Trifunctional photoinitiators based on a triazine skeleton for visible light source and UV LED induced polymerizations

Article abstract of DOI:10.1021/ma301931p

Trifunctional photoinitiators (tPIs) based on benzophenone, anthracene, and pyrene chromophores linked to a triazine moiety are proposed as new initiating systems. In combination with an iodonium salt and a silane, these structures are able to initiate the radical polymerization RP of acrylates and the cationic polymerization CP of epoxides and vinylethers under Xe-Hg lamp, LED and very soft irradiation (i.e., halogen lamp). Upon addition of an amine, these new photoinitiators were also able to start the radical polymerization of acrylates. Excellent RP and CP polymerization profiles are obtained i.e. better than those recorded using the reference compounds (benzophenone, anthracence and pyrene). In CP, some of these compounds combined with thianthrenium salts can also be used. The mechanisms involved in the different multicomponent initiating systems were analyzed by ESR, fluorescence, steady state photolysis, and laser flash photolysis experiments.

Full text of DOI:10.1021/ma301931p

Article
pubs.acs.org/Macromolecules
Trifunctional Photoinitiators Based on a Triazine Skeleton for Visible
Light Source and UV LED Induced Polymerizations
Mohamad-Ali Tehfe,† Frederic Dumur,‡ Bernadette Graff,† Fabrice Morlet-Savary,† Jean-Pierre Fouassier,§
́
́
Didier Gigmes,‡ and Jacques Lalevee†,*
́
†Institut de Science des Mater
Cedex, France
‡Aix-Marseille Universite,
́
iaux de Mulhouse IS2M, LRC CNRS 7228, ENSCMu-UHA, 15 rue Jean Starcky, 68057 Mulhouse
́
CNRS, Institut de Chimie Radicalaire, UMR 7273, F-13397 Marseille, France
§UHA-ENSCMu, 3 rue Alfred Werner 68093 Mulhouse
S
* Supporting Information
ABSTRACT: Trifunctional photoinitiators (tPIs) based on
benzophenone, anthracene, and pyrene chromophores linked
to a triazine moiety are proposed as new initiating systems. In
combination with an iodonium salt and a silane, these
structures are able to initiate the radical polymerization RP
of acrylates and the cationic polymerization CP of epoxides
and vinylethers under Xe−Hg lamp, LED and very soft
irradiation (i.e., halogen lamp). Upon addition of an amine,
these new photoinitiators were also able to start the radical polymerization of acrylates. Excellent RP and CP polymerization
profiles are obtained i.e. better than those recorded using the reference compounds (benzophenone, anthracence and pyrene). In
CP, some of these compounds combined with thianthrenium salts can also be used. The mechanisms involved in the different
multicomponent initiating systems were analyzed by ESR, fluorescence, steady state photolysis, and laser flash photolysis
experiments.
compared to those of the individual starting PI units. These
known mPIs absorb in the UV or near UV/visible range.
Decreasing the length of the spacer or using appropriate
spacers in dPIs should allow an efficient coupling of the
molecular orbitals MO of the two PI units and could result in
enhanced light absorption properties (in term of molar
extinction coefficients ε and red-shifted wavelengths). This
was first achieved several years ago2k,l in dPIs such as HAP-Sp-
HAP where Sp = −O−, −CH2−. The π−π* transitions are red-
shifted by 25−35 nm (and centered at ∼260 and 280 nm for Sp
= −O− and −CH2−, respectively compared to 245 nm for
HAP itself) and the ε are increased by a 2-fold factor. The
delocalization of the π orbitals of the HAP moieties takes place
through a conjugative interaction with the 2p orbital of the
central oxygen atom in HAP−O−HAP or a through-space
hyperconjugation in the slightly twisted HAP−CH2−HAP.2s
The search for new photoinitiators PI and/or new photo-
initiating systems for radical and/or cationic polymerization
reactions upon visible lights and/or LED irradiations (365, 395
nm) remains a great challenge to avoid the use of Hg or Xe−
Hg lamps.1 In this aim, search of new architectures involving
dPIs or even trifunctional photoinitiator arrangements tPIs
potentially exhibiting a strong coupling of the molecular
INTRODUCTION
■
Development of multifunctional photoinitiators mPIs (that can
be defined as molecular or macromolecular arrangements
where several low molecular weight photoinitiator PI units are
incorporated) have received a constant and particular attention
of researchers (see, e.g., a book in ref 1 and original papers2).
Reasons justifying the interest for such mPIs have been
mentioned for many years3 and a recent paper4 pointed out the
possible advantages: reduced migratability, reduced release of
photolysis products, less odor, better compatibility into the
resin... Examples of mPIs (see, e.g., in refs1 and 2) include (i)
polymeric PI (where PI = benzophenone, thioxanthone,
camphorquinone are generally pendant groups of polymer
chains, e.g.;2a,f,o,p,r a dendritic structure has also been
proposed2e), (ii) oligomeric PI (with PI = hydroxyacetophe-
none (HAP) as pendent units),2b and (iii) difunctional
photoinitiators dPIs4 where two PI units (such as phenyl-
glyoxylate, benzophenone, thioxanthone; e.g., ref 2m) are
usually linked using a rather long ethylene glycol chain spacer
Sp. As far as the absorption is concerned in all these systems,
the PI units obviously behave as independent single moieties.
