1 ACYCLIC DIENE METATHESIS POLYMERIZATION FOR THE SYNTHESIS OF FUNCTIONALIZED POLYMERS By PAULA ANDREA DELGADO SALDARRIAGA 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 2011
2 2011 Paula Andrea Delgado Saldarriaga
3 To my lovely husband Henry, my mom and my brothers for their endless love and for supporting my crazy ideas
4 ACKNOWLEDGMENTS There are many people who I would like to thank for their support during my graduate career at the University of Florida. I need to start by thanking God for giving me the health, strength and wisdom thorough these years, and for not letti ng my spirit fall during the most difficult circumstances. I would like to thank my soul mate Henry who has been my rock, my happiness, and my shoulder. Without him this success would not be the same. I would like to thank my Father, who taught me that lim itations only exist in your mind. To my inspiration, my Mother, thank you for showing me the perseverance that is needed for success in life, for your unconditional love and your prayers, and for being the foundation of our wonderful family. I would like t o thank my two brothers Diego and David for their love and for the shared joys and sorrows. I would like to thank my grandma for sharing her priceless life experiences and her prayers. I would like to have a special acknowledgement to my uncle Ricardo, who has always helped and provided advice to me during my career, thank you Tio. I also would like to thank the members of my committee, Dr. Kenneth B. Wagener, Dr. Kenneth Sloan, Dr. Aaron Aponick, Dr. Steven Miller, and Dr. Ben Smith for their assistance an d time. To the supportive scientific and friendly environment of the Butler Laboratory that made an unforgettable multidisciplinary experience in my career. Thanks are given to the present members of the Wagener group, for making every day a joyful and mem orable experience. To the former members Dr. Piotr Matloka, Dr. Eric Berda, Dr. James Leonard, and Dr. Yuying Wei thank you for your unconditional help and advice.
5 Appreciation is given to Sara Klossner for her kind help, advice and our unforgettable share d experiences. I would like to thank the National Science Foundation (NSF, DMR 0703261) and ARO (W911NF 09 1 0290) for their support of my work. And last but not least, I also have special acknowledgment to Professor Fabio Zuluaga, who believed in me, and gave me the opportunity to work with Dr. Wagener, to whom I have no words to express my gratitude. For his unconditional support, understanding, and guidance throughout these five years of graduate school at the University of Florida, a life of gratitude Dr. Wagener.
6 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 9 LIST OF FIGURES ................................ ................................ ................................ ........ 10 LIST OF SCHEMES ................................ ................................ ................................ ...... 13 ABSTRACT ................................ ................................ ................................ ................... 15 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 17 1.1 Olefin Metathesis ................................ ................................ .............................. 17 1.1.1 General Olefin Metathesis Transformations ................................ ............ 17 1.1.2 Brief History of Olefin Metathesis ................................ ............................ 19 1.1.3 Acyclic Diene Metathesis (ADMET) Polymerization ................................ 23 1.2 Solid State Polymerization ................................ ................................ ................ 27 1.2.1 Solid state Polymerization of Semicrystalline Polymers .......................... 27 1.2.2 Acyclic Diene Metathesis Pol ymerization under Solid State Conditions .. 29 1.3 Purpose of this Dissertation ................................ ................................ .............. 31 2 SYNTHESIS AND THERMAL CROSSLINKING OF CARBOSILOXANE AND OLIGO(OXYETHYLENE) POLYMERS ................................ ................................ ... 32 2.1 Introductory Remarks ................................ ................................ ........................ 32 2.2 Results and Discussion ................................ ................................ ..................... 35 2. 2.1 Monomer Design ................................ ................................ ..................... 35 2.2.2 ADMET Polymerization of Carbosiloxane or Oligo(oxyethylene) based Monomers with Silacyclobutane as Cha in end Telechelic Derivative ............ 36 2.2.3 Spectroscopic Characterization ................................ ............................... 38 2.2.4 Thermal and Molecular Weight Characterization of Glycol and Siloxane based Polymers ................................ ................................ .............. 40 126.96.36.199 Thermal analysis of chain end telechelic polymers ........................ 41 2.2.4. 2 Thermal end group crosslinking via opening of silacyclobutane ring ................................ ................................ ................................ .......... 46 2.2.5 Mechanical Properties of Cured Polymers ................................ .............. 49 2.3 Experimental Conditions ................................ ................................ ................... 51 2.3.1 Chemicals ................................ ................................ ................................ 51 2.3.2 Instru mentation ................................ ................................ ........................ 51 2.3.3 Monomer Synthesis ................................ ................................ ................. 52 2.3.4 General Procedure for Bulk Polymerization ................................ ............. 56 2.3.5 Hydrogenated Polymers ................................ ................................ .......... 57
7 3 SYNTHESIS AND CHARACTERIZATION OF POLY(3 ALKYL 2,5 THIENYLENE VINYLENE) BY SOLID STATE METATHESIS POLYCONDENSATION ................................ ................................ ......................... 60 3.1 Introd uctory Remarks ................................ ................................ ........................ 60 3.2 Results and Discussion ................................ ................................ ..................... 61 3.2.1 Monomer Synthesis ................................ ................................ ................. 61 3.2. 2 Polymer Synthesis ................................ ................................ ................... 64 188.8.131.52 1 H NMR analysis of 3 dodecyl PTV (P3DDTV) .............................. 65 184.108.40.206 Different attempts for the synthesis of 3 dodecyl PTV, (42a) ......... 66 3.2.3 Poly(3 hexyl 2,5 thienylene vinylene), P3HTV ................................ ........ 68 3.2.4 Truly Intractable Polymer: 3 methyl De rivative ................................ ........ 70 3.2.5 Thermal and Electrochemical Analysis ................................ .................... 71 220.127.116.11 Thermal analysis of synthesized PTVs ................................ .......... 71 18.104.22.168 Optoelectronic and electrochemical properties of soluble PTVs derivatives ................................ ................................ ............................... 74 3.3 Experimental Data ................................ ................................ ............................ 77 3.3.1 Materials ................................ ................................ ................................ .. 77 3.3.2 Instrumentation ................................ ................................ ........................ 77 3.3.3 Monomer and Precursors Synthesis ................................ ........................ 79 3.3.4 General Metathesis Conditions in the Solid State ................................ ... 82 4 SYNTHESIS AND THERMAL PROPERTIES OF POLY(NAPHTHALENE VINYLENES) ................................ ................................ ................................ .......... 84 4.1 Introductory Remarks ................................ ................................ ........................ 84 4.2 Results and Discussion ................................ ................................ ..................... 87 4.2.1 Monomer and Polymer Synthesis ................................ ..................... 87 4.2.2 Thermal Properties ................................ ................................ ........... 93 4.2.3 Optical Studies ................................ ................................ .................. 94 4.2.4 Electrochemical Studies ................................ ................................ .... 95 4.3 Experimental Methods ................................ ................................ ...................... 97 4.3.1 Instrumentation and Analysis ................................ ................................ .. 98 4.3.2 Monomer and Precursors Synthesis ................................ ...................... 100 4.3.3 Polymer Synthesis ................................ ................................ ................. 104 5 INTRODUCTION OF TRIPTYCENE UNITS INTO THE POLYOLEFIN BACKBONE ................................ ................................ ................................ .......... 106 5.1 Introductory Remarks ................................ ................................ ...................... 106 5.2 Results and Discussion ................................ ................................ ................... 108 5.2.1 Monomer Synthesis ................................ ................................ ............... 108 5.2.2 Homopolymerization of Triptycene Monomers ................................ ...... 109 5.2.3 Spectroscopic and Thermal Analysis of Triptycene Homopolymers ...... 111 5.2.4 Thermal Characterization of Triptycene Homopolymers ........................ 115 5.2.5 Block Copolymerization between Triptycene Monomers and Cis cyclooctene ................................ ................................ ................................ 119
8 5.2.6 Random Copolymerization ................................ ................................ .... 121 5.2.7 Thermal Characterization of Block and Random Copolymers ............... 123 5.2.8 Spectroscopic Analysis of Triptycene Copolymers ................................ 125 5.3 Experimental Details ................................ ................................ ....................... 126 5.3.1 Instrumentation and Analysis ................................ ................................ 126 5.3.2 Monomer Synthesis ................................ ................................ ............... 128 5.3.3 Polymer Synthesis ................................ ................................ ................. 129 6 CONCLUSIONS ................................ ................................ ................................ ... 135 6.1 Synthesis and Thermal Cr osslinking of Carbosiloxane and Oligo(oxyethylene) Polymers ................................ ................................ ............. 135 6.2 Carbosiloxane and Oligo(oxyethylene) thermoset polymers ........................... 135 6.3 Synthesis of PTVs by Solid State Metathesis Polycondensation .................... 136 6.4 Synthesis Of Poly(Naphthalene Vinylenes) ................................ .................... 137 6.5 Introd uction of Triptycene Units into the Polyolefin Backbone ........................ 138 APPENDIX A VOLTAMMOGRAMS ................................ ................................ ............................ 140 B GPC TRACES ................................ ................................ ................................ ...... 142 C THE 1 H NMR S PECTRA OF TRIPTYCENE COPOLYMERS ............................... 143 LIST OF REFERENCES ................................ ................................ ............................. 144 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 152
9 LIST OF TABLES Table page 2 1 GPC data for saturated and unsaturated telechelic polymers. ........................... 41 2 2 Thermal analysis of the saturated and unsaturated polymers before crosslinking. ................................ ................................ ................................ ........ 42 2 3 Thermal analysis of the saturate d and unsaturated polymers before crosslinking. ................................ ................................ ................................ ........ 44 2 4 Mechanical properties of thermally crosslinked oxyethylene and carbosiloxane based polymers. ................................ ................................ ......... 51 3 1 Molecular weight analysis for the synthesis of P3DDTV ................................ ..... 68 3 2 Electrochemical properties of 3 hexyl and 3 dodecyl PTV derivatives ............... 76 4 1 Different attempts for the polymerization of monomer ( 43b ). ............................. 90 4 2 Optical properties of PNV derivative ( 62 ) ................................ ........................... 96 4 3 Electrochemical properties of PNV derivative ( 62 ). ................................ ............ 96 5 1 Molecular weight summary for triptycene homopolyme rs ................................ 111 5 2 Thermal analysis of saturated and unsaturated triptycene homopolymers. ...... 118 5 3 Molecular weight analysis of block copolymers ................................ ................ 121 5 4 Thermal analysis of triptycene copolymers. ................................ ...................... 123
10 LIST OF FIGURES Figure page 1 1 Most common olefin metathesis transformations. ................................ ............... 18 1 2 Metallacyclobutane mechanism. ................................ ................................ ......... 19 1 3 Formation of the 14 electron species by the two possible pathways. ................. 21 1 4 Most used metathesis catalysts. ................................ ................................ ......... 21 1 5 Release/return mechanism for Hoveyda type catalysts. ................................ ..... 23 1 6 Some examples of functionalized olefin polymers synthesized by ADMET polymerization. ................................ ................................ ................................ ... 25 1 7 ADMET proposed mechanism ................................ ................................ ............ 26 2 1 Latent reactive siloxane and oligo(oxyethylene) materials. A) Internal crosslinking. B) Chain end alkoxy functionalized crosslinking. ........................... 33 2 2 1 H NMR spectra of glycol derivatives. A) Monomer 5 (9sp4gl) B) Polymer 9 (Si_9sp4gl) C) Hydrogenated polymer 13 (Si_H_9sp4gl). ................................ 37 2 3 13 C NMR spectra of glycol derivatives. A) Monomer 18 (9sp4gl). B) Polymer 20 (Si_9sp4gl). C) Hydrogenated polymer 22 (Si_H _9sp4gl) ............................ 38 2 4 1 H NMR spectra of siloxane derivatives. A) Monomer 23 (6sp3Si).B) Polymer 25 C) Hydrogenated polymer 27. ................................ ................................ ....... 40 2 5 13 C NMR spectra of siloxane derivatives. A) Monomer 23 (6sp3Si). B) Polymer 25 C) Hydrogenated polymer 27. ................................ ........................ 41 2 6 TGA traces of glycol based telechelic polymers ( 19 22 ) in an inert atmosphere. ................................ ................................ ................................ ........ 43 2 7 TGA traces of carbosiloxane telechelic polymers ( 25 28 ) in an inert atmosphere. ................................ ................................ ................................ ........ 44 2 8 DSC thermograms of telechelic glycol based polymers. ................................ .... 45 2 9 DSC thermograms of telechelic carbosiloxane based polymers ( 25 28 ). ........... 46 2 10 DSC curves of telechelic polymer Si_9s4gl ( 20 ) before and after crosslinking. .. 47 2 11 FT IR spectra of glycol derivatives ................................ ................................ .... 49 2 12 Stress/strain curves of selected thermosets. ................................ ...................... 50
11 3 1 1 H NMR of 3 dodecyl 2,5 dipropenylthiophene monomer 40a. .......................... 63 3 2 Solid state polymerization o f the 3 dodecyl 2,5 dipropenylthiophene monomer 40a. ................................ ................................ ................................ .... 65 3 3 1 H NMR correlation for dodecyl thiophene derivatives. ................................ ...... 66 3 4 1 H NMR correlation of hexyl derivatives. A) 3 hexyl 2,5 dipropenyl monomer 40b. B) P3HTV prepolymer 41b C) P3HTV final polymer 42b. .......................... 69 3 5 1 H NMR correlation between methyl thiophene derivatives. ............................... 72 3 6 TGA thermogram of PTVs ( 42a c) at 20 o C/min rate in N 2 ................................ 72 3 7 DSC thermograms for polymer PTVs ( 42a c) at 10 o C/min rate .......................... 73 3 8 Spectroelectrochemistry of P3DDTV. ................................ ................................ 74 3 9 Spectroelectrochemistry of P3HTV. ................................ ................................ .... 75 3 10 Cyclic voltammogram of soluble PTVs. ................................ .............................. 76 4 1 Different linkages for naphthalene vinylene polymers. ................................ ....... 84 4 2 1,1 vinyl substituted aromatic species. ................................ ............................... 85 4 3 Different Ru based catalysts for the synthesis of tetrasubstituted olefins ........... 87 4 4 1 H NMR spectra of naphthalene derivatives. A) Monomer ( 61 ). B) Polymer ( 62 ). ................................ ................................ ................................ .................... 92 4 5 TGA thermogram of polymer ( 62 ). ................................ ................................ ...... 93 4 6 Differential scanning calorimetry thermogram for PNV derivative ( 62 ). Top trace heating ramp; bottom trace, cooling rap; 10 o C/min in He. ......................... 94 4 7 Absorption and emission spectra of PNV derivative ( 62 ) in methylene chloride solution. The sample was excited at 394 nm. ................................ ....... 95 4 8 Cyclic voltammogram of PNV derivative ( 62 ) in dichloromethane with 0.1 M TBAPF 6 /ACN supporting electrolyte. Scan rate of 25 mV/s ................................ 97 4 9 Differential pulse voltammogram of PNV derivative ( 62 ) in dichloromethane with 0.1 M TBAPF 6 supporting electrolyte at 100 mV. ................................ ........ 97 5 1 Mechanical interlocking mechanism of triptycene. ................................ ............ 107 5 2 Different linkages to the triptycene structure. ................................ .................... 108
12 5 3 1 H NMR spectra of bridgehead triptycene derivatives. A) Monomer ( 65 ). B) Homopolymer ( 68 C) Hydrogenated homopolymer ( 69 ). ................................ 112 5 4 13 C NMR spectra of bridgehead triptycene derivatives. A) Monomer ( 65 ). B) Homopolymer ( 68 ). C) Hydrogenated homopolymer ( 69 ). ................................ 113 5 5 1 H NMR spectra of 1,4 benzene substituted triptycene derivatives. A) Monomer ( 67 ). B) Homopolymer ( 70 ). C) Hydrogenated homopolymer ( 71 ). ... 114 5 6 13 C NMR spectra of 1,4 benzene substituted triptycene derivatives. ................ 115 5 7 Thermogravimetric analysis for triptycene homopolymers and polyoctenamer at 20 o C/min in N 2 ................................ ................................ ............................. 117 5 8 Differential scanning calorimetry thermograms of bridgehead homopolymers ( 68 and 69 ) and 1,4 benzene substituted homopolymers ( 70 and 71 ) .......... 118 5 9 GPC traces of the triptycene derivataives. A) Homopolymer (first block, 72a ). B) Final block copolymer ( 74a ), using Grubbs first generation catalyst. ........... 122 5 10 Thermogravimetric analysis for random copolymers between 1,4 benzene substituted block copolymers ................................ ................................ ........... 124 5 11 Differential scanning calorimetry thermograms of Block copolymers ( 74c d ) and random copolymers ( 75a b ) at a heating rate of 10 o C/min. ....................... 125 5 12 1 H NMR spectra of triptycene copolymers. ................................ ....................... 127 A 1 Cyclic voltammogram of P3DDTV ................................ ................................ ... 140 A 2 Differential pulse voltammogram o f P3DDTV ................................ .................. 140 A 3 Cyclic voltammogram of P3HTV ................................ ................................ ...... 141 A 4 Differential pulse voltammogram of P3HTV ................................ ..................... 141 B 1 GPC Traces of the first block of the block copolymers ................................ .... 142 C 1 1 H NMR spectra. A ) homopolymer 70 B ) block copolymer 74a C ) random copolymer 76d in a 5:5 ratio of cyclooctene:triptycene ................................ ..... 143
13 LIST OF SCHEMES Scheme page 1 1 The principle of olefin metathesis. ................................ ................................ ...... 17 1 2 Synthesis of PET by solid state polymerization conditions. ................................ 29 1 3 Melt prepolymerization of 1,9 decadiene (10) followed by polymerization in the solid state. ................................ ................................ ................................ .... 30 1 4 Melt prepolymerization of 1,4 dipropoxy 2,5 divinylbenzene followed by solid state polymerization. ................................ ................................ ........................... 30 2 1 Synthesis of carbosiloxane based polymers possessing thermally crosslinkable chain ends. ................................ ................................ ................... 36 2 2 Thermal induced crosslinking reaction of silac yclobutane end capped polymers. ................................ ................................ ................................ ............ 48 3 1 Synthesis of 3 dodecyl 2,5 dipropenylthiophene monomer ( 40) ........................ 62 3 2 Solid state polymerization of the 3 hexyl 2,5 dipropenylthiophene monomer 40b. ................................ ................................ ................................ .................... 69 3 3 Solid state polymerization of 3 methyl 2,5 dipropenylthiophene 40c ................ 70 4 1 Monomer synthesis by Kumada coupling using Ni(dmpe)Cl 2 catalyst. ............... 88 4 2 Synthesis of monomer 43b by Pd PEPSI iPr catalyzed Kumada coupling. ........ 88 4 3 Polymerization of 2,6 di(1 octen 2 yl)naphthalene ( 43b ). ................................ ... 89 4 4 Synthesis of 2,6 d i(1,3 decadien 4 yl)naphthalene (55) ................................ .... 90 4 5 Synthesis of 2,6 bis(( Z ) 2 vinyl 1 octenyl)naphthalene ( 61 ). .............................. 91 4 6 Polymerization of 2,6 bis(( Z ) 2 vinyl 1 octenyl)naphthalene ( 61 ). ...................... 92 5 1 Synthesis of bridgehead triptycene monomer ( 65 ). ................................ .......... 109 5 2 Synthesis of 1 4 benzene substituted triptycene monomer ( 67 ). ...................... 109 5 3 ADMET polymerization and hydrogenation of bridgehead and 1 4 benzene substituted triptycene monomers. ................................ ................................ ..... 110 5 4 Block copolymerization of 1,4 benzene substituted triptycene monomer ( 67 ) and cis cyclooctene ( 73 ). ................................ ................................ .................. 119
14 5 5 ADMET copolymerization of 1,4 benzene substituted triptycene monomer ( 69 ) and 1,9 decadiene ( 10 ). ................................ ................................ ............ 122
15 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 ACYCLIC DIENE METATHESIS POLYMERIZATION FOR THE SYNTHESIS OF FUNCTIONALIZED POLYMERS By Paula Andrea Delgado Saldarriaga December 2011 Chair: Kenneth B. Wagener Major: Chemistry Acyclic diene metathesis polymerization (ADMET) has been used in the synthesis of functio nal polymers, as previous reports demonstrated that ADMET can be used for the synthesis of ionomers, elastomers, model polyethylene, and conjugated polymers, among others. The well established mechanism, high selectivity for new trans olefins, mild reactio n conditions, tolerance for different functionalities, well defined end groups, absence of branching within the polymer structure, and the possibility of bulk polymerization make the ADMET polymerization a useful tool for the synthesis of functionalized po lymers. The research described herein explains the synthesis of thermosets, conjugated polymers and elastomers by this methodology. As an overview, C hapter 1 highlights the history of ADMET and solid state polymerization as a methodology for polymer synth esis. Chapter 2 describes a series of saturated and unsaturated carbosiloxane and oligo(oxyethylene) polymers synthesized using silacyclobutane as a chain end. Thermally crosslinking these polymers led to thermosets, with moduli from 0.6 to 9.3MPa, tensile strengths from 0.3 to 1.0MPa and elongations from 12 to 76%. Chapter 3 describes how solid state metathesis
16 polymerization (SSP) can be used for the direct synthesis of intractable poly(thienylene vinylenes), polymers which are unattainable by any other m ethodology. The progress of this method was evaluated from the synthesis of soluble PTVs, where a prepolymer exhibited 3.5 fold increase in its molecular weight while in the SSP. Synthesized PTVs exhibited thermal and electrochemical properties similar to those of PTVs synthesized by traditional methodologies. The synthesis of vinyl substituted poly(naphthalene vinylenes), PVN is described in C hapter 4. Herein, modification on monomer architecture demonstrated the essentials for an efficient metathesis tran sformation. PNV systems were obtained by placing the alkyl solubilizing groups (to obtain a hydrocarbon soluble polymer) one carbon away of the active olefin. Incorporation of triptycene units into the polymer backbone induces its mechanical interlocking p roperties that led to polymers with enhanced mechanical properties. The successful introduction of triptycene into polyolefin backbone by ADMET polymerization is described in C hapter 5. The influence on the triptycene architecture and triptycene concentration in the polymer influenced the thermal behavior of the resulting polymers. Collectively, the research described herein again proves the versatility of ADMET polymerization as a tool for the synthesis of functionalized polymers.
17 CHAPTER 1 INTRODUCTION 1. 1 Olefin M etathesis Olefin metathesis which is a powerful method for the formation of carbon carbon bonds, is very valuable for synthetic purposes as evidenced by usage in about 4500 research reports in the last ten years. Olefin metathesis is defined as a chemical transformation in which two carbon carbon double bonds interchange with one another in the presenc e of catalyst resulting in formation of two new olefins as illustrated in scheme 1 1. 1 The importance is recognized throughout the scientific world, most notably in the 2005 Nobel award to professors Grubbs, Schrock and Chauvin, who are the key developers of the process. Scheme 1 1 The principle of olefin metathesis. 1.1.1 General Olefin Metathesis T ransformations A broad variety of compounds can be synthesized by this methodology and F igure 1 1 represents seven of the most common olefin meta thesis transformations: a) Self metathesis (SM) : M etathesis exchange between two olefins of the same compound. b) Cross metathesis (CM): Exchange olefins between two different olefins. This type of reaction is the most used of all olefin metathesis, as it allows the double bond formation from a variety of functional group structures. c) Ring clos ing metathesis (RCM): I ntramolecular metathesis exchange to form cyclic structures, driven by the entropy of the transformation 3 4 d) Ring opening metathesis polymerization ( ROMP ): Chain growth polymerization, where high molecular weight polymers (up to millions) can be attained, driven by the release of a strain ring With a certain catalyst, It can perform as a living polymerization. 5
18 e) ADMET polymerization (Acyclic diene metathesis polymerization): S tep growth equilibrium polymerization usually of a diene monomer, in which polymerization is driven by the release of an olefin condensate (usually ethylene). 6 f) Ethenolysis: O lefin metath esis reaction, where an internal double bond of a high molecular weight structure or polymer reacts with ethylene to break its structure into a smaller molecular weight product. 7 g) Acyclic triene metathesis polymerization (AT MET polymerization): D erivative o f ADMET polymerization, where the monomer is a tri functional olefin, which leading to the formation of branched polymers 8 9 Figure 1 1 Most common olefin metathesis transformations.
19 The development of these olefin metathesis transformations has been closely related to the progress of the catalyst development and understanding of the reaction mechanism as described in the next section. 1.1.2 Brief History of Olefin Metathesis The first investigation of olefin metathesis occurred early 1960 s in the industrial settings of Dupont, Standard O il and Phillips Petroleum 10 with the ROP (ring opening polymerization) of norbornene using t itanium tetrachloride and l ithium aluminum tetraalky l. The process was called at the time 11 Later in 1964 butene and ethylene emerged. 12 However the real understanding of th is type of reaction began with the works of Calderon et al. in 1967, 13 who realized 14 Different mechanisms were also proposed for this reaction, with the aim to expand the methodology by developing more active catalysts T met al complex proposed by Bradshow (supported by Calderon) 15 and mechanism suggested by Grubbs. 16 However it was not until Chauvin and Hrisson proposed the formation of the metal carbene complex as an active catalyst and meta llacyclobutane i ntermediate that a full understanding o f this reaction started to emerge (Figure 1 2) 17 Figure 1 2 Metallacyclobutane mechanism.
