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Modeling Linear-Low Density Polyethylene: Copolymers Containing Precise Structures

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Title:
Modeling Linear-Low Density Polyethylene: Copolymers Containing Precise Structures
Creator:
SWOREN, JOHN CHRISTOPHER ( Author, Primary )
Copyright Date:
2008

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Carbon ( jstor )
Copolymers ( jstor )
Hydrogenation ( jstor )
Macromolecules ( jstor )
Melting ( jstor )
Molecular weight ( jstor )
Monomers ( jstor )
Polyethylenes ( jstor )
Polymerization ( jstor )
Polymers ( jstor )

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University of Florida
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University of Florida
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Copyright John Christopher Sworen. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
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8/31/2005
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436098561 ( OCLC )

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MODELING LINEAR-LOW DENSITY POLYETHYLENE: COPOLYMERS CONTAINING PRECISE STRUCTURES By JOHN CHRISTOPHER SWOREN 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 2004

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Copyright 2004 by John Christopher Sworen

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For You.... Christine, John, and Christie Sworen, Thanks.

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ACKNOWLEDGMENTS I would like to acknowledge my advisor, Professor Ken Wagener, for all the guidance, friendship, and tolerance over these many years. He is a true role model for any graduate student’s professional career helping students understand all aspects of lab and life. His love for polymer chemistry and telling of those famous life stories have made my time at Florida most enjoyable. In addition, Professor Wagener’s most enduring quality, without question, is his love and constant concern for the well-being of students and people, past and present, which truly make him a person to remember. The stay at Florida would not be complete without thanking and acknowledging the people who have in some fashion made graduate school a pleasure. I have to thank Dr. and Mrs. Butler for their friendship and all their contributions to Florida’s polymer expansion. In addition, I would like to thank them for their continued support personally through the Butler Polymer Research Award. I thank Mrs. Lorraine Williams for all her early help with manuscript preparations and many funny and delightful lunch conversations. Further, I would like to thank all secretaries within the polymer office for their supplemental joy and help throughout the years. Also, special thanks go to Mrs. Sara Klossner for all her help with job searching and sending all those letters in the final year. In addition, I have to thank my committee members (Professors John Reynolds, Eric Enholm, Elliot Douglas, C. Russell Bowers and James Boncella) for their help throughout my tenure at the University of Florida. iv

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I have had the pleasure of working and conversing with some truly amazing colleagues at the University of Florida. Specifically, I have been blessed to sit next to and know the best lab mate, Dr. Timothy Hopkins. I have missed all those late night talks and problem solving sessions, writing on any piece of paper we could find no matter the size. Of course, I will never forget some of those late filtering nights. I would like to thank my other classmates in the Wagener Group, Dr. Ed Lehman, Dr. Jason Smith, and Dr. Cameron Church (Pawlow). They have contributed to my graduate career both inside and outside the lab and will never be forgotten. In addition, my list would not be complete without acknowledging my true friend, Dr. James Pawlow. I would not be in my current position or have the background to understand my ongoing and more than likely future chemistry questions without him. I thank Jim for everything he hase done; his advice and friendship are unparallelled and I wish him continued luck and good fortune. I have to acknowledge the many past and current Reynolds group members and lab mates (Mr. Barry Thompson, Mr. Ryan Walczak, Mr. Ben Reeves, Mr. Genay Jones, and Dr. Kyukwan Zong, Dr. Shane Waybright and Dr. Dean Welsh) for their friendship and help on the polymer floor. In addition, there are many selective Reynolds group members that need special recognition. I have to thank my Dr. Hopkins replacement, Ms. Emilie Galand, for all those funny singing moments, laughter in the lab, and French candy. I would like to thank Dr. Carl Gaupp (Josey Wales) and Janet for all their support and friendship throughout our overlapping stay at Florida. With that, I can not forget Dr. C.J. Dubois and his wife Sonya Dubois. They have been my second family and have v

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helped and supported me in countless ways. In fact, words can not thank them enough for their kindness; I love them both. My gratitude and special thanks go out to the most recent graduate students in Wagener’s group; without them my life at the University of Florida would be incomplete. I have the extreme pleasure to work and collaborate with the best hood buddy a graduate student can ask for, Ms. Florence Courchay. Over the years, she has become a true and loving friend and I would help her in anyway possible, even run countless TLCs. We have had our share of arguments about chemistry and even clothes, laughed, and even shared a close and scary moment in the stockroom, thanks to Walt. I appreciate her concerns and questions and truly enjoyed our time together; I will miss her immensely. Also, I have had the pleasure of meeting, talking, and knowing Ms. Violeta Petkovska. The time we have spent together has produced the most memorable conversations about life and family and I have learned from each moment. She truly deserves to become rich and famous and pimp around in a big SUV. Of course, this section would be lacking without mentioning the Polish friends who have made Florida feel like home the last couple of years. Both Mr. Piotr Matloka and his wife Kornelia’s generosity and kindness have been unsurpassed and I consider them family. They will always be missed but never ever forgotten. Finally, I could not have succeeded without the support and guidance of my family. I am truly blessed and thankful for all their love, patience, and sacrifice to better both my sister and me. These sacrifices have given us unseen advantages and have allowed the pursuit of many endeavors enabling us to become successful not only in our careers but in life. I will always cherish the smile and emotions brought to their faces from even the vi

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smallest accomplishments in our lives, brought about by their generosity and love. I hope they realize that they made all this possible. vii

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TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iv LIST OF TABLES.............................................................................................................xi LIST OF FIGURES..........................................................................................................xii ABSTRACT.....................................................................................................................xvi CHAPTER 1 THE ESSENCE OF POLYETHYLENE......................................................................1 1.1 Historic Significance..............................................................................................1 1.2 Advent of High-Density and Specialized Polyethylene.........................................4 1.3 Nomenclature of Polyethylene...............................................................................7 1.4 Polyethylene Morphology and Attributes.............................................................10 1.5 Morphological Studies and Branch Modeling......................................................15 1.6 Application of Metathesis in the Synthesis of Precise Structures........................20 1.7 Dissertation Purpose.............................................................................................23 2 RANDOM METHYL BRANCHED ETHYLENE/1-PROPENE COPOLYMERS..24 2.1 Introduction...........................................................................................................24 2.2 Results and Discussion.........................................................................................26 2.2.1 Polymer Synthesis and Hydrogenation......................................................26 2.2.2 Molecular Weight and Branching Analysis of ADMET Polymers............30 2.2.3 Thermal Analysis and Behavior.................................................................36 2.2.4 IR and Diffraction Data..............................................................................44 2.3 Conclusions...........................................................................................................48 2.4 Experimental Section............................................................................................49 2.4.1 Instrumentation...........................................................................................49 2.4.2 Materials.....................................................................................................53 2.4.3 General ADMET Copolymerizations.........................................................54 2.4.4 Hydrogenation of Unsaturated ADMET Polymers....................................58 3 PRECISE ETHYL BRANCHED ETHYLENE/1-BUTENE COPOLYMERS.........61 viii

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3.1 Introduction...........................................................................................................61 3.2 Results and Discussion.........................................................................................63 3.2.1 Monomer Synthesis and Characterization..................................................63 3.2.2 ADMET Polymerization and Hydrogenation Chemistry...........................67 3.3.3 Structure Determination using NMR and IR..............................................70 3.3.4 Thermal Analysis........................................................................................76 3.3.5 Wide-angle X-ray Scattering......................................................................84 3.3 Conclusions...........................................................................................................86 3.4 Experimental Section............................................................................................87 3.4.1 Instrumentation and Analysis.....................................................................87 3.4.2 Materials.....................................................................................................89 3.4.3 Synthesis and Characterization of 3-(4-pentenyl)-7-octene (1).................90 3.4.4 Synthesis and Characterization of 3-(10-undecenyl)-13-tetradecene (2)...90 3.4.5 Monomer Synthesis and Characterization of Wittig Monomers................93 3.4.6 General Polymerization Conditions...........................................................94 3.4.7 General Hydrogenation Conditions............................................................96 4 LINEAR-LOW DENSITY POLYETHYLENE CONTAINING PRECISELY PLACED HEXYL BRANCHES................................................................................99 4.1 Introduction...........................................................................................................99 4.2 Results and Discussion.......................................................................................102 4.2.1 Monomer Synthesis and Characterization................................................102 4.2.2 ADMET Polymerization and Hydrogenation Chemistry.........................105 4.2.3 Structural Data Solution.........................................................................108 4.2.4 Thermal Behavior.....................................................................................110 4.2.5 Structural Data – Solid State....................................................................117 4.3 Conclusions.........................................................................................................123 4.4 Experimental Section..........................................................................................124 4.4.1 Instrumentation and Analysis...................................................................124 4.4.2 Materials...................................................................................................125 4.4.3 General Monomer Synthesis....................................................................126 4.4.4 General Polymerization Conditions.........................................................129 4.4.5 General Hydrogenation Conditions..........................................................131 5 SIDE CHAIN MOTION IN PRECISE DEUTERATED METHYL BRANCHED POLYETHYLENE...................................................................................................133 5.1 Introduction.........................................................................................................133 5.2 Results and Discussion Characterization.........................................................140 5.2.1 Monomer Synthesis and Characterization................................................140 5.2.2 Nomenclature and Comonomer Content..................................................143 5.2.3 ADMET Polymerization and Hydrogenation...........................................144 5.2.4 Thermal Behavior.....................................................................................147 5.3 Results and Discussion – 2 H-n.m.r. Spectroscopy..............................................151 5.4 Conclusions.........................................................................................................161 5.5 Experimental Section..........................................................................................162 ix

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5.5.1 Instrumentation and Analysis...................................................................162 5.5.2 Materials...................................................................................................163 5.5.3 Monomer Synthesis..................................................................................164 5.5.4 Synthesis of Precise Deuterated Methyl ADMET Dienes.......................166 5.5.5 General Polymerization Conditions.........................................................167 5.5.6 General Hydrogenation Conditions..........................................................169 APPENDIX ADDITIONAL WAXD AND NMR DATA..............................................172 LIST OF REFERENCES.................................................................................................182 BIOGRAPHICAL SKETCH...........................................................................................202 x

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LIST OF TABLES Table page 1-1 General polyethylene classification requirements.......................................................9 2-1 Molecular weight data shown for the saturated ADMET copolymers gathered using three detection methods...................................................................................31 2-2 Branching content and comonomer content for the random series...........................33 2-3 Heat flow and crystallinity data for the random methyl branched series..................37 3-1 Molecular weights for ADMET model EB materials................................................70 4-1 Molecular weights and structural data for ADMET model EO materials...............107 5-1 Molecular weights for deuterated model ADMET copolymers..............................144 xi

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LIST OF FIGURES Figure page 1-1 Fringed-micelle morphology....................................................................................11 1-2 Chain-folding model for polyethylene recrystallization..........................................12 1-3 Representative crystallization model for polyethylene including the orthorhombic subcell.......................................................................................................................13 1-4 Three-phase crystallization model...........................................................................14 1-5 Polyethylene orthorhombic crystal lattice................................................................17 1-6 Metastable polyethylene unit cells...........................................................................19 1-7 General ADMET reaction scheme...........................................................................21 1-8 Schrock’s catalyst (C1) and Grubbs’ first generation catalyst (C2)........................22 2-1 General synthetic scheme for the synthesis of EP model copolymers.....................27 2-2 Infrared characterization data for both the ADMET prepolymer PE-97.4 and its hydrogenated analog PE-97.4H................................................................................29 2-3 A comparison of endgroups and chemical shifts for all the polymerization combinations.............................................................................................................35 2-4 DSC endothermic traces for PE-OCT, PE-1.5, PE-7.1, and PE-13.6....................38 2-5 DSC endothermic traces for PE-OCTH, PE-1.5H, PE-7.1H, and PE-13.6H.......39 2-6 DSC endothermic traces for PE-25.0, PE-43.3, and PE-55.6.................................40 2-7 DSC endothermic traces for PE-25.0H, PE-43.3H, and PE-55.6H........................41 2-8 Thermal comparison of random (PE-43.3H) versus precise methyl branching (PE-45PH)..............................................................................................42 2-9 Thermal correlations using the Flory equation........................................................43 2-10 IR Spectral Changes with increased branch content................................................45 xii

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2-11 Wide-angle scattering pattern for the random copolymers......................................47 3-1 Controlling ethyl branch content using ADMET polymerization............................62 3-2 Ethyl branch synthetic methodology for short methylene monomers......................64 3-3 Synthesis for longer methylene run length monomers shown for 3-(10-undecenyl)-13-tetradecene (2).....................................................................................................66 3-4 Synthesis of Wittig monomers.................................................................................67 3-5 Typical 13 C NMR transformation for ADMET copolymers....................................71 3-6 Infrared comparison for the ADMET EB series......................................................76 3-7 DSC comparison between a methyl and ethyl on every 9 th carbon..........................78 3-8 Structural comparison based on the collected DSC and NMR data.........................80 3-9 Annealing experiments for HPEB21W....................................................................82 3-10 WAXD of precise ethyl branched EB copolymer HPEB21W (Top) and precise methyl branched EP copolymer HPEP21 (bottom).................................................85 4-1 Modeling precisely branched ethylene/1-octene copolymers using organic methods...................................................................................................................101 4-2 Synthetic method utilized to produce model EO monomers..................................104 4-3 Acyclic Diene METathesis (ADMET) polymerization.........................................106 4-4 A comparison of 13 C NMR spectra for a typical ADMET polymerization transformation........................................................................................................109 4-5 Thermal profile of the model EO copolymer containing a hexyl branch on each and every 9 th backbone carbon, HPEO9......................................................................111 4-6 The DSC melting and recrystallization thermograph for HPEO15.......................112 4-7 The DSC melting and recrystallization thermograph for HPEO21.......................113 4-8 Thermal comparison of HPEO21, HPEB21, and HPEP21.................................115 4-9 Graphic comparison for the precise branched ADMET series...............................116 4-10 Infrared absorbencies for the ADMET model EO copolymers..............................118 4-11 Initial solid state magic angle 13 C-n.m.r. of HPEO21 taken at -30 o C..................121 xiii

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5-1 Equation of spin states............................................................................................135 5-2 Hamiltonians governing quadrupole couplings......................................................135 5-3 Singularities observed for 2 H-n.m.r. and the overlapped Pake pattern..................137 5-4 The experimental 2 H-n.m.r. spectrum....................................................................138 5-5 Synthetic methodology used to produce symmetrical placed deuterated methyl monomers...............................................................................................................141 5-6 Typical NMR data produced for ADMET monomers, 1 H and 13 C-n.m.r. illustrated for monomer 1.......................................................................................142 5-7 1 H and 13 C-n.m.r. for HPEP-d 3 -9 and 1 H-n.m.r. for its hydrogen analog HPEP9...................................................................................................................146 5-8 Thermal profile for the ADMET model copolymer containing a deuterated methyl group on every 9 th carbon, HPEP-d 3 -9......................................................149 5-9 Thermal profile for the ADMET model copolymer containing a deuterated methyl group on every 15 th carbon, HPEP-d 3 -15..................................................150 5-10 Thermal profile for the ADMET model copolymer containing a deuterated methyl group on every 21 th carbon, HPEP-d 3 -21..................................................151 5-11 Cooling and heating 2 H-n.m.r. spectra for HPEP-d 3 -9..........................................154 5-12 The collective heating 2 H-n.m.r. data set for HPEP-d 3 -9......................................156 5-13 Cooling and heating 2 H-n.m.r. spectra for HPEP-d 3 -15........................................157 5-14 The collective heating 2 H-n.m.r. data set for HPEP-d 3 -15....................................158 5-15 Cooling and heating 2 H-n.m.r. spectra for HPEP-d 3 -21........................................159 5-16 The collective heating 2 H-n.m.r. data set for HPEP-d 3 -21....................................160 A-1 WAXD pattern for unbranched ADMET polyethylene.........................................172 A-2 WAXD pattern for PE-1.5H..................................................................................173 A-3 WAXD pattern for PE-7.1H..................................................................................174 A-4 WAXD pattern for PE-13.1H................................................................................175 A-5 WAXD pattern for PE-25.0H................................................................................176 A-6 WAXD pattern for PE-43.3H................................................................................177 xiv

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A-7 WAXD pattern for PE-55.6H................................................................................178 A-8 Combined cooling wide-line 2 H-n.m.r spectra for HPEP-d 3 -9..............................179 A-9 Combined cooling wide-line 2 H-n.m.r spectra for HPEP-d 3 -15............................180 A-10 Combined cooling wide-line 2 H-n.m.r spectra for HPEP-d 3 -21............................181 xv

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Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy MODELING LINEAR-LOW DENSITY POLYETHYLENE: COPOLYMERS CONTAINING PRECISE STRUCTURES By John Christopher Sworen August 2004 Chair: Kenneth B. Wagener Major Department: Chemistry The incorporation of precise defects and ultimately the control of polyethylene’s primary structure have been sought after since the macromolecule’s inception in the 1930s. Considerable research has been directed towards controlling the polymer’s behavior either by the branch type or branch frequency being introduced within the copolymer. Due to the simplistic nature of polyethylene, controlling these factors allows for wide-ranging perturbations to the final material and their performance. Consequently, the control and modeling of such incorporation and behavior would allow for predictions and structural correlations Acyclic diene metathesis (ADMET) has been used to produce exact models of ethylene copolymers in an attempt to investigate structure/property relations. It was found that the materials produced by controlled and exact placement of branch defects produce new polyethylene-based materials exhibiting behavior not observed previously. Also, the homogeneous branch distributions obtained using metathesis is the ultimate xvi

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factor contributing to the observed behavior and ultimately allowing for the access to these new materials. The branched models have been split into separate chapters throughout the dissertation based on their branch identity. Chapter 2 focuses on the modeling of randomly branched ethylene/1-propene (EP) copolymers producing the first example of a room temperature EP copolymer containing a hexagonal phase. Chapter 3 probes the behavior of an ethylene/1-butene (EB) copolymer series as well as their crystal packing. The copolymers yield unique behavior and produce materials not obtainable via other polymerization techniques. Chapter 4 is an attempt to model and investigate a special class of linear branched ethylene copolymers. These macromolecules are based on ethylene/1-octene (EO) and represent the first example of precise models of linear-low density polyethylene. The final chapter focuses on attempts of understanding chain motion and side chain location within the semi-crystalline state of model EP copolymers. Conclusions about branch location and mobility are derived and the techniques, such as 2 H-n.m.r, are described. Regardless of the chapter or subject chosen, metathesis has been used successfully to better understand and answer fundamental polymer questions and behavior. xvii

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CHAPTER 1 THE ESSENCE OF POLYETHYLENE 1.1 Historic Significance The term “macromolecule” was coined by Staudinger in 1922 to help distinguish molecules of high molecular weight from their smaller weight analogs. These principles followed his first decisive paper on the subject in 1920, which, for example, proposes linear molecules for polyoxymethylene and polystyrene. 1-2 The following ten years saw indisputable proof that macromolecules exist, separate from associated colloidal materials. The most convincing evidence was seen through the work of W. H. Carothers and others at the duPont company. Cathors’ work on polyesters and polyamides led to the development and the commercialization of synthetic polymers worldwide. However, the basic understanding of macromolecule materials can be traced back to the principles governing the valences brought about by the cohesion of simple organic structural building blocks. These rules constructed to explain small molecule structural behavior were developed in the 1870s, predating the idea of macromolecules by almost fifty years. 3 Throughout the decades preceding the interesting debates sparked by Staudinger, polyethylene (PE) had an already long, rich history despite its simplistic structure and inexpensive design. The synthesis of the linear polyolefin, first conducted by the German chemist Hans von Pechmann4 in 1898, followed shortly after by Bamberger and Tschirner5 (1900), was accidentally prepared from the decomposition of diazomethane. The macromolecule was characterized as a waxy, white solid containing simple and long 1

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2 repeating methylene units, thus termed polymethylene. Unlike polyethylene, which must contain an even number of repeating carbon atoms, polymethylene can have any number of repeating carbon atoms. Friedrich and Marvel, in 1930, reported the first low molecular weight polyethylene by an incidental polymerization of ethylene sighting the production of a “non-gaseous” product.6 Also in 1930, Carothers et al. published the synthesis of paraffin waxes by the sodium reduction of decamethylene bromide.7 A few years later, Koch and Ibing (1935) reported higher molecular weight paraffins by the Fisher-Tropsch reduction of carbon dioxide with hydrogen.8 Despite the numerous syntheses published, the important discovery of a polyethylene-based material was missed. In the 1930s, the British chemical company Imperial Chemical Industries (ICI) began the first high-pressure research program of small molecules, including ethylene. The first existence of polyethylene was reported on March 29 th , 1933, by a research team at ICI. The discovery, reported by Eric Fawcett and Reginald Gibson, was conducted under high ethylene pressure in the presence of benzaldehyde producing the familiar waxy, white solid lining the reaction vessel. 9 The polymerization was initiated by trace amounts of oxygen, unknown to Fawcett and Gibson at that time. The development of a reproducible set of polymerization conditions was not found until December 1935 by a fellow ICI chemist, Michael Perrin. The first set of experimental conditions yielded 8 g of the highly ductile polyethylene having a melting point in the range of 110 o C. His discovery is the basis for all future low-density polyethylene materials produced to date. The advent of World War II led ICI to take the first manufacturing patent out in 1936. 10

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3 The first high-pressure production plant in 1937 realized the successful development of polyethylene, and by the outbreak of WWII, ICI was commercially producing polyethylene. At the time, the inherent flexibility and chemical inertness of this new material were investigated for potential electrical insulating and barrier materials. The development of polyethylene was most extensively seen in the areas of insulator materials, and by the end of the war, polyethylene was utilized in insulating radar components, submarine communication cables, and telecommunication cables linking France and England. The benefits brought about by using polyethylene materials were so great that both Union Carbide and the duPont company bought the rights from ICI to commercially produce polyethylene in the United States. Commercial output of polyethylene began in 1943 overtaking the initial production by Great Britain. The years following the conclusion of WWII saw a decreasing demand for polyethylene and manufacturing shifted towards consumer development. The expansion of products made from polyethylene opened new markets for molding small parts and extruded cable wire insulation. Despite the numerous applications and good mechanical properties, polyethylene production and expansion into other various markets had been limited. The majority of the discourse lay with the high-pressure polymerization mode needed to produce the desired materials. The principles governing the polymerization created by ICI lead to highly branched materials producing materials with low tensile strength, flexibility, and softening temperature. Subsequent landmarks in polyethylene’s history were the modification and control of these factors influencing the overall behavior and performance of this simple material.

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4 1.2 Advent of High-Density and Specialized Polyethylene The initial hurdle for further polyethylene commercialization was to produce catalysts that would polymerize ethylene under more mild temperature and pressures conditions as those used in the initial studies performed at ICI. Similar to the development of low-density polyethylene, high-density materials were overlooked by both the duPont and U.S. Rubber Company in the early 1930s. 11 Marvel and Mayo independently produced the high melting material from lithiumalkyl reagents as well as Hall and Nash in 1937. In 1943, Fisher used aluminum powder and titanium fluorides to polymerize ethylene, a patent later assigned to BASF in 1953. The realization of low-pressure and temperature polyethylene was being investigated by two separate groups after the end of World War II. The most recognizable advancement in polyethylene materials was made by the German chemist Karl Ziegler, who headed a research group at the Max Planck Institute in West Germany investigating transition metal chemistry. The commercialization of HDPE was made possible by Karl Ziegler’s discovery of the “Aufbau” reaction in which ethylene was dimmerized using triethylaluminum to form 1-butene. 12 Its application in the polymerization of ethylene was realized after the discovery that the “Aufbau” reaction was being terminated by nickel from the reaction vessel. The significance of this discovery lies in the extension of alkyaluminum to zirconium metal, instead of nickel, which seems to produce a significant amount of highly linear polyethylene. Further studies by Martin, a Ziegler staff member, succeeded in polymerizing ethylene with a titanium complex at such low pressure and temperature that the polymerization was conducted in a glass vessel. 12 Around the same time, researchers at the Phillips Petroleum company were investigating solid supported

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5 transition metal oxides. The company, not considered part of the polyolefin field, had a base interest in the synthesis of lubrication oils from either an ethylene or propylene feedstock. Its initial investigation in the area was the production of butadiene from ethylene using supported chromium trioxide. Observations made by John Hogan and Robert Banks during these early experiments yielded a waxy, highly linear version of polyethylene. 13 The properties resembled the materials made by Ziegler and by the end of the 1950s both systems were being commercially used to produce high density polyethylene. The new form of polyethylene had superior properties to those of higher branched resins opening the market to PE materials previously unavailable. Dr. Ziegler wrote his own patent application and confined his claim to the polymerization of ethylene. Inspired by the polyethylene development, Giulio Natta applied this technology to produce the first polypropylene resin in Spain in 1954. The significance of this discovery was recognized by the Nobel Prize Committee in 1963 and the committee awarded the Nobel Prize to both Karl Ziegler and Giulio Natta for their work in the field of ethylene/propylene polymerization. To this day, the initial heterogeneous catalyst systems developed by them both in the 1950s are now collectively known as Ziegler-Natta catalysts. The development of Ziegler-Natta catalysts has revolutionized the range of materials possible and has solidified polyethylene as the world’s leading synthetic macromolecule. From the 1940s onward, research devoted to the copolymerization of ethylene led by such catalysts has allowed the incorporation of numerous aliphatic and even polar comonomers. The copolymerization of ethylene was commercialized in the

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6 1950s with incorporation of pendent side chains to inhibit crystallization and reduce shrinking upon cooling. The copolymerization of ethylene produces polymers falling into the linear-low density (LLDPE) class as a result of modifying the linear backbone of HDPE. The copolymers are usually comprised of a statically inserted alpha-olefin, principally 1-propylene, 1-butene, 1-hexane, and 1-octene. The incorporation of the comonomer typically gives rise to long run lengths of unbranched linear polyethylene producing heterogeneous polymer structures. The control of monomer insertion and polymer microstructure has been a continuing problem of heterogeneous systems like that of Ziegler-Natta. These shortcomings have fueled researchers to study ethylene homoand copolymerizations with the most recent advancements coming from the ability to control comonomer incorporation by the development well-defined catalyst systems. Initially investigated by the German chemist Walter Kaminsky in 1976, the catalysts are based on metallocene structures; these catalyst systems have since proven to be efficient for both the homoand copolymerization of ethylene. 14 Metallocene-based catalysts are dramatically different for previous systems producing very well-defined structures, lower polydispersities and more uniform polymer microstructures. 15-25 In general, the control offered by metallocene systems has been applied to produce branched analogs of linear polyethylene. In recent years, the highly oxophilic nature of the early transition metals that constitute both Ziegler-Natta and metallocene catalyst has come under investigation. The lower oxophilicity of late transition metals has undergone a revolutionary development focusing on the work conducted by Maurice Brookhart and coworkers. 26 In contrast to

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7 early transition metals, little information has been discovered using late metals for the polymerization of ethylene due to high -elimination rates. However, the discovery of -diimine ligands has produced numerous complexes based on cationic palladium and nickel. The bulkiness of the ligated diimine restricts the agnostic hydrogen interaction normally responsible for chain termination and transfer. Controlling the sterics around the metal center allows for polymerization/elimination ratio manipulation producing polymers containing long-chain branches derived from a single monomer, ethylene. Further modification can be conducted by the addition of branched comonomers, randomly inserting controlled defects yielding wide ranging materials based on the identity of the chosen comonomer and its percent incorporation. 1.3 Nomenclature of Polyethylene As motioned many types of polyethylene exist today; in order to delineate the synthesis origin of a selective polyethylene, which can be directly related to the material behavior, a variety of standard classes have been developed in which all versions of polyethylene are placed. The nomenclature, based on the mode of polymerization, spans all possible material densities as measured for purely crystalline (1.00 g/cm 3 ) and totally amorphous materials (0.850 g/cm 3 ). Variations to the simple polyethylene theme chiefly arise from the production of defects, specifically, the addition of differing branch lengths and content. Also, chain-end manipulation is seen but to a lesser extent. In general, the higher concentration of randomly placed defects yields lower crystalline and less dense materials. Until recently, three base classes, low-density polyethylene (LDPE), high-density polyethylene (HDPE), and linear-low density polyethylene (LLDPE), have been designated to categorize both linear and branched polyethylene. However, recent

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8 advances in the area of metallocene catalysts have broadened the nomenclature to include numerous subsets, most notably ultra-high molecular weight polyethylene (UHMWPE) and very-low density polyethylene (VLDPE). Polyethylene produced by radical polymerizations is referred to as low-density polyethylene (LDPE) or high-pressure polyethylene. These low-density materials are the first examples of polyethylene relating back to the initial work of Fawcett and Gibson. Microstructural defects caused by the high temperatures and ethylene pressures produce highly branched macromolecules by interchain radical transfer, resulting in poor packing behavior and as a result low densities and crystallinity. The high pressures produce high concentrations of ethyl and butyl branches, which are frequently clustered together, separated by long run lengths of unbranched material. Typically, the name LDPE has been designated to materials containing 40-60% crystallinity and densities in the range of 0.91-0.93 g/cm 3 . High-density polyethylene (HDPE) or low-pressure polyethylene, initially synthesized by the work of Ziegler and Phillips Petroleum are highly linear version with little or no side chain branches. The low reaction pressure required limits the intramolecular back biting seen in radical chemistry producing tight chain packing and high crystallinity. The narrow inter-chain heterogeneity gives this class of polyethylene good mechanical strength with molecular weights in the area of 500,000-1,000,000 g/mol. In most cases, the polymers exhibit 70-90% crystallinity with respective densities between 0.94-0.96 g/cm 3 . As mentioned, the advent of single site metallocene catalysts has been able to produce completely linear polyethylene with extremely high molecular weights. These special polymers have been deemed ultra-high molecular weight

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9 polyethylene (UHMWPE) encompassing the higher crystallinity and density values seen in HDPE. Typically, the molecular weight range for UHMWPE is 6-12 times that of HDPE materials producing extremely entangled polymer chains. When spun, UHMWPE produces tuff fibers coined Spectra1000, rivaling the properties of Kevlar. Table 1-1. General polyethylene classification requirements. Property HDPE LDPE LLDPE VLDPE Density (g/cm 3 ) 0.94 – 0.97 0.91 – 0.94 0.90 – 0.94 0.86 – 0.90 Crystallinity (% from density) 62 – 80 42 – 60 34 – 62 4 – 35 Tensile Modulus (x 10 -3 psi) 155 – 200 25 – 50 38 – 130 < 38 Tensile Strength (x 10 -3 psi) 3.2 – 4.5 1.2 – 4.5 1.9 – 6.5 2.5 – 5.0 Melting Temperature ( o C) 125 134 98 – 115 100 – 125 60 – 100 Distortion Temperature ( o C @ 66 psi) 80 – 90 40 – 45 55 – 80 Heat of Fusion (cal/g) 38 – 58 21 – 37 15 – 43 0 15 The final class of polyethylene is actually based on copolymers of ethylene systematically produced using metallocene systems. Linear-low density polyethylene (LLDPE) combines the density of LDPE materials with control defect placement. The key is the production of a purely linear backbone with selective branch incorporation via the addition of a branched comonomer. On average 25-100 backbone carbons separate the branches producing fairly long-run lengths of crystallizable material. Industrially, LLDPEs are mainly produced using metallocene single site catalyst systems owning to 34% of the total polyethylene sold. Of course, the material behavior and properties are controlled by comonomer type and content. The narrow intraand interchain heterogeneity offered by metallocenes enables the copolymer to obtain extremely low crystallinites and material densities. Addition of long chain branched comonomers (<

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10 C 8 ), a subset of LLDPE regarded as very low-density polyethylene (VLDPE), produces useful materials with densities approaching purely amorphous polyethylene. The low-densities are realized by the high local concentration of branches, typically every 7-20 backbone carbon atoms. Table 1-1 summarizes the generalizations and illustrates the overlaps observed for each branching classification. Regardless of the catalyst system employed, polyethylene is the world’s largest synthetically produced macromolecule in the world with an estimated 120 billion pounds produced in 2003. 1.4 Polyethylene Morphology and Attributes Polyethylene in its simplest form consists of a long backbone of an even number of carbons covalently bonded, each having a pair of hydrogens. Unlike simple compounds, polyethylene does not exist as a single or identical molecule but as a collection of chemical different macromolecules. Polyethylene materials between the lower and higher density limits (0.85 – 1.00 g/cm 3 ) exist in a semi-crystalline form, in which the material contains both highly ordered and unordered segments. This structural tangent to small organic molecules yields various behavior and morphologic responses depending on the homogeneity of these molecules within the material. In polyethylene’s purest form, C 2n H 4n+2 , the value most frequently describing this modulation in behavior is its weight(M w ) to number average (M n ) molecular weight ratio. Values for M w /M n for commercial resins can vary from 1.2 – 25, or more. The measured breadth in the molecular weight distribution is used to predict polyethylene’s properties in both the solid and molten state. In the case of LDPE and LLDPE, the composition and homogeneity of branches have a greater affect on the polymer’s behavior. In fact, branch manipulation produces better responsive materials over the structural pure HDPE and consequently is responsible for the highest volume polyethylene.

