Chemistry & Technology of UV & EB formulation for Coating, Inks and Paints

Chemistry & Technology of UV & EB formulation for Coating, Inks and Paints
Volume III Photoinitiators for free radical and cationic polymerization
By K. Dietliker

Chapter I Introduction
Contents
I Introduction
II Absorption - the primary process
1. principles of absorption
2. electronic structures
i. electronic transitions
ii. electron spins
III Secondary process
1. unimolecular reactions
i. direct fragmentation
a) Norrish type I reaction
b) Norrish type II reaction
2. Bimolecular reactions
i. Complex formation
a) Electron – donor acceptor complexes
b) Aggregation complexes
c) Intramolecular interactions
d) Dipole – dipole interactions
e) Charge transfer interactions
ii. Hydrogen abstraction
3. Combination of type I and type II free radical photoinitiators
4. Hybrid curing
IV Solvent cage
V Cationic photoinitiation and radical photoinitiation
VI Overview of volume III
VII Reference

Chapter II Free radical polymerization
I Introduction
II Principles of photoinduced radical polymerization
1. System undergoing photocrosslinking
2. Photopolymerisable formulations
III Photoinitiators
1. Type I photoinitiators
i. Photoinduced a-cleavage
2. Type II photoinitiators
i. Hydrogen abstraction
ii. Photoinduced electron transfer process
V Selection of a photoinitiator
1. Abstraction characteristics
i. Clear coationg
ii. Pigments formulations
iii. Fillers and stabilizers
2. Photoinitiator efficiency
3. Yellowing
4. Photoinitiator concentration
i. Cost of a formulation
ii. Influence on the uncured formulation
iii. Curing properties
iv. Influence on the Properties of the cured coating
5. Selection Chart
6. Photoinitiators for special applications
i. Photoinitiators for silicon-based formulations
ii. Photoinitiators for Water-borne systems
VI Unimolecular UV-photoinitiator systems (Type I photoinitiators)
1. Photoinitiators undergoing a-cleavage
i. Benzoin derivatives
a) Photochemistry
b) Initiation of polymerization
c) Stability and yellowing
d) Benzoin derivatives containing polysiloxane residues
ii. Methylolbenzoin and 4-Benzoyl-1.3-dioxolane derivatives
iii. Benzilketals
a) Photochemistry
b) Initiation of polymerization
c) Yellowing
d) Benzilketals substituted by Polysiloxane residues
iv. a,a-dialkoxyacetophenones
a) Photochemistry
b) a,a-dialkoxyacetophenones derivatives containing Polysiloxane residues
v. a-Hydroxy alkylphenones
a) Photochemistry
b) Initiation of polymerization
c) Influences of substituents
d) Yellowing
e) Stability
f) a-Hydroxy alkylphenones bearing polysiloxane substituents
g) 1-Hydroxycyclohexylphenylketone/Benzophenone Blends
vi. a-Aminoalkylphenones
a) Absorption characteristics
b) Photochemistry
c) Sensitization of a-Aminoalkylphenone derivatives
d) Initiation of polymerization
e) Influences of substituents
f) Yellowing
vii. Acylphosphine oxides
a) Absorption characteristic
b) Photochemistry
c) Initiation of polymerization
d) Stability
e) Acylphosphines and acylphosphine sulphides
2. Other unimolecular photoinitiators
i. O-acyl-a-oximinoketones
a) Photochemistry
ii. Peroxy compounds
iii. Halogenated acetophenone derivatives
iv. Phenylglyoxylates
v. Miscellaneous Fragmenting Photointiators
VII Bimolecular UV photoinitiators
1. Aromatic ketone/coinitiator systems
i. Benzophenone/Amines
ii. Michler’s Ketone/Benzophenone
iii. Thioxanthone/Amines
iv. Miscellaneous aromatic ketones
2. Transition metal complexes/polyhalogen systems
i. Ferrocene/Polyhalogen system
ii. Transition metal carbonyl/polyhalogen system
VIII Macromolecular UV photoinitiators
1. Polymer-bound unimolecular photoinitiators
i. Polymer-bound a-cleavage photoinitiators
ii. Polysilanes
iii. Other polymer-bound fragmentation photoinitiators
2. Polymer-bound bimolecular photoinitiators
i. Polymer-bound Benzophenone derivatives
ii. Polymer-bound thioxanthone derivatives
3. Copolymerisable photoinitiaotors
IX Visible photoinitiators
1. Titanocene photoinitiators
i. Absorption characteristics and photosensitivity
ii. Photochemistry
iii. Initiation of polymerization
iv. Stability
2. Dye/coinitiator systems
i. Photoreducible Dyes
ii. Coinitiators
a) Amine coinitiators
b) Arylsulphinates
c) Enolates
d) Miscellaneous coinitiators
iii. Dye/monomer initiating systems
3. Dye-group 4A organometallic coinitiator systems
4. Dye/Borate salt coinitiator systems
i. Absorption characteristics
ii. Coinitiators
iii. Mechanism of initiation
5. Dye/trichloromethyl-s-triazine coinitiator systems
6. Dye/bisimidazole systems
7. Dye/peroxides or a,a-azo-bis(isobutyromitrile) systems
8. 1,2-diketone/coinitiator systems
9. Ketocoumarine/coinitiator systems
10. Water soluble dibenzylidene ketones/cointiator system
X Conclusions
XI Commercial sources of free radical photoinitiators
XII Acknowledgement
XIII References
XIV Appendix

