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Photoinitiators
Photoinitiators
Structures,ReactivityandApplicationsinPolymerization
Volume1
Writtenby
Jean-PierreFouassier
JacquesLalevée
Photoinitiators
Structures,ReactivityandApplicationsinPolymerization
Volume2
Writtenby
Jean-PierreFouassier
JacquesLalevée
Authors
Prof.Jean-PierreFouassier 15,rueduChâteau 68590SaintHippolyte France
Prof.JacquesLalevée UniversityofHauteAlsace UMRCNRS7361 15,rueJeanStarcky 68057MulhouseCedex France
Allbookspublishedby WILEY-VCH arecarefully produced.Nevertheless,authors,editors,and publisherdonotwarranttheinformationcontained inthesebooks,includingthisbook,tobefreeof errors.Readersareadvisedtokeepinmindthat statements,data,illustrations,proceduraldetailsor otheritemsmayinadvertentlybeinaccurate.
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PrintISBN: 978-3-527-34609-7
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PartIPhotopolymerizationReactionsandPhotoinitiators: Backgrounds 1
1BackgroundsinPhotopolymerizationReactions:AShort Overview 3
1.1PhotopolymerizationandPhoto-cross-linking 3
1.1.1Reactions 3
1.1.2PhotoinitiationStep 4
1.1.3DifferentKindsofPhotopolymerizationReactions 4
1.1.4MonomersandOligomers 4
1.1.5PhotopolymerizableFormulations 6
1.1.6UVCuring 6
1.1.7Imaging 6
1.1.8ControlledPhotopolymerization 7
1.2PhotopolymerizationReactions 7
1.2.1MonomersandOligomersinPhotopolymerizationReactions 7
1.2.1.1Monomers/OligomersinRadicalPhotopolymerization 8
1.2.1.2Monomers/OligomersinCationicPhotopolymerization 10
1.2.1.3MonomersinThiol–enePhotopolymerization 11
1.2.1.4MonomersinChargeTransferPhotopolymerization 12
1.2.1.5MonomersinAnionicPhotopolymerization 12
1.2.1.6MonomersinPhotoinducedCopper-CatalyzedAzide–Alkyne Cycloaddition 12
1.2.1.7MonomersinPhotoactivatedHydrosilylationReactions 12
1.2.2MonitoringthePhotopolymerizationReaction 13
1.2.3KineticLawsinPhotopolymerizationReactions 13
1.2.3.1RadicalPhotopolymerization 13
1.2.3.2CationicPhotopolymerization 15
1.2.3.3DependenceofPhotopolymerizationRate 15
1.2.3.4Laser-InducedPhotopolymerization 16
1.2.3.5KineticsofthePhotopolymerizationinBulk 17
1.2.4OxygenInhibition 18
1.2.5RoleofLightStabilizers 18
1.2.6CompetitiveAbsorptionofLightbyaPigment 20
1.2.7RoleofEnvironmentinthePolymerizationReaction 21
1.3ImplementationofPhotopolymerizationReactionsandBriefOverview oftheApplications 22
1.3.1LightSourcesforPhotopolymerizationReactions 22
1.3.1.1ElectromagneticRadiation 22
1.3.1.2CharacteristicsofaLightSource 23
1.3.1.3AvailableLightSources 23
1.3.2BriefOverviewoftheApplicationAreas 27 References 29
2PhotoinitiatingSystem 35
2.1CharacteristicsofaPhotoinitiatingSystem 35
2.1.1GeneralProperties 35
2.1.2AbsorptionofLightbyaMolecule 35
2.1.2.1AbsorptionSpectrum 35
2.1.2.2MolecularOrbitalsandEnergyLevels 36
2.1.2.3AbsorptionofLightandOpticalTransitions 36
2.1.2.4AbsorptionIntensity 37
2.1.2.5ReciprocityLaw 38
2.1.2.6MultiphotonicAbsorption 38
2.1.3Jablonski’sDiagram 39
2.1.4KineticsoftheExcitedStateProcesses 40
2.1.5PhotoinitiatorandPhotosensitizer 40
2.1.6AbsorptionofaPhotosensitiveSystem 42
2.1.7InitiationStepofaPhotoinducedPolymerization 42
2.1.7.1ProductionofInitiatingSpecies 43
2.1.7.2CompetitiveReactionsintheExcitedStates 43
2.1.7.3ReactivityinBulkvs.Solution:RoleofDiffusion 43
2.1.7.4CageEffects 44
2.2ApproachofPhotochemicalandChemicalReactivity 45
2.3ReactivityofaPhotosensitiveSystem 46
2.4Efficiencyvs.Reactivity 48 References 49
PartIIPhotoinitiators:Structures,ExcitedStates,Reactivity, andEfficiency 55
3CleavableRadicalPhotoinitiators 59
3.1BenzoylChromophore-BasedPhotoinitiators 59
3.1.1BenzoinDerivatives 61
3.1.2BenzoinEtherDerivatives 62
3.1.2.1AbsorptionofBenzoinEthers 62
3.1.2.2PhotolysisofBenzoinEthers 63
3.1.2.3CleavageProcessinBenzoinEthers 64
3.1.2.4InitiatingRadicalsinBenzoinEthers 64
3.1.2.5SubstitutionEffectsinBenzoinEtherDerivatives 64
3.1.2.6EffectofLewisAcidsonBenzoinEthers 65
3.1.3HalogenatedKetones 65
3.1.4DialkoxyacetophenonesandDiphenylacetophenones 65
3.1.5MorpholinoandAminoKetones 66
3.1.6HydroxyAlkylAcetophenones 67
3.1.7KetoneSulfonicEsters 69
3.1.8ThiobenzoateDerivatives 70
3.1.9SulfonylKetones 70
3.1.10OxysulfonylKetones 71
3.1.11OximeEsters 71
3.2HydroxyAlkylHeterocyclicKetones 72
3.3BenzophenoneandThioxanthoneMoiety-BasedCleavableSystems 72
3.3.1BenzophenonePhenylSulfides 72
3.3.2Ketosulfoxides 72
3.3.3BenzophenoneThiobenzoates 73
3.3.4BenzophenoneSulfonylKetones 73
3.3.5SilylMoietyContainingCleavableBenzophenoneandThioxanthone Derivatives 73
3.4BenzoylPhosphineOxideDerivatives:aC—PBondBreaking 73
3.5TrichloromethylTriazines 76
3.6BiradicalGeneratingKetones 76
3.7Diketones 76
3.8SilylGlyoxylates 77
3.9Peroxides 77
3.10Peresters 78
3.11AzidesandAromaticBis-azides 79
3.12Carbon–GermaniumCleavableBond-BasedDerivatives 79
3.13Carbon–TinCleavableBond-BasedPIs 81
3.14Carbon–SiliconCleavableBond-BasedPIs 81
3.14.1BisSilylKetones 81
3.14.2Tetraacylsilanes 82
3.15Carbon–NitrogenCleavableBondContainingPIs 82
3.15.1AzoDerivatives 82
3.15.2PhenacylPyridiniumDerivatives 83
3.15.3PhenacylEthylCarbazoliumDerivatives 83
3.15.4N-substitutedDiazabicyclononanes 83
3.16Boron–SulfurCleavableBondContainingPIs 84
3.17Boron–NitrogenCleavableBondContainingPIs 84
3.18DisilaneDerivatives 84
3.19DiselenideandDiphenylditellurideDerivatives 85
