New push-pull dyes derived from Michler's ketone for polymerization reactions upon visible lights.

Article abstract of DOI:10.1021/ma400766z

Among other photoinitiating systems, aromatic ketone based compounds have been largely exploited as photoinitiators (PIs). However, none of these compounds efficiently absorb above 420 nm. The search of novel architectures of PIs for getting an important

Full text of DOI:10.1021/ma400766z

Article
pubs.acs.org/Macromolecules
New Push−Pull Dyes Derived from Michler’s Ketone For
Polymerization Reactions Upon Visible Lights.
Mohamad-Ali Tehfe,† Frederic Dumur,‡ Bernadette Graff,† Fabrice Morlet-Savary,† Jean-Pierre Fouassier,§
́
́
Didier Gigmes,*,‡ and Jacques Lalevee*,†
́
†Institut de Science des Mater
France
‡Aix-Marseille Universite,
́
iaux de Mulhouse IS2M − UMR CNRS 7361 − UHA; 15, rue Jean Starcky, 68057 Mulhouse Cedex −
́
CNRS, Institut de Chimie Radicalaire, UMR 7273, F-13397 Marseille, Cedex 20, France
§UHA-ENSCMu, 3 rue Alfred Werner, 68093 Mulhouse, France
S
* Supporting Information
ABSTRACT: Among other photoinitiating systems, aromatic
ketone based compounds have been largely exploited as
photoinitiators (PIs). However, none of these compounds
efficiently absorb above 420 nm. The search of novel
architectures of PIs for getting an important red-shift of the
absorption is crucial for the use of visible lights for polymer
synthesis. Novel bifunctional dyes derived from the Michler’s
ketone structure are proposed here as photoinitiators for the
free radical polymerization of acrylates and the cationic
polymerization of epoxides upon exposure to 457, 473, and
532 nm laser diodes and even to a green LED bulb at 514 nm.
Excellent polymerization profiles are obtained. These original dyes exhibit a push−pull molecular character for a remarkable
covering of the visible lights. The formation of the radicals and the ions in the two- and three-component photoinitiating systems
is described and the initiation steps are discussed.
tris(trimethylsilyl) silyloxy (BP−OSi), an alkoxylamine (BP−
N(−X)−Y) or a N-phenylglycine moiety, several perester
groups....
INTRODUCTION
■
The development of photoinitiators PI of polymerization is an
attractive research field (see e.g. in1,2). Among other PI
systems, aromatic (and aliphatic to a lesser extent) ketone
based compounds (benzophenones, thioxanthones, anthraqui-
nones, fluorenones, ketocoumarines, camphorquinones...) have
been largely exploited as photoinitiators. Benzophenone BP,
originally one of the model molecule for photochemists,3 has
been undoubtedly considered all along the years as an
interesting starting structure (and presumably the most widely
used) where structural modifications can be easily introduced
to improve the absorption properties or the photochemical
reactivity. Benzophenone is a Type II PI working through
electron/proton transfer or hydrogen abstraction. A huge
number of Type II BP derivatives have been synthesized and
studied. They involved (i) compounds bearing somewhat usual
substituents4 linked by a carbon atom (alkyl, phenyl, benzoyl,
trimethylsilyl, acrylate, ...), an oxygen (alkoxy, phenoxy, ...), a
sulfur (thioether...), or a nitrogen (4,4′-dimethylaminobenzo-
phenone or Michler’s ketone MK, 4,4′-diethylaminobenzophe-
none EAB...), (ii) water-soluble derivatives,5 (iii) slightly
modified skeletons,6 oligomeric or polymeric arrangements,7
and tailor-made two-photon absorbing compounds.8 Type I
cleavable benzophenone derivatives (that can also behave as
Type I PIs) have been developed;9 they contain, e.g., a
sulfoxide, a thiobenzoate, a phenyl sulfide, a sulfonyl (BPSK), a
The one-photon π−π* absorption properties of most of
these benzophenone derivatives remain close to that of BP itself
(λmax ∼ 250 nm, εmax = 18700 M−1 cm−1; forbidden n−π*
transition at ∼350 nm, εmax = 200 M−1 cm−1), the best red-
shifts being typically observed for MK or EAB (λmax ∼ 365 nm,
εmax = 44000 M−1 cm−1 in acetonitrile), BPSK (λmax ∼ 313 nm,
εmax = 18900 M−1 cm−1), BMS (λmax ∼ 310 nm, εmax = 18200
M−1 cm−1) or BP−OSi (no clear absorption maximum is
observed at λ > 300 nm despite extinction coefficients higher
than for benzophenone; ε350 nm ∼ 400 M−1 cm−1). None of
these compounds efficiently absorb above 420 nm.
In the frame of our recent works devoted to the design of
highly absorbing PIs in the visible wavelength range through
the search of novel architectures of modified existing PIs or di-
and trifunctional PIs,10 we look for another new way for getting
a more important red-shift of the absorption of BP related
compounds. Indeed, usual electron delocalization cannot
ensure important modifications in the ground state absorption
spectra. On the opposite, as known in photochemistry,
Received: April 13, 2013
Revised: April 29, 2013
Published: May 14, 2013
© 2013 American Chemical Society
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Scheme 1
reported in the literature, in other Knoevenagel conditions and in
lower yield.14 The three dyes M_1-M_3 were prepared by
Knoevenagel condensation of 3,3-bis(4-(dimethylamino)phenyl)-
acrylaldehyde with the corresponding electron acceptor.
Synthesis of 5-(3,3-Bis(4-(dimethylamino)phenyl)allylidene)-
pyrimidine-2,4,6(1H,3H,5H)-trione, M_1. Michler’s aldehyde (1 g,
3.40 mmol) and barbituric acid (0.43 g, 3.40 mmol) were dissolved in
absolute ethanol (20 mL). A few drops of piperidine were added.
Immediately, the solution turned indigo. The solution was refluxed for
4 h. After cooling, the solvent was removed under reduced pressure.
