Photoinitiators based on a phenazine scaffold: High performance systems upon near-UV or visible LED (385, 395 and 405 nm) irradiations

Article abstract of DOI:10.1016/j.polymer.2014.04.005

Novel photoinitiators based on a phenazine scaffold are proposed for the ring opening polymerization of epoxy monomers as well as the free radical polymerization of (meth)acrylates. Good to excellent polymerization profiles can be obtained upon different easily accessible, energy saving and cheap LEDs (385, 395 and 405 nm) as well as a diode laser at 405 nm or halogen lamp opening new fields for polymer synthesis upon soft and convenient irradiations. These compounds can be particularly attractive as high performance photoinitiators in the 350-425 nm range. The initiation mechanisms are investigated in detail through fluorescence, cyclic voltammetry, steady state photolysis and electron spin resonance (ESR) experiments.

Full text of DOI:10.1016/j.polymer.2014.04.005

Polymer 55 (2014) 2285e2293
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Photoinitiators based on a phenazine scaffold: High performance
systems upon near-UV or visible LED (385, 395 and 405 nm)
irradiations
Mohamad-Ali Tehfe a, Frédéric Dumur b, Pu Xiao a, Jing Zhang a, Bernadette Graff a,
,
a
,
b
,
,
*
Fabrice Morlet-Savary a, Didier Gigmes b , Jean-Pierre Fouassier 1, Jacques Lalevée a
*
a Institut de Science des Matériaux de Mulhouse IS2M, UMR CNRS 7361, UHA, 15, rue Jean Starcky, 68057 Mulhouse Cedex, France
b Aix-Marseille Université, CNRS, Institut de Chimie Radicalaire, UMR 7273, F-13397 Marseille Cedex 20, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel photoinitiators based on a phenazine scaffold are proposed for the ring opening polymerization of
epoxy monomers as well as the free radical polymerization of (meth)acrylates. Good to excellent poly-
merization profiles can be obtained upon different easily accessible, energy saving and cheap LEDs (385,
395 and 405 nm) as well as a diode laser at 405 nm or halogen lamp opening new fields for polymer
synthesis upon soft and convenient irradiations. These compounds can be particularly attractive as high
performance photoinitiators in the 350e425 nm range. The initiation mechanisms are investigated in
detail through fluorescence, cyclic voltammetry, steady state photolysis and electron spin resonance
(ESR) experiments.
Received 27 February 2014
Received in revised form
22 March 2014
Accepted 3 April 2014
Available online 15 April 2014
Keywords:
Phenazine
Photoinitiators
LEDs
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
FRPCP upon highly attractive near UV or visible LED lights. Phena-
zines PHs are encountered in e.g. the medical area (see e.g. Ref. [4]),
The photoinitiating systems PISs play an important role in free
radical polymerization (FRP), thiol-ene polymerization (TEP),
cationic polymerization (CP) or free radical promoted cationic
polymerization (FRPCP) and interpenetrated polymer networks
(IPN) synthesis (see e.g. in Refs. [1,2]). Huge efforts are devoted to
the design of UV, visible and near IR sensitive PISs working upon
exposure to monochromatic or polychromatic lights, under high or
low intensity sources, in laminate, inert atmosphere or under air
(Ref. [3] and references therein) The search for novel skeletons or
novel derivatives of existing structures operating in more and more
complicated experimental conditions required by the industrial
applications is a fascinating topic. Particularly, the recent develop-
ment of cheap, energy saving and easily accessible LEDs operating
upon soft irradiations has opened new fields for polymer synthesis.
In the frame of our works on the design of PISs, we propose here to
develop phenazine derivatives as photoinitiators (PI) of FRP, CP and
optics (see e.g. Ref. [5]), photoconductive materials (see e.g. Ref. [6]),
solar cells and photovoltaics (see e.g. Refs. [7,8]). They have been
mentioned in the photopolymerization area (in FRP as additives, see
e.g. Refs. [9e11]; in CP as photosensitizers for the decomposition of
onium salts, see e.g. Refs. [12e16]; in solid-state photo-
polymerization, see e.g. Ref. [17]). More recently, synthetized benzo
[2,3-b]ephenazines were found to be quite efficient photo-
sensitisers in radical as well as cationic polymerization processes
[18] but upon high intensity Xenon lamp exposure.
