa) Modulus (MPa) Elongation (%) Tensile Strength (MPa) Modulus (MPa) Elongation (%) Tensile Strength (MPa) Modulus (MPa) Elongation (%) xlink 17 0.16 0.5 49 xlink 25 0.86 1.8 80 xlink 33 0.67 2.0 49 xlink 18 0.36 1.9 24 xlink 26 0.75 2.1 52 xlink 34 0.55 1.7 47 xlink 19 0.54 1.7 45 xlink 27 0.32 0.5 100 xlink 35 0.38 0.8 72 xlink 20 0.91 2.3 63 xlink 28 1.05 2.6 68 xlink 36 4.79 1.4 507 xlink 21 xlink 29 0.88 1.6 105 xlink 37 1.86 1.4 298 xlink 22 8.72 30.5 422 xlink 30 7.79 59.5 346 xlink 38 xlink 23 10.42 74.5 710 xlink 31 5.52 115.3 170 xlink 39 8.60 54.6 335 xlink 24 10.34 19.1 710 xlink 32 8.36 59.4 285 xlink 40 6.82 33.3 258

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78 A reversed trend is observed in the seri es of thermosets where the number of methylene groups increases and the length of oxyethylene units remains the same. As was shown above thermal properties of hom opolymers varies from totally amorphous to semicrystalline as the length of carbon chai ns increases. These crystalline regions are effective physical crosslinks that makes mate rial stronger but brittle and observed trends are typical for these kinds of structures. Moreover, these results once again confirmed that introducing chain-end cr osslinker evidently improves mechanical properties e.g. xlink 12 containing only chain-inte rnal crosslinker shows TS = 0.9 MPa and E= 4.3 MPa, while for tricomponent xlink 36 TS= 4.8 MPa and E= 1.8 MPa. Although there is an obvious decrease in the modulus, with value in the range typical for elastomers, the augmentation of tensile strength is eviden t and higher values ar e desired since it corresponds to the force at wh ich material fractures. Subsequently, a series of tricomponent networks were prepared and their structure/property relationship was investig ated. Ttricomponent materials shows similar trends to bicomponent thermosets as presen ted by the stress/str ain curves shown in Figures 3-19. Results obtained for series of xlink 22 xlink 23 and xlink 24 unequivocally show how small changes in th e composition such as one oxyethylene unit can produce materials with flexible plastic or elastic behavior. Thermosets that contain longer carbon chains between oxyethylene segments are tougher and shows typical plastic behavior, while the ones w ith shorter carbon chai ns reveal their true elastic nature. Figure 3-20 shows stress/strain curves of xlink 24 xlink 36 and xlink 37 with exceptionally good properties for elastomers when compared to other thermosets. Observed values of tensile st rength for these three materials range from 2 to 10 MPa,

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79 while elongation ranges from 300 to 700 %. Th e other thermosets show either elastic behavior with low elongation, or plastic behavior with plastic plateau in the stress/strain curves. In addition, fractured specimen of xlink 24 and xlink 36 presented in Figure 320 show good elastic recovery of these materi als. The 1 inch length of each specimen used in the test did not ch ange after the rapture. Figure 3-20. Stress/strain curves and picture of thermosets with good elastic properties. 3.5 Conclusions Family of oligo(oxyethylene) dienes monomers has been synthesized, characterized, and subjected to olefin metath esis polymerization. Ch aracterization of the resultant polymers revealed a wide spectru m of properties dependant on both the length of oxyethylene segments and also the lengt h of carbon chains in between them. Consequently, these monomers were copolymer ized to obtain targeted linear “latent reactive” elastomers, exposure to atmospheric mo isture triggered crosslinking that led to the formation of thermoset. Thermal analysis and mechanical testing were performed on crosslinked materials to asses their properties. Am ong fifty different compositions that were prepared many of them revealed purely elastic beha vior while some exhibit propert ies of flexible plastics.

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80 These thermoset materials may be suitabl e for biological app lications such as semipermeable membranes or can be used in sealant or adhesive industry. 3.6 Experimental Methods 3.6.1 Materials All reactions were conducted in flamedried glassware under an argon atmosphere unless otherwise noted. Reagents were purchas ed from Fischer or Aldrich and were used as received unless otherwise not ed. The first-generation Gru bbs’ catalyst used in this study was graciously provided by Materia, Inc. 5-bromo-1-pentene, 8-bromo-1-octene, 1-undecene-11-ol, 11-chloro-1-undecene, 11-bromo-1-undecene were synthesized according to literature procedures.137 3.6.2 Instrumentation and Analysis All 1H NMR (300 MHz) and 13C NMR (75 MHz) spectra were recorded on a Varian Associates Mercury 300 spec trometer. Chemical shifts for 1H and 13C NMR were referenced to residual signals from CDCl3 (1H = 7.26 ppm and 13C = 77.00 ppm) with 0.03% v/v TMS as an internal reference. Reaction conversions and relative purity of crude products were monitored by thin la yer chromatography (TLC) performed on EMD silica gel coated (250 m thickness) glass plates and 1H NMR. Developed TLC plates were stained with iodine abso rbed on silica or vanillin solu tion (5 wt% in 50mL ethanol with 2mL H2SO4) to produce a visible signature. Low and high-resolution mass spectral (LRMS and HRMS) data were obtained on a Finnegan 4500 gas chromatograph/mass spectrometer using the chemi cal ionization (EI) mode. Fourier transform infrared (FT-IR) sp ectroscopy was performed using a Bio-Rad FTS-40A spectrometer. Monomer was prep ared by droplet depos ition and sandwiched

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81 between two KBr salt plates. Unsaturated polymer samples were prepared by solution casting a thin film from tetrahydr ofuran onto a KBr salt plate. Differential scanning calorimetry (DSC) analysis was performed using a TA Instruments Q1000 series equipped with a controlled cooling accessory (LNCS) at a heating rate of 10 C/min. Calibrations were made using indium and freshly distilled n octane as the standards for peak temperature transitions and indium for the enthalpy standard. All samples were prepared in herm etically sealed pans (6-15 mg/sample) and were run using an empty pan as a reference. Thermogravimetric analysis (TGA) was pe rformed either on a Perkin-Elmer TGA7 at 20 C/min or on TA Instruments T GA Q500 Series using dynamic scans under an inert (nitrogen) and oxidative (air) atmospheres. Gel permeation chromatography (GPC) was performed at 40 C using a Waters Associates GPCV2000 liquid chromatography sy stem with an internal differential refractive index detector (D RI) and two Waters Styragel HR-5E columns (10 microns PD, 7.8 mm ID, 300 mm length) in HPLC grade tetrahydrofuran as the mobile phase at a flow rate of 1.0 mL/minute. Injectio ns were made at 0.05-0.07 % w/v sample concentration using a 220.5 l injection volume. Retention times were calibrated against narrow molecular weight polystyrene standa rds (Polymer Laboratories; Amherst, MA) selected to produce Mp and Mw values below and above the expected copolymer molecular weight. Mechanical tests were performed at the Univ ersity of Florida facility by courtesy of Dr. Brenan’s research group, using an Inst ron model 1122 load frame upgraded with an

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82 MTS ReNew system running MTS TestWorks 4 software and a 500 g load cell for the experiments. Tensile specimens were cut from the cured freestanding films using an ASTM D1822-68 type L dogbone die. Each specimen was individually measured to account for thickness variability in calcula tions. The grip separation for the samples was set at 25.4 mm and the width of the testing portion was se t at 3.1 mm. Tensile measurements were made according to ASTM D412-97 at rate of 2 inch/min. 3.6.3 Monomer Synthesis Monomer 1 and 2 were synthesized according to a literature procedure75. 3.6.3.1 Synthesis of di(oxyethylene) -di-4-pentenyl ether (3sp2gl) (86) Monomer 3sp2gl was synthesized according to th e procedure described in Chapter 2 for monomer 83 Monomer was purified using colu mn chromatography (1:1 ethyl acetate:hexane), followed by vacuum distil lation over calcium hydride yielded 9.6 g (58.7% yield) colorless liquid. The follo wing spectral properties were observed: 1H NMR (CDCl3): = 1.64 (m, br, 4H), 2.10 (m, br, 4H), 3.47 (m, br, 4H), 3.59 (m, br, 8H), 4.95 (m, br, 4H), 5.77 (m, br, 2H). 13C NMR (CDCl3): = 28.82, 30.23, 70.15, 70.66, 70.71, 114.64, 138.30. FT-IR: (cm-1) 3077, 2938, 2865, 1641, 1448, 1415, 1350, 1323, 1296, 1247, 1120, 993, 911, 873. MS (70 eV): m/z = 243.1957 (M+H)+. (C14H26O3) (242.35): Calcd. C 69.38, H 10.81; Found C 69.23, H 10.89. 3.6.3.2 Synthesis of tri(oxyethylene) -di-4-pentenyl ether (3sp3gl) (87) Monomer 3sp3gl was prepare and purify using the same methodology as described for 3sp2gl yielded 8.5 g (65% yield) of colorl ess liquid. The following spectral properties were observed: 1H NMR (CDCl3): = 1.63 (m, br, H4), 2.07 (m, br, H4), 3.37 (m, br, H4), 3.57 (m, br, H12), 4.87 (m, br, H4), 5.74 (m, br, H2). 13C NMR (CDCl3): =

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83 28.77, 30.22, 70.12, 70.62, 70.70, 114.65, 138.28. FT-IR: (cm-1) 3077, 2865, 1641, 1449, 1416, 1350, 1323, 1296, 1248, 1119, 993, 912, 872. MS (70 eV): m/z = 287.2230 (M+H)+. (C16H30O4) (286.40): Calcd. C 67.10, H 10.56; Found C 67.05, H 10.61. 3.6.3.3 Synthesis of tetra(oxyethylene) -di-4-pentenyl ether (3sp4gl) (88) Monomer 3sp4gl was prepare and purify using the same methodology as described for 3sp2gl yielded 10.5 g (72% yield) of colo rless liquid. The following spectral properties were observed: 1H NMR (CDCl3): = 1.64 (m, br, H4), 2.07 (m, br, H4), 3.43 (m, br, H4), 3.62 (m, br, H16), 4.93 (m, br, H4), 5.74 (m, br, H2). 13C NMR (CDCl3): = 28.78, 30.22, 70.10, 70.61, 70.69, 114.65, 138.28. FT-IR: (cm-1) 3076, 2866, 1640, 1449, 1416, 1350, 1323, 1296, 1248, 1118, 993, 912, 871. MS (70 eV): m/z = 330.2395 (M)+. (C18H34O5) (330.44): Calcd. C 65.42, H 10.37; Found C 65.12, H 10.39. 3.6.3.4 Synthesis of tri(oxyethylene) -di-7-octenyl ether (6sp3gl) (89) Monomer 6sp3gl was prepare and purify using the same methodology as described for 3sp2gl yielded 9.2 g (55% yield) of colorl ess liquid. The following spectral properties were observed: 1H NMR (CDCl3): = 1.30 (m, br, H12), 1.51 (m, br, H4), 1.98 (m, br, H4), 3.40 (m, br, H4), 3.53 (m, br, H12), 4.88 (m, br, H4), 5.70 (m, br, H2). 13C NMR (CDCl3): = 25.87, 28.77, 28.86, 29.51, 33.63, 70.00, 70.55, 71.37, 114.10, 138.96. FT-IR: (cm-1) 3076, 2929, 2858, 1640, 1458, 1350, 1323, 1297, 1248, 1120, 995, 909, 726. MS (70 eV): m/z = 371.3168 (M+H)+. (C22H42O4) (370.56): Calcd. C 71.31, H 11.42; Found C 71.33, H 11.53. 3.6.3.5 Synthesis of tetra(oxyethylene) -di-7-octenyl ether (6sp4gl) (90) Monomer 6sp4gl was prepare and purify using the same methodology as described for 3sp2gl yielded 6.7 g (58% yield) of colorl ess liquid. The following spectral properties were observed: 1H NMR (CDCl3): = 1.31 (m, br, H12), 1.54 (m, br, H4), 1.98

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84 (m, br, H4), 3.40 (m, br, H4), 3.55 (m, br, H12), 4.89 (m, br, H4), 5.72 (m, br, H2). 13C NMR (CDCl3): = 25.90, 28.81, 28.90, 29.54, 33.67, 70.03, 70.57, 70.59, 71.42, 114.14, 139.02. FT-IR: (cm-1) 3076, 2929, 2865, 1640, 1457, 1350, 1297, 1249, 1119, 995, 910, 877. MS (70 eV): m/z = 415.3434 (M+H)+. (C24H46O5) (414.61): Calcd. C 69.52, H 11.18; Found C 69.46, H 11.19. 3.6.3.6 Synthesis of di(oxyethylene) -di-10-undecenyl ether (9sp2gl) (91) Sodium hydride was placed in A flam e-dried, Ar-purged, th ree-necked 500 mL round-bottom flask equipped with a stir bar, condenser, and an additional funnel was charged with (7.0 g, 0.017 mo l) di-ethylene glycol -ditosyl, sodium hydride (1.8 g, 0.44 mol, 60% dispersion) and anhydrous dimethylformamide (DMF) (50 ml). The reaction mixture was cooled down to 0 C and 6.3 g (0.037 mol) of 10-undecene -1-ol was added slowly over 20 minutes under consta nt stirring. After 12 hours of stirring at 0 C the mixture was warmed to room temper ature and then was quenched with successive additions of water (50mL) and 6N HCl (100 mL) over thirty minutes. The organic phase was collected in two ether (150mL) washings, washed with brine (2 x150mL), and dried with MgSO4. Filtration and solvent removal afford ed slightly yellow oil. Purification using column chromatography (1:4 ethyl acetate:hexanes) followed by vacuum distillation over calcium hydride afforded 4.7 g (68% yield) of colorless liquid. The following spectral properties were observed: 1H NMR (CDCl3): = 1.16 (m, br, H24), 1.53 (m, br, H4), 1.96 (m, br, H4), 3.40 (m, br, H4), 3.57 (m, br, H12), 4.87 (m, br, H4), 5.72 (m, br, H2). 13C NMR (CDCl3): = 26.07, 28.91, 29.10, 29.41, 29.45, 29.51, 29.64, 33.77, 70.08, 70.65, 71.50, 114.06, 139.16. FT-IR: (cm-1) 3077, 2924, 2855, 1641, 1446, 1415, 1351, 1298, 1248, 1121, 993, 909, 722. MS (70 eV): m/z = 411.3818 (M+). (C28H55O4) (410.67): Calcd. C 76.04, H 12.27; Found C 76.02, H 12.31.

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85 3.6.3.7 Synthesis of tri(oxyethylene) -di-10-undecenyl ether (9sp3gl) (92) Monomer 9sp3gl was prepare and purify using the same methodology as described for 9sp2gl yielded 5.7 g (78% yield) of colorl ess liquid. The following spectral properties were observed: 1H NMR (CDCl3): = 1.25 (m, br, H24), 1.60 (m, br, H4), 2.10 (m, br, H4), 3.53 (m, br, H4), 3.60 (m, br, H12), 4.95 (m, br, H4), 5.85 (m, br, H2). 13C NMR (CDCl3): = 26.10, 28.94, 29.14, 29.45, 29.49, 29.51, 29.55, 29.62, 29.66, 33.81, 70.04, 70.64, 71.53, 114.06, 139.18. FT-IR: (cm-1) 3076, 2926, 2855, 1640, 1464, 1350, 1298, 1249, 1120, 993, 909. MS (70 eV): m/z = 455.4121 (M+). (C28H55O4) (454.72): Calcd. C 73.96, H 11.97; Found C 73.91, H 12.18. 3.6.3.8 Synthesis of tetra(oxyethylene) -di-10-undecenyl ether (9sp4gl) (93) Monomer 9sp4gl was prepare and purify using the same methodology as described for 9sp2gl yielded 6.5 g (73% yield) of colorl ess liquid. The following spectral properties were observed: 1H NMR (CDCl3): = 1.27 (m, br, H24), 1.54 (m, br, H4), 2.02 (m, br, H4), 3.41 (m, br, H4), 3.57 (m, br, H12), 4.90 (m, br, H4), 5.74 (m, br, H2). 13C NMR (CDCl3): = 26.07, 28.91, 29.10, 29.41, 29.45, 29.51, 29.63, 33.77, 70.06, 70.60, 71.63, 71.51, 114.06, 139.17. FT-IR: (cm-1) 3076, 2926, 2855, 1640, 1464, 1350, 1298, 1249, 1120, 993, 909, 722. MS (70 eV): m/z = 499.4373 (M+). (C28H55O4) (498.78): Calcd. C 72.24, H 11.72; Found C 72.40, H 11.80. 3.6.3.9 Synthesis of 10-undecenyldimeth oxymethylsilane 9sp2OMe (97) A 250 mL three-necked round bottom flask equipped with an additional funnel, condenser, and stir bar was flame-dried unde r vacuum, and then flushed with argon. Magnesium turnings (1.1 g, 0.044 mol) and dr y diethyl ether (50 mL) were added. A solution of 11-chloro-1-undecene (7.5 g, 0.040 mo l) in 50 mL of diethyl ether was added drop-wise to maintain consta nt reflux. After addition, th e mixture was refluxed for an

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86 additional hour, followed by cooling to room temperature. Upon cooling, the mixture was filtered via canula into the addition funne l attached to another 250 mL three-necked round bottom flask equipped with condens er, and stir bar. A solution of trimethoxymethylsilane (7.2 g, 0.060 mol) in dried Et2O was added followed by dropwise addition of the Grignard reagent. Th e solution was refluxed for 2 hours, cooled, and the product was diluted with 50 mL of dry pentane and filtered via cannula. The combined organics were evaporated under re duced pressure yieldi ng 8.2 g of a clear, colorless liquid. The crude product was purif ied by vacuum distillation over calcium hydride. Monomer 97 was collected in 80% and the following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.1 (s, 3H), 0.6 (t, 2H), 1.27 (m, br, 14H), 2.03 (m, br, 2H), 3.51 (s, 6H), 4.9 (m, br, 2H), 5.7 (m, br, 1H), 13C NMR (CDCl3): (ppm) -5.80, 13.03, 22.68, 28.94, 29.13, 29.29, 29.47, 29.51, 33.27, 33.82, 50.14, 114.08, 139.26; EI/HRMS: [M+H]+ calcd. for C14H31SiO2: 259.2093, found: 259.2103; Elemental analysis calcd. for C14H31SiO2: 65.06 C, 11.70 H; found: 64.86 C, 11.75 H. 3.6.3.10 Synthesis of di(4-pentenyl)dimethoxysilane 3sp2OMe (100) A 250 mL three-necked round bottom flask equipped with an additional funnel, condenser, and stir bar was flame-dried unde r vacuum, and then flushed with argon. Magnesium turnings (2.1 g, 0.087 mol) and dr y diethyl ether (50 mL) were added. A solution of 5-bromo-1-pentene (11.8 g, 0.080 mol) in 50 mL of diethyl ether was added drop wise to maintain consta nt reflux. After addition, th e mixture was refluxed for an additional hour, followed by cooling to room temperature. Upon cooling, the mixture was filtered via canula into the addition funne l attached to another 250 mL three-necked round bottom flask equipped with condens er, and stir bar. A solution of tetramethylorthosilicate ( 5.44 g, 0.040 mol) in dried Et2O was added followed by drop-

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87 wise addition of the Grignard reagent. Th e solution was refluxed for 2 hours, cooled, and the product was diluted with 50 mL of dry pentane and filtered via cannula. The combined organics were evaporated under re duced pressure yieldi ng 5.5 g of a clear, colorless liquid. The crude product was purif ied by vacuum distillation over calcium hydride. Monomer 100 was collected in 78% and the following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.6 (s, 4H), 1.45 (m, br, 4H), 2.05 (m, br, 4H), 3.55 (s, 6H), 5.0 (m, br, 4H), 5.8 (m, br, 2H), 13C NMR (CDCl3): (ppm) 11.61, 22.36, 37.51, 50.55, 115.01, 138.81; EI/HRMS: [M-C5H9]+ calcd. for C12H24SiO2: 181.1412, found: 181.1412; Elemental analysis Calcd. for C16H30Si: 63.14 C, 10.59 H; found: 63.10 C, 10.69 H. 3.6.4 General Metathesis Conditions All monomers used in polymerization were distilled from CaH2 and degassed prior to polymerization. All glassware was thor oughly cleaned and dried under vacuum before use. The reactions were initiated in the bulk under an argon-filled glove box by placing the appropriate amount of monomer or monomers in 50-mL round-bottom flasks equipped with a magnetic Teflon™ stir bar followed by 1st Generation Grubbs’ catalyst [Ru=C] (4) and slowly stirred for 2 minutes. Th e monomer-to-catalyst ratios typically used were 250 : 1. In all cases of copolym erization all reactant were stirred before catalyst addition to yield hom ogenous mixture. The flasks were then fitted with an adapter equipped with a Teflon™ vacuum valv e, which after were sealed and removed from the glove box and placed immediately on the vacuum line. Slow exposure to the moderate vacuum yielded in slow bubbling of ethylene. After stirring for couple minutes the flasks were submerged into an oil bath at 50 C until the viscosity increased and stirring continued for 72 h.

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88 3.6.4.1 Synthesis of poly3sp2gl The monomer was polymerized using the above procedure. Monomer 86 (0.51 g, 2.06 mmol) was added to the reactio n tube charged with Grubbs’ 1st generation catalyst (6.80 mg, 8.25x10-6 mol). The reaction tube was seal ed using a Kontes Teflon valve and placed under an intermediate vacuum until the mixture became viscous. The reaction flask was then placed in a 40 C oil bath a nd high vacuum (<0.01 mm Hg) was applied. The temperature was gradually raised to 55 C over 72 hours. After three days, the polymerization was quenched via dissolution in toluene and exposed to air. The following properties were observed: 1H NMR (CDCl3): = 1.57 (m, br, H4), 2.01 (m, br, H4), 3.41 (m, br, H4), 3.56 (m, br, H12), 5.33 (br, H2); 13C NMR (CDCl3): = 23.64, 28.97, 29.40, 29.52, 70.07, 70.58, 70.78, 129.55, 129.97. GPC data (THF vs. polystyrene standards): Mn = 35 766 g/mol; PDI ( Mw/Mn) = 1.77. DSC Results: Tg (glass transition) = -79 C, Cp = -0.78 J/g C 3.6.4.2 Synthesis of poly3sp3gl Monomer 87 (0.51 g, 1.74 mmol) was added to th e reaction tube charged with Grubbs’ 1st generation catalyst (5.72 mg, 6.96x10-6 mol). The following properties were observed: 1H NMR (CDCl3): = 1.59 (m, br, H4), 2.01 (m, br, H4), 3.40 (m, br, H4), 3.55 (m, br, H12), 5.33 (br, H2); 13C NMR (CDCl3): = 23.64, 28.97, 29.40, 29.62, 70.04, 70.56, 70.78, 129.54, 129.96. GPC data (THF vs. polystyrene standards): Mn = 34 565 g/mol; PDI ( Mw/Mn) = 1.89. DSC Results: Tg (glass transiti on) = -76 C, Cp = -0.83 J/g C 3.6.4.3 Synthesis of poly3sp4gl Monomer 88 (0.51 g, 1.51 mmol) was added to th e reaction tube charged with Grubbs’ 1st generation catalyst (5.00 mg, 6.05x10-6 mol). The following properties were

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89 observed: 1H NMR (CDCl3): = 1.56 (m, br, H4), 2.01 (m, br, H4), 3.40 (m, br, H4), 3.55 (m, br, H16), 5.35 (br, H2); 13C NMR (CDCl3): = 23.67, 28.98, 29.44, 29.56, 32.31, 32.94, 70.07, 70.58, 70.79, 129.56, 129.98. GPC data (THF vs. polystyrene standards): Mn = 34 890 g/mol; PDI ( Mw/Mn) = 1.91. DSC Results: Tg (glass transitio n) = -74 C, Cp = -0.88 J/g C; Tm (melting peak) = -35.4 C, hm = 4.8 J/g; 3.6.4.4 Synthesis of poly6sp3gl The following properties were observed: 1H NMR (CDCl3): = 1.30 (m, br, H12), 1.54 (m, br, H4), 1.95 (m, br, H4), 3.41 (m, br, H4), 3.56 (m, br, H12), 5.31 (br, H2); 13C NMR (CDCl3): = 25.96, 26.02, 26.07, 27.17, 29.01, 29.16, 29.50, 29.59, 29.62, 29.71, 32.52, 70.06, 70.64, 70.51, 129.82, 130.29, 130.35, 130.38. GPC data (THF vs. polystyrene standards): Mn = 36 193 g/mol; PDI ( Mw/Mn) = 1.74. DSC Results: Tg (glass transition) = -75 C, Cp = -0.29 J/g C; Tm (melting peak) = 12.9 C, hm = 53.7 J/g; Recrystallization Tc (recrystallization peak) = -12.4 C, hc = 41.21 J/g 3.6.4.5 Synthesis of poly6sp4gl The following properties were observed: 1H NMR (CDCl3): = 1.29 (m, br, H12), 1.54 (m, br, H4), 1.95 (m, br, H4), 3.40 (m, br, H4), 3.56 (m, br, H12), 5.32 (br, H2); 13C NMR (CDCl3): = 25.94, 26.01, 27.16, 28.99, 29.08, 29.14, 29.47, 29.57, 29.60, 29.69, 32.12, 32.50, 70.05, 70.59, 70.62, 71.49, 129.80, 130.27. GPC data (THF vs. polystyrene standards): Mn = 30 734 g/mol; PDI ( Mw/Mn) = 1.60. DSC Results: Tg (glass transition) = -76 C, Cp = -0.33 J/g C; Tm (melting peak) = 13.3 C, hm = 46.6 J/g; Recrystallization Tc (recrystallizati on peak) = -16.2 C, hc = 44.54 J/g 3.6.4.6 Synthesis of poly9sp2gl The following properties were observed: 1H NMR (CDCl3): = 1.26 (m, br, 24H), 1.54 (m, br, 4H), 1.96 (m, br, 4H), 3.41 (m, br 4H), 3.57 (m, br, 8H), 5.33 (br, 2H); 13C