Addition of chloroform followed by pentane precipitated a black solid,
which was filtered off, washed several times with pentane, and dried
under vacuum. The title molecule was obtained in 84% yield (1.15 g)
1H NMR (CDCl3), δ (ppm): 3.08 (s, 12H), 6.66 (d, 2H, J = 8.9 Hz),
introducing push−pull effects in the coupled moieties of di- or
trifunctional compounds allows dramatic changes in the
absorption through a substantial charge transfer CT: this
property was recently used for the design of blue to yellow, blue
to green or blue to red photosensitive systems.11 We explore
here structurally related Michler’s ketone derivatives allowing
the use of true visible light irradiation sources. In the present
paper, novel Ar−(CC−Y)−Ar bifunctional dye structures
where Y stands for a barbituric, a thiobarbituric, an
indanedione, a pyridinium, a dicyanovinyl, or an aldehyde
moiety are proposed (Scheme 1). They can be considered as a
Michler’s ketone (Ar−(CO)−Ar) derivative where the C
O bond is changed for a CC−Y moiety. The use of these
dyes in two- and three-component photoinitiating systems for
the free radical polymerization of acrylates and the cationic
polymerization of epoxides upon exposure to 457, 473, and 532
nm laser diodes and even to a green LED bulb at 514 nm is
studied. The formation of the radicals and the ions in two- and
three-component photoinitiating systems is described and the
initiation steps are also discussed.
6.74 (d, 2H, J = 8.9 Hz), 7.21 (d, 2H, J = 8.9 Hz), 7.45 (d, 2H, J = 8.9
1
Hz), 8.14 (d, 1H, J = 13.1 Hz), 8.32 (d, 1H, J = 13.1 Hz). H NMR
(DMSO-d6), δ (ppm): 3.04 (s, 12H), 6.78 (d, 2H, J = 9.1 Hz), 6.83 (d,
2H, J = 8.9 Hz), 7.10 (d, 2H, J = 8.8 Hz), 7.28 (d, 2H, J = 9.0 Hz),
7.85 (d, 1H, J = 12.8 Hz), 8.20 (d, 1H, J = 12.8 Hz). 13C NMR
(DMSO-d6), δ (ppm): 44.2, 109.7, 111.3, 111.7, 118.3, 124.5, 127.3,
131.8, 133.2, 150.4, 151.7, 152.3, 163.5, 164.0, 166.3; HRMS (ESI
MS) m/z: theor, 404.1848; found, 404.1845 (M+• detected).
Synthesis of 5-(3,3-Bis(4-(dimethylamino)phenyl)allylidene)-2-
thioxodihydropyrimidine-4,6(1H,5H)-dione, M_2. Michler’s aldehyde
(1 g, 3.40 mmol), thiobarbituric acid (0.49 g, 3.40 mmol) were
dissolved in absolute ethanol (20 mL). A few drops of piperidine were
added. Immediately, the solution turned dark violet. The solution was
refluxed for 4 h. After cooling, the solvent was removed under reduced
pressure. Addition of chloroform followed by pentane precipitated a
solid which was filtered off, washed several times with pentane and
dried under vacuum. The chromophore was obtained in 78% yield
(1.11 g). 1H NMR (CDCl3), δ (ppm): 3.10 (s, 6H), 3.11 (s, 6H), 6.66
(d, 2H, J = 8.9 Hz), 6.73 (d, 2H, J = 8.9 Hz), 7.21 (d, 2H, J = 8.8 Hz),
7.49 (d, 2H, J = 8.9 Hz), 8.09 (d, 1H, J = 13.3 Hz), 8.39 (d, 1H, J =
EXPERIMENTAL SECTION
■
i. Synthesis of the Different Dyes. All reagents and solvents
were purchased from Aldrich or Alfa Aesar and used as received
without further purification. Mass spectroscopy was performed by the
Spectropole of Aix-Marseille University. ESI mass spectral analyses
were recorded with a 3200 QTRAP (Applied Biosystems SCIEX)
mass spectrometer. The HRMS mass spectral analysis was performed
with a QStar Elite (Applied Biosystems SCIEX) mass spectrometer.
Elemental analyses were recorded with a Thermo Finnigan EA 1112
elemental analysis apparatus driven by the Eager 300 software. 1H and
13C NMR spectra were determined at room temperature in 5 mm o.d.
1
13.3 Hz). H NMR (DMSO-d6), δ (ppm): 3.06 (s, 12H), 6.79−6.85
1
tubes on a Bruker Avance 400 spectrometer of the Spectropole: H
(m, 4H), 7.13 (d, 2H, J = 8.7 Hz), 7.32 (d, 2H, J = 8.9 Hz), 7.84 (d,
1H, J = 12.3 Hz), 8.24 (d, 1H, J = 12.3 Hz). 13C NMR (DMSO-d6), δ
(ppm): 44.8, 111.3, 111.41, 111.45, 111.8, 118.9, 124.5, 127.1, 132.4,
133.6, 152.0, 152.7, 163.6, 174.0, 177.7; HRMS (ESI MS) m/z: theor,
420.1620; found, 420.1622 (M+• detected).
(400 MHz) and 13C (100 MHz). The 1H chemical shifts were
referenced to the solvent peak DMSO-d6 (2.49 ppm), CDCl3 (7.26
ppm) and the 13C chemical shifts were referenced to the solvent peak
DMSO-d6 (39.5 ppm), CDCl3 (77 ppm). 3,3-Bis(4-(dimethylamino)-
phenyl)acrylaldehyde M_6 (Michler’s aldehyde)12 and M_4 were
synthesized as previously reported.13 Synthesis of 2-(3,3-bis(4-
(dimethylamino)phenyl)allylidene)malononitrile M_5 was previously
Synthesis of 2-(3,3-Bis(4-(dimethylamino)phenyl)allylidene)-1H-
indene-1,3(2H)-dione, M_3. Michler’s aldehyde (1 g, 3.40 mmol) and
indane-1,3-dione (0.49 g, 3.40 mmol) were dissolved in absolute
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Scheme 2
ethanol (20 mL). Immediately, the solution turned deep red. The
solution was refluxed for 4 h. After cooling, the solvent was removed
under reduced pressure. Addition of a minimum of ether followed by
pentane precipitated a deep green solid which was filtered off, washed
several times with ether and dried under vacuum. The title
chromophore was obtained in 72% yield (1.03 g). 1H NMR
(DMSO-d6), δ (ppm): 3.06 (s, 6H), 3.07 (s, 6H), 6.66 (d, 2H, J =
8.9 Hz), 6.76 (d, 2H, J = 8.7 Hz), 7.20 (d, 2H, J = 8.7 Hz), 7.45 (d,
2H, J = 8.9 Hz), 7.67−6.72 (m, 3H), 7.83−7.86 (m, 2H), 8.29 (d, 1H,
J = 12.7 Hz). 13C NMR (DMSO-d6), δ (ppm): 40.1, 40.2, 111.40,
111.44, 118.7, 122.1, 122.3, 123.8, 125.6, 128.7, 132.2, 133.4, 133.6,
133.9, 134.1, 134.3, 140.6, 142.0, 145.5, 151.7, 152.1, 165.7, 191.4,
191.5; HRMS (ESI MS) m/z: theor, 422.1994; found, 422.1995 (M+.
detected).
