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- Herausgeber: Wiley-VCH
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Photoinitiating systems for polymerization reactions are largely encountered in a variety of traditional and high-tech sectors, such as radiation curing, (laser) imaging, (micro)electronics, optics, and medicine.
This book extensively covers radical and nonradical photoinitiating systems and is divided into four parts:
* Basic principles in photopolymerization reactions
* Radical photoinitiating systems
* Nonradical photoinitiating systems
* Reactivity of the photoinitiating system
The four parts present the basic concepts of photopolymerization reactions, review all of the available photoinitiating systems and deliver a
thorough description of the encountered mechanisms. A large amount of experimental and theoretical data has been collected herein. This
book allows the reader to gain a clear understanding by providing a general discussion of the photochemistry and chemistry involved.
The most recent and exciting developments, as well as the promising prospects for new applications, are outlined.
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Seitenzahl: 808
Veröffentlichungsjahr: 2013
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Table of Contents
Related Titles
Title Page
Copyright
Dedication
Abbreviations
Introduction
Part I: Basic Principles and Applications of Photopolymerization Reactions
Chapter 1: Photopolymerization and Photo-Cross-Linking
References
Chapter 2: Light Sources
2.1 Electromagnetic Radiation
2.2 Characteristics of a Light Source
2.3 Conventional and Unconventional Light Sources
References
Chapter 3: Experimental Devices and Examples of Applications
3.1 UV Curing Area: Coatings, Inks, Varnishes, Paints, and Adhesives
3.2 Conventional Printing Plates
3.3 Manufacture of Objects and Composites
3.4 Stereolithography
3.5 Applications in Microelectronics
3.6 Laser Direct Imaging
3.7 Computer-to-Plate Technology
3.8 Holography
3.9 Optics
3.10 Medical Applications
3.11 Fabrication of Nano-Objects through a Two-Photon Absorption Polymerization
3.12 Photopolymerization Using Near-Field Optical Techniques
3.13 Search for New Properties and New End Uses
3.14 Photopolymerization and Nanotechnology
3.15 Search for a Green Chemistry
References
Chapter 4: Photopolymerization Reactions
4.1 Encountered Reactions, Media, and Experimental Conditions
4.2 Typical Characteristics of Selected Photopolymerization Reactions
4.3 Two-Photon Absorption-Induced Polymerization
4.4 Remote Curing: Photopolymerization Without Light
4.5 Photoactivated Hydrosilylation Reactions
References
Chapter 5: Photosensitive Systems
5.1 General Properties
5.2 Absorption of Light by a Molecule
5.3 Jablonski's Diagram
5.4 Kinetics of the Excited State Processes
5.5 Photoinitiator and Photosensitizer
5.6 Absorption of a Photosensitive System
5.7 Initiation Step of a Photoinduced Polymerization
5.8 Reactivity of a Photosensitive System
References
Chapter 6: Approach of the Photochemical and Chemical Reactivity
6.1 Analysis of the Excited-State Processes
6.2 Quantum Mechanical Calculations
6.3 Cleavage Process
6.4 Hydrogen Transfer Processes
6.5 Energy Transfer
6.6 Reactivity of Radicals
References
Chapter 7: Efficiency of a Photopolymerization Reaction
7.1 Kinetic Laws
7.2 Monitoring the Photopolymerization Reaction
7.3 Efficiency versus Reactivity
7.4 Absorption of Light by a Pigment
7.5 Oxygen Inhibition
7.6 Absorption of Light Stabilizers
7.7 Role of the Environment
References
Part II: Radical Photoinitiating Systems
Chapter 8: One-Component Photoinitiating Systems
8.1 Benzoyl-Chromophore-Based Photoinitiators
8.2 Substituted Benzoyl-Chromophore-Based Photoinitiators
8.3 Hydroxy Alkyl Heterocyclic Ketones
8.4 Hydroxy Alkyl Conjugated Ketones
8.5 Benzophenone- and Thioxanthone-Moiety-Based Cleavable Systems
8.6 Benzoyl Phosphine Oxide Derivatives
8.7 Phosphine Oxide Derivatives
8.8 Trichloromethyl Triazines
8.9 Biradical-Generating Ketones
8.10 Peroxides
8.11 Diketones
8.12 Azides and Aromatic Bis-Azides
8.13 Azo Derivatives
8.14 Disulfide Derivatives
8.15 Disilane Derivatives
8.16 Diselenide and Diphenylditelluride Derivatives
8.17 Digermane and Distannane Derivatives
8.18 Carbon–Germanium Cleavable-Bond-Based Derivatives
8.19 Carbon–Silicon and Germanium–Silicon Cleavable–Bond-Based Derivatives
8.20 Silicon Chemistry and Conventional Cleavable Photoinitiators
8.21 Sulfur–Carbon Cleavable-Bond-Based Derivatives
8.22 Sulfur–Silicon Cleavable-Bond-Based Derivatives
8.23 Peresters
8.24 Barton's Ester Derivatives
8.25 Hydroxamic and Thiohydroxamic Acids and Esters
8.26 Organoborates
8.27 Organometallic Compounds
8.28 Metal Salts and Metallic Salt Complexes
8.29 Metal-Releasing Compound
8.30 Cleavable Photoinitiators in Living Polymerization
8.31 Oxyamines
8.32 Cleavable Photoinitiators for Two-Photon Absorption
8.33 Nanoparticle-Formation-Mediated Cleavable Photoinitiators
8.34 Miscellaneous Systems
8.35 Tentatively Explored UV-Light-Cleavable Bonds
References
Chapter 9: Two-Component Photoinitiating Systems
9.1 Ketone-/Hydrogen-Donor-Based Systems
9.2 Dye-Based Systems
9.3 Other Type II Photoinitiating Systems
References
Chapter 10: Multicomponent Photoinitiating Systems
10.1 Generally Encountered Mechanism
10.2 Other Mechanisms
10.3 Type II Photoinitiator/Silane: Search for New Properties
10.4 Miscellaneous Multicomponent Systems
References
Chapter 11: Other Photoinitiating Systems
11.1 Photoinitiator-Free Systems or Self-Initiating Monomers
11.2 Semiconductor Nanoparticles
11.3 Self-Assembled Photoinitiator Monolayers
References
Part III: Nonradical Photoinitiating Systems
Chapter 12: Cationic Photoinitiating Systems
12.1 Diazonium Salts
12.2 Onium Salts
12.3 Organometallic Derivatives
12.4 Onium Salt/Photosensitizer Systems
12.5 Free-Radical-Promoted Cationic Photopolymerization
12.6 Miscellaneous Systems
12.7 Photosensitive Systems for Living Cationic Polymerization
12.8 Photosensitive Systems for Hybrid Cure
References
Chapter 13: Anionic Photoinitiators
13.1 Inorganic Complexes
13.2 Organometallic Complexes
13.3 Cyano Derivative/Amine System
13.4 Photosensitive Systems for Living Anionic Polymerization
References
Chapter 14: Photoacid Generators (PAG) Systems
14.1 Iminosulfonates and Oximesulfonates
14.2 Naphthalimides
14.3 Photoacids and Chemical Amplification
References
Chapter 15: Photobase Generators (PBG) Systems
15.1 Oxime Esters
15.2 Carbamates
15.3 Ammonium Tetraorganyl Borate Salts
15.4 N-Benzylated-Structure-Based Photobases
15.5 Other Miscellaneous Systems
15.6 Photobases and Base Proliferation Processes
References
Part IV: Reactivity of the Photoinitiating System
Chapter 16: Role of the Experimental Conditions in the Performance of a Radical Photoinitiator
16.1 Role of Viscosity
16.2 Role of the Surrounding Atmosphere
16.3 Role of the Light Intensity
References
Chapter 17: Reactivity and Efficiency of Radical Photoinitiators
17.1 Relative Efficiency of Photoinitiators
17.2 Role of the Excited-State Reactivity
17.3 Role of the Medium on the Photoinitiator Reactivity
17.4 Structure/Property Relationships in Photoinitiating Systems
References
Chapter 18: Reactivity of Radicals toward Oxygen, Hydrogen Donors, Monomers, and Additives: Understanding and Discussion
18.1 Alkyl and Related Carbon-Centered Radicals
18.2 Aryl Radicals
18.3 Benzoyl Radicals
18.4 Acrylate and Methacrylate Radicals
18.5 Aminoalkyl Radicals
18.6 Phosphorus-Centered Radicals
18.7 Thiyl Radicals
18.8 Sulfonyl and Sulfonyloxy Radicals
18.9 Silyl Radicals
18.10 Oxyl Radicals
18.11 Peroxyl Radicals
18.12 Aminyl Radicals
18.13 Germyl and Stannyl Radicals
18.14 Boryl Radicals
18.15 Lophyl Radicals
18.16 Iminyl Radicals
18.17 Metal-Centered Radicals
18.18 Propagating Radicals
18.19 Radicals in Controlled Photopolymerization Reactions
18.20 Radicals in Hydrosilylation Reactions
References
Chapter 19: Reactivity of Radicals: Towards the Oxidation Process
19.1 Reactivity of Radicals toward Metal Salts
19.2 Radical/Onium Salt Reactivity in Free-Radical-Promoted Cationic Photopolymerization
References
Conclusion
Index
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The Authors
Prof. Jean Pierre Fouassier
formerly University of Haute Alsace
Ecole Nationale Supérieure de Chimie
3 rue Alfred Werner
68093 Mulhouse Cedex
France
Prof. Jacques Lalevée}
University of Haute Alsace
Institut Science des Matériaux
IS2M-LRC 7228, CNRS
15 rue Jean Starcky
68057 Mulhouse Cedex
France
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Library of Congress Card No.: applied for
British Library Cataloguing-in-Publication Data
A catalogue record for this book is available from the British Library.