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90 NMR (CDCl3): = 26.09, 26.19, 27.21, 28.99, 29.13, 29.17, 29.26, 29.31, 29.34, 29.37, 29.46, 29.49, 29.65, 29.77, 32.19, 32.60, 70.07, 70.65, 71.53, 129.85, 130.31. GPC data (THF vs. polystyrene standards): Mn = 51 750 g/mol; PDI ( Mw/Mn) = 2.06. DSC Results: Tg (glass transition) = -50 C, Cp = -0.39 J/g C; Tm (melting peak) = 57.1 C, hm = 82.4 J/g; Recrystallization Tc (recrystallization peak) = 35.8 C, hc = 82.4 J/g 3.6.4.7 Synthesis of poly9sp3gl The following properties were observed: 1H NMR (CDCl3): = 1.26 (m, br, 24H), 1.54 (m, br, 4H), 1.95 (m, br, 4H), 3.41 (m, br 4H), 3.56 (m, br, 12H), 5.31 (br, 2H); 13C NMR (CDCl3): = 26.09, 27.21, 29.13, 29.18, 29.31, 29.47, 29.49, 29.57, 29.66, 29.77, 32.60, 70.06, 70.62, 71.53, 129.84, 130.31. GPC data (THF vs. polystyrene standards): Mn = 40 103 g/mol; PDI ( Mw/Mn) = 1.89. DSC Results: Tg (glass transitio n) = -55 C, Cp = -0.44 J/g C; Tm (melting peak) = 45.9 C, hm = 70.6 J/g; Recrystallization Tc (recrystallization peak) = 26.1 C, hc = 68.3 J/g 3.6.4.8 Synthesis of poly9sp4gl The following properties were observed: 1H NMR (CDCl3): = 1.26 (m, br, 24H), 1.54 (m, br, 4H), 1.95 (m, br, 4H), 3.41 (m, br 4H), 3.57 (m, br, 16H), 5.36 (br, 2H); 13C NMR (CDCl3): = 26.01, 26.07, 27.19, 28.46, 29.13, 29.16, 29.22, 29.28, 29.32, 29.45, 29.47, 29.55, 29.59, 29.63, 29.75, 32.25, 32.58, 70.03, 70.58, 71.61, 70.68, 70.70, 71.51, 129.83, 130.45. GPC data (THF vs. polystyrene standards): Mn = 46 840 g/mol; PDI ( Mw/Mn) = 2.06. DSC Results: Tg (glass transitio n) = -56 C, Cp = -0.34 J/g C; Tm (melting peak) = 42.5 C, hm = 55.8 J/g; Recrystallization Tc (recrystallization peak) = 19.4 C, hc = 55.6 J/g

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91 3.6.5 Preparation of Copolymers and Thermosets “Latent reactive” copolymers have been synthesized according to general metathesis conditions described in section 3.6.4 by mixing appropriate monomers. Five general formulations have been made. First, two dicomponent copolymers we re prepared by mixing appropriate oligo(oxyethylene) diene monomer (1.3 g) with 0.065 g of either 3sp2OMe (100) or 3sp4OMe (75) chain-internal crosslinker. Second, endcapped oligomers were synthe sized by mixing 1.3 g of proper glycolbased diene monomer with end9sp2OMe (97) The amount of the endcapper 97 was calculated in the fashion to obtain an appropriate oligomer with DP~5. Third, two tricomponent compositions were prepared by mixing 1.3 g of oligo(oxyethylene) diene, 0.065 g of either 3sp2OMe or 3sp4OMe and end9sp2OMe In this cases the amount of 97 was calculated to be approximately equal to 2.5% by mol of oligo(oxyethylene) diene. Characteristic shifts were observed: 1H NMR (CDCl3): (ppm) = 0.55-0.60 [m, (CH2-Si)], 1.26 [m, br, (CH2-)], 1.54 [m, br, ([CH2CH2O]nCH2CH2-)], 1.95 [m, br, (CH=CHCH2), 3.41 [m, br, ([CH2CH2O]nCH2-CH2-)], 3.48 [s, (Si-O CH3)], 3.57 [m, br, ([ CH2CH2O]n-CH2-CH2-)], 5.36 [br, (CH = CH -)]; 13C NMR (CDCl3): (ppm) = -5.8 [Si(OCH3)2CH3], 2.55 [-SiCH2CH2-Si], 10.4-13.2 [-CH2CH2-Si], 21.9-23.4 [CH2-CH2Si], 26.1 [(CH2CH2O)n-CH2-CH2CH2-)], 27.1 [ trans -CH=CHCH2-(CH2)n], 28.9-29.7 [CH=CH-CH2-( CH2)n-CH2], 32.5 [ cis -CH=CHCH2-(CH2)n], 37.2 [-CH=CHCH2(CH2)2-Si], 50.3 [Si-O CH3] 70.03-71.61 [ CH2CH2O]n, 129.83-130.45 [ cis & trans CH2= CH2-].

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92 Films of thermosets have been prepared by dissolving copolymers in dry toluene (7 mL) and cast onto a poly(tetrafluoroethylene) mold. The mold was then placed along with 10 mL of deionized water in the oven at 55 C and left to cure for 8 hours. Obtained films of crosslinked materials were then sectioned for subsequent characterization.

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93 CHAPTER 4 SYNTHESIS AND CHARACTERIZATION OF CARBOSILOXANE/CARBOSILANE COPOLYMERS AND THERMOSETS 4.1 Introduction Polysiloxanes, mostly known as silicones, are by far the most important group of organosilicon polymers. Polysiloxanes’ bac kbone consists of an alternating chain of silicon and oxygen atoms, where two organic gr oups are attached to the silicon atoms. The nature of these substituents dictates the physical and chemical properties of the resulting polymer. Modification of the si licone backbone with these groups offers unlimited possibilities for their use as specia lty polymers or as modifiers for carbonbased polymers.1,4,139-141 Silicones, in particular polydimethylsil oxanes (PDMS), are the most popular and most characterized organosilicon polymer. They exhibit unique properties such as: high hydrophobicity, thermal and oxidative stability, electrical resistance, low glass transition temperature, low environmental toxicity, gas permeability, antiadhesive properties and etc3,142-145. Differences in properties between carbon-based polymers and organosilicon based polymers arise from carbon and silicon differences at the molecular level as discussed in Chapter 1. The physical propert ies of polysiloxanes result from the chain flexibility that arises from the length of th e Si-O bond along with the lack of substituents on every atom in the backbone. This results in a large angle of the Si-O-Si (145) and OSi-O (110) linkages1,4. Long bonds between atoms cause the activation energy of bond rotation along the siloxane bond in PDMS to be practically equal zero. Consequently,

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94 this free rotation allows for the orientati on of alkyl groups on the polymer surface making surface low in energy and chemically inert. However, despite the numerous unique properties that polyorg anosiloxanes can offer, as those mentioned above, their relative mechanical performance is weak (TS~ 0.34 MPa)146. Addition of fillers is desired in order to improve the overall phys ical properties of siloxane el astomers that can results in a 40 times increase in tensile strength. Over 30 years ago, these distinctive and ex traordinary properties of silicones were recognized and introduced in sealants formulation. Silicone-based sealants exhibit prolonged durability in harsh environments, ther efore they are preferred over polyethers, polyurethanes and acrylic based sealants. However as in the case of glycol-based sealants described in chapter 3, the presence of fillers, plasticizers, and a curing catalyst to obtain a room temperature cu ring composition is required. In this chapter the attempt to synthe size filler-free carbosilane/carbosiloxane elastomers is presented. The synthesis and characterization of mono mers used in this study as well as their polymeri zation is described. Conse quently, their preparation and mechanical testing results of th ermoset elastomers are reported. 4.2 Monomer Synthesis Since there are no known organosilicon com pounds that naturally occur, several processes have been developed for the fo rmation of silicon-carbon bond. There are two general synthetic approaches: the su bstitution method and the direct method.7 The first method involves silicon halide or ester whos e substituents are successively replaced by an organometallic compound. In the sec ond method, elemental silicon reacts with hydrocarbon halide under certain conditions to produce a mixture of organosilicon halides.

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95 Kipping’s147 and Dilthey’s148 pioneering work in the preparation of organic derivatives of silicon tetrachloride using Gri gnard chemistry became one of the most and widely used method in preparation of orga nosilicon compounds. Another effective and frequently used mode of synthesis for organos ilicon compounds is alkyl lithium reagents. However, the main drawback of these two r eactions is the multiple alkylation of silicon, which leads to the mixture of multiple alkyl ated compounds. Purifi cation and separation of these products can be a very challenging task. An attempt was made to synthesize a family of siloxane-based dienes, similar to glycol-b ased monomers described in previous chapter, using the Grignard chemis try. Unfortunately traces of products from multiple substitutions along with desired product were detected. Mo reover, the use of column chromatography and vacuum distil lation to separate and purify the product diene was unsuccessful. HSi O Si O Si H 2+ [Pt] toluene Si O Si O Si 4 4 4sp3Si (192) xs [Pt] = Karstedt's catalyst (191) (190) Si O Si Si O Si Pt Pt Si O Si Figure 4-1. Synthesis of siloxane-based dienes via hydrosilylation. Our focus then turned to hydrosilylation, wh ich is described as the addition reaction of Si-H across a bond. It is a well known and impor tant technique for making siliconcarbon bonds that are widely used commercially and in the laboratory. This process may be initiated by radical or, more often by transiti on metal catalysis. We decided to attempt

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96 synthesis of siloxane-based dienes using this technique. As was shown in previous studies by Smith et al ., longer siloxane linkages or l onger alkenyl appendages within monomers are required in order to suppress ring-closing metathesis.73 The reaction of hydrogen terminated trisiloxane (190) with an excess of 1,5 hexadiene (191) in the presence of Karstedt’s catalyst resulted in desired product, Figure 4-1. The reaction is fast and efficient in giving spectroscopically pure monomer after removing the excess 1,5 hexadiene (191) and toluene by rotavap. It is imperati ve to have an excess of the diene relative to the amount of Si-H bonds in order to inhi bit polymerization, as reported by Smith et al Only 2.5 eq. of (191) leads to the formation of the oligomeric product73. Si O Si O Si 6 6 Si O Si O Si 4 4 Si O Si O Si 6 O Si 6 Si O Si O Si 4 O Si 4 Si O Si 4 4 4sp2Si (76) 4sp3Si (192) 4sp4Si (193) 6sp3Si (194) 6sp4Si (195) Figure 4-2. Siloxane-based diene monomers. Figure 4-2 shows a family of siloxane-based dienes with different lengths of siloxane and alkenyl chains th at were successfully synthesi zed via hydrosilylation. Once again, the abbreviated nomencla ture was used instead of the full names of the monomers as shown in Figure 4-2. Similar to the glycol-based monomers, the first number corresponds to the number of methylene units (“ sp ”) between silicon a nd the vinyl group; the second number corresponds to the number of silicon atoms present in siloxane unit

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97 (“ Si ”). Consequently, for the polymers, “ poly ” followed by the monomer abbreviation is used. Product synthesis, workup, and purifi cation via column chromatography was followed by vacuum distillation over calci um hydride to yield analytically pure monomers, which were stored in thr in ert atmosphere of a glove box. Common spectroscopic methods such as 1H NMR, 13C NMR, and FT-IR were used to characterize all monomers. 4.3 ADMET Polymerization 4.3.1 Synthesis of Oligo(siloxane)/Oligo(ethylene) Copolymers Acyclic diene metathesis (ADMET) polycondensation catalyzed by 1st generation Grubbs’ catalyst [Ru]* was used to synthesize oli go(siloxane)/oligo(ethylene) copolymers. All of these polymers are visc ous liquids and the standard spectroscopic methods (1H NMR, 13C NMR, FT-IR), gel-permeati on chromatography (GPC) and thermal analysis (DSC, TGA) were used for the structural characterization and verification of the monomers’ conversion to hi gh molecular weight polymers. Table 4-1 summarizes the results obtained from GPC analysis on the unsaturated polymers, while a more detailed discussion regarding 1H NMR, 13C NMR, FT-IR and the thermal analysis is described in the following sections. Table 4-1. GPC data for unsat urated polycarbosiloxanes. GPC (g/mol)a Polymer Mn Mw PDI poly4sp3Si (196) 44,305 77,363 1.74 poly4sp4Si (197) 41,998 75,912 1.80 poly6sp3Si (198) 57,214 110,115 1.92 poly6sp4Si (199) 49,859 91,947 1.84 a) referenced to PS standards in THF at 40C;

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98 As shown in Table 4-1, similar to glycol-based polymers described in Chapter 3, high molecular weights were obtained with an expected polydisper sity index close to two. 4.3.1.1 Structural characterization Figure 4-3 shows the 1H NMR spectra for 6sp4Si and its high molecular weight polymer poly6sp4Si The characteristic terminal olef in signal present at 4.9 and 5.9 ppm in monomer spectrum (top) are not observed in the spectrum of the poly6sp4Si (bottom) that confirms high conversion of monomer (195) As illustrated in Figure 4-3 proton signals from Si-CH3 and Si-CH2are present at 0.1 and 0.6 ppm respectively and are present in both spectra of the monomer and polymer. Figure 4-3. 1H NMR spectra of 6sp4Si (top) and poly6sp4Si (bottom).

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99 Figure 4-4. 13C NMR spectra of 6sp4Si (top) and poly6sp4Si (bottom). Close inspection of the 13C NMR spectra of monomer and its polymer shown in Figure 4-4 leads to the analogous observati ons. The spectra show distinctive carbon signals of methyl groups resi ding on silicon atoms present at 0.4 and 1.4 ppm. As in the olefinic region of 6sp4Si (195) and poly6sp4Si (199) 1H NMR spectra, similar 13C NMR spectral changes are also observed. The tw o signals for the vinyl carbons at 114.1 and 139.8 ppm present in the monomer disappear while two new peaks at 130.3 ppm (major) and 129.5ppm (minor) are formed in the polymer. As described earlier in chapter 3, these two new signals correspond to trans and cis isomers of the 1,2-di substituted double bonds along the polymer backbone, further conf irming high conversion of monomer to unsaturated polymer. Characteristic splitting of the resonance of the allylic carbon in the

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100 monomer spectrum at 34.1 ppm results in tw o new signals (33.2 and 27.1 ppm) in the spectrum of polymer that correspond to the trans and cis geometries around this carbon. The relative proportion of cis and trans carbons by 13C NMR show approximately 80% content of the later, which is in an agreement with previous reports on ADMET polymerization.52,53 The high content of the trans olefin in ADMET products is attributed to the most stable conformati on of the metallacyclobutane intermediate.53 Figure 4-5. FT-IR spectra of 6sp4Si (blue) and poly6sp4Si (red). Further verification of the polymer’s al ong with complete conversion of monomer to polymer was made by Fourier transform infr ared spectroscopy. An example of an FTIR spectrum of monomer (195) and spectrum of its corresponding polymer (199) are shown in Figure 4-5. Typical for diene monomers, distinctive wavenumber bands that correspond to the vinyl group ar e present in the spectrum of 6sp4Si at 3078, 1642

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101 and 910 cm-1. The absence of these peak s in the spectrum of polymer (199) along with the appearance of a new sharp absorbance at 968 cm-1, assigned to the trans carboncarbon double bond again, confirms the total co nversion of monomer to high molecular weight polymer. The ex pected band at 730-665 cm-1 that corresponds to the cis conformation was not obser ved as in the case of poly6sp3gl described in the previous chapter. FT-IR also provides insight a bout organic groups attached to silicon atoms.149 Perhaps the most characteristic band in th e spectra of organosilicon compounds is the symmetrical methyl deformation that appear s as an intense and sharp band at 1262 cm-1, which is shown in Figure 4-5. Due to the presence of siloxane linkages in both the monomer and the corresponding polymer, di stinctive peaks ar e present at 1040 cm-1. Moreover, visible splitting of the band conf irms presence of coupled siloxane units. 4.3.1.2 Thermal analysis Differential scanning calorimetry (DSC) has been used to determine thermal behavior of unsaturated pol ycarbosiloxanes and these obtained results have been summarized in Table 4-2. As expected for polymers incorporating the very flexible siloxane linkages4,145, low glass transition te mperatures were observed for all polymers. Figure 4-6 shows actual DSC thermograms for polymers (196) (197) (198) and (199) theyt exhibit glass transi tion endotherms ranging from -104 to -97 C. These low glass transition temperature values, in compar ison with previously de scribed glycol-based polymers (Table 3-2), illustrate the great enhancement in flexibility observed with siloxane-based polymers. In addition, glycol -based polymer melting transitions have not been observed for siloxane-based polymers. An increase in the number of -Si-O-Silinkages results in a decrease of Tg, within the series of polym ers with the same number of methylene groups.

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102 Table 4-2. Thermal analysis of the unsaturated polymers DSC TGA (C)b Polymer Tg (C)a Cp (J/g C) TN2 Tair poly4sp2Si (200)c -91.0 429 poly4sp3Si (196) -99.2 -0.45 427 256 poly4sp4Si (197) -104.1 -0.52 433 277 poly6sp3Si (198) -97.0 -0.46 434 280 poly6sp4Si (199) -102.5 -0.49 439 298 a) values taken from the mid-point; b) recorded at 10% total mass loss under nitrogen gas or air, 20 C/min; c) literature values75 Figure 4-6. DSC traces of polycarbosiloxanes. As in the case of unsaturated glycol-b ased polymers, the thermal-degradation behavior has been investigated using thermo -gravimetric analysis (TGA). The analysis was performed for each polymer both in inert (n itrogen) and oxidative (air) atmospheres. The TGA experiments were conducted at a scan rate of 20 C/min from 50 to 800 C and summarized results are presented in Table 4-2.

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103 Figure 4-7. Thermogravimetric analysis of polymer (198) in nitrogen and air. As discussed previously polysiloxanes exhibit good thermal stability1,150, hence there is a great interest in in corporating siloxane units into carbon-based polymers. This high thermal stability of siloxanes compared to their carbon count erparts comes from their fundamental propert ies such as strength1,140,151 and high flexibility of Si-O-Si bond4,145,150. Figure 4-7 illustrates typical TGA curves for unsaturated polycarbosiloxanes along with showing wei ght-loss versus temp erature traces for poly6sp3Si (189) in both atmospheres. Good thermal stability of the polymer is observed up to 425 C in nitrogen, after which rapid but uniform decomposition follows. On the other hand, decomposition in oxidative atmosphere not only begins at lower temperatures, but also seems to follow a mo re complex degradative pathway that is visible by the presence of steps in the TGA trace (red curve) Figure 4-7. It is a typical behavior of siloxanes due to the natura l tendency of silicon to bond with oxygen that leads essentially to the formation of pu re silica on the end of the scan.

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104 4.3.2 Synthesis of “Latent Reactive” Carbosilane/Carbosiloxane Copolymers As in the case of glycol-based dienes described in Chapter 3 shown above, carbosiloxadiene monomers have been used in the preparation of the “latent reactive” carbosilane/carbosiloxane copolymers. Howe ver, only tricomponent compositions that constitute siloxane-based m onomers with 2.5% by mol of the “chain-end” crosslinker (97) and with 5% by weight of eith er “chain-internal” crosslinker (75) or (100) have been synthesized. Structure and abbreviate d names are presented in Figure 4-8. y 9 Si O Si Si y 3 Si OMe OMe OMe OMe Si 9 3 n m5% wt content OMe OMe Si MeO MeO z Si O Si Si z y 3 Si OMe OMe n mcopolymer 41 (201) z = 1; y = 4; 42 (202) z = 2; y = 4; 43 (203) z = 3; y = 4; 44 (204) z = 2; y = 6; 45 (205) z = 3; y = 6; 5% wt content 9 3 y OMe OMe Si MeO MeO 9 copolymer 46 (206) z = 1; y = 4; 47 (207) z = 2; y = 4; 48 (208) z = 3; y = 4; 49 (209) z = 2; y = 6; 50 (210) z = 3; y = 6; Figure 4-8. “Latent reactive” carbos ilane/carbosiloxane copolymers. Structures of obtained copolymers have been verified by NMR spectroscopy, and examples of both the 1H and 13C NMR spectra for copolymer 48 (208) are shown in Figure 4-9. As predicted in the case of unsaturated ADMET polymers, the benchmark signals of internal olefin are pr esent in both spectra at 5.4 ppm in 1H NMR spectrum (top, Figure 4-9) and at 130 ppm in 13C NMR spectrum (bottom, Figure 4-9). Due to the presence of additional linkages between diffe rent repeat units in the copolymer when compared to homopolymer, multiple signals of cis and trans isomers are present in the olefinic region in the 13C NMR spectrum.

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105 Figure 4-9. 1H (top) and 13C (bottom) NMR spectra for copolymer 48 (208) Characteristic peaks of Si-CH2 and Si-OCH3 protons are observed in 1H NMR spectrum at 0.6 and 3.5 ppm respectively. Wh ile the proton signals of the methylene groups adjacent to the silicon from 3sp4OMe (75) 4sp4Si (193) and end9sp2OMe (97) overlap in the proton spec trum, carbon signals in the 13C NMR spectrum can be recognized and assigned accordingly. Due to the low content of crosslinkers (75) and (97) the intensity of these signals is low wh en compared to the carbon signals from the 4sp4Si unit. 4.4 Preparation and Characterization of Thermosets As described in Chapter 3, presence of alkoxy groups on a silicon atom in copolymers enable crosslinking to form thr ee-dimensional network. Therefore using the

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106 same procedures as in the case of gl ycol-based thermosets, “latent reactive” carbosilane/carbosiloxane copolymers have been exposed to moisture that triggers the crosslinking process to produ ce thermosets. Generic structures and the short names assigned to each respective composition are presented in Figure 4-10. y 9 Si O Si Si y 3 Si O O O O Si 9 3 n m5% wt content O O Si O O z Si O Si Si z y 3 Si O O n mxlink 41 (211) z = 1; y = 4; 42 (212) z = 2; y = 4; 43 (213) z = 3; y = 4; 44 (214) z = 2; y = 6; 45 (215) z = 3; y = 6; 5% wt content 9 3 y O O Si O O 9 xlink 46 (216) z = 1; y = 4; 47 (217) z = 2; y = 4; 48 (218) z = 3; y = 4; 49 (219) z = 2; y = 6; 50 (220) z = 3; y = 6; Figure 4-10. Siloxane-based thermosets. Mechanical properties of these tricomponent thermosets have been investigated as in the case of earlier described glycol-based thermosets. The main goal of this research was to improve the overall physical propertie s of the initial thermosets prepared by Brzezinska75 et al ., which exhibit very low modulus (E= 0.16 MPa) and tensile strength (TS= 0.2 MPa)121. Table 4-3. Mechanical properties of carbosiloxane/carbosilane thermosets. Tensile Strength (MPa) Modulus (MPa) Elongation (%) Tensile Strength (MPa) Modulus (MPa) Elongation (%) xlink 41 0.53 0.9 92 xlink 46 0.37 1.5 31 xlink 42 0.26 0.6 63 xlink 47 0.33 1.1 37 xlink 43 0.41 0.8 75 xlink 48 0.39 1.1 48 xlink 44 0.40 1.1 50 xlink 49 0.51 0.8 96 xlink 45 0.48 0.7 104 xlink 50 0.47 1.2 62

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107 Table 4-3 summarizes some of the mechanical properties of carbosiloxane/carbosilane thermosets after curing with moisture. Similar for unfilled siloxane elastomer, values of modulus and te nsile strength range from 0.6 to 1.5 MPa and from 0.26 to 0.53 MPa respectively. Although th ese values show some improvement in physical properties when compar ed to our initial materials121, they are not as satisfactory as the ones obtained for the glycol-based thermosets presented in Chapter 3. These siloxane-based thermosets differ in their compositions by the amount of possible crosslink sites introdu ce by chain-internal crossli nkers. Thermosets obtained from homopolymer of 3sp2OMe exhibit rubber like behavior while thermosets prepared from poly3sp4OMe have a rigid plastic behavior. Fr om these results one would expect that the resultant thermoset that contains 3sp4OMe should exhibit higher values of modulus and tensile strength than the one that constitute the same amount of 3sp2OMe Unfortunately, the differences in the modulus or tensile strength are too small to draw some definitive conclusion when comparing th ose thermosets side by side that was more vivid in the case of glyc ol-based examples. As expected for these amorphous copolymers, all thermosets s how a 100% elastic recovery which is illustrated by lack of plastic deformation plateau in the stress/strain curves which are presented in Figure 4-11. As mentioned above silicon-containing pol ymers exhibit better thermal stability than their organic counterparts152. This is attributed to the strength of the Si-O bond versus C-O, as presented in Table 1-1. Ther mal stability of the resultant thermosets has been investigated using TGA, Table 4-4. Re ported values of temper ature at 10% weight loss are very similar to those obtained by th e same analysis of homopolymers discussed

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108 above (Table 4-2). Similar to the behavi or of the above described polycarbosiloxanes these thermosets decompose in the same manne r, i.e. uniform decomposition in nitrogen, while multistep decomposition is observed in air, as was shown in Figure 4-7. Figure 4-11. Stress/strain curves of carbosiloxane/carbosilane thermosets. Table 4-4. Thermal degradation da ta of carbosiloxane thermosets. TGA (C)a TGA (C)a TN2 Tair TN2 Tair xlink 41 349 292 xlink 46 389 343 xlink 42 311 292 xlink 47 402 286 xlink 43 340 307 xlink 48 421 347 xlink 44 403 338 xlink 49 403 361 xlink 45 413 291 xlink 50 434 354 a) recorded at 10% total mass loss unde r nitrogen gas or air, 20 C/min; 4.5 Conclusions Acyclic diene metathesis polymerization has been used to synthesize “latent reactive” carbosiloxane/carbosilane elastomers These linear unsaturated copolymers have been cured by exposure of the resultan t copolymers to moisture. An enhancement in physical properties has been observed when compared to previously synthesized materials by Brzezinska et al .75, yet desired enhancement has not been reached most likely due to the low inter actions between the chains.