Synthesis of 2-(3,3-Bis(4-(dimethylamino)phenyl)allylidene)-
malononitrile, M_5. Michler’s aldehyde (1 g, 3.40 mmol) and
malononitrile (0.22 g, 3.40 mmol) were dissolved in absolute ethanol
(50 mL). A few drops of piperidine were added. Immediately, the
solution turned deep red. The solution was refluxed for 2 h. After
cooling, the solvent was removed under vacuum. Addition of a
minimum of ether followed by pentane precipitated a Bordeaux-black
solid which was filtered off and dried under vacuum. The
chromophore was obtained in 95% yield (1.11 g). 1H NMR
(CDCl3), δ (ppm): 3.06 (s, 6H), 3.07 (s, 6H), 6.64 (d, 2H, J = 9.1
Hz), 6.73 (d, 2H, J = 8.8 Hz), 6.95 (d, 1H, J = 12.3 Hz), 7.10 (d, 2H, J
= 9.1 Hz), 7.35 (d, 2H, J = 8.8 Hz), 7.48 (d, 1H, J = 12.3 Hz). 13C
NMR (CDCl3), δ (ppm): 40.1, 40.2, 74.5, 111.40, 111.44, 113.9,
116.1, 116.6, 125.0, 127.1, 132.1, 133.0, 151.8, 152.5, 159.1, 163.8;
HRMS (ESI MS) m/z: theor, 343.1917; found, 343.1919 ([M + H]+
detected).
ii. Chemical Compounds. N-Methyldiethanolamine (MDEA),
phenacyl bromide (R−Br), N-vinylcarbazole (NVK), and tris-
(trimethylsilyl)silane ((TMS)3SiH) were obtained from Aldrich and
used with the best purity available (Scheme 2). [Methyl-4 phenyl-
(methyl-1-ethyl)-4-phenyl]iodonium tetrakis(pentafluorophenyl)-
borate (Iod) was obtained from Bluestar Silicones-France. (3,4-
Epoxycyclohexane)methyl 3,4-epoxycyclohexylcarboxylate (EPOX;
Uvacure 1500) and trimethylolpropane triacrylate (TMPTA) were
obtained from Cytec (Scheme 2). EPOX and TMPTA were selected
as representative multifunctional monomers for cationic and radical
polymerizations, respectively. The formation of polymer networks is
expected.
iii. Irradiation Sources. Several lights were used: (i) Poly-
chromatic light from a halogen lamp (Fiber-Lite, DC-950 - incident
light intensity: I0 ≈ 12 mW cm−2; in the 370−800 nm range); (ii)
Monochromatic light delivered by laser diodes at 457, 473, and 532
nm (MBL-III-BFIOPTILAS; I0 ≈ 100 mW cm−2). A laser diode at 405
nm was also used (I0 ≈ 12 mW cm−2). The emission spectra of these
laser beams are given in ref 15a. (iii) Green light (514 nm; ∼ 15 mW/
cm2) emitted by a LED bulb already presented in ref 15b.
iv. Free Radical Photopolymerization (FRP) Experiments.
Trimethylolpropane triacrylate (TMPTA from Cytec) was used as a
low viscosity monomer. The experiments were carried out in
laminated conditions. The films (25 μm thick) deposited on a BaF2
pellet were irradiated (see the irradiation sources). The evolution of
the double bond content was continuously followed by real time FTIR
spectroscopy (JASCO FTIR 4100) at about 1630 cm−1 as in ref 16.
v. Cationic Polymerization (CP) and Free Radical Promoted
Cationic Polymerization (FRPCP). The two- and three-component
photoinitiating systems are based on dye/iodonium salt (0.3%/2% w/
w) and dye/iodonium salt/NVK (0.3%/2%/3% w/w), respectively.
The experimental conditions are given in the figure captions. The
residual weight content is related to the monomer. The photosensitive
formulations (25 μm thick) were deposited on a BaF2 pellet under air.
The evolution of the epoxy group content was continuously followed
by real time FTIR spectroscopy (JASCO FTIR 4100) at about 790
cm−1, respectively.16
vi. Computational Procedure. Molecular orbital calculations
were carried out with the Gaussian 03 suite of programs. The
electronic absorption spectra for the different compounds were
calculated with the time-dependent density functional theory at
B3LYP/6-31G* level on the relaxed geometries calculated at
UB3LYP/6-31G* level.17
vii. ESR Spin Trapping (ESR-ST) Experiments. The ESR-ST
experiments were carried out using an X-Band spectrometer (MS 400
Magnettech). The radicals were produced at RT under a halogen lamp
exposure under N2 and trapped by phenyl-N-tert-butylnitrone (PBN)
according to a procedure described in detail in ref 18. The ESR spectra
simulations were carried out with the PEST WINSIM program.
viii. Fluorescence Experiments. The fluorescence properties of
the compounds were studied using a JASCO FP-750 spectrometer.
ix. Redox Potentials. The redox potentials were measured in
acetonitrile by cyclic voltammetry with tetrabutyl-ammonium
hexafluorophosphate 0.1 M as a supporting electrolyte. The free
energy change ΔGet for an electron transfer reaction is calculated from
the classical Rehm−Weller equation (eq I)19 where Eox, Ered, Es, and C
are the oxidation potential of the donor, the reduction potential of the
acceptor, the excited state energy and the Coulombic term for the
initially formed ion pair, respectively. C is neglected as is usually done
in polar solvents.20
ΔGet = EOX − Ered − ES + C
(I)
x. Laser Flash Photolysis. Nanosecond laser flash photolysis
(LFP) experiments were carried out using a Qswitched nanosecond
Nd/YAG laser (λexc = 355 nm, 9 ns pulses; energy reduced down to 10
mJ) from Continuum (Minilite) and an analyzing system consisting of
a ceramic xenon lamp, a monochromator, a fast photomultiplier and a
transient digitizer (Luzchem LFP 212).10
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Figure 1. UV−visible absorption spectra of (A) M_1, M_2, M_3, M_4 and (B) M_5, M_6 in acetonitrile.