Bibliographic information published by the Deutsche Nationalbibliothek
The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at <http://dnb.d-nb.de>.
© 2012 Wiley-VCH Verlag &Co. KGaA, Boschstr. 12, 69469 Weinheim, Germany
All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law.
Print ISBN: 978-3-527-33210-6
ePDF ISBN: 978-3-527-64827-6
ePub ISBN: 978-3-527-64826-9
mobi ISBN: 978-3-527-64825-2
oBook ISBN: 978-3-527-64824-5
Dedication
To Geneviève F., Gaëlle, Hugo and Emilie L. for their patience and understanding
To our colleagues over the world for the marvellous time we spent together during all these years.
Abbreviations
AA
acrylamide
ABE
allylbutylether
ABP
aminobenzophenone
ADD
acridinediones
AH
electron/proton donor
AIBN
azo bis-isobutyro nitrile
ALD
Aldehydes
ALK
Alkoxyamines
AN
acrylonitrile
AOT
bis-2 ethyl hexyl sodium sulfosuccinate
APG
alkylphenylglyoxylates
AQ
anthraquinone
ATR
Attenuated reflectance
ATRP
atom transfer radical polymerization
BA
butylacrylate
BAc
[2-oxo-1,2-di(pheny)ethyl]acetate
BAPO
Bis-acyl phosphine oxide
BBD
Benzoyl benzodioxolane
BBDOM
bisbenzo-[1,3]dioxol-5-yl methanone
BC
borane complexes
BD
Benzodioxinone
BDE
bond dissociation energy
BE
benzoin esters
BIP-T
bis-(4-tert-butylphenyl) iodonium triflate
BMA
butylmethacrylate
BME
benzoin methyl ether
BMS
benzophenone phenyl sulfide
BP
benzophenone
BPO
benzoyl peroxide
BPSK
1-Propanone,1-[4-[(4-benzoylphenyl)thio]phenyl]-2-methyl-2-[(4-methylphenyl)sulfonyl]
BTTB
4-Benzoyl(4′-tert-butylperoxycarboxyl) tert-butylperbenzoate
BVE
butylvinylether
Bz
benzil
BZ
benzoin
C1
7-diethylamino-4-methyl coumarin
C6
3-(2′-benzothiazoryl)-7-diethylaminocoumarin
CA
cyanoacrylates
CD
cyclodextrin
CIDEP
chemically induced electron polarization
CIDNP
chemically induced nuclear polarization
CL
caprolactone
CNT
photopolymerized lipidic assemblies
co-I
co-initiator
CPG
cyano N-phenylglycine
CQ
camphorquinone
CT
charge transfer
CTC
charge transfer complex
CTP
computer-to-plate
CTX
chlorothioxanthone
CumOOH
cumene hydroperoxide
CW
continuous-wave
DB
deoxybenzoin
DCPA
dicylopentenyl acrylates
DDT
diphenyldithienothiophene
DEAP
2,2-dietoxyacetophenone
DEDMSA
N
,
N
-diethyl-1,1-dimethylsilylamine
DEEA
2-(2-ethoxy-ethoxy) ethyl acrylate
DFT
density functional theory
DH
hydrogen donor
DMAEB
dimethylamino ethyl benzoate
DMPA
2,2-dimethoxy -2 phenyl-acetophenone
DMPO
5,5′-dimethyl-1-pyrroline N-oxide
DPA
diphenyl acetylene
dPI
difunctional photoinitiators
DSC
differential scanning calorimetry
DTAC
dodecyl trimethylammonium chloride
DUV
deep UV
DVE
divinylether
EA
electronic affinity
EAB
diethyl amino benzophenone
EDB
ethyl dimethylaminobenzoate
EHA
2-ethyl hexyl ester
EL
ethyl linoleate
EMP
N
-ethoxy-2-methylpyridinium
EMS
epoxy-modified silicone
Eo
Eosin Y
EP
epoxy acrylate
EpAc
epoxy acrylate; see Section 16 p359
EPDM
ethylene-propylene-diene monomers
EPHT
electron/proton hydrogen transfer
EPOX
3,4-epoxycyclohexane)methyl 3,4-epoxycyclohexylcarboxylate
EPT
ethoxylated pentaerythritol tetraacrylate
ERL
exposure reciprocity law
ESO
epoxidized soybean oil
ESR
electron spin resonance
ESR-ST
Electron spin resonance spin trapping
ET
energy transfer
eT
electron transfer
EtBz
ethylbenzene
EUV
extreme UV
EVE
ethylvinylether
FBs
fluorescent bulbs
Fc(+)
ferrocenium salt derivative
FRP
free radical photopolymerization
FRPCP
free-radical-promoted cationic polymerization
FTIR
Fourier transform infrared
FU
fumarate
GRIN
gradient index
HABI
2,2′,4,4′,5,5′-hexaarylbiimidazole
HALS
Hindered amine light stabilizer
HAP
2-hydroxy-2- methyl-1- phenyl-1- propanone
HCAP
1-hydroxy- cyclohexyl-1- phenyl ketone
HCs
hydrocarbons
HDDA
hexane diol diacrylate
hfc
hyprefine splitting
HFS
hyperfine splitting
HOMO
highest occupied molecular orbital
HQME
hydroquinone methyl ether
HRAM
Highly reactive acrylate monomers
HSG
hybrid sol–gel
HT
hydrogen transfer
IP
ionization potential
IPNs
Interpenetrating polymer networks
IR
infrared
ISC
intersystem crossing
ITX
isopropylthioxanthone
JAW
julolidine derivative
K-ESR
kinetic electron spin resonance
KC
ketocoumarin
2K-PUR
two-component polyurethane
LAT
light absorbing transients
LCAO
linear combination of atomic orbitals
LCD
liquid crystal display
LDI
Laser direct imaging
LDO
limonene dioxide
LED
light-emitting diode
LFP
laser flash photolysis
LIPAC
laser-induced photoacoustic calorimetry
LS
light stabilizers
LUMO
lowest unoccupied molecular orbital
MA
methylacrylate
MA
monomer acceptor
MAL
maleate
MB
methylene blue
MBI
mercaptobenzimidazole
MBO
mercaptobenzoxazole
MBT
mercaptobenzothiazole
MD
monomer donor
MDEA
methyldiethanolamine
MDF
medium-density fiber
MEK
methyl ethyl ketone
MIR
multiple internal reflectance
MK
Mischler's ketone
MMA
methylmethacrylate
MO
molecular orbitals
mPI
Multifunctional photoinitiators
MPPK
2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-1-butanone
MWD
molecular weight distribution
NAS
2-[p-(diethyl-amino)styryl]naphtho[1,2-d]thiazole
NHC
N-heterocyclic carbene
NIOTf
N
-(trifluoromethanesulfonyloxy)-1,8-naphthalimide
NIR
near-IR reflectance
NMP2
nitroxide-mediated photopolymerization
NMP
nitroxide-mediated photopolymerization
NMR
Nuclear magnetic resonance
NOR
norbornenes
NP
nanoparticles
NPG
N
-phenyl glycine
NQ
naphthoquinone
NVET
nonvertical energy transfer
NVP
N
-vinylpyrolidone
OD
optical density
OLED
organic light-emitting diode
OMC
organometallic compounds
On
+
onium salt derivative
OrM
organic matrixes
P
+
pyrilium salt derivative
PAG
Photoacid generators
PBG
photobase generator
PBN
phenyl-
N
-tertbutyl nitrone
PC
photocatalyst
PCBs
printed circuit boards
PCL
polycaprolactone
PDO
1-phenyl 2-propanedione-2 (ethoxycarbonyl) oxime
PEG
polyethyleneglycol
PES
potential energy surface
PETA
pentaerythritol tetraacrylate
PHS
Poly(hydrosilane)s
PHT
pure hydrogen transfer
PI
photoinitiator
PIS
photoinitiating system
PLA
Polylactic acid
PLP
pulsed laser polymerization
PLP
Pulsed laser-induced polymerization
PMK
2-methyl-1-(benzoyl)-2-morpholino-propan-1-one
PMMA
polymethylmethacrylate
POH
phenolic compounds
PPD
1-phenyl-1,2-propanedione
PPK
2-benzyl-2-dimethylamino-1-(phenyl)-1-butanone
PS
photosensitizer
PS/PI
photosensitizer/photoinitiator
PSAs
Pressure-sensitive adhesives
PVC
polyvinylchloride
PWBs
printed wiring boards
PYR
pyrromethene
RAFT
reversible addition-fragmentation transfer
RB
Rose Bengal
RFID
radiofrequency identification
ROMP
Ring-opening metathesis photopolymerization
ROOH
peroxide derivative
ROOH
hydroperoxide derivative
ROP
ring-opening polymerization
RP
radical pair
RPM
radical pair mechanism
RSH
mercaptan
RT-FTIR
real-time Fourier transform infrared
SCM
solvatochromic comparison method
SCRP
spin-correlated radical pair
SDS