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109 Hydrosilylation has been proven a very c onvenient and effective synthetic method in obtaining siloxane dienes in good quantities. Fam ilies of such monomers have been synthesized and subjected to olefin metathesis polymerization yielding linear unsaturated polycarbosiloxanes. Carbosiloxa nediene monomers suitable for olefin metathesis have been synthesized and characterized 4.6 Experimental Methods 4.6.1 Materials All reactions were conducted in flamedried glassware under an argon atmosphere unless otherwise noted. Reagents were purchas ed from Gelest or Aldrich and were used as received unless otherwise not ed. The first-generation Gru bbs’ catalyst used in this study was graciously provided by Materia, Inc. 4.6.2 Instrumentation and Analysis Instrumentation for NMR, HRMS, FT-IR, DSC, TGA and GPC are discussed in Chapter 3. Elemental analyses were performed by Atlantic Microlab, Inc (Norcross, GA). Mechanical tests were performed at the Univ ersity of Florida using an Instron model 1122 load frame upgraded with an MTS ReNew system running MTS TestWorks 4 software and a 500 g load cell for the experime nts. Specimen preparation was detailed in Chapter 2. 4.6.3 Monomer Synthesis Monomer 75 and 76 were synthesized according to a literature procedure75, while synthesis of monomer 97 and 100 has been described in Chapter 3. 4.6.3.1 Synthesis of 1,5-bis(hexenyl)-1,1,3,3,5,5-h examethyltrisiloxane 4sp3Si (192) A flame-dried, Ar-purged, three-necked 500 mL round-bottom flask equipped with a stir bar, condenser, and an additional funnel was char ged with (5.0 g, 0.013 mol) H-

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110 terminated 1,1,3,3,5,5-hexamethyltrisiloxane, 1,5-hexadiene (10.7 g, 0.13 mol) and dry toluene (50 ml). The reaction mixture was stirred for couple minutes to ensure its homogeneity and tris(divi nyltetramethyldisiloxane)Pt2 (Karstedt’s catalyst) (0.6 mg of 10.6% soln. in xylenes, 10-5eq). An exotherm was produced thus an ice bath was used to keep solution below 30 C. The solution was allowed to stir for 30 minutes after which the excess of 1,5-hexadiene and to luene was distilled off using the rotary evaporator. The monomer was passed through silica plug to remove catalyst, dried over CaH2 and distilled under vacuum resulting in pure m onomer in 95% yield. The following spectral properties were observed: 1H NMR (CDCl3): = 0.04 (d, 18H), 0.53 (m, br, 4H), 1.37 (m, br, 8H), 2.04 (m, br, 4H), 4.95 (m, br, 4H), 5.77 (m, br, 2H). 13C NMR (CDCl3): = 0.21, 1.29, 18.13, 22.76, 32.64, 33.56, 114.12, 139.13. FT-IR: (cm-1) 3078, 2958, 2924, 2856, 1641, 1439, 1412, 1257, 1051, 910, 841, 795. MS (70 eV): m/z = 357.2113 (MCH3)+. (C18H40O2Si3) (372.76): Calcd. C 58.00, H 10.82; Found C 58.21, H 10.07. 4.6.3.2 Synthesis of 1,7-bis(hexenyl )-1,1,3,3,5,5,7,7-octamethyltetrasiloxane 4sp4Si (193) Monomer 4sp4Si was prepared and purified using the same methodology as described for 4sp3Si yielded 8.5 g (92% yield) of colorless liquid. The following spectral properties were observed: 1H NMR (CDCl3): = 0.04 (s, 12H), 0.06 (s, 12H), 0.52 (m, br, 4H), 1.31 (m, br, 8H), 2.02 (m, br, 4H), 4.91 (m, br, 4H), 5.74 (m, br, 2H). 13C NMR (CDCl3): = 0.21, 1.20, 18.11, 22.76, 32.63, 33.56, 114.12, 139.12. FT-IR: (cm-1) 3078, 2959, 2924, 2856, 1641, 1440, 1412, 1258, 1080, 1041, 910, 840, 798. MS (70 eV): m/z = 447.2602 (M+H)+. (C20H46O3Si4) (446.92): Calcd. C 53.75, H 10.37; Found C 53.93, H 10.39.

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111 4.6.3.3 Synthesis of 1,5-bis(octenyl)-1,1,3,3,5,5hexamethyltrisiloxane 6sp3Si (194) Monomer 6sp3Si was prepared and purified using the same methodology as described for 4sp3Si yielded 10.5 g (94% yield) of colorless liquid. The following spectral properties were observed: 1H NMR (CDCl3): = 0.02 (s, 6H), 0.06 (s, 12H), 0.51 (m, br, 4H), 1.32 (m, br, 16H), 2.03 (m, br, 4H), 4.91 (m, br, 4H), 5.77 (m, br, 2H). 13C NMR (CDCl3): = 0.22, 1.31, 18.31, 23.21, 28.91, 33.32, 33.87, 114.10, 139.22. FT-IR: (cm-1) 3078, 2957, 2925, 2855, 1641, 1440, 1411, 1257, 1051, 993, 909, 840, 795. MS (70 eV): m/z = 413.2395 (M-CH3)+. 4.6.3.4 Synthesis of 1,7-bis(octenyl )-1,1,3,3,5,5,7,7-octaamethyltrisiloxane 6sp4Si (195) Monomer 6sp4Si was prepared and purified using the same methodology as described for 4sp3Si yielded 7.8 g (92% yield) of colorless liquid. The following spectral properties were observed: 1H NMR (CDCl3): = 0.04 (s, 12H), 0.06 (s, 12H), 0.51 (m, br, 4H), 1.32 (m, br, 16H), 2.03 (m, br, 4H), 4.91 (m, br, 4H), 5.77 (m, br, 2H). 13C NMR (CDCl3): = 0.21, 1.20, 18.28, 23.20, 28.90, 33.30, 33.86, 114.10, 139.24. FT-IR: (cm-1) 3078, 2959, 2925, 2855, 1641, 1441, 1412, 1258, 1080, 1041, 910, 840, 798. MS (70 eV): m/z = 503.3222 (M+H)+. (C24H54O3Si4) (503.02): Calcd. C 57.30, H 10.82; Found C 57.58, H 10.87. 4.6.4 General Metathesis Conditions All monomers used in polymerization were distilled from CaH2 and degassed prior to polymerization. All glassware was thor oughly cleaned and dried under vacuum before use. The reactions were initiated in the bulk under an argon-filled glove box by placing the appropriate amount of monomer or monomers in 50-mL round-bottom flasks equipped with a magnetic Teflon™ stir bar followed by 1st Generation Grubbs’ catalyst

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112 [Ru=C] (4) and slowly stirred for 2 minutes. Th e monomer-to-catalyst ratios typically used were 250 : 1. In all cases of copolym erization all reactant were stirred before catalyst addition to yield hom ogenous mixture. The flasks were then fitted with an adapter equipped with a Teflon™ vacuum valv e, which after were sealed and removed from the glove box and placed immediately on the vacuum line. Slow exposure to the moderate vacuum yielded in slow bubbling of ethylene. After stirring for couple minutes the flasks were submerged into an oil bath at 50 C until the viscosity increased and stirring continued for 72 h. 4.6.4.1 Synthesis of poly4sp3Si The monomer was polymerized using the above procedure. Monomer 192 (0.5 g, 0.0013 mol) was added to the reactio n tube charged with Grubbs’ 1st generation catalyst (4.41 mg, 5.36 x10-6 mol). The reaction tube was seal ed using a Kontes Teflon valve and placed under an intermediate vacuum until the mixture became viscous. The reaction flask was then placed in a 40 C oil bath a nd high vacuum (<0.01 mm Hg) was applied. The temperature was gradually raised to 55 C over 72 hours. After three days, the polymerization was quenched via dissolution in toluene and exposed to air. The following properties were observed: 1H NMR (CDCl3): = 0.31 (d, 18H), 0.77 (m, 4H), 1.6 (m, 8H), 2.23 (m, br, 4H), 5.65 (br, 2H); 13C NMR (CDCl3): = 049, 1.61, 18.56, 18.63, 23.29, 23.45, 27.52, 32.90, 33.88, 34.01, 130.11, 130.67. FT-IR: (cm-1) 2957, 2922, 2854, 1409, 1256, 1049, 965, 840, 794. GPC data (THF vs. polystyrene standards): Mn = 44 305 g/mol; PDI ( Mw/Mn) = 1.74. DSC Results: Tg (glass transition) = -99.2 C, Cp= -0.45 J/g C.

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113 4.6.4.2 Synthesis of poly4sp4Si Monomer 193 (0.5 g, 0.0011 mol) was added to th e reaction tube charged with Grubbs’ 1st generation catalyst (3.68 mg, 4.47 x10-6 mol). The following properties were observed: 1H NMR (CDCl3): = 0.04 (d, 12H), 0.06 (d, 12H), 0.50 (m, 4H), 1.35 (m, 8H), 1.97 (m, br, 4H), 5.38 (br, 2H); 13C NMR (CDCl3): = 0.19, 1.19, 18.06, 21.87, 22.77, 27.00, 31.86, 32.35, 32.90, 33.40, 33.52, 129.73, 130.23, 130.50. FT-IR: (cm-1) 2958, 2922, 2854, 1410, 1258, 1079, 1040, 966, 840, 797. GPC data (THF vs. polystyrene standards): Mn = 41 998 g/mol; PDI ( Mw/Mn) = 1.80. DSC Results: Tg (glass transition) = -104.1 C, Cp= -0.52 J/g C. 4.6.4.3 Synthesis of poly6sp3Si Monomer 194 (0.5 g, 0.0011 mol) was added to th e reaction tube charged with Grubbs’ 1st generation catalyst (3.83 mg, 4.66 x10-6 mol). The following properties were observed: 1H NMR (CDCl3): = 0.31 (d, 18H), 0.77 (m, 4H), 1.6 (m, 8H), 2.23 (m, br, 4H), 5.65 (br, 2H); 13C NMR (CDCl3): = 049, 1.61, 18.56, 18.63, 23.29, 23.45, 27.52, 32.90, 33.88, 34.01, 130.11, 130.67. FT-IR: (cm-1) 2956, 2923, 2853, 1462, 1256, 1049, 966, 840, 795. GPC data (THF vs. polystyrene standards): Mn = 57 214 g/mol; PDI ( Mw/Mn) = 1.92. DSC Results: Tg (glass transitio n) = -97.0 C, Cp= -0.46 J/g C. 4.6.4.4 Synthesis of poly6sp4Si Monomer 195 (0.5 g, 0.001 mol) was added to th e reaction tube charged with Grubbs’ 1st generation catalyst (3.27 mg, 3.97 x10-6 mol). The following properties were observed: 1H NMR (CDCl3): = 0.04 (s, 12H), 0.06 (s, 12H), 0.57 (m, 4H), 1.29 (m, 16H), 1.97 (m,4H), 5.38 (br, 2H); 13C NMR (CDCl3): = 0.19, 1.18, 18.27, 23.20, 27.26, 28.96, 29.08, 32.67, 33.33, 129.86, 130.32. FT-IR: (cm-1) 2958, 2923, 2854, 1462, 1410, 1257, 1081, 1040, 967, 840, 797. GPC data (THF vs. polystyrene standards): Mn = 49

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114 859 g/mol; PDI ( Mw/Mn) = 1.84. DSC Results: Tg (glass transition) = -102.5 C, Cp= 0.49 J/g C. 4.6.5 Preparation of Copolymers and Thermosets “Latent reactive” copolymers have been synthesized according to general metathesis conditions described in secti on 4.6.4 by mixing appropriate monomers. Two formulation of tricomponent compos itions were prepared by mixing 1.3 g of carbosiloxane diene, 0.065 g of either 3sp2OMe or 3sp4OMe and end9sp2OMe Similar to preparation tricomponent gl ycol-based compositions, the amount of 97 was calculated to be approximately equal to 2.5% by mol of carbosiloxane diene. Characteristic shifts were observed: 1H NMR (CDCl3): (ppm) = 0.04-0.06 [Si( CH3)2-O-], 0.55-0.60 [m, (CH2-Si)], 1.26 [m, br, (CH2-)], 1.95 [m, br, (CH=CHCH2), 3.52 [s, (Si-O CH3)], 5.36 [br, (CH = CH -)]; 13C NMR (CDCl3): (ppm) = -5.8 [Si(OCH3)2CH3], 0.2 [-CH2-Si(O CH3)2-O-], 1.2 [-O-Si(O CH3)2-O-], 2.55 [-SiCH2CH2Si], 10.4-13.2 [-CH2CH2-Si], 18.1-18.2 [-CH2CH2-Si(CH3)2-O-], 21.9-23.4 [CH2-CH2Si], 27.1 [ cis -CH=CHCH2-], 32.3 [-Si-CH2-CH2CH2-CH2], 33.4 [ trans -CH=CHCH2], 37.2 [-CH=CHCH2-(CH2)2-Si], 50.3 [Si-O CH3], 129.83-130.45 [ cis & trans CH = CH -]. Films of thermosets have been prepared by dissolving copolymers in dry toluene (7 mL) and cast onto a poly(tetrafluoroethylene) mold. The mold was then placed along with 10 mL of deionized water in the oven at 55 C and left to cure for 8 hours. Obtained films of crosslinked material s were then sectioned for subsequent characterization.

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115 APPENDIX A 1. Results of mechanical tests on dicomponent thermosets Thermoset Tensile Strength (MPa) Modulus (MPa) Elongation (%) xlink 1 (150) 0.78 3.3 29 xlink 2 (151) 0.83 2.9 39 xlink 3 (152) 0.72 2.6 38 xlink 4 (153) 1.02 4.2 33 xlink 5 (154) 0.72 3.8 24 xlink 6 (155) 0.40 1.1 50 xlink 7 (156) 0.41 0.9 75 xlink 8 (157) 0.48 0.7 104 A 2. Results of mechanical tests on dicomponent thermosets xlink 9-16 Thermoset Tensile Strength (MPa) Modulus (MPa) Elongation (%) xlink 9 (158) 0.53 1.7 38 xlink 10 (159) 0.68 2.3 44 xlink 11 (160) 0.65 2.4 37 xlink 12 (161) 0.89 4.3 27 xlink 13 (162) 0.84 3.1 37 xlink 14 (163) 13.75 126.5 144 xlink 15 (164) 5.48 68.8 241 xlink 16 (165) 5.30 42.4 150

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116 A B A 1. Stress/strain curves of dicomponent thermosets. A) xlink 1-5 B) xlink 6-8

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117 A B A-2. Stress/strain curves of dicomponent ther mosets xlink 9-16 A) xlink 9-13 B) xlink 14-16

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127 BIOGRAPHICAL SKETCH Piotr Pawe Mat oka was born on May 14, 1976, to Maria and Stanis aw Mat oka, in Gniezno, Poland, where he spent 19 years. After graduation from high school in 1995, he successfully passed his chemistry qualifie r, and was accepted to the Department of Chemistry at the University of Adam Mick iewicz, Poznan. In fall 1997, he joined Professor Marciniec’s research group. Under his supervision, Piotr conducted research in the field of organosilicon synthesis via metath esis and silylative coupling. In June 2000, he defended his thesis “Chemistry investigation of vinyl-, allyltris ubstituted silanes with ally-, vinyl-alkyl ethers catalyzed by ruthenium comp lexes” and graduated with Departmental Honors with a Mast er of Science. That summ er he got married, and that same year he left Poland and attended gradua te school at the Univer sity of Florida under the direction of Professor Kenneth Wagener. Piotr’s work there involved the synthesis of latent reactive carbosilane/carbosiloxane elastomers via acyclic diene metathesis (ADMET).


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Title: Synthesis and Characterization of Latent Reactive Oligo Oxyethylene Carbosilane and Carbosiloxane Carbosilane Copolymers via Acyclic Diene Metathesis Polymerization ADMET for Thermoset Materials
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Title: Synthesis and Characterization of Latent Reactive Oligo Oxyethylene Carbosilane and Carbosiloxane Carbosilane Copolymers via Acyclic Diene Metathesis Polymerization ADMET for Thermoset Materials
Physical Description: Mixed Material
Copyright Date: 2008

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Table of Contents
    Title Page
        Page i
        Page ii
    Dedication
        Page iii
    Acknowledgement
        Page iv
        Page v
        Page vi
        Page vii
        Page viii
        Page ix
        Page x
    List of Tables
        Page xi
    List of Figures
        Page xii
        Page xiii
        Page xiv
        Page xv
    Abstract
        Page xvi
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    Acyclic diene metathesis polymerization (ADMET) approach to silicon-containing materials
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    Synthetic modification of crosslink density and soft segment in polycarbosilane/polycarbosiloxane elastomers
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    Synthesis and characterization of oligo (oxyethylene)/carbosilane copolymers and thermosets
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    Synthesis and characterization of carbosiloxane/carbosilane copolymers and thermosets
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    Appendix
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    References
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    Biographical sketch
        Page 127
Full Text






SYNTHESIS AND CHARACTERIZATION OF LATENT REACTIVE
OLIGO(OXYETHYLENE)/CARBOSILANE AND
CARBOSILOXANE/CARBOSILANE COPOLYMERS VIA ACYCLIC DIENE
METATHESIS POLYMERIZATION (ADMET) FOR THERMOSET MATERIALS















By

PIOTR PAWEL MATLOKA


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA


2006






























Copyright 2006

by

Piotr Pawel Mattoka



























Mojej ukochanej zonie Komelii i moim rodzicom za ich bezgraniczn4 miloC6,
wyrozumialtoS i przyjaili.





To my lovely wife Komelia and my parents for their eternal love, understanding, and
friendship.








ACKNOWLEDGMENTS

There are a great number of people who have given me their support,

encouragement, and support during my graduate career. First and foremost, I must thank

my wife Komelia. She has been everything for me during the course of my dissertation

work. She has been my rock, my motivation and my friend. Without her I would be

incomplete.

I would like to thank my parents for their endless love, devotion, support and

sacrifices they have made that allowed me to become a person that I am today. They

taught me at a young age what was important in life, and showed me how to work hard to

achieve my goals.

I need to acknowledge the people that molded my career as a student of chemistry

before going to collage and finally to graduate school. I would like to thank my

secondary school chemistry teacher Mrs. Krystyna Swiqch and my high school chemistry

teacher Mrs. Danuta Bolifiska for being wonderful teachers.

At Adam Mickiewicz University I would like to express my sincere thanks to Dr.

Wioleta Patroniak for her friendship and help in making right decision at my

undergraduate career. Sincere gratitude also goes to Prof. Bogdan Marciniec, my

undergraduate advisor whose encouragement and support made my undergraduate

research career extremely rewarding experience. I cannot leave out my best friend that I

had pleasure to study with Dr. Piotr Pawlu6, whose friendship I value very much.





During my career at University of Florida I have had pleasure to meet and work

among extraordinary people, such Dr. John Sworen, who I would like to thank for taking

the time to teach me good laboratory techniques, for introducing me to my project early

in my graduate career, and for being a true friend. I extend my thanks to my

classmates/friends Dr. Florence Courchay (aka BMB) and Dr. Travis Baughman for all

wonderful time we have spend together, especially marvelous time we had during our trip

to Europe. I cannot omit my "Polish fellow" Dr. Ryan Walczak who I thank for all

scientific and non-scientific discussion that we had. There have been many people that

have enriched my life, both inside and outside of the laboratory sincere thanks goes to

all of the past and current members of the Wagener research group for their helpful

discussions and friendship including Dr. Jason Smith, Dr. Tim Hopkins, Dr. Violeta

Petkovska, Dr. Garrett Oakley, Giovanni Rojas, Erik Berda, James Leonard, Meghan

Greenfield and Zach Kean. I have to thank also other members of the floor who I had

pleasure to meet. My experience at the University of Florida would not have been

complete without making the acquaintances of Dr. Carl Gaupp, Dr. C.J. DuBois, Dr. Ben

Reeves, Tim Steckler, Bob Brookins, Merve "Marwa" Ertas, Sophie Bernard, and

Victoria Broadstreet.

Enough thanks cannot be expressed to Lorraine Williams and Sara Klossner in the

polymer office. Without them, the little things that make everything run smoothly, but no

one wants to think about, would never get done. I also extend my thanks to Lori Clark for

her help in the graduate office.




Many thanks are extended to my committee members, Dr. John R. Reynolds, Dr.

Michael J. Scott, Dr. Daniel R. Talham, and Dr. Anthony B. Brennan for their help

throughout my journey at the University of Florida

Finally, I would like to express my sincere appreciation to my research advisor

Professor Ken Wagener. First, I would like to thank him for his encouragement,

guidance, patience, and understanding during the course of my graduate career. Second,

I gratefully value his advice and his confidence in my abilities as a chemist. Most

importantly I would like to thank him for having always time to sit and talk about not

only chemistry but simply everyday life. I will forever be thankful for his presence in my

life.








TABLE OF CONTENTS

page

A C K N O W LED G M EN TS ............................................................ .................................. iv

L IST O F T A B L E S ............................................................................... .......................... xi

LIST O F FIG U R ES .............................................. ............ ......... ......................... xii

A B S T R A C T ..................................................................................................................... xv i

CHAPTER

1 ACYCLIC DIENE METATHESIS POLYMERIZATION (ADMET)
APPROACH TO SILICON-CONTAINING MATERIALS.....................................1

1.1 Introduction ....................................................... ... ............... ......................1
1.2 Silicon C hem istry .......................................................... ................................ 3
1.3 O lefin M etathesis............................. ................................................................. 4
1.3.1 Brief History of Olefin Metathesis...........................................................6
1.3.2 Introduction to ADMET Polymerization................................................8
1.4 Olefin Metathesis Chemistry of Compounds Containing Silicon ........................12
1.4.1 Acyclic Diene Oligomerization and Polymerization of Containing
S silicon D ien es ..................................................................................................14
1.4.2 ADMET Catalyzed by "Ill-Defined" Catalytic Systems.......................... 15
1.4.3 ADMET Catalyzed by "Well-Defined" Catalytic Systems....................... 18
1.4.3.1 Polycarbosilanes.............................................................................. 18
1.4.3.2 Polycarbosiloxanes........................................................................ 21
1.4.3.3 Telechelic oligom ers .....................................................................24
1.4.3.4 Functionalized polycarbosilanes .................................................26
1.4.3.5 Latent reactive elastomers................................................................27
1.5 Silylative Coupling (SC) Polycondensation.................................................28
1.6 Crosslinking Methods for Silicon-Containing Materials................................... 31
1.7 Purpose of Study .................................................................................................33

2 SYNTHETIC MODIFICATION OF CROSSLINK DENSITY AND SOFT
SEGMENT IN POLYCARBOSILANE/POLYCARBOSILOXANE
E L A ST O M E R S ....................................................................................................34

2 .1 Introdu action ....................................................................... ....................................34
2.2 Synthetically Modified Crosslink Density..........................................................36





2.3 Synthetic Soft Segment Modification.................................................................39
2 .4 C on clusion s............. ................ ..... ..... ........ ...... ...... .............. ............43
2.5 Experim mental M ethods.................................................................................... 44
2.5.1 G general Considerations ................................... ......................................44
2.5.2 M materials. .............................................. ..... ................... ............ 45
2.5.3 M onom er Synthesis................................................................................. 46
2.5.3.1 Tris(4-pentenyl)methylsilane (80).................................................46
2.5.3.2 Diundecenyltriethylene glycol (83)..................................................47
2.5.4. General Metathesis Conditions...............................................................47
2.5.4.1 Polymerization of diundecenyltriethylane glycol (83)...................48
2.5.4.2 Terpolymerization of monomers 75, 76, and 80 to produce
terpolym er 81 ........................................... .................. .........................48
2.5.4.3 Terpolymerization of monomers 75, 83, and 80 to produce
terpolym er 84.................................................................... .................... ..49

3 SYNTHESIS AND CHARACTERIZATION OF
OLIGO(OXYETHYLENE)/CARBOSILANE COPOLYMERS AND
T H E R M O SE T S .................................................................... ............................. 50