Bifunctional photoinitiators bPIs (e.g., refs 2h, j, n, and q)
where two chemically different PI units (e.g., a benzophenone
and a sulfonyl ketone) are linked also refer to dPIs: in that case,
a more or less important delocalization of the molecular orbitals
occurs leading to improved light absorption properties
Received: September 14, 2012
Revised: October 16, 2012
Published: October 30, 2012
© 2012 American Chemical Society
8639
dx.doi.org/10.1021/ma301931p | Macromolecules 2012, 45, 8639−8647

Macromolecules
Article
Scheme 1
Scheme 2
1
Avance 400 spectrometer of the Spectropole: H (400 MHz) and 13
C
orbitals of the PI units with those of the spacer thus resulting in
better light absorption properties is of crucial interest. In the
present paper, we propose, for the first time, the design of tPIs
based on a triazine scaffold with benzophenone, pyrene or
anthracene moieties as the peripheral photoabsorbing units
(Tz_BP, Tz_Py, and Tz_An in Scheme 1). Their ability in
photoinitiating systems as photoinitiators/photosensitizers for
the cationic polymerization CP of epoxides and vinylethers and
the radical polymerization RP of acrylates under very soft
irradiation conditions (halogen lamp, LED bulbs, ...) as well as
their excited state processes are investigated.
1
(100 MHz). The H chemical shifts were referenced to the solvent
peak DMSO-d6 (2.49 ppm) and the 13C chemical shifts were
referenced to the solvent peak DMSO d6 (39.5 ppm). 2,4,6-Tri(1-
pyrenylamino)-1,3,5-triazine Tz-Py was synthesized according to a
procedure previously reported.5 The initiators are yellow powders for
Tz_An, Tz_BP and Tz_Py. All the synthesized compounds were
prepared with analytical purity up to accepted standards for new
organic compounds (>98%) which was checked by high field NMR
analysis.
Synthesis of 2,4,6-Tri(2-anthracenylamino)-1,3,5-triazine, Tz_An.
The reactions were carried out in a 100 mL Parr autoclave under
autogenous pressure. The reactor was charged with acetone (50 mL),
cyanuric chloride (0.17 g, 0.92 mmol), 2-aminoanthracene (0.87 g, 4.6
mmol) and NaHCO3 (0.3 g, 3.6 mmol). The reaction mixture was
heated at 100 °C for 10 h, resulting in a pressure of approximately 6
bar in the reactor. After cooling to room temperature, the greenish
precipitate was collected by filtration and washed with acetic acid. The
EXPERIMENTAL PART
■
i. Triazine-Based Photoinitiators (Tz_BP, Tz_Py, and Tz_An).
The investigated triazine derivatives (Tz_BP, Tz_Py, and Tz_An)
shown in Scheme 1 were readily prepared by reacting five equivalents
of the corresponding amines with cyanuric chloride. 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. 1H and 13C NMR spectra were
determined at room temperature in 5 mm o.d. tubes on a Bruker
1
yield was 0.49 g (82%). H NMR (DMSO-d6), δ (ppm): 7.31−7.48
(m, 8H), 7.83−7.89 (brs, 4H), 8.07−8.09 (m, 8H), 8.51−8.58 (m,
4H), 8.65−8.80 (m, 3H), 9.77 (brs, 3H). HRMS: m/z calcd for
C45H31N6 ([M + H]+ detected), 655.2605; found, 655.2608.
Synthesis of 2,4,6-Tri(4-benzoylphenylamino)-1,3,5-triazine,
Tz_BP. The reactions were carried out in a 100 mL Parr autoclave
under autogenous pressure. The reactor was charged with acetone (50
mL), cyanuric chloride (0.17 g, 0.92 mmol), 4-aminobenzophenone
8640
dx.doi.org/10.1021/ma301931p | Macromolecules 2012, 45, 8639−8647

Macromolecules
Article
(0.91 g, 4.6 mmol), and NaHCO3 (0.3 g, 3.6 mmol). The reaction
mixture was heated at 160 °C for 4 h, resulting in a pressure of
approximately 13 bar in the reactor. After cooling to room
temperature, the brown precipitate was collected by filtration and
washed with acetic acid. The yield was 0.53 g (86%). HRMS: m/z
calcd for C42H31N6O3 ([M + H]+ detected), 667.2452; found,
667.2455. Anal. Calcd for C42H30N6O3: C, 75.7; H, 4.5; N, 12.6.
Found: C, 75.5; H, 4.4; N, 12.4.
ii. Compounds. Tris(trimethylsilyl)silane ((TMS)3Si−H), diphe-
nyliodonium hexafluorophosphate (Iod1), N-Methyldiethanolamine
(MDEA), triethylene glycol divinyl ether (DVE), anthracene (An),
pyrene (Py), and benzophenone (BP) were obtained from Aldrich and
used with the best purity available (Scheme 2). [Methyl-4-phenyl-
(methyl-1-ethyl)-4-phenyl]iodonium tetrakis(pentafluorophenyl) bo-
rate (Iod2)6 was obtained from Bluestar Silicones. (4-
Hydroxyethoxyphenyl)thianthrenium hexafluorophosphate (TH) was
obtained from Lamberti Spa (recrystallized form of Esacure 1187).
(3,4-Epoxycyclohexane)methyl 3,4-epoxycyclohexylcarboxylate
(EPOX; Uvacure 1500) and trimethylol−propane triacrylate
(TMPTA) were obtained from Cytec and selected as representative
monomers for cationic and radical polymerization, respectively
(Scheme 2).
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 380−800 nm range); (ii)
polychromatic light delivered by a Xe−Hg lamp (Hamamatsu, L8252,
150 W, λ > 300 nm) or Hg lamp (Omnicure S1000); (iii) 365 nm
(LED from Hamamatsu: LC-L1, Δλ ∼ 20 nm; I0 ∼ 50 mW cm−2).