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11 All together, the combination of polyethylene’s unique structural characteristics causes variations between neighboring macromolecules resulting in less ideal (versus small molecules) and more disordered structures. For a number of years, this fact complicated the deduction of long-range structural information for polyethylene, mainly from the belief single crystal growth in such heterogonous structures was improbable. Early investigations into the repeating morphology of polyethylene led to the creation of two schools of thought regarding crystallite formation in macromolecules. It is now universally accepted that polymers with flexible chains crystallize as thin lamellae with the advent of chain folding. Initially reported by Sauter 27 and Stork 28 in the 1930s, the concept of folding macromolecules was dismissed and believed to be unlikely due to effects caused by molecular entanglements. Figure 1-1. Fringed-micelle morphology. Crystalline lamellae are the basic building blocks for the larger morphologies observed in macromolecules such as spherulites, row-structures, transcrystalline layers, or dendrites, etc. Much debate has surrounded the questions regarding the origin of these structures begining with Herrmann et al. in 1930. 29 His group postulated a fringe-micelle

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12 crystallization model (Figure 1-1) which proposes that a single, chain-extended polymer stem can contribute to several different crystallite and amorphous domains. Through the use of x-ray powder diffraction analysis, he concluded that the scattering pattern was indicative of small crystallite size, thus leading to a fringed-micelle. Unfortunately, diffuse reflections from semi-crystalline polymers can result from either small crystallite size or lattice defects making predictions not straight-forward. The concept did predict the observed mechanical properties of polyethylene; however, the model was unable to associate the fine details (tie molecules and loops) seen with spherulties or helix formation in polypropylene. Figure 1-2. Chain-folding model for polyethylene recrystallization. A) sharp folds, B) switchboard model, C) adjacent loop reentry and D) complete recrystallization pictorial. Several groups 30-34 in the 1950s showed it was possible to grow single crystals of polymeric materials, sparking detailed investigations into the ideas brought out by Stork and Sauter. Thereafter, Keller, 35 Fischer, 36 and Till 37 independently published the first evidence for a chain-folded, solution grown polyethylene. Although the electron diffraction studies performed on the material revealed thin platelets (~100 ), crystal

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13 thickness varies as a function of recrystallization conditions. The aftermath has led to several models for chain-folding illustrated in Figure 1-2 including the most recognizable switchboard model proposed by Flory. 38 Of course, the reasons for the observation of thin crystal platelets are entirely kinetic: a thin crystal grows faster and the entropic barrier for the crystallization of short segments is smaller than extended chains. Figure 1-3. Representative crystallization model for polyethylene including the orthorhombic subcell. Observations made by Keller and others on PE’s crystal thickness (100 – 200 ) and typical polymer chain have to be at least 1000 , they contended that chain-folding must occur. The model depicting their observations is illustrated in Figure 1-3, as well as the outlined orthorhombic lattice known to exist in polyethylene. The chain-folding model accounts for the observed material properties and also accounts for structural defects including spherulites, dendrites, and crystal twinning. To be sure, the ideas brought about by single crystal observations have revolutionized the theories governing crystallization, crystal growth, and growth kinetics. 39-43

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14 Figure 1-4. Three-phase crystallization model. The collection of the entire present day observations produces the crystallization model, based on the repeating lamellae structure, outlined in Figure 1-4. Since the time of adjunct reentry the consensus is that polyethylene can be represented in terms of a three-phase model. The model constitutes a well-defined and understood highly order phase surrounded by a well understood ‘liquid-like’ disordered phase. Investigations into polyethylene crystallization has uncovered a disorderd-ordered phase in which has been the source of much debate. It is accepted that an undetermined amount of chain stems within crystallites are connected to the nearest neighbor through tight folding loops; however, a majority of the stems have connectivity through this slightly disordered phase, coined the interfacial region. Although the nature of this disordered phase is not well understood Figure 1-4 represents the presently accepted model.

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15 1.5 Morphological Studies and Branch Modeling As mentioned, semi-crystalline polymers can be considered to be a composite of dense, crystalline segments imbedded within an unorganized, amorphous matrix. Unlike ceramics or inorganic minerals, the semi-crystalline nature complicates a general structure common to the entire material. The picture gets distorted by such considerations as morphology, percent crystallinity, interfacial regions, and branch homogeneity. Since commercial inception in the 1930s, considerable research has focused on the structure-property relationships of ethylene based polymers. The ultimate effect that branching has on the behavior of polyolefins is quite important; in fact, this topic has been examined in great detail for more than 60 years. 44-61 Due to polyethylene’s simplistic nature, the material has been the standard with which to compare when investigating and modeling structure-property functions. Typically, direct detection methods (WAXD, SAXS, diffraction, microscopy, and NMR) have been used to determine and investigate polymeric microstructure while indirect methods (DSC, density, and mechanical analysis) have been used to explain the properties achieved by said structure. Over the years, numerous attempts to correlate properties to structures have been developed. However, in order to understand the origins of molecular behavior, the repeating unit cell of the simplest known structure, polyethylene, must be used as a starting point. Of course, the information gathered using single crystal X-ray is unsurpassed when trying to produce a valid model to which to compare structural perturbations. The molecular study of polyethylene, in its infancy, was complicated due to uncontrollable branch production and wide molecular weight distributions. In an attempt to overcome these problems linear, unbranched polyethylene paraffins and long-chain n

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16 alkanes have been used as models to investigate such behavior. 62 The synthesis of these model molecules produces uniform and homogeneous structures with extreme narrow polydispersities uncommon in polyethylene using polymerization techniques. Correlations between paraffins/alkanes to polyethylene can be made, if of sufficient molecular weight, yielding property functions. Alex Mller 63-66 completed the most exhaustive study on n-paraffins obtaining the single crystal diffraction pattern for C 29 H 60 in the mid 1920s. It was concluded that the material packed in parallel zigzag planes which can be drawn normal to the repeating axis through the end-groups separating layers. In fact, it was found out that the oligomer contained two distinct repeating layers, translationally identical to its neighbor. This repeating structure observed by n-alkanes was determined as orthorhombic, geometry later observed for linear polymeric alkanes, such as polyethylene. 67-76 Due to these similarities, crystalline n-alkanes have been studied as chain models for crystal growth and morphology, 69,70,77-79 melting temperature, 80-81 chain mobility, 82 conformational defects, 83-84 and self-diffusion. 85-86 The extension is also valid to the metastable states (hexagonal) in high pressure polyethylene which have counterparts in n-alkanes up to 40 carbons. 87-88 As mentioned, the investigation of higher molecular weight, unbranched hydrocarbon materials reveals the same orthorhombic structure observed by Mller for n-paraffins. The structure of polyethylene was uncovered in a landmark paper by C. W. Bunn in 1939. 89 In contrast to the small molecules studied by Mller, Fourier transformation was able to map the electron density for the repeating cell. This contouring of the different densities allowed for methylene stem location and their

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17 positional locality. The mapping of individual cells was further categorized by Vand 90 in accordance with the repeating methylene sequences. By far, Vand’s rendition of the orthorhombic unit cell, outlined for the ab face in Figure 1-5, is the most common structural representation encountered in aliphatic polymers. Upon close inspection, it would seem that the structure of polyethylene is quite simple. However, the fact that polymers are a heterogeneous collection of macromolecules the generalization of a uniform unit cell is unrealistic. In fact, the unit cell portrayed for polyethylene is an idealistic rendition of an otherwise impure structure. Figure 1-5. Polyethylene orthorhombic crystal lattice. A) Orthogonal view and B) along the c axis.

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18 The various branched versions of polyethylene tend to generate more attention since a wider range and of properties can be produced when compared to the high-density analogs. The properties and performance of ethylene-based copolymers, above that of pure polyethylene, is dependent primarily on branch content and comonomer incorporation along a single chain and, most importantly, between polymer chains. 91-102 Linear and branched polyethylene exhibit a multitude of properties based on the molecular homogeneity and morphological make-up of the material based on catalyst design. Consequently, structural modeling of each branched division can lead to a better understanding of not only polymer processing but also the overall effect microstructural branch perturbations have on polyethylene (PE) based materials. Until now, modeling random (statistical) methyl branching in polyethylene has been restricted to polymers produced by chain addition chemistry using either free radical chemistry, 10 Ziegler-Natta chemistry, 103-106 homogeneous metallocene, 107-113 and/or late transition metal catalytic systems. 114-129 The synthetic methodology used to study these copolymers are ill-defined causing ill-defined structures via chain transfer or chain walking occurs causing unwanted branching, broad molecular weight distributions, and heterogeneous comonomer distribution. 130-133 In fact, the modeling of random copolymers of higher copolymers of ethylene are produced using the same systems: Ziegler-Natta, 134-140 and metallocene catalysts, 141-146 anionically synthesized hydrogenated butadienes, 50,147-151 and when using other late transition metals. 152-155 In every case, these “defects” in the polymer structure, exploited to create wider and varying material responses, can be unfavorable when attempting to synthesize ideal models for ethylene/-olefin copolymers. These defects, even in small quantities, can alter the

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19 polymer’s macromolecular behavior and thermal response depending on their frequency and identity. Realization of these defects beyond that of the expansion of polyethylene’s orthorhombic unit cell is seen in the formation of metastable crystal forms under various conditions. Of course, the existence of these new unit cells can coincide with each other making them available under normal conditions. Figure 1-6 illustrates the common metastable states seen in modified polyethylenes. The monoclinic (Figure 1-6a), also referred to as the triclinic cell, is a phase normally expressed in elongated samples or polyethylene that undergoes an injection molding process. Typically, in random copolymers of ethylene the monoclinic unit cell is unstable above temperatures of 60 o C. The hexagonal form of polyethylene is produced under high pressure and temperature conditions which can not form under any commercial fabrication process. As mentioned, the hexagonal phase of polyethylene has numerous examples in linear paraffins up to 40 carbons in which the phase is referred as the ‘rotator’ phase. Figure 1-6. Metastable polyethylene unit cells. A) Monoclinic and B) hexagonal unit cell. The dimensions of the unit cells, each axis having different lengths, produce polymers having different densities with respect to each unit cell. Inspection of the unit cells indicates that the intermolecular distance between neighboring zigzag chains,

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20 responsible for the a axis, is the factor determining the macromolecular behavior. Also, regardless of the unit cell, the repeating c axis is relatively undisturbed to changes in packing. The origin of the monoclinic is a simple translational shift of the orthorhombic center stem while the hexagonal phase of polyethylene is the highest disordered phase due to an inconstant rotation, at random angles, of chain stems with respect to it’s nearest neighbor. 1.6 Application of Metathesis in the Synthesis of Precise Structures As observed in the previous sections, the fundamental importance of predicting the behavior of either ethylene homopolymers or their copolymers can not be overlooked and has been an on going focus for decades. In the past, the modeling of this behavior has been centered on using chain-addition polymerization either mediated by a high energy center (radical, cation, or anion) or transition metal. In any case, this type of polymerization exhibits uncontrolled monomer incorporations, heterogeneous branch distributions, large polydispersities, and ill-defined branch identities producing imprecise polymer structures. Of course, a polymer’s behavior can easily be manipulated by such factors, either by a single or combination of these events, to produce a variety of materials. However, the problems arising from chain-addition polymerizations, even in the smallest percent, are unwanted when attempting to produce structure/property relationships or model the behavior of such polymers. The majority of the problems derived from chain-addition conditions, such as chain transfer or commoner incorporation, can be circumvented by using step-condensation type polymerization. The rules governing step polymerization and its mechanism allows for the control and elimination of these unwanted defects. In most cases, traditional step polymers are produced by simple organic transformations repeated

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21 many times producing high molecular weight polymers. However, step-condensation macromolecules are highly functionalized polymers having simple dislocations, such as esters or amides. For example, one of the most common condensation polymers, polyester, is produced by the repeating esterification of a difunctional carboxylic acid and a corresponding diol. Unlike polyester, polyethylene has no functional handle thus making typical step-condensation mechanisms unrealistic. In recent years, the development of a non-traditional step-condensation, coined metathesis polymerization, has allowed the production of polyolefins using simple olefinic dislocations. RCatalystRxH2C=CH2 Figure 1-7. General ADMET reaction scheme. The most widely applied step-condensation modeling mechanism for a variety of macromolecules has been acyclic diene metathesis (ADMET). The advent of ADMET has allowed the synthesis of functionalized polyolefins without the defects produced by chain-addition. 156 As illustrated in Figure 1-7, ADMET involves the coupling of an ,-diene mediated by a transition metal (W, Mo, Ru) carbene complex to yield a linear unsaturated polyolefin. The historic background and utility of ADMET as been reviewed in detail; thus, only its application in modeling precise branched copolymers will be discussed herein. In this light, ADMET was limited in its application due to ill-defined catalysts and unknown mechanistic details. However, the development of Schrocks’ catalysts 157-162 as well as Grubbs’ first generation ruthenium catalyst 163-169 (Figure 1-8) has help make metathesis an accepted mechanism to investigate polyethylene behavior.

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22 CHCH3CH3MoNOOF3CCF3CH3F3CF3CH3CRuCClClHPPSchrock'sGrubbs' First Generation C 1 C 2 Figure 1-8. Schrock’s catalyst (C1) and Grubbs’ first generation catalyst (C2). As discussed earlier, the architecture of ethylene copolymers produced using chain-addition is modified by a selective choice of either catalyst choice, monomer type, or monomer feed control. To correctly make valid correlations between defects or perturbations caused by branch incorporation, these factors need to be controlled and manipulated selectively. Ultimately, ones ability to control all these factors in an attempt to synthesis precise model copolymers is futile. On the other hand, the use of ADMET allows organic synthesis instead of indirect manipulation (control) to modify the polymer’s primary structure. In this fashion, the repeating unit of any ethylene-based copolymer is only dependent on one variable and independent on catalyst choice or monomer feed ratios. The major advantage of this approach is its’ inherent ability to govern the copolymer’s properties by the appropriate organic building block. The cornerstone in producing precise branched structures is the coupling of the error free ADMET polymerization to produce linear polymers and the symmetrically functionalized dienes. The diene functionality produced using organic chemistry is directly transferred to the growing polymer chain owning to only one symmetrical repeat

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23 unit. In fact, this direct monomer/polymer relationship is inherent to the polymerization of a single monomer unit using step-condensation and in particular ADMET. In general, the single monomer polymerization technique alleviates the heterogeneous branching distributions caused by reactive ratio differences and multi-site reaction centers. 1.7 Dissertation Purpose This document describes the on going investigation into the utility of ADMET to produce precisely branched models of polyethylene. An initial systematic study was performed to model precise linear-low density polyethylene as well as producing random models of ethylene/1-propene copolymers. Also, an investigation into side chain motion is discussed aided by the production of precisely placed deuterated methyl branches. The continuation of this earlier research has lead to the synthesis of precise models of ethylene/1-butene (EB) and ethylene/1-octene (EO) containing ethyl or hexyl branches, respectively. Regardless of the branch identity, metathesis has produced a linear polyethylene backbone with homogeneous branch distributions yielding unique, never before observed structures, which seem to be unattainable using chain-addition chemistry.

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CHAPTER 2 RANDOM METHYL BRANCHED ETHYLENE/1-PROPENE COPOLYMERS 2.1 Introduction Polyethylene is the largest volume synthetic macromolecule made today and is the fastest growing petrochemical market in the world, with over 100 billion pounds produced in 2001. 170 Since commercial inception in the 1930s, considerable research has focused on the structure-property relationships of ethylene based polymers. The ultimate effect that branching has on the behavior of polyolefins is quite important; in fact, this topic has been examined in great detail for more than 60 years. 44-61 Indeed, the melting behavior and branch analysis of ethylene/-olefin random copolymers has garnered considerable attention due to wide-ranging perturbations in the final materials response associated with the distribution of the -olefin within the copolymer. 91-102 The properties and performance of ethylene-based copolymers is dependent primarily on branch content and comonomer incorporation along a single chain and, most importantly, between polymer chains. 91-102 Consequently, modeling such behavior can lead to a better understanding of not only polymer processing but also the overall effect microstructural branch perturbations have on polyethylene (PE) based materials. Until now, modeling random (statistical) branching in polyethylene has been restricted to polymers produced by chain addition chemistry using either free radical chemistry, 10 Ziegler-Natta chemistry, 103-106 homogeneous metallocene, 107-113 and/or late transition metal catalytic systems. 114-129 Inevitably, chain transfer or chain walking occurs causing unwanted branching, broad molecular weight distributions, and 24

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25 heterogeneous comonomer distribution. 130-133 These “defects” in the polymer structure, exploited to create wider and varying material responses, can be unfavorable when attempting to synthesize ideal models for ethylene/-olefin copolymers. Our approach to this problem is quite different from previous studies. We have chosen step polycondensation chemistry to model PE, a methodology that precludes the random branching resulting from chain transfer reactions. The Acyclic Diene METathesis (ADMET) reaction has been used to produce linear polyethylene via polymerization of 1,9-decadiene to polyoctenamer, followed by subsequent hydrogenation to yield what we term as ADMET PE. 156 Further, ADMET also has been used to create ethylene/propylene copolymers wherein the methyl branch is precisely placed along the macromolecular backbone. Previously, we reported that model EP copolymers with a precise sequence length distribution between methyl branches exhibit properties not seen in model EP copolymers produced by chain addition polymerization to date. 171 In this paper we expand our ADMET model approach by synthesizing a series of random EP materials containing varying degrees of propylene incorporation, focusing primarily on characterization of chain structure and thermal behavior. Copolymerizing the appropriate methyl branched ,-diene monomer with a linear, unbranched hydrocarbon ,-diene, followed by subsequent exhaustive hydrogenation leads to statistical methyl branching along the chain, where the final microstructure is controlled both by the monomers chosen and the molar ratios used during the polymerization. Herein, we report our findings for six copolymer systems with varying degrees of short-chain branching (SCB) content.

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26 2.2 Results and Discussion 2.2.1 Polymer Synthesis and Hydrogenation ADMET polycondensation was used as the modeling polymerization mechanism of choice, since it offers control of the molecular weight distribution, branch type, and comonomer distribution in the final copolymer. Manipulation of these variables for PE has been sought for some time, since doing so provides a protocol to fine tune the mechanical properties, morphology, and response of the final copolymer. It is our intent to define macromolecular structure/property relationships for PE copolymers using this approach. For example, stiffness, tensile strength, processability, and softening are all properties affected by short chain branching (SCB) and short chain branch distribution (SCBD) in PE based materials. 172 ADMET can control the branching sequence length distribution in the microstructure of the final copolymer by allowing for total conversion of monomer(s). Since this is step polycondensation chemistry, the initial molar ratio of the two monomers is directly transferred to the final copolymer; one does not have to deal with reactivity ratios. Further, ADMET copolymerization produces a random copolymer as a result of the transmetathesis reaction of internal olefins, a phenomenon exactly analogous to transesterification which occurs in the synthesis of polyethylene terephthalate. The nomenclature for the unsaturated ADMET copolymers is designed to describe the actual branch content (PE-43.3, 43.3 being the number of CH 3 branches/1000 total carbons measured by NMR), while the hydrogenated samples contain an "H" after the branch number (i.e. PE-43.3H). In this study, six model EP copolymers were synthesized by combining 6-methyl-1,10-undecadiene (1) and 1,9-decadiene (2) with

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27 Schrock’s molybdenum metathesis catalyst under ADMET polymerization conditions (Figure 2-1). Additionally, homopolymers derived from monomers 1 and 2 have been synthesized for comparison. Monomer 1 and PE-97.4H used in this study were synthesized following literature procedure. 171 The homopolymers of 1,9-decadiene are designated PE-OCT and PE-OCTH (“polyoctenamer”). HCH333(1)+6HCH3336xy(2)(PE-OCT) (PE-97.4)[Mo]-C2H496 hours40-50 oCExhaustive Hydrogenation(PE-OCTH) (PE-97.4H)5HCH33xynnCompoundPE-1.5PE-7.1PE-13.6PE-25.0PE-43.3PE-55.61(mol %)2(mol %)25102040509895908060508PE-OCT0100PE-97.40100 Figure 2-1. General synthetic scheme for the synthesis of EP model copolymers. All monomers were dried over metal, and the highest molar ratio of monomer to catalyst was employed. The chemistry proceeds smoothly to produce linear unsaturated polymers with no side reactions detectable by NMR analysis. The three copolymers containing the highest branch content (PE-43.3, PE-55.6, and homopolymer PE-97.4, which carries a methyl “branch” in every repeat unit) remained viscous liquids throughout the polymerization, whereas the remaining polymers solidified within five minutes of initiation. These observations are a direct reflection of the effect that methyl SCB and SCBD have on the behavior of the resulting materials.

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28 Prior to saturation with hydrogen, the unsaturated copolymers were characterized by quantitative 13 C NMR spectroscopy, which determined the cis:trans ratio of the double bond for all eight polymers. When polymerizing unhindered monomers such as 1,9-decadiene Schrock’s [Mo] catalyst produces polymers with a trans content greater than 90%; 156 however, when the molar ratio of the “methyl” monomer 1 is increased, the trans content decreases. 171 The homopolymerization of 1,9-decadiene produces a polymer with a trans fraction of 96%, a value which decreases to 85% for the copolymerization of a 50/50 molar ratio 1,9-decadiene and 6-methyl-1,10-undecadiene and 77% for the homopolymer of 6-methyl-1,10-undecadiene. This change in cis: trans ratio is due to the increased methyl branching (defect) content. Further, an increase in branch content leads to more chain-folded gauche interactions during crystallization of these materials, which leads to a better understanding of the crystallization kinetics in these unsaturated materials and may permit the modeling of ethylene propylene diene monomer (EPDM) rubbers. Research is currently underway to model EPDM elastomeric materials to further substantiate this observation. The unsaturated ADMET copolymers described above were transformed into model EP analogs by exhaustive hydrogenation using Wilkinson’s catalyst. A homogeneous hydrogenation method was chosen to accommodate the insolubility of the resulting saturated polymers, thereby offering more facile purification after complete saturation of the olefin bond present in each repeat unit. Previously, Wilkinson’s catalyst has been shown to successfully hydrogenate radically produced branched polybutadienes, a fact that guided our choice of hydrogenation systems. 147,173-174 The complete hydrogenation of PE-43.3 and PE-55.6 was accomplished in 96 hours using toluene as

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29 the solvent, while the copolymers PE-OCTH – PE-25.0H required a higher boiling solvent (xylene at 145 o C) to maintain homogeneous hydrogenation conditions. In both cases, full hydrogenation was achieved. The hydrogenation proceeds more efficiently with the exclusion of moisture and oxygen from the reaction vessel. Figure 2-2. Infrared characterization data for both the ADMET prepolymer PE-97.4 and its hydrogenated analog PE-97.4H. While there are several analytical techniques to monitor successful hydrogenation ( 1 H NMR, 13 C NMR, bromine uptake, and infrared (IR) spectroscopy), IR spectroscopy

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30 offers the most sensitive method to observe whether or not exhaustive saturation has occurred. Figure 2-2 depicts IR data for a typical transformation of an unsaturated ADMET polymer to saturated model polymer in the series studied here. The 967-969 cm -1 absorption in the unsaturated polymer, which corresponds to the out-of-plane C-H bend in the alkene, completely disappears after successful hydrogenation. Further purification of the saturated polymers was accomplished via dissolution in xylene followed by precipitation in acidic methanol, repeating this procedure if necessary, until the polymers were white. The polymers seem to purify more easily and effectively if the saturated polymers were precipitated in warm acidic methanol (40 o C) using a blender to agitate the solution. 2.2.2 Molecular Weight and Branching Analysis of ADMET Polymers Prior work in our group has shown that the number average molecular weight of ADMET polyethylene M w s must exceed 24,000 g/mol versus polystyrene (PS) standards before a constant melting behavior is observed; 156,171 consequently, measuring the molecular weight of the polymers prepared in this study is essential. The molecular weight data before and after hydrogenation for the precipitated polymers is summarized in Table 2-1. The GPC data for the unsaturated polymers was compiled using simple differential refractive index (DRI) calibration with polystyrene standards. The M w s for all polymers range from 29,000 – 63,000 g/mol (versus PS standards) and exhibit a polydispersity index (PDI) in the range of 2.0, which is sufficient for modeling conventional PE materials. Variance in molecular weight can be attributed to differences in solubility of the polymers as they form, as well as to catalyst decomposition.

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31 Table 2-1. Molecular weight data shown for the saturated ADMET copolymers gathered using three detection methods. Saturated Copolymers versus PS c Saturated Copolymers versus EP d Saturated Copolymers LALLS e EP Model Polymers Methyls/1000 Total Carbons a M w x 10 -3 PDI b M w x 10 -3 PDI b M w x 10 -3 PDI b PE-OCTH 0 34.4 1.6 14.5 1.5 16.2 1.6 PE-1.5H 1.5 37.2 1.6 15.6 1.6 15.3 1.6 PE-7.1H 7.1 41.8 1.7 17.6 1.7 23.2 1.9 PE-13.6H 13.6 58.3 1.7 24.6 1.7 26.2 1.6 PE-25.0H 25.0 56.5 1.9 24.7 1.9 27.0 1.8 PE-43.3H 43.3 62.9 2.0 27.3 2.0 30.5 1.4 PE-55.6H 55.6 29.0 2.2 12.9 2.1 13.7 1.5 PE-97.4H 97.4 f 34.4 1.6 10.6 1.9 15.7 2.1 A) Determined by an average of both the 1 H NMR (300 MHz) and 13 C NMR (125 MHz) data. B) Polydispersity index (M w /M n ). C) Molecular weight data taken using using trichlorobenzene at 135 o C relative to polystyrene standards. D) Molecular weight data taken using using trichlorobenzene at 135 o C relative to an EP calibration curve using the appropriate Mark-Houwink equation (Equation 2). E) Molecular weight data taken using LALLS and trichlorobenzene at 135 o C. F) The statically determined value of 111 (mathematically determined by dividing 1000 backbone carbons by 9) differs from the experimentally determined branch content. The saturated EP copolymers were analyzed by three molecular weight determination methods. The molecular weights were determined using low-angle laser light scattering (LALLS), universal calibration method calibrated using polystyrene (PS), and universal calibration by converting the PS calibration curve to an ethylene/propylene calibration curve using the Mark-Houwink equation shown in the experimental section (Equation 2). The variances in the molecular weights between saturated and unsaturated copolymers (Table 2-1) are a direct result of these different methods of data collection. We have looked at the effects on molecular weight caused by hydrogenation when going from unsaturated to saturated polymers and concluded that molecular weights are not affected by the hydrogenation process. 156,171 All GPC traces were essentially unimodal demonstrating that copolymers are formed rather than mixtures of homopolymers. A more detailed study of these EP model copolymers, discussed here, is underway using

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32 triple detection methods (laser light scattering and viscometry) in order to gather data on the branching, branching uniformity, and dilute solution behavior. Carbon and proton NMR data are presented in Table 2-2. The proton spectra were acquired with 160 co-added transients and used to determine the molar content of monomer 1 and branch content of the polymer. The proton NMR spectra are dominated by the sharp singlet from the linear backbone methylenes at 1.34 ppm. Methyl signals are observed for the branch methyls, 1B 1 , (doublet centered at 0.915 ppm, with a J HH coupling to the backbone methine of 6.4 Hz), and chain end methyls, 1s, (triplet at 0.945 ppm, with a J HH of 6.3 Hz). Deconvolution of these overlapping resonances with an 85% Lorentzian/15% Gaussian lineshape allowed segregation of signal intensity into contributions from methyl branches (6-methyl-1,10-undecadiene) and chain ends (6-methyl-1,10-undecadiene and 1,9-decadiene.) The branch content was determined by dividing the multiplicity-corrected integral of the 1B 1 methyl signal (derived from the deconvolution) into the sum of this value and the multiplicity-corrected methylene/methine integral. The molar composition values were calculated as follows. The number of monomer 1 repeat units in the polymer was measured from the multiplicity-corrected 1B 1 methyl integral. After correction for methylene/methine contributions from monomer 1, the remainder of the aliphatic integral was assigned to 1,9-decadiene. Semi-quantitative 13 C NMR spectra were acquired using 4,000 coadded transients, and allowing a 20 second recycle delay. Monomer 1 content was determined by integrating not only the resonance of the branch methyl ( 20.1) but also the carbons alpha ( 37.5) and beta ( 27.5) to the branch point and using the average to determine

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33 the comonomer content. Since the carbon resonances close to the branch point are easily distinguished, the calculation is somewhat more facile when compared to the 1 H data. Subtracting the average branched monomer count from the rest of the carbon backbone gave the average monomer count that originated from 1,9-decadiene. For both proton and carbon NMR, the mole percent of 1 can be calculated by dividing the branch monomer count by the total monomer count arising from both 1 and 2, which is given in Table 2-2 as mol% by NMR. Table 2-2. Branching content and comonomer content for the random series. Property 1.5H 7.1H 13.6H 25.0H 43.3H 56.6H 111H Feed ratio 1:2 a 2 5 10 20 40 50 100 Mol % 1 e 1.2 5.8 11.2 21.1 38.0 50.2 97.0 Mol % 99.69 98.57 97.24 94.86 90.94 88.21 78.31 wt % ethylene 99.54 97.85 95.91 92.48 86.98 83.27 70.66 Mol % 0.31 1.13 2.76 5.13 9.06 11.80 21.63 wt % propylene 0.46 2.15 4.08 7.52 13.02 16.73 29.33 Branching d,e 1.5 7.1 13.6 25.0 43.3 55.6 100 f A) The molar percent of 6-methyl-1,10-undecadiene added to the polymerization flask. B) The equivalent molar percent of ethylene in a EP copolymer produced by addition polymerization. C) The equivalent molar percent of propylene in an EP copolymer produced by addition polymerization. D) Methyl branches/1000 carbons. E) Determined by averaging the 1 H and 13 C NMR data. F) The statically determined value of 111 methyls/1000 carbons differs from the experimentally determined branch content, however is within the error of the NMR measurement. Summarized in Table 2-2 are the corresponding ethylene and propylene contents calculated as if these systems had been produced by chain-addition (insertion-type) mechanism. The data given in Table 2-2 is an average of values obtained by 1 H and 13 C NMR. The calculation assumes that four moles of ethylene originate from the 1,9-decadiene repeat unit after hydrogenation of the ADMET polymer. It also assumes that an average of 3.5 moles of ethylene and 1 mole of propylene originate from the 6-methyl

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34 1,10-undecadiene repeat unit after hydrogenation. Multiplying these values by the mole percent of each monomer, respectively, will generate the hypothetical mole percentages of ethylene and propylene. The monomer weight percentages were calculated for use in GPC-LALLS and in-line viscometry analysis. Carbon NMR was also used to determine the exact nature of the endgroups associated with these ADMET EP copolymers. Figure 3a shows the carbon spectrum for PE-OCTH (hydrogenated polyoctenamer) produced using Schrock’s metathesis catalyst, a spectrum which unequivocally shows that the endgroups produced after hydrogenation by this type of metathesis (ADMET) polymerization are methyls. This fact is vital when modeling polyethylene, as well as scientifically important since endgroups previously have never been observed in a hydrogenated ADMET high polymer. In the past, instrument limitations precluded spectroscopic determination of chain-end methyls (after hydrogenation). In this study, the high magnetic field and number of coadded transients (>4,000) allowed us to make this observation for the first time. Throughout the catalyst mediated ADMET cycle, high polymer is produced through the coupling of two terminal dienes (on separate monomer units) via a 2+2/retro 2+2 cycloaddition reaction. The coupling of the monomer units produces vinyl (H 2 C=CH-Polymer-CH=CH 2 ) endgroups, giving methyl endgroups when hydrogenated. It is also possible to distinguish the two different endgroups produced during the ADMET copolymerization of 6-methyl-1,10-undecadiene (1) with 1,9 decadiene (2). These differences arise from the use of two structurally different comonomers, causing different local environments at the chain end. Termination of the copolymer by 1,9 decadiene produces endgroups (after hydrogenation) equivalent to the homopolymer PE

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35 OCTH. Figure 2-3a shows six distinct resonances for hydrogenated poly(octenamer), 14.22 (1s), 22.91 (2s), 32.23 (3s), 29.59 (4s), 29.68 (5s), and 29.99 for the PE backbone. Figure 2-3. A comparison of endgroups and chemical shifts for all the polymerization combinations. A) 13 C NMR of unbranched PE-OCTH, B) PE-55.6H, and C) precisely methyl branched PE-97.4H (methyl on every 9 th carbon). Since ADMET copolymerization is random, the resulting copolymer contains endgroups from 6-methyl-1,10-undecadiene (1). The effect this methyl branch has on the endgroups can only be seen when examining the 4s and 3s carbons, or the carbons beta and gamma to the branch point. The methyl branch point shifts the 4s (upfield) and 3s (downfield) carbons with respect to the endgroups produced by PE-OCTH. The resonances produced by the chain-end carbons of 6-methyl-1,10-undecadiene are 14.22 (1s), 22.91 (2s), 32.60 (3s), 27.04 (4s), and 37.57 for the methylene alpha to the branch

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36 point (Figure 2-3c). Additionally, Figure 2-3 shows that both the 1s and 2s carbons of the chain-end are indistinguishable for both monomers; therefore, both resonances overlap in the copolymer. The equivalent carbon chemical shifts in solution for two possible chain ends suggests that the methyl branch in the copolymer affects carbons no greater than three positions from an individual branch located on the polymer backbone. 2.2.3 Thermal Analysis and Behavior Differential scanning calorimetry was performed using a Perkin-Elmer DSC-7 equipped with Pyris TM software, with calibration accomplished using indium and n-octane as standards for all thermal transitions. Heats of fusions were referenced to indium. To erase thermal and crystallization history, samples were taken through several heating/cooling cycles with data collected on the third cycle in the series. The DSC technique was chosen as the principal mode to examine of the morphology and structure for random methyl branched ADMET EP random copolymers. Numerous literature studies are available concerning the structure and thermal properties of branched PE (LDPE and HDPE), particularly for ethylene/propylene (EP) copolymers made by chain-addition chemistry. 91-133 The unsaturated polymers were also examined to better understand the melting behavior and crystallization kinetic trends observed for the saturated counterparts. A wide range of initiation procedures can be used to produce EP copolymers made by chain-addition chemistry; consequently, the branch identity, branch content, and branch homogeneity of these polymers differ considerably. These differences, which are direct results from chain transfer or chain walking mechanisms, give rise to variances in thermal properties that affect the use and processing of these polymers. Whereas, the model ADMET EP copolymers reported herein contain a single, known branch identity

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37 (methyl), which is determined by the initial monomer’s identity, a priori. The thermal behavior of the model EP polymers is summarized in Table 2-3. This study is focused on random methyl branched defects in PE; therefore, PE-97.4 and PE-97.4H, described earlier, 19 containing precise methyl branch placement have not been discussed in Table 2-3 or the thermal behavior section. Table 2-3. Heat flow and crystallinity data for the random methyl branched series. ADMET Polymers Methyl Branches/ T m ( o C) Peak b h m (J/g) b % Crystallinity c PE-OCTH 0 133.0 230.0 0.785 PE-1.5H 1.5 129.0 207.6 0.713 PE-7.1H 7.1 123.2 183.4 0.621 PE-13.6H 13.6 119.0 165.8 0.563 PE-25.0H 25.0 111.6 137.3 0.476 PE-43.3H 43.3 80.7 85.0 0.296 PE-55.6H 55.6 52.1 87.0 0.290 ( Unsaturated ) PE-OCT 0 74.2 163.0 PE-1.5 1.5 72.6 103.0 PE-7.1 7.1 68.6 98.7 PE-13.6 13.6 67.8 88.7 PE-25.0 25.0 61.5 57.1 PE-43.3 43.3 8.2 18.7 PE-55.6 55.6 -7.6 9.0 A) Branch content determined by averaging the 1 H (300 MHz) and 13 C NMR (125 MHz) branch data. The branch content of unsaturated polymers is assumed to be equivalent to the saturated EP polymers. B) Scan rate of 10 o C/min used to obtain data. C) Percent crystallinity determined by dividing the heat of fusion by 293 J/g. 177 The melting temperatures for model ADMET EP copolymers follow a similar trend found for branched commercial materials. As the methyl branch (defect) content

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38 increases, the melting point, percent crystallinity, and heat of fusion decrease. The relationship between defect content and thermal behavior is well known and has been studied in great detail by Flory, 175 Eby, 176 and Mandelkern. 47-48 The DSC thermographs for the unsaturated and saturated versions of the first three polymers in the series are given in Figures 2-4 (unsaturated) and 2-5 (saturated) along with the traces for the unsubstituted homopolymer PE-OCT/PE-OCTH. The polymers exhibit both a sharp primary melting peak as well as a broad, diffuse secondary endothermic region. This secondary area, commonly referred to as the premelting region, is thought to be a regime in which quantities of smaller crystallites are melting, recrystallizing, and remelting prior to the onset of the primary melting peak. Figure 2-4. DSC endothermic traces for PE-OCT, PE-1.5, PE-7.1, and PE-13.6 [Scan rate = 10 o C/min]. The second set of data in the series is provided in Figure 2-6 (unsaturated) and Figure 2-7 (saturated). The polymers with the highest methyl branch content (PE-43.3H

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39 and PE-55.6H) have no distinct melting point (T m ); however, they do manifest DSC endotherms with relatively the same low heat of fusion values. Similar behavior has been observed for ethylene-co-propylene polymers made by chain techniques with higher propylene content. 46,48,115 For example, random copolymers made using Ziegler-Natta catalysis with greater than 15% propylene incorporation generate the same type of broad, indistinct thermal curves shown here. 46,48 However, the model EP copolymers produced by ADMET exhibit this broad, indistinct melting at lower branch density than Ziegler-Natta produced polymers, around 10-13% by weight propylene. Unsaturated copolymers PE-43.3H and PE-55.6H greatly decrease their percent crystallinity upon moderate incorporation of methyl branching. These two materials with sub-ambient melting points, are viscous liquids at room temperature. Figure 2-5. DSC endothermic traces for PE-OCTH, PE-1.5H, PE-7.1H, and PE-13.6H [Scan rate = 10 o C/min].