RESULTS AND DISCUSSION
■
1. Absorption Properties of the New Dyes. The ground
state absorption spectra of the proposed dyes (Figure 1) allow a
large and efficient matching with the various visible light
sources (halogen lamp and laser diodes at 405, 457, 473, and
532 nm). Remarkably, high molar extinction coefficients are
determined for a green light, e.g., ∼28 500, 16 200, 14 400,
7000, and 32 750 M−1 cm−1, for M_1, M_2, M_3, M_4, and
M_5, respectively at ∼532 nm. These visible light absorptions
can be advantageously compared to that of the classical
Michler’s ketone (see the Introduction). For M_6, the
absorption is red-shifted compared to the Michler ketone
MK (λmax = 385 nm vs 365 nm) but the visible light absorption
remains weak, i.e., ε450 nm ∼ 1000 M−1 cm−1.
These dyes can be considered as push−pull aromatic
chromophores. The unsymmetrically substituted D−π−A
arrangements bearing electron donor (D) and electron
acceptor (A) functionalities at both ends of a planar conjugated
spacer are well-known to feature a large change in their
absorption spectra and/or emission spectra as a function of the
solvent polarity and the respective strength of the electron
releasing and electron withdrawing groups.
Molecular orbital MO calculations (using the time-depend-
ent density functional theory at B3LYP/6-31G* level on the
relaxed geometries calculated at UB3LYP/6-31G* level) show
that the lowest energy transition (that exhibits a π → π*
character) involves strongly delocalized highest occupied
molecular orbitals (HOMO) and lowest unoccupied molecular
orbitals (LUMO) for all the investigated new dyes (Figure 2).
For M_1 to M_3 and M_5 and M_6, the HOMO and
LUMO are mainly localized on the donor (dimethylamino
phenyl moiety) and the acceptor (barbituric for M_1,
thiobarbituric for M_2, indanedione for M_3, dicyanovinyl
for M_5, or aldehyde for M_6) fragment, respectively. This
highlights a charge transfer character in agreement with a
push−pull structure (Figure 2). For M_4, the situation is
different as the HOMO and LUMO are localized on the
pyridinium moiety (Figure 2).
A solvatochromic study was carried out for M_1, this
compound being characterized by the highest efficiency in the
associated photoinitiating systems (see below). The maximum
absorption wavelengths in different solvents are gathered in
Table 1. The important Stoke shifts confirm the charge transfer
character of the transition. No direct relationships were found
with the empirical solvatochromic scales evidencing a behavior
Figure 2. Molecular orbitals (HOMO (left) and LUMO (right)) for
M_1 to M_6 (at UB3LYP/6-31G* level); the dimethyl amino group is
indicated by an arrow; the hydrogens are not depicted.
more complex than that recently encountered in other
proposed push−pull systems.11
2. Cationic Photopolymerization of EPOX. The best
typical conversion−time profiles of an epoxy monomer
(EPOX) under air upon visible lights (laser diode irradiations
at 457, 473, or 532 nm; green LED bulb at 514 nm; halogen
lamp) are shown in Figures 3 and 4. Quite slow conversions are
obtained with the dye/Iod initiating systems (e.g., Figure 3
curve 1). The presence of NVK drastically improves the
polymerization profiles (e.g., Figure 3 curve 1 vs curve 2). NVK
only absorbs in the UV range and can not be used as a
photosensitizer upon visible light i.e. the two-component
system NVK/Iod is not efficient for polymerization upon
laser diode. The dye is required for an efficient sensitization
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Table 1. Absorption and Emission Maxima (nm) of M_1
Measured by UV−Visible Spectroscopy and Fluorescence
Spectroscopy
dielectric
refractive
λmax
λem
Stoke
shift
solvent
constant (ε) index (n) (M_1) (M_1)
tert-butylbenzene
toluene
2.3
2.4
1.493
1.497
1.446
1.407
1.424
1.359
1.328
1.344
540
542
567
526
563
537
561
548
581
582
588
598
584
600
42
46
31
58
37
−
38
52
−
chloroform
THF
4.8
7.4
CH2Cl2
8.9
a
acetone
20.6
32.7
37.5
−
n.e.
methanol
acetonitrile
599
600
water
([acetonitrile] =
0.2 M)
−
n.e.
a
n.e.: non-evaluated (too weak to be measured).
Figure 4. Photopolymerization profiles of EPOX under air. (A) Upon
a laser diode, exposure at 532 nm in the presence of (1) M_1/NVK/
Iod (0.3%/3%/2% w/w), (2) M_3/NVK/Iod (0.3%/3%/2% w/w),
(3) M_2/NVK/Iod (0.3%/3%/2% w/w), (4) M_5/NVK/Iod (0.3%/
3%/2% w/w), and (5) M_6/NVK/Iod (0.3%/3%/2% w/w). (B) In
the presence of M_1/NVK/Iod (0.3%/3%/2% w/w) using different
laser diode irradiations: (1) 532 nm; (2) 457 nm; (3) 473 nm.
compound at the laser line (457 < 473 < 532 nm).
Interestingly, the M_1/Iod/NVK can also be highly effective
for the polymerization upon very low intensity sources: (i)
green LED bulb exposure (a final conversion of ∼55% can be
reached after 30 min of irradiation), (ii) halogen lamp exposure
(Figure S1 in the Supporting Information), or (iii) 405 nm
laser diode exposure. Excellent polymerization profiles were
also obtained for these soft irradiations conditions for the
M_1/Iod/(TMS)3Si−H initiating system. Interestingly, the
M_1/Iod/NVK system is also able to initiate the polymer-
ization of Triethylene glycol divinyl ether (DVE-3) for these
low intensities sources i.e. > 90% of conversion for 10 min of
irradiation with green LED bulb or halogen lamp.
3. Free Radical Photopolymerization. The best typical
conversion−time profiles of trimethylolpropane triacrylate
(TMPTA) in laminated conditions under, e.g., a laser diode
irradiation at 532 nm are shown in Figure 5. A quite slow
conversion is obtained when using the M_1 (to M_6)/MDEA
(Figure 5 curve 1) or M_1 (to M_6)/R−Br photoinitiating
systems whereas a very fast rate of polymerization and relatively
high conversions are reached with the three-component system
Figure 3. Photopolymerization profiles of EPOX under air upon a
laser diode exposure at 532 nm in the presence of (1) M_1/Iod
(0.3%/2% w/w) or (2) M_1/NVK/Iod (0.3%/3%/2% w/w); Inset:
conversion of NVK for run 2.
process. The dye efficiency follows the M_1 > M_3 > M_2 ∼
M_5 > M_6 series (Figure 4A); i.e., M_4 is not stable in
presence of the iodonium salt, leading to a degradation of the
sample: this latter compound will not be investigated further.
