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Mechanisms of Poly(Vinyl Chloride) Pyrolysis in the Presence of Transition Metals

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Mechanisms of Poly(Vinyl Chloride) Pyrolysis in the Presence of Transition Metals W&M ScholarWorks Dissertations, Theses, and Masters Projects Theses, Dissertations, & Master Projects 1995 Mechanisms of Poly(Vinyl Chloride) Pyrolysis in the Presence of Transition Metals William Stephen Bryant College of William & Mary - Arts & Sciences Follow this and additional works at: https://scholarworks.wm.edu/etd Part of the Physical Chemistry Commons, and the Polymer Science Commons Recommended Citation Bryant, William Stephen, "Mechanisms of Poly(Vinyl Chloride) Pyrolysis in the Presence of Transition Metals" (1995). Dissertations, Theses, and Masters Projects. Paper 1539626994. https://dx.doi.org/doi:10.21220/s2-3ya0-ks60 This Thesis is brought to you for free and open access by the Theses, Dissertations, & Master Projects at W&M ScholarWorks. It has been accepted for inclusion in Dissertations, Theses, and Masters Projects by an authorized administrator of W&M ScholarWorks. For more information, please contact [email protected]. MECHANISMS OF POLY(VINYL CHLORIDE) PYROLYSIS IN THE PRESENCE OF TRANSITION METALS A Thesis Presented to The Faculty of the Department of Chemistry The College of William and Mary in Virginia In Partial Fulfillment Of the Requirements for the Degree of Master of Arts by William Stephen Bryant 1995 APPROVAL SHEET This thesis is submitted in partial fulfillment of the requirements for the degree of Master of Arts Author Approved, August 4, 1995 W. H. Starnes, Jr. TABLE OF CONTENTS Acknowledgments vi List of Tables vii List of Figures viii List of Schemes xi Abstract xiii I. Introduction A. PVC Smoke and Fire 2 B. Thermal Degradation of PVC 4 C. Mechanisms for Benzene Formation 11 D. Current Smoke Suppression Additives 14 E. Reductive Coupling Mechanism 19 F. Low-Valent or Zero-Valent Metal Additives for Smoke Suppression 22 II. Experimental A. Instrumentation 1. Gas Chromatography-Mass Spectroscopy (GC-MS) 24 2. Nuclear Magnetic Resonance (NMR) 25 3. Infrared Spectroscopy (IR) 25 iii 4. Melting Point Apparatus 25 5. Thermogravimetric Analysis (TGA) 25 B. Model-Compound Reactions 1. General 27 2. Open System (External Flame) 28 3. Open System (Oil Bath) 29 4. Closed System 30 C. PVC Gel Reactions 1. General 32 2. Solid State Gel Reactions 32 3. IR Analysis Reactions 33 4. Solvated Gel Reactions 33 D. Synthesis of 3,-4-Dimethyl-1,5-hexadiene and Its Isomers 34 E. Synthesis of 4-Chloromethylbiphenyl 35 F. Synthesis of 4,4’-Diphenylbibenzyl 42 G. Synthesis of Cobalt(II) Formate 47 III. Results and Discussion A. Model Compounds 49 1. 3-Chloro-l-butene 50 2. Benzyl Chloride 62 iv 3. Cinnamyl Chloride 71 4 .4-Chloromethylbiphenyl 80 B. Solid State Degradation of PVC 91 C. Gelation of PVC in Solution 105 IV. Conclusions 106 References 108 v ACKNOWLEDGMENTS The author wishes to express his appreciation to Professor William H. Starnes, Jr., under whose guidance this investigation was conducted, for his patient counsel and criticism. Appreciation is also expressed to Professors Robert D. Pike and Michael A. G. Berg for their careful review and criticism of the manuscript. Particular gratitude goes to my parents, Mr. and Mrs. Julian A. Bryant, Jr., without whom this experience could not have been made possible. Finally, the author is especially grateful to his wife, Kerry L. Bryant, for her love, sacrifice, and caring encouragement during this research. VI List of Tables 1. Coupling of 3-chloro-1 -butene (1) with metal additives. 60 2. GC area percentages for pyrolysis products from benzyl chloride and metal . additives. 64 3. Gel yields. 92 vii List of Figures 1. Weight loss vs. temperature profile for PVC. 4 2. Most thermally unstable defect sites in PVC. 5 3. Model-compound reactions with molybdenum-containing Lewis acids. 16 4. Experimental setup for the open system (external flame) reactions. 28 5. Experimental setup for the open system (oil bath) reactions. 29 6. Experimental setup for the closed system reactions. 30 7 . Experimental setup for the solid state gel reactions. 32 8. GC-MS results for 4-biphenylmethanol. 39 9. *H NMR spectrum of 4-chloromethylbiphenyl. 40 10. 13C NMR spectrum of 4-chloromethylbiphenyl. 41 11. GC-MS results for 4-chloromethylbiphenyl. 41 12. *11 NMR spectrum of 4,4'-diphenylbibenzyl. 44 13. 13C NMR spectrum of 4,4'-diphenylbibenzyl. 45 14. GC-MS results for 4,4'-diphenylbibenzyl. 46 15. IR spectrum for cobalt(II) formate. 48 16. GC-MS data for the coupled products from 3-chloro-1 -butene. 51 -57 17. Isomers of 3-chloro-1 -butene reductive coupling product. 58 18. Major contributing structures of the cis radical. 59 viii 19. GC-MS results for bibenzyl. 63 20. GC chromatogram of pyrolysis products from Mo(CO)6 and benzyl chloride. 