Table Of ContentPHOTOSTABILIZATION OF POLYMERS
Principles and Applications
PHOTOSTABILIZATION
OF
POLYMERS
Principles and Applications
J. F. RABEK
Department ofPolymer Technology,
The Royal Institute ofTechnology,
Stockholm, Sweden
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BritishUbraryCatalqguing in Publication Data
Rabek,J. F. (Jan F.)
Photostabilization ofpolymers.
1. Polymers. Stabilization
I. Title
668.4'1
ISBN-13:978-94-010-6821-5
UbraryofCongressCataloging-in-PublicationData
Rabek,J. F.
Photostabilization ofpolymers: principlesand applications/
J. F. Rabek.
p. cm.
Includesbibliographical references.
ISBN-13:978-94-010-6821-5 e·ISBN·13:978·94·009·0747·8
001:10.1007/978-94-009-0747-8
1. Polymers-Deterioration. 2. Photochemistry. I. Title.
OD381.9.P56R34 1990
620.1'920422-dc20 89-16993
CIP
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Dedicated to my aunt Irena Gawronska, chemist, her
family Adam and Mary and their lovely children Jan,
Anna, Ronan and Paula
'Noneofusisasgoodasallofus'
Peopleinvolvedinpolymerstabilization
Preface
During the last two decades, the production of polymers and plastics
has been increasing rapidly. In spite of developing new polymers and
polymeric materials, only 40-60 are used commercially on a large
scale. It has been estimated that half of the annual production of
polymers is employed outdoors. Increasing the stability of polymers
and plastics towards heat, light, atmospheric oxygen and other
environmental agents and weathering conditions has always been a
very important problem. The photochemical instability of most of
polymers limits them to outdoor application, where they are photo
degraded fast over periods ranging from months to a few years.
To the despair of technologists and consumers alike, photodegrada
tion and environmental ageing ofpolymers occur much faster than can
be expected from knowledge collected in laboratories. In many cases,
improved methods of preparation and purification of both monomers
and polymers yield products of better quality and higher resistance to
heat and light. However, without stabilization of polymers by applica
tion of antioxidants (to decrease thermal oxidative degradation) and
photostabilizers (to decrease photo-oxidative degradation) it would be
impossible to employ polymers and plastics in everyday use. At
best, the choice of suitable stabilizers is at present governed not only
by the data collected in practical outdoor or indoor ageingofpolymers
and plastics, but also by the collected knowledge of thermal oxidative
and photo-oxidative degradation mechanisms, stabilization mechan
isms, interactions of additives (synergistic and antagonistic effects),
etc. The main task has been to bridge the gap between the theory of
thermal degradation and/or photodegradation of polymers and their
practical stabilization.
This book represents the author's attempt, based on his 20 years'
experience in research on photodegradation and photostabilization, to
collect and generalize a number of available data on the photo-
vii
Vlll PREFACE
stabilization of polymers. The space limitation and the tremendous
number of publications in the past decade have made a detailed
presentation of all important results and data difficult. The author
apologizes to those whose work has not been quoted or widely
presented in this book. Because many published results are very often
contradictory, it has been difficult to present a fully critical review of
collected knowledge, without antagonizing the authors. For that
reason, all available theories, mechanisms and different suggestions
have been presented together, and only practice can evaluate which of
them are valid.
Very different chemical nomenclature of antioxidants and photo
stabilizers is sometimesused for the samecompounds; therefore in this
book the nomenclature employed is the same as was used by authors
in their original publications. However, all available chemical nomen
clature has been collected in tables and it should be very easy to find
one's way through the jungle of different names.
This is an effort to integrate this vitally needed information on
photostabilization ofpolymersin asingle book written as a monograph
ofthe subject. This book should be a useful aid to all people from the
polymer and plastics industries, but also to graduate or advanced
undergraduate students.
The following figures and tables were reproduced by permission of
John Wiley & Sons, Inc: Figs 1.8, 1.9, 2.12, 2.14, 3.1, 3.6, 4.2-4.4,
4.14, 5.3, 5.4, 5.9, 5.24, 5.30, 5.31, 5.34, 5.37, 6.4, 6.5, 8.4, 9.1, 9.2,
9.8, 9.9, 9.16, 9.17, 9.20, 9.23-9.25, 9.30; Tables 2.5, 3.1, 3.3-3.6,
3.11,4.5,4.7,4.10,5.2-5.4,5.10,6.7, 7.3, 7.5.