The emission spectrum for halogen lamp was already given in ref 7a.
iv. Radical Polymerization (RP). For film photopolymerization
experiments, TMPTA (Scheme 2) was used as the monomer. The
experiments were carried out in laminate (polypropylene films). 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.7
v. Cationic Polymerization CP. The epoxy films (25 μm thick)
were irradiated on a BaF2 pellet under air. The evolution of the epoxy
group content was continuously followed by real time FTIR
spectroscopy (JASCO FTIR 4100) as in.7a,c,d The absorbance of the
epoxy group was monitored at about 790 cm−1. The conversion of the
Si−H group of (TMS)3Si−H is followed at about 2050 cm−1. The
formation of the polyether was well characterized at 1080 cm−1.
vi. ESR Spin Trapping (ESR-ST) Experiments. ESR-ST
experiments were carried out using an X-Band spectrometer (MS
400 Magnettech). The radicals were produced at room temperature
under a halogen lamp exposure and trapped by phenyl-N-tert-
butylnitrone (PBN) according to a procedure described in detail in
refs 8 and 9.
vii. Fluorescence Experiments. The fluorescence properties of
the different triazine based photoinitiators were studied in toluene
using a JASCO FP-750 spectrometer and the fluorescence lifetimes
were determined with a Fluoromax 4 spectrofluorimeter (Jobin-Yvon).
The rate constants were extracted from a Stern−Volmer treatment as
presented in ref 7a.
Figure 1. (A) UV−visible absorption spectra of the different triazine
derivatives (Tz_Py in toluene; Tz_An and Tz_BP in toluene/
acetonitrile). Inset: zoom for Tz_BP. (B) HOMO and LUMO of a
model Tz_Py derivative (UB3LYP/6-31G* level).
different light source emission spectra: (i) the halogen lamp
that mostly delivers visible light (e.g., for both Tz_Py and
Tz_An having ε > 2000 M−1 cm−1 at 400 nm), (ii) the Xe−Hg
lamp that delivers a UV−visible light (λ > 300 nm), and (iii)
the LED at 365 nm. Remarkably, when going from Py to
Tz_Py or An to Tz_An, a noticeable bathochromic shift of the
UV absorption spectra is observed (Figure S1, Supporting
Information: λmax ∼ 334 nm; ε ∼ 33 000 M−1 cm−1 for Py vs
λmax ∼ 348 nm; ε ∼ 38 000 M−1 cm−1 for Tz_Py and λmax
∼
356 nm; ε ∼ 9000 M−1 cm−1 for An vs λmax ∼ 404 nm; ε ∼
8500 M−1 cm−1 for Tz_An). For Tz_BP, the absorption
properties are moderately improved compared to the parent
compound BP (λmax ∼ 330 nm; ε ∼ 120 M−1 cm−1 for BP vs
λmax ∼ 330 nm; ε ∼ 330 M−1 cm−1 for Tz_BP; Figure 1).
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 MOs involved in the π → π* transition are strongly
delocalized for Tz-Py i.e. the two different pyrene units are
involved and a participation of the triazine linker is also noted
(Figure 1B). This is in line with the improved light absorption
properties of Tz_Py compared to that of Py; a rather similar
behavior is observed for Tz_An. For Tz_BP, the MOs are less
affected by the presence of the triazine skeleton and
accordingly, the absorption properties are less modified
viii. Laser flash photolysis. Nanosecond laser flash photolysis
(LFP) experiments were carried out using a Q-switched 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).7
RESULTS AND DISCUSSION
■
1. Photochemical Properties of Tz_BP, Tz_An, and
Tz_Py. Because of their absorption spectra (Figure 1A) and
their high molar extinction coefficients (about 38 000, 8500,
and 330 M−1 cm−1 for Tz_Py, Tz_An, and Tz_BP at ∼348,
∼404 and ∼330 nm, respectively), the absorption of the
selected triazine derivatives allows a good matching with the
8641
dx.doi.org/10.1021/ma301931p | Macromolecules 2012, 45, 8639−8647

Macromolecules
Article
compared to that of the parent compound. Tz_Py exhibiting
the best absorption properties of the new photoinitiators, the
mechanistic investigation will be reported only for this
compound in the rest of the discussion (moreover, the reduced
solubility of Tz-An and the fast degradation of Tz_BP in laser
flash photolysis experiments prevent a thorough investigation of
their excited state processes).
The excitation of Tz_Py in laser flash photolysis reveals the
presence of a transient specie characterized by an absorption
maximum at about 420 nm (Figure 3). This is close to the 3Py
a. The Tz_Py/Iod1 and Tz_Py/Silane/Iod1 Initiating
Systems. In fluorescence experiments (Figure S2A, Supporting
1
Information), a strong quenching of the Tz_Py by Iod1 is
found (i.e., k = 1.2 × 1010 M−1 s−1); the fluorescence lifetime
under air is 16 ns. For 1Py/Iod1, a diffusion controlled reaction
rate constant is also found7a indicating that a Py moiety of
1
Tz_Py is involved. This Tz_Py/Iod1 interaction corresponds
to an efficient electron transfer process which promotes (as in
the known thermodynamically favorable process calculated in
1Py/Iod1)10 the decomposition of the iodonium salt r2.
TzPy → 1TzPy(hν)
(r1)
1TzPy + Ph2I+ → (TzPy)•+ + Ph2I•
•
→ (TzPy)•+ + Ph + Ph − I
(r2)
Interestingly, upon a halogen lamp exposure, a very fast
bleaching of the Tz_Py/Iod1 solution occurs (e.g., in less than
2 min for Tz_Py/Iod1; Figure S2B, Supporting Information).