20 Based on this proposed mechanism, a vast number of either homogenous or heterogeneous catalysts have been developed to date, each having different group tolerance, lifetime of the active specie s activity, and selectivity of cis vs trans olefin form ation Star t ing with Schrock and coworkers in the mid 80s, neutral carbene complexes based on t ungsten or m olybdenum catalyst s containing bulky imido ligands were synthesized. 18 These catalysts presented high metathesis activity, and because of their adequate stability and product control 19 T he catalysts, especially m olybdenum type (1), presented high metathesis activity as a result of the high oxidation state metal, but they were sensitive to oxygen, polar and protic f unctional groups that limit its experimental practice. 19 Therefore, an effort to synthesize catalyst s tolerant to ai r, moisture and some functional groups started growing. In early 1990s Grubbs synthesized (based on previous experience with Ru catalysts) a la te transition metal Ru catalyst having bulky basic phosphine ligands (specially tricyclohexylphosphine) (2) that showed higher stability but lower activity than ( 1) However this Ru catalyst could not be produced in big scale. 19 Different studies on r uthenium catalysts indicated that a dissociative pathway was associated in the formation of the ac tive catalyst. Thus, the most labile ligand dissociates, forming a 14 electron specie s (Figure 1 3B) that is considered to be the active metathesis catalyst. This specie s then coordinates with the olefin to form the metallacyclobutane intermediate. Taking this dissociative mechanism into consideration, Grubbs and coworkers investigated various ligand s to stabilize the 14 electron specie s and there by increas ing the stabili ty and activity of the catalyst.
21 Figure 1 3 Formation of the 14 electron specie s by the two possible pathways. In 1992, Grubbs synthesized what is today called the first generation Grubbs catalyst (3) with higher activity than previous Ru based cata lyst s but still lower than H catalyst has the great advantage of being tolerant to air, moisture, and many polar functional groups. Figure 1 4. Most used metathesis catalysts.
22 In order to stabilize the 14 electron specie s and facilitate their formation, a stronger electron don ating ligand a substituted N heterocyclic carbene (NHC), was introduced to replace one of the phosphine groups Many substitutions were analyzed, showing that without substitution the 14 electron specie s decomposes too rapidly to give productive metathesis products. 19 Mesyl substituted NHC (4) was found to be more active than the previous ly synthesized Ru based catalyst, while maintaining the stability and the functional group tol (3) Nevertheless, later studies demonstrated than this catalyst facilitate d olefin isomerization, which lessened the precision on certain type s of substrate. 20 Numerous catalysts have been synthesized attempting to improve the catalyst activity, functional group tolerance, lifetime of the 14 electron specie s and selectivity over cis over trans olefin s (Figure 1 4) Among these, Hoveyda reported a family of very active and stable r uthenium systems der ived from the Grubbs catalysts (e g catalyst (5) and (6) ). In these catalysts, the phosphine and the benzylidene were replaced by a bid e ntate benzylidene ether ligand, in which the oxygen atom coordinates with the r uthenium center, giving it remarkable ac tivity. 21 Although the metathesis mechanism of this type of catalysts is still under investigation, the established general mechanism is based on a release/return or boomerang mechanism (Figure 1 5 ). The first step in the mechanism involves dissociation of the benzylidene ether, activated by the presence of the olefin substrate, to form complex I, which forms the metallacyclobutane intermediate II. Cycloreversion of this complex leads to the formation of complex III, which enters into the catalytic cycle after the olefin exchange (Figure 1 5). 22 23
23 Greatest advantage of these types of catalysts is that they are able to regenerate themselves once the substrate is depleted, thereby decreasing decomposition of the active 14 electron species V. Taking into th e account the history of the olefin metathesis and the most used catalysts, ADMET polymerization will be the transformation applied in this study. Figure 1 5 Release/return mechanism for Hoveyda type catalysts. 1. 1. 3 Ac yclic Diene Metathesis (ADMET) P olymerization Acyclic Diene Metathesis is the principal polymerization react ion used in this dissertation. As previously mentioned, ADMET polymerization involves a step growth condensation with the removal of ethylene (in most of the cases) as driven forc e. The diene with an early transition metal catalyst was described in the late 1970s. In this case low molecular weight oligomers were reported in the reaction of
24 1,5 hexadiene and 1,7 octadiene with a combination of nitrosyl mol ybdenum and t ungsten compounds with organoaluminium halides as catalytic systems. 14 Later, Wagener and coworkers showed that th ese catalytic systems (Lewis acids) not only promote metathesis reaction s but can also serve as a cid cataly st for vinyl addition polymerization. 24 Subsequently, the Lewis acid free systems developed by Schrock facilitated the successful metathesis polymerization of 1,6 hexadiene and 1,9 decadiene, resulting in polymers of about 12, 000 g/mol molecular weight. 25 26 However, as previously mentioned, the high oxophilicity of molybdenum Schrock catalyst limited the synthesis of variety functional polymers. It was in 1992, when ere first tried in an ADMET polymerization study. The polymerizatio n of 1,9 decadiene, with Grubbs first generation catalyst (3) le d to polymer wi th a molecular weight of 20,000 g/mol. 27 Due to the high functional group tolerance of this catalyst, a vast number of functionalized polyolefins have been synthesized since th en. Figure 1 6 show s some examples of functionalized olefin polymers synthesized by ADMET polymerizations. The functionalit ies of these polymers have led to many different studies. For instance, alkyl and deuterated alkyl substituents o n the polyethylene b ackbone have been studied as models for the commercially synthesized HDPE (high density polyethylene) and LDPE (low density polyethylene), as well as for morphological studies. 28 Additional studies have been performed with precisely placed acids and ionic groups on the poly olefin backbone to model cel l membranes, and for crystallographic studies. 29 Siloxanes and glycol linkage s have also been synthesized by this
25 methodology and they provide an opportunity to synthesize hybrid soft/hard phase materials in the elastomeric polymer field. 30 Polyolefins containing precisely placed halogen functionalit ies have served as models for morphological studies, as the halogen interfere s in their crystal line behavior of the polymer. 31 Recently, precisely placed pendant chromophores have been incorporated into the family to study the ir interaction s of the emission color of the polymer. 32 Moreover, ADMET polymerization h as been recently used for the synthesis of defect free conjugated polymers, allowing different copolymerization compositions, and therefore controlling electronic properties of the final polymer. 33 Figure 1 6. Some examples of functionalized olefin polym ers synthesized by ADMET polymerization. transformation the polymerization described in Figure 1 7 must be considered. The polymerization starts by the dissociation or decoordina tion of one of the labile ligands of
26 the catalyst to form the 14 electron specie s I (previously described in Figure 1 3) This metathesis active system coordinates with the olefin followed by formation of the metallacyclobutane II which after productive cleavage forms the metathesis active alkylidene complex III Subsequent reaction with a new monomer leads to the formation of the metallacyclobutane IV which after productive cleavage start s form ation of polymer chains with a mixture of cis and trans stereoisomers, where the catalyst and the substitution of the olefins play an important role on the ratio of the stereoisomers. Then, another olefin coordinates with the methylidene carbene V which after another productive cleavage of the metallacyclob utane VI regenerates the metal alkylidene III and produces ethylene. Removal of ethylene out from the sys tem drives the reaction towards polymer formation. 14,29 Figure 1 7. ADMET proposed mechanism Many experimental conditions haven used for the synthes is of polymers by ADMET polymerization. Bulk polymerization is most common where polymerization is carried out close to the melting temperature of the monomer. However, once high monomer conversion is obtained, stirring of the polymerization mixture becom es tedious, limiting the removal of ethylene. Another method for ADMET polymerization
27 involves use of high boiling solvents under dynamic vacuum conditions. This methodology is necessary when the monomer is a solid or when the polymer mixture ha s reached a viscosity that does not allow stirring under bulk conditions. However, polymers made by this methodology should be partially or highly solub le in the high boiling solvent used, usually 1,2 dichlorobenzene and o xylene. Although these two methodologies al low the formation of high molecular weight polymers intractable material cannot be used under these circums tances. The next subchapter introduce s solid state polymerization as a methodology for the synthesis of rigid rod polymers. 1. 2 Solid State P olymerization Solid state polymerization (SSP) is an alternative polymerization methodology that takes place with little motion, where all the starting materials are present as crystals or powders. There are two types of solid state polymerization: topoche mical polymerization and polymerization for semi crystalline polymers. Topochemical polymerization starts with the crystalline monomer and proceeds all the way to the polymer in the solid s t ate. This method is usually used for the synthesis of polyacety lenes and polyarenes with rigid crystalline phases. The second type is the equilibrium polycondensati on of semicrystalline polymers, will be described in more detail. 1.2.1 Solid state Polymerization of Semicrystalline P olymers This type of solid state po lymerization which was f irst reported in 1964, 34,35 is widely practiced in the polyester, polyamide, and polycarbonate industries. 36 These polymerizations start with bulk formation of a low molecular weight polymer (prepolymer), which reacts further under the solid state conditions to increase the molecular weight
28 Th e monomer is polymerized in bulk (molten state) at temperatures higher than the melti ng temperature of the polymer. W ith the release of a small condensate a prepolymer with a molecular weight of about 15,000 g/mol can be achieved This prepolymer is typically extruded to chips or flakes to increase its surface area, using tumble dryers or moving bed reactors to prevent the small particles from stick ing to each other Once the prepolymer has been shaped, it is placed it in the reactor to continue the polymerization in the solid state. The prepolymer is then heated to a temperature lower than the onset of its melting temperature (T m ) and above its glass transition temperature (T g ). T he poly mer has the highest mobility in the se micrystalline region (usually 5 40 o C lower than the melting temperature of the polymer). Therefore the maximum mobility of the amorphous region is used while the crystal line region remains intact. Many studies have de monstrated that reacting groups remain in the amorphous region The closeness of these reacting groups in the solid state facilitate end group encounters, yielding higher molecular weight polymers. In the s ynthesis of p oly(ethylene terephthalate) (PET) a typical example of the industrial use of this methodology, t he prepolymer molecular weight increased 1.7 times. 36 The synthesis of PET starts with the polymerization of bis(2 hydroxyethyl terephthalate) ( 7) at about 280 o C to produce the prepolymer (8) w ith an average molecular weight of 15,000 g/mol which is sufficient enough for use in most industrial applications. This PET prepolymer is then cooled and extruded to chips to increase its su rface area. The polymerization continues in the solid state above T g and below T m (usually 150 o C) to obtain a polymer (9) with an approximate molecular weight of 25,000 g/mol. ( Scheme 1 2 ).
29 Scheme 1 2 Synthesis of PET by solid state polymerization conditions. Solid state polymerization presents several advantages over the use of melt polymerization. 37 It requires lower operating temperatures, which constrain side reactions and lead to higher purity polymers. It is an environmentally friendly procedure, as it does not require hazardous solvents. Polymers are simpler to collect, as the crystalline phase has not been affected. Higher molecular weight polymers can be obtained with an elevated degree of crystallinity As disadvantages, solid state polymerization s exhibit low reaction rates and slower diffusion of the byp roduct 36 and these factors significantly influence the molecular weight of the final polymer. 1.2. 2 Acy clic Diene Metathesis Polymerization u nder Solid State C onditions Solid diene monomer s. Oakley studied the influence of solid state polymerization in a variety of functional monomers: olefins, ketone s alcohols, aromatics, and a comb graft copolymer
30 with polystyrene grafted onto the polyolefin backbone. As an example, 1,9 decadiene ( 10 ) w as exposed to solid state metathesis condit ions. Following the industrial methodology for this approach a prepolymer (11) of 1,300 g/mol was obtained which after solid state reaction yielded a 20 fold increase in molecular weight (Scheme 1 3 ). 38 Scheme 1 3 Melt prepolymerization of 1,9 decadiene (1 0 ) followed by polymerization in the solid state. Oakley also studied the polymerization of a rigid rod system by ADMET polymerization in order to understand the feasibility of preparing defect free PPV in the solid state. The bulk polymerization of 1,4 dipropoxy 2,5 divinylbenzene (13 ) produced an oligomer with a molecular weight of 500 g/mol followed by an increment in the solid state to 1 100 g/mol after 7 days of solid state polymerization (Scheme 1 4 ). This low monomer conversion was explained by the proximity of the propoxy group that can coordinate with the active alkylidene carbene making a stable complex that does not continue with a productive metathesis reaction. 39 Scheme 1 4 Melt prepolymerization of 1,4 dipropoxy 2,5 divinylbenzene followed by solid state polymerization. Taking advantage of the solvent free conditions and the proximity of the reacting groups in the amorphous region of semi crystalline polymers d ifferent types of
31 polymers functionalities can be explored by this methodology, preferably those polymers that are unattainable in the liquid or molten state. 1.3 Purpose of this Dissertation The following text describes the on going investigation into the application of ol efin metathesis, mainly ADMET polymerization, to produce functionalized polymers with specific applications T he research presented in this dissertation is significant to the development of structure property relationships for widely applied chemical and p hysical crosslinked materials as well as for the synthesis of common conjugated polymers through novel synthetic methods. Chapter 2 describes the synthesis of a series of s ilacyclobutane chain end siloxane/ oligo(oxyethylene) telechelic polymers. The therm al crosslinking of these polymers led to thermoset materials with mechanical properties comparable to thermosets cured by alternative methodologies. Chapter 3 involves the preparation and characterization of a series of poly(thienylene vinylene), PTVs by s olid state metathesis polymerization in a Teflon mold. This methodology allows the direct synthesis of intractable materials that unattainable by any other direct methodology Chapter 4 describes the progress on the synthesis of poly(naphthalene vinylene) derivatives by the use of state of the art metathesis catalysts. Finally, Chapter 5 describes the incorporation of triptycene units into the polyolefin backbone by different metathesis copolymeriz ations. Different ratios of triptycene co olefins polymers were investigated for further mechanical properties studies. As a summary, the research described in this document involves the development of synthetic methodology for the preparation of functiona lized olefins and conjugated polymers with control over the polymer st ructures, and their application.
32 CHAPTER 2 SYNTHESIS AND THERMA L CROSSLINKING OF CA RBOSILOXANE AND OLIGO(OXYETHYLENE) P OLYMER S 2. 1 Introductory Remarks The search for new thermoplastics with high moduli and elongation characteristics has involved a variety of combinations of soft and hard phases. 1 It is well known that introducing siloxanes as a soft phase increases the thermal and oxidative stability of the polymer and its electrical resistance, with the added advantages of low glass transition temperatures (~ 120 o C) and low toxicity. 40 44 Likewise, oligo(oxyethylene) linkages can also serve as a soft phase to enhance the elongation, thermal and chemical stability, and hydr ophobicity of the material, 45,46 making these polymers useful in membranes, hydrogels, amphiphilic copolymers and biomaterials. 47 51 However, these polymers usually exhibit low weather resistance and limited tensile strength. 41,43 In order to improve thei r stress strain behavior, they are usually copolymerized with glassy or crystalline hard phases and/or are reinforced with the addition of crosslinkers. 45 46 The latter process provides control over the primary structure of the polymer, because the crossli nker usually remains intact during the polymerization. 52 Olefin metathesis has been used as a tool for the synthesis of silicon/hybrid elastomer materials. In particular, acyclic diene metathesis polymerization (ADMET), Partial information of this chapter has been published and reproduced in part with the permission. J. Polym. Sci., Part A: Polym. Chem. 2009 47 5180 5183 License number: 2784350042300,and J. Polym. Sci., Part A: Polym. Chem ASAP License number: 2784571 138872
33 offers efficient chemistry and tole rance to different functional groups, both of which are important for the design of organosilicon and organo glycol linear polymers. Over the past ten years, our group has studied a variety of soft and hard phase compositions. 53 Brzenzinska et al. 54 carbosilane/carbosiloxane hybrid materials in which a series of alkoxy substituted carbosilanes (hard phase) and carbosiloxanes (soft phase) were incorporated in a random copolymer by ADMET polymerization (Figure 2 1 A ) The alkoxy functionalities served as hydrolytically driven internal crosslinkers; the density of crosslinker and soft phase in the polymer backbone allowed tailoring of the physical properties of the crosslinked materials. Figure 2 1 Latent react ive siloxane an d oligo(oxyethylene) materials. A) Internal crosslinking. B) C hain end alkoxy functionalized crosslinking. Although these hydrolytic thermoset polymers exhibited interesting elastomeric behavior, their tensile strengths were not particularl y high, possibly due to insufficient crosslinker concentration. 54,55 Later, Matlok a et al. introduced internal and/or chain end alkoxy substituted silicon crosslinkers into oligo(oxyethylene) and carbosiloxane based polymers and studied their structure/pr operty relationships. 55,56 They found that incorporation of chain end crosslinked materials enhanced the mechanical properties,
34 possibly by limiting the formation of dangling chains (Figure 2 1 B ) and that the mechanical properties of thermo sets depended o n the soft/hard phase formulations. Moduli between 2.0 10.0 MPa and elongations between 300 700% were observed for oligo(oxyethylene) based polymers, 57 while carbosiloxane homologues exhibited modu li in the range of 1.5 6.0 MPa and elongations of 30 to 100%. 55,57 While mechanical properties were improved, hydrolytically driven latent crosslinked materials have the disadvantages associated with inherently hydrophobic materials water is unable to completely penetrate the polymer system. Consequently, sever al researchers designed thermoset materials with thermally polymerizable chain ends. Different reactive functionalities were investigated as crosslinkers, including benzocyclobutane, 58,59 ethylene, 60 acethylene, 61 epoxides, 62 norbornene derivatives, 63 and disilacyclobutane. 64 Particularly, silacyclobutane has been used as chain end crosslinker, where the possibility of using anionic, cationic, organometallic, and/or thermal initiation conditions make it useful for the synthesis of chain end telechelic materials. 64,65 To further investigate the mechanical properties of carbosilane and oligo(oxyethylene) based polymers, our group has synthesized thermal chain end silacyclobutane functionalized hybrid materials by ADMET polymerization. 30 Chapter 2 will f ocus on the synthesis and characterization of the unsaturated and saturated telechelic polymers possessing silacyclobutane as a chain end thermally induced crosslinker. The mechanical properties of crosslinked polymers are also described.
35 Monomers and poly s to the number of glycol linkages. The polymer has a polymer backbone. When the polymer is hydrogenated, they and the corresponding polymer backbon e name. Once polymers are thermally cured, 2. 2 Results and D iscussion 2. 2 .1 Monomer D esign Carbosiloxanes and oligo(oxyethylene) based monomers were synthesized based on the requirements nee ded for a productive ADMET polymerization: no interference of the monomer functional group with the catalysis activity, and sufficiently long distance between the double bonds to avoid ring closing reaction during polymerization. Based on these requirement s, two different oligo(oxyethylene) based monomers ( 17 6sp4gl), and ( 18 9sp4gl) were synthesized as previously reported, 56 both possessing four glycol units, but with the number of methylene units (spacers) varying from six to nine. Scheme 2 1 shows the two different carbosiloxane monomers were synthesized ( 23 6sp3Si) and ( 24 6sp4Si) both having the same number of methylenes units, but with 3 to 4 siloxane linkages, by the hydrosilylation reaction of 1,6 hexadiene with the two different hydrogen termina 57 Previous work in our group has shown that placing chain end crosslinking units in the polymer backbone highly decreases the numbers of dangling chains, leading to
36 increased tensile strengths of the crosslinked materials. Thus, a chain end crosslinker active towards metathesis ( 16 ), 1 methyl 1 (10 undecenyl) silacyclobutane, was synthesized by a Grignard reaction between 1 chloro 1 methylsylacyclobutane and 10 undece nyl magnesium bromide in 65% yield. Scheme 2 1 Synthesis of carbosiloxane based polymers possessing thermally crosslinkable chain ends. 2.2.2 ADMET P olymerization of C arbosiloxane or O ligo(oxyethylene) based M onomers with Silacyclobutane as Chain end Telechelic D erivative Metathesis polymerization of oligo(oxyethylene) based ( 17 18 ) / carbosiloxanes ( 23 24 ) monomers and silacyclobutane derivative ( 16 ) led to the corresponding end capped polymers ( 19 20 and 25 26 ), all of which were viscous liquids. The se polymers were synthesized under standard ADMET polymerization conditions, using first ( 3 ) to prevent isomerization reactions during the polymerization. In order to promote low molecular weight polymers, the monomer/chain end crosslinker ratio used was 5/1. Decreasing the molecular weight of the polymer, leads to a higher concentration of chain end crosslinker in the system, leading to higher tensile strengths in the thermally cured polymers. Previously reported elastomeric
37 materials demonstrated that the stoichiometric control of the monomer addition, directly influences the molecular weight of the desired polymer. 30 methodology, 64,66 which is based on the in situ formed hydrogenation agent, diimide, obtained from the thermolysis of p toluenesulfonylhydrizide (TSH) in the pr esence of tripropylamine (TPA) and o xylene as solvent Thus, high pressure H 2 is not required, and it functions under mild conditions (100 110 o C) to prevent premature ring opening of the silacyclobutane crosslinker. ( Scheme 2 1 and 2 2 ). Standard 1 H, 13 C NMR spectroscopy, FT IR, gel permeation chromatography (GPC) and thermal analysis (TGA and DSC) were used to determine the primary structures of the polymers and their hydrogenation products. Figure 2 2 1 H NMR spectra of glycol derivatives. A) M onomer 5 (9sp4gl) B) P olymer 9 (Si_9sp4gl) C) H ydrogenated polymer 13 (Si_H_9sp4gl).
38 2.2.3 Spectroscopic C haracterization 1 H NMR spectroscopy have been a useful tool for the understanding on the dienes monomers possess different shifts than the polymer olefin. Therefore, Figure 2 2 A shows the 1 H NMR spectrum of the distin ctive terminal olefins of monomer 18 (9sp4g l) at 4.9 and 5.7 ppm, while the oxyethylene linkage is observed between 3.53 and 3.63 ppm. Figure 2 2B shows signals at 0.25, 0.73 and 0.96 ppm corresponding to the presence of the silacyclobutane in the polymer 2 0 (Si_9sp4gl). In this spectrum, the metathesis polymerization can be clearly analyzed by the appearance of an internal olefin at 5.4 Figure 2 3 13 C NMR spectra of glycol derivatives A) M onomer 18 (9sp4gl). B) P olymer 20 (Si_9sp4gl). C) H ydrogenated polymer 22 (Si_H_9sp4gl)
39 Evidence for complete hydrogenation without prema ture ring opening of the chain end crosslinker is observed in spectrum c where the hydrogenated polymer 22 (Si_H_ 9sp 4gl) does not exhibit any olefin peaks. The same type of 1 H NMR data was obtained for 6sp4gl family having the same behavior as the 9sp4gl. The 13 C NMR spectra (Figure 2 3) show analogous resonances. Characteristic signals of the oxyethylene segment can be observed at 71.3 and 70.8 ppm. Moreover, monomer 18 (9sp4gl) shows terminal olefin peaks at 114.1 and 139.2 ppm, which disappear upon polymerization. Two new internal olefin peaks are observed at 130.6 and 129.8 ppm, corresponding to ~80% trans and ~20% c is configuration in polymer 20 (Si_9sp4gl), which is in agreement with the thermodynamically preferred olefins. 1,29 The absence of any olefin peak in the hydrogenated homologue confirmed that complete hydrogenation occurred. Similar to the 1 H NMR analysis for the glycol based polymers, siloxane family presents the same olefin transformation. Figure 2 4 shows the 1 H NMR spectra for the siloxane derivative 6sp3Si ( 23 ), its polymerization and hydrogenation. Figure 2 4A shows the monomer 6sp3Si ( 23 ), which presents the characteristic terminal olefin signal at 4.9 and 5.9 ppm, which vanish upon polymerization, to become an internal olefin signal visible at 5.6 ppm. Siloxane linkage (Si CH 3 and Si CH 2 ) can be observed at 0.2 and 0.6 ppm respectivel y, which maintain unaltered during the polymerization and hydrogenation. Interpretation of the 13 C NMR of the 6sp3Si monomer ( 23 ), its polymer ( 25 ) and hydrogenated derivative ( 27 ) leads to a similar observation (Figure 2 5). As for the siloxane linkage, m ethyl groups on the silicon atoms can be observed at 0.4 and 1.4
40 ppm. Terminal olefins of the monomer are observed at 114.1 and 139.2 ppm, which disappear to convert into two internal olefins at 130.5 and 130.1 ppm trans and cis respectively in a 77% and 23% ratio, in agreement with the most stable conformation of the metallacyclobutane intermediate. 29 Figure 2 4 1 H NMR spectra of siloxane derivatives. A) M onomer 23 (6sp3Si).B) P olymer 25 C) H ydrogenated polymer 27 2.2.4 Thermal and Molecular Weight Characterization of Glycol and Siloxane based Polymers GPC analysis of the telechelic polymers (Table 2 1) shows that the polymers have molecular weight values (M n ) between 4,000 and 8,000 g/mol, which correspond with an average degree of polymerization of 13. These values were our targeted goals, since decreasing the degree of polymerization relative to the amount of crosslinker results in an increase in the molar concentration of thermally crosslinkable end groups, leading to higher tensile strength.
