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ADMET Linear-Low Density Polyethylene

Permanent Link: http://ufdc.ufl.edu/UFE0022675/00001

Material Information

Title: ADMET Linear-Low Density Polyethylene Synthesis, Characterization and Thermal Behavior of Precisely and Irregularly Sequenced Copolymers
Physical Description: 1 online resource (197 p.)
Language: english
Creator: Rojas, Giovanni
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: acyclic, admet, decyanation, polyethylene, polymerization, polyolefin
Chemistry -- Dissertations, Academic -- UF
Genre: Chemistry thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Step-growth acyclic diene metathesis (ADMET) polymerization chemistry followed by exhaustive hydrogenation offers a new alternative in modeling ethylene/alpha-olefin copolymers. In contrast to chain-growth chemistry, this new approach produces well-defined, defect-free primary structures. This dissertation describes the synthesis, characterization and thermal behavior of ADMET-produced polyethylene materials containing either precisely or irregularly spaced alkyl branches, the latter to serve as models for ethylene/alpha-olefin copolymers made via chain-growth chemistry. The thermal behavior of the new materials was studied using differential scanning calorimetry, and detailed NMR and IR analyses permitted the characterization of the primary structures. Controlling the comonomer content allowed formation of polymers with a wide range of thermal properties, from semicrystalline to fully amorphous. This research explores a two step universal synthesis for ADMET monomers, which is described as a synthetic pathway that produces alkylcyano alpha,omega-dienes in quantitative yields. The chemistry is based on simple ?,?-dialkenylation of primary nitriles. Optimization leads to essentially quantitative conversions for every substrate/example reported, which will prove useful in many synthetic schemes. Decyanation chemistry for the synthesis of pure alkyl alpha,omega-dienes in quantitative yields is here presented. Deuteration labeling and structural mechanistic investigations were completed to decipher this chemistry. Deuterium labeling experiments reveal the precise nature of this radical decyanation chemistry, where an alcohol plays the role of hydrogen donor. The correct molecular design to avoid competing intramolecular cyclization, and the necessary reaction conditions to avoid olefin isomerization during the decyanation process are reported herein. Polymerization followed by exhaustive hydrogenation renders ADMET linear low density polyethylene model materials. Here it is investigated the effect of incorporating butyl branches along the polyethylene backbone, focusing on the synthesis, characterization and thermal behavior of ADMET-produced polyethylene materials containing either precisely or irregularly spaced butyl branches, the latter to serve as models for ethylene/1-hexene copolymers made via chain-growth chemistry. By keeping the branch-to-branch distance constant while the branch identity is changed, a better understanding of the effect of linear and non-linear bulkier short-chain branching along the polyethylene chain is studied. Different linear (methyl to hexyl) and non-linear bulkier branches (iso-propyl, tert-butyl, and cyclohexyl) were synthesized using the chemistry developed during this work. Detailed NMR, IR and DSC analyses reveled that the presence of small linear branches (methyl and ethyl) produces organized structures with very different melting temperatures and degrees of crystallinity, while linear and non-linear bulkier branches (propyl to hexyl, iso-propyl, tert-butyl, and cyclohexyl) are less organized and have similar melting temperatures and degrees of crystallinity.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Giovanni Rojas.
Thesis: Thesis (Ph.D.)--University of Florida, 2008.
Local: Adviser: Wagener, Kenneth B.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2009-02-28

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0022675:00001

Permanent Link: http://ufdc.ufl.edu/UFE0022675/00001

Material Information

Title: ADMET Linear-Low Density Polyethylene Synthesis, Characterization and Thermal Behavior of Precisely and Irregularly Sequenced Copolymers
Physical Description: 1 online resource (197 p.)
Language: english
Creator: Rojas, Giovanni
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: acyclic, admet, decyanation, polyethylene, polymerization, polyolefin
Chemistry -- Dissertations, Academic -- UF
Genre: Chemistry thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Step-growth acyclic diene metathesis (ADMET) polymerization chemistry followed by exhaustive hydrogenation offers a new alternative in modeling ethylene/alpha-olefin copolymers. In contrast to chain-growth chemistry, this new approach produces well-defined, defect-free primary structures. This dissertation describes the synthesis, characterization and thermal behavior of ADMET-produced polyethylene materials containing either precisely or irregularly spaced alkyl branches, the latter to serve as models for ethylene/alpha-olefin copolymers made via chain-growth chemistry. The thermal behavior of the new materials was studied using differential scanning calorimetry, and detailed NMR and IR analyses permitted the characterization of the primary structures. Controlling the comonomer content allowed formation of polymers with a wide range of thermal properties, from semicrystalline to fully amorphous. This research explores a two step universal synthesis for ADMET monomers, which is described as a synthetic pathway that produces alkylcyano alpha,omega-dienes in quantitative yields. The chemistry is based on simple ?,?-dialkenylation of primary nitriles. Optimization leads to essentially quantitative conversions for every substrate/example reported, which will prove useful in many synthetic schemes. Decyanation chemistry for the synthesis of pure alkyl alpha,omega-dienes in quantitative yields is here presented. Deuteration labeling and structural mechanistic investigations were completed to decipher this chemistry. Deuterium labeling experiments reveal the precise nature of this radical decyanation chemistry, where an alcohol plays the role of hydrogen donor. The correct molecular design to avoid competing intramolecular cyclization, and the necessary reaction conditions to avoid olefin isomerization during the decyanation process are reported herein. Polymerization followed by exhaustive hydrogenation renders ADMET linear low density polyethylene model materials. Here it is investigated the effect of incorporating butyl branches along the polyethylene backbone, focusing on the synthesis, characterization and thermal behavior of ADMET-produced polyethylene materials containing either precisely or irregularly spaced butyl branches, the latter to serve as models for ethylene/1-hexene copolymers made via chain-growth chemistry. By keeping the branch-to-branch distance constant while the branch identity is changed, a better understanding of the effect of linear and non-linear bulkier short-chain branching along the polyethylene chain is studied. Different linear (methyl to hexyl) and non-linear bulkier branches (iso-propyl, tert-butyl, and cyclohexyl) were synthesized using the chemistry developed during this work. Detailed NMR, IR and DSC analyses reveled that the presence of small linear branches (methyl and ethyl) produces organized structures with very different melting temperatures and degrees of crystallinity, while linear and non-linear bulkier branches (propyl to hexyl, iso-propyl, tert-butyl, and cyclohexyl) are less organized and have similar melting temperatures and degrees of crystallinity.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Giovanni Rojas.
Thesis: Thesis (Ph.D.)--University of Florida, 2008.
Local: Adviser: Wagener, Kenneth B.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2009-02-28

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0022675:00001


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1 ADMET LINEAR-LOW DENSITY POLYETHYLENE: SYNTHESIS, CHARACTERIZATION AND THERMAL BEHAVIOR OF PRECISELY AND IRREGULARLY SEQUENCED COPOLYMERS By GIOVANNI ROJAS A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2008

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2 2008 Giovanni Rojas

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3 To my lovely wife, son, and Mom

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4 ACKNOWLEDGMENTS I would like to acknowledge my wife, Yeneir e Orozco; my incredible son, Sebastian Rojas; my mother, Miriam Jimenez, and my fa ther, Armando Rojas for the endless love and support during all these years of academic career. I also acknow ledge Professor Fabio Zuluaga from Universidad del Valle for hi s guidance, support, and friendship that finally developed into a Ph.D degree. During my time at the University of Florida, I have had the privilege of working on the Butler Polymer Floor, Center for M acromolecular Science & Engineering among scientists, faculty, high caliber visitor professors and exceptional students that have made my time in Florida unforgettable. I thank Prof essors George Butler, Ken Wagener and John Reynolds for the creation and development of the Po lymer Program at the University of Florida, place that enriches education and creates highly competent scientists I also thank Sara Klossner, Lorraine Williams, Lori Clark, and Professor Benjamin Smith for their work in the administration and managing of the Polymer Fl oor and Chemistry Graduate School. Also I would like to express my gratitude to all the agencies that contri buted with financ ial support that made possible this research, the National Scie nce Foundation, the Army Research Office, Dr. Lisa S. Baugh at ExxonMobil Research and Engi neering Company, and Mr. Yuki Iseki at the Petrochemicals Research Laborator y, Sumitomo Chemical Company. In addition to all agencies, I thank the Polymer Floor for thei r facilities for the opportunity of being part of the Polymer Program Family, as well as University of Florid a for allowing me to enjoy the experience of being a Teaching Assistant during a few years of school. In fact, the teaching experience was grateful and full of joy, allowing me to be an educator in both classr ooms and laboratory. Such experience permitted me to work very closel y with Mr. Wei Li, a wonderful undergraduate student who acquired incredible skills in laborato ry that led him to gra duate school in Pharmacy. There are some colleagues that I must acknowle dge for the time we spent talking chemistry,

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5 eating breakfast, lunch and dinner, and enjoying free time. I am in debt with Dr. John Sworen and Dr. Travis W. Baughman for teaching me how to work in an organic laboratory synthesizing several compounds and mainly for teaching me how to solve real problems in lab. Dr. Piotr Matloka for being my lab mate sitting next to me for about 4 years, thanks to him Poland and Europe is one place where I would like to spend some time. I would like to extend my special thanks to Dr. Ryan M. Walczak for being kind a nd patience, and also for sharing some of his coffee during our long conversations about chemistr y, politics, religion, family and other topics. I would like to express my grat itude to both Mr. James Leonard, and Dr. Erik Berda for sharing their beds during our business trips to Pasa dena CA, Atlanta GA, Kingsport TN, and New Orleans LA., and for the unforgettable time we spen t together walking the streets and drinking a few beers during conferences. During conferences and daily bases, I had the opportunity to know better some of the Wagener and Reynolds past a nd present members, people who left a sense of friendship in my heart, people like Kathryn Opper, Yuying Wei, Bob Brookings, Tim Steckler, Emine Boz, Fernando Gomez, Dr. Violeta Petk ovska, Dr. Florence Courchay, Dr. Garrett Oakley, Dr. Timothy Hopkins, Dr Stephen E. Lehman, Dr. Jason Smith, Dr. Jim Pawlow, Frank A. Arroyave, Pierre Beaujuge, JJ Cowart, Jiangu o Mei, Dr. Aubrey Dyer, Dr. Stefan Ellinger and Professor Dr. Mark Watson. And last but no t least, I thank all members of LEI 322 and 314 laboratories.

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6 TABLE OF CONTENTS page ACKNOWLEDGMENTS...............................................................................................................4 LIST OF TABLES................................................................................................................. ..........8 LIST OF FIGURES................................................................................................................ .........9 LIST OF SPECTRAL DATA BY COMPOUND.........................................................................12 ABSTRACT....................................................................................................................... ............16 CHAPTER 1 PRECISION POLYOLEFIN STRUCT URE: MODELING POLYETHYLENE CONTAINING ALKYL BRANCHES..................................................................................18 Introduction................................................................................................................... ..........18 Linear ADMET Polyethylene.................................................................................................21 Models of Ethylene/ -Propylene Copolymers.......................................................................23 Irregularly Placed Methyl Branches................................................................................30 Precise Models of Ethylene/ -Olefin Copolymers.................................................................33 Polyethylene Containing Geminal Dimethyl Branches...................................................33 Polyethylene Containing Ethyl Branches........................................................................36 Polyethylene Containing Hexyl Branches.......................................................................40 Conclusions.................................................................................................................... .........43 2 QUANTITATIVE -ALKYLATION OF PRIMARY NITRILES........................................44 Introduction................................................................................................................... ..........44 Results and Discussion......................................................................................................... ..44 Conclusions.................................................................................................................... .........47 Experimental................................................................................................................... ........48 3 AVOIDING OLEFIN ISOMERIZAT ION DURING DE CYANATION OF ALKYLCYANO -DIENES: A DEUTERIUM LABELING AND STRUCTURAL STUDY OF MECHANISM...................................................................................................53 Introduction................................................................................................................... ..........53 Results and Discussion......................................................................................................... ..53 Synthetic Approach to Alkyl -Dienes Via Decyanation Chemistry..........................53 Deuterium Labeling and Mechanistic Considerations....................................................60 Conclusions.................................................................................................................... .........67 Experimental Section........................................................................................................... ...67

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7 4 PRECISELY AND IRREGULARLY SEQUENCED ETHYLENE/1-HEXENE COPOLYMERS: A SYNTHESI S AND THERMAL STUDY..............................................78 Introduction................................................................................................................... ..........78 Results and Discussion......................................................................................................... ..80 Polyethylene Models with Precisely Placed Butyl Branches..........................................80 Monomer synthesis and ADMET polymeri zation of precisely sequenced EH copolymers............................................................................................................80 Structural data for precisel y sequenced EH copolymers..........................................85 Thermal behavior for precisel y sequenced EH Copolymers....................................91 Polyethylene Models with Irregularly Placed Butyl Branches........................................96 Monomer Synthesis and ADMET polymeri zation of Irregularly Sequenced EH Copolymers...........................................................................................................97 Structural Data for Irregula rly Sequenced EH Copolymers.....................................99 Thermal Behavior for Irregularly Sequenced EH Copolymers..............................104 Conclusions.................................................................................................................... .......108 Experimental Section........................................................................................................... .108 5 LINEAR-LOW DENSITY POLYETHYLENE CONTAINING PRECISELY PLACED LINEAR AND NON-LINEAR BULKIER BRANCHES....................................................120 Introduction................................................................................................................... ........120 Results and Discussion.........................................................................................................122 Monomer Synthesis and ADMET Polyme rization of Precisely Sequenced Ethylene/ -olefin Copolymers...................................................................................122 Structural Data for Precisely Sequenced Ethylene/ -Olefin Copolymers.....................124 Thermal Behavior for Precisely Sequenced Ethylene/ -Olefin Copolymers................133 Conclusions.................................................................................................................... .......136 Experimental Section........................................................................................................... .137 APENDIX The 1H AND 13C NUCLEAR MAGNETIC RESO NANCE SPECTRA FOR SELECTED INTERMEDIATES AND TARGET MATERIALS.......................................146 Compounds Described in Chapter 2.....................................................................................146 Compounds Described in Chapter 3.....................................................................................150 Compounds Described in Chapter 4.....................................................................................156 Compounds Described in Chapter 5.....................................................................................168 LIST OF REFERENCES......................................................................................................186 BIOGRAPHICAL SKETCH................................................................................................197

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8 LIST OF TABLES Table page 1-1. Effect of molecular weight on thermal behavior in linear ADMET PE............................22 1-2. Precise short chain branch distribu tion and its effect on thermal behavior.......................26 1-3. Effect of increasing branch content on thermal behavior and crystallinity in random EP copolymers.................................................................................................................. .31 1-4. Thermal transitions of the ADMET gem -dimethyl branched and methyl branched model polyethylenes..........................................................................................................34 1-5. Thermal transitions of the ADMET ethyl branched model polyethylenes........................36 2-1. Different reaction conditions for alkenylation of hexanenitrile.........................................45 2-2. Dialkylation of primary nitriles in presence of LDA.........................................................46 3-1. Different decyanation systems for the reduction of 1d to 12-butyltricosa-1,22-diene......56 3-3. Decyanation of 1a in presence of deuterated compounds..................................................61 4-1 Molecular weights for ADMET models............................................................................85 4-2. Molecular weights for unsaturated and saturated EH i rregularly sequenced copolymers prepared by ADMET......................................................................................99 5-1. Molecular weights and thermal da ta for precisely sequenced ethylene/ -olefin copolymers..................................................................................................................... ..124

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9 LIST OF FIGURES Figure page 1-1. The ADMET reaction....................................................................................................... .20 1-2. The ADMET polymerization of 1,9-decadiene followed by hydrogenation.....................22 1-3. Synthesis of diverse methyl monomers.............................................................................24 1-4. General synthetic scheme for synt hesis of symmetrical methyl-branched polyethylene models by ADMET......................................................................................24 1-5. General synthetic scheme for shor t ethylene run length monomers for ADMET.............25 1-6. Synthesis of EP7 copolymer..............................................................................................26 1-7. Differential scanning calorimetry cu rves for EP9, EP15 and EP21 copolymers...............27 1-8. Differential scanning calori metry curves of EP5 and EP7................................................29 1-9. Synthesis of irregular placed methyl branching PE copolymers by varying diene comonomer ratios...............................................................................................................30 1-10. Differential scanning calorimetry curves of precise sequenced EP and irregularly sequenced EP polymers having similar branch content.....................................................32 1-11. Synthesis of symmetrical gemdimethyl substituted -diene monomers and their ADMET polymers.............................................................................................................34 1-12. Differential scanning calo rimetry curves of precise gemdimethyl polyethylene. EIB9, EIB15, and EIB21...................................................................................................35 1-13. Ethyl branched monomer synthe sis via alkylation of acetoacetate...................................37 1-14. Synthetic pathway to ethyl branched monomers via mal onate modification....................37 1-15. Comparison of EP9, EIB 9, EB9, and EO9 DSC traces.....................................................38 1-16. Differential scanning calorime try curves of EB9, EB15 and EB21..................................39 1-17. Synthesis of symmetrical hexyl substituted -diene monomers and their ADMET polymers....................................................................................................................... ......41 1-18. Differential scanning calorimetry curves of EO9, EO15 and EO21 copolymers obtained via ADMET.........................................................................................................42 2-1. Dialkenylation of hexane nitrile in presence of base..........................................................45

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10 2-2. Formation an internal olefin initiated by olefin isomerization..........................................47 3-1. Synthesis of alkyl -dienes.............................................................................................54 3-2. Synthesis of 12-butyltricosa-1,22-diene............................................................................55 3-3. Proposed mechanism for the olefin isomeri zation via formation of an allylic radical......57 3-4. Expanded 1H NMR spectrum of 12-butyltricosa-1,22diene at three different degrees of olefin isomerization.......................................................................................................58 3-5. Decyanation of (1a) in presence of deuterated tert -butanol...............................................60 3-6. Deuterium NMR of 12-d12-Methyl-tricosa-1,22-diene...................................................61 3-7. Comparison of 13C NMR for 12-methyltricosa-1 ,22-diene and 12-d-12-Methyltricosa-1,22-diene............................................................................................................. ..62 3-8. Comparison of 1H NMR for methyl resonances of 12-d-12-Methyl-tricosa-1,22-diene and 12-methyltricosa-1,22-diene.......................................................................................63 3-9. Decyanation of 2-alkyl-2 -pent-4-enyl-hept-6-enenitrile....................................................65 3-10. Decyanation of alkenylnitriles.......................................................................................... .66 3-11 Proposed mechanism for the reductive elimination of nitrile............................................67 4-1. Retrosynthesis of precisely se quenced ethylene/1-hexene copolymer..............................80 4-3. Synthesis of EH15 and EH21 vi a ADMET polymerization-hydrogenation......................82 4-4. Synthesis of EH5 via ADMET polymerization-hydrogenation.........................................84 4-5. Comparison of 1H NMR spectra for a typical ADMET polymerization transformation EH5............................................................................................................87 4-6. Comparison of 13C NMR spectra for a typical ADMET polymerization transformation EH5............................................................................................................88 4-7. Infrared spectra for the ADMET unsa turated and saturated polymers EH5 .....................89 4-8. Infrared spectra for the ADMET sa turated polymers EH5, EH15, and EH21..................91 4-9 Differential scanning calorimetry cu rves for ADMET polymers: EH5, EH15, and EH21........................................................................................................................... .......92 4-10 Differential scanning calorimetry cu rves for ADMET polymers possessing alkyl branches on every 21st carbon............................................................................................93

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11 4-11 Differential scanning calorimetry cu rves for ADMET polymers possessing alkyl branches on every 15th carbon...........................................................................................95 4-12 Differential scanning calorimetry cu rves for ADMET polymers possessing alkyl branches on every 5th carbon.............................................................................................96 4-13 Synthesis of EH random materi als by ADMET copolymerization of 9butylheptadeca-1,16-diene and 1,9-decadiene...................................................................97 4-14 Comparison of 13C NMR spectra for non-branched irregularly sequenced, and precisely sequenced ADMET polymer............................................................................100 4-15. Infrared spectra for the irregul arly placed ADMET copolymers EH0-EH43.5...............102 4-16. Differential scanning calorimetry cu rves for ADMET polymers: EH0, EH-2.5, EH6.0, and EH-11.5..............................................................................................................105 4-17 Differential scanning calorimetry curv es for ADMET polymers: EH-21.3, EH-37.0, and EH-43.5.................................................................................................................... .106 4-18 Differential scanning calorimetry curves for precisely sequenced ADMET copolymer EH21 and irregularly se quenced EH-43.5 ADMET copolymer....................107 5-1. Synthesis of 12-alkyltricosa-1,22-dienes.........................................................................122 5-2. Synthesis of precisely sequenced ethylene/ -olefin copolymers.....................................123 5-3. Comparison of 1H NMR spectra for a typical ADMET polymerization transformation ENH21.....................................................................................................128 5-4. Comparison of 13C NMR spectra for a typical ADMET polymerization transformation ENH21.....................................................................................................129 5-5. Comparison of 13C NMR spectra for a typical ADMET polymerization transformation posesing bulkier branches.......................................................................130 5-6. Infrared spectra for the ADMET satura ted polymers posesing bulkier branches............132 5-7. Differential scanning calorimetry cu rves for ADMET polymers possessing linear branches....................................................................................................................... ....133 5-8. Differential scanning calorimetry cu rves for ADMET polymers possessing bulkier branches....................................................................................................................... ....135

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12 LIST OF SPECTRAL DATA BY COMPOUND Data page NC 9 92-Methyl-2-(undec-10-enyl )tridec-12-enenitrile....................................................146 NC 9 9 2-Ethyl-2-(undec-10-enyl)t ridec-12-enenitrile......................................................147 NC 9 9 2-butyl-2-(undec-10-enyl)t ridec-12-enenitrile.......................................................148 NC 9 9 2-Hexyl-2-(undec-10-enyl)t ridec-12-enenitrile...............................................149 9 9 12-Methyltricosa-1,22-diene...................................................................................150 9 9 12-Ethyltricosa-1,22-diene......................................................................................151 9 9 12-Propyltricosa-1,22-diene...................................................................................152 9 9 12-Butyltricosa-1,22-diene......................................................................................153 9 9 12-Pentyltricosa-1,22-diene.................................................................................154 9 9 12-Hexyltricosa-1,22-diene..............................................................................155 6 6 9-butylheptadeca-1,16-diene................................................................................156

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13 CN CN 2,7-diallyl-2,7-dibutyl octanedinitrile.....................................................157 5,10-diallyltetradecane............................................................................158 n EH5u......................................................................................................159 4 n EH5............................................................................................................................ .160 6 6 n EH15u...................................................................................................................161 14 n EH15........................................................................................................................... .162 9 9 n EH21u.................................................................................................................163 20 n EH21........................................................................................................................... .164 n EH0u............................................................................................................165 6 n EH0...........................................................................................................................166 86 8 xy n EH-43.5.......................................................................................................167

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14 CN 3,3-dimethylbutanenitrile..............................................................................................168 CN 2-cyclohexylacetonitrile.............................................................................................169 NC 9 9 2-isopropyl-2-(undec-10-enyl )tridec-12-enenitrile................................................170 NC 9 9 2-tert-butyl-2-(undec-10-e nyl)tridec-12-enenitrile................................................171 NC 9 9 2-cyclohexyl-2-(undec-10-e nyl)tridec-12-enenitrile..............................................172 9 9 12-isopropyltricosa-1,22-diene..............................................................................173 9 9 12-tert-butyltricosa-1,22-diene...............................................................................174 9 9 tricosa-1,22-dien-12-ylcyclohexane.......................................................................175 9 9 n EPent21u.............................................................................................................176 20 n EPent21.......................................................................................................................177 9 9 n EHept21u.............................................................................................................178 20 n EHept21.....................................................................................................................179

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15 9 9 n E3MB21u............................................................................................................180 20 n E3MB21......................................................................................................................181 9 9 n ENH21u...............................................................................................................182 20 n ENH21.........................................................................................................................183 9 9 n EVCH21u............................................................................................................184 20 n EVCH21......................................................................................................................185

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16 Abstract of Dissertation Pres ented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy ADMET LINEAR-LOW DENSITY POLYETHYLENE: SYNTHESIS, CHARACTERIZATION AND THERMAL BEHAVIOR OF PRECISELY AND IRREGULARLY SEQUENCED COPOLYMERS By Giovanni Rojas August 2008 Chair: Kenneth B. Wagener Major: Chemistry Step-growth acyclic diene metathesis (ADMET) polymerization chemistry followed by exhaustive hydrogenation offers a new alternative in modeling ethylene/ -olefin copolymers. In contrast to chain-growth chemistry, this ne w approach produces well-defined, defect-free primary structures. This dissert ation describes the synthesis, characterization and thermal behavior of ADMET-produced polyet hylene materials containing eith er precisely or irregularly spaced alkyl branches, the latter to serve as models for ethylene/ -olefin copolymers made via chain-growth chemistry. The thermal behavior of the new materials was studied using differential scanning calorimetry, and detailed NMR and IR analyses permitted the characterization of the primary structures. Controlling the comonomer content allowed formation of polymers with a wide range of thermal propert ies, from semicrystalline to fully amorphous. This research explores a two step univers al synthesis for ADMET monomers, which is described as a synthetic path way that produces alkylcyano -dienes in quantitative yields. The chemistry is based on simple -dialkenylation of primary nitriles. Optimization leads to essentially quantitative conversions for ever y substrate/example reported, which will prove useful in many synthetic schemes.

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17 Decyanation chemistry for the synthesis of pure alkyl -dienes in quantitative yields is here presented. Deuteration labeli ng and structural mechanistic inve stigations were completed to decipher this chemistry. Deuterium labeling experime nts reveal the precise na ture of this radical decyanation chemistry, where an alcohol play s the role of hydrogen donor. The correct molecular design to avoid competing intramol ecular cyclization, and the necessary reaction conditions to avoid olefin isomerization during the decyanation process are reported herein. Polymerization followed by exhaustive hydr ogenation renders ADMET linear low density polyethylene model materials. Here it is investigat ed the effect of incorporating butyl branches along the polyethylene backbone, focusing on th e synthesis, characterization and thermal behavior of ADMET-produced polyet hylene materials containing eith er precisely or irregularly spaced butyl branches, the latter to serve as m odels for ethylene/1-hexene copolymers made via chain-growth chemistry. By keeping the branch-to-branch distance consta nt while the branch id entity is changed, a better understanding of the effect of linear and no n-linear bulkier short-ch ain branching along the polyethylene chain is studied. Di fferent linear (methyl to hexyl) and non-linear bu lkier branches ( iso -propyl, tert -butyl, and cyclohexyl) were synthesized using the chemistry developed during this work. Detailed NMR, IR and DSC analyses reveled that the presence of small linear branches (methyl and ethyl) produces organize d structures with very different melting temperatures and degrees of crystallinity, while li near and non-linear bulkie r branches (propyl to hexyl, iso -propyl, tert -butyl, and cyclohexyl) are less or ganized and have similar melting temperatures and degrees of crystallinity.

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18 CHAPTER 1 PRECISION POLYOLEFIN STRUCTURE: MODELING POLYETHYLENE CONTAINING ALKYL BRANCHES 1.1 Introduction Polyethylene (PE) is the largest volume pol ymer produced worldwide with an annual demand of over 60 million tons.1, 2 An average growth rate of 5.2% in terms of demandproduction during this decade is expected.3 Oligomers of PE were firs t observed in 1898 by Hans von Pechmann, Eugen Bamberger and Friedrich Ts chirner by accident during high pressure experiments with diazomethane.4 In 1933, Imperial Chemical Industries (ICI) reported the existence of high molecular weight polyethylene and in 1937 ICI obtained the patent for its commercial production.5 A significant contribution to polymer chemistr y was made in the 1950s by Karl Ziegler, where he synthesized high density polyethylene (HDPE) at low pr essure and temperature using a heterogeneous titanium catalyst. Inspired by Zieg lers work, in 1954 Giulio Natta applied this technology to synthesize polypropylene. Ziegler a nd Natta jointly received the Nobel Prize in chemistry for polymerization and the development of these catalysts, which today bear their names.6, 7 Polymerization of ethylene using Ziegler6-11 and homogenous metallocene-based catalysts12, 13 produces highly crystalline (62-80%) materi als. The degree of crystallinity can be controlled by the copolymerization of ethylene with -olefins; linear-low density polyethylene (LLDPE) is the result. The incorporation of th e comonomer, typically 1-propene, 1-butene, 1hexene, or 1-octene, produces long run lengths of unbranched linear polyethylene with random branched regions. These branched polyethyle nes are known for their enhanced mechanical properties and industrial importance. Diverse type s of materials can be obtained by controlling the mode of polymerization, catalyst nature, pressure and temperature.8, 11-25

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19 The physical properties of PE obtained via -olefin copolymerization depend on the branch content, which is directly related to the amount of comonomer incorporated into the polyethylene backbone. For LLDPE, the physical properties ca n vary depending on the molecular weight, molecular weight distribution, branch identity, branch content and branch distribution. Control over LLDPE physical properties can be achieve d using diverse methods based on choice of catalyst, initiator, comonomer, as well as types of temperature and pressure.18-20, 25-30 Commercial LLDPE is usually prepared by chain-growth polymeri zation using ZieglerNatta or metallocene chemistry. Because of multisite initiation on the heterogeneous catalyst, Ziegler systems produce primary structures with low-molecular weights and broad molecularweight distributions. By compar ison, metallocenes, which are singl e-site homogeneous catalysts, provide LLDPEs with narrower molecular weight distributions and higher levels of comonomer incorporation. Both types of cat alyst have the disadvantage of generating random errors in the main backbone, causing defects or heterogeneity in the primary structure; the problem is less severe in the case of metallocene-based PE. Th e frequency of appearance of these defects along the main chain is widely used to manipulate the product to obtain material s with desired physical properties. Studies of model branched PEs can lead to a better unde rstanding of polymer processing and the overall microstructural effects produced by branch perturbations on PE-based materials.17, 31, 32 Chain transfer and/or chain walking can occu r if the PE is prepared by free-radical, Ziegler-Natta or metallocene chemistry,17, 22, 23, 33 and attempts to produce model materials with well-defined primary structures have failed using these methods.20, 25, 28, 34-36 As a result, most of the PE research has focused on the study of shor t chain branching (SCB) and short chain branch distribution (SCBD).2, 17, 19, 20, 25, 28-32, 34-40

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20 Model systems are often employed to study the behavior of these commercial materials. Many of the methods available i nvolve chain propagation chemistr y which are still subjected to the incorporation of unwanted defects via head-to-head or tail-to-tail monomer coupling.41-45 The problems associated with chain-growth polym erization can be overcome using step-growth condensation polymerization. The step-growth acyclic diene metathesis (ADMET) process produces model polyolefins with well-defined primary structures, since the chemistry is controlled by the nature of the monomer rather than the catalyst or comonomer incorporation. Catalyzed copolymerization of ethylene with -olefins produces ill-defined primary structures; use of a single symmetric monomer in an ADMET polymerization produces PE with a precisely known primary structure.46-50 Consequently ADMET polymeri zation chemistry followed by exhaustive hydrogenation offers a new approach to the synthesis of PE backbones either without branches47 or with specific branches preci sely placed along the main backbone.48, 49 While these are not models for industrial ethylene copolymers in the true sense of the wo rd, they represent an excellent starting point for the study of stru cture property in ethyl ene-based materials by isolating the effects of specific structural features. These polymer s can be seen as benchmarks for industrial copolymers with similar composition. R R n catalyst + n C2H4 123 Figure 1-1. The ADMET reaction ADMET chemistry is illustrated in Figure 11. The driving force of this step-growth polycondensation is the removal of the condensate ethylene, a ccomplished by applying vacuum

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21 under normal polymerization conditions between 25 and 55 C. As is shown in Figure 1-1, an unsaturated polymer is formed and subsequent h ydrogenation produces saturated PE models with well-defined primary structures.48-53 Polyethylene with methyl, gemdimethyl, ethyl and hexyl branches have been synthesized, and their ther mal behavior, among other parameters, is being used to model the properties of ethylene/1-pr opene, ethylene/isobutylene, ethylene/1-butene and ethylene/1-octene random copolym ers obtained via typical chain polymerization methods. Below is a review of the synthesis and thermal behavior of a series of model linear and branched PEs, as well as random ethylene/1-propene c opolymers made via the ADMET approach.47-50, 53, 54 1.2 Linear ADMET Polyethylene Synthesis of high-molecular-weight linear PE without undesired defects is important for studies of crystallization behavior.20 Previous studies of such macromolecules have been limited to large n -paraffins (monodisperse ethylene ol igomers) up to 390 carbons in length.37, 55 These models have perfect primary stru ctures, but the presence of a hi gh molar concentration of methyl endgroups leads to inexact results when morphol ogical behavior is ex trapolated to highmolecular-weight systems, because these end groups impede crystallization. Such extrapolations can be useful in studying primary struct ure, but the results can be ambiguous.1, 37-39 On the other hand, ADMET polymerization yields defect-free linear PE of molecular weight up to Mn ~ 15,000 g/mol and a most probable molecular weight distribution ( Mw ~ 30,000 g/mol) by bulk polymerization of 1,9-decadiene in the presence of Grubbs or Schrocks catalyst, as shown in Figure 1-2. The resulti ng polyoctanemer is exhaustively hydrogenated to produce completely saturated PE. The ADMET method also allows control of the PE molecular weight by regulating the reaction time, te mperature, and monomer/catalyst ratio.

