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A. Introduction 11-169B. Tables 11-170
Table 1. Rate Constants of Cleavage, ElectronTransfer and Monomer Quenchingin Radical Photoinitiators 11-170
Annex to Table 1. PhotoinitiatorCompound Chemistries 11-173
Table 2. Bimolecular Rate Constants forthe Reaction of Phosphonyl Radicalswith Various Monomers inCyclohexane at Room Temperature 11-176
Table 3. Bimolecular Rate Constants forthe Reaction of Various Radicalswith Various Olefinic Monomersat Room Temperature 11-176
Table 4. Bimolecular Rate Constants forthe Reaction of Ph2P=O andPh2P = S with Various Monomers 11-176
Table 5. Electron Transfer Reaction of Radicalswith Diphenyliodonium Salts 11-176
Table 6. Electron Transfer Rate Constants (ke)Between Photosensitizers and CationicPhotoinitiators and Quenching RateConstants (fcq) for Cyclohexene Oxidein Methanol (M) and Acetonitrile(AN) 11-177
Table 7. Excitation Transfer Rate Constants(kj) for Thioxanthones andPhotoinitiators 11-178
Annex to Table 7. CompoundChemistries 11-178
Table 8. Triplet State Lifetimes (rT) of theSensitizer (TXI) in Different Media,and Rate Constant (A:T) of theInteraction between TXI and TPMK 11-179
Table 9. Some Values of the Triplet StateEnergy Levels of Photoinitiators andMonomers 11-179
Table 10. Values of r f , rT, and k%in Solution 11-179
Table 11. Rate Constant of Interaction ofKetones and Light Stabilizersin Solution 11-179
Annex to Table 11 11-179C. References 11-180
A. INTRODUCTION
UV curing technologies use light beams to start photo-chemical and chemical reactions in organic materials(monomers, oligomers, prepolymers, polymers), mostlythrough a Photo-Induced Polymerization (PIP) reaction.This leads to the formation of a new polymeric materialwhose applications lie in various industrial sectors, such ascoatings, graphic arts, imaging, microelectronics, etc.Specific advantages of these technologies over the usualthermal operations are rapid through-cure, solvent-freeformulation, room temperature treatment and low energyrequirements.
This PIP process is concerned with the creation of apolymer P through a chain radical or cationic reactioninitiated by light in the presence of a photoinitiator (PI) anda coupled Pl/photosensitizer (PS):
The reactivities of PI and PS govern, for a large part, thepractical efficiency of the PIP reaction. The present chapterreports typical data obtained (through time-resolved laserspectroscopy experiments) on the excited state processes inPI and PS occurring after the absorption of the photon. Rateconstants reported in the following tables correspond to thefollowing processes:
P h o t o p o l y m e r i z a t i o n R e a c t i o n s
J. P. FouassierLaboratoire de Photochimie Generale, Mulhouse, Cedex, France
light
lightadd species :X
lightexcited PS
excited PI R* or acid species
3Pi*triplet state
1PI*first excitedsinglet state
lightPI
(ground singletstate)
1.
cleavage
H abstraction
monomer quenching
electron transfer
2. R' (or A# or S*...) + M — ^ - RM'
3. 3 PF + light stabilizer — -(LS)
k
4. 3PS* + PI —- excitation transfer
5. Tj'. Triplet state lifetime under the given conditions(equal to the reciprocal value of the sum of the first-orderrate constants of the different processes)Tj: Triplet state lifetime in the presence of a givenadditive
6- 3PS* + cationic photoinitiator C+ —- PS"+ C*(a) Energy transfer can sometimes occur:
3PS*+ C+ - PS+ C+*
B. TABLES
(b) Energy and electron transfer can also occur in thefirst excited singlet state 1PS*.