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40 Figure 2-6. DSC endothermic traces for PE-25.0, PE-43.3, and PE-55.6 [Scan rate = 10 o C/min]. Several interesting results are observed in the melting behavior of the EP copolymers with randomly situated methyl branches, compared to EP model copolymers containing precisely placed branch defects reported earlier. 171 In our earlier study, sharp, well-defined distinct melting temperatures were observed for polymers with moderate to high branch content (48-111 methyls/1000 backbone carbons). Figure 2-8 shows PE-45PH ("P" stands for precise branch placement) contains methyl branches on every 21 st carbon along the polymer backbone which corresponds to a branch density of 45 methyls/1000 total carbons (or 48 methyls per 1000 backbone carbons). The precisely branched EP model materials exhibit a higher order in regards to their packing ability, as

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41 compared to either the ADMET randomly branched copolymers or the PEs made by chain addition with equivalent levels of methyl branch content (Figure 2-8). Figure 2-7. DSC endothermic traces for PE-25.0H, PE-43.3H, and PE-55.6H [Scan rate = 10 o C/min]. No distinct melting point was observed for the randomly branched PE-43.3H copolymer model made by metathesis chemistry (Figure 2-8). With respect to SCBD, Figure 2-8 demonstrates how important the uniformity of branch dispersion is in determining the final material’s response. The sharp, well-defined endotherm generated by the precisely branched material 171 is a striking result when compared to its randomly branched counterpart studied here. Evidently, the well-controlled SCBD has invoked a special crystal ordering never before observed in randomly branched PEs within the regime of comonomer content(s) studied here.

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42 Figure 2-8. Thermal comparison of random (PE-43.3H) versus precise methyl branching (PE-45PH) [Scan rate = 10 o C/min]. The thermal behavior of the randomly branched ADMET polymers illustrates a dependence on the branch content or methyl comonomer composition. Plotting the branch content of these polymers versus their respective peak T m s (in Kelvin), an approach similar to the Flory equation, 175 corresponds to an unbranched PE having a T m = 134 o C (Figure 2-9a). ADMET PE produced by the hydrogenation of poly(octenamer) exhibits the same peak melting temperature (134 o C), within the T m range of commercially produced HDPE (134 – 138 o C). Further, a comparison was made to Flory’s infinite molecular weight linear polyethylenes by plotting percent crystallinity versus peak melting temperature (T m ). In this case, percent crystallinity was calculated using DSC techniques by dividing the heats of fusion obtained for each model polymer by 293 J/g. 177 The percent crystallinities are provided in Table 2-3. The data, when plotted in this fashion, illustrates that the ADMET polymers agree with the commonly

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43 accepted observations by Flory, Wunderlich, and Mandelkern, which demonstrates that unbranched ultra-high molecular weight PE should have a T o m = 141.5-145.5 o C. 175,177-178 The data provided by these ADMET PEs lead to the conclusion that perfectly linear, chain extended ADMET PE should have a T m = 143.5 o C (at a 10 o C/min scan rate), when using Wunderlich’s heat of fusion data (Figure 2-9b). Extrapolation to the samples’ equilibrium melting temperature (scan rate = 0 o C/min) to avoid superheating was not performed in this initial study. Figure 2-9. Thermal correlations using the Flory equation. A) Plot of melting temperature vs. methyl branching and B) Plot of percent crystallinity vs. melting temperature [Scan rate = 10 o C/min].

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44 2.2.4 IR and Diffraction Data In addition to using DSC and NMR to characterize ADMET model PE and EP copolymers, we have examined the crystal structure of our ADMET EP systems via infrared spectroscopy. The IR absorbance spectra are given in Figure 2-10 for a sampling of the random EP ADMET copolymers synthesized in this study. Previously, Tashiro et al. conducted a detailed study concerning polyethylene crystal structures and their corresponding IR absorbances. They concluded that the scissoring at 1466 cm -1 and methylene rock at 721 cm -1 indicate a hexagonal crystal structure for linear PE, while the double methylene rock at 719 cm -1 and 730 cm -1 and single band at 1471 cm -1 arises from the orthorhombic crystal of PE. 77,179 In our case, the polymer arising from the polymerization of 6-methyl-1,10-undecadiene (PE-97.4H) exhibits absorbances at 722 cm -1 corresponding to the CH 2 rocking of the backbone, and a singlet scissoring absorbance at 1465 cm -1 indicating a hexagonal crystal, whereas ADMET PE (PE-OCTH) shows absorbances at 729 cm -1 and 720 cm -1 and 1470 cm -1 resulting from an orthorhombic crystal. However, when comparing the copolymer series, as the molar ratio of 6-methyl-1,10-undecadiene increases, the absorbance characteristics approach and eventually convert to those exhibited for PE-97.4H. This can be seen by the transformation from a double to a single absorbance peak in the CH 2 rocking region (720-728 cm -1 region) in going from PE-OCTH to PE-97.4H. The sharp peak at 1377 cm -1 (Figure 2-10) corresponds to the symmetrical methyl bend, which increases in relative absorbance as the methyl branch content increases.

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45 Figure 2-10. IR Spectral Changes with increased branch content. The behavior observed for the polymers throughout this study supports the conclusions made by Tashiro. 179 The absorbances seen at 722 and 1465 cm -1 correspond to a hexagonal crystal structure, which correlate to findings for EP model materials with precise methyl branching 171 as determined by electron diffraction. 180 ADMET PE shows orthorhombic nature when compared to Tashiro’s observations and an orthorhombic-hexagonal crystal transition is seen with moderate incorporation of methyl branches (defects). In order to further substantiate these IR findings, wide-angle x-ray diffraction (WAXD) was performed on the series of copolymers to demonstrate that the absence of Davidov splitting in the methylene rocking and bending modes is a result of a hexagonal phase, and not the result of a highly distorted orthorhombic crystal (Figure 2-11). Inspection of Figure 2-11 provides substantial proof for the formation of a new crystalline phase in these ADMET polyethylenes when the number of statistically placed methyl branches is increased. PE-OCTH produced two main intensities at d-spacings of

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46 4.11 and 3.70 (Figure 2-11a). Respectively, these maxima correspond precisely with the normally observed, characteristic 110 and 200 reflections for the orthorhombic unit cell of high-density polyethylene (HDPE). 89,181-184 This result is in agreement with what is expected for a defect-free ethylene-based material. However, as illustrated in Figure 2-11b, the diffraction pattern changes substantially for the ADMET EP copolymer containing 55.6 methyl branches per 1000 carbons (PE-55.6H). Noteworthy differences become evident when comparing Figure 2-11a (PE-OCTH) to Figure 2-11b (PE-55.6H). First, Figure 2-11b shows only one intense peak for the ADMET EP copolymer (PE-55.6H) with a d-spacing of 4.23 —this differs substantially from the diffractogram of PE-OCTH (Figure 2-11a), which contains two clear maxima. Second, the Bragg reflection for the 110 peak (4.11 ) for PE-OCTH shifts to 4.23 in Figure 2-11b. In fact, in PE-OCTH there is no existence whatsoever of the 200 reflection observed in Figure 2-11a. The peak also increases in its relative intensity and broadening is evident when compared to the 110 reflection obtained in the WAXD of PE-OCTH (Figure 2-11a). These results point to the presence of another crystallite form; indeed, the dspacing of 4.23 is not predicted for the orthorhombic form and could possibly originate from three known structures of PE: a) monoclinic 185 b) triclinic 186-188 or c) hexagonal. 181-184 The most likely explanation is that the d-spacing observed at 4.23 (Figure 2-11b) arises from the reflection of the 100 Bragg plane in the hexagonal phase of polyethylene. 181-184 Moreover, simple division of the unit cell parameter a by b deduces the a/b ratio for PE-55.6H equaling 3 , which is the expected value for a hexagonal crystal (see inset, Figure 11b).

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47 Figure 2-11. Wide-angle scattering pattern for the random copolymers. A) ADMET polyethylene (PE-OCTH) and B) PE-55.6H. The figure shows the a and b dimensions of the unit cell (referred to orthohexagonal axes for PE-55.6H). The hexagonal phase found in paraffinoid substances and in some cases polyethylene primarily is caused by chemical defects within the crystal. In fact, the hexagonal phase in PE has been observed previously at room temperature in irradiated (gamma or electron energy) samples and in copolymers containing small diene components. 189-193 The effect on the polymers crystal lattice in both cases is the same. The observed changes are brought about by defects produced by main chain scission,

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48 double bond formation, or crosslinking. 189-193 This disordered phase can also be produced in highly extended fibers, albeit at higher temperatures 194-196 or under high hydrostatic pressure. 181-184 We are able to force this hexagonal change at room temperature in our ADMET copolymers by the addition of randomized branch defects which in this case are only methyl groups. In cases where lattice defects are produced (irradiation, diene addition, and randomized methyl branches) the orthorhombic-hexagonal transition decreases below the polymers observed T m allowing for its observability. Therefore, varying the branch content in these ADMET EP systems represents the first example of an orthorhombic-to-hexagonal phase transition in an ethylene-based copolymer without any previous external manipulation of the material (i.e. high temperature, high pressure, irradiation, etc.). 2.3 Conclusions Acyclic diene metathesis (ADMET) polymerization has proven useful in modeling random ethylene/-olefin copolymers. In these EP random copolymers, as the weight percent propylene is increased, both the melting points and heats of fusion decrease. Therefore, the thermal behavior of the methyl branched random copolymers correlates well to Flory’s and Wunderlich’s observations based on linear chain extended PE. By using this methodology, the theoretical melting point (T m ) for ADMET PE was found to be 143.5 o C (at a 10 o C/min scan rate) by extrapolation. Copolymers produced via ADMET polymerization have shown properties unique in both their thermal behavior and morphology. These random EP copolymers show the ability to change conformation in crystal packing/arrangement, depending on propylene content. On incorporation of approximately 10 mol % propylene, a switch from an orthorhombic to a hexagonal crystal arrangement can be observed by IR spectroscopy

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49 and WAXD. This is the first example of conformational switching to the hexagonal phase in ethylene/propylene copolymers containing moderate methyl branch (defect) content without external sample manipulation prior to analysis. A more detailed study of this conformational switching in ADMET EP copolymers is in progress. The exact nature of the endgroups produced by ADMET polymerization has been observed for the first time by carbon NMR. The methyl endgroups produced after hydrogenation must originate from vinyl endgroups, which are produced throughout the ADMET polymerization cycle. Therefore, these model EP copolymers and all hydrogenated polymers produced by ADMET chemistry contain methyl endgroups independent of monomer type and polymerization conditions. It is possible to distinguish between the two different endgroups produced in an ADMET random copolymerization. We are continuing this research by gathering x-ray diffraction data to better understand the differences between random and precise branching in ethylene/propylene model copolymers. In addition, we are currently expanding our study of short chain branching in PE to ethyl, butyl, and hexyl branches incorporated in both a precise and a random arrangement. 2.4 Experimental Section 2.4.1 Instrumentation All 1 H NMR (300 MHz) and 13 C NMR (75 MHz) spectra of the unsaturated ADMET polymers were recorded on either a Varian Associates Gemini 300 or a Varian Associates Mercury 300 spectrometer. Chemical shifts for 1 H and 13 C NMR data were referenced to residual signals from CDCl 3 (7.23 for 1 H and 77.23 for 13 C) with 0.03% v/v TMS as an internal reference.

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50 The saturated ethylene/propylene model copolymers were prepared for NMR spectroscopic analysis by dissolution in tetrachloroethane-d 2 as an approximately 5 weight-% solution. Sample preparation and data acquisition were performed at a temperature of 120C. Proton NMR spectra were acquired on a Varian Unity INOVA 300 spectrometer using a 5mm switchable probe. For each 1 H spectrum, 160 transients were co-averaged using a 90-acquire pulse sequence, with a total pulse delay of 10.8 seconds. Spectra were Fourier transformed to 64K complex points with line broadening of 0.2 Hz. The chemical shift scale was referenced by setting the resonance from residual tetrachloroethane protons to 5.98 ppm. The same samples were run for carbon NMR on a Varian UnityPlus 500, also in a 5mm switchable probe. For each 13 C spectrum, 4000 transients were coaveraged, using a 90-acquire pulse sequence with full decoupling to obtain optimal nuclear Overhauser enhancement (nOe). Broadband decoupling was performed with WALTZ-16 modulation. A total pulse delay time of 20.9 seconds was employed. The spectra were Fourier transformed to 64K points, with 1Hz line broadening. Gel permeation chromatography (GPC) of the unsaturated ADMET polymers was performed using two 300 mm Polymer Laboratories gel 5m mixed-C columns. The instrument consisted of a Rainin SD-300 pump, Hewlett-Packard 1047-A RI detector (254 nm), TC-45 Eppendorf column heater set to 35 o C, and Waters U6K injector. The solvent used was THF at a flow rate of 1.0 mL/min. Polymer samples were dissolved in HPLC grade THF (approximately 0.1% w/v) and filtered before injection. Retention times were calibrated to polystyrene standards from Polymer Laboratories (Amherst,

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51 MA). In all cases, peak integration has been truncated to exclude any contribution from lower molecular weight cyclic materials. High temperature gel permeation chromatography (HTGPC) of the saturated EP model copolymers was performed on a Waters 150C with its internal differential refractive index detector (DRI), a Viscotek differential viscosity detector (DP), and a Precision light scattering detector (LS). The light scattering signal was collected at a 15 degree angle, and the three in-line detectors were operated in series in the order of LS-DP-DRI. The chromatography was performed at 135C using three Polymer Laboratory mixed-bed type B columns (10 microns PD, 7.8 mm ID, 300 mm length) with inhibited trichlorobenzene as the mobile phase at a flow rate of 0.5 ml/minute. Injection mass for the samples varied between 0.600 and 0.750 mg using a 300 l injection volume. Data analysis for the high temperature GPC was performed using an in-house program developed at ExxonMobil. 172 This program calculates the molecular weight distributions in two ways: (1) by triple detection (LALLS), directly from the detector signals using the Zimm equation, and (2) by DRI detector using universal calibration and the Mark-Houwink relationship. Methodology for LALLS: Molecular weight was calculated from the LS and DRI signals. The DP detector was used to measure sample intrinsic viscosity and to examine the Mark-Houwink relationship, log (intrinsic viscosity) – log (molecular weight), to be presented in a future paper [since EP copolymers are well characterized, it was not necessary to use the intrinsic viscosity to estimate the virial coefficient, A2, for purposes of molecular weight calculations in this work]. The inter-detector volumes were determined by shifting their values in the software to obtain the best overlap of the three

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52 normalized signals for two suitably narrow polystyrene standards. The detector response factors used to convert the raw data to polymer molecular weights were determined by running a series of polymer standards (the two polystyrene standards used to determine the inter-detector volume, three narrow, and one broad PE standards from NIST and one broad PP standard), for which the M w , intrinsic viscosity, and injection mass are known. The DRI response factor was determined by first optimizing the agreement between the concentration calculated from the integrated peak areas and from the injection mass for the seven samples. The light scattering response factor was then determined by optimizing the agreement between the M w values calculated for each of the narrow standards compared to the literature values. Similarly, the intrinsic viscosity response factor was calculated by optimizing the agreement between the calculated and literature values for the five narrow standards. Methodology for high temperature DRI detection: Retention times were calibrated using 17 Polymer Laboratory EZ-Cal polystyrene standards. For each sample, the PS calibration curve is converted to a corresponding EP calibration curve using the appropriate Mark-Houwink equation for the polymer composition. The Mark-Houwink parameters for each EP composition were calculated from PE using Equation 1. [] EP = [] PE * (10.0053015*wt% propylene) If it is assumed that the molecular weight exponent does not vary significantly with copolymer composition (a reasonable assumption since for PE and PP are very similar), this equation can be rewritten as Equation 2, where wt % propylene is determined by NMR and K PE is taken from the literature (Equation 2). 20 K EP = K PE *(1 – 0.0053015* wt% propylene)

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53 Fourier transform infrared (FT-IR) spectrometry was performed using a Bio-Rad FTS-40A spectrometer. The hydrogenation of the unsaturated ADMET polymers was monitored by the disappearance of the out-of-plane bend for the trans internal double bond at 967 cm -1 . The samples were prepared by grinding the polymer with IR grade KBr into a homogeneous mixture and analyzed using a KBr pellet formed from the mixture. Differential scanning calorimetry (DSC) was performed using a Perkin-Elmer DSC 7 at a heating rate of 10 o C/min. Thermal calibrations were made using indium and freshly distilled n-octane as references for thermal transitions. Heats of fusion were referenced against indium. The samples were scanned for multiple cycles to remove recrystallization differences between samples and the results reported are of the third scan in the cycle. The results are listed in the experimental section and in tabular form within the text. Reported values are given as T m (melting peak) and h m (enthalpy of melting). Wide-angle X-ray Diffraction (WAXD) patterns were collected in point collimated, monochromatic Cu K radiation on a Bruker platform goniometer. The source was a Kristalloflex 760 2.2 kW generator and long fine focus tube equipped with cross coupled Gble mirror monomchromator and 200 m collimation. A HI-STAR area detector was mounted for data collection at 5.9 cm and referenced to corundum (alumina). Data were processed using GADDS program. The data presented are shown at 30 degrees 2theta and unwarped for inhomogeneous response in the flood field of the detector. 2.4.2 Materials Monomer 6-methyl-1,10-undecadiene (1) used in this study was synthesized following literature procedures. 171 Schrock’s molybdenum metathesis catalyst,

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54 [(CF 3 ) 2 CH 3 CO] 2 (N-2,6-C 6 H 3 -i-Pr 2 )Mo=CHC(CH 3 ) 2 Ph was also synthesized following literature procedures. 157-162 Wilkinson’s rhodium hydrogenation catalyst RhCl(PPh 3 ) 3 was purchased from Strem Chemical and used as received. Xylenes (Fisher) and 1,9-decadiene (Aldrich) were freshly distilled over Na metal using benzophenone as the indicator. Additional reagents were used as received. 2.4.3 General ADMET Copolymerizations All glassware was thoroughly cleaned, oven-dried, and finally flame-dried under vacuum prior to use. The monomers were dried over a potassium mirror, vacuum transferred into a Schlenk flask, and subsequently degassed (3X) prior to storage in an argon-filled dry box. Monomers were weighed based on the needed molar ratios, (X:Y) shown below, of the resulting ethylene/propylene copolymers. All metathesis reactions were initiated in the bulk, inside the dry box using 50 mL round-bottom flasks equipped with a Teflon stirbar. The flasks were then fitted with a Teflon vacuum valve, brought out of the dry box, and placed on a high vacuum line (<10 -3 mmHg) while vigorously stirring. The polymerization vessel was exposed to intermittent vacuum at room temperature until the reaction either became highly viscous or solid (stirring ceased). The flask was then placed in a 40 o C oil bath at high vacuum (<10 -3 mmHg) for 48 hours upon which the temperature was raised to 50 o C for an additional 48 hours. The polymerization vessel was cooled to room temperature, and finally, the unsaturated polymer was taken up into toluene and precipitated into cold acidic methanol (1 M HCl) to remove catalyst residue. The ADMET unsaturated polymers were then fully characterized and subsequently hydrogenated. Synthesis and Characterization of PE-55.6. Polymerization of (50:50) 6-Methyl-1,10-undecadiene (1) and 1,9-decadiene (2). Monomer 1, 0.960 g (5.78 mmol)

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55 and 2 0.800 g (5.78 mmol) were combined and stirred for 3 hours to produce a homogeneous mixture. To this mixture was added 0.009 g (1.095 x 10 -2 mmol) of Schrock’s molybdenum catalyst. Precipitation from methanol (-78 o C), PE-55.6 gave: Yield: 90 % (after precipitation). The following spectral properties were obtained: 1 H NMR (CDCl 3 ) 0.83 (d, 1.63 H, methyl), 1.10 (br, 1.19 H), 1.32 (br, 8.0 H), 1.98 (br, 4.29 H), 5.38 (br, 2 H, internal olefin); 13 C NMR (CDCl 3 ) 20.0, 27.3, 27.4, 29.2, 29.8, 32.8, 33.2, 36.9, 129.9 (cis), 130.4 (trans). 13 C NMR integration of cis:trans peaks: 15:85. GPC data (DRI vs. PS): M w = 26 100 g/mol; PDI = 1.7 (M w /M n ). DSC results: T m (peak) = -7.6 o C, h m = 9.0 J/g. Synthesis and Characterization of PE-43.3. Polymerization of (40:60) 6-Methyl-1,10-undecadiene (1) and 1,9-decadiene (2). Synthesized as above using 0.800 g (4.82 mmol) 1, 1.00 g (7.20 mmol) 2, and 0.009 g (1.095 x 10 -2 mmol) of Schrock’s molybdenum catalyst. Precipitation from methanol (-78 o C), PE-43.3 gave: Yield: 92 % (after precipitation). The following spectral properties were obtained: 1 H NMR (CDCl 3 ) 0.83 (d, 1.34 H, methyl), 1.10 (br, 1.09 H), 1.32 (br, 8.2 H), 1.98 (br, 4.3 H), 5.38 (br, 2 H, internal olefin); 13 C NMR (CDCl 3 ) 20.0, 27.3, 27.4, 29.2, 29.8, 32.8, 33.2, 36.9, 129.9 (cis), 130.4 (trans). 13 C NMR integration of cis:trans peaks: 13:87. GPC data (DRI vs. PS): M w = 69 400 g/mol; PDI = 1.8 (M w /M n ). DSC results: T m (peak) = 8.2 o C, h m = 18.7 J/g. Synthesis and Characterization of PE-25.0. Polymerization of (20:80) 6-Methyl-1,10-undecadiene (1) and 1,9-decadiene (2). Synthesized as above using 0.432 g (2.60 mmol) 1, 1.44 g (10.4 mmol) 2, and 0.008 g (1.087 x 10 -2 mmol) of Schrock’s molybdenum catalyst. Precipitation from methanol, PE-25.0 gave: Yield: 97 % (after

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56 precipitation). The following spectral properties were obtained: 1 H NMR (CDCl 3 ) 0.83 (d, 0.70 H, methyl), 1.10 (br, 0.59 H), 1.32 (br, 8.0 H), 1.98 (br, 4.2 H), 5.38 (br, 2 H, internal olefin); 13 C NMR (CDCl 3 ) 20.0, 27.3, 27.4, 29.2, 29.8, 32.8, 33.2, 36.9, 129.9 (cis), 130.4 (trans). 13 C NMR integration of cis:trans peaks: 11:89. GPC data (DRI vs. PS): M w = 60 200 g/mol; PDI = 2.4 (M w /M n ). DSC results: T m (peak) = 61.5 o C, h m = 57.1 J/g. Synthesis and Characterization of PE-13.6. Polymerization of (10:90) 6-Methyl-1,10-undecadiene (1) and 1,9-decadiene (2). Synthesized as above using 0.220 g (1.32 mmol) 1, 1.70 g (12.3 mmol) 2, and 0.009 g (1.095 x 10 -2 mmol) of Schrock’s molybdenum catalyst. Precipitation from methanol, PE-13.6 gave: Yield: 97 % (after precipitation). The following spectral properties were obtained: 1 H NMR (CDCl 3 ) 0.83 (d, 0.27 H, methyl), 1.10 (br, 0.23 H), 1.32 (br, 7.6 H), 1.98 (br, 4.0 H), 5.38 (br, 2 H, internal olefin); 13 C NMR (CDCl 3 ) 20.0, 27.3, 27.4, 29.2, 29.8, 32.8, 33.2, 36.9, 129.9 (cis), 130.4 (trans). 13 C NMR integration of cis:trans peaks: 9:91. GPC data (DRI vs. PS): M w = 57 500 g/mol; PDI = 2.0 (M w /M n ). DSC results: T m (peak) = 67.8 o C, h m = 88.7 J/g. Synthesis and Characterization of PE-7.1. Polymerization of (5:95) 6-Methyl-1,10-undecadiene (1) and 1,9-decadiene (2). Synthesized as above using 0.113 g (0.681 mmol) 1, 1.77 g (13.0 mmol) 2, and 0.010 g (1.37 x 10 -2 mmol) of Schrock’s molybdenum catalyst. Precipitation from methanol, PE-7.1 gave: Yield: 98 % (after precipitation). The following spectral properties were obtained: 1 H NMR (CDCl 3 ) 0.83 (d, 0.14 H, methyl), 1.10 (br, 0.15 H), 1.32 (br, 8.13 H), 1.98 (br, 4.14 H), 5.38 (br, 2 H, internal olefin); 13 C NMR (CDCl 3 ) 20.0, 27.3, 27.4, 29.2, 29.8, 32.8, 33.2, 36.9, 129.9

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57 (cis), 130.4 (trans). 13 C NMR integration of cis:trans peaks: 7:93. GPC data (DRI vs. PS): M w = 35 000 g/mol; PDI = 1.8 (M w /M n ). DSC results: T m (peak) = 68.6 o C, h m = 98.7 J/g. Synthesis and Characterization of PE-1.5. Polymerization of (1:99) 6-Methyl-1,10-undecadiene (1) and 1,9-decadiene (2). Synthesized as above using 0.021 g (0.124 mmol) 1, 1.70 g (12.3 mmol) 2, and 0.008 g (1.087 x 10 -2 mmol) of Schrock’s molybdenum catalyst. Precipitation from methanol, PE-1.5 gave: Yield: 98 % (after precipitation). The following spectral properties were obtained: 1 H NMR (CDCl 3 ) 0.83 (d, 0.04 H, methyl), 1.10 (br, 0.08), 1.32 (br, 7.25 H), 1.98 (br, 4.0 H), 5.38 (br, 2 H, internal olefin); 13 C NMR (CDCl 3 ) 20.0, 27.3, 27.4, 29.2, 29.8, 32.8, 33.2, 36.9, 129.9 (cis), 130.4 (trans). 13 C NMR integration of cis:trans peaks: 4:96. GPC data (DRI vs. PS): M w = 30 100 g/mol; PDI = 1.9 (M w /M n ). DSC results: T m (peak) = 72.6 o C, h m = 103.0 J/g. Synthesis and Characterization of PE-OCT. Polymerization of 1,9-Decadiene (2). Monomer 2, 2.00 g (14.47 mmol), was combined with 0.011 g (1.446 x 10 -2 mmol) of Schrock’s molybdenum catalyst. The resulting unsaturated polymer (PE-OCT) was analyzed after precipitation from methanol. Yield: 98 % (after precipitation). The following spectral properties were obtained: 1 H NMR (CDCl 3 ) 1.32 (br, 8.0 H), 1.98 (br, 4.0 H), 5.38 (br, 2 H, internal olefin); 13 C NMR (CDCl 3 ) 29.2, 29.8, 32.8, 129.9 (cis), 130.4 (trans). 13 C NMR integration of cis:trans peaks: 4:96. GPC data (DRI vs. PS) : M w = 27 600 g/mol; PDI = 1.8 (M w /M n ). DSC results: T m (peak) = 74.2 o C, h m = 163 J/g.

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58 2.4.4 Hydrogenation of Unsaturated ADMET Polymers Synthesis and Characterization of PE-55.6H. Hydrogenations were performed using a 150 mL Parr high-pressure reaction vessel equipped with a glass liner and Teflon stirbar. Unsaturated polymer PE-50 (1.00 g) and Wilkinson’s catalyst (0.020 g) were added to the glass liner under a nitrogen blanket. Finally, 20 mL of xylenes were added. The vessel was sealed and attached to a grade 5 hydrogen tank and purged with hydrogen several times. The bomb was charged with 700 psi of H 2 and stirred for 96 hours at 120 o C. The hydrogenated polymer PE-55.6H was dissolved in boiling toluene, filtered, and precipitated into 40 o C methanol. The polymer was then filtered and then dried under reduced pressure until a constant weight was obtained. Yield: 97 % (after precipitation). The following spectral properties were obtained: 1 H NMR (TCE-d 2 ) 0.915 (d, CH 3 , 95 H), 1.19 and 1.34 (br, CH 2 , 1000 H). 13 C NMR (TCE-d 2 ) 14.22, 20.13 (CH 3 ), 22.91, 27.04, 27.44, 29.59, 29.68, 29.99, 30.00, 30.37, 32.23, 32.60, 33.25, 37.57 (CH). GPC data (LALLS): M w = 13 700 g/mol; PDI = 1.5 (M w /M n ). DSC results: T m (peak) = 52.1 o C, h m = 87.0 J/g. Synthesis and Characterization of PE-43.3H. Synthesized following procedure shown above. Yield: 98 % (after precipitation). The following spectral properties were obtained: 1 H NMR (TCE-d 2 ) 0.915 (d, CH 3 , 73.1 H), 1.19 and 1.34 (br, CH 2 , 1000 H). 13 C NMR (TCE-d 2 ) 14.22, 20.13 (CH 3 ), 22.91, 27.04, 27.44, 29.59, 29.68, 29.99, 30.00, 30.37, 32.23, 32.60, 33.25, 37.57 (CH). GPC data (LALLS): M w = 30 500 g/mol; PDI = 1.4 (M w /M n ). DSC results: T m (peak) = 80.7 o C, h m = 85.0 J/g. Synthesis and Characterization of PE-25.0H. Synthesized following procedure shown above. Yield: 98 % (after precipitation). The following spectral properties were obtained: 1 H NMR (TCE-d 2 ) 0.915 (d, CH 3 , 44.57 H), 1.19 and 1.34 (br, CH 2 , 1000

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59 H). 13 C NMR (TCE-d 2 ) 14.22, 20.13 (CH 3 ), 22.91, 27.04, 27.44, 29.59, 29.68, 29.99, 30.00, 30.37, 32.23, 32.60, 33.25, 37.57 (CH). GPC data (LALLS): M w = 27 000 g/mol; PDI = 1.8 (M w /M n ). DSC results: T m (peak) = 111.6 o C, h m = 137.3 J/g. Synthesis and Characterization of PE-13.6H. Synthesized following procedure shown above. Yield: 99% (after precipitation). The following spectral properties were obtained: 1 H NMR (TCE-d 2 ) 0.915 (d, CH 3 , 38.72 H), 1.19 and 1.34 (br, CH 2 , 1000 H). 13 C NMR (TCE-d 2 ) 14.22, 20.13 (CH 3 ), 22.91, 27.04, 27.44, 29.59, 29.68, 29.99, 30.00, 30.37, 32.23, 32.60, 33.25, 37.57 (CH). GPC data (LALLS): M w = 26 200 g/mol; PDI = 1.6 (M w /M n ). DSC results: T m (peak) = 119.0 o C, h m = 165.8 J/g. Synthesis and Characterization of PE-7.1H. Synthesized following procedure shown above. Yield: 98 % (after precipitation). The following spectral properties were obtained: 1 H NMR (TCE-d 2 ) 0.915 (d, CH 3 , 24.23 H), 1.19 and 1.34 (br, CH 2 , 1000 H). 13 C NMR (TCE-d 2 ) 14.22, 20.13 (CH 3 ), 22.91, 27.04, 27.44, 29.59, 29.68, 29.99, 30.00, 30.37, 32.23, 32.60, 33.25, 37.57 (CH). GPC data (LALLS): M w = 23 200 g/mol; PDI = 1.9 (M w /M n ). DSC results: T m (peak) = 123.2 o C, h m = 183.4 J/g. Synthesis and Characterization of PE-1.5H. Synthesized following procedure shown above. Yield: 99 % (after precipitation). The following spectral properties were obtained: 1 H NMR (TCE-d 2 ) 0.915 (d, CH 3 , 11.72 H), 1.19 and 1.34 (br, CH 2 , 1000 H). 13 C NMR (TCE-d 2 ) 14.22, 20.13 (CH 3 ), 22.91, 27.04, 27.44, 29.59, 29.68, 29.99, 30.00, 30.37, 32.23, 32.60, 33.25, 37.57 (CH). GPC data (LALLS): M w = 15 300 g/mol; PDI = 1.6 (M w /M n ). DSC results: T m (peak) = 129.0 o C, h m = 207.6 J/g. Synthesis and Characterization of PE-OCTH. Synthesized following procedure shown above. Yield: 98 % (after precipitation). The following spectral

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60 properties were obtained: 1 H NMR (TCE-d 2 ) 0.915 (d, CH 3 , 10.63 H), 1.19 and 1.34 (br, CH 2 , 1000 H). 13 C NMR (TCE-d 2 ) 14.22 (1s), 22.91 (2s), 29.59 (4s), 29.68 (5s), 29.99, 32.23 (3s). GPC data (LALLS): M w = 16 200 g/mol; PDI = 1.6 (M w /M n ). DSC results: T m (peak) = 133 o C, h m = 230.0 J/g.