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22 n catalyst 6 6 Exhaustive hydrogenation Ru PCy3 PCy3 Cl Cl Mo N i-Pr F3C F3C F3C F3C O O Ph Schrock's catalystFirst generation Grubbs catalyst i-Pr 4 5 6 7 8 n Figure 1-2. ADMET polymerization of 1,9-decadiene followed by hydrogenation Table 1-1 shows the melting temperatures and enthalpies for ADMET PEs of varying number-average molecular weights determined by differential scanning calorimetry (DSC). All of these samples, including those with low-molecu lar-weights, show sharp Tms at temperatures above 130 C, even with molecula r weight values as low as Mn = 2400 g/mol. Based on these results, the thermal behavior of lower molecula r weight ADMET PE are cons istent with that of conventional HDPE.47, 51, 52 Table 1-1. Effect of mol ecular weight on thermal behavior in linear ADMET PE Mn (g/mol) Polydispersity Index (PDI) Tm (C) (peak) hm (J/g) 2400 2.4 130.7 252 7600 2.4 131.3 213 11000 1.9 132.0 221 15000 2.6 133.9 204 HDPE 3.1 134.0 210

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23 1.3 Models of Ethylene/ -Propylene Copolymers Methyl branched ADMET polymers model a large family of statistically random ethylene/ -olefin copolymers.1, 29, 51 For example polypropylene (PP) is crystalline material when the tacticity of the pendant methyl group is high ly regular, but it is completely amorphous when the methyl groups are randomly or iented, as in atactic PP. Betw een the extremes of amorphous PP and defect-free polyethylene lie EP copolymer s where the defect is always a methyl group. By varying the number and placement of the incor porated methyl defects, the response of the final material can be significantly altered. Although numerous methods are available for pr oducing such systems, only those modeled by ADMET have controlled comonomer content and distribution, there by leading to fewer ambiguities relative to other model systems when relating structure on the molecular level to macroscopic properties. Precisely sequen ced EP copolymers can be obtained via ADMET polymerization of a symmetrical -diene monomer bearing a pendant methyl group, followed by exhaustive saturation. It is important to note that all polymers obtained by this methodology are atactic with respect to the relative stereo chemistry of the alkyl branch. These models are named according to the frequency of the pendant defect. For example EP9 refers to polyethylene containing a methyl branch on every ninth carbon; EP15 has a methyl branch on every fifteenth carbon, etc. The -diene monomers were first prepar ed by alkylating ethyl acetoacetate.48, 51 Figure 1-3 shows the synthetic scheme employe d for preparation of diverse methyl -diene monomers. First, alkylation of ethyl acet oacetate with alkenyl bromide produces a -alkenylketoester, which is then deacy lated via a retro-Claisen condensation. The resulting ester is reduced to a primary alcohol, tosylated, followe d by displacement with hydride, producing the required methyl branched diene monomer 14a-e

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24 OEt O O 1) 2) Br n t-BuOK COOEt H3COC nn NaOEt nn EtOH COOEt LAH Et2O nn OH TsCl, pyr CHCl3 nn OTs LAH Et2O nn CH3 n Compound 3 14a 4 14b 6 14c 8 14d 9 14e 910 11 13 14a-e 12 Figure 1-3. Synthesis of diverse methyl monomers n Compound 3 EP9 4 EP11 6 EP15 8 EP19 9 EP21 n n CH3 n n CH3 x catalyst n H2C=CH2 2n+2 CH3 x Exhaustive hydrogenation 14a-e 15 EP9-EP21, 16a-e Schrock's Figure 1-4. General synthetic scheme for s ynthesis of symmetrical methyl-branched polyethylene models by ADMET Polymerization of methyl -diene monomers 14a-e is carried out with Schrocks catalyst (Figure 1-4). The resultant unsaturated ADMET polymer is then exhaustively hydrogenated

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25 yielding ADMET PE with methyl groups precisely placed along the PE backbone. This strategy has been used to synthesize a pool of ADMET PE materials containing me thyl groups on every 9th, 11th, 15th, 19th, or 21st carbon ( EP9 trough EP21 ).48 Because ring closing metathesis is observed if the reaction is carried out with 1,6heptadiene-based struct ures, synthesis of EP copolymers with higher dens ity of precisely placed CH3 side groups requires a different approach, where polymerization of monomers c ontaining two methyl gr oups on each monomeric unit is effective. Figure 1-5 shows the scheme s for synthesizing ADM ET monomers containing two methyl groups placed 7 ( 23 ) and 5 ( 26 ) carbons apart.56 OEt EtO O O NaH, THF Br Br O O O O OEt EtO OEt EtO NaOH EtOH/H2O LAH THF O O OEt EtO OEt EtO O O EtOOC COOEt OEt EtO O O Br NaH, THF NaH, THF Br Br Decalin O O OH HO OH HO O O COOH COOH HO OH 1) MsCl, pyr 2) LAH, THF 1718 19 20 21 2223 24 25 26 Figure 1-5. General synthetic scheme for s hort ethylene run length monomers for ADMET Both schemes are based on diethyl malona te chemistry. Dialkylation of either 1,6dibromohexane or 1,4-dibromobutane with diethyl al kenyl malonate yields a tetraester diene,

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26 which is converted to the respective tetraaci d diene after saponification and decarboxylation. Reduction to the diol is achieved with lithium aluminum hydride. Subsequent double-mesylation of the respective diol followed by reductive cleavage with hydrid e yields the desired monomer 23 or 26 .56 Schrock's [Mo] catalyst 10-3 torr n n Exhaustive Hydrogenation 23 EP7u, 27 EP7, 28 Figure 1-6. Synthesis of EP7 copolymer Polymerization of monomers 23 and 26 is carried out in the bul k with Schrocks catalyst under high vacuum, as is shown in Figure 1-6 for EP7 High molecular weight unsaturated polymers EP5u Mn = 26000 g/mol and EP7u Mn = 12700 g/mol were isolated, and exhaustive hydrogenation yielded EP5 and EP7 respectively. Table 1-2. Precise short chain branch distri bution and its effect on thermal behavior ADMET PE Methyl branches per 1000 carbon atoms Tm (C) (peak) hm (J/g) Mn (g/mol) EP5 200 Amorphous 28400 EP7 143 60 19 12900 EP9 111 -14 28 17500 EP11 91 11 66 8500 EP15 67 39 82 17100 EP19 53 57 96 17400 EP19 53 57 84 72000 EP21 48 62 103 20200 Linear ADMET PE 0 134 204 15000

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27 Table 1-2 presents thermal an alysis data for ADMET polymers EP5 to EP21 The effects of branch distribution are obvious. The peak melting temperatures and heats of fusion of ADMET EPs increase as the branch content decreas es, a clear indication of increasing crystalline content.48, 51 Due to the highly organized primary mi crostructure, these precise models are semicrystalline even at branch contents high enough to render random EP copolymers completely amorphous. Only when methyl groups are placed every 5th carbons do these precise ADMET EP copolymers lose the ability to crystallize. Semicrystalline polymers EP9 to EP21 show sharp and well-defined endothermic transitions, as shown in Figure 1-7.29 In contrast EP copolymer s obtained via Ziegler-Natta polymerization exhibit a broad and indistinct melting behavior wh en the percentage of propylene incorporated in the fina l material exceeds 15%.57, 58 Figure 1-7. Differential scanni ng calorimetry curves for EP9 EP15 and EP21 copolymers. Data taken from Wagener et al .48

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28 It is also interesting to compare the DS C data for ADMET EPs with the results for ADMET PE, where Tm = 134 C and hm = 204 J/g are significantly higher than Tm and hm for any of the EP products. The data in Table 1-2 sh ow that the amorphous contribution can be tuned by the frequency of the methyl branches pr oducing totally amorphous or semicrystalline materials. Two versions of ADMET EP19 copolymers were prepared w ith significantly different number average molecular weights, Mn =17400 and Mn = 72000 g/mol to investigate the effect of molecular weight. A sharp melting endotherm of 57 C is observed for both polymers, indicating that a number average molecular weight of approximately 17400 is sufficient for the thermal comparison of this model with commercial EP copolymers.48, 55, 59 EP21 and EP15 polymers have been characterized further by x-ray diffraction, wide-angle x-ray diffraction (WAXD) and small-angle x-ra y scattering (SAXS) as well as transmission electron microscopy (TEM), and Raman spectrosc opy to further understand their structure and morphology.60 According to the TEM results, the lamellar thickness far exceeds the inter-branch distance along the backbone, indica ting that the methyl group is incl uded within the crystal. This finding was verified by crystallography, which shows th at the chains pack in to a triclinic lattice that allows inclusion of methyl branches as la ttice defects. Further, the methylene sequences between defects participat e in a hexagonal sublattice. In order for the chains to pack in this way, the defects must all be contai ned within planes oblique to the chain stems, leading to conformationally distorted crystals. This is more prevalent in the case of EP15 than in EP21 due to the greater defect content, a result conf irmed by Raman spectroscopy, as well as the melting temperature data in Table 1-2. Scatte ring and DSC experiments performed on EP21 led to the same conclusion.61 The defects are concentrat ed in planes between stacks of hexagonally packed

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29 methylene sequences; the unit cell which houses th e defected planes and hexagonal sublattice is described as monoclinic, rather than triclinic.61 Figure 1-8. Differential scanni ng calorimetry curves of EP5 and EP7 Data taken from Wagener et al .56 Additional differential scanni ng calorimetry studies of EP5 and EP7 copolymers illustrate the effects of the short run length on thermal behavior, as is shown in Figure 1-8. ADMET EP copolymers from EP9 to EP21 exhibit semicrystalline behavior, EP5 exhibits fully amorphous behavior. While a glass transition temperature for semicrystalline ADMET EP9 to EP21 copolymers is observed at 43 C,48 EP5 shows a Tg at -65 C, 20 C lower. The dramatic shift to a lower temperature of the observed Tg is attributed to the high me thyl branch density. Similar effects have been observed in random EP copolymers when the propylene content exceeds 50 wt%.21 However, when propylene content exceeds 84 wt%, the polymer exhibits residual

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30 crystallinity resembling homopolypropylene, and the material can be classified as ethylene-poor ethylene/propylene copolymer.21, 56 Copolymer EP5 is the first example of fully amorphous materials within the family of sequenced EP copolymers. 1.3.1 Irregularly Placed Methyl Branches Copolymers with irregularly placed met hyl branches can be synthesized by copolymerization of ADMET EP mo nomers with an unbranched -diene. For example, copolymerization of a methyl-substituted -diene with 1,9-decadiene, followed by exhaustive hydrogenation, yields ADMET EP copolymers with irregular branch placement.50 Figure 1-9 shows six copolymers, which model thei r industrial EP copolymer analogs. CH3 33 + 6 CH3 33 6 xy -C2H4Exhaustive Hydrogenation 5 CH3 3 x y n n 14a (mol %) 29 (mol %) 2 5 10 20 40 50 98 95 90 80 60 50 8 14a 29 30a-f 31a-f [Mo] 40-50 oC 96 hours Figure 1-9. Synthesis of irregular placed met hyl branching PE copolymers by varying diene comonomer ratios The melting temperatures for irregularly placed methyl branches EP copolymers follow a pattern similar to that of commercial materials obtained via chain propagation chemistry. As the

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31 methyl branch content increases, the peak me lting, percent crystallinit y, and heat of fusion decrease. (Table 1-3).50 Table 1-3. Effect of increasing branch content on thermal behavior and crystallinity in random EP copolymers Polymer Methyl branches per 1000 carbon atoms Tm (C) (peak) hm (J/g) % Crystallinity Linear ADMET PE 0 134.0 230.0 78.5 31a 1.5 129.0 207.6 71.3 31b 7.1 123.2 183.4 62.1 31c 13.6 119.0 165.8 56.3 31d 25.0 111.6 137.3 47.6 31e 43.3 80.7 87.0 29.6 31f 55.6 52.1 85.0 29.0 Polymers with the highest amount of propylen e incorporation (43.3 a nd 55.6 branches per 1000 carbons) show broad and indistinct DSC prof iles as do commercial materials. However, lowering the amount of propylene results in shar p and well-defined endotherms similar to those obtained for precisely sequenced EP copolymers. Figure 1-10 shows the DSC thermograms for two polymers with 45 methyl branches per 1000 carbons.50, 51 The top trace, co rresponding to the polymer with equally spaced methyl groups, has a sharp well-defined endotherm, this is in contrast with the thermogram of the irregula rly sequenced analog, which shows a broad and illdefined melting transition. The difference in thermal behavior may be attributed to microstructural characterist ics of the two polymers.

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32 Figure 1-10. Differential scanning calorimetry curves of precise sequenced EP (top) and irregularly sequenced EP (bottom) polymers having similar branch content. Data taken from Wagener et al .48, 50 The polymer with precise branch spacing has a unique lamellar thickness and a sharp welldefined endotherm. The irregular branch spacin g system exhibits broad thermal response and a lower heat of fusion due to the variable lame llar thickness imparted by uneven ethylene run length. These facts illustrate th e effect of irregular and unifo rm SCBD on EP copolymers. ADMET has proven to impart control over the bran ch content, and more importantly, branch regularity, allowing formation of model polymers which cannot be made in any EP copolymerization via conventional chain-growth chemistry.50-52

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33 1.4 Precise Models of Ethylene/ -Olefin Copolymers Polyethylene with precisely pla ced alkyl branches larger th an methyl groups have also been prepared via ADMET, where such material s are models for copolymers of ethylene and olefins larger than propylene. ADM ET models with precisely placed gem -dimethyl, ethyl, and hexyl branches have been examined to furt her understand the morphology of these precise materials and to investigate the size limit for inclusion of defects within the crystal. 1.4.1 Polyethylene Containing Ge minal Dimethyl Branches Polyethylene containing gemdimethyl branches can be regarded as an ethylene/isobutylene (EIB) copolym er. While these structures have proven to be elusive via chain propagation techniques due to the vas tly differing reactivities of the comonomers,62 EIB models have been prepared in high yields via ADMET polymerization.53 Figure 1-11 illustrates the chemistry us ed to synthesize three symmetrical gemdimethyl substituted -diene monomers. Sequential addition of tw o equivalents of an alkenyl bromide to ethyl propionoate using lithium diisopropyl amide (LDA) to form the enolate intermediate, leads to the carboxylic acid intermediate 33 Reduction with LiAlH4 generates the alcohol 34 which is converted to the tosylate 35 Finally, the tosylate is reduced with LiAlH4 to give the symmetrical gemdimethyl substituted -diene 36 Polymerization of gemdimethyl -diene monomers is carried out with Schrocks cat alyst. The resulting unsatur ated ADMET polymer is then exhaustively hydrogenated yieldi ng EIB models of polyethylene with geminal dimethyl groups precisely placed on every 9th, 15th and 21st carbon.53

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34 OEt O 1) 2) Br n 3eq LDA COOH nn LiAlH4 nn Ether Pyridine LiAlH4Ether nn OH TsCl n C o m p o u n d 3 EIB9 6 EIB15 9 EIB21 n n x catalyst n H2C=CH2 2n+2 x Exaustive hydrogenation 32 33 34a-c 35a-c 36a-c 37a-c 38a-c nn OTs Figure 1-11. Synthesis of symmetrical gemdimethyl substituted -diene monomers and their ADMET polymers Precision gemdimethyl ADMET EIBs serve as models to show the effect of increasing steric bulk. The DSC data for EIB9 EIB15 and EIB21 are presented in Figure 1-12 and Table 1-4. These results can be compared to the data for EP9 EP15 and EP21 in Figure 1-7 and Table 1-2. In the case of EIB9 the addition of the second methyl group disrupts the polymers ability to pack into crystals resulting in a totally amorphous material, compared to semicrystalline EP9 Extending the inter-defect sequence length to 14 or 20 carbons renders the polymer semicrystalline, with depressed melting temp erature when compared to the analogous EP models. Table 1-4. Thermal transitions of the ADMET gem -dimethyl branched and methyl branched model polyethylenes. Branches per 1000 carbon gem -dimethyl polymer Tm (C) Tg (C) Methyl polymer Tm (C) Tg (C) 111 EIB9 Amorphous-47 EP9 -14 -44 67 EIB15 32 -42 EP15 39 48 EIB21 45 -22 EP21 62 -43

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35 Figure 1-12. Differential scanning calorimetry curves of precise gemdimethyl polyethylene. EIB9 (top), EIB15 (center) and EIB21 (bottom). Data taken from Wagener et al .53 Interestingly, the difference between the Tms for EIB15 and EP15 is only 7 C, compared to a 17 C decrease between EP21 and EIB21 Extensive DSC studies on this polymer have revealed that much of this behavior is depende nt on thermal history. The rather broad hysteresis between the melting and crystallizat ion transitions suggests that th ese polymers crystallize fairly slowly. This possibility is supported by the nding that the samples undergo a cold crystallization.53 Wide angle x-ray diffr action (WAXD) studies show reflections associated with hexagonal, monoclinic, and triclinic packin g, pointing towards polymorphism as a possible cause of this complex behavior. The melting beha vior was found to be very similar with the melting of a 20 carbon n -paraffin, suggesting that cr ystallization behavior of EIB21 is strongly related to the branch to branch distance.61

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36 1.4.2 Polyethylene Containing Ethyl Branches Copolymers of ethylene with 1-butene are obtained industr ially by copolymerization via Ziegler-Natta and metallocene chemistry.17, 31, 32 While many studies deal with modification of the catalyst and optimization of the reactions conditions, precise models of LLDPE are more important for understanding the morphology a nd thermal behavior of these materials.20, 25, 28, 30, 34-36, 40 Inspired by the success in modeling EP a nd EIB copolymers via ADMET polymerization, we have synthesized ethylene/1-butene (EB) copolymers featuring precisely placed ethyl branches, thus extending behavioral studies moving from two single-carbon defects (EIB copolymers) to a single two-carbon defect (EB co polymers). Multiple synthetic procedures were attempted in order to obtain perfectly spaced et hyl-branched LLDPE materials. The first strategy to produce ethyl-branched -diene monomers was based on al kenylation of ethyl acetoacetate, as shown in Figure 1-13. However, pr oblems during reduction of tosylate 42 impeded the application of this methodology to longer chain lengths. The prefe rred approach for synthesizing monomers with longer spacers between ethyl groups is shown in Figure 1-14. Diethyl malonate is alkenylated in the presence of sodium hydride to give diester 45 Saponification of compound 45 followed by decarboxylation, reduction, and bromination yields bromo alkyl -diene 48 A single carbon homologation is th en achieved by addition of CO2 to the respective Grignard of 50 .49, 51 Using this scheme, monomers with n = 3, 6, and 9 were produced. Table 1-5. Thermal transitions of the ADM ET ethyl branched model polyethylenes. Ethyl Branches per 1000 carbon Ethyl polymer Tm (C) Tg (C) 111 EB9 Amorphus -76 67 EB15 -33 & -6 NA 48 EB21 35 NA

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37 OEt O O O O OEt 33 33 33 33 33 1.) 2.) Br 3 LiCl DMSO / H2O LiAlH4Et2O TsCl, pyr CHCl3 33 + t-BuO-K+ O OH OTs 939 40 41 42 43 44a Super Hydride 1M Li(Et)3BH, THF Figure 1-13. Ethyl branched monomer synt hesis via alkylation of acetoacetate O O OEt O O OEt nn HO O nn nn nn 1.) 2.) Br n NaOH THF/EtOH Decalin 1.) LAH/ THF 1.) Mg/THF EtO EtO OH O 2.) CBr4/PPh3CH2Cl22.) Solid CO21.) LAH/ THF 2.) CBr4/PPh3CH2Cl2 nn 1.) Mg/THF 2.) H2O/H+NaH 17 45a-c COOH Br nn COOH nn Br 46a-c 47a-c 48a-c 49a-c 50a-c 44a-c n = 3, 6, 9 Figure 1-14. Synthetic pathway to ethyl bran ched monomers via malonate modification The thermal data for EB copolymers are presented in Table 1-5. Similar to EP copolymers, precisely sequenced EB copolymers show an in crease peak melting temperature, enthalpy, and

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38 crystallinity with increasing run length. Like EP copolymers, SCB influences the thermal behavior of ADMET EB copolymers, but the final physical propert ies seem to depend mostly on the identity of the branch.49 Figure 1-15 shows the DSC therm ograms for the polymers with a variety of branch types, in all case s with the branch occurring on every 9th carbon. Polyethylene with a methyl branch on every 9th carbon ( EP9 ) shows a peak melt at 14 C, while the ethyl branch version ( EB9 ) is fully amorphous with only a glass transition temperature of 76 C and no apparent melting behavior. The on ly viable explanation for this change in thermal behavior is the difference in branch size. In the case of EP9 the pendant methyl branches are too small to inhibit crystallization.48-51, 60 On the other hand, the ethyl branches on EB9 are large enough to completely prevent crystalliza tion. An increment of one carbon un it in the branch length results in a significant change in the thermal behavior. Figure 1-15. Comparison of EP9 EIB9 EB9 and EO9 DSC traces. Data taken from Wagener et al .48, 49, 53, 54

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39 Similar to EP copolymers, crystal formation a nd crystallization kinetics of EB copolymers is directly affected by the branch spacing, as is shown in Figure 116. Increasing the spacing from every 9th carbon to every 21st carbon results in a change from fully amorphous EB9 to semicrystalline EB21 However, EB15 produces a bimodal profile w ith a melting temperature of -33 C and -6 C, unlike the corresponding polymer with methyl branches on every 15th carbon ( EP15 shown in Figure 1-7), which s hows only a single melting endotherm. Figure 1-16. Differential sca nning calorimetry curves of EB9 EB15 and EB21. Data taken from Wagener et al .49

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40 WAXD investigations as well as extensive DS C analysis explain this behavior. Like EIB21 the melting behavior of EB21 can be correlated to that of eicosane, indicating a high dependence on the branch to branch distance. Th e WAXD results show some lattice expansion implying the partial inclusion of ethyl groups into th e crystal, but to a much lesser extent than in EP21 This suggests that polymorphism resulting fr om inclusion and exclusion of the ethyl defect may be responsible for these observations. Comparing the WAXD results for EIB21 and EB21 suggests that much of the melting behavior is attributed to crystallization of methylene sequences between defects. The inclusion of th ese crystallized segments into higher melting crystals results in bimodal thermal behavior in both cases. Regardless of whether the branch is included or excluded from the crystal, there is a very obvious effect of the increased volume requirements resulting from add ition of a single methylene group.60, 61 1.4.3 Polyethylene Containing Hexyl Branches ADMET can also be used to prepare polymers w ith precisely placed branches longer than two carbons. Figure 1-17 shows the scheme for su ch polymers containing hexyl branches, which serve as models for ethylene/1-o ctene (EO) copolymers; in fact the method can be applied to alkyl branches of any length. Ini tial steps to prepare carboxylic acid 47 are explained above in relation to Figure 1-14. The acid is reduced to the primary alcohol and directly converted to the sulfonic acid ester 52 using mesyl chloride. A modified Gr ignard/Gilman reaction was developed for insertion of a branch functionality of any length to form symmetrical -diene monomers, as shown in Figure 1-17 for a hexyl substituent.

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41 Decalin OOH n n 180 oC OH n n LiAlH4THF O EtO O OEt O EtO O OEt nn 1) NaH, THF 1) KOH/EtOH O HO O OH nn 2) HCl / H2O Br n 2) OMs nn nn CuBr:S(CH3)2LiBr, LiSPh Mg/THF CH3(CH2)4Br n = 3, 6, 9 MsCl Et3N CHCl3 ADMET nn x Pd(C), H2 1000psi Toluene 2n+2 x n C o m p o u n d 3 EO9 6 EO15 9 EO21 17 45a-c 46a-c 47a-c 51a-c 52a-c 53a-c 54a-c 55a-c Figure 1-17. Synthesis of sy mmetrical hexyl substituted -diene monomers and their ADMET polymers Thermograms for EO model polymers are shown in Figure 1-18. The trends are similar to those observed for the families discussed above. The melting temperatures and heat of fusion decrease with increasing branch content. EO9 is totally amorphous, which is no surprise considering that the ethyl branch is able to comp letely disrupt crystallinity at the same branch concentration. A semicrystalline morphology is observed for EO15 which is quite surprising since all other known EO copolymers with similar branch content are amorphous.63 Semicrystalline behavior is also noted for EO21 where the low melting temperature is indicative of small crystallites. In terestingly, the h eat of fusion of EO21 (53 J/g) is similar to that

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42 of EB21 (57 J/g). This observation is unexpected c onsidering the notable d ecrease in heat of fusion from EP21 (103 J/g) to EIB21 (61 J/g) and EB21 (57 J/g). The melting profile of the EO21 closely mimics that of EP21 rather than either EIB21 or EB21 This implies a uniform crystal structure for EO21 rather than the apparent polymorphism displayed by EIB21 and EB21 One possible explanation is that the hexyl branch is large enough to be completely excluded from the crystal, with the result th at the observed behavior is due solely to crystallization of interdefect methylene units. An other possible explanation is that the branch is included to give a single crys talline form as seen in EP21 Figure 1-18. Differential sca nning calorimetry curves of EO9 EO15 and EO21 copolymers obtained via ADMET. Data taken from Wagener et al .54

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43 1.5 Conclusions Acyclic diene metathesis polymerization is us eful in modeling precisely and irregularly sequenced ethylene/ -olefin copolymers. Considering the results for the entire precise alkyl branch ADMET family, it is clear that both defect placement and identity have a defin itive effect on the overall properties of the resulting polymers. Small alkyl branches are includ ed within the crystal la ttice. The limits have been delineated regarding the amount of alkyl def ects that can be incorporated into these precise systems before crystallinity is completely disrupted. In addition, relative to irregularly sequenced systems, precise models can endure a much highe r defect concentration without destroying the ability of the chains to pack into lamellae. Ou r work in this area continues, focusing on much longer defect to defect spacing and a variety of branch ident ities. By creating a complete catalogue of polymers with precise alkyl branch placement, we aim to fully understand the intriguing behavior of these precision model materials.