41 Figure 2 5 13 C NMR spectra of siloxane derivatives. A) M onomer 23 (6sp3Si ). B) P olymer 25 C) H ydrogenated polymer 27 2. 2.4.1 Thermal a nalysis of c hain end t elechelic p olymers The thermal behavior of the polymer family was investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Table 2 1. GPC data for saturated and unsaturated telechelic polymers. GPC a Polymer M n ( KDa ) M w ( KDa ) PDI DP 19, (Si_6sp4gl) 6.0 10.0 0 1.67 16 20, (Si_9sp4gl) 5.6 9.7 1.73 11 25, (Si_6sp3Si) 4.4 6.6 1.51 10 26, (Si_6sp4Si) 5.2 8.3 1.60 10 21 (Si_H_6sp4gl) 8.3 20.0 0 2.36 23 22 (Si_H_9sp4gl 7.2 13.0 0 1.81 14 27 (Si_H_6sp3Si) 5.2 8.3 1.60 12 28 (Si_H_6sp4Si) 5.3 8.5 1.59 10 a. Referred to PS standards in THF at 40 o C
42 T hermogravimetric analysis (TGA) was taken using both inert (nitrogen) and oxidative (air) atmospheres, at a scan rate of 20 o C/min from 30 to 700 o C. Table 2 2 presents the TGA values for saturated and unsaturated oligo(oxyethylene) and carbosiloxane based polymers ( 19, 20, 25 and 26 ) before and after thermal crosslinking. Table 2 2. Thermal analysis of the saturated and unsaturated polymers before crosslinking. TGA Polymer T(N 2 ) (C) T(Air) (C) 19 (Si_6sp4gl) 276 242 20 (Si_9sp4gl) 232 215 25 (Si_6sp3Si) 347 290 26 (Si_6sp4Si) 367 250 21 (Si_H_6sp4gl) 298 198 22 (Si_H_9sp4gl 220 182 27 (Si_H_6sp3Si) 234 185 28 (Si_H_6sp4Si) 329 288 Values recorded at 5% total mass loss under nitrogen and air gas at 20C/min As previously mentioned, incorporation of siloxane and glycol linkages induces thermal stability in the polymer backbone. This stability is observed in TGA behavior (Figures 2 6 and 2 7 ), where polymers do not degrade until 220 o C for glycol based polymers and about 340 o C for the s iloxane homologues. Rapid decomposition follows hydrogenated versions for siloxane and glycol derivated polymers with similar thermal stability. With an oxidative atmosphere, the decomposition temperature decreases in all cases, preserving the same degrad ation pathway. The DSC data in Table 2 3 reveals the thermal transition values for saturated and unsaturated oligo(oxyethylene) and carbosiloxane based polymers ( 19, 20, 25, and
43 26 ) before and after thermal crosslinking. Glass transition temperatures (T g ) were taken at the mid point of the transition; the melting temperatures (T m ) were obtained as the highest temperature peak of the melting transition in the second heating cycle. Figure 2 6 TGA traces of glycol based telechelic polymers ( 19 22 ) in an i nert atmosphere. Crosslinking temperatures (T crosslinking ) were taken as the starting point of the exotherm, as some samples start decomposing before the end of the crosslinking transition. Since the presence of soft phases like siloxane and glycol units in the polymer backbone increases flexibility, low glass transition temperatures are observed. Oxyethylene based polymers ( 19 22 ) exhibited T g values between 40 to 58 o C, in agreement with those for similar reported polymers. 43 Enhanced flexibility is observed for siloxane based polymers ( 25 28 ), which have glass transition temperatures as low
44 as 103 o C. These values decreased in proportion to the number of siloxane linkages present in the polymers, being 99 o C for Si_6sp3Si and 103 o C for Si_6sp4Si. 42 Figure 2 7 T GA traces of carbosiloxane telechelic polymers ( 25 28 ) in an inert atmosphere. Table 2 3. Thermal analysis of the saturated and unsaturated polymers before crosslinking. DSC Polymer T g Cp T m T c m T crosslinking ( C) a (J/gC) ( C) b (C) c J/g) (C) d 19 (Si_6sp4gl) 58 0.13 17 34 48 165 20 (Si_9sp4gl) 47 0.22 30 18 62 162 25 (Si_6sp3Si) 99 0.11 ------208 26 (Si_6sp4Si) 103 0.17 ------207 21 (Si_H_6sp4gl) 57 0.11 16 35 46 163 22 (Si_H_9sp4gl 40 0.14 43 15 35 161 27 (Si_H_6sp3Si) 46 0.12 ------210 28 (Si_H_6sp4Si) 49 0.13 ------211 a ) Values taken from the mid point; b ) values assigned to the peak of the melt; c ) values assigned to the peak of the recrystallization; d ) recorded from onset
45 Thermal behavior of all the telechelic oxyethylene based polymers ( 19 2 2 ), summarized Table 2 3 can be observed in the Figure 2 8 Therefore, these polymers present a semicrystalline behavior which can be attributed to the large number of methylene units present, with melting temperatures (T m ) between 17 and 30 o C, increas ing upon hydrogenation. The same behavior was analyzed by Matloka for chain end oxyethylene polymers. 43 Moreover, their low glass transition temperatur es between 58 and 47 o C were in agreement with similar end capped polymers reported previously, 43 where glass transition temperatures values increase as the hydrocarbon segment increases. Thermal crosslinking can al so be observed as an exotherm around 160 o C, which is not observed in subsequent cycles Figure 2 8 DSC thermograms of telechelic glycol based polymers.
46 Likewise, thermal analysis of siloxane based polymer family (25 28) is summariz ed in Table 2 3, and s howed in F igure 2 9 These polymers present purely amorphous behavior with glass transitions temperatures from 103 o C to 46 o C, and curing temperatures from 208 to 210 o C 2. 2.4.2 Thermal e nd group c rosslinking via o pening of s ilacyclobutane r ing Thermal chain end crosslinking was measured by DSC, where samples were heated to the crosslinking temperature range of 160 to 210 o C at a rate of 10 o C/min. Figure 2 9 DSC thermograms of telechelic carbosiloxane based polymers ( 25 28 ) The DSC thermogram of poly mer 20 (Si_9sp4gl, Figur e 2 10 ) shows a glass transition temperature of 47 o C (second run value) followed by a melting peak at 30 o C m = 62 J/g) and an exotherm corresponding to the ring opening crosslinking of silacyclobutane. After cooling, the sample was heated one more time. A sharp melting
47 peak was observed at 25 o m = 47 J/g) with no crosslinking endotherm between 162 210 o C. Thus, co mplete crosslinking reaction can be inferred during the third heat. These 60 in which the ring opening reaction of silacyclobutane was observed as an endotherm at 160 o C. Figure 2 10 DSC curves of telechelic polymer Si_9s4gl ( 20 ) before and after crosslinking. According with the DSC thermogram of every family of polymer, the crosslinking temperature was determined by the exotherm value between 160 210 o C. Interestingly, siloxane based polymers showed higher curing values than the glycols homologues. Having these values in hand, the polymers were subjected to thermal chain end crosslinking by heating them on a Teflon plate at the correspo nding temperatures for 6 days (S cheme 2 2 ). A change in morphology was evident d uring the curing process,
48 and the final elastomeric films were insoluble in all organic solvents. There is no question that the polymers were chain end crosslinked into thermosets Scheme 2 2 Thermal induced crosslinking reaction of silacyclobutane end capped polymers. Infrared spectroscopy (F igure 2 1 1 ) confirmed the polymerization procedure and was used to evaluate the crosslinking reaction. Characteristic wavelengths of the corresponding vinyl group were observed in monomer 9sp4gl ( 17 ) and silacyclob utane end capper ( 16 ) before polymerization at 3080 cm 1 1640 cm 1 and 999 cm 1 These absorptions disappeared upon polymerization, and new sharp bands appeared at 966 cm 1 and 724 cm 1 corresponding to the trans and cis out of plane bend of the internal olefin. In addition to the olefin peaks, the characteristic absorption of the oligo(oxyethylene) linkag e was observed at 1120 and 1038 cm 1 and between 1085 1041 cm 1 for the siloxane units The ring opening reaction of the silacyclobutane has been previousl y observed by IR spectroscopy. 67,68 The ch aracteristic absorption at 1119 cm 1 corresponding to the closed ring, di sappears and a new band at 1140 cm 1 of the open Si CH 2 CH 2 CH 2 Si
49 should be observed. The ring opening reaction could not be confirmed for t he new family of polymers, due to overlap of the characteristic bands with the previously mentioned C O C and Si O vibrations. However, there is no question that ring opening crosslinking occurred. Figure 2 1 1 FT IR spectra of glycol derivatives. A) M on omer 9sp4g ( 18 ). B) silacyclobutane crosslinker ( 16 ) C) P olymer ( 20 ), Si_9sp4gl D) crosslinked polymer ( 31 ) x Si_9sp4gl 2.2.5 Mechanical P roperties of C ured P olymers Mechanical properties of thermally cured polymers were measured for comparison with previously reported internal and chain end moisture crosslinked polymers, while selected stress strain curves are shown in Figure 2 1 2 I t can be observed that crosslinked siloxane based and oxy(ethylene) based polymers present similar stress/strain behavi or, except for X Si_H_6sp4gl ( 30 ) which has a brittle character.
50 A summary of elongation, tensile strength, and modulus values is presented in Table 2 4. Oligo(oxyethylene) derivatives exhibited very similar stress strain profiles. Elongation s up to 60%, and moduli of ~0.7 MPa were observed, which are comparable with those of most of the moisture chain end crosslinked polymer values reported by Matloka. Upon hydrogenation, the crystallinity of the polymer increased, and as a consequence, the network became stronger but more brittle as in the case of polymer. The opposite behavior was observed for the carbosiloxane derivative polymers (33 36) where elongation increased in the hydrogenated homologues, possibly due to the inability of these derivatives to cry stallize. The stress strain values of these siloxane based polymers were in the same range as those of the high molecular weight polymers reported previously by Matloka with internal and chain end moisture crosslinkers. 30,56 Figure 2 1 2 Stress/strain curves of selected thermosets.
51 Table 2 4. Mechanical properties of thermally crosslinked oxyethylene and carbosiloxane based polymers. Polymer Tensile Strength (MPa) Elongation (%) Modulus (MPa) 29 (X Si_6sp4gl) 0.3 61 0.6 31 (X Si_9sp4gl) 0.4 56 0.8 35 (X Si_6sp4Si) 0.4 26 1.7 30 (X Si_H_6sp4gl) 1.0 12 9.3 34 (X H_Si_6sp3Si) 0.5 76 1.1 36 (X H_Si_6sp4Si) 0.5 53 1.1 2. 3 Experimental C onditions 2.3.1 Chemicals Chemicals were purchased from Aldrich Chemical Company and used as received unless otherwise noted. Magnesium turnings were activated by vacuum drying at 100C and stor ed in an argon filled dry box prior to use. 2.3.2 Instrumentation Solution 1 H NMR (300 MHz) and 13 C NMR (75 MHz) spectra were recorded on a Varian Associates Mercury 300. All chemical shifts for 1 H and 13 C NMR were referenced to residual signals from CDC l 3 ( 1 H = 7.27 pp m and 13 C = 77.23 ppm). Compounds were examined by high resolution mass spectrometry (HRMS) data, obtained on a Finnigan 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). Infrared spectroscopy (IR) was performed on a Bruker Vector 22 spectrometer. Gel permeation chromatography (GPC) was performed with a Waters Associates GPCV2000 liquid chrom atography system with an internal differential refractive index detector. Differential Scanning Calorimetry (DSC) was performed using a Thermal Analysis (TA) Q1000 at a heating rate of 10 C/min under
52 helium purge, using indium and freshly distilled n octa ne as the standards for peak temperature transitions and indium for the enthalpy standard. All samples were prepared in hermetically sealed pans (4 7 mg/sample) with an empty pan as a reference. The samples were scanned for multiple cycles to erase therma l history, and the results are reported from the second scan cycle. Thermogravimetric analysis (TGA) was performed on a TA Q5000 using the dynamic high resolution mode. Sumitomo Chemical Company measured the mechanical properties of the samples. The tensil e modulus measurements were performed at room temperature on a single column type tensile tester STA series (A D Co., Lt d.). Rectangular specimens (18 mm ( length), 4.5 mm (width), 0.2 1.2 mm (thickness)) were stretched with a cross head speed of 20 mm/m in until samples were broken. The initial cross head distance was 4 mm. Each tensile modulus was calculated by averaging three tensile test results. 2.3.3 Monomer S ynthesis Synthesis and characterization of the necessary monomers was performed as previous ly reported in the literature. 56,57 C hain end crosslinker 1 methyl 1 (10 undecenyl)silacyclobutane, ( 16 ) Magnesium (4.89g, 0.20 mol) was added to a 500 mL three necked flask equipped with a reflux condenser and an addition funnel. Argon was used to backfill the reaction vessel three times, with flame drying after the second backfill. Dry diethyl ether was added (100 mL), followed by dropwise addition of 10 undecenylchloride (32.25 mL, 0.17 mol) in 60 mL of diethyl ether. The reaction mixture was refl uxed for 2.5 hours, followed by dropwise addition of 1 methyl 1 chlorosilacyclobutane (22.90 mL, 0.187 mol) at 0C. After allowing the reaction mixture to stir at 0 5 C for 2.5 h, 1 M aqueous HCl solution
53 (40 mL) was added slowly. The layers were separated and the aqueous solution was extracted with ether (2x60 mL). The combined organic layers were washed with H 2 O (50 mL) and brine (2 x50 mL), and were then dried with MgSO 4 The solvent was evaporated and the crude mixture was purified by silica gel column chromatography using hexane as solvent to yield 8.2 g of the pure product (65%); bp 124 126 C. 1 H NMR (CDCl 3 (m, 4H), 0.70 (m, 2H), 0.21 (s, 3H). 13 C NMR (CDCl 3 14.4, 34.8, 33.5, 34.6, 29.8, 29.7, 29.5, 24.1, 22.3, 18.4, 13.6, 1.2 FT IR: (cm 1 ) 1119, 1242, 1450, 2970. MS (70 eV): m/z = 237.2069 (M H) + Synthesis of 6sp4gl monomer ( 17 ) T he published procedure 69 was modified as follows: 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 addition funnel. Dried tetraethylene 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 addition funnel and the mixture was added drop wise under constant stirring. After 24 h, 8 bromo 1 octene (40 g, 0.17 mol) in 240 mL of THF was added and stirred for an additional 72 h under 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 MgSO 4 filtered, and evaporated under reduced pressure. The crude product was then purified by column chromatography using hexanes/diethyl ether (80:20%) yielding 6.7g (58%) of 6sp4gl monomer. The following spectral properties were observed: 1 H NMR (CDCl 3 1.63 (m, br, 4H), 2.07 (m, br, 4H), 3.37(m, br, 4H), 3.57 (m, br, 12H), 4.87 (m, br, 4H),
54 5.74 (m, br, 2H). 13 C NMR (CDCl 3 70, 114.65, 138.28. FT IR: (cm 1 ) 3077, 2865, 1641,1449, 1416, 1350, 1323, 1296, 1248, 1119, 993, 91 2, 872. MS (70 eV): m/z = 287.2230 (M + H) + (C 16 H 30 O 4 ) (286.40): Calcd. C 67.10, H 10.56; Found C 67.05, H 10.61. Synthesis of 9sp4gl monomer ( 18 ) Sodium hydride was placed in a flame dried, Ar purged, three necked 500 mL round bottom flask equipped with a stir bar, condenser, and an addition funnel was ch arged with (7.0 g, 0.017 mol) tetra ethylene ditosyl, sodium hydride (1.8 g, 0.44 mol, 60% dispersion) and anhydrou s dimethylformamide (DMF) (50 mL ). The reacti on 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 constant stirring. After 12 hours of stirring at 0C the mixture was warmed to room temperature and then quenched with successive additions of water (50mL) and 6M HCl (100 mL ) over 30 minutes. The organic phase was extracted with ether (2x150 mL), washed with brine (2 x150 mL), and dried with MgSO 4 Filtration and solvent evaporation afforded yellow oil. Purification using column chromatography (1:4 ethyl acetate:hexanes) foll owed by vacuum distillation ov er calcium hydride afforded 6.5 g (73% yield) of colorless liquid. The following spectral properties were observed: 1 H NMR (CDCl 3 3.57 (m, br, 12H), 4.90 (m, br, 4H), 5.74 (m, br, 2H). 13 C NMR (CDCl 3 28.9, 29.1 29.4, 29.5 29.5, 29.6 33.8, 70.1 70.6, 71. 5 71 6 114. 1 139. 2 FT IR: (cm 1 ) 3076, 2926, 2855, 1640, 1464, 1350, 1298, 1249, 1120, 993, 909, 722. MS (70 eV): m/z = 4 99.4373 (M + ). (C 28 H 55 O 4 ) (498.78): Calcd. C 72.24, H 11.72; Found C 72.40, H 11.80.
55 Synthesis of 6sp3Si monomer ( 23 ) A flame dried, Ar purged, three necked 500 mL round bottom flask equipped with a stir bar, condenser, and an addition funnel was charged with (5.0 g, 0.013 mol) H 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 two minutes to ensure its homogeneity and 0.6 mg of 10.6% soln. in xylenes, 10 5 eq, of tris(divinyltetramethyldisiloxane)Pt 2 was exothermic, an ice bath was used to keep the temperature below 30 C. The solution was allowed to stir for 30 minutes after which the excess of 1,5 hexadiene and tol uene was distilled off using the rotary evaporator. The monomer was passed through a silica plug to remove the catalyst, dried over CaH 2 and distilled under vacuum resulting in a pure colorless liquid monomer in 94% yield. The following spectral properties were observed: 1 H NMR (CDCl 3 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). 13 C NMR (CDCl 3 33 .9, 114.1, 139.2 FT IR: (cm 1 ) 30 78, 2957, 2925, 2855, 1641, 1440, 1411, 1257, 1051, 993, 909, 840, 795. MS (70 eV): m/z = 413.2395 (M CH 3 ) + Synthesis of 6sp4Si monomer ( 24 ) Monomer 6sp4Si was synthesized and purified using the same methodology as described for 6sp3Si yielding 7.8 g ( 92% yield) of colorless liquid. The following spectral properties were observed: 1 H NMR (CDCl 3 4H), 4.91 (m, br, 4H), 5.77 (m, br, 2H). 13 C NMR (CDCl 3 1.2 18. 3 23.2, 28.9, 33.3, 33. 9 114.1, 139.2. FT IR: (cm 1 ) 3078, 2959, 2925, 2855, 1641, 1441, 1412,
56 1258, 1080, 1041, 910, 840, 798. MS (70 eV): m/z = 503.3222 (M+H) + (C 24 H 54 O 3 Si 4 ) (503.02): Calcd. C 57.30, H10.82; Found C 57.58, H 10.87 2.3.4 General Procedure for B ulk P olymerization All monomers used in polymerization were distilled from CaH 2 and degassed prior to polymerization. All glassware was cleaned and dried under vacuum before use. The reactions were initiated in the bulk inside an argon filled glove box by placing the appropriate amount of monomer in a 50 mL round bottomed flask equip ped with a catalyst and slow stirring for 2 minutes. The monomer to catalyst ratios were 250:1. In all copolymerizations, all reactants were stirred before catalyst addition to yield a from the glove box and placed immediately on the vacuum line. Slow exposure to moderate vacuum (<0.01mmHg) removed the evolved ethylene. After stirring for 15 minut es, the flasks were submerged in a silicon oil bath at 50C and then left under vacuum and stirred for 72 h. The reactions were quenched by addition of ethylvinyl ether. Polymer (Si_6sp4gl) ( 19 ) 1 H NMR (CDCl 3 1.28 (m, 88H), 1.54 (m, 20H), 1.94 (m, 34H), 3.42 (t, 20H), 3.58 (m, 80H), 5.35(m, 12H). 13 C NMR (CDCl 3 70.6, 70.0, 32.5 29. 6, 29.0, 25.9 18.5 16.9, 13.8. FT IR (cm 1 ): 3080, 2926, 2853, 1642, 1631, 1462, 1120, 1038, 994, 967, 914, 7 22. GPC data (THF vs. PS standards): M n = 6.0 x 10 3 g/mol; M w =1.0 x 10 4 g/mol; PDI = 1.67. DSC results: T g : 58 o C; T m = 17 o C; T c = 34 o C; T crosslink =165 o C. TGA (20 o C/min.): N 2 ( 5%) = 276 o C.
57 Polymer (Si_9sp4gl) ( 20 ) 1 H NMR (CDCl 3 1.32 (m, 92H), 1.66 (m, 20H), 1.98 (m, 24H), 3.48 (t, 20H), 3.63 (m, 80H), 5.40 (m, 12H). 13 C NMR (CDCl 3 18.4 16.8 13.8 FT IR (cm 1 ): 2919, 2852, 1632, 1468, 1153 1121, 1029, 965, 719. GPC data (THF vs. PS standards): M n = 5.6 x 10 3 g/mol; M w = 9.7 x 10 3 g/mol; PDI = 1.73. DSC results: T g = 47 o C; T m =30 o C; T c =18 o C; T crosslink =162 o C; TGA (20 o C/min.): N 2 ( 5%) = 232 o C. Polymer ( Si_6sp3Si) ( 25 ) 1 H NMR (CDCl 3 20H), 1.32 (m, 32H), 1.98 (m, 24H), 5.40 (m, 12H). 13 C NMR (CDCl 3 6, 130.1 33. 6, 32.9 29. 9, 29.2 23. 9, 23.4, 18.5, 16.8, 13.8, 1.5 0. 5 FT IR (cm 1 ): 2957, 2923, 2854, 1463, 1257, 1051, 967, 7 05. GPC data (THF vs. PS standards): M n = 4.4 x 10 3 g/mol; M w = 6.6 x 10 3 g/mol; PDI = 1.51 DSC results: T g = 99 o C; T crosslink =208 o C. TGA (20 o C/min.): N 2 ( 5%) = 347 o C. Polymer (Si_6sp4Si) ( 26 ) 1 H NMR (CDCl 3 4H), 0.96 (m, 20H), 1.30 (m, 32H), 1.97 (m, 24H), 5.40 (m, 12H). 13 C NMR (CDCl 3 5. FT IR (cm 1 ): 2958, 2923, 2854, 1462, 1258, 1078, 10 45, 967, 705. GPC data (THF vs. PS standards): M n = 5.2 x 10 3 g/mol; M w = 8.3 x 10 3 g/mol; PDI = 1.60. DSC results: T g = 103 o C; T crosslink =207 o C. TGA (20 o C/min.): N 2 ( 5%) = 367 o C. 2.3.5 Hydrogenated P olymers Hydrogenation was performed according to the li terature. 64,66 ca. 0.9 g (1 equiv repeat unit) of the corresponding polymer was dissolved in 60 mL of dry o xylene and added to a two necked round bottom flask with a reflux condenser. Then 2.5 equiv. of
58 dry tripropylamine (TPA) and 2 equiv. of p toluenesu lfonhydrazide (TSH) were added to the flask under inert atmosphere and stirred until dissolved. The mixture was heated at 100 o C in an oil bath and stirred for about 5 hours under argon. After cooling to room temperature, an additional equivalent each of TP A and TSH was added to the reaction mixture, and the mixture was allowed to react at 100 o C for an additional 14 hours. After removing the solid by filtration, the filtrate was dissolved in toluene (250 300 mL) and slowly added to methanol (ca. 3.5L). The s olution was placed in the refrigerator for 5 hours, and the product was recovered by decantation or filtered by osmosis and subsequently dried under vacuum, yielding saturated polymers. Si_H_6sp4gl polymer ( 21 ) 1 H NMR (CDCl 3 62H), 1.61 (m,18H), 3.45 (m,10H), 3.62 (m,50H). 13 C NMR (CDCl 3 70.8, 70.3, 29.9, 26.3 17.8, 15.3, 10.4. FT IR (cm 1 ): 2917, 2851, 1640, 1471, 1152, 1019. GPC data (THF vs. PS standards): M n = 8.3 x 10 3 g /mol; M w = 2.0 x 10 4 g/mol; PDI = 2.36. DSC results: T g = 57 o C; T m = 16 o C; T c = 35 o C; T crosslink =163 o C. TGA (20 o C/min.): N 2 ( 5%) = 298 o C. Si_H_9sp4gl polymer ( 22 ) 1 H NMR (CDCl 3 92H), 1.73 (m,56H), 3.42 (m, 20H), 3.61 (m, 80H). 13 C NMR (CDCl 3 70.7 70.2, 29.8, 26.3 17.9, 16.0, 10.8. FT IR (cm 1 ): 2918, 2852, 1470, 1262, 1153, 1020. GPC data (THF vs. PS standards): M n = 7.2 x 10 3 g/mol; M w = 1.3 x 10 4 g/mol; PDI = 1.81. DSC results: T g = 40 o C; T m = 43 o C; T c =15 o C; T crosslink = 161 o C. TGA ( o C at 20 o C/min.): N 2 ( 5%) = 220 o C.