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CHAPTER 3 PRECISE ETHYL BRANCHED ETHYLENE/1-BUTENE COPOLYMERS 3.1 Introduction Ethylene-based macromolecules, both homoand copolymers, without question constitute the highest volume of synthetically produced polymers in the world. The structural simplicity and industrial importance have led these materials to be among the most thoroughly studied macromolecules. Although such factors as mode of polymerization (radical, Ziegler-Natta, metallocene, etc.), catalyst choice, reaction temperature/pressure, and molar mass bare significant importance on ethylene/-olefin copolymers, the short-chain branching (SCB) content and its distribution are the most prominent factors in linear low density polyethylenes (LLDPEs). 197-201 Linear low density polyethylene is a statistical copolymer of ethylene and an alpha-olefin (butene, hexene, and octene) where the type, concentration, and distribution of these branches vary and are highly dependent on the chosen polymerization mechanism. Typically, these random copolymers are produced using Ziegler-Natta, 134-140 and metallocene catalysts, 141-146 anionically synthesized hydrogenated butadienes, 50,147-151 and when using other late transition metals. 152-155 Similar to the results obtained for ethylene/propylene (EP) copolymers, 77,92-101 studies on randomly-branched ethylene/butylenes (EB) copolymer systems have shown that the density, enthalpy, degree of crystallinity, and peak melting/crystallization points all decrease as the amount of defect content (ethyl branch) is increased. In the past, the interest of EB copolymers has been limited relative to ethylene/propene versions of LLDPE. These butylene based 61

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62 copolymers and homopolymers have garnered attention due to their unusual combination of toughness and flexibility as well as their resistance to creep and external stress. 202-203 However, the synthetic methodology used to study these copolymers may produce unwanted side reactions and as a result unknown primary structures. These defects, even in small quantities, can alter the polymer’s macromolecular behavior and thermal response depending on their frequency and identity. Recently we presented a way to obviate the random nature of branching in polyethylene along with unwanted side products. 156,171 Doing so has been accomplished using the clean, step polymerization chemistry offered by acyclic diene metathesis (ADMET). This mild chemistry avoids chain transfer and other catalyst “mistakes” encountered during chain propagation processes, thereby producing a branched polymer with a homogeneous composition distribution and known branch identity (Figure 3-1). Figure 3-1. Controlling ethyl branch content using ADMET polymerization. A short time ago we reported the synthesis and thermal behavior for a series of five model ethylene/propylene (EP) copolymers in which the methyl branch was precisely

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63 placed on each and every 9 th , 11 th , 15 th , 19 th , and 21 st carbon along the backbone, respectively. 171 We have also reported polyethylene containing precise methyl content, but with a statistical placement along the backbone using ADMET copolymerization. 204 The thermal behavior and morphological analysis for this series of EP copolymers have yielded unique results, in effect creating a new class of PE based materials using metathesis, based on the structural control offered by precise branch identity coupled with their precise or random placement. In an effort to extend our LLDPE structural library, a synthetic methodology was sought to lengthen the alkyl branch in these model materials. This has proven to be a difficult task, for the structural simplicity of symmetrically disposed, substituted dienes is deceptive. We now report the successful synthesis of , -diene monomers in which the ethyl branch has been symmetrically substituted on the hydrocarbon backbone. The ADMET polymerization of these monomers and subsequent hydrogenation has yielded the first ADMET model ethylene/1-butene (EB) copolymers wherein the ethyl branch is placed on each and every 9 th , 15 th , and 21 st carbon along the backbone (Figure 3-1). Herein, we present the monomer/polymer synthesis, characterization, and thermal analysis for these new LLDPE model materials. 3.2 Results and Discussion 3.2.1 Monomer Synthesis and Characterization The mild chemistry afforded by ADMET polymerization has proven a useful mechanism for the modeling of perfectly branched structures. 156,171 The cornerstone of this perfectly branched PE model study has been to produce a monomer (, -diene) with pure alpha olefin functionality along with perfect branch identity (Figure 3-1).

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64 Fulfilling both requirements has proven difficult when expanding the branch length beyond the methyl group, 171 leading to significant effort in formulating a synthetic pathway that would successfully extend the branch identity without sacrificing the integrity of the diene. Several methodologies were investigated throughout the synthesis work to generate perfectly branched LLDPE materials; multiple synthetic procedures were used to complete this study starting either from ethyl acetoacetate (Figure 3-2), diethyl malonate (Figure 3-3), or ketodienes (Figure 3-4). The first successful synthetic strategy to produce a pure , -diene monomer with a symmetrically substituted ethyl branch is presented in Figure 3-2. OOOEtOOOEt33O33H67733HOH33HOTs89933HCH2CH31.)2.)tBuO-K+Br3LiClDMSO / H2OLiAlH4Et2OTsCl, pyrCHCl31M Li(Et)3BH/THFTHF33+110Obtained 7.1 : 1 mixture of ethyl branch monomer (1) to eliminated product (10).(Super Hydride)Step 6 to 1 & 8 = 83.0%95.1%72.3%28.5%5 Figure 3-2. Ethyl branch synthetic methodology for short methylene monomers. The conditions in step 1 (Figure 3-2) were modified from the work of Krapcho, et al. 205-208 Ethyl acetoacetate is deprotonated with base and readily effects the S N 2 displacement of bromide upon addition of 5-bromo-1-pentene. Subsequently, in the same pot, the monosubstituted product is reacted with a second equivalent of base and alkenyl halide, affording the disubstituted -keto ester (6). Compound 6 was decarboxylated

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65 using a dimethylsulfoxide (DMSO)/water/salt mixture 205-208 to produce an , -diene with a pendant methyl ketone that is symmetrically substituted along the monomer backbone (7). Reduction using lithium aluminum hydride (LAH) yields the secondary alcohol (8), which is further tosylated (9). The reducing agent Li(Et) 3 BH, coined Super Hydride, first employed by H.C. Brown and coworkers in the late 1970s is used to reduce compound 9. 17 This final step yields a mixture of the symmetrical diene of interest (1) and eliminated by-product (10). These products can be separated using HPLC or careful column chromatography with hexane. The use of the hindered boron reducing agent is evident since the reduction of the tosylated alcohol (9) with LAH produces no traceable amount of compound 1, whereas a 68 % conversion was observed for the olefinic monomer 10. Although monomer 1 (three methylenes) was successfully produced by the method shown in Figure 3-2, difficulties were encountered when trying to synthesize monomers containing longer chain lengths. Complications arise during the reduction of the secondary tosylated or mesylated alcohol derivatives. The preferred synthesis for these longer run length monomers is shown in Figure 3-3, outlined for 3-(10-undecenyl)-13-tetradecene (2), to produce precisely placed ethyl branches. The synthesis was modified according to the procedure for our precisely placed methyl monomers (Figure 3-3). 171 Compound 11 is synthesized using sodium hydride with 11-bromo-1-undecene, followed by decarboxylation of the resulting diacid. The monoacid is reduced into the primary alcohol and directly converted to the bromide (13) using CBr 4 . A single carbon homologation was performed by the addition of solid CO 2 to the Grignard of compound 13. Once again its reduction was followed by the formation of the bromide 15.

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66 Monomer 2 was obtained by quenching the Grignard of 15 with water. Noteworthy, the formation of the Grignard must be achieved using sonication, for production of the Grignard thermally causes compound 15 to dimerize. Again, the key difference between either methods (Figures 3-2 and 3-3) is the formation and reduction of the primary bromide (15) in Figure 3-3 using Mg/H 2 O or if preferred the reduction of the tosylated alcohol with Super Hydride. The displacement of a primary tosylate using boron can produce the desired hydrocarbon monomer with minimal amounts of the eliminated compound (< 5 %). 99HO99HBr12131399H1.) LAH/ THF1.) Mg/THFHO2.) CBr4/PPh3CH2Cl295.3 %2.) Solid CO2OHO1.) LAH/ THF2.) CBr4/PPh3CH2Cl293.8 %99HBr14151599HCH2CH321.) Mg/THF2.) H2O/H+65.3%99OEtO111.) NaOH/EtOHOEtO2.) Decalin Figure 3-3. Synthesis for longer methylene run length monomers shown for 3-(10-undecenyl)-13-tetradecene (2). The synthesis of symmetrical ethyl branched dienes can be accomplished using either methodologies outlined in Figures 3-2 or 3-3. However, in an attempt to simplify our monomer synthetic procedure we sought easier and more efficient ways to afford any length branch through simple organic transformations. Our initial endeavor focused on using Wittig couplings to produce monomers containing a “masked” branch yielding the correct ethyl branch upon exhaustive hydrogenation. In fact, the model PEs derived from

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67 monomers made through Wittig coupling (Figure 3-4) and ethyl acetoacetate addition (Figure 3-3) yields polymers having the exact primary structure. Their comparison will be discussed further. Onn(CH3CH2)PPh3BrtBuO-K+/THFnn16) n = 917) n = 63) n = 94) n = 6 Figure 3-4. Synthesis of Wittig monomers. Wittig monomers (Figure 3-4) were synthesized using an in-situ formation of the phosphorus ylide followed by direct attack on the corresponding ketone. The starting ketones were synthesized according to literature procedures. 210 The branch identity can be controlled by the starting bromoalkane used in the ylide precursor; for example, ethyl branches would be obtained from bromoethane. Their synthesis is done by refluxing the necessary bromoalkane with triphenylphosphine in diethyl ether, where the resulting salt is filtered, washed with excess ether, and dried prior to use. Upon addition of base to the salt/ketone slurry the solution turns yellow indicative of ylide formation. The reaction is complete within 30 minutes of base addition and the product can be purified by flash chromatography in hexane. The clean chemistry and easy synthesis afforded by Wittig chemistry will allow formation of any branch length monomers readily from available, inexpensive starting bromoalkanes. 3.2.2 ADMET Polymerization and Hydrogenation Chemistry The proper choice of the appropriate catalyst system throughout this model study was crucial due to the differing monomer structures employed; only Grubbs’ first generation 163-169 or Shrock’s 157-162 catalyst could be used for pure , -diene

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68 polymerizations. The Wittig monomers were polymerized only with Grubbs’ catalyst, due to the presence of the “masked” branch, the trisubsituted olefin. Since we are modeling polymers containing exact primary structures, we have avoided all other ruthenium based catalyst systems due to their propensity to isomerize external and internal olefins. 211-214 Monomer 1 was exposed to Schrock’s catalyst 157-162 under mild ADMET step polymerization conditions using typical catalyst loadings (1000:1, monomer:catalyst). All other monomers were polymerized using Grubbs’ first generation catalyst. The chemistry proceeds cleanly to yield a linear, unsaturated polymer that is comprised of only one type of repeat unit, plus the usual amount of cyclics (<1-2%) found in bulk polycondensation conversions. Exhaustive hydrogenation of the unsaturated prepolymer was accomplished using either palladium on carbon (10 wt% Pd/C) or RuHCl(CO)(PCy 3 ) 2 (5 wt%); the homogeneous Ru catalyst was used with the trisubstituted olefinic prepolymers due to its literature applications in this area. 215-217 In both cases the hydrogenations were carried out over 5 days using 500 p.s.i for Pd; however, higher pressure was needed (2000 p.s.i) for the homogeneous catalyst to unsure complete hydrogenation. The polymers were purified by filtration and simple precipitation of the hydrogenation solution in acidic methanol (1 M). No side reaction was detectable by TLC or NMR, and hydrogenation was verified by both infrared (IR) spectroscopy and NMR analysis. As previously observed, hydrogenation effectiveness is best monitored by IR. The 967-969 cm -1 absorption in the unsaturated polymer, which corresponds to the out-of-plane C-H bend in the alkene, completely disappears after successful hydrogenation. This is the first example of any model EB copolymer being

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69 prepared containing precisely placed ethyl branches on each and every 9 th , 15 th , and 21 st carbon along polyethylene’s linear backbone. In the following sections, all polymers are named using the prefix HP (hydrogenated polymer) followed by the comonomer type (EB, ethylene/butene or EP, ethylene/propylene) and the precise branch frequency (21); for example HPEB21, is designated as hydrogenated ethylene/butene copolymer containing an ethyl branch on every 21 st carbon. Due to the exact nature of the polymers produced, the comonomer content can be easily calculated using the branch frequency (n) following the relationship: mol % comonomer =2n 100x Table 3-1 confirms that the hydrogenation process does not alter the molecular weight of the unsaturated polymers in this study, which is consistent with our earlier experiments. 156,171,204 The saturated EB copolymers were analyzed by three molecular weight determination methods consisting of the use of an internal differential refractive index detector (DRI), differential viscosity detector (DP), and a Precision light scattering detector (LS). Using these three detectors in series, the molecular weights were determined by universal calibration (a plot of log intrinsic viscosity [] x molecular weight vs. retention time) calibrated using polystyrene (PS) and low-angle laser light scattering (LALLS). The results are shown in table 3-1. The universal calibration data was generated by calibrating the retention times using 10 Polymer Laboratory polystyrene standards. As previously discussed for EP copolymer models, 171 these ADMET model EB copolymers exhibit molecular weights and polydispersities within a

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70 sufficient range to make it an excellent model for commercial grades of LLDPE produced via metallocene catalysis. 141-146 Table 3-1. Molecular weights for ADMET model EB materials. Model EB Polymer Ethyl on every n th backbone Carbona Unsaturated Copolymers (Relative) b Saturated Copolymers Relative (PS) b Universal c LALLS d n M w x 10 -3 PDI e M w x 10 -3 PDI e M w x 10 -3 PDI e M w x 10 -3 PDI e HPEB9 9 56.5 1.8 58.6 1.8 37.8 1.8 29.2 1.7 HPEB15W 15 53.1 1.9 54.2 1.9 31.2 1.9 23.8 1.8 HPEB21 21 56.1 2.0 54.1 1.8 36.5 1.9 28.6 1.7 HPEB21W 21 50.2 1.9 50.7 1.9 27.3 1.8 25.4 1.8 A) Branch content based on the hydrogenated repeat unit. B) Molecular weight data taken in tetrahydrofuran (40 o C) relative to polystyrene standards. C) Molecular weight data taken in tetrahydrofuran (40 o C) using viscosity law calibration relative to polystyrene standards. D) Molecular weight data taken using low-angle laser light scattering (LALLS) in tetrahydrofuran at 40 o C. D) Polydispersity index (M w /M n ). 3.3.3 Structure Determination using NMR and IR Our goal in modeling PE based materials is to develop an understanding of the relationship between the exact effect branch content and identity and a given model copolymer’s microand macromolecular properties. A direct transfer of monomer branch content to the polymer is achieved using step metathesis chemistry (ADMET). As a starting point we have used semi-quantitative 13 C NMR as the primary tool for investigation to verify primary structure. Figure 3-5 displays the 13 C NMR spectra for the conversion of monomer 1 to unsaturated polymer, UPEB9 (Figure 3-5b); the 13 C spectrum for the fully saturated ADMET model EB copolymer possessing an ethyl branch on every 9 th carbon, HPEB9 is presented in Figure 3-5c. These NMR data confirm that the ADMET reaction has taken place. The absence of visible end-groups (114.5 and 139.2 ppm) implies that high polymer has been obtained, a result consistent with the GPC results given earlier.

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71 Further, the internal olefin resonance at 130.62 ppm (Figure 3-5b) completely vanishes upon exhaustive hydrogenation of the double bonds (confirmed by IR, Figure 3-6). Figure 3-5. Typical 13 C NMR transformation for ADMET model copolymers. A) Monomer 1, B) UPEB9, and C) HPEB9.

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72 The clean and complete nature of the transformations depicted in the spectra is typical for all ADMET model LLDPEs synthesized thus far, 171 data which illustrate the level of structural control that is possible when choosing step condensation chemistry as the method to model ethylene-co-alpha-olefin systems. Moreover, the 13 C NMR spectra of these ADMET copolymers reveal the exact chemical shifts of a particular branch point and its subsequent carbons. In effect, acyclic diene metathesis allows for a direct correlation between branch identity and observed NMR shift (ppm) due to the exact primary structure of the polymers. In the case of precise ethyl branched copolymers, the observed shifts are 33.45 (), 26.99 (), 30.43 (), 30.31 (), 39.09 (methine), 26.12 (’), and 11.12 (1B n ) ppm, which is in very good agreement with experimental 218-222 and predicted values. 223-225 These data suggest that ADMET model LLDPEs, in conjunction with high field NMR experiments, could be used to derive new and improved mathematical parameters in the structural study of branched polyethylene. A wealth of information can be collected concerning the amount, nature, and partitioning of branched PE materials using 13 C NMR studies. 226-227 The precisely-branched ADMET PEs synthesized thus far offer a tremendous potential to study/model the direct impact a short-chain branch and its distribution have on the final structure-property relationships in ethylene-based materials. Nowhere is this more evident than in the NMR results presented here. As previously observed in our model EP model copolymers, the utility of IR to observe and understand changes in structure is invaluable. In the past, Tashiro et al. 179 carried out a detailed study on the IR response of differing polyethylene crystal structures. In Figure 3-6, the saturated ADMET EB copolymer models clearly exhibit the

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73 characteristic shapes and absorption values (two single peaks at 1461 and 720 cm -1 ) which suggests an unorganized packing structure. The limited correlation between IR and x-ray data in EB copolymers means that the exact structure cannot be determined from the absorbance spectra alone. However, following the vibrational analysis made for n-alkenes and disordered polyethylene we can make certain observations using the 1366, 1305 and 1352 cm -1 bands. 83,228-229 Previously, the bands observed at 1366 and 1305 cm -1 were assigned to a kink and the 1352 cm -1 to a double gauche defect in PE materials. 179 The overall concentration of gauche and kink methylene sequences for our ADMET EB copolymers is reduced with the decrease in branch defect content. This trend can be observed by the comparison of these defect bands versus the -CH 2 scissoring at 1461 cm -1 . Also, the ratio of these defect bands (1366, 1305, and 1352 cm -1 ) relative to the methylene wagging vibration at 1261 cm -1 shows a unique pattern. Close inspection reveals that the ratio of all three disordered vibrations are equal relative to each other; however, their ratio to the 1461 cm -1 changes depending on branch content and crystallinity. Of course, both HPEB9 and HPEB15 are amorphous at the recorded spectra temperature while HPEB21 is semicrystalline. The observed disordered ratio trend can also be observed using and the 801 and 769 cm -1 vibration (visible with EB copolymers 230-231 ). The peaks most likely originate from a methylene rock and proceed with a similar up/down ratio when the defect content and crystallinity change. While at present the exact cause of these vibrations and variable intensities cannot be correlated to structural information in our EB copolymers, we can compare them to our precise methyl branched copolymers as well as theoretical models (Figure 3-6b).

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74 The higher content of these defects is in accord with the higher steric demand of the ethyl branch over the methyl branch. Further, the majority of the methyl branches are known to incorporate into the repeating methylene sequences. 232-234 Of course, under equilibrium conditions the branches, even methyl, are assumed to be rejected from the crystallites. 175,235 Equilibrium is seldom reached during crystallization however, thereby favoring an intermediate situation where the partial segregation of branches exists between the amorphous and crystal regions. 236 This equilibrium, for branches longer than methyl, can be shifted by the crystallization conditions to favor inclusion or exclusion. 232,237 On this basis, the bulk of the ethyl side group is at the boundary between total exclusion and inclusion within the crystal lattice. The intermediate situation of phase partitioning chain defects seems most likely, and there have been numerous experimental, 226,227,233,238-245 theoretical, 246-257 and molecular modeling studies 258-259 to help define a mechanism for branch inclusion. Typically, x-ray diffraction coupled with high field 13 C NMR has been used to determine branch inclusion. For ethyl branched polymers, the proportion of ethyl branch inclusion was determined to be a function of SCB concentration and was estimated at 10:1 (17 SCB/1000C) and 5:1 (21 SCB/1000C) between the amorphous and crystalline regions. 226,233,237 More recently, studies have assumed the existence of branch incorporation by considering possible structural perturbations and conformational defects. These studies have proposed interstitial sites along the polymer chains, known as kinks, 246-250 arising from conformational gauche defects (2g1 defects) being the most common. 253 These 2g1 defects have been proposed to be large enough for ethyl

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75 branches. 246,254-257 In fact, the gt (2g1) conformation can be observed using IR and assigned the 1366 and 1305 cm -1 absorptions. As mentioned earlier, our EB copolymers exhibit high concentrations of the kink (tttgtttt) defect. The concentration of these defects in relative to the double gauche (1351 cm -1 ) remains constant throughout the branch content. Also, it would seem that the distorted trans segments (shoulder of the 1461 cm -1 absorption) hold this constant relationship as well. The nearly constant ratio of these bands versus defect content for our EB copolymers suggests that defect equilibrium is independent of methylene sequence length. The thermal analysis of these polymers, discussed later, shows that HPEB9 is amorphous most likely because of the short sequences of trans methylenes between branch kinks. As the branch frequency decreases, the resulting longer run length of trans segments enables the polymer to crystallize, depending on the temperature as seen for HPEB21. The larger steric demand has brought about a large increase in the gauche and kick defects relative to ADMET EP copolymers (Figure 3-6b) as well as a new observed vibration (wag) at 769 cm -1 . These defects are small and only slightly observed for the methyl branched HPEP21. There is also a shift in the methylene scissoring vibration from 1472 cm -1 for HPEP21 to 1461 cm -1 for HPEB21. Although the band positions are slightly different from a typical orthorhombic crystal of PE, 179 observed at 1472 and 1463 cm -1 , our EP and EB copolymers encompass both peaks respectively. In order to further delineate the copolymers structure, the thermal behavior of these materials was explored as well as WAXD of HPEB21.

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76 Figure 3-6. Infrared comparison for the ADMET EB series. A) Infrared spectra for ADMET EB copolymers and B) IR comparison of precise methyl and ethyl branched copolymers (on every 21 st ). 3.3.4 Thermal Analysis Numerous thermal behavior studies have been performed on commercially produced LLDPEs 260-263 and EB copolymers containing a statistical distribution of ethyl branches. 48,56,59,115,143,145-146,150,226,264-274 Similar to the results obtained for EP copolymers, studies on randomly-branched EB copolymer systems have shown that the

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77 density, enthalpy, degree of crystallinity, and peak melting/crystallization points all decrease as the amount of defect content (ethyl branches) is increased. Like EP copolymers, the melting behavior of EB systems is influenced by the amount of short-chain branching (SCB); however, the SCB distribution (SCBD) is by far the most determinant factor on the final physical properties of a given material. The major problem arising during modeling studies on ethylene-based polymers is the compositional heterogeneity normally encountered for these statistically branched materials. In this way, ADMET EB copolymers present the advantage of being well-defined materials with a homogeneous distribution of defects along the backbone. Thus they make excellent substances with which to model the effect that SCB and SCBD have on the final materials response of ethylene-based materials. Figure 3-7 shows a calorimetric comparison between the saturated ethyl (HPEB9) versus fully saturated methyl branched polymer (HPEP9). Both materials possess precise branch distribution along the hydrocarbon backbone. Previously studied model EB copolymers, made from hydrogenated poly(butadienes), have exhibited ill-defined melts for branch contents as high as 106 ethyls/1000 carbons. 226 In contrast, the ADMET model EB copolymer HPEB9, possessing 111 ethyls/1000 carbons, shows no detectable melting point in the range studied here, suggesting a completely amorphous behavior. This result is interesting when compared to the narrow melting point exhibited by the ADMET model EP copolymer (HPEP9) with the same branch content (Figure 3-7). The only viable explanation for this difference is that methyl branches are readily incorporated into the crystal lattice, whereas the steric demands of the ethyl branch preclude its taking part in the crystallization process at this level of precise branch

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78 distribution. In an effort to produce EB copolymers containing crystalline segments the average methylene run length (MSL) was increased to produce both model polymers HPEB15 and HPEB21. Our modeling polymerization chemistry, ADMET, lends itself perfectly for this task. Figure 3-7. DSC comparison between a methyl and ethyl on every 9 th carbon. As shown previously we are able to modify the backbone of our model polymers by simple monomer manipulation. Figure 3-2 and 3-3 illustrate that we have developed a routine synthesis to create monomers containing an ethyl branch and any level of branch content (‘R’/1000 carbons). In fact, the model copolymers containing an ethyl branch on every 21 st backbone carbon were synthesized with two different methodologies. Utilizing the Wittig reaction along with the appropriate ruthenium polymerization catalyst, we were able to make the total synthesis viable for modeling PE on a large scale. Overall this new synthetic approach allows for modeling material properties and perhaps polymer

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79 blends on industrial scales. Of course, for the Wittig methodology to be a viable method for monomer synthesis, the tri-substituted olefin must remain inactive throughout the polymerization. If at any time the tri-substituted olefin engages in metathesis, even after all terminal olefins have reacted, the polymer primary structure would be altered. In order to determine if the pendent olefin in the Wittig monomers were actually inactive in the ADMET polymerization cycle both monomers 2 and 3 were synthesized and compared (Figure 3-8). To prove the Wittig method of producing monomers was adequate for modeling EB branched polyolefins, HPEB21 was synthesized from a purely , diene monomer obtained by the procedure outlined in Figure 3-3. The polymer was then used as the reference and compared to the Wittig produced copolymer (HPEB21W). The easiest and most effective method to make a structure comparison between HPEB21 and HPEB21W was close inspection of both 13 C NMR and DSC. This comparison would lead to an identical response to the external stimuli if both polymer’s macromolecular behavior were the same. Further, the thermograph and carbon spectra of both polymers would be equal if the primary structures were equal. In fact, if at anytime throughout the metathesis cycle the trisubstituted olefin in UPEB21W becomes metathesis active, one or both of these techniques would detect the structural change. Figure 3-8 reveals that both polymers have an identical carbon spectrum and exhibit the same nearly monomodal melting profile containing two distinct peak melting temperatures. The enthalpy ratio between these two melting peaks is the same regardless of the polymer synthetic methodology.

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80 Figure 3-8. Structural comparison based on the collected DSC and NMR data. A) DSC comparison for HPEB21, HPEB15W, and HPEB21W. B) 13 C NMR of HPEB21 and HPEB21W. The precise nature of the branch location or constant MSL produces a semi-crystalline polymer favoring a single crystalline region (T m = 34.3 o C). Comparison of model EB copolymers synthesized using either metallocene 264,267 or hydrogenated polybutadienes, 150,226 at the same level of branch content, show very ill-defined endotherms. However, when HPEB21 (ethyl branch) is compared to the precise methyl branched model HPEP21, studied previously, the latter has a higher peak melting temperature (62 o C) and a higher melting enthalpy (103 J/g). The EP model copolymer also exhibits a sharp melting profile with no premelting in contrast to the rather large premelting thermograph seen for HPEB21. To ascertain the semi-crystallinity limit in our model EB copolymers, the methylene sequence length was reduced to produce HPEB15W. This model copolymer, containing an ethyl branch on every 15 th carbon, was synthesized using the Wittig approach only. The reduction of the methylene sequence length causes the melting point to drop below room temperature. The polymer still exhibits semi-crystallinity, but increasing the

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81 defect content results in a bimodal melting profile. Similar results have been observed for continuously cooled hydrogenated polybutadienes at much higher branch content. 226 Apparently, precisely placed ethyl branched EB copolymers have a single sharp melting profile for copolymers containing approximately 50-60 ethyl branches per 1000 total carbons. The crystal formation and/or the crystallization kinetics also change when the overall branch content is increased. For example, when going from the amorphous HPEB9 to the semi-crystalline HPEB21, the melting profile becomes bimodal. These two different melting crystals may originate from the same source when comparing HPEB15 and HPEB21, but regardless of crystal origin the enthalpy ratio increases when going from HPEB15 to HPEB21, favoring the higher melting crystal. We have used annealing experiments on HPEB21W in an effort to force the copolymer to prefer a single crystal form. The same experiments could have been conducted with HPEB15W; however, we focused on HPEB21W primarily because of its higher melting temperature (above room temperature). Figure 3-9 illustrates that the EB copolymer HPEB21W can be manipulated by annealing the sample. The sample was initially annealed in the DSC at the leading edge of the higher melting crystal; in the case of HPEB21 the ideal temperature was found at 28 o C. Upon annealing the sample for 14 days (Figure 3-9), the reduction of the lower melting crystal was substantial and produced a polymer with a precise narrow peak melting temperature of 34.4 o C. In an effort to reduce the premelting in HPEB21W, the annealing experiment was carried outside in an isothermal bath at 28 o C for 28 days (Figure 3-9). Figure 3-9 illustrates that the polymer’s small endotherms and premelting observed after 14 days have been eliminated, producing a distinct, narrow single melting

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82 peak for HPEB21(W). The melting profile for our copolymer containing an ethyl branch precisely placed on every 21 st carbon exhibits the same behavior as our model EP copolymers, albeit at lower temperatures. Figure 3-9. Annealing experiments for HPEB21W. DSC thermograph of A) HPEB21W, B) annealed HPEB21W for 14 days at 28 o C, and C) annealed HPEB21W for 28 days at 28 o C. In this light, consensus has it that melting temperatures, crystallinity, and lamella thickness are a function of branch content and are relatively independent of branch size (excluding methyl). Since the identity of the branch (again, excluding methyl) has little effect on the crystal nature of LLDPE due to branch exclusion, the comonomer incorporation is the most important factor influencing the polymer’s behavior. These issues are a direct result of catalyst choice and polymerization conditions; for example, a metallocene EB copolymer (homogeneous) has a lower T m (26 o C) than a polymer with the same average branch content (30 SCB/1000C) but synthesized with a heterogeneous

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83 catalyst system. 267 These melting differences have been suggested to originate from the thick unbranched crystal formation witnessed in all heterogeneous systems. The more homogeneous branched system lacks the longer unbranched sequences, thinner crystals, and lower melting temperatures. Our ADMET produced polymers have perfect and constant MSL through every repeating sequence so a comparison between homogeneous, heterogeneous, and our copolymers is important. Correlations between branch content and melting temperature in EB copolymers have been investigated for metallocene, Ziegler-Natta, and hydrogenated polybutadienes (HPB). 48,59,266-267,274 From the data reported, the peak melting temperature decreases with more controlled polymerization conditions. For the same branch content the T m follows the trend 95 o C, 88 o C, and 62 o C for HPB, Z-N, and metallocene, respectively. Of course, ADMET copolymers have more control of the polymer’s primary structure, even more than observed for any metallocene catalyst. Having theoretically no heterogeneity in branch incorporation (or MSL), ADMET copolymers should exhibit lower melting points than metallocene copolymers, most likely resulting from smaller crystallite formation. Relating the branch content of our ADMET copolymers to the derived chain-addition models agrees with this assumption. Indeed, if HPEB21 was produced by chain-addition the level of branch content (43.5 SCB/1000 carbons) would predict a melting point of ~60 o C (actual T m = 34.5 o C). 267 Furthermore, the enthalpy of fusion of our ADMET EB copolymers is much higher (~57 J/g) than either metallocene (~30 J/g) or Z-N (~42 J/g) copolymers. These results are consistent with ADMET producing more homogeneous sequence lengths relative to any chain-addition polymerization.