In the present paper, we will revisit this kind of scaffold and
synthesize new derivatives (Scheme 1), check their ability (when
incorporated in various PISs) in photopolymerization reactions
induced under soft lights delivered by near UV LEDs (385 and
395 nm). Additional lights (low intensity laser diode@405 nm and
halogen lamp; higher intensity (w100 mW/cm2) LED@405 nm) will
also be used. High performance initiating systems will be proposed
for radical and cationic polymerizations and for the synthesis of
interpenetrated polymer networks. The photochemical mecha-
nisms of the initiation species formation will be investigated by
steady state photolysis, fluorescence, cyclic voltammetry, and
electron spin resonance spin trapping, and laser flash photolysis
techniques.
* Corresponding authors. Institut de Science des Matériaux de Mulhouse IS2M,
UMR CNRS 7361, UHA, 15, rue Jean Starcky, 68057 Mulhouse Cedex, France.
E-mail addresses: didier.gigmes@univ-amu.fr (D. Gigmes), jacques.lalevee@uha.
fr (J. Lalevée).
1
Formerly: UHA-ENSCMu, 3 rue Alfred Werner, 68093 Mulhouse, France.
http://dx.doi.org/10.1016/j.polymer.2014.04.005
0032-3861/Ó 2014 Elsevier Ltd. All rights reserved.

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M.-A. Tehfe et al. / Polymer 55 (2014) 2285e2293
Scheme 1.
2. Experimental section
The reaction mixture was then filtered and the blue-violet solid was
washed with water and pentane. The solid was then treated with
refluxing 30% nitric acid (20 mL) for 3 h. Upon cooling, no precip-
itate formed. The solution was poured into water. The yellow solid
was filtered off, and dissolved in DCM. The organic phase was dried
over magnesium sulfate and the solvent removed under reduced
pressure. The solid was purified by dissolution in a minimum of
DCM and precipitation with pentane (1.92 g, 86% yield). 1H NMR
2.1. Synthesis of the different photoinitiators
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. tubes
on a Bruker Avance 400 spectrometer of the Spectropole: 1H
(400 MHz) and 13C (100 MHz). The 1H chemical shifts were refer-
enced to the solvent peak CDCl3 (7.26 ppm) and the 13C chemical
shifts were referenced to the solvent peak CDCl3 (77 ppm). All these
dyes were prepared with analytical purity up to accepted standards
for new organic compounds (>98%) which was checked by high
field NMR analysis. Diquinoxalino[2,3-a:20,30-c]phenazine PH_1,
(CDCl3)
d (ppm): 7.55e7.74 (m, 6H), 7.78e7.99 (m, 5H), 8.27e8.47
(m, 2H), 8.50e8.59 (m, 4H), 8.68e8.84 (m, 4H), 8.88e8.98 (m, 3H);
HRMS (ESI MS) m/z: theor: 697.1983 found: 697.1981 ([M þ H]þ
detected); Anal. Calc. for C45H24N6O3 : C, 77.6; H, 3.5; O, 6.9; Found:
C, 77.7; H, 3.4; O, 6.8%.
2.1.2. Synthesis of 6,7,15,16-tetramethylquinoxalino[20,30:9,10]phe-
nanthro[4,5-abc]phenazine PH_4
Pyrene-4,5,9,10-tetraone (0.5 g, 1.91 mmol) and 4,5-dimethyl-
1,2-diaminobenzene (0.65 g, 4.77 mmol, 2.5 eq.) were suspended in
acetic acid (50 mL) and the solution was refluxed for 48 h. After
cooling, the solvent was removed under reduced pressure. Water
was added and the precipitate was filtered off, washed with water
and pentane. The solid was dissolved in concentrated HNO3 (10 mL)
and the solution was refluxed overnight. After cooling, the orange
precipitate was filtered off, washed with pentane and dried under
[19]
2,3,8,9,14,15-hexamethyldiquinoxalino[2,3-a:20,30-c]phena-
zine PH_2 [20] were synthesized according to literature pro-
cedures. Pyrene-4,5,9,10-tetraone used for the synthesis of PH_2
was synthesized as previously reported, without modification and
in similar yield [21].
vacuum (0.81 g, 92% yield). 1H NMR (CDCl3)
d (ppm): 2.59 (s, 12H),
7.99e8.10 (m, 6H), 9.53 (s, 4H); HRMS (ESI MS) m/z: theor:
458.2035 found: 458.2037 (Mþ. detected); Anal. Calc. for C36H26 : C,
94.3; H, 5.7; Found: C, 94.5; H, 5.5%.