Chapter III Photoinitiators for cationic polymerization
I Introduction
II Photoinduced cationic polymerization
1 Characteristics of light-induced cationic polymerization
2 The role of cationic photoinitiator
(i) Direct excitation of the photoinitiator
(ii) Indirect excitation of the photoinitiator
a) Classic energy transfer
b) Sensitization via exciplex
(iii) Initiation of polymerization
III Application of cationic photoinitiators
1 cationic polymerization of epoxides
2 cationic polymerization of vinyl compounds
3 high energy ray induced cationic polymerization
4 photoinitiated acid catalyzed polymerization
5 photoinitiated acid catalyzed polymerization reactions
6 photolithography
(i) Negative working photoresists
(ii) Positive working photoresists
IV Characteristics of cationic photoinitiators
V Onium salt photoinitiators
1 Dizonium salts
2 Halonium salts
(i) Diaryliodonium salts
(a) Synthesis
(b) Substituent influences on diaryliodonium salts
(c) Influence of the counterion
(d) Photochemistry of diaryliodonium salts – direct irradiation
(e) Photochemistry of diaryliodonium salts – sensitized decomposition
(f) Photoredox induced decomposition of iodonium salts
(ii) Polymer-bound iodonium salts
(iii) Other diarylhalonium salts
3 Sulphonium salts
(i) Triarylsulphonium salts
(a) Synthesisi
(b) Substituent influences on triarylsulphonium salts
(c) Influence of the counterion
(d) Photochemistry of triarylsulphonium salts – direct irradiation
(e) Photochemistry of triarylsulphonium salts – sensitized decomposition
(f) Photoredox induced decomposition of sulphonium salts
(ii) Polymer bound triarylsulphonium salts
4 Triarylselenonium salts
5 Sulphoxonium salts
6 Onium salts which undergo reversible photodissociation
(i) Dialkyl-4-hydroxyphenylsulphonium salts
(ii) Dialkylphenacylsulphonium salts
(iii) Dialkylacylsulphoxonium salts
7 Miscellaneous onium salts photoinitiators
VI Organometallic photoinitiators
1 Iron arene complexes
(i) Synthesis of iron arene complexes
(ii) Spectral sensitivity
(iii) Photochemistry of iron arene complexes
(iv) Application of iron arene photoinitiators
2 Miscellaneous organometallic photoinitiators
VII Metal salts as cationic photoinitiators
VIII Photodecomposable organosilanes
1 o-nitrobenzyl triarylsilyl ethers
2 Triarylsilyl peroxides
3 Acylsilanes
IX Latent sulphonic acids
1 a-sulphonyloxy ketones
2 a-hydroxymethylbenzoin sulphonates
3 Nitrobenzyl esters
4 Aryl diazidonaphthaquinone-4-sulphonates
5 a-sulphonyl acetophenones
6 Other latent sulphonic acids
X Miscellaneous acid generating compounds
1 Halomethyl-s-triazines
2 Chlorinated acetophenones
XI Commercially available cationic photoinitiators
XII Conclusions
XIII Acknowledgement
XIV References
XIV Appenix