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84 3.3.5 Wide-angle X-ray Scattering In addition to using DSC, NMR, and IR spectroscopy to characterize the structure of these precise models of ethylene/1-butene copolymers, we examined the crystal packing of the lowest defect content copolymer (HPEB21) using WAXD, limiting our study to polymers whose endotherms were above room temperature. Figure 3-10 shows the WAXD spectra of both the precise ethyl branched ADMET copolymer HPEB21W and the previously synthesized precise ADMET methyl branched copolymer, HPEP21. It is somewhat surprising to find that both polymers exhibit the same two maxima profile with an amorphous-like halo centered around 39 (2 theta). Also, the Bragg reflections observed are specific to our precise ADMET copolymers. In fact, the lowest angle reflection is common to both polymers, resulting in a d-spacing value of approximately 4.60 . The detailed examination of our precise methyl branched ADMET EP copolymers using WAXD, SAXS, and electron diffraction suggests that the packing of these polymers as triclinic. 180 A triclinic lattice enables better packing of pendent groups due to the inherent staggering, producing less free volume. There is an important difference between the methyl branched and the ethyl branched polymer. Polymers possessing precise methyl branching also contain a hexagonal sublattice, as suggested by the typical reflections of the basal plane. Based on the data observed for our EP model copolymers we can assign the 4.59 reflection or the (100) of the triclinic cell to HPEB21W. It is also apparent that the increased size of the branch causes a broadening of the main peaks as well as a merging of the two maxima. With this in mind, we can make defect correlations between the data obtained for the precise methyl and the ethyl branched polymers may be drawn.

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85 Figure 3-10. WAXD of precise ethyl branched EB copolymer HPEB21W (Top) and precise methyl branched EP copolymer HPEP21 (bottom). Since the polymers contain the same methylene sequence length, correlations based on defect identity alone can be made without the influence of inter and intra-chain inconsistencies or defects. Based on the x-ray similarities of HPEP21 and HPEB21, it seems that the ethyl branches get incorporated to some extent within the interior of the crystallite. They must act as packing defects; however, based on the WAXD data alone we cannot determine whether the ethyl branch is a favored point to initiate a chain fold. The broadening of the reflections is most likely caused by the

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86 smaller crystallite size produced by the increased steric demand of the ethyl group. Of course, the ethyl branch puts a larger constraint on the chain packing, which may result either in a large amorphous domain (typically centered around 19 2theta) or in a larger decrease in the long range order. When compared to the methyl copolymer, the precise ethyl branch polymer does exhibit a smaller enthalpy of melting; for example, 140 J/g for HPEP21 versus 58 J/g for HPEB21W. The IR study described earlier has shown a high content of defects relative to the normal trans conformation. These data support metathesis being a useful modeling tool producing unique material behavior by offering non-stereoregular branch placement, homogeneous primary structure, and interchain consistencies not available by chain-addition polymerization. 3.3 Conclusions Acyclic diene metathesis polymerization has proven to control the primary structure of ethylene/1-butene copolymers resulting in linear polyethylene containing only ethyl branches. In this effort, a simple synthetic method has been developed to produce exact linear model polymers on an industrial scale using ketodienes. The inherent ability of metathesis to control the polymers branch identity and placement has profound effects on the thermal and crystal behavior of these distinct EB materials resulting in a new class of LLDPEs. The structural investigation has shown that these ADMET EB copolymers favor ethyl branch inclusion producing a similar triclinic/hexagonal crystal structure obtained for our EP model copolymers. Moreover, these copolymers exhibit distorted methylene sequences with high concentrations of kink, gauche, and double gauche defects. The interand intra-homogeneity of the sequence length distribution in these materials produces lower melting points and higher melting enthalpies when compared to chain

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87 propagated EB polymers. In fact, the thermal behavior of these materials concludes that the MSL and its distribution are more controlled versus chain-addition chemistry and single site metallocene systems. Step polymerization also produces narrow monomodal melting profiles when branch content reaches approximately 45 ethyl branches/1000 carbons or 9 mol percent 1-butene. We are currently continuing this branched polyethylene research by gathering a better base of scattering data and understanding the differences between random and precise branch content. In addition, we are investigating precisely branched liner-low density materials containing hexyl and ultimately longer defects. 3.4 Experimental Section 3.4.1 Instrumentation and Analysis All 1 H NMR (300 MHz) and 13 C NMR (75 MHz) spectra were recorded on either a Varian Associates Gemini 300 or Mercury 300 spectrometer. Chemical shifts for 1 H and 13 C NMR were referenced to residual signals from CDCl 3 ( 1 H = 7.27 ppm and 13 C = 77.23 ppm) with 0.03% v/v TMS as an internal reference. Reaction conversions and relative purity of crude reactions were monitored by chromatography and NMR. Gas chromatography (GC) was performed on a Schimadzu GC-17 gas chromatograph equipped with a 25 m capillary column packed with a 5% crosslinked PH ME and flame ionization detector. Thin layer chromatography (TLC) was performed on Watman TM aluminum backed, 250 mm silica gel coated plates. Reverse phase chromatography was performed using C 18 functionalized silica gel (Aldrich) eluted with 3:2 acetonitrile/toluene. TLC plates for UV inactive olefin monomers were stained with either potassium permanganate (2%) in an aqueous solution of sodium bicarbonate (4%) or phosphomolybdic acid (10%) in ethanol after development to produce a visible

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88 signature. Low and high-resolution mass spectral (LRMS and HRMS) data were obtained on a Finnegan 4500 gas chromatograph/mass spectrometer using the electron ionization (EI) mode. Elemental analyses were carried out by Atlantic Microlabs Inc., Norcross, GA. HPLC was accomplished using a Ranin instrument equipped with Dynamax SD1 pumps, Dynamax UV-1 variable wavelength UV/VIS absorbance detector, and a Varian Star 9042 Refractive Index (RI) detector in series, and Dynamax FC-1 fraction collector. Two columns were utilized: 1) analytical or scout scale column with dimensions of 10.0 mm (inner diameter) by 250.0 mm. 2) preparative scale with dimensions of 41.4 mm (inner diameter) by 250.0 mm. Both columns were silica packed with a particle size of 8m 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. Gel permeation chromatography (GPC) was performed using a Waters Associates GPCV2000 liquid chromatography system with its internal differential refractive index detector (DRI), internal differential viscosity detector (DP), and a Precision 2 angle light scattering detector (LS). The light scattering signal was collected at a 15 degree angle, and the three in-line detectors were operated in series in the order of LS-DRI-DP. The chromatography was performed at 45 C using two Waters Styragel HR-5E columns (10 microns PD, 7.8 mm ID, 300 mm length) with HPLC grade tetrahydrofuran as the mobile phase at a flow rate of 1.0 mL/minute. Injections were made at 0.05-0.07 % w/v sample concentration using a 322.5 l injection volume. In the case of universal calibration, retention times were calibrated against narrow molecular weight polystyrene standards (Polymer Laboratories; Amherst, MA). All standards were selected to produce M p or M w

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89 values well beyond the expected polymer's range. The Precision LS was calibrated using narrow polystyrene standard having an M w = 65,500 g/mol. Fourier transform infrared (FT-IR) spectroscopy was performed using a Bio-Rad FTS-40A spectrometer. The hydrogenation of the unsaturated ADMET prepolymer was monitored by the disappearance of the out-of-plane C-H bend for the internal olefin at 967 cm -1 . Monomer was prepared by droplet deposition and sandwiched between two KCl salt plates. Unsaturated and hydrogenated polymer samples were prepared by solution casting a thin film from tetrachloroethylene onto a KCl salt plate. Differential scanning calorimetry (DSC) analysis was performed using a Perkin-Elmer DSC 7 equipped with a controlled cooling accessory (CCA-7) at a heating rate of 10 C/min. Calibrations were made using indium and freshly distilled n-octane as the standards for peak temperature transitions and indium for the enthalpy standard. All samples were prepared in hermetically sealed pans (5-10 mg/sample) and were run using an empty pan as a reference and empty cells as a subtracted baseline. Wide-angle X-ray Diffraction (WAXD) patterns were collected in point collimated, monochromatic Cu K radiation on a Bruker platform goniometer. The source was a Kristalloflex 760 2.2 kW generator and long fine focus tube equipped with cross coupled Gble mirror monomchromator and 200 m collimation. A HI-STAR area detector was mounted for data collection at 5.9 cm and referenced to corundum (alumina). Data were processed using GADDS program. The data presented are shown at 30 degrees 2theta and unwarped for inhomogeneous response in the flood field of the detector. 3.4.2 Materials Schrock's molybdenum catalyst [(CF 3 ) 2 CH 3 CO] 2 (N-2,6-C 6 H 3 -i-Pr 2 ) Mo=CHC(CH 3 ) 2 Ph was synthesized according to the literature procedure. 157-162 Grubbs’

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90 first generation ruthenium catalyst, bis(tricyclohexylphosphine)benzylidine ruthenium (IV) dichloride, was purchased from Strem and stored in an Argon filled dry box prior to use. The hydrogenation catalyst RuHCl(CO)(PCy 3 ) 2 was synthesized along with all starting ketones used in the Wittig approach according to literature procedures. 210,215-217 The corresponding phosphonium salts were synthesized via S n 2 displacement of the required bromoalkane with triphenylphosphine. Tetrahydrofuran (THF), dimethoxyethane (DME), toluene, and diethyl ether (Et 2 O) were freshly distilled from Na/K alloy using benzophenone as the indicator. A solution of 2 M potassium tert-butoxide (KOt-Bu) was prepared in a flame dried, argon purged Schlenk tube by combining the salt (Aldrich) with DME. All starting bromoalkenes were distilled from CaH 2 prior to use. Ethyl acetoacetate and diethylmalonate (Aldrich) were also distilled from CaH 2 prior to use. All other reagents were used as received. 3.4.3 Synthesis and Characterization of 3-(4-pentenyl)-7-octene (1) The synthesis has been reported in a previous dissertation by Dr. Jason A. Smith and been excluded from this experimental section. 3.4.4 Synthesis and Characterization of 3-(10-undecenyl)-13-tetradecene (2) Synthesis of 2-undec-10-enyl-tridec-12-enoic acid (12). The starting diester (11) was synthesized according to a previously published synthetic procedure. The saponification of compound 11 (11.5 g, 2.93 mmol) was done in the same reaction flask by addition of 100 mL of ethanol and 250 mL of 6 M NaOH. The reaction was refluxed for 48 hours. The solution was acidified using 12 M HCl and the organic layer was washed with DI water, dried over Na 2 SO 4 , and evaporated under reduced pressure. The crude diacid was then decarboxylated at 180 o C in decalin to aid the heat transfer. The mixture was then purified using flash column chromatography (4:1 ethyl acetate/hexane)

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91 to yield 10.5 g of 12. Yield 98.1 % (isolated). The following spectral properties were observed: 1 H NMR (CDCl 3 ): (ppm) 1.22-1.55 (m, br, 28H), 1.63 (m, 4H), 2.06 (m, br, 4H, allylic CH 2 ), 2.37 (m, 1H), 4.98 (m, 4H, vinyl CH 2 ), 5.82 (m, 2H, vinyl CH); 13 C NMR (CDCl 3 ): (ppm) 27.58, 29.34, 29.65, 29.68, 29.75, 29.77, 32.37, 34.03, 45.75, 114.31, 139.44, 183.14; EI/LRMS: [M] + cald. for C 24 H 44 O 2 : 364, found: 364. Synthesis of 12-bromomethyl-tricosa-1,22-diene (13). The reduction of the compound 12 was performed following a similar synthesis as compound 8 above. In this case, THF was used instead of diethyl ether. The product was not purified prior to bromide synthesis; however, the alcohol can be purified via flash chromatography using 4:1 hexane/ethyl acetate. The crude alcohol (8.20 g, 23.3 mmol) along with 100 mL of CH 2 Cl 2 and 7.94 g (24.0 mmol) of carbon tetrabromide were combined in an Ar purged 500 ml round bottom flask. Triphenylphosphine (7.35 g, 28.1 mmol) was added slowly to the reaction mixture to control heat evolution. Once the solution turns orange, it was allowed to stir for 4 hours and methanol was added to remove any excess orange color. The crude product was concentrated under reduced pressure and phosphine oxide was recrystallized from diethyl ether at -20 o C. The solution was filtered and the product was purified by flash chromatography using 100 % hexane as the eluent, recovering 9.18 g. Yield of 13: 95.3 % (Isolated). The following spectral properties were observed: 1 H NMR (CDCl 3 ): (ppm) 1.29 (m, br, 32H), 1.60 (m, 1H), 2.06 (m, 4H, allylic CH 2 ), 3.34 (d, 2H, CH 2 Br), 4.98 (m, 4H, vinyl CH 2 ), 5.82 (m, 2H, vinyl CH); 13 C NMR (CDCl 3 ): (ppm) 26.81, , 29.4, 29.74, 29.82, 30.03, 32.82, 34.07, 39.75, 39.90, 114.35, 139.45; EI/LRMS: [M] + cald. for C 24 H 45 Br: 413, found: 413.

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92 Synthesis of 3-undec-10-enyl-tetradec-13-enoic acid (14). In a flame dried, Ar purged 500 mL three-neck round bottom flask equipped with a condenser, 9.00 g (21.7 mmol) of 13, 0.793 g (32.6 mmol) of magnesium turnings, and 20 mL of diethyl ether were combined. The flask was placed in a sonicator for 2 hours. The flask was removed and solid CO 2 was added. The reaction was monitored by TLC using 4:1 hexane:ethyl acetate after acidic workup of the reaction aliquot. After completion, 3 N HCl was added, washed with DI water, dried over Na 2 SO 4 , filtered, and evaporated under reduced pressure affording 7.80 g. Yield of 14: 95.1 % (Crude). The crude product was purified via flash chromatography using 4:1 hexane:ethyl acetate yielding 5.31 g (64.7 %). The following spectral properties were observed: 1 H NMR (CDCl 3 ): (ppm) 1.29 (m, br, 33H), 1.85 (br, 1H), 2.06 (m, 4H, allylic CH 2 ), 2.28 (d, 2H, CH 2 COOH), 4.98 (m, 4H, vinyl CH 2 ), 5.82 (m, 2H, vinyl CH); 13 C NMR (CDCl 3 ): (ppm) 27.58, 29.34, 29.65, 29.68, 29.75, 29.77, 32.37, 34.03, 41.20, 114.35, 139.45, 176.89; EI/LRMS: [M] + cald. for C 25 H 46 O 2 : 378, found: 378. Synthesis of 12-(2-bromo-ethyl)-tricosa-1,22-diene (15). Compound 15 was synthesized and purified following the procedure used above for compound 13. Yield of 15: 93.8 % (Isolated). The following spectral properties were observed: 1 H NMR (CDCl 3 ): (ppm) 1.20-1.58 (br, 33H), 1.82 (q, 2H, CH 2 CH 2 Br), 2.06 (m, 4H, allylic CH 2 ), 3.42 (t, 2H, CH 2 Br), 4.96 (m, 4H, vinyl CH 2 ), 5.81 (m, 2H, vinyl CH); 13 C NMR (CDCl 3 ): (ppm) 26.63, , 29.36, 29.72, 29.81, 30.20, 32.53, 33.31, 34.04, 36.69, 37.48, 114.32, 139.48; EI/LRMS: [M] + cald. for C 25 H 47 Br: 427, found: 427. Synthesis of 3-(10-undecenyl)-13-tetradecene (2). In a flame dried, Ar purged 500 mL three-neck round bottom flask equipped with a condenser, 3.00 g (7.01 mmol) of

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93 15, 0.255 g (10.5 mmol) of magnesium turnings, and 20 mL of diethyl ether were added. The flask was placed in a sonicator for 2 hours. The flask was removed and quenched with 1 N HCl. The organic layer was then washed with DI water, dried with MgSO 4 , filterd, and evaporated under reduced pressure yielding 2.68 g (Crude). The product was purified using reverse-phase flash chromatography (C 18 functionalized silica gel) using 3:2 aetonitrile:toluene as the eluent (R f = 0.65), yielding 1.58 g (65.3 %) of monomer 2. 1 H NMR (CDCl 3 ): (ppm) 0.84 (t, 3H, -CH 2 CH 3 ), 1.28 and 1.37 (m, br, 35H), 2.05 (m, 4H), 4.96 (m, 4H, vinyl CH 2 ), 5.81 (m, 2H, vinyl CH); 13 C NMR (CDCl 3 ): (ppm) 11.14 (-CH 2 CH 3 ), 26.18 (-CH 2 CH 3 ), 27.00, 29.19, 29.40, 29.72, 29.90, 29.99, 30.36, 33.41, 34.12, 39.10 (-C(H)(CH 2 CH 3 ), 114.29 (vinyl CH 2 ), 139.49 (vinyl CH); EI/HRMS: [M] + calcd. for C 25 H 48 : 348.3756, found: 348.3758. Elemental analysis calcd. for C 25 H 48 : 86.12 C, 13.88 H; found: 86.25 C, 13.97 H. 3.4.5 Monomer Synthesis and Characterization of Wittig Monomers Synthesis of 3-(10-undecenyl)-2,13-tetradecadiene (3). The starting ketone was synthesized according to the literature procedure. 210 In a flame dried, Ar purged 250 mL round bottom flask equipped with a stirbar and 125 mL addition funnel, 5.00 g (14.9 mmol) of pure 16 and 8.31 g (22.4 mmol) of (ethyl)triphenylphosphonium bromide were added. A suspension was created using 50 mL of dry THF. A solution of 1 M (2.52 g, 22.4 mmol) potassium tert-butoxide (KOt-Bu) in THF was prepared and added to the addition funnel. The base was added drop wise over a 30 minute period at room temperature producing a yellow solution. After four hours, diethyl ether (50 mL) and 1 M HCl (50 mL) were added. The organic layer was washed with DI water, dried over MgSO 4 , filtered, and evaporated under reduced pressure. The resulting product was

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94 washed pentane, concentrated, and purified by flash chromatography using 100 % hexanes as eluent to yield 4.65 g. Yield of 3: 90 % (Isolated). The following spectral properties were observed: 1 H NMR (CDCl 3 ): (ppm) 1.34 (m, br, 28H), 1.63 (d, 3H, methyl), 2.06 (m, br, 8H, allylic CH 2 ), 5.01 (m, 4H, vinyl CH 2 ), 5.24 (q, 1H, internal olefin), 5.86 (m, 2H, vinyl CH); 13 C NMR (CDCl 3 ): (ppm) , 28.47, 29.20, 29.42, 29.78, 29.86, 29.92, 30.02, 34.07, 37.28, 114.30, 118.22 (vinyl CH 2 ), 139.32 (vinyl CH), 140.80; EI/HRMS: [M] + cald. for C 25 H 46 : 346.3599, found: 346.3591; Elemental analysis calcd. for C 25 H 46 : 86.62 C, 13.38 H; found: 86.57 C, 13.50 H. Synthesis of 3-(7-octenyl)-2,10-undecadiene (4). Compound was synthesized as above. Yield of 4: 92.4 % (Isolated). The following spectral properties were observed: 1 H NMR (CDCl 3 ): (ppm) 1.34 (m, br, 28H), 1.63 (d, 3H, methyl), 2.06 (m, br, 8H, allylic CH 2 ), 5.01 (m, 4H, vinyl CH 2 ), 5.24 (q, 1H, internal olefin), 5.86 (m, 2H, vinyl CH); 13 C NMR (CDCl 3 ): (ppm) , 28.38, 29.15, 29.34, 29.56, 29.82, 29.86, 34.05, 37.21, 114.34, 118.31 (vinyl CH 2 ), 139.38 (vinyl CH), 140.74; EI/HRMS: [M] + cald. for C 19 H 34 : 262.2660, found: 262.2653; Elemental analysis calcd. for C 19 H 34 : 86.94 C, 13.06 H; found: 86.93 C, 13.09 H. 3.4.6 General Polymerization Conditions All glassware was thoroughly cleaned and flame dried under vacuum prior to use. The monomers were dried over CaH 2 and Na mirror, and subsequently degassed prior to polymerization. All metathesis reactions were initiated in the bulk, inside an Argon atmosphere glove box. The monomers were placed in a 50 mL round-bottomed flask equipped with a magnetic Teflon TM stirbar. The flasks were then fitted with an adapter equipped with a Teflon TM vacuum valve. After addition of catalyst, slow to moderate

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95 bubbling of ethylene was observed. 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 while stirring in an oil bath at 30 C until the viscosity increases. Generally after 4 h, the polymerization was exposed to full vacuum (<10 -1 mm Hg) for 24 h and then high vacuum (<10 -3 mm Hg) for 96 h, gradually increasing temperature to 50 C during the last 24 h of polymerization. The reaction vessel was then cooled to room temperature, exposed to air and toluene was added. The mixture was heated to 80 C in order to dissolve the resultant polymer and decompose any remaining active catalyst. The polymer/toluene solution was taken up and precipitated dropwise into a vigorously stirred beaker containing 1500 mL of acidic methanol (1 M). Polymerization of 3-(4-pentenyl)-7-octene (1) to give UPEB9. The synthesis has been reported in a previous dissertation by Dr. Jason A. Smith and been excluded from this experimental section. Polymerization of 3-(10-undecenyl)-13-tetradecene (2) to give UPEB21. Grubbs’ first generation [Ru] catalyst (2.62 mg, 3.18x10 -3 mmol) was added to monomer 2 (0.50 g, 1.4 mmol). Precipitation yielded 0.47 g of a spongy white solid. Yield: 94.2 % (after precipitation). 1 H NMR (CDCl 3 ): (ppm) 0.83 (t, 3H, methyl), 1.26 (m, br, 35H), 1.97 (m, br, 4H), 5.38 (m, br, 2H, internal olefin); 13 C NMR (CDCl 3 ): (ppm) 11.11, 26.13, 27.00, 27.47, 29.45, 29.59, 29.81, 29.94, 29.99, 30.43, 32.87, 33.48, 39.11, 130.12 (cis olefin), 130.59 (trans olefin). 13 C NMR (CDCl 3 ) integration of cis:trans peaks gives: 12:88. GPC data (THF vs. polystyrene standards): M w = 56 100 g/mol; P.D.I. (M w /M n ) = 2.01.

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96 Polymerization of 3-(10-undecenyl)-2,13-tetradecadiene (3) to give UPEB21W. Grubbs’ first generation [Ru] catalyst (7.91 mg, 9.61x10 -3 mmol) was added to monomer 3 (1.50 g, 4.32 mmol). Precipitation yielded 1.47 g of a white spongy solid. Yield: 98.0 % (after precipitation). 1 H NMR (CDCl 3 ): (ppm) 1.26 (m, br, 28H), 1.58 (d, 3H, methyl), 1.97 (m, br, 8H), 5.19 (q, 1H, olefin), 5.38 (br, 2H, internal olefin); 13 C NMR (CDCl 3 ): (ppm) 13.75, 27.50, 28.49, 28.54, 29.45, 29.58, 29.80, 29.87, 29.90, 29.96, 30.03, 32.87, 37.29, 118.20, 130.12 (cis olefin), 130.59 (trans olefin), 140.95. 13 C NMR (CDCl 3 ) integration of cis:trans peaks gives: 15:85. GPC data (THF vs. polystyrene standards): M w = 50 200 g/mol; P.D.I. (M w /M n ) = 1.93. Polymerization of 3-(7-octenyl)-2,10-undecadiene (4) to give UPEB15W. Grubbs’ first generation [Ru] catalyst (8.37 mg, 1.02x10 -3 mmol) was added to monomer 4 (1.20 g, 4.57 mmol). Precipitation yielded 1.15 g of a white solid. Yield: 95.8 % (after precipitation). 1 H NMR (CDCl 3 ): (ppm) 1.29 (m, br, 16H), 1.57 (d, 3H, methyl), 1.96 (m, br, 8H), 5.17 (q, 1H, olefin), 5.38 (br, 2H, internal olefin); 13 C NMR (CDCl 3 ): (ppm) 13.41, 27.44, 28.40, 28.44, 29.35, 29.60, 29.88, 32.84, 37.21, 118.22, 130.08 (cis olefin), 130.58 (trans olefin), 140.84. 13 C NMR (CDCl 3 ) integration of cis:trans peaks gives: 18:82. GPC data (THF vs. polystyrene standards): M w = 53 100 g/mol; P.D.I. (M w /M n ) = 1.96. 3.4.7 General Hydrogenation Conditions Hydrogenation was performed using a 150 mL Parr high-pressure stainless steel reaction vessel equipped with a glass liner and a Teflon TM stirbar. The unsaturated polymer was first taken up into 50 mL of toluene (UPEB9 and UPEB21) or 100 mL of chlorobenzene (UPEB21W and UPEB15W). To the pre-tared glass liner was added 1

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97 eq. of 10 % palladium on activated carbon (UPEB9 and UPEB21) or 5 w/w % of RuHCl(CO)(PCy 3 ) 2 (UPEB21W and UPEB15W) followed by pipette addition of the polymer solution. The glass liner was placed into the bomb and the bomb sealed. The Parr vessel was purged with 150 p.s.i. (3x) of Grade 5 hydrogen gas (H 2 ) in order to minimize oxygen and water introduced from the atmosphere. The bomb was charged to 500 p.s.i. (Pd systems) or 2000 p.s.i. (Ru systems) and the mixture was stirred for 24 h at 50 C followed by 96 h at 80 C (120 h total). The resultant polymer was filtered and precipitated into acidic methanol (1N stock solution prepared with HCl) to obtain a finely dispersed white solid. The polymer was filtered and dried under high vacuum (3 x 10 -4 mm Hg) at 70 C for 5 days. Hydrogenation of UPEB9 to produce HPEB9. The synthesis has been reported in a previous dissertation by Dr. Jason A. Smith and been excluded from this experimental section. Hydrogenation of UPEB21 to produce HPEB21. Hydrogenation was performed using palladium on carbon according to the above procedure. Precipitation yielded 1.12 g (98.1 %) of a white spongy material. 1 RCDCl 3 (ppm) 0.83 (t, 3H, methyl), 1.25 (br, 43H); 13 C NMR (CDCl 3 ): (ppm) 11.14, 26.15, 27.01, 30.01, 30.44, 33.48, 39.12. GPC data (THF vs. polystyrene standards): M w = 54 100 g/mol; P.D.I. (M w /M n ) = 1.78. DSC Results: T m (peak melting temperature) = 34.6 o C; h m = 50.9 J/g. Hydrogenation of UPEB21 to produce HPEB21W. Hydrogenation was performed using ruthenium according to the above procedure. Precipitation yielded 0.990 g (96.1 %) of a white spongy material. 1 RCDCl 3 (ppm) 0.83 (t, 3H, methyl), 1.25 (br, 43H); 13 C NMR (CDCl 3 ): (ppm) 11.14, 26.15, 27.01, 30.01, 30.44, 33.48,

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98 39.12. GPC data (THF vs. polystyrene standards): M w = 50 700 g/mol; P.D.I. (M w /M n ) = 1.90. DSC Results: T m (peak melting temperature) = 34.3 o C; h m = 50.2 J/g. Hydrogenation of UPEB15W to produce HPEB15W. Hydrogenation was performed using ruthenium according to the above procedure. Precipitation yielded 1.10 g (95.9 %) of a white spongy material. 1 RCDCl 3 (ppm) 0.84 (t, 3H, methyl), 1.27 (br, 31H); 13 C NMR (CDCl 3 ): (ppm) 11.13, 26.12, 26.98, 29.97, 30.41, 33.44, 39.09. GPC data (THF vs. polystyrene standards): M w = 54 200 g/mol; P.D.I. (M w /M n ) = 1.91. DSC Results: T m 1 (peak melting temperature) = -32.8 o C; h m 1 = 16.7 J/g and T m 2 (peak melting temperature) = -5.6 o C; h m 2 = 6.6 J/g.

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CHAPTER 4 LINEAR-LOW DENSITY POLYETHYLENE CONTAINING PRECISELY PLACED HEXYL BRANCHES 4.1 Introduction Polymers based around the selective homopolymerization of ethylene or through its copolymerization with -olefins have been produced for almost 60 years to manipulate linear polyethylene’s base material properties. 44-61,91-102 Enhancements to the world’s simplest macromolecule can be accomplished using numerous methods based on catalyst or initiator choices, chain transfer events, monomer types (or feed), reactivity ratio manipulations, or temperature and pressure variations. Overall, these events produce defects to alter the polymers stiffness, tensile strength, processability, and softening temperature due to changes in branching and its distribution (SCBD). 172 The various types of copolymers can be classified into groups based on the nature or method of this “defect” incorporation. In the current polyolefin market, linear-low density polyethylene (LLDPE), the linear copolymers of ethylene and an -olefin offer enhanced behavior over all other structural version of polyethylene. The widespread interest in LLDPE materials is due to the excellent combination of processability and good mechanical performance caused by their low densities and relative homogeneous linear backbone. Commercial LLDPEs are produced using a multitude of systems based on either Ziegler-Natta or metallocene catalysts. The less effective Ziegler-Natta systems tend to favor high ethylene insertion rates yielding ill-defined and heterogeneous primary structures. 275-277 Also, these systems tend to produce low-molecular weight materials and 99

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100 high molecular weight distributions originating from their tendencies for multi-site initiation. In contrast to conventional Ziegler-Natta catalysts, metallocenes provide copolymers with narrower composition distributions, narrower molecular weight distributions, and higher levels of comonomer incorporation. 278-302 Several researchers have shown that the coordination geometry of metallocenes play an important role in the final structure of the copolymer. 300 In fact, the manipulation of such catalytic systems is often used to alter and vary the behavior of LLDPEs. Practical application of these systems has been the development of constrained geometry catalysts (CGC) based on ansa-monocyclopentadienylamido group 4 metal complexes. Initially developed by Bercaw and researchers at Exxon, their high catalytic activity and ability to generated macromonomers have produced copolymers with excellent processablitiy and mechanical properties. 298 The plethora of materials synthesized using either metallocene or Zeigler-Natta systems have motivated research groups to study the behavior of LLDPEs produced using these chain-addition techniques. 303-345 Regardless of the polymerization method random errors introduce unavoidable defects causing molecular heterogeneity, and hence, heterogeneous structures. Overall the documented average defect content in metallocene synthesized polyolefins has been narrow, reactivity ratio variations yield copolymers with locally heterogeneous structures due to uncontrollable insertion rates. The addition of these defects is widely used to manipulate the base polyolefin material, however detrimental when attempting to model structure/property behavior. Our approach in the modeling of ethylene-based copolymers has been based on organic synthesis instead of indirect catalyst/comonomer adjustment. In this fashion, the primary structure of any

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101 LLDPE can be predetermined through the easily purified macromonomers in contrast to indirect methods (catalyst and temperature) which tend to cause an additional level of encumbrance when modeling systems based on a sole comonomer. Figure 4-1 demonstrates the retro-synthesis using the clean, step polymerization chemistry offered by acyclic diene metathesis (ADMET) to produce compositionally precise LLDPEs, outlined for ethylene/1-octene owning to known branch identity and placement. Figure 4-1. Modeling precisely branched ethylene/1-octene copolymers using organic methods. The first example of this methodology was the synthesis of five model ethylene/propylene (EP) copolymers in which the methyl branch was precisely placed on each and every 9 th , 11 th , 15 th , 19 th , and 21 st carbon along the backbone, respectively. 171 Continuation of this research led to the development of structural homogeneous copolymers of ethylene and 1-butene (EB) containing symmetrically displaced ethyl branches. 346 The copolymers produced using these methods have exhibited unique thermal and structural behavior in effect creating a new class of PE based materials. In order to validate the behaviors observed in the precise studies, a series of random methyl branched polyethylene was produced using ADMET copolymerization. 204 Through these

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102 initial studies it was concluded that the morphology of these model copolymers results solely from the precise control of primary structure in turn enabling access to never observed behavior. We now report the polymer synthesis, characterization, and thermal analysis for our most recent attempt to produce LLDPEs as models for chain-addition copolymers of ethylene and 1-octene. The ADMET polymerization of the symmetrically hexyl substituted monomers and their subsequent hydrogenation has yielded copolymers containing a hexyl on each and every 9 th , 15 th , and 21 st carbon. The resulting ADMET copolymers are based on a linear polyethylene backbone without the influences from unwanted branch content, heterogeneous branch distributions, and inter-chain heterogeneity. Herein, we also present a universal synthesis to yield pure , -diene monomers containing any length alkyl branch using commercially available alkyl bromides. 4.2 Results and Discussion 4.2.1 Monomer Synthesis and Characterization The study of ethylene copolymers, largely their linear-low density analogs, has centered on chain-addition polymerization where the copolymers architecture is modified by a selective choice of either transition metal, monomer type, or monomer feed control. 103-129,134-155,275-302 As mentioned, our approach to investigate LLDPEs was to allow organic synthesis instead of indirect manipulation to modify the polymer’s primary structure. The major advantage of this approach is the inherent ability to govern the copolymer’s properties by the appropriate organic building block resulting in a single repeating unit independent of catalyst choice or monomer feed ratios. Coupling the

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103 correct monomer synthesis with a consistent and error free polymerization mechanism allows for the production of precise macromolecules. In the past, monomer synthesis to consistently produce pure alpha olefin functionality and branch purity has proven difficult and numerous methodologies have been investigated to encompass both purity requirements. 171,346 Figure 4-2 illustrates the first example of a universal synthetic methodology with the ability to produce any branch identity/frequency from a common starting material. The starting compounds used to synthesize the precise EO monomers, outline in Figure 4-2, were modified from an earlier published procedure by Wagener. 347 Compound 7 was synthesized using sodium hydride and a respective bromoalkene, followed by decarboxylation of the resulting diacid. The monoacid is reduced into the primary alcohol and directly converted to the sulfonic acid ester (9) using mesyl chloride. The protected alcohol can be made in batch quantities and used as the starting point for any symmetrical displaced alkyl branch. Using the above materials as a starting point, a detailed study centered on developing a universal coupling reaction to insert the branch functionality regardless of the starting alcohol. To add further utility, the use of a simple and inexpensive branch precursor was also investigated. Typically, the coupling of carbon moieties to existing structures is mediated via a transition metal complex; such has nickel or palladium, which tends to have high -olefin binding affinities. These large binding rates compete with substitution leading to olefin isomerization even with low metal concentrations (0.5 mol %). Of course, olefinic binding kinetics restricts the choice of possible routes used to produce pure -olefin branched diene monomers. However, using softer metals to perform the catalytic branch/monomer coupling can effectively alleviate isomerization.