MK itself does not work under such conditions. M_6 does not
work at 532 nm (i.e., this compound does not absorb for this
wavelength) but can be used for halogen lamp or 405 nm laser
diode irradiations (final conversions >40% can be reached using
M_6/Iod/NVK).
M_1 being the most reactive, its associated polymerization
initiating ability was investigated upon different laser diode
irradiations (457, 473, and 532 nm; Figure 4B; tack free
coatings can be obtained at 532 and 473 nm). The efficiency
order is in line with the amount of light absorbed by this
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(1−2) to PhI, (M_1)•+ and a phenyl radical Ph• as supported
by ESR-ST and ESR experiments. Ph• (Figure 7A) and M_1•+
(Figure 7B) are clearly observed: the hyperfine coupling
constants hfc (aN = 14.2 G; aH = 2.2 G) agree with the known
data for the PBN/Ph• adduct;18,21 the radical cation is
characterized by a distinct singlet signal with g ∼ 2.003 in
agreement with.22 Upon identical light absorbed intensities, the
photolysis of the dye decreases in the series M_1 > M_3 >
M_2 ∼ M_5 (M_4/Iod is not stable; see above; M_6 has not
been investigated i.e. this compound does not absorb at 532
nm) in the same way as the polymerization efficiency, thereby
highlighting the role of the dye/Iod interaction in the global
efficiency of the processes. Upon photolysis of dye/Iod
solutions, a new product can be observed at about 650 nm;
based on the ESR data, this absorption can be potentially
ascribed to dye•+ (see below). For the dye/Iod systems, dye•+
corresponds to the initiating species for cationic polymerization
of epoxides.
Figure 5. Photopolymerization profiles of TMPTA in laminated
conditions upon a laser diode exposure at 532 nm in the presence of
(1) M_1/MDEA (0.3%/4% w/w), (2) M_1/R−Br (0.3%/3% w/w),
(3) M_1/MDEA/R−Br (0.3%/4%/3% w/w), (4) M_2/MDEA/R−
Br (0.3%/4%/3% w/w), (5) M_3/MDEA/R−Br (0.3%/4%/3% w/
w), and (6) M_4/MDEA/R−Br (0.3%/4%/3% w/w).
dye → 1dye (hv)
1
dye + Ph2I+ → dye•+ + Ph2I•
(1)
•
Ph2I• → Ph + Ph−I
(M_1/MDEA/R−Br; Figure 5 curve 3; final tack-free coatings
within 10 min). The efficiency of the three-component systems
decreases in the series M_1 > M_2 > M_4 > M_3 ∼ M_5 ∼
M_6.
4. Chemical Mechanisms. a. The Dye/Iod/NVK for
Cationic Polymerization. When exposed to the laser diode at
532 nm, a very fast bleaching of the M_1/Iod solution is found
(Figure 6). It results from the oxidation of M_1 by Iod leading
(2)
The free energy change ΔGet for the dye/Ph2I+ electron
1
transfer reaction is favorable according to the redox properties
of the reactants (Table 2) (e.g., Eox = 0.75 V for M_1 [from this
work; see Figure 8A]; Ered(Ph2I+) ∼ −0.2 V;1 E(1M_1) ∼ 2.15
eV (Figure 8B; from the crossing of fluorescence and
absorption spectra)). In laser flash photolysis experiments, no
Figure 6. Photolysis of M_1/Iod (A), M_2/Iod (B), and M_3/Iod (C) in acetonitrile, under air, with a laser diode exposure at 532 nm (identical
light absorption intensity). [Iod] = 0.011 M; the UV−visible spectra are recorded at the same irradiation times.
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Figure 7. (A) ESR−spin trapping spectrum of M_1/Iod; [Iod] = 0.01 M. (B) ESR spectrum of the cation radical (M_1)•+ at room temperature; in
tert-butylbenzene; laser diode exposure at 532 nm; under N2; experimental (a) and simulated (b) spectra. Phenyl-N-tert-butylnitrone (PBN) is used
as spin trap in part A.
affected by different parameters: (i) the relative dye light
absorption properties, (ii) the radical or radical cation
formation quantum yields in the singlet state and (iii) the
ability of dye•+ to initiate a ring-opening polymerization
process.
Table 2. First Excited Singlet State Energy and Oxidation
Potentials Eox of M_1 to M_6
a
λabs (nm)
ES1 (eV)
Eox (SCE) (V)
ΔGet (eV)
M_1
M_2
M_3
M_4
M_5
M_6
548
586
556
476
491
385
2.15
2.01
2.13
−
0.75
0.8
−1.2
−1.01
−1.43
b
As usually in presence of NVK,23 the phenyl radicals (Ph•)
generated in eq 2 are easily converted into NVK• by an
addition to the double bond of NVK (eq 3). The formation of
the NVK radicals (NVK•) upon irradiation of M_1/Ph2I+/
NVK (aN = 14.4 G; aH = 2.5 G in agreement with18,23) is
clearly observed in ESR spin trapping experiments. As
previously discussed in other related systems,16b,24 the NVK+
cations are easily formed, i.e., NVK• is an electron rich radical
that can be easily oxidized (eqs 4a, 4b). These NVK+ can very
efficiently initiate the ROP of the epoxide (eq 5). Reaction 4b
allows a partial regeneration of the dye as supported by
photolysis experiments i.e. the photolysis of the dye in the
three-component system (dye/Iod/NVK) is slower than in the
two-component (dye/Iod) in agreement with 4b. The dye is
only partially regenerated during the polymerization; i.e., the
presence of radical cations inserted in the final polymer
network is easily observed in ESR experiments (Figure S2 in
the Supporting Information). These species are very stable and
0.5
−
0.8
2.46
−1.46
−1.86
2.81
0.75
a
Free energy changes ΔGet of the M_1 (to M_6)/Iod interaction; in
b
acetonitrile. Not stable in presence of Iod.
transient ascribable to a triplet state can be observed for M_1
which is the most reactive dye: this confirms the S1 pathway
(on the opposite, MK works in its triplet state). Reaction 1
being favorable for all the investigated dyes (see ΔGet, Table 2),
the lower photolysis found for different dye/Iod systems can be
explained by a back electron transfer regenerating the starting
compounds. Such a deactivation pathway decreases the yield in
Ph• and dye•+ in line with the very low efficiency of these
systems in polymerization experiments (see above). Therefore,
the relative efficiency of these dye/Iod combinations will be
Figure 8. (A) Cyclic voltammogram of M_1 in acetonitrile. (B) (a) Absorption and (b) fluorescence spectra of M_3 in acetonitrile.
