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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