This bleaching is ascribed to the oxidation of Tz_Py by Iod1 r2.
Reaction r2 is also strongly supported by ESR-ST experiments
where the formation of a phenyl radical (Ph•) during the
irradiation of Tz_Py/iod1 is clearly observed (Figure 2): the
Figure 3. Time-resolved absorption spectra after laser excitation (355
nm) of Tz_Py in toluene. Inset: transient decay at 420 nm under air.
spectrum reported in the literature12 and can be safely ascribed
to 3Tz_Py. Considering the concentration of the iodonium salt
used in the polymerization experiments (e.g., [iod1] = 0.048 M;
see below), the resulting strong singlet state quenching (see
above) will prevent, in these conditions, a significant triplet
state pathway in Tz_Py/Iod1.
In the presence of a silane, reactions r4-r5 occur as observed
in the other related systems:1,7a the formation of the silyliums
(TMS)3Si+ (known as efficient structures for the epoxide ring-
opening reaction) explains the excellent polymerization
initiating ability of Tz_Py/(TMS)3SiH/Iod1 (see below).
(TMS)3Si• + (TzPy)•+ → (TMS)3Si+ + TzPy
Figure 2. ESR spectra obtained after a halogen lamp irradiation of
Tz_Py/Iod1 (in tert-butylbenzene), [Iod1] = 0.01 M: experimental
(a) and simulated (b) spectra. Phenyl-N-tert-butylnitrone (PBN) is
used as spin-trap.
(r4)
•
(TMS)3Si• + Ph2I+ → (TMS)3Si+ + Ph + Ph − I
(r5)
In the absence of a possible experimental support (see
above), we could assume, as the behavior of Tz_Py is rather
close to that of Py, that Tz_BP and Tz_An should behave as
BP (triplet state reactivity) and An (singlet state reactivity),
respectively.
b. Tz_Py/Amine Initiating System. For this part, triethyl-
amine will be used as a representative amine to avoid a high
polarity of the sample ensuring the ESR investigation. An
aminoalkyl radical is generated upon a halogen lamp irradiation
of Tz_Py/amine as observed in ESR-ST experiments, i.e., the
aminoalkyl radical adduct onto PBN is characterized by
hyperfine coupling constants hfc (aN = 14.5 G; aH = 2.5 G)9e
in agreement with the reported data. This highlights a α(C−H)
hydrogen abstraction between Tz_Py and the amine according
hyperfine coupling constants hfc (aN = 14.2 G; aH = 2.2 G)
agree with the known data for the PBN adduct of this radical.9
For the irradiation of a Tz_Py/(TMS)3Si−H/Iod1 solution,
these Ph• radicals are easily converted into silyl radicals
(TMS)3Si• by a hydrogen abstraction reaction r3 on
(TMS)3Si−H7,11 as revealed in ESR-ST experiments by the
formation of silyl radicals (aN = 15.0 G; aH = 5.7 G in
agreement with ref 9 for the associated PBN radical adduct). In
the irradiation of Tz_Py/(TMS)3Si−H, no free radicals were
observed indicating that the presence of Iod1 is required in
agreement with r3.
•
Ph + (TMS)3Si−H → Ph−H + (TMS)3Si•
(r3)
8642
dx.doi.org/10.1021/ma301931p | Macromolecules 2012, 45, 8639−8647

Macromolecules
Article
Figure 4. (A) Photopolymerization profiles of EPOX under air. Upon a Xe−Hg lamp exposure (λ > 300 nm) in the presence of (1) Tz_BP/Iod1
(1%/2% w/w); (2) (TMS)3Si−H/Iod1 (3%/2% w/w); (3) Tz_BP/(TMS)3Si−H/Iod1 (1%/3%/2% w/w); (4) Tz_Py/(TMS)3Si−H/Iod1 (1%/
3%/2% w/w); (5) Tz_An/(TMS)3Si−H/Iod1 (1%/3%/2% w/w); (6) Py/(TMS)3Si−H/Iod1 (1%/3%/2% w/w); insert: Si−H conversion during
the photopolymerization of curve 4. (B) Photopolymerization profiles of EPOX under air. Upon a Xe−Hg lamp exposure (λ > 300 nm) in the
presence of (1) Tz_BP/(TMS)3Si−H/Iod1 (1%/3%/2% w/w) and (2) Tz_BP/(TMS)3Si−H/Iod1 (1%/3%/2% w/w) after 7 days of storage.
to an electron/proton transfer r6. The rate constant for this
process r6 has been determined from fluorescence quenching
experiments: 2 × 108 M−1 s−1 (Figure S3, Supporting
Information). The same reactions should likely arise in
Tz_BP and Tz_An.
final conversions of EPOX as exemplified by curves 3, 4, or 5 in
Figure 4A (presence of the silane) compared to curve 1
(absence of the silane). Final conversions of about 90%, 80%
and 70% for Tz_BP, Tz_Py, and Tz_An, respectively, are
reached after 5 min of irradiation and tack free coatings are
obtained. The Si−H conversions are also high (i.e., ∼ 80% for
Tz_Py): this demonstrates that these Si−H conversions are
directly related to the efficiency of the initiation step in
agreement with reactions r3−r5. Remarkably, a quite slow
conversion is obtained when using (TMS)3Si−H/Iod1 (Figure
4A, curve 2) in line with the very low absorption of the
iodonium salt (Iod1) under the Xe−Hg lamp (λ > 300 nm).