2.1.1. Synthesis of diquinoxalino[2,3-a:20,30-c]phenazine-2,8,14-
triyltris(phenylmethanone) and diquinoxalino[2,3-a:20,30-c]
phenazine-2,8,15-triyltris(phenylmethanone) PH_3
2.2. Chemical compounds
N-vinylcarbazole
(NVK),
diphenyliodonium
hexa-
fluorophosphate (Ph2Iþ or Iod), N-methyldiethanolamine (MDEA),
phenacylbromide (ReBr), tris(trimethylsilyl)silane ((TMS)3SiH) and
2,4,6-tris(trichloromethyl)-1,3,5-triazine (Tz or R0-Cl) were ob-
tained from Aldrich with the best purity available and used as
received (Scheme 2). (3,4-epoxycyclohexane)methyl 3,4-
epoxycyclohexylcarboxylate
(EPOX;
Uvacure
1500)
and
trimethylol-propane triacrylate (TMPTA) were obtained from Cytec
(Scheme 2); these monomers were selected as benchmark multi-
functional monomers for cationic and radical polymerizations,
respectively. The formation of polymer networks at room temper-
ature is expected preventing a full conversion of the reactive
functions [1]. The polymerization of methacrylates was also
investigated: bisphenol A-glycidyl methacrylate (Bis-GMA) and
triethyleneglycol dimethacrylate (TEGDMA) were obtained from
Aldrich and used with the highest purity available.
Hexaketocyclohexane octahydrate (1 g, 3.2 mmol) and 3,4-
diaminobenzophenone (2.04 g, 9.6 mmol, 3 eq.) were refluxed in
1:1 glacial acetic acid/ethanol (50 mL) at 140 ꢀC for 24 h. After
cooling, the solution was concentrated until a precipitate formed.
2.3. Irradiation sources
Several lights were used: i) polychromatic light from a halogen
lamp (Fiber-Lite, DC-950 e incident light intensity: I0 z 12 mW/

M.-A. Tehfe et al. / Polymer 55 (2014) 2285e2293
2287
Scheme 2.
cm2; in the 370e800 nm range); ii) monochromatic light delivered
2.6. Computational procedure
by a laser diode at 405 nm (I0 z 2 mW/cm2) and iii) LEDs @385 and
395 nm (ThorLabs; I0 z 10 mW/cm2) and @405 nm (ThorLabs;
All the molecular orbital (MO) 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 [23]. The
geometries were frequency checked.
I
0 z 110 mW/cm2).
2.4. Free radical photopolymerization (FRP) of acrylates
The experiments were carried out in laminated conditions or
under air. The prepared formulations deposited on a BaF2 pellet
(25
mm thick) were irradiated (see the irradiation devices). The
2.7. ESR spin trapping (ESR-ST) experiments
evolution of the double bond content was continuously followed by
real time FTIR spectroscopy (JASCO FTIR 4100) at about 1630 cmꢁ1
as in Ref. [22].
The ESR-ST experiments were carried out using an X-Band
spectrometer (MS 400 Magnettech). The radicals were produced at
RT upon a light exposure (see the irradiation devices) under N2 and
trapped by phenyl-N-tert-butylnitrone (PBN) according to a pro-
cedure described in detail in Ref. [24]. The ESR spectra simulations
were carried out with the PEST WINSIM program.
2.5. The ring opening polymerization of epoxy
The photosensitive formulations were deposited (25 mm thick)
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 cmꢁ1, respectively [22].
2.8. Fluorescence experiments
The fluorescence properties of the compounds were studied
using a JASCO FP-750 spectrometer.
2.9. Redox potentials
The redox potentials (vs. SCE) were measured in acetonitrile by
cyclic
voltammetry
with
tetrabutyl-ammonium
hexa-
fluorophosphate 0.1 M as a supporting electrolyte. The free energy
Table 1
Molar extinction coefficients (in Mꢁ1 cmꢁ1) of PH_1 to PH_4 at typical irradiation
device wavelengths (LEDs @365, 385, 395 or 405 nm or laser diode@405 nm).