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Figure 9. Photolysis of M_1/MDEA ([MDEA] = 0.25M) (A); M_1/MDEA/R−Br ([MDEA] = 0.25M; [R−Br] = 0.08M) (B); in acetonitrile;
under N2; low intensity laser diode exposure at 532 nm. Identical light absorption intensity.
Figure 10. (A) ESR−spin trapping spectrum of M_1/ethyldimethylaminobenzoate (EDB); (B) ESR-Spin Trapping spectrum of M_1/(EDB)/
phenacyl bromide (R−Br); laser diode exposure at 532 nm; experimental (a) and simulated (b) spectra. Phenyl-N-tert-butylnitrone (PBN) is used as
spin trap; under N2.
persistent during several weeks. The investigation of the
magnetic properties of these materials is beyond the scope of
the present paper but can be worthwhile for different
magnetism applications.
Remarkably, only phenacyl radicals (aN = 14.9 G; aH =4.6 G)
are observed in ESR-ST experiments upon the irradiation of the
M_1/MDEA/R−Br three-component system (Figure 10B).25
Their formation is explained on the basis of (6) and (8). As no
aminoalkyls are detected, reaction 7 must be considered as
unable to compete with (8). Interestingly, reaction 8 ensures a
regeneration of the dye. This is fully consistent with the
photolysis of M_1/MDEA/R−Br that is much slower than that
of M_1/MDEA (Figure 9A vs Figure 9B). This behavior
highlights a photocatalyst behavior for M_1. The phenacyl
radicals initiate the FRP of TMPTA (9).
•
Ph + NVK → Ph−NVK•
(3)
•
Ph−NVK• + Ph2I+ → Ph−NVK+ + Ph−I + Ph
(4a)
Ph−NVK• + dye•+ → Ph−NVK+ + dye
(4b)
Ph−NVK+ + EPOX → Ph−NVK−EPOX+
(5)
dye → 1dye (hv)
b. Dye/Amine/Alkyl Halide for Free Radical Polymer-
ization. As above, a bleaching of the M_1/amine (MDEA)
solution is found upon the laser diode exposure at 532 nm
(Figure 9). It results (eq 6) from the reduction of M_1 by
MDEA leading to (M_1)•− and a subsequent proton transfer
1
•+
dye + MDEA → dye•− + MDEA
(6)
(7)
dye•− + MDEA•+ → dye−H• + MDEA(•−H)
dye•− + R−Br → dye + R• + Br−
leading to aminoalkyl radical MDEA•
(eq 7). This is
(‑H)
supported by ESR-ST experiments; i.e., an aminoalkyl radical is
clearly observed in an irradiated M_1/ethyldimethylaminoben-
zoate (EDB) solution: the hyperfine coupling constants hfc (aN
= 14.3 G; aH = 2.4 G; Figure 10) agree with the known data for
the PBN/aminoalkyl radical adduct;18 EDB (instead of MDEA)
is used to avoid a high polarity of the sample preventing an ESR
analysis.
(8)
(9)
R• + TMPTA → R−TMPTA
•
The relative efficiency of the dye/MDEA/R−Br combina-
tions is rather complex and can be affected by different
parameters: (i) the relative dye light absorption properties, (ii)
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347. (g) Wang, H.; Shi, Y.; Wei, J.; Jiang, X.; Yin, J. J. Appl. Polym. Sci.
2006, 101, 2347−2354. (h) Tanaka, M.; Yago, T.; Wasaka, M. Chem.
Lett. 2009, 38, 1086−1087. (i) Decker, C.; Moussa, K. J. Polym. Sci.,
Polym. Lett. 1989, 27, 347−354.
(5) (a) Green, W. A.; Timms, A. W. In Radiation Curing in Polymer
Science and Technology; Fouassier, J. P., Rabek, J. F., Eds.; Elsevier:
Barking, U.K., 1993; Vol. II, pp 375−434. (b) Fouassier, J. P., Lougnot,
D. J. In Lasers in Polymer Science and Technology; Fouassier, J. P.;
Rabek, J. F., Eds.; CRC Press: Boca Raton, FL, 1990; Vol. II, pp 145−
168. (c) Corrales, T.; Catalina, F.; Allen, N. S.; Peinado, C. In
Photochemistry and UV Curing: new trends; Fouassier, J. P., Ed.;
Research Signpost: Trivandrum, India, 2006; pp 31−45. (d) Liska, R.;
Knaus, S.; Gruber, H.; Wendrinsky, J. Surf. Coat. Int. 2000, 83, 297−
303.
(6) (a) Neckers, D. C.; Valdes-Aguilera, O. M. In Advances in
Photochemistry; Hammond, D. H., Gollnick, G. S.; Eds.; Wiley: New
York, 1993. (b) Tasdelen, M. A.; Kumbaraci, V.; Talinli, N.; Yagci, Y.
Macromolecules 2007, 40, 4406−4408. (c) Wang, K.; Ma, G.; Yin, R.;
Nie, J.; Yu, Q. Mater. Chem. Phys. 2010, 124, 453−457. (d) Cui, R.;
Wang, K.; Ma, G.; Qian, B.; Yang, J.; Ju, Q.; Nie, J. J. Appl. Polym. Sci.
the radical or radical cation formation quantum yields and (iii)
the rate constants for eqs 6 and 8.
CONCLUSION
■
In this paper, we showed that bifunctional dyes derived from
the Michler’s ketone structure allow efficient radical polymer-
ization of TMPTA and cationic polymerization of EPOX upon
exposure to 405, 457, 473, and 532 nm laser diodes (100 mW/
cm2) as well as to a green LED bulb at 514 nm or a halogen
lamp. Five of these original dyes exhibit a unique push−pull
molecular character which explains their remarkable red-shifted
absorptions. Once again, it appeared that free radical promoted
cationic polymerization (and obviously free radical polymer-
ization) can be easily carried out under exposure to visible light
sources. Other colored photoinitiators will be proposed in the
future.
ASSOCIATED CONTENT
* Supporting Information
■
́
2011, 120, 2754−2759. (e) Pietrzak, M.; Wrzyszczynski, A. J. Appl.