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44 CHAPTER 2 QUANTITATIVE -ALKYLATION OF PRIMARY NITRILES 2.1 Introduction Organonitriles long have been used for the pr eparation of numerous organic structures due to the ease and variety of synthetic transf ormations that can be performed with them.64-72 -Alkylation of aliphatic nitriles often is employed in synthetic strategies, since -anions are easily generated with common bases such as sodium amide,65, 71, 73, 74 n -butyl lithium,75 lithium diethylamide,65, 76 potassium hexamethyl disilazane,77 lithium 2,2,6,6-tetramethylpiperidide (LTMP),78 and lithium diisopropylamide (LDA).65, 71, 79 Once -alkylation is completed, further chemical modification can be performed on the remaining nitrile functionality, for example reductive elimination of the nitrile func tionality will lead to the formation of -dienes. The literature is mature, detailing such transformati ons in multi-step syntheses; however, to our knowledge none of the -cyanodiolefins presented in here have been prepared before, but similar products have been reported in low yield.73, 76, 80-84 We report quantitative conversions of organonitriles to -cyanodiolefins, using rather conventional chemistry, manipulating simple concep ts such as basicity while focusing on the elimination of competing reactions, stru ctural isomerization in particular. 2.2 Results and Discussion Current synthetic approaches towards alkyl -diolefins are based on diethyl malonate chemistry involving multiple steps, resulting in 10-60% product yields.48-50, 85, 86 Herein, we report essentially quantitative ( 96-99%) alkylation of a family of primar y alkyl nitriles using a variety of bromide and tosylate alkenyl substrates in the presence of various amide bases. In many cases, structural isomerization of the olefin occurs in these transformations as a detrimental side reaction not only reduci ng yield but rendering product -olefin purification difficult. We

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45 describe the reaction conditions necessary to avoid this side reaction, a result which is particularly useful when preparing -diolefins used in metathesis chemistry.87, 88 CN X 9 + 2eq of Base NC 99 1c 2b 3c X = OTs, Br Figure 2-1. Dialkenylation of hexa nenitrile in presence of base Figure 2-1 shows the -dialkenylation of hexanenitril e, our test reaction for the development of this chemistry. Once deprotonated the -anion nucleophile monoalkylates either a brominated or tosylated -olefin 2b ; a second alkylation follows to yield the desired tertiary nitrile. While the chemistry a ppears straightforward, achieving quantitative conversions yielding -cyanodiolefins has not been reported until now. Table 2-1. Different reaction conditions for alkenylation of hexanenitrile Base Solvent Reaction Time (h) Temp (C) Yield (%)a Isomerization (%)b LTMP THF 3 -78 99 0 LDA THF 3 -78 99 0 NaNH2 THF 6 -78 0 N/A NaNH2 THF 6 0 0 N/A NaNH2 THF 6 25 0 N/A NaNH2 Toluene 12 110 57 7 a Isolated yield after purifi cation by column chromatography b Percentage of olefin isom erization detected by NMR. Table 2-1 illustrates the eff ect of different reaction temp eratures and three bases on reaction yield. Using freshly prepared LTMP (pKa = 37) or LDA (pKa = 36) in THF, 3c is quantitatively produced at low temperature (-78 C) after 3 hours, whereas a weaker base, sodium amide (pKa = 33), leads to no reaction wh atsoever even at room temperature. At 110 C reaction temperature, sodium amide results in considerably lower yields than for the lithium

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46 bases, plus performs undesired olefin isomerizat ion as described in Figur e 2-2. Ultimately, this side reaction causes double bond w alking along the aliphatic chai n generating more stable 1,2disubstituted olefins, a transformation facilitate d by higher reaction temperat ure or use of the less selective base. Table 2-2. Dialkylation of primary nitriles in presence of LDA Entry Primary Nitrile Alkylating Substrate Dialkylation Product Overall Yield (%)a 1 CN 1a OTs 9 2a NC 99 3a 99 2 CN 1a Br 9 2b NC 99 3a 99 3 CN 1b OTs 9 2a NC 99 3b 96 4 CN 1c Br 9 2b NC 99 3c 99 5 CN 1d Br 9 2b NC 99 3d 99 6 CN 1a 2c Br 3e Ph Ph NC 98 7 CN 1a 2d Br 3f NC 98 8 CN 1a 2e Br 3g NC 97 9 CN 1a 2f Br 3h NC 99 10 NC COOEt 1e OTs 9 2a NC COOEt 99 3i 97 a Isolated yield after purifi cation by column chromatography

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47 NC R 99 OlefinIsomerization NC R 89 + Other isomers 45 Figure 2-2. Formation an internal olefin initiated by olefin isomerization The scope of this reaction was studied by the dialkylation of different nitriles ( 1a-d) with tosylate 2a or bromide 2b All cases showed quantit ative dialkenylation of th e respective nitriles, creating a family of alkylcyano -dienes potentially useful for ADMET chemistry. Various alkylating agents ( 2c-f ) were also introduced to verify th e adaptability of the reaction while probing functional group tole rance (Table 2-2, entrie s 6-9). Dialkylation of 1a with benzylbromide produced 3e in 98% yield, demonstrating that the substitution initiated by the anion is not limited to alkenyl bromides; additionally, no length dependence was observed during the alkylation of 1a which can be afforded with long chain alkenyl substituents 2a or short chain alkenyl substituents 2d as is shown in Table 2-2 en try 1 and 7. The effect of the -anion formation in the presence of a different functionality to the nitrile group was examined (Table 2-2 entry 10); dialkylation yields were 97%, de monstrating that an ad jacent carbonyl group does not interfere with this reaction. 2.3 Conclusions We believe this optimized met hodology for preparing alkylcyano -diolefins in quantitative yields will prove usef ul in many synthetic schemes, th at is the case of metathesis chemistry where pure -dienes are needed, ADMET and ring cl osing (RC). This approach will reduce the number of synthetic steps to onl y two transformations, alkenylation followed by decyanation. In contrast to pr eviously reported methodologies wh ere low yields were obtained, this methodology in combination to reductive el imination of nitriles promises to afford dienes in high yields, merging this strategy in to a universal synthetic pathway for the production

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48 of -dienes useful for ADMET. The versatility of this transformation is shown by the use of common reagents such as LTMP and LDA and the prevention of olefin isomerization. 2.4 Experimental General Procedure for Dialkylation of Nitr iles Using LDA or LTMP, Synthesis of 2butyl-2-(undec-10-enyl)tridec-12-enenitrile (3c) A 1M solution of hexanenitrile (1.733 g, 18 mmol) in dry THF (17.8 mL) was prepared in a three-necked round bo ttomed flask equipped with a stir bar and argon inlet adaptor. The solu tion was cooled to -78 C and a freshly prepared solution of lithium diisopropylamide (LDA) (2.18 g, 22 mmol) or lithium 2,2,6,6tetramethylpiperidide (LTMP) (3.11g, 22 mmol) in THF ( 21.5 mL) was added via cannula transferring. The mixture was warmed to 0 C a nd stirred for 30 min, then cooled to -78 C. The alkylating 11-bromoundec-1-ene (5 g, 22 mmol) was a dded at -78 C, then st irred at 0 C for 30 min. After the first alkylation, the solution was cooled to -78 C followed by the addition of LDA (2.18 g, 22 mmol) or LTMP (3.11g, 22 mmol) in THF (21.5 mL ) via cannula transferring. The mixture was warmed to 0 C and stirred for 30 min, then cooled to -78 C. The second alkylation was performed by addition of 11-br omoundec-1-ene (5 g, 22 mmoles) and stirring the solution at 0 C for 30 min, followed by 3 hour s at room temperature. The reaction was quenched with water (100 mL), extracted three ti mes with ether (200 mL) and washed with brine (50 mL). After drying over MgSO4, the solution was filtered, con centrated by rotary evaporation, and purified by flash column chromatography (5% v/v ethyl acetate/hexane ). After purification, 7.16 g (99% yield) of a pale yellow liquid was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.94 (t, 3H, CH3), 1.23-1.56 (m, 39H), 2.04 (q, 4H), 4.97 (m, 4H, vinyl CH2), 5.82 (m, 2H, vinyl CH); 13C NMR (CDCl3): (ppm) 14.18 (CH3), 23.12, 24.50, 26.66, 29.15, 29.34, 29.67, 29.73, 30.00, 34.04, 36.05, 36.33, 40.82, 114.32 (vinyl CH2), 124.71 (-CN), 139.39 (vinyl CH); EI/HRMS: [M]+ calculated for C28H51N: 401.4022, found:

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49 401.4031. Elemental analysis calculated for C28H51N: 83.72 C, 12.80 H, 3.49 N; found 83.71 C, 12.81 H, 3.48 N. 2-Methyl-2-(undec-10-enyl)tr idec-12-enenitrile (3a). After purification, 6.41 g (99% yield) of a pale yellow liquid was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm), 1.20-1.64 (m, 33H), 2.04 (q, 4H), 4.96 (m, 4H, vinyl CH2), 5.81 (m, 2H, vinyl CH); 13C NMR (CDCl3): (ppm) 24.77 (CH3), 23.95, 28.88, 29.06, 29.40, 29.45, 29.66, 33.77, 36.66, 39.41, 114.08 (vinyl CH2), 124.68 (-CN), 139.13 (vinyil CH); EI/HRMS: [M]+ calculated for C25H45N: 359.3552, found: 359.3697. Elemental an alysis calculated for C25H45N: 83.49 C, 12.61 H, 3.89 N; found 83.23 C, 12.59 H, 4.18 N. 2-Ethyl-2-(undec-10-enyl)tr idec-12-enenitrile (3b). After purification, 6.46 g (96% yield) of a pale yellow liquid was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.99 (t, 3H, -CH3), 1.29-1.56 (m, 35H), 2.04 (q, 4H), 4.97 (m, 4H, vinyl CH2), 5.82 (m, 2H, vinyl CH); 13C NMR (CDCl3): (ppm) 8.89 (CH3), 14.33, 22.87, 24.46, 29.13, 29.32, 29.63, 29.65, 29.71, 29.98, 31.81, 34.01, 35.83, 41.31, 114.33 (vinyl CH2), 124.52 (-CN), 139.39 (vinyil CH); EI/HRMS: [M]+ calculated for C26H47N: 373.3709, found: 373.3710. Elemental analysis calculated for C26H47N: 83.57 C, 12.68 H, 3.75 N; found 83.59 C, 12.67 H, 3.74 N. 2-Hexyl-2-(undec-10-enyl)tridec-12 -enenitrile from LTMP (3d). After purification, 7.66 g (99% yield) of a pale yellow liquid was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.90 (t, 3H, -CH3), 1.29-1.56 (m, 42H), 2.04 (q, 4H), 4.97 (m, 4H, vinyl CH2), 5.82 (m, 2H, vinyl CH); 13C NMR (CDCl3): (ppm) 14.24 (CH3), 22.80, 24.48, 24.51, 29.15, 29.33, 29.62, 29.66, 29.71, 29.99, 31.83, 34.01, 36.38, 40.88, 114.34 (vinyl CH2), 124.69 (-CN), 139.41 (vinyil CH); EI/HRMS: [M]+ calculated for C30H55N: 429.4335,

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50 found: 429.4346. Elemental anal ysis calculated for C30H55N: 83.84 C, 12.90 H, 3.26 N; found 83.41 C, 13.37 H, 3.49 N. 2-Benzyl-2-methyl-3-phenylpropanenitrile (3e). After purification, 4.1 9 g (98% yield) of a pale yellow liquid was collected. The follo wing spectral properti es were observed: 1H NMR (CDCl3): (ppm) 1.50 (s, 3H, -CH3), 2.83 (s, 4H), 7.40 (m, 10H); 13C NMR (CDCl3): (ppm) 22.12 (CH3), 30.81 (quaternary carbon), 41.56 (CH2), 120.91 (-CN), 125.51, 128.11, 128.91, 140.32 (aromatic carbon); EI/HRMS: [M]+ calculated for C17H17N: 235.1361, found: 235.1309. Elemental analysis calculated for C17H17N: 86.77 C, 7.28 H, 5.95 N; found 86.59 C, 5.41 H, 5.99 N. 2-Allyl-2-methylpent-4-enenitrile (3f). After purification, 2.41 g (98% yield) of a pale yellow liquid was collected. The followi ng spectral properties were observed: 1H NMR (CDCl3): (ppm) 1.53 (s, 3H, -CH3), 2.27 (d, 4H, CH2), 5.01 (m, 4H, vinyl CH2), 5.82 (m, 2H, vinyl CH); 13C NMR (CDCl3): (ppm) 23.41 (CH3), 25.65 (quaternary carbon), 41.35 (CH2), 115.33 (vinyl CH2), 124.51 (-CN), 136.39 (vinyl CH); EI/HRMS: [M]+ calculated for C9H13N: 135.1048, found: 135.1059. Elemental anal ysis calculated for C9H13N: 79.95 C, 9.69 H, 10.36 N; found 79.99 C, 9.61 H, 11.39 N. 2-Methyl-2-propylpentanenitrile (3g). After purification, 2.45 g ( 97% yield) of a pale yellow liquid was collected. The followi ng spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.98 (t, 6H, -CH3), 1.29-1.56 (m, 4H, CH2), 1.53 (s, 3H, -CH3) 1.61 (t, 4H, CH2); 13C NMR (CDCl3): (ppm) 10.89 (CH3), 15.33, 24.87, 25.46, 46.48 (C-CH2), 122.9 (CN); EI/HRMS: [M]+ calculated for C9H17N: 139.1361, found: 139.1321. Elemental analysis calculated for C9H17N: 77.63 C, 12.31 H, 10.06 N; found 77.48 C, 12.41 H, 10.11 N.

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51 2-Methyl-2-pentylheptanenitrile (3h). After purification, 3.51 g (99% yield) of a pale yellow liquid was collected. The followi ng spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.99 (t, 6H, -CH3), 1.29-1.56 (m, 12H), 1.61 (s, 3H, -CH3), 1.72 (t, 4H, C-CH2-CH2); 13C NMR (CDCl3): (ppm) 13.12 (CH3), 22.71, 23.57, 24.56, 28.23, 31.65, 43.25, 124.50 (-CN); EI/HRMS: [M]+ calculated for C13H25N: 195.1987, found: 195.1877. Elemental analysis calculated for C13H25N: 79.83 C, 12.90 H, 7.17 N; found 79.54 C, 12.99 H, 7.46 N. Ethyl 2-cyano-2-(undec-10-en yl)tridec-12-enoate (3i). After purification, 3.58 g (97% yield) of a pale yellow liquid was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 1.29-1.56 (m, 31H), 2.04 (t, 4H), 2.21 (m, 4H, vinyl CH2), 4.15 (q, 2H, O-CH2-CH3), 5.01 (m, 4H, vinyl CH2), 5.82 (m, 2H, vinyl CH); 13C NMR (CDCl3): (ppm) 14.13 (CH3), 22.87, 24.46, 29.13, 29.32, 29.63, 29.65, 29.71, 29.98, 33.81, 38.01, 61.15 (O-CH2CH3), 114.33 (vinyl CH2), 124.51 (-CN), 139.39 (vinyl CH), 173.85 (C=O); EI/HRMS: [M]+ calculated for C27H47NO2: 417.3607, found: 417.3594. Elemental analysis calculated for C27H47NO2: 77.64 C, 11.34 H, 3.35 N, 7.66 O; found 77.61 C, 11.41 H, 3.28 N, 7.70 O. General Procedure for Dialkylation of Nitr iles Using Sodium Amide, Synthesis of 2butyl-2-(undec-10-enyl)tridec-12-enenitrile (3b) A 1M solution of nitrile (hexanenitrile, 1.50 g, 15 mmol) in dry THF (15.4 mL) was prepared in a three-necked round bottomed flask equipped with a stir bar, condens er, and argon inlet adaptor. The reaction flask was loaded with NaNH2 (1.44 g, 37 mmol) and the alkylating 11-bromoundec-1-ene (8.630 g, 37 mmol). The mixture was refluxed for 12 hours and then quenc hed with 1M HCl (100 mL), extracted three times with ether (500 mL) and washed with br ine (100 mL). After drying over MgSO4, the solution was filtered, concentrated by rotary evaporation, and purified by flash column chromatography (5% v/v ethyl acetate/hexane). After purification, 3.19 g (57% yield) of a pale

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52 yellow liquid was collected. The followi ng spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.94 (t, 3H, -CH3), 1.23-1.56 (m, 41H), 2.04 (q, 4H), 4.97 (m, 4H, vinyl CH2), 5.42 (m, 0.30H, internal olefin CH), 5.82 (m, 2H, vinyl CH); 13C NMR (CDCl3): (ppm) 14.39 (CH3), 23.34, 24.74, 26.90, 29.39, 29.57, 29.68, 29.90, 29.96, 30.23, 34.26, 36.31, 36.58, 41.05, 114.55 (vinyl CH2), 124.88 (-CN), 139.58 (vinyl CH); EI/HRMS: [M]+ calculated for C28H51N: 401.4022, found: 404.4029. Elemental anal ysis calculated for C28H51N: 83.72 C, 12.80 H, 3.49 N; found 83.71 C, 12.81 H, 3.49 N. The olefin is omerization was quantified by relating the integrals of the isomerized olefin at 5.42 ppm and the terminal olefin at 4.90-5.04 ppm and the percentage of isomerization is then given by th e formula: 100x[Integral at 5.42 ppm / (integral at 5.42 + integral at 4.90-5.04 ppm)].

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53 CHAPTER 3 AVOIDING OLEFIN ISOMERIZATION DU RING DECYANATION OF ALKYLCYANO -DIENES: A DEUTERIUM LABELING AND STRUCTURAL STUDY OF MECHANISM 3.1 Introduction Olefin metathesis has proven to be an excellent synthetic tool for carbon-carbon bond formation via a variety of methodologi es, two of which require dienes. -Dienes are usually employed in ring closing metathesis (RCM) and acyclic diene metathesis (ADMET) chemistry, where the preparation of pure terminal ol efins can be synthetically challenging.89 In many cases, alkene isomerization occurs as a detrimental side reaction, not only reducing yield but also generating a difficult-to-purify mixture of products with inte rnal olefins. Nitrile chemistry is often employed because of the high alkylation yield and ease of subsequent decyanation,90 where decyanation is usually carried out by electron transfer chemistry initiated by alkali metals, such as Li,69, 91, 92 Na,68, 93, 94 or K.72, 95 The reaction proceeds in excellent yield via a radica l anion intermediate, which eliminates a cyanide moiety with concomitant formation of a radical.96, 97 Even so, reaction conditions can be harsh when other functionalities not compatible with alkali metals or radical species are present. For example, compounds containing olefin func tionalities can undergo structural isomerization via radical intermediates. This is the case for -dienes, which can isomerize to internal olefins. To circumvent this isomerization problem, we have applied a previously reported method for the decyanation of alkylcyano -dienes while completely avoiding isomerization.98 This chapter describes the necessary conditions to do so. 3.2 Results and Discussion 3.2.1 Synthetic Approach to Alkyl -Dienes Via Decyanation Chemistry Most methods for the preparation of alkyl -dienes require as many as 9 synthetic steps resulting in low yields.46, 51, 52 We have reduced the number of steps to 2, previously reported

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54 alkylation90 followed by decyanation, while producing an alytically pure dienes. Further yet, a variety of synthetic routes can be required just for the preparation -dienes simply possessing different alkyl substituents. For example, thr ee independent methodologies have been used for synthesizing -dienes possessing methyl,48, 50, 85 ethyl,49, 52 and hexyl54 substituents. The need for a high yield, universal synthesis ha ving fewer steps motivated us to explore more sophisticated nitrile chemistry, since primary nitriles 19 have been dialkenylated using lithium diisopropylamide (LDA) in quantitative yields.90 Subsequent decyanation of the resulting alkylcyano -dienes 1 produces alkyl -dienes 2 as shown in Figure 3-1. This chapter focuses on alkyl -dienes with 9 methylene spacers betw een the double bond and the tertiary carbon. Syntheses of analogous compounds with vari ous spacer lengths can also be achieved and will be presented in chapter 4. R CN 99 R 99 a. Methyl b. Ethyl c. Propyl d. Butyl e. Pentyl f. Hexyl 1a-f2a-f R = Ko, HMPA t -BuOH, Et2O Br 9 R CN LDA, THF 2 eq 19 Figure 3-1. Synthesis of alkyl -dienes Previous work has shown that reductive elimin ation of nitriles by el ectron transfer works for primary, secondary and te rtiary nitriles usi ng various alkali metals in ammonia,68, 69, 91-94 potassium in hexamethylphosphoramide (HMPA),70, 99-101 or potassium with dicyclohexyl-18-C6 in toluene.102 Although decyanation of alkylnitriles by al kali metals in liquid ammonia is quite versatile, it does not offer utility when other func tionalities are present in the molecule, such as olefins. For example, Marshall and Bi erenbaum reported the decyanation of -unsaturated

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55 nitriles using alkali metals in liquid ammonia with yields greater than 90 %, yet they obtained a mixture of products due to olefin isomerization.103 Cuvigny reported the use of alkali metals in HMPA and ether in the presence of various alcohols with yields from 16 to 89%.98 Other groups have modified Cuvignys methodology for the synthe sis of vitamin D derivatives with yields from 70 to 90%.70, 99, 100 While this methodology has proven to be useful with various substrates, studies containing alkene molecu les susceptible to promote olef in isomerization as described here have not been reported. Our investigation began by exploring several me thods for the reductive elimination of the nitrile functional group from model compound 1d The different reaction conditions and observed results are shown in Figure 3-2 and table 3-1. Decyanation NC 99 1d 99 2d Figure 3-2. Synthesis of 12-butyltricosa-1,22-diene ( 2d ) The first experiment (Entry 1) involved th e use of potassium metal on alumina in dry hexane, yielding 20% decyanation and giving 7% olefin isomerization after 5 minutes of reaction. After 10 minutes, the same reaction c onditions produced 30% decyanation with 20% olefin isomerization, where the extent of isomerization was calculated from 1H NMR spectra by comparison of the relative areas of the terminal a nd internal olefin signals (see Figure 3-4). The observed results suggested that a tertiary radica l is formed after the re ductive elimination of nitrile, where the translocation of this radical to a more stable allyl radical, leads to the olefin isomerization product (Figure 3-3).

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56 Table 3-1. Different decyanation systems for the reduction of 1d to 12-butyltricosa-1,22-diene ( 2d ) Entry System Solvent Reaction Time Yield (%)* Olefin Isomerization (%)** Hexane 5 min 20 7 1 K0, Al2O3 Hexane 10 min 30 20 Hexane/Toluene (1:1) 10 min 19 63 2 K0, Al2O3, Toluene Toluene 10 min 22 75 3 K0, Ph3CH Hexane/Ether (1:1) 3 h 41 B.D 4 K0, HMPA, t -BuOH Ether 3 h 99 B.D Yield after purification by column chromatography, ** Percentage of olefin isomerization detected by NMR and confirmed by GC, B.D: Below 1H and 13C NMR detection limit. Different systems involving a radical trap were developed in order to prove the concept of radical translocation. Formation of a more stable species must occu r to avoid transl ocation of the tertiary radical to an allylic radical. Furthermore, the stable species must be produced at a higher rate than the allylic radical formation in order to tune the reaction towa rd decyanation without olefin isomerization. Toluene was added to the reaction mixture with the intent of forming a stable benzyl radical, as indicat ed in table 3-1, entry 2. Decyan ation occurred in 19-22% yield with 63-75% olefin isomerization. Although forma tion of benzyl radical cannot be ruled out, formation of the allylic radical seems to occu r at a faster rate, t hus promoting olefin isomerization.

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57 9 9 R 8 9 R 8 9 R H H 9 9 R 8 9 R H Nonisomerized olefin Useful for RCM & ADMET Isomerized product Figure 3-3. Proposed mechanism for the olefin isom erization via formation of an allylic radical The third entry in table 3-1 shows the result of incorporation of triphenylmethane as a radical trap. The reductive elimination of the nitrile functional group in the presence of Ph3CH in hexane/ether (1:1) produced the desired decy anation product in 41% yield; hydrogen radical transfer from the triphenylmethane molecule to th e tertiary radical formed by decyanation occurs to produce the desired product withou t structural olefin isomeriza tion. The absence of isomerized internal double bonds suggests that the more stable triphenylmet hyl radical forms more quickly than does the allylic radical which would lead to olef in isomerization. Although the triphenylmethyl radical was obs erved during the reaction by th e appearance of a yellowish solution, competition between the radical tr apping process and deprotonation of Ph3CH initiated by potassium metal is also plausible.92, 104-107 The initial yellow soluti on gradually converted to an intense red color due to formation of th e triphenylmethyl anion, which deactivates the decyanation process and d ecreases the reaction yield.

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58 Figure 3-4. Expanded 1H NMR spectrum of 12-butyltricosa-1,22-diene ( 2d ) at three different degrees of olefin isomerization Entry 4 in table 3-1 shows the decyanation of 1d using potassium metal, HMPA and tBuOH with quantative yields without apparent olef in isomerization. The absence of isomerized product suggests that the te rtiary radical formed after the reduc tive elimination of nitrile, before producing an allylic radical, quickly abstracts hydrogen from the al cohol or it is reduced yielding a carbanion, which inactivates the tertiary radical and consequently its structural isomerization. Although formation of t -butoxyl-radicals from t -butanol is not common,108-110 alkoxyl-radicals rapidly abstract hydrogen from the -carbon in the alcohol, solvent, or disproportionate yielding a t -butoxide anion.111-114 To further expand the scope of th is method, a series of alkylcyano -dienes was decyanated resulting in quantitative yields with no apparent olefin isomerization, as shown in table 3-2. Obviously the method has broad utili ty. Prior methodologies fo r the preparation of alkyl -dienes require six to nine synt hetic steps; this approach re quires two steps, alkylation90

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59 and decyanation, and circumvents side reactions providing a universal, high yielding route to pure alkyl -dienes. Table 3-2. Decyanation of alkylcyano -dienes using potassium metal, HMPA and tBuOH in ether. Substrate Product Overall Yield (%)* Olefin Isomerization (%)** NC 99 1a 99 2a 99 B.D NC 99 1b 99 2b 98 B.D NC 99 1c 99 2c 99 B.D NC 99 1d 99 2d 99 B.D NC 99 1e 99 2e 98 B.D NC 99 1f 99 2f 99 B.D Yield after purification by co lumn chromatography, ** Percentage of olefin isomerization detected by NMR and confir med by GC, B.D: Below 1H and 13C NMR detection limit.

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60 3.2.2 Deuterium Labeling and Mechanistic Considerations Cuvigny speculated that HMPA is the hydroge n donor in the reductive elimination of nitriles, but no chemical or spectroscopic proof has been reported to date.98 Two possible sources of hydrogen radicals are present in th e reactions we describe, HMPA and t -BuOH.115 The reaction is carried out as a mixture of pota ssium metal and HMPA in ether, followed by dropwise addition of the nitrile dissolved in t -BuOH and ether. Experiments in deuterated alcohol were performed to dete rmine the origin of the hydrogen captured after the reductive elimination of nitrile (table 3). The first test involved the dropwise a ddition of a mixture of 1a and t -BuOD in ether to a solution of potassium metal and HMPA in ether, yielding the decyanation product 3 (Figure 3-5) in quantitative yield wi thout apparent olefin isomerization. Figure 3-6 shows the deuterium NMR spectrum of 3 where one singlet at 1.38, corresponding to the monodeuteration of the tertiary carbon, is observed. Figure 3-7 shows the 13C NMR spectra of the products formed in the presence t -BuOH (Figure 3-7a) and t -BuOD (Figure 3-7b). The intensity of the tertiary carbon signal at 33.02 ppm is much smaller in the monodeuterated product 3 due to the larger 13C relaxation time in the absence of directly bonded protons. The extent of deuteration of the final pro duct was calculated by integration of the 1H NMR signals from the methyl at the branch point, singlet in the deuterated product vs doublet in the product with 1H on the tertiary carbon, as shown in Fi gure 3-8. The results indicated that 3 was 92% deuterated. The high extent of deuteration c onfirms that the hydrogen from the alcohol is captured by the tertiary radical from th e reductive elimination of nitrile. Ko, HMPA t -BuOD, Ether NC CH3 99 1a D CH3 99 3 Figure 3-5. Decyanation of ( 1a ) in presence of deuterated tert -butanol

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61 Table 3-3. Decyanation of 1a in presence of deuterated compounds Entry Decyanation System Yield (%)* Extent of Deuteration (%)** Olefin Isomerization (%)*** 1 K0, HMPA, t -BuOD 99 92 B.D 2 K0, HMPAd18, t -BuOH 99 Not detected B.D 3 K0, t -BuOD 12 91 B.D 4 t -BuO-K+ 0 --* Yield after purification by column chromatography ** Extend of deuteration detected by 1H NMR and deuterium NMR *** Percentage of isomerized product detected by 1H NMR and confirmed by GC B.D: Below 1H and 13C NMR detection limit Figure 3-6. Deuterium NMR of 12d-12-Methyl-tricosa-1,22-diene The second entry in table 3-3 describes the de cyanation experiment using HMPA with all methyl groups isotopically labeled with deuter ium. As with the previous experiments, the reaction produced decyanation in quantitative yield without apparent olefin isomerization. Deuterium NMR experiments showed no apparent deuteration in the final product when the

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62 isotopic label is carried by the HMPA, clearly showing that the hydrogen from the alcohol, and not from HMPA, is captured by th e tertiary radical during the reductive elimination of nitrile. Figure 3-7. Comparison of 13C NMR for (a) 12-methyltricosa-1,22-diene and (b) 12-d-12Methyl-tricosa-1,22-diene The third entry in table 3-3 shows the reacti on conditions when decyanation occurs in the absence of HMPA, resulting in 12% decyanatio n with no apparent olefin isomerization. Deuterium NMR showed a singlet at 1.38, which corresponds to the formation of 3 The low yield in this reaction is expl ained by the absence of HMPA, wh ich apparently stabilizes the formation of the intermediate species.

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63 Figure 3-8. Comparison of 1H NMR for methyl resonances of (a) 12-d-12-Methyl-tricosa-1,22diene (singlet with a small contribution of residual doubl et) and (b) 12-methyltricosa1,22-diene (doublet) The fourth experiment in table 3-3 was designe d to determine if reductive elimination is carried out by potassium metal or by the potassium t -butoxide possibly formed in situ The reaction was performed vi a dropwise addition of 1a in ether to a solution of potassium metal and t -BuOD in ether. The starting material 1a was recovered and no decyanation product 3 was detected. These results demonstrate that reduc tive elimination of nitrile occurs by electron transfer from potassium metal and not via t -BuOK formed in situ

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64 Although decyanation methodology using potassi um metal and HMPA appears to occur through a radical-intermediate mechanism, no defin itive proof of this has been clearly presented to date.65 Formation of a carbanion via reduction of the radical-int ermediate species cannot be ruled out.115 One way to provide evidence for a free ra dical-intermediate would be to capture it via intramolecular cyclization befo re reduction to the carbanion o ccurs. Alkenes capture radical moieties which can subsequently undergo rapid intraradical cyclization to form cyclic radicals.116-119 To prove the point, decyanation was performed using alkylcyano -dienes 4a and 4b possessing only three methylene un its between the terminal double bonds and the nitrile, in order to enhance the likelihood for cyc lization to occur (Figure 3-9).120-122 In fact, bicyclic products 10 and 11 form as a result of intramolecular radical capture. Decyanation of 4 produces a tertiary radical 5 which undergoes 5exo and 6endo ring closures 6 and 7 leading to the bicyclic structures 10 and 11 To further determine the influence of spacer length on the cyclization pathway, a series of experiments were performed using alkylcyano -alkenes 13 possessing spacers of 3, 4, 5 and 6 methylene groups (Figure 3-10). Compounds with three and four methylene units between the terminal double bond and the nitr ile formed cyclic products 15 and 16 Structures with five and six methylene spacers yielded only linear structures These results verified that at least five CH2 spacers are needed between the double bond and th e carbon bearing the nitrile group to prevent radical induced cyclization.123-125

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65 5exo Ring closure 6endo Ring closure CN R K0, HMPA t-BuOH, Ether R = a = Methyl b = Butyl R R R R R R R 4a,b 5a,b 6a,b 7a,b 8a,b 9a,b 10a,b 11a,b 7exo Ring closure 7exo Ring closure Hydrogen abstraction Hydrogen abstraction Figure 3-9. Decyanation of 2-alkyl -2-pent-4-enyl-hept-6-enenitrile

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66 R CN R K0, HMPA t-BuOH, Ether x x a, c, e, g = Methyl b, d, f, h = Butyl R y R z 13a-h 14a-h 15a-d 16a-d When x = 3, y = 1 and z = 1 x = 4, y = 2 and z = 2 x = 5 Linear structures were formed ( 17a,b ) x = 6 Linear structures were formed ( 18a,b ) R = H H exo closure endo closure 15a y = 1, R = Methyl 15b y = 1, R = Butyl 15c y = 2, R = Methyl 15d y = 2, R = Butyl 16a z = 1, R = Methyl 16b z = 1, R = Butyl 16c z = 2, R = Methyl 16d z = 2, R = Butyl Figure 3-10. Decyanatio n of alkenylnitriles All these results suggest a plausible mechan ism involving a radical-intermediate for the reductive elimination of CN in th e presence of potassium, HMPA and tBuOH (Figure 3-11). Transfer of one electron from potassium metal to the nitrile group results in formation of a radical anion. Subsequent elimina tion of cyanide yields a tertiary radical that is rearranged to form cyclic molecules 10 11 15 and 16 quenched by abstraction of hydrogen from t -BuOH to yield 2a-f or reduced to a carbanion followed by protonation from t -BuOH to yield 2a-f

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67 Abstraction of hydrogen from t -BuOH avoids formation of allylic radicals and consequent olefin isomerization. 9 9 CH3 N Ko+K 9 9 CH3 9 9 CH3 D 9 9 C CH3 N Ko CH3 CH3 CH3 O D CH3 CH3 CH3 O + + CH3 CH3 CH3 O + K CN Figure 3-11 Proposed mechanism for the reductive elimination of nitrile 3.3 Conclusions The understanding of the mechanism for reducti ve elimination of nitriles opens the possibility for the synthesis of alkyl -dienes. Previously repor ted methodologies for the preparation of 2a 2b and 2f require six to nine synthetic steps. This new methodology allows quantitative synthesis of such dienes in two steps and circ umvents side reactions such as structural olefin isomerization and intramolecular cyclization. We believe this to be a universal synthesis route for the preparation of alkyl -dienes. 3.4 Experimental Section Materials. All starting materials were used as received, except for 11-bromoundec-1-ene, and the alkylcyano -dienes, which were synthesized accord ing to the literature procedures.89, 90 Tetrahydrofuran, toluene and ether were freshl y distilled from Na/K alloy using benzophenone as an indicator. The 11-bromoundec-1-ene, hexamethylphosphoramide, diisopropylamine, propiononitrile, butyronitrile, pentan enitrile, hexanenitrile, heptanen itrile, and octanenitrile were

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68 freshly distilled from CaH2 prior to use. The tert -butanol was dried over calcium oxide and freshly distilled before use. Decyanation of 2-Butyl-2-(undec-10-enyl)tr idec-12-enenitrile (1d) with Potassium Metal and Neutral Alumina. The decyanation of 1d (0.10 g, 0.3 mmol) was carried out in slurry of potassium and neutral alumina as reported by Umani-Ronchi.72 The reaction was monitored by TLC plate using 5% ethyl acetate in hexane. When no trac e of starting material was observed by TLC, the remaining excess of unreacted potassium was removed from the reaction flask. The reaction was quenched with wate r (20 mL), extracted three times with ether (600 mL), and washed with brine (150 mL). After drying over MgSO4, the solution was filtered, concentrated by rotary evapor ation, and purified by flash colu mn chromatography (hexane). Decyanation was carried out in hexane, hexane:t oluene (1:1), and toluene as described below: Decyanation of 2-Butyl-2-(undec-10-enyl) tridec-12-enenitrile (1d) in Hexane. Synthesis of 12-Butyltricosa-1,22-diene (2d). After purification, 19 mg (20% yield) of a colorless liquid was collected. The follo wing spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.90 (t, 3H), 1.23-1.41 (m, 39H), 2.04 ( q, 4H), 4.97 (m, 4H), 5.42 (m, 0.15H), 5.82 (m, 2H); 13C NMR (CDCl3): (ppm) 14.4, 23.4, 24.5, 26.9, 29.2, 29.4, 29.8, 29.9, 29.9, 30.4, 33.6, 33.9, 34.1, 37.6, 114.3, 139.5; EI/HRMS: [M]+ calculated for C27H52: 376.4069, found: 376.4050. Elemental anal ysis calculated for C27H52: 86.09 C, 13.91 H; found 86.02 C, 13.98 H. Decyanation of 2-Butyl-2-(undec-10-enyl)trid ec-12-enenitrile (1d) in Hexane:Toluene 1:1. Synthesis of 12-But yltricosa-1,22-diene (2d) After purification, 18 mg (19% yield) of a colorless liquid was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.90 (t, 3H), 1.23-1.41 (m, 39H), 2.04 ( q, 4H), 4.97 (m, 4H), 5.42 (m, 3.4H),