3.20Sulfur–CarbonCleavableBond-BasedDerivatives 85
3.21DisulfideDerivatives 86
3.22Oxyamines 86
3.22.1Alkoxyamines 86
3.22.2Silyloxyamines 86
3.23Barton’sEsterDerivatives 87
3.24HydroxamicandThiohydroxamicAcidsandEsters 87
3.25IonPairPIs 87
3.25.1Organoborates 88
3.25.2Polyoxometalate–oniumSaltIonPairs 88
3.25.3Naphthalimide–IodoniumSaltIonPairs 89
3.26OrganometallicCompounds 90
3.26.1Titanocenes 90
3.26.2MiscellaneousOrganometallicPIs 90
3.26.2.1ChromiumComplexes 90
3.26.2.2AluminateComplexes 90
3.26.2.3ZirconoceneDichloride 91
3.26.2.4ZincComplexes 91
3.27MetalSaltsandMetallicSaltComplexes 91
3.28MiscellaneousSystems 91
3.28.1Acetone 91
3.28.2PhosphineOxideDerivatives 92
3.28.3Sulfur–SiliconCleavableBond-BasedDerivatives 92
3.28.4DigermaneandDistannaneDerivatives 92
3.28.5HalogenatedKetones 92
3.28.6HydroxyAlkyl-ConjugatedKetones 92
3.28.7Dibenzothiophenes 93
3.28.8Self-initiatingMonomers 93
3.28.9Self-assembledPIMonolayers 93
3.28.10Silicon–HydrideTerminatedSurface 93
3.28.11SemiconductorNanoparticles 93
3.28.12Perovskites(Nanocrystals) 94 References 95
4Two-ComponentRadicalPhotoinitiators 117
4.1Ketone/HydrogenDonorandKetone/Electron/ProtonDonor Couples 117
4.1.1BasicMechanism 117
4.1.2HydrogenDonorsandElectron/ProtonDonors 119
4.1.2.1Amines 119
4.1.2.2ThioDerivatives 121
4.1.2.3Benzoxazines 121
4.1.2.4Aldehydes 122
4.1.2.5Acetals 122
4.1.2.6Hydroperoxides 122
4.1.2.7Silanes 122
4.1.2.8Silylamines 123
4.1.2.9Metal(IV)andAmineContainingStructures 123
4.1.2.10Silyloxyamines 123
4.1.2.11GermanesandStannanes 124
4.1.2.12BoraneComplexes 124
4.1.2.13PhosphorusContainingCompounds 124
4.1.2.14Monomers 125
4.1.2.15PhotoinitiatorItself 125
4.1.2.16AlcoholsandTHF 125
4.1.2.17PolymerSubstrates 125
4.2Ketone/ElectronAcceptorSystems 125
4.2.1Ketone/IodoniumSalt 125
4.2.1.1Benzophenone(orThioxanthone)/IodoniumSalt 125
4.2.1.2SilylKetone/IodoniumSalt 126
4.2.1.3Silylglyoxylate/IodoniumSalt 126
4.2.1.4Ketone/NovelIodoniumSalts 126
4.2.2Ketone/Triazine 126
4.3Ketone/DiethoxyacetateSalt 127
4.4Well-KnownandNovelTypeIIKetones 127
4.4.1BenzophenoneDerivatives 127
4.4.1.1Benzophenone 127
4.4.1.2ModifiedBenzophenones 128
4.4.2ThioxanthoneDerivatives 132
4.4.2.1Thioxanthone:AbsorptionandExcitedStates 132
4.4.2.2Well-KnownThioxanthonesasModels 134
4.4.2.3NovelThioxanthones 136
4.4.3Diketones 138
4.4.3.1AromaticDiketones 138
4.4.3.2Camphorquinone 139
4.4.4Ketocoumarins 140
4.4.5Coumarins 140
4.4.6AlkylPhenylglyoxylates 141
4.4.7SilylKetones 141
4.4.8SilylGlyoxylates 141
4.4.9OtherTypeIIKetoneSkeletons 142
4.4.9.1Anthraquinones 142
4.4.9.2Fluorenones 142
4.4.9.3Naphthoquinones 142
4.4.9.4AliphaticKetones 142
4.4.9.5Ketoesters 142
4.4.9.6CleavableKetonesasTypeIIPhotoinitiators 143
4.4.9.7Aldehydes 143
4.4.9.8Acetals 143
4.5Dye-BasedSystems 143
4.5.1UsualDye/AmineSystems 143
4.5.1.1EosinorRoseBengalasModels 143
4.5.1.2Dye/AmineInteraction:SomeKineticData 144
4.5.2Dye/AdditiveSystems:SomeExamples 144
4.5.2.1Dyes:Overview 144
4.5.2.2Additives 146
4.5.2.3SomeTypicalExamplesofDye/AdditiveSystems 147
4.5.3Dye-LinkedAdditiveIonPairs 149
4.5.4Dye-LinkedPhotoinitiatororCo-initiator-BasedSystems 149
4.5.5Dye/OniumSalts:ARevivalofInterest 150
4.5.5.1DyeswithD–π-A–π-DArrangements 150
4.5.5.2NIRPolymethineDyes 150
4.5.5.3SquaraineDye 151
4.5.5.4OtherExamplesofNovelDyesforNovelApplications 151
4.6OrganometallicCompound-BasedSystems 165
4.6.1Metallocene/Additive 165
4.6.2MetalCarbonyl/Additive 165
4.6.3MetalComplex/Olefin 168
4.6.4OrganometallicComplex/Amine 168
4.6.5CopperComplex/IodoniumSalt 168
4.6.6MiscellaneousOrganometallicCompound/AdditiveCouples 168
4.6.6.1OrganometallicCompound/Ketone-BasedSystems 168
4.6.6.2FerroceniumSalt/Additive 169
4.7Ketone/Ketone-BasedSystems 169
4.8Photoinitiator/Peroxide(orHydroperoxide)-BasedSystems 170
4.8.1RadicalPhotoinitiator/PeroxideInteractions 170
4.8.2Photobase/Peroxide 170
4.9TypeIPhotoinitiator/Additive 171
4.10Donor/AcceptorChargeTransferSystems 172
4.10.1OldSystems 172
4.10.2Amine/IodoniumSaltSystems 172 References 173
5CationicPhotoinitiatingSystems 199
5.1DiazoniumSalts 199
5.2OniumSalts 200
5.2.1IodoniumandSulfoniumSalts 200
5.2.1.1BasicModelCompounds 200
5.2.1.2PhotopolymerizationReaction 201
5.2.1.3AbsorptionProperties 202
5.2.1.4DecompositionProcessesofIodoniumSalts 202
5.2.1.5DecompositionProcessesofSulfoniumSalts 205
5.2.2DevelopmentofN,P,O(andOthers)CenteredOniumSalts 206
5.2.3DevelopmentintheIodoniumandSulfoniumSaltSeries 206
5.2.3.1SubstitutionEffectsinIodoniumandSulfoniumSaltDerivatives 207
5.2.3.2RecentDevelopmentsinIodoniumandSulfoniumSaltDerivatives 209
5.3OrganometallicDerivatives 212
5.3.1TransitionOrganometallicComplexes 212
5.3.2InorganicTransitionMetalComplexes 214
5.3.3NontransitionMetalComplexes 214
5.4PhotosensitizedDecompositionofOniumSalts 214
5.4.1Backgrounds 214
5.4.1.1PhotosensitizationThroughEnergyTransfer 214
5.4.1.2PhotosensitizationThroughElectronTransfer 215
5.4.2NovelDevelopmentsinElectronTransferReactions 219
5.4.2.1Photosensitizer-LinkedCationicMonomer 219
5.4.2.2PyriliumSalt/Hydroperoxide 219
5.4.2.3NovelSeriesofPhotosensitizers 219
5.5UnconventionalCationicSystems 222
5.5.1UpconversionNanoparticles 222
5.5.2CarbonNanotubes 222 References 222
6Anionic,Photoacid,andPhotobaseInitiatingSystems 241
6.1AnionicPhotoinitiators 241