Compared to the well-known parent compounds Py and
An,10 a higher efficiency of the triazine derivatives is clearly
observed (e.g., Figure 4A, curve 4 vs curve 6; Xe−Hg lamp
exposure); the same holds true upon a 365 nm LED irradiation
(Figure 5 curve 1 vs curve 2). The much better absorption
properties of Tz_Py (compared to Py) at 365 nm (Figure S1,
Supporting Information) are presumably the driving factor for
its enhanced initiating ability.
•+
1TzPy + MDEA → (TzPy)•− + MDEA
•
→ (TzPyH)• + MDEA (−H)
(r6)
2. Cationic Photopolymerization. 2.a. Photopolymeriza-
tion of EPOX upon UV Light. The best conversion−time
profiles of EPOX using Tz_Py (or Tz_BP, Tz_An)/
(TMS)3Si−H/Iod1 and Tz_Py (or Tz_BP, Tz_An)/Iod1 are
depicted in Figures 4 and 5. All the experiments were carried
out under air. Interestingly, when using the Xe−Hg lamp (λ >
300 nm), the addition of the silane to triazine derivatives/Iod1
drastically improves both the polymerization rates Rp and the
The storage of all the triazine-containing formulations (e.g.,
Tz_BP/(TMS)3SiH/Iod1) is quite good as similar polymer-
ization profiles are obtained either immediately after prepara-
tion (Figure 4B, curve 1) or after 7 days of storage at room
temperature without the presence of inert atmosphere (Figure
4B, curve 2).
2.b. Photopolymerization of EPOX upon Visible Light.
While comparing the different triazine derivatives for the EPOX
photopolymerization under the halogen lamp irradiation
(Figure 6), a decrease of the polymerization rates in the series
Tz_An > Tz_Py > Tz_BP could be evidenced. A very fast
polymerization is however noted with the multicomponent
initiating system Tz_An/(TMS)3Si−H/Iod1. This trend of
reactivity has to be related to the light absorption properties of
the different initiators at λ > 380 nm: Tz_An > Tz_Py >
Tz_BPsee Figure 1A. No polymerization is observed when
using the Tz_BP/(TMS)3Si−H/Iod1 initiating system in
Figure 5. Photopolymerization profiles of EPOX under air upon a 365
nm LED exposure in the presence of (1) Py/(TMS)3Si−H/Iod1 (1%/
3%/2% w/w) and (2) Tz_Py/(TMS)3Si−H/Iod1 (1%/3%/2% w/w).
8643
dx.doi.org/10.1021/ma301931p | Macromolecules 2012, 45, 8639−8647

Macromolecules
Article
Scheme 3
∼9000 M−1 cm−1 at 404 nm for Tz_An and TX-An,
respectively), Tz_An exhibits the highest efficiency (Figure
S5, Supporting Information) again highlighting its excellent
reactivity.
2.c. Sensitization of Thianthrenium Salts. Sulfonium (and
also thianthrenium) salts and iodonium salts correspond to
well-known cationic photoinitiators.1,3 Different anthracene
derivatives being efficient structures to sensitize the sulfonium
salts decomposition,10 the effect of the Tz_An addition to 4-
(hydroxyethoxyphenyl) thianthrenium hexaflorophosphate
(TH) has also to be investigated. In the EPOX photo-
polymerization, the Tz_An/TH couple is better than TH alone
(both the polymerization rates and the final conversions are
increased) (Figure 7, curve 1 vs curve 2). This highlights the
Figure 6. Photopolymerization profiles of EPOX under air. Upon a
halogen lamp irradiation in the presence of (1) Tz_Py/Iod1 (1%/2%
w/w), (2) Tz_BP/(TMS)3Si−H/Iod1 (1%/3%/2% w/w), (3)
Tz_Py/(TMS)3Si−H/Iod1 (1%/3%/2% w/w), (4) Tz_An/
(TMS)3Si−H/Iod1 (1%/3%/2% w/w), (5) An/(TMS)3Si−H/Iod1
(1%/3%/2% w/w), and (6) Py/(TMS)3Si−H/Iod1 (1%/3%/2% w/
w). Inset: Photobleaching of the polymer film under air of curve 3;
UV−vis absorption spectra before (a) and after (b).
agreement with the lack of absorption of Tz_BP at λ > 380 nm
(Figure 1A). The photobleaching of the polymer film in these
conditions is also quite remarkable (Figure 6). This can be
useful for applications requiring colorless coatings. This
bleaching clearly indicates that these initiators are strongly
inserted in the polymer network as initiating structures.
Accordingly, the extractability of the initiator evaluated as
presented by us in [2d] is found to be very low. The three-
component systems based on the parent compounds
(benzophenone, pyrene, anthracene) does not lead to an
efficient polymerization (i.e., final conversion <30%; Figure 6,
curves 5 and 6). This clearly highlights that the new proposed
compounds are very attractive for very soft irradiation
conditions.
Figure 7. Photopolymerization profiles of EPOX under air, upon Hg
lamp irradiation in the presence of (1) TH (3% w/w) and (2) Tz_An/
TH (1.2%/3% w/w).
high versatility of these triazines derivatives that can be used in
combination of iodonium or thianthrenium salts in CP
initiating systems.
2.d. Photopolymerization of DVE/EPOX Blends. Interest-
ingly, when using Tz_An/Iod2 to polymerize a DVE/EPOX
blend (20%/80% w/w) upon a halogen lamp irradiation in
laminate, a copolymer is readily formed and a tack free coating
is obtained after only 10 min. At this time, the EPOX and
divinyl ether double bond (CC) conversions are about 50%
and 80%, respectively (Figure S6, Supporting Information).