PAGE 69

69 5.82 (m, 2H); 13C NMR (CDCl3): (ppm) 14.4, 23.4, 24.5, 26.9, 29.2, 29.4, 29.8, 29.9, 29.9, 30.4, 33.6, 33.9, 34.1, 37.6, 114.3, 139.5; EI/HRMS: [M]+ calculated for C27H52: 376.4069, found: 376.4035. Elemental anal ysis calculated for C27H52: 86.09 C, 13.91 H; found 86.09 C, 13.90 H. Decyanation of 2-Butyl-2-(undec-10-enyl)tr idec-12-enenitrile (1d) in Toluene. Synthesis of 12-Butyltricosa-1,22-diene (2d). After purification, 21 mg (22% yield) of a colorless liquid was collected. The follo wing spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.90 (t, 3H), 1.23-1.41 (m, 39H), 2.04 (q, 4H), 4.97 (m, 4H), 5.42 (m, 6H), 5.82 (m, 2H); 13C NMR (CDCl3): (ppm) 14.4, 23.4, 24.5, 26.9, 29.2, 29.4, 29.8, 29.9, 29.9, 30.4, 33.6, 33.9, 34.1, 37.6, 114.3, 139.5; EI/HRMS: [M]+ calculated for C27H52: 376.4069, found: 376.4074. Elemental analysis calculated for C27H52: 86.09 C, 13.91 H; found 86.11 C, 13.91 H. Decyanation of 2-Butyl-2-(undec-10-enyl)tr idec-12-enenitrile (1d) with Potassium Metal and Triphenylmethane. Synthesis of 12-butyltricosa1,22-diene (2d). Potassium metal (49 mg, 1.25 mmol) and hexane (10 mL) were tr ansferred to a threeneck round bottom flask equipped with a stir bar, addition funnel, and argon inlet adaptor. A solution of 1d (0.10 g, 0.3 mmol) and triphenylmethane (183 mg, 0.75 mmol) in hexane (10 mL) and ether (1.5 mL) was added dropwise to the reactor and stirred for 3 hours. The reaction was quenched with water (5 mL), extracted three times with ether (300 mL), and washed with brine (100 mL). After drying over MgSO4, the solution was filtered, concentrated by rotary evaporation, and purified by flash column chromatography (hexane). After purificat ion, 38 mg (41% yield) of a colorless liquid was collected. The following spect ral properties were observed: 1H NMR (CDCl3): (ppm) 0.90 (t, 3H), 1.23-1.41 (m, 39H), 2.04 (q, 4H), 4.97 (m, 4H), 5.82 (m, 2H); 13C NMR (CDCl3): (ppm) 14.4, 23.4, 24.5, 26.9, 29.2, 29.4, 29.8, 29.9, 30.4, 33.6, 33.9, 34.1, 37.6, 114.3, 139.5;

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70 EI/HRMS: [M]+ calculated for C27H52: 376.4069, found: 376.4061. Elemental analysis calculated for C27H52: 86.09 C, 13.91 H; found 86.10 C, 13.90 H. General Methodology of Decyanat ion Using Potassium Metal and Hexamethylphosphoramide. Potassium metal (8.285 g, 212 mmol), HMPA (27.238 g, 152 mmol), and ether (185 mL) were transferred to a three-neck round bottom fl ask equipped with a stir bar, addition funnel, and argon inlet adaptor. A solution of the alkylcyano -diolefin (30 mmol) and tBuOH (5.841 g, 79 mmol) in ether (130 mL) was added dropwise to the reactor and stirred for 3 hours at 0 C. The reaction was mon itored by TLC plate using 5% ethyl acetate in hexane. When no trace of starting material was observed by TLC, the remaining excess of unreacted potassium was removed from the reacti on flask. The reaction was quenched with water (20 mL), extracted three times with ether (600 mL), and washed with brine (150 mL). After drying over MgSO4, the solution was filtered, concentrated by rotary evaporation, and purified by flash column chromatography (hexane). 12-Methyltricosa-1,22-diene (2a). After purification, 9.93 g (99% yield) of a colorless liquid was collected. The following sp ectral properties were observed: 1H NMR (CDCl3): (ppm) 0.84 (d, 3H), 1.23-1.39 (m, 33H), 2.04 (q, 4H), 4.97 (m, 4H), 5.82 (m, 2H); 13C NMR (CDCl3): (ppm) 20.0, 27.4, 29.2, 29.4, 29.8, 29.9, 30.0, 30.3, 33.0, 34.1, 37.4, 114.3, 139.4; EI/HRMS: [M]+ calculated for C24H46: 334.3600, found: 334.3607. Elemental analysis calculated for C24H46: 86.14 C, 13.86 H; found 86.15 C, 13.79 H 12-Ethyltricosa-1,22-diene (2b). After purification, 10.24 g (98% yield) of a colorless liquid was collected. The following sp ectral properties were observed: 1H NMR (CDCl3): (ppm) 0.84 (t, 3H), 1.28-1.37 (m, 35H), 2.04 ( q, 4H), 4.96 (m, 4H), 5.82 (m, 2H); 13C NMR (CDCl3): (ppm) 11.1, 26.1, 27.0, 29.2, 29.4, 29.8, 29.9, 30.0, 30.4, 33.4, 34.1, 39.1, 114.3, 139.5;

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71 EI/HRMS: [M]+ calculated for C25H48: 348.3756, found: 348.3758. Elemental analysis calculated for C25H48: 86.12 C, 13.88 H; found: 86.25 C, 13.97 H. 2-Propyltricosa-1,22-diene (2c). After purification, 10.76 g (99% yield) of a colorless liquid was collected. The following sp ectral properties were observed: 1H NMR (CDCl3): (ppm) 0.90 (t, 3H), 1.23-1.41 (m, 37H), 2.04 ( q, 4H), 4.97 (m, 4H), 5.82 (m, 2H); 13C NMR (CDCl3): (ppm) 14.8, 20.1, 27.0, 29.2, 29.4, 29.8, 29.9, 30.0, 30.4, 34.0, 34.1, 36.4, 37.5, 114.3, 139.4; EI/HRMS: [M]+ calculated for C26H50: 362.3913, found: 362.3918. Elemental analysis calculated for C26H50: 86.10 C, 13.90 H; found 86.09 C, 13.91 H. 12-Butyltricosa-1,22-diene (2d). After purification, 11.18 g (99% yield) of a colorless liquid was collected. The following sp ectral properties were observed: 1H NMR (CDCl3): (ppm) 0.90 (t, 3H,), 1.23-1.41 (m, 39H), 2.04 (q, 4H), 4.97 (m, 4H), 5.82 (m, 2H); 13C NMR (CDCl3): (ppm) 14.4, 23.4, 27.0, 29.2, 29.4, 29.8, 29.9, 30.0, 30.4, 33.7, 34.0, 34.1, 37.6, 114.3, 139.4; EI/HRMS: [M]+ calculated for C27H52: 376.4069, found: 376.4061. Elemental analysis calculated for C27H52: 86.09 C, 13.91 H; found 86.10 C, 13.90 H. 12-Pentyltricosa-1,22-diene (2e). After purification, 11.48 g (98% yield) of a colorless liquid was collected. The following sp ectral properties were observed: 1H NMR (CDCl3): (ppm) 0.90 (t, 3H), 1.23-1.41 (m, 41H), 2.04 ( q, 4H), 4.97 (m, 4H), 5.82 (m, 2H); 13C NMR (CDCl3): (ppm) 14.4, 23.0, 26.7, 27.0, 29.2, 29.4, 29.7, 29.8, 29.9, 30.0, 30.4, 32.7, 33.9, 34.0, 34.1, 37.7, 114.3, 139.4; EI/HRMS: [M]+ calculated for C28H54: 390.4226, found: 390.4228. Elemental analysis calculated for C28H54: 86.07 C, 13.93 H; found 86.05 C, 13.96 H. 12-Hexyltricosa-1,22-diene (2f). After purification, 12.01 g (99% yield) of a colorless liquid was collected. The following sp ectral properties were observed: 1H NMR (CDCl3): (ppm) 0.89 (t, 3H), 1.15-1.48 (m, 43H), 2.04 ( q, 4H), 4.97 (m, 4H), 5.82 (m, 2H); 13C NMR (CDCl3):

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72 (ppm) 14.4, 23.0, 26.9, 29.2, 29.4, 29.8, 29.9, 29.9, 30.1, 30.4, 32.2, 33.9, 34.1, 37.6, 114.3, 139.5; EI/HRMS: [M]+ calculated for C29H56: 404.4382, found: 404.4386. Elemental analysis calculated for C29H56: 86.05 C, 13.95 H; found 86.38 C, 13.97 H. Decyanation Using Isotopic Labeling with Deuterium. The decyanation of 1a was carried out in presence of deuterated t -butanol or HMPAd18 using the general decyanation procedure described before. Decyanation using potassium metal, he xamethylphosphoramide and 2-methyl-2propan-[2H]-ol. Synthesis of [12-2H]-12-Methyltricosa-1,22-diene (3). After purification, 9.9 g (99% yield) of a colorless liquid was co llected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.84 (s, 3H), 1.23-1.39 (m, 32H), 2.04 (q, 4H), 4.97 (m, 4H), 5.82 (m, 2H); 13C NMR (CDCl3): (ppm) 19.9, 27.3, 27.4, 29.2, 29.4, 29.8, 29.9, 30.0, 30.3, 34.1, 37.3, 37.4, 114.3, 139.4; deuterium NMR (CDCl3): (ppm) 1.38 (s, CH2CD(CH3)CH2). EI/HRMS: [M]+ calculated for C24H45D: 335.3662, found: 335.3657. Elemental analysis calculated for C24H45D: 85.89 C, 14.11 H; found 85.92 C, 14.09 H. Decyanation using potassium metal, hexamethylphosphoramided18 and tert -butanol. Synthesis of 12-Methyltricosa-1,22-diene (2a) After purification, 9.91 g (99% yield) of a colorless liquid was collected. The follo wing spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.84 (d, 3H), 1.23-1.39 (m, 33H), 2.04 (q, 4H), 4.97 (m, 4H), 5.82 (m, 2H); 13C NMR (CDCl3): (ppm) 20.0, 27.4, 29.2, 29.4, 29.8, 29.9, 30.0, 30.3, 33.0, 34.1, 37.4, 114.3, 139.4; deuterium NMR (CDCl3): No signal detected for CH2CD(CH3)CH2; EI/HRMS: [M]+ calculated for C24H46: 334.3600, found: 334.3605. Elemental analysis calculated for C24H46: 86.14 C, 13.86 H; found 86.12 C, 13.88 H.

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73 Decyanation of Alkylcyano-1,10-und ecadienes and Alkenenitriles. The decyanation of 4 and 13 was carried out as described in the ge neral decyanation methodology. Characterization and purification of the resp ective products was carried out by NMR and HPLC/MS. Two columns were utilized: (1) analy tical or scout scale column w ith dimensions of 10.0 mm (inner diameter) by 250.0 mm; (2) prepar ative scale with dimensions of 41.4 mm (inner diameter) by 250.0 mm. Both columns were silica packed with a pa rticle size of 8 m and a pore size of 60 Crude samples were diluted in a 25% solution (w/v ) of HPLC grade hexanes and filtered prior to injection. 3a,7-Dimethyl-decahydroazulene (10a). After purification, 0.84 g (85% yield) of a colorless liquid was collected. The follo wing spectral properties were observed: 1H NMR (CDCl3): (ppm) 1.06 (d, 3H), 1.16 (s, 3H), 1.25-1.45 (m, 10H) 1.61-1.75 (m, 6H); 13C NMR (CDCl3): (ppm) 21.3, 22.6, 22.1, 23.5, 32.0, 33.3, 38.2, 39.0, 39.9, 41.4, 47.0, 48.0. EI/HRMS: [M]+ calculated for C12H22: 166.1722, found: 166.1725. Elemental analysis calculated for C12H22: 86.67 C, 13.33 H; found 86.63 C, 13.36 H. 3a-Butyl-7-methyl-decah ydroazulene (10b). After purification, 0.82 g (83% yield) of a colorless liquid was collected. The follo wing spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.96 (t, 3H), 1.06 (d, 3H), 1.16-1.48 (m, 14H), 1.60-1.75 (m, 8H); 13C NMR (CDCl3): (ppm): 14.1, 21.3, 22.4, 23.4, 23.8, 27.8, 32.3, 33.3, 36.4, 37.7, 38.2, 39.2, 39.3, 44.8, 54.7; EI/HRMS: [M]+ calculated for C15H28: 208.2191, found: 208.2193. Elemental analysis calculated for C15H28: 86.46 C, 13.54 H; found 86.48 C, 13.52 H. 1,5-Dimethylbicyclo[4.3.1]decane (11a). After purification, 27 mg (3% yield) of a colorless liquid was collected. The follo wing spectral properties were observed: 1H NMR (CDCl3): (ppm) 1.06 (d, 3H), 1.16 (s, 3H), 1.10-1.26 (m, 9H), 1.31-1.51 (m, 6H), 1.61-1.70 (m,

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74 1H); 13C NMR (CDCl3): (ppm) 18.8, 21.4, 22.1, 25.4, 31.7, 35.7, 37.2, 40.1, 40.9, 41.6, 42.7, 43.4 ; EI/HRMS: [M]+ calculated for C12H22: 166.1722, found: 166.1720. Elemental analysis calculated for C12H22: 86.67 C, 13.33 H; found 86.61 C, 13.39 H. 1-Butyl-5-methylbicycl o[4.3.1]decane (11b). After purification, 18 mg (2% yield) of a colorless liquid was collected. The follo wing spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.96 (t, 3H), 1.06 (d, 3H), 1.10-1.51 (m, 21H), 1.61-1.70 (m, 1H); 13C NMR (CDCl3): (ppm): 14.1, 18.8, 21.7, 22.4, 23.4, 27.5, 31.7, 35.7, 37.5, 39.2, 39.4, 40.1, 40.5, 41.2 ; EI/HRMS: [M]+ calculated for C15H28: 208.2191, found: 208.2188. Elemental analysis calculated for C15H28: 86.46 C, 13.54 H; found 86.43 C, 13.56 H. 1,2-Dimethylcyclopentane (15a). After purification, 0.94 g (95% yield) of a colorless liquid was collected. The following sp ectral properties were observed: 1H NMR (CDCl3): (ppm) 1.06 (d, 6H), 1.25-1.75 (m, 8H); 13C NMR (CDCl3): (ppm): 17.9, 25.4, 36.1, 45.3 ; EI/HRMS: [M]+ calculated for C7H14: 98.1096, found: 98.1094. Elemental analysis calculated for C7H14: 85.63 C, 14.37 H; found 85.61 C, 14.39 H. 1-Butyl-2-methylcyclopentane (15b). After purification, 0.89 g (90% yield) of a colorless liquid was collected. The following sp ectral properties were observed: 1H NMR (CDCl3): (ppm) 0.96 (t, 3H), 1.06 (d, 3H), 1.29-1.60 (m, 14H); 13C NMR (CDCl3): (ppm): 14.1, 18.2, 23.1, 25.7, 30.0, 31.8, 33.9, 36.4, 43.1, 46.4 ; EI/HRMS: [M]+ calculated for C10H20: 140.1565, found: 140.1568. Elemental analysis calculated for C10H20: 85.63 C, 14.37 H; found 85.61 C, 14.40 H. 1,2-Dimethylcyclohexane (15c). After purification, 0.71 g (71% yield) of a colorless liquid was collected. The following sp ectral properties were observed: 1H NMR (CDCl3): (ppm) 1.06 (m, 6H), 1.20-1.65 (m, 10H); 13C NMR (CDCl3): (ppm): 18.2, 25.8, 33.3, 40.3 ; EI/HRMS:

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75 [M]+ calculated for C8H16: 112.1252, found: 112.1250. Elemental an alysis calculated for C8H16: 85.63 C, 14.37 H; found 85.67 C, 14.31 H. 1-Butyl-2-methylcyclohexane (15d). After purification, 0.68 g (68% yield) of a colorless liquid was collected. The following sp ectral properties were observed: 1H NMR (CDCl3): (ppm) 0.96 (t, 3H), 1.06 (d, 3H), 1.20-1.50 (m, 16H); 13C NMR (CDCl3): (ppm): 14.1, 18.5, 23.1, 25.8, 26.1, 30.0, 31.1, 32.1, 33.6, 38.1, 42.5 ; EI/HRMS: [M]+ calculated for C11H22: 154.1722, found: 154.1721. Elemental analysis calculated for C11H22: 85.63 C, 14.37 H; found 85.61 C, 14.36 H. Methylcyclohexane (16a). After purification, 42 mg (4% yi eld) of a colorless liquid was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.96 (d, 3H), 1.01-1.75 (m, 11H); 13C NMR (CDCl3): (ppm): 22.9, 26.5, 26.6, 32.9, 35.6 ; EI/HRMS: [M]+ calculated for C7H14: 98.1096, found: 98.1097. Elemental analysis calculated for C7H14: 85.63 C, 14.37 H; found 85.64 C, 14.32 H. Butylcyclohexane (16b). After purification, 91 mg (9% yiel d) of a colorless liquid was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.96 (t, 3H), 1.01-1.8 (m, 17H); 13C NMR (CDCl3): (ppm): 14.2, 23.1, 26.6, 26.9, 29.3, 33.6, 37.4, 37.8 ; EI/HRMS: [M]+ calculated for C10H20: 140.1565, found: 140.1561. Elemental analysis calculated for C10H20: 85.63 C, 14.37 H; found 85.60 C, 14.40 H. Methylcycloheptane (16c). After purification, 0.27 g (28% yiel d) of a colorless liquid was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.96 (d, 3H), 1.01-1.4 (m, 12H), 1.65 (m, 1H); 13C NMR (CDCl3): (ppm): 21.0, 26.5, 29.3, 34.9, 37.3 ; EI/HRMS: [M]+ calculated for C8H16: 112.1252, found: 112.1256. Elemental analysis calculated for C8H16: 85.63 C, 14.37 H; found 85.59 C, 14.41 H.

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76 Butylcycloheptane (16d). After purification, 0.31 g (31% yi eld) of a colorless liquid was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.96 (t, 3H), 1.25-1.45 (m, 18H), 1.50 (m, 1H); 13C NMR (CDCl3): (ppm): 14.1, 23.1, 26.8, 29.3, 29.7, 34.9, 35.1, 40.4 ; EI/HRMS: [M]+ calculated for C11H22: 154.1722, found: 154.1719. Elemental analysis calculated for C11H22: 85.63 C, 14.37 H; found 85.67 C, 14.31 H. Non-1-ene (17a). After purification, 0.98 g (98% yield) of a colorless liquid was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.86 (t, 3H), 1.231.39 (m, 10H), 2.04 (q, 2H), 4.97 (m, 2H), 5.82 (m, 1H); 13C NMR (CDCl3): (ppm) 11.1, 22.8, 29.5, 29.8, 31.9, 33.9, 114.3, 139.5. EI/HRMS: [M]+ calculated for C9H18: 126.1409, found: 126.1410. Elemental analysis calculated for C9H18: 85.63 C, 14.37 H; found 85.67 C, 14.31 H. Dodec-1-ene (17b). After purification, 0.99 g (99% yiel d) of a colorless liquid was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.89 (t, 3H), 1.23-1.39 (m, 16H), 2.04 (q, 2H), 4.97 (m, 2H), 5.82 (m, 1H); 13C NMR (CDCl3): (ppm) 11.1, 22.8, 29.4, 29.7, 29.8, 31.9, 33.9, 114.3, 139.5. EI/HRMS: [M]+ calculated for C12H24: 168.1878, found: 168.1875. Elemental anal ysis calculated for C12H24: 85.63 C, 14.37 H; found 85.61 C, 14.40 H. Dec-1-ene (18a). After purification, 0.97 g (97% yield) of a colorless liquid was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.89 (t, 3H), 1.231.39 (m, 12H), 2.04 (q, 2H), 4.97 (m, 2H), 5.82 (m, 1H); 13C NMR (CDCl3): (ppm) 11.1, 22.8, 29.4, 29.7, 29.8, 31.9, 33.9, 114.3, 139.5. EI/HRMS: [M]+ calculated for C10H20: 140.1565, found: 140.1563. Elemental anal ysis calculated for C10H20: 85.63 C, 14.37 H; found 85.65 C, 14.39 H.

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77 Tridec-1-ene (18b). After purification, 0.98 g (98% yiel d) of a colorless liquid was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.89 (t, 3H), 1.23-1.39 (m, 18H), 2.04 (q, 2H), 4.97 (m, 2H), 5.82 (m, 1H); 13C NMR (CDCl3): (ppm) 11.1, 22.8, 29.4, 29.7, 29.8, 31.9, 33.9, 114.3, 139.5. EI/HRMS: [M]+ calculated for C13H26: 182.2035, found: 182.2033. Elemental anal ysis calculated for C13H26: 85.63 C, 14.37 H; found 85.60 C, 14.42 H.

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78 CHAPTER 4 PRECISELY AND IRREGULARLY SEQUENCED ETHYLENE/1-HEXENE COPOLYMERS: A SYNTHESI S AND THERMAL STUDY 4.1 Introduction During the past decade, ethylene-based copol ymers have been the most widely used thermoplastic materials.3 Within the polyethylene (PE) fam ily, linear low-density polyethylene (LLDPE) plays an important role,126 because of the diversity of ma terials that can be produced. The physical properties of LLDPE can be tuned by manipulating the amount of short-chain branching (SCB) and the short-ch ain branch distribution (SCBD),127, 128 by controlling the mode of polymerization, catalyst type, pressure, and te mperature. Of course, the identity of the comonomer is also important. Commonly, 1-buten e is chosen because of its low cost, but the use of 1-hexene or 1-octene has shown to im prove the mechanical properties of the final material.128-138 It has also been observed that th e properties of LLDPE are affected by interactions between the polymer chains.18-20, 25-30 Commercial LLDPE is usually prepared by chain-growth polymeri zation using ZieglerNatta or metallocene chemistry.4, 139 Multisite-initiated Ziegler catal ysis favors the insertion of ethylene and produces ill-define d and heterogeneous primary st ructures and polymers possessing low-molecular-weights and high molecular-weight distributions.140-142 In contrast, single-site catalysis by metallocene systems produces c opolymers with narrower molecular weight distribution and highe r comonomer content,129, 139, 143-147 but the problem of ill-defined primary structures still remains. Complete characterization of commercial PE requires detailed study of intraand intermolecular properties, incl uding molecular weight distri bution, chemical composition, sequence length distribution and lo ng chain branching level. M odel systems are often employed, because the results can lead to a better understanding of polym er processing and the overall

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79 microstructural effects produced by branch perturbations on PE-based materials.17, 31, 32 In the past, these materials were made by chainpropagation chemistry, which results in the incorporation of unwanted def ects via head-to-head or ta il-to-tail monomer coupling.41-45 The resulting random distribution of alkyl branches along the PE backbone alters the polymer morphology and thermal behavior, thereby precl uding effect use as model systems. The problems associated with chain-growth polymerization can be overcome using stepgrowth condensation polymerizat ion, in particular acyclic diene metathesis (ADMET) polymerization. In this process, the final polym er structure is contro lled by using monomers which undergo solely olefin metathesis to produce PE with perfectly known primary structures. In ADMET, elimination of ethylene gas drives the reaction to yield an unsaturated high molecular weight polymer in the bulk. While chain-growth methods require indirect manipulation of the primary structure,4 ADMET dictates the final primary structure of the polymer based on the monomer design.47 The advantage of this approa ch is the ability to control the polymer architecture by choosing the approp riate building block, ther eby circumventing the use of comonomers and monomer feed ratios or the design of specializ ed catalysts. Model PE copolymers can be prepared by ADMET using symmetrically designed diolefin monomers to produce polymers with well -defined branch identity and distribution along the polymer backbone.46-49, 54, 56, 148 The polymerization is carried out using Schrocks or first generation Grubbs catalyst,149-154 followed by exhaustive satura tion with hydrogen. Figure 4-1 shows the retrosynthesis of ADMET copolymers, with butyl branches precisely placed along the polymer backbone. Initial modeling studies have been performed on PE containing methyl branches on every 9th, 11th, 15th, 19th, and 21st carbon along the backbone.48 Continuation of this research led to the

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80 development of ethyl-branched polyethylene,49 and subsequently to the development of hexylbranched polyethylene.54 These polymers have proven to be ideal models of PE copolymers of sequenced ethylene/1-propylene, ethylene/1-butene and ethylene /1-octene, respectively. This chapter reports the synthesis, characterization an d thermal behavior of model ethylene/1-hexene copolymers. The ADMET process was used to pr oduce PE containing butyl branches precisely spaced along the main backbone, as well as the randomly spaced analogs. 2x+2 n x x n x x Exhaustive Hydrogenation Exhaustive Hydrogenation ADMET ADMET Route (b) More frequently spaced branching Route (a) Less frequently spaced branching 4a when x = 6 4b when x = 9 EH15u, EH21u EH5, EH15, EH21 10 n EH5u Figure 4-1. Retrosynthesis of precisely sequenced ethylene/1-hexene copolymer 4.2 Results and Discussion 4.2.1 Polyethylene Models with Precisely Placed Butyl Branches 4.2.1.1 Monomer synthesis and ADMET polymeri zation of precisely sequenced EH copolymers In the past, attempts to synthesize -diene monomers functionalized only with alkyl branches met with limited success.48, 49, 54 Methodologies were base d on the synthesis of the diene, followed by incorporation of the alkyl branch into the monomeric unit.49, 54 Typically,

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81 extension of the alkyl branch was carried out by coupling of ca rbon moieties mediated via metal complexes, but that strategy resulted in lo w yields and required many synthetic steps. Instead of coupling the alkyl br anch after formation of the -diene, incorporation of the alkyl branch during formation of the -diene can produce monomers with a variety of branch lengths in high yields with fewer synthetic step s. Nitriles are important precursors in these syntheses, because of the reactions that can be performed on the car bon alpha to the nitrile functionality. Double alkenylation of the -carbon, followed by the redu ctive elimination of the nitrile moiety, allows the synt hesis of virtually any alkyl -diene. This alkenylation/decyanation strategy has proven to be useful for the synthesis of a variety of alkyl -dienes with only two synthetic steps in quantitative yields.90, 96 CN Br x 2) 1 eq x x NC x x Ko, HMPA t -BuOH, Ether 1) 1eq LDA, THF, 0 oC 4a when x = 6 4b when x = 9 1 3a-b Br x 4) 1 eq 3) 1eq LDA, THF, 0 oC2a-b Figure 4-2. Synthesis of -olefins via dialkylation/decy anation of hexanenitrile Figure 4-2 illustrates the s ynthetic methodology to produce -diene monomers 4a and 4b from the alkenylation of hexanenitrile 1 with alkenyl bromides 2a and 2b Alkenylation of 1 in the presence of lithium diisopropyl amide (LDA) and 8-bromooct-1-ene ( 2a ) or 11bromoundec-1-ene ( 2b ) produces the cyano -dienes 3a and 3b in quantitative yields.90 Decyanation of nitriles 3a and 3b is achieved by transferring one electron from potassium metal to the nitrile group to form a ra dical anion, which promotes elim ination of the cyanide anion. The resulting tertiary radi cal is further quenched by ab straction of hydrogen from t -BuOH to

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82 give -diene monomers 4a and 4b in quantitative yields.96 Synthesis of -dienes containing longer runs of methylene units between the term inal olefins is under current investigation. x x x x n CH2=CH2 x x n (PPh3)3RhCl H2 (400 p.s.i) 20 n EH21 14 n EH15 When x = 6 When x = 9 4a-b EH15u, EH21u 5 Ru PCy3 PCy3 Ph Cl Cl 1st Gen. Grubbs 1st Generation Grubbs catalyst Toluene, 100 oC Figure 4-3. Synthesis of EH15 and EH21 via ADMET polymerization-hydrogenation As shown in Figure 4-3, polymerization of -diolefin monomers 4a and 4b is carried out with first generation Grubbs catalyst ( 5 ) in the absence of solvent. Similar to any step-growth polycondensation, ADMET require s pure monomers to obtain high conversion. The polymerization proceeds efficiently yielding unsaturated polymers EH15u and EH21u with less than 1-2% cyclization side reac tions. Subsequent exhaustive satu ration of the internal olefins with hydrogen gas and Wilkinson catalyst in toluene yields saturated polymers EH15 and EH21 The efficiency of hydrogenation can be followed by the disappearance of the olefin signals in 1H NMR (Figure 4-5) and 13C NMR (Figure 4-6), and by the di sappearance of the out-of-plane alkene C-H bend using infrared (IR) spectroscopy (Figure 4-7). The nomenclature of ADMET products is base d on the comonomers for the corresponding copolymer formed by chain addition.. All copolymers include the prefix E for ethylene,

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83 followed by the comonomer type H for 1-hexene. Saturation or unsaturation of the main backbone is given by the absence or presence of the suffix u and the branch frequency is indicated by number. For example, EH21 designates the satura ted precisely sequenced ethylene/1-hexene copolymer w ith a butyl branch on every 21st carbon, while EH21u refers to the unsaturated analog. Although the synthetic approach described above can be us ed to prepare EH models containing butyl branches on every 15th and 21st carbon (route (a) in Figure 4-1), the synthesis of the monomers for EH copolymer with shorter me thylene run lengths between branches has been difficult to accomplish. During the decyanation pro cess (Figure 4-2), the intermediate tertiary radical can undergo intraradical cyclization. Unwa nted cyclization products were isolated when decyanation chemistry was used to synthesize the -diene monomers containing 3 and 4 methylene groups, 6-butylundeca-1,10diene and 7-butyltrideca-1,2,12-triene.96, 116-122 In addition, ADMET polymerization based on 1,6-hept adiene monomers will also result in cyclization by ring closing metathes is. Therefore, a different approa ch was used for the synthesis of EH copolymer models possessing butyl bran ches spaced by fewer than 15 methylene units. Previous success in the synthesis of EP copolymers containing methyl groups on every 5th and 7th carbon56 led us to try ADMET polymerization of monomers containing two butyl groups on each monomeric unit. Figure 4-4 shows the synthetic approach for obtaining EH5 polyethylene containing a butyl branch on very 5th carbon. Monoalkenylati on of hexanenitrile 1 with allyl bromide 6 in presence of LDA yields nitrile 7 Disubstitution of 1,4-dibromobutane quantitatively yields 2,7-diall yl-2,7-dibutyloc tanedinitrile 9 which undergoes decyanation to produce 5,10-diallyltetradecane (monomer 10 ). Polymerization of 10 in presence of first generation Grubbs catalyst proceeds sm oothly to produce unsaturated polymer EH5u

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84 Exhaustive hydrogenation of the unsaturat ed polymer in the presence of p -toluenesulfonyl hydrazide, tripropyl amine and xylene yields EH5 This methodology allows the synthesis of highly branched sequenced ethylene/1-hexene copol ymers. The correct design of the monomeric unit circumvents ring closing metathesis nor mally observed in structures based on 1,6heptadiene. Ru PCy3 PCy3 Ph Cl Cl Br CN CN Br Br CN CN Ko, HMPA t-BuOH Ether n 4 n EH5 pTSH TPA Xylene, 130 oC1st Gen. Grubbs 6 7 8 9 10 EH5u 11) 1eq LDA, THF, 0 oC 2) 1 eq 1) 1eq LDA, THF, 0 oC 2) 1 eq Figure 4-4. Synthesis of EH5 via ADMET polymerization-hydrogenation. Regardless of the strategy employed for the -diene monomer preparation, high molecular weight polymers were afforded via ADMET for both monoalkyl ( 4a and 4b ) and dialkyl diolefins ( 10 ). Table 1 shows the molecular weights for the precisely sequenced ethylene/1hexene copolymer models obtained via ADMET po lymerization. The weight-average molecular weights were obtained by gel permeation chroma tography (GPC) versus polystyrene standards. The small difference in molecular weight before and after hydrogenation suggests that the main PE chains are not affected by the saturation proce ss. This is expected, because of the difference in dilute solution behavior of polyethylene comp ared to the polystyrene GPC standards, and is not due to cleavage of the polymer chains. The range of molecular weights (20,000 to 40,000 g/mol by GPC) is sufficient to model the ther mal behavior of commerc ially available LLDPEs.48

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85 Table 4-1 Molecular weights for ADMET models, EH precisely sequenced copolymers. wM x 103 (PDI)c Model EH copolymer Butyl on every nth backbone carbon na Butyl branch content per 1000 carbons Unsaturated b Saturated b Tm (C) (peak) hm (J/g) EH5 5 200 21.2 (1.7) 20.8 (1.8) Amorphous EH15 15 67 47.6 (1.9) 48.1 (1.9) 33 & -53 13 EH21 21 48 41.5 (1.8) 40.3 (1.7) 14 47 a Branch content based on th e hydrogenated repeat unit. b Weight-average molecular weight data obtained using GPC in THF (40 C) re lative to polystyrene standards (g/mol). c PDI, polydispersity index ( n wM M / ) 4.2.1.2 Structural data for precisel y sequenced EH copolymers Control over the polymer primary struct ure by ADMET makes it possible to obtain information about the macromolecular structur e of linear low-densit y polyethylene having defects intentionally and evenly placed along the main chain. Examination of 1H and 13C NMR spectra of monomers and polymers indicates co mplete transformation and control over the primary structure. Figure 4-5 shows the 1H NMR spectra for the ADMET polymer EH5 and its precursors. The transformation begins w ith the decyanation of 2,7-diallyl-2,7dibutyloctanedinitrile (9) yielding 5,10-diallyltetradecane monomer (10), shown in Figures 4-5a and 4-5b, respectively. Polymerization of 10 yields the unsaturated polymer EH5u. Analysis of the olefin region (5-6 ppm) supports the fact that the polymer is fo rmed from a single repeat unit, which is evidenced by the disappearance of the term inal olefin signals (5.1 and 5.9 ppm in Figure 4-5b) and the formation of the in ternal olefin (5.3 ppm in Figur e 4-5c). Further hydrogenation of the internal olefins yields EH5, a perfectly sequenced ethyle ne/1-hexene copolymer, which shows no observable traces of olefin by 1H NMR (Figure 4-5d).