Polym. Sci. 2011, 122, 2604−2608. (f) Yang, J.; Shi, S.; Xu, F.; Nie, J.
Photochem. Photobiol. Sci. 2013, 12, 323−329.
S
Figure S1, photopolymerization profiles of EPOX under air
upon a halogen lamp exposure in the presence of M_1/Iod and
M_1/NVK/Iod; Figure S2, ESR spectrum for a polymer
synthesized upon irradiation of EPOX at 532 nm (initiating
system M_1/Iod/NVK 0.3/2/3% w/w). This material is
available free of charge via the Internet at http://pubs.acs.
org/.
(7) (a) Wang, Y.; Jiang, X.; Yin, J. Eur. Polym. J. 2009, 45, 437−447.
(b) Wei, J.; Liu, F.; Lu, Z.; Song, L.; Cai, D. Polym. Adv. Tech. 2008,
19, 1763−1770. (c) Sun, F.; Zhang, N.; Nie, J.; Du, H. J. Mater. Chem.
2011, 21, 17290−17296. (d) Temel, G.; Aydogan, B.; Arsu, N.; Yagci,
Y. Macromolecules 2009, 42, 6098−6106. (e) Allen, N. S. J. Photochem.
Photobiol. A 1996, 100, 101−107. (f) Temel, G.; Aydogan, B.; Arsu,
N.; Yagci, Y. J. Polym. Sci., Part A: Polym. Chem. 2009, 47, 2938−2947.
(g) Wei, J.; Liu, F. Macromolecules 2009, 42, 5486−5491.
(h) Pouliquen, L.; Coqueret, X.; Morlet-Savary, F.; Fouassier, J. P.
Macromolecules 1995, 28, 8028−8034. (i) Matsushima, H.; Hait, S.; Li,
Q.; Zhou, H.; Shirai, M.; Hoyle, C. E. Eur. Polym. J. 2010, 46, 1278−
1287. (j) Chen, Y.; Loccufier, J.; Vanmaele, L.; Frey, H. J. Mater. Chem
2007, 17, 3389−3392. (k) Wang, H.; Wei, J.; Jiang, X.; Yin, J. J.
Photochem. Photobiol. A: Chem. 2007, 186, 106−114. (l) Sandholzer,
M.; Schuster, M.; Liska, R.; Turecek, C.; Varga, F.; Stelzer, F.; Slugovc,
C. Polym. Prepr. 2007, 48, 925−926. (m) Wei, J.; Wang, B. Macromol.
Chem. Phys. 2011, 212, 88−95. (n) Wen, Y.; Jiang, X.; Yin, J. Prog. Org.
Coatings 2009, 66, 65−72. (o) Xiao, P.; Dai, M.; Nie, J. J. Appl. Polym.
Sci. 2008, 108, 665−670. (p) Xiao, P.; Zhang, H.; Dai, M.; Nie, J. Prog.
Org. Coatings 2009, 64, 510−514. (q) Allen, N. S. Photochemistry 2007,
36, 232−297.
AUTHOR INFORMATION
Corresponding Author
*E-mail: (J.L.) jacques.lalevee@uha.fr; (D.G.) didier.gigmes@
univ-amu.fr.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was partly supported by the “Agence Nationale de la
Recherche” Grant ANR 2010-BLAN-0802. J.L. thanks the
Institut Universitaire de France for the financial support.
REFERENCES
(1) Fouassier, J.-P.; Lalevee
Scope, Reactivity and Efficiency: Wiley-VCH: Weinheim, Germany,
2012.
(8) (a) Li, Z.; Siklos, M.; Pucher, N.; Cicha, K.; Ajami, A.; Husinsky,
W.; Rosspeintner, A.; Vauthey, E.; Gescheidt, G.; Stampfl, J.; Liska, R.
J. Polym. Sci., Part A: Polym. Chem. 2011, 49, 3688−3699. (b) Baldeck,
P.; Stephan, O.; Andraud, C. In Basics of Photopolymerization Reactions;
Fouassier, J. P., Allonas, X., Eds., Researchsignpost: Trivandrum, India,
2010; Vol. 3, pp 200−220.
■
́
, J. Photoinitiators for Polymer Synthesis:
(2) (a) Dietliker, K. A Compilation of Photoinitiators Commercially
Available for UV Today: Sita Technology Ltd.: Edinburgh and London,
2002; (b) Green, W. A.; Industrial photoinitiators: CRC Press: Boca
Raton, FL, 2010, (c) Allen, N. S.; Photochemistry and Photophysics of
Polymer Materials; Wiley: New York, 2010; (d) Photoinitiated
Polymerization, Belfied, K. D., Crivello, J. V., Eds.; ACS Symposium
Series 847; American Chemical Society: Washington, DC, 2003.
(3) Turro, N. J. Modern Molecular Photochemistry; University Science
Books: New York, 1991.
(4) (a) Schnabel, W. in Lasers in Polymer Science and Technology,
Fouassier, J. P., Rabek, J. F., Eds.; CRC Press: Boca Raton, FL, 1990,
Vol. II, pp 95−143; (b) Rulhman, D.; Fouassier, J. P. Eur. Polym. J.
1991, 27, 991; Eur. Polym. J. 1992, 28, 591−597. (c) Fouassier, J. P. In
Radiation Curing in Polymer Science and Technology; Fouassier, J. P.,
Rabek, J. F., Eds.; Elsevier: Barking, U.K., 1993; Vol. 1, pp 49−118;
1993, Vol. 2, pp 1−62; (d) Lissi, E. A., Encinas, M. V. In
Photochemisrty and Photophysics; Rabek, J. F., Ed.; CRC Press: Boca
Raton, FL, 1991; Vol. 4, pp 221−293. (e) Wang, H.; Wei, J.; Jiang, X.;
Yin, J. Macromol. Chem. Phys. 2006, 207, 1080−1086. (f) Nagarajan,
R., Jr.; Bowers, J. S.; Wu, Z.; Cui, H.; Bao, R.; Jonsson, S.; McCartney,
R., Jr.; Pittman, C. U.; Cao, L.; Ran, R. Surf. Coat. Int. 1999, 82, 344−
(9) (a) Fouassier, J. P.; Lougnot, D. J.; Avar, L. Polymer 1995, 36,
5005−5010. (b) Morlet - Savary, F.; Fouassier, J. P.; Tomioka, H.
Polymer 1992, 33, 4202−4206. (c) Fouassier, J. P.; Lougnot, D. Polym.