The conversion of the divinyl ether DVE is faster than that of
EPOX (Figure S6, Supporting Information) as resulting from
the usual higher reactivity of vinylethers in cationic polymer-
ization. The polymerization initiation can be easily explained by
eq r7, where the VE+ cation is the initiating structure produced
by the oxidation of the VE• radical (obtained by addition of the
(TMS)3Si• or Ph• radicals to the vinylether double bond) by
the iodonium salt.
A similar behavior is observed when substituting Iod1 by
Iod2 in the three-component photoinitiating system using a
halogen lamp irradiation, a LED 365 nm or Xe−Hg lamp
(Figure S4, Supporting Information).
The ability of Tz_An for the initiation of the EPOX
photopolymerization was also compared to that of a bifunc-
tional PI (TX-An, Scheme 3) synthesized here (see in
Supporting Information) according to the procedure men-
tioned in.13 Such thioxanthone-anthracene derivatives (a
thioxanthone bearing an anthracene unit) were elegantly
proposed13 as efficient radical photoinitiators being able to
reduce the oxygen inhibition of the polymerization. Although
these compounds are characterized by excellent and rather
close light absorption properties at λ > 400 nm (ε ∼ 8500 and
•
(TMS)3Si•(or Ph) + VE → VE•
(r7a)
8644
dx.doi.org/10.1021/ma301931p | Macromolecules 2012, 45, 8639−8647

Macromolecules
Article
Figure 8. (A) Photopolymerization profiles of TMPTA upon a Xe−Hg lamp irradiation (λ > 300 nm) in laminate in the presence of (1) Tz_BP/
Iod1 (1%/2% w/w), (2) Tz_BP/(TMS)3Si−H/Iod1 (1%/3%/2% w/w), (3) Tz_Py/(TMS)3Si−H/Iod1 (1%/3%/2% w/w), and (4) Tz_An/
(TMS)3Si−H/Iod1 (1%/3%/2% w/w). (B) Photopolymerization profiles of TMPTA upon a halogen lamp irradiation in laminate in the presence of
(1) Tz_Py (1% w/w), (2) Tz_Py/Iod1 (1%/2% w/w), and (3) Tz_Py/(TMS)3Si−H/Iod1 (1%/3%/2% w/w). (C) Evolution of the IR band of
(TMS)3Si−H recorded during the photopolymerization of Tz_Py/(TMS)3Si−H/Iod1 (1%/3%/2% w/w) under air and upon a halogen lamp
irradiation. (D) Photopolymerization profiles of TMPTA upon a Xe−Hg lamp irradiation (λ > 300 nm) under air in the presence of (1) Tz_Py/
Iod1 (1%/2% w/w) and (2) Tz_Py/(TMS)3Si−H/Iod1 (1%/3%/2% w/w).
•
VE• + Ph2I+ → VE+ + Ph + Ph − I
(Figure 8A). The high reactivity of the new three-component
(r7b)
system is ascribed to the formation of free radicals (Ph• and
R3Si•) through r1-r3 that can initiate the polymerization of
3. Radical Photopolymerization of Acrylates. 3.a. Tri-
azine Derivative/Silane/Iod1 Photoinitiating Systems. The
TMPTA (Figure 8). Indeed, Ph• and (TMS)3Si• are excellent
polymerization initiating radicals exhibiting high rate constants
for their addition to the acrylate double bond (k > 106 M−1
s−1).7b,c,14,15
The same holds true when using a halogen lamp irradiation
with Tz_Py/(TMS)3Si−H/Iod1 (Figure 8B). A final con-
version higher than 50% is reached within 5 min of irradiation
and a tack-free coating is obtained. A high Si−H consumption
is still found in agreement with eq r3 (Figure 8C).
best typical conversion−time profiles of trimethylolpropane
triacrylate TMPTA are shown in Figures 8 and 9. The triazine
derivatives/(TMS)3Si−H/Iod1 combination is a good initiating
system; i.e., high polymerization rates and final conversions are
obtained in laminate under a Xe−Hg lamp exposure and tack-
free coatings are formed (see Tz_Py or Tz_An in Figure 8A).
Using Tz_BP, the conversion reaches a maximum of ∼20%
Remarkably, no polymerization is observed when using
Tz_Py/Iod1 upon a Xe-lamp exposure under air. The addition
of (TMS)3Si−H improves the photopolymerization of
TMPTA. Rather high polymerization rates and conversions
(∼35%) are obtained (Figure 8D). This rather interesting
behavior of the proposed silane containing photoinitiating
systems under air is in line (as already shown elsewhere, see e.g.
in7b,c,15) with the ability of the silanes to convert the stable
peroxyls into new polymerization initiating silyls.
3.b. Triazine Derivative/Amine Photoinitiating Systems.
Interestingly, when using N-methyl diethanolamine (MDEA) as
a co-initiator (triazine derivative/MDEA initiating systems),
good photopolymerization profiles are recorded (Figure 9).
With Tz_Py/MDEA, a final conversion >70% is reached within
5 min of irradiation, forming a tack-free coating. A final
conversion >70% is excellent for a trifunctional acrylate
monomer.[1] The aminoalkyl radicals generated from the
Tz_Py/MDEA initiating system (see above in reaction r6) are
known as very efficient structures for the addition to acrylates.16
Figure 9. Photopolymerization profiles of TMPTA upon a Xe−Hg
lamp irradiation (λ > 300 nm) in laminate in the presence of (1)
Tz_Py (1% w/w) and (2) Tz_Py/MDEA (1%/5% w/w).