3.1 Introduction..........................................................................................................50
3.2 Synthesis of M onom ers .................................................................................... 51
3.2.1 Monomers for Soft Phase Modification ..................................................51
3.2.2 Monomers for Crosslink Density Modification .......................................53
3.3 ADMET Polymerization.................................................... .....................54
3.3.1 Synthesis of Oligo(oxyethylene)/Oligo(ethylene) Copolymers .................54
3.3.1.1 Structural characterization................................................................ 56
3.3.1.2 Thermal behavior of unsaturated polymers....................................59
3.3.1.3 Thermal stability of unsaturated polymers.....................................64
3.3.2 Polymerization of "Chain-Internal" Crosslinker 3sp20Me .......................65
3.3.3 Synthesis and Characterization of "Latent Reactive" Copolymers...........66
3.4 Preparation and Characterization of Thermosets.................................................69
3.4.1 Thermal Behavior and Degradation of Thermosets ..................................71
3.4.2 M echanical Properties ................................... .........................................74
3.5 C onclusions.................................... .......................................... ................... .. 79
3.6 Experim mental M ethods................................. ...............................................80
3.6.1 M materials .......................... .................. ................................................ 80
3.6.2 Instrumentation and Analysis..................................................................80
3.6.3 M onom er Synthesis.................................................................................. 82
3.6.3.1 Synthesis of di(oxyethylene) a,o-di-4-pentenyl ether (3sp2gl)
(8 6 )............. ............... .................. ...................................................... ... 82
3.6.3.2 Synthesis oftri(oxyethylene) a,a-di-4-pentenyl ether (3sp3gl)
(8 7 ).............. ............... ................................................................ ... ..... 8 2
3.6.3.3 Synthesis oftetra(oxyethylene) a,co-di-4-pentenyl ether (3sp4gl)
(88)............................... ...................... .............. ................... ..... 83
3.6.3.4 Synthesis of tri(oxyethylene) a,co-di-7-octenyl ether (6sp3gl) (89).83
3.6.3.5 Synthesis oftetra(oxyethylene) a,o-di-7-octenyl ether (6sp4gl)
(90) .................................................... ............ ................................. 83





3.6.3.6 Synthesis of di(oxyethylene) a,o-di-10-undecenyl ether (9sp2gl)
(9 1).............................. ........... .......................................... ........... ... 8 4
3.6.3.7 Synthesis of tri(oxyethylene) a,o-di-10-undecenyl ether (9sp3gl)
(9 2 )................................. ....................................... ...... .................. ...... 8 5
3.6.3.8 Synthesis of tetra(oxyethylene) a,o-di- 10-undecenyl ether
(9sp4gl) (93) ............................................................... .................... 85
3.6.3.9 Synthesis of 10-undecenyldimethoxymethylsilane 9sp2OMe (97) .85
3.6.3.10 Synthesis of di(4-pentenyl)dimethoxysilane 3sp20Me (100) .......86
3.6.4 General Metathesis Conditions.............................................................. 87
3.6.4.1 Synthesis of poly3sp2gl ................................................... .............88
3.6.4.2 Synthesis of poly3sp3gl .................................................... ...........88
3.6.4.3 Synthesis of poly3sp4gl ..................................................................88
3.6.4.4 Synthesis of poly6sp3gl .................................................... ...........89
3.6.4.5 Synthesis of poly6sp4gl ..................................................................89
3.6.4.6 Synthesis of poly9sp2gl ..................................................................89
3.6.4.7 Synthesis of poly9sp3gl .................................................... ...........90
3.6.4.8 Synthesis of poly9sp4gl .................................................... ...........90
3.6.5 Preparation of Copolymers and Thermosets ............................................91

4 SYNTHESIS AND CHARACTERIZATION OF
CARBOSILOXANE/CARBOSILANE COPOLYMERS AND THERMOSETS.....93

4.1 Introduction............................. ...........................................................................93
4.2 M onom er Synthesis ................................................................... ................... 94
4.3 A D M ET Polym erization..................................... .......................................... 97
4.3.1 Synthesis of Oligo(siloxane)/Oligo(ethylene) Copolymers .......................97
4.3.1.1 Structural characterization.............................................................. 98
4.3.1.2 Therm al analysis .......................................................................101
4.3.2 Synthesis of "Latent Reactive" Carbosilane/Carbosiloxane Copolymers 104
4.4 Preparation and Characterization of Thermosets................................................105
4 .5 C conclusion s............................ ... ... .............................................................108
4.6 Experim ental M ethods..................................................... ................................. 109
4 .6.1 M materials ................................................. ............................................... 109
4.6.2 Instrum entation and Analysis................................................................. 109
4.6.3 M onom er Synthesis ......... ............................................ ........................109
4.6.3.1 Synthesis of 1,5-bis(hexenyl)-1,1,3,3,5,5-hexamethyltrisiloxane
4sp3Si (192)............................... ............. ...........................109
4.6.3.2 Synthesis of 1,7-bis(hexenyl)-1,1,3,3,5,5,7,7-
octamethyltetrasiloxane 4sp4Si (193)................................................ 110
4.6.3.3 Synthesis of 1,5-bis(octenyl)-1,1,3,3,5,5-hexamethyltrisiloxane
6sp3Si (194)..................................................... ............ ...................... 111
4.6.3.4 Synthesis of 1,7-bis(octenyl)-1,1,3,3,5,5,7,7-
octaamethyltrisiloxane 6sp4Si (195) .................................................111
4.6.4 G general M etathesis Conditions................................................................111
4.6.4.1 Synthesis of poly4sp3Si ................................................................112
4.6.4.2 Synthesis of poly4sp4Si .................................................................113
4.6.4.3 Synthesis of poly6sp3Si .............................................................. 13




4.6.4.4 Synthesis of poly6sp4Si .................................................................113
4.6.5 Preparation of Copolymers and Thermosets ............. ..........................1. 14

APPENDIX.................................. ....... .... ....................................................... .....115

LIST OF REFERENCES................................................... ...........................................118

BIOGRAPHICAL SKETCH ........................................................................................127








LIST OF TABLES


Table page

1-1 Comparison of various silicon and carbon bond lengths and energies ..................3

2-1 Mechanical properties of the unsaturated ADMET copolymers and a
com m ercially available elastom er. ................................... ....................................35

2-2 Synthetic research objectives. ................................................................ ................36

3-1 GPC data of unsaturated polym ers.............................................. ...................... 55

3-2 Thermal analysis of the unsaturated polymers ....................................................60

3-3 Physical properties of selected thermosets compositions.................................77

4-1 GPC data for unsaturated polycarbosiloxanes. .....................................................97

4-2 Thermal analysis of the unsaturated polymers.....................................................102

4-3 Mechanical properties of carbosiloxane/carbosilane thermosets...........................106

4-4 Thermal degradation data of carbosiloxane thermosets.........................................108

A-1 Results of mechanical tests on dicomponent thermosets xlink 1-8......................1115

A-2 Results of mechanical tests on dicomponent thermosets xlink 9-16......................115








LIST OF FIGURES


Figure page

1-1 Types ofolefin metathesis: a) simple exchange reactions; b, c) metathesis
polymerization and ring-closing metathesis; c) metathesis degradation ..................

1-2 M etallacyclobutane m echanism ................................................... .....................6

1-3 W ell-defined m etathesis catalysts. ................................... ................ .................7

1-4 Acyclic diene metathesis (ADMET) and ring-opening metathesis (ROMP)
polym erizations. .. .................... ................. ........................... ............................... 8

1-5 Theoretical degree of polymerization vs. conversion in condensation type
polym erization ............................................... ....................................................... 10

1-6 ADMET polymerization of 1,9-decadiene................................................... ............10

1-7 The catalytic cycle of ADMET polymerization.....................................................11

1-8 Ring-opening metathesis polymerization of 1,1-dimethyl-l-silacyclopent -3-ene..13

1-9 ROMP of silylsubstituted norbornens................................................................. 13

1-10 ROMP using Casey's carbene complex............................................................... 13

1-11 Polymerization of diallyl- and allyl-butenyl derivatives of disubstituted silanes.... 15

1-12 Polymerization of diallyltetramethyldisiloxane .................................................. 16

1-13 M etathesis of diallyltetramethyldisilane. ........................................... ....................17

1-14 M etathesis of dialkenylsilacyclobutane. ..................................................................17

1-15 Copolymerization of divinyldimethylsilane (32) with 1,9-decadiene (10).............. 18

1-16 Productive and non-productive metathesis. ........................................................19

1-17 Polycarbosilanes via ADM ET................................................................................20

1-18 Polycarbosilanes with the disilacyclobutane rings.................................................21





1-19 Non-productive ADMET polymerization. .......................................................21

1-20 ADMET polymerization of siloxane containing dienes.........................................22

1-21 Controlled diene insertion via ADMET. .............................................................23

1-22 ADMET copolymerization of divinyltetraethoxydisiloxane...................................24

1-23 Telechelic polym ers via AD M ET. ................................... .....................................25

1-24 ADMET polymerization of a,co-telechelic diene macromonomer. .........................25

1-25 Chloro- and dichloro-functionalized polycarbosilanes via ADMET.....................26

1-26 Two routes to polym er m odification...................................................................... 26

1-27 Latent reactive carbosiloxane/carbosilane copolymer. ..........................................27

1-28 The latent reactivity concept to attain diverse behavior of materials....................28

1-29 Catalytic cycle of silylative coupling. ..................................................................29

1-30 SC polycondensation of divinylsubstituted silicon monomers ..............................30

1-31 Starburst oligom er via SC ................................................................................31

2-1 Atmospherically crosslinked ADMET copolymers ..................................... ..34

2-2 Chain-end crosslinking molecules. ............................................................. 37

2-3 Chain-end crosslinking in the polycarbosilanes via ADMET..................................38

2-4 1H NMR spectra of monomer 83.................................................................................40

2-5 Glass transition temperatures for various lengths of polyoxyethylene ....................41

2-6 High elastic material containing increased soft phase and chain-end crosslinker. ..43

3-1 G lycol-based m onom ers..........................................................................................52

3-2 Synthesis of 9sp4gl (93)........................................................................................ 52

3-3 Synthesis of end9sp20Me and 3sp20Me. .............................................................54

3-4 H NMR spectra of monomer 6sp3gl and polymer poly6sp3gl .............................56

3-5 13C NMR spectra of monomer 6sp3gl and polymer poly6sp3gl ............................57

3-6 FT-IR spectra of 6sp3gl and poly6sp3gl. .............................................................58





3-7 DSC traces of unsaturated 3sp microblock copolymers...................................62

3-8 DSC traces of unsaturated 6sp microblock copolymers...........................................62

3-9 DSC traces of unsaturated 9sp microblock copolymers...........................................63

3-10 TG A traces of poly6sp4gl..................................................................................... 64

3-11 1H NMR spectra of 3sp20Me and poly3sp20Me................................................65

3-12 Compositions of "latent reactive" unsaturated copolymers .................................67

3-13 H (A) and 13C (B) NMR spectra of copolymer 38 (147). ....................................68

3-14 Composition and structure of crosslinked materials ..............................................70

3-15 Moisture cured xlink 39 at room temperature. ...................................................71

3-16 DSC curves of poly6sp4gl, copolymer 29 and xlink 29........................................72

3-17 TGA traces in an oxidative atmosphere. .............................................................73

3-18 TGA traces in an inert atmosphere........................................................................74

3-19a Stress/strain curves. ............................................................................. ............... 75

3-19b Stress/strain curves. .......................... ........................................ ....................... 75

3-19c Stress/strain curves........................... ..................................................................... 76

3-20 Stress/strain curves and picture ofthermosets with good elastic properties...........79

4-1 Synthesis of siloxane-based a, o dienes via hydrosilylation ..................................95

4-2 Siloxane-based a, o diene monomers. ....................................................................96

4-3 1H NMR spectra of 6sp4Si (top) and poly6sp4Si (bottom) .....................................98

4-4 3C NMR spectra of 6sp4Si (top) and poly6sp4Si (bottom)...................................99

4-5 FT-IR spectra of 6sp4Si (blue) and poly6sp4Si (red)...........................................100

4-6 DSC traces of polycarbosiloxanes.................................................................102

4-7 Thermogravimetric analysis of polymer (198) in nitrogen and air ......................103

4-8 "Latent reactive" carbosilane/carbosiloxane copolymers. ...................................104

4-9 1H (top) and 13C (bottom) NMR spectra for copolymer 48 (208). ......................105




4-10 Siloxane-based therm osets. ...............................................................................106

4-11 Stress/strain curves of carbosiloxane/carbosilane thermosets ..............................108

A-1 Stress/strain curves of dicomponent thermosets xlink 1-8.....................................116

A-2 Stress/strain curves of dicomponent thermosets xlink 9-16...................................117








Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

SYNTHESIS AND CHARACTERIZATION OF LATENT REACTIVE
OLIGO(OXYETHYLENE)/CARBOSILANE AND
CARBOSILOXANE/CARBOSILANE COPOLYMERS VIA ACYCLIC DIENE
METATHESIS POLYMERIZATION (ADMET) FOR THERMOSET MATERIALS

By

Piotr Pawel Mattoka

May 2006

Chair: Kenneth B. Wagener
Major Department: Chemistry

Elastomeric materials can be found in many aspects of our life and the spectrum of

their use is broad. From shoe soles, cable insulators, and automotive parts to advanced

medical equipment, these polymeric materials are based on natural or synthetic rubbers

such as butyl rubber or silicones. Although many of these products have been used for

years, the development of novel synthetic methods for the improvement and creation of

new classes of elastomers are continuously being sought.

Acyclic diene metathesis (ADMET) has been proven to be an effective tool in the

synthesis of latent reactive carbosilane/carbosiloxane copolymers bearing a methoxy-

functional group on each repeat unit. The polymerization results in a linear thermoplastic

polymer. The latent reactive methoxy groups remain inert during polymerization;

however, exposure to moisture triggers hydrolysis and the formation of a chemically




crosslinked thermoset. The thermoset's properties can be modified by varying the ratio

of carbosilane and carbosiloxane repeat units in the final material.

Synthetic modification of the crosslink density and run length in the soft phase in

polycarbosilane/polycarbosiloxane elastomers is discussed. The incorporation of "chain-

end" crosslinks has improved mechanical performance by limiting the formation of

dangling chains. In addition, increasing the run length of the soft phase, to achieve a

better balance between soft phase concentration and crosslink density, generates a

material showing significantly improved mechanical performance.

Various oligo(oxyethylene) and carbosiloxane a, o-dienes with different lengths of

oxyethylene or siloxane units and alkenyl chains have been synthesized to investigate

their influence on the properties of the resultant materials.

Consequently, numerous thermoset materials that show physical properties from

elastic to flexible plastic behavior were prepared and analyzed. The results obtained from

mechanical testing and thermal analysis can be directly related to the structure of the

thermoset.


xvii







CHAPTER 1
ACYCLIC DIENE METATHESIS POLYMERIZATION (ADMET) APPROACH TO
SILICON-CONTAINING MATERIALS

1.1 Introduction

As an inherent part of organometallic chemistry, organosilicon chemistry is one of

the rapidly developing fields of science. Throughout nature, many well-known inorganic

and polymeric compounds contain silicon; however, there are no naturally occurring

organosilanes. Organosilicon chemistry has blossomed since Kipping's pioneering work

at the beginning of the 20th century. Numerous applications1-4 have been reported in the

manufacture of synthetic reagents and intermediates, bioactive molecules, biomedical

materials, electronic devices, specialty plastics, elastomers, coatings, and fibers.

Throughout the years, researchers have focused on silicon-carbon hybrids compounds

rather than purely inorganic structures.

Silicon/carbon hybrid polymeric materials have garnered considerable attention for

their enhanced properties (some that cannot be attained by using polymers based only on

carbon). The uniqueness of the silicon-carbon copolymers comes from their high thermal

stability, good electrical resistance, low surface tension, release and lubrication

properties, high hydrophobicity, low glass transition, and low toxicity for the natural

environment.4 The siloxane unit or the silicon atom can be incorporated into carbon-

based polymer backbone to tailor desired properties of the resultant material.2'' Several

synthetic methods involving anionic ring-opening polymerization, thermal








cyclopolymerization, condensation, and coupling reactions have been applied to

synthesize such hybrids.1,4

The simplest and most widely known organosilicon polymers are based on

silicones or polysiloxanes. This general class, well known for over 100 years, has many

valuable and unique properties. Silicones in particular, like polydimethylsiloxanes

(PDMS), exhibit hydrophobicity, thermal and oxidative stability, electrical resistance,

low glass-transition temperature, low environmental toxicity, gas permeability, and

antiadhesive properties. However, silicone elastomers based on polydimethylsiloxane

(PDMS) alone have relatively weak mechanical properties.2,'46,7 To improve their

mechanical performance (thereby extending their commercial use), researchers have

modified these silicon-based materials. The most economically viable method has been

to incorporate silica-based fillers in the polymer's matrix. For example, fillers have been

shown to impart elongation and overall mechanical properties of the resultant material.

These silicon-based materials (PDMS) can also be enhanced by incorporating carbon

segments resulting in silicon/carbon copolymers, which can be achieved via block or

grafted copolymers. There are numerous examples of these hybrid materials based on

PDMS-block-polysulfone,9 PDMS-block-poly(methyl methacrylate),'0 PDMS-block-

polyamide-6,11 PDMS-block-poly( -methylstyrene),12 PDMS-block-(bisphenol A

polycarbonate),1314 PDMS-block-polystyrene,1 poly(vinyl alcohol)-graft-PDMS,16 and

segmented polyurethane-graft-PDMS.17

Silicon-based hybrids are not the only example of organosilicon copolymers.

Progress in organometallic chemistry and in the chemistry of novel materials led to

production of new silicon-containing materials such as polycarbosilanes and








polycarbosiloxanes. These saturated or unsaturated materials offer many potential

industry applications, and produce new challenges for organosilicon chemists. Recently,

these materials have found uses in gas-separation membranes or as ceramics precursors.

1.2 Silicon Chemistry

Silicon is a second-row element, directly under carbon in the periodic table,

suggesting similar chemistry and reactivity to that of carbon. Silanes when compared to

their analogous carbon compounds (particularly in nucleophilic substitution) show

enhanced reactivity and relative rates. This trend relates to silicon's larger size and lower

electronegativity, and the atom's availability to impart low-energy orbital bonding (Table

1-1).1s

Table 1-1. Comparison of various silicon and carbon bond lengths and energies
Bond Bond Length Bond Energy
(A) (kJ/mol)
Si-C 1.90 318
C-C 1.54 334
Si-O 1.63 531
C-O 1.44 340
Si-Cl 2.11 471
C-C1 1.81 335

Correlations to silicon's reactivity or stability can be made and explained using

Table 1-1. For example, silicon-halogen bonds are easily cleaved by nucleophiles while

resistant to homolytic fission. These observation are realized by the large

electronegativity differences and high polarizability of both atoms producing highly ionic

bond in character.19 Also, silicon-oxygen bonds (siloxanes and silanols) are not

analogous to carbon-oxygen sigma bonds (ethers and alcohols). The lone pairs on

oxygen can overlap with an empty d-orbital on silicon, resulting in a highly polarized








bond. Recently, it was shown that o* orbitals can participate in back-bonding because of

their lower energy versus empty d-orbitals.1 This interaction justifies the fact that

silanols are stronger proton donors than aliphatic alcohols and that the decreased basicity

of oxygen is observed in the following order: C-O-C > Si-O-C > Si-O-Si.

1.3 Olefin Metathesis

Olefin metathesis has been investigated for over 50 years as one of the most

motivating discoveries in organometallic chemistry, widely used in both academic and

industrial settings.2022 In 2005, professors Yves Chauvin, Robert H. Grubbs, and

Richard R. Schrock were awarded the Nobel Prize in Chemistry "for the development of

the metathesis method in organic synthesis." The name, proposed by Calderon, Chen,

and Scott23 in 1967, originates from the Greek word metathesiss" meaning changing or

exchanging positions. The metathesis process involves reaction of two carbon-carbon

double bonds that yields two new olefins (Figure 1-1) and is described as an

intramolecular and intermolecular exchange of substituents on 1, 2 di-, tri-, or

tetrafunctional double bonds and "can be compared to a dance in which the couples

change partners." 24 This process can be divided into four categories:

* Simple exchange reactions

> Metathesis reaction involving two equal olefins
>Cross-metathesis (CM) reaction involving two different olefins

* Metathesis polymerizations

> Ring-opening metathesis polymerization (ROMP)
> Acyclic diene metathesis polymerization (ADMET)

* Ring-closing metathesis (RCM)

* Metathesis degradation of unsaturated polymers








a)


R R

b, c)

RCM













d)
Degradative R'
Metathesis of
SR' Unsaturated
Polymers +
Figure 1-1. Types of olefin metathesis: a) simple exchange reactions; b, c) metathesis
polymerization and ring-closing metathesis; c) metathesis degradation.

Many applications benefit from olefin metathesis, making this mild method for

creating a new carbon-carbon double bond a convenient tool for synthesis of small

molecules and for macromolecular synthesis. While the pharmaceutical industry has

embraced ring-closing metathesis to synthesize complex cyclic structures, acyclic diene

metathesis and ring-opening polymerizations are widely used by polymer chemists to

produce a vast number of functionalized hydrocarbon polymers and silicon-carbon based

hybrids.

In the next sections some background information on the ADMET approach to

silicon-containing polymers and copolymers catalyzed by "well-defined" catalyst systems

is described. Complementary method to ADMET polymerization such as silylative








coupling (SC) polycondensation of divinyl organosilicon derivatives (which shows low

metathesis activity) is also discussed.

1.3.1 Brief History of Olefin Metathesis

The first research on olefin metathesis and its industrial application that led to

publication was by Banks and Bailey25 from Philips Petroleum in 1964. The observed

reaction was called olefin disproportionate and was performed in the presence of the

heterogeneous catalyst. The publication, however, was foreshadowed by Eleuterio's26

and Peters'27 patent disclosures few years earlier.

Several mechanisms were initially proposed to account for all observed exchange

reaction products. The process consistently involves subsequential bond breaking and

reformation after a transition metal 2+2 cycloaddition/retroaddition mechanism. The

Chauvin mechanism (Figure 1-2) was initially ignored, only to become the most widely

accepted mechanism with both metalla-cycle and metalla-carbene intermediates.28

R R' R R' R R'


M] [M] [M]
R" R" R"
Figure 1-2. Metallacyclobutane mechanism.

Olefin metathesis is a catalytically initiated reaction with numerous active catalytic

systems. These catalysts, either homogeneous or heterogeneous, contain transition

metals such as molybdenum, tungsten, rhenium, tantalum, ruthenium, rhodium, or

titanium.20 Common to industrial applications, the catalyst systems are typically

heterogeneous versions of either Mo, W, or Rh oxides or carbonyls supported on highly

developed A1203 or Si02. The presence of co-catalyst is often required in these systems,

usually a Lewis acid (a main group tri- or tetravalent metal). On the other hand,







homogeneous systems (coordination complexes) can be active with or without the

presence of the co-catalyst.

In the early days of olefin metathesis, organometallic chemists raced to synthesize

metal carbene complexes that might improve understanding of the metathesis process.29-

33 Further investigations during the mid-1980s led Schrock and coworkers to the

development of neutral carbene complexes based on tungsten34-36 and molybdenum37-39

(Figure 1-3). These catalysts were active in metathesis transformations and were called

"well-defined" because the catalytically active species were easy too identify by

spectroscopic methods. Because of the oxophyllic nature and low-tolerance to

polar-functional groups, there were some limitations in the utility of these catalysts.

Efforts were made to develop catalyst systems based on late transition metals that in

complexes form catalysts more tolerant to air, moisture and functional groups.




H3C N CH3 H3C N CH3
F3C O-W-O- CF3 F3C -0Mo-Ok CF3
F3C CHR CF3 F3C CHR" CF3
R'= t-Bu; R"= -C(Me)2Ph
[W] [Mo]
(1) (2)


PCy Ph PCy3Ph
ClRu j Ph Ru C1=\ Y
PCyz PCy3Ph
[Ru] [Ru]* [Ru]**
(3) (4) (5)

Figure 1-3. Well-defined metathesis catalysts.

In 1992 Grubbs and coworkers40 introduced the first well-defined ruthenium based

catalyst [Ru] (3) (Figure 1-3), where their increased stability allowed for manipulations








outside an inert atmosphere. The ligation sphere of the first-generation ruthenium-based

catalyst [Ru]* (4) was soon modified by substitution of one phosphine ligand with a

N-heterocyclic carbene ligand.41'42 In some cases this change achieved catalytic activity

comparable to one of the molybdenum Schrock's catalyst41 [Mo] (2), and a higher

tolerance of functional groups was observed than in the first-generation Grubbs' catalyst

[Ru]* (4).42 Structural isomerization 43,44 of the olefin can accompany olefin metathesis,

an event that influences the synthesis of the exact structures through RCM and ADMET.

Despite of vast number of "well-defined" catalysts that have been synthesized, none of

them have proven to be applicable for all substrates or transformations.

1.3.2 Introduction to ADMET Polymerization

The discoveries and developments in the field of olefin metathesis and

organometallic chemistry have made olefin metathesis a convenient synthetic tool for the

synthesis of functionalized and non-functionalized polyolefins.21 As previously

mentioned there are two modes of olefin metathesis polymerization: ring-opening

metathesis polymerization (ROMP)21 and acyclic diene metathesis polymerization

(ADMET)21 (Figure 1-4).

ADMET
cat.
-CH4
(6) (7)


ROMP

cat.


(8) (9)

Figure 1-4. Acyclic diene metathesis (ADMET) and ring-opening metathesis (ROMP)
polymerizations.








ROMP falls into chain-addition type polymerization category. It is an exothermic

reaction, thermodynamically driven by the release of ring strain in a cyclic olefin

monomer. ADMET is step-growth condensation type polymerization and thermally

neutral. It is important to understand requirements and consequences for these

classifications.

Acyclic diene metathesis is a step-growth condensation type polymerization that

normally employs an a,wo-diene in conjunction with a metathesis catalyst to produce high

molecular unsaturated polymer. The reaction is driven by removal of a small condensate,

usually ethylene. ADMET follows the same rules as any other polycondensation

reaction, meaning that high conversions (>99%) with no side reactions are necessary to

produce high molecular weight polymers.45 This reaction, as in the case any

condensation polymerization, is an equilibrium process, which proceeds in a stepwise

fashion to form dimer, trimer, tetramer, and so on to obtain high molecular polymer. The

size of the polymer increases continuously with time (conversion) at relatively slow rate.