sodium dodecyl sulfate
SG1
N-(2-methylpropyl)-N-(1-diethylphosphono-2,2-dimethylpropyl)-N-oxyl
SHOMO
singly highest occupied molecular orbital
SOMO
singly occupied molecular orbital
STY
styrene
SU
suberone
SWNT
single-wall carbon nanotube
TEA
triethyl amine
TEMPO
2,2,6,6, tetramethylpiperidine N-oxyl radical
THF
tetrahydrofuran
ThP
thiophene
TI
titanocene derivative
TIPNO
2,2,5-tri-methyl-4-phenyl-3-azahexane-3-nitroxide
TLS
thermal lens spectroscopy
TM
triplet mechanism
TMP
2,2,6,6-tetramethylpiperidine
TMPTA
trimethylolpropane triacrylate
TP
+
thiopyrilium salt derivative
TPA
two-photon absorption
TPGDA
tetrapropyleneglycol diacrylate
TPK
1-[4-(methylthio) phenyl]-ethanone
TPMK
2-methyl-1-(4-methylthiobenzoyl)-2-morpholino-propan-1-one
TPO
2,4,6-trimethyl benzoyl-diphenylphosphine oxide
TPP
triphenylphosphine
TR-ESR
time resolved electron spin resonance
TR-FTIR
time-resolved Fourier transform infra red
TR-S2FTIR
Laser-induced step-scan FTIR spectroscopy
TS
transition state
TST
transition state theory
TTMSS
tris(trimethyl)silylsilane
TX
thioxanthone
TX-SH
2-mercaptothioxanthone
Tz
triazine derivative
ULSI
ultra large scale integration
UV
ultraviolet
UVA
UV absorbers
VA
vinyl acetate
VC
vinylcarbazole
VE
vinyl ethers
VE
vinylacetate
VET
vertical energy transfer
Vi
violanthrone
VIE
vitamin E
VLSI
very large scale integration
VOC
volatile organic compounds
VP
vinylpyrrolidone
VUV
vacuum ultraviolet
XT
xanthones
Introduction
Light-induced polymerization reactions are largely encountered in many industrial daily life applications or in promising laboratory developments. The basic idea is to readily transform a liquid monomer (or a soft film) into a solid material (or a solid film) on light exposure. The huge sectors of applications, both in traditional and high-tech areas, are found in UV curing (this area corresponds to the largest part of radiation curing that includes UV and electron beam curing), laser imaging, microlithography, stereolithography, microelectronics, optics, holography, medicine, and nanotechnology.
UV curing represents a green technology (environmentally friendly, nearly no release of volatile organic compounds (VOCs), room temperature operation, possible use of renewable materials, use of convenient light sources (light-emitting diodes (LEDs), household lamps, LED bulbs, and the sun) that continues its rapid development. The applications concern, for example, the use of varnishes and paints (for a lot of applications on a large variety of substrates, e.g., wood, plastics, metal, and papers), the design of coatings having specific properties (for flooring, packaging, release papers, wood and medium-density fiber (MDF) panels, automotive, pipe lining, and optical fibers), the development of adhesives (laminating, pressure sensitive, and hot melt), and the graphic arts area (drying of inks, inkjets, overprint varnishes, protective and decorative coatings, and the manufacture of conventional printing plates).
Other applications of photopolymerization reactions concern medicine (restorative and preventative denture relining, wound dressing, ophthalmic lenses, glasses, artificial eye lens, and drug microencapsulation), microelectronics (soldering resists, mask repairs, encapsulants, conductive screen inks, metal conductor layers, and photoresists), microlithography (writing of complex relief structures for the manufacture of microcircuits or the patterning of selective areas in microelectronic packaging using the laser direct imaging (LDI) technology; direct writing on a printing plate in the computer-to-plate technology), 3D machining (or three-dimensional photopolymerization or stereolithography) that gives the possibility of making objects for prototyping applications, optics (holographic recording and information storage, computer-generated and embossed holograms, manufacture of optical elements, e.g., diffraction grating, mirrors, lenses, waveguides, array illuminators, and display devices), and structured materials on the nanoscale size.
Photopolymerization reactions are currently encountered in various experimental conditions, for example, in film, gas phase, aerosols, multilayers, (micro)heterogeneous media or solid state, on surface, in ionic liquids, in situ for the manufacture of microfluidic devices, in vivo, and under magnetic field. Very different aspects can be concerned with gradient, template, frontal, controlled, sol–gel, two-photon, laser-induced or spatially controlled, and pulsed laser photopolymerization.
As a photopolymerization reaction involves a photoinitiating system, a polymerizable medium, and a light source, a strong interplay should exist between them. The photoinitiator has a crucial role as it absorbs the light, converts the energy into reactive species (excited states, free radicals, cations, acids, and bases) and starts the reaction. Its reactivity governs the efficiency of the polymerization. A look at the literature shows that a considerable number of works are devoted to the design of photosensitive systems being able to operate in many various (and sometimes exotic) experimental conditions. This research field is particularly rich. Fantastic developments have appeared all along the past three decades. Significant achievements have been made since the early works on photopolymerization in the 1960s and the traditional developments of the UV-curing area. At present, high-tech applications are continuously emerging. Tailor-made photochemistry and chemistry have appeared in this area. The search for a safe and green technology has been launched. Interesting items relate not only to the polymer science and technology field but also to the photochemistry, physical chemistry, and organic chemistry areas.
We believe that the proposed book focused on this exciting topic related to the photosensitive systems encountered in photopolymerization reactions will be helpful for many readers. Why a new book? Indeed, in the past 20 years, many aspects of light-induced polymerization reactions have been obviously already discussed in books and review papers. Each of these books, however, usually covers more deeply selected aspects depending first on the origin (university, industry) and the activity sector of the author (photochemistry, polymer chemistry, and applications) and second on the goals of the book (general presentation of the technology, guide for end users, and academic scope). Our previous general book published more than 15 years ago (1995) and devoted to the three photoinitiation-photopolymerization-photocuring complementary aspects already provided a first account on the photosensitive systems.