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86 Figure 4-6 shows the 13C NMR spectra for the same comp ounds. In the spectrum for the 2,7-diallyl-2,7-dibut yloctanedinitrile (9, Figure 4-6a), the singlets at 120.1 and 132.0 ppm show the presence of terminal olefin s, and the signal at 123.7 ppm corresponds to the nitrile carbon. Absence of the signal at 123.7 ppm after decyan ation (Figure 4-6b) demonstrates complete elimination of the CN group. Based on the values of the chemical shifts for the singlets corresponding to the terminal olefin (120.1 and 132.0 ppm in pre-monomer 9 versus 115.8 and 137.8 ppm in monomer 10) and the data obtained from 1H NMR, it can be concluded that the change in chemical shifts is due solely to the absence of the nitrile functionality and not to isomerization of the terminal olefin to an internal olefin. ADMET polymerization of 10 yields the unsaturated polymer EH5u. Comparison of Figures 4-6b and 4-6c shows the disappearance of the signals belonging to the terminal olefin at 115.8 and 137.8 ppm and formation of the new internal olefin (cis at 129.4 pp m and trans at 130.1 ppm) produced from the effective metathesis polymerization. Subsequent hydroge nation of the internal olefin yields the saturated polymer EH5, whose 13C NMR spectrum (Figure 4-6d) shows no det ectable trace of olefins. Upon close inspection of the 13C NMR data during the transformation, it can be concluded that the ADMET polymer EH5 is formed only by symmetrical repeati ng units, in which the methyl from the pendant side chain butyl branch resona tes at 14.5 ppm (C H3), the methylene alpha to the terminal methyl group at 23.6 ppm (C H2CH3) and the carbon at the branch point at 37.8 ppm.

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87 Figure 4-5. Comparison of 1H NMR spectra for a typi cal ADMET polymerization transformation: (a) Premonomer 9, 2,7-diallyl-2,7-dibutyl octanedinitrile, (b) Monomer 10, 5,10-diallyltetradecane, (c ) ADMET unsaturated polymer EH5u, (d) ADMET saturated polymer EH5.

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88 Figure 4-6. Comparison of 13C NMR spectra for a typical ADMET polymerization transformation: (a) Premonomer 9, 2,7-diallyl-2,7-dibutyl octanedinitrile, (b) Monomer 10, 5,10-diallyltetradecane, (c ) ADMET unsaturated polymer EH5u, (d) ADMET saturated polymer EH5

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89 Further studies of these precisely sequenced ethylene/1-hexene copolymer models were performed using infrared (IR) spectroscopy. Although 1H and 13C NMR showed no detectable remaining traces of olefins after exhaustive hyd rogenation, IR spectroscopy offers the most sensitive method to observe whether complete saturation has occurred.46, 47, 148 Figure 4-7 shows the IR spectra before and after exhaustive hydr ogenation of the model ma terial. The unsaturated material EH5u (Figure 4-7, bottom curve) show s an absorption band at 969 cm-1 due to the outof-plane C-H bend in the alkene, which di sappears after complete hydrogenation to EH5 (Figure 4-7, top curve). Figure 4-7. Infrared spectra for the ADMET unsaturated and saturated polymers EH5u (bottom) and EH5 (top)

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90 In the past, Tashiro et al carried out a study of branching behavior on ultra high molecular weight polyethylene using complementary data from wide angle x-ray diffraction (WAXD), IR and Raman spectroscopy.155 They concluded that the scissoring at 1466 cm-1 and methylene rock at 721 cm-1 indicate a hexagonal crystal structure, wh ile the double methylene rock at 719 and 730 cm-1 and single band at 1471 cm-1 correspond to an orthorhombi c crystal structure. Similar IR studies and WAXD measurements showed the same connections of inter-chain defects to crystal behavior and crystal packing for ADMET PE containi ng methyl branches randomly placed along the backbone.50 As described below, the lo w melting transitions of our semicrystalline EH model copolymers made it di fficult to obtain solid-state data. However, detailed IR analysis for the synthesized EH copolymers gives an idea of their crystal structures. The IR spectra for EH5, EH15, and EH21 in Figure 4-8 are dominated by two sets of absorption bands (2900 and 1464 cm-1), which are usually obser ved when the packing is disorganized. While orth orhombic crystals show the charact eristic Davidov splitting at 720 cm-1 due to the methylene rocking,133, 156 our EH models display a si ngle rocking absorbance at 728 cm-1, indicating the absence of orthorhombic crysta l behavior. Moreover, the two experimental absorption bands at 728 and 1464 cm-1 are characteristic of a highly disordered phase, similar to the pattern observed in previous studies containing precisely spaced methyl,48 ethyl,49 and hexyl branches.54 Similar to PE models possessing hexyl branches,55 EH models displa y characteristic bands at 2955, 1464 and 728 cm-1, which suggest that the larger defect volume imparted by evenly spaced butyl branches does not alter the methylene scissori ng and wagging regions. The IR data presented above indicates that the precisely sequenced model copolymers EH5, EH15 and EH21 contain high defect concentrati ons. Although we cannot rule out the presence of hexagonal crystals, th e absence of the characteristic orthorhombic signature is clear

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91 in the IR spectra. In order to understand how the crystal packi ng occurs in our EH models, a series of solid-state NMR expe riments and subambient x-ray di ffraction experiments (SAXS and WAXD) are currently underway. Figure 4-8. Infrared spectra for the ADMET saturated polymers EH5 (bottom), EH15 (center), and EH21 (top) 4.2.1.3 Thermal behavior for precisely sequenced EH Copolymers Numerous reports are available concerning the structure and thermal properties of branched PE, particularly for LLDPE a nd HDPE made by chain-addition chemistry.20, 25, 27-30, 157 Although the ultimate goal has been to understand th e relationship between structure and physical properties, many previous investigations attempted to correlate initial monomer feed ratios to the final properties of the produced materials. A major draw back to this approach is the problem of imperfect primary structures, whic h are always present in materials produced by

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92 chain-addition chemistry. In contrast, our well-d efined primary structures permit studies of the thermal properties of precisely sequ enced ethylene/1-hexene copolymers. Figure 4-9. Differential scanning calorimetr y curves for ADMET polymers: EH5 (bottom), EH15 (center) and EH21 (top). Figure 4-9 shows the DSC analysis for EH5, EH15, and EH21, and the physical data are summarized in table 4-1. Similar to previous st udies involving polyethylen e containing regularly spaced methyl (EP),48 ethyl (EB),49 and hexyl branches (EO),54 the precisely sequenced ethylene/1-hexene (EH) copolymer s display sharp and well-defined endothermic transitions, with none of the broadening observed for copol ymers obtained via chain polymerization.20, 25, 27-30, 157 The data in table 4-1 show that the EH models follow the trend previous ly observed for EP, EB, and EO model copolymers, for which melting te mperature, heat of fusion, and degree of

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93 crystallinity all decrease as the perc entage of 1-olefin increases. The EH21 and EH15 copolymers are both semicrystalline materials, with percent crystallinity d ecreasing as the branch content increases. When the branch content incr eases to 200 branches per 1000 backbone carbons (EH5), a fully amorphous material is produced. Figure 4-10. Differential scanning calorimetry cu rves for ADMET polymers possessing alkyl branches on every 21st carbon. Data for EP21, EB21, and EO21 taken from Wagener et al .48, 49, 54 The DSC profiles for a series of precisely se quenced copolymers containing alkyl branches on every 21st carbon (Figure 4-10) show an obvious correlation between branch size and thermal behavior. While EP21 depicts a sharp and welldefined melting point at 62 C, one-carbon homologation on the side branch (EB21) produces a 40 C lower bimodal melting transition at 24 C (major peak) and 15C (minor peak). Th is bimodal behavior co uld be produced by many factors; for example, the presence of a pre-meltin g endotherm due to the existence of two distinct

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94 arrays packing differently in the crystal structur e. Increasing the branch size from two to four carbons (EH21) produces a sharp, well-defi ned single endotherm at 14 C, the same temperature as the small endotherm for EB21. This indicates that EH21 contains only one packing array, which is different from that observed for EP21. Interestingly, addition of two more carbons to the side branch (EO21), seems to have no effect on the thermal behavior, suggesting that EH21 and EO21 are quite similar in nature. The same trends are observed when the bran ch spacing is14 methylene units, as shown in Figure 4-11. Incorporation of a methyl defect on every 15th carbon (EP15) renders a material with a well-defined endotherm w ith a peak melting of 39 C. When the side chain is extended to two carbons (EB15) a bimodal transition is observed. In contrast to the behavior of EB21, the smaller fraction corresponds to the higher meltin g component (-6C, minor fraction, vs -33C, major fraction). As in the case of EB21 and EH21, the larger overall he at flow observed for EH15 corresponds to the lower temperature endotherm for EB15, but there is an additional small contribution at -53 C. The peak at -53 C for EH15 overlaps the endotherm previously reported for EO15 at -48 C, but the latter also shows a small peak at -17 C. When the branch distance is maintained constant, whether 20 carbons (Figur e 4-10) or 14 carbons apart from each other (Figure 4-11), a clear depression of the melting point of the model mate rials is observed when the branch size is gradually increased from one carbon unit (EP models) to six carbon units (EO models). Although EO and EH copolymers made via chain-growth chemistry are amorphous due to their high comonomer content (13-14%), pr ecisely sequenced ethylene/1-olefin models containing an alkyl branch on every 21st and 15th carbon contain more organized primary structures and are semicrystalline materials.

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95 Figure 4-11. Differential scanning calorimetry cu rves for ADMET polymers possessing alkyl branches on every 15th carbon. Data for EP15, EB15, and EO15 taken from Wagener et al .48, 49, 54 When the defects are evenly and precisely distributed along the polye thylene main chain, the well-organized primary structures permit the formation of semicrystalline materials. However, regardless of the branch identity or the order imparted by the perfectly sequenced comonomer incorporation, the ability to form se micrystalline materials is lost if the defect becomes more frequent along th e polyethylene backbone, as show n in Figure 4-12. The DSCs of both EP5 and EH5 model copolymers indicate that these compounds are fully amorphous materials. It is noteworthy that the pr esence of the bulkier butyl branch on EH5 causes the glass transition previously observed for EP5 at -65C to decrease to -73 C. Thus, even the amorphous state is affected by the size of the branch on the polyethylene backbone.

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96 Figure 4-12. Differential scanning calorimetry cu rves for ADMET polymers possessing alkyl branches on every 5th carbon. Data for EP5 taken from Baughman, Sworen and Wagener.56 4.2.2 Polyethylene Models with Irregularly Placed Butyl Branches The first part of this chapter has describe d the ADMET synthesis of polyethylene with precisely spaced butyl branches. While these are not models for the industrial ethylene copolymers in the true sense of the word, they represent an excellent st arting point for the study of structure/property relationships in ethylene-based materials, b ecause they allow the effects of specific structural features to be isolated and investigated. As described above, DSC results show that these well-organized primary stru ctures display unique thermal behavior. In contrast, because of inevitable chain transf er or chain walking, industrially prepared LLDPE made by copolymeri zation of ethylene with -olefins produces structures with alkyl branches of varying lengths randomly spaced alo ng the main chain.. Thus, realistic models of

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97 commercial ethylene/1-alkene copo lymers should have branches of known chain length, but with random spacing. These materials can also be synthesized by the ADMET process, as demonstrated previously for EP copolymers and halogen-substituted polyethylene.50, 158 4.2.2.1 Monomer Synthesis and ADMET polymeriza tion of Irregularly Sequenced EH Copolymers Using metathesis chemistry for modeling PE structures, the branch frequency can be controlled by copolymerization of monomeric units with the correct architecture. Because the comonomers have similar reactivit ies, total conversion of the monomers into copolymer permits manipulation of the branch cont ent of the final material. For example, ADMET copolymerization of a monomer containing the required branch id entity (butyl branch) along with 1,9-decadiene produces an irregularly sequenced ethylene/1-hexene copolymer. In chain-growth chemistry the branch content is directly related to both th e molar and reactivity ratios, but step-growth chemistry permits manipulation of the branch cont ent of the final material by controlling only the initial molar ratio of the two monomers without dealing with reactivity ratios. 66 + 6 66 6 xy n 86 8 xy n Random EH copolymer Random Unsaturated PE EH-2.5u to EH-43.5u Ru PCy3 PCy3 Ph Cl Cl CH2=CH24a 11 EH-2.5 to EH-43.5pTSH TPA Xylene, 130 oC Figure 4-13. Synthesis of EH random materi als by ADMET copolymerization of 9butylheptadeca-1,16-diene (4a) and 1,9-decadiene (11). As shown in Figure 4-13, ADMET copolymer ization of 9-butylheptadeca-1,16-diene (4a) with 1,9-decadiene (11) in the presence of first generation Grubbs catalyst yi elds unsaturated polymers EH-2.5u to EH-43.5u. Exhaustive hydrogenation of th e unsaturated polymers using p -

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98 toluenesulfonyl hydrazide, tripr opyl amine and xylene yields i rregularly sequenced ethylene/1hexene copolymers EH-2.5 to EH-43.5. The nomenclature for the unsaturated/saturated polymers is based on the comonomer content. The prefix E denotes for polyethylene, followed by the comonomer type H for 1-hexene. Saturation or unsat uration of the main backbone is given by the absence or presence of the suffix u. The branch content is given by number; e.g., EH-2.5 designates the saturated irregularly seque nced ethylene/1-hexene copolymer, which contains 2.5 butyl branches per 1000 backbone carbons, while EH-2.5u refers to its unsaturated analog. Copolymerization of different molar ratios of 4a and 11 yields a series of materials with varying butyl branch content, as shown in table 4-2. The lo wer limit of comonomer content incorporation is set by perfectly linea r PE made by homopolymerization of 11, which yields perfectly linear polyethylene with no alkyl branches EH0.47 Incorporation of 2 mol % of 4a renders EH-2.5u, which has wM = 40,000 g/mol and a polydisper sity index (PDI) of 1.7 via GPC versus polystyrene standards. Subsequent saturation yields EH-2.5 with a wM = 39,800 g/mol and PDI = 1.8. The small change in mol ecular weight after satu ration suggests that the main chain is not affected by the hydrogenation process. Weight-average molecular weights of materials with higher comonomer content, from EH-6.0 to EH-43.5, are also listed on table 4-2. Incorporation of 5, 10, 20, 40, and 50 mol % of comonomer 4a yields materials containing 6.0, 11.5, 21.3, 37.0, and 43.5 butyl branches per 1000 backbone carbons, respectively. The models in table 4-2 have weight-average molecula r weights ranging from 37,000 to 45,000 g/mol by GPC. Regardless of the molecular weight de termination method, the molecular weights displayed in table 4-2 for our irregularly sequenced ethylen e/1-hexene copolymers are sufficiently high to serve as mode ls for LLDPE or EH copolymers.

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99 Table 4-2. Molecular weights for unsaturated and saturate d EH irregularly sequenced copolymers prepared by ADMET wM x 103 (PDI)c Copolymer with irregularly placed butyl branches Butyl branch content per 1000 backbone carbons a 9-butylheptadeca1,16-diene (4a) mol % 1,9decadiene (11) mol % Unsaturated b Saturated b EH0 0.0 0 100 42.5 (1.8) 44.9 (1.8) EH-2.5 2.5 2 98 40.1 (1.7) 39.8 (1.8) EH-6.0 6.0 5 95 39.5 (1.7) 40.7 (1.6) EH-11.5 11.5 10 90 38.7 (1.6) 37.8 (1.8) EH-21.3 21.3 20 80 48.4 (1.6) 45.1 (1.6) EH-37.0 37.0 40 60 37.5 (1.8) 38.1 (1.7) EH-43.5 43.5 50 50 38.4 (1.8) 37.3 (1.8) EH15 66.7 100 0 47.6 (1.9) 48.1 (1.9) a Determined by an average of both the 1H NMR (300 MHz) and 13C NMR (125 MHz) data. b Weight-average molecular weight data obtained by GPC in THF ( 40 C) relative to polystyrene standards (g/mol). c Weight-average molecular weight da ta obtained by low-angle laser light scattering (LALLS) in THF at 40 C (g/mol). d PDI, polydispersity index ( n wM M /) 4.2.2.2 Structural Data for Irregularly Sequenced EH Copolymers The butyl branch content initially dete rmined by the molar content of monomer 4a was verified for the final materials, EH-2.5 to EH-43.5, by a combination of 1H and 13C NMR spectroscopy, as previous ly reported by Wagener et al for ethylene/propene copolymers.50 For each 1H NMR spectrum, 160 transients were co-ave raged using a 90 acqu isition pulse and a total relaxation delay of 10.8 s. All spectra we re Fourier transformed to 64 K complex points with line broadening of 0.2 Hz. The chemical shift scale was referenced to the residual tetrachloroethane (TCEd2) protons at 5.98 ppm. Likewise, for each 13C NMR spectrum, 4000 transients were co-averaged, us ing a 90 acquisition pulse with fu ll decoupling to obtain optimal nuclear Overhauser enhancement. Broadba nd decoupling was performed with WALTZ-16

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100 modulation. A total relaxation de lay time of 20.9 s was employed. The spectra were Fourier transformed to 64 K points, with 1 Hz line broa dening. The butyl branch contents calculated using both the 1H and 13C data are given in table 4-2. Figure 4-14. Comparison of 13C NMR spectra for: (a) Non-branched ADMET PE EH0, (b) irregularly sequenced EH-43.5 ADMET polymer, and (c) precisely sequenced EH15 ADMET polymer. Figure 4-14a shows the 13C NMR spectrum for the homopolymerization of 1,9-decadiene after exhaustive hydrogenation (EH0). The linear polyethylene presents a dominant signal at 29.99 ppm (signal E), which corresponds to the methylene units forming the polyethylene main chain. Detailed 13C NMR analysis allows visu alization of signals A ( 14.31 ppm), B ( 22.94 ppm), C ( 32.22 ppm), and D ( 29.60 ppm), which correspond to the endgroups of the terminal

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101 polyethylene chain, as shown in Figure 4-14a. In-depth 13C NMR analysis for the perfectly sequenced EH15 copolymer permits the visualization of the carbon at the branch point at 37.62 ppm (signal V), as shown in Fi gure 4-14c. Similar to the spectr um shown in Figure 4-14a, the 13C NMR for EH15 (Figure 4-14c) is domi nated by the signal at 29.99 ppm corresponding to the PE backbone. Close inspection of spectra 4-14c and 4-14a shows that the terminal CH2CH2CH3 linkage (A, B, and C) is present in bo th, indicating that the presence of butyl branches precisely placed on every 15th carbon affects carbons no greater than three positions from an individual branch located on the pol ymer backbone. The same effect was observed by Wagener et al during 13C NMR experiments of polyethylen e containing methyl branches.50 Moreover, the spectrum in Figure 4-14c shows the resonances belonging to the butyl branch, I ( 14.39 ppm), II ( 23.40 ppm), III ( 30.40 ppm), and IV ( 33.63 ppm) and the three carbons on the main chain around the branch point, VI ( 33.95 ppm), VII ( 26.95 ppm), and VIII ( 29.20 ppm). Figure 4-14b shows the 13C NMR spectrum for the irregularly sequenced ethylene/1hexene model copolymer containing 43.5 butyl branches per 1000 backbone carbons (EH-43.5). Like the spectra in Figure 4-14a and 4-14c, th e spectrum in Figure 4-14b is dominated by the signal at 29.99 ppm corresponding to the PE backbone Detailed analysis of the resonances observed for EH-43.5 indicates that both EH0 and EH15 characteristics are pr esent; the terminal endgroups (A, B, and C) are present, as well as the resonances correspondi ng to the butyl branch (I, II, III and IV). The main differences between the spectra in Figure 4-14b and 4-14c are the relative areas for the signals corres ponding to the butyl branch (signa ls I, II, III, and IV), which are all smaller for EH-43.5 (43.5 butyl branches per 1000 ba ckbone carbons, 4-14b), compared to EH5 (200 butyl branches per 1000 backbone carbons 4-14c).

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102 Figure 4-15. Infrared spectra for the irregularly placed ADMET copolymers EH0-EH43.5, (a) recorded in the region of 1400-1335 cm-1, (b) recorded in the region of 1490-1440 cm-1, and (c) recorded in the region of 750-690 cm-1.

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103 In addition to the NMR characterization of the irregularly sequenced ethylene/1-hexene ADMET copolymers, infrared (IR) spectro scopy was used to study EH copolymers EH-2.5 to EH-43.5. Although x-ray diffraction tec hniques provide the absolute crystal structure, IR spectroscopy can give an idea of the order or cr ystal structure for these model polymers. Pracella et al reported the structural ch aracterization of EH copolymers made via chain-growth chemistry.133 In their report, detailed IR study for EH copolymers facilitated the determination of the comonomer contents in the 1-5 mol% range. Similarly to Pracellas work, we have focused the IR analysis on three main re gions: 1490-1440, 1400-1330, and 750-690 cm-1. The region from 1400 to 1330 cm-1 is useful for compositional analysis of ethylene/ -olefin copolymers. In this region (Figure 4-15 a), linear polyethylene EH0 shows an absorption band at 1369 cm-1 corresponding to the methylene wagging.133, 159 Incorporation of butyl branches along the PE backbone results in formation of a new absorption band at 1378 cm-1, corresponding to the symmetric deformation of the terminal methyl on the butyl branch. While the band at 1378 cm-1 is very weak for EH-2.5 due to the low comonomer content, IR analysis of materials with higher comonomer contents present more intense bands with areas proportional to the branch content. Figure 4-15b shows spectra of the 1490-1440 cm-1 region, which contains bands at 1473 cm-1 and 1463 cm-1 due to the bending of methylene uni ts in the crystalline and amorphous phases. Linear ADMET polyethylene EH0 exhibits two well-defined bands at 1473 and 1463 cm-1, suggesting the presence of a well-organized hi ghly crystalline structure. However, gradual incorporation of butyl branches decreases the ar eas of both bands, indicating a reduction in the degree of crystallinity, because of the formation of less organized structures in the polymers with high butyl branch content.

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104 While the precisely sequenced EH model copolymers, EH5, EH15, and EH21 showed no signs of orthorhombic crystal behavior (Figure 48), usually observed as a Davidov splitting at 719 and 730 cm-1 due to the methylene rocking, the irre gularly sequenced EH model copolymers show the characteristic pattern of an orthorhombic lattice.133, 160 It is important to note that the characteristic bands suggesting the orthorhombi c crystal behavior are most pronounced in the linear ADMET polyethylene possessing no branches (EH0). Increasing the comonomer content causes the intensities of the absorption bands at 719 and 730 cm-1 to decrease. In order to clarify how the crystallization process occurs in our irregularly seque nced EH model copolymers, a series of solid-state NMR, SAXS and WA XD experiments are currently under study. 4.2.2.3 Thermal Behavior for Irregularly Sequenced EH Copolymers While numerous investigations are availa ble concerning the structure and thermal properties of ethylene/1-hexene copo lymers made via chain chemistry,128, 129, 131-135 the new ADMET copolymers have the well-defined, defect-f ree primary structures needed to gain an understanding of the relationship between comono mer content and thermal behavior. The first attempt in modeling LLDPE with randomly placed alkyl branches prepared by ADMET chemistry was carried out using ethylene/propene (EP) copolymers.50 Although sharp and welldefined endotherms were observed for EP rando m models containing up to 25 methyl branches per 1000 backbone carbons, broad and ill-defined endotherms were observed for EP random models with 43 methyl branches per 1000 b ackbone carbons (~10 mol% of propylene). The same effect has been observed for EP random copo lymers made via Ziegler-Natta chemistry with comonomer content greater than 15 mol %.

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105 Figure 4-16. Differential scanning calor imetry curves for ADMET polymers: EH0, EH-2.5, EH6.0, and EH-11.5 Similar to ADMET EP random model copol ymers, the ADMET EH model copolymers give sharp and well-defined endotherms at lower comonomer content, as shown in Figure 4-16. Linear polyethylene without branches (EH0) has the highest melting temperature (Tm = 134 C) and heat of fusion ( hm = 205 J/g). Incorporation of small am ounts of butyl branches irregularly placed along the PE backbone has only a small eff ect on the melting temperature of the material. For example, incorporation of 2.5 (EH-2.5) and 6 butyl branches (EH-6.0) per 1000 backbone carbons reduces the melting temperature to 126 and 122 C, respectively. In contrast, the enthalpies of fusion of such material s decrease significantly, by 12 J/g for EH-2.5 and 76 J/g for EH-6.0. This effect can be attributed to the decrease in crystallinity when larger numbers of butyl branches are incorporated.

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106 Similarly to previously reported ADMET EP random models, our ADMET EH models showed a broad and ill-defined endotherms at lo wer comonomer content th at their counterpart chain-growth-based materials. For example, random copolymers made using chain-growth chemistry with greater than 5% 1-hexene incorpor ation generate the same type of broad and illdefined curves shown here.128, 134 However, EH-11.5 copolymer produced by ADMET exhibit this broad and ill-defined melting at lower bran ch density than that their counterpart chaingrowth-based materials, being EH-11.5 a pproximately 3% 1-hexene incorporation. Figure 4-17. Differential scanning calorimet ry curves for ADMET polymers: EH-21.3, EH-37.0, and EH-43.5 Figure 4-17 shows the DSC profiles for irre gularly sequenced EH model copolymers possessing higher branch content, EH-21.3, EH-37.0, and EH-43.5. As expected, increasing the branch content along the PE backbone results in br oadening of the endotherms. In addition, these copolymers have very indistinct Tms, an indication that, along with branch identity, branch

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107 distribution plays a significant role in determining the final thermal properties of the material. This observation is very evident when a copolymer with precisely spaced branches is compared to an irregular copolymer with the same total branch content. Figure 4-18 shows the DSCs for EH-43.5 and EH21, which are EH models containing 43.5 and 48 butyl branches per 1000 backbone carbons, respectively. While EH-43.5 shows a broad and ill-defined melting endotherm due to the irregularity in placi ng butyl branches al ong the PE backbone, EH21 shows a sharp and well-defined melting point because of the higher degree of crys tallinity imparted to the tertiary structure by the ev enly spaced primary structure. Because ADMET chemistry results in known primary structures, we are able to manipulate the tertiary structure of the EH copolymers simply by choosing the correct monom er or comonomer. Materials with a wide range of thermal properties, from semicrystallin e to fully amorphous, can be prepared simply by control of monomer arch itecture, without manipulation of external conditions, such as high temperature, pressure or irradiation. Figure 4-18. Differential scanning calorimetry cu rves for precisely sequenced ADMET copolymer EH21 (48 branches/1000 backbone car bons) and irregularly sequenced EH-43.5 ADMET copolymer (43.5 branches/1000 backbone carbons).

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108 4.3 Conclusions Acyclic diene metathesis polymerization ha s proven to produce polyethylene materials with perfectly well-defined, defect-free primar y structures. ADMET allows the intentional incorporation of defects regul arly or irregularly placed along the polyethylene main chain. Structural and thermal study of ADMET model copolymers containing butyl branches (ethylene/1-hexene (EH) copolymers) reveal s unique properties never observed for EH copolymers made via chain-propagation chemis try. Thus, the ADMET EH copolymers may be considered as a new class of LLDPE. Analogous to observations on previously reported model copolymers (EP, EB, and EO), increasing the am ount of comonomer content, 1-hexene, has a pronounced lowering effect on the density, enthalpy of melting, degree of crystallinity, and peak melting transition of such materials. Moreover, manipulation of the primary structure by simple choice of monomer or comonomer architecture makes it possible to form LLDPEs with a wide range of properties, from semicrystalline to am orphous materials. Although in the past, synthesis of alkyl -diene monomers has required many synt hetic steps affording only low yields, production of monomers in two s ynthetic steps in quantitative yields is now possible using alkylation/decyanation chemistry. Our work in this area continues, focusing on much longer defect-to-defect spacing and a va riety of bulkier and longer bran ch identities. By creating a complete catalogue of polymers with precise and irregular alkyl branch placement, we aim to understand the intriguing physical and chemical behavior of polyethyl ene-based materials. 4.4 Experimental Section Instrumentation and Analysis. All 1H NMR (300 MHz) and 13C NMR (75 MHz) spectra were recorded in CDCl3 unless otherwise stated. Chemical sh ifts were referenced to residual signals from CDCl3 (7.27 ppm for 1H, 77.23 ppm for 13C) with 0.03% v/v TMS as an internal

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109 reference. The NMR splitting patterns are designat ed as follows: s, single t; d, doublet; t, triplet; m, multiplet; and br, broad signal. Analysis of samples by gas chromatography (GC) was performed on a gas chromatograph, equipped with a flame ionization detector, using a capillary column coated with 5% diphenyl 95% dimethylpolysiloxane. High-resolution mass spectrometry (HRMS) was performed using a mass spectrometer in the electron ionization (EI) mode. The mass resolution was ~6000 for EI meas ured at Full-Width-Half-Maximum (FWHM) in the high resolution detection mode. Thin laye r chromatography (TLC) was used to monitor all reactions and was performed on aluminum plates coated with silica gel (250 m thickness). TLC plates were developed to produ ce a visible signature by any of the following: ultraviolet light, iodine, vanillin, KMnO4, or phosphomolybdic acid. Flas h column chromatography was performed using ultra pure silica gel (40-63 m, 60 pore size). All reactions were performed in flame-dried glassware under argon unless otherwise stated. Gel permeation chromatography (GPC) was pe rformed using an internal differential refractive index detector (DRI), internal differ ential viscosity detector (DP), and a Precision 2 angle light scattering detector (LS). The light scattering sign al was collected at a 15 degree angle, and the three in-line dete ctors were operated in series in the order of LS-DRI-DP. The chromatography was performed at 45 C using two columns (10 microns PD, 7.8 mm ID, 300 mm length) with HPLC grade tetr ahydrofuran as the mobile pha se at a flow rate of 1.0 mL/minute. Injections were made at 0.050.07 % w/v sample concentration using a 322.5 l injection volume. In the case of universal calibration, retention times were calibrated against narrow molecular weight polystyrene standards. MA). All standards were selected to produce pM or wM values well beyond the expected polymer's range. The Precision LS was calibrated using narrow polystyrene standard having an wM = 65,500 g/mol.