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104 In the past, copper based complexes have shown a wide range of utility in carbon-carbon bond formation from either the starting Grignard or lithium reagents and are softer than nickel or palladium. The most common routes are based on organocuprate (I) or Gilman reagents, R 2 CuLi, which have shown high selective substitutions with alkyl, alkenyl, aryl halides or tosylates. 348-350 However, the available starting lithium reagents limit the production of Gilman complexes as well as the need for high excess of the organocuprate (500%) to achieve moderate yields. Also, “lower order” cuprates have difficulty in substitutions at highly hinder reaction centers. “Higher order” cuprates overcome these shortcomings but still at the expense of high catalyst loadings and the starting lithium reagent. Figure 4-2. Synthetic method utilized to produce model EO monomers. The highly hindered center in our monomers and the lack of commercially available lithium reagents resulted in an investigation into modifying and softening the basicity of Grignard reagents. Selective conjugated additions and homoaddition of Grignards have been well documented by the addition of copper iodine and can be

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105 realized with copper loadings as low as one mol percent. 351 In fact, the addition of copper iodine to a solution of compound 9 with the respective alkyl magnesium reagent generated low yields (<5%) of the hexyl branched monomer. Complete uptake of the starting mesylated alcohol was obtained, however conversion was to the reduced methyl branched monomer. Two basic approaches can be used to alleviate this competing reduction mode of alkyl cuprates thru the formation of heterocuprates. The fundamental idea is the addition of a nontransferable group aids in alkyl transfer and hinders the intermolecular reduction. These heterocuprates are produced through the bonding of copper with either a sp or sp 2 carbon (e.g. alkenyl or 2-thienyl) or the attachment of a heteroatom based ligand such as sulfur or nitrogen. In the past, Burns et al. have investigated the coupling of alkyl sulfonates with Grignard regents using highly efficient soluble thiocuprates. 352 A series of model reactions were performed to investigate the substrate effects encountered in the synthesis of our symmetrically positioned hexyl branched dienes. Overall, the optimal results were obtained using the mesylated-protected alcohol (9), 10 mol percent of the cuprate, and the addition of HMPA with mild heating of the reaction mixture. The clean and efficient chemistry afforded using this system (illustrated in Figure 4-4a) and the availability of starting alkyl magnesium reagents has expanded the scope of ADMET to model long chain branching in LLDPEs. 4.2.2 ADMET Polymerization and Hydrogenation Chemistry In the past Acyclic Diene Metathesis (ADMET) has been shown useful for the synthesis and modeling of perfectly branched polymer structures (Figure 4-3). 156,171 The mechanism of step-condensation metathesis offers control over molecular weight, polydispersity, branch identity, and branch frequency in the final material. Also,

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106 metathesis allows for complete conversion of the monomer functionality to the growing polymer chain without influences of chain transfer resulting in a purely linear PE backbone. As illustrated in Figure 4-3, ADMET produces high polymer from a metal mediated coupling of two terminal olefins driven by the condensation of ethylene. The consequence of this polymerization control allows for branch identity and type to be a function of monomer selection. Figure 4-3. Acyclic Diene METathesis (ADMET) polymerization. The ADMET chemistry proceeds cleanly to yield a linear, unsaturated polymer that is comprised of only one type of repeat unit, plus the usual amount of cyclics (<1-2%) found in bulk polycondensation conversions. Metathesis, similar to all step-condensations, requires high monomer purity to obtain high conversion. The most effective methods have been outlined in the past, ultimately leading to monomers dried over metal mirrors. The polymerization proceeds efficiently using Schrock’s catalyst 157-162 with typical catalyst loadings (750:1, monomer:catalyst) followed by the exhaustive hydrogenation over palladium on carbon (10 wt% Pd/C). The hydrogenations can be completed over 4 days and purified by simple precipitation in acidic methanol (1 M). As noted previously, the efficiency of hydrogenation can easily be quantified by both infrared (IR) spectroscopy, gathered by observation of the out-of-plane C-H bend in the alkene, and NMR analysis. 204

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107 The molecular weights of the model copolymers are displayed in Table 4-1 and confirm that the ADMET prepolymer is not affected by the hydrogenation conditions employed. The decrease in the molecular weight data observed for LLALS should be expected because of the differing dilute solution behavior of PE versus PS not due to scissoring of the polymer chains. Independent of determination method, the molecular weights for the ADMET EO copolymers are sufficiently high to model 1-octene LLDPEs coinciding with earlier experiments. 156,171,204 Table 4-1. Molecular weights and structural data for ADMET model EO materials. Model EO Copolymer Hexyl on every n th backbone carbon a Branch Content Methyls b Hexyls c Unsaturated Relative d Saturated Relative d LALLS e n Per 1000 carbons b,c M w x 10 -3 (PDI) f HPEO9 9 67 111 58.2 (1.8) 55.6 (1.7) 27.1 (1.8) HPEO15 15 48 67 44.5 (1.8) 47.2 (1.8) 26.2 (1.8) HPEO21 21 37 48 44.6 (1.8) 46.1 (1.7) 25.8 (1.8) A) Branch content based on the hydrogenated repeat unit. B) Branch content measured as methyls/1000 total carbons (include the branch carbons). C) Branch content measured as hexyls/1000 backbone carbons (excluding the branch). D) Molecular weight data taken in tetrahydrofuran (40 o C) relative to polystyrene standards. E) Molecular weight data taken using low-angle laser light scattering (LALLS) in tetrahydrofuran at 40 o C. F) Polydispersity index (M w /M n ). As with all our metathesis generated model copolymers their nomenclature is based on the parent chain-addition copolymer. All copolymers begin with the prefix HP (hydrogenated polymer) followed by the comonomer type (EO, ethylene/1-octene) and the precise branch frequency (21); for example HPEO21, is designated as the hydrogenated ethylene/1-octene copolymer containing a hexyl branch on every 21 st carbon. Due to the exact nature of the polymers produced, the comonomer content can be easily calculated using the branch frequency (n) following the relationship:

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108 mol % comonomer =2n 100x In order to develop a better understanding of polyethylene behavior during crystallization, copolymers with high comonomer content were pursued and attempts to determine the minimal methylene sequence length were investigated. Table 4-1 lists the branch content of the copolymers produced either based on the total number of carbons or backbone carbons alone. As mentioned earlier, the polymers have exact primary structures and are the first examples of EO copolymers containing precisely placed hexyl branches on each and every 9 th , 15 th , and 21 st carbon along polyethylene’s linear backbone. 4.2.3 Structural Data – Solution The ability to control the copolymers primary structure allows for an opportunity to gather a wealth of information on the macromolecular structure of any ethylene-based material without chain transfer influences and heterogeneous comonomer incorporation. Metathesis has been proven a useful tool to control the primary and secondary structure of polymers and this unique control and insight into branch effects can be realized by examination of the 13 C spectra of a monomer/copolymer transformation. The solution behavior of these model copolymers tends to mimic our previously synthesized model LLDPEs. Due to the high comonomer incorporation the copolymers are highly soluble in typical organic solvents used for polyolefin macromolecules. Figure 4-4 shows the carbon spectra for an ADMET polymerization from monomer to unsaturated polymer followed by its complete hydrogenation to produce the model copolymer HPEO9. Comparisons to either linear small molecules or our methyl and ethyl branched copolymers indicates precise structures with distinct branch and main chain resonances.

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109 Figure 4-4. A comparison of 13 C NMR spectra for a typical ADMET polymerization transformation. A) Monomer 1, B) ADMET unsaturated prepolymer, and C) HPEO9. The clean and complete nature illustrated in Figure 4-4 results from carbons observed for one polymeric repeat unit, typical of ADMET polymerizations. The spectral data supports the formation of a single repeating unit as evident by the disappearance of the external olefins from monomer 1 (114 and 139 ppm) to a single cis:trans internal

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110 olefin observed at 129.9 and 130.3 ppm, respectively. Further, the 13 C NMR confirms the exhaustive hydrogenation by the lack of the internal sp 2 carbons found in the unsaturated polymer. Upon close inspection HPEO9’s repeating unit and the spectral data both consist of eleven different carbons. The model copolymers give the typical side chain hexyl branch resonances, specifically 14.4 ppm (-CH 3 ) and 23.0 ppm (-CH 2 CH 3 ) along with the branch point carbon resonating at 37.7 ppm. 4.2.4 Thermal Behavior Commercially ethylene/1-octene (EO) copolymers constitute the largest volume LLDPE with numerous studies being performed on their thermal and material behavior annually. 303-345 Attempts to correlate initial monomer feed ratios to final material’s responses are under investigation in order to develop structure/property functions to cost effectively mass-produce LLDPEs. Our goal is to develop a separate and fundamental understanding of the relationship between comonomers and branch frequency. The initial approach is to investigate the model copolymers crystallization behavior and probe the crystallization kinetics of these new materials. Similar to the results obtained for our ADMET synthesized EP 171 or EB 346 copolymers, density, enthalpy, degree of crystallinity, and peak melting/recrystallization points all decrease as the amount of comonomer (1-octene) is increased. Figure 4-5 shows the thermal profile for HPEO9, the model copolymer containing a hexyl branch on every 9 th backbone carbon of polyethylene suggesting a completely amorphous behavior. The data presented comes as no surprise due to the short methylene sequences between branch points resulting in small sequence lengths. In fact, the ADMET copolymer exhibits the exact same glass transition temperature (-78 o C) and behavior as for metallocene synthesized EO copolymers. 278-302 However, repeated DSC

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111 scans reveal a common and reproducible transition with an onset of o C. It is unclear at this point if the onset is either a melt transition based on small crystallizable regions or a second relaxation endotherm. For HPEO9, annealing experiments and heating rate variations seem to indicate the heat flow originates from a relaxational mode not semi-crystallinity. It should be pointed out that a similar profile is commonly observed in semi-crystalline branched chain-addition copolymers. Upon sample annealing the onset of the observed peak is unaltered. Moreover, a plot of molar branch content versus peak melting point, a complete series comparison to HPEO15 and HPEO21, would suggests a melting point below that of the glass transition temperature. Figure 4-5. Thermal profile of the model EO copolymer containing a hexyl branch on each and every 9 th backbone carbon, HPEO9. The second model copolymer, HPEO15, turns out to exhibit semi-crystalline nature as illustrated in Figure 4-6. An increase in the methylene sequence length in turn produces a sharp and well-defined melting profile having a peak melting point of -48 o C.

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112 Also, at high sample loadings a second profile can be observed at -17 o C owning to only a small fraction of the overall heat flow. It is uncertain if this transition is caused by kinetic restraints brought out by its high concentration in the DSC pan or a second thicker crystal regime. Regardless of HPEO15’s melting profile it’s the first semi-crystalline example of a precise melting EO copolymer containing high comonomer content (13-14%) and uniform methylene sequence length. Similar results have been observed for metallocene produced copolymers of ethylene and 1-octene with an average branch distribution centered on our ADMET content. It should be noted that the peak melting temperature in the metallocene samples are substantially higher (~150 o C) with a considerable premelting region. 310 Figure 4-6. The DSC melting and recrystallization thermograph for HPEO15. The initial attempt to synthesis and model ethylene/1-octene copolymers was completed by examination of HPEO21 producing the thermal profile shown in Figure 4-7. Similar to all previous model copolymers a sharp and well-defined endotherm is

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113 observed having a peak melting temperature of 16 o C. Unlike the previous copolymer HPEO15, the placement of a hexyl branch on every 21 st carbon produces only a single melting peak. It is interesting to note the well-defined endotherm, lacking any visible premelting region, is similar to HDPE materials exhibiting little or no branch defects. In fact, the peak observed for HPEO21 mimics the melting nature of our EP copolymer, HPEP21, albeit at a lower temperature. Of course, the thermal analysis of well-defined structures produces well-defined transitions. The heat flow for HPEO21 is rather high (53 J/g) when compared to either the EP or EB coinciding with the previous HPEB21 containing an ethyl branch on every 21 st carbon. Figure 4-7. The DSC melting and recrystallization thermograph for HPEO21. It is also interesting to note the reappearance of the transition at -51 0 C. It would seem that our precise hexyl branched polymer series show the same relaxation temperature independent of methylene length. Moreover, the transition seems to be common to all ADMET LLDPE materials and can be commonly observed in the majority of branched chain-addition copolymers. The transitions independence on sequence

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114 length and crystallinity indicates its correspondence to the -relaxation produced by pendent side group motional relaxation. The consistent behavior of side group motion is not uncommon as they have also been observed to be independent of pressure effects in polypropylene indicating main chain methylene segments act independently of side motion or their positional local. Under the conditions used to monitor the thermal behavior of these copolymers, HPEO9 yields two distinct relaxational pathways reinforcing the idea of branch motional segregation. Examination of the copolymers presented in this series and further comparisons to other ADMET models has brought about interesting questions. For example, the crystallization kinetics observed across the documented ADMET series shows unique trends. The crystallization kinetics observed for HPEO15 seems to be unique to this class of ADMET copolymers. Comparisons to previously synthesized ADMET model EP and EB copolymers show different rates of super cooling dependent on branch type. In all cases the copolymers were examined under a cooling rate of 10 o C/min; however, the temperature differences between the peak melting and recrystallization endotherms gets narrower. The series following the trend HPEP15, HPEB15, and HPEO15 have observed differences of 12 o C, 10 o C, and 8 o C, respectively. These differences may be realized by the formation of smaller crystallites and as a result faster recrystallization kinetics. On the other hand, comparisons of the 21 st branch frequency copolymers do not observe this trend. The data follows a 12 o C, 18 o C, and 11 o C temperature lag between the crystallization and recrystallization peaks for the copolymers HPEP21, HPEB21, and HPEO21. The observed differences may be a function of defect content or the longer run methylene run lengths produced by an increase in trans-segments. Without further

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115 investigation, a complete change in crystal structure or morphology between HPEO15 and HPEO21 can not be ruled out. Figure 4-8. Thermal comparison of HPEO21, HPEB21, and HPEP21. As indicated thermal analysis seems to indicate small crystallite structures represented by the lower melting peaks when compared to the EP copolymer series; 171 however, the crystallization/recrystallization enthalpies seem to be completely non-uniform across the same series. Also, increasing the branch length when spanning the copolymers containing the same methylene sequences results in a distinct change of the characteristic melting peak following the apparent kinetic fluctuations observed during crystallization. The major distinction can be observed by the loss and reappearance of a well-defined endotherm when spanning the series (Figure 4-8). This trend is observed regardless of the frequency subset compared perhaps offering information about branch crystallization and crystal incorporation. Figure 4-8 illustrates the calorimetric

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116 differences collected by keeping the branch frequency constant while systematically increasing the branch length. Figure 4-9. Graphic comparison for the precise branched ADMET series. Colored bars and solid black bars represent peak melting data and heat of fusions respectively. In the case of multimodal melting two bars are presented. Closer inspection of the entire ADMET copolymer series with the aid of Figure 4-9 reveals that an increase in the side chain bulk produces inconsistent trends not easily understandable. The melting point depression should not come as a surprise as this phenomenon is well documented, but the leveling of enthalpies can be observed regardless of branch bulkiness or frequency with the exclusion of methyl defects raises some questions. Also, the formation of well-defined thermal profiles for the EO copolymer series is interesting, having no comparison in either homogeneous metallocene or CGC systems produced by chain-addition. As mentioned, throughout the study the ADMET EO copolymers resemble our EP copolymers perhaps indicating some branch inclusion. The lack of density measurements, crystal structure data, and long

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117 spacing measurements for these ADMET EO polymers limits the correlations between branched models. However, formation of lamellae structures or any crystalline structure seems highly unlikely in HPEO15 due to the small methylene sequence length and high concentration of trans-segments without side chain involvement. The question of side chain self-crystallization can be ruled out since HPEO9, containing the highest concentration of branch defects, yields no melting endotherms in conjunction with only a single well-defined melting peak for HPEO21. In order to answer question about branch position and inclusion, a series of solid state experiments were conducted using both infrared spectroscopy and NMR analysis. 4.2.5 Structural Data – Solid State A wealth of information can be collected using infrared (IR) spectroscopy to observe and understand chain defects brought about by an increase in defect content. Efficient correlations have been demonstrated between absorbance values and macromolecular packing as well as the assignment of chain defects modes in polyethylene materials. Also, detailed infrared studies on previous ADMET copolymers have revealed connections of inter-chain defects to crystal behavior and crystal packing. 204 The limited correlation between defect content and crystal structure using these techniques is somewhat surprising based on the ease of measurement. In the past, Tashiro et al. carried out a study of branching behavior on polyethylene packing using wide-angle x-ray diffraction (WAXD) supplemented by infrared spectroscopy. 179 Unfortunately, our ability to further compare the solid state data gathered using IR with WAXD is limited due to the rather low melting points of either semi-crystalline copolymer. However, detailed structural analysis can be made based on

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118 the well-defined absorbencies for the kink and double gauche defects following the 1366 cm -1 (1305 cm -1 ) and 1352 cm -1 bands, respectively. Figure 4-10. Infrared absorbencies for the ADMET model EO copolymers. In Figure 4-10, the IR spectra for the saturated ADMET EO copolymers are dominated by the two peak absorbencies observed for an unorganized packing structure. Moreover, the ADMET EO copolymers exhibit no signs of the characteristic absorbencies of an orthorhombic crystal or the symbolic Davidov splitting in the methylene rock region (~720 cm -1 ). However, a faint doublet is witnessed in the methylene scissoring band (~1460 cm -1 ) containing a broader lower wavenumber shoulder resulting from the highly distorted trans-polyethylene segments. Increasing the methylene sequence length causes the two distinct absorbencies (1461 and 1465 cm -1 ) to become more defined forgoing any influences to the methylene wagging band (722 cm -1 ). The two experimental peaks at 722 cm -1 and 1465 cm -1 have been assigned to the

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119 hexagonal phase of polyethylene and have been observed in the previously synthesized ADMET copolymer containing a methyl group on every 9 th backbone carbon. 171 Also, the additional observed scissoring absorbance at 1461 cm -1 and the accompanied shoulder is consistent with observation made in our detailed EB copolymer study. 346 Previously, the observed resonances have had separate origins in each copolymer series based on different branch incorporation mechanisms. The EO LLDPE series causing the merging of these previous separate resonances despite the larger steric demand brought about by the precise hexyl branch. Interestingly, the larger defect volume does not seem to further alter either the methylene scissoring or wagging regions with the observed methylene wagging absorbance (722 cm -1 ) being more consistent with the methyl copolymer series. The consensus that the majority of hexyl branches are excluded from crystallizing lamellae and their higher free volume should suggest the observed spectra (IR and DSC) would tend to mimic the EB copolymers. However, this is not the case. As discussed previously, the thermal investigation of the precise EO copolymers tends to resemble and mimic the profiles obtained for the precise methyl branch series. The present data collection set favors partial hexyl branch inclusion particularly based on the thermal profiles. Of course, under equilibrium conditions the branches, even methyl, are assumed to be rejected from the growing crystallites. 175,235 Over the years, Flory’s equilibrium theory has been modified to allow for short chain (methyl and ethyl) branch inclusion accounting for the collected experimental evidence. 175,235 Specifically, ethyl side groups have been thought to be on a boundary condition between inclusion and exclusion with segregation being a function of crystallization conditions. Up to this point there has been some debate whether larger branches, such has hexyl, could be included within the

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120 growing lamellae, favoring total branch exclusion. 353-355 Typically, studies have proposed interstitial sites along the polymer chain, known as kinks, which yield excess free volume allowing for branch incorporation. Arising from conformational gauche defects, the 2g1 is the most common defect proposed to be large enough for ethyl branches. 246-257 There has been some suggestion that larger defects can enter the crystal (< 2%), however there is no real experimental evidence for a 2g1 mechanism. The IR bands at 1366 and 1305 cm -1 correspond to the 2g1 defect and can be easily quantified using infrared techniques. The overall concentration of this defect as well as the double gauche defect, observed at 1352 cm -1 , in the ADMET EO copolymers is constant regardless of methylene sequence length. This trend tends to follow the concentration of methyl end groups realized as an absorbance at 1377 cm -1 corresponding to the total branch concentration due to the polymer’s high molecular weight. The longer methylene sequence lengths cause a broadening of these observed bands especially the 1301 cm -1 kink resonance when compared to our EB series. It should be noted that the EP copolymers do not exhibit these defect bands due to the methyls incorporation into the growing crystal without the need for methylene rearrangement. While at the present time the exact cause of these defects can not be correlated to any secondary or higher order structure, comparisons tend to indicate that the copolymers contain high defect concentrations. These defects seem to correspond to branch concentrations independent of branch frequency. On the other hand, the highly branched copolymers contain two distinct methylene scissoring modes either deriving from main chain and side chain methylene vibrations or differing local environments. At the present time, it seems unlikely that the different vibrations are caused by methylene

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121 heterogeneity since the observed vibrations are common to short chain branched copolymers. In order to help elucidate the packing tendencies of our ADMET EO copolymers a series of solid state NMR experiments were conducted in the polymers plastic regime. The initial study has been localized to HPEO21 with hopes for further structural analysis using SAXS and WAXD. Figure 4-11. Initial solid state magic angle 13 C-n.m.r. of HPEO21 taken at -30 o C. 356 Up to now, numerous solid state NMR studies have been conducted on semi-crystalline polyethylene providing detailed information on phase structure and morphology. 226-227,353-355 A 13 C cross-polarized magic angle spinning (CPMAS) spectrum of linear polyethylene is dominated by a peak at 33.1 ppm due to the all-trans segment stem constituenting the orthorhombic crystal along with a broader shoulder at 31 ppm from the non-crystalline component. In certain oriented samples, the methylene carbons for the metastable monoclinic cell of linear polyethylene show a resonance at 34.4 ppm.

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122 Of course, the designated line widths and positions just mentioned are dynamic based on the local mobility and gauche defect concentrations around the carbon of interest. For example, the peaks observed in EO copolymers containing low 1-octene concentrations yield lower ppm values versus linear unbranched polyethylene due to higher gauche concentrations. In both cases, the orthorhombic crystal cell dominates producing resonances at 32.7 and 33.1 ppm for EO and PE, respectively indicating more disorder. However, carbons situated three bonds from a gauche defect tend to be 4-6 ppm higher when compared to the corresponding trans-segments. Figure 4-11 illustrates the solid state carbon spectrum for HPEO21 containing three distinct resonances centered on 14.3, 23.3, and 32.8 ppm corresponding to the methyl (1B 1 ), first branch methylene, and rigid methylene backbone, respectively. 356 It would seem that the broad resonances correspond to low mobility resulting from the polymer’s crystalline phase. As mentioned, the lower observed resonance at 32.8 versus linear PE suggesting a more disordered crystalline phase. The lower field shoulder observed for the methyl resonance has been indicative of “locked” methyl branches in other branched polyolefins. It appears that the methyl resonance (14.3 ppm) and its nearest CH 2 is quite broad indicating restricted movement of the branch carbons. The low resolution or the overlapping methylene resonances seen in the acquired spectrum precludes any peak assignment or deconvolution. However, the combination of the methyl shoulder and the broadness of the observed resonances seem to point to branch inclusion. It should be mentioned that the thermal data as well as the IR spectra tend to favor the idea of partial branch inclusion. Further CP studies in tandem with varying

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123 delay times are underway to separate the contributions for the mobile and crystalline phases. 4.3 Conclusions Acyclic diene metathesis polymerization has proven to control the primary structure of ethylene/1-octene copolymers resulting in linear polyethylene containing only hexyl branches. In this effort, a simple synthetic method has been developed to produce exact linear model polymers of any short chain or long chain branching sequence. The inherent ability of metathesis to control the polymers branch identity and placement has profound effects on the thermal and crystal behavior of these distinct EO materials resulting in a new class of LLDPEs. The precise model EO copolymers tend to structural mimic previously synthesized ADMET EP copolymers rather than our EB copolymers, specifically crystallization kinetics. The structural investigation has shown that these ADMET EO copolymers seem to indicate side chain involvement in the crystallizing structures. Thermal analysis has indicated well-defined crystal structures albeit smaller when compared to metallocene structures while demonstrating a more homogeneous branching distribution over previously made EO copolymers. Moreover, these copolymers exhibit distorted methylene sequences with high concentrations of kink, gauche, and double gauche along the same concentration has methyl concentrations. We are currently continuing this branched polyethylene research by gathering a better base of scattering data and understanding the differences between random and precise branch content. In addition, we are investigating precisely branched liner-low density materials containing deuterated hexyl branches and attempting to locate and investigate molecular side chain motion.

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124 Ultimately, the syntheses of longer defects are underway with investigations into side chain cocrystallization and radically produced LDPEs. 4.4 Experimental Section 4.4.1 Instrumentation and Analysis All 1 H NMR (300 MHz) and 13 C NMR (75 MHz) spectra were recorded on either a Varian Associates Gemini 300 or Mercury 300 spectrometer. Chemical shifts for 1 H and 13 C NMR were referenced to residual signals from CDCl 3 ( 1 H = 7.27 ppm and 13 C = 77.23 ppm) with 0.03% v/v TMS as an internal reference. Reaction conversions and relative purity of crude reactions were monitored by chromatography and NMR. Gas chromatography (GC) was performed on a Schimadzu GC-17 gas chromatograph equipped with a 25 m capillary column packed with a 5% crosslinked PH ME and flame ionization detector. High-resolution mass spectral (LRMS and HRMS) data were obtained on a Finnegan 4500 gas chromatograph/mass spectrometer using the electron ionization (EI) mode. Elemental analyses were carried out by Atlantic Microlabs Inc., Norcross, GA. Gel permeation chromatography (GPC) was performed using a Waters Associates GPCV2000 liquid chromatography system with its internal differential refractive index detector (DRI), internal differential viscosity detector (DP), and a Precision 2 angle light scattering detector (LS). The light scattering signal was collected at a 15 degree angle, and the three in-line detectors were operated in series in the order of LS-DRI-DP. The chromatography was performed at 45 C using two Waters Styragel HR-5E columns (10 microns PD, 7.8 mm ID, 300 mm length) with HPLC grade tetrahydrofuran as the mobile phase at a flow rate of 1.0 mL/minute. Injections were made at 0.05-0.07 % w/v sample concentration using a 322.5 l injection volume. In the case of universal calibration,

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125 retention times were calibrated against narrow molecular weight polystyrene standards (Polymer Laboratories; Amherst, MA). All standards were selected to produce M p or M w values well beyond the expected polymer's range. The Precision LS was calibrated using narrow polystyrene standard having an M w = 65,500 g/mol. Fourier transform infrared (FT-IR) spectroscopy was performed using a Bio-Rad FTS-40A spectrometer. The hydrogenation of the unsaturated ADMET prepolymer was monitored by the disappearance of the out-of-plane C-H bend for the internal olefin at 967 cm -1 . Monomer was prepared by droplet deposition and sandwiched between two KCl salt plates. Unsaturated and hydrogenated polymer samples were prepared by solution casting a thin film from tetrachloroethylene onto a KCl salt plate. Differential scanning calorimetry (DSC) analysis was performed using a Perkin-Elmer DSC 7 equipped with a controlled cooling accessory (CCA-7) at a heating rate of 10 C/min. Calibrations were made using indium and freshly distilled n-octane as the standards for peak temperature transitions and indium for the enthalpy standard. All samples were prepared in hermetically sealed pans (5-10 mg/sample) and were run using an empty pan as a reference and empty cells as a subtracted baseline. 4.4.2 Materials Schrock's molybdenum catalyst [(CF 3 ) 2 CH 3 CO] 2 (N-2,6-C 6 H 3 -i-Pr 2 ) Mo=CHC(CH 3 ) 2 Ph was synthesized according to the literature procedure. 157-162 Tetrahydrofuran (THF) was freshly distilled from Na/K alloy using benzophenone as the indicator. The starting diethylmalonate and alkenyl bromides along with hexamethylphosphoramide and triethylamine were distilled over CaH 2 . All other materials were used as received from the Aldrich chemical company.

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126 4.4.3 General Monomer Synthesis The starting protected alcohols were synthesized according to a previously published procedure. 347 Also, the protection of the primary alcohols was modified from a procedure outlined by Wagener using p-toluenesulfonyl chloride. 171 The characterization data observed for each protected alcohol is listed below. The crude mesylated alcohol was used without further purification in the copper coupling. In general, to flame dried and Ar purged 100 mL round bottom flask equipped with a stir bar, 224 mg (2.58 mmol) of LiBr and 530 mg (2.58 mmol) of CuBr•S(CH 3 ) 2 were dissolved 23.4 mL of dry THF. After stirring for 10 mins, the flask was cooled to 0 o C and 2.58 mL (2.58 mmol) of a 1M lithium thiophenoxide (Aldrich) solution was added producing a yellow cuprate complex. In a separate flame dried three-neck RBF equipped with a additional funnel and stir bar, the previously synthesized mesylated alcohol (9) was dissolved in THF:HMPA (3:1 v/v) to produce a 1M solution followed by cooling to 0 o C. Once chilled, 10 mol % of the 0.1 M cuprate complex was added and allowed to stir for 15 mins. Pentylmagnesium bromide (1.5 eq, 1M in THF) was added dropwise over an hour while warming the solution to room temperature. Overall, the reaction concentration was kept at 0.5 M and the reaction was allowed to proceed for 24 hours. Additional heating (30 o C) was required for good conversion of the longer methylene monomers. Workup was done by the addition of 100 mL of ether, extraction with 1M HCl (100 mL), and saturated sodium chloride followed by drying over MgSO 4 . The solution was filtered, concentrated, and purified by column chromatography using hexane. In addition, further purification was performed to remove any eliminated byproduct by distillation or reverse phase HPLC. Characterication of 6-methanesulfonyl methyl-1,10-undecadiene (9a). Purification of compound 9a was performed as noted by Wagener. 171 Yield of compound

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127 9a: 98.2 %. The following spectral properties were observed: 1 H NMR (CDCl 3 ): (ppm) 1.20-1.50 (m, 8.5H), 1.62 (m, 0.5H), 2.05 (m, 4H), 3.00 (s, 3H), 4.12 (d, 2H), 4.96 (m, 4H, vinyl CH 2 ), 5.81 (m, 2H, vinyl CH); 13 C NMR (CDCl 3 ): (ppm) 26.75, 29.10, 29.90, 33.99, 37.42, 38.01, 72.7, 114.41 (vinyl CH 2 ), 139.50 (vinyl CH); EI/LRMS calcd. for C 13 H 24 O 3 S: 260, found: 260. Elemental analysis calcd. for C 13 H 24 O 3 S: 59.96 C, 9.29 H, 12.31 S; found: 59.6 C, 9.53 H, 12.01 S. Characterization of 9-methanesulfonyl methyl-1,16-undecadiene (9b). Purification of compound 9b was performed as noted by Wagener. 171 Yield of compound 9b: 99.2 %. The following spectral properties were observed: 1 H NMR (CDCl 3 ): (ppm) 1.20-1.50 (m, 20.5H), 1.62 (m, 0.5H), 2.05 (m, 4H), 3.00 (s, 3H), 4.12 (d, 2H), 4.96 (m, 4H, vinyl CH 2 ), 5.81 (m, 2H, vinyl CH); 13 C NMR (CDCl 3 ): (ppm) 26.75, 29.10, 29.24, 29.90, 30.87, 33.99, 37.42, 38.01, 72.7, 114.41 (vinyl CH 2 ), 139.50 (vinyl CH); EI/LRMS: [M] calcd. for C 19 H 36 O 3 S: 344, found: 344. Elemental analysis calcd. for C 19 H 36 O 3 S: 66.23 C, 10.53 H, 9.31 S; found: 66.01 C, 10.51 H, 8.99 S. Characterization of 12-methanesulfonyl methyl-1,22-undecadiene (9c). Purification of compound 9c was performed as noted by Wagener. 171 Yield of compound 9c: 96.2 %. The following spectral properties were observed: 1 H NMR (CDCl 3 ): (ppm) 1.20-1.50 (m, 33.5H), 1.62 (m, 0.5H), 2.05 (m, 4H), 3.00 (s, 3H), 4.12 (d, 2H), 4.96 (m, 4H, vinyl CH 2 ), 5.81 (m, 2H, vinyl CH); 13 C NMR (CDCl 3 ): (ppm) 26.75, 29.10, 29.24, 29.55, 29.90, 29.99, 30.01, 30.87, 33.99, 37.42, 38.01, 72.7, 114.41 (vinyl CH 2 ), 139.50 (vinyl CH); EI/LRMS calcd. for C 26 H 50 O 3 S: 427, found: 427. Elemental analysis calcd. for C 26 H 50 O 3 S: 73.18 C, 13.64 H; found: 86.36 C, 13.58

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128 Synthesis and Characterization of 6-hexyl-undeca-1,10-diene (1). Monomer 1 was synthesized as described above using the mesylated alcohol produced using 5-bromo-1-pentene. After column and distillation (70 o C at 0.156 mmHg) monomer 1 was collected as a colorless liquid. Yield of monomer 1: 67.2 %. The following spectral properties were observed: 1 H NMR (CDCl 3 ): (ppm) 0.88 (t, 3H, -CH 3 ), 1.20-1.50 (m, 19H), 2.05 (m, 4H), 4.96 (m, 4H, vinyl CH 2 ), 5.81 (m, 2H, vinyl CH); 13 C NMR (CDCl 3 ): (ppm) 14.39 (-CH 3 ), 22.99, 26.31, 26.93, 30.07, 32.22, 33.41, 33.89, 34.51, 37.48, 114.41 (vinyl CH 2 ), 139.50 (vinyl CH); EI/HRMS: [M] calcd. for C 17 H 32 : 236.2504, found: 236.2507. Elemental analysis calcd. for C 17 H 32 : 86.36 C, 13.64 H; found: 86.36 C, 13.58 H. Synthesis and Characterization of 9-hexyl-heptadeca-1,16-diene (2). Monomer 2 was synthesized as described above using the mesylated alcohol produced using 8-bromo-1-octene. After column and distillation (135 o C at 0.135 mmHg) monomer 2 was collected as a colorless liquid. Yield of monomer 2: 62.2 %. The following spectral properties were observed: 1 H NMR (CDCl 3 ): (ppm) 0.88 (t, 3H, -CH 3 ), 1.15-1.48 (m, 34H), 2.05 (q, 4H), 4.96 (m, 4H, vinyl CH 2 ), 5.81 (m, 2H, vinyl CH); 13 C NMR (CDCl 3 ): (ppm) 14.42 (-CH 3 ), 23.01, 26.95, 26.98, 29.28, 29.50, 30.13, 30.29, 32.26, 33.98, 33.99, 34.14, 37.69, 114.34 (vinyl CH 2 ), 139.49 (vinyl CH); EI/HRMS: [M] calcd. for C 23 H 44 : 320.3443, found: 320.3446. Elemental analysis calcd. for C 23 H 44 : 86.17 C, 13.83 H; found: 86.20 C, 13.82 H. Synthesis and Characterization of 12-hexyl-tricosa-1,22-diene (3). Monomer 3 was synthesized as described above using the mesylated alcohol produced using 11-bromo-1-undecene. After column monomer 3 was collected as a colorless liquid. Yield