6.1.1InorganicComplexes 241
6.1.2OrganometallicComplexes 242
6.1.3CyanoDerivative/AmineSystem 243
6.1.4Ketoprofen 243
6.1.5Amines 243
6.2NonionicPhotoacidGeneratorsSystems 243
6.2.1Sulfonates 244
6.2.2 N -Arylsulfonimides 244
6.2.3Naphthalimides 245
6.2.4Non-saltPyreneDerivatives 245
6.2.5 α-Disulfones 245
6.2.6Fullerenes 245
6.2.7Terarylene-BasedCompounds 246
6.3PhotobaseGeneratorsSystems 246
6.3.1OximeEsters 246
6.3.2Carbamates 246
6.3.3N-benzylatedStructure-BasedPhotobases 246
6.3.4Benzoylformamides 247
6.3.5AmmoniumChromophoreContainingBorateSalts 247
6.3.6AnionicChromophoreContainingAmmoniumSalts 248
6.3.7SuperBaseContainingPBGs 248
6.3.8OtherMiscellaneousSystems 249 References 249
7ReactivityofRadicalsTowardVariousSubstrates: UnderstandingandDiscussion 257
7.1Backgrounds 257
7.1.1DirectDetectionofRadicals 257
7.1.2AdditionofRadicalstoDoubleBonds 258
7.2ReactivityofRadicalsTowardOxygen,HydrogenDonors,Monomers, andAdditives 259
7.2.1AlkylandRelatedCarbon-CenteredRadicals 259
7.2.2ArylRadicals 261
7.2.3BenzoylRadicals 262
7.2.4AcrylateandMethacrylateRadicals 263
7.2.5AminoalkylRadicals 265
7.2.5.1Reactivity 265
7.2.5.2RoleoftheClassoftheAmine 268
7.2.5.3 N -PhenylGlycineDerivatives 268
7.2.5.4ChainLengthEffect 268
7.2.5.5RegioselectivityoftheHydrogenAbstractionReaction 269
7.2.5.6AminoalkylRadicalsandtheHalogenAbstractionReaction 270
7.2.5.7ReactivityUnderAir 270
7.2.6Phosphorus-CenteredRadicals 271
7.2.7ThiylRadicals 273
7.2.8SulfonylandSulfonyloxyRadicals 276
7.2.9SilylRadicals 277
7.2.9.1Characteristics 277
7.2.9.2ParticularBehavioroftheTris(trimethylsilyl)silylRadical 279
7.2.9.3ReactivityandPhotoinitiationUnderAir 280
7.2.9.4Silylamines 281
7.2.9.5OtherSourcesofSilylRadicals 282
7.2.10OxylRadicals 283
7.2.11PeroxylRadicals 284
7.2.11.1Characteristics 284
7.2.11.2InteractionwithH-Donors 286
7.2.11.3InteractionwithMonomers 287
7.2.11.4InteractionwithTriphenylphosphine 287
7.2.11.5SH 2Substitution 288
7.2.11.6OtherOxylsandPeroxyls 288
7.2.12AminylRadicals 288
7.2.13GermylandStannylRadicals 290
7.2.13.1Characteristics 290
7.2.13.2Reactivity 290
7.2.13.3ReactivityUnderAir 290
7.2.13.4ReactivityandStructureof(TMS)3 Ge• vs.(TMS)3 Si• 291
7.2.14BorylRadicals 292
7.2.14.1Characteristics 292
7.2.14.2Reactivity 293
7.2.14.3ReactivityUnderAir 295
7.2.14.4PhotoinitiationUnderAir 295
7.2.15LophylRadicals 295
7.2.16IminylRadicals 296
7.2.17Metal-CenteredRadicals 296
7.2.18PropagatingRadicals 298
7.2.19RadicalsinControlledPhotopolymerizationReactions 299
7.2.19.1PhotoinifertersandDithiocarbamylRadicals 299
7.2.19.2Light-SensitiveAlkoxyaminesandGenerationofNitroxides 300
7.2.20ReactivityofRadicalsTowardMetalSalts 302
7.2.21Radical/OniumSaltReactivityinFreeRadicalPromotedCationic Photopolymerization(FRPCP) 302 References 305
8RoleofExperimentalConditionsonthePerformanceof aRadicalPhotoinitiator 321
8.1RoleofViscosity 322
8.2RoleoftheSurroundingAtmosphere 324
8.3RoleoftheLightSource 325
8.4RoleofMonomerMatrix:AnExample 327 References 328
9ReactivityandEfficiencyofRadicalPhotoinitiators 333
9.1ReactivityofPhotoinitiators 334
9.1.1ExcitedStateProcesses 334
9.1.2CleavageProcesses 335
9.1.3ElectronandHydrogenTransferReactions 336
9.1.4ElectronTransferReactions 337
9.1.5RoleofBondDissociationEnergy 337
9.1.5.1RoleofBondDissociationEnergyinCleavableSystems 338
9.1.5.2RoleofBondDissociationEnergyinNon-cleavableSystems 340
9.1.6PhotoinitiatorQuenchingbyMonomers 340
9.1.7ReactivityoftheInitiatingRadical:AdditiontoDoubleBonds 342
9.1.8ReactivityoftheInitiatingRadical:InteractionwithHydrogen Donors 344
9.2Reactivity/EfficiencyofPhotoinitiators:ExamplesofStructural Effects 345
9.2.1Reactivity/EfficiencyRelationshipsinFluidMedia 345
9.2.1.1ExamplesofOil-SolublePhotoinitiatingSystems 345
9.2.1.2ExamplesofWater-SolublePhotoinitiatingSystems 349
9.2.2Reactivity/EfficiencyRelationshipsinHeterogeneousMedia 350
9.2.3Reactivity/EfficiencyRelationshipsinBulk 352
9.2.4PolymerizationEfficiencyinBulk:ExamplesofSomeEffects 354
9.3Up-to-dateApproachoftheReactivityandtheStructure/Property Relationships 359 References 362
Introduction xv
PartIIIHighPerformancePhotoinitiatingSystems: Achievements,Trends,Challenges,Opportunitiesand Applications 375
10DesignofPhotoinitiatorsforEnhancedPerformance:A MechanisticApproach 377
11MulticomponentRadicalPhotoinitiatingSystemsfor EnhancedReactivity 399
12PhotoinitiatingSystemsforFreeRadicalPromotedCationic Polymerization 435
13PhotoinitiatorsforNovelSpecificProperties 463
14IndustrialPhotoinitiators:ABriefOverview 531
PartIVPhotoinitiatorsforSpecificReactionsandTraditional orEmergingInnovativeApplications 537
15PhotoinitiatorsandLightSources:NovelDevelopments 539
16PhotoinitiatorsforControlled/LivingPolymerization Reactions 559
17PhotoinitiatorsinSpecificPolymerizationProcesses 591
18PhotoinitiatorsfortheCuringofThickorFilledSamples 641
19PhotoinitiatorsinVariousSectorsofIndustrial Applications 657 Conclusion 699 Index 703
Introduction xv
PartIPhotopolymerizationReactionsandPhotoinitiators: Backgrounds 1
1BackgroundsinPhotopolymerizationReactions:AShort Overview 3
2PhotoinitiatingSystem 35
PartIIPhotoinitiators:Structures,ExcitedStates,Reactivity, andEfficiency 55
3CleavableRadicalPhotoinitiators 59
4Two-ComponentRadicalPhotoinitiators 117
5CationicPhotoinitiatingSystems 199