LED@365 nm
LED@385 nm
LED@395 nm
Laser diode
or LED@405 nm
PH_1
PH_2
PH_3
PH_4
16 300
8100
17 100
10 300
19 000
9100
20 900
14 100
17 900
10 300
19 100
20 050
19 100
9980
19 600
15 300
Fig. 1. UVevisible absorption spectra of PH_1, PH2, PH_3, PH_4 in CHCl3.

2288
M.-A. Tehfe et al. / Polymer 55 (2014) 2285e2293
Fig. 2. Molecular Orbitals involved in the lowest energy transition.
change
DGet for an electron transfer reaction is calculated from the
the coulombic term for the initially formed ion pair, respectively. C
classical Rehm-Weller equation (Eq. (1)) [25] where Eox, Ered, Es and
C are the oxidation potential of the donor, the reduction potential of
the acceptor, the excited state energy (singlet or triplet state) and
is neglected as usually done in polar solvents [26].
D
Get ¼ Eox ꢁ Ered ꢁ ES þ C
(1)
Fig. 3. Photolysis of (A) PH_2/Iod; (B) PH_3/Iod; (C) PH_4/Iod upon a laser diode@405 nm for irradiation times of 0, 1, 3 and 5 min; [Iod] ¼ 0.037 M in acetonitrile/chloroform 25 V/
75 V.

M.-A. Tehfe et al. / Polymer 55 (2014) 2285e2293
2289
Table 2
Table 3
Oxidation potentials (Eox); singlet state energy levels (ES1 from the UV and fluo-
rescence spectra); triplet state energy levels (ET1 calculated at UB3LYP/6-31G* level)
Free Radicals observed in ESR spin-trapping experiments for different photo-
initiating systems in tert-butylbenzene (spin trap ¼ PBN).
and free energy changes D
Get for the 1PH/Iod and 3PH/Iod interactions.
Photoinitiating
system
PBN radical
adduct
Hyperfine coupling
constants hfcs
PH
ES1
(eV)
ET1
(eV)
Eox
(V) SCE
D
Get
DGet
(1PH/Iod) (eV)
(3PH/Iod) (eV)
PH/Iod
PH/Iod/NVK
PH/Iod/(TMS)3SiH
Phꢂ
aN ¼ 14.2 G; aH ¼ 2.2 G
aN ¼ 14.5 G; aH ¼ 2.5 G
aN ¼ 14.8 G; aH ¼ 5.5 G
PH_1
PH_2
PH_3
PH_4
3.01
2.93
2.96
2.91
2.39
2.38
2.25
2.2
Ph-NVKꢂ
(TMS)3Siꢂ
a
a
a
0.61
0.32
0.67
ꢁ2.12
ꢁ2.44
ꢁ2.04
ꢁ1.57
ꢁ1.73
ꢁ1.33
a
The solubility is poor in acetonitrile preventing accurate electrochemistry
the rate constant of interaction and the fluorescence lifetime,
respectively). The electron transfer quantum yield FeT for r1a
measurements.
calculated according to FeT ¼ kq
1PH_4/Iod (FeT w 0.5 for [Iod] w 0.07 M in polymerization ex-
periments e see below). The Get for r1a (Table 2) were evaluated
s
0 [Iod]/(1 þ kq
s
0 [Iod])1 is high for
3. Results and discussion
D
3.1. Light absorption properties of the different PHs
according to the Rehm-Weller equation (Eq. (1)). A reduction po-
tential of ꢁ0.2 V was used for Ph2Iþ according to the literature value
[1]. A triplet state pathway can not be ruled out i.e. the associated
The UVeVis absorption spectra of the proposed PHs are depic-
ted in Fig. 1; the maximum absorption wavelengths are gathered in
Table 1. All these proposed structures exhibit good to excellent light
absorption properties in the 350e425 nm; their respective
extinction coefficients for typical irradiation devices (LEDs @365,
385, 395, 405 nm or laser diode@405 nm) are gathered in Table 1.
Molecular orbital MO calculations show that the lowest energy
D
Get(3PH/Iod) being also highly negative (see Table 2).
transition exhibits a
p / p* character and involves strongly
delocalized molecular orbitals (Fig. 2) in full agreement with the
enhanced light absorption properties of these derivatives
compared to the phenazine which exhibit only UV light absorption
i.e. the associated absorption spectrum presents band at 365 nm
with shoulders at 351 and 387 nm [27].