Growth of molecular weight is described the Carother's equation that relates the number-


average degree of polymerization Xn (also known as the degree of polymerization, DP)

to the extent of reaction p or conversion of the diene monomer.

1
Xn = -
l-p
Figure 1-5 shows a typical plot of theoretical X" versus conversion of the

monomer in any condensation type polymerization. High molecular weight polymer is

obtained at the end of polymerization when the conversion of monomer is larger than that

of 99%. Thus, a highly active catalytic system is required throughout the polymerization;

most catalysts however, show higher activity towards terminal olefins for steric hindrance









reasons, and so a,oo-diene monomers are often used in acyclic diene metathesis

polymerization.


200


S150


o 100

I-1
50




0 20 40 60 80 100
% Conversion

Figure 1-5. Theoretical degree of polymerization vs. conversion in condensation type
polymerization.

Early investigations of polymerization of 1,5-hexadine (6) and 1,9-decadine (10)

(Figure 6), by Wagener and co-workers in the mid-1980s, demonstrated that "classical"

catalysts such as WC16/EtAlC12 can lead to both cationic vinyl addition chemistry and in

addition to polycondensation chemistry,20'46 thereby defining the need for active and

well-defined catalyst for metathesis. Fortunately, in 1986, Schrock34 and co-workers

successfully prepared the first well-defined, single site catalyst, a breakthrough in this

field. This breakthrough led to more stable ruthenium based catalytic systems discovered

by Grubbs.

cat.
'' CA- C2H4
(10) (11)
Figure 1-6. ADMET polymerization of 1,9-decadiene.








Like many other polycondensation reactions, ADMET polymerization is best

performed in the bulk (neat) to maximize the molar concentration of monomer (terminal

olefins) and to promote a shift in the equilibrium of the reaction from monomer towards

unsaturated polymer formation. Bulk polymerization also minimizes undesired

cyclization, a well known concurrent reaction in polycondensation chemistry.45

Moreover, high vacuum is applied to remove the condensate ethylene, which further

shifts reaction towards polymer formation.





[n1-,R R



H2C=CH LnM R

LnMn- Ln R- R

I I



R LnM'CH2 'R
Figure 1-7. The catalytic cycle of ADMET polymerization.

The mechanism of the ADMET polymerization cycle, Figure 1-7, has been well

documented.46'47 Each step in this mechanism is in true chemical equilibrium, and the

ultimate driving force for the reaction is removal of ethylene. The catalytic cycle starts

with coordination of an olefin, followed by formation of a metallacyclobutane

intermediate and productive cleavage that leads to the formation of the metathesis active

alkylidene complex. These subsequent reactions produce a methylidene complex








followed by the coordination of another monomer. Productive cleavage of another

metallacyclobutane results in release of one ethylene molecule per each catalytic cycle.

The developments in the field of well-defined catalysts along with the clean

mechanism of ADMET have become instrumental in the synthesis of novel polymers

with controlled architectures. The design starts with the preparation of a,c-diene bearing

desired type of functionality or specific type of branching. The resultant polymer retains

this functionality and a specific backbone sequence. ADMET has produced unsaturated

polymers where the functionalities have been ethers,48 esters,49 carbonates,50 sulfides,51

and many more functionalities.52'53 Consequently, ADMET bypass typical synthetic

obstacles in the synthesis of polymers and copolymers, and allows creating polymer

structures that cannot be prepared via other routes.

1.4 Olefin Metathesis Chemistry of Compounds Containing Silicon

In the early seventies, research on metathesis was predominantly focused on

producing materials from simple silicon functionalized olefins. In 1971, Friedman

described the first example of these materials by the metathesis of monoalkenylsilanes in

the presence of MoO3/A1203.54 In addition to these simple materials, a variety of

organosilicon compounds can be produced using metathesis and can be divided into three

categories based on choice of polymerization method and structure of monomer:

* ROMP of unsaturated silacycloalkenes

* ROMP of silylsubstituted cycloalkenes

* ADMET of a,o-dienes containing silicon

First, the ROMP of the unsaturated silacycloalkenes leads to polymers containing

silicon atoms incorporated in the carbon backbone, as exemplified in Figure 8. The








metathesis of 1,1- dimethyl- 1-silacyclopent- 3-ene (12) proceeds in the presence of

tungsten55 or alumina-rhenium56 and offers a broad scope for all silacycloalkenes, except

for the thermodynamically stable silacyclohexene derivatives.

CH3
n cat IN
Si Si
H3C 'CH3 CH3 Jn
(12) (13)
Figure 1-8. Ring-opening metathesis polymerization of 1,1-dimethyl- 1-silacyclopent
-3-ene.

Second, the ROMP of silylsubstituted olefins leads to unsaturated polymers

(Figure 1-9) containing pendant silyl groups used to modify the properties of the

polymer's backbone. One such example is the ROMP of silylsubstituted norbornenes in

the presence of either a homogeneous tungsten catalyst or a heterogeneous alumina-

rhenium catalyst.57


I R cat.
R
(12) (13)

R = SiMe3, SiMe2CH2SiMe3, SiC13, Si(OEt)3
Figure 1-9. ROMP of silylsubstituted norbornens.

An interesting example of ROMP is the reaction of 1-(trimethylsilyl)cyclobut- -ene

(16) in the presence of Casey's carbene complex (Figure 1-10).58

SiMe3 cSiMe

i-n
(16) (17)

cat. = (CO)5W=CPh2
Figure 1-10. ROMP using Casey's carbene complex.

The resultant polymer shows a repeating head-to-tail structure containing only the cis

double bond configuration. Moreover, this trimethylsilyl groups can be easily converted








into different functionality making them a surrogate for the functional group before

metathesis.

Third, the ADMET polymerization of a,co-dienes containing silicon leads to

formation of unsaturated polymers which, depending on the structure of monomer, can

either include silicon functionality incorporated into polymer backbone or as a pendant

groups along the polymer chain. Contrary to ROMP which can be limited to the use of

strained cyclic monomers, ADMET offers wide spectrum of polymer structures. Thus,

utility of ADMET polymerization will be discussed in the next section.

1.4.1 Acyclic Diene Oligomerization and Polymerization

Acyclic diene metathesis polymerization of silicon-containing compounds is the

most universal method amenable for the synthesis of unsaturated organosilicon oligomers

and polymers. The clean and efficient chemistry of ADMET combine desired material

properties of both carbon and silicon based polymers in the random linear copolymer.

Moreover, the high selectivity of olefin metathesis facilitates an introduction of a wider

range of possible "functional handles" to manipulate the overall material properties.

Metathesis of dialkenylsilicon derivatives can be achieved either by an

intramolecular or an intermolecular approach. The intermolecular ADMET reaction

between a,o-dienes (with exceptions of divinyl derivatives) produces linear, unsaturated

polycarbosilane or polycarbosiloxane oligomers or polymers. Unsaturated heterocyclic

organosilicons can also be produced by an intramolecular reaction if preferred. The

mechanism of reaction is strictly dependent on the structure of the initial a,o-diene and

substituents on silicon; note that in some cases a six membered ring compound will be

preferentially formed as the most thermodynamically stable product. Since all possible








pathways are in equilibrium, both the seven and five membered rings are rarely observed.

Product formation can be influenced to some extent by the presence or absence of solvent

in the reaction environment.

As mentioned, the divinyl derivatives of silicon compounds do not undergo

homometathesis, mainly due to the steric and electronic effects of two silyl groups

present on the adjacent carbon atoms in the intermediate metallacyclobutane.35 However,

while studying the hydrosilative activity of simple Ru(II) and Ru(III) complexes,

Marciniec and coworkers59-62 have shown that catalytic metathesis of alkoxyvinylsilanes

is a competing reaction. However, soon after was found that this process does not

operate through metallacyclobutane mechanism. Thus, application of this silylative

coupling (SC) polycondensation in the formation of macromolecular structures

containing silicon will be described in the later in separate section.

1.4.2 ADMET Catalyzed by "Ill-Defined" Catalytic Systems.

Ill-defined catalyst systems do not easily lend themselves to metathesis

polymerization chemistry, thus the practical utility and the scope of olefin metathesis

have been limited toward functional groups, such the ones based on silicon.

R ,R2 [Re] R R R, R2
S1 +
S -C2H4,35 0C I<- n
F2 XR
(18) (19) (20)
R1 RI
+ 4 ySi.,,. -^ A
R2 2 X
(21)
[Re] = Re207/A1203 + Sn(or Pb)R4
R1 = R2 = Me, Et or R1 = Me, R2 = Ph where: n = 1; R = R2 = Me where n = 2; x = 1-4
Figure 1-11. Polymerization of diallyl- and allyl-butenyl derivatives of disubstituted
silanes.










The first information regarding metathesis and co-metathesis reactions in the

presence of these aforementioned catalytic systems were published in early eighties. The

reactions reported by Vdovin et al.63 utilized the heterogeneous Re207/A1203 catalyst

along with a tetraalkyltin or tetraalkyllead co-catalysts. Vdovin's and Finkelshtein's6366

research interests were focused on polymerization of diallyl and the allyl-butenyl

derivatives of methyl, ethyl, and phenyl substituted silanes, as presented in Figure 1-11.

Predominantly, cyclic products (20) were formed along with some traces of oligomeric

compounds.

The attempted polymerization of diallyltetramethyldisiloxane (22)67, Figure 1-12,

performed in the presence of Re207/Al203+Sn(Pb)R4, was accompanied by partial

cleavage of the Si-Callyl and Si-O bonds, resulting in dissproportionation of the Si-O

bonds and formation ofpolysiloxane chains.

Me Me Me 1 Me
cat. I
Si-O-Si^ _HSi-O -Si +Me S
Me Me 4Me JMe Met O Me
(22) (23) (24)


SMe Me
+ Si-O-Si
Me Me
n
(25)
Figure 1-12. Polymerization of diallyltetramethyldisiloxane.

Similarly to what is observed during attempted polymerization of diallyl and the

allyl-butenyl derivatives of disubstituted silanes, polymerization of

diallyltetramethyldisilane (26) resulted in formation of both linear and cyclic products,

where the former predominates (Figure 1-13). In this case, cyclized product is formed







over the linear structure, what one can be attributed to the higher stability of the six

membered disilane product.

Me Me Me Me
I I I Me S-Me
f Si-Si t Si + iMe
Me Me Me Me

(26) (27) (28)
Figure 1-13. Metathesis of diallyltetramethyldisilane.

Many attempts have been taken to introduce a secondary functionality ("latent

reactive sites") to silicon-based monomer other than those used by ADMET. An

interesting example shows ADMET polymerization of dialkenysilanes containing the

highly reactive silacyclobutane 68,69 (Figure 1-14). Hence, Finkelshtein observed that

ADMET chemistry occurs in the same manner as for any other dialkenylsilanes, while

maintaining the highly reactive silacyclobutane in every repeat unit. The resultant

oligomer's expansion, when heated, cleavage of Si-C bonds in the four-membered ring

yielding a crosslinked, waxy material.


cat + + /Qn
-m
.C2H4"-
(29) (30) (31)
n=l,2
m=l-3
Figure 1-14. Metathesis of dialkenylsilacyclobutane.

In spite of the lack of metathetical conversion for divinyl organosilicon derivatives,

Kawai and coworkers70'71 have recently reported successful synthesis of O-2t conjugated

oligo(silylene-vinylene)s from tetravinylsilanes and divinylsilanes in the presence of

Re203/A1203 promoted with SnBu4. These polymers are important class of partly

conjugated optical materials, which based on the ab initio molecular calculation, should

exhibit high transparency and relatively high second and third hyperpolarizability. It was








found that the addition oftetrabutyltin is essential for ADMET to occur. The reactivity

of Schrock's and Grubbs' catalysts was also examined; however the catalysts did not

succeeded, for reasons described previously. All products were linear oligomers, and

cyclic products were not detected.

1.4.3 ADMET Catalyzed by "Well-Defined" Catalytic Systems

In the early 90's Wagener and co-workers72-75 opened a new chapter in the

synthesis of unsaturated polymers and copolymers containing silicon by preparing

polycarbosilanes and polycarbosiloxanes with acyclic diene metathesis polymerization

using well-defined ADMET catalysts (Figure 1-2).

1.4.3.1 Polycarbosilanes

Polycarbosilanes are an interesting class of polymers due to the presence of

covalent bond between silicon and carbon atoms in the backbone. Potential applications

of these materials in the broad range of fields have triggered considerable interest in their
-2
preparation.2


r l] I
Si ~+ #- % L~4. J Si
CH3 6 -C2H4
CH3 LCH3 m -- m
(32) (10) (33)
Figure 1-15. Copolymerization of divinyldimethylsilane (32) with 1,9-decadiene (10).

The first silane diene, dimethyldivinylsilane (32),72 subjected to ADMET

polymerization did not polymerize in the presence of the tungsten based Schrock's

catalyst [W] (1), where the lack of productive metathesis was attributed to the steric

influence of the trisubstituted silicon atom adjacent to the double bond. Similar results

were obtained by Schrock and coworkers36 in the attempted metathesis of

vinyltrimethylsilane. The steric influence was further demonstrated via copolymerization








of divinylsilane (32) with 1,9-decadiene (10) where the divinyl repeat unit was found

to insert in a singular manner along the backbone, Figure 15.

Metathesis
CH CH13
CH3
LnW=CH2 + -'iHi ,i
CH I CH3
L (35) CH3
LW Si (36)
H3C, CH3
H3C -Si LnW IH3 CH3
S L + Si
(34) I
CH3 CH3
(37) (32)
Co-Metathesis

CH
SLnW=CH2 + 1 Si"

LnW H i (39) CH3
1 (40)
SCH3
R
CH3
(38) LnW R +
(41) CH3
(32)

Figure 1-16. Productive and non-productive metathesis.

Finkelshtein 66 provides a different explanation for the lack of reactivity of

divinyldimethylsubstituted silanes in the ADMET polymerization. His rationalization is

based on the formation of the highly stable silylated carbene complex, Figure 1-16, and

its reactivity under copolymerization conditions. During the homopolymerization of

divinylsilanes, formation of the metathesis active methylidene complex (35) competes

with an inactive silylated carbene (37). The reaction goes through the

thermodynamically more favorable process that leads to formation of the stronger

stabilized silylated carbene, and thus the metathesis product is not observed. In the case







of copolymerization, the stability of both carbene complexes does not differ significantly

and two pathways are possible. The productive copolymer formation is realized along

with the unproductive formation of the starting divinylsilanes.

Further investigations have shown that monomers with the methylene spacers

incorporated between the silicon atom and the olefin are able to undergo productive

metathesis polymerization (Figure 1-17) 72. Successful ADMET polymerization

produces unsaturated polymers containing predominately (80%) trans double bonds.

Exceptions are observed while polymerizing stiffer carbon segments; for example, the

polymerization of 1,4-bis-(dimethylallylsilyl)benzene results in a 47% cis configuration

along the unsaturated backbone. 72

CH3 CH3
I [W] {
CH3 4 .CH3
(42) (43)

CH3 CH3
CH3 ]. CH3
H CH3 -C2H4 CHzi I
CH, CH3 n
(44) (45)

CH CH3 CH3 CH3

CH3 CH3 _CH3 CH3 .
(46) (47)
Figure 1-17. Polycarbosilanes via ADMET.

As shown in Figure 1-14 Finkelshtein68'69 has successfully polymerized a,co-diene

bearing highly reactive silacyclobutane using ADMET methodology. Similar study using

"well-defined" catalytic system was conducted by Interrante and coworkers.76 The

carbosilane polymers and copolymers were synthesized with the disilacyclobutane rings

imbedded into the copolymer's backbone (Figure 1-18).








Me Me Me
Si Si [Ru]** Si SiTPA SSi
Me -CH2CH2 Me 2 Tn T Me
(48) (49) (50)

TPA: tripropylamine
TSH: p-toluenesulfonydrizide
Figure 1-18. Polycarbosilanes with the disilacyclobutane rings.

Unsaturated materials were hydrogenated using methodology developed by Hahn77

which does not require the use of high-pressure H2, and the disilacyclobutane rings were

thermally induced to open resulting in a transparent, crosslinked solid material.

1.4.3.2 Polycarbosiloxanes

A similar to carbosilanes, investigation of ADMET has shown that siloxanes are

also polymerizable with the Schrock's molybdenum catalyst [Mo] (2) (Figure 1-19 and

Figure 1-20). Polymerization leads to formation of unsaturated polycarbosiloxanes.73'74

CH3 CH3
3 3 [Mo]
Si-O-Si no metathesis
I I
CH3 CH3
(51)

CH3 CH3 H3C CH3
e3 e3 [Mo]i SiN. -0
Si-O-Si o H3 C-S CH3
I I -CH4
CH3 CH3 -
(52) (53)
Figure 1-19. Non-productive ADMET polymerization.

As in the case of divinyldimethylsilane, sterics has a predominant effect on both the

productive and non-productive metathesis rates of vinylcarbosiloxane (51) (Figure 1-19).

On the other hand, the reaction of 1,3-diallyl-l,1,3,3-tetramethyldisiloxane (52) where

siloxane group is "spaced out" by one methylene unit, leads to the ring formation (53)78

and essentially quantitative conversion for cyclization of diallyldisiloxane was observed.

This exclusive and fast cyclization with no oligomerization indicates great







thermodynamic stability of this seven membered ring (Figure 1-19). Thus, an increased

flexibility of siloxanes requires longer distances between the olefin and silicon to produce

ADMET linear polymers, as shown in Figure 1-20.

CH3 CH3 CH3 rCH3 CH3 CH3
I I I [M o] I I I
,-Si-O-Si-O-Si [S. IN Si-O-Si-O-Si1
CH3 CH3 CH3 4 3 CH3 CH3

(54) (55)

CH3 CH3 CH3 CH3 CH3 CH3
I |I 3 CMo] iO "S N
Si-O-Si-O-Si [ i-O- i-O-i
SCH3 CH3 CH3"3 -C2H4 CH3 CH3 CH3 .n
(56) (57)

CH3 CH-a CH3 CH3
Si-O-S i---r ---i-O-Si %
CH3 CH3 CH3 CH3
(58) [Mo]




CMH3 CH32 CH3 CHi
(59)
Figure 1-20. ADMET polymerization of siloxane containing dienes.

Another noteworthy example of ADMET copolymerization is an insertion of an

aromatic diene repeat unit into an unsaturated polycarbosiloxane.74 Smith et al. have

shown that slow addition of small diene monomer to unsaturated oligomer offers more

than statistical control of copolymer by kinetically inhibiting homometathesis of the

added diene (Figure 1-21).

As previously shown in Figure 1-19 divinyl siloxane derivatives are reluctant to

homometathesis; however, like divinyl silane they undergo copolymerization. The first

successful copolymerization of divinyltetraethoxydisiloxane (63) with 1,9-decadiene (10)

in the presence of the Grubbs' catalyst [Ru]** (5) was reported by Malecka et al. Figure












1-22.79 No consecutive linkage of divinyltetraethoxydisiloxane was observed.

Surprisingly, in the similar experiment where divinyltetraethoxydisiloxane (63) was

substituted with divinyltetramethyldisiloxane (51), copolymerization failed and no

polymeric or oligomeric products were detected. The lack of metathetical activity of

divinyltetramethyldisiloxane (51) in copolymerization was attributed to the

decomposition of the Grubbs' catalyst [Ru] ** (5) due to the p-transfer of silyl group to

ruthenium in the metallacyclobutane, previously observed by Pietraszuk et al.80

CH3 CH3 CH3
I I I CH3 CH3 CH
Si-O-Si-O-Si I I I
I I I Si-O-Si-O-Si
CH3 CH3 CH 3 I I I
CH3 CH3 CH3
(60)


Toluene
[w] / \/ \/
(61)



Si-O-Si-O-Si I I I C /
CH3 CH3 CH3 I ,C
SCH3 CH3 CH3 Y

(62)
Figure 1-21. Controlled diene insertion via ADMET.

Marciniec and Majchrzak81 have subjected divinyltetradisiloxane to ADMET

copolymerization conditions in the presence of 1,4-divinylbenzene (65) (Figure 1-22).

Analysis of this copolymer showed the structure to be perfectly linear and trans(stereo)-

regular.










OEt OEt OEt OEt
I I ,, [Ru]
Si-O-Si- + i-O- '
6I CH2CH2
OEt OEt OEt OEt
(63) (10) (64)


OEt OEt [Ru]* OEt OEt /
i"Si-O-sOSi + / -- -
I I/1 CH2CH2 I i
OEt OEt OEt OEt

(63) (65) (66)
Figure 1-22. ADMET copolymerization of divinyltetraethoxydisiloxane.

1.4.3.3 Telechelic oligomers

Telechelic polymers are macromolecules which contain one or more functional end

groups that can form bonds with another molecule. They offer potential use e.g. in the

formulation of model networks82 or in the preparation of thermoplastic elastomers.83

Preparation of this type of macromolecule is not trivial, especially those possessing

functionality of 2.0 essential for the stoichiometric balance in the polycondensation

reactions.84

ADMET polymerization is a convenient route to prepare an a,o-telechelic

polyoctenamers with the functionality close to 2.0.85'86 1,9-decadiene (10) was

polymerized in the presence of the Schrock's catalyst [Mo] (2) using dimers (71) of

5-hexenyl-methoxydimethylsilane or 5-hexenyl-chlorodimethylsilane as chain limiters

Figure 1-23. As expected, the number average molecular weights for these telechelic

oligomers were proportional to the ratio of the monomer to the chain limiter. Further,

these highly reactive macromonomers were exploited to synthesize ABA block

copolymer of polydimethylsiloxane-polyoctenamer-polydimethylsiloxane.









CH CH3 CH3
X-S CH + [Ru]* or [Mo] X-Si Si-
i+ # i3S -CH2CH2 CH3L3 JY CH3
6H3 IiH3 kIn3
CH3
(71) (10) (72)

where: X= -Cl, -OCH3
Figure 1-23. Telechelic polymers via ADMET.

Smith and Wagener73 synthesized a,o-oligodiene via hydrosilation of

1,4-pentadiene (68) with 1,1,3,3-tetramethyldisiloxane (67), which then was exposed to

ADMET conditions as shown in Figure 1-24. This nonvolatile, quick flowing liquid is an

ideal monomer for ADMET polymerization due to the fact that continuous high vacuum

can be applied during polymerization.


CH3 CH3
H-Si-O-Si-H
I I
CH3 CH3
(67)


+ s


I IN


X
(69)


[Mo]
- CH2CH2
i


[Pt] = Karstedt's catalyst
Figure 1-24. ADMET polymerization of a,o-telechelic diene macromonomer.









1.4.3.4 Functionalized polycarbosilanes

The polycarbosilanes presented in Section 1.3.1.2.1 possess a simple silicon-carbon

backbone. In order to introduce functionality along the polymer's backbone, Cummings

et al. 8788 synthesized chloro- and dichlorosilane a,co-dienes (73), that undergo successful

ADMET polymerization (Figure 1-25) in the presence of the Schrock's catalyst [Mo] (2).

Cl Cl
I I
S ^ [Mo] 4 *Si N >
I CHzCH I ^ '"x
SJ-n
(73) (74)
where: R= Cl, CH3
Figure 1-25. Chloro- and dichloro-functionalized polycarbosilanes via ADMET.

These chlorofunctionalized thermoplastic materials were exposed to different

nucleophilic organolithium salts yielding polymers with various physical properties

depending on the bulkiness of the nucleophiles. This concept was previously used by

Allcock4 to tailor desired properties ofpolyphosphazanes. Allcock has also showed that

cyclolinear phosphazane containing polymers that can be obtained via ADMET

polymerization.89,90

Nuc
Si
I N




Nuc [Cl
N I
X Nucx Cl x


Cl


Figure 1-2. Two routes to polymer modification.
Figure 1-26. Two routes to polymer modification.







Subsequently, Church et al.9192 demonstrated the utility and flexibility of ADMET

in the one-pot synthesis of alkoxy-functionalized carbosilanes. They demonstrated that

functionalization can be facilitated either via macromolecular substitution or substitution

on the a,o-diene monomer (Figure 1-26). As noted above both pendant groups on the

carbosilane polymer backbone have a significant effect on the physical properties of

resultant polymer. These alkoxy-functionalized polymers can be further crosslinked to

yield a polymer network.

1.4.3.5 Latent reactive elastomers

The functionalized polycarbosilanes via ADMET described above offer a new

approach to the synthesis of materials exhibiting variable physical properties. This

research has led to a new type of synthesis involving "latent reactive"

carbosilane/carbosiloxane copolymers by Brzezinska75 (Figure 1-27), illustrating the

random incorporation of "latent reactivity" throughout polycarbosiloxane backbone in the

form of the alkoxy-substituted carbosilane.
S CH3 CH3 CH3
OCH I I

CH OCH3 CH3 CH3
OCH3
(75) (76)
Latent Reactive Carbosilane HARD [Mo] Carbosiloxane SOFT


OCH3 CH3 CH3
OCH3 I I I

OCH OCH3 X CH 3 CH3 y
OCH3
(77)
Figure 1-27. Latent reactive carbosiloxane/carbosilane copolymer.

It is well known that the methyl silyl ether bond, which inert during ADMET

chemistry, easily hydrolyzes in the presence of moisture and condenses to form stable

siloxane linkage.7 Consequently, the physical properties of ADMET








polycarbosilane/polycarbosiloxane copolymers can be tuned by selecting the appropriate

molar concentrations of each monomer. Figure 1-28 illustrates this modular approach

and shows its extensive application in the generation a large number of materials

exhibiting physical properties from elastic materials to plastics.