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129 of monomer 3: 59.2 %. The following spectral properties were observed: 1 H NMR (CDCl 3 ): (ppm) 0.89 (t, 3H, -CH 3 ), 1.15-1.48 (m, 44H), 2.05 (q, 4H), 4.96 (m, 4H, vinyl CH 2 ), 5.81 (m, 2H, vinyl CH); 13 C NMR (CDCl 3 ): (ppm) 14.40 (-CH 3 ), 22.98, 26.96, 29.23, 29.44, 29.80, 29.91, 29.97, 30.11, 30.41, 32.24, 33.96, 34.09, 37.66, 114.24 (vinyl CH 2 ), 139.42 (vinyl CH); EI/HRMS: [M] + calcd. for C 29 H 56 : 404.4382, found: 404.4385. Elemental analysis calcd. for C 29 H 56 : 86.05 C, 13.95 H; found: 86.17 C, 13.96 H. 4.4.4 General Polymerization Conditions All glassware was thoroughly cleaned and flame dried under vacuum prior to use. The monomers were dried over CaH 2 and Na mirror, and subsequently degassed prior to polymerization. All metathesis reactions were initiated in the bulk, inside an Argon atmosphere glove box. The monomers were placed in a 50 mL round-bottomed flask equipped with a magnetic Teflon TM stirbar. The flasks were then fitted with an adapter equipped with a Teflon TM vacuum valve. After addition of catalyst, slow to moderate bubbling of ethylene was observed. 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 while stirring in an oil bath at 30 C until the viscosity increases. Generally after 4 h, the polymerization was exposed to full vacuum (<10 -1 mm Hg) for 24 h and then high vacuum (<10 -3 mm Hg) for 96 h, gradually increasing temperature to 50 C during the last 24 h of polymerization. The reaction vessel was then cooled to room temperature, exposed to air and toluene was added. The mixture was heated to 80 C in order to dissolve the resultant polymer and decompose any remaining

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130 active catalyst. The polymer/toluene solution was taken up and precipitated dropwise into a vigorously stirred beaker containing 1500 mL of acidic methanol (1 M). Polymerization of 6-hexyl-undeca-1,10-diene (1) to give UPEO9. Schrock’s [Mo] catalyst (6.4 mg, 8.5x10 -3 mmol) was added to monomer 1 (1.5 g, 6.3 mmol). Precipitation (-78 o C) yielded 1.3 g of an off white, stringy material. Yield: 88 % (after precipitation). 1 H NMR (CDCl 3 ): (ppm) 0.88 (t, 3H, methyl), 1.28 (m, br, 19H), 1.97 (m, br, 4H), 5.40 (m, br, 2H, internal olefin); 13 C NMR (CDCl 3 ): (ppm) 14.37, 22.96, 26.91, 26.98, 27.09, 27.90, 30.06, 32.21, 33.30, 33.44, 33.59, 33.88, 37.45, 130.15 (cis olefin), 130.62 (trans olefin). 13 C NMR (CDCl 3 ) integration of cis:trans peaks gives: 19:81. GPC data (THF vs. polystyrene standards): M w = 58 200 g/mol; P.D.I. (M w /M n ) = 1.8. Polymerization of 9-hexyl-heptadeca-1,16-diene (2) to give UPEO15. Schrock’s [Mo] catalyst (3.2 mg, 4.1x10 -3 mmol) was added to monomer 1 (1.0 g, 3.1 mmol). Precipitation (-78 o C) yielded 0.95 g of an off white, stringy material. Yield: 95 % (after precipitation). 1 H NMR (CDCl 3 ): (ppm) 0.86 (t, 3H, methyl), 1.15-1.50 (m, br, 31H), 1.97 (m, br, 4H), 5.40 (m, br, 2H, internal olefin); 13 C NMR (CDCl 3 ): (ppm) 14.41, 23.05, 26.96, 27.52, 29.54, 29.66, 29.99, 30.10, 30.13, 30.31, 32.25, 32.93, 33.97, 37.68, 130.15 (cis olefin), 130.62 (trans olefin). 13 C NMR (CDCl 3 ) integration of cis:trans peaks gives: 14:86. GPC data (THF vs. polystyrene standards): M w = 44 500 g/mol; P.D.I. (M w /M n ) = 1.8. Polymerization of 12-hexyl-tricosa-1,22-diene (3) to give UPEO21. Schrock’s [Mo] catalyst (3.1 mg, 3.9x10 -3 mmol) was added to monomer 1 (1.2 g, 2.9 mmol). Precipitation (-78 o C) yielded 1.1 g of an off white, stringy material. Yield: 96 % (after

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131 precipitation). 1 H NMR (CDCl 3 ): (ppm) 0.84 (t, 3H, methyl), 1.00-1.5 (m, br, 43H), 1.97 (m, br, 4H), 5.40 (m, br, 2H, internal olefin); 13 C NMR (CDCl 3 ): (ppm) 14.37, 22.97, 26.93, 26.98, 29.46, 29.60, 29.81, 29.94, 29.98, 30.05, 30.09, 30.42, 32.22, 32.87, 33.97, 37.68, 130.09 (cis olefin), 130.55 (trans olefin). 13 C NMR (CDCl 3 ) integration of cis:trans peaks gives: 16:84. GPC data (THF vs. polystyrene standards): M w = 44 600 g/mol; P.D.I. (M w /M n ) = 1.8. 4.4.5 General Hydrogenation Conditions Hydrogenation was performed using a 150 mL Parr high-pressure stainless steel reaction vessel equipped with a glass liner and a Teflon TM stirbar. The unsaturated polymers were taken up in 75 mL of toluene and added to the glass liner with 1 eq. of 10 % palladium on activated carbon. The glass liner was placed into the bomb and the bomb sealed. The Parr vessel was purged with 150 p.s.i. (3x) of Grade 5 hydrogen gas (H 2 ) in order to minimize oxygen and water introduced from the atmosphere. The bomb was charged to 1000 p.s.i. and the mixture was stirred for 24 h at 80 C followed by 48 h at 100 C. The resultant polymer was filtered and precipitated into acidic methanol (1N stock solution prepared with HCl) to obtain a finely dispersed white solid. The polymer was filtered and transferred to a 50 mL round bottom flask, evaporation under reduced pressure for 6 h, and further drying under high vacuum (3 x 10 -4 mm Hg) at 70 C for 5 days. Hydrogenation of UPEO9 to give HPEO9. Precipitation yielded 0.800 g (90.7 %) of a translucent, tacky material. 1 RCDCl 3 (ppm) 0.84 (t, 3H, methyl), 1.1-1.5 (br, 27H); 13 C NMR (CDCl 3 ): (ppm) 14.42, 23.01, 26.96, 27.03, 30.07, 30.14, 30.50, 32.26, 33.99, 34.00, 37.71. GPC data (THF vs. polystyrene standards): M w = 55

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132 600 g/mol; P.D.I. (M w /M n ) = 1.7. DSC Results: Glass Transition Temperature Data: Tg o CC p = 0.59 J/gC. Hydrogenation of UPEO15 to give HPEO15. Precipitation yielded 1.01 g (97.5 %) of a white spongy material. 1 RCDCl 3 (ppm) 0.89 (t, 3H, methyl), 1.27 (br, 39H); 13 C NMR (CDCl 3 ): (ppm) 14.43, 23.03, 26.98, 27.02, 30.04, 30.14, 30.48, 32.27, 34.01, 37.70. GPC data (THF vs. polystyrene standards): M w = 47 200 g/mol; P.D.I. (M w /M n ) = 1.8. DSC Results: T m (peak melting temperature) = -48 o C; h m = 19 J/g; T c (peak recrystallization temperature) = -56 o C; h m = 18 J/g. Hydrogenation of UPEO21 to give HPEO21. Precipitation yielded 1.12 g (98.1 %) of a white spongy material. 1 RCDCl 3 (ppm) 0.89 (t, 3H, methyl), 1.27 (br, 51H); 13 C NMR (CDCl 3 ): (ppm) 14.40, 22.99, 26.96, 26.99, 30.01, 30.12, 30.45, 32.24, 33.98, 37.67. GPC data (THF vs. polystyrene standards): M w = 46 100 g/mol; P.D.I. (M w /M n ) = 1.7. DSC Results: T m (peak melting temperature) = 16 o C; h m = 53 J/g; T c (peak recrystallization temperature) = 4 o C; h m = 51 J/g

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CHAPTER 5 SIDE CHAIN MOTION IN PRECISE DEUTERATED METHYL BRANCHED POLYETHYLENE 5.1 Introduction The investigation of molecular motion and chain relaxation pathways in semi-crystalline polymers has been extensively studied to better understand the macromolecule’s mechanical properties. Knowledge and understanding of the type, origin, and time scale of molecular motions in the solid state allows for precise polymer modifications and ultimately final material manipulation. 357-359 Over the years, polyethylene (PE) has become the model polymer to investigate molecular motion due to its simplicity and well-documented mechanical behavior. In an attempt to measure these transitions, modifications to polyethylene’s amorphous region have been conducted using various sample preparation and branch incorporation techniques. 357-359 The majority of the literature procedures have focused on using differential scanning calorimetry (DSC) to observe these altercations and probe the effects of semi-crystalline motion. 44-61 However, the analysis of these modified samples by these techniques yield complications arising from branch motion when attempting to relate motion to morphology. Despite these shortcomings, the industrial and fundamental scientific importance of this subject cannot be overlooked. However, a direct experimental method to elucidate the details of motion and investigate defect perturbations within polyethylene materials remains scarce. Among the various techniques, nuclear magnetic resonance (NMR) is a well-established standard for measuring motion, along with the small 133

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134 timescales associated with such transitions. 360-367 These direct measurements, collected by NMR, can be interpreted into quantitative information not easily attainable with indirect detection or bulk methods. The examination of motion in solid PE using NMR spectroscopy dates back to the 1950s and has successfully developed into a standard method for the study of amorphous and crystalline motion. 368 In particular, wide line 1 H-n.m.r. 363,369 and more recently high resolution 13 C-n.m.r. 226-227,370 and 2 H-n.m.r. 371-378 have been used extensively to study solid chain relaxation. If synthetically feasible, the study of selectively deuterated polymers using wide line 2 H-n.m.r. offers numerous benefits over the other techniques mentioned. In order to understand and appreciate the benefits of 2 H-n.m.r., a discussion and comparison to 1 H-n.m.r. will be reviewed. The origin and explanation of the observed resonances will also be provided. The solid state 1 H-n.m.r. analysis of semi-crystalline polymers with respect to a particular motional model is difficult due to the signal origins observed in the NMR spectrum. The use of higher quantum spin states (I = 1) overcomes these shortcomings generating spectral resonances governed by separate interactions; specifically, proton-proton dipolar interactions ( 1 H-n.m.r.) or the coupling of C-D bonding electrons with the magnetic field. 375 The source of this difference can be explained by simple NMR theory as well as quantum Hamiltonians. Regardless of the nucleus, simple NMR theory predicts one should observe a doublet of NMR lines found with the frequency splitting outlined in Figure 5-1. Differences arise within the variable ‘C’ (Figure 5-1) when comparing nuclei with different spin states.

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135 v = C(3cos2 1) Figure 5-1. Equation of spin states. The spectra obtained either by 1 H or 2 H-n.m.r. analysis for a single interaction, to simplify the discussion, would produce indistinguishable resonance data. In this case, single proton pair motion reduces the angle to H the angle of the dipolar coupling in the direction of the applied magnetic field. For protons (I = ), C = C H = 3 H 2 h/(8 2 r 2 ) is the dipolar coupling constant where H is the gyromagnetic ratio, h is Plank’s constant, and r is the distance across the dipolar interaction. In the case of deuterons (I = 1), C = C D = 3e 2 Qq/4h is the quadrupole coupling constant where eQ is the quadrupole moment and eq as the electric field gradient (axially symmetric). Similar to proton pairs, the application of a single interaction reduces to D the angle of the C-D vector in the direction of the magnetic field. A more detailed quantum mechanical treatment for a single C-D bond (above that illustrated in Figure 5-1) leads to the collection and combination of the Zeeman and quadrupole Hamiltonians. The Hamiltonians illustrated in Figure 5-2 explain the same two observed resonances as Figure 5-1, where D is the deuteron Zeeman frequency and D = C D (Figure 5-1). The additional term involving the asymmetry parameter, accounts for non-axial imperfections in the EFG tensor which in aliphatic C-D bonds is nearly axial ( = 0). In the case of polyethylene, is assumed to be zero yielding the simpler expression outline in Figure 5-1. D D(3cos21 + sin2cos2)+Figure 5-2. Hamiltonians governing quadrupole couplings. Application of 1 H-n.m.r. beyond single crystals even at low temperatures (< 100 K), where the line shapes are governed by dipolar interactions, creates confusion.

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136 Specifically, the examination of high molecular weight polymers produces interactions with neighboring protons that are not of immediate interest. In the solid state above these temperatures (100 K), the proton spectrum is complicated through both inter-chain and long-range intra-chain dipolar couplings. The multiple nearest protons contribute to the observed line shape, and deconvolution of these signals is nearly impossible. However, there has been experimental information gathered on polyethylene using 1 H-n.m.r. coupled with higher temperatures, generally above the -transition, yielding a series of dynamic models based on methylene motion. 362-363,379 The higher temperatures give rise to peak narrowing through one, 364-365 two, 366-367 and more componential motion, 380 which allows the decomposition of this complex pattern revealing information on polymer crystallinity and amorphous content. In this light, the resonances observed in 2 H-n.m.r. become unique and drastically different compared to 1 H-n.m.r., when investigating motion in non-crystalline (100 %) solids. The dominating interaction for deuterons is the coupling of the quadrupole moment with the external field gradient (EFG). In fact, the dipole-dipole coupling from neighboring deuterons, similar to 1 H-n.m.r. resonances, is negligible, hence the resonances are only a function of the local C-D vector environment. The independent nature observed by a single deuteron allows for local vector motional quantization in macromolecules. The average of all C-D vector distributions and orientations produces the typical spectra observed for semi-crystalline polyethylene. In this case, low temperature 2 H-n.m.r. data collection produces two singularities derived from the Zeeman frequency plus/minus D , experienced at the rigid limit. Figure 5-3 illustrates the typical Pake

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137 doublet characteristic of rigid aliphatic deuterons. 377 Of course, the well-defined motions of deuterated polyethylene caused by interactions of the methylene C-D bonds lead to well-defined spectra. In the glassy state, the nearly immobile main chain produces a 121 kHz splitting between the observed singularities. + DD Figure 5-3. Singularities observed for 2 H-n.m.r. and the overlapped Pake pattern. 377 On the other hand, the examination of glassy perdeuterated polypropylene leads to a spectrum consisting of two well-defined Pake patterns (Figure 5-4). The superposition of singularities is derived from the motion of both main chain as well as side chain methyl deuterons. As observed for unbranched deuterated polyethylene, the broad component owning to a distance of 121 kHz originates from the main chain. However, under the conditions used to measure semi-crystalline motion, axial methyl group reorientation of the EFG tensor is in the fast time scale regime. As a result, the side chain methyl deuterons experience an averaging of the EFG tensor of approximately 1/3 that of the main chain. The motional averaging yields a distance of 35 kHz between singularities as observed in Figure 5-4.373 Regardless of deuteron placement or of its environment, a narrowing is observed for all singularities, implying increased molecular motion. In fact, a system in isotropic motion, observed above a polymer’s melting point,

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138 results in a single narrow resonance. Coupling the data collection offered with 2H-n.m.r. through the modeling of isotropic motional deconvolution allows for the quantization of branch inclusion as well as information on polymer crystallinity and relaxation modes. However, the origins of these relaxation modes and their corresponding thermal transitions have been debated for years.381-387 Figure 5-4. The experimental 2 H-n.m.r. spectrum for A) glassy perdeuterated polypropylene 373 and B) rapid isotropic deuteron motion. In contrast to small molecules, three relaxation mechanisms have been reported in simple polymeric hydrocarbons. In general, branched polyethylene exhibits an process related to chain jumps in the crystalline domains close to the melting point (300 – 390 K). 373 Also, a relaxation corresponds to a limited motion of distorted main chains associated with interfacial regions of semi-crystalline copolymers. In addition, the process is connected to side chain reorientation in branched polyethylenes. The final relaxation has been generally accepted to be associated with the glass transition of PE and is seemed to originate from local conformational transitions only. In atactic PP, the relaxation can be described as small-step rotational diffusion. These pathways have been measured indirectly mainly through dielectric relaxation, dynamic mechanical analysis, and thermal analysis. 388 However, magnetic resonance, especially 2 H-n.m.r., delineates

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139 these pathways directly along the C-D vector and can be correlated to spectral peak shape and line broadening. Moreover, the well-defined line shape of ‘rigid’ deuterons can be subtracted from the total line shape observed for semi-crystalline polymers. In an attempt to better understand these processes and bridge the information gap between linear PE and atactic PP, precisely positioned deuterated models of highly branched linear EP copolymers need to be investigated. In the past, acyclic diene metathesis (ADMET) has been utilized to produce model copolymers of ethylene with precise primary structures. 171 Our efforts in this area have focused on producing exact structures through monomer selection alone. This has enabled our group to produce ethylene/alpha-olefin materials by simple organic transformations without the influence of catalytic chain transfer. Most notably, this ability has also allowed the formation of polymers inaccessible through usual polymerization modes with the benefit of precise branch location and identity as well as homogeneous short chain branch distributions (SCBDs). 91-102 The first example of this methodology was the synthesis of five model ethylene/propylene (EP) copolymers, 371 followed by a series of ethylene/1-butene (EB) 346 copolymers containing precise methyl and ethyl branches respectively. Recently, our group has synthesized the complimentary ethylene/1-octene (EO) materials in an attempt to investigate linear-low density behavior. In fact, the controlled structures enable the macromolecule to access never before observed behavior; in effect creating a new class of PE based materials. In contrast to our previous hydrocarbon modeling studies we now report the synthesis and characterization for a series of precisely deutero-methyl branched polyethylene. The monomers and polymers are deuterated analogs of our previously

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140 published EP copolymers yielding a deuterated methyl on each and every 9 th , 15 th , and 21 st carbon. The resulting ADMET copolymers are based on a linear polyethylene backbone without influences from unwanted branch content, heterogeneous SCBDs, and inter-chain heterogeneity. Herein, we also present the initial study on the polymers solid state side chain motion from the data collected through wide line 2 H-n.m.r. 5.2 Results and Discussion Characterization 5.2.1 Monomer Synthesis and Characterization Over recent years, acyclic diene metathesis (ADMET), a non-classical step condensation polymerization, has been utilized to synthesize various hydrocarbons and functionalized linear ethylene copolymers. The polymerization of the appropriate functionalized pure ,-diene monomer produces an unsaturated polymer, where functional group placement is controlled completely by monomer selection. 156,171 Upon hydrogenation, linear analogs of chain addition copolymers are obtained without the drawbacks of chain transfer, large polydispersities, and heterogeneous branch distributions. In this light, the methodology used to synthesize these symmetric monomers is the key for producing exact primary structures in which monomer functional purity dominates. In the past, the monomer synthesis to consistently produce these pure alpha olefin functionalities and branch purities has proven difficult. However, extensive synthetic examinations have been outlined to yield a variety of functional pure ADMET monomers. Our initial methyl branch idea was extended to synthesis of monomers containing precisely displaced deuterated methyl groups by using metal deuterides. 171 However, the intermediates used throughout the synthetic procedure, outlined in Figure 5-5, were adopted from a more efficient procedure. In general, the starting monoacids

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141 (6a-c) can be made easily by the disubstitution of diethylmalonate with an alkenyl halide possessing the appropriate methylene spacing. Saponification of the resulting diester (5) followed by decarboxylation affords the pure monoacid 6. Selective reduction with lithium aluminum deuteride (LAD) yields the primary alcohol (7), which is mesylated (8), then reduced via deuteride displacement into the symmetrical diene of interest. EtOOEtOO1) NaH2)BrnOEtEtOOOnn1) KOH/EtOH2) Decalin, OHHOnn66THFHnn1) MsCl2) NEt3/CHCl3CD2OMsHnn88HnnCD2OHTHFCD3LiAl(2H)4LiAl(2H)4n = 3, 6, 94571 n = 32 n = 63n=9 Figure 5-5. Synthetic methodology used to produce symmetrical placed deuterated methyl monomers. Three symmetrical monomers were made in this manner where n = 3, 6, 9 (Figure 5-5) and were found to be isocharacteristic to our previous methyl monomers. As mentioned earlier, due to the nature of step condensation polymerization and due to our attempt to produce exact macromolecules, monomer purity is crucial. Nuclear magnetic resonance can be used to investigate and characterize monomer functionality effectively. Figure 5-6 illustrates both the 1 H and 13 C-n.m.r. for monomer 1 made through the procedure outlined in Figure 5-5. Close inspection and integration of the observed residual methyl resonance at 0.88 ppm indicates that in this case, monomer 1 contains 98

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142 % deuterated methyl groups. Also, the carbon spectrum obtained for monomer 1 shows six distinct resonances which are relatively unaffected by the deuteron placement with respect to its hydrogen analog. However, the resonance observed for the methyl group shifts downfield (18.9 ppm) and indicates multiple carbon-deuteron couplings. The collection of three deuterons produces the faint septet (inset, Figure 5-6) with a coupling constant of 18.9 hertz. The spectrum observed collected for monomer 1 is typical of the entire series and is consistent with the formation of a perdeuterated methyl group. Figure 5-6. Typical NMR data produced for ADMET monomers, 1 H and 13 C-n.m.r. illustrated for monomer 1.

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143 5.2.2 Nomenclature and Comonomer Content The well-defined structures produced by metathesis in conjunction with the precise nature of the starting monomers yields a direct relationship between monomer and polymer branch content. The comonomer content, as described by ‘chain-made’ copolymers of ethylene, can be easily calculated using the branch frequency observed in the monomer or hydrogenated ADMET copolymer following the relationship: mol % comonomer =2n 100x The molar branch content only depends on the branch frequency produced by the appropriate monomer and is independent of the chosen polymerization mechanism. This allows for the calculation of the comonomers weight percent as well as the branch content per 1000 carbons, permitting direct correlations to metallocene and radically synthesized copolymers. The ability of ADMET to produce precise and homogeneous primary structures has allowed us to create a library of model copolymers bearing a variety of linear comonomers. In order to avoid confusion, all our metathesis generated model copolymers have their names derived from the parent chain-addition copolymer and are designed to describe the actual branch content and frequency. All copolymers, past and present, begin with the prefix HP (hydrogenated polymer) or UP (unsaturated polymer) followed by the comonomer type (EP, ethylene/1-propene) and the precise branch frequency (21). The deuterated model copolymers synthesized in this study contain an additional d 3 designation preceding the branch frequency. For example, HPEP-d 3 -9 is designated as hydrogenated ethylene/1-propene copolymer containing a perdeuterated

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144 methyl (CD 3 ) on each and every 9 th carbon along the linear polyethylene backbone. In comparison, HPEP9 synthesized previously contains a CH 3 group on every 9 th carbon. 171 5.2.3 ADMET Polymerization and Hydrogenation ADMET polycondensation was used as the modeling polymerization mechanism of choice, since it offers control of the molecular weight distribution, branch type, and comonomer distribution in the final copolymer. 171,204 In an effort to produce the highest polymer purity, all three monomers were exposed to Schrock’s catalyst under mild ADMET step polymerization conditions. 171 In all cases, thoroughly drying and distilling the appropriate monomers over a potassium mirror followed by vaccum transfer can achieve these conditions. This purification method allows the use of low catalyst loadings (1000:1 monomer: catalyst) while still maintaining high step condensation molecular weights. The chemistry proceeds cleanly to produce linear, unsaturated precisely branched polymers containing one type of repeat unit. Typical molecular weights were obtained through this step-addition process as well as the polydispersities, which were calculated after purification via precipitation. The ability to model chain-addition aliphatic polyolefins requires definite molecular weight requirements. Similar to other macromolecules, polyethylene’s thermal and physical characteristics are a direct function of molecular weight. Of course, polyolefin behavior eventually tends to plateau, reaching a maximum fairly low in the molecular weight profile. Extensive work in our group has shown that the weight-average molecular weight (M w ) of ADMET polyethylene must exceed 24,000 g/mol versus polystyrene (PS) standards before a constant melting behavior is observed. 156 Table 5-1. Molecular weights for deuterated model ADMET copolymers.

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145 Model Copolymer Methyl on Every n th Backbone Carbona Comonomer 3d 3 -1-Propene Content b Unsaturated Copolymers (Relative) c Saturated Models Relative (PS) c LALLS d n Mol % M w x 10 -3 PDI e M w x 10 -3 PDI e M w x 10 -3 PDI e HPEP-d 3 -9 9 22.2 46.5 1.8 56.5 1.8 27.3 1.6 HPEP-d 3 -15 15 13.3 51.3 1.9 53.1 1.9 29.6 1.8 HPEP-d 3 -21 21 9.5 48.1 2.0 56.1 1.9 31.1 1.9 A) Branch content based on the hydrogenated repeat unit. B) Comonomer content based on the chain-addition analogs. C) Molecular weight data taken in tetrahydrofuran (40 o C) relative to polystyrene standards. D) Molecular weight data taken using low-angle laser light scattering (LALLS) in tetrahydrofuran at 40 o C. E) Polydispersity index (M w /M n ). Table 5-1 illustrated this data obtained using two molecular weight determination methods consisting of an internal differential refractive index detector (DRI) and a Wyatt three-angle light scattering detector (LS). Using these detectors in series, the molecular weights were determined based on a relative retention time calibration to 10 Polymer Laboratory polystyrene standards and low-angle laser light scattering (LALLS). As observed in the past, the molecular weight data obtained for this series are sufficiently high to model the behavior of industrially produced polyethylene and therefore sufficiently high to model and correctly predict copolymer behavior. These unsaturated polyethylene analogs were converted to their corresponding deuterated methyl branched polymers via exhaustive hydrogenation. In addition to monomer purity, hydrogenation must be complete and avoid any side reactions in order to make valid comparisons to chain-addition polymers. In the past, complete hydrogenation was conducted using a heterogeneous palladium 171 or ruthenium catalyst system, 346 homogeneous Wilkinson’s catalyst, 204 or stoichiometric diimine reduction. 156,171 Regardless of the hydrogenation system chosen, exhaustive hydrogenation can be accomplished with the appropriate conditions without any

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146 detrimental side reaction. However, the deuterated ADMET unsaturated polymers synthesized in this study are sensitive to the competing hydrogen abstraction observed in most catalytic hydrogenations. If observed, a possible scrambling of hydrogen and deuterons will then produce ill-defined deuteron placement and irregular copolymers, complicating future experiments. Figure 5-7. 1 H and 13 C-n.m.r. for HPEP-d 3 -9 and 1 H-n.m.r. for its hydrogen analog HPEP9 (inset). The stoichiometric diimine reduction method was chosen to eliminate this side reaction and was accomplished according to Hahn. 389 Hydrogenation was completed in

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147 nine hours by the successive addition of toluenesulfonylhydrazide (TSH) and triproylamine (TPA), three equiv of each every three hours, to the unsaturated polymer in refluxing o-xylene. After cooling, the saturated polymer was recovered by precipitation in methanol, and filtered. To insure complete byproduct removal, the polymer was dissolved in toluene and reprecipitated in acidic methanol through an alumina plug. Infrared detection is the method of choice to monitor hydrogenation effectiveness along the polymer backbone. The easiest and most reliable proof is the out-of-plane C-H bend in the alkene (967 cm -1 ), which completely disappears after successful hydrogenation. 204 Figure 5-7 shows the 1 H and 13 C-n.m.r. for the fully hydrogenated copolymer generated from monomer 1. Due to the high molecular weight obtained during the ADMET polymerization (Table 5-1), integration of the methyl region (0.90 ppm) directly indicates the percentage of perdeuterated methyl groups in the resulting hydrogenated copolymer. Indeed, the diimine reduction does not scramble deuteron placement, as the integration values are constant before and after the hydrogenation. The inset of Figure 5-7 provides the reference, HPEP9, as the model EP copolymer. The observed methyl resonance, illustrated as the triplet at 0.88 ppm, is nonexistent in HPEP-d 3 -9. Also, the observed septet in the carbon spectrum, typical for perdeuterated methyl groups, is consistent with precise hydrogen transfer as well as the 25.1-Hz J C-D coupling constant. The NMR results obtained for the complete transformation of monomer 1 to its model copolymer, HPEP-d 3 -9, were observed for the entire series independent of branch frequency. 5.2.4 Thermal Behavior Since the inception of polyethylene in the 1930s, numerous variations on this simple repeating structure are produced annually; however, each type has varying levels

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148 of defects leading to intraand inter-chain differences, and heterogeneity. 91-102 Of course, these “defects” in the polymer structure are exploited and manipulated to create wider and varying material responses. Traditionally, these variations derived from chain transfer events and multi-site catalyst systems have direct effects on the polymer’s thermal and mechanical properties. Thermal profiling using differential scanning calorimetry (DSC) is a simple method for illustrating these heterogeneous structures. As mentioned earlier, acyclic diene metathesis (ADMET) polymerization alleviates these problems and allows the polymer to access a unique behavior resulting from precise branch placement. In general, these more precise and homogeneous polymers produced via ADMET yield sharper, more well-defined melting endotherms and recrystallization exotherms when analyzed by calorimetry. The melting profiles obtained in this deuterated methyl study coincide with our previously synthesized model EP copolymers. Unsurprisingly, the deuterated methyl replacement does not alter the copolymer’s thermal behavior. In all cases comparing analysis was performed using a Perkin-Elmer DSC 7, erasing the polymer’s thermal history prior to data collection. The thermal data collected for the undeuterated model EP copolymers was published previously; however, to make the most valid comparison the samples were run simultaneously. Similarly the methyl branched copolymers, this precise deuterated methyl system follows the same decreasing trend in enthalpy and peak melting point as a function of increasing branch content. When directly compared to the previous methyl systems 171 the crystallization/recrystallization heat flow and peak melting/crystallization temperature perfectly matches within experimental error. Figure 5-8 illustrates the thermal profile for

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149 both the heating and cooling of the polymer containing a deuterated methyl on every 9 th carbon, with the data collected on the third heating/cooling cycle. The observed well-defined profiles prove the homogeneous structures produced using metathesis. For HPEP-d 3 -9, this structural control has lead to a peak melting temperature of -10 o C and a corresponding melting enthalpy of 30 J/g. The sample also shows thermodynamical equilibrium with reversible melting and constant heat flow exchange. Figure 5-8. Thermal profile for the ADMET model copolymer containing a deuterated methyl group on every 9 th carbon, HPEP-d 3 -9. Figure 5-9 shows the calorimetric data collected for HPEP-d 3 -15, containing a deuterated methyl on every 15 th carbon, which exhibit the same profile as our methyl series. The increasing methylene sequence length produces a sharp exothermal heat flow and well-defined melting. Of course, compared to HPEP-d 3 -9 the decrease in branch content has raised the melting and recrystallization points above room temperature.