Commun. 1990, 31, 417−422. (d) Allonas, X.; Lalevee
P.; Visconti, M. J. Polym. Sci., Part A: Polym. Chem. 2000, 38, 4531−
4541. (e) Lalevee, J.; Blanchard, N.; El Roz, M.; Graff, B.; Allonas, X.;
Fouassier, J. P. Macromolecules 2008, 41, 4180−4186. (f) Guillaneuf,
Y.; Bertin, D.; Gigmes, D.; Versace, D. L.; Lalevee, J.; Fouassier, J. P.
́
, J.; Fouassier, J.
́
́
Macromolecules 2010, 43, 2204−2212. (g) Griesser, M.; Dvorak, C.;
Jauk, S.; Hofer, M.; Rosspeintner, A.; Grabner, G.; Liska, R.;
Gescheidt, G. Macromolecules 2012, 45, 1737−1745.
́
(10) (a) Lalevee, J.; Tehfe, M. A.; Dumur, F.; Gigmes, D.; Morlet-
Savary, F.; Graff, B.; Fouassier, J. P. Macromol. Rapid Commun. 2013,
34, 239−245. (b) Tehfe, M. A.; Dumur, F.; Graff, B.; Clement, J. L.;
Gigmes, D.; Morlet-Savary, F.; Fouassier, J. P.; Lalevee, J. Macro-
molecules 2013, 46, 736−746. (c) Tehfe, M. A.; Lalevee, J.; Telitel, S.;
́
́
́
Contal, E.; Dumur, F.; Gigmes, D.; Bertin, D.; Nechab, M.; Graff, B.;
Morlet-Savary, F.; Fouassier, J. P. Macromolecules 2012, 45, 4454−
4460.
3769
dx.doi.org/10.1021/ma400766z | Macromolecules 2013, 46, 3761−3770

Macromolecules
Article
(11) Tehfe, M.-A.; Dumur, F.; Graff, B.; Gigmes, D.; Fouassier, J.-P.;
́
Lalevee, J. Macromolecules 2013, DOI: ma-2013-005082.
(12) Mayr, H.; Ofial, A. R.; Sauer, J.; Schmied, B. Eur. J. Org. Chem.
2000, 11, 2013−2020.
(13) Dumur, F.; Mayer, C.; Dumas, R. E.; Miomandre, F.; Frigoli,
́
M.; Secheresse, F. Org. Lett. 2008, 10, 321−324.
(14) Boger, D. L.; Wysocki, R. J., Jr. J. Org. Chem. 1988, 53, 3408−
3421.
́
(15) (a) Tehfe, M. A.; Lalevee, J.; Dumur, F.; Zein-Fakih, A.; Telitel,
S.; Gigmes, D.; Contal, E.; Bertin, D.; Morlet-Savary, F.; Graff, B.;
Fouassier, J. P. Eur. Polym. J. 2013, DOI: 10.1016/j.eurpo-
lymj.2013.01.023. (b) Tehfe, M. A.; Lalevee, J.; Morlet-Savary, F.;
Graff, B.; Blanchard, N.; Fouassier, J. P. Macromolecules 2012, 45,
1746−1752.
(16) (a) Lalevee
́
, J.; Tehfe, M. A.; Gigmes, D.; Fouassier, J. P.
, J.; Tehfe, M. A.;
Macromolecules 2010, 43, 6608−6615. (b) Lalevee
Zein-Fakih, A.; Ball, B.; Telitel, S.; Morlet-Savary, F.; Graff, B.;
Fouassier, J. P. ACS Macro Lett. 2012, 1, 802−806.
́
(17) (a) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A.;
Stratmann, R. E. J.; Burant, C.; Dapprich, S.; Millam, J. M.; Daniels, A.
D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.;
Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford,
S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.;
Salvador, P.; Dannenberg, J. J.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Baboul,
A. G.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi,
I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.; Gonzalez, C.;
Head-Gordon, M. E.; Replogle, S.; Pople, J. A. Gaussian 03, Revision B-
2; Gaussian, Inc.: Pittsburgh, PA, 2003. (b) Foresman, J. B.; Frisch, A.
Exploring Chemistry with Electronic Structure Methods; 2nd ed.,
Gaussian. Inc.: Pittsburgh, PA, 1996.
(18) (a) Tordo, P. Spin-trapping: recent developments and applications;
Atherton, N. M., Davies, M. J., Gilbert, B. C., Eds.; Electron Spin
Resonance 16; The Royal Society of Chemistry: Cambridge, U.K.,
1998. (b) Landolt Bornstein: Magnetic Properties of Free Radicals;
Fischer, H., Ed.; Springer Verlag: Berlin, 2005;, Vol. 26d. (c) Chandra,
H.; Davidson, I. M. T.; Symons, M. C. R. J. Chem. Soc. Faraday Trans.
1 1983, 79, 2705−2711. (d) Alberti, A.; Leardini, R.; Pedulli, G. F.;
Tundo, A.; Zanardi, G. Gazz. Chim. Ital. 1983, 113, 869−871.
(19) Rehm, D.; Weller, A. Isr. J. Chem. 1970, 8, 259−265.
(20) Lalevee
Fouassier, J. P. Macromolecules 2008, 41, 2003−2010.
(21) Lalevee, J.; Blanchard, N.; Tehfe, M. A.; Morlet-Savary, F.;
́
, J.; Dirani, A.; El Roz, M.; Graff, B.; Allonas, X.;
́
Fouassier, J. P. Macromolecules 2011, 43, 10191−10195.
(22) Kim, S. J.; Jang, H.-G.; Lee, J. K.; Min, H.-K.; Hong, S. B.; Seo,
G. Chem. Commun. 2011, 47, 9498−9500.
́
(23) Lalevee, J.; Dumur, F.; Mayer, C. R.; Gigmes, D.; Nase, G.;
Tehfe, M. A.; Telitel, S.; Morlet-Savary, F.; Graff, B.; Fouassier, J. P.
Macromolecules 2012, 45, 4134−4141.
(24) Hua, Y.; Crivello, J. V. J. Polym. Sci., Part A: Polym. Chem. 2000,
38, 3697−3709.
́
(25) Lalevee, J.; Tehfe, M. A.; Dumur, F.; Gigmes, D.; Blanchard, N.;
Morlet-Savary, F.; Fouassier, J. P. ACS Macro Lett 2012, 1, 286−290.
3770
dx.doi.org/10.1021/ma400766z | Macromolecules 2013, 46, 3761−3770