3.2. Photoreactivity for the PH/iodonium salt systems
The PH/Iod solutions are characterized by photolysis experi-
ments upon light exposure; this behavior is clearly observed upon a
diode laser@405 nm exposure in Fig. 3. For PH_1/Iod, no photolysis
is detected. For a similar absorption at 405 nm, the photolysis rate
follows the series PH_3 w PH_4 >> PH_2 or PH_1. A similar trend
is observed for the polymerization rate (see below) when using the
PH/Iod based initiating systems.
This very fast photolysis is in agreement with a favorable
reduction process (r1a). Accordingly, a strong 1PH_4/Iod fluores-
cence quenching is shown with a SterneVolmer coefficient kq.
Fig. 5. Photolysis of a PH_4/MDEA solution upon a laser diode@405 nm for irradiation
times of 0, 1, 3, 5 and 10 min; [MDEA] ¼ 0.1 M in chloroform.
s0 ¼ 16.5 Mꢁ1 (Fig. 1 in supporting information; kq and
s0 stand for
a
b
a
b
3320
3330
3340
3350
3360
3370
3310
3320
3330
3340
3350
3360
3370
B (G)
B (G)
Fig. 6. ESR-Spin Trapping spectrum of PH_2/ethyldimethylaminobenzoate;
LED@395 nm exposure; experimental (a) and simulated (b) spectra. Phenyl-N-tert-
butylnitrone (PBN) is used as spin trap; under N2. The hyperfine coupling constants are
aN ¼ 14.3 G; aH ¼ 2.4 G for the PBN adduct of the aminoalkyl radical in agreement with
[28].
Fig. 4. ESR-Spin Trapping spectrum of PH_2/Iod; LED@395 nm exposure; experi-
mental (a) and simulated (b) spectra. Phenyl-N-tert-butylnitrone (PBN) is used as spin
trap; under N2. The hyperfine coupling constants hfcs are aN ¼ 14.2 G; aH ¼ 2.2 G for
the PBN adduct of phenyl radical in agreement with [28].

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M.-A. Tehfe et al. / Polymer 55 (2014) 2285e2293
Phꢂ þ NVK / Ph-NVKꢂ
(r1d)
(r1e)
Phꢂ þ (TMS)3SiH / Ph-H þ (TMS)3Siꢂ
a
b
3.3. Photoreactivity of the PH/amine systems
The PH/amine solutions are characterized by an efficient
photolysis upon a diode laser@405 nm (Fig. 5). This photolysis is
associated with the observation of aminoalkyl radicals in ESR-spin
trapping experiments (Fig. 6) in agreement with r2. Accordingly,
strong 1PH/amine fluorescence quenchings are observed (Fig. 2 in
supporting information) e.g.
a SterneVolmer coefficient kq.
3320
3330
3340
3350
3360
3370
s0 ¼ 5.5 Mꢁ1 is found for 1PH_4/MDEA; the associated electron
transfer quantum yield FeT for r2 is very high (w0.6) for
[MDEA] w 0.25 M in polymerization experiments.
B (G)
Fig. 7. ESR-Spin Trapping spectrum of PH_2/phenacylbromide; LED@395 nm expo-
sure; experimental (a) and simulated (b) spectra. Phenyl-N-tert-butylnitrone (PBN) is
used as spin trap; under N2. The hyperfine coupling constants are aN ¼ 14.6 G;
aH ¼ 4.4 G for the PBN adduct of the phenacyl radical in agreement with [28].
1,3PH þ MDEA / PHꢂꢁ þ MDEAꢂþ / PH-Hꢂ þ MDEAꢂ(ꢁH)
(r2)
In the PH/amine/phenacylbromide (ReBr) three-component
system, the phenacyl radical is also clearly observed in the ESR-
spin trapping experiments (Fig. 7). This shows the occurrence of
r3 in addition to r2. Using Tz (noted R0-Cl in Scheme 2) instead of Re
Br, a similar behavior can be expected.
(r1a) being favorable for all the PHs, the difference observed in
their photolysis rates can be ascribed to a back electron transfer
process (r1b) that is affected by the PH structure.
