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. Fouassier Laboratoire de Photochimie Generale, Mulhouse, Cedex, France
A. Introduction 11-169 B. Tables 11-170 Table 1. Rate Constants of Cleavage, Electron Transfer and Monomer Quenching in Radical Photoinitiators 11-170 Annex to Table 1. Photoinitiator Compound Chemistries 11-173 Table 2. Bimolecular Rate Constants for the Reaction of Phosphonyl Radicals with Various Monomers in Cyclohexane at Room Temperature 11-176 Table 3. Bimolecular Rate Constants for the Reaction of Various Radicals with Various Olefinic Monomers at Room Temperature 11-176 Table 4. Bimolecular Rate Constants for the Reaction of Ph 2 P=O and Ph2P = S with Various Monomers 11-176 Table 5. Electron Transfer Reaction of Radicals with Diphenyliodonium Salts 11-176 Table 6. Electron Transfer Rate Constants (ke) Between Photosensitizers and Cationic Photoinitiators and Quenching Rate Constants (fcq) for Cyclohexene Oxide in Methanol (M) and Acetonitrile (AN) 11-177 Table 7. Excitation Transfer Rate Constants (kj) for Thioxanthones and Photoinitiators 11-178 Annex to Table 7. Compound Chemistries 11-178 Table 8. Triplet State Lifetimes (rT) of the Sensitizer (TXI) in Different Media, and Rate Constant (A:T) of the Interaction between TXI and TPMK 11-179 Table 9. Some Values of the Triplet State Energy Levels of Photoinitiators and Monomers 11-179 Table 10. Values of r f , rT, and k% in Solution 11-179 Table 11. Rate Constant of Interaction of Ketones and Light Stabilizers in Solution 11-179 Annex to Table 11 11-179 C. References 11-180
A.
INTRODUCTION
UV curing technologies use light beams to start photochemical and chemical reactions in organic materials (monomers, oligomers, prepolymers, polymers), mostly through a Photo-Induced Polymerization (PIP) reaction. This leads to the formation of a new polymeric material whose applications lie in various industrial sectors, such as coatings, graphic arts, imaging, microelectronics, etc. Specific advantages of these technologies over the usual thermal operations are rapid through-cure, solvent-free formulation, room temperature treatment and low energy requirements. This PIP process is concerned with the creation of a polymer P through a chain radical or cationic reaction initiated by light in the presence of a photoinitiator (PI) and a coupled Pl/photosensitizer (PS): light
light
light
add species :X
excited PS excited PI
R* or acid species
The reactivities of PI and PS govern, for a large part, the practical efficiency of the PIP reaction. The present chapter reports typical data obtained (through time-resolved laser spectroscopy experiments) on the excited state processes in PI and PS occurring after the absorption of the photon. Rate constants reported in the following tables correspond to the following processes: 1.
PI (ground singlet state)
light
1 PI* first excited singlet state
cleavage H abstraction monomer quenching electron transfer
3 Pi* triplet state
2. R' (or A# or S*...) + M — ^ 3. 3 P F + light stabilizer (LS) 3
(b) Energy and electron transfer can also occur in the first excited singlet state 1 PS*.
RM'
—-
k
4. PS* + PI —- excitation transfer 5. Tj'. Triplet state lifetime under the given conditions (equal to the reciprocal value of the sum of the first-order rate constants of the different processes) Tj: Triplet state lifetime in the presence of a given additive 6 3
- PS* + cationic photoinitiator C+ —- PS" + C* (a) Energy transfer can sometimes occur: 3 PS*+ C+ - PS+ C+*
Detailed data are available, especially in several chapters of two edited books (1) and in a recent monograph (2). Few data are known on the photopolymerization itself and largely depend on the practical formulation used as well as the experimental conditions. Typically, one photon absorbed can lead to ~10000 polymerized double bonds (3). Rate constants of propagation kp and termination fct for a polyurethane acrylate resin containing an acrylate monomer (weight ratio, 1:1) as reactive diluent are ~10 4 1/mol/s and 3 x 10 4 l/mol/s respectively (when half of the double bonds have been polymerized) (3).
B. TABLES TABLE 1. RATE CONSTANTS OF CLEAVAGE, ELECTRON TRANSFER AND MONOMER QUENCHING IN RADICAL PHOTOINITIATORS0 10~9A:e (1/mol/s)
10~6A:q (1/mol/s)
Monomers famines 7 solventsd
Ha Hb Hc lid lie Hf Hg Hh Hi Ha
1.3 2.0 1.2 1.2 0.2 0.07 1.5 0.6 0.27
Mi, AHi, Si
Ha
0.003e 0.001^ 7 2 1.9 2 0.56
66 150 2.5 2 1 13 180 8 0.05 3200 360 5.4 34
Compound
10 "8Jk0 (s"1)
Ha
Hj Ilk 111 Hm Hn Up Hq Hr Hs Ilr Hs Hr Hs Hr Ils Ilr Hs I2a I2b I2c I2d I2e I2f I2g I2h I2i
10 0.5 0.9 0.0064* 0.0025e 0.0056e 0.0043*
7.14 0.87 0.003 0.00025 0.83 0.003 0.67 1.18 0.80
0.26 < 0.001 0.08 0.20 0.08 0.17 0.15 0.05
1500 1550
56 110 5500 7400 5100 6500 49 140 9.4 50 250 20 4.5 8 22 10 29 20 21
M2, M5, M3, M4,
Refs. 4
S2 S2 S2 S2
21 21 21 21 22
S 2 , AH3 S 2 , AH4 S 2 , AH2 S 2 , AH5 S 2 , AH6 S3 M 7 , AH2, S 4
26
S2
26
S 6 , Mi
26
S6, M2
26
S6, M5
26
S6, M3
26
S6, M4
26
Mi, AHi, Si
23 25
5
TABLE 1. cont'd Compound Ba I3b 13c I3d I3e I3f I3g I3h I4a I4b I4c I4d I4e I4f I4g I4h I4i I4e I4f I4g I4h I4i I4f I4g I4h I4i I4f I4g I4h I4i I5a I6a I7a I7b I8a I9a HOa Ilia IHb IHc Hid I12a I12b I12c I12d I12e I12a I12b I12c I12d I12e I12b I12c I12d I12e I12b I12c I12d I12e I13a I14a I14b I14c I14d I15a I15b I15c
10 8A: c (s"1) 10 1 25 0.005 10 0.006 0.007 0.13 >100 >100 > 100 >100
W~9ke (1/mol/s)
10 6 A: q (I/moI/s) >200 2
0.7 6 XlO" 5 0.85 2.5
0.9 0.4
0.7 0.05 440 0.35 11
700 1200 480 800 1000 200 13 8100 4800 6500 1500 190 6 17 5 4 >5
Mi5AHi5S1
6
Si
7
M2, S2
7
Mi, S 2
7
M3, S2
7
M4, S2
7
Mj5S1 Mi, AHi, Si
8 9 9
«10 ~4