59 Si_H_6sp3Si polymer, ( 27 ) 1 H NMR (CDCl 3 18H), 0.53 (m, 12H), 0.74 (m, 4H), 0.96 (m, 20H), 1.30 (m, 44H), 1.97 (m, 24H). 13 C NMR (CDCl 3 3.5, 30.0 29. 7, 23. 9, 23. 5 18. 6 16.8 13.8, 1.5, 0. 5. FT IR (cm 1 ): 2958, 2923, 2854, 1462, 1258, 1078, 1045, 967, 705. GPC data (THF vs. PS standards): M n = 5.2 x 10 3 g/mol; M w = 8.3 x 10 3 g/mol; PDI = 1.60. DSC results: T g = 46 o C; T crosslink = 210 o C. TGA (20 o C/min.): N 2 ( 5%) = 234 o C. Si_H_6sp4si polymer, ( 28 ) 1 H NMR (CDCl 3 16H), 0.96 (m, 20H), 1.23 (m, 108H). 13 C NMR (CDCl 3 30.0 29. 7, 23.9, 23.49, 18.5, 16.5, 16.8, 13.8, 1.4, 0.4 FT IR (cm 1 ): 2958, 2923, 2854, 1465, 1258, 1079, 705. GPC data (THF vs. PS standards): M n = 5.3 x 10 3 g/mol; M w = 8.5 x 10 3 g/mol; PDI = 1.59. DSC results: T g = 49 o C; T crosslink =211 o C. TGA (20 o C/min.): N 2 ( 5%) = 329 o C.
60 CHAPTER 3 SYNTHESIS AND CHARACTERIZATION OF POLY(3 ALKYL 2,5 THIENYLENE VINYLENE) BY SOLID STATE METATHESIS POL YCONDENSATION 3.1 Introductory Remarks The synthesis of polythienylene vinylenes (PTVs) is an active research area in the manufacture of electroactive materials, due to th e relatively low band gaps and high conductivities achieved upon doping of PTV materials. 70 72 Unfunctionalized PTV is an intractable polymer and its polymerization is usually carried out by indirect synthes is of a processable prepolymer. H owever, th is route produces defects in the final polymer. 73 76 In contrast, substituted PTVs (with alkyl solubilizing groups with more than four carbons) are processable and usually synthesized by various methods like Wittig 77 or Wittig Horner 78 cross coupling re actions (e.g. Stille, 79 80 H eck, 79 and K umada 81 reactions), oxidative polymerization, 81 or ROMP. 82,83 Nevertheless functionalization may limit the applications of the resulting polymers. 84 Acyclic diene metathesis (ADMET) polymerization has been used in the synthe sis of conjugated polymers such as polyacetylene 85 functionalized poly(phenylene vinylene s ) 86,87 polyfluorenes, 87 silylene/siloxane functionalized conjugated polymers, 88 and PTVs, 89 in bulk or in the presence of high boiling solvents. The well established mechanism, high selectivity for new trans olefins, mild reaction conditions, tolerance for different functionalities, well defined end groups, absence of branching within the polym er structure, and the possibility of bulk polymerization make this methodology a useful tool for the synthesis of conjugated polymers. 6, 89 Solid state polymerization (SSP) has been widely practiced in the polyester, polyamide, and polycarbonate industries. This polymerization starts in bulk at high
61 temperatures with the release of a small molecule to achieve a low molecular weight polymer (prepolymer), which is then cooled to obtain a powder or flakes. Polymerization then continues in the solid state, at a temperature lower than the onset melting temperature to increa se the molecular weight while in the solid state 36,90 Our group has been investigating the influence of solid state polymerization on the molecular weights of polymers obtained by ADMET polymeri zation for a variety of functionalized polyolefins. Results for the polymerization of 1,9 decadiene showed an approximately 20 fold increase in molecular weight using solid state conditions. 38 We have extended these investigations to the synthesis of a pro cessable PTV by solid state ADMET polymerization in order to characterize the polymer structure and compare its electronic properties with those made by other methodologies This undertaking would be quite difficult for truly intractable material. Therefor e, this report presents results for 3 alkyl poly(thienylene vinylenes) P3DDTV to demonstrate the reliability of this process in the eventual synthesis of intractable PTV 3.2 Results and D iscussion To demonstrate the versatility of the solid state polymerization in the synthesis of intractable polymers, two processable pol ymers were synthesized: poly(3 dodecyl 2,5 thienylene vinylene ) ( P3DDTV ), and poly(3 hexyl 2,5 thienylene vinylene ) ( P3HTV ). After establishing this methodology, a truly intractable polymer poly(3 methylthiophene vinylene) ( P3MTV ), was synthesized to demonstrate that solid state polymerization can be used in the synthesis of truly intractable polymers. 3.2.1 Monomer S ynthesis Monomers 3 alkyl 2, 5 dipropenyl t hiophene ( 4 0 a c ) w ere synthesized a ccording to a literature method 89 as shown in Scheme 3 1 The 3 bromothiophene was alkylated
62 with the proper 1 bromo alkane by a Kumada coupling reaction with 80% yield. 91 Under Wittig reaction conditions, the 3 alky lthiophene s (38 a c ) w ere then lithiated with n butyllithium and formylated using DMF in the presence of tetramethylethylenediamine (TMEDA). 92 A Wittig reaction using the synthesized aldehyde and ethyl triphenyl phosphonium bromide was performed to obtain monomer s ( 4 0 a c ) which w ere purified by distillation after passing through a fi ltration column to remove the tr iphenylphosphine oxide. The monomer s proved to be unstable in air and light, especially in the presence of oxygen, they form aldehydes wi th in a short period of time. This i nstability to oxygen increases as the size of the alkyl group decreases the m ethyl derivative being the most unstable o f the series. Thus, the monomer was always synthesized a short number of days prior to the polymerization and kept cold in the dark under inert conditions. Unsubstituted PTV was also synthesized, but it readily decomposes. Therefore, the mono mer was properly characterized but it decomposed before it could be polymerized. Scheme 3 1 Synthesis of 3 dodecyl 2,5 dipropenylthiophene monomer ( 4 0 ) The first reported PTV by ADMET polymerization was in 199 9 by Tsuie with the synthesis of poly(3 dodecyl 2,5 thienylene vinylene) P3DDTV 73 Despite t he low
63 molecular weight polymer s that were obtained (2 700 g/mol) from the 3 dodecyl 2,5 divinylthiophene monomer using Schrock catalyst ( 1 ), this was the first investigation on using ADMET polymerization for the synthesis of this type of syste m. 73 Years later, Hillmyer et al. 89 reported the synthe sis of an analogous monomer 3 hexyl 2,5 dipropenylthiophene ( 4 0b ) yielding a mixture of stereoisomers from the Wittig reaction. Similar to his reported monomer, our synthesized monomers ( 40a c ) resulted in four diastereomers from the Wittig reaction all showing preference for E product over the Z stereoisomer. Figure 3 1. 1 H NMR of 3 dodecyl 2,5 dipropenylthiophene monomer 40a. Dodecyl (40a) : 32% 2 E 5 E 26% 2 E 5 Z 1 5 % 2 Z 5 Z and 27% 2 Z 5 E Hexyl (40b) : 43% 2 E 5 E 19% 2 E 5 Z 8% 2 Z 5 Z and 30% 2 Z 5 E Methyl (40c) : 44% 2 E 5 E 24% 2 E 5 Z 12% 2 Z 5 Z and 20% 2 Z 5 E The percentage of each diastereomer ( marked as c,d,e,f in the aromatic proton H 1 Figure 3 1) was evaluated by 1 H NMR spectroscopy. As an example, the 1 H NMR
64 spectrum of 3 dodecyl 2,5 dipropenylthiophene monom er (40a) shows that protons c, d, and e are well resol ved, an d their proportions can be identified But b ecause peak f overlaps with the olefinic protons, its integration was obtained indirectly. The total integration c+d+e+f should equal one six of total integration for the methyl end groups (multiplets b). Therefore th e peak f integral was obtained by subt racting the sum of c+d+e from one sixth of the integration for b. 3.2. 2 Polymer S ynthesis In order to establish the best solid state polymerization conditions for monomers (40 a c) t he most stable monomer of the series (3 dodecyl 2,5 dipropenylthiophene, 40a ) was examined first. Thi s monomer was placed in a Teflon mold (Figure 3 2 A ) and generation catalyst (4) at 70 o C for three hours to yield a solid prepolymer (41 a ) with a number average mo lecular weight of 4,000 g/mol (Figure 3 2 B ). Since step growth polymerization can continue in the solid state under the proper conditions (e .g. polyesters, Nylon, etc. ), the increase in the molecular weight of the solid prepolymer ( 41 a ) was investigated. The key to success was generation catalyst (4) over the prepolymer ( 41 a ) which resulted in an increase of molecular weight under vacuum at 70 o C. The c atalyst was then sprinkled every three days (0.2 mol% dose) under an inert atmosphere to ensure the catalyst activity and ensure a productive metathesis polymerization. Since the polymer was designed to be soluble in organic solvents (the dodecyl chain left in place), the molecular weight increase under solid state conditions was determined by gel permeation chromatography (GPC) and 1 H NMR spectroscopy
65 Figure 3 2 Solid state polymerization of the 3 dodecyl 2,5 dipropenylthiophene monomer 4 0 a Figures represent the Teflon mold and the different stages of the polymerization, with the cataly st represented as brown dots. A) Liquid monomer 4 0 a before the polymerization. B ) Prepolymer 41 a re presented as a red shiny film. C ) Final polymer 42 a 3.2. 2 .1 1 H NMR analysis of 3 dodecyl PTV ( P3DDTV ) The 1 H NMR spectrum of monomer (40 a ) is shown on Figure 3 3 A and the presence of four possible diastereomers is observed in the aromatic region Terminal methyl units give peaks between 1.90 1.82 ppm with methyl groups resulting from the combination of Z stereoisomers at 1.90 ppm and from E stereoisomers at 1.85 ppm. Because the monomer is unstable in air and light, its decomposition is identified by the presence of aldehyde protons between 9.0 and 9.5 ppm which can result after five minutes of monomer e xposure to these conditions. After the monomer was rigorously purified, it was sub jected to ADMET polymerization conditions ( Figure 3 3 B ). T he progress of the polymerization was analyzed by the peak area ratios of the terminal methyl unit ( b ) and the methylene unit s ( a ). Monomer (40 a ) presents a ratio of 3:1, while prepolymer ( 41 a ) exhibits a 1:5 ratio, confirming the diminution of term inal methyl units in the system and corroborating the GPC results of a number average molecular weight of 4,000 g/mol. Aromatic protons were observed as three broad peaks, which became less shielded as the degree of
66 polymerization increased. After the third week of polymerization under sol id state conditions ( Figure 3 3 C ), the methyl group units in the polymer backbone were almost undetectable (in a 1:16 ratio), confirming the increase of the molecular weight to 14,000 g/mol indicated by GPC. Figure 3 3 1 H NMR correlation for dodecyl thiophene derivatives. A) 3 dodecyl 2,5 dipropenyl monomer 40a B)P 3DDTV prepolymer 4 1a C) P3DDTV final polymer 42a 3.2. 2 .2 Different attempts for the synthesis of 3 dodecyl PTV (42 a ) Different conditions were attempted in order to obtain the highest molecular weight by this methodology (Table 3 1) Formation of prepolymer ( 41 a ) was st udied at 40 o C and 70 o generation catalyst (4) At 40 o C, low molecular weight films were obtained (M n = 2,300 g/mol, entry 2) after 10 hours, while a M n of 4,000 g/mol was obtained after three hours of polymerization at 70 o C (entry 3). Af ter a sprinkle of
67 catalyst (0.2 mol% ) was added to prepolymer ( 41a ) the molecular weight was analyzed every week. During the first two weeks only a slight increase was noticed (M n = 5,300 g/mol, entry 4). The largest increase was observed after the thir d week when the molecular weight increased to 14 ,000 g/mol (entry 5 Table 3 1 ). Values that are in agreement with a polycondensation mechanism, where high monomer conversion is needed to obtain a high molecular weight polymer. After the third week, polym erization growth decreased substantially. Bulk polymerization (rather than solid state polymerization) was also attempted in order to compare the two techniques. With this methodology, only low molecular weight polymers (M n = 2,400 g/mol) were obtained (en try 7 Table 3 1). This can be explained by the decreased accessibility of the propenyl units to the active catalyst species as polymers solidify into clumps. Hillmyer et al. also obtained molecular weights of 2,500 g/mol using the same bulk conditions. 89 first generation catalyst (3) but only pentamers were obtained, possibly because of the lower reactivity of the catalyst (entry 1 Table 3 1). Hillmyer et al studied the synthesis of 3 hexyl PTV ( P3HTV 42b ) by ADMET polymerization using a variety of high boiling solvents, catalysts and temperatures. They concluded that P3HTV can be obtained by ADMET polymerization with a molecular o C for 48 hours with thrichlorobenzene as a solvent 89
68 O ur results show that solid state polymerization in a Teflon mold can definitely increase the accessibility of active propenyl units without the need for solvents to obtain higher molecular weight polymers wit h the desired final shape. Table 3 1 Molecular weight analysis for the synthesis of P3DDTV Entr y Conditions (Temp., catalyst, time) Catalyst (mol % ) M n ( KDa ) c M w ( KDa ) a M w /M n a DP Yield b 1 40 o C, 3 24 h 0.6 1.3 1.8 1.5 5 35 2 40 o C, 4 10 h 0.6 2.3 4.4 1.9 8 80 3 70 o C, 4 3 h 0.6 4.0 7.7 1.9 14 87 4 70 o C, 4 2 weeks 1.2 5.3 10.8 0 2.1 18 86 5 70 o C, 4 3 weeks 1.8 14.0 0 33.3 0 2.3 48 88 6 70 o C, 4 4 weeks 2.4 14.5 0 31.8 0 2.2 50 85 7 60 o C, 4 3 weeks bulk 1.8 2.4 4.4 1.9 8 55 a Molecular weight determined using GPC analysis (PS standards) and corroborated by 1 H NMR spectroscopy. 3 and 4 b Isolated yield after quenching with ethyl vinyl ether and precipitation from methanol. 3.2. 3 Poly(3 hexyl 2,5 thienylene vinylene), P3HTV Based on the optimized conditions for the solid sate polymerization of the dodecyl derivative (42 a ) a 3 hexyl version was used to determine the reproducibility of the solid state methodology. M onomer 3 hexyl 2,5 dipropenylthiophene ( 40b) was synthesized by the same methodology as described in the literature in 40% yield. 68 Solid state polymerization was performed according with to the best conditions for the P3DDTV derivative (42a ) as is repre sented in Scheme 3 2 Therefore, P3HTV was synthesized by the polymerization of the 3 hexyl monomer ( 40b) with Grubbs second generation catalyst (4) in a Teflon mold after 3 hours, which resulted in a prepolymer of a number average molecular weight of 4,50 0 g/mol. Subsequent polymerization in the solid state with addition of catalyst every three days at 70 o C for three weeks allow ed the formation of dark red film with a molecular weight of 7,000 g/mol. As observed for the P3DDTV, 1 H NMR spectroscopy indicated that the solid sta te metathesis transformation of the hexyl derivative was successful (Figure 3 3). The ratio
69 between the methyl end groups (b) with respect to the methylene units (a) decreased as the degree of polymerization i ncreased. Therefore, the integral ratio between these two groups could be used to estimate the number average molecular weight of 3,900 g/mol for the prepolymer ( 41b ), which agrees with the GPC value of M n = 4,500 g/mol (Figure 3 3 B ). S imilar NMR analysis provided a number average molecular weight of 6,700 g/mol for the final polymer (Figure 3 3 C ), which corresponds with the GPC analysis of M n = 7,000 g/mol. Scheme 3 2. Solid state polymerization of the 3 hexyl 2,5 dipropenylthiophene monomer 40b. Figure 3 4. 1 H NMR correlation of hexyl derivatives. A) 3 hexyl 2,5 dipropenyl monomer 40b B) P3HTV prepolymer 41b C) P3HTV final polymer 42b
70 3.2. 4 Truly Intractable Polymer: 3 methyl Derivative Having the solid state methodology set for the soluble polymers P3DDTV ( 42a ) and P3HTV ( 42b ), the next step was to prove that this methodology can be used in the synthesis of truly intractable materials. Thus, 3 methyl 2,5 dipropenyl monomer ( 40c ) was synthesized by the same methodology illustrated in Scheme 3 1, keeping in mind that this methyl derivative is very reactive towards oxygen and light. Polymerization of 3 methyl 2,5 dipropenylthiophene ( 40c ) was carried out according to the optimized conditions for the P3DDTV derivative ( 42c ) In this manner, m ono mer ( 40c ) was submitted to ADMET polymerization conditions in a TEFLON mold generation catalyst under vacuum conditions at 70 o C (Scheme 3 3 ) The monomer became a red film after 3 hours of polymerization and catalyst was added every t hree days in 2 mol% dose s Subsequent addition of Grubbs second generation catalyst for a four week period allow ed the formation of an intractable polymer that does not solubilize in any organic solvent. For that reason o nly low molecular weight structures could be characterized by 1 H NMR spectroscopy. Scheme 3 3 Solid state polymerization of 3 methyl 2,5 dipropenylthiophene 40c Figure 3 5 displays the monomer transformation. Spectrum a shows the methyl units (a) att ached to the t hiophene between 2.24 to 2.17 ppm for the four possible diastereomers, as well as the methyl end groups (b) between 2.02 to 1.89 ppm (with a 1:2 ratio) Figure 3 5B shows the downshifting of the olefin protons upon polymerization
71 between 7.11 to 6. 43 ppm with some remaining protons from the monomer structure at 6.15 ppm and 5.67 ppm. The Methyl end groups (b) integration ratio respect to the methyl attached ring (a) decreased to 0.26:1 giving an approximate molecular weight of 738 g/mol. This low molecular weight represents only the soluble oligomers in the system, but not the actual molecular weight of the intractable polymer. In order to identify higher molecular weight oligomers, P3MTV ( 42c ) was submitted to high temperature (110 o C) 1 H NMR analysis, using DMSO d 6 as the solvent (Figure 3 4 C ). Although higher molecular weight oligomers (M n = 982 g/mol) were observed, most of the polymer was still insoluble in DMSO at that temperature. The nature of this polymer (P3MTV) does not allow molecula r weight determination by GPC or 1 H NMR, but the presence of the intractable material corroborates the successful polymerization of the 3 methyl derivative monomer under solid state metathesis conditions. 3.2. 5 Thermal and E lectrochemical A nalysis I n orde r t o determine if the electronic and morphological characteristics of the synthesized PTV s obtained under solid state conditions are consistent with those of the previously reported PTVs Thermal Gravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), optical spectroscopy and cyclic voltammetry (CV) were performed. 3.2. 5 1 Thermal a nalysis of s ynthesized P TV s The thermogravimetric analysis (TGA) of the three poly( thienylene vinylene) systems is presented in Figure 3 6 Every thermogra m was performed under inert (nitrogen) atmosphere at a scan rate of 20 o C/min from 30 to 600 o C Th e s e thermogram s show ed that the soluble P TV s series were stable up to 3 5 3 o C above w hich they decompose in a single pathway. P 3M TV instead, is more stable with a 5% weight loss of 373 o C and only 50% of weight loss at 600 o C.
72 Figure 3 5. 1 H NMR correlation between methyl thiophene derivatives. A) 3 methyl 2,5 dipropenyl monomer 40c. B) P3MTV prepolymer 41c C) P3MTV final polymer 42c Figure 3 6 TGA thermogram of PTV s ( 42 a c ) at 20 o C/min rate in N 2
73 The d ifferentia l scanning calorimetry (DSC) thermogram for the poly( thienylene vinylene) series is shown in Figure 3 7 Polymer P3DDPTV shows a glass transition temperature at 43 o C and a broad exotherm at 115 o C ( m = 4.3 J/g ) which could correspond to a melting transition of some of the dodecyl solubilizing groups. The melting transition was confirmed in the cooling cycle with observation of crystallization transition at 86 o C ( c = 3.8 J/g ) In contrast, P3HTV has a smaller alkyl group that does not organize properly to show a melting transition i n the polymer and only the gla ss transition temperature was detected at 49 o C. Analogous to the hexyl derivative polymer, P3MTV shows only a glass transition temperature at 40 o C, which is typical of a PTV derivative polymer. Figure 3 7 DSC thermogram s for polymer PTVs ( 42 a c ) at 10 o C/min rate
74 3.2. 5 2 Optoelectronic and electrochemical properties of soluble PTVs derivatives The electronic properties of the soluble synthesized PTVs were determined by spectroelectrochemistry, and cyclic voltammetry to evaluate the HO MO LUMO levels and analyze the electrochromic behavior. These data are summarized in Table 3 2. Figure 3 8 Spectroelectrochemistry of P3DDTV. Film was spray cast onto ITO coated glass from dichloromethane solutions (~1 mg mL 1 ). Electrochemical oxidation of the film was carried out in 0.1 M TBAPF6/ACN supporting electrolyte using an Ag/AgCl reference electrode and a platinum counter electrode. The applied potential was increased in 100 mV increments from 0.1 to +0.2V, in 25 mV steps from +0.225 to +0.35V, and in 100 mV steps from +0.4 to +0.8V. Figure s 3 8 and 3 9 display the s pectroelectrochemistry of the solu ble P3DDTV ( 42a ) and P3HTV ( 42b ) polymers in dichloromethane solutions. Th e UV Vis absorption spectra for P3DDTV (Figure 3 8 ) exhibit an onset of th e low energy absorption edge (onset of the transition) for the neutral spectrum at 750 nm correspond ing to an optical band gap of 1.65 eV. The electrochromic behavior was observed by recording the spectral changes upon oxid ation of the polymer thin film that as shown in Figure 3 8. The results agree with those for previously reported P3DDPTV synthesized by other methodologies. Likewise, the spectroelectrochemi cal data of P3HTV ( Figure 3 9 ) show
75 an absorption onset at 744 nm, correspond ing to a HOMO LUMO bandgap of 1.67 e V This is a cha racteristic value for a P 3H TV. 89 Cyclic voltammetry (CV) was used for confirming the optoelectronic properties of the synthesized soluble PTVs. Figure 3 10 A displays the CV for P3DDTV polymer showing a reversible onset of polymer oxidation at +0.25 V vs. Fc/Fc + corresponding to a HOMO energy level of 5.35 eV. (The conversio n of the HOMO energy was accomplished by adding 5.1 eV to the onset of the oxidation of the polymer, assuming that Fc/Fc+ is at 5.1 eV below the vacuum level). 93 These results all agree with the corresponding data for previously synthesized P3DDPTV by cros s coupling reactions. 56 75 Figure 3 9 Spectroelectrochemistry of P3HTV. Film was spray cast onto ITO coated glass from dichloromethane solutions (~1 mg mL 1 ). Electrochemical oxidation of the film was carried out in 0.1 M TBAPF 6 /ACN supporting electrolyte using Ag/Ag + the reference electrode and a platinum wire as the counter electrode. The applied potentials was increased in 100 mV increments from 0.1 to +0.2, in 25 mV steps from +0.225 to +0.35, and in 100 mV from +0.4 to +0.7. In addition, the cyclic vol tammogram of P3HTV (Figure 3 10B ) displays a reversible onset potential at 0.17 V vs Fc/Fc+, corresponding to a HOMO energy level
76 of 5.27 eV. These are similar values to those reported by Hillmyer et al. for the same P3HTV synthes ized by ADMET polymerization under high boiling solvent conditions (Table 3 2). 89 Figure 3 10 Cyclic voltammogram of soluble PTVs. A ) P3DDTV B ) P3HTV. Every sample was run 10 repeated cycles at 50 mV/s in 0.1 M TBAPF 6 /ACN supporting electrolyte. Because d ifferential pulse voltammetry (DPV) yields sharper redox onsets along the elect rochemical process and increases the accuracy of the estimated energy band gaps DPV was used to verify the energy bang gap estimated from U V V isible and t he cyclic voltammogram ( Appendix A ) Table 3 2 summarizes the DPV values, where the HOMO leve l potentials were very close to the values estimated from the cyclic voltammogram. Table 3 2 Electr ochemical properties of 3 hexyl and 3 dodecyl PTV derivatives Polymer Onset HOMO (CV) Onset HOMO (DPV) max absorption Optical band gap (CV) (DPV) P3DDTV 0.25 V 5.35 eV 0.13 V 5.23 eV 750 nm 1.65 eV PHTV 0.17 V 5.27 eV 0.13 V 5.23 eV 744 nm 1.67 eV All potentials are reported vs. Fc/Fc+ and all HOMO and LUMO energies are derived from the electrochemical data based on the assumption that the Fc/Fc+ redox couple is 5.1 eV relative to vacuum. a ) b)
77 The thermal and electrochemical results indicate that the solid state methodology can be used to synthesize conjugate d polymers that are similar to those made by cross coup l ing reactions or by ADMET polymerization under high boiling solvent conditions 3. 3 Experimental Data 3.3.1 Materials All reagents were used as received unless otherwi se noted. The 3 bromothiophene and ethyltriphenyl phosphonium bromide were purchased from Sigma second and first generation catalysts were provided by Materia, Inc. and stored under N 2 3.3.2 Instrumentat ion 1 H NMR (500 MHz) and 13 C NMR ( 125 MHz) spectra were recorded on an Inova 2 spectrophotometer, and 1 H NMR (300 MHz) and 13 C NMR ( 75 MHz) were recorded on a Mercury300 spectrometer using CDCl 3 as solvent All chemical shifts for 1 H and 13 C NMR were refer enced to residual signals from CDCl 3 ( 1 H = 7.27 ppm, and 13 C = 77.23 ppm). Differential scanning calorimetry (DSC) was performed using a Thermal Analysis (TA ) Q1000 at a heating rate of 10 o C/min under nitrogen purge. 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 (2 4 mg/sample), and an empty pan was used as the reference. The samples were scanned for multiple cycles to remove recrystallization differences between samples, and the results were reported from the second scan cycle. Thermogravimetric analysis (TGA) was performed on a TA Q5000 using the
78 dynamic high resolution analysis cap ability at a h eating rate of 20 o C/min under nitrogen purge. Gel permeation chromatography was performed with a Waters Associates GPC V2000 liquid chromatography system with internal differe ntial refractive index detector For the electrochemistry analysis, a standard three electrode electrochemical cell was used with a platinum button working electrode, a platinum wire counter electrode, and a silver wire pseudo reference electrode calibrated vs. Fc/Fc + All potentials are reported vs. Fc/Fc + in accord with the IUPAC s tandard for electrochemistry in organic solvents. Electrochemistry was performed using an EG&G Princeton Applied Research model 273A potentiostat / galvanostat operated with Corrware II software from Scribner and Associates. The primary techniques used wer e cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Polymers were adsorbed to the working electrode by electropolymerization or drop casting of a soluble polymer from a 1 2%(w /w) solutio n of the polymer in chloroform, using 0.1M tetrabutyla mmonium hexafluorophosphate (TBAPF 6 ) as electrolyte. Spectroelectrochemical experiments were performed using a Cary 500 UV Vis NiR specrophotometer for bench top experiments equipped with a InGaAs diode array detector with fiber optic capabilities for dry box studies. In all cases, a three electrode cell was utilized, as described above, with indium tin oxide (ITO) coated glass used as the working electrode (Delta Technologies 8 electropolymerization or by spray coati ng of the soluble polymer from a 1 2%(w/w) solution of the polymer in dichloromethane using an Iwata HP BC airbrush. In this experiment, the evolution of the polymer absorption spectra is monitored as a function of applied potential.