6Anionic,Photoacid,andPhotobaseInitiatingSystems 241
7ReactivityofRadicalsTowardVariousSubstrates: UnderstandingandDiscussion 257
8RoleofExperimentalConditionsonthePerformanceof aRadicalPhotoinitiator 321
9ReactivityandEfficiencyofRadicalPhotoinitiators 333
Introduction xv
PartIIIHighPerformancePhotoinitiatingSystems: Achievements,Trends,Challenges,Opportunitiesand Applications 375
10DesignofPhotoinitiatorsforEnhancedPerformance:A MechanisticApproach 377
10.1TraditionalSearchofSubstituentEffectsinRadicalPhotoinitiators 377
10.1.1UsualSubstituentEffects 377
10.1.2LimitoftheUsualSubstituentEffect:AnIllustration 378
10.1.3NewlyDevelopedPossibilities 379
10.1.4SubstituentEffectsandReactivity 381
10.1.5SubstituentEffectsandNovelProperties 381
10.2SearchofNovelCleavableBonds 382
10.3MultifunctionalPhotoinitiatorsforanIncreasedVisibleLight Absorption 382
10.3.1BichromophoricPhotoinitiators 383
10.3.2DifunctionalRadicalPhotoinitiators 384
10.3.2.1BehaviorofaTypicalDifunctionalSystem 385
10.3.2.2NovelDifunctionalSystemsforRadicalandCationic Polymerization 385
10.3.3HighlyCoupledTri-functionalPhotoinitiatorsforRadicalandCationic Polymerization 385
10.3.3.1AvailableSystems 385
10.3.3.2Example:ATrifunctionalBenzoinether 386
10.3.3.3TetrafunctionalPhotoinitiators 387
10.3.4Push–PullPhotoinitiators 387
10.3.5PanchromaticPhotoinitiators 388
10.3.6SpecificReactivityofMultifunctionalPhotoinitiators 388
10.4PhotoinitiatorswithaThermallyActivatedDelayedFluorescence (TADF) 389
10.5AmineorPhosphine/IodoniumSaltChargeTransferComplexes 390
10.6MechanosynthesizedPhotoinitiators 391 References 392
11MulticomponentRadicalPhotoinitiatingSystemsfor EnhancedReactivity 399
11.1Photoinitiator/Amine/IodoniumSalt 399
11.1.1AromaticKetone/Amine/IodoniumSalt 400
11.1.2Camphorquinone/Amine/IodoniumSalt 400
11.1.3SilylKetone/Amine/IodoniumSalt 400
11.1.4Dye/Amine/IodoniumSalt 400
11.2Photoinitiator/Amine/OrganicHalide 402
11.2.1Dye/Amine/OrganicHalide 402
11.2.2Ketone/Amine/OrganicHalide 403
11.2.3OrganometallicCompound/Amine/OrganicHalide 403
11.2.3.1CopperComplex/Amine/OrganicHalide 403
11.2.3.2IronComplex/Amine/OrganicHalide 404
11.2.3.3IridiumComplex/Amine/OrganicHalide 404
11.3Photoinitiator/Amine/OtherAdditive 406
11.3.1Ketone/Amine/Bromocompound 406
11.3.2Dye/Amine/Bromocompound 406
11.3.3Ketone/Amine/Ketone 406
11.3.4Dye/Amine/Ketone 406
11.3.5Ketone/Amine/Silane 407
11.3.6Ketone/Amine/Germane 407
11.3.7Ketone/Amine/MetalSalt 407
11.3.8Dye/Amine/MetalSalt 407
11.3.9Ketocoumarin/Amine/FerroceniumSalt 407
11.3.10Ketone/Amine/ImideDerivatives 408
11.3.11Photoinitiator/Amine/Peroxide 408
11.4Photoinitiator/Borate/Additive 408
11.4.1Cyanine/Borate/Triazine 408
11.4.2Cyanine/Borate/PicoliniumSalt 409
11.4.3StyrylbenzothiazoliniumSalt/Borate/PyridiniumSalt 409
11.4.4Cyanine/Borate/Thiol 409
11.4.5Ketone/Borate/RutheniumSalt 409
11.5Photoinitiator/Cl-HABI/Thiol 409
11.6Photoinitiator/Silane/IodoniumSalt:AVeryVersatileSystem 410
11.6.1Dye/Silane/IodoniumSalt 410
11.6.2Ketone/Silane/IodoniumSalt 411
11.6.3OrganometallicCompound/Silane/IodoniumSalt 411
11.6.3.1Ruthenium(orIridium)/Silane/IodoniumSalt 411
11.6.3.2ZincComplex/Silane/IodoniumSalt 412
11.6.3.3Polyoxometallate/Silane/IodoniumSalt 412
11.7Photoinitiator/N -Vinylcarbazole/IodoniumSalt 412
11.7.1Ketone/N -Vinylcarbazole/IodoniumSalt 412
11.7.2Dye/N -Vinylcarbazole/IodoniumSalt 413
11.7.3OrganometallicCompound/N -Vinylcarbazole/IodoniumSalt 413
11.7.3.1CopperComplex/N -Vinylcarbazole/IodoniumSalt 413
11.7.3.2IronComplex/N -vinylcarbazole/IodoniumSalt 413
11.7.3.3MOFCompound/N -Vinylcarbazole/IodoniumSalt 415
11.7.3.4Perovskite/N -vinylcarbazole/IodoniumSalt 415
11.8Photoinitiator/Germane/IodoniumSalt 415
11.9Photoinitiator/CARET/IodoniumSalt 415
11.10Photoinitiator/TriphenylphosphineDerivative/IodoniumSalt 417
11.10.1CopperComplex/TriphenylphosphineDerivative/IodoniumSalt 417
11.10.2VanadiumorManganeseComplex/Triphenylphosphine Derivative/IodoniumSalt 417
11.10.3FerroceneDerivative/TriphenylphosphineDerivative/Iodonium Salt 418
11.11MiscellaneousPhotoinitiator/Additive/IodoniumSalt 418
11.11.1Photoinitiator/TinDerivative/IodoniumSalt 418
11.11.2Dye/Arylsulfinate/IodoniumSalt 419
11.11.3Dye/Dihydropyridine/IodoniumSalt 419
11.11.4KetoneorDye/Thiol/IodoniumSalt 419
11.11.5Ketone/Sulfinate/IodoniumSalt 419
11.12Photoinitiator/Additive/SulfoniumSalt 420 11.13ChargeTransferComplex/Peroxide 420
11.14Photoinitiator/Additive/Hydroperoxide 420
11.14.1Dye/FerroceniumSalt/Hydroperoxide 420
11.14.2MetalCarbonylCompound/Silane/Hydroperoxide 420
11.15OtherMiscellaneousThree-ComponentSystems 421
11.15.1Ketone/Triazine/Thiol 421
11.15.2PhosphineOxide/Silane/Borane 421
11.15.3Dye/Disulfide/NHCBorane 421
11.16Four-ComponentSystems:Examples 421
11.16.1Dye/FerroceniumSalt/Amine/Hydroperoxide 421
11.16.2Ketone/HABIDerivative/Amine/IodoniumSalt 422
11.16.3Cyanine/Borate/IodoniumSalt/Phosphine 422
11.16.4NIRDye/IodoniumSalt/Phosphine/ThermalInitiator 423 References 423
12PhotoinitiatingSystemsforFreeRadicalPromotedCationic Polymerization 435
12.1FRPCPProcess 435
12.2TypeIPhotoinitiator/IodoniumSaltTwo-ComponentSystems 436
12.2.1Ketone/IodoniumSalt 436
12.2.2Silylglyoxylate/IodoniumSalt 437
12.2.3Polysilane/IodoniumSalt 437
12.2.4Acylgermane/IodoniumSalt 437
12.2.5VinylHalide/IodoniumSalt 437