In conclusion, I should like to express my gratitude to members of
my family for their patience while this book was being prepared,
having to forego my company during innumerable evenings, weekends
and holidays.
J. F. RABEK
Contents
Preface . .vii
Chapter 1 Introduction to the Photo-oxidative Degradation
Mechanisms ofPolymers
1.1 DefinitionsofPhotostabilityofPolymericMaterials 1
1.2 GeneralMechanismofPolymerPhoto-oxidation 2
1.3 PhotoinitiationofPolymerDegradation 3
1.4 ChainPropagation. . . . . . . . . 5
1.5 ChainBranching . . . . . . . . . . 6
1.6 Photo-reactionsofCarbonylGroups . . 7
1.7 HydrogenAbstraction . . . . . . . . 8
1.8 PhotodecompositionofHydroperoxideGroups 9
1.9 FormationofAcidsand Peracids . 11
1.10 FormationofUnsaturatedGroups. . . . . . 13
1.11 TerminationReactions. . . . . . . . . . . 14
1.12 PhenylRingOpeningPhoto-reactions . . . . 15
1.13 KineticsofPhoto-oxidativeDegradationofPolymers 15
1.14 RoleofPolymerMorphologyinPhoto-oxidation . . 17
1.15 RoleofPolymerManufacturing . . . . . . . . . . 18
1.16 RoleofMetalsorMetallicCompoundsinThermaland/or
Photo-oxidativeDegradationofPolymers 18
1.17 RoleofProcessinginThermalOxidationofPolymers . 22
1.18 MechanismsInvolvedinthe PhotolysisoftheThermally
OxidizedPolyolefinsDuringProcessing .. . . . . . 25
1.19 PhysicalProcessesinthe Photo-oxidationofPolymers . 30
Chapter 2 Introduction to the Oxidative and Photo
stabilization ofPolymers
2.1 Antioxidants . . . . . . . . 42
2.2 Photostabilizers. . . . . . . . . 44
2.3 StabilizersinaPolymerMatrix . . 45
2.4 DistributionofStabilizersinaPolymerMatrix 47
2.5 Quenchers . . . . . . . . . . . . . . . . 63
2.6 SingletOxygenDeactivators . . . . . . . . 67
2.7 PhotostabilityofAdditives . . . . . . . . . 69
2.8 SynergismandAntagonismbetweenAdditives 69
ix
x CONTENTS
Chapter 3 Antioxidants
3.1 HinderedPhenols . . . . . . . . . . . . 80
3.2 Hydroxygalvinol/GalvinoxyRadicalSystem. 109
3.3 PhenolicSulphides. . . . . . . . 114
3.4 Monosulphides . . . . . . . . . . . . . 117
3.5 Thiophenolsand Dithiobisphenols. . . . . 117
3.6 SulphoxidesandSulphones . . . . . . . . 122
3.7 SynergisticEffects betweenHinderedPhenolsandSulphur-
ContainingCompounds . . . . . . . . . . 125
3.8 DixanthogensandThiophosphorylDisulphides 128
3.9 MetalDithiolatesasAntioxidants . . . . . . 131
3.10 4-Alkyl-2-mercaptothiazolines. . . . . . . . 134
3.11 SulphurDioxideRole in AntioxidizingSystems 136
3.12 Roleofthe AntioxidantStructureinStabilizationProcesses 137
3.13 OvenAgeingAntioxidantPerformance 138
3.14 PolyquinonesasAntioxidants. . 140
3.15 LigninDerivativesasStabilizers. 143
3.16 OrganophosphorusAntioxidants 145
3.17 PentaerythritylDiphosphites . 151
3.18 OrganoboronAntioxidants . . . 152
3.19 MacrocyclicLigands. . . . . . 152
3.20 AromaticAmine Antioxidants . 153
3.21 NitrosoCompoundsand Nitrones 158
3.22 AntioxidantPropertiesofNitrosoamines 161
3.23 AntioxidantPropertiesofAntistaticAgents(Tensides) . 165