79 3.3.3 Monomer and P recursors S ynthesis Synt hesis of 3 dodecyl 2,5 diformyl thiophene, 39 a The synthetic procedure was taken from literature. 89 92 To a mixture of 3 dodecylthiophene (8.4 g, 0.10 mol), TMEDA (27.8 g, 0.24 mol), and dry hexane (50 mL) at room temperature was added 140 mL of n butyllithium (0.24 mol in hexane) to prepare the 2,5 dilithiothiophene intermediate. The reaction mixture was then heated at 40C for 30 minutes, after whic h 180 mL of dry THF were added. T he solution was cooled to 40C, and excess DMF (0.27 mol) was added dropwise over a 15 min period. The temperature was gradually increased to room temperature with continuous stirring over a 30 min period. The suspension was then poured into a mixture of 167 mL of HCl (37%) and 1700 mL of ice water, while vigorously stirring. Saturated NaHCO 3 solution was slowl y added under vigorous stirring until the solution reached a pH of 6 where some of the dialdehyde was removed by precipitation. The organic layer was separated and the aqueous layer extracted with diethyl ether four times. The organic solution was dried with MgSO 4 and recrystallized from THF/Ether (4:1) to afford 7.91 g ( 77 % ) of product ( 39a) as a light brown powder m.p. 110 114C. 1 H NMR (300 MHz, CDCl 3 10.09 (s, 1 H) 9.92 (s, 1 H) 7.61 (s, 1 H) 2.95 (t, J =7.60 Hz, 2 H) 1.58 1.72 (m, 2 H) 1.10 1.39 (m, 18 H) 0.82 (t, J =11.00 Hz, 3 H). 13 C NMR (75 MHz, CDCl 3 183.6, 183.2, 28.7, 22.9, 14.3 ( Aliphatic Synthesis of 3 dodecyl 2,5 dipropenyl thiophene, 40 a 89 A flame dried, Ar purged, three necked 200 mL round bottom flask equipped with a stir bar and additional funnel was charged with ethyl triphenyl phosphonium bromide (19.86g, 53.50 mmol) and dry tetrahydrofuran (THF, 40 mL). The reaction mixture was cooled to 40 C, and a
80 solution of 2.5 M n butyl lithium in hexane (20.7 mL, 51.71mmol) was added dropwise. After 30 min of stirring at 40 C, the mixture was warmed to room temperature for a three hour period. The mixture was then cooled to 78 o C, and a soluti on of 3 dodecyl 2,5 diformylthiophene in THF (17.83 mmol) was added dropwise. The reaction flask was then wrapped with aluminum foil. After 90 min of stirring at 78 o C, the reaction was warmed to room temperature and allowed to stir overnight. The reactio n was quenched at 10 C with deionized water (25 mL). Dichloromethane (DCM, 70 mL ) was added and the organic portion was washed with deionized water, while the aqueous portion was extracted three times with dichloromethane. The combined organic phases were washed with brine (2x50 mL) and dried with MgSO 4 Filtration and solvent evaporation afforded a dark orange liquid, which was flashed through silica with hexane as eluent to give monomer free of triphenylphosphine oxide. Vacuum distillation (230 o C at 10mmH g) afforded pure monomer in 30% yield. 1 H NMR (30 0 MHz, CDCl 3 6.77, 6.68, 6.63, 6.54 (s, Th H 4 1H), 6.58 6.34 (m, H 6 olefin attach ed to thiophene, 2H), 6.11 5.55 (m, H 7 olefin attach ed to the methyl unit, 2H), 1.98, 1.86 (m, propenyl, 3H), 2.50 1.52, 1.40 13 C NMR (126 MHz, CDCl 3 141.2, 141.0, 140.8, 139.2, 139.1, 138.5, 138.3, 137.1, 136.5, 132.7, 130.2, 130.0, 129.2, 127.0, 126.3, 126.0, 125.3, 125.0, 124.9, 124.8, 124.7, 124.5, 124.4, 124.3, 124.2, 124.1, (m), 29.8, 29.7, 29.6, 28.8, 28.7, 28.4, 28.3, 23.0, 18.8 (d), 18.5 (d), 15.4, 15.3, 14.4 11.20%. HR MS (DART): [M] + = 332.2548, [M+H] + = 664.5070, [2M] + = 665.5148
81 Sy nthesis of 3 hexyl 2,5 diformyl thiophene, 39b Compound ( 39b ) was synthesized according to the synthes is of the 3 dodecyl derivative, to give 7.2 g (64%) as a light brown powder. 1 H NMR (300 MHz, CDCl 3 10.02 (s, 1H) 9.98 (s, 1H) 7.62 (s, 1H) 3.02 (t, J =7.58 Hz, 2H) 1.56 1.68 (m, 2H) 1.17 1.41 (m, 6H) 0.88 (t, J =11.18 Hz, 3H). 13 C NMR (75 MHz, CDCl 3 183. 4 18 2.9 15 3 4 148.1, 143. 4 137. 8 13 31. 4 31.2, 29.8, 2 8 6 13 C NMR (75 MHz, CDCl 3 183.6, 183.2, 152.2, 148.1, 143.5, 137.3, 135.8 Synt hesis of 3 hexyl 2,5 dipropenyl thiophene, 40b 89 Monomer ( 40b ) was synthesized according to the synthesis of the dodecyl derivative. Vacuum distillation (220 o C at 0.5 mmHg) afforded pure monomer in 63% yield. 1 H NMR (500 MHz, CDCl 3 6.80, 6.71, 6.66, 6.57 (s, Th H 4 1H), 6.56 6.39 (m, H 6 olefin attach ed to thiophene, 2H), 6.11 5.61 (m, H 7 olefin attach ed to the methyl unit, 2H), 2.05, 1.81 (m, 13 C NMR (126 MHz, CDCl 3 141.2, 141.0, 140.4, 139.2, 1 39.1, 138.6, 137.2, 136.5, 134.3, 131.9, 130.0, 129.2, 127.1, 126.3, 125.4, 125.3, 125.1, 124.9, 124.8, 124.7, 124.6, 124.4, 124.2, 123.5, analysis: calc. C 77.36%, H 9.74%; found C 77.08%, H 10.02%. HR MS (DART): [M+ H] + = 249.1671 [2M+H] + = 497.3270, [3M+H] + = 745.4869. Synthesis of 3 methyl 2,5 diformyllthiophene, ( 39c ) 89 Compound ( 39c ) was synthesized according with the synthesis of 3 dodecyl derivative, 11.5 g (87%) as a light brown powder. 1 H NMR (300 MHz, CDCl 3 10.14 (s, 1H) 9.97 (s, 1H) 7.61 (s,
82 1H) 2.63 (s, 3 H). 13 C NMR (75 MHz, CDCl 3 183.5, 183.2, 152.1, 148 .4, Aliphatic Synthesis of 3 methyl 2,5 dipropenyllthiophene, ( 40c ) 89 Monomer ( 40c ) was synthesized according with the synthesis of the dodecyl derivative. Vacuum distillation (70 o C at 0.06 mmHg) afforded pur e monomer in 25 % yield. 1 H NMR (500 MHz, CDCl 3 6.79, 6.70, 6.65, 6.55 (s, Th H 4 1H), 6.61 6.38 (m, H 6 olefin attach to thiophene, 2H), 6.16 5.61 (m, H 7 olefin attach to the methyl unit, 2H), 2.02, 1.89 (m, 13 C NMR (126 MHz, CDCl 3 140.9, 139.1, 138.9, 137.0, 136.5, 135.6, 135.1, 134.4, 134.2, 133.4, 133.0, 132.1, 130.7, 130.0, 128.0, 127.2, 12 5.4, 125.3, 125.0, 124.8, 124.7, 124.6, 124.5, 124.4, calc. C 79.45%, H 10.91 %; found C 79.20%, H 11.20%. HR MS (DART): [M H] + = 177.0904, [M] + = 178.0827, [M+H] + = 179.0875 3.3.4 General Metathesis Conditions in the S olid S tate Monomer was degassed prior to polymerization and all glassware w as cleaned and dried under vacuum before u se. The reactions were initiated by placing the appropriate amount of monomer (0.4g) in a 5 mL flat Teflon TM mold (outside dimensions: 2.4x1.6x0.6 cm; inside dimensions: 1.4x1.1x0.5 cm) followed by the generation catalyst (0.2 mo l%). The mold was then placed into an Schlenk flask and exposed to high vacuum to yield 2 butene as the released molecule. The temperature was controlled using a heating mantle and set to 70 o C. Catalyst was then added every three days (in a 0.2 mol% dose), at which time a polymerization sample was taken (under oxygen free conditions) to determine the
83 extent of polymerization. To terminate ADMET polymerization, the polymer was dissolved in 15 mL of chloroform containing 1 mL of ethyl vinyl ether, stirred for 4 hours and then precipitated from cold methanol. Synthesis of poly ( 3 dodecyl thienylene vinylene ) P 3DD TV, ( 4 2a ) 1 H NMR (500 MHz, CDCl 3 7.01 1.10, 0.88 13 C NMR (126 MHz, CDCl 3 99.7, 32.2, 31.0 (m), 29.9 (m), 29.7 (m), 29.6, 28.6, 22.7, 14.4. GPC (Mn= 14,000 g/mol, Mw= 32,000 g/mol, PDI: 2.3), TGA ( o C at 20 o C/min.) N 2 ( 5%) = 353 o C, DSC results: T g = 43 o C, T m = 115 o C H m = 4.1 J/mol, T c =86.3 o C H c = 11.4 J/mol. UV(DCM) max abs nm: 750 E HOMO ( CHCl 3 )=5.23 eV, E HOMO LUMO gap= 1.65 eV. Synthesis of poly(3 hexylthienylene vinylene), P 3H TV, ( 42b ) Monomer was polymerized according to general solid state polymerization conditions 1 H NMR (500 MHz, CDCl 3 6.73 7.12 (Aromatic 6.61 6. 42 ( vinylene linkage), 2.65, 1.63, 1.37, 0. 94 ( ) 1.86 1.94 (methyl end groups). 13 C NMR (126 MHz, CDCl 3 119.4, 31.9, 31.0, 22.9, 28.6, 22.9, 14.40 TGA ( o C at 20 o C/min.) N 2 ( 5%) = 350 o C, DSC results: T g = 49 o C. UV(CHCl 3 ) max abs nm: 744, E HOMO (DPV)=5.23 eV, E HOMO LUMO gap=1.67 eV. Synthesis of poly(3 methylthienylene vinylene), P 3M TV, ( 42c ) Monomer was polymerized according to general solid state polymerization conditions. 1H NMR (500 MHz, CDCl 3 6.96 2.01 (methyl end groups). TGA (oC at 20oC/min.) N2 ( 5%) = 373oC, DSC results: Tg = 40 o C.
84 CHAPTER 4 SYNTHESIS AND THERMAL PROPERTIES OF POLY(NAPHTHALENE VINYLENES) 4.1 Introductory Remarks Poly(arylene vinylenes) comprise one of the most promising class es of conjugated polymers for understanding fundamental electronic process es and their applications in optoelectronics. 94 ,95 As an example, poly(phenylene vinylenes) (PPV) play important roles in electroluminescent materials photoconductors solar energy cells, and laser materials. Due to these high impact applications, many derivatives and copolymer s derived from PPV ha ve been studied. Of particular interested in t h is dissertation are P oly( naphthalene vinylenes ), PNV, which are modification s of PPV, having special phot oluminescence and emission properties. 9 6,97 Poly(n aphthalene vinylen es ) can occur in the polymer via three differ ent linkages : 1,4 1,5 and 2,6 PNV (Figure 4 1). Among these structural isomers, 1 ,4 PNV is the most studied since it occurs in more commercially available materials However, the 2,6 analogue is considered the most desirable as its quinoid al structure do es not interrupt the conjugation length along the polymer backbone. 9 5,9 7 98 Figure 4 1. Different link ages for naphthalene vinylene polymers. Poly(naphthalene vinyl enes) are usually synthesized by Horner Emmons 99 101 Knoevenagel 102 Gilch, 103 and Wessli ng 104 polymerization s, all of which result in defects in the polymer backbone
85 I t is well known that the i ntroduction of solubilizing group s is necessary for the pr ocessability of a fully conjugated polymer. However these groups may affect the conjugated chain configuration and thereby affect the thermal stability and optoelectronic properties of the material 9 4,105,106 One of the purposes of this research is t o study the stacking interactions of the naphthalene vinylene poly mers. Numerous previous s tu interaction s have shown that substitution ca stacking of the aromatic molecules 107 108 In order to study these inter molecular interactions without s acrificing processability, the substitution can be incorpo rated in to the v inylene linkage instead of the aromatic system. In 1989, Dr. Schl ter et al synthesized a series of polycyclic aromatic hydrocarbons with terminal olefin s that could be poly m erized by ADMET polymerization (Figure 4 2). 10 9 1 10 Figure 4 2. 1,1 vinyl su bstituted aromatic species S tructures 43a e are not only potential monomers for ADMET polymerization, they also posses a 1,1 substituted vinyl group that will form a new tetrasubstituted double bond after the metathesis reaction T he bulkiness around the metallacyclobutane intermediate, makes this reaction a challenging transformation that can still be considered an unsolved problem in olefin metathesis. 111 11 3 Studies on metathesis
86 reactions of 1,1 vinyl substituted olefins (such a n enyene cross metathesis or RCM) have demonstrated the challenging nature o f this type of transformati on 114 115 For these reasons, Grubbs and coworkers have developed a new series of catalyst s to increase the ir efficiency i n hindered olefins Therefore, bulky, electron rich N heterocyclic carbene (NHC) ligand s which give excellent reactivity and stability to the catalyst, have been replaced by new less bulky N heterocyclic carbenes ( NHC s ) 11 6 11 8 Use of these c atalyst s for synthesis of tetrasubstituted olefins has primarily involved r ing closing metathesis and cross metathesis reactions Thus, Grubbs and coworkers reported that the exchang e of the mesyl group for the ortho tolyl group on the NHC of Ru most common catalysts results in efficient synthesis of tetrasubstituted olefins by ring closing metathesis. 11 9 1 21 This modification of Grubbs Hoveyda second generation catalyst has led to the most active commercially available catalyst ( 44 ) for the synthesis of tetrasubstitut ed rings of strain ed alkenes (Figure 4 3) The free space around the r uthenium atoms allows the coordination of bulkier substrates without significant reduction o f catalyst activity. Accordingly, other types of unhindered ortho tolyl, and ortho isopropylphenyl Grubbs second generation and Grubbs Hoveyda second generation catalyst derivatives have been studied (Figure 4 3). Since reducing the bulkiness o f the N aryl substituent o n the NHC increases the activity of the catalysts the activity sho uld further improve by removing both ortho substituents on the N Aryl group The catalyst with N phenyl group s is unstable and difficult to synthesize 116 but I ntroduction of bulky substituents on the NHC core increases the stability Grubbs and coworkers have synthesized a new se ries of stable catalysts derived from Grubbs Hoveyda second generation catalys t with tetramethyl
87 substitution at the NHC ( 47 ) resulting in high er efficiency for hindered olefins 11 6 ,12 2 Figure 4 3 shows some examples of Ru catalyst s providing between 8 9 9 9 % yields in the formation of tetrasubstituted olefins in ring closing transformations, of these the most reactive catalyst is compound ( 47 ). 12 2 Figure 4 3 Different Ru based catalysts for the synthesis of tetrasubstituted olefins Taking into consideration the special photoluminescence and emission properties of poly(naphthalene vinylenes), the goal of the present work is to synthesize vinyl substituted PNVs by ADMET polymerization for further studies. 4.2 Results and D iscussion 4.2.1 Monomer and P olymer S ynthesis The synthesis of naphthalene derivative monomers was accomplished in collaboration of Yuichiro Tokoro, a graduate student from Kyoto University. The f irst series of monomers was performed according to the methodology reported by Schlter
88 et al. 109 110 The 1,1 vinyl disubstitut ed monomer 1,4 di(1 octen 2 yl)naphthalene ( 43 b ) was synthesized as shown in scheme 4 1, 1 O ctyne was brominated with HBr in the presence of tetrabutylammonium bromide to afford 2 bromo 1 octene ( 49 ) in 88% yield, 123 which, after subsequent formation of the Grignard reagent, allowed the synthesis of the monomer by Kumada coupling in low yield. M onomer ( 43 b ) exhibited olefin isomerization in the presence of Ni catalyst, 124 resulting in loss of precision of the final polymer, as well as a reduction of the metathesis activity. 125 Different Ni based catalysts systems (i.e Ni(dppp)Cl 2) and Ni(dppe)Cl 2 ) were attempted in order to d ecrease the isomerization process. However, these methods did not yield any product at all. Scheme 4 1 Monomer synthesis by Kumada coupling using Ni(dmpe)Cl 2 catalyst. Based on the work of Organ et al. Pd PEPPSI i P r catalyzed Kumada reactions show no isomerization product for allylic Grignard intermediates. 126 127 Using the same reaction conditions as Organ monomer ( 43b ) w as obtained in 71% yield respectively, with no indication of isomeriz ed products (Scheme 4 2) Scheme 4 2 S ynthesis of monomer 43 b by Pd PEPSI iPr catalyzed Kumada coupling. Having naphthalene monomer ( 43b ) synthesized the next step was to try the polymerization with the state of the art catalyst s for hindered olefins. Since tetra
89 substituted polyolefins have never been studied, a scan o f all possible catalyst was needed to find the optimum reaction conditions (Scheme 4 3) Scheme 4 3 Polymerization of 2,6 di(1 octen 2 yl)naphthalene ( 43b ) M onomer ( 43b ) was subjected ADMET polymerization under dynamic vacuum conditions at different temperatures Dynamic vacuum conditions are needed, because the polymer wi ll be fully a conjugated system that could form film s or cl u mps that inhibit formation of high molecular weight material Previous reports of ADMET polymerization under dynamic vacuum conditions have indicated that 1,2 dichlorobenzene was the best solvent for standard ADMET polymerizations 32 33,87 The polymerization was carried out with different catalyst s at 40 o C using 1,2 dichlorobenzene as solvent However polymerization did not take place under any of these conditions (Table 4 1) In order to increase the catalyst activity, t he tempe rature was raised f ro m 40 to 80 o C but no polymer was obtained. In order to im prove the formation of the tetrasubstituted olefin, Blechert et al. stud ied the efficiency of tetramethyl substituted Ru c atalysts with different solvents Th e y found that instead of using 2 mol% of catalyst in 1,2 dichlorobenze, 5 mol% of catalyst in a low dielectric constant solvent such as hexafluorobenzene or octafluorotoluene promote d the synthesis of tetrasubstituted olefins up to 99% yield. 12 7 Thus, the polymerization was attempted with the sam e conditions as reported by Pederson However, metath esis polymerization did not take place (Table 4 1)
90 Table 4 1. Different attempts for the polymerization of monomer ( 43b ). entry catalyst solvent P ( Torr ) T ( C ) t ( h ) conversion ( % ) 1 44 (1 mol%) 1,2 DCB 70 40 90 0 2 45 (1 mol%) 1,2 DCB 70 75 44 0 3 4 (1 mol%) 1,2 DCB 70 75 44 0 4 46 (1 mol%) 1,2 DCB 70 75 44 0 5 6 (2 mol%) 70 70 48 0 6 47 (5 mol%) 1,2 DCB 70 75 65 0 7 47 (5 mol%) octafluorotoluene 760 80 24 0 1,2 DCB= 1,2 dichlorobenzene Taking into account that the bulkiness around the double bond is the main factor in the polymerization failure and that the main objective was the synthesis of poly(naphthalene vinylenes), t he next step was to extend the terminal double bound so that the hexyl solubilizing g roup is two carbons away of the active terminal olefins thereby giving room for the metathesis to take place. As shown in Scheme 4 4, t he synthesis of monomer ( 55 ) s tart s from the condensation of terephthaloyl chloride ( 53 ) with 1 bromohexane in the prese nce of ZnCl 2 to produce 1,1' (naphthalene 2,6 diyl) 1 diheptanone ( 54 ). 128 Subsequent Wittig reaction of the diketone ( 54 ) with allyltriphenylphosphonium bromide in the presence of potassium t ert butoxide yield ed monomer ( 55 ) in low yields (<10%) Due to low yields another attempt to synthesize analogous monomers were explored Scheme 4 4 Synthesis of 2,6 di(1,3 decadien 4 yl)naphthalene ( 55 ) As shown in scheme 4 5, the synthesis of a new vinyl substituted monomer started by the conversion of 1 octyne ( 48 ) to the pinacol boronic ester ( 57 ). Subsequent N e gishi cross coupling reaction of ( 57 ) with vinylzinc chloride in the presence of Pd
91 PEPPSI iP r catalyst produced the boronic ester ( 58 ) with an extended double bond, which was then iodinated to produce ( 59 ) in 73% yield. Treatment of ( 59 ) with the Grignard reagent, transme ta llation with ZnCl 2 formed the organozinc intermediate ( 60 ). Negishi cross coupling of the resulting organozinc reagent ( 60 ) and 2,6 dibromonaphthalene ( 50 ) in the presence of Pd PEPPSI iPr catalyst gave the monomer ( 61 ) in 40% yield purified by preparative HPLC. 129, 130 Polymerization was then performed with Grubbs Hoveyda second generation catalyst ( 6 ), as it is the most active catalyst for unhindered monomers. 129 Toluene was used as solvent as previously reported experiments suggested for ADMET polymerization with Grubbs Hoveyda type catalysts under dynamic vacuum conditions. 33 A polymer with molecular weight of 4,000 g/mol (by GPC) was obtained after 48 hours of polymerization (Scheme 4 6). Scheme 4 5 Synthesis of 2,6 bis(( Z ) 2 vinyl 1 octenyl)naphthalene ( 61 ).