For obvious reasons, all these three fascinating aspects that continuously appear in the literature cannot be unfortunately developed now (in 2011) in detail in a single monograph because of the rapid growth of the research. A book that mostly concentrates on the photosensitive systems that are used to initiate the photopolymerization reaction, their adaptation to the light sources, their excited state processes, the reactivity of the generated initiating species (free radicals, acids, and bases), their interaction with the different available monomers, their working out mechanisms, and the approach for a complete understanding of the (photo)chemical reactivity was missing. This prompted us to write the present book. It aims at providing an original and up-to-date presentation of these points together with a discussion of the structure/reactivity/efficiency relationships observed in photoinitiating systems usable in radical, cationic, and anionic photopolymerization as well as in acid and base catalyzed photocrosslinking reactions. We wish to focus on the necessary role of the basic research toward the progress of the applied research through the large part we have devoted to the involved mechanisms. In fact, everybody is aware that there is no real technical future development without a present high-quality scientific research. In our opinion, such an extensive and complete book within this philosophy has never been written before.
Science is changing very fast. During the preparation of a book, any author has the feeling of walking behind the developments that unceasingly appear. It is rather difficult to have the latest photography of the situation by the end of the manuscript; this is also reinforced by the necessary delay to print and deliver the book. Therefore, we decided here to give not only the best up-to-date situation of the subject but also to take time to define a lot of basic principles and concepts, mechanistic reaction schemes, and examples of reactivity/efficiency studies that remain true and are not submitted to a significant aging on a 10-year timescale.
The book is divided into four parts. In Part I, we deliver a general presentation of the basic principles and applications of the involved photopolymerization reactions with a description of the available light sources, the different monomers and the properties of the cured materials, the various aspects and characteristics of the reactions, and the role of the photosensitive systems and the typical examples of applications in different areas. The part especially concerned with the polymer science point of view (as other books have already dealt in detail with this aspect) focuses on general considerations and latest developments and to what is necessary to clearly understand the following parts. Then, we enter into the heart of the book.
In Parts II and III, we give (i) the most exhaustive presentation of the commercially and academically used or potentially interesting photoinitiating systems developed in the literature (photoinitiators, co-initiators, photosensitizers, macrophotoinitiators, multicomponent combinations, and tailor-made compounds for specific properties), (ii) the characteristics of the excited states, and (iii) the involved reaction mechanisms. We provide an overview of all the available systems but we focus our attention on newly developed photoinitiators, recently reported studies, and novel data on previous well-known systems. All this information is provided for radical photopolymerization (Part II) and cationic and anionic photopolymerization and photoacid and photobase catalyzed photocrosslinking (Part III).
In Part IV, we gather and discuss (i) a large set of data, mostly derived from time-resolved laser spectroscopy and electron spin resonance (ESR) experiments, related to both the photoinitiating system excited states and the initiating radicals (e.g., a complete presentation of the experimental and theoretical reactivity of more than 15 kinds of radicals is provided); (ii) the most recent results of quantum mechanical calculations that allow probing of the photophysical/photochemical properties as well as the chemical reactivity of a given photoinitiating system; and (iii) the reactivity in solution, in micelle, in bulk, in film, under air, in low viscosity media, or under low light intensities.
The book also outlines the latest developments and trends for the design of novel molecules. This concerns first the elaboration of smart systems exhibiting well-designed functional properties or/and suitable for processes in the nanotechnology area. A second direction refers to the development of an evergreen (photo)chemistry elaborating, for example, safe, renewable, reworkable, or biocompatible materials. A third trend is related to the use of soft irradiation conditions for particular applications, which requires the design of low oxygen sensitivity compounds under exposure to low-intensity visible light sources, sun, LEDs, laser diodes, or household lamps (e.g., fluorescence or LED bulbs).
When questioning the Chemical Abstract database, many references appear. We have not intended to give here an exhaustive list of references or a survey of the patent literature. We used, however, more than 2000 references. Pioneer works are cited but our present list of references mainly refers to papers dispatched during the past 15 years. The selection of the articles is most of the time a rather hard and sensitive task. We have done our best and beg forgiveness for possible omissions.
This research field has known a fantastic evolution. We would like now to share the real pleasure we had (and still have) in participating and contributing to this area. Writing this book was really a great pleasure. We hope that our readers, R and D researchers, engineers, technicians, University people, and students involved in various scientific or/and technical areas such as photochemistry, polymer chemistry, organic chemistry, radical chemistry, physical chemistry, radiation curing, imaging, physics, optics, medicine, nanotechnology will appreciate this book and enjoy its content.
And now, it is time to dive into the magic of the photoinitiator/photosensitizer world!
Part I
Basic Principles and Applications of Photopolymerization Reactions
In this first part of the book, we give a general presentation of the photopolymerization reactions, the light sources, the experimental devices and the applications, the role of the photosensitive systems, the evaluation of the practical efficiency of a photopolymerizable medium, and the approach of the photochemical and chemical reactivity. As stated in the introduction, the different aspects related to photopolymerization reactions are currently presented and discussed in books (see, e.g., [1–31]) and review papers (see, e.g., [32–96]). As a consequence, some of the above-mentioned topics that have formerly received a deeper analysis are not exhaustively treated here. In that case, we only provide a basic and rather brief description that should allow an easy understanding of the three subsequent parts.
1
Photopolymerization and Photo-Cross-Linking
Everybody knows that a polymerization reaction [97] consists in adding many monomer units M to each other, thereby creating a macromolecule (Eq. (1.1)).
1.1
The initiation step of this reaction corresponds to the decomposition of a molecule (an initiator I) usually obtained through a thermal process (Eq. (1.2)). This produces an initiating species (e.g., a free radical R·) able to attack the first monomer unit. Other units add further to form the macromolecule.
1.2
Instead of a thermal activation of the polymerization, other stimuli such as light, electron beam, X-rays, γ-rays, plasma, microwaves, or even pressure can be used [85]. Among them, the exposure of a resin (monomer/oligomer matrix) to a suitable light appeared as a very convenient way for the initiation step: in that case, the reaction is called a photopolymerization reaction (Eq. (1.3)).
1.3
Owing to their absorption properties, monomers or oligomers are usually not sensitive to the available lights (except a few cases involving specifically designed light-absorbing structures). The addition of a photoinitiator (PI) is at least necessary (Eq. (1.4)). Excited states are generated under the light exposure of PI (Chapters 2 and 3). Then, an initiating species is produced. Its nature –radical (R·), cationic (C+), and anionic (A−) –is dependent on the starting molecule.
1.4
Accordingly, the usual types of photopolymerization reactions (radical, cationic, and anionic photopolymerization or acid and base catalyzed photo-cross-linking reactions) can be encountered (Eq. (1.5)) in suitable resins.
1.5
The term photopolymerization is very general and relates to two different concepts (Scheme 1.1). A photoinduced polymerization reaction is a chain reaction where one photon yields one initiating species and induces the incorporation of a large number of monomer units. A photo-cross-linking reaction refers to a process involving a prepolymer or a polymer backbone in which a cross-link is formed between two macromolecular chains. This kind of polymer can be designed in such a way that it contains pendent (e.g., in polyvinylcinnamates) or in-chain photo-cross-linkable moieties (e.g., in chalcone-type chromophore-based polymers).
Scheme 1.1
A monomer (1) is a rather small molecule having usually one or several chemical reactive functions (e.g., acrylates), whereas an oligomer (2) is a large molecular structure consisting of repetitive units of a given chemical structure that constitutes the backbone (e.g., a polyurethane) and containing one or more reactive chemical functions. The oligomer skeleton governs the final physical and chemical properties of the cured coating.
When using multifunctional monomers or oligomers, the photoinduced polymerization reaction does not obviously proceed to form a linear polymer. As it develops in the three directions of space, it also leads to a cross-linking reaction, thereby creating a polymer network (see, e.g., Scheme 1.2 for a free radical reaction). Sometimes, the reaction is depicted as a cross-linking photopolymerization.
Scheme 1.2
A photopolymerizable formulation [25] consists of (i) a monomer/oligomer matrix (the monomer plays the role of a reactive diluent to adjust the viscosity of the formulation; it readily copolymerizes), (ii) a PI or a photoinitiating system (PIS) (containing a PI and other compounds), and (iii) various additives, for example, flow, slip, mist, wetting, dispersion agents, inhibitors for handling and fillers, plasticizers, matting or gloss agents, pigments, and light stabilizers according to the applications.
UV curing is a word that defines an ever-expanding industrial field [6, 10, 16, 25] where the light, often delivered by a mercury lamp, is used to transform a liquid photosensitive formulation into an insoluble solid film for coating applications through a photopolymerization reaction. Photocuring is a practical word that refers to the use of light to induce this rapid conversion of the resin to a cured and dried solid film. Film thicknesses typically range from a few micrometers to a few hundred micrometers depending on the applications. In photostereolithography, the idea consists in building up a solid object through a layer-by-layer photopolymerization procedure.