Detailed data are available, especially in several chaptersof two edited books (1) and in a recent monograph (2). Fewdata are known on the photopolymerization itself andlargely depend on the practical formulation used as well asthe experimental conditions. Typically, one photonabsorbed can lead to ~10000 polymerized double bonds(3). Rate constants of propagation kp and termination fct fora polyurethane acrylate resin containing an acrylatemonomer (weight ratio, 1:1) as reactive diluent are~1041/mol/s and 3 x 104l/mol/s respectively (when halfof the double bonds have been polymerized) (3).
TABLE 1. RATE CONSTANTS OF CLEAVAGE, ELECTRON TRANSFER AND MONOMER QUENCHING IN RADICAL PHOTOINITIATORS0
10 "8Jk0 10~9A:e 10~6A:q Monomers famines 7Compound (s"1) (1/mol/s) (1/mol/s) solventsd Refs.
Ha 1.3 66 Mi, AHi, Si 4Hb 2.0 150Hc 1.2 2.5lid 1.2 2lie 0.2 1Hf 0.07 13Hg 1.5 180Hh 0.6 8Hi 0.27 0.05Ha 3200 M2, S2 21
360 M5, S2 215.4 M3, S2 21
34 M4, S2 21Ha 0.003e 22
0.001^Ha 7 S2, AH3 26
2 S2, AH4
1.9 S2, AH2
2 S2, AH5
0.56 S2, AH6
Hj 10 S3 23Ilk 0.5 1500 M7, AH2, S4 25111 0.9 1550Hm 0.0064* S2 26Hn 0.0025e
Up 0.0056e
Hq 0.0043*Hr 56 S6, Mi 26Hs 110Ilr 5500 S6, M2 26Hs 7400Hr 5100 S6, M5 26Hs 6500Hr 49 S6, M3 26Ils 140Ilr 9.4 S6, M4 26Hs 50I2a 7.14 250 Mi, AHi, Si 5I2b 0.87 0.26 20I2c 0.003 < 0.001 4.5I2d 0.00025 0.08 8I2e 0.83 0.20 22I2f 0.003 0.08 10I2g 0.67 0.17 29I2h 1.18 0.15 20I2i 0.80 0.05 21
TABLE 1. cont'd
10 8A: c W~9ke 106A:q Monomers famines 7Compound (s"1) (1/mol/s) (I/moI/s) solvents^ Refs.
Ba 10 >200 M i 5 A H i 5 S 1 6I3b 1 213c 25I3d 0.005 <10~4
I3e 10I3f 0.006 «10 ~4
I3g 0.007 <10~4
I3h 0.13 <10~4
I4a >100 Si 7I4b >100I4c > 100I4d >100I4e 8100 M2, S2 7I4f 4800I4g 6500I4h 1500I4i 190I4e 480 Mi, S2 7I4f 800I4g 1000I4h 200I4i 13I4f 60 M3, S2 7I4g 17I4h <1I4i 5.7I4f 1300 M4, S2 7I4g 700I4h 380I4i 180I5a > 10 8I6a 7 x l O - 3 0.7 M j 5 S 1 9I7a 0.7 0.05 Mi, AHi, Si 9I7b 6 XlO"5 440I8a 0.85 0.35 M i 7 A H i 9 S 1 9I9a 2.5 11 Mi 5 AH 1 9 Si 9HOa > 10 10Il ia 0.8 Mi, AHi, Si 10IHb > 1IHc 0.12 0.9 700Hid 0.01 0.4 1200I12a 480 M 1 5 S 2 11I12b 800I12c 1000I12d 200I12e 13I12a 8100 M 2 5 S 2 11I12b 4800I12c 6500I12d 1500I12e 190I12b 6 M3, S2 11I12c 17I12d <10I12e 5.7I12b 1300 M4, S2 11I12c 700I12d 380I12e 180I13a 1.4 1.6 AH2, S2 12I14a 11000 M 1 9 AH 1 5 S 1 13I14b 6.5 2900I14c 6.0 15I14d 3.5 1200I15a >5 S2 14I15b 4I15c >5
References page 11-180
TABLE 1. cont'd
10*kc 10~9ke 10~6kq Monomers famines 7Compound ( s 1 ) (1/mol/s) (1/mol/s) solvents^ Refs.
