Well-defined second-order nonlinear optical polymers by controlled radical polymerization, via multifunctional macromolecular chain transfer agent: Design, synthesis, and characterizations

Article abstract of DOI:10.1016/j.polymer.2013.12.059

To address the issue of the aggregation in second-order nonlinear optical (NLO) polymers we developed an approach based on the synthesis of a multifunctional macromolecular chain transfer agent. The controlled monomer insertion polymerization into the main chain by a 'reversible addition-fragmentation chain transfer' (RAFT) mechanism allows the spatial arrangement of the NLO chromophores along the polymeric chain in order to obtain sequence-ordered polymers. In a first step, a novel trithiocarbonate based macroinitiator containing the disperse red 19 (DR19) units in the main chain was synthesized by polycondensation; in a second step, this polymeric precursor was applied to the synthesis of a sequentially ordered polymer by controlled insertion radical polymerization of styrene. Size exclusion chromatography (SEC), nuclear magnetic resonance (NMR) data revealed that, (i) for the first time, polystyrenes (PS) bearing DR19 dyes covalently bounded were obtained, and (ii) both the insertion reaction and the length of the polystyrene segments were accurately controlled. Whatever the incorporated dye amount, all the copolymers were soluble in common solvents. Second-order optical nonlinearity in corona-poled thin films was evaluated, and second harmonic coefficients up to 80 pm/V were determined for loading ratio lower than 10 wt-% (DR19/PS). This approach opens up opportunities for the incorporation of more efficient chromophores even in apolar matrices.

Full text of DOI:10.1016/j.polymer.2013.12.059

Accepted Manuscript
Well-Defined Second-Order Nonlinear Optical Polymers by Controlled Radical
Polymerization, via Multifunctional Macromolecular Chain Transfer Agent: Design,
Synthesis, and Characterizations
Anne-Lise Roy, Chong Bui, Ileana Rau, François Kajzar, Bernadette Charleux, Maud
Save, David Kreher, André-Jean Attias
PII:
S0032-3861(13)01177-4
10.1016/j.polymer.2013.12.059
JPOL 16696
DOI:
Reference:
To appear in: Polymer
Received Date: 20 November 2013
Revised Date: 24 December 2013
Accepted Date: 27 December 2013
Please cite this article as: Roy A-L, Bui C, Rau I, Kajzar F, Charleux B, Save, M, Kreher D, Attias A-
J, Well-Defined Second-Order Nonlinear Optical Polymers by Controlled Radical Polymerization, via
Multifunctional Macromolecular Chain Transfer Agent: Design, Synthesis, and Characterizations,
Polymer (2014), doi: 10.1016/j.polymer.2013.12.059.
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ACCEPTED MANUSCRIPT
Well-Defined Second-Order Nonlinear Optical Polymers by Controlled
Radical Polymerization, via Multifunctional Macromolecular Chain
Transfer Agent: Design, Synthesis, and Characterizations.
Anne-Lise Roy, Chong Bui, Ileana Rau, François Kajzar, Bernadette Charleux, Maud Save,
David Kreher, André-Jean Attias*
S
B
B
Trithiocarbonate
1) Polycondensation
NLO Chromophore
derivative
+
A
S
S
A
S
S
S
S
S
S
S
S
S
S
S
S
MultifunctionalMacromolecular RAFT agent
2) Controled Monomer Insertion Polymerization
Monomer (spacer)
S
S
S
S
S
S
S
S
S
l
l
l
l
Controlled length
Controlled length

ACCEPTED MANUSCRIPT
Well-Defined Second-Order Nonlinear Optical Polymers by Controlled
Radical Polymerization, via Multifunctional Macromolecular Chain Transfer
Agent: Design, Synthesis, and Characterizations.
Anne-Lise Roy,1 Chong Bui,1 Ileana Rau,2 François Kajzar,2,3 Bernadette Charleux,4 Maud
Save,5 David Kreher, 1,6 André-Jean Attias1*
1 UMR 7610 CNRS – UPMC, Laboratoire de Chimie des Polymères, 3 rue Galilée, 94200 Ivry,
France.
andre-jean.attias@upmc.fr.
2 University POLITEHNICA of Bucharest, Faculty of Applied Chemistry and Materials Science,
Dept. of General Chemistry, 1 Polizu Street, 011061 Bucharest, Romania.
3 Institut des Sciences et Technologies Moléculaires d’Angers, MOLTECH Anjou – UMR
CNRS 6200, Université d’Angers, 2 bd Lavoisier, 49045 Angers Cedex, France.
4 Université de Lyon, Univ. Lyon 1, CPE Lyon, CNRS, UMR 5265, Laboratoire de Chimie,
Catalyse, Polymères et Procédés (C2P2), LCPP group, 43, Bd. du 11 Novembre 1918, F-69616
Villeurbanne, France.
5 CNRS, University of Pau & Pays Adour, UMR 5254, IPREM, Equipe de Physique et Chimie
des Polymères, 2 avenue du Président Angot, Pau, F-64053, France
6 ENSTA – Synthèse Organique et Réactivité, Ecole Polytechnique – UMR CNRS 7652, 91128
Palaiseau Cedex, France.
† Electronic supplementary information (ESI) available: The NLO set-up description is given,
this material being available free of charge.
1