In the imaging area, an image is obtained according to a process largely described in the literature [8, 9, 17, 90]. The resin layer is irradiated through a mask. A reaction takes place in the irradiated areas. Two basically different reactions can occur: (i) a photopolymerization or a photo-cross-linking reaction that renders the film insoluble (using a suitable solvent allows to dissolve the monomer present in the shadow areas; after etching of the unprotected surface and a bake out of the polymerized film, a negative image is thus formed) and (ii) a depolymerization or a hydrophobicity/hydrophilicity change (that leads to a solubilization of the illuminated areas, thereby forming a positive image). Free radical photopolymerization and photo-cross-linking (Scheme 1.3) lead to a negative image through (i). The acid or base catalyzed reaction (Scheme 1.3) leads either to a negative image (i) or a positive image (ii).
Scheme 1.3
In microelectronics, such a monomer/oligomer or polymer matrix sensitive to a light source is named a photoresist. In imaging technology, the organic matrix is called a photopolymer. Strictly speaking, photopolymer refers to a polymer sensitive to light but this word is often used to design a monomer/oligomer matrix that polymerizes under light exposure. The new term photomaterial refers to an organic photosensitive matrix that leads, on irradiation, to a polymer material exhibiting specific properties useful in the nanotechnology field; it could also design the final material formed through this photochemical route.
References
1. Roffey, C.G. (1982) Photopolymerization of Surface Coatings, John Wiley & Sons, Inc., New York.
2. Rabek, J.F. (1987) Mechanisms of Photophysical and Photochemical Reactions in Polymer: Theory and Practical Applications, John Wiley & Sons, Ltd, New York.
3. Hoyle, C.E. and Kinstle, J.F. (eds) (1990) Radiation Curing of Polymeric Materials, ACS Symposium Series, Vol. 417, American Chemical Society.
4. Fouassier, J.P. and Rabek, J.F. (eds) (1990) Lasers in Polymer Science and Technology: Applications, CRC Press, Boca Raton, FL.
5. Bottcher, H. (1991) Technical Applications of Photochemistry, Deutscher Verlag fur Grundstoffindustrie, Leipzig.
6. Pappas, S.P. (1986) UV-Curing: Science and Technology, Technology Marketing Corporation, Stamford, CT; Plenum Press, New York (1992).
7. Fouassier, J.P. and Rabek, J.F. (eds) (1993) Radiation Curing in Polymer Science and Technology, Chapman & Hall, London.
8. Krongauz, V. and Trifunac, A. (eds) (1994) Photoresponsive Polymers, Chapman & Hall, New York.
9. Reiser, A. (1989) Photoreactive Polymers: The Science and Technology of Resists, John Wiley & Sons, Inc., New York.
10. Fouassier, J.P. (1995) Photoinitiation, Photopolymerization, Photocuring, Hanser, Münich.
11. Allen, N.S., Edge, M., Bellobono, I.R., and Selli, E. (eds) (1995) Current Trends in Polymer Photochemistry, Ellis Horwood, New York.
12. Scranton, A.B., Bowman, A., and Peiffer, R.W. (eds) (1997) Photopolymerization: Fundamentals and Applications, ACS Symposium Series, Vol. 673, American Chemical Society, Washington, DC.
13. Olldring, K. and Holman R. (eds) (1997) Chemistry and Technology of UV and EB Formulation for Coatings Inks and Paints, vol. I - VIII, John Wiley & Sons, Ltd and Sita Technology Ltd, London.
14. Fouassier, J.P. (1998) Photoinitiated Polymerization: Theory and Applications, Rapra Review Reports, Vol. 9(4), Rapra Technology Ltd, Shawbury.
15. Holman, R. (ed.) (1999) UV and EB Chemistry, Sita Technology Ltd, London.
16. Davidson, S. (1999) Exploring the Science, Technology and Application of UV and EB Curing, Sita Technology Ltd, London.
17. Neckers, D.C. (1999) UV and EB at the Millennium, Sita Technology Ltd, London.
18. Fouassier, J.P. (ed.) (1999) Photosensitive Systems for Photopolymerization Reactions, Trends in Photochemistry and Photobiology, Vol. 5, Research Trends, Trivandrum.
19. Crivello, J.V. and Dietliker, K. (1999) Photoinitiators for Free Radical, Cationic and Anionic Photopolymerization, Surface Coatings Technology Series, vol. III (ed. G. Bradley), John Wiley & Sons, Inc.
20. Fouassier, J.P. (2001) Light Induced Polymerization Reactions, Trends in Photochemistry and Photobiology, Vol. 7, Research Trends, Trivandrum.
21. Dietliker, K. (2002) A Compilation of Photoinitiators Commercially Available for UV Today, Sita Technology Ltd, London.
22. Drobny, J.G. (2003 and 2010) Radiation Technology for Polymers, CRC Press, Boca Raton, FL.
23. Belfied, K.D. and Crivello, J.V. (eds) (2003) Photoinitiated Polymerization, ACS Symposium Series, Vol. 847, American Chemical Society, Washington, DC.
24. Fouassier, J.P. (ed.) (2006) Photochemistry and UV Curing, Research Signpost, Trivandrum.
25. Schwalm, R. (2007) UV Coatings: Basics, Recent Developments and New Applications, Elsevier, Oxford.
26. Schnabel, W. (2007) Polymer and Light, Wiley-VCH Verlag GmbH, Weinheim.
27. Lackner, M. (ed.) (2008) Lasers in Chemistry, Wiley-VCH Verlag GmbH, Weinheim.
28. Mishra, M.K. and Yagci, Y. (eds) (2009) Handbook of Vinyl Polymers, CRC Press, Boca Raton, FL.
29. Allen, N.S. (ed.) (2010) Photochemistry and Photophysics of Polymer Materials, John Wiley & Sons, Inc., Hoboken, NJ.
30. Fouassier, J.P. and Allonas, X. (eds) (2010) Basics of Photopolymerization Reactions, Research Signpost, Trivandrum.
31. Green, W.A. (2010) Industrial Photoinitiators, CRC Press, Boca Raton, FL.
32. Fouassier, J.P. (2000) Recent Res. Devel. Photochem. Photobiol., 4, 51–74.
33. Fouassier, J.P. (2000) Recent Res. Devel. Polym. Sci., 4, 131–145.
34. Fouassier, J.P. (1999) Curr. Trends Polym. Sci., 4, 163–184.
35. Fouassier, J.P. (1990) Prog. Org. Coat., 18, 227–250.
36. Paczkowski, J. and Neckers, D.C. (2001) Electron Trans. Chem., 5, 516–585.
37. Schnabel, W. (1990) in Lasers in Polymer Science and Technology, vol. II (eds J.P. Fouassier and J.F. Rabek), CRC Press, Boca Raton, FL, pp. 95–143.
38. Urano, T. (2003) J. Photopolym. Sci. Technol., 16, 129–156.
39. Fouassier, J.P., Allonas, X., and Burget, D. (2003) Prog. Org. Coat., 47, 16–36.
40. Fouassier, J.P., Ruhlmann, D., Graff, B., Morlet-Savary, F., and Wieder, F. (1995) Prog. Org. Coat., 25, 235–271.
41. Fouassier, J.P., Ruhlmann, D., Graff, B., and Wieder, F. (1995) Prog. Org. Coat., 25, 169–202.
42. Fouassier, J.P. (1993) in Radiation Curing in Polymer Science and Technology, vol. 1 (eds J.P. Fouassier and J.F. Rabek), Elsevier, Barking, pp. 49–118.
43. Fouassier, J.P. (1993) in Radiation Curing in Polymer Science and Technology, vol. 2 (eds J.P. Fouassier and J.F. Rabek), Elsevier, Barking, pp. 1–62.
44. Lissi, E.A. and Encinas, M.V. (1991) in Photochemistry and Photophysics, vol. IV (ed. J.F. Rabek), CRC Press, Boca Raton, FL, pp. 221–293.
45. Fouassier, J.P. (1990) in Photochemistry and Photophysics, vol. II (ed. J.F. Rabek), CRC Press, Boca Raton, FL, pp. 1–26.
46. Timpe, H.J. (1993) in Radiation Curing in Polymer Science and Technology, vol. 2 (ed. J.P. Fouassier), Elsevier, Barking, pp. 529–554.