I15d 3.3I16a 1.5 180 AH19S1 15I16b >3I17a 0.05 300 S1 16I18a 0.16 S1 17I19a 0.3 0.7 100 S1 18I20a 29 S2 18I21a 60 S2 18I22a -10 S3 19I22b - 5 93I22c 0.02 2.3I22d 0.014 2.0I23a 6 15 M1, AH3, S2 20I23b 5 2I23c 4 3I23d 4 3I23e 0.01 AH2, S5 24I23f 0.017I23a 2.5 3000 M2, S2, AH2 20I23b 6000I23c 6000I23d 6000I23a 0.2 M3, S2 20I23b 0.02I23c 0.03I23d 0.04I23a 4 M4, S2 20I23b 0.4I23c 1I23d 1I23a 40 M5, S2 20I23b 30I23c 5I23d 6I23a 1 M6, S2 20I23b 1I23c 0.3I23d 0.3I23a 8 S2, AH4 26I23b 6I23c 6I23d 6I23a 26 S1, M8 13I23a 23 S19M9 13I23b 8 S2, AH7 26I23b 0.85 S2, AH8 26I23g <10~5 65 M7, S4 25I23h <10~5 37124 0.016 S2, Mi 37125 0.006 S2, M10 37126 0.007 S2, M10 37127 4.4-f S2 39128 0.3129 0.015 S7, AH9 41a Compound chemistries given in Annex to Table 1.1}Monomers: Mi - methyl methacrylate; M2 - styrene; M3 - vinyl acetate; M4 - acrylonitrile; M5 - vinyl pyrrolidone; M6 - butylvinylether; M 7 - acrylamide; Mg -PETA; M 9 - TMPTA; M10 - butylmethacrylate.cAmines: AHi - methyl diethanolamine; AH2 - triethylamine; AH3 - ethyl-4-(dimethylamino)-benzoate; AH4 - bis-(2-hydroxy ethyl)-methylamine; AH5 - methyl-4-amino benzoate; AH 6 - 1,4-diazabicyclo [2.2.2] octane (DABCO); AH7 - dimethylamine; AHg - 2-(dimethyl aminoethyl)-benzoate; AH 9 - diethylaniline.dSolvents: Si - toluene; S 2 - benzene; S 3 - acetonitrile; S 4 - water; S5 - 2-propanol; S 6 - acetone; S 7 - ethanol.eRate constant of H abstraction by THF.^Rate constant of H abstraction by isopropanol.
ANNEX TO TABLE 1. PHOTOINITIATOR COMPOUND CHEMISTRIES
Compound R Ri R2 R3 R4
HaliblieHdHeiifHgHhin
Hj
Ilk
111HmHnUpHq
Hr
Hs
I2aI2bI2cI2dI2eI2fI2gI2hI2i
BaI3b13cDd
I3e
I3f
Bg
Dh
I4a
I4bI4cI4dI4eI4fI4gI4h
I4i
References page 11-180
ANNEX TO TABLE 1. cont'd
Compound R Ri R2 R3 R4
I5a
I6a
I7a HI7b CH2SOjNa +
I8a
I9a
I9b
HOa C2H5
Ilia H HIHb H CH3
IHc CH3 HIHd CH3O H
I12a OH112b OCOCH3
I12c HI12d CH3
I12e
I13a CH3
I14a HI14b /-C3H7
I14c OC2H5
I14d J-C4H9
I15a
I15b HI15c CH3
I15d
I16a
Fluorenone
ANNEX TO TABLE 1. cont'd
Compound R Ri R2 R3 R4
I16b
I17a
I18a
I19a
I20a
I21a
I22aI22b
I22c
I22d
I23a HI23b ClI23c CH3
I23d CH3(CH3)2
I23e HI23f H
I23g -OCH2COOH
I23h OCH2CH2CH2N(CH3)3SO3Me-
124
125126
127
128
129
AcridinePhenazine
References page 11-180
akRU in 107l/mol/s.foRef. 26.cFrom Ref. 40.+From Ref. 16.