8645
dx.doi.org/10.1021/ma301931p | Macromolecules 2012, 45, 8639−8647

Macromolecules
Article
Tz_Py is also able to initiate alone the polymerization (Figure 9
curve 1) but to a lower extent (Figure 9, curve 2 vs curve 1).
This can be ascribed to a hydrogen abstraction reaction
between *Tz_Py and the monomer M thereby generating an
initiating radical M(−H)• , reaction r8.
REFERENCES
■
(1) Fouassier, J. P.; Lalevee
Scope, Reactivity and Efficiency; Wiley-VCH, Weinheim, Germany,
2012.
(2) (a) Liska, R. J. Polym. Sci., Part A: Polym. Chem. 2002, 40, 1504−
1510. (b) Fouassier, J. P.; Lougnot, D. J.; Li Bassi, G.; Nicora, C.
Polym. Commun. 1989, 30, 245−248. (c) Rosspeintner, A.; Griesser,
M.; Pucher, N.; Iskra, K.; Liska, R.; Gescheidt, G. Macromolecules
́
, J. Photoinitiators for Polymer Synthesis:
*TzPy + M → (TzPy − H)• + M(−H
)
•
(r8)
́
2009, 42, 8034−8038. (d) Lalevee, J.; Blanchard, N.; Fries, C.; Tehfe,
M. A.; Morlet-Savary, F.; Fouassier, J. P. Polym. Chem. 2011, 2, 1077−
1084. (e) Chen, Y.; Loccufier, J.; Vanmaele, L.; Frey, H. J. Mater.
Chem. 2007, 17, 3389−3392. (f) Jiang, X.; Luo, J.; Yin, J. Polymer
2009, 50, 37−41. (g) Bertens, F.; Qingjin, Y.; Gu, D. Proc. RadTech
Eur. 2005, 1, 471−478. (h) Yilmaz, G.; Aydogan, B.; Temel, G.; Arsu,
N.; Moszner, N.; Yagci, Y. Macromolecules 2010, 43, 4520−4526.
(i) Yilmaz, G.; Tuzun, A.; Yagci, Y. J. Polym. Sci., Part A: Polym. Chem.
2010, 48, 5120−5125. (j) Visconti, M.; Belloti, E.; Cattaneo, M. Proc.
RadTech Eur. 2005, 2, 313−318. (k) Visconti, M.; Cattaneo, M. Proc.
RadTech Eur. 2003, 1, 205−209. (l) Fuchs, A.; Bolle, T.; Ilg, S.; Husler,
R. Proc. RadTech Eur. 2003, 1, 507−511. (m) Herlily, S. Proc
RadTech, U. S. A., 2002, 1, 413−417; (n) Visconti, M. Proc. RadTech
USA 2002, 1, 1033−1037. (o) Corrales, T.; Catalina, F.; Peinado, C.;
Allen, N. S. J. Photochem. Photobiol. A. 2003, 159, 103−109.
(p) Angiolini, L.; Caretti, D.; Carlini, C.; Corelli, E.; Salatelli, E.
Polymer 1999, 40, 7197−7202. (q) Allonas, X.; Grotzinger, C.;
CONCLUSION
■
In the present paper, original trifunctional photoinitiators tPIs
comprising anthracenes, pyrenes and benzophenones as
peripheral chromophores of a triazine central core are
proposed. The strong molecular orbital coupling existing
between the peripheral chromophores and the triazine moiety
enabled to significantly improve the light absorption properties
of the new photoinitiators. The three-component (tPI/silane/
iodonium salt) systems in RP and CP and the two-component
(tPI/amine) combination in RP are more efficient than the
reference systems. Very soft irradiation conditions as well as
visible lights (Xe−Hg lamp, 365 nm LED, halogen lamp) can
be successfully employed. Some of these compounds can also
sensitize the thianthrenium salt decomposition; this can likely
be extended to other sulfonium salts. Development of triazine
based organic photocatalysts should likely be proposed in the
future. This work should also open the way to highly efficient
light harvesting photoinitiators where the PI/spacer coupling is
much more important.
Lalevee
902. (r) Pouliquen, L.; Coqueret, X.; Morlet Savary, F.; Fouassier, J. P.
, J.;
́
, J.; Fouassier, J. P.; Visconti, M. Eur. Polym. J. 2001, 37, 897−
Macromolecules 1995, 28, 8028−8035. (s) Dietlin, C.; Lalevee
́
Allonas, X.; Fouassier, J. P.; Visconti, M.; Li Bassi, G.; Norcini, G. J.
App. Polym. Sci. 2008, 107, 246−252.
(3) (a) Radiation Curing in Polymer Science and Technology;
Fouassier, J. P., Rabek, J. F., Eds., Chapman & Hall: London, 1993.
(b) Fouassier, J. P. Photoinitiation, Photopolymerization, Photocuring;
ASSOCIATED CONTENT
Hanser: Munich, 1995. (c) Crivello, J. V.; Dietliker, K. Photoinitiators
̈
■
for Free Radical, Cationic and Anionic Photopolymerization; Surface
Coatings Technology Series; Bradley, G., Ed.; Wiley: New York, 1999;
Vol. III. (d) Dietliker, K. A Compilation of Photoinitiators Commercially
Available for UV Today; Sita Technology Ltd.: London, 2002. (e)
Photoinitiated Polymerization; Belfied, K. D., Crivello, J. V., Eds.; ACS
Symposium Series 847; American Chemical Society: Washington DC,
2003. (f) Handbook of Vinyl Polymers; Mishra, M. K., Yagci, Y., Eds.,
CRC Press: Boca Raton, FL, 2009.