47. Cunningham, A.F. and Desobry, V. (1993) in Radiation Curing in Polymer Science and Technology, vol. 2 (eds J.P. Fouassier and J.F. Rabek), Elsevier, Barking, pp. 323–374.
48. Green, W.A. and Timms, A.W. (1993) in Radiation Curing in Polymer Science and Technology, vol. 2 (eds J.P. Fouassier and J.F. Rabek), Elsevier, Barking, pp. 375–434.
49. Carlini, C. and Angiolini, L. (1993) in Radiation Curing in Polymer Science and Technology, vol. 2 (eds J.P. Fouassier and J.F. Rabek), Elsevier, Barking, pp. 283–322.
50. Li Bassi, G. (1993) in Radiation Curing in Polymer Science and Technology, vol. 2 (eds J.P. Fouassier and J.F. Rabek), Elsevier, Barking, pp. 239–282.
51. Murai, H. and Hayashi, H. (1993) in Radiation Curing in Polymer Science and Technology, vol. 2 (eds J.P. Fouassier and J.F. Rabek), Elsevier, Barking, pp. 63–154.
52. Steiner, U.E. and Wolff, H.J. (1991) in Photochemistry and Photophysics, vol. IV (ed. J.F. Rabek), CRC Press, Boca Raton, FL, pp. 1–130.
53. Hayashi, H. (1990) in Photochemistry and Photophysics, vol. I (ed. J.F. Rabek), CRC Press, Boca Raton, FL, pp. 59–136.
54. Fouassier, J.P. and Lougnot, D.J. (1990) in Lasers in Polymer Science and Technology, vol. II (eds J.P. Fouassier and J.F. Rabek), CRC Press, Boca Raton, FL, pp. 145–168.
55. Jacobine, A. (1993) in Radiation Curing in Polymer Science and Technology, vol. 3 (eds J.P. Fouassier and J.F. Rabek), Elsevier, Barking, pp. 219–268.
56. Peeters, S. (1993) in Radiation Curing in Polymer Science and Technology, vol. 3 (eds J.P. Fouassier and J.F. Rabek), Elsevier, Barking, pp. 177–218.
57. Broer, D.J. (1993) in Radiation Curing in Polymer Science and Technology, vol. 3 (eds J.P. Fouassier and J.F. Rabek), Elsevier, Barking, pp. 383–444.
58. Higashi, M. and Niwa, M. (1993) in Radiation Curing in Polymer Science and Technology, vol. 3 (eds J.P. Fouassier and J.F. Rabek), Elsevier, Barking, pp. 367–382.
59. Hasegawa, M., Hashimoto, Y., and Chung, C.M. (1993) in Radiation Curing in Polymer Science and Technology, vol. 3 (eds J.P. Fouassier and J.F. Rabek), Elsevier, Barking, pp. 341–366.
60. Dworjanyn, P.A. and Garnett, J.L. (1993) in Radiation Curing in Polymer Science and Technology, vol. 1 (eds J.P. Fouassier and J.F. Rabek), Elsevier, Barking, pp. 263–328.
61. Dreeskamp, H. and Palm, W.U. (1990) in Lasers in Polymer Science and Technology, vol. II (eds J.P. Fouassier and J.F. Rabek), CRC Press, Boca Raton, FL, pp. 47–56.
62. Mc Lauchlan, K.A. (1990) in Lasers in Polymer Science and Technology, vol. I (eds J.P. Fouassier and J.F. Rabek), CRC Press, Boca Raton, FL, pp. 259–304.
63. Phillips, D. and Rumbles, G. (1990) in Lasers in Polymer Science and Technology, vol. I (eds J.P. Fouassier and J.F. Rabek), CRC Press, Boca Raton, FL, pp. 91–146.
64. Mc Gimpsey, W.G. (1990) in Lasers in Polymer Science and Technology, vol. II (eds J.P. Fouassier and J.F. Rabek), CRC Press, Boca Raton, FL, pp. 77–94.
65. Bortolus, P. (1993) in Radiation Curing in Polymer Science and Technology, vol. 2 (eds J.P. Fouassier and J.F. Rabek), Elsevier, Barking, pp. 603–636.
66. Timpe, H.J., Jockush, S., and Korner, K. (1993) in Radiation Curing in Polymer Science and Technology, vol. 2 (ed. J.P. Fouassier), Elsevier, Barking, pp. 575–602.
67. Crivello, J.V. (1993) in Radiation Curing in Polymer Science and Technology, vol. 2 (eds J.P. Fouassier and J.F. Rabek), Elsevier, Barking, pp. 435–472.
68. Hacker, N.P. (1993) in Radiation Curing in Polymer Science and Technology, vol. 2 (eds J.P. Fouassier and J.F. Rabek), Elsevier, Barking, pp. 473–504.
69. Sahyun, M.R., De Voe, R.J., and Olofson, P.M. (1993) in Radiation Curing in Polymer Science and Technology, vol. 2 (ed. J.P. Fouassier), Elsevier, Barking, pp. 505–529.
70. Davidson, R.S. (1993) in Radiation Curing in Polymer Science and Technology, vol. 3 (eds J.P. Fouassier and J.F. Rabek), Elsevier, Barking, pp. 153–176.
71. Decker, C. and Fouassier, J.P. (1993) in Radiation Curing in Polymer Science and Technology, vol. 3 (eds J.P. Fouassier and J.F. Rabek), Elsevier, Barking, pp. 1–36.
72. Castle, P.M. and Sadhir, R.K. (1993) in Radiation Curing in Polymer Science and Technology, vol. 3 (eds J.P. Fouassier and J.F. Rabek), Elsevier, Barking, pp. 37–72.
73. Cabrera, M., Jezequel, J.Y., and André, J.C. (1993) in Radiation Curing in Polymer Science and Technology, vol. 3 (eds J.P. Fouassier and J.F. Rabek), Elsevier, Barking, pp. 73–97.
74. Allen, N.S. (2005) Photochemistry, vol. 35, The Royal Society of Chemistry, London, pp. 206–271.
75. Decker, C. (1999) in Macromolecules, vol. 143 (ed. K.P. Ghiggino), Wiley-VCH Verlag GmbH, Weiheim, pp. 45–63.
76. Decker, C. and Hoang Ngoc, T. (1998) in Functional Polymers, Modern Synthetic Methods and Novel Structures, ACS Symposium Series (eds A.O. Patil, D.N. Schultz, and B.M. Novak), American Chemical Society, pp. 286–302.
77. Decker, C. (1998) Des. Monom. Polym., 1, 47–64.
78. Decker, C. and Elzaouk, B. (1997) in Current Trends in Polymer Photochemistry (eds N.S. Allen, M. Edge, I. Bellobono, and E. Selli), Ellis Horwood, New York, pp. 131–148.
79. Decker, C. (1997) in Materials Science and Technology, vol. 18 (ed. H.E.H. Meijer), Wiley-VCH Verlag GmbH, Weinheim, pp. 615–657.
80. Decker, C. (1996) in Polymeric Materials Encyclopedia, vol. 7 (ed. J.C. Salamone), CRC Press, Boca Raton, FL, pp. 5181–5190.
81. Decker, C. (2001) in Specialty Polymer Additives (eds S. Al Malaika, A. Golovoy, and C.A. Wilkic), Backwell Science, Oxford, pp. 139–154.
82. Decker, C. (2003) in Photoinitiated Polymerization, ACS Symposium Series, Vol. 847, Chapter 23 (eds K.D. Belfield and J. Crivello), American Chemical Society, p. 266.
83. Sipani, V. and Scranton, A.B. (2004) in Encyclopedia of Polymer Science and Technology (ed. H.F. Mark), Wiley-Interscience, New York. doi: 10.1002/0471440264.pst491
84. Cai, Y. and Jessop, J.L.P. (2004) in Encyclopedia of Polymer Science and Technology (ed. H.F. Mark), Wiley-Interscience, New York. doi: 10.1002/0471440264.pst490
85. Fouassier, J.P., Allonas, X., and Lalevée, J. (2007) in Macromolecular Engineering: from Precise Macromolecular Synthesis to Macroscopic Materials Properties and Applications, vol. 1 (eds K. Matyjaszewski, Y. Gnanou, and L. Leibler), Wiley-VCH Verlag GmbH, Weinheim, pp. 643–672.
86. Allonas, X., Crouxte-Barghorn, C., Fouassier, J.P., Lalevée, J., Malval, J.P., and Morlet-Savary, F. (2008) in Lasers in Chemistry, vol. 2 (ed. M. Lackner), Wiley-VCH Verlag GmbH, pp. 1001–1027.