OCH3
S Latent Reactive Carbosilane HarC + VVSof
OCH3



Low (10%) High (> 90%)
Hard Segment Hard Segment
Content Equal RatioE Content
(50/50)


|m0--- pwvwwF --- I JA
Hard Soft Hard Soft Hard Soft
Elastomer Intermediate Properties Plastic
Figure 1-28. The latent reactivity concept to attain diverse behavior of materials.

1.5 Silylative Coupling (SC) Polycondensation

Previously mentioned, ADMET polymerization is a universal method to obtain

unsaturated organosilicon polymers. A vast number of a,co-dienes containing silicon

functionality tend to be active in this process, when catalyzed by well-defined carbene

complexes. On the other hand divinyl organosilicon compounds are an exception, since

they remain inert under conditions of acyclic diene metathesis polymerization. It

happens that the sterics of silyl groups stimulate a nonproductive cleavage of

disilylmetallacyclobutane.35

The Marciniec research group has found an important way to solve this problem.

Divergent to well-defined olefin metathesis catalysts, numerous ruthenium and rhodium

complexes that contain or generate in situ metal-hydrogen or metal-silicon bonds catalyze

intermolecular polycondensation of divinyldiorganosilicon derivatives.








SiR3 SiR3 [Ru]-H
SiR3 R3 Si





Ru]S SiR [Ru] SiR3 [Ru] SiR
H H H SiR3 H



SiR3
]Ru]-SiR3


[Ru] = RuHC1(CO)(PPh3)n
Figure 1-29. Catalytic cycle of silylative coupling.

At first, Marciniec et al.60 proposed a mechanism in which carbene is formed by

rearrangement of a metal hydride complex. Soon after it was found that catalysis

operates via non-metallacarbene mechanism;93'94 where series of o-complexes are formed

via insertion-elimination, as depicted in Figure 1-29. These transformations were termed

silylative coupling polycondensation (SC) (or as referred by Finkelshtein66 may as well

be called Marciniec's metathesis). Complexation of the olefin to electrophilic metal

center is followed by metal insertion into the C-H bond. Elimination of ethylene yields

metal-silyl complex that coordinates another vinylsilane, which inserts into M-Si bond

followed by reductive elimination of homometathesis product while regenerating hydride

complex. Formation of the 1,1-bis(silyl)ethene as product along with cis/trans 1,2-

bis(silyl)ethenes distinguish this reaction from olefin metathesis where only former two

are formed.

Early attempts at polymer synthesis via SC polycondensation of divinylsilanes and

bisvinylsiloxanes (Figure 1-30) catalyzed by RuCl2(PPh3)3 and RuHCl(CO)(PPh3)3








yielded polymers in moderate conversions, too low for step-growth polymer

chemistry.


S cat. Si
-CHCH2 Si Si
n m

where:
Si = silane, siloxane
cat.= RuCl2(PPh3)3 or RuHCl(CO)(PPh3)3
Figure 1-30. SC polycondensation of divinylsubstituted silicon monomers.

While rhodium-based catalysts were used two monomers of

divinyltetramethyldisiloxane have undergone ring closure which subjected to X-ray

spectroscopy revealed a boat conformation.97

Further studies in the synthesis of polycarbosilanes and polycarbosiloxanes from

divinyl organosilicon derivatives were conducted by Malecka et al.9-'100 who

demonstrated the dependence of catalyst identity on polymer's morphology. SC

polycondensation of divinyl organosilicon compounds catalyzed by ruthenium-phosphine

complexes, such as shown in Figure 1-30, yielded linear polycarbosilanes or

polycarbosiloxanes. Both trans-1,2- and gem-1,1- fragments were present in the

polymer's backbone, while highly stereoselective trans-tactic structures were formed

when [RuCl2(CO)3]2 was used. Moderate molecular weights of polymers were obtained

as well.

Majchrzak et al.81,01-103 have successfully synthesized numerous phenylene-

silylene-vinylene and siloxylene-vinylene-phenylene polymers and copolymers via SC

polycondensation, producing highly stereo- and regioselective structures with values of

Mw from 13,100 to 34,800 g/mol.103 Alternate ruthenium complexes were screened in

order to find a catalyst that promotes these regular structures. Furthermore, they have








extended the utility of SC polycondensation to the synthesis of organosilicon starburst

materials that contains the silicon-bridged x-conjugated structure,104'105 as shown in

Figure 1-31.


Figure 1-31. Starburst oligomer via SC.

1.6 Crosslinking Methods for Silicon-Containing Materials.

Elastomers are described as ,,materials that can be stretched many times its original

length without breaking, and will snap back to its original size when it is released."106 To

prevent polymer chains from slipping past each other during elongation, either physical

or chemical crosslinks have to be present.

Elastomers containing physical crosslinks e.g. glassy polymer (with Tg above room

temperature) or semi-crystalline polymer (with Tm above room temperature) are termed

thermoplastic elastomers, because they can be reshaped upon heating above Tg or Tm. On








the other hand, elastomers that contain chemical crosslinks are called thermoset

elastomers, and polymer chains are hold together through covalent bonds forming a

single networked molecule. The degree of crosslinking is very important for the final

properties of materials. Too many crosslinks make material stronger, but brittle, and only

lightly crosslinked materials are effective elastomers.

Applications of silicon-based materials in elastomers, coatings, and resins require

that the materials do not flow; therefore crosslinking of these materials is necessary.

In general, crosslinking requires presence oftri- or tetrafunctional silanes that can

react under ionic conditions, or organic groups that are pendant or are on the end of the

silicone polymer. Most silicone elastomers are prepared via one of the three crosslinking

routes: moisture cure, heat-activated radical cure, or addition cure.1,4

First, moisture cure crosslinking, very often referred to as room-temperature

vulcanization (RTV), takes advantage of the susceptibility of the silicon atom to

nucleophilic substitution. Very often hydroxy-terminated polysiloxanes are crosslinked

by reacting with tri- or tetrafunctional silanes at room temperature. The rate of the cure is

strictly dependent on the rate of hydrolysis of the leaving groups, thus very often these

reactions are catalyzed by acids, bases, and by tin or titanium alkoxy/acyloxy derivatives.

Second, heat-activated radical cure (high-temperature vulcanization HTV) involves

formation of free radicals from peroxides e.g. m-chlorobenzoyl peroxide or

di-t-butyl peroxide. Two main reactions are observed while using these systems: the

hydrogen radical abstraction from the methyl group attached to the silicon and the radical

addition to vinyl groups. The reactivity of the latter reaction is higher than the hydrogen

radical abstraction; therefore lower temperatures can be used to crosslink vinyl-











substituted silicones. The distribution of vinyl groups along polymer backbone plays

important role in the characteristics of the cured materials. The formation of the polymer

network is more efficient in the systems where vinyl groups are distributed

homogenously, rather than the blocky systems where vinyl groups tend to react with each

other. In the latter case this reactions do not contribute to formation of the network.

Third, addition cure requires presence of the vinyl-terminated and hydrogen-

terminated polymers in the system. The addition reaction occurs under mild conditions

and in most cases is catalyzed by platinum based catalysts. Since this is an addition

reaction no by products are formed, however the residual catalyst remains trapped in the

network.

1.7 Purpose of Study.

This document reports the progress in the investigation of ADMET application in

production of solvent resistant elastomeric materials and plastics. The objective is to

create a "common denominator" in materials (shown in Figure 1-27), wherein mechanical

performance can be varied from highly elastomeric to flexible plastic, depending on the

molar ratio of monomers used during polymerization. Improvements of processability,

durability, and elasticity are sought.

The study has focused on the improvement of previously synthesized materials

through variation of the length of the soft phase, and introduction of the labile silicon-

alkoxy end group. In result numerous new siloxane or oxyethylene based materials have

been synthesized and characterized.








CHAPTER 2
SYNTHETIC MODIFICATION OF CROSSLINK DENSITY AND SOFT SEGMENT
IN POLYCARBOSILANE/POLYCARBOSILOXANE ELASTOMERS

2.1 Introduction

The clean and efficient chemistry afforded by ADMET, mentioned in the previous


chapter, allows for the combination of the best material properties of both carbon and


silicon into a precise random linear copolymer. Moreover, the high selectivity of olefin


metathesis allows for a wider range of possible functional handles to manipulate the


overall material properties. The behavior of ADMET carbosilane/carbosiloxane


copolymers can be achieved by selecting the appropriate molar concentrations of each


monomer, as demonstrated in Figure 1-27, to generate a large number of materials.

OCH3 CH3 CH3

OCH3 + C HH
CH I I


(75) [Mo] (76)



OCH3
101 (77)
10 '/. 1/
H2O
Single Elastic Link
Chain-Internal Crosslinks in Backbone

/ \ ri3 3cm
CH3 CH3




I H3 CH3 n CH30H
OH3 L,
0 (78) Single Elastic Link
I in Backbone
Chain-Internal Crosslinks
Figure 2-1. Atmospherically crosslinked ADMET copolymers.








The production of these previously obtained hybrid systems using ADMET

chemistry is described in Figure 2-1.75,107 These carbon/silicon copolymers contain

"chain-internal" crosslinks only, where the ratio of 75 to 76 co-monomers determines its

fundamental mechanical performance, varying from a rigid to an elastic behavior.

However co-monomer identity, functionality, and ratio are predominant factors in

controlling the elastic properties of the material. While our initial silicon thermoset

copolymers of this type are freestanding films, they are relatively weak (low tensile

strength) (Table 2-1).

Table 2-1. Mechanical properties of the unsaturated ADMET copolymers and a
commercially available elastomer.

Materis Modulus Tensile Strength Elongation
Materials
(MPa) (MPa) (%)
Polymer 78 0.16 0.2 20
Polymer 82 0.7 0.4 84
Polymer 85 6.0 0.6 400
Gelest Zipcone fSeriesa 2.0 0.7 150
a) Filler free Fast Cure pure silicon-based elastomer purchased from Gelest

Since the goal of the research is to produce solvent resistant and durable thermosets

based on polycarbosilanes, we focused on the factors influencing tensile strength and

other properties in order to improve our initial material (Figure 2-1). The successful

production of silicon hybrid polymers via ADMET requires that our methodology

conform to certain thermoplastic material criteria. First, crosslink density in such

materials is important and must be tailored precisely to balance mechanical strength and

brittleness while maintaining chemical and solvent resistance. Second, the soft phase

should be amorphous and sufficient in length to observe elastomeric behavior; moreover,

the run length of the soft phase between crosslink sites plays an important role in








elasticity allowing for low crosslink density, yet still enabling solvent resistance. While

our initial materials are interesting (Figure 2-1, material 78) they lack sufficient tensile

strength, most likely from an imbalance in crosslink density and soft phase morphology

generated from the presence of dangling-chains in the three dimensional network.'08

Thus, in Table 2-2 we have outlined synthetic modification to our initial materials that in

our opinion should improve their overall performance

Table 2-2. Synthetic research objectives.
Research Objectives Schematic Representation Benefit

Synthetically modified H3CO Will enhance tensile
crosslink density H3CO-Si^ 1 ^ strength and mechanical
H3CO UIx durability.

Chain-end latent crosslinking

Synthetic soft segment H3 Will significantly improve
modification s-o si degree of elasticity, degree
i~HO 4H3 CHi -- of elastic recovery, and the
Y propensity for phase
Increased run length in soft segment (y>1) separation.


2.2 Synthetically Modified Crosslink Density

The architecture of our initial hybrid copolymers are composed of a carbosiloxane

soft phase containing a siloxane bond (Si-O-Si), giving flexibility and mobility, while the

carbosilane hard monomer lacks this motional freedom since the Si-O-Si link is pendant

to and therefore not part of the linear polymer backbone. Thus, as illustrated in

Figure 2-1, these crosslinks, which we term "chain-internal", are found exclusively in the

hard phase of the copolymer, where their presence is critical since placing them in the

soft segment would limit elasticity. As a result, the latent reactive sites are placed in the

hybrid material by the carbosilane monomer alone, in which its content does not exceed

10% by weight. These low monomer concentrations are necessary to produce flexible








materials. As was shown by Brzezinska75 this chain-internal crosslinker is randomly

incorporated into polymer backbone, therefore crosslinking will occur at random points

to the neighboring chains. This will result in formation of uncapped chain-ends

(dangling-chains). Dangling chains are described as chains that are connected to the

junction at only one end point. These mobile chains, which are elastically ineffective,

represent network imperfections diluting the ultimate properties of the ADMET

elastomer. In fact Andrady et al., has shown that both the ultimate strength and

maximum extensibility of a material are lower for networks containing dangling-

chains.109 In an effort to circumvent this problem, we have introduced the concept of

"chain-end" crosslinking to complement "chain-internal" crosslinking in attempt to

produce more perfect networks. Figure 2-2 shows two different molecules that can be

used as chain-end crosslinkers.



OCH3
B Si-OCH li
xOCH3 CH3
(79) (80)
Figure 2-2. Chain-end crosslinking molecules.

This approach to increase the crosslink density comprises two distinct concepts.

First, note that a polymer synthesized using compound 79 (Figure 2-2) would produce a

latent reactive, end-capped linear polymer. The mention of compound 61 is only for

comparison and introduction of our new latent concept and its use will be discussed in

Chapter 3. On the other hand, compound 80, synthesized by a Grignard reaction of 5-

bromo-1-pentene with trichloromethylsilane, contains three ADMET active terminal

olefins (f = 3), therefore, using chain-end crosslinker 80 will result in a crosslinked









network via the ADMET polymerization mechanism. Initially, we focused on proving

the chain-end crosslinking concept using monomer 80 by combining it with our

previously reported75 the hard and soft carbosiloxane and carbosilane monomers

described in Figure 2-1. As mentioned above, introduction of monomer 80 should

produce better-defined networks in material 82, and an observable improvement in its

mechanical response when compared to material 78..

ADMET polymerization is a step-growth type of polycondensation, where the

initial monomer molar ratios are directly transferred to the polymer produced. Also, due

to the nature of the substrates polymerized, all monomers are incorporated randomly in

the polymer.



0 OCH 3 I I
^ l -OH + CH3I I +YI
OCH3 H 3 x0

OCH, (76)
(75) ) (80)
cat





H O





Chain-End
I CCH3 CH3
1CH3 OCH 3H



H20

Chain-End
Single Elastic Link Crosslinks
Chain-Internal Crosslinks in Backbone


Chain-Internal Crosslinks

Figure 2-3. Chain-end crosslinking in the polycarbosilanes via ADMET.







Figure 2-3 illustrates the synthesis of a copolymer possessing both types of

crosslinks using an initial soft/hard/chain-end crosslinker molar ratio of 20:1:1 ratio,

respectively. The use of metathesis (ADMET) generates polymers in which all

monomers are randomly incorporated. Also, the high conversions needed in metathesis

chemistry allows for a direct transfer of monomer feed ratios to the growing polymer

chains. Both Schrock's molybdenum catalyst [Mo] (2) (at room temperature) and 2nd

generation Grubbs' catalyst [Ru]** (5) (at 67-700 C) were examined in this study.

Polymerizations were initiated using a 250:1 monomer: catalyst ratio regardless of

catalyst chosen. Following initiation the reaction mixture was poured onto a Teflon

plate and placed either in a room temperature vacuum desiccator (Schrock's catalyst), or

in a high temperature vacuum oven for second-generation Grubbs' catalyst. Both catalyst

systems produce free standing films, where solvent resistance is rendered by the chain-

end crosslinker 82. These freestanding films were then exposed to atmospheric moisture

to activate the "chain-internal" latent crosslinks. The resultant material (82) containing

chain-end crosslinks shows significant improvement in tensile strength (Table 2-1), when

compared with our initial material (78) without chain-end crosslinks. Preliminary

mechanical data recorded a modulus of 0.7 MPa and 84% extensibility for material 82.

When compared to material 78 (modulus 0.16 MPa, 20% extension) the importance of

chain-end crosslinking concept is evident.

2.3 Synthetic Soft Segment Modification

The minimization of network defects by using "chain-end" crosslinks has a

profound enhancement over the material's bulk properties. In an attempt to obtain better

elongation, further modification was investigated by the incorporation of a different soft

phase monomer. Throughout our initial study, we have solely employed the carbosilane








monomer 76, a monomer possessing an inherently low Tg reflective of the Si-O-Si base

unit. The homopolymer of monomer 76 has an observed glass transition onset of -91 C

making it a desirable soft phase.75 However, when this monomer is employed in a

random copolymer (material 82) array with the hard phase monomer 75, overall

elongations are limited to approximately 80%.

The most efficient way to enhance elasticity would be to increase the run length of

the siloxane soft phase. However, due to obstacles encountered during the synthesis and

purification of such monomers, we initially focused on an easily synthesizable soft phase.

Diene versions of polyoxyethylene are well known and have found wide application as

soft phase segments, 110-117 while this soft phase is not siloxane based the synthesis of

these dienes are trivial and can be produced in large quantities. Treatment of a

representative bromoalkene with a glycolic alkoxide yields analytically pure monomer 83

after purification.11s Other method used in the synthesis of family of glycol-based dienes

will be discussed in Chapter 3.



S8 f d d d c a

di "b








Figure 2-4. NMR spectra of monomer 83.




Figure 2-4. H NMR spectra of monomer 83.








For example, the NMR spectrum for monomer 83 is shown in Figure 2-4. The

characteristic integration of the polyoxyethylene segment at 3.6 ppm, as well as, the

observed resonances for the diene can be seen at 5.8 and 5.0 ppm.

While polyoxyethylene are excellent soft segments; their glass transition is

dependent on the number of repeating ethylene oxide units. An increase in Tg is

observed with larger numbers of ethylene oxide, Figure 2-5.119 For example, the small

molecule ethylene glycol (n=l) exhibits a Tg = 930C while an increase to -500C is

observed when n=9. Initially, monomer 83 was chosen as the model soft phase due to its

low glass transition (-75C) relative to monomer 76 (-91C). Hopefully, the close

proximity of the two Tgs would reduce the effects caused by the monomers' molecular

differences. The goal in the future is to produce soft phases based solely on siloxane, in

effect utilizing the purely amorphous nature of silicon; in fact, the best-known

elastomers, polydimethylsiloxane (PDMS), exhibit Tgs as low as -1230C.




n Tg (oC)
1 -93
2 -83

3 -75

4 -70
9 -50

Figure 2-5. Glass transition temperatures for various lengths of polyoxyethylene

The homopolymer synthesized with monomer 83 under standard bulk ADMET

polycondensation conditions generated a linear polymer having an M = 28,000 g/mol.

Thermal analysis of this oxyethylene-based ADMET homopolymer yielded a melting

temperature of 35.7 C and a recrystallization temperature of 16.6 C revealing semi-










crystalline properties typical for pristine polyoxyethylene. Repeated DSC scans led to

identical enthalpies of melting and recrystallization for this macromolecule.

Given the viability of this oxyethylene-based monomer in homometathesis, it was

employed in the ADMET terpolymerization scheme describing earlier (Figure 2-3),

substituting the new oxyethylene diene for the carbosiloxane monomer (Figure 2-6).

Identical monomer ratios (20:1:1) and catalyst loadings (250:1) were employed

comparable to the siloxane based terpolymer. A 10 fold increase in elongation-to-break

was observed, from less than 80% to 400% (Figure 2-6). It is apparent that 4 ethylene

oxide units are sufficient to generate highly elastic materials, and this data suggests that

fewer ethylene oxide units (perhaps 2 or 3) may prove of value.

The data in Table 2-1 also illustrates a clear enhancement in modulus and tenacity

for polymer 85, as compared with polymer 78 and 82. The modulus, tenacity, and

elongation increase along with presence of chain-end crosslinking and with a longer soft

phase, as expected. Moreover, the tenacity matches that of commercial silicone

elastomers, combined with a significantly higher modulus and elongation. It is evident

that "chain-end" crosslinking combined with the soft phase modification offer enhanced

elasticity and performance over our initial materials. In order to produce materials that

are more UV stable and offer the lowest possible Tgs, investigations to generate all-

siloxane copolymers possessing fully latent chain-internal and chain-end crosslink sites,

including the use of siloxane chain-end crosslinkers such as 79 (Figure 2-2), are

described in following chapters.






43




OCH, |
I OCH, X I
(75) (83)
[Rul (80)



\ I IH /\ I 9 i\ I /
OCH x \ y\ CH, /
(84)
Atmospheic
Hp
Chain-End
Chain-Internal Crosslinks
Crosshlinks


9 II
Longer Length Soft Phase + CH30H



Chain-End
Chain-Internal (85) Crosslinks
Crosslinks




Apply Tension

Release Tension




Figure 2-6. High elastic material containing increased soft phase and chain-end
crosslinker.

2.4 Conclusions

ADMET polymerization of carbosilane/carbosiloxane copolymers bearing "latent

reactive sites" offers a new approach to the synthesis of materials exhibiting variable

physical properties. Latent reactive methoxy groups remain inert during metathesis

polymerization; exposure of the copolymer to moisture triggers hydrolysis (latent

crosslinking). The incorporation of "chain-end" crosslinks has improved mechanical

performance by limiting the formation of dangling chains. In addition increasing the run








length of the soft phase, in order to achieve a better balance between soft phase

concentration and crosslink density, generates a material exhibiting significant

mechanical performance. The material where the soft phase was changed from the

siloxane unit to the polyoxyethylene glycol leads to formation of crosslinked film 70 that

exhibits good material properties (modulus 6 MPa, elongation 500%). We are pursuing

this research with the goal of generating all-siloxane copolymers possessing fully latent

chain-internal and chain-end crosslink sites.

2.5 Experimental Methods

2.5.1 General Considerations

IH NMR (300 MHz) and 13C NMR (75 Hz) spectra of the ADMET polymers and

monomers were recorded in CDC13 or C6D6 on either a Mercury series or Varian VXR-

300 NMR super-conducting spectrometer. Chemical shifts were referenced to residual

CHC13 (7.25 for IH and 77.23 for 1C) and to residual C6D6 (7.15 for H and 128.39 for

13C). High-resolution mass spectral (HRMS) data were obtained on a Finnegan 4500 gas

chromatograph/mass spectrometer using either the chemical ionization (CI) or

electrospray ionization (ESI) mode. Elemental analysis was carried out by Atlantic

Microlab Inc. (Norcross, GA).

Gel permeation chromatography (GPC) of the unsaturated ADMET polymer was

performed using two 300 mm Polymer Laboratories gel 5pm mixed-C columns. The

instrument consisted of a Rainin SD-300 pump, Hewlett-Packard 1047-A RI detector

(254 nm), TC-45 Eppendorf column heater set to 35 C, and Waters U6K injector. The

polymer samples were dissolved in HPLC grade THF (approximately 0.1% w/v), filtered

before injection, and collected at a flow rate of 1.0 mL/min. Retention times were








calibrated to polystyrene standards purchased from Polymer Laboratories (Amherst,

MA).

Differential scanning calorimetry (DSC) was performed using a Perkin-Elmer DSC

7 at a heating rate of 10 C/min. Thermal calibrations were made using indium and

freshly distilled n-octane as references. Heats of fusion were referenced against indium.

All samples were prepared in hermetically sealed pans (4-7 mg/sample) and were run

using an empty pan as a reference. The samples were scanned for multiple cycles to

remove recrystallization differences between samples, and the results reported from the

second scan cycle.

Mechanical tests were performed at the University of Florida facility by courtesy of

Dr. Brenan's research group, using an Instron model 1122 load frame upgraded with an

MTS ReNew system running MTS TestWorks 4 software and a 500 g load cell for the

experiments.

Tensile specimens were cut from the cured freestanding films using an ASTM

D1822-68 type L dogbone die. Each specimen was individually measured to account for

thickness variability in calculations. The grip separation for the samples was set at 25.4

mm and the width of the testing portion was set at 3.1 mm. Tensile measurements were

made according to ASTM D412-97 at rate of 2 inch/min.

2.5.2 Materials.

All reagent grade solvents were freshly distilled over a Na/K alloy, except for THF

which was dried using K-benzophenone ketyl. 5-bromo-1-pentene and 11-bromo-1-

undecene were purchased from Aldrich and dried over activated 4A sieves. Magnesium

turnings (Aldrich) were activated by vacuum drying at 100 OC prior to use. Triethylene







glycol (Aldrich) was dried by azeotropic distillation using toluene and

bis(trimethoxysilyl)ethane (Gelest) was distilled over CaH2. Any necessary chlorosilanes

were purchased from Gelest and used as received. Deuterated solvents (Cambridge

Isotope Laboratories) were stored over activated 4A sieves. Filler Free fast Cure pure

Silicon based elastomer was purchased from Gelest. The metathesis catalysts

Cl2Ru(IMes)(PCy3)[=CHPh]42 and [Mo=CHCMe2Ph(=N-C6H3-2,6-i-Pr2-)

(OCMe(CF3)2)2]38,120 were synthesized according to literature procedure. All other

compounds were used as received.

2.5.3 Monomer Synthesis

Monomer 75 and 76 were synthesized according to a literature procedure.75

2.5.3.1 Tris(4-pentenyl)methylsilane (80)

A 250 mL three-necked round bottom flask equipped with an additional funnel,

condenser, and stir bar was flame-dried under vacuum, and then flushed with argon.

Magnesium turnings (2.1 g, 0.087 mol) and dry diethyl ether (50 mL) were added. A

solution of 5-bromo- -pentene (11.8 g, 0.0800 mol) and 50 mL of diethyl ether was

added drop-wise to maintain a constant reflux. The solution was refluxed for an

additional hour, cooled to room temperature, and a mixture oftrichloromethylsilane (3.32

g, 0.0221 mol) in Et20 (10 mL) was slowly added. Upon addition, the solution was

refluxed (2 hours), cooled and the product was diluted with 50 mL of dry pentane and

separated via cannula. The organic were evaporated under reduced pressure yielding 6.5

g of a clear, colorless liquid. The crude product was purified by column chromatography

using straight hexanes. Monomer 80 was collected in 80% and the following spectral

properties were observed: 1H NMR (CDCl3): 8 = -0.05 (s, H3), 0.5 (m, br, H6), 1.4 (m, br,

H6), 2.05 (m, br, H6), 5.0 (m, br, H6), 5.8 (m, br, H3). 13C NMR (CDCl3): 6 = -5.25,







13.36, 23.40, 37.79, 114.43, 138.99. MS (70 eV): m/z = 181.1412 (M+-CsH9).

