ESR Spectroscopy in Polymer Research

Thirty years ago, Zavoisky, in Moscow (USSR), reported the first successful experi­ mental observations of the ESR phenomenon. Its application to polymer problems began about 20 years ago. ESR belongs to the most specific and useful methods in the study of polymer reactions. The main purpose of this book is to collect the present available information on the applications of electron spin resonance (ESR) spectroscopy in polymer research. The book has been written both for those who want an introduction to this field, and for those who are aheady familiar with ESR and are interested in application to polymers. Therefore, the fundamental principles of ESR spectroscopy are first out­ lined, the experimental methods including computer applications are described in more detail, and the main emphasis is on the application of ESR methods to polymer problems. Many results obtained are only briefly treated for lack of space. The authors hope that this book will provide a useful source of information by giving a coherent treatment and extensive references to original papers, reviews, and discussions in monographs and books. In this way we hope to encourage polymer chemists, organic chemists, biochemists, physicists, and material scientists to apply ESR methods to their research problems.

1. Generation of Free Radicals.- 1.1. Free Radicals, Biradicals, and Radical Ions.- 1.2. Basic Properties of Free Radicals.- 1.3. Free Radical Reactions.- 1.4. Interaction of Electromagnetic Radiation with Matter.- 1.4.1. Interaction of Low Energy Photons with Matter.- 1.4.2. Interaction of High Energy Photons with Matter.- 1.5. Interaction of Charged Particles with Matter.- 1.6. Physical Sources of Free Radicals.- 1.6.1. Ionizing Radiation.- 1.6.1.1. Charged Particle Accelerators.- 1.6.1.2. Radioisotope Sources.- 1.6.1.3. Nuclear Reactors.- 1.6.2. Light Irradiation.- 1.6.3. Other Physical Sources for the Production of Free Radicals.- 1.7. Chemical Sources for the Production of Free Radicals.- 2. Principles of ESR Spectroscopy.- 2.1. Introduction.- 2.2. Interaction Between the Electron Spin and Internal Magnetic Field.- 2.3. Spin Relaxation.- 2.4. The Shape of ESR Resonance Lines.- 2.4.1. Line Shape.- 2.4.2. Line Width.- 2.4.3. Intensity.- 2.5. g-Value.- 2.6. Interaction Between the Electron and the Nuclear Spins.- 2.6.1. Hyperfine Structure Spectrum due to a Single Proton.- 2.6.2. Spectra with Hyperfine Structure due to Equivalent Protons.- 2.6.3. Hyperfine Structure Spectra due to Nonequivalent Protons.- 2.6.4. Second Order Splittings of Lines.- 3. Experimental Instrumentation of Electron Spin Resonance.- 3.1. ESR Spectrometers.- 3.2. Field Sweep Calibration.- 3.3. Measurements of Spin Concentration.- 3.4. Measurements of ESR Spectra at Different Temperatures.- 3.5. Computer Application into ESR Spectroscopy.- 3.6. Preparation of Samples for ESR Experiments.- 3.6.1. Gases.- 3.6.2. Liquids.- 3.6.3. Solids.- 3.6.4. Stabilization of Free Radicals.- 3.6.5. Apparatus for High Pressure Annealing of Samples.- 3.6.6. Loading Apparatus for ESR Stretching Experiments.- 3.6.7. Milling Devices for Grinding Samples.- 3.6.8. Preparation of Samples Containing Free Radicals by Sawing Technique.- 3.7. Special Techniques for ESR Spectroscopy.- 4. ESR Study of Polymerization Processes.- 4.1. Homogeneous Chain-growth Polymerization.- 4.2. Ionizing Polymerization.- 4.2.1. Solid-state Polymerization.- 4.2.1.1. Olefin Monomers.- 4.2.1.2. Dienes.- 4.2.1.3. Cyclic Olefines.- 4.2.1.4. Vinyl Monomers.- 4.2.1.4.1. Acrylic and Methacrylic Acide Monomers.- 4.2.1.4.2. Acrylamides.- 4.2.1.4.3. Methyl Methacrylate.- 4.2.1.4.4. Acrylonitrile and Methacrylonitrile.