TABLE 4. BIMOLECULAR RATE CONSTANTS 0 FOR THE REAC-T I O N OF P h 2 R = O A N D Ph2P-=* W I T H VARIOUS M O N O M E R S * 0
Radical
Monomer Ph2P = O Ph2P = S
Methacrylonitrile 1.9 0.9Styrene 4.6 0.4Methylmethacrylate 4.1 0.19Acrylonitrile 1.3 0.52Methyl acrylate 1.7 0.62rc-Butyl vinyl ether 5.0 0.15Vinyl acetate 1.4 0.042akRM in 107l/mol/s*Ref. 27.cExperiments were carried out in CH 2C^ solution at room temperature.
TABLE 5. ELECTRON TRANSFER REACTION OF RADICALS W I T HD I P H E N Y L I O D O N I U M SALTS
Radicals 10"9Jt6 (1/mol/s) Refs.
Ph2PO <10"3 42Ph2COH 0.03 43(CHs)2COH 0.06
TABLE 2. BIMOLECULAR RATE CONSTANTS0 FOR THE REACTION OF PHOSPHONYL RADICALS WITH VARIOUS MONOMERS INCYCLOHEXANE AT ROOM TEMPERATU RE *
Radical
Monomer
Methacrylonitrile 5.0 4.6 4.5 9.2 11
Styrene 6.0 4.5 8.0 22 25Methylmethacrylate 8.0 5.0 5.8 5.8 5.3Acrylonitrile 2.0 2.0 0.18 0.58 0.26Methyl acrylate 3.5 2.1 1.3 1.7 1.6n-Butyl vinyl ether 0.4 0.3 0.23 2.1 1.4Vinyl acetate 0.16 0.13 0.082 0.29 0.18akRM in 107l/mol/s.bRef. 26.
TABLE 3. BIMOLECULAR RATE CONSTANTS" FOR THE REACTION OF VARIOUS RADICALS W I T H VARIOUS OLEFINIC MONOMERS ATR O O M TEMPERATURE*
Radical
Monomer
Styrene 3.5 x 10"2 7 x 10~4 1.2 x 10 ~2 6Methylmethacrylate 9xlO~ 4 5.4xlO~2 4x lO" 5 0.9xl0~2 6 18C 10"3t IO"1*Acrylonitrile 4 x 10 ~4 1.6 x 10~2 2 x 10 ~3 2Methyl acrylate 2n-Butyl vinyl ether < 10 "6 0.5Vinyl acetate 6 x 10 ~4 2 x 10 ~2 0.2Af-Vinyrpyrrolidone 4xlO~ 5
TABLE 6. ELECTRON TRANSFER RATE CONSTANTS (ke) BETWEEN PHOTOSENSITIZERS AND CATIONIC PHOTOINITIATORS ANDQUENCHING RATE CONSTANTS (kq) FOR CYCLOHEXENE OXIDE IN METHANOL (M) AND ACETONITRILE (AN)
Photosensitizer Cationic photoinitiator Anion Solvent (1/mol/s) (1/mol/s) Refs.