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110 Fourier transform infrared (FT-IR) sp ectroscopy was carried out for monomers, unsaturated and saturated polymers. Monomer s were prepared by droplet deposition and sandwiched between two KCl salt plates. Unsatu rated and hydrogenated polymer samples were prepared by solution casting a th in film from tetrachloroethylene onto a KCl salt plate. Differential scanning calorimetry (DSC) anal ysis was performed using a DSC equipped with a controlled cooling accessory at a heating rate of 10 C/min. Calibrations were made using indium and freshly distilled n -octane as the standards for p eak temperature transitions and indium for the enthalpy standard. All samples were prepared in hermetically sealed pans (5-10 mg/sample) and were run using an empty pan as a reference and empty cells as a subtracted baseline. The samples were scanned for multiple cy cles to remove recrystallization differences between the samples and the results reporte d are of the third scan in the cycle. Materials. Chemicals were purchased from th e Aldrich Chemical Co. and used as received unless noted. Grubbs first generation catalyst, bis(tricyclohexylphosphine)benzylid ineruthenium (IV) dichloride, was obtained from Materia, Inc and stored in an argon-filled drybox pr ior to use. Wilkinsons rhodium hydrogenation catalyst RhCl(PPh3)3 was purchased from Strem Chemical a nd used as received. Tetrahydrofuran (THF) and xylenes was freshly distilled from Na /K alloy using benzophen one as the indicator. The starting hexanenirtile and alkenyl br omides along with hexamethylphosphoramide, triethylamine, and 1,9-decadiene were distilled over CaH2. General Monomer Synthesis. Monomers 4a and 4b were synthesized according to previously published procedures.90, 96 A modification of the prev iously reported methodology was used for the synthesis of monomer 10, 5,10-diallyltetradecane.

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111 Synthesis and characterization of 5,10-diallyltetradecane (10). A 1M solution of hexanenitrile (2.136 g, 22 mmol) in dry THF ( 17.8 mL) was prepared in a three-necked round bottomed flask equipped with a stir bar and argon inlet adaptor. The solution was cooled to -78 C and a freshly prepared solution of lithium d iisopropylamide (LDA) (2.18 g, 22 mmol) in THF (21.5 mL) was added via cannula transferring. The mixture was warmed to 0 C and stirred for 30 min, then cooled to -78 C. The alkenylating 3-bromoprop-1-ene (6) (2.639 g, 22 mmol) was added at -78 C, then stirred at 0 C for 30 mi n. The mixture was gradually warmed to room temperature and stirred for 2 h, and then was quenched with water (100 mL), extracted three times with ether (200 mL) and washed with br ine (50 mL). After dr ying over MgSO4, the solution was filtered, concentrated by rotary evaporation, and purified by flash column chromatography (5% v/v ethyl acetate/hexane). Afte r purification, 3.011 g (99% yield) of a pale yellow liquid was collected, 2-allylhexanenitrile (7). A 1M solution of 7 (3.011 g, 22 mmol) in dry THF (17.8 mL) was prepared in a three-neck ed round bottomed flask equipped with a stir bar and argon inlet adaptor. The soluti on was cooled to -78 C and a freshly prepared solution of lithium diisopropylamide (LDA) (2.18 g, 22 mmol ) in THF (21.5 mL) was added via cannula transferring. The mixture was warm ed to 0 C and stirred for 30 min, then cooled to -78 C. 1,4dibromobutane (4.706 g, 22 mmol) was added at 78 C, then stirred at 0 C for 30 min. The mixture was gradually warmed to room temperature and stirred for additional 2 h, and then was quenched with water (100 mL), extracted three ti mes with ether (200 mL) and washed with brine (50 mL). After drying over MgSO4, the solution was filtered, concentrated by rotary evaporation, and purified by flash column chro matography (5% v/v ethyl acetate/hexane). After purification, 7.20 g (99% yield) of a pale yellow liquid was collected, 2,7-diallyl-2,7dibutyloctanedinitrile (9).The following spectral properties were observed: 1H NMR (CDCl3):

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112 (ppm) 0.93 (t, 6H, CH3), 1.30-1.60 (m, 20H), 2.32 (d, 4H), 5.20 (m, 4H, vinyl CH2), 5.82 (m, 2H, vinyl CH); 13C NMR (CDCl3): (ppm) 14.06, 22.97, 24.80, 26.65, 35.94, 36.08, 40.56, 40.64, 120.05, 123.69, 131.97; EI/HRMS: [M]+ calculated for C22H36N2: 328.2878, found: 328.2876. Elemental analysis calculated for C22H36N2: 80.43 C, 11.04 H, 8.53 N; found 80.40 C, 11.06 H, 8.51 N. Decyanation of compound 9 was carried out using potassium metal (6.01 g, 154 mmol). HMPA (19.891 g, 111 mmol), and ether (185 mL) we re transferred to a three-neck round bottom flask equipped with a stir bar, addition funnel, and argon inlet adaptor. A solution of 2,7-diallyl2,7-dibutyloctane-dinitrile (9) (7.20 g 22 mmol) and tBuOH (4.15 g, 56 mmol) in ether (130 mL) was added dropwise to the reactor and st irred for 3 hours at 0 C. The reaction was monitored by TLC plate using 5% ethyl acetate in hexane. When no trac e of starting material was observed by TLC, the remaining excess of unreacted potassium was removed from the reaction flask. The reaction was quenched with wa ter (20 mL), extracted three times with ether (600 mL), and washed with brine (150 mL). After drying over MgSO4, the solution was filtered, concentrated by rotary evapor ation, and purified by flash co lumn chromatography (hexane). After purification, 6.10 g (99% yiel d) of 5,10-diallyltetradecane (10) was obtained as a colorless liquid. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.90 (t, 6H), 1.16-1.40 (m, 22H), 2.02 (t, 4H), 4.95 (m, 4H), 5.74 (m, 2H); 13C NMR (CDCl3): (ppm) 14.41, 23.41, 26.88, 29.20, 29.44, 30.22, 33.60, 33.90, 34.07, 37.59, 114.30, 139.49; EI/HRMS: [M]+ calculated for C20H38: 278.2974, found: 278.2978. Elemental analysis calculated for C20H38: 86.25 C, 13.75 H; found 86.23 C, 13.76 H General Polymerization Conditions. All glassware was flame dried under vacuum prior to use. Monomers 4a, 4b, 10, and 11 were dried over K mirror and degassed prior to

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113 polymerization. All metathesis reactions were initiated in the bulk, inside an argon atmosphere drybox. For the case of homopolymerization, monomers 4a, 4b, and 10 were placed in a 50 mL round-bottomed flask equipped with a magnetic stir bar, respectively. Grubbs first generation catalyst (400:1 monomer:catalyst) was added to the flask, and the flask was then fitted with a Schlenk adapter equipped with a vacuum valve. The reaction was monitored by formation of ethylene gas as a moderate observed bubbling. Th e sealed reaction vessel was removed from the drybox and immediately placed on the vacuum line. The reaction vessel was then exposed to intermittent vacuum. After 4 h, the poly merization was exposed to full vacuum (10-4 torr) for 96 h at 45-50 C. The reaction vessel was then cooled to room temp erature, exposed to air, and 50 mL of a mixture of ethyl vinyl ether in toluen e 1% v/v was added. The polymer/toluene solution was precipitated in methanol by dropwise addi tion of the solution to a beaker containing 1500 mL of acidic methanol (1 M), yielding pure EH5u, EH15u and EH21u polymers, respectively. For the case of copolymer ization of monomers 4a and 11, monomers were weighted based on the needed molar ratios, as shown in table 2. The adequate mixture of monomers was placed in a 50 mL round-bottomed flask equipped with a magnetic stirbar, and Grubbs fi rst generation catalyst (400:1 monomer:catalyst) was added to the flask. Application of the same polymerization and purification procedure previously men tioned afforded the model copolymers EH-2.5u EH43.5u. Polymerization of 5,10-diallyltetra decane (10) to give EH5u. After purification, 820 mg (90% yield) of material was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.91 (t, 7H,), 1.25 (br, 23H), 1.97 (m, 4H), 5.35 (m, 2H); 13C NMR (CDCl3): (ppm) 14.44, 23.38, 27.43, 29.23, 29.34, 33.29, 33.75, 36.95, 38.01, 129.40, 130.11; GPC data (THF vs. polystyrene standards): wM = 21,200 g/mol; P.D.I. ( n wM M /) = 1.7

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114 Polymerization of 9-butylheptadeca -1,16-diene (4a) to give EH15u. After precipitation, 860 mg (93% yield) of material was collected. The following spect ral properties were observed: 1H NMR (CDCl3): (ppm) 0.90 (t, 3H,), 1.23 (br, 29H), 1.98 (m, 4H), 5.40 (m, 2H); 13C NMR (CDCl3): (ppm) 14.43, 23.41, 26.92, 29.19, 29.49, 29.62, 29.95, 30.26, 32.88, 33.59, 33.93, 37.61, 130.12, 130.58; GPC data (THF vs. polystyrene standards): wM = 47,600 g/mol; P.D.I. ( n wM M /) = 1.9 Polymerization of 12-butyltricosa -1,22-diene (4b) to give EH21u. After precipitation, 980 mg (91% yield) of material was collected. The following spect ral properties were observed: 1H NMR (CDCl3): (ppm) 0.90 (t, 3H,), 1.27 (br, 34H), 1.98 (m, 4H), 5.39 (m, 2H); 13C NMR (CDCl3): (ppm) 14.42, 23.41, 26.96, 29.20, 29.44, 29.79, 29.92, 29.97, 30.41, 32.86, 33.60, 33.95, 37.62, 130.11, 130.57; GPC data (T HF vs. polystyrene standards): wM = 41,500 g/mol; P.D.I. ( n wM M /) = 1.8 Copolymerization of 9-butylheptadeca-1,16-di ene (4a) and 1,9-decadiene (11) to give EH-2.5u. After precipitation, 2.501 g (93% yield) of material was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.90 (t, 0.07H,), 1.30 (br, 8H), 1.98 (m, 4H), 5.39 (m, 2H); 13C NMR (CDCl3): (ppm) 14.25, 23.23, 26.73, 29.01, 29.29, 29.68, 29.75, 30.23, 32.69, 33.41, 33.73, 37.41, 129.90, 130.40; GPC data (THF vs. polystyrene standards): wM = 40,100 g/mol; P.D.I. ( n wM M /) = 1.8 Copolymerization of 9-butylheptadeca-1,16-di ene (4a) and 1,9-decadiene (11) to give EH-6.0u. After precipitation, 2.027 g (89% yield) of material was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.90 (t, 0.2H,), 1.30 (br, 9H), 1.98 (m, 4H), 5.39 (m, 2H); 13C NMR (CDCl3): (ppm) 14.25, 23.23, 26.73, 29.01, 29.29, 29.68,

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115 29.75, 30.23, 32.69, 33.41, 33.73, 37.41, 129.90, 130.40; GPC data (THF vs. polystyrene standards): wM = 39,500 g/mol; P.D.I. ( n wM M /) = 1.7 Copolymerization of 9-butylheptadeca-1,16-di ene (4a) and 1,9-decadiene (11) to give EH-11.5u. After precipitation, 1.875 g (91% yield) of material was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.90 (t, 0.5H,), 1.30 (br, 10H), 1.98 (m, 4H), 5.39 (m, 2H); 13C NMR (CDCl3): (ppm) 14.25, 23.23, 26.73, 29.01, 29.29, 29.68, 29.75, 30.23, 32.69, 33.41, 33.73, 37.41, 129.90, 130.40; GPC data (THF vs. polystyrene standards): wM = 38,700 g/mol; P.D.I. ( n wM M /) = 1.6 Copolymerization of 9-butylheptadeca-1,16-di ene (4a) and 1,9-decadiene (11) to give EH-21.3u. After precipitation, 1.572 g (95% yield) of material was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.90 (t, 1.3H,), 1.30 (br, 14H), 1.98 (m, 4H), 5.39 (m, 2H); 13C NMR (CDCl3): (ppm) 14.25, 23.23, 26.73, 29.01, 29.29, 29.68, 29.75, 30.23, 32.69, 33.41, 33.73, 37.41, 129.90, 130.40; GPC data (THF vs. polystyrene standards): wM = 48,400 g/mol; P.D.I. ( n wM M /) = 1.6 Copolymerization of 9-butylheptadeca-1,16-di ene (4a) and 1,9-decadiene (11) to give EH-37.0u. After precipitation, 1.350 g (91% yield) of material was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.90 (t, 2.2H,), 1.30 (br, 20H), 1.98 (m, 4H), 5.39 (m, 2H); 13C NMR (CDCl3): (ppm) 14.25, 23.23, 26.73, 29.01, 29.29, 29.68, 29.75, 30.23, 32.69, 33.41, 33.73, 37.41, 129.90, 130.40; GPC data (THF vs. polystyrene standards): wM = 37,500 g/mol; P.D.I. ( n wM M /) = 1.8 Copolymerization of 9-butylheptadeca-1,16-di ene (4a) and 1,9-decadiene (11) to give EH-43.5u. After precipitation, 1.170 g (88% yield) of material was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.90 (t, 3H,), 1.30 (br, 25H), 1.98

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116 (m, 4H), 5.39 (m, 2H); 13C NMR (CDCl3): (ppm) 14.25, 23.23, 26.73, 29.01, 29.29, 29.68, 29.75, 30.23, 32.69, 33.41, 33.73, 37.41, 129.90, 130.40; GPC data (THF vs. polystyrene standards): wM = 38,400 g/mol; P.D.I. ( n wM M /) = 1.8 General hydrogenation methodology using Wilkinsons catalyst. Hydrogenation was performed using a 150 mL high-pr essure stainless steel reacti on vessel equipped with a glass liner, temperature probe, pressure gauge, and a paddle wheel stirrer. A solution of unsaturated polymer (EH15u and EH21u) (~1.0 g) was dissolved in a toluene (100mL), followed by degasification by bubbling nitrogen gas into the stirred solutio n for 30 minutes. Wilkinsons catalyst (3.7 mg, 4 mol) [RhCl(PPh3)3] was added to the solution, and the glass liner was placed into the bomb and then sealed. The bomb was ch arged with hydrogen gas to 400 p.s.i. and the mixture was stirred for 24 h at 80 C follo wed by 48 h at 100 C.. Upon cooling to room temperature, the resultant polymer solution wa s precipitated into acidic methanol (1N stock solution prepared with HCl), filtered, and dried affording saturated polymers EH15 and EH21, respectively. Hydrogenation of EH15u to give EH15. After precipitation, 855 mg (99% yield) of material was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.90 (t, 3H,), 1.27 (br, 31H); 13C NMR (CDCl3): (ppm) 14.39, 23.40, 26.95, 29.20, 29.96, 30.40, 33.63, 33.95, 37.62; GPC data (THF vs. polystyrene standards): wM = 48,100 g/mol; P.D.I. ( n wM M /) = 1.9; DSC Results: Melting Temperature Data: Tm = -33 C, hm = 13 J/g and Tm = -53 C Hydrogenation of EH21u to give EH21. After precipitation, 973 mg (99% yield) of material was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.90 (t, 3H,), 1.27 (br, 47H); 13C NMR (CDCl3): (ppm) 14.43, 23.42, 24.49, 26.95,

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117 29.21, 29.97, 30.41, 33.62, 33.94, 37.61; GPC data (THF vs. polystyrene standards): wM = 40,300 g/mol; P.D.I. ( n wM M / ) = 1.7; DSC Results: Melting Temperature Data: Tm = 14 C, hm = 47 J/g General hydrogenation methodology using diimide. This method was applied for the saturation of polymer EH5u and copolymers EH-2.5 through EH-43.5 due to solubility issues that were eventually overcome. A so lution of unsaturated polymer (~1.0 g) was dissolved in xylenes (30 mL) in a 350 mL three-neck round bo ttomed flask. Tripropyl amine (3.79 g, 26.3 mmol) was added via syringe followed by addition of p -toluenesulfonhydrazide (4.33 g, 23.3 mmol) using a powder funnel. The reaction mixture was heated to 135C for 2 hours. The reaction was monitored by the produced nitroge n observed through a mine ral oil bubbler. When production of nitrogen gas was ceased, the solutio n was cooled to room temperature, and a second batch of tripropyl amine (3.79 g, 26.3 mmol) and p -toluenesulfonhydrazide (4.33 g, 23.3 mmol) was added. The reaction mixture was heated to 135C for 2 h, and its performance was monitored by the evolution of nitrogen gas. Pr ecipitation of the crude mixtures into acidic methanol (1N stock solution prepared with HCl), followed by filtration afforded the saturated EH5 polymer and copolymers EH-2.5 through EH-43.5. Hydrogenation of EH5u to give EH5. After precipitation, 817 mg ( 99% yield) of material was collected. The following spect ral properties were observed: 1H NMR (CDCl3): (ppm) 0.90 (t, 3H,), 1.27 (br, 14H); 13C NMR (CDCl3): (ppm) 14.55, 23.55, 27.58, 29.37, 33.77, 34.15, 37.81; GPC data (THF vs. polystyrene standards): wM = 20,800 g/mol; P.D.I. ( n wM M /) = 1.8; DSC Results: Glass Tr ansition Temperature Data: Tg = -73 C, Cp = 0.63 J/g C Hydrogenation of EH-2 .5u to give EH-2.5. After precipitation, 2. 489 g (99% yield) of material was collected. The following spectral properties were observed: 1H NMR (TCEd2):

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118 (ppm) 0.92 (t, CH3, 3H,), 1.19 and 1.34 (br, CH2, 129H); 13C NMR (TCEd2): (ppm) 14.29, 14.39, 22.94, 23.40, 26.95, 29.20, 29.60, 29.99, 30.40, 32.22, 33.63, 33.95, 37.62; GPC data (THF vs. polystyrene standards): wM = 39,800 g/mol; P.D.I. ( n wM M /) = 1.8; DSC Results: Melting Temperature Data: Tm = 126 C, hm = 193 J/g Hydrogenation of EH-6 .0u to give EH-6.0. After precipitation, 1. 993 g (98% yield) of material was collected. The following spectral properties were observed: 1H NMR (TCEd2): (ppm) 0.92 (t, CH3, 3H,), 1.19 and 1.34 (br, CH2, 93H); 13C NMR (TCEd2): (ppm) 14.29, 14.39, 22.94, 23.40, 26.95, 29.20, 29.60, 29.99, 30.40, 32.22, 33.63, 33.95, 37.62; GPC data (THF vs. polystyrene standards): wM = 40,700 g/mol; P.D.I. ( n wM M /) = 1.6; DSC Results: Melting Temperature Data: Tm = 122 C, hm = 129 J/g Hydrogenation of EH-1 1.5u to give EH-11.5. After precipitation, 1. 868 g (99% yield) of material was collected. The following spectral properties were observed: 1H NMR (TCEd2): (ppm) 0.92 (t, CH3, 3H,), 1.19 and 1.34 (br, CH2, 76H); 13C NMR (TCEd2): (ppm) 14.29, 14.39, 22.94, 23.40, 26.95, 29.20, 29.60, 29.99, 30.40, 32.22, 33.63, 33.95, 37.62; GPC data (THF vs. polystyrene standards): wM = 37,800 g/mol; P.D.I. ( n wM M /) = 1.8; DSC Results: Melting Temperature Data: Tm = 113 C, hm = 105 J/g Hydrogenation of EH-2 1.3u to give EH-21.3. After precipitation, 1. 469 g (93% yield) of material was collected. The following spectral properties were observed: 1H NMR (TCEd2): (ppm) 0.92 (t, CH3, 3H,), 1.19 and 1.34 (br, CH2, 50H); 13C NMR (TCEd2): (ppm) 14.29, 14.39, 22.94, 23.40, 26.95, 29.20, 29.60, 29.99, 30.40, 32.22, 33.63, 33.95, 37.62; GPC data (THF vs. polystyrene standards): wM = 45,100 g/mol; P.D.I. ( n wM M /) = 1.6; DSC Results: Melting Temperature Data: Tm = 94 C, hm = 95 J/g

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119 Hydrogenation of EH-3 7.0u to give EH-37.0. After precipitation, 1. 280 g (95% yield) of material was collected. The following spectral properties were observed: 1H NMR (TCEd2): (ppm) 0.92 (t, CH3, 3H,), 1.19 and 1.34 (br, CH2, 42H); 13C NMR (TCEd2): (ppm) 14.29, 14.39, 22.94, 23.40, 26.95, 29.20, 29.60, 29.99, 30.40, 32.22, 33.63, 33.95, 37.62; GPC data (THF vs. polystyrene standards): wM = 38,100 g/mol; P.D.I. ( n wM M /) = 1.7; DSC Results: Melting Temperature Data: Tm = 45 C, hm = 93 J/g Hydrogenation of EH-4 3.5u to give EH-43.5. After precipitation, 1. 152 g (98% yield) of material was collected. The following spectral properties were observed: 1H NMR (TCEd2): (ppm) 0.92 (t, CH3, 3H,), 1.19 and 1.34 (br, CH2, 33H); 13C NMR (TCEd2): (ppm) 14.29, 14.39, 22.94, 23.40, 26.95, 29.20, 29.60, 29.99, 30.40, 32.22, 33.63, 33.95, 37.62; GPC data (THF vs. polystyrene standards): wM = 37,300 g/mol; P.D.I. ( n wM M /) = 1.8; DSC Results: Melting T emperature Data: Tm = 10 C, hm = 85 J/g

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120 CHAPTER 5 LINEAR-LOW DENSITY POLYETHYLENE CONTAINING PRECISELY PLACED LINEAR AND NON-LINEAR BULKIER BRANCHES 5.1 Introduction Polyethylene (PE) is the most widely utilized thermoplastic polymer today.3 Since its discovery in the 1930s, PE has been of increas ing interest in both i ndustrial and academic settings, due primarily to the ability to produce ma terials with a wide rang e of physical properties and unique polymer architectures.126 Physical properties of lin ear low-density polyethylene (LLDPE), an important member of the polyeth ylene family, can be tuned by manipulating the amount of short-chain branching (SCB) and the short-chain branch distribution (SCBD),127, 128 as well as by controlling the mode of polymerization, catalyst type pressure, and temperature. Clearly, the identity of the com onomer is also important, with propene, 1-butene, 1-hexene and 1-octene being the most common choices, because of their low cost a nd their effects on the mechanical properties of the final material.18-20, 25-30, 128-138 Commercial LLDPE is usually prepared by chain-growth polymeri zation using ZieglerNatta or metallocene chemistry.4, 139 Single-site catalysis by metallocene systems produces copolymers with narrower molecular weight dist ributions and higher comonomer content than Ziegler-Natta products.129, 139, 143-147 Due to the similar ethylene/ -olefin comonomer reactivity, metallocene systems produce mate rials with linear and bulky -olefins not suitable with ZieglerNatta chemistry. Copolymerization via metallo cene chemistry of ethylene with odd carbonnumber -olefins (e.g. 1-pentene or 1-heptene) is also feasible because such compounds are available using the Fisher-Tropsch olefin synthesi s process. These possibilities have led to the creation of a significan t number of ethylene/ -olefin copolymers with a wide range of applications.161-169 Furthermore, metallocene copolymeri zation of ethylene with non-linear, bulkier -olefins such as 3-methyl-1-butene (3MB),170-173 4-methyl-1-pentene (4MP),174-177

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121 vinylcyclohexene (VCH),178-181 and norbornene 173 has created a new class of materials with better impact strength than that of traditional ethylene linear -olefin copolymers. In the past, it has been demonstrated that copolymerization of ethylene with -olefins via chain-propagation chemistry results in the incorpor ation of unwanted defects via head-to-head or tail-to-tail monomer coupling. Additionally, inevit able chain transfer or chain walking produces structures with alkyl branches of varyi ng lengths randomly spaced along the main chain.41-45 However, the problems associated with chaingrowth polymerization can be overcome using step-growth condensation polymer ization, in particular acycl ic diene metathesis (ADMET) polymerization. In ADMET, elimination of et hylene gas drives the reaction to yield an unsaturated high molecular weight polymer, and subsequent exhaustive hydrogenation of the resultant polymer yields pe rfectly sequenced ethylene/ -olefin copolymers.47 This new synthetic route presents the advantage of controlling the polymer architect ure by choosing th e appropriate building block, thereby circumventing the use of comonomers and monomer feed ratios or the design of specialized catalys ts typically needed for chain-growth chemistry. The first synthesized ADMET-LLDPE contained methyl branches precisely placed along the backbone.48 Continuation of this research led to the development of ethyl-branched polyethylene,49 and subsequently to the developm ent of hexyl-branched polyethylene.54 This chapter reports the synthesis, characterization an d thermal behavior of model ethylene/1-pentene (EPent21), ethylene/1-heptene (EHept21), ethylene/3-methyl-1-butene (E3MB21), ethylene/neohexene (ENH21), and ethylene/vinylcyclohexane (EVCH21) copolymers.

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122 5.2 Results and Discussion 5.2.1 Monomer Synthesis and ADMET Polyme rization of Precisely Sequenced Ethylene/ -olefin Copolymers In the past, different methodol ogies for the synthesis of -dienes have rendered functionalized monomers in only moderate yields.48, 49, 54 Lately, we have produced -diene monomers functionalized with al kyl branches of various length s by alkylation/d ecyanation of primary nitriles in near ly quantitatively yields.90, 96 This approach is based on the double alkenylation of the carbon alpha to the nitrile, followed by the reduc tive elimination of the nitrile moiety. Figure 5-1 shows the synthetic approach for the preparation of alkyl -diene monomers (4a to 4i) from primary nitriles 2a-i. While most of nitriles were commercially available, nitriles 2h and 2i were synthesized by cyanation of bromides 1h and 1i. Alkenylation of nitriles 2a-i in the presence of lithium diisopropyl amide (LDA) and 11bromoundec-1-ene produces the alkylcyano -dienes 3a-i in quantitative yields.90 Decyanation of nitriles 3a-i is achieved with potassium metal via radical chemistry.96 The resulting tertiary radical after decyanation is further qu enched by abstraction of hydrogen from t -BuOH to give -diene monomers 4a-i in quantitative yields. R CN Br 9 2) 1 eq 9 9 NC R 9 9 R Ko, HMPA t -BuOH, Ether 1) 1eq LDA, THF, 0 oC Br 9 4) 1 eq 3) 1eq LDA, THF, 0 oCR = Methyl Ethyl Propyl Butyl Pentyl Hexyl iso -propyl tert -butyl Cyclohexyl R1 Br KCN, acetone 18-crown-6 R1 CN R1 = t -butyl cyclohexyl (4a) (4b) (4c) (4d) (4e) (4f) (4g) (4h) (4i) 2a-i3a-i4a-i 1h, i 2h, i (2h) (2i) Figure 5-1. Synthesis of 12-al kyltricosa-1,22-dienes (4a-i)

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123 As shown in Figure 5-2, polymerization of alkyl -diolefin monomers 4a-i is carried out with first generation Grubbs catalyst (5) in the absence of solvent. The polymerization proceeds efficiently, yielding unsaturated polymers EP21u to EVCH21u. Exhaustive hydrogenation of the unsaturated polymers using p -toluenesulfonyl hydrazide, trip ropyl amine and xylene yields sequenced ethylene/ -olefin copolymers EP21u to EVCH21u. As described further below, the efficiency of hydrogenation can be followed by the disappearance of the olefin signals in 1H NMR (Figure 5-3) and 13C NMR (Figure 5-4), and by the absen ce of the out-of-plane alkene C-H bend (969 cm-1) using infrared (IR) sp ectroscopy (Figure 5-6). 20 nR 9 9 R n 9 9 R Methyl Ethyl Propyl Butyl Pentyl Hexyl iso -propyl tert -butyl Cyclohexyl EP21 EB21 EPent21 EH21 EHept21 EO21 EIH21 ENH21 EVCH21 4a-i Branch (R) Unsaturated polymer Saturated polymer EP21u EB21u EPent21u EH21u EHept21u EO21u EIH21u ENH21u EVCH21u 5 Ru PCy3 PCy3 Ph Cl Cl 1st Generation Grubbs catalyst CH2=CH21st Gen. GrubbspTSH TPA Xylene, 130 oC EP21u EVCH21u EP21 EVCH21 (a) (b) (c) (d) (e) (f) (g) (h) (i) Figure 5-2. Synthesis of pr ecisely sequenced ethylene/ -olefin copolymers The nomenclature for the unsaturated/satur ated polymers is based on the comonomer content. The prefix E for polyethylene is followed by th e different comonomer types, for example 3MB for 3-methyl-1-butene. Saturation or uns aturation of the main backbone is given by the absence or presence of the suffix u. The branch frequency is indicated by number; e.g., E3MB21 designates the saturated sequenced ethy lene/3-methyl-1-butene copolymer, which

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124 contains iso -propyl branches on every 21st backbone carbon, while E3MB21 u refers to its unsaturated analog. Table 5-1. Molecular weights and therma l data for precisely sequenced ethylene/ -olefin copolymers wM x 103 (PDI) b Copolymer with precisely placed alkyl branches Branch on every 21st carbon Comonomer -olefin Unsaturate a Saturate a Tm (C) (peak) hm (J/g) EP21 Methyl Propene 20.2 (1.7) 20.2 (1.7) 63 104 EB21 Ethyl Butane 50.2 (1.9) 50.7 (1.9) 24 65 EPent21 Propyl Pentene 41.2 (1.7) 41.4 (1.7) 12 60 EH21 Butyl Hexane 41.5 (1.8) 40.3 (1.7) 12 57 EHept21 Pentyl Heptene 45.1 (1.8) 45.8 (1.8) 14 58 EO21 Hexyl Octene 44.6 (1.8) 46.1 (1.7) 12 49 E3MB21 iso -propyl 3-Methylbutene 45.5 (1.7) 46.0 (1.7) 11 37 ENH21 tert -butyl Neohexene 30.6 (1.7) 32.1 (1.7) 13 50 EVCH21 Cyclohexyl Vinylcyclohexane 32.5 (1.6) 33.6 (1.6) 9 37 a Weight average molecular weight data obt ained by GPC in THF (40 C) relative to polystyrene standards (g/mol). b PDI, polydispersity index ( n wM M /) Table 5-1 shows the molecular weights for the precisely sequenced ethylene/ -olefin copolymers obtained via ADMET poly merization. The weight-average molecular weights were obtained by gel permeation chromatography (GPC) ve rsus polystyrene standards. The molecular weights measured indicate absence of cleavage of the polymer chains during the hydrogenation process.48 5.2.2 Structural Data for Precisely Sequenced Ethylene/ -Olefin Copolymers Using ADMET, it is possible to produce polymers with perfectly know primary structures,48, 49, 54 solely by the design of the -diene. The resulting LLDPE has defects intentionally and evenly placed along th e polyethylene chain. Examination of 1H and 13C NMR