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Abstract
To address the issue of the aggregation in second-order nonlinear optical (NLO) polymers we
developed an approach based on the synthesis of a multifunctional macromolecular chain
transfer agent. The controlled monomer insertion polymerization into the main chain by a
‘reversible addition-fragmentation chain transfer’ (RAFT) mechanism allows the spatial
arrangement of the NLO chromophores along the polymeric chain in order to obtain sequence-
ordered polymers. In a first step, a novel trithiocarbonate based macroinitiator containing the
disperse red 19 (DR19) units in the main chain was synthesized by polycondensation; in a
second step, this polymeric precursor was applied to the synthesis of a sequentially ordered
polymer by controlled insertion radical polymerization of styrene. Size exclusion
chromatography (SEC), nuclear magnetic resonance (NMR) data revealed that, (i) for the first
time, polystyrenes (PS) bearing DR19 dyes covalently bounded were obtained, and (ii) both the
insertion reaction and the length of the polystyrene segments were accurately controlled.
Whatever the incorporated dye amount, all the copolymers were soluble in common solvents.
Second-order optical nonlinearity in corona-poled thin films was evaluated, and second harmonic
coefficients up to 80 pm/V were determined for loading ratio lower than 10 wt-% (DR19/PS).
This approach opens up opportunities for the incorporation of more efficient chromophores even
in apolar matrices.
2