(C16H3oSi) (250.49): Calcd. C 76.72, H 12.07; Found C 76.69, H 12.18.

2.5.3.2 Diundecenyltriethylene glycol (83).

The synthetic procedure was modified from published procedure.'18 Sodium

hydride (6.5 g, 0.27 mol, 60% dispersion) was placed in a flame-dried, Ar-purged, three-

necked 1000 mL round-bottom flask equipped with a stir bar, condenser, and an

additional funnel. Dried triethylene glycol (8.1 g, 0.068 mol) and 260 mL of dry THF

were combined in a flame-dried 500 mL Schlenk flask. The solution was transferred to

the additional funnel and the mixture was added drop-wise under constant stirring. After

24 h, 11-bromo-1-undecene (40 g, 0.17 mol) in 240 mL of THF was added and stirred for

an additional 72 h at reflux. Upon cooling, 50 mL of water was added, stirred for 15

minutes, and extracted using ether. The combined organic extracts were washed with a

saturated NaCl solution, dried over MgSO4, filtered, and evaporated under reduced

pressure. The crude product was then purified by column chromatography using

hexanes/diethyl ether (80:20%). The fractions were concentrated yielding 15 g of

monomer 83. The following spectral properties were observed: 1H NMR (CDCl3): 8 =

1.25 (m, br, H24), 1.60 (m, br, H4), 2.10 (m, br, H4), 3.53 (m, br, H4), 3.60 (m, br, H12),

4.95 (m, br, H4), 5.85 (m, br, H2). 13C NMR (CDC13): 6 = 26.10, 28.94, 29.14, 29.45,

29.49, 29.51, 29.55, 29.62, 29.66, 33.81, 70.04, 70.64, 71.53, 114.06, 139.18. MS (70

eV): m/z = 455.4121 (M+). (C2sH5504) (454.72): Calcd. C 73.96, H 11.97; Found C

73.91, H 12.18.

2.5.4. General Metathesis Conditions

All monomers used in polymerization were purified and degassed prior to

polymerization. All glassware was thoroughly cleaned and dried under vacuum before







use. The polymerizations were initiated in an argon-filled glove box by placing the

appropriate amount of monomer followed by either metathesis catalyst and slowly stirred

for 2 minutes. In all cases the monomer: catalyst ratios were 250:1.

2.5.4.1 Polymerization of diundecenyltriethylane glycol (83)

The monomer was polymerized using the above procedure. Monomer 83 (0.51 g,

0.0021 mol) was added to the reaction tube charged with Grubbs' 2nd generation catalyst

(7.30 mg, 8.58x10-6 mol). The reaction tube was sealed using a Kontes Teflon valve and

placed under an intermediate vacuum until the mixture became viscous. The reaction

flask was then placed in a 40 C oil bath and high vacuum (<0.01 mm Hg) was applied.

The temperature was gradually raised to 70 oC over 72 hours. After three days, the

polymerization was quenched via dissolution in toluene followed by precipitation in

acetone. The following properties were observed: 'H NMR (CDCl3): 6 = 1.25 (m, br,

H24), 1.60 (m, br, H4), 2.10 (m, br, H4), 3.53 (m, br, H4), 3.60 (m, br, H12), 5.56 (br, H2);

"C NMR (CDC13): 6 = 25.91, 26.06, 27.17, 28.96, 29.10, 29.16, 29.31, 29.43, 29.46,

29.60, 29.73, 32.49, 32.57, 70.01, 70.57, 70.58, 71.50, 130.30. GPC data (THF vs.

polystyrene standards): M, = 27 770 g/mol; PDI (MA/n) = 1.55. DSC Results: T,

(melting peak) = 35.7 C, Ah,,, = 86.8 J/g; Recrystallization Tc (recrystallization peak)

20.1 oC, Ah, = -88.8 J/g

2.5.4.2 Terpolymerization of monomers 75, 76, and 80 to produce terpolymer 81

Terpolymer 81 was prepared at 1: 20: 1 monomeric ratio using monomer 75 (0.17

g, 5.0 x 10-4 mol), monomer 76 (3.0 g, 0.010 mol) and monomer 80 (0.13 g, 5.2 x 10-4

mol). The monomers were stirred for 5 minutes to ensure a homogeneous mixture before

the addition of either 2nd generation Grubbs' catalyst (0.0372 g, 4.41 x 10-5 mol), or

Schrock's catalyst (0.0341 g, 4.41 x 10-4 mol). The reaction mixture was sealed,














removed from the glove box, and stirred under vacuum for 10 minutes. The

polymerization mixture was then poured out on a Teflon plate and placed in a vacuum

oven at 700 C for 72 h. In the case of Schrock's catalyst, the reaction mixture was cast in

the glove box and placed inside a vacuum desiccator. The desiccator was removed from

the glove box, and placed on a high vacuum line at room temperature for 72 h. Vigorous

bubbling of the ethylene gas byproduct was observed, followed by formation of a thin

film. After 72 h the Teflon plate was removed from a vacuum oven and exposed to 80%

moist atmosphere having a pH 6.5-7.0, for a period of 3 weeks.

2.5.4.3 Terpolymerization of monomers 75, 83, and 80 to produce terpolymer 84

Terpolymer 84 was prepared by mixing monomer 75 (0.11 g, 3.3 x 10-4 mol),

monomer 83 (3.1 g, 6.6 x 10-3 mol), and monomer 80 (0.0862 g, 3.46 x 10-4 mol)

resulting in a 1: 20: 1 monomer ratio. Following the same procedure as for terpolymer

81, all monomers were mixed and stirred prior to the addition of the catalyst. In this case,

2nd generation Grubbs' catalyst (0.035 g, 4.1 x 10-5 mol) was added and the reaction

mixture was stirred, sealed, removed from the glove box, and placed for 10 minutes on a

high vacuum line. The mixture was then transferred to the Teflon plate and placed in a

vacuum oven at 70 C. After 72 h, the Teflon plate was removed and the thin film was

exposed to 80% moist atmosphere having pH 6.5-7.0 for a period of 3 weeks.







CHAPTER 3
SYNTHESIS AND CHARACTERIZATION OF
OLIGO(OXYETHYLENE)/CARBOSILANE COPOLYMERS AND THERMOSETS

3.1 Introduction

Encouraged by results obtained from the previous investigation,121 we synthesized

fully latent reactive processable and durable materials. Although our ultimate goal is to

produce carbosiloxane/carbosilane based materials, our focus shifted to materials based

on the oxyethylene segments. The previous studyl21 has proven that the incorporation of

these segments can result in a thermoset that exhibits good physical properties.

As mentioned in the previous chapter, polyethylene glycol has found wide

application as a soft phase segment.110,112,122 This hydrophilic polyether received

considerable attention for use in biomaterials due to its low interfacial energy with water,

relative structural stability, lack of binding sites for reactive proteins, and high chain

mobility.123 It has been used extensively in the preparation of polymer electrolytes,124-126

crosslinked hydrogels,127-129 membranes130-132 and amphiphilic copolymers.118,133,134

In the preparation of membranes for biological applications, control over the pore

size and good mechanical properties are a necessity in order to enhance the transport of

hydrophilic entities. Thus the preparation of such membranes requires highly

monodisperse polyethylene glycol chains, which are further terminated with allyl groups

susceptible to hydrosilylation. The synthesis involves the random cohydrosilylation of

a,o-diallyl-PEG and a, o-diallyl-PIB segments with pentamethylcyclopentasiloxane131

resulting in the formation of a network that restrains post reaction shaping.







Silylated polyethers have found applications in the sealant industry. For example

MS Polymer developed by Kaneka Corporation in Japan, composed of high molecular

weight polypropylene oxide endcapped with silyl groups, has been used in formulation of

sealants and caulks.135 The synthesis of silyl terminated polyethers involves reaction of

polypropylene glycol with allyl chloride in the presence of alkali metals which produces

allyl terminated polyether, followed by hydrosilylation with methyldimethoxysilane in

the presence of the platinum chloride catalyst. The resultant silyl terminated polyether is

subsequently mixed with fillers, plasticizers, and a curing catalyst to obtain a room

temperature curing composition.

This chapter describes the design and synthesis of unsaturated "latent reactive"

oligo(oxyethylene)/carbosilane copolymers prepared via acyclic diene metathesis

polymerization. Methoxy groups attached to silicon atoms have been chosen as the

"latent reactive" sites that have previously been proven to be inert during

metathesis.75'85'121'136 Exposure to moisture triggers the hydrolysis of methoxy groups,

which undergo condensation reaction to yield crosslinked materials. The synthesis and

characterization of monomers, polymers, and both linear and crosslinked copolymers is

reported.

3.2 Synthesis of Monomers

3.2.1 Monomers for Soft Phase Modification

A family of monomers (Figure 3-1), with different lengths of oligo(oxyethylene)

and methylene spacers between the carbon-carbon double bond and the

oligo(oxyethylene) unit, has been synthesized in order to investigate the influence of the

structural modifications on the properties of the resulting materials. For clarity, the

nomenclature shown in Figure 3-1 is used instead of the full names of the monomers.









The first number corresponds to the number of methylene units ("sp") between oxygen

and the vinyl group; the second number corresponds to a glycol ("gl") used in the

monomer synthesis (e.g. 2 for diethylene glycol). Consequently, abbreviations used for

the polymers are "poly" followed by the monomer abbreviation.



3sp2gl 6 9 9sp2gl
(86) 6sp3gl (91)
O^{4A) (89)
3sp3gl O 9sp3gl
(87) 4 (92)
O^ O^ 606sp4gl O4
3 (90) 9
3sp4gl 9sp4gl
(88) (93)

Figure 3-1. Glycol-based monomers.

Williamson's ether synthesis, described in Chapter 2, was used to prepare the 3sp

and 6sp monomers. The 9sp monomers were synthesized via another synthetic route that

involves reaction of 1-undecene-11-ol and an appropriate ditosylated oligo(oxyethylene)

glycol in the presence of sodium hydride (example presented in Figure 3-2). The 1-

undecene-11-ol used in this reaction was synthesized according to literature procedure.137


OH + Ts O OT DMF, oOC 0
9 4
(94) (95) (93)

Figure 3-2. Synthesis of 9sp4gl (93).

The synthesis, workup, and product purification via column chromatography was

followed by vacuum distillation over calcium hydride to yield analytically pure

monomers, which were stored in an inert atmosphere of a glove box. Common







spectroscopic methods such as 1H NMR, 13C NMR, and FT-IR were used to characterize

all monomers.

3.2.2 Monomers for Crosslink Density Modification

As described in Chapter 2 our initial materials were composed of two monomers:

the "soft phase" monomer 76 and the latent reactive "chain-intemal" crosslinker 75.

From previous studies75'121 we have learned that the ratio of used monomers dictates

properties of the final thermoset. Moreover, we have found that the crosslink density

modification via an incorporation of the "chain-end" crosslinker as the third component

enhances properties of our materials by limiting the formation of dangling chains.121

However, due to the nature of this "chain-end" crosslinker 80 used in this study, a

thermoset is formed already during the polymerization restraining further processing of

the polymer.

Since the ultimate goal of this research is the synthesis of fully "latent reactive",

linear processable materials for thermoset elastomers, we have decided to synthesize a

latent reactive "chain-end" crosslinker. The synthesis of such monomer shown in Figure

3-3, involves the Grignard coupling of 11-chloro-1-undecene with

trimethoxymethylsilane (96). The use of this monofunctional metathesis active monomer

97 in the synthesis of latent reactive materials has a dual purpose. First, the placement of

97 on the end of chains will ensure linearity of the resultant polymer and facilitate further

processing. Second, presence of labile methoxy groups on the silicon atom that

participate in the crosslinking process will limit the formation of dangling chains in the

final thermoset.

The crosslink density of our materials can be further modified using "chain-

internal" crosslinker 100 (Figure 3-3) bearing only two methoxy groups on the silicon









atom instead of four as used in previous studies.121 Using the same synthetic

methodology as in the case of 97, the Grignard coupling of 5-magnesiumbromo-1-

pentene (98) and tetramethylorthosilicate (99) was applied.

OCH3 OCH3
I Et2O
MgC1 + H3CO-Si-CH3 -CH3
OCH3 OCH3
OCH3 end9sp20Me OC
(95) (96) (97)
OCH3 OCH3
I EtzO I
./ MgBr + H3CO-Si-OCH3 2' 3
OCH3 OCH3
3sp20Me
(98) (99) (100)

Figure 3-3. Synthesis of end9sp20Me and 3sp20Me.

In both cases after workup and distillation an analytically pure monomer was obtained as

proven by 1H NMR, 13C NMR, and FT-IR.

Once again short names were assigned for clarity, as shown in Figure 3-3. The first

part of the name depicts number of methylene groups between silicon atom and the vinyl

group, whereas the second part describes number of the latent reactive methoxy groups

present in the monomer. Consequently, the short name for monomer 75, described in

Chapter 2, will be 3sp40Me. In order to distinguish the a,co-diene monomers from a

monofunctional "chain-end" monomer, the word "end" was placed before an

abbreviation.

3.3 ADMET Polymerization

3.3.1 Synthesis of Oligo(oxyethylene)/Oligo(ethylene) Copolymers

Polymers were synthesized from monomers presented in Figure 3-1 under standard

bulk ADMET polycondensation conditions using the 1st generation Grubbs' catalyst

[Ru]* (4). Although our initial polymerization of monomer 9sp3gl was catalyzed by 2nd











generation Grubbs' catalyst [Ru]** (5), the [Ru]* (4) was used to conduct metathesis in

mild conditions and to prevent olefin isomerization during polymerization.43'138

Resulting linear unsaturated polymers can be described as alternating (AB)n microblock

copolymers of oligo(oxyethylene) and oligo(ethylene). All polymers are viscous liquids

except for ones made from 9sp monomers.

Table 3-1. GPC data of unsaturated polymers.

Polymer GPC (g/mol)a
Polymer
Mn Mw PDI
poly3sp2gl (101) 35,766 63,306 1.77
poly3sp3gl (102) 34,565 65,328 1.89
poly3sp4gl (103) 34,890 66,634 1.91
poly6sp3gl (104) 36,193 62,976 1.74
poly6sp4gl (105) 30,734 49,174 1.60
poly9sp2gl (106) 51,750 106,605 2.06
poly9sp3gl (107) 40,103 72,185 1.80
poly9sp4gl (108) 46,840 96,490 2.06
a) referenced to PS standards in THF at 40'C;

The standard spectroscopic methods (1H NMR, 13C NMR, FT-IR), the gel-

permeation chromatography (GPC) and the thermal analysis (DSC, TGA) were used for

the structural characterization and verification of the monomers' conversion to high

molecular weight polymers. Table 3-1 summarizes the results obtained from the gel-

permeation chromatography analysis on unsaturated polymers, while a more detailed

discussion regarding 1H NMR, 13C NMR, FT-IR and the thermal analysis is described in

the following sections.









3.3.1.1 Structural characterization

The spectra of monomers with the same alkenyl group length or the same number

ofoligo(oxyethylene) units are homologous. Thus the spectra of polymers obtained from

these monomers are very similar as well.


c l g g .




I I
H NMR spectra of monomer 6sp3g and polymer poly6sp3gl.
In Figure 3-4, a representative H NMR spectra of monomer 6sp3g (89) and

2, 3 6 6 I \
S 6 4 I /n
U 6


4 5


1 1 ElF T 1 1 1 T V ,T f F I
6.0 5.0 4.0 3.0 2.0 1.0
Figure 3-4. 'H NMR spectra of monomer 6sp3gl and polymer poly6sp3gl.

In Figure 3-4, a representative Hc NMR spectra of monomer 6sp3gl (89) and

polymer poly6sp3gl (104) is presented. The top of the figure shows 'H NMR spectra

with characteristic peaks between 3.53-3.63 ppm that correspond to protons on the

oxyethylene segment. As shown in Figure 3-4, the chemical shifts for the monomer and

the unsaturated polymer remain the same, but the intensity of signals depends on the

length of the oxyethylene segment.

The 'H NMR spectra clearly illustrates quantitative conversion of the monomer to

the high molecular weight unsaturated polymer. This can be observed by the complete

disappearance of the vinyl groups in the monomer, (peaks at 4.9 and 5.7 ppm in the top









spectra), and by the newly formed peak at 5.3 ppm of the internal olefin that appears in

the spectrum of polymer (bottom).


[ c d h g a
6* 3 f g C b


S3 4 8 7 2
V 6 7 5 1 I


5 trans


130 120 110 100 90 80 70 60 50 40 30 20 10

Figure 3-5. 3C NMR spectra of monomer 6sp3gl and polymer poly6sp3gl.

The chemical structures of the monomer and the polymer were characterized by 3C

NMR and are shown in Figure 3-5. The spectra of the monomer and the polymer show

characteristic carbon signals of oxyethylene segments present at 71.3 and 70.8 ppm. As

in the olefinic region of 6sp3gl (89) and poly6sp3gl (104) of the 1H NMR spectra, the

13C NMR spectral changes are also observed. Two signals of vinyl carbons at 114.1 and

139.8 ppm present in the monomer disappear while two new peaks at 130.3 ppm (major)

and 129.5ppm (minor) are formed in the polymer. These two new signals correspond to








trans and cis isomers of the 1,2-disubstituted double bonds along the polymer backbone,

further confirming high conversion of a monomer to the unsaturated polymer. Moreover,

the resonance of the allylic carbon in the monomer spectrum at 33.6 ppm splits into two

new signals (32.5 and 27.1 ppm) in the spectrum of polymer due to the trans and cis

geometries around this carbon. The relative proportion of cis and trans carbons by 3C

NMR show approximately 80% content of the later, which is in an agreement with

previous reports on ADMET polymerization.52'53 The high content of the trans olefin in

AMDET products is attributed to the most stable conformation of the metallacyclobutane

intermediate.5

-- 6sp4gl
-- poly6sp4gl


3080

914

S* 1121




SI I *\ 968
-968

1121\



3500 3000 2500 2000 1500 1000 500
Wavenumber (cm")

Figure 3-6. FT-IR spectra of 6sp3gl and poly6sp3gl.

Chemical structures of the monomer and the polymer were also verified by FT-IR

spectroscopy. For example FT-IR spectra of 6sp3gl and poly6sp3gl shown in Figure 3-6

contain a strong band at 1121 cm-1 that corresponds to the asymmetric stretch of the C-O-











C ether bonds from the oxyethylene segment and is present in both the monomer and the

polymer. Characteristic wavenumber bands that correspond to the vinyl group in the

monomer are observed at 3080, 1642, 994 and 914 cm-1. These peaks were not observed

in the poly6sp3gl, instead a new sharp absorbance assigned to the trans carbon-carbon

double bond appeared at 968 cm-1. Due to the low concentration of the cis conformation

in the polymer, the expected band at 730-665 cm1 was not detected. These results

further demonstrate high conversion of monomer to corresponding polymer.

3.3.1.2 Thermal behavior of unsaturated polymers

Thermal analysis of the family of alternating (AB)n microblock copolymers was

performed by differential scanning calorimetry (DSC). Detailed characteristics of

thermal transitions for unsaturated polymers are summarized in Table 3-2. Values of

glass transition temperatures (Tg) were taken at the mid-point of the transition and the

melting transition temperatures (Tm) were taken as the temperature at the peak of the

melting transition in the second heating scan. Similarly, the crystallization temperature

(Tc) was taken as the temperature at the peak of crystallization transition in the second

cooling scans. The data was collected by scanning samples from -150 to 80 C at 10

C/min and reported from second heating and cooling scans. All polymers described

below exhibit unique thermal properties. The combination of melting, crystallization,

and glass transition, three phenomena that are important with respect to the design and

processing of polymeric materials, have been observed for this family of unsaturated

(AB)n microblock copolymers.








Table 3-2. Thermal analysis of the unsaturated polymers.

Polymer DSC TGA (oC)e
Polym er-------------------- -
Tg Cp Tm Tc AH g/T TN2 Tda
(oC)a (J/(g OC) (OC)b (oC)c (J/g) g/m
poly3sp2gl -79.0 -0.78 242 250
poly3sp3gl -76.2 -0.83 -- 245 245
poly3sp4gl -74.1 -0.88 -35.4 4.8 0.80 252 251
poly6sp3gl -75.0 -0.29 12.9 -12.4 53.7 0.69 231 235
poly6sp4gl -76.0 -0.33 13.3 -16.2 46.6 0.68 239 227
poly9sp2gl -50.4 -0.39 57.1 35.8 82.4 0.67 314 295
poly9sp3gl -55.2 -044 45.9 26.1 70.6 0.68 282 248
poly9sp4gl -56.4 -0.34 42.5 19.4 55.8 0.68 276 258
a) values taken from the mid-point; b) values assign to the top of the melt; c) values
assign to the bottom of the recrystallization; d) calculated from obsolete temperatures;
e) recorded at 5% total mass loss under nitrogen gas or air, 20 oC/min

The glass transition temperatures reported in Table 3-2 for poly3sp2gl, poly3sp3gl,

and poly3sp4gl polymers were essentially identical with the values published by Baker et

al.124 for the same polymers obtained from ADMET polycondensation catalyzed by [Mo]

(2). The actual DSC thermograms of unsaturated polymers are presented in Figures 3-7 -

3-9 and are grouped into three graphs based on the number of methylene units in the

polymer. Thermograms of poly3sp2gl and poly3sp3gl display glass transition

temperatures at -79 and -76 OC respectively, revealing the purely amorphous character of

these polymers. In the case of poly3sp4gl after relaxation at -74 C, a cold crystallization

at -50 OC is observed, followed by melting peak at -35 oC. Comparison of Tg's in the

series of 3sp polymers shows their dependence on the length of the ethylene oxide

segment. The glass transition values increase as the content of the ethylene oxide

increases, a trend observed previously by Faucher119 in a series of ethylene oxide

polymers.












The thermal behavior of polymers poly6sp3gl and poly6sp4gl (Figure 3-8) is

basically the same. In the heating scan a low relaxation temperature can be seen at-75

and -76 'C for poly6sp3gl and poly6sp4gl respectively, followed by a sharp melt at -13

C with the heats of fusion of 53.7 J/g for poly6sp3gl and of 46.6 J/g for poly6sp4gl.

Upon cooling both thermograms display sharp crystallization peaks at -12 and -16 C and

both the enthalpy of melting and the enthalpy ofrecrystallization exhibit the same energy

for both polymers. Moreover, similar AH values for the melt and recrystallization

suggest a similar crystal packing of these polymers.

Analysis of thermograms for poly9sp3gl and poly9sp4gl exhibit similar trends as

described above for the 6sp polymers. Heating scans reveal very weak glass transition

temperatures at -55 and -56 C for poly9sp3gl and poly9sp4gl correspondingly,

presumably due to the semicrystalline nature of these materials. Sharp melting peaks are

present in both thermograms at 46 OC for poly9sp3gl and 42 C for poly9sp4gl. After

repeated scanning, both the heat of fusion of the melt and the enthalpy of recrystallization

exhibit the same energy. Thermal analysis performed on poly9sp2gl showed relaxation

at -50 C followed by a melt, cold crystallization and another melt at 57 C and a single

sharp recrystallization peak upon cooling scan at 35 C. Overall heats of fusion for the

heating run and the cooling run are virtually identical varying only by 0.08 J/g. Similar

to the series of 3sp polymers, dependence of Tg and Tm values on the number of ethylene

oxide segments present in the repeat unit is evident.










0.2-




0.0-




-0.2-



-0.4-




-0.6-


- poly3sp3gl
p013 o '1p:P4g


-0.81
-155 -125 -95 65 -35 -5 10 25 40 55 70 85
E 'I" Temperature (OC)

Figure 3-7. DSC traces of unsaturated 3sp microblock copolymers.


poly6sp3'l1
poly6sp4gl


0-









,-1


-155 -125 -95 -65 -35 -5 10 25 40 55 70 85
IL-o Dn Temperature (OC)

Figure 3-8. DSC traces of unsaturated 6sp microblock copolymers.












.- poly9sp3gl
1.5
Spoly9sp4gl


0.5-



-0.5-



-1.5



-2.5



-3.5
-155 -125 -95 -65 -35 -5 10 25 40 55 70 85
xo U n Temperature (OC)
Figure 3-9. DSC traces of unsaturated 9sp microblock copolymers.

However, reverse trends are observed when compared to the 3sp polymers, as the

number of oxyethylene units increase the values of melting temperature and glass

transition temperature decrease. The oxygen atoms of the ethylene oxide segment can be

considered as irregularities in the carbon chain of polyolefins. Thus short ethylene oxide

segments and long hydrocarbon segments will contribute to higher melting points and

higher relaxation temperatures as observed for poly9sp2gl, where there are only three

oxygen atoms per repeat unit in the polymer. Hence, by increasing the content of the

oxygen atoms in the polymers' repeat unit (five oxygen atoms present in the poly9sp4gl)

decreases glass transition and melting temperatures accordingly.

As suggested by the Boyer-Beaman rule for nonsymmetrical crystalline polymers

the ratio of Tg/Tm should be close to 2/3. Table 3-2 shows the calculated Tg/Tm ratio





64


values for the unsaturated polymers fall between 0.67 and 0.80, which is in close

agreement with the Boyer-Beaman rule.