12.2.6OrganotelluriumCompound/IodoniumSalt 438
12.3TypeIPhotoinitiator/SulfoniumSalt 438
12.4TypeIPhotoinitiator/PyridiniumSalt 438
12.5TypeIPhotoinitiator/ZincSalt 438
12.6TypeIIPhotoinitiator/IodoniumSaltThree-ComponentSystems 439
12.6.1Photoinitiator/Amine/IodoniumSalt 439
12.6.2Photoinitiator/Silane/IodoniumSalt 439
12.6.2.1GeneralMechanism 439
12.6.2.2BasicKetone/Silane/IodoniumSaltSystems 440
12.6.2.3NovelDye/Silane/IodoniumSaltSystems 440
12.6.2.4OrganometallicCompound/Silane/IodoniumSalt 441
12.6.3Photoinitiator/Germane/IodoniumSalt 447
12.6.4Photoinitiator/Alcohol/IodoniumSalt 447
12.6.5Photoinitiator/N -Vinylcarbazole/IodoniumSalt 448
12.6.5.1Visible-Light-InducedFRPCP 448
12.6.5.2FRPCPUnderRedLights 449
12.6.5.3MulticolorPhotoinitiatorsandPanchromaticCationic Formulations 449
12.6.5.4CopperComplex/N -Vinylcarbazole/IodoniumSalt 449
12.6.5.5IronComplex/N -Vinylcarbazole/IodoniumSalt 450
12.6.5.6Perovskite/N -Vinylcarbazole/IodoniumSalt 451
12.6.6Photoinitiator/CARET/IodoniumSalt 451
12.6.7Photoinitiator/Alkylhalide/IodoniumSalt 451
12.6.8UpconversionNanoparticle-BasedSystems 451
12.7Addition/FragmentationReaction 452
12.8Photoinitiator/MetalSalt/Additive-BasedSystems 452 References 452
13PhotoinitiatorsforNovelSpecificProperties 463
13.1One-ComponentTypeIIPhotoinitiators 463
13.1.1BenzoylBenzodioxolaneDerivatives 463
13.1.2ThioxanthoneDerivatives 464
13.1.3Naphthoquinones 464
13.1.4Photoinitiator–Amine 465
13.1.5Photoinitiator–Monomer 466
13.1.6Photoinitiator–amine–monomer 466
13.1.7Photoinitiator–PolymerChainIonicPair 466
13.1.8Photoinitiator–thiol 466
13.1.9AldehydesasOne-ComponentSystems 467
13.1.10Bis-pyridiniumDerivatives 467
13.1.11MaskedPhotoinitiators 467
13.1.12Photoinitiator–Photosensitizer 468
13.1.13Photoinitiator–oniumsaltsystem 468
13.1.14Photoinitiator-ProtonatedBase 468
13.1.15ChargeTransferComplex(CTC)Systems 469
13.2Macrophotoinitiatiors 469
13.2.1TypeIMacrophotoinitiators 470
13.2.1.1Examples 470
13.2.1.2TypeIPhotoinitiator-LinkedPhotosensitizerMacrophotoinitiators 471
13.2.2TypeIIMacrophotoinitiators 471
13.2.2.1Examples 471
13.2.2.2Reactivity/Efficiency:aLimit 473
13.2.3SupportedandImmobilizedPhotoinitiators 474
13.2.4CopolymerizablePhotoinitiators. 475
13.2.5PolymericOniumSalts 476
13.2.6PolymericCross-linkablePhotoinitiators 476
13.3Water-SolublePhotoinitiators 477
13.3.1Water-SolubleTypeIPhotoinitiators 477
13.3.2Water-SolubleTypeIIPhotoinitiators 478
13.3.3CationicPhotoinitiators 480
13.3.4IncorporationofPhotoinitiatorsinacavity 480
13.3.5IncorporationofPhotoinitiatorsinaHeterogeneousEnvironment 480
13.4PhotoredoxCatalystsasPhotoinitiators 480
13.4.1PhotoinitiatorsInvolvingOxidationCycles 481
13.4.1.1Photoinitiator/Silane/IodoniumSalt 481
13.4.1.2Photoinitiator/Silane/SulfoniumSalt 482
13.4.1.3Photoinitiator/N -Vinylcarbazole/IodoniumSalt 482
13.4.1.4Photoinitiator/Amine/AlkylBromide 483
13.4.1.5Photoinitiator/Amine/IodoniumSalt 483
13.4.1.6Photoinitiator/IodoniumSalt/TinDerivative 483
13.4.1.7Photoinitiator/Thiol/Oxygen 483
13.4.2PhotoinitiatorsInvolvingReductionCycles. 484
13.4.2.1Photoinitiator/Amine/AlkylHalide 484
13.4.2.2Photoinitiator/Dye/Silane/IodoniumSalt 484
13.4.3SimultaneousOxidationandReductionCycle 484
13.4.4ExamplesofPolymerizationProfiles 485
13.5Two-PhotonAbsorptionPhotoinitiators 485
13.5.1CleavablePhotoinitiatorsforTwo-PhotonAbsorption 486
13.5.2TypeIIPhotoinitiatorsforTwo-PhotonAbsorption 486
13.5.3CationicPhotoinitiatorsforTwo-PhotonAbsorption 487
13.5.4PhotobasesforTwo-PhotonAbsorption 488
13.6PhotoinitiatorsforOvercomingOxygenInhibition 488
13.6.1DesignofHighlyReactivePhotoinitiators 489
13.6.2DesignofMigratedPhotoinitiators 489
13.6.2.1DesignofFluorinatedPhotoinitiators 489
13.6.2.2DesignofSiloxaneGroupContainingPhotoinitiators 489
13.6.3DesignofOxygen-TolerantSystems 489
13.6.4OxygenSelf-consumingPhotoinitiators 490
13.6.4.1OxygenSelf-consumingThioxanthoneDerivatives 490
13.6.4.2OxygenSelf-consumingAldehydeDerivatives 491
13.6.5Oxygen-MediatedRadicalFormation 491
13.6.5.1UseofSilanesasCo-initiatorsandOxygenScavenger 491
13.6.5.2CleavablePhotoinitiator/Thiol-ContainingThioxanthone 492
13.6.5.3UseofaSH2 Reaction 492
13.6.5.4UseofBoranes 493
13.6.6UseofPhosphines 493
13.6.7UseofOrganozirconiums 494
13.7PhotoinitiatorswithOtherMiscellaneousProperties 494
13.7.1Host–GuestSupramolecular-StructuredPhotoinitiators 494
13.7.2OrthogonalPhotoinitiators:DualInitiation 495
13.7.3MultiwavePhotoinitiators:Wavelength-SelectiveInitiation 496
13.7.4ChiralPhotoinitiators 497
13.7.5Self-initiatedMonomersasPhotoinitiators 497
13.8Eco-friendlyPhotoinitiators 498
13.8.1SafePhotoinitiators 498
13.8.2NaturalorBiosourcedPhotoinitiatorsandCo-initiators 499 References 500
14IndustrialPhotoinitiators:ABriefOverview 531
14.1RadicalIndustrialPhotoinitiators 532
14.2CationicIndustrialPhotoinitiators 534
14.3Tailor-MadeFormulationsofIndustrialPhotoinitiators 534
14.4ToxicityandREACHRegistrationofPhotoinitiators 535 References 535
PartIVPhotoinitiatorsforSpecificReactionsandTraditional orEmergingInnovativeApplications 537
15PhotoinitiatorsandLightSources:NovelDevelopments 539
15.1PhotoinitiatorsUnderSoftIrradiationConditions 539
15.2PhotoinitiatorsUnderSunlight 540
15.3PhotoinitiatorsUnderLEDandLaserDiodeIrradiationConditions 541
