THE CHEMISTRY OF RADICAL POLYMERIZATION THE CHEMISTRY OF RADICAL POLYMERIZATION GRAEME MOAD CSIRO Molecular and Health Technologies Bayview Ave, Clayton, Victoria 3168, AUSTRALIA and DAVID H. SOLOMON Department of Chemical and Biomolecular Engineering. University of Melbourne, Victoria 3010, AUSTRALIA Dr Graeme Moad CSIRO Molecular and Health Technologies Bayview Ave, Clayton, Victoria 3168 AUSTRALIA Email: [email protected] Prof David H. Solomon Department of Chemical and Biomolecular Engineering. University of Melbourne Victoria 3010 AUSTRALIA Email: [email protected] Contents Contents............................................................................................................................ v Index to Tables.............................................................................................................xvi Index to Figures ............................................................................................................ xx Preface to the First Edition .....................................................................................xxiii Preface to the Second Edition..................................................................................xxv Acknowledgments......................................................................................................xxvi 1 INTRODUCTION.................................................................................................. 1 1.1 References ............................................................................................................ 8 2 RADICAL REACTIONS.................................................................................... 11 2.1 Introduction....................................................................................................... 11 2.2 Properties of Radicals...................................................................................... 12 2.2.1 Structures of Radicals .................................................................................... 12 2.2.2 Stabilities of Radicals..................................................................................... 14 2.2.3 Detection of Radicals..................................................................................... 14 2.3 Addition to Carbon-Carbon Double Bonds................................................ 16 2.3.1 Steric Factors................................................................................................... 19 2.3.2 Polar Factors.................................................................................................... 21 2.3.3 Bond Strengths................................................................................................ 22 2.3.4 Stereoelectronic Factors................................................................................. 23 2.3.5 Entropic Considerations................................................................................. 24 2.3.6 Reaction Conditions....................................................................................... 24 2.3.6.1 Temperature............................................................................................. 24 2.3.6.2 Solvent ..................................................................................................... 25 2.3.7 Theoretical Treatments .................................................................................. 26 2.3.8 Summary.......................................................................................................... 28 2.4 Hydrogen Atom Transfer ............................................................................... 29 2.4.1 Bond Dissociation Energies .......................................................................... 30 2.4.2 Steric Factors................................................................................................... 30 2.4.3 Polar Factors.................................................................................................... 31 2.4.4 Stereoelectronic Factors................................................................................. 32 2.4.5 Reaction Conditions....................................................................................... 33 2.4.6 Abstraction vs Addition ................................................................................. 34 2.4.7 Summary.......................................................................................................... 36 v vi Contents 2.5 Radical-Radical Reactions.............................................................................. 36 2.5.1 Pathways for Combination............................................................................ 37 2.5.2 Pathways for Disproportionation.................................................................. 38 2.5.3 Combination vs Disproportionation ............................................................. 39 2.5.3.1 Statistical factors..................................................................................... 39 2.5.3.2 Steric factors............................................................................................ 40 2.5.3.3 Polar factors............................................................................................. 41 2.5.3.4 Stereoelectronic and other factors ........................................................ 41 2.5.3.5 Reaction conditions................................................................................ 42 2.5.4 Summary.......................................................................................................... 43 2.6 References .......................................................................................................... 44 3 INITIATION ......................................................................................................... 49 3.1 Introduction....................................................................................................... 49 3.2 The Initiation Process...................................................................................... 50 3.2.1 Reaction with Monomer ................................................................................ 51 3.2.2 Fragmentation ................................................................................................. 54 3.2.3 Reaction with Solvents, Additives, or Impurities....................................... 55 3.2.4 Effects of Temperature and Reaction Medium on Radical Reactivity .... 55 3.2.5 Reaction with Oxygen.................................................................................... 56 3.2.6 Initiator Efficiency in Thermal Initiation .................................................... 57 3.2.7 Photoinitiation................................................................................................. 58 3.2.8 Cage Reaction and Initiator-Derived Byproducts ...................................... 60 3.2.9 Primary Radical Termination........................................................................ 61 3.2.10 Transfer to Initiator ........................................................................................ 62 3.2.11 Initiation in Heterogeneous Polymerization................................................ 63 3.3 The Initiators..................................................................................................... 64 3.3.1 Azo-Compounds............................................................................................. 68 3.3.1.1 Dialkyldiazenes....................................................................................... 68 3.3.1.1.1 Thermal decomposition..................................................................... 72 3.3.1.1.2 Photochemical decomposition.......................................................... 74 3.3.1.1.3 Initiator efficiency.............................................................................. 74 3.3.1.1.4 Transfer to initiator ............................................................................ 77 3.3.1.2 Hyponitrites............................................................................................. 78 3.3.2 Peroxides.......................................................................................................... 79 3.3.2.1 Diacyl or diaroyl peroxides................................................................... 82 3.3.2.1.1 Thermal decomposition..................................................................... 82 3.3.2.1.2 Photochemical decomposition.......................................................... 83 3.3.2.1.3 Initiator efficiency.............................................................................. 84 3.3.2.1.4 Transfer to initiator and induced decomposition............................ 85 3.3.2.1.5 Redox reactions .................................................................................. 85 3.3.2.2 Dialkyl peroxydicarbonates................................................................... 87 3.3.2.3 Peroxyesters............................................................................................. 88 Contents vii 3.3.2.3.1 Thermal decomposition..................................................................... 88 3.3.2.3.2 Photochemical decomposition.......................................................... 90 3.3.2.4 Dialkyl peroxides.................................................................................... 90 3.3.2.5 Alkyl hydroperoxides............................................................................. 92 3.3.2.6