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125 spectra of monomers and polymers indicates co mplete transformation and control over the primary structure. Figure 5-3 shows the 1H NMR spectra for the ADMET polymer ENH21 and its precursors. The transformation begins with the cyan ation of 1-bromo-2, 2-dimethylpropane (1h) yielding 3,3dimethylbutanenitrile (2h), shown in Figure 5-3a. Double alkenylation of nitrile 2h with 11bromoundec-1-ene yields premonomer 3h, 2tert -butyl-2-(undec-10-enyl)tri dec-12-enenitrile, is shown in Figure 5-3b. Decyanation of nitrile 3h forms monomer 4h, 12tert -butyltricosa-1,22diene in quantitative yield, as shown in Figure 5-3c. ADMET polymerization of 4h yields the unsaturated polymer ENH21u. Analysis of the olefin region (5-6 ppm) supports formation of polymer, which is evidenced by the disappearance of the terminal olefin signals (5.1 and 5.9 ppm in Figure 5-3c) and the formati on of the internal olefin (5.3 ppm in Figure 5-3d). Further hydrogenation of the internal olefins yields ENH21, a perfectly sequenced ethylene/neohexene copolymer, corresponding to polyethylene with t -butyl branches on every 21st backbone carbon, with no observable tr aces of olefin by 1H NMR (Figure 5-3e). Figure 5-4 shows the 13C NMR spectra for the same transformations. In the spectrum for the 3,3-dimethylbutanenitrile (2h, Figure 5-4a), the resonance at 118.67 shows the presence of the nitrile functionality. After th e double alkenylation of nitrile 2h, the spectrum for 2tert -butyl2-(undec-10-enyl)tridec-12-enenitrile (3h, Figure 5-4b) shows the pr esence of the nitrile functionality at 122.95 ppm along w ith the characteristic terminal olefin signals at 114.27 and 139.26 ppm, respectively. Absence of the signal at 122.95 ppm after decyanation (Figure 5-4c) demonstrates complete eliminati on of the CN group yielding monomer 4h, 12tert -butyltricosa1,22-diene. ADMET polymerization of 4h yields the unsaturated polymer ENH21u. Comparison of Figures 5-4c and 5-4d shows the disappearance of the signals belonging to the terminal olefin

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126 at 114.31 and 139.44 ppm and formation of the new internal olefin ( cis at 130.12 ppm, minor component, and trans at 130.58 ppm, major component) produ ced from the effective metathesis polymerization. Subsequent exhaustive hydrogenation of the internal olefin yields the saturated polymer ENH21, whose 13C NMR spectrum (Figure 5-4e) shows no detectable trace of olefins. This observation is further supported by the absen ce of the out-of-plane C-H bend in the alkene region at 969 cm-1 in the infrared (IR) spectrum, as described below. Upon close inspection of the 13C NMR data for the ADMET polymers, it can be concluded that the branches are precisely placed along th e polyethylene main backbone with no unwanted defects due to chain walking typically obser ved during chain-growth chemistry. Figure 5-5 shows a portion (10-55 ppm) of the 13C NMR spectra for the precisely sequenced ethylene/ olefins, Epent21, EHept21, E3MB21, ENH21, and EVCH21. All spectra are dominated by a singlet at 29.99 ppm corresponding to methylenes on the main polyethylene chain. However, the presence of alkyl branches precisely placed along the main chain affects the chemical shifts of carbons located w ithin three CH2 units from an individual branch.50 In the spectrum for EPent21 which is polyethylene containi ng propyl branches on every 21st backbone carbon (Figure 5-5a), the resonances belonging to the propyl branch, 1 ( 14.80 ppm), 2 ( 20.07 ppm), 3 ( 36.37 ppm), and the carbon at the branch point 4 ( 37.42 ppm) indicates that only propyl branches are present, in agreement with previously repor ted data on chain-growth materials obtained by copolymerization of ethylene with 1-pentene.138, 162, 182-184 While EPent21 spectrum shows resonances for three carbons at the propyl branch, the EHept21 spectrum, Figure 5-5b, shows five resonances corresponding to the pe ntyl branch precisely placed on every 21st backbone carbon: a ( 14.80 ppm), b ( 22.97 ppm), c ( 26.62 ppm), d ( 26.94 ppm), and e ( 33.89

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127 ppm). In agreement with the EPent21 spectrum, which shows a resonance for the branch point carbon at 37.42 ppm, EHept21 shows the corresponding branch -point peak at 37.64 ppm.166-169 In addition to spectra 5-5a and 5-5b for polye thylene with precisely placed linear branches, Figures 5-5c, 5-5d and 5-5e present the 13C NMR spectra for polyethy lene containing non-linear bulkier branches on every 21st carbon: iso -propyl (E3MB21), tert -butyl (ENH21), and cyclohexyl (EVCH21). In the spectrum for E3MB21, the resonances belonging to the iso -propyl branch (A at 19.46 ppm and B at 30.45 ppm), as well as the resonance from the carbon at the branch point C ( 43.96 ppm), indicate that only iso -propyl branches are present. Peak assignments are based on prev ious detailed NMR studies.170-177, 185-188 It is not surprising that the presence of a bulkier branch, iso -propyl, causes a shift in the resonance corresponding to the carbon at the br anch point, 37.42 and 37.64 ppm for the carbons at propyl and pentyl branches, respectively, vers us 43.96 ppm for the carbon directly attached to an iso -propyl branch. Following the same trend, the resonance for the backbone carbon at a tert butyl branch is shifted from 43.96 ppm (E3MB21) to 49.02 ppm (ENH21), due to the highly branched functionalization, as show n in Figure 5-5d. The spectrum for ENH21 (Figure 5-5d) also shows the characteristic re sonances belonging to pendant tert -butyl branches, I ( 28.06 ppm), and II ( 34.11 ppm). In the spectrum for EVCH21 (fig 5-5e), the cyclohexyl carbons resonate at 27.21 ppm, m; 27.26 ppm, n; 30.03 ppm, o; and 43.53 ppm,p., The backbone branch carbon for EVCH21 with pendant cyclohexyl groups (peak q in Figure 5.5e) appears at 40.41 ppm, which is downfield compared to the resona nces at propyl and pent yl branches, although not shifted as greatly as the branch carbons in the polymers with iso -propyl and tert -butyl pendant groups. Peak assignments are based on previous detailed NMR studies.173, 178-181, 189

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128 Figure 5-3. Comparison of 1H NMR spectra for a typical ADM ET polymerization transformation ENH21: (a) 3,3-dimethylbutanenitrile (2h) (b) Premonomer 3h, 2tert -butyl-2(undec-10-enyl)tridec-12-e nenitrile, (c) Monomer 4h, 12tert -butyltricosa-1,22-diene, (d) ADMET unsaturated polymer ENH21u, (e) ADMET saturated polymer ENH21.

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129 Figure 5-4. Comparison of 13C NMR spectra for a typical ADMET polymerization transformation ENH21: (a) 3,3-dimethylbutanenitrile (2h) (b) Premonomer 3h, 2tert -butyl-2-(undec-10-enyl)tridec12-enenitrile, (c) Monomer 4h, 12tert butyltricosa-1,22-diene, (d ) ADMET unsaturated polymer ENH21u, (e) ADMET saturated polymer ENH21.

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130 Figure 5-5. Comparison of 13C NMR spectra for a typical ADMET polymerization transformation posesing bulky branches (a) EPent21, (b) EHept21, (c) E3MB21, (d) ENH21, (e) EVCH21

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131 In addition to the NMR characterization of the precisely sequenced ethylene/ -olefin ADMET materials, infrared (IR) sp ectroscopy was used to study the Epent21, EHept21, E3MB21, ENH21, and EVCH21 copolymers. Although x-ray diffr action techniques provide the absolute crystal structure, IR spectroscopy is a complementary technique that provides an estimation of the crystal structure. In the past, Tashiro et al carried out a study of branching behavior on ultra-high molecular weight polye thylene using wide angle x-ray diffraction (WAXD), IR and Raman spectroscopy. They concluded that the scissoring at 1466 cm-1 and the methylene rock at 721 cm-1 indicate a hexagonal crystal stru cture, while the double methylene rock at 719 and 730 cm-1 and single band at 1471 cm-1 correspond to an orthorhombic crystal structure.133, 155, 156 Figure 5-6 shows the IR spectra for the Epent21, EHept21, E3MB21, ENH21, and EVCH21 copolymers, with the spectra of previous ly reported precisely sequenced ethylene/ olefin copolymers, EP21,48 EB21,49 EH21, and EO21,54 included for comparison. As mentioned above, there is no out-of-plane C-H bend absorption at 969 cm-1, indicating complete absence of C=C in the saturated polymers. All sp ectra are dominated by two sets of absorption bands (~2900 and 1472 cm-1) belonging to C-H stretchi ng and methylene scissoring, respectively. In addition to the stretching and scissoring, the met hylene rocking band is observed for all copolymers at 718 cm-1. Although orthorhombic crystals show the characteristic Davidov splitting around 720 cm-1,155, 156 all of our precisely sequenced ethylene/ -olefin copolymers display a single absorption band at 718 cm-1, indicating the absence of orthorhombic crystal behavior. Moreover, the two experime ntal absorption bands at 718 and 1472 cm-1 are characteristic of a highly di sordered phase, similar to th e pattern previously observed.48, 49, 54 Comparison of all spectra in Figure 5-6 suggests th at incorporation of lin ear defects (methyl to

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132 hexyl) and non-linear bulkier branches ( iso -propyl, t -butyl and cyclohexane) evenly spaced along the polyethylene chain does not alter the C-H st retching, or methylene scissoring and methylene rocking regions in the IR. However, there is significant variation in the intensity of the absorption band at 1378 cm-1 corresponding to the symmetrical bend for the terminal methyls on the the pendant branches. As Fi gure 5-6 shows, the intensity of the absorption band at 1378 cm-1 is smaller when linear alkyl branches are incor porated, while higher intensity is observed when bulkier branches ( iso -propyl and tert -butyl) are placed along the PE chain. On the other hand, when cyclohexane groups are precisely placed on every 21st backbone carbons, the absorption at 1378 cm-1 almost disappears, because of the absence of methyl groups at the branch. The very weak absorption at 1378 cm-1 corresponds to the terminal met hyl groups of the PE backbone of EVCH21. Figure 5-6. Infrared spectra for the ADMET saturated polymers EP21, EB21, EPent21, EH21, EHept21, EO21, EIH21, ENH21, and EVCH21

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133 5.2.3 Thermal Behavior for Preci sely Sequenced Ethylene/ -Olefin Copolymers Numerous thermal studies have been perf ormed on commercially produced chain-growth LLDPE,28, 36, 40, 181, 190-192 as well as for ADMET-produced random and precisely sequenced ethylene/ -olefin copolymers.46, 48-52, 54, 56, 148 Those studies showed that the melting behavior of ethylene-based copolymers is influenced by th e amount of short-chain branching (SCB). However, the determining factor on the final phy sical properties of the resulting LLDPE is the short-chain-branch distribution (S CBD). Interpretation of results for chain-growth PE has been limited, due to the heterogeneity of the material and the presence of unwan ted defects. However, due to their perfectly known primary structur es, ADMET PE materials contain regularly spaced branches of known identity. By keeping the bran ch-to-branch distance cons tant while the branch identity is changed, a better understanding of the eff ect of linear and non-linear bulkier shortchain branching can be observed Figure 5-7. Differential scanning calorimetr y curves for ADMET polymers possessing linear branches

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134 Figure 5-7 shows the DSC thermogr ams for the previously reported EP21, EB21, EH21, and EO21 copolymers,48, 49, 54 along with the Epent21, and EHept21 copolymer models. (Refer to Table 5-1 for physical data.) Similar to previous studies involving ADMET LLDPE,48, 49, 54 Epent21 and EHept21 (i.e., polyethylene containing propyl and pentyl branches on every 21st backbone carbon) display sharp and well-define d endothermic transitions, with none of the broadening observed for copolymers obtained via chain polymerization.20, 25, 27-30 The data in Figure 5-7 show that incorporat ion of defects precisely spaced by 20 backbone carbons causes the melting temperature of the material to decrease. While high density polyethylene with practically no defects along th e main chain shows a melting transition at Tm = 134 C with a heat of fusion hm = 210 J/g,47 incorporation of met hyl branches on every 21st backbone carbon (EP21) decreases the melting point to 63 C and the enthalpy of fusion to 104 J/g. This effect is explained by the disruption of the crystal structure due to the presence of the precisely placed methyl defects. The same tre nd is observed when the alkyl branch is extended to two carbons (EB21), as shown in Figure 5-7. Incorpora tion of an ethyl branch defect on every 21st backbone carbon renders a material with a melting point below that of EP21 (Tm = 24 C with a heat of fusion hm = 65 J/g). This indicates that in corporation of the larger ethyl groups disrupts the crystal structure even mo re, resulting in depression of both the melting temperature and the heat of fusi on. Crystal structures of both EP21 and EB21 obtained using wide-angle x-ray diffraction (WAXD) and small-an gle x-ray scattering (SAXS ) revealed that the chains pack into a triclinic latt ice that allows inclusion of me thyl and at some extent ethyl branches as lattice defects.49, 50 Similar to EP21 and EB21 model copolymers, the ADMET copolymers EPent21, EH21, EHept21, and EO21 give sharp and well-defined endotherms, as shown in Figure 5-7. Extension

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135 of the branch size from two carbons in EB21 to three carbons in EPent21 follows the same pattern of decreasing the melting te mperature and heat of fusion (Tm = 24 C and hm = 65 J/g for EB21; Tm = 12 C and hm = 60 J/g for EPent21). However, incorporation of more than three carbons into the side branch produces no additional effect on the melting endotherm and degree of crystallinity. As show n in Figure 5-7, polymers contai ning linear branches with three or more carbons on every 21st backbone carbon (propyl EPent21, butyl EH21, pentyl EHept21, and hexyl EO21) show similar melting points (Tm ~ 13 C with hm ~ 58 J/g). The similar behavior of polymers with threeto six-carbon side chains may be due to exclusion of the branch from the crystal lattice, producing materials with comparable degrees of crystallinity. On the other hand, the short methyl and ethyl branches can be accommodated into the lattice, resulting in more organized structures. In this re gard, it is noteworthy that the endotherm for EB21 shows a shoulder on the lower melting side. This may i ndicate that there is part ial exclusion of ethyl branches, and that the material contai ns two types of crystalline regions. Figure 5-8. Differential scanni ng calorimetry curves for ADMET polymers possessing bulkier branches

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136 Further DSC studies were performed on materi als containing non-linear bulkier branches, iso -propyl (E3MB21), tert -butyl (ENH21), and cyclohexyl (EVCH21), as shown in Figure 5-8 and table 5-1. Similar to previous ADMET LLDPE models,48, 49, 54 the copolymers with nonlinear bulkier branches display sh arp and well-defined endothermic transitions, with none of the broadening observed for copolymers obtained via chain polymerization.170-181 Materials with non-linear bulkier branches ( iso -propyl, tert -butyl, and cyclohexyl) follow the same pattern as those with linear defec ts of three to six side -branch carbons, with Tms in the range of 9 to 13C and similar enthalpies of fusion. It is in teresting that polymers with non-linear branches display the same thermal properties as polymers with linear side chains of three or more carbons. As mentioned above, this behavior may be due to exclusion of large de fects from the crystal lattice. A series of solid-state NMR and suba mbient x-ray diffraction experiments (SAXS and WAXD) will help to prove whether or not the def ects are included or excluded from the crystal lattice. 5.3 Conclusions Acyclic diene metathesis polymerization has been used to produce perfectly sequenced polyethylenes having linear and non-linear bulkier alkyl branches on every 21st backbone carbon. Detailed NMR studies have shown that the ne w linear low-density polyethylenes are formed from one single repeat unit featuring precise branch identity. The structural and thermal investigations have shown that th e chain branches affect the crys talline regions. Thermal analysis has shown that well-defined primary structures have sharp endothermic transitions with none of the broadening observed for the copolymers obtaine d via chain-growth chemistry. Based on DSC analysis, it has been observed that the presen ce of small linear bran ches (methyl and ethyl) produces organized structures with very di fferent melting temperat ures and degrees of crystallinity, while linear and non-linear bulkier branches (propyl to hexyl, iso -propyl, tert -butyl,

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137 and cyclohexyl) are less organized and have si milar melting temperatures and degrees of crystallinity. Our work in this area continues, focusing on solid-state NMR and x-ray diffraction experiments with the intent of understanding the morphology and physical properties of ADMET based materials. By creating a complete catalogu e of polymers with linear and non-linear bulkier alkyl branch placement, we aim to further th e understanding of the physical and chemical behavior of polyethyl ene-based materials. 5.4 Experimental Section Instrumentation and Analysis. All 1H NMR (300 MHz) and 13C NMR (75 MHz) spectra were recorded in CDCl3 unless otherwise stated. Chemical sh ifts were referenced to residual signals from CDCl3 (7.27 ppm for 1H, 77.23 ppm for 13C) with 0.03% v/v TMS as an internal reference. The NMR splitting patterns are designat ed as follows: s, single t; d, doublet; t, triplet; m, multiplet; and br, broad signal. Analysis of samples by gas chromatography (GC) was performed on a gas chromatograph, equipped with a flame ionization detector, using a capillary column coated with 5% diphenyl-95% dimet hylpolysiloxane. High-resolution mass spectrometry (HRMS) was performed using a mass spectromete r in the electron ionization (EI) mode. The mass resolution was ~6000 for EI measured at Full-Width-Half-Maximum (FWHM) in the high resolution detection mode. Thin layer chromatogr aphy (TLC) was used to monitor all reactions and was performed on aluminum plates coated with silica gel (250 m thickness). TLC plates were developed to produce a visibl e signature by any of the following: ultraviolet light, iodine, vanillin, KMnO4, or phosphomolybdic acid. Flash column chromatography was performed using ultra pure silica gel (40-63 m, 60 pore size). All reactions were performed in flame-dried glassware under argon unless otherwise stated. Gel permeation chromatography (GPC) was pe rformed using an internal differential refractive index detector (DRI), internal differ ential viscosity detector (DP), and a Precision 2

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138 angle light scattering detector (LS). The light scattering sign al was collected at a 15 degree angle, and the three in-line dete ctors were operated in series in the order of LS-DRI-DP. The chromatography was performed at 45 C using two columns (10 microns PD, 7.8 mm ID, 300 mm length) with HPLC grade tetr ahydrofuran as the mobile pha se at a flow rate of 1.0 mL/minute. Injections were made at 0.050.07 % w/v sample concentration using a 322.5 l injection volume. In the case of universal calibration, retention times were calibrated against narrow molecular weight polystyrene standards. All standards were selected to produce Mp or Mw values well beyond the expected polymer's range. The Precision LS was calibrated using narrow polystyrene standard having an Mw = 65,500 g/mol. Fourier transform infrared (FT-IR) sp ectroscopy was carried out for monomers, unsaturated and saturated polymers. Monomer s were prepared by droplet deposition and sandwiched between two KCl salt plates. Unsatu rated and hydrogenated polymer samples were prepared by solution casting a th in film from tetrachloroethylene onto a KCl salt plate. Differential scanning calorimetry (DSC) anal ysis was performed using a DSC equipped with a controlled cooling accessory at a heating rate of 10 C/min. Calibrations were made using indium and freshly distilled n -octane as the standards for p eak temperature transitions and indium for the enthalpy standard. All samples were prepared in hermetically sealed pans (5-10 mg/sample) and were run using an empty pan as a reference and empty cells as a subtracted baseline. The samples were scanned for multiple cy cles to remove recrystallization differences between the samples and the results reporte d are of the third scan in the cycle. Materials. Chemicals were purchased from th e Aldrich Chemical Co. and used as received unless noted. Grubbs first genera tion catalyst, bis(tr icyclohexylphosphine)benzylidineruthenium (IV) dichloride, was obtaine d from Materia, Inc and stored in an argon-

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139 filled drybox prior to use. Wilkinson s rhodium hydrogenation catalyst RhCl(PPh3)3 was purchased from Strem Chemical and used as re ceived. Tetrahydrofuran (THF) and xylenes was freshly distilled from Na/K all oy using benzophenone as the indicat or. The starting hexanenirtile and alkenyl bromides along with hexamethylphos phoramide, triethylamine, and 1,9-decadiene were distilled over CaH2. Synthesis and Characterization of 3,3-dimethylbutanenitrile (2h). 1-bromo-2,2dimethylpropane (1h) (5.0 g, 33.10 mmol), NaCN (4.87 g, 99.31 mmol), and acetone (30 mL) were transferred to a three-n eck round bottom flask equipped w ith a stir bar, condenser, and argon inlet adaptor. The solution was stirred and refluxed for 3 hours at 63 C. After cooling the solution at room temperature 30 mL of water wa s added, extracted three times with ether (100 mL), and washed with brine (150 mL). After drying over MgSO4, the solution was filtered, concentrated by rotary evapor ation, and purified by flash co lumn chromatography (hexane). After purification 2.0 g (62 % yi eld) of material was collected The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 1.08 (s, 9H), 2.21 (s, 2H); 13C NMR (CDCl3): (ppm) 29.07, 30.78, 32.27, 118.67; EI/HRMS: [M]+ calculated for C6H11N: 97.0891, found: 97.0888. Elemental analysis calculated for C6H11N: 74.17 C, 11.41 H, 14.42 N; found 74.19 C, 11.39 H, 14.40 N Synthesis and Characterization of 2-cyclohexylacetonitrile (2i). After purification 2.03 g (66 % yield) of material was collected. Th e following spectral pr operties were observed: 1H NMR (CDCl3): (ppm) 1.14 (m, 5H), 1.70 (m, 6H), 2.20 (d, 2H) ; 13C NMR (CDCl3): (ppm) 24.76, 25.74, 32.42, 34.80, 118.99; EI/HRMS: [M]+ calculated for C8H13N: 123.1048, found: 123.1043. Elemental analysis calculated for C8H13N: 77.99 C, 10.64 H, 11.37 N; found 77.95 C, 10.66 H, 11.38 N

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140 General Monomer Synthesis. Nitriles 3a-1 and monomers 4a-f were synthesized according to previously published procedures.90, 96 2-isopropyl-2-(undec-10-enyl)tridec-12-enenitrile (3g). After purification, 4.60 g (99% yield) of a pale yellow liquid was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm), 1.32 (d, 6H), 1.59 (br, 32H), 2.32 (m, 4H), 5.26 (m, 4H, vinyl CH2), 6.09 (m, 2H, vinyl CH); 13C NMR (CDCl3): (ppm) 17.88, 24.53, 29.13, 29.31, 29.64, 29.72, 30.09, 32.07, 33.12, 34.01, 45.22, 114.30, 123.83, 139.25; EI/HRMS: [M]+ calculated for C27H49N: 387.3865, found: 387.3861. Elemen tal analysis calculated for C27H49N: 83.65 C, 12.74 H, 3.61 N; found 83.62 C, 12.75 H, 3.62 N 2-tert-butyl-2-(undec-10-enyl)tridec-12-enenitrile (3h). After purification, 4.0 g (97% yield) of a pale yellow liquid was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm), 1.05 (s, 9H), 1.29 (br, 32H) 2.03 (q, 4H), 4.96 (m, 4H, vinyl CH2), 5.80 (m, 2H, vinyl CH); 13C NMR (CDCl3): (ppm) 26.38, 27.46, 29.12, 29.31, 29.59, 29.64, 29.73, 30.39, 33.71, 34.00, 37.29, 48.84, 114.27, 122.95, 139.26; EI/HRMS: [M]+ calculated for C28H51N: 401.4022, found: 401.4019. Elemen tal analysis calculated for C28H51N: 83.72 C, 12.80 H, 3.49 N; found 83.73 C, 12.79 H, 3.48 N 2-cyclohexyl-2-(undec-10-enyl)tridec-12-enenitrile (3i). After purification, 3.40 g (98% yield) of a pale yellow liquid was collected. Th e following spectral proper ties were observed: 1H NMR (CDCl3): (ppm), 1.16-1.82 (br, 43H), 2.06 (q, 4H), 4.96 (m, 4H, vinyl CH2), 5.83 (m, 2H, vinyl CH); 13C NMR (CDCl3): (ppm) 24.62, 26.42, 26.76, 27.83, 29.14, 29.32, 29.65, 29.73, 30.11, 33.25, 34.01, 41.94, 44.91, 114.3, 124.12, 139.34; EI/HRMS: [M]+ calculated for C30H53N: 427.4178, found: 427.4175. Elemen tal analysis calculated for C30H53N: 84.24 C, 12.49 H, 3.27 N; found 84.21 C, 12.50 H, 3.29 N

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141 12-isopropyltricosa-1,22-diene (4g). After purification, 4.25 g ( 99% yield) of a colorless liquid was collected. The following sp ectral properties were observed: 1H NMR (CDCl3): (ppm) 0.85 (d, 6H), 1.30 (br, 33H), 1.71 (br, 1H), 2.08 (q, 4H), 4.97 (m, 4H), 5.85 (m, 2H); 13C NMR (CDCl3): (ppm) 19.45, 28.04, 29.23, 29.43, 29.5, 29.79, 29.91, 29.97, 30.44, 30.82, 34.08, 43.97, 114.3, 139.42; EI/HRMS: [M]+ calculated for C26H50: 362.3913, found: 362.3910. Elemental analysis calculated for C26H50: 86.10 C, 13.90 H; found 86.08 C, 13.91 H 12tert -butyltricosa-1,22-diene (4h). After purification, 3.70 g ( 99% yield) of a colorless liquid was collected. The following sp ectral properties were observed: 1H NMR (CDCl3): (ppm) 0.86 (s, 9H), 1.30 (br, 33H), 2.05 (q, 4H), 4.97 (m, 4H), 5.85 (m, 2H); 13C NMR (CDCl3): (ppm) 28.04, 29.2, 29.42, 29.77, 29.91, 30.34, 30.6, 31.81, 34.08, 49.01, 114.3, 139.44; EI/HRMS: [M]+ calculated for C27H52: 376.4069, found: 376.4070. Elemen tal analysis calculated for C27H52: 86.09 C, 13.91 H; found 86.11 C, 13.89 H tricosa-1,22-dien-12-ylcyclohexane (4i). After purification, 4.25 g (99% yield) of a colorless liquid was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 1.03-1.75 (br, 44H), 2.04 (q, 4H), 4.97 (m, 4H), 5.84 (m, 2H); 13C NMR (CDCl3): (ppm) 27.21, 27.26, 28.06, 29.19, 29.4, 29.76, 29.89, 29.94, 30.03, 30.42, 31.03, 34.07, 40.4, 43.54, 114.29, 139.47; EI/HRMS: [M]+ calculated for C29H54: 402.4226, found: 402.4230. Elemental analysis calculated for C29H54: 86.49 C, 13.51 H; found 86.50 C, 13.49 H General Polymerization Conditions. All glassware was flame dried under vacuum prior to use. Monomers were dried over K mirror and degassed prior to polymerization. All metathesis reactions were initiated in the bulk, inside an argon atmosphere drybox. Monomer was placed in a 50 mL round-bottomed flask equi pped with a magnetic stirbar. Grubbs first generation catalyst (400:1 mono mer:catalyst) was added to the flask, and the flask was then

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142 fitted with a Schlenk adapter equipped with a vacuum valve. The reaction was monitored by formation of ethylene gas as a moderate obser ved bubbling. The sealed reaction vessel was removed from the drybox and immediately placed on the vacuum line. The reaction vessel was then exposed to intermittent vacuum. After 4 h, the polymerization was exposed to full vacuum (10-4 torr) for 96 h at 45-50 C. The reaction vess el was then cooled to room temperature, exposed to air, and 50 mL of a mixture of ethyl vinyl ether in toluene 1% v/v was added. The polymer/toluene solution was precipitated in metha nol by dropwise addition of the solution to a beaker containing 1500 mL of acidic methanol (1 M), yielding pure EPent21u, EHept21u, E3MB21u, ENH21, and EVCH21 polymers, respectively. Polymerization of 2-propyltricosa1,22-diene (4c) to give EPent21u. After purification, 980 mg (98% yield) of material was collected. The following spect ral properties were observed: 1H NMR (CDCl3): (ppm) 0.88 (t, 3H,), 1.27 (br, 30H), 1.55 (s 1H), 1.98 (br, 3H), 5.39 (br, 2H); 13C NMR (CDCl3): (ppm) 14.79, 20.07, 26.95, 27.46, 29.43, 29.57, 29.79, 29.92, 29.96, 30.41, 32.85, 33.96, 36.37, 37.44, 130.12, 130.58; GPC da ta (THF vs. polystyrene standards): wM = 41,200 g/mol; P.D.I. ( n wM M /) = 1.7 Polymerization of 12-pentyltricosa1,22-diene (4e) to give EHept21u. After purification, 970 mg (97% yield) of material was collected. Th e following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.89 (t, 3H,), 1.27 (br, 32H), 1.55 (s, 1H), 1.98 (br, 3H), 5.39 (br, 2H); 13C NMR (CDCl3): (ppm) 14.36, 22.95, 26.61, 26.96, 27.46, 29.36, 29.44, 29.57, 29.62, 29.68, 29.79, 29.82, 29.92, 29.96, 30.03, 30.4, 32.63, 32.85, 33.89, 33.96, 37.66, 130.11, 130.58; GPC data (THF vs. polystyrene standards): wM = 45,100 g/mol; P.D.I. ( n wM M /) = 1.8

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143 Polymerization of 12-isopropyltrico sa-1,22-diene (4g) to give E3MB21u. After purification, 960 mg (96% yield) of material was collected. Th e following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.84 (d, 6H,), 1.28 (br, 32H), 1.69 (br, 1H), 1.98 (br, 4H), 5.40 (br, 2H); 13C NMR (CDCl3): (ppm) 19.43, 28.01, 29.38, 29.44, 29.58, 29.8, 29.94, 29.97, 30.44, 30.74, 32.86, 43.91, 130.09, 130.56; GPC data (THF vs. polystyrene standards): wM = 45,500 g/mol; P.D.I. ( n wM M /) = 1.7 Polymerization of 12tert -butyltricosa-1,22-diene (4h) to give ENH21u. After purification, 915 mg (92% yield) of material was collected. Th e following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.85 (s, 8H,), 1.02 (br, 2H), 1.28 (br, 26H), 1.98 (br, 4H), 5.40 (br, 2H); 13C NMR (CDCl3): (ppm) 28.07, 29.47, 29.60, 29.81, 29.85, 29.94, 30.05, 30.35, 30.63, 31.82, 32.87, 34.12, 49.05, 130.12, 130.58; GPC data (THF vs. polystyrene standards): wM = 30,600 g/mol; P.D.I. ( n wM M /) = 1.7 Polymerization of tricosa-1,22-dien-12ylcyclohexane (4i) to give EVCH21u. After purification, 938 mg (94% yield) of material was collected. Th e following spectral properties were observed: 1H NMR (CDCl3): (ppm) 1.27 (br, 40H), 1.53-1.71 (m, 5), 1.98 (br, 4H), 5.39 (br, 2H); 13C NMR (CDCl3): (ppm) 27.22, 27.27, 28.09, 29.45, 29.58, 29.80, 29.95, 29.97, 30.04, 30.45, 31.05, 32.87, 40.41, 43.56, 130.11, 130.57; GPC data (THF vs. polystyrene standards): wM = 32,500 g/mol; P.D.I. ( n wM M /) = 1.6 General hydrogenation methodology using diimide. A solution of unsaturated polymer (~1.0 g) was dissolved in xylenes (30 mL) in a 350 mL three-neck round bottomed flask. Tripropyl amine (3.79 g, 26.3 mmol) was added via syringe followed by addition of p toluenesulfonhydrazide (4.33 g, 23.3 mmol) usi ng a powder funnel. The reaction mixture was heated to 135C for 2 hours. The reaction was monitored by the produced nitrogen observed

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144 through a mineral oil bubbler. When production of nitrogen gas was ceased, the solution was cooled to room temperature, and a second batc h of tripropyl amine (3.79 g, 26.3 mmol) and p toluenesulfonhydrazide (4.33 g, 23.3 mmol) was added. The reaction mixture was heated to 135C for 2 h, and its performance was monitored by the evolution of nitrogen gas. Precipitation of the crude mixtures into acidic methanol (1M HCl), followed by filtration afforded the saturated polymers EPent21, EHept21, E3MB21, ENH21 and EVCH21. Hydrogenation of EPent21u to give EPent21. After precipitation, 912 mg (91% yield) of material was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.89 (t, 3H,), 1.27 (br, 36H); 13C NMR (CDCl3): (ppm)14.80, 20.07, 26.94, 29.99, 30.42, 33.93, 36.37, 37.42; GPC data (THF vs. polystyrene standards): wM = 41,400 g/mol; P.D.I. ( n wM M /) = 1.7; DSC Results: Melting Temperature Data: Tm = 12 C, hm = 60 J/g Hydrogenation of EHept21u to give EHept21. After precipitation, 860 mg (86% yield) of material was collected. The followi ng spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.88 (t, 3H,), 1.26 (br, 41H);13C NMR (CDCl3): (ppm) 14.80, 22.97, 26.62, 26.94, 29.99, 30.41, 33.89, 33.93, 37.64; GPC data (THF vs. polystyrene standards): wM = 45,800 g/mol; P.D.I. ( n wM M /) = 1.8; DSC Results: Melting Temperature Data: Tm = 14 C, hm = 58 J/g Hydrogenation of E3MB21u to give E3MB21. After precipitation, 985 mg (99% yield) of material was collected. The followi ng spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.84 (br, 6H,), 1.28 (br, 43H), 1.69 (br, 1H);13C NMR (CDCl3): (ppm) 19.46, 28.03, 29.48, 29.99, 30.45, 30.80, 43.96; GPC data (THF vs. polystyrene standards): wM = 46,000

PAGE 145

145 g/mol; P.D.I. ( n wM M /) = 1.7; DSC Results: Melting Temperature Data: Tm = 11 C, hm = 37 J/g Hydrogenation of ENH21u to give ENH21. After precipitation, 895 mg (90% yield) of material was collected. The following spectral properties were observed: 1H NMR (CDCl3): (ppm) 0.85 (s, 9H,), 1.01 (br, 3H), 1.27 (br, 36H);13C NMR (CDCl3): (ppm) 28.06, 29.99, 30.33, 30.61, 31.80, 34.11, 49.02; GPC data (THF vs. polystyrene standards): wM = 32,100 g/mol; P.D.I. ( n wM M /) = 1.7; DSC Results: Melting Temperature Data: Tm = 13 C, hm = 50 J/g Hydrogenation of EVCH21u to give EVCH21. After precipitation, 950 mg (95% yield) of material was collected. The followi ng spectral properties were observed: 1H NMR (CDCl3): (ppm) 1.27 (br, 14H), 1.53-1.74 (m, 2H);13C NMR (CDCl3): (ppm) 27.21, 27.26, 28.06, 29.99, 30.03, 30.44, 31.03, 40.41, 43.53; GPC data (THF vs. polystyrene standards): wM = 33,600 g/mol; P.D.I. ( n wM M /) = 1.6; DSC Results: Melting Temperature Data: Tm = 9 C, hm = 37 J/g

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146 APPENDIX 1H AND 13C NUCLEAR MAGNETIC RESONA NCE SPECTRA FOR SELECTED INTERMEDIATES AND TARGET MATERIALS 6.1 Compounds Described in Chapter 2 2-Methyl-2-(undec-10-enyl)tr idec-12-enenitrile (3a)

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147 2-Ethyl-2-(undec-10-enyl)tr idec-12-enenitrile (3b)

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148 2-butyl-2-(undec-10-enyl)tridec-12-enenitrile (3c)

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149 2-Hexyl-2-(undec-10-enyl)tr idec-12-enenitrile (3d)

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150 6.2 Compounds Described in Chapter 3 12-Methyltricosa-1,22-diene (2a)

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151 12-Ethyltricosa-1,22-diene (2b)

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152 12-Propyltricosa-1,22-diene (2c)

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153 12-Butyltricosa-1,22-diene (2d)

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154 12-Pentyltricosa-1,22-diene (2e)

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155 12-Hexyltricosa-1,22-diene (2f)

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156 6.3 Compounds Described in Chapter 4 9-butylheptadeca-1,16-diene (4a) 12-Butyltricosa-1,22-diene (2d) See the appendix for compounds described in chapter 3.