15.4NIRLight-InducedPolymerization 542
15.5NIRLight-InducedThermalPolymerization 544
15.6PhotoinitiatorsandPulsedLightIrradiation 545
15.7PhotoinitiatorsUnderVisibleLights:ResidualColorationofthe Coating 546
15.8ExamplesofEfficientPhotoinitiatorStructuresvs.theIrradiation Wavelengths 551 References 551
16PhotoinitiatorsforControlled/LivingPolymerization Reactions 559
16.1Dithiocarbamates 560
16.2 O-Alkoxyamines 562
16.3OrganometallicCompounds 563
16.3.1IridiumComplexes 563
16.3.2RutheniumComplexes 564
16.3.3CopperComplexes 564
16.3.3.1Copper(II)Complexes 564
16.3.3.2Copper(I)Complexes 565
16.3.4IronComplexes 566
16.3.5ZincComplexes 567
16.3.6MagnesiumComplexes 568
16.3.7CobaltComplexes 568
16.3.8ManganeseCarbonyls 569
16.3.9GoldComplexes 569
16.3.10Nobium-BasedCompounds 570
16.4Metal-FreeCompounds 570
16.4.1OrganicDyes 570
16.4.2OrganicTypeIPhotoinitiators 572
16.4.3Iodine-ContainingCompounds 572
16.4.4Hydrocarbons,Phenazines,andPhenothiazines 572
16.4.5ThiocarbonylthioCompounds 573
16.4.6Ketones 574
16.4.7MiscellaneousOrganicPhotoinitiators 574
16.5TiO2 –graphiticCarbonNitrideComposite 574
16.6IronOxidesandSalts 575
16.7PhotoinitiatorsinLivingCationicPolymerization 575
16.8PhotoinitiatorsinLivingAnionicPolymerization 577 References 577
17PhotoinitiatorsinSpecificPolymerizationProcesses 591
17.1PhotoinitiatorsforThiol–EneReactions 591
17.2PhotoinitiatorsinRelatedThiol–EneChemistries 593
17.2.1Silane–EneChemistry 593
17.2.2Phosphane–EneChemistry 594
17.2.3Iodo–EneChemistry 594
17.2.4Germane–EneChemistry 594
17.3PhotoinitiatorsforInterpenetratingPolymerNetworksSynthesis 595
17.3.1IPNSynthesisUnderIntenseUVLightExposure 595
17.3.1.1One-StepProductionofIPN 595
17.3.1.2Two-StepProductionofIPN 596
17.3.2IPNSynthesisUnderVisibleLights 596
17.3.2.1Visible-Light-InducedOne-StepFormationofIPN 596
17.3.2.2IPNSynthesisUsingTwo-ColorResponsiveInitiatingSystems 598
17.4PhotoinitiatorsinPhotoactivatedRedoxPolymerization 598
17.4.1Amine-andPeroxide-ContainingSystems 598
17.4.1.1Amine/Phosphine/IodoniumSalt/BenzoylPeroxide 598
17.4.1.2MABLIComplex/IodoniumSalt/Phosphine 599
17.4.1.3FerroceneDerivative/IodoniumSalt/Phosphine/Ammonium Persulfate 600
17.4.1.4LatentSuperbase/Peroxide 600
17.4.1.5ControloftheGelTime 600
17.4.2Amine-FreeandPeroxide-FreeSystems 600
17.5PhotoinitiatorsinPhoto-CuAACReactions 601
17.6PhotoinitiatorsinHydrosilylationReactions 601
17.7PhotoinitiatorsinHybridSol–GelPhotopolymerization 602
17.8PhotoinitiatorsfortheInSituGenerationofNanoparticles 603
17.8.1Photoinitiator/MetalSalt-BasedSystems 603
17.8.1.1CleavablePhotoinitiators 603
17.8.1.2TypeIIPhotoinitiators 604
17.8.1.3One-ComponentPhotoinitiators 604
17.8.1.4Metal-FunctionalizedPhotoinitiators 605
17.8.2Metal-CenteredPhotoinitiators 605
17.9PhotoinitiatorsinParticularExperimentalConditions 605
17.9.1PhotoinitiatorsforHydrogelSynthesis 605
17.9.2PhotoinitiatorsforPolymerizationofSelf-assembledSystems 606
17.9.2.1Photopolymerizationin(Micro)heterogeneousMedia 606
17.9.2.2Polymerization-InducedSelf-assembly(PISA) 608
17.9.3PhotoinitiatorsinIonicLiquids 609
17.9.4PhotoinitiatorsfortheElaborationofNovelArchitecturesThrough Grafting 610
17.10PhotoinitiatorsinMiscellaneousNovelReactions 614
17.10.1PhotoinitiatorsinSelf-HealingReactions 614
17.10.2PhotoinitiatorsinEpoxy-AminePolyadditionReactions 614
References 615
18PhotoinitiatorsfortheCuringofThickorFilledSamples 641
18.1PenetrationofLightinaThickSample 641
18.2UseofBleachablePhotoinitiators 642
18.3UseofHighIrradiances 643
18.4UseofTemperatureEffects 643
18.4.1Light-InducedTemperatureIncrease 643
18.4.2TemperatureControl 644
18.4.3ThermalCuringinDual-CureStrategies 644
18.4.4RoomTemperatureDualCuring 644
18.5UCNP-AssistedPhotopolymerizationUnderNIRLights 645
18.6UseofCatalyticPhotoredoxProcesses 645
18.7DesignofNovelPhotoinitiatingSystems 646
18.7.1PhotoinitiatorsforNIRLights 646
18.7.2SemiconductorNanoparticles 646
18.7.3ChargeTransferComplexes 647
18.7.4NovelPhotoinitiatingSystemsfortheManufactureofComposites 647 References 650
19PhotoinitiatorsinVariousSectorsofIndustrial Applications 657
19.1PhotoinitiatorsintheRadiationCuringArea 657
19.2PhotoinitiatorsinGraphicArts 661
19.3Photoinitiatorsin3DPrintingTechnologies 662
19.3.1Stereolithography 662
19.3.23DPrinting 662
19.3.3Two-Photon3DPrinting 664
19.3.4DirectLaserWriting 664
19.3.54DPolymerMicropatterning 665
19.3.6ExamplesofNovelPhotoinitiatorsin3DPrinting 665
19.4PhotoinitiatorsforBiomaterials 666
19.5PhotoinitiatorsforDentistryApplications 667
19.5.1Camphorquinone/Germane/IodoniumSaltSystem 668
19.5.2NovelGermylKetones 668
19.5.3NovelSilylKetone-BasedSystems 668
19.5.4NovelAcylsilanes 669
19.5.5Dyes 669
19.5.6NIRPhotoinitiatingSystems 669
19.5.7DesignofWater-CompatibleVisibleLightPhotoinitiators 669
19.5.8PhotoinitiatorsinDentalCompositesInvolvingaDifferent Chemistry 670
19.6Photoinitiatorsin(Micro)Electronics 670
19.7PhotoinitiatorsintheOpticsArea 672
19.7.1ManufactureofOpticalElements 672
19.7.2Holography 673
19.7.3PhotopolymerizationUsingNear-FieldOpticalTechniques 674
19.8PhotoinitiatorsinOrganicElectronics 674 References 674
Conclusion 699 Index 703
Introduction
Asalreadyknown,aphotoinitiator(PI)oraphotoinitiatingsystem(PIS),wherea PIisintroduced,allowstheinitiationofapolymerizationreactionunderexposure toalightsource.