1,3PH þ Ph2Iþ / PHꢂþ þ Ph2Iꢂ
PHꢂþ þ Ph2Iꢂ / PH þ Ph2Iþ
Ph2Iꢂ / Phꢂ þ Ph-I
(r1a)
(r1b)
(r1c)
1,3PH þ ReBr (or R0-Cl) / PHꢂþ þ (ReBr)ꢂꢁ (or R0-Clꢂꢁ
)
(r3a)
(r3b)
(r3c)
PH-Hꢂ þ ReBr (or R0-Cl) / PH þ Hþ þ (ReBr)ꢂꢁ (or R0-Clꢂꢁ
)
ꢂ
ReBrꢂꢁ (or R0-Cl) / Rꢂ þ Brꢁ (or R0 þ Clꢁ)
The processes r1a, r1c are also in agreement with the observa-
tion of phenyl radicals upon irradiation of the four PH/Iod solutions
in ESR-spin trapping experiments (Fig. 4).
3.4. The initiation steps using the PH based photoinitiating systems
In the PH/Iod/NVK three-component system, Ph-NVKꢂ radicals
are observed in agreement with (r1d) (Table 3). In PH/Iod/(TMS)3
For the ROP of epoxides, PHꢂþ can be considered as the initiating
species when using the PH/Iod combinations (see r1a). In the PH/
-
SiH, silyl radicals ((TMS)3Siꢂ) are formed (r1e) (Table 3).
Fig. 8. ROP profiles of EPOX under air upon (A) a LED@385 nm exposure in the presence of (1) PH_3/Iod (0.5%/3% w/w); (2) PH_4/Iod (0.5%/3%/3% w/w); (3) PH_3/Iod/(TMS)3SiH
(0.5%/3%/3% w/w); (4) PH_4/Iod/(TMS)3SiH (0.5%/3%/3% w/w). (B) A LED@395 nm lamp exposure in the presence of (1) PH_4/Iod (0.5%/3% w/w); (2) PH_4/Iod/(TMS)3SiH. Insert:
conversion of SieH for run (2).

M.-A. Tehfe et al. / Polymer 55 (2014) 2285e2293
2291
Fig. 9. ROP profiles of EPOX under air upon a halogen lamp exposure in the presence of (A) (1) PH_4/Iod (0.5%/3% w/w); (2) PH_4/Iod/NVK (0.5%/3%/3% w/w); (B) conversion of NVK
for run (2) in (A).
Iod/NVK and PH/Iod/(TMS)3SiH three-component systems, Ph-
NVKꢂ and (TMS)3Siꢂ are oxidized by the iodonium salt to generate
the Ph-NVKþ and (TMS)3Siþ cations, respectively. These latter
species are very efficient to initiate a ring opening polymerization
(ROP). The relative efficiencies of the different PH/Iod/NVK (or
(TMS)3SiH) combinations (see below) should be affected by i) the
relative PH light absorption properties, ii) the radical or radical
cation formation quantum yields, iii) the possible back electron
transfer (r1b) and iv) the relative ability of PHꢂþ to initiate a ROP
process.
The aminoalkyl and phenacyl radicals generated in the PH/
amine or PH/amine/phenacylbromide systems through r2, r3 can
initiate the FRP. The relative PH light absorption properties as well
as the radical formation quantum yields in r2 and r3 will affect the
performance of the PH in the different systems.
coatings are obtained. The efficiency of the different phenazine
derivatives decreases in the series PH_3wPH_4 >> PH_1, PH_2.
3.6. Free radical photopolymerization of acrylates and
methacrylates
The conversion-time profiles of TMPTA in laminate under a
diode laser@405 nm are shown in Figs. 10e12. Only the PH_3 and
PH_4 based three-component systems (PH/MDEA/ReBr) lead to
good polymerizations (Fig. 10 curves 5 and 6; final tack-free coating
with PH_4/MDEA/RBr). The efficiency decreases in the series
PH_4 > PH_3 >> PH_2, PH_1. Interestingly, in the PH/MDEA/alkyl
halide three-component systems, the 2,4,6-tris(trichloromethyl)-
1,3,5-triazine (Tz) is an additive better than the phenacylbromide
(Fig. 11, curve 1 vs. curve 2; a tack free coating is obtained).