S
* Supporting Information
(i) Synthesis of thioxanthone−anthracene, (ii) UV−visible
absorption spectra of Py, Tz_Py, An, and Tz_An, (iii)
1
fluorescence quenching of Tz_Py by Iod1, (iv) fluorescence
1
quenching of Tz_Py by triethylamine, (v) photopolymeriza-
tion profiles of EPOX in the presence of Tz_Py/Iod2 and
Tz_Py/(TMS)3Si−H/Iod2, (vi) photopolymerization profiles
of EPOX in the presence of Tz_An/(TMS)3Si−H/Iod1 and
thioxanthone−anthracene/(TMS)3Si−H/Iod1, and (vii) pho-
topolymerization profiles of an EPOX/DVE blend in the
presence of Tz_An/Iod2.This material is available free of
charge via the Internet at http://pubs.acs.org.
(4) Visconti, M. In Photochemistry and UV Curing: new trends,
Fouassier, J. P., Ed., Research Signpost: Trivandrum, 2006; pp 153−
163.
(5) Almonasy, N.; Nepras, M.; Hykova, S.; Lycka, A.; Cerma, J.;
Dvorak, M.; Michl, M. Dyes Pigm. 2009, 82, 416−421.
(6) Castellanos, F.; Fouassier, J. P.; Priou, A.; Cavezzan, J. J. Appl. Sci.
1996, 60, 705−711.
(7) (a) Tehfe, M. A.; Lalevee
Gigmes, D.; Bertin, D.; Nechab, M.; Graff, B.; Morlet-Savary, F.;
Fouassier, J. P. Macromolecules 2012, 45, 4454−4460. (b) Lalevee, J.;
El-Roz, M.; Allonas, X.; Fouassier, J. P. J. Polym. Sci., Part A: Polym.
Chem. 2008, 46, 2008−2014. (c) Tehfe, M. A.; Lalevee, J.; Gigmes, D.;
Fouassier, J. P. Macromolecules 2010, 43, 1364−1370. (d) Tehfe, M.
A.; Lalevee, J.; Gigmes, D.; Fouassier, J. P. J. Polym. Sci., Part A: Polym.
Chem. 2010, 48, 1830−1837. (e) Souane, R.; Tehfe, M. A.; Lalevee, J.;
Gigmes, D.; Fouassier, J. P. Macromol. Chem. Phys. 2010, 211, 1441−
1445. (f) Lalevee, J.; Tehfe, M. A.; Gigmes, D.; Fouassier, J. P.
Macromolecules 2010, 43, 6608−6615.
(8) Lalevee, J.; Blanchard, N.; Tehfe, M. A.; Morlet-Savary, F.;
́
, J.; Telitel, S.; Contal, E.; Dumur, F.;
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: (J.L.) jacques.lalevee@uha.fr; (D.G.) didier.gigmes@
univ-provence.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. JL thanks the
Institut Universitaire de France for the financial support. The
authors thank G. Norcini (Lamberti Spa) for the gift of
recrystallized (4-hydroxyethoxyphenyl) thianthrenium hexaflor-
ophosphate (TH). The authors also thank Dr. Nicolas
Blanchard and Cedric Tresse (COB-UHA, Mulhouse, France)
for the preparation of the thioxanthone−anthracene.
Fouassier, J. P. Macromolecules 2011, 43, 10191−10195.
(9) (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.;
8646
dx.doi.org/10.1021/ma301931p | Macromolecules 2012, 45, 8639−8647

Macromolecules
Article
́
Tundo, A.; Zanardi, G. Chim. Ital. 1983, 113, 869−871. (e) Lalevee, J.;
Gigmes, D.; Bertin, D.; Graff, B.; Allonas, X.; Fouassier, J. P. Chem.
Phys. Lett. 2007, 438, 346−350.
(10) (a) Pappas, S. P. Progr. Org. Coatings 1985, 13, 35−64. (b) Hua,
Y.; Jiang, F.; Crivello, J. V. Chem. Mater. 2002, 14, 2369−2377.
(c) Crivello, J. V.; Jang, M. J. Photochem. Photobiol. A: Chem. 2003,
159, 173−188.
(11) (a) Lalevee
P. J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 3042−3047. (b) Tehfe,
M.-A.; Lalevee, J.; Allonas, X.; Fouassier, J. P. Macromolecules 2009, 42,
8669−8674.
́
, J.; Dirani, A.; El-Roz, M.; Allonas, X.; Fouassier, J.
́
(12) Bensasson, R. V.; Land, E. J. Trans. Faraday Soc. 1971, 67,
1904−1915.
(13) (a) Balta, D. K.; Arsu, N.; Yagci, Y.; Jockusch, S.; Turro, N. J.
Macromolecules 2007, 40, 4138−4141. (b) Balta, D. K.; Arsu, N.; Yagci,
Y.; Sundaresan, A. K.; Jockusch, S.; Turro, N. J. Macromolecules 2011,
44, 2531−2535.
(14) Lalevee
108, 4326−4334.
(15) Lalevee, J.; Blanchard, N.; Alloas, X.; Fouassier, J. P. J.
Organomet. Chem. 2008, 693, 3643−3649.
(16) Lalevee, J.; Graff, B.; Alloas, X.; Fouassier, J. P. J. Phys. Chem. A.
2007, 111, 6991−6998.
́
, J.; Allonas, X.; Fouassier, J. P. J. Phys. Chem. A. 2004,
́
́
8647
dx.doi.org/10.1021/ma301931p | Macromolecules 2012, 45, 8639−8647