3.3.1.3 Thermal stability of unsaturated polymers

The thermal-degradation behavior of unsaturated polymers has been investigated

using thermo-gravimetric analysis (TGA). The analysis was performed for each polymer

both in inert (nitrogen) and oxidative (air) atmospheres. The TGA experiments were

conducted at a scan rate of 20 C/min from 50 to 800 C and summarized results are

presented in Table 3-2.


95. poly6sp4gl N2
poly6sp4gl Air

75


55


35


15

-5 ....
50 150 250 350 450 550 650 750
Temperature (C)
Figure 3-10. TGA traces of poly6sp4gl.

Figure 3-10 illustrates typical TGA curves for unsaturated polymers plotted as

weight-loss versus temperature for poly6sp4gl (105) in both atmospheres. The polymer

exhibits good thermal stability up to 250 OC, after which rapid decomposition follows.

As shown in Figure 3-8 there is no significant difference in thermal stability for

poly6sp4gl in nitrogen and in air. Essentially complete volatilization of the sample is

achieved at 460 OC under both mediums. This rapid and complete elimination of mass is








indicative of the structural purity exhibited by these regular polymers. Moreover, due to

the fact that these polymers completely decompose thermally in a linear fashion over a

narrow temperature range implies that only one mechanism of decomposition, more

likely ether breakdown, is responsible for their decomposition.

3.3.2 Polymerization of "Chain-Internal" Crosslinker 3sp20Me

To ensure metathesis compatibility the monomer was homopolymerized in the

presence of 1st generation Grubbs' catalyst (4). The 'H NMR spectra for the monomer

and resulting ADMET polymer (poly3sp20Me (109)) are shown in Figure 3-11. Indeed,

metathesis does occur and can be easily observed by the disappearance of both the

internal and external olefin protons at 5.8 and 5.0 ppm, respectively. This unsaturated

carbosilane has been previously synthesized by Church91 et al. during investigation of

nucleophilic substitution on silicon-containing am(-dienes; however, 2nd generation

Grubbs' ruthenium complex (5) was used to promote ADMET polymerization.

C C

)OC 13






-
2 2






1 3 4 5


6.0 5.0 4.0 3.0 2.0 1.0
Figure 3-11. 'H NMR spectra of 3sp20Me and poly3sp20Me.







The presence of reactive groups in each repeat unit of the polymer makes the

characterization and handling of polymer challenging. Hydrolytic sensitivity makes GPC

analysis unavailable, instead 1H NMR end-group analysis was performed indicating a Mn

of 45,000 g/mol, four times higher than previously reported. Differential scanning

calorimetry was performed yielding in the same glass transition (Tg= -800C) as observed

by Church et al.

3.3.3 Synthesis and Characterization of "Latent Reactive" Copolymers

Given the compatibility of monomers mentioned in previous section and ADMET

viability to produce high molecular weight unsaturated polymers, their copolymerization

under bulk reaction conditions at mild temperatures is relatively trivial. Our previous

studies of carbosilane or carbosiloxane-based monomers75 have shown that their

copolymerization yields completely random copolymers. Copolymerization of the

glycol-based monomers with the "chain-internal" crosslinkers and/or "chain-end"

crosslinker produced random linear copolymers as well. Three general formulations have

been made where glycol-based monomers have been copolymerized with 10% by weight

of either "chain-internal" crosslinker (75) or (100), or with only "chain-end" crosslinker

to yield endcapped oligomers with approximate degree of polymerization equal to five

(DP-5), or with both "chain-internal" (5% by weight) and "chain-end" (2.5% by mol)

crosslinkers. Figure 3-12 shows general structures of each composition.

Figure 3-13 displays an example of the 'H NMR and 13C NMR spectra for

copolymer 38 (147). Characteristic presence of the internal olefin signal at 5.34 ppm for

all the polymers prepared by ADMET polymerization is visible in the H NMR spectrum.

Three additional peaks are present in the 1H NMR spectrum of copolymer (147), when

compared to the 'H NMR spectrum of poly9sp2gl i.e. at 0.1, 0.6, 3.5 ppm that





67



corresponds to proton signals of Si-CH3, Si-CH2-, Si-OCH3 groups respectively. The


comonomers feed ratio dictates the ratio of monomers present in the copolymer and can


be verified by 1H NMR spectroscopy by relating signals of Si-CH3 groups either to Si-


CH2- or CH2-CH2-O- groups.


10% wt content

OMe

9 OMe3 m
n m




10% wt content
OMe OMe

OM OMe
S- OMe I m




OMe
MeO I /
MOkO\ Si-Me
Me-Si 9 -o O -
Me/ g 9 OMe
MeO n
n-5




5% wt content

OMe
MeO OMe
Me-Si 0 O M'^ SiMeSi-Me




MeO0 OMe O Me

5% wt content
OOMe Me OMe
O\ Si-Me
Me-Si Si 3
/ x 3 Me OMe
MeO OMe
h m


copolymer 1 (110): g
2 (111): g
3 (112): g
4 (113): g
5 (114): g
6 (115): g
7 (116): g
8 (117): g


copolymer 9 (118): g
10 (119): g
11(120): g
12 (121): g
13 (122): g
14 (123): g
15 (124): g
16 (125): g



copolymer 17(126): g
18 (127): g
19 (128): g
20 (129): g
21 (130): g
22 (131): g
23 (132): g
24 (133): g



copolymer 25 (134): g
26 (135): g
27(136): g
28 (137): g
29 (138): g
30 (139): g
31(140): g
32 (141): g



copolymer 33 (142): g:
34 (143): g:
35 (144): gy
36 (145): g:
37(146): g=
38 (147): g
39 (148): g:
40 (149): g


Figure 3-12. Compositions of "latent reactive" unsaturated copolymers.

'3C NMR spectroscopy further confirms formation of copolymer by presence of the


internal olefin carbons at 129.5-131.2 ppm. However, multiple signals are present in this










region rather than only two signals (trans and cis) that are observed in the 3C NMR


spectrum of homopolymers. These multiple signals correspond to presence of additional

linkages between different repeat units in the copolymer. Signals from Si-CH3 at -5.8


ppm, Si-CH2- at 2.5 ppm, and Si-OCH3 at 50.3 ppm groups are also observed; however,

the intensity of these peaks is low due to the low content of both "chain-internal" and


"chain-end" crosslinkers in the copolymer.


5% wt content

Me S i oOMe -OMC
Me-Si--W1 Sii-'
1/ 9 2 OMe I 9 IOMC
MeO OMe
n im




Si-OCH,


I Ik f -CH,-Si
A L .,1t 1 : '.,o'o|oSi-CH
CH,=CH, S -CH3
3.6 3.5 3. 0 6 0.2 0.0

S' I i '' I I
5.0 4.0 3.0 2.0 1.0 0.0
5.0 4.0 3.0 2.0 1.0 0.0


CH,=CH,


-CH,-Si Si-CH,





r 131 130 |51 -- 50 49 -


125 100 75 50 25 0

Figure 3-13. 'H (A) and 3C (B) NMR spectra of copolymer 38 (147).


"' ^""












3.4 Preparation and Characterization of Thermosets

It is well known fact that silicon-alkoxy bonds as silicon-halide bonds are

susceptible to hydrolysis leading to formation of silanol groups (Si-OH), which can

undergo condensation at appropriate conditions. In result a thermodynamically stable

silicon-oxygen-silicon bond is formed and a byproduct such as alcohol or HX is released.

Although good efficiency and availability of compounds containing the silicon-halide

bond, due to formation of acids during crosslinking process the alkoxy groups are

preferred over the later. The process just described is well known as room-temperature

vulcanization (RTV) and has been used in sealant industry for over 30 years. This

opportunity exists for copolymers shown in Figure 3-12 that contain chain-internal and

chain-end crosslink sites. Consequently, when these copolymers are exposed to moisture

the latent reactivity is triggered yielding in thermoset materials. The composition and

short name assigned for simplicity are presented in Figure 3-14.

The first attempt to produce thermoset was performed on xlink 39, whose

composition with exception of latent reactive chain-end crosslinker showed good material

properties in previous study, as described in Chapter 2. An attempt was made to cast a

film of copolymer 39. The polymer was dissolved in toluene, poured into a Teflon mold,

and placed on the lab bench to trigger crosslinking. Unfortunately after one day the

resultant film started to crack yielding after two days a very brittle material as shown in

Figure 3-15.









10% wt content


10% wt content
0A

o1 ASi
J 0 1 xJ
-4 0 i


O\ Si-Me
Me-Si S-e
O n-n


5% wt content


5% wt content


xlink 1 (150): g
2 (151): g
3 (152): g
4 (153): g
5 (154): g
6 (155): g
7 (156): g
8 (157): g



xlink 9(158): g
10 (159): g
11 (160): g
12 (161): g
13 (162): g
14 (163): g
15 (164): g
16 (165): g



xlink 17(166): g
18(167): g
19 (168): g
20 (169): g
21 (170): g
22 (171): g
23 (172): g
24 (173): g



xlink 25 (174): g
26(175): g
27(176): g
28(177): g
29 (178): g
30 (179): g
31 (180): g
32(181): g



xlink 33 (182): g
34 (183): g
35(184): g
36 (185): g
37(186): g
38(187): g
39 (188): g
40 (189): g


Figure 3-14. Composition and structure of crosslinked materials.


The formation of this brittle material can be justify by information obtained from


DSC analysis ofpoly9sp3gl that showed semi-crystalline nature (Tm=46 C) of this


polymer. This kinetic phenomenon, namely crystallization takes place before chemical


crosslinking occurs yielding in physical crosslinks. It is well known fact that crystallinity


makes material strong, but it also makes it brittle. Thus we have decided to increase


2; x=
:3; x=
:4; x=
:3; x=
:4; x
:2; x=
:3; x=
4; x



2; x
3; x=
:4; x=
:3; x=
:4; x=
:2; x=
3; x=
:4; x=



:2; x=
3; x
4; x
=3; x
4; x
2; x
3; x
4; x



:2; x
=3; x
4; x
=3; x
=4; x
=2; x
=3; x
=4; x










































































































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29 and to -6 OC for xlink 29. In the case of xlink 29 the presence of chemical crosslinks

limits mobility of the polymer chains to form highly ordered arrangements; as a result the

extent of crystallization is suppressed even more. But not only decreasing changes in

melting temperatures are observed. An increase in values of the glass temperature

transition is evident in the series of poly6sp4gl (Tg= -77 OC), copolymer 29 (Tg= -76 OC)

and xlink 29 (Tg= -73 'C); however, the changes are by far more discrete than for the

melts.

1.5-

copol mer 29
1.0 xlink 29



0.5 -



g 0.0



i
-0.5



-1.0.




-150 -100 -50 0 50
Exo Down Temperature (C)
Figure 3-16. DSC curves ofpoly6sp4gl, copolymer 29 and xlink 29.

The thermal degradation behavior ofthermosets has been also investigated. Figure

3-17 and 3-18 shows traces of a few selected crosslinked materials in both an oxidative

and inert atmosphere respectively as percentage weight loss versus temperature in the 50-












800 OC range. Good thermal stability for the series ofthermosets presented in Figure 3-

17 and 3-18 is observed where essentially zero percent weight is lost upon heating from

50-300 OC, except for those based on 3sp glycols. The linear decomposition of these

materials implies that only one mechanism is responsible for their decomposition.

Thermal stability of these selected thermosets has been improved in both medium

when compared with the TGA results for homopolymers, which is expected for

crosslinked materials.

Thermal analysis results for the remaining thermosets are collected in Appendix.


loo. Air
100-

xlink 35
xlink 36

0xlink 38
xlink 39
S xlink 40

60

toi


50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800
Temperature (C)
Figure 3-17. TGA traces in an oxidative atmosphere.









Nitrogen


xlink 35
xlink 36
xlink 38
xlink 39
xlink 40


40



20-



0
50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800
Temperature (C)
Figure 3-18. TGA traces in an inert atmosphere.

3.4.2 Mechanical Properties

The mechanical properties of moisture cured thermosets were examined. As shown

in Figure 3-14 couple series of different composition networks were prepared and their

stress/strain profiles were analyzed in regard of their composition; Table 3-3 summarizes

data for these compositions.

In order to gain insight into the effect of the relative chain-internal/chain-end/soft

phase composition on mechanical properties a series ofbicomponent (chain-internal/soft

phase) thermosets were prepared and their properties investigated. Results from these

tests and stress/strain curves for these bicomponent thermosets have been placed in

appendix. A decrease in modulus (E) and tensile strength (TS) is observed as the length

of ethylene glycol increases in the series of thermosets with the same number of













methylene groups.


/
.Si-Me

0


n-5


--xlink 17
- link 18
- xlink 19
- xlink 20


12-


10-


8-


6-


4-


0.0 I 0.2 0.3 0.4 0.5 0.6 0.7
Strain (mmimm)


Figure 3-19a. Stress/strain curves.


xlink 22
--xlink 23
xlink 24









in /





1 1 2 3 4 5 6 7 8
Strain (mm/mm)


5% wt content


\
Me-Si'
-S


0.8


0.6-


0.4-

0.2


0.0
0.0 0.2 0.4 0.6 0.8
Strain (mm/mm)
Figure 3-19b. Stress/strain curves.


6-


4-


xlink 30
-- xlink 31
link 32


0 .i I I I
1.0 1.2 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Strain (mm/mm)


1.0-


0.8-


S0.6-


" 0.4-


0.2-


I:
i




































-Si-Me
0


xlink 36
xlink 37
xlink 39
xlink 40


Strain (m/
Strain (mm/mm)


4 5


Strain (mm/mm)
Figure 3-19c. Stress/strain curves.























Table 3-3. Physical properties of selected thermosets compositions.

Tensile Modulus Elongation Tensile Modulus Elongation
Strength (MPa) (%) Strength (MPa) (%)
(MPa) (MPa)
xlink 17 0.16 0.5 49 xlink 25 0.86 1.8 80
xlink 18 0.36 1.9 24 xlink 26 0.75 2.1 52
xlink 19 0.54 1.7 45 xlink 27 0.32 0.5 100
xlink 20 0.91 2.3 63 xlink 28 1.05 2.6 68
xlink 21 xlink 29 0.88 1.6 105
xlink 22 8.72 30.5 422 xlink 30 7.79 59.5 346
xlink 23 10.42 74.5 710 xlink 31 5.52 115.3 170
xlink 24 10.34 19.1 710 xlink 32 8.36 59.4 285


xlink 33
xlink 34
xlink 35
xlink 36
xlink 37
xlink 38
xlink 39
xlink 40


Tensile Modulus Elongation
Strength (MPa) (%)
(MPa)
0.67 2.0 49
0.55 1.7 47
0.38 0.8 72
4.79 1.4 507
1.86 1.4 298


8.60
6.82


54.6
33.3


335
258


I








A reversed trend is observed in the series ofthermosets where the number of

methylene groups increases and the length of oxyethylene units remains the same. As

was shown above thermal properties of homopolymers varies from totally amorphous to

semicrystalline as the length of carbon chains increases. These crystalline regions are

effective physical crosslinks that makes material stronger but brittle and observed trends

are typical for these kinds of structures. Moreover, these results once again confirmed

that introducing chain-end crosslinker evidently improves mechanical properties e.g.

xlink 12 containing only chain-internal crosslinker shows TS= 0.9 MPa and E= 4.3 MPa,

while for tricomponent xlink 36 TS= 4.8 MPa and E= 1.8 MPa. Although there is an

obvious decrease in the modulus, with value in the range typical for elastomers, the

augmentation of tensile strength is evident and higher values are desired since it

corresponds to the force at which material fractures.

Subsequently, a series of tricomponent networks were prepared and their

structure/property relationship was investigated. Ttricomponent materials shows similar

trends to bicomponent thermosets as presented by the stress/strain curves shown in

Figures 3-19. Results obtained for series of xlink 22, xlink 23, and xlink 24

unequivocally show how small changes in the composition such as one oxyethylene unit

can produce materials with flexible plastic or elastic behavior. Thermosets that contain

longer carbon chains between oxyethylene segments are tougher and shows typical

plastic behavior, while the ones with shorter carbon chains reveal their true elastic nature.

Figure 3-20 shows stress/strain curves of xlink 24, xlink 36, and xlink 37 with

exceptionally good properties for elastomers when compared to other thermosets.

Observed values of tensile strength for these three materials range from 2 to 10 MPa,







while elongation ranges from 300 to 700 %. The other thermosets show either elastic

behavior with low elongation, or plastic behavior with plastic plateau in the stress/strain

curves. In addition, fractured specimen of xlink 24 and xlink 36 presented in Figure 3-

20 show good elastic recovery of these materials. The 1 inch length of each specimen

used in the test did not change after the rapture.

1 -- xlink 24
lxlink 36
9-`

7-









Strain (mm/mm)
5-`

3-`






Figure 3-20. Stress'strain curves and picture of thermosets with good elastic properties.

3.5 Conclusions

Family of oligo(oxyethylene) c, co dienes monomers has been synthesized,

characterized, and subjected to olefin metathesis polymerization. Characterization of the

resultant polymers revealed a wide spectrum of properties dependant on both the length

of oxyethylene segments and also the length of carbon chains in between them.

Consequently, these monomers were copolymerized to obtain targeted linear "latent

reactive" elastomers, exposure to atmospheric moisture triggered crosslinking that led to

the formation of thermoset.

Thermal analysis and mechanical testing were performed on crosslinked materials

to asses their properties. Among fifty different compositions that were prepared many of

them revealed purely elastic behavior while some exhibit properties of flexible plastics.








These thermoset materials may be suitable for biological applications such as

semipermeable membranes or can be used in sealant or adhesive industry.

3.6 Experimental Methods

3.6.1 Materials

All reactions were conducted in flame-dried glassware under an argon atmosphere

unless otherwise noted. Reagents were purchased from Fischer or Aldrich and were used

as received unless otherwise noted. The first-generation Grubbs' catalyst used in this

study was graciously provided by Materia, Inc. 5-bromo-1-pentene, 8-bromo-1-octene,

1-undecene-11-ol, 11-chloro- 1-undecene, 11-bromo-1-undecene were synthesized

according to literature procedures.37

3.6.2 Instrumentation and Analysis

All 1H NMR (300 MHz) and 13C NMR (75 MHz) spectra were recorded on a

Varian Associates Mercury 300 spectrometer. Chemical shifts for 1H and 13C NMR were

referenced to residual signals from CDCl3 (1H = 7.26 ppm and 13C = 77.00 ppm) with

0.03% v/v TMS as an internal reference. Reaction conversions and relative purity of

crude products were monitored by thin layer chromatography (TLC) performed on EMD

silica gel coated (250 pm thickness) glass plates and 1H NMR. Developed TLC plates

were stained with iodine absorbed on silica or vanillin solution (5 wt% in 50mL ethanol

with 2mL H2S04) to produce a visible signature. Low and high-resolution mass spectral

(LRMS and HRMS) data were obtained on a Finnegan 4500 gas chromatograph/mass

spectrometer using the chemical ionization (EI) mode.

Fourier transform infrared (FT-IR) spectroscopy was performed using a Bio-Rad

FTS-40A spectrometer. Monomer was prepared by droplet deposition and sandwiched









between two KBr salt plates. Unsaturated polymer samples were prepared by solution

casting a thin film from tetrahydrofuran onto a KBr salt plate.

Differential scanning calorimetry (DSC) analysis was performed using a TA

Instruments Q1000 series equipped with a controlled cooling accessory (LNCS) at a

heating rate of 10 "C/min. Calibrations were made using indium and freshly distilled n-

octane as the standards for peak temperature transitions and indium for the enthalpy

standard. All samples were prepared in hermetically sealed pans (6-15 mg/sample) and

were run using an empty pan as a reference.

Thermogravimetric analysis (TGA) was performed either on a Perkin-Elmer TGA-

7 at 20 C/min or on TA Instruments TGA Q500 Series using dynamic scans under an

inert (nitrogen) and oxidative (air) atmospheres.

Gel permeation chromatography (GPC) was performed at 40 oC using a Waters

Associates GPCV2000 liquid chromatography system with an internal differential

refractive index detector (DRI) and two Waters Styragel HR-5E columns (10 microns

PD, 7.8 mm ID, 300 mm length) in HPLC grade tetrahydrofuran as the mobile phase at a

flow rate of 1.0 mL/minute. Injections were made at 0.05-0.07 % w/v sample

concentration using a 220.5 tl injection volume. Retention times were calibrated against

narrow molecular weight polystyrene standards (Polymer Laboratories; Amherst, MA)

selected to produce Mp and Mw values below and above the expected copolymer

molecular weight.

Mechanical tests were performed at the University of Florida facility by courtesy of

Dr. Brenan's research group, using an Instron model 1122 load frame upgraded with an







MTS ReNew system running MTS TestWorks 4 software and a 500 g load cell for the

experiments.

Tensile specimens were cut from the cured freestanding films using an ASTM

D1822-68 type L dogbone die. Each specimen was individually measured to account for

thickness variability in calculations. The grip separation for the samples was set at 25.4

mm and the width of the testing portion was set at 3.1 mm. Tensile measurements were

made according to ASTM D412-97 at rate of 2 inch/min.

3.6.3 Monomer Synthesis

Monomer 1 and 2 were synthesized according to a literature procedure75.

3.6.3.1 Synthesis of di(oxyethylene) a,o-di-4-pentenyl ether (3sp2gl) (86)

Monomer 3sp2gl was synthesized according to the procedure described in Chapter

2 for monomer 83. Monomer was purified using column chromatography (1:1 ethyl

acetate:hexane), followed by vacuum distillation over calcium hydride yielded 9.6 g

(58.7% yield) colorless liquid. The following spectral properties were observed: 1H

NMR (CDCl3): 6 = 1.64 (m, br, 4H), 2.10 (m, br, 4H), 3.47 (m, br, 4H), 3.59 (m, br, 8H),

4.95 (m, br, 4H), 5.77 (m, br, 2H). 13C NMR (CDC13): 6 = 28.82, 30.23, 70.15, 70.66,

70.71, 114.64, 138.30. FT-IR: (cm-1) 3077, 2938, 2865, 1641, 1448, 1415, 1350, 1323,

1296, 1247, 1120, 993, 911, 873. MS (70 eV): m/z = 243.1957 (M+H)+. (C14H2603)

(242.35): Calcd. C 69.38, H 10.81; Found C 69.23, H 10.89.

3.6.3.2 Synthesis of tri(oxyethylene) a,o-di-4-pentenyl ether (3sp3gl) (87)

Monomer 3sp3gl was prepare and purify using the same methodology as described

for 3sp2gl, yielded 8.5 g (65% yield) of colorless liquid. The following spectral

properties were observed: 1H NMR (CDCl3): 6 = 1.63 (m, br, H4), 2.07 (m, br, H4), 3.37

(m, br, H4), 3.57 (m, br, H12), 4.87 (m, br, H4), 5.74 (m, br, H2). 13C NMR (CDC13): 6 =







28.77, 30.22, 70.12, 70.62, 70.70, 114.65, 138.28. FT-IR: (cm-1) 3077, 2865, 1641,

1449, 1416, 1350, 1323, 1296, 1248, 1119, 993, 912, 872. MS (70 eV): m/z= 287.2230

(M+H)+. (C16H3004) (286.40): Calcd. C 67.10, H 10.56; Found C 67.05, H 10.61.

3.6.3.3 Synthesis of tetra(oxyethylene) a,wo-di-4-pentenyl ether (3sp4gl) (88)

Monomer 3sp4gl was prepare and purify using the same methodology as described

for 3sp2gl, yielded 10.5 g (72% yield) of colorless liquid. The following spectral

properties were observed: 1H NMR (CDC13): 6 = 1.64 (m, br, H4), 2.07 (m, br, H4), 3.43

(m, br, H4), 3.62 (m, br, H16), 4.93 (m, br, H4), 5.74 (m, br, H2). 13C NMR (CDC13): 8 =

28.78, 30.22, 70.10, 70.61, 70.69, 114.65, 138.28. FT-IR: (cm-1) 3076, 2866, 1640,

1449, 1416, 1350, 1323, 1296, 1248, 1118, 993, 912, 871. MS (70 eV): m/z= 330.2395

(M)+. (C18H3405) (330.44): Calcd. C 65.42, H 10.37; Found C 65.12, H 10.39.

3.6.3.4 Synthesis of tri(oxyethylene) a,to-di-7-octenyl ether (6sp3gl) (89)

Monomer 6sp3gl was prepare and purify using the same methodology as described

for 3sp2gl, yielded 9.2 g (55% yield) of colorless liquid. The following spectral

properties were observed: 1H NMR (CDC13): 6 = 1.30 (m, br, H12), 1.51 (m, br, H4), 1.98

(m, br, H4), 3.40 (m, br, H4), 3.53 (m, br, H12), 4.88 (m, br, H4), 5.70 (m, br, H2). 13C

NMR (CDC13): 6 = 25.87, 28.77, 28.86, 29.51, 33.63, 70.00, 70.55, 71.37, 114.10,

138.96. FT-IR: (cm-1) 3076, 2929, 2858, 1640, 1458, 1350, 1323, 1297, 1248, 1120,

995, 909, 726. MS (70 eV): m/z = 371.3168 (M+H)+. (C22H4204) (370.56): Calcd. C

71.31, H 11.42; Found C 71.33, H 11.53.

3.6.3.5 Synthesis of tetra(oxyethylene) a,o-di-7-octenyl ether (6sp4gl) (90)

Monomer 6sp4gl was prepare and purify using the same methodology as described

for 3sp2gl, yielded 6.7 g (58% yield) of colorless liquid. The following spectral

properties were observed: 1H NMR (CDC13): 6 = 1.31 (m, br, H12), 1.54 (m, br, H4), 1.98