- 4.2.1.4.5. Vinyl Acetate.- 4.2.1.4.6. Styrene.- 4.2.1.4.7. N-Vinylcarbazole.- 4.2.1.4.8. Radical Pairs in ?-Irradiated Vinyl Monomers.- 4.2.1.5. Cyclic Monomers.- 4.2.2. Polymerization in Organic Glass Matrices.- 4.2.2.1. ESR Studies of Ionic Processes in ?-Irradiated Organic Glasses.- 4.2.2.2. ESR Studies of Ionic Polymerization in Organic Glass Matrices.- 4.2.2.2.1. Nitroethylene.- 4.2.2.2.2. Isobutene.- 4.2.2.2.3. 1,3-Butadiene.- 4.2.2.2.4. Vinyl Ethers.- 4.2.2.2.5. Acrylic Acid.- 4.2.2.2.6. Methyl Methacrylate.- 4.2.2.2.7. Acrylonitrile.- 4.2.2.2.8. Styrene and ?-Methylstyrene.- 4.2.3. Ionizing Polymerization ― Miscellaneous Problems.- 4.3. Photopolymerization.- 4.3.1. Photosensitized by Hydrogen Peroxide.- 4.3.2. Photosensitized by Hydroperoxides and Peroxides.- 4.3.3. Photosensitized by Diacyl Peroxides and Tert-Butyl Peresters.- 4.3.4. Photosensitized by Dialkyl Peroxydicarbonates.- 4.3.5. Photosensitized by Benzophenone.- 4.3.6. Quinones.- 4.3.7. Photosensitized by Azo-Compounds.- 4.3.8. Photosensitized by Metal Halides.- 4.3.9. Photosensitized by Metal Acetylacetonates.- 4.4. Thermal Polymerization.- 4.4.1. Application of a Polymer Matrix for Studies of Growing Chain Radicals at High Pressure.- 4.4.2. Stabilization of Free Radicals on the Surface of Synthetic Zeolites.- 4.4.3. Popcorn Polymerization.- 4.4.4. Thermal Polymerization ― Miscellaneous Problems.- 4.5. Polymerization Initiated by Mechano-radicals.- 4.6. Polymerization Initiated by Various Free Radical Initiation Systems.- 4.6.1. Hydroperoxide-SO2 System.- 4.6.2. Tetraphenylborate-Organic Acid Systems.- 4.6.3. Redox Systems.- 4.6.3.1. Polymerization Initiated by Redox Systems.- 4.6.3.1.1. Acrylic and Methacrylic Acid Monomers.- 4.6.3.1.2. Acrylamides.- 4.6.3.1.3. Acrylonitrile.- 4.6.3.1.4. Vinyl Esters.- 4.6.3.1.5. Copolymerization of Vinyl Acetate and Acrylonitrile with Various Comonomers.- 4.6.3.1.6. Allyl Monomers.- 4.6.3.1.7. Miscellaneous Monomers.- 4.7. Anionic Polymerization.- 4.7.1. Introduction.- 4.7.2. ESR Study of Ion Pairs, Free Ions, and Electron-transfer Reactions.- 4.7.3. Initiation of Polymerization by Electron Transfer.- 4.7.4. Initiation of Polymerization with Stable Alkali Metal Complexes.- 4.7.4.1. Polycyclic Aromatic Complexes.- 4.7.4.2. Ketyl Complexes.- 4.7.4.3. Aromatic Nitrile Complexes.- 4.7.4.4. Pyridyl Complexes.- 4.7.4.5. Organic Sulphur Complexes.- 4.8. Cationic Polymerization.- 4.8.1. Photo-Induced Cationic Polymerization.- 4.8.2. Cationic Polymerization Initiated with Lewis Acids.- 4.9. Heterogenous Chain-Growth Polymerization.- 4.9.1. Ziegler-Natta Catalysts.- 4.9.2. Phillips Catalysts.- 4.9.3. Other Metal Catalysts for Polymerization.- 4.9.4. Polymerization Initiated by Clays.- 4.9.5. Polymerization Initiated by Silica Gel.- 4.9.6. Polymerization Initiated by Molecular Sieves.- 5. ESR Study of Degradation Processes in Polymers.- 5.1. Radiation and Photo-Degradation of Polymers.- 5.1.1. Polyolefines.- 5.1.1.1. n-Alkane Single Crystals.- 5.1.1.2. Polyethylene.- 5.1.1.2.1. Radical Formation Under Ionizing Radiation.- 5.1.1.2.2. Radical Formation Under UV-Irradiation.- 5.1.1.2.2.1. ESR Studies on Photosensitized Degradation of Polyethylene.- 5.1.1.2.3. Conversion of Free Radicals Under Light Irradiation and Warming.- 5.1.1.2.4. Morphological Effects on the Formation and Behavior of Radicals.- 5.1.1.2.5. Decay of Free Radicals.- 5.1.1.2.6. Ethylene Copolymers.- 5.1.1.3. Polypropylene.- 5.1.1.3.1. Radical Formation Under Ionizing Radiation.- 5.1.1.3.2. Radical Formation Under UV-Irradiation.- 5.1.1.4. Molecular Motions in Solid Polyolefmes.- 5.1.1.5. Radical Pairs in ?-Irradiated Polyolefines.- 5.1.1.6. Poly-1-butene.