Chapter 4 Pigments
4.1 PhotostabilizingPropertiesofPigments 167
4.2 TitaniumDioxide . . 182
4.3 ZincOxide . . . . . 195
4.4 MetalSaltsCoatings . 196
4.5 CarbonBlack. . . . 196
Chapter 5 Photostabilizers
5.1 Alkyl-Substitutedp-Hydroxybenzoates . 202
5.2 PhenylEstersofBenzoicAcid 203
5.3 SalicylanilidesandOxanilides. . . . . 209
5.4 Diketones . . . . . . . . . . . .. 212
5.5 BenzylideneMalonate . . . . . . .. 213
5.6 Estersofa-Cyano-(J-phenylcinnamicAcid 213
5.7 Hydroxybenzophenones . . . . . . . . 215
5.8 ChromanoneandTetralonePhotostabilizers 229
5.9 Hydroxybenzotriazoles. . . . 229
5.10 OrganicMetalPhotostabilizers 241
5.11 MetalStearates . . . . . . . 249
CONTENTS xi
5.12 MetalSaltsofOrganicAcids . . . . 250
5.13 MetalOximeChelates . . . . . . . 253
5.14 Nickel(II)Mono-oxime(Hydrazone)Chelates 256
5.15 MetalSalicylateChelates. . . . . . . . 257
5.16 Nickel(II)Bis(stilbenedithiolate) Chelates . . 258
5.17 PyrazoleChelates . . . . . . . . . . . . . 258
5.18 Nickel(II)ThiopicolineAnilideChelate . . . 261
5.19 Nickel(II)2,2'-Thiobis(4-tert.-octylphenolato)-n-butylamine. 262
5.20 Nickel(II)Bis(o-butyl-3,5-di-tert.-butyl-4-hydroxybenzyl)-
phosphonate . . . . . . . . . . . . . . . . . . . . 263
5.21 MetalDithiolatesas Photostabilizers. . . . . . . . . . 264
5.22 MetalChelatesasPro-oxidantsand Photoinitiators 267
5.23 DithiocarbamateIronComplexActingasPhotoinitiatorof
PolymerDegradation . . . . . . . . . . . . 269
5.24 Metal Acetylacetonates . . . . . . . . . . . 272
5.25 Metal Deactivators . . . . . . . . . . . . . 275
5.26 OrganotelluriumCompoundsasPhotostabilizers 278
Chapter 6 HinderedAmineLightStabilizers(HALS)
6.1 MechanismsofHALS Reactions . . . . . . . . . 279
6.2 MechanismsofNitroxy Radical Reactions . . . . . 298
6.3 TransformationsofHinderedAminesandNitroxy Radicals
DuringProcessingofPolymers . . . . . . . . . . . . . 317
6.4 StabilizingPropertiesofHALSinCommercialPolymers . . 318
6.5 Synergistic/AntagonisticEffectsofHALSwithOtherAdditives 327
6.6 NovelHALS . . . . . . . . . . . . . . . . . . . . .. 342
Chapter 7 Polymer-BoundAdditives
7.1 PropertiesofPolymer-BoundAdditives 357
7.2 PolymericAntioxidants . . . . . . . 358
7.3 PolymericPhotostabilizers . . . . . . 368
7.4 HinderedAmine(HALS)MonomersandPolymers 391
7.5 PolymerswithHinderedN-oxyGroupintheMainChain 393
Chapter 8 IndustrialAspectsofPolymerStabilization
8.1 IndustrialMethodsofIncorporatingAdditives ... . 396
8.2 ToxicityofPhotostabilizers . . . . . . . . . . . . . 397
8.3 'WorldIndexofPolyolefineStabilizers' 399
8.4 IndustrialApplicationofAntioxidants . . . . . . . . . .. 401
8.5 PhotostabilizationofLow-DensityPolyethylenefor Agricultural
Applications . . . . . . . . . . . . . . . . . . 408
8.6 CommerciallyProducedPolymericHALS . . . . . 409
8.7 PhotostabilizationofPolypropyleneTapesand Fibres 415
8.8 PhotostabilizationofRubber-Modified Plastics . . . 417