92 Scheme 4 6 Polymerization of 2,6 bis(( Z ) 2 vinyl 1 octenyl)naphthalene ( 61 ). Figure 4 4. 1 H NMR spectra of naphthalene derivatives. A) M onomer ( 61 ). B) P olymer ( 62 ). Figure 4 4 displays a representative comparison between the 1 H NMR spectrum of monomer ( 61 ) and its corresponding polymer ( 62 ). The olefin vinyl proton in the monomer (Figure 4 4A) was observed as a do u blet of do u blets at 7. 70 ppm. Upo n polymerization, these signals decrease d with respect to the aliphatic peaks. The degree of polymerization was calculated from the ratio between the vinyl protons (a) and the methylene protons (b) in the polymer spectrum. The number average molecular weight calculated by 1 H NMR was 3,800 g/mol which is consistent with the GPC value (4,000
93 g/mol) These results also demonstrate that the hindrance around the vinyl group was the impediment in attempting the polymerization of the previou s synthesized monomer ( 43b ). Because the hexyl group is still too close in the monomer ( 61 ) only low molecular weight polymer was obtained. F urther studies on different monomer architectures and polymerization s with unhindered catalysts are on going. 4.2.2 Thermal P roperties Thermal analysis of the poly(2,6 nap hthalene vinylene ) derivative s w ere performed by DSC and TGA analysis in a nitrogen environment. Figure 4 5 shows t he thermal gravimetric performance of polymer ( 62 ) which shows an onset degradation temperature at 3 26 o C ( 5% weight loss ) indicat ive of good th ermal stability any further heating results in one pathway decomposition of the polymer. Figure 4 5. TGA thermogram of polymer ( 62 )
94 Differential Scanning Calorimetry (D SC) was used to analyze the thermal properties of the polymer. Figure 4 6 shows the DSC thermogram o f PNV derivative ( 62 ), indicating that polymer present a glass transition temperature of 30 o C. 4.2.3 Optical S tudies Optical properties of poly(naphthalene vinylene) derivative ( 62 ) were measured by electronic (UV vis) and photoluminescence (PL) spectroscopy. The optica l data is summarized in Table 4 2. Figure 4 7 shows the UV vis absorption and PL spectra ( max abs =456 nm and max emission =527nm) of the dilu te polymer solutions in DCM Figure 4 6. Differential scanning calorimetry thermogram for PNV derivative ( 62 ). Top trace heating ramp; bottom trace, cooling rap; 10 o C/min in He The UV vis spectra demonstrated two absorption s bands in the range of 500 2 50 nm. A maximum absorption was observed at 394 nm with another smaller absorption
95 centered at 286 nm. The absorption edge to the onset of the transition was observed at 456 nm (2.72 eV) in dichloromethane. While there are no published reports of poly(n aphthalene vinylenes) alkyl substituted on the naphthalene ring or alkyl substituted in the vinylene linkage to provide baseline comparison, alkoxyl substituted PNVs present maximum absorptions at 440 nm, demonstrating that the insertion of electron donor substituents red shift the spectrum. Figure 4 7 also shows the fluorescence spectrum of poly(naphthalene vinylene) derivative ( 62 ) obtained upon excitation at 394 nm (maximum absorption wavelength) in dichloromethane. The emission band of the polymer peaks at 527 nm, correspondingly, the solution appears to emit green light. Figure 4 7. Absorption and emission spectra of PNV derivative ( 62 ) in methylene chloride solution. The sample was excited at 394 nm. 4.2. 4 Electrochemical Studies Electrochemical pro perties of the polymer were studied by employing cyclic voltammetry (CV) and differential pulse voltammetry (DPV) experiments on the
96 poly(naphthalene vinylene) derivative ( 62 ). The cyclic voltammetry measurements were carried out in dichloromethane in an a rgon filled glovebox at 25 mV/s rate using 0.1 M TBAPF 6 as the electrolyte (Figure 4 8). An irreversible oxidation band was observed at ca. 0.44V (vs Fc/Fc + ), while the irreversible reduction process showed the onset at ca. 2.02(vs Fc/Fc + ). Table 4 2 Optical properties of PNV derivative ( 62 ) max abs (nm) max emission (nm) Optical band gap 456 527 2.72eV Values estimated from onset absorption edge in DCM solution. Differential pulse voltammetry (DPV) was used to calculate the E HOMO LUMO gap as it yields sharper redox onsets along the electrochemical process and therefore increases the accuracy of the estimated energy gaps. Figure 4 9 shows that the oxidation onset on the DPV voltammogram occurs at ca. 0.42V (vs Fc/Fc + ) and the reduction onset at ca. 2.18V (vs Fc/Fc + ). The conversion of the HOMO and LUMO energies was accomplished by adding 5.1 eV to the onset of the oxidation and reduction of the polymer, assuming that Fc/Fc+ is at 5.1 eV below the vacuum level). 93 Thus, the polymer prese nt an E HOMO value of 5.52 eV, an E LUMO value of 2.92 eV, and therefore, an E HOMO LUMO gap of 2.60eV. This HOMO LUMO energy gap is in accordance with the spectroscopy gap (2.72eV) calculated form the onset of the absorption transition. Table 4 3 Electroch emical properties of PNV derivative ( 62 ) E ox Onset E Red Onset E ox Onset E Red Onset HOMO from DPV LUMO from DPV E HOMO LUMO gap (CV) (CV) (DPV) (DPV) 0.44V 2.02V 0.42V 2.18 5.52eV 2.92eV 2.60eV All potentials are reported vs. Fc/Fc + and all HOMO and LUMO energies are derived from the electrochemical data based on the assumption that the Fc/Fc+ redox couple is 5.1 eV relative to vacuum.
97 4.3 Experimental M ethods All reactions were conducted in flame dried glassware under an argon atmos phere unless otherwise noted. Reagents were purchased from Fischer or Aldrich and were catalysts used in this study. Figure 4 8 Cyclic voltammogram of PNV derivative ( 62 ) in dichloromethane with 0.1 M TBAPF 6 /ACN supporting electrolyte. Scan rate of 25 mV/s Figure 4 9. Differential pulse voltammogram of PNV derivative ( 62 ) in dichloromethane with 0.1 M TBAPF 6 supporting electrolyte at 100 mV.
98 4.3.1 Instrumentation an d Analysis The 1 H NMR (300 MHz) and 13 C NMR (75 MHz) spectra were recorded on a Mercury 300 spectrometer, and the 1 H NMR (500 MHz) and 13 C NMR (125 MHz) spectra recorded on a Varian Associates Innova 500 spectrometer. Chemical shifts for 1 H and 13 C NMR were referenced to residual signals from CDCl 3 ( 1 H = 7.26 ppm and 13 C = 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 si lica gel coated (250 m thickness) glass plates and 1 H and 1 3 C NMR. 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 o C/min. Calib rations 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 performe d either on a TA Instruments TGA Q 4000 Series using dynamic scans under an inert (nitrogen) atmosphere Gel permeation chromatography (GPC) was performed at 40 C 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. I njections 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 standards (Polymer Laboratories; Amherst, MA)
99 selected to produce M p and M w values below and above the expected copolymer molecular weight. UV Vis absorpt ion spectra were recorded on a Varian Cary 500 UV Vis NIR spectrophotometer. Electrochemistry was performed in a three electrode cell consisting of an ITO coated glass or platinu m button working electrode, a platinum wire/flag counter electrode, and a Ag/Ag+ reference electrode or a silver wire pseudo reference electrode in a 0.1 M [nBu 4 N] [PF 6 ] / acetonitrile solution calibrated using the ferrocene ferrocenium redox couple, assumi ng the values of [FeCp 2 ] +/0 = 0.40 V (0.1 M [nBu4N] [PF6] /acetonitrile solution) vs. Ferrocene. Electrochemical measurements were made with an EG&G PAR model 273A potentiostat/galvanostat or BAS 100B electrochemical analyzer, and optical data were measure d with a Cary 500 UV Vis NIR spectrophotometer or a StellerNet Diode Array UV Vis NIR Electrochemistry was performed in a three electrode electrochemical cell used with a platinum button working electrode, a platinum wire counter electrode, and a silver wi re pseudo reference electrode calibrated vs. Fc/Fc + in a 0.1 M TBAPF 6 / acetonitrile solution calibrated using the ferrocene ferrocenium redox couple All potentials are reported vs. Fc/Fc+ in accord with the IUPAC standard for electrochemistry in organic solvents. Electrochemistry was performed using an EG&G Princeton Applied Research model 273A potentiostat / galvanostat operated with Corrware II software from Scribner and Associates. The primary techniques used were cyclic voltammetry (CV) and differenti al pulse voltammetry (DPV). Polymers were adsorbed to the working electrode by drop casting of a soluble polymer from a 1 2% (w /w) solution of the polym er in dichloromethane.
100 4.3. 2 Monomer and Precursors S ynthesis 2 bromo 1 oc tene ( 49 ) To a solution of tetrabutylammonium bromide (145 g, 300mmol) and HBr (36.9 mL, 534 mmol in 33% acetic acid) in CH 2 Cl 2 was added 1 octyne ( 12 mL 60 mmol) slowly. After stirring for 17 h at room temperature, the reaction mixture was quenched with sat d aq. NaHCO 3 solution. T he organic phase was dried over MgSO 4 and concentrated in vacuo, and hexane was added to the residue. The mixture was washed with water, dried over MgSO 4 and concentrated in vacuo. The remaining oil was purified by si lica gel column chromatography using he xane as the eluent distill ated under vacuum to give a colorless oil in 88% yield (10.1 g, 52.6 mmol). 1 H NMR (300 MHz, CDCl 3 5.55 (d, J=1.00 Hz, 1 H) 5.38 (t, J=1.00 Hz, 1 H) 5.38 (s, 1 H) 2.41 (d, J=14.66 Hz, 2 H) 2.41 (s, 2 H) 1.55 (br. s., 2 H) 1.30 (s, 6 H), 0.89 (td, J=6.20, 1.17 Hz, 3 H) ppm. 13 C NMR (75 MHz, CDCl 3 135.18, 116.39, 41.65 31.74 28.30 28.08 22.77 14.26 ppm. Ni(dmpe)Cl 2 catalyst 131 A Schlenk flask was placed under N2 and equipped with a stir bar. EtOH and acetone were sparged for 30 min prior to starting the reaction. NiCl 2 2 O (0.4 g, 2 mmol, 1.0 equiv) was added to the flask. Next, EtOH (11 mL) was added using a double sided needle. Finally, 1,2 bis(dimethylphosphino)ethane (dm pe) (0.55 mL, 3.3 mmol, 2.0 equiv) was added to the flask by syringe. After 30 min, acetone (8 mL) and toluene (16 mL) were added. A precipitate formed which was collected by filtration under N2 using a Schlenk filter frit Next, 0.52g of the precipitate w as combined with another portion of NiCl 2 2 O (0.52 g) in 26 mL of EtOH. The reaction was refluxed at 85 C for 45 min and the solution turned red/brown. After cooling to rt an orange precipitate formed. The solid was filtered and washed with hexanes to g ive 0.35 g of 1 as a n orange/brown solid (75% yield). HRMS (EI): Calcd. for C 6 H 16 Cl 2 NiP 2 : 277.9458
101 [M]+; found, 277.9470. Elemental Analysis: Calcd, C 25.76, H 5.76; found, C 25.952 H H 5.701. 2.6 bis(1 hexylethenyl)naphthalene, ( 43 b ) 109,110 Magnesium tunings (1.03 g, 42.2 mmol) and LiCl (1.68 g, 39.6 mmol) were dried at 120 C under vacuum. After cooling to room temperature, THF (26.4 mL) and 2 bromo 1 octene (5,05 g, 26.4 mL) were added and stirring was continued for 2 h at room temperature. The resu lting Mg reagent was added to a solution of 2,6 dibromonaphthalene (3.41 g, 12.0 mmol) and Pd PEPPSI IPr (0.163 g, 0.24 mmol) in THF (60 mL). The resulting mixture was stirred for 15 h at room temperature. Then, the reaction mixture was quenched with sat d aq. NH 4 Cl solution (100 mL), extracted by Et 2 O (100 mL), dried over MgSO 4 and concentrated in vacuo. The crude residue was purified by silica gel column chromatography using hexane as the eluent and recrystallized in Et 2 O/EtOH to give a white solid in 71% yield (2.96 g, 8.51 mmol). 1 H NMR (299 MHz, CDCl 3 7.77 (dd, J=8.78, 1.70 Hz, 4 H) 7.56 (dd, J=8.49, 1.70 Hz, 2 H), 5.40 (d, J=1.42 Hz, 2 H) 5.14 (d, J=1.20 Hz, 2 H) 2.60 (t, J=7.60 Hz, 4 H) 1.43 1.55 (m, 6 H) 1.22 1.41 (m, 12 H), 0.87 (t, J=6.80 Hz, 6 H) ppm. 13 C NMR (75 MHz, CDCl 3 148.8, 138.8, 132.9, 128.2, 125.2, 124.5, 112.7, 35.6, 31.9, 29.3, 28.6, 22.8, 14.3 ppm. 1,1' (2,6 naphthy lene)diheptan 1 one (54). LiCl ( 1.8 g, 64 mmol) and ZnCl 2 (3.0 g, 22 mmol) were dried at 120 C under vacuum for two hours After cooling down the system to 0 o C 40 mL of dry THF were added. Keeping the system at this temperature, Hexyl magnesium bromide solution ( 21 mL 42 mmol ) w as added dropwise and stirring was continued for 1 h at 0 o C to ensure complete conversion to the di n hexylzinc Pd PEPPSI IPr (0.136 g, 0.2 mmol) in THF ( 32 mL) was added to the system To this
102 mixture, naphthalene 2,6 dicarbonyl dichloride (10.1g, 40 mmol) in 50 mL of THF was added over a 1 h period at 0 o C. The resulting mixture was allowed to reach room temperature and stirred for 15 h. Then, it was quenched with satd. aq. NH 4 Cl solution (100 mL), extracted by Et 2 O (100 mL), dried over MgSO 4 and concentrated in vacuo. The crude residue was purified by silica gel column chromatography using hexane as the eluent to give colorless oil in 75 % yield 1 H NMR (299 MHz, CDCl 3 8.49 (s, 2 H) 7.97 8.18 (m, 4 H) 3.11 (t, J =7.50 Hz, 4 H) 1.72 1.92 (m, 4 H) 1.22 1.49 (m, 12 H) 0.83 ( t J =6.80 Hz, 6 H) 13 C NMR (74 MHz, CDCl 3 202.1, 136.7, 134.6, 129.9, 129.3, 124.7, 38.6, 31.6, 29.0, 28.8, 22.6, 14.3 ppm. ( Z ) 2 bromo 1 octenyl) 4,4,5,5 tetramethyl 1,3,2 dioxaborolane ( 57 ) To a solution of boron tribromide (25.0 g, 99.8 mmol) in CH 2 Cl 2 (90 mL) was added 1 octyne ( 13.4 mL 90.7 ) at 78 C. After 1 h at 78 C, the reaction mixture was warmed to room temperature, and kept a t this temperature for 2 h. A solution of pinacol (12.9 g, 109 mmol) in CH 2 Cl 2 (80 mL) was added at 78 C The resul tant reaction mixture was warmed to room temperature, stirred for 11 h, washed with sat d aq. NaHCO 3 solution and brine, and dried over MgSO 4 After evaporation of the solvent, the residue was purified by silica gel c olumn chromatography using hexane/EtOAc (20:1 4:1) as the eluent to give pale yellow oil in 97 % yield (22.0 g, 87.1 mmol). 1 H NMR (299 MHz, CDCl 3 5.85 5.88 (m, 1 H) 2.51 (t, J =6.80 Hz, 2 H) 1.54 (m, 2 H) 1.24 1.36 (m, 18 H) 0.88 (t, J =6.80 Hz, 3 H) ppm. 13 C NMR (75 MHz, CDC l 3 145.5, 83.8, 45.5, 31.7, 28.3, 28.2, 25.0, 22.7, 14.2 ppm. ( Z ) 2 hexyl 1,3 butadienyl) 4,4,5,5 tetramethyl 1,3,2 dioxaborolane ( 58 ) A solution of 57 (12.7 g, 40.0 mmol) and Pd PEPPSI IPr (0.272 g, 0.400 mmol) in THF (60
103 mL) was added to a solution of organozinc reagent (48 mmol, generated by treating vinylmagnesium bromide (30 mL, 48 mmol, 1.6 M solution in THF) with a solution of ZnCl 2 (6.54 g, 48.0 mmol) and LiCl (3.05 g, 72.0 mmol) in THF for 40 min at 0 C) at 0 C. The resultant rea ction mixture was stirred at room temperature for 14 h, quenched with sat d aq. NH 4 Cl solution (150 mL), extracted with Et 2 O (150 mL), dried over MgSO 4 and concentrated in vacuo. The remaining oil was purified by silica gel column chromatography using hex ane/EtOAc (19:1) as the eluent to give a pale yellow oil in 80% yield (8.01 g, 32.0 mmol). 1 H NMR (299 MHz, CDCl 3 7.26 (dd, J =18.0, 10.0 Hz, 1 H) 5.39 (dd, J =17.8, 1.4 Hz, 1 H) 5.33 5.35 (m, 1 H) 5.19 (dd, J =11.0, 1.4 Hz, 1 H), 2.30 (t, J =6 .50 Hz, 2 H), 1.42 1.55 (m, 2 H) 1.20 1.38 (m, 18 H), 0.88 (t, J =6.5 Hz, 3 H) ppm. 13 C NMR (75 MHz, CDCl 3 159.9, 137.5, 115.9, 83.2, 34.7, 32.0, 29.6, 28.92, 25.1, 22.8, 14.3 ppm. ( Z ) 1 iodo 2 hexyl 1,3 butadiene, ( 59 ) To a solution of 58 (7.51 g, 30.0 mmol) in THF (60 mL) was added a solution of NaOH (30 mL 90 mmol, 3 M in water). The resultant mixture was stirred for 30 min at roo m temperature, followed by addition of a solution of I 2 (15.1 g, 60.0 mmol) in THF (300 mL). After 15 h at ro om temperature the reaction mixture was quenched with aq. Na 2 S 2 O 3 solution, extracted with Et 2 O, washed with sat d aq. NaHCO 3 solution, dried over MgSO 4 and concentrated in vacuo. The remaining oil was purified by silica gel column chromatography using h exane as the eluent to give pale yellow oil in 73% yield (5.81 g, 22.0 mmol). 1 H NMR (300 MHz, CDCl 3 6.63 (dd, J =17.0, 11.0 Hz, 1 H) 6.18 (s, 1 H) 5.45 (dd, J =18.2, 1.0 Hz, 1 H) 5.32 (dd, J =10.5, 1.0 Hz, 1 H) 2.35 (t, J =8.20 Hz, 2 H) 1.40 1.53 (m, 2 H)
104 1.20 1.37 (m, 6 H) 0.88 (t, J =7.0 Hz, 3 H) ppm. 13 C NMR (75 MHz, CDCl 3 146.8, 137.79, 117.9, 80.3, 34.5, 31.8, 29.3, 28.7, 22.8, 14.3 ppm. 2,6 bis(( Z ) 2 vinyloct 1 en 1 yl)naphthalene ( 61 ) A solution of 59 (2.54 g, 9. 60 mmol) and LiCl (0.427 g, 10.08 mmol) in THF (15 mL) was cooled to 40 C and iPr MgCl (5.0 mL, 10 mmol, 2.0 M in THF) was added dropwise and stirring was continued at 0 C for 3 h. The resulting magnesium reagent was transmetalated by the addition of ZnC l 2 2LiCl (10 mL, 5.0 mmol, 0.5 M in THF) and stirred at 0 C for 30 min. To this mixture was added a solution of 2,6 dibromonaphthalene (1.14 g, 4.00 mmol) and Pd PEPPSI i Pr (0.082 g, 0.120 mmol) in THF (20 mL). The resulting mixture was stirred for 15 h at room temperature. Then, the reaction was quenched with sat d aq. NH 4 Cl solution (75 mL) extracted with Et 2 O (75 mL), dried over MgSO 4 and concentrated in vacuo. The crude residue was purified by C 18 HPLC using with acetone/CH 3 CN (3:2) as the eluent 1 H NMR (300 MHz, CDCl 3 7.74 (d, J =8.5 Hz, 2 H) 7.66 (s, 2 H) 7.37 (dd, J =8.5, 1.47 Hz, 2 H) 6.86 (dd, J =18.0, 12.0 Hz, 2 H) 5.42 (dd, J =18.00, 1.00 Hz Hz, 2 H) 5.21 (dd, J =11.00, 1.00 Hz, 2 H), 2.41 (t, J =8.20 Hz, 4 H), 1.54 1.67 (m, 4 H) 1.28 1.48 (m, 12 H) 0.91 (t, J =6.70 Hz, 6 H) ppm. 13 C NMR (75 MHz, CDCl 3 139.9, 135.3, 134.6, 132.2, 129.3, 128.3, 128.1, 127.7, 115.4, 34.2, 32.0, 29.6, 29.2, 22.9, 14.4 ppm. 4.3. 3 Polymer Synthesis Synthesis of poly(naphthalene vinylene) derivative, ( 6 2 ) In a S chlenck flask, a saturated solution of monomer in toluene (50 wt % ) was degassed by bubbling a rgon through the solution for three hours. Under strong a rgon flow, 1 mol% of Grubbs Hoveyda second generation catalyst was added. The system was then placed under dynamic vacuum at 70 torr absolute pressure via an aspirator attached to one arm. The
105 reactor was heated to 60 o C and left to sti r for 48 hours. After this time, ADMET was terminated by dissol ving the polymer in a solution of 20 mL of chloroform and 2 mL of ethyl vinyl ether. The solution was allowed to stir for 3 hours. After that time, the product was precipitated from methanol giving 200 mg of polymer 1 H NMR (500 MHz, CDCl 3 7.83 7.73 ( m 4 H) 7. 49 7.39 ( m, 2 H) 7. 13 7.06 ( m 2 H) 6.69 6.62 ( m 2 H) 2.4 1 ( m 4 H) 1.64 ( m 4 H) 1.47 1.20 ( m 12 H) 0.87 ( t 6 H ) 13 C NMR (75 MHz, CDCl 3 140.5, 135.7, 135.4 132.3, 132.2, 129.9, 129.3, 128.4, 128.3, 128 .3, 128.2, 128.1, 127.8, 127.7 94.1, 35.1, 34.2, 32.0, 29.9, 29.8, 29.6, 29.2, 22.9, 15.8, 14.3. GPC: M n : 4 ,000 g/mol, M w : 9 8 00 g/mol, PDI: 2.4 TGA: 326 o C (5 % weight loss). DSC: Tg: 3 0 o C UV(DCM) max abs nm: 456, PL(DCM) max emission nm: 527, E HOMO LUMO gap (uV Vis)=2.60eV, E HOMO (DPV)=5.52eV, E HOMO (DPV)=2.92eV.
106 CHAPTER 5 INTRODUCTION OF TRIP TYCENE UNITS INTO THE POLYOLEFIN BACKBONE 5 1 Introductory Remarks The search for elastomers with enhanced mechanical properties ( i.e. high modulus, strength and strain of failure) has involved a consideration of a variety of interaction s between adjacent chains in the polymer. For instance, hydrogen bonding, ionic interactio ns and covalent bonds have been used as chemical and physic al crosslinkers to increase the strength of the interchain interaction s 132 Introduction of a rigid pendant group on the polymer backbone ha s been used to e nhance the polymer properties. For example, the integration of an adamantyl group increase s the glass transition temperature of the polymer, but because of its bulkiness, it reduce s the intermolecular chain entanglements. 133 136 In contrast, the i ntroduction of bulky pendant such as silsesquioxanes POSS, improve s the stiffness of the pol ymer by increasing the intramolecular interactions due to aggregation of the POSS cages. 132, 137 It is usually the case that while increasing the stiffness of the polymer, the ductility decreases Swager and Thomas introduced another concept for intramole cular interactions where t he incorporation of the rigid triptycene units induces mechanical interlocking that minimizes the internal molecular free volume (IMFV) of this unit. 138 The eometry of a 139 As shown in Figure 5 1, t riptycene has a rigid structure compose d of three benzene ring s and is part of the family of iptycenes, all of which have IMFV characteristics. W hen tript ycene is introduced into a polymer, the modulus and ductility are increased even at low temperature ( 30 o C). 132 The explanation of this behavior relies on the threading of the
10 7 polyme r after a mechanical stress is applied Before the polymer is strained so me of the neighboring chains occupy the cavities of the triptycenes to minimize the free energy ar ising from the IMFV (Figure 5 1) Once the material is strained neighboring chains align parallel to each other, threading through the cavity until opposite triptycene units meet and interlock 140 This interlocking increase s the inter molecular interaction s in the polyme r without the loss of ductility, making materials useful in molecular devices such as rachers, gear systems, and propellers. 1 41 142 Figure 5 1. Mechanical interlocking mechanism of triptycene. In order to study the influence of triptycene units o n the mechanical properties of polymers, Swager and Thomas studied a series of triptycene containing polyesters and polycarbonates. 132, 138 In the cas e of polyesters 21 wt% of triptycene was necessary to obtain a successful increment of modulus, strength, and strain to failure while also i ncreasing stiffness and ductility. Authors also found that an aliphatic chain is necessary for success i n the propo sed interlocking mechanism. On the other hand, polycarbonate blended with 8 2 6 wt% triptycene exhibited a significant improvement in the stiffness of
108 the polymer making it competitive with commercial materials for lightweight, and high impact resistance applications. 138 Taking into consideration the properties that triptycene impart s to a polymer, t he present work will focus on the incorporation of tript ycene into the polyolefin backbone. Homopolymerization and copolymerization reactions will be used to m odify the ratio of triptycene in the polymer. 5 2 Results and Discussion 5 2 1 Monomer Synthesis Two different monomers (bridgehead and 1,4 benzene substituted Figure 5 2 ) were synthesized in order to study how the architecture of the triptycene in the po lymer backbone influences the thermal and mechanical properties of the material The bridgehead monomer ( 65 ) and the 1,4 benzene substituted monomer ( 6 7 ) were provided by Dr. Swager at MIT. 143 Monomer s synthesis was carried out taking into consideration the conditions for a successful ADMET polymerization (i.e. sufficient space between the dienes, non protic functionalities, and non bulky olefins). Figure 5 2. Different linkages to the triptycene structure T he synth esis of the brid gehead monomer ( 65 ) is illustrated in the Scheme 5 1. Triptycene diol ( 64 ) was synthesized by the rhodium catalyzed alkyne cyclotrimerization
109 reaction in 75% yield. Further alkylation of ( 64 ) with 11 bromo 1 undecene in the presence of sodium hydride produ ced monomer ( 65 ) in 40% yield 143 Scheme 5 1. Synthesis of b ridg ehead triptycene monomer ( 65 ) Scheme 5 2 shows the synthesis of 1,4 benzene di substituted monomer ( 6 7 ). A lkylation of triptycene hydroquinone ( 6 6 ) by 1 bromo 10 undecene in the presence of s odium hydroxide and sodium sulfoxylate produced monomer ( 67 ) in 81% yield Scheme 5 2 Synthesis of 1 4 benzene substituted triptycene monomer ( 67 ) 5 2 2 Homopolymerization of T riptycene M onomers Having these two monomers, ADMET polymerization s w ere carried out under dynamic vacuum conditions using 1,2 dichlorobenze as solvent at 40 o C, which are the standard conditions for ADMET polymerization of a solid monomer. 21,32 generation catalyst was used since it does not cause isomeriz ation of the terminal olefin of the monomer und er th ese conditions. 125 By a void ing i somerization the triptycene units could be precisely spaced in the polymer and therefore, homopolymers will present 44.7% triptycene in the poly mer backbone. Scheme 5 3 shows the polymerization process es for the b ridgehead triptycene monomer and 1 4 benzene
110 substituted monomer Successful ADMET polymerization was demonstrated by the molecular weight of the polymers found by GPC (Gel P erme ation Chromatography) analysis (M n =49,000 g/mol for bridgehead polymer ( 6 8 ) and M n =44,000 g/mol for the 1,4 benzene substituted analogue ( 70 ) ). Table 5 1 summarize the molecular weights of obtained polymers. Scheme 5 3 ADMET polymerization and hydrogenation of bridgehead and 1 4 benzene substituted triptycene monomer s Metathesis polymerization products ( 6 8 and 70 ) were subsequently hydrogenated w ith Wilkinson catalyst under 400 PSI of hydrogen gas in a Parr Bomb This method because it is highly efficient, and can be performed at any temperature. Spectroscopic characterization demonstrated the compl ete saturation of the materials, and the hydrogenated polymers preserved their molecular weight as it is described in Table 5 1. F ew studies have been performed with the more active Grubbs Hoveyda first generation catalysts ( 5 3 ) for olefin polymerization without isomerization side products. 125 W e attempted ADMET polymerization under the same dynamic conditions using the bridgehead monomer ( 65 ) and the Grubbs Hoveyda first generation catalysts ( 5 ) in order to study its efficiency.