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150 Increasing the sequence length has allowed crystallization to occur at a greater extent which is illustrated by the increased heat flow (88 J/g). Figure 5-9. Thermal profile for the ADMET model copolymer containing a deuterated methyl group on every 15 th carbon, HPEP-d 3 -15. Finally, the thermal profile of the model copolymer containing a deuterated methyl on every 21 st carbon, HPEP-d 3 -21, is shown in Figure 5-10. Once again the sharp melting and recrystallization range is indicative of precise and uniform structures. The data obtained in this side chain motion study has the same melting and recrystallization peaks as reported for the methyl copolymer. In this study, HPEP-d 3 -21 has a melting point of 62 o C owning to a heat flow of 105 J/g while a value of 54 o C and 103 J/g obtained by cooling the sample. Regardless of the sample or branch frequency, these deuterated methyl copolymers are exact models for their methyl analogs, allowing for

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151 direct correlations. 171 In this light, these deuterated copolymers were explored as models to investigate side chain methyl group motion. Figure 5-10. Thermal profile for the ADMET model copolymer containing a deuterated methyl group on every 21 th carbon, HPEP-d 3 -21. 5.3 Results and Discussion – 2 H-n.m.r. Spectroscopy 390 Polyethylene’s structural simplicity has made it one of the most thoroughly studied polymeric materials, but the copolymer of ethylene with 1-propene has been the subject of the most intensive structural-property investigation.44-61,91-102 Specifically, relationships of branch content, heterogeneity, and identity to macromolecular behavior has been the focus of the majority of these publications. In most cases, the correlations of structural perturbations have been made on the basis of bulk properties such as heat capacity, dielectric relaxation, and dynamical analysis.360 Presently, nuclear magnetic resonance is the only experimental method yielding microscopic information of

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152 molecular order and detailed solid state dynamics. In the past, main chain motion in polyethylene360 and more recently polypropylene373 with side chain methyl motional behavior has been extensively studied by 2H-n.m.r. However, the polymers produced using chain-addition polymerization conditions yield perdeuterated PE or PP. For polypropylene, this leads to overlapping Pake patterns, which complicates spectral deconvolution. In 2000, we investigated the structure of model ethylene/1-propene copolymers containing precise structures synthesized via ADMET polymerization. 171 Under standard detection methods the structure and material properties of our ADMET EP copolymers have shown unique behavior specific to our systems. In an effort to delineate the source of this behavior, a series of precisely deuterated model copolymers were synthesized, and molecular motion in these samples was investigated using 2 H-n.m.r. The ability of ADMET to synthesize controlled polymer structures allowed for selective side chain deuteration, eliminating spectra complications observed in perdeuterated PP. The concepts of chain motion in deuterated polyethylene and polypropylene have been modeled based on either the four tetrahedral jumps of a diamond lattice 391-392 or through the allowed states of pentane using the rotational isomeric state developed by Flory. 393 Regardless of the model, the predicted line shapes and total spectral width are proportional to the total number of available chain conformations. Statistically, these conformations (diamond model) as well as the 2 H-n.m.r. line shapes are determined by the probability of finding the C-D vector in one of the four orientations found in the diamond lattice. With this in mind, the use of only two lattice points would result in the smallest local motional averaging. On the other hand, the availability of the polymer to

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153 rapidly access all four tetrahedral positions results in isotropic orientation and in the complete narrowing of the spectrum. Similar to polyethylene’s glass transition, polypropylene side chain methyl group motion is locked through temperatures reaching the -transition. Of course, the methyl groups experience an additional narrowing of the rigid ‘Pake’ pattern from anisotropic motion (rotating around the C 3 axis) in the fast time regime. However, the concepts developed for deuterated polyethylene should remain valid to investigate side chain motion. The line shapes observed in the fully relaxed solid echo spectra of ADMET EP copolymers can be treated as a superposition of a rigid ‘Pake’ pattern and a motionally narrowed central region with decreasing widths as a function of temperature. The shape of the rigid pattern can also be dynamic at higher temperatures due to the finite symmetry of the gradient field tensor. The copolymer study was conducted in two steps to observe these differences and attempt to decompose the resulting line shapes. First, the investigation of side chain motion was conducted by melting the polymer (T m + 20 o C), achieving isotropic motional averaging, followed by stepwise cooling. The respective samples were then cooled to -70 o C in 10 o C intervals through the polymer’s thermal profile resulting in rigid methyl groups. Secondly, the study was completed by heating the respective polymer in 10 o C intervals following the polymer’s macroscopic melting behavior. In all cases, the polymer was allowed to equilibrate at each temperature to eliminate kinetic differences between melting and cooling of the sample. Figure 5-11 illustrates the solid echo 2 H-n.m.r. spectrum for the ADMET EP copolymer containing a perdeuterated methyl group on every 9 th carbon, HPEP-d 3 -9. The observed ‘Pake’ pattern (-70 o C) is common to all polyethylenes corresponds to

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154 locked methyl groups based on the ~35 kHz distance between singularities. Also, it seems side chain motion is independent of sample crystallization or melting since there is no difference between the spectra collected for either heating of cooling at the same temperature. Similar to previous studies on perdeuterated polypropylene, the initial spectral evidence for side group motional averaging, in our ADMET copolymers, is seen around the -relaxation plus 20 o C. As the temperature is increased within the polymer’s premelting region, theoretically reaching at the -relaxation, the spectra becomes dominated by isotropic methyl group motion. However, the spectral series still clearly shows signs of rigid methyl groups. The existence of the wide-line pattern indicates restricted motion even when the sample is melted. Similar observations have been seen for aPP and PE systems. Figure 5-11. Cooling and heating 2 H-n.m.r. spectra for HPEP-d 3 -9.

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155 A more detailed collection of the heating profiles is illustrated in Figure 5-12 for HPEP-d 3 -9 and the narrowing of the residual Pake pattern can be clearly observed. The characteristic line shapes within the overlapping pattern is common to the entire series (shown below). In this case, the slight narrowing of the Pake pattern within the temperature range of -70 o C < T < -30 o C is characteristic of axial reorientation caused by limited methyl group diffuse motion (2 vector jumps). Extension of the temperature range enables the methyl group to access an additional mode of rotation (3 vectors) causing increased freedom. Further, the line shape indicates that the methyl groups do not take part in non-axial reorientation which yields splitting of the allowed singularities. In addition to the lack of visible doublets, axial motion can also be seen by closer inspection of the overlapping line shapes (Figure 5-12). The reduction of line width is common and uniform when comparing the peak and leading edge of the corresponding singularity. In the past, motional modeling of main chain methylene groups in deuterated polyethylene and polypropylene has shown that non-uniform spectral averaging is manifested as non-uniform narrowing or, as mentioned, as an increase in the singularities multiplicity. Ideally, the appearance of isotropic methyl motion should be a function of methyl rotation within the amorphous and interstitial regions when appproaching the -relaxation temperature. On the same note, methyl branch inclusion within the crystal region for random EP copolymers was previously determined to be approximately 40 percent. 48 As a reminder, HPEP-d 3 -9 has a peak melting point of -10 o C when measured at 10 o C/min and a corresponding enthalpy of 30 J/g. So based on heat capacity measurements, the ADMET EP copolymer’s crystallinity, containing a methyl branch on every 9 th carbon, is

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156 10-15 %. If these ideas hold true only 4-6 % of the crystalline region contains incorporated (locked) methyl groups. The residual ‘Pake’ pattern observed at -10 o C in HPEP-d 3 -9 is most probably derived from methyl groups residing in this remaining crystalline material when approaching the -relaxation temperature. Figure 5-12. The collective heating 2 H-n.m.r. data set for HPEP-d 3 -9. An extensive morphological study has been conducted on our ADMET EP model copolymers containing a methyl on every 15 th and 21 st carbon. Continuation of this study was conducted using 2 H-n.m.r. as illustrated in Figure 5-13 and 5-14 for HPEP-d 3 -15. As observed for HPEP-d 3 -9, side chain motion is independent of sample preparation or whether the relaxation transitions are approached during a heating or cooling cycle. The temperature range studied on HPEP-d 3 -15 produced an interesting data set due to the last temperature (30 C) ending up directly on the sloping melting peak. As seen for HPEP-d o 3 -9 the narrowing of the basic ‘Pake’ pattern and the emergence of isotropic motion is

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157 visible at -30 o C. However, the narrow center peak is masked due to the higher percent of locked methyl groups and broadening at the lower temperatures. Figure 5-13. Cooling and heating 2 H-n.m.r. spectra for HPEP-d 3 -15. The combination of the heating spectral series, shown in Figure 5-14, better illustrates the increase diffusivity brought about by the higher crystallinity and the formation of thicker crystal morphology. Increasing the methylene sequence length by placing a branch on every 15 th carbon yields a melting point of 39 o C and a melting enthalpy of 80 J/g. In previous studies, the -relaxation temperature is independent of branch frequency but a two and a half fold increase in crystallinity (25-30 %) is observed here. Typically, an increase in crystallizable run lengths of polyethylene produces a larger concentration of methyl groups in the crystalline phase. At this point we are unable to calculate the exact percent of methyl groups in motion or their contribution to the three phase crystallizing model. However, the motional behavior with respect to accessible conformational states remains constant and independent of branch frequency.

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158 As outlined for HPEP-d 3 -9, diffuse methyl motion as well as the absence of non-axial reorientation is observed within the same temperature range. Figure 5-14. The collective heating 2 H-n.m.r. data set for HPEP-d 3 -15. The stacked 2 H-n.m.r. data set for the lowest branch content material, HPEP-d 3 -21, is shown in Figure 5-15 followed by the overlapping heating series in Figure 5-16. In this case, the deuterated methyl group on every 21 st carbon produces a model copolymer of moderate crystallinity. Thermal analysis has yielded a peak melting point of 61 o C owning to 52-55 % crystalline. Of course, the higher melting point allows for a greater range of plasticity and easier data interpretation. The precise structures, when annealed in the NMR tube, produce a very narrow melting peak with almost no premelting region. Once again, a narrowing of the Pake pattern is observed with increased temperature, whereas an isotropic methyl resonance appears around 0 o C. It seems that the increased crystallinity has hindered the emergence of the isotropic peak until 50 degrees higher

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159 than the -relaxation temperature. As mentioned, the motion measured around the side group relaxational transition should originate from the methyl groups within the unorganized material surrounding the crystalline segments. In this light, it seems that HPEP-d 3 -21 has little to no interstitial regions or very little amorphous content. Figure 5-15. Cooling and heating 2 H-n.m.r. spectra for HPEP-d 3 -21. The inherent discrepancy between the crystallinity determined by DSC and inferred from the NMR data originates from assumptions based on polyethylene’s theoretical melting point and enthalpy. In the case of ADMET EP copolymers, the crystal structure differs from that of random ethylene copolymers making crystallinity correlations from thermal analysis incorrect, even though it remains the easiest method for structural comparisons. In fact, a detailed crystal investigation determined the density of HPEP-d 3 -21 to reside in the vicinity of pure crystalline polyethylene. As measured,

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160 the density would place 80-90 % of all methyl groups in a locked position at lower temperatures. Figure 5-16. The collective heating 2 H-n.m.r. data set for HPEP-d 3 -21. Further studies are underway to quantify the amount of rigid methyl groups and distinguish the amount of methyl groups in the interstitial region. The side group motion is also being investigated at one degree intervals along the thermal profile collected using DSC. Also, the information gathered is currently being modeled with respect to NMR equation given in Figure 5-1 and 5-2 as well as application of the 3 and 5 bond models. In addition, the polymers are being studied using small angle neutron scattering to investigate the methyl position within the present three-phase model. The ultimate goal is to produce a valid correlation of data sets for molecular motion and methyl group placement within the macromolecular material. Hopefully, this will allow a better

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161 understanding of these ADMET copolymers’ relaxational transitions and model for crystalline morphology. 5.4 Conclusions Acyclic diene metathesis polymerization has proven to control the primary structure of ethylene/1-propene copolymers by selective deuterated methyl placement. The model copolymers exhibit isocharacteristic behavior with our previous EP models regardless of deuteron replacement and are successfully used as models for the parent EP copolymers containing precise structures. The inherent ability of metathesis and the effective hydrogenation techniques allows for a plethora of potential model copolymers containing precise deuteron placement without the effects of chain transfer. The structural investigation using 2 H-n.m.r. has shown that these ADMET EP copolymers yield textbook wide-line spectra, enabling easy deconvolution of methyl motion. Moreover, these copolymers exhibit characteristic methyl motion with respect to the collected thermal data gathered using DSC. Correlations to the polymers relaxation temperatures have been developed with relation to the three-phase crystallization model. Further modeling and simulation of the gather 2 H-n.m.r. spectra are needed using to selectively eliminate the contribution of rigid methyl groups using spin-lattice relaxation techniques. Additional spectral data is currently being collected as well as deconvolution of the NMR data. Also, comparisons to neutron scattering data are underway to confirm the methyl group motion and location observed by wide-line NMR. The uniqueness of the ADMET model EP copolymers, offers a better understanding of a new structure in polyethylene materials. Overall, the correlations and experimental conclusions for these ADMET model copolymers are helping improve our understanding of the relationship between structure and material behavior.

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162 5.5 Experimental Section 5.5.1 Instrumentation and Analysis All 1 H NMR (300 MHz) and 13 C NMR (75 MHz) spectra were recorded on either a Varian Associates Gemini 300 or Mercury 300 spectrometer. Chemical shifts for 1 H and 13 C NMR were referenced to residual signals from CDCl 3 ( 1 H = 7.27 ppm and 13 C = 77.23 ppm) with 0.03% v/v TMS as an internal reference. Reaction conversions and relative purity of crude reactions were monitored by chromatography and NMR. Gas chromatography (GC) was performed on a Schimadzu GC-17 gas chromatograph equipped with a 25 m capillary column packed with a 5% crosslinked PH ME and flame ionization detector. High-resolution mass spectral (LRMS and HRMS) data were obtained on a Finnegan 4500 gas chromatograph/mass spectrometer using the electron ionization (EI) mode. Elemental analyses were carried out by Atlantic Microlabs Inc., Norcross, GA. Gel permeation chromatography (GPC) was performed using a Waters Associates GPCV2000 liquid chromatography system with its internal differential refractive index detector (DRI), internal differential viscosity detector (DP), and a Wyatt 3 angle light scattering detector (LS). The light scattering signal was collected at three angles (39-90-141) and the three in-line detectors were operated in series in the order of LS-DRI-DP. The chromatography was performed at 45 C using two Waters Styragel HR-5E columns (10 microns PD, 7.8 mm ID, 300 mm length) with HPLC grade tetrahydrofuran as the mobile phase at a flow rate of 1.0 mL/minute. Injections were made at 0.05-0.07 % w/v sample concentration using a 322.5 l injection volume. In the case of universal calibration, retention times were calibrated against narrow molecular weight polystyrene

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163 standards (Polymer Laboratories; Amherst, MA). All standards were selected to produce M p or M w values well beyond the expected polymer's range. The Precision LS was calibrated using toluene and normalized to two narrow polystyrene standards (M w = 30,000 g/mol and 200,000 g/mol). Fourier transform infrared (FT-IR) spectroscopy was performed using a Bio-Rad FTS-40A spectrometer. The hydrogenation of the unsaturated ADMET prepolymer was monitored by the disappearance of the out-of-plane C-H bend for the internal olefin at 967 cm -1 . Monomer was prepared by droplet deposition and sandwiched between two KCl salt plates. Unsaturated and hydrogenated polymer samples were prepared by solution casting a thin film from tetrachloroethylene onto a KCl salt plate. Differential scanning calorimetry (DSC) analysis was performed using a Perkin-Elmer DSC 7 equipped with a controlled cooling accessory (CCA-7) at a heating rate of 10 C/min. Calibrations were made using indium and freshly distilled n-octane as the standards for peak temperature transitions and indium for the enthalpy standard. All samples were prepared in hermetically sealed pans (5-10 mg/sample) and were run using an empty pan as a reference and empty cells as a subtracted baseline. 5.5.2 Materials Schrock's molybdenum catalyst [(CF 3 ) 2 CH 3 CO] 2 (N-2,6-C 6 H 3 -i-Pr 2 ) Mo=CHC(CH 3 ) 2 Ph was synthesized according to the literature procedure. 157-162 Tetrahydrofuran (THF) was obtained from an Aldrich keg and dried by filtration through alumina. All other materials were used as received from the Aldrich chemical company.

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164 5.5.3 Monomer Synthesis The conditions used in the synthesis of all monomers were modified from previously published procedures by Wagener. 171 In an effort to produce the deuterated version of the precise methyl branched monomers lithium aluminum deuteride (LAD) was used in place of lithium aluminum hydride (LAH). For convenience and ease, deuterons are labeled ‘D’ within both the text and figures. Additional characterization information about the deuterated intermediates used and final precise monomers is discussed; however, the exact reaction conditions employed are referenced in each section. Characterization of 2-(4-pentenyl)-hept-6-en-1-d 2 -ol (7a). The starting monoacid (6a) was synthesized according to the literature procedure. 347 Modification of the synthesis using LAD and purification of compound 7a was performed as noted by Wagener. 171 Yield of compound 7a: 98.2 %. The following spectral properties were observed: 1 H NMR (CDCl 3 ): (ppm) 1.30-1.50 (m, 9H), 2.05 (m, 4H), 4.96 (m, 4H, vinyl CH 2 ), 5.78 (m, 2H, vinyl CH); 13 C NMR (CDCl 3 ): (ppm) 26.28, 30.49, 34.24, 40.22, 64.56 (-CD 2 -), 114.46 (vinyl CH 2 ), 139.00 (vinyl CH); EI/LRMS calcd. for C 12 H 20 D 2 O: 184, found: 184. Characterization of 2-(7-octenyl)-dec-9-en-1-d 2 -ol (7b). The starting monoacid (6b) was synthesized according to the literature procedure. 347 Modification of the synthesis using LAD and purification of compound 7b was performed as noted by Wagener. 171 Yield of compound 7b: 99.2 %. The following spectral properties were observed: 1 H NMR (CDCl 3 ): (ppm) 1.30-1.50 (m, 21H), 2.05 (m, 4H), 4.96 (m, 4H, vinyl CH 2 ), 5.78 (m, 2H, vinyl CH); 13 C NMR (CDCl 3 ): (ppm) 27.29, 29.37, 29.56,

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165 30.49, 31.33, 34.22, 40.78, 64.56 (-CD 2 -), 114.56 (vinyl CH 2 ), 139.50 (vinyl CH); EI/LRMS calcd. for C 18 H 32 D 2 O: 268, found: 268. Characterization of 2-(10-undecenyl)-tridec-12-en-1-d 2 -ol (7c). The starting monoacid (6c) was synthesized according to the literature procedure. 347 Modification of the synthesis using LAD and purification of compound 7c was performed as noted by Wagener. 171 Yield of compound 7c: 99.4 %. The following spectral properties were observed: 1 H NMR (CDCl 3 ): (ppm) 1.30-1.50 (m, 33H), 2.05 (m, 4H), 4.96 (m, 4H, vinyl CH 2 ), 5.78 (m, 2H, vinyl CH); 13 C NMR (CDCl 3 ): (ppm) 27.03, 29.08, 29.29, 29.65, 29.76, 29.79, 30.23, 31.03, 33.95, 40.48, 64.76 (-CD 2 -), 114.21 (vinyl CH 2 ), 139.29 (vinyl CH); EI/LRMS calcd. for C 24 H 44 D 2 O: 352, found: 352. Characterization of 6-methanesulfonyl methyl-d 2 -1,10-undecadiene (8a). The synthesis a purification of compound 8a was adopted from a previous literature procedure. 171 Yield of compound 8a: 98.2 %. The following spectral properties were observed: 1 H NMR (CDCl 3 ): (ppm) 1.30-1.50 (m, 8H), 1.71 (m, 1H), 2.05 (m, 4H), 2.99 (s, 3H), 4.96 (m, 4H, vinyl CH 2 ), 5.78 (m, 2H, vinyl CH); 13 C NMR (CDCl 3 ): (ppm) 25.94, 30.17, 33.97, 37.35, 37.56, 71.78 (-CD 2 -), 114.94 (vinyl CH 2 ), 138.60 (vinyl CH); EI/LRMS calcd. for C 13 H 22 D 2 O 3 S: 262, found: 262. Characterization of 9-methanesulfonyl methyl-d 2 -1,16-undecadiene (8b). The synthesis and purification of compound 8b was adapted from a previous literature procedure. 171 Yield of compound 8b: 97.9 %. The following spectral properties were observed: 1 H NMR (CDCl 3 ): (ppm) 1.25-1.50 (m, 20H), 1.71 (m, 1H), 2.05 (m, 4H), 2.99 (s, 3H), 4.96 (m, 4H, vinyl CH 2 ), 5.78 (m, 2H, vinyl CH); 13 C NMR (CDCl 3 ):

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166 (ppm) 26.64, 28.99, 29.13, 29.80, 30.71, 33.87, 37.30, 37.70, 71.88 (-CD 2 -), 114.33 (vinyl CH 2 ), 139.16 (vinyl CH); EI/LRMS calcd. for C 19 H 34 D 2 O 3 S: 346, found: 346. Characterization of 12-methanesulfonyl methyl-d 2 -1,22-undecadiene (8c). The synthesis and purification of compound 8c was adapted from a previous literature procedure. 171 Yield of compound 8c: 96.7 %. The following spectral properties were observed: 1 H NMR (CDCl 3 ): (ppm) 1.30-1.50 (m, 32H), 1.71 (m, 1H), 2.05 (m, 4H), 2.99 (s, 3H), 4.96 (m, 4H, vinyl CH 2 ), 5.78 (m, 2H, vinyl CH); 13 C NMR (CDCl 3 ): (ppm) 26.78, 29.15, 29.35, 29.70, 29.76, 29.77, 30.05, 30.81, 34.03, 37.39, 37.79, 72.33 (-CD 2 -), 114.34 (vinyl CH 2 ), 139.20 (vinyl CH); EI/LRMS calcd. for C 25 H 46 D 2 O 3 S: 431, found: 431. 5.5.4 Synthesis of Precise Deuterated Methyl ADMET Dienes The outlined synthesis is modified from an early literature procedure. In flame dried, Ar purged 100 mL three-neck round bottom flask equipped with an addition funnel and stir bar, lithium aluminum deuteride (1.5 eq) and dry THF were combined creating a 1M slurry. The flask was cooled to 0 o C, and a 1.0M solution of the mesylated alcohol in THF was added drop-wise. After 30 minutes, the flask was refluxed for an additional hour, cooled, and quenched by the sequential addition of water (1eq), 15% NaOH (1 eq), followed by 3 equivalents (versus LAD) of water. The precipitate was filtered and the organic layer was dried over MgSO 4 . Filtration and concentration of the organics yielded a yellow liquid which was purified by column chromatography using hexane as the mobile phase. Characterization of 6-methyl-d 3 -1,10-undecadiene (1). Yield of compound 1: 95.3 %. The following spectral properties were observed: 1 H NMR (CDCl 3 ): (ppm)

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167 0.92 (t, 0.06H), 1.15 (m, 1.5H), 1.39 (m, 7.5H), 2.05 (m, 4H), 4.96 (m, 4H, vinyl CH 2 ), 5.81 (m, 2H, vinyl CH); 13 C NMR (CDCl 3 ): (ppm) 18.93 (-CD 3 , J C-D = 18.89 Hz) , 26.65, 32.56, 34.37, 36.67, 114.37 (vinyl CH 2 ), 139.37 (vinyl CH); EI/HRMS calcd. for C 12 H 19 D 3 : 169.3213, found: 169.3210. Elemental analysis calcd. for C 12 H 19 D 3 : 85.12 C, 13.10 H & D; found: 85.19 C, 13.14 H. Characterization of 9-methyl-d 3 -1,16-undecadiene (2). Yield of compound 2: 90.8 %. The following spectral properties were observed: 1 H NMR (CDCl 3 ): (ppm) 0.92 (t, 0.08H), 1.11 (m, 2H), 1.20-1.50 (m, 19.5H), 2.05 (m, 4H), 4.96 (m, 4H, vinyl CH 2 ), 5.81 (m, 2H, vinyl CH); 13 C NMR (CDCl 3 ): (ppm) 18.99 (-CD 3 , J C-D = 18.89 Hz), 27.30, 29.24, 29.47, 30.14, 34.10, 37.27, 114.32 (vinyl CH 2 ), 139.39 (vinyl CH); EI/HRMS calcd. for C 18 H 31 D 3 : 253.4807, found: 253.4811. Elemental analysis calcd. for C 18 H 31 D 3 : 85.29 C, 13.68 H & D; found: 85.25 C, 13.65 H. Characterization of 12-methyl-d 3 -1,22-undecadiene (3). Yield of compound 3: 86.8 %. The following spectral properties were observed: 1 H NMR (CDCl 3 ): (ppm) 0.92 (t, 0.07H), 1.11 (m, 2H), 1.20-1.50 (m, 31H), 2.05 (m, 4H), 4.96 (m, 4H, vinyl CH 2 ), 5.81 (m, 2H, vinyl CH); 13 C NMR (CDCl 3 ): (ppm) 19.01 (-CD 3 , J C-D = 18.89 Hz), 27.33, 29.20, 29.41, 29.77, 29.88, 29.95, 30.28, 32.75, 34.10, 37.27, 114.30 (vinyl CH 2 ), 139.46 (vinyl CH); EI/HRMS calcd. for C 24 H 43 D 3 : 337.6402, found: 337.6414. Elemental analysis calcd. for C 24 H 43 D 3 : 85.38 C, 13.86 H & D; found: 85.34 C, 13.81 H. 5.5.5 General Polymerization Conditions All glassware was thoroughly cleaned and flame dried under vacuum prior to use. The monomers were dried over CaH 2 and K mirror, and subsequently degassed prior to

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168 polymerization. All metathesis reactions were initiated in the bulk, inside an Argon atmosphere glove box. The monomers were placed in a 50 mL round-bottomed flask equipped with a magnetic Teflon TM stirbar. The flasks were then fitted with an adapter equipped with a Teflon TM vacuum valve. After addition of catalyst, slow to moderate bubbling of ethylene was observed. 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 while stirring in an oil bath at 30 C until the viscosity increases. Generally after 4 h, the polymerization was exposed to full vacuum (<10 -1 mm Hg) for 24 h and then high vacuum (<10 -3 mm Hg) for 96 h, gradually increasing temperature to 50 C during the last 24 h of polymerization. The reaction vessel was then cooled to room temperature, exposed to air and toluene was added. The mixture was heated to 80 C in order to dissolve the resultant polymer and decompose any remaining active catalyst. The polymer/toluene solution was taken up and precipitated drop-wise into a vigorously stirred beaker containing 1500 mL of acidic methanol (1 M). Polymerization of 6-methyl-d 3 -undeca-1,10-diene (1) to give UPEP-d 3 -9. Schrock’s [Mo] catalyst (9.0 mg, 1.1x10 -3 mmol) was added to monomer 1 (1.0 g, 5.9 mmol). Precipitation (-78 o C) yielded 0.83 g of an off white, stringy material. Yield: 99 % (after precipitation). 1 H NMR (CDCl 3 ): (ppm) 0.88 (t, 0.05H, methyl), 1.10 (m, 2H), 1.28 (m, br, 7H), 1.97 (m, br, 4H), 5.40 (m, br, 2H, internal olefin); 13 C NMR (CDCl 3 ): (ppm) 19.02 (-CD 3 , J C-D = 24.3 Hz), 27.39, 27.43, 27.79, 32.59, 33.20, 36.76, 36.90, 130.17 (cis olefin), 130.64 (trans olefin). 13 C NMR (CDCl 3 ) integration of cis:trans peaks gives: 13:77. GPC data (THF vs. polystyrene standards): M w = 46 500 g/mol; P.D.I. (M w /M n ) = 1.8.

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169 Polymerization of 9-methyl-d 3 -heptadeca-1,16-diene (2) to give UPEP-d 3 -15. Schrock’s [Mo] catalyst (6.0 mg, 7.9x10 -3 mmol) was added to monomer 2 (1.0 g, 3.9 mmol). Precipitation (-78 o C) yielded 0.87 g of an off white, stringy material. Yield: 99 % (after precipitation). 1 H NMR (CDCl 3 ): (ppm) 0.88 (t, 0.07H, methyl), 1.10 (m, 2H), 1.28 (m, br, 19H), 1.97 (m, br, 4H), 5.40 (m, br, 2H, internal olefin); 13 C NMR (CDCl 3 ): (ppm) 19.02 (-CD 3 , J C-D = 25.1 Hz), 27.35, 27.49, 29.52, 29.65, 29.97, 30.07, 30.18, 32.78, 32.91, 37.31, 130.15 (cis olefin), 130.62 (trans olefin). 13 C NMR (CDCl 3 ) integration of cis:trans peaks gives: 19:81. GPC data (THF vs. polystyrene standards): M w = 51 300 g/mol; P.D.I. (M w /M n ) = 1.9. Polymerization of 12-methyl-d 3 -tricosa-1,22-diene (3) to give UPEP-d 3 -21. Schrock’s [Mo] catalyst (5.0 mg, 6.5x10 -3 mmol) was added to monomer 1 (1.1 g, 3.3 mmol). Precipitation (-78 o C) yielded 1.0 g of an off white, stringy material. Yield: 98 % (after precipitation). 1 H NMR (CDCl 3 ): (ppm) 0.88 (t, 0.08H, methyl), 1.10 (m, 2H), 1.28 (m, br, 31H), 1.97 (m, br, 4H), 5.40 (m, br, 2H, internal olefin); 13 C NMR (CDCl 3 ): (ppm) 19.07 (-CD 3 , J C-D = 26.1 Hz), 27.40, 27.50, 29.48, 29.62, 29.85, 29.88, 29.97, 30.03, 30.07, 30.34, 32.81, 32.91, 37.34, 130.15 (cis olefin), 130.62 (trans olefin). 13 C NMR (CDCl 3 ) integration of cis:trans peaks gives: 17:83. GPC data (THF vs. polystyrene standards): M w = 48 100 g/mol; P.D.I. (M w /M n ) = 2.0. 5.5.6 General Hydrogenation Conditions The procedure used was a modified diimide reduction published by Hahn. 389 Also, the procedure outline has been successfully applied to ADMET synthesized hydrocarbon polymers in the past. 156,171 The hydrogenation was performed in a flame dried, Ar purged, 500 mL round bottom flask equipped with a reflux condenser and stir bar. The

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170 vessel was charged with 1.50 g of the respective ADMET prepolymer followed by the addition of 100 mL of dry o-xylene. Upon dissolution, 2.30 g (2.5 eq) of TSH and 1.80 g (2.5 eq) of TPA was added and the solution was refluxed for 3 hours. The solution was cooled and an additional 2.5 eq of TSA and TPA were added. The solution was refluxed again for 3 additional hours and the preceding procedure was conducted once again. After a total of 9 hours, the solution was cooled and precipitated directly into methanol (1000 mL), chilled, and the solid was filtered. The resultant solid was dissolved in 30 mL of toluene and precipitated into 500 mL of acidic methanol (1M HCl) through an alumina plug. The methanol/toluene was chilled (-78 o C) and the white saturated polymer filtered and dried overnight under high vaccum. Hydrogenation of UPEP-d 3 -9 to give HPEP-d 3 -9. Precipitation yielded 0.98 g (95.3 %) of a translucent, tacky material. 1 RCDCl 3 (ppm) 0.84 (t, 0.04H, methyl), 1.1-1.5 (br, 17H); 13 C NMR (CDCl 3 ): (ppm) 19.02 (-CD 3 , J C-D = 25.1 Hz), 27.38, 30.04, 30.34, 32.79, 37.32. GPC data (THF vs. polystyrene standards): M w = 56 500 g/mol; P.D.I. (M w /M n ) = 1.8. DSC Results: T m (peak melting temperature) o Ch m = 30 J/g; T c (peak crystallization temperature) = -34 o Ch c = 30 J/g.. Hydrogenation of UPEP-d 3 -15 to give HPEP-d 3 -15. Precipitation yielded 0.97 g (98.6 %) of a white spongy material. 1 RCDCl 3 (ppm) 0.84 (t, 0.06H, methyl), 1.1-1.5 (br, 29H); 13 C NMR (CDCl 3 ): (ppm) 19.07 (-CD 3 , J C-D = 25.1 Hz), 27.39, 30.00, 30.04, 30.34, 32.79, 37.32. GPC data (THF vs. polystyrene standards): M w = 53 100 g/mol; P.D.I. (M w /M n ) = 1.9. DSC Results: T m (peak melting temperature) o Ch m = 79 J/g; T c (peak crystallization temperature) = 29 o Ch c = 75 J/g.

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171 Hydrogenation of UPEP-d 3 -21 to give HPEP-d 3 -21. Precipitation yielded 1.00 g (96.6 %) of a white spongy material. 1 RCDCl 3 (ppm) 0.84 (t, 0.06H, methyl), 1.1-1.5 (br, 41H); 13 C NMR (CDCl 3 ): (ppm) 19.07 (-CD 3 , J C-D = 25.1 Hz), 27.39, 30.00, 30.34, 32.80, 37.32. . GPC data (THF vs. polystyrene standards): M w = 56 100 g/mol; P.D.I. (M w /M n ) = 1.9. DSC Results: T m (peak melting temperature) o Ch m = 101 J/g; T c (peak crystallization temperature) = 56 o Ch c = 100 J/g.

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APPENDIX ADDITIONAL WAXD AND NMR DATA Figure A-1. WAXD pattern for unbranched ADMET polyethylene. 172

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173 Figure A-2. WAXD pattern for PE-1.5H as referenced in Chapter 2.

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174 Figure A-3. WAXD pattern for PE-7.1H as referenced in Chapter 2.

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175 Figure A-4. WAXD pattern for PE-13.1H as referenced in Chapter 2.

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176 Figure A-5. WAXD pattern for PE-25.0H as referenced in Chapter 2.

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177 Figure A-6. WAXD pattern for PE-43.3H as referenced in Chapter 2.

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178 Figure A-7. WAXD pattern for PE-55.6H as referenced in Chapter 2.

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179 Figure A-8. Combined cooling wide-line 2 H-n.m.r spectra for HPEP-d 3 -9.

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180 Figure A-9. Combined cooling wide-line 2 H-n.m.r spectra for HPEP-d 3 -15.

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181 Figure A-10. Combined cooling wide-line 2 H-n.m.r spectra for HPEP-d 3 -21.

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BIOGRAPHICAL SKETCH John Christopher Sworen, son of John and Christine Sworen, was born in Scranton, Pennsylvania, on September 8, 1976. He lived in Dickson City, Pennsylvania, throughout his entire youth, and attended Mid Valley High School. After high school he continued his education by attending The Pennsylvania State University regional campus in Dunmore, Pennsylvania. Academically, he pursued a general science degree while working in the chemistry lab under a work study program. After two years, he moved to the main campus at University Park, Pennsylvania, home of the Nittany Lions and happy valley. That following fall he joined Dr. Ayusman Sen’s research group and found his love of chemistry and polyolefins. His research under the direct advisement of Dr. Jim Pawlow was the synthesis via chain-addition of hyper-branched polyethylene for new synthetic oil additives. He graduated from Penn State in December 1998. John Sworen then followed his former mentor, Jim Pawlow, to the University of Florida to work under the Ph.D. advisement of Kenneth B. Wagener. While at Florida, he was able to expand and develop the ongoing modeling polyethylene project and set up numerous worldwide collaborations. After a successful graduate career, he completed the requirements for the degree of Doctor of Philosophy in August 2004. 202