The PH_3/MDEA/Tz (0.5%/3%/3% w/w) system is also excellent to
initiate radical polymerization of acrylates upon LED@405 nm
(Fig. 12). The intensity of this latter LED (w110 mW/cm2) ensures
excellent polymerization profiles. The performance of this PH_3/
MDEA/Tz system for the polymerization of methacrylates (i.e. Bis-
GMA/TEGDMA blend (70%/30%, w/w)) is also remarkable with a
final conversion of w60% under air (Fig. 12) i.e. this demonstrates
the high performance of this initiating system to overcome the
oxygen inhibition.
3.5. ROP of EPOX
The conversion-time profiles of EPOX under air under exposure
to LEDs or a halogen lamp are shown in Figs. 8 and 9; the conver-
sions reached after 1000 s of irradiation are gathered in Table 4.
When using the different PH/Iod initiating systems, the poly-
merization does not occur (e.g. Fig. 8A curves 1 and 2; Table 4). This
shows the low ability of PHꢂþ generated in r1a to initiate a ROP
process. The presence of NVK or (TMS)3SiH drastically improves the
polymerization profiles (e.g. Fig. 8A curve 1 vs. curve 3 and Table 4)
i.e. the cations Ph-NVKþ and (TMS)3Siþ are now the initiating
species. The consumption of the SieH and NVK functions (Figs. 8B
and 9B) in the course of the photopolymerization is in line with r1d
and r1e. With PH_3 (or PH_4)/Iod/NVK (or (TMS)3SiH), tack free
Table 4
Final conversion reached after 1000 s of irradiation using different photoinitiating
systems.
PISs (0.5%/3% w/w or
0.5%/3%/3% w/w)
LED@385
nm
LED@395 nm
Laser diode
@405 nm
Halogen
lamp
PH_1/Iod or PH_1/Iod/
(TMS)3SiH
PH_2/Iod or PH_2/Iod/
(TMS)3SiH
np
np
np
np
np
np
PH_3/Iod
np
np
np
PH_3/Iod/(TMS)3SiH
PH_3/Iod/NVK
PH_4/Iod
PH_4/Iod/(TMS)3SiH
PH_4/Iod/NVK
50%
35%
np
48%
38%
52%
52%
np
57%
np
50%
np
60%
52%
Fig. 10. FRP profiles of TMPTA in laminated conditions upon exposure to a laser
diode@405 nm in the presence of (1) PH_1/MDEA/RBr; (2) PH_2/MDEA/RBr (0.5%/3%/
3% w/w); (3) PH_3/MDEA; (4) PH_4/MDEA (0.5%/3% w/w); (5) PH_3/MDEA/RBr; (6)
PH_4/MDEA/RBr (0.5%/3%/3% w/w).
np: No polymerization.

2292
M.-A. Tehfe et al. / Polymer 55 (2014) 2285e2293
60
Acrylate
Epoxide
50
40
30
20
10
0
0
200
400
600
800
1000
Time (s)
Fig. 11. FRP profiles of TMPTA in laminate upon exposure to a laser diode@405 nm in
the presence of (1) PH_4/MDEA/RBr or (2) PH_4/MDEA/Tz (0.5%/3%/3% w/w).
Fig. 13. Polymerization profiles of an EPOX/TMPTA blend (50%/50% w/w) upon a
halogen lamp exposure in the presence of PH_4/Iod/NVK (0.5%/3%/3% w/w); in
laminate.
3.7. Synthesis of interpenetrated polymer networks (IPNs)
delocalized molecular orbitals are promising for the development
of other derivatives exhibiting a red-shifted absorption.
The synthesis of IPNs was also carried out (Fig. 13). High con-
versions for both the acrylate and the epoxide functions were ob-
tained using the PH_4 (or PH_3)/Iod/NVK system; tack free
coatings). The formations of free radicals and cations (see above)
ensure the simultaneous radical and ROP processes.
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.
4. Conclusion
This paper shows that novel phenazine derivative based three-
component photoinitiating systems allow efficient radical poly-
merization of TMPTA, cationic polymerization of EPOX and TMPTA/
EPOX interpenetrated polymer network synthesis upon exposure
to easily accessible, energy saving and cheap LEDs at 385, 395 and
405 nm as well as a laser diode at 405 nm or a halogen lamp. Their
photochemical reactivity toward the production of initiating spe-
cies is rather good. Their excellent absorption properties in the
380e425 nm range resulting from the presence of strongly
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.polymer.2014.04.005.
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