Light-inducedpolymerizationreactionsarelargelyencounteredinmanyindustrialapplicationsorinpromisinglaboratorydevelopments.Thebasicideaistoreadilytransformaliquidmonomer(orasoftfilm)intoasolidmaterial(orasolidfilm) uponlightexposureatambienttemperature.Thehugesectorsofapplicationsare foundinbothtraditionalandhightechareassuchasradiationcuring,laserimaging,3Dprinting,microelectronics,optics,biosciences,dentistry,nanotechnology, etc.Radiationcuringisconsideredasagreentechnologythatcontinuesitsrapid development.
Photopolymerizationreactionscanbecarriedoutinvariousexperimentalconditions,suchasinfilms,gasphase,aerosols,multilayers,(micro)heterogeneousmedia orsolidstate,onsurface,inionicliquids,insituinthemanufacturingofmicrofluidic devices,invivo,evenundermagneticfield,etc.Verydifferentaspectsareconcerned ingradient,template,frontal,controlled,sol–gel,two-photon,redox,laser-induced, orspatiallycontrolledphotopolymerizations,etc.
AphotopolymerizationreactioninvolvesaPIoraPIS,apolymerizablemedium, andalightsource.Thephotoinitiatorplaysacrucialroleasitabsorbsthelight andstartsthereaction.Itsreactivitygovernstheefficiencyofthepolymerization. Theliteratureshowsthataconsiderablenumberofworksaredevotedtothedesign ofphotosensitivesystemsbeingabletooperateinmanyvarious(andsometimes exotic)experimentalconditions.
Fantasticdevelopmentshaveoccurredallalongthepastfivedecades.Significant achievementshavebeendonesincetheearlyworksonphotopolymerizationinthe 1960sandthetraditionaldevelopmentsoftheradiationcuringarea.Today,hightech applicationsarecontinuouslyemerging.Atailor-madephotochemistryandchemistryforthedesignofhigh-performancesystems(thatcanoperateatanywavelength, underlowlightintensityandunderair,ensureabettersafety,andprovidenovel handlingorenduseproperties)haveappearedinthisareaandhasachievedremarkablesuccess.Thesearchforasafeandgreentechnologyisgrowing.Interestingitems firstrelatetothepolymerscienceandtechnologyfieldbutalsotothephotochemistry,physicalchemistry,andorganicchemistryareas.
Inthepast40years,manyaspectsoflight-inducedpolymerizationreactionshave beendiscussedinbooksandreviewpapers.Eachofthesebooks,however,usually covermoredeeplyselectedaspectsdependingfirstontheorigin(universityand industry)andactivitysectoroftheauthor/editor(photochemistry,polymerchemistry,applications,etc)andsecondonthegoalsofthebook(generalpresentation ofthetechnology,guideforendusers,andacademicscope,etc).Ourprevious generalbookpublishedmorethan20yearsago(Hanser,1995)anddevotedtothe threephotoinitiation/photopolymerization/photocuringcomplementaryaspects alreadyprovidedafirstaccountonthephotosensitivesystems.Unfortunately,for obviousreasons,allthesethreefascinatingaspectsthatcontinuouslyappearedin theliteraturecouldnolongerbedevelopedindetailinasinglemonographbecause oftherapidgrowthoftheresearch.Thiswasthereasonwhyoursecondbook (PhotoinitiatorsforPolymerSynthesis)publishedin2012(Wiley)wasonlyfocused onthephotosensitivesystemsthatareusedtoinitiatethephotopolymerization reaction,theiradaptationtothelightsources,theirexcitedstateprocesses,their interactionwiththedifferentavailablemonomers,theirworkingoutmechanisms, andtheapproachforacompleteunderstandingofthe(photo)chemicalreactivity. Thissecondbookshowedthehugeprogressmadebetween1995and2012.
Whyanewbook?Indeed,bytheendof2010,onecouldhavehadthefeelingthat almosteverythinghadbeenforeseenandverifiedinthedesignofphotoinitiators andPISs.However,scienceisevergoingon!Thankstonovelmethodsofinvestigation(bothexperimentalandtheoretical)andnovelideasaccompaniedbysearches inotherareas(fineproductcatalogs,naturalcompounds,optoelectronics,organic light-emittingdiodes(OLEDs),solarcells,composites:lightweightmaterials,etc), ahugeprogresshasbeendoneinthepast10years!Alotofnovelstructurespreviouslyunimaginableandusableinnovelandpromisingapplicationshavebeen publishedandhaveopenednewunsuspectedhorizons.
HugechallengesremainintheareaofPIsandPISs,butaconstantdevelopmentisnotedin(i)nontoxic(orlesstoxic)systems,e.g.biologicalandmedical applications,foodpackaging,andforthesafetyoftheendusers(thetoxicityof manyclassicalPIshasbeenre-evaluatedinthecontextoftheREACHregistration); (ii)high-performancesystemsfortheaccesstolargerobjectsin3Dprinting,the highproductivityforthecuringofinks,coatings,paints,composites,theability tophotopolymerizepigmentedorhighlyfilledthicksamplesforcompositeswith improvedmechanicalproperties,andtheworkingoutinhydrogels,eco-friendly water-basedformulations,orself-assembledsystems;(iii)systemsoperatingunder safeirradiationdevicesandvisible,red,andnear-infrared(NIR)lightsources;and (iv)systemsfornewphotopolymerizationprocesses,e.g.controlledpolymerization, hybridpolymerizationtoreducepolymerizationstressandshrinkage,dualcure polymerizationcombiningredoxandlightactivationforreactionsinshadowareas, polymerizationofbiosourcedmonomers,two-photonphotopolymerization,and emulsionphotopolymerizationuponvisiblelights.
Thefollowingpictureschematicallydepicts60yearsofevolutionoftheresearch anddevelopmentinthisarea.Originally,thescreeningoftheavailablechemicals,thesynthesisofsuitablederivatives,andthelargeuseoftrialanderror
experimentsallowedtosatisfactorilyphotocuremonomer/oligomerformulations accordingtotheratherundemandingrequestedconditionsatthisperiod.Then, theinvestigationoftheexcitedstateprocessesandtheproposalofmechanistic schemeshelpedtodesignmorepowerfulsystemsforanimprovedperformance. Finally,themolecularorbital(MO)calculationsprovidednewsolutionsforthe constructionofefficientmoleculesandtheinterpretationofthechemicalreactivity. Questionsarisingfromendusersorresearchersforthedevelopmentofnovel applicationsleadtoademandofnovel“five-legged”photoinitiatorsthat,along time,aremoreandmoresophisticated.Moreover,goodfortune,closeattention,or brilliantideas,evenwithoutanyheavyexperimentalortheoreticalapproach,have alsoplayedakeyroleinthediscoveryofnovelstructuressomewhereonourplanet.