111 Polymer ( 6 8 ) was obtained with number average m olecular weight of 44,000 g/mol (s imilar values to those provided by ( 3 ) The 1 H and 13 C NMR characterization of this polymer also showed exact placement of the aliphatic linkage, which demonstrates that no isomerization was formed. In contrast to previous ly reported investigations on the Grubbs Hoveyda first generation catalyst 147 our results show that this catalyst can be used as an alternative for the synt hesis of precisely functionalized polymers. Table 5 1. Molecular weight summary for triptycene homopolymers Polymer Catalyst M n a. M w a M w / M n a ( KDa ) ( KDa ) Bridgehead homopolymers 68 3 49 .0 91 .0 1.8 69 Wilkinson 42 .0 90 .0 2.1 68 5 44 .0 80 .0 1.8 69 Wilkinson 37 .0 76 .0 2.1 1,4 benzene substituted homopolymers 70 3 44 .0 83 .0 1.9 71 Wilkinson 46 .0 87 .0 1.9 a ) Values obtained by GPC using polystyrene standards in THF at 40 o C 5 2 .3 Spectroscopic and T hermal A nalysis of T riptycene H omopolymers Progress of t he ADMET polymerization was monitored by 1 H NMR spectroscopy because the terminal olefins of the monomer have different chemical shift s than the olefins of the polymer or the hydrogenated analogue. Figure 5 3 A shows the characteristic termina l olefins of the diene monomer ( 65 ) at 5.0 and 5.8 ppm (protons c and d) The distinctive aromatic protons of the triptycene units can be observed at 7.56 and 7.05 ppm, and t he aliphatic spacer linkage can be observed between 4.57 to 1.35 ppm (protons e to f) Figure 5 3 B verifies the metathesis transformation by the disappearance of the terminal olefins and the presence of the
112 internal olefin at 5.4 ppm. Finally, Figure 5 3 C corroborates the quantitative hydrogenation of the polymer backbone, evidenced by complete loss of olefin peaks. Figure 5 3 1 H NMR spectra of bridgehead triptycene derivatives. A ) M onomer ( 65 ). B ) H omopolymer ( 68 C ) H ydrogenated homopolymer ( 69 ). Further verification of the metathesis polymerization and hydrogenation was achieved by 13 C NMR spectroscopy. Figure 5 4 shows the corresponding 13 C NMR spectra of the bridgehead monomer ( 65 ), polymer ( 68 ) and the hydrogenated polymer ( 69 ). The characteristic triptycene aroma tic carbons are observed at 145.0, 125.1 and 121.2 ppm, the characteristic bridge carbon is observed at 85.2 ppm (carbon f), and the aliphatic linkage s are detected between 67.5 to 26.5 ppm. The terminal olefin peak s of monomer ( 65 ) (Figure 5 4 A ) at 139.5 and 114.4 ppm disappear upon polymerization (Figure 5 4 B ), and t wo new internal olefin peaks can be observed at 130.6 and 129.9 ppm, correspond ing to approximately 79% trans and 21 % cis olefins (calculated by the
113 ratio between these two signals) This observation is in agreement with previously reported ADMET polymers where the trans olefin product is favored. 6 Figure 5 4 1 3 C NMR spectra of br idgehead triptycene derivatives. A ) M onomer ( 65 ). B ) H omopolymer ( 68 ). C ) H ydrogenated homopolymer ( 69 ). The 1 H and 13 C NMR spectroscopy were also used for the characterization of the 1,4 benzene substituted polymer analogs Figure 5 5 A displays the 1 H NMR spectr um of the 1,4 substituted triptycene monomer. The characteristics peaks for this series of compoun ds include the aromatic protons at 7.38, 6.96, and 6.47 ppm (carbons a c) and the bridgehead proton at 5.90 ppm (proton d) Aliphatic linkage is observed at the same chemical shift as for the bridgehead substituted analogues ( 65 and 68 ) between 3.91 to 1.24 ppm. In Figure 5 5B t he metathesis transformation is observed by conversion of
114 the terminal olefins at 4.9 and 5.8 ppm to the internal olefin at 5.50 ppm. Complete hydrogenation is verified in Figure 5 5 C which shows no olefin resonances. Figure 5 5 1 H NMR spectra of 1,4 benzene substituted triptycene derivatives. A ) M onomer ( 67 ). B ) H omopolymer ( 70 ). C) H ydrogenated homopolymer ( 71 ). Polymerization and hydrogenation steps were also followed by 13 C NMR spectroscopy of the 1,4 benzene substituted polymer Figure 5 6 exhibited t he characteristic aromatic carbons at 1 48.7, 146.0, 135.9, 125.1, 1 23.9 and 110.9 ppm and the bridgehead carbon at 47.7 ppm. The aliphatic carbons presented the same chemical shift s as the ca rbons in the bridgehead substituted monomer (34.1 to 26.4 ppm). The c omplete conversion from monomer to polymer was verified by the transformation of the terminal olefins at 139.5 and 114.4 ppm to the internal olefins at 130.7 and 130.2. A 76% trans 24% c is olefin ratio was also found in agreement with
115 results for previous ADMET polymers. 6 Upon hydrogenation (Figure 5 6 C ), aliphatic carbons were reduced to four peaks, an the absence of olefin carbons demonstrated the complete saturation of the polymer bac kbone. Figure 5 6. 1 3 C NMR spectra of 1,4 benzene substituted triptycene derivatives. A ) M onomer ( 67 ). B) H omopolymer ( 70 ). C ) H ydrogenated homopolymer ( 71 ). 5.2 4 Thermal Characterization of Triptycene H omopolymers The thermal analysis of the triptycene homopolymers family was performed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Detailed characteristics of thermal transitions for unsaturated and saturated polymers are summarized in Table 5 2. Thermo gravimetric analysis was performed in an inert atmosphere (nitrogen) from 30 to 700 o C. As shown in Figure 5 7, b ridgehead polymer ( 68 ), and its hydrogenated derivative ( 69 ) exhibited high thermal stability (5% weight loss) at 420 and 450 o C,
116 respectively compared with the olefin polyoctenamer (5% weight loss at 409 o C) Further heating of the hydrogenated version resulted in a maximum of weight loss of 20% at 700 o C, indicating remarkabl e stability for the polymer. However, the 1,4 benzene substituted anal og s show lower stability The u nsaturated polymer ( 70 ) degrades at 203 o C, while its hydrogenated derivative ( 71 ) is stable until 390 o C. Further heating of all homopolymers show similar degradation pathway. Comparison of the t hermal stability of the homopolymers indicates that the degradation temperature for the bridgehead polymers is higher than those for 1,4 benzene substituted analogs demonstrating that the polymer architecture affects the decomposition temperature of the polymers Differential sc anning calorimetry was performed to observe the thermal behavior of the bridgehead and 1,4 benzene substituted polymers (Figure 5 8). Table 5 2 shows the thermal data for the saturated and unsaturated triptycene homopolymers. Glass transition temperatures (T g ) were attained at the inflection point of the transition; the melting (T m ) and crystallization (T c ) temperatures were obtained from the peak point of the transition in the second heating cycle. The unsaturated version of the bridgehead triptycene polym er exhibits an amorphous character with a T g of 37 o C. Upon hydrogenation, the aliphatic chains organize, allowing the polymer to show a semicrystalline behavior, with a glass transition temperature at 50 o C and a broad endotherm at 122 o C ( H m =14.7 J/g). We assume the melting character of this endotherm, as an exotherm at 117 o C ( H c =9.4 J/g) is observed upon cooling.
117 Figure 5 7 Thermogravimetric analysis for triptycene homopolymers and polyoctenamer at 20 o C/min in N 2 DSC thermograms for 1,4 benzene substituted polymers ( 70 and 71 ) are illustrated in Figure 5 8, indicating the amorphous character of the polymers with a glass transition temperature of 22 o C. Upon hydrogenation, the glass transition temperature increases to 43 o C, reduced values compare to th ose of the bridgehead polymers ( 68 and 69 ). Comparing the glass transition temperature of triptycene containing polymers with polyoctenamer (T g = 40 o C), it is possible to confi rm that the addition of a rigid structure to th e polymer backbone increases its glass transition temperature. 148
118 Figure 5 8 Differential scanning calorimetry thermograms of bridgehead homopolymers ( 68 and 69 ) and 1,4 benzene substituted homopolymers ( 70 and 71 ) at a heating rate of 10 o C/min. Table 5 2. Thermal analysis of saturated and unsaturated triptycene homopolymers. Polymer TGA ( o C) a DSC T g ( o C) b C p (J/g o C) T m ( o C) c H m (J/g) T c ( o C) c H c (J/g) Bridgehead polymers 68 420 37 3.1 ----69 450 50 2.1 122 14.7 117 9. 4 1,4 benzene substituted polymers 70 203 22 2.8 ----71 390 43 2.6 ----Polyoctenamer 409 30 1.7 61 105 16 69 a ) R ecorded at 5% total mass loss under nitrogen and air gas at 20C/min ; b ) Values taken from the mid point ; c ) Peak maximum peak of the melt transition The triptycene concentration in the polymer backbone (44.7%) systematically decreased with the copolymerization of a metathesis active olefin (i.e. cyclooctene or 1,9 decadi ene) T wo different types of copolymers were synthesized to change the polymer architecture and examine the effect of copolymerization on the threading
119 properties. B lock copolymerization and random copolymerization both using the 1,4 benzene substituted triptycene monomer ( 67 ) were achieved The 1,4 benzene substituted system was selected for the copolymerization, as previous reports demonstrated that the attachment of the polymer chains at the bridgehead position decrease s the IMFV properties. 132 Scheme 5 4. Block copolymerization of 1,4 benzene substituted triptycen e monomer ( 67 ) and cis cyclooctene ( 73 ). 5.2. 5 Bl o c k C o polymerization b etween T riptycene Monomers and C is c yclooctene B lock copolymerization is one of the alternatives to decrease the concentration of triptycene in the polyolefin backbone where the polymers should have different mechanical properties compared to those from random copolymerizations. In this case, t h e block copolymers will contain two phases : the ADMET polymer of the previously synthesized 1,4 benzene substituted triptycene monomer ( 67 ), and the ROMP (ring opening metathesis polymerization) product of cis cyclooctene, which will decrease the concentration of triptycene in the polymer backbone (Scheme 5 4). The ROMP transformation was cho sen for copolymerization of the second block, because of the
120 high reactivity of the monomer and high molecular weight of the resulting polymers. 63 Two different cyclooctene/triptycene molar formulations were attempted: 5 : 5 and 3 : 1 ratio which form polymers with about 37 and 28 wt % triptycene. These conditions were preferred as they provided the best intramolecular interactions for previous reported triptycene containing polymers 138 139 The triptycene monomer was subjected to standard ADMET polymerization under dynamic vacuum cond itions (as used for the homopolymer analogs) for 72 hours In order to veri f y the efficacy of the polymerization, a sample of the polymer was removed before t he addition of the cis cyclooctene, quenched and analyzed by 1 H NMR and GPC. Table 5 3 summarizes the molecular weight data for the first part of the block polymer ( 74a d ) and the AB diblock copolymer. Number average m olecular weights va ry from 12,000 to 47,000 g/mol, indicating successful ADMET polymerization. Subsequent addition of cis cyclooctene ( 73 ) to the system initiated the ROMP transformation After six hours of polymerization, the molecular weight increase d 1. 5 times for the 3: 1 formulation ( 74a ) producing a polymer with 30.4 wt% triptycene However, because the 5: 5 formulation ( 74b ) did not exhibit a considerable molecular weight increment (1.08 fold increment) additional trials were attempted to obtain th is desired formulation. In this way, new copolymers present ed higher molecular weight s (4 1,000 and 69,000 g/mol) with a 1.5 fold m olecular weight increment and with 31.0 and 30.5wt% triptycene in the polymer backbone The copolymer ratio s were analyzed by 1 H NMR spectroscopy (Figure 5 1 2) as the triptycene structure present unequivocal signals that can be corroborated with the new d ouble bond formed afte r the metathesis transformation. A 2.4:1 .0 ratio was
121 obtained for the 3:1 proposed polymer ( 74 a ) due probably to partial reaction between the cyclooctene monomer and the Ru alkylidene polymer (active growing chains) For the 5:5 formulation a 2.26:1 .0 ( 74c ) and 2.3 9 :1 .0 ratio s ( 74 d ) were observed instead of 1:1 indicating the high reactivity of the ROMP chain prop agation. Table 5 3. Molecular wei ght analysis of block copolymer s Polymer Ratio a Ratio by 1 H NMR b Y ield c GPC(homopolymer) ( KDa ) d GPC (copolymer) ( KDa ) d m : n M n M w M w / M n M n M w M w / M n Block copolymers 74a 3:1 2.40:1.0 82 13.1 34.5 2.6 2 8.8 52 .2 1.8 74b 5:5 0.08:1.0 77 11.7 24.1 2.0 13 .4 24 .4 1.8 74c 5:5 2.26:1.0 89 28.1 53.6 1.9 40.8 73 .4 1.8 74d 5:5 2.39:1.0 94 47.3 89.8 1.9 69.6 111 .2 1.6 Random copolymers 75a 3:1 2.60:1.0 73 ---33.5 59.8 1.8 75b 5:5 0.81:1.0 81 ---44.4 77.7 1.8 a) C yclooctene:triptycene molar ratio ; b) Calculated from integrals ratio of a triptycene characteristic proton and the olefin protons; c) Isolated yield after quenching with ethyl vinyl ether and precipitation from methanol; d) V alues r eferred to polystyrene standards in THF at 40 o C The GPC traces of block copolymers were evaluated in order to corroborate the reaction between the homopolymer and cis cyclooctene. As an example, GPC traces of first block ( 72a ) and final diblock copolymer ( 74a ) are shown in Figure 5 9 indicating the expecte d shift in the retention time to higher molecular weight region after addition of the cis cyclooctene. M ulti traces were not observed, confirming the introduction of polyoctenamer in the polymer backbone. The complete series of GPC chromatograms can be fou nd in Appendix B. 5.2.6 Random C opolymerization Another attempt to decrease the concentration of triptycene in the polyolefin backbone was the random copolymerization between the diene triptycene monomer ( 67 ) and 1,9 decadiene ( 10 ), which provides the same number of methylene units as cyclooctene (Scheme 5 5). Previous ADMET random copolymerization have
122 introduced 1,9 decadiene comonomers to decrease the concentration of alkyl branches in the polyolefin backbone. 145 Thus, using pre viously reported methodology, 1,4 benzene substituted triptycene monomer ( 67 ) with 1,9 decadiene ( 10 ) was subjected to standard ADMET polymerization under dynamic vacuum conditions using Grubbs first generation catalyst ( 3 ). To compare the mechanical prope rties, the same 3:1 and 5:5 ratios were attempted, corresponding to 37 and 28wt% triptycene in the polymer backbone. Figure 5 9 GPC traces of the triptycene derivataives. A) H omopolymer (first block 72a ) B) F inal block copolymer ( 74a ) using Grubbs fi rst generation catalyst. Scheme 5 5 ADMET copolymerization of 1,4 benzene substituted triptycene monomer ( 69 ) and 1,9 decadiene ( 10 ). Table 5 3 presents the molecular weight data for these two new copolymers. The triptycene repeat unit concentration in the polyolefin backbone was also studied by 1 H NMR spectroscopy. The observed ratio of the 3:1 preparation was 2.6:1 .0 and for the 5:5 preparation was 0.8 :1.0 demonstrating that by selecting one metathesis
123 transformation the copolymer ratios can be controlled by the stoichiometric addition of the two comonomers. 5.2. 7 Thermal C haracterization of B lock and R andom C opolymers The thermal behavior of the triptycene block and random copolymers w as analyzed by TGA and DSC the rmograms TGA was performed using the same conditions as for the homopolymers ( 68 71 ) and the thermal values are summarized in Table 5 4 Figure 5 10 shows that block copolymers were stable until 420 o C with very similar thermal values between the two block copolymers. These block copolymers also presented higher stability than those of the random copolymers, which started degrading between 350 to 380 o C. By increasing the concentration of triptycene in the polymer backbone the thermal stability of the p olymers is enhancement. For instance the random copolymer ( 75b ) contains 38.6wt% of triptycene and has a decomposition temperature of 380 o C, while its analog ( 75a ) present s 29.6wt% of triptycene and its decomposition temperature starts at 350 o C. Further heating of the copolymers resulted in total weight loss in one pathway Table 5 4 Thermal analysis of triptycene copolymers. Polymer Copolymer ratio a Triptycene % a TGA ( o C) b DSC T g ( o C) c C p (J/g o C) Block copolymers 74a 2.40:1.0 30.4 -32 1.0 74b 0.08:1.0 43.9 -10 0.5 74c 2.26:1.0 31.0 420 16 2.8 74d 2.39:1.0 30.5 421 24 3.7 Random copolymers 75a 2.60:1.0 29.6 350 17 2.5 75b 0.81:1.0 38.6 380 12 3.2 Homopolymer ( 70 ) -44.7 203 22 2.8 Polyoctenamer d ---40 2.3 a). C yclooctene :triptycene 1 H NMR ratio b) wt% triptycene in the polymer b) Values recorded at 5% total mass loss under anhydrous nitrogen and air at 20C/min. c ) Values taken from the mid point of the melt transition. d) Reported thermal data of polyoctenamer. 145
124 Fig ure 5 1 0 Thermogravimetric analysis for random copolymers between 1,4 benzene substituted block copolymers ( 74c d ) and random copolymers ( 75a b ) at 20 o C/min under N 2 Differential scanning calorimetry was performed for the block and random copolymers to compare their glass transition temperatures with those of the homopolymer ( 67 ). Figure 5 11 displays that, upon increase of polyoctenamer by ROMP, the glass transition temperatures of the copolymers decrease (Polyoctenamer Tg= 40 o C) 145, 146 Block copolyme rs present glass transition temperatures well below room temperature ( 16 o C or lower ) influenced by local concentration of polyoctenamer in the block copolymer. The triptycene concentration in the polymer backbone influences the glass transition temperatu re of the polymers, usually an increase on the T g of the polymer is observed Therefore, polymer with 30.5w t % triptycene ( 74d ) present ed a T g of 24 o C, while the 31wt% analog ( 74c ) has a Tg is of 16 o C.
125 Figure 5 11. Differential scanning calorimetry thermograms of Block copolymers ( 74c d ) and random copolymers ( 75a b ) at a heating rate of 10 o C/min. Random copolymers showed similar glass transition temperatures trend s (Figure 5 11) 17 o C for the 29.6wt% triptycene polymer ( 75a ) and 12 o C for the 38.6wt % triptycene polymer ( 75b ) These results indicate that when the polyoctenamer is localized in blocks, the thermal properties of the polymer have more influence from the polyolefin than from the rigid block triptycene. In contrast, when the polymer is rand omly copolymerized, the thermal properties are averages of the two homopolymers 5 2 8 Spectroscopic A nalysis of T riptycene C opolymers In order to calculate the copolymer ratios in the block and random copolymers, 1 H NMR spectroscopy was used, as 1,4 benzene substituted triptycene present unequivocal signals that differ from the po lyolefin backbone For instance, the
126 methylene groups (c), observed at 3.9 ppm in Figure 5 1 2 A can be correlated with the internal olefins (d) of the polymer. Therefore, the homopolymers ( 70 ) contain four methylene groups per two internal olefins, a 4:2 ratio. If the homopolymer is block copolymerize d with cis cyclooctene, any increment of the olefin concentration is indicative of the ratio of polyoctenamer in the polymer backbone. Figure 5 1 2 B shows the 1 H NMR spectrum of the block copolymer of cis cyclooctene and triptycene monomer in a 3:1 calculated ratio. The 4.4:4 .0 experimental ratio founded by 1 H NMR corresponds to a 2.4:1 .0 polyoctenamer:triptycene co polymer ratio Using the same analysis for ADMET random 3:1 copolymer ( Figure 5 1 2 C ), the ratio of 4.6:4 .0 obtained by 1 H NMR corresponds to a 2. 6 :1 .0 incorporation of polyoctenamer with r espect to triptycene. The same 1 H NMR analysis was used to determine the po lyoctenamer:triptycene ratios for random copolymers (Appendix C ) In addition to thermal and spectroscopic analysis of homopolymers and copolymers, the ultimate goal of this project is to study the mechanical properties of triptycene functionalized polyole fins. These studies are ongo ing in the Swager group at MIT. 5 3 Experimental Details 5.3.1 Instrumentation and Analysis The 1 H NMR (300 MHz) and 13 C NMR (75 MHz) spectra were recorded on a Mercury 300 spectrometer, and the 1 H NMR (500 MHz) and 13 C NMR (125 MHz) spectra were obtained on a Varian Associates Innova 500 spectrometer. Chemical shifts for 1 H and 13 C NMR were referenced to residual signals from CDCl 3 ( 1 H = 7.26 ppm and 13 C = 77.00 ppm) with 0.03% v/v TMS as an internal reference. Reactio n conversions and relative purity of crude products were monitored by thin layer
127 chromatography (TLC) performed on EMD silica gel coated (250 m thickness) glass plates and 1 H and 1 3 C NMR. Figure 5 12. 1 H NMR spectra of triptycene copolymers A ) H omopol ymer 70 B ) B lock copolymer 74a C) R andom copolymer 76a in a 3:1 ratio of cyclooctene:triptycene 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 o 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 m g/sample) and were run using an empty pan as a reference. Thermogravimetric analysis (TGA) was performed either on a TA Instruments TGA Q4000 Series using dynamic scans under an inert (nitrogen) atmosphere.