65 21. GC chromatogram of pyrolysis products from copper powder and benzyl chloride. 67 22. GC chromatogram of pyrolysis products from (methylcyclopentadienyl)- manganese tricarbonyl and benzyl chloride. 68 23. GC chromatogram of pyrolysis products from tetrakis(acetonitrile)- copper(I) hexafluorophosphate and benzyl chloride. 69 24. GC-MS results for pyrolysis products from copper(II) formate and benzyl chloride. 70 25. GC chromatogram of “95%” cinnamyl chloride. 72 26. GC chromatogram of “97%” cinnamyl chloride. 73 27. GC chromatogram of “97%” cinnamyl bromide. 74 28. ]H NMR spectrum of “97%” cinnamyl chloride. 75 29. Partial GC chromatogram of “97%” cinnamyl chloride. 77 30. GC-MS data for products from the lithium coupling reaction of cinnamyl chloride. 78 31. GC-MS data for control run with neat 4-chloromethylbiphenyl. 82 32. GC-MS data for pyrolysis products from iron nonacarbonyl and 4- ix chloromethylbiphenyl. 84 33. GC-MS data for pyrolysis products from copper powder and 4-chloro­ methylbiphenyl. 85 34. GC-MS data for products resulting from copper(H) formate decomposition followed by addition of 4-chloromethylbiphenyl. 87 35. GC-MS data for pyrolysis products from copper(II) formate and 4-chloromethylbiphenyl. 89 36. IR spectra for PVC degraded in the presence of copper additives. 95 37. IR spectra for PVC degraded in the presence of a tungsten additive. 96 38. IR spectra for PVC degraded in the presence of molybdenum additives. 97 39. IR spectra for PVC degraded in the presence of cobalt additives. 98 40. IR spectra for PVC degraded in the presence of nickel additives. 99 41. IR spectra for PVC degraded in the presence of a manganese additive. 100 42. IR spectra for PVC degraded in the presence of iron additives. 101 x List of Schemes 1. Combustion of PVC. 3 2. Ion-pair mechanism. 6 3. Radical mechanism. 7 4. Chloronium cation intermediate mechanism. 8 5. Four-membered cyclic transition state mechanism. 9 6. Thermal degradation of PVC. 10 7. Hexatriene mechanism for formation of benzene. 11 8. Octatetraene mechanism for formation of benzene. 12 9. PVC pyrolysis scheme. 15 10. Mo(VI)-catalyzed olefin dimerization and chloroalkylation. 17 11 Possible mechanism for Mo(VI)-catalyzed crosslinking in pyrolyzing PVC. 17 12. Metal-catalyzed reductive coupling mechanism. 19 13. Allylic and alkyl site coupling. 20 14. Homocoupling of alkyl halides via activated zero-valent copper. 23 15. Synthesis of 3,4-dimethyl-1,5-hexadiene and its isomers. 34 16. Conversion of 4-biphenyl carboxyl ic acid into the corresponding alcohol. 35 17. Conversion of 4-biphenylmethanol into 4-chloromethylbiphenyl. 36 xi 18. Synthesis of 4,4-diphenylbibenzyl. 42 19. Synthesis of cobalt formate. 47 20. Formation of radical intermediate from 3-chloro-1-butene. 59 21. Possible fragmentation routes for cinnamyl chloride coupled product. 79 22. Possible fragmentation route for 4,4'-diphenylbibenzyl. 81 23. Lewis-acid-catalyzed dehydrochlorination with subsequent crosslinking. 93 24. Crosslinking of PVC chains via Friedel-Crafts alkylation. 103 25. Crosslinking of PVC chains via reductive coupling. 103 xii ABSTRACT Many metal additives used as smoke suppressants and fire retardants for the thermal degradation of poly (vinyl chloride) (PVC) utilize a Lewis acid catalyzed crosslinking mechanism. However, this mechanism involves cracking reactions that generate volatile hydrocarbons which, in turn, increase flame spread. An alternative mechanism involving reductive coupling has been studied using zero-valent and low-valent transition metal additives (e.g., carbonyls, formates, and other compounds). The studies with low-molecular-weight models have shown that the reductive coupling mechanism is possible. Many of the metal carbonyls coupled 3-chloro-1- butene when decomposed prior to the introduction of the model compound. Copper- containing additives were the most effective for the coupling of the other model compounds studied. The solid-state PVC studies have also indicated the possible occurrence of a reductive coupling mechanism during the pyrolysis of the polymer. Several of the additives caused significant polymer gelation but did not cause the extensive double bond formation that would have indicated the operation of a Lewis- acid-catalyzed process. MECHANISMS OF POLY(VINYL CHLORIDE) PYROLYSIS IN THE PRESENCE OF TRANSITION METALS 2 I. INTRODUCTION A. PVC Smoke and Fire The industrial production of poly(vinyl chloride) (PVC), (-CH2CHCl-)n, is second only in terms of tonnage to that of polyethylene.1 It is considered to be the most important bulk polymer to the plastics industry today.2 It is well-known that PVC is widely used in the construction market as insulation for electrical and communication wiring, water pipes, home interior furnishings, and many other construction applications.3,4 In 1992, 5.6 billion pounds of PVC were utilized in construction in the
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