Theaboveconsiderationspromptedustowritetodayanewbookonphotoinitiatorsinwhichthemostrecentdevelopmentshavebeenstressed.Here,weintend (i)togivethebestup-to-datesituationofthesubjectandtaketimetobrieflydefinea lotofbasicprinciplesandconcepts,mechanisticreactionschemes,andexamplesof studiesthatremaintrueandarenotsubmittedtoasignificantagingona10year timescale,(ii)tokeepacompletepresentationoftheencounteredPISstogether withadiscussionofthestructure/excitedstateprocesses/reactivity/efficiencyrelationships,(iii)tofocusontheinvolvedmechanisms(theroleofthebasicresearch towardtheprogressoftheappliedresearchbeingabsolutelynecessary),and(iv)to outlinethelatestdevelopmentsandtrendsinthedesignofnoveltailor-madephotoinitiators/PISs(basedonexperimentalandtheoreticalapproaches)aswellasthe correspondingexisting,emerging,promising,orchallengingapplicationswherecurrentornewsystemsareemployed.Toouropinion,suchanextensiveandcomplete bookwithinthisphilosophyremainstotallyoriginaltoday.
Thebookisdividedintofourpartsincluding19chapters.Asmentionedbefore, wedecidedtoprovideabasicthoroughdescriptionoftheprocessesandmechanisms togetherwithanin-depthtreatmentofthedesignofPIsandPISsandageneralpresentationofthecurrentapplications.
InPartI,wedeliverageneralbutconcisepresentationofthebasicprinciples ofphotopolymerizationreactionswithadescriptionoftheavailablelightsources, thedifferentmonomers,thecharacteristics,kinetics,andmonitoringofthereactionstogetherwithafewwordsontheapplicationareas(Chapter1).Asitspecially concernsthepolymersciencepointofview,thischapterwillonlyfocusonwhatis necessarytoclearlyunderstandthefollowingchapters.Thecharacteristics,therole, thedifferentbasicprocesses,andthereactivity/efficiencyofthePISsaredescribed inChapter2togetherwithafewphotochemistrychecks.
PartIIisdevotedtothestructures,excitedstateprocesses,reactivity,andefficiency ofphotoinitiators.Inafirststep,weprovide(i)themostexhaustivepresentation ofthecommerciallyoracademicallyusedorpotentiallyinterestingPISsdeveloped intheliteraturesofar(photoinitiators,co-initiators,andphotosensitizers),(ii)the characteristicsoftheexcitedstates,(iii)theinvolvedreactionmechanisms,and (iv)acompletepresentationoftheexperimentalandtheoreticalreactivityofmore than15kindsofradicals.Beingawareoftheimportanceofatotalhomogeneity throughoutthebook,wekeepacompletequalitativeoverviewofalltheavailablesystemsdevelopedalongyears,butwewillfocusourattentiononnewly developedphotoinitiators,recentlyreportedstudies,andnoveldataonprevious well-knownsystems.Allthisinformationisprovidedforradicalphotoinitiators (Chapters3and4);cationicphotoinitiators(Chapter5);anionicphotoinitiators, photoacids,andphotobases(Chapter6);andinitiatingradicals(Chapter7).Ina secondstep,wediscusstheroleoftheexperimentalconditions,e.g.formulation viscosity,surroundingatmosphere,lightsourceemissionspectrum,andintensity ontheefficiencyofaphotopolymerizationreaction(Chapter8).Thereactivityand efficiencyofPISsinsolution,bulk,orfilm,underair,inhigh/low-viscositymedia orunderhigh/lowlightintensitiesaswellastheelaborationofstructure/property relationships(Chapter9)willberestrictedtoradicalstructuresasalmostnothing concernscationicsystems;thereactivity/efficiencyinmicroheterogeneousmedia willalsobeevoked.
InPartIII,weintroducespecificchapters(whichdidnotappearatallinthe previous2012book)todealwiththedesignofhigh-performancePISs:these chaptersallowtounderstandthenoveldirectionsofresearch,thebuildingupof novelchemicalstructuresofphotoinitiators,thesearchofadditiveswithmore suitablebonddissociationenergies(BDEs)andredoxproperties,thespecificrole ofPIsandPISsinup-to-datepossibilitiesofapplicationsandenduses,etc.We successivelypresentthesynthesisandmechanisticapproachofnovelarchitectures ofphotoinitiators(Chapter10);thedesignofmulticomponentradicalPISsfor anenhancedreactivity(Chapter11);therecenthugeprogressmadeinPISsfor freeradicalpromotedcationicphotopolymerization(Chapter12);theproposalof photoinitiatorsfornovelspecificandimprovedpropertiessuchasone-component, water-soluble,two-photonabsorptionoroxygen-tolerantcompounds,orthogonal photoinitiators,safephotoinitiators,andnaturalphotoinitiators(Chapter13);and theindustrialphotoinitiators(Chapter14).
PartIVisdevotedtotheroleofphotoinitiatorsinspecificreactionsandcurrentoremerginginnovativeapplications.Thedevelopmentofphotoinitiators
Introduction xix adaptedtonovellightsources(LEDs,sun,pulsedsources,NIRlights,etc.)is showninChapter15.Chapter16reviewsphotoinitiatorsincontrolledpolymerizationreactions.Photoinitiatorsusableinspecificpolymerizationprocesses (thiol–ene,interpenetratingpolymernetwork[IPN],redox,polymerization-induced self-assembly[PISA],copper-catalyzedazide-alkynecycloaddition[CUAAC],ionic liquids,hydrogels,incorporationofnanoparticles,etc.)aredetailedinChapter17. TherecentprogressinthedesignofphotoinitiatorsandPISsforthepolymerization ofthickfilmsisdescribedinChapter18.Finally,Chapter19coverssomeaspects ofphotoinitiatorsinindustrialapplications,e.g.coatings,graphicarts,3Dprinting, medical,optics,andelectronics.
WhenquestioningtheChemicalAbstractdatabase,manyreferencesappear.We havenotintendedtogivehereanexhaustivelistofreferencesorasurveyofthe patentliterature.Morethan1000referencesappearedeachyear.Pioneerworksare cited,butourpresentlistofreferencesmainlyrefersnowtopapersdispatchedduring thepast30/20yearswithanemphasisonthe2010–2019period.Theselectionof thearticlesismostofthetimearatherhardandsensitivetask.Wehavedoneour bestandbegforgivenessforpossibleomission.
Thisresearchfieldcontinuouslyknowsafantasticevolution.Wewouldlikenow tosharetherealpleasurewehad(andstillhave)inparticipatingandcontributing tothisarea.Writingthissecondbookwasreallyagreatpleasure.Wehopethatour readers,R&Dresearchers,engineers,technicians,Universitypeople,andstudents, involvedinvariousscientificand/ortechnicalareassuchasphotochemistry,polymerchemistry,organicchemistry,radicalchemistry,physicalchemistry,radiation curing,imaging,physics,optics,medicine,andnanotechnology,willappreciatethis bookandenjoyitscontent.