128 Gel permeation chromatography (GPC) was performed at 40 C 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 mob ile phase at a flow rate of 1.0 mL/minute. In jections 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 standards (Polymer Laboratories; Amherst, MA) selected to produce M p and M w values below and above the expected copolymer molecular weight. 5.3.2 Monomer S ynthesis Synthesis of trypticene diol, ( 64 ) 143 Compound 63 (5 g, 19.2 mmol), and [Rh(cod)Cl] 2 (237 mg, 0.48 m mol) were suspended in 150 mL dry toluene under argon. Norbornadiene (8.8 g, 96 mmol) was added and the flask was sealed and heated at 105 C for 20 h. The volatiles were removed in vacuo and the residue was purified by column chromatography (4:1, Hexanes:EtOAc) to give 64 (75%). 1 H NMR (400 MHz, CDCl 3 7.56 (dd, J =5.6, 3.2, 6H), 7.12 (dd, J =5.6, 3.2, 6H), 3.4 (s, 2H). 13 C NMR (125 MHz, CDCl 3 144.7, 125.7, 118.8, 79.6. HRMS (ESI) calcd. for C 20 H 14 O 2 [M+H] 287.1072, found 287.1080. Synthesis of bridgehead monomer, ( 65 ) Compound 64 (4 g, 14 mmol), 11 bromo 1 undecene (25 mL, 107 mmol), and NaH (5 g, 130 mmol) were dissolved in 100 mL of DMF and heated at 70 o C for 15 h. The reaction was cooled to room temperature and partitioned between water and diethyl ether. The a queous phase was extracted with diethyl ether twice more and the combined organic fractions were washed with water, brine, dried over Mg 2 SO 4 and evaporated in vacuo The residue was recrystallized from
129 EtOH twice to give 3 (40%) m.p. 133 134 o C. 1 H NMR (400 MHz, CDCl 3 7.56 (dd, J =5.2, 3.2, 6H), 7.05 (dd, J =5.2, 3.2, 6H), 5.90 5.79 (m, 2H), 5.05 4.99 (m, 2H), 4.97 4.94 (m, 2H), 4.57 (t, J =7, 4H), 2.18 2.05 (m, 8H), 1.67 (m, 4H), 1.52 1.35 (m, 20H). 13 C NMR (125 MHz, CDCl 3 145.0 139.5, 125.1, 121.2, 114.4, 85.2, 67.5, 34.1, 32.0, 29.9, 29.7, 29.4, 29.2, 26.5. HRMS (ESI) calcd. for C 42 H 54 O 2 [M+H] 591.4197, found 591.4179. Synthesis of 1,4 benzene sub stituted monomer, ( 67 ) Compound 66 2 (7 g, 24.5 mmol), Na 2 S 2 O 4 (4.26 g, 24.5 mmol ), Bu 4 NBr (2.37 g, 7.3 mmol), NaOH (12.7 g, 318 mmol), 11 bromo 1 undecene (21 mL, 98 mmol), were dissolved 100 mL THF:H 2 O (1:1) and refluxed 8 h. The reaction was cooled to room temperature and partitioned between water and diethyl ether. The aqueous phas e was extracted with diethyl ether once more and the combined organic fractions were washed with 3M NaOH three times, dried over Mg 2 SO 4 and evaporated in vacuo The residue was dissolved in a minimum amount of dichloromethane and precipitated from EtOH at 0 o C twice to give 67 (94%) m.p. 94 95 o C. 1 H NMR (400 MHz, CDCl 3 7.41 (dd, J =5.2, 3.2, 4H), 6.99 (dd, J =5.2, 3.2, 4H), 6.50 (s, 2H), 5.90 5.79 (m, 2H), 5.89 (s, 2H), 5.06 5.01 (m, 2H), 4.98 4.95 (m, 2H), 3.94 (t, J =6.4, 4H), 2.09 (m, 4H), 1.84 ( m, 4H), 1.55 (m, 4H), 1.50 1.33 (m, 20H). 13 C NMR (125 MHz, CDCl 3 148.7, 146.0, 139.4, 135.9, 125.1, 123.9, 114.4, 110.9, 69.9. 47.7, 34.1, 29.9, 29.7, 29.6, 29.4, 29.2, 26.4. HRMS (ESI) calcd. for C 42 H 54 O 2 [M+Na] 613.4016, found 613.4016. 5.3. 3 Polymer S ynthesis Synthesis of bridgehead homopolymer, ( 68 ) In an S chlenck flask, a saturated solution of monome r in 1,2 dichlorobenzene (50 wt %) was degassed by bubbling a rgon through the solution for three hours. Under strong a rgon flow, 1 mol%
130 generation catalyst was added. The system was then placed under dynamic vacuum at 70 torr absolute pressure via an aspirator attached to one ar m. The reactor was heated to 45 o C and left to stirr for 72 hours. Then ADMET was terminated by dissolving p olymer in a solution of 20 mL chloroform and 2 mL ethyl vinyl ether. The solution was allowed to stir for 3 hours. After that time, polymers were precipitated from methanol, and 500 mg of polymers was obtained. 1 H NMR (500MHz, CDCl 3 7.58 (dd, J = 5.3, 3.2 Hz, 6H), 7.03 (dd, J = 5.3, 3.0 Hz, 6H), 5.52 5.33 (m, 2 H), 4.55 (t, J = 7.0 Hz, 4 H), 2.25 1.92 (m, 8 H), 1.65 (m, 4H), 1.57 1.21 (m, 20 H). 13 C NMR (125 MHz, CDCl 3 145.0, 130.6, 130.1, 125.1, 121.2, 85.2, 67.5, 3 2.9, 29.9, 29.8, 29.5, 26.5. GPC: M n : 49,000 g/mol, M w : 9 1,000 g/mol, PDI: 1.8. TGA: 420 o C (5 % weight loss). DSC: Tg: 37 o C. Synthesis of 1,4 benzene substituted homopolymer, ( 70 ) The same polymerization method described for 68 was used, obtaining 500 mg of polymer 70 1 H NMR (500MHz CDCl 3 7.40 (dd, J = 3.2, 2.0 Hz, 4H), 6.98 (dd, J = 3.3, 1.8 Hz, 4H), 6.49 (s, 2H), 5.89 (s, 2H), 5.50 5.36 (m, 2H), 3.93 (t, J= 3.9, 4H), 2.10 1.95 (m, 4H), 1.84 (m, 4H), 1.55 (m, 4H) 1.50 1.30 (m, 20H).). 13 C NMR (125 MHz, CDCl 3 148.7, 146.1, 135.9, (130.7, 130.2, 125.1, 124.0, 110.9, 69.9, 47.7, 32.9, 30.0, 29.9, 29.8, 29.7, 29.5, 27.5, 26.5. GPC: M n : 44,000 g/mol, M w : 83,000 g/mol, PDI: 1.9. TGA: 150 o C (5 % weight loss). DSC: Tg: 22 o C. Hydrogenated b ridge head homo polymer ( 69 ) In a 125 mL Parr bomb glass sleeve, unsaturated polymer (0.4 00 g) was dissolved in 40 mL degassed toluene. A few milligrams of Wilkinson`s hydrogenation catalyst w ere added, and the bomb was charg ed with 400 psi of hydrogen. The reaction was allowed to proceed for three days
131 at 70 0 C. The polymer solution was concentrated and precipitated in cold methanol to yield 0.350 g of hydrogenated polymer. 1 H NMR (500MHz, CDCl 3 7.59 (dd, J = 5.3, 3.2 Hz, 6H), 7.04 (dd, J = 5.3, 3.2 Hz, 6H), 4.57 (t, J = 6.8 Hz, 4 H), 2.23 2.04 (m, 4H), 1.65 (m, 4H), 1.58 1.18 (m, 22 H). 13 C NMR (125 MHz, CDCl 3 145.0, 125.0, 121.2, 85.2, 67.5, 32.0, 30.0, 29.9, 26.5. GPC: M n : 42,000 g/mol, M w : 9 9,000 g/mol, PDI: 2.1. TGA: 450 o C (5 % weight loss). DSC: Tg: 50 o C, Tm: 122 o 14.7 J/g), Tc: 117 o Hydrogenated 1,4 benzene substituted homopolymer, ( 71 ). The same method as d escribed above for hydrogenated polymer ( 6 9 ) was used, using 0.5 of polymer ( 70 ) Yield: 90% 1 H NMR (500MHz CDCl 3 (s, 2H), 3.95 (s, 4H), 1.85 (s, 2H), 1.56 (s, 2H), 1.33 (m, 14H). 13 C NMR (125 MHz, CDCl 3 151.2, 148.5, 138.5, 138.4, 127.6, 126.4, 113. 4, 72.4, 50.2, 32.5, 32.4, 32.2, 29.0. GPC: M n : 46,000 g/mol, M w : 8 7,000 g/mol, PDI: 1.9. TGA: 390 o C (5 % weight loss). DSC: Tg: 43 o C. Block copolymer in 3:1 ratio, ( 74a ) The same ADMET polymerization method described for 68 was used. Instead of quenching the polymerization with ethyl vinyl ether, a degassed solution cyclooctene in 1,2 dicholorobenzene as added, followed by the addition of Grubbs first generation catalyst. The solution was sealed under argon atmosphere for ab out 48 hours. After this period of time, polymerization was terminated by the addition of degassed ethyl vinyl ether (2 mL), and the solution was allowed to stir for 3 hours. Polymer was then precipitated from cold methanol to yield 500 mg of polymer. 1 H N MR (500 MHz, CDCl 3 7.40 (dd, J =3.30, 1.90 Hz, 4 H) 6.98 (dd, J =3.57, 2.06 Hz, 4 H) 6.49 (s, 2 H) 5.88 (s, 2 H) 5.33 5.49 (m, 7 H) 3.93 (t, J =6.18
132 Hz, 4 H) 1.93 2.13 (m, 14 H) 1.79 1.88 (m, 4 H) 1.50 1.59 (m, 5 H) 1.25 1.47 (m, 41 H). 13 C NMR (126 MHz, CDCl 3 148.6, 146.0, 135.8, 130.7, 130.6, 130.6, 130.5, 130.1, 127.9, 125.1, 123.9, 110.8, 69.9, 47.7, 32.9, 32.8, 30.1, 30.0, 30.0, 29.9, 29.9, 29.8, 29.8, 29.7, 29.7, 29.6, 29.5, 29.4, 29.4, 29.3, 29.2, 27.5, 27.4, 26.5. GPC: M n( 72a ) : 13,100 g/mol, M w( 72a ) : 34,500 g/mol, PDI ( 72a ) : 2.6. M n( 74a ) : 28,800 g/mol, M w( 74a ) : 52,200 g/mol, PDI ( 74a ) : 1.8 B lock copolymer in 5:5 ratio, ( 74b ) The same method as described above for the block copolyme r ( 74a ) was used, in a 5:5 cis cyclooctene:triptycene monomer molar ratio. 1 H NMR (500 MHz, CDCl 3 7.36 (dd, J =3.16, 2.06 Hz, 4 H) 6.95 (dd, J =3.16, 2.20 Hz, 4 H) 6.45 (s, 2 H) 5.85 (s, 2 H) 5.32 5.46 (m, 2 H) 3.89 (t, J =6.45 Hz, 4 H) 1.92 2.09 (m, 4 H) 1.76 1.85 (m, 4 H) 1.46 1.56 (m, 4 H) 1.23 1.44 (m, 22 H) 13 C NMR (126 MHz CDCl 3 148.6, 145.9, 135. 8, 130.5, 130.1, 125.0, 123.8, 110.8, 69.8, 47.6, 32.8, 30.0, 29.9, 29.8, 29.8, 29.7, 29.7, 29.7, 29.6, 29.6, 29.5, 29.4, 29.3, 27.4, 26.4. GPC: M n(11) : 11,700 g/mol, M w(11) : 24,100 g/mol, PDI (11) : 2.1. M n(12) : 13,400 g/mol, M w(12) : 24,400 g/mol, PDI (11) : 1.8 Block copolymer in 5:5 ratio, (74 c ). The same method as described above for the block copolymer ( 74a ) was used, in a 5:5 cis cyclooctene:triptycene monomer molar ratio. 1 H NMR (500 MHz, CDCl 3 7.40 (dd, J =3.29, 2.05Hz, 4 H) 6.94 7.02 (m, 4 H) 6.49 (s, 2 H) 5.88 (s, 2 H) 5.33 5.48 (m, 9 H) 3.93 (t, J =6.10 Hz, 4 H) 1.92 2.12 (m, 18 H) 1.78 1.89 (m, 4 H) 1 .49 1.59 (m, 5 H) 1.23 1.47 (m, 49 H) 13 C NMR (126 MHz, CDCl 3 148.7, 146.05, 135.9, 130.6, 130.1 29.3, 27.5, 26.5, 1.28. M n(72c ) : 28,1 00 g/mol, M w( 72c ) : 53,6 00 g/mol, PDI ( 72c ) : 1.9 M n( 74c ) : 40,8 00 g/mol,
133 M w( 74c ) : 73,4 00 g/mol, PDI ( 74c ) : 1.8 TGA: 420 o C (5 % weight loss). DSC: Tg: 16 o C, C p =2.8 J/g o C. Block copolymer in 5:5 ratio, (74 d ). The same method as described above for the block copolymer ( 74a ) was used, in a 5:5 cis cyclooctene :triptycene monomer molar ratio. 1 H NMR (500 MHz, CDCl 3 7.42 (br. s., 4 H), 7.00 (br. s., 4 H), 6.51 (br. s., 2 H), 5.90 (br. s., 2 H), 5.34 5.53 (m, 7 H), 3.95 (br. s., 4 H), 2.03 (d, J =11.67 Hz, 15 H), 1.85 (br. s., 4 H), 1.57 (d, J =7.14 Hz, 6 H), 1.38 (br. s., 43 H). 13 C NMR (126 MHz, CDCl 3 pp 148.7, 146.1, 135.9, 130.6, 130.1, 127.9, 125.1, 123.9, 110.9, 69.9, 47.7, 32.9, 30.0 29.3, 27.5, 26.5. M n(72d) : 47.300 g/mol, M w(72d) : 89,800 g/mol, PDI (72d) : 1.9. M n(74c) : 69,600 g/mol, M w(74c) : 111,200 g/mol, PDI (74d) : 1.6. TGA: 421 o C (5 % weig ht loss). DSC: Tg: 24 o C, C p =3.7 J/g o C. R andom copolymers in a 3:1 ratio ( 7 5 a ) The same method as described above for ADMET homopolymerization was used, with a degassed solution of 5:5 or 3:1 1,9 decadiene ( 10 ) / triptycene monomer ( 67 ) ratio in 1,2 dichlorobenzene with 1 mol% Grubbs first generation catalyst After 3 days of reaction, polymerization was terminated by the addition of degassed ethyl vinyl ether (2 mL), and the solution was allowed to stir for 3 hours. Polymer was then precipitated from cold methanol to yield 1.0 g of polymer. 1 H NMR (500 MHz, CDCl 3 7.41 (dd, J =3.30, 1.90 Hz, 4 H) 6.99 (dd, J =3.30, 1.80 Hz, 4 H) 6.50 (s, 2 H) 5.89 (s, 2 H) 5.35 5.50 (m, 7 H) 3.94 (t, J =6.31 Hz, 4 H) 1.94 2.12 (m, 16 H) 1.85 (m, 4 H ) 1.51 1.60 (m, 6 H) 1.26 1.48 (m, 42 H) 13 C NMR (126 MHz, CDCl 3 148. 6 145.9, 135. 8 130.5, 130.5 130.0 125.0 123. 9 110. 8 69.8 47.6 32.8, 32. 8 30.0 29.9 29. 9 29.8 29.8 29.7 29.7 29. 7 29.6
134 29.5 29.4, 29.3 29.2 29.2 27. 4 26.4 GPC: M n : 33,500 g/mol, M w : 5 9,800 g/mol, PDI: 1.8. TGA: 409 o C ( 5 % weight loss). DSC: Tg: 17 o C C p =3.2 J/g o C. Random copolymers in a 5:5 ratio, (75b). The same method as described above for ADMET random copolymer ( 7 5a ) was used. 1 H NMR (500 MHz, CDCl 3 7.42 (dd, J =3.30, 1.80 Hz, 4 H) 7.00 (dd, J =3.20, 1.80 Hz, 4 H) 6.50 (s, 2 H) 5.90 (s, 2 H) 5.34 5.52 (m, 4 H) 3.94 (t, J =6.25 Hz, 4 H) 1 .95 2.13 (m, 8 H) 1.79 1.91 (m, 4 H) 1.51 1.62 (m, 6 H) 1.23 1.49 (m, 28 H) 13 C NMR (12 6 MHz, CDCl 3 148.7, 146.1, 135.9, 130.8, 130.7, 130.6, 130.2 130.1, 128.0, 125.1, 124.0, 110.9, 69.9, 47.5, 32.9, 32.9, 30.1, 30.0, 30.0, 29.9, 29.9, 29.8, 29.8, 29.7, 29.6, 29.5, 29.4, 29.3, 27.3, 26.5. GPC: M n : 44,400 g/mol, M w : 77 ,700 g/mol, PDI: 1.8. TGA: 403 o C (5 % weight loss). DSC: Tg: 12 o C, Cp=3.2 J/g o C.
135 CHAPTER 6 CONCLUSIONS Acyclic diene metathesis polymerization has proved one more time to be a successful methodology for the synthesis of functionalized polymers. We had the opportunity to study a different ADMET methodology, the influence of the monomer architecture on the success of the polymerization, and the applica tion of the resulting polymers. The conclusions of these studies have been divided into each individual project. 6.1 S ynthesis and T hermal C rosslinking of C arbosiloxane and O ligo(oxyethylene) P olymers Acyclic diene metathesis polymerization has again proved to be a successful methodology for the synthesis of functionalized polymers. We had the opportunity to study: ADMET polymerization under alternative, solid state conditions, the influence of the mono mer architecture on the success of the polymerization, and the applicability of the resulting polymers. The conclusions of these studies have each been divided into individual projects. 6.2 Carbosiloxane and Oligo(oxyethylene) thermoset polymers ADMET pol ymerization was used for the synthesis of a series of unsaturated telechelic carbosiloxane and oligo(oxyethylene) based telechelic polymers, using silacyclobutane as an end capped thermally induced crosslinker. Subsequent hydrogenation resulted in complete saturation of the polymer backbone without preliminary ring opening of the silacyclobutane. The telechelic polymers demonstrated amorphous behavior, while oligo(oxyethylene) derivatives exhibited semicrystalline properties. Thermal and mechanical properti es analyses were performed on cured materials (where the crosslinking reaction occurred between 160 210 o C). The tensile
136 strength obtained values that were comparable with most of the previously hydrolytically driven chain end cured materials, with the adva ntage that thermally induced crosslinking can be easily controlled and is not affected by the hydrophilicity of the polymer system. The complete series of hydrolytic and thermal crosslinking approaches for carbosilanes and oligo(oxyethylene) based teleche lic polymers suggests an important trend in the work being done. While modulus and percent elongation can be varied depending upon composition and the type of crosslinking (hydrolytic or thermal), there is little improvement in tensile strength observed. W hen internal hydrolytic crosslinking is performed, tensile strength is at a minimum. When internal and chain end hydrolytic crosslinking is done, there is an improvement in thermal crosslinking, but nothing of great significance. When thermal crosslinking is done only on the chain end (the work reported in this manuscript), tensile strengths are about the same. The next step in terms of approaching higher tensile strengths for siloxane based elastomers becomes obvious. The best approach should be to introdu ce thermal crosslinking both internally and at the chain end. If this is done, then we anticipate complete conversion of the silacyclobutane unit both internally as well as at chain ends. We believe these will ultimately lead to the highest tensile stren gth for such polymers, making siloxane based materials competitive with butyl rubber tensile strengths. 6.3 Synthesis of PTVs by Solid State Metathesis Polycondensation Poly(3 dodecyl 2,5 thienylene vinylene) and poly(3 hexyl 2,5 thienylene vinylene) were synthesized by ADMET polymerization under solid state conditions. These two soluble polymers were obtained to demonstrate that polymers prepared by this methodology presented the same spectroscopic, thermal, optical and electrochemical
137 properties as the on es synthesized using ADMET polymerization in high boiling solvents or by cross coupling reactions. There is no question that solid state polymerization creates the same polymer, poly(3 hexyl 2,5 thienylene vinylene), as reported by Hillmyer using conventio nal polymerization procedures. The approach is simple: sprinkle catalyst (2 mol% every three days) on the solid state polymerizing allowing the release of 2 butene, in this c ase. Molecular weights are similar to, and actually slightly larger, than those reported by conventional techniques. This polymerization was chosen to demonstrate the viability of solid state methodology. The real opportunity lies in using solid state pol ymerization techniques to polymerization method (for example, leaving off the C 12 H 25 alkyl branch in the case of thienylene vinylenes). This hypothesis was demonstrated by t he synthesis of a methyl substituted PTV derivative that yielded an insoluble polymer that could not be characterized. The lack of solubility proved that the metathesis reaction took place, demonstrating that solid state metathesis polymerization can be us ed for the direct synthesis of intractable materials. 6.4 Synthesis Of Poly(Naphthalene Vinylenes) In order to synthesize vinyl substituted poly(naphthalene vinylene) systems by ADMET polymerization, a variety of monomer methodo logies were developed. A 1 ,1 vinyl su bstituted naphthalene derivative comprised the first monomer, which was synthesized by a modifie d reported methodology using Pd PEPPSI iPr catalyst. As this monomer contained 1,1 vinyl su bstituted terminal olefins, its ADMET polymerization forms a tetrasubstituted vinyl linkage that requires special metathesis catalysts. The
138 state of the art catalysts for the synthesis of tetrasubstituted olefins were utilized to attempt this transformation. Different temperatures, solvents, and catalyst addition s were employed. However, polymerization did not take place, presumably because of the steric hindrance of the terminal olefins. The next step became clear, the synthesis of a monomer with less bulky olefins. A new naphthalene monomer with extended vinyl l inkage, where the solubilizing hexyl group was placed one carbon away from the active terminal olefin was synthesized by Negishi c ross coupling reaction using Pd PEPPSI iPr catalyst. The successful ADMET polymerization of this monomer was attempted using G rubbs Hoveyda second generation catalyst, obtaining polymers with number average molecular weight of 4,000 g/mol. The optical and electrochemical properties of this new vinyl substituted poly(naphthalene vinylene) systems were also analyzed. Further studie s on different monomer architectures and polymerization with unhindered catalysts are ongoing. 6.5 Introduction of Triptycene Units into the Polyolefin Backbone Triptycene units induce mechanical interlocking properties to a polymer, which increase the pol ymer intermolecular interactions, and therefore enhance the mechanical properties. The introduction of triptycene units into a polyolefin backbone by ADMET polymerization was studied, and its influence on the thermal properties of the polymers was analyzed Incorporation of triptycenes into a polyolefin was achieved by two different triptycene architectures: bridgehead and 1,4 benzene substituted systems. These different architectures comprise an important factor on the thermal behavior of the resulting pol ymers: the bridgehead analog presented higher thermal stability and glass transition temperature than those of 1,4 benzene substituted analog. Triptycene concentration in the polymer backbone was systematically decreased with the
139 copolymerization of an act ive metathesis olefin. Two different copolymers were obtained in order to examine the effect of the copolymer architecture with the mechanical properties of the polymers. Block and random copolymers were obtained from the synthesis of 1,4 benzene substitut ed monomer with cis cyclooctene and 1,9 decadiene, respectively. Copolymers with molar ratios of 3:1 and 5:5 were synthesized in order to study the influence of the triptycene concentration on the thermal and mechanical properties of the polymers. Between copolymers presented higher thermal stability and lower glass transition temperatures than those for random copolymers; between copolymers of the same architecture, the thermal stability and glass transition tempera ture increase as the triptycene concentration increases. The mechanical properties of synthesized triptycene containing polymers are ongoing in the Swager group at MIT.
140 APPENDIX A VOLTAMMOGRAMS Figure A 1 Cyclic voltammogram of P3DDTV drop cast from CHCl 3 solution (2 mg mL 1 ) onto a platinum button electrode (0.02 cm 2 ) in 0.1 M TBAPF6/ACN supporting electrolyte using a scan rate of 50 mV/s. Figure A 2. Differential pulse voltammogram of P3DDTV drop cast from CHCl 3 solution (2 mg mL 1) onto pl atinum button electrode (0.02 cm2) in 0.1 M TBAPF6/ACN supporting electrolyte using a step time of 0.03 s, a step size of 2 mV, and an amplitude of 100 mV.
141 Figure A 3. Cyclic voltammogram of P3HTV drop cast from CHCl 3 solution (2 mg mL 1 ) onto platinum b utton electrode (0.02 cm 2 ) in 0.1 M TBAPF 6 /ACN supporting electrolyte using a scan rate of 50 mV/s. Figure A 4 Differential pulse voltammogram of P3HTV drop cast from CHCl 3 solution (2 mg mL 1 ) onto platinum button electrode (0.02 cm 2 ) in 0.1 M TBAPF 6 /A CN supporting electrolyte using a step time of 0.03 s, a step size of 2 mV, and an amplitude of 100 mV.
142 APPENDIX B GPC TRACES Figure B 1 GPC Traces of the first block of the block copolymers and the final diblock copolymers in THF a) First block ( 72a ) and copolymer ( 74a ); b) First block ( 72b ) and copolymer ( 74b ); c) First block ( 72c ) and copolymer ( 74c ); d) First block ( 72d ) and copolymer ( 74d ).
143 APPENDIX C THE 1 H NMR SPECTRA OF TRIPTYCENE COPOLYMERS Figure C 1 1 H NMR spectra. a) homopolymer 70 b ) block copolymer 74a c) random copolymer 76 d in a 5:5 ratio of cyclooctene:triptycene
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152 BIOGRAPHICAL SKETCH Paula Andrea Delgado Saldarriaga was born in 1983 to Jose Alonso Delgado and Piedad Zolanye Saldarriaga, in Palmira, Colombia, being the second kid of the family. After graduation from high school in 2000, Paula was accepted to study chemistry in Universid ad del Valle, Cali, Colombia, the third most important university in Colombia, in which Paula earned scholarship for outstanding academic records during the entire the synthesis of heterocyclic compounds. After one year of research, Paula defended her thesis titled: Synthesis of novel 1,7 Dihydro 6 H pyrazolo[3,4 b ][1,3]thiazolo[5,4 e ]pyridin 6 thiones and evaluation as antifungal and anticancer agents. After the presenta tion, Paula was awarded for her meritorious research work. In September of 2005, s he graduated with honors as best graduating candidate in chemistry major. In the summer of 2006, Paula left Colombia and attended graduate school at the University of Florida under the direction of Professor Kenneth B. Wagener. During her graduate career, s he worked in the synthesis of telechelic siloxane/oligo(oxyethylene) polymers, the synthesis of poly(ethylenene vinylenes) under solid state conditions, and in the synthesis functionalized olefins by ADMET polymerization. She got married in December of 2008 in Colombia to Henry Martinez Gonzalez, who met while she was doing the undergraduate studies in Colombia