87. Arsu, N., Reetz, I., Yagci, Y., and Mishra, M.K. (2008) in Handbook of Vinyl Polymers (eds M.K. Mishra and Y. Yagci), CRC Press, pp. 50–75.
88. Fouassier, J.P., Allonas, X., Lalevée, J., and Dietlin, C. (2010) in Photochemistry and Photophysics of Polymer Materials (ed. N.S. Allen), John Wiley & Sons, Inc., Hoboken, NJ, pp. 351–420.
89. Kahveci, M.U., Gilmaz, A.G., and Yagci, Y. (2010) in Photochemistry and Photophysics of Polymer Materials (ed. N.S. Allen), John Wiley & Sons, Inc., Hoboken, NJ, pp. 421–478.
90. Ivan, M.G. and Scaiano, J.C. (2010) in Photochemistry and Photophysics of Polymer Materials (ed. N.S. Allen), John Wiley & Sons, Inc., Hoboken, NJ, pp. 479–508.
91. Muftuogli, A.E., Tasdelen, M.A., and Yagci, Y. (2010) in Photochemistry and Photophysics of Polymer Materials (ed. N.S. Allen), John Wiley & Sons, Inc., Hoboken, NJ, pp. 509–540.
92. Gisjman, P. (2010) in Photochemistry and Photophysics of Polymer Materials (ed. N.S. Allen), John Wiley & Sons Inc., Hoboken, NJ, pp. 627–680.
93. Lalevée, J., El Roz, M., Allonas, X., and Fouassier, J.P. (2009) in Organosilanes: Properties, Performance and Applications, Chapter 6 (eds E. Wyman and M.C. Skief), Nova Science Publishers, Hauppauge, NY, pp. 164–193.
94. Lalevée, J., Tehfe, M.A., Allonas, X., and Fouassier, J.P. (2010) in Polymer Initiators, Chapter 8 (ed. W.J. Ackrine), Nova Science Publishers, Hauppauge, NY, pp. 203–247.
95. Yagci, Y. and Retz, I. (1998) Prog. Polym. Sci., 23, 1485–1538.
96. Lalevée, J. and Fouassier, J.P. (2011) Polym. Chem., 2, 1107–1113.
97. Matyjaszewski, K., Gnanou, Y., and Leibler, L. (eds) (2007) Macromolecular Engineering: From Precise Macromolecular Synthesis to Macroscopic Materials Properties and Applications, vol. 1, Wiley-VCH Verlag GmbH, Weinheim, pp. 643–672.
2
Light Sources
2.1 Electromagnetic Radiation
2.1
The electromagnetic spectrum spans a large frequency range that varies by many orders of magnitude. Owing to the absorption properties of the photosensitive systems, the light used in photopolymerization reactions typically consists of (i) ultraviolet (UV) light (200–400 nm range classified as UVA: 320–400 nm, UVB: 290–320 nm, and UVC: 190–290 nm); (ii) visible light (400–700 nm); and (iii) sometimes near-infrared (IR) light (700–1000 nm). Light has a dual wave–particle nature: it behaves like a wave, for example, in interference phenomena and like a particle (the photon), for example, in the photoelectric effect.
2.2
2.3
The intensity of the radiation received by a sample at a given wavelength I0 (λ0) is usually defined in photochemistry by the number of photons delivered by the source at this wavelength, in a defined wavelength interval, per surface unit and time unit. The amount of energy transported by the light beam Ebeam(λ0) in J cm−2 s−1 is expressed in Eq. (2.4): it corresponds to a power density (W cm−2). In the case of a laser source, I0 (λ0) usually refers to the number of photons per time unit, the irradiated area having the dimension of the laser spot; Ebeam (λ0), which is thus expressed in J s−1, corresponds to a power P (in W).
2.4
The overall intensity I0 (or the total number of photons) delivered over a part of the electromagnetic spectrum is thus defined by an integral (Eq. (2.5)). The total energy Ebeam is also an integral.
2.5
2.2 Characteristics of a Light Source
When using a polychromatic light, a careful selection of wavelengths (Figure 2.1) can be achieved through the use of various filters [1]:
The measurement of the light intensity is done in practice by radiometers, which provide a calibrated flat output response in a given wavelength range in terms of the luminous energy per second and surface unit (J s−1cm−2 or W cm−2). As usually encountered in photochemistry [1–5], chemical actinometers can be also used to calculate the number of photons.
2.3 Conventional and Unconventional Light Sources
Typical light sources are conventional artificial light sources, laser beams, and the sun [6–10].
2.3.1 Xenon Lamp
The emission spectrum is continuous in wavelengths (Figure 2.1). Xenon (Xe) as well as mercury (Hg) (Section 2.3.2) lamps have high electrical power requirements and give off a lot of heat but emit a high light intensity over a wide spectral range. For laboratory equipment, the light intensities are relatively low compared to the Xe–Hg lamp (e.g., typically 200 and ∼ 60 mW cm−2 for Hg–Xe and Xe lamps, respectively).
2.3.2 Mercury Arc Lamp
An electrical discharge in a Hg vapor produces excited atomic energy levels. Characteristic narrow transitions occur between some of these levels and the ground state. A set of particular wavelengths is thus emitted: 254, 313, 366, 405, 435, 546, and 579 nm. The reflector used also affects the output spectrum and can be selected for an appropriate wavelength (254 and 366 nm). The relative intensity of the different lines also depends on the Hg vapor pressure. Commercial medium pressure Hg lamps for the UV-curing technologies (electrical power ∼ 60–240 W cm−1; length of the lamp: 100–2300 mm) exhibit the spectrum shown in Figure 2.2c. High fluxes of photons (typically > 1.2 W cm−2 in the 280–445 nm range) are available. Hg lamps emit heat (>50%).
Figure 2.2 (a,b) Typical emission spectra of different microwave lamps. (Source: Reproduced with permission of Fusion Inc.) (c) Typical emission spectrum of a mercury lamp. (d) Emission spectrum of a doped mercury lamp (Xe–Hg lamp) equipped with a 366 nm reflector.
Low-pressure Hg lamps or germicidal lamps mostly deliver photons around 254 nm. They can be used to produce a wrinkled surface cure.
2.3.3 Doped Lamps
Mercury lamps can be doped (e.g., by xenon, gallium, indium, and iron halides) in order to change the emission spectrum and generally to increase the light emission in the near-UV-visible region around 410–420 nm, as seen in Figure 2.2d.
Low-pressure fluorescent lamps are Hg lamps that contain a fluorescent agent: the spectrum is changed and the intensity is very low. They are used as pregelification lamps to increase the core polymerization.
2.3.4 Microwave Lamps
Contrary to usual Hg lamps, where the Hg atoms are excited by an electric field, the excitation in the radio-frequency-excited electrodeless lamps is provided by microwaves. Doped lamps are also available. This allows to mostly adjust the emission around, for example, 420 or 380 nm as shown in Figure 2.2a,b. These lamps have a high input power (300–600 W in−1; lamp design with 6 or 10 in width) and emit a lower IR amount.
2.3.5 Excimer Lamps
Excimer lamps are discharge lamps. The emitted wavelength is a function of the gases that form the excimer. In particular, they can work at 308 nm or even at 222 or 172 nm in vacuum ultraviolet (VUV) devices (see, e.g., in [11] and references therein). They have a limited commercial use. Applications in photopolymerization are under development.
2.3.6 Light-Emitting Diodes (LEDs)
A light-emitting diode (LED) is based on a semiconductor material device [12, 13]. At present, according to the technical developments, the proposed LEDs emit a light with an almost Gaussian distribution in a narrow wavelength range centered at 365 nm (345–385 nm) or 395 nm (380–420 nm) with an intensity about a few 10–100 mW cm−2 (Figure 2.3). Highly packed arrays of LED are possible (up to 400 LED per cm2). This allows light intensities up to 2 and 8 W cm−2 at 365 and 395 nm, respectively. As the light is delivered within a small wavelength interval, the output luminous power density per nanometer is typically 0.1 and 0.5 W cm−2 nm−1 (at 365 and 395 nm) compared to 0.2 W cm−2 nm−1 for a 100 W short arc lamp in the 365–440 nm range. However, the total power density (in W cm−2) over the whole emission spectrum is obviously noticeably lower for an LED arrangement than for a mercury lamp.