AsF6" M 24 0.3 28Cl" 24PF6- 26BF4; 24AsF6 AN 290
AsF6 M 400
36
AsF6 M 15 0.33Cl" 1BF4" 47
BF4 M 6.4 0.04
M 14 29
PF6 35
PF6 28
SbF6 4
AsF6 8
BF 4 570
BF4 110
PF6 14
AsF6 100
BF4 38
15
References page 11-180
Chlorothioxanthone
Chlorothioxanthone
Benzophenone
Ketocoumarin
Chlorothioxanthone
TABLE 6. cont'd
Photosensitizer
Xanthone
Michler's ketone 0.7Thioxanthone 20010-Methylacridone 350Acridone 740Anthracene M l 31Chlorothioxanthone (NO2Cp)2I
+ Cl" 400 28Pyrene 130Benzophenone 500Isopropylthioxanthone 250
TABLE 7. EXCITATION TRANSFER RATE CONSTANTS (kT) FOR THIOXANTHONES AND PHOTOINITIATORSa
Thioxanthone Initiator Solvent 10 "6^x (1/mol/s)
TXI HMK Toluene 100Methanol 290
OMK Toluene 75Methanol 380
TPMK Toluene 240Methanol 630
NMK Toluene 4700Methanol 7900
ETX TPMK Toluene 12Methanol 110
ITX TPMK Toluene 60Methanol 55
"Ref. 32.
ANNEX TO TABLE 7. COMPOUND CHEMISTRIES
Triplet stateenergy level
TX's R Ri R2 R3 R4 Abbrev. (kcal/mol)
H Cl H H CTX 62H CH(CH3)2 H H ITX 61
CH3 H COOET H ETX 58,5H H H COOET TXI 63
H HMK 65SCH3 TPMK 61OCH3 OMK 65
N(CH3) 2 NMK 63
Mok's
10-7Are 10~7A:q
Cationic photoinitiator Anion Solvent (1/mol/s) (1/mol/s) Refs.
Cl" M 140 30
TABLE 8. TRIPLET STATE LIFETIMES (TT) OF THE SENSITIZER(TXI) IN DIFFERENT MEDIA*, AND RATE CONSTANT (kj) OF THEINTERACTION BETWEEN TXI AND TPMK*
XT tl H r 6 J k x
Medium (ns) (cp at 28° C) (I/moI/s)
TMPTAC (100%) 650 40 80Acrylate (66/33) 2200 185 31Toluene-Ep. acrylate 1500 9.5 35
(50/50)Toluene-TMPTA (25/75) 270 5.8 135Toluene-TMPTA (50/50) 200 1.7 <40Toluene-TMPTA (75/25) 280 0.9 150HDDA^ (100%) 650 5.2 95HDDA-Ep. acrylate 2500 58 22
(50/50)Toluene-HDDA (50/50) 1000 1.2 140Toluene-HDDA-Ep. 850 5.8 68
acrylate (25/50/25)Toluene-PETAe (50/50) 220 3.1 40Toluene-PETA-Ep. 360 6.9 69
acrylate (43/43/14)Toluene 50 0.53 240Methanol 140 0.52 630aViscosity: 77.&Ref. 33; for formula, see Annex to Table 7.Trimethylolpropane triacrylate.^Hexanedioldiacrylate.Tentaerythritol triacrylate.
TABLE 9. SOME VALUES OF THE TRIPLET STATE ENERGYLEVELS OF PHOTOINITIATORS AND MONOMERS
Compound Triplet state energy (AE) (kcal/mol)
Ila 69 Cited in Ref. 13I4a 73I7a 53I8a 53I9b 59M2 61I14a 75 Cited in Ref. 38124 57
TABLE 10. VALUES OF T°, T1, AND IrJt IN SOLUTION
10"6JkJPhotoinitiators t j (ns) Xj (ns) (1/mol/s)
TABLE 11. RATE CONSTANT OF INTERACTION OF KETONESAND LIGHT STABILIZERS IN SOLUTION
l<T6A:a
Photoinitiator Light stabilizer (1/mol/s) Refs.
Benzophenone LSI 6500 34LS2 8550LS3 10300LS4 15000LS5 7050SL6 5900 35
Acetone LSI 500 36LS7 700
ANNEX TO TABLE 11.
4200 4000 0.85
3300 2000 14
470 470 < 5
4000 1750 24
determined in bulk epoxyacrylate-HDDA (60:4OwAv); a in solution b in thepresence of LSI (2%).; Ref. 34.
References page 11-180
LSI:
LS2:
LS3:
LS4:
LS5:
LS6:
LS7:
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