- 5.1.1.7. Polyisobutylene.- 5.1.1.8. Poly-3-methyl-1-butene.- 5.1.1.9. Poly-4-methyl-1-pentene.- 5.1.1.10. Trapped Electrons in Polyolefines.- 5.1.2. Polydienes.- 5.1.2.1. Polybutadiene.- 5.1.2.2. Polyisoprene.- 5.1.2.3. Polypiperylene.- 5.1.2.4. Polychloroprene.- 5.1.3. Poly(methyl acrylate) and Poly(methyl methacrylate).- 5.1.4. Polystyrenes.- 5.1.5. Poly(vinyl chloride) and Poly(vinylidene chloride).- 5.1.6. Fluorinated Polymers.- 5.1.7. Poly(vinyl acetate).- 5.1.8. Polyvinyl alcohol).- 5.1.9. Polynitroethylene.- 5.1.10. Polyvinylpyridines.- 5.1.11. Poly(vinyl pyrrolidone).- 5.1.12. Polyethers.- 5.1.12.1. Polyoxymethylene.- 5.1.12.2. Polyoxyethylene.- 5.1.12.3. Poly-3,3-bis(chloromethyl)oxethane.- 5.1.12.4. Poly(2,6-dimethyl-1,4-phenyleneoxide).- 5.1.12.5. Polyglycols.- 5.1.13. Polycarbonates.- 5.1.14. Polyesters.- 5.1.14.1. Poly(?-propiolactone).- 5.1.14.2. Linear Aliphatic Polyesters.- 5.1.14.3. Poly(ethylene terephthalate).- 5.1.14.4. Poly(ethylene-2,6-naphthalene-dicarboxylate.- 5.1.15. Polyamides.- 5.1.16. Polyurethanes.- 5.1.17. Sulphur-Containing Polymers.- 5.1.18. Polysiloxanes.- 5.1.19. Biopolymers.- 5.1.19.1. Cellulose.- 5.1.19.2. Starch.- 5.1.19.3. Other Polysaccharides.- 5.1.19.4. Lignin.- 5.1.19.5. Wool.- 5.1.19.6. Polynucleotides.- 5.2. Free Radicals Formed in Glow Discharge of Polymers.- 5.3. Anionic Degradation of Vinylaromatic Polymers.- 5.4. Reaction of Polymers with Hydroxy Radicals.- 6. ESR Study of Polymers in Reactive Gases.- 6.1. Molecular Oxygen.- 6.2. Singlet Oxygen.- 6.3. Atomic Oxygen.- 6.4. Atomic Hydrogen.- 6.5. Atomic Nitrogen.- 6.6. Noble Gases.- 6.7. Other Gases.- 7. ESR Studies of the Oxidation of Polymers.- 7.1. Radiation-Induced Oxidation of Polymers.- 7.2. Polyethylene.- 7.3. Polypropylene.- 7.4. Poly(tetrafluoroethylene).- 7.5. ESR Studies of Antioxidants.- 8. ESR Studies of Molecular Fracture in Polymers.- 8.1. Introduction.- 8.2. Generation of Submicrocracks.- 8.3. Generation of Free Radicals in Mechanically Deformed Polyethylene.- 8.4. ESR Study of Free Radicals Formed During Fracture in Rubber.- 8.5. ESR Study of Fatigue Processes in Polymers.- 8.6. ESR Study of Free Radicals Formed During Grinding and Machining of Polymers.- 8.7. Anomalous Behavior of Free Radicals Obtained by Sawing Technique.- 8.8. Mechanical Degradation of Polymers in Frozen Solution Matrix.- 9. ESR Studies of Graft Copolymerization.- 9.1. Graft Copolymerization of Polyethylene.- 9.2. Cellulose Graft Copolymers.- 9.3. Miscellaneous Problems.- 10. ESR Studies of Crosslinking.- 10.1. ESR Study of Enhanced Crosslinking of Polymers.- 10.2. ESR Study of Free Radicals Observed During the Curing of Unsaturated Polyester Resins.- 10.3. ESR Study of the Vulcanization of Rubber.- 10.4. ESR Spectra of Light-Irradiated Poly(vinyl cinnamate).- 11. Application of Stable Free Radicals in Polymer Research.- 11.1. Nitroxide Radicals.- 11.2. Spin-Probe Technique.- 11.3. Spin-Trapping Technique.- 11.4. Spin-Labeling Technique.- 12. ESR Spectroscopy of Stable Polymer Radicals and their Low Molecular Analogues.- 12.1. Poly(triphenylmethyl) Radicals.- 12.2. Poly(?,??-diphenyl-p-xylene) Radicals.- 12.3. Polyphenoxy Radicals.- 12.4. Poly(triphenylhydrazyl) Radicals.- 12.5. Polymers Containing Stable Free Radicals of the Nitroxide Type.- 12.6. Poly(pyridinyl) Radicals.- 12.7. Poly(verdazyl) Radicals.- 12.8. Polymers Containing Stable Free Radicals of the Tetrazine Type.- 12.9. Polyradical Anions.- 12.10. ESR Study of Donor-Acceptor Polymer Complexes.- 12.11. Organic Polymeric Semiconductors.- 12.12. Free Radicals Formed by Pyrolysis of Polymers.- 12.13. Free Radicals in Carbon Black.- 13. ESR Study of Ion-Exchange Resins.- References.