Figure 2.3 Typical emission spectra of (a) 365 nm LED, (b) 532 nm diode laser, and (c) 635 nm diode laser (J. Lalevée unpublished data).
The main benefits of LEDs are (i) low heat generation (no IR light); (ii) low energy consumption; (iii) low operating costs, less maintenance, a ∼ 50000 h life and portability; and (iv) a possible incorporation in programmed robots that can move the lamps to improve the curing of shadow areas. LEDs have a high potential for digital inkjet printing, adhesive curing, curing of thin heat-sensitive plastic foils, spot curing (automotive topcoat repair), and dentistry (UV handhold for curing teeth inlay). Development of the LED technology is fully under way and holds great promise. A spray gun equipped with LEDs allows the resin application and the photocuring step in a single operation [14]. The performance of LEDs versus conventional light sources in UV-curing experiments has been evaluated [15, 16] and is discussed in the following chapters. The emission spectra exhibit a higher full width half maximum (FWHM) (∼20–30 nm) for LED compared to a diode laser irradiation (<1.5 nm), as seen in Figure 2.3.
2.3.7 Pulsed Light Sources
While all the lamps described above emit a light whose intensity is constant as a function of time, flash lamps and pulsed UV light sources deliver the photons in a single flash or pulse of light. Examples can be found in [17]. Pulsed Xe lamps deliver lower heat. They are suited to specialty applications. The pulsed laser polymerization (PLP) techniques can be useful compared to continuous irradiations and lead to specific properties, that is, the initiation takes place only during the irradiation, and the propagation and termination processes can be observed in the dark period so that the molecular weights and the molecular weight distributions (MWDs) can be modulated by the frequency as well as the pulse width.
2.3.8 Laser Sources
Details on lasers [18] and laser applications in photopolymerization can be found in [19–21]. Laser beams present specific characteristics: (i) a monochromatic light (this allows a control of the light absorption and then the photochemical reactions; side reactions and local heating are reduced), (ii) large possibilities in wavelength selection, (iii) a high energy concentration onto a small surface (this ensures a quasi-instantaneous curing and a reduced oxygen inhibition), (iv) a high spatial resolution, spectral selectivity, narrow bandwidth of the emission (these properties are useful in holography), (v) an easy focalization (the photochemical event can be produced in a sample placed at a long distance from the light source), and (vi) a very short exposure time allowing a possible scanning of a surface by the laser spot, which behaves as a pencil of light (the direct imaging is affordable; high-resolution images can be obtained).
As in conventional sources, many lasers deliver the light continuously as a function of time. Some lasers can also emit the light as a (very) short pulse. In that case, very high power P or power density DP can be attained as the amount of energy is divided by the pulse duration: for example, a continuous-wave (CW) laser (100 mJ s−1) gives P values, for example, ∼ 0.1 W, whereas a low-intensity pulsed laser (e.g., 100 ns, 1 mJ) leads to P ∼ 10 kW. Compared to a conventional light source (typically DP ∼ 0.2 W cm−2), this CW laser yields higher DP (DP ∼ 10 W cm−2) because of its small beam diameter. In the same way, the pulsed laser considered above would lead to DP ∼ 1000 kW cm−2.
Many different lasers are available in the market; among them are the following:
2.3.9 Sun
The sun is a very convenient and inexpensive source of light but delivers a low intensity (typically < 5 mW cm−2 in the near-UV-visible wavelength range; see the emission spectrum in Figure 2.1). This intensity is strongly affected by the weather, the location, and the year period. It might be of interest for particular outdoor or daylight indoor applications. Visible-light-induced polymerization is well documented, as seen in Parts II and III, but works devoted to sunlight curing itself are rather scant.
2.3.10 Household Lamps
With the actual need for green technologies, the development of new (photo)chemical systems and new soft irradiation conditions for photopolymerization reactions is ever required. For example, the basic interest in household fluorescent bulbs (FBs) (Figure 2.4), which already appeared in organic synthesis [23], might be (i) the available higher luminous power in the 380–800 nm range ( ∼ 15 mW cm−2 compared to < 5 mW cm−2 for solar irradiation); (ii) the stability of this irradiation source, which is not affected by the weather and location (iii); the disposal of very safe light sources; and (iv) the use of commercial and cheap standard devices.
Figure 2.4 Emission spectra (intensity in μW cm−2) of (a) a household fluorescent bulb, (b) a household blue LED bulb, and (c) a household white LED bulb.
In the same way, compared to FBs, household LED bulbs (Figure 2.4) emit 7–20 mW cm−2 in a selected spectral range (e.g., λmax ∼ 462 nm for a blue LED bulb) with no IR or UV radiation and are more rugged and damage resistant. Other advantages are (i) lower electrical energy consumption, (ii) longer lifetimes, (iii) safe and environmentally friendly lamps (no mercury; cool to the touch), (iv) no frequency interference, (v) large range of color (no filter; white lights can be delivered in a variety of color temperatures), and (vi) relatively low divergence of the light beam (their directional output can be exploited by clever designs such as light strips or concentrated arrays).
2.3.11 UV Plasma Source
It is known that UV lights can be generated from plasma produced by a microwave excitation of suitable gases. This was recently applied [14] to the complete and regular curing of complicated objects (even a car body) in a plasma chamber with an integrated roller bed.
References
1. Braun, A., Maurette, M.T., and Oliveros, E. (1986) Technologie Photochimique, Presses Polytechniques Romandes, Lausanne, CH.
2. Wayne, R.P. (1988) Principles and Applications of Photochemistry, Oxford Science and Publications, Oxford.
3. Turro, N.J. (1978and 1990) Modern Molecular Photochemistry, Benjamin, New York.
4. Gilbert, A. and Baggot, J. (1991) Essentials of Molecular Photochemistry, Blackwell Scientific Publications, Oxford.
5. Suppan, P. (1994) Chemistry and Light, The Royal Society of Chemistry.
6. Fouassier, J.P. (1995) Photoinitiation, Photopolymerization, Photocuring, Hanser, Münich.
7. Davidson, S. (1999) Exploring the Science, Technology and Application of UV and EB Curing, Sita Technology Ltd, London.
8. Drobny, J.G. (2010) Radiation Technology for Polymers, CRC Press, Boca Raton, FL.
9. Schwalm, R. (2007) UV Coatings: Basics, Recent Developments and New Applications, Elsevier, Oxford.
10. Rabek, J.F. (1993) in Radiation Curing in Polymer Science and Technology, vol. 1 (eds J.P. Fouassier and J.F. Rabek), Chapman & Hall, London, pp. 453–502.
11. Vicente, J.S., Gejo, J.L., Rothenbacher, S., Sarojiniamma, S., Gogritchiani, E., Miranda, M.A., Wörner, M., Oliveros, E., Kasper, G., and Braun, A.M. (2010) in Basics of Photopolymerization Reactions, vol. 3 (eds J.P. Fouassier and X. Allonas), Research Signpost, Trivandrum, pp. 47–66.
12. Mills, P. (2005) Proceeding of the RadTech Europe Conference, http://www.radtech-europe.com/.
13. Karsten, R. (2009) Proceeding of the RadTech Europe Conference, http://www.radtech-europe.com/.
14. Dietliker, K., Braig, A., and Ricci, A. (2010) Photochemistry, 38, 344–368.
15. Anyaogu, K.C., Ermoshkin, A.A., Neckers, D.C., Mejiritski, A., Grinevich, O., and Fedorov, A.V. (2007) J. Appl. Polym. Sci., 105, 803–808.
16. Brandl, B., IST Metz GmbH (2007) Proceeding of the RadTech Europe Conference., Germany, http://www.radtech-europe.com/.
17. Kinpling, K. (2008) Proceeding of the RadTech USA, Chicago, http://www.radtech.org/.
18. Duarte, F.J. (ed.) (2009) Tunable Laser Applications, CRC Press, Bocca Raton, FL.
19. Fouassier, J.P. and Rabek, J.F. (eds) (1990) Lasers in Polymer Science and Technology: Applications, CRC Press, Boca Raton, FL.
20. Lackner, M. (ed.) (2008) Lasers in Chemistry, Wiley-VCH Verlag GmbH, Weinheim.
21. Allonas, X., Crouxte-Barghorn, C., Fouassier, J.P., Lalevée, J., Malval, J.P., and Morlet-Savary, F. (2008) in Lasers in Chemistry, vol. 2 (ed. M. Lackner), Wiley-VCH Verlag GmbH, pp. 1001–1027.