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157 2,7-diallyl-2,7-dibutyl octanedinitrile (9)

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158 5,10-diallyltetradecane (10)

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159 EH5u

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160 EH5

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161 EH15u

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162 EH15

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163 EH21u

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164 EH21

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165 EH0u

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166 EH0

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167 EH-43.5

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168 6.4 Compounds Described in Chapter 5 3,3-dimethylbutanenitrile (2h)

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169 2-cyclohexylacetonitrile (2i)

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170 2-isopropyl-2-(undec-10-enyl)tr idec-12-enenitrile (3g).

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171 2-tert-butyl-2-(undec-10-enyl)tridec-12-enenitrile (3h)

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172 2-cyclohexyl-2-(undec-10-enyl)tridec-12-enenitrile (3i)

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173 12-isopropyltricosa-1,22-diene (4g)

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174 12-tert-butyltricos a-1,22-diene (4h)

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175 tricosa-1,22-dien-12-ylcyclohexane (4i)

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176 EPent21u

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177 EPent21

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178 EHept21u

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179 EHept21

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180 E3MB21u

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181 E3MB21

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182 ENH21u

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183 ENH21

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184 EVCH21u

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185 EVCH21

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186 LIST OF REFERENCES 1. Gedde, U. W.; Mattozzi, A. Long-Term Properties of Polyolefins 2004, 169 29-73. 2. Knuuttila, H.; Lehtinen, A.; Nummila-Pakarinen, A. Long-Term Properties of Polyolefins 2004, 169 13-27. 3. Univation Technologies Market Information, http://www.univation.com 4. Peacock, A. J.; Handbook of Polyethylene: St ructures, Properties, and Applications ; Marcel Dekker: New York, 2000, 534pp. 5. Fawcett, E. W.; Gibson, R. Q.; Perrin, M. H.; Patton, J. G.; Williams, E. G. Brit. Pat. 2, 816, 883, Sept. 6, 1937, (Imperial Chemical Industries, Ltd). 6. Ziegler, K. Patent, Belg. Pat. 533,326, May 535, 1955. 7. Ziegler, K. Kunststoffe 1955, 45 506. 8. Forte, M. M. D.; da Cunha, F. O. V.; dos Santos, J. H. Z.; Zacca, J. J. Polymer 2003, 44 1377-1384. 9. Usami, T.; Gotoh, Y.; Takayama, S. Macromolecules 1986, 19 2722-2726. 10. Mirabella, F. M. Journal of Polymer Science Part B-Polymer Physics 2001, 39 28192832. 11. Dias, M. L.; Barbi, V. V.; Pereira, R. A.; Mano, E. B. Materials Research Innovations 2001, 4 82-88. 12. Villar, M. A.; Ferreira, M. L. Journal of Polymer Science Part a-Polymer Chemistry 2001, 39 1136-1148. 13. Vanden Eynde, S.; Mathot, V.; Koch, M. H. J.; Reynaers, H. Polymer 2000, 41 34373453. 14. Al-Hussein, M.; Strobl, G. Macromolecules 2002, 35 8515-8520. 15. DesLauriers, P. J.; Rohlfing, D. C.; Hsieh, E. T. Polymer 2002, 43 159-170. 16. Fernyhough, C. M.; Young, R. N.; Poche, D.; Degroot, A. W.; Bosscher, F. Macromolecules 2001, 34 7034-7041. 17. Gates, D. P.; Svejda, S. K.; Onate, E.; Killian, C. M.; Johnson, L. K.; White, P. S.; Brookhart, M. Macromolecules 2000, 33 2320-2334.

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187 18. Hadjichristidis, N.; Xenidou, M.; Iatrou, H. ; Pitsikalis, M.; Poulos Y.; Avgeropoulos, A.; Sioula, S.; Paraskeva, S.; Velis, G.; Lohse, D. J.; Schulz, D. N.; Fetters, L. J.; Wright, P. J.; Mendelson, R. A.; Garcia-Franco, C. A.; Sun, T.; Ruff, C. J. Macromolecules 2000, 33 2424-2436. 19. Haigh, J. A.; Nguyen, C.; Alamo, R. G.; Mandelkern, L. Journal of Thermal Analysis and Calorimetry 2000, 59 435-450. 20. Jokela, K.; Vaananen, A.; Torkkeli, M.; Star ck, P.; Serimaa, R.; Lofgren, B.; Seppala, J. Journal of Polymer Science Part B-Polymer Physics 2001, 39 1860-1875. 21. Mader, D.; Heinemann, J.; Walter, P.; Mulhaupt, R. Macromolecules 2000, 33 12541261. 22. Mattice, W. L. Macromolecules 1983, 16 487-490. 23. Mattice, W. L.; Stehling, F. C. Macromolecules 1981, 14 1479-1484. 24. Rangwala, H. A.; Lana, I. G. D.; Szymura, J. A.; Fiedorow, R. M. Journal of Polymer Science Part a-Polymer Chemistry 1996, 34 3379-3387. 25. Zhang, F. J.; Song, M.; Lu, T. J.; Liu, J. P.; He, T. B. Polymer 2002, 43 1453-1460. 26. Ungar, G.; Zeng, K. B. Chemical Reviews 2001, 101 4157-4188. 27. Bracco, S.; Comotti, A.; Simonutti, R.; Camurati, I.; Sozzani, P. Macromolecules 2002, 35 1677-1684. 28. Starck, P.; Malmberg, A.; Lofgren, B. Journal of Applied Polymer Science 2002, 83 1140-1156. 29. Wright, K. J.; Lesser, A. J. Macromolecules 2001, 34 3626-3633. 30. Pak, J.; Wunderlich, B. Macromolecules 2001, 34 4492-4503. 31. Johnson, L. K.; Killian, C. M.; Brookhart, M. Journal of the American Chemical Society 1995, 117 6414-6415. 32. Quijada, R.; Rojas, R.; Bazan, G.; Komon, Z. J. A.; Mauler, R. S.; Galland, G. B. Macromolecules 2001, 34 2411-2417. 33. Roedel, M. J. Journal of the Americ an Chemical Society 1953, 75 6110-6112. 34. Adisson, E.; Ribeiro, M.; Deffieux, A.; Fontanille, M. Polymer 1992, 33 4337-4342. 35. Alamo, R. G.; Mandelkern, L. Macromolecules 1991, 24 6480-6493. 36. Starck, P.; Rajanen, K.; Lofgren, B. Thermochimica Acta 2003, 395 169-181.

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188 37. Tracz, A.; Ungar, G. Macromolecules 2005, 38 4962-4965. 38. Ungar, G.; Keller, A. Polymer 1980, 21 1273-1277. 39. Vaughan, A. S.; Ungar, G.; Bassett, D. C.; Keller, A. Polymer 1985, 26 726-732. 40. Mirabella, F. M. Journal of Polymer Science Part B-Polymer Physics 2001, 39 28002818. 41. Carella, J. M.; Graessley, W. W.; Fetters, L. J. Macromolecules 1984, 17 2775-2786. 42. Colby, R. H.; Milliman, G. E.; Graessley, W. W. Macromolecules 1986, 19 1261-1262. 43. Gotro, J. T.; Graessley, W. W. Macromolecules 1984, 17 2767-2775. 44. Krishnamoorti, R.; Graessley, W. W.; Balsara, N. P.; Lohse, D. J. Macromolecules 1994, 27 3073-3081. 45. Morton, M.; Clarke, R. G.; Bostick, E. E. Journal of Polymer Science Part A General Papers 1963, 1 475-482. 46. Baughman, T. W.; Wagener, K. B. Metathesis Polymerization 2005, 176 1-42. 47. O'Gara, J. E.; Wagener, K. B. Makromolekulare Chemie-Rapid Communications 1993, 14 657-662. 48. Smith, J. A.; Brzezinska, K. R.; Valenti, D. J.; Wagener, K. B. Macromolecules 2000, 33 3781-3794. 49. Sworen, J. C.; Smith, J. A.; Berg, J. M.; Wagener, K. B. Journal of the American Chemical Society 2004, 126 11238-11246. 50. Sworen, J. C.; Smith, J. A.; Wagener, K. B.; Baugh, L. S.; Rucker, S. P. Journal of the American Chemical Society 2003, 125 2228-2240. 51. Berda, E. B.; Baughman, T. W.; Wagener, K. B. Journal of Polymer Science Part A: Polymer Chemistry 2006, 44 4981-4989. 52. Rojas, G.; Wagener, K. In Metathesis Chemistry 2007, pp 305-324. 53. Schwendeman, J. E.; Wagener, K. B. Macromolecular Chemistry and Physics 2005, 206 1461-1471. 54. Sworen, J. C.; Wagener, K. B. Macromolecules 2007, 40 4414-4423. 55. Wunderlich, B.; Czornyj, G. Macromolecules 1977, 10 906-913. 56. Baughman, T. W.; Sworen, J. C.; Wagener, K. B. Macromolecules 2006, 39 5028-5036.

PAGE 189

189 57. Mirabella, F. M.; Ford, E. A. Journal of Polymer Science Part B-Polymer Physics 1987, 25 777-790. 58. Wunderlich, B.; Poland, D. Journal of Polymer Science Part A 1963, 1 357. 59. Wilski, H.; Grewer, T. Journal of Polymer Science Part C 1964, 33. 60. Lieser, G.; Wegner, G.; Smith, J. A.; Wagener, K. B. Colloid and Polymer Science 2004, 282 773-781. 61. Qiu, W. L.; Sworen, J.; Pyda, M.; Nowak-Pyda, E.; Habenschuss, A.; Wagener, K. B.; Wunderlich, B. Macromolecules 2006, 39 204-217. 62. Shaffer, T. D.; Canich, J. A. M.; Squire, K. R. Macromolecules 1998, 31 5145-5147. 63. Alizadeth, A.; Richardson, L.; Xu, J.; McCa rtney, S.; Marand, H.; Cheung, Y. W.; Chum, S. Macromolecules 1999, 32 6221-6235. 64. Caddick, S.; Judd, D. B.; Lewis, A. K. D.; Reich, M. T.; Williams, M. R. V. Tetrahedron 2003, 59 5417-5423. 65. Fleming, F. F.; Zhang, Z. Y. Tetrahedron 2005, 61 747-789. 66. Gregory, G. B.; Johnson, A. L.; Ripka, W. C. Journal of Organic Chemistry 1990, 55 1479-1483. 67. Khurana, J. M.; Kukreja, G. Synthetic Communications 2002, 32 1265-1269. 68. Kraus, G. A.; Hon, Y. S. Journal of Organic Chemistry 1985, 50 4605-4608. 69. Rychnovsky, S. D.; Griesgraber, G.; Kim, J. S. Journal of the Americ an Chemical Society 1994, 116 2621-2622. 70. Sicinski, R. R.; Perlman, K. L.; Prahl, J.; Smith, C.; DeLuca, H. F. Journal of Medicinal Chemistry 1996, 39 4497-4506. 71. Dauben, W. G. Organic Reactions ; John Willey: New York, 1984. 72. Savoia, D.; Tagliavini, E.; Trombini, C.; Umani-Ronchi, A. Journal of Organic Chemistry 1980, 45 3227-3229. 73. Drake, C. A.; Rabjohn, N.; Tempesta, M. S.; Taylor, R. B. Journal of Organic Chemistry 1988, 53 4555-4562. 74. Lortie, F.; Boileau, S.; Bouteiller, L. Chemistry European Journal 2003, 9 3008-3014. 75. Taber, D. F.; Kong, S. Journal of Organic Chemistry 1997, 62 8575-8576.

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190 76. Fleming, F. F.; Gudipati, S.; Zha ng, Z. Y.; Liu, W.; Steward, O. W. Journal of Organic Chemistry 2005, 70 3845-3849. 77. Stork, G.; Gardner, J. O.; Boeckman, R. K.; Parker, K. A. Journal of the American Chemical Society 1973, 95 2014-2016. 78. Tripathy, S.; Hussain, H.; Durst, T. Tetrahedron Letters 2000, 41 8401-8405. 79. Viteva, L.; Gospodova, T.; Stefanovsky, Y.; Simova, S. Tetrahedron 2005, 61 58555865. 80. Baek, S.; Jo, H.; Kim, H.; Kim, H.; Kim, S.; Kim, D. Organic Letters 2005, 7 75-77. 81. Hartmann, R. W.; Batzl, C. Journal of Medicinal Chemistry 1986, 29 1362-1369. 82. Kaliappan, K. P.; Gowrisankar, P. Tetrahedron Letters 2004, 45 8207-8209. 83. Magomedov, N. A. Organic Letters 2003, 5 2509-2512. 84. Odinets, I.; Vinogradova, N.; Petrov skii, P.; Lyssenko, K.; Mastryukova, T. Phosphorus Sulfur and Silicon and the Related Elements 2002, 177 1787-1791. 85. Wagener, K. B.; Valenti, D.; Hahn, S. F. Macromolecules 1997, 30 6688-6690. 86. Sworen, J. C. 2004, PhD. Dissertation, University of Florida,. 87. Baughman, T. W.; Wagener, K. B. Advances in Polymer Science 2005, 176 1-42. 88. Lehman, S. E.; Schwendeman, J. E.; O'Donnell, P. M.; Wagener, K. B. Inorganica Chimica Acta 2003, 345 190-198. 89. Baughman, T. W.; Sworen, J. C.; Wagener, K. B. Tetrahedron 2004, 60 10943-10948. 90. Rojas, G.; Baughman, T. W.; Wagener, K. B. Synthetic Communications 2007, 37 39233931. 91. Franck-Neumann, M.; Miesch, M.; L acroix, E.; Metz, B.; Kern, J. M. Tetrahedron 1992, 48 1911-1926. 92. Arapakos, P. G.; Scott, M. K.; Huber, F. E. Journal of the American Chemical Society 1969, 91 2059-2062. 93. Nemoto, H.; Hashimoto, M.; Kur obe, H.; Fukumoto, K.; Kametani, T. Journal of the Chemical Society-Perkin Transactions 1 1985, 927-934. 94. Nemoto, H.; Nagai, M.; Abe, Y.; Mo izumi, M.; Fukumoto, K.; Kametani, T. Journal of the Chemical Society-Perkin Transactions 1 1987, 1727-1733. 95. Ra, C. S.; Kim, Y. S. Bulletin of the Korean Chemical Society 1997, 18 151-155.

PAGE 191

191 96. Rojas, G.; Wagener, K. B. Journal of Organic Chemistry 2008, 73 4962-4970. 97. Mattalia, J. M.; Marchi-Delapie rre, C.; Hazimeh, H.; Chanon, M. Arkivoc 2006, 90-118. 98. Cuvigny, T.; Larcheve.M; Normant, H. Comptes Rendus Hebdomadaires Des Seances De L Academie Des Sciences Serie C 1972, 274 797-799. 99. Fall, Y.; Torneiro, M.; Castedo, L.; Mourino, A. Tetrahedron Letters 1992, 33 66836686. 100. Torneiro, M.; Fall, Y.; Castedo, L.; Mourino, A. Tetrahedron Letters 1992, 33 105-108. 101. Debal, A.; Cuvigny, T.; Larcheveque, M. Synthesis-Stuttgart 1976, 391-393. 102. Ohsawa, T.; Kobayashi, T.; Miz uguchi, Y.; Saitoh, T.; Oishi, T. Tetrahedron Letters 1985, 26 6103-6106. 103. Marshall, J. A.; Bierenbaum, R. Journal of Organic Chemistry 1977, 42 3309-3311. 104. Gomberg, M. Journal of the American Chemical Society 1900, 22 757-771. 105. Gomberg, M. Journal of the American Chemical Society 1901, 23 496-502. 106. Lankamp, H.; Nauta, W. T.; MacLean, C. Tetrahedron Letters 1968, 9 249-254. 107. McBride, J. M. Tetrahedron 1974, 30 2009-2022. 108. Yan, X. M.; Robbins, M. D.; White, J. M. Journal of Physical Chemistry B 2004, 108 18925-18931. 109. Ashworth, B.; Gilbert, B. C.; Norman, R. O. C. Journal of Chemical Research (S) 1977, 94-95. 110. Brainard, R. L.; Madix, R. J. Journal of the American Chemical Society 1987, 109 80828083. 111. Mortensen, A.; Skibsted, L. H. FEBS Letters 1998, 426 392-396. 112. Moger, C.; Gyor, M. Tetrahedron Letters 1989, 30 7467-7468. 113. Stolze, K.; Udilova, N.; Nohl, H. Free Radical Biology and Medicine 2000, 29 10051014. 114. Verdin, D. International Journal for Radiation Physics and Chemistry 1970, 2 201-208. 115. Cuvigny, T.; Larcheveque, M.; Normant, H. Bulletin de la Socit Chimique de France 1973, 3 1174-1178. 116. Denisova, T. G.; Denisov, E. T. Russian Chemical Bulletin 2002, 51 949-960.

PAGE 192

192 117. Ha, C.; Horner, J. H.; Newcomb, M.; Varick, T. R.; Arnold, B. R.; Lusztyk, J. Journal of Organic Chemistry 1993, 58 1194-1198. 118. Sturino, C. F.; Fallis, A. G. Journal of Organic Chemistry 1994, 59 6514-6516. 119. Beckwith, A. L. J.; Bowry, V. W.; Schiesser, C. H. Tetrahedron 1991, 47 121-130. 120. Beckwith, A. L. J. Tetrahedron 1981, 37 3073-3100. 121. Stork, G.; Baine, N. H. Journal of the Americ an Chemical Society 1982, 104 2321-2323. 122. Beckwith, A. L. J.; Phillipou, G.; Serelis, A. K. Tetrahedron Letters 1981, 22 28112814. 123. Gomez, A. M.; Company, M. D.; Uriel, C.; Valverde, S.; Lopez, J. C. Tetrahedron Letters 2002, 43 4997-5000. 124. Julia, M. Accounts of Chemical Research 1971, 4 386-392. 125. Beckwith, A. L.; Moad, G. Journal of the Chemical Soc iety, Chemical Communications 1974, 472-473. 126. McKnight, A. L.; Waymouth, R. M. Chemical Reviews 1998, 98 2587-2598. 127. Muller, A. J.; Hernandez, Z. H.; Arnal, M. L.; Sanchez, J. J. Polymer Bulletin 1997, 39 465-472. 128. Czaja, K.; Sacher, B.; Bialek, M. Journal of Thermal Analysis and Calorimetry 2002, 67 547-554. 129. Anantawaraskul, S.; Soares, J. B. P.; Jirachaithorn, P. Macromolecular Symposia 2007, 257 94-102. 130. James, D. E.; Encyclopedia of Polymer Science and Engineering, Mark, H. F, Bikales, N. M, Overberger, C. G, Menges, G, Wiley-Interscience, New York, 1985, 6, p429. 131. Alobaidi, F.; Ye, Z. B.; Zhu, S. P. Journal of Polymer Science Part A-Polymer Chemistry 2004, 42 4327-4336. 132. Seger, M. R.; Maciel, G. E. Analytical Chemistry 2004, 76 5734-5747. 133. Pracella, M.; D'Alessio, A.; Giaiacopi, S.; Galletti, A. R.; Carlini, C.; Sbrana, G. Macromolecular Chemistry and Physics 2007, 208 1560-1571. 134. Zhang, J. W.; Li, B. G.; Fan, H.; Zhu, S. Journal of Polymer Science Part A-Polymer Chemistry 2007, 45 3562-3569. 135. Hsieh, E. T.; Randall, J. C. Macromolecules 1982, 15 1402-1406.

PAGE 193

193 136. Dorman, D. E.; Bovey, F. A.; Otocka, E. P. Macromolecules 1972, 5 574-577. 137. Randall, J. C.; Polymer characterizati on by ESR and NMR, ACS Symposium Series, Arthur E. Woodward and Frank A. Bovey, American Chemical Society, Washington, DC,1980,142,309 pp. 138. Randall, J. C. Journal of Polymer Science Part B Polymer Physics 1973, 11 275-287. 139. Shan, C. L. P.; Soares, J. B. P.; Penlidis, A. Journal of Polymer Science Part a-Polymer Chemistry 2002, 40 4426-4451. 140. Da Silva, A. A.; Soares, J. B. P.; De Galland, G. B. Macromolecular Chemistry and Physics 2000, 201 1226-1234. 141. Czaja, K.; Bialek, M. Polymer 2001, 42 2289-2297. 142. Takaoka, T.; Ikai, S.; Tamura, M.; Yano, T. Journal of Macromolecular Science-Pure and Applied Chemistry 1995, A32 83-101. 143. Quijada, R.; Dupont, J.; Miranda, M. S. L.; Scipioni, R. B.; Galland, G. B. Macromolecular Chemistry and Physics 1995, 196 3991-4000. 144. Madkour, T. M.; Goderis, B.; Mathot, V. B. F.; Reynaers, H. Polymer 2002, 43 28972908. 145. Suhm, J.; Schneider, M. J.; Mulhaupt, R. Journal of Polymer Science Part a-Polymer Chemistry 1997, 35 735-740. 146. Schneider, M. J.; Mlhaupt, R. Journal of Molecular Catalysis A: Chemical 1995, 101 11-16. 147. Suhm, J.; Schneider, M. J.; Mulhaupt, R. Journal of Molecular Catalysis A Chemical 1998, 128 215-227. 148. Rojas, G.; Berda, E. B.; Wagener, K. B. Polymer 2008, 49 2985-2995. 149. Schrock, R. R.; Murdzek, J. S.; Bazan, G. C.; Robbins, J.; Dimare, M.; Oregan, M. Journal of the American Chemical Society 1990, 112 3875-3886. 150. Bazan, G. C.; Khosravi, E.; Schrock, R. R.; Feast, W. J.; Gibson, V. C.; Oregan, M. B.; Thomas, J. K.; Davis, W. M. Journal of the American Chemical Society 1990, 112 83788387. 151. Bazan, G. C.; Oskam, J. H.; Cho, H. N.; Park, L. Y.; Schrock, R. R. Journal of the American Chemical Society 1991, 113 6899-6907. 152. Fox, H. H.; Schrock, R. R. Organometallics 1992, 11 2763-2765.

PAGE 194

194 153. Feldman, J.; Murdzek, J. S.; Davis, W. M.; Schrock, R. R. Organometallics 1989, 8 2260-2265. 154. Oskam, J. H.; Schrock, R. R. Journal of the American Chemical Society 1992, 114 75887590. 155. Tashiro, K.; Sasaki, S.; Kobayashi, M. Macromolecules 1996, 29 7460-7469. 156. Rueda, D. R.; Baltacalleja, F. J.; Hidalgo, A. Journal of Polymer Science Part B-Polymer Physics 1977, 15 2027-2031. 157. Ke, B. Journal of Polymer Science 1960, 42 15-23. 158. Boz, E.; Ghiviriga, I.; Nemeth, A. J.; Jeon, K.; Alamo, R. G.; Wagener, K. B. Macromolecules 2008, 41 25-30. 159. Krimm, S. Fortschr. Hochpolym-Forsch. 1960, 2 S 51. 160. Zerbi, G.; Modern Polymer Spectroscopy, Wiley-VCH, New York, 1999, 304pp. 161. Da Silva, M. A.; Galland, G. B. Journal of Polymer Science Part A Polymer Chemistry 2008, 46 947-957. 162. Luruli, N.; Heinz, L.-C.; Grumel, V.; Brll, R.; Pasch, H.; Raubenheimer, H. G. Polymer 2006, 47 56-66. 163. Halasz, L.; Belina, K.; Vorster, O. C.; Juhasz, P. Plastics, Rubber & Composites 2004, 33 205-211. 164. Neves, C. J.; Monteiro, E.; Habert, A. C. Journal of Applied Polymer Science 1993, 50 817-824. 165. Luruli, N.; Pijpers, T.; Brull, R.; Grumel, V.; Pasch, H.; Mathot, V. Journal of Polymer Science Part B-Polymer Physics 2007, 45 2956-2965. 166. Halasz, L.; Vorster, O. Polymers for Advanced Technologies 2006, 17 1004-1008. 167. Joubert, D. J.; Goderis, B.; Reynaers, H.; Mathot, V. B. F. Journal of Polymer Science Part B-Polymer Physics 2005, 43 3000-3018. 168. Joubert, D.; Tincul, I. Macromolecular Symposia 2002, 178 69-79. 169. Tincul, I.; Smith, J.; van Zyl, P. Macromolecular Symposia 2003, 193 13-28. 170. Derlin, S.; Kaminsky, W. Macromolecules 2007, 40 4130-4137. 171. Kirshenb.I; Feist, W. C.; Isaacson, R. B. Journal of Applied Polymer Science 1965, 9 3023-3031.

PAGE 195

195 172. Endo, K.; Fujii, K.; Otsu, T. Journal of Polymer Science Part A Polymer Chemistry 1991, 29 1991-1993. 173. Kaminsky, W.; Beulich, I.; Arndt-Rosenau, M. Macromolecular Symposia 2001, 173 211-225. 174. Mauler, R. S.; Galland, G. B.; Scipioni, R. B.; Quijada, R. Polymer Bulletin 1996, 37 469-474. 175. Losio, S.; Tritto, I.; Zannoni, G.; Sacchi, M. C. Macromolecules 2006, 39 8920-8927. 176. Irwin, L. J.; Reibenspies, J. H.; Miller, S. A. Journal of the American Chemical Society 2004, 126 16716-16717. 177. Xu, G.; Cheng, D. Macromolecules 2001, 34 2040-2047. 178. Aitola, E.; Puranen, A.; Setala, H.; Lipponen, S.; Leskela, M.; Repo, T. Journal of Polymer Science Part A Polymer Chemistry 2006, 44 6569-6574. 179. Nomura, K.; Itagaki, K. Macromolecules 2005, 38 8121-8123. 180. Gendler, S.; Groysman, S.; Goldschmidt, Z.; Shuster, M.; Kol, M. Journal of Polymer Science Part A Polymer Chemistry 2006, 44 1136-1146. 181. Starck, P.; Lofgren, B. Journal of Macromolecular Science-Physics 2002, B41 579-597. 182. Blitz, J. P.; Mcfaddin, D. C. Journal of Applied Polymer Science 1994, 51 13-20. 183. Striegel, A. M.; Krejsa, M. R. Journal of Polymer Science Part B-Polymer Physics 2000, 38 3120-3135. 184. Sarzotti, D. M.; Soares, J. B. P.; Penlidis, A. Journal of Polymer Science Part B-Polymer Physics 2002, 40 2595-2611. 185. Lindeman, L. P.; Adams, J. Q. Analytical Chemistry 1971, 43 1245-1252. 186. Borriello, A.; Busico, V.; Derosa, C.; Schulze, D. Macromolecules 1995, 28 5679-5680. 187. Asakura, T.; Nakayama, N. Polymer Communications 1991, 32 213-216. 188. Randall, J. C. Journal of Polymer Science Part B Polymer Physics 1975, 13 1975-1990. 189. Keaton, R. J.; Jayaratne, K. C.; Hennings en, D. A.; Koterwas, L. A.; Sita, L. R. Journal of the American Chemical Society 2001, 123 6197-6198. 190. Wilfong, D. L.; Knight, G. W. Journal of Polymer Science Part B Polymer Physics 1990, 28 861-870. 191. Starck, P. Polymer International 1996, 40 111-122.

PAGE 196

196 192. McKenna, T. F. European Polymer Journal 1998, 34 1255-1260.

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BIOGRAPHICAL SKETCH Giovanni Rojas, son of Miriam Jimenez and Armando Rojas, was born in the country of Colombia on October 31st, 1976, in Cali, Valle. In 1988 afte r finishing elementary school, he joined a technical school, Ins tituto Nacional de Enseanza Media Diversificada I.N.E.M, where he received a degree in Industrial Chemis try in 1993. In 1994, he began his professional education at Universidad del Valle. During the last two years of college, Giovanni was focused on the field of food chemistry working specifica lly on enzymology and biochemistry of the juice obtained from passion fruit. In 1999, he receiv ed the degree in Chemistry. In 2000, Giovanni began his industrial career as chemist in the area of quality control in Bayer. S.A. After one year in Bayer, he decided to move to Unilever S. A for working on laundry and house hold products at the Research and Development department. In 2002, Giovanni joined the research group of Professor Fabio Zuluaga at the ch emistry department in Universidad del Valle for working in the graft copolymerization of polysiloxanes with -lactones. Before finishing his master in organic chemistry, he began graduate st udies in organic and polymer ch emistry under the advisement of Professor Kenneth B. Wagener at University of Florida in 2003. Giovanni received his degree of Master in Organic Chemistry in 2005. Upon comple tion of Ph.D. requirement s in the summer of 2008, Dr. Giovanni Rojas relocated to Mainz, Ge rmany to begin a post-doctoral research under the supervision of Professor Dr. Klaus Mllen and Dr. Markus Klapper at the Max Planck Institute for Polymer Research.