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Introduction
Organic second-order nonlinear optical (NLO) polymers have attracted considerable attention
in the past two decades for their potential applications in information processing and
telecommunications [1-2]. The interest in these materials derives from the high electro-optic (E-
O) coefficients (r33) measured with NLO chromophore-containing polymeric materials [3-4]. In
general, an E-O polymer system consists of NLO chromophores dispersed in a host matrix
(guest-host system) or covalently attached to a polymer backbone (side-chain polymer, main
chain polymer), the second-order nonlinear effect resulting from an asymmetric alignment of the
chromophores using electric field poling.
Currently, one of the most challenging task in the 2nd order NLO polymeric material
development is to efficiently translate molecular optical nonlinearity (β) into macroscopic
second-order NLO activity (second harmonic generation, electro-optic modulation, optical
rectification etc, that is to say to reduce chromophore-chromophore interactions in the bulk state)
[5-6]. First, a majority of the efforts addressing the improvement of the E-O polymer
performances have concentrated on the systematic design of chromophores with large
hyperpolarizability (β) [7]; second, beside increasing the number and efficiency of
chromophores, efforts were mainly devoted to improve poling efficiency.
In this purpose, several strategies have been proposed, such as either optimization of the guest-
host interactions in the case of doped polymers [8-9], or matrix/chromophore compatibility
improvement, or self-assembly, and/or shape engineering of the chromophores [10-13]. The
latter approach has been intensively studied through the nanoscale tailoring of NLO
chromophores and polymers leading to dendritic modified NLO chromophores [10, 14-17], side-
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chain dendronized NLO polymers [18-19], pendant diazobenzene NLO linear polymers [20-21]
or crosslinkable polymers via Diels-Alder type reaction for lattice hardening [22-26]. In the latter
case, the poled/cured polymers showed very large E-O coefficients (up to 263 pm/V at the
wavelength of 1.31 µm).
Here, we propose an alternative complementary way to minimize the chromophore-
chromophore interactions, based on controlled radical polymerization. To validate this approach,
we will use a non polar matrix (polystyrene, PS) which usually leads to poor solvatation of
highly polar chromophores, resulting in very low electro-optic (E-O) coefficients (r33) (0.5 for
10% wt chromophore ratio) [8]. This strategy enables us to expect the synthesis of polystyrene
containing NLO chromophore groups distributed homogeneously along the polymer chain and
separated by PS blocks with narrow dispersity.
Since their emergence in the nineties, the controlled radical polymerization (CRP) methods
[27], recently named by IUPAC reversible deactivation radical polymerization (RDRP) [28],
have known an increasing interest as they proved to be efficient methods to control the
macromolecular architectures (molar masses, narrow chain length distribution and topology)
while preserving the versatility and the easy implementation of radical polymerization. The
design of various polymers with complex topologies has been possible by the development of
different CRP techniques: nitroxide-mediated living free-radical polymerization (NMP) [29-30],
atom transfer radical polymerization (ATRP) [27, 31-32], reversible addition fragmentation
chain transfer (RAFT) [33-34], cobalt-mediated radical polymerization [35] and
organotellurium-mediated living radical polymerization (TERP) [36]. Among these methods,
RAFT and NMP allowed the synthesis of multisegmented polymers via the vinylic monomer
insertion into either a multifunctional polyalkoxyamine macro-initiator [37-39], or a
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multifunctional macromolecular RAFT agent [40-48]. Well-defined multiblock copolymers were
successfully prepared by this way [36-40, 46, 49]. Multisegmented polymers have also been
prepared by consecutive radical addition-coupling reaction of α,ω-macrobiradicals onto nitroso
compound [50], dithioester [51], dinitroxides [52] or by click chemistry of telechelic polymers
synthesized by RAFT and ATRP polymerization [53-54]. A theoretical study highlighted that
multiblock copolymers of higher homogeneity are rather prepared with RAFT strategy through a
polyfunctional chain transfer agent than with the commonly used coupling of functionalized
prepolymers [55]. The originality of the present study lies in the synthesis of a chromophore
based polyfunctional RAFT agent to implement the synthesis of a multisegmented polymer with
the block interconnected by the functional group.
Experimental section
Chemicals. All commercially available chemicals were used without further purification.
Solvents were carefully dried and distilled prior to use. All glassware was also heat-dried under
vacuum with a hot air gun before using. Reactions were performed under an inert atmosphere.
Column chromatography was performed on Geduran Silica 60 (40-63 µm, Merck). Styrene
(Acros, 99 %) was distilled under vacuum before use. Carbon disulfide (Acros, 99%),
nonahydrated sodium sulphur (Extra pur, Acros), methyltributylammonium chloride (Aldrich, 75
wt-% in water), 2-bromopropionyl bromide (Aldrich, 96%), Disperse Red 19 (Aldrich, 96 %),
triethylamine (Acros, 99 %), tetrabutylammonium hydrogensulfate (TBAHS, Aldrich, 97%),
azo-bis-isobutyronitrile (AIBN, Fluka, 98 %) were used as supplied.
Monomer Synthesis. Synthesis of Trithiocarbonate disodium in aqueous solution (1). Carbon
disulfide (6.6 g, 0.087 mol) was slowly added to a mixture of nonahydrated sodium sulfur (0.083
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mol), methyltributylammonium chloride (0.42 g, 1.8 mmol) and water (28 mL). After stirring for
one night at ambient temperature, a red aqueous solution was recovered and stored at 4 °C.
Synthesis of DR19-di-2-bromopropionate (2). 2-bromopropionyl bromide (13 mL, 0.121 mol)
in anhydrous tetrahydrofuran (50 mL) was added dropwise under stirring to a cooled solution
containing Disperse Red 19 (6.1 g, 0.018 mol) and triethylamine (17 mL, 0.121 mol) in 100 mL
anhydrous tetrahydrofurane. The solution was stirred at room temperature for 48h. Additional
water (100 mL) was added to dissolve the triethylamine bromohydrate salts. The organic phase
was extracted with diethyl ether, washed with a saturated aqueous solution of NaHCO3 (50 mL),
and water (3 × 50 mL) until neutral pH of the aqueous phase was reached, dried over MgSO4,
filtered and solvent was evaporated. The crude product was purified by column chromatography
on silica gel, using dichloromethane as an eluent, to give 7.5 g of a red solid (yield = 68 %).
1H NMR (CDCl3; 200 MHz) δ (ppm): 1.79 (d, 6H, 3J = 7.0 Hz, CH3), 3.83 (t, 4H, 3J = 6.2 Hz,
3
3
CH2-N), 4.43 (m, 6H, CH-Br, CH2-O), 6.87 (d, 2H, J = 9.2 Hz, CHarom), 7.93 (d, 2H, J = 9.2
Hz, CHarom), 7.95 (d, 2H, 3J = 9.2 Hz, CHarom), 8.35 (d, 2H, 3J = 9.2 Hz, CHarom).
Multifunctional Macromolecular RAFT Agent (MM-RAFT): synthesis of DR19-based
polytrithiocarbonate (3). The DR19-di-2-bromopropionate and the crude aqueous solution of
disodium trithiocarbonate were used for the synthesis of the desired DR19-based
polytrithiocarbonate by step polymerization. DR19-di-2-bromopropionate (2.08 g, 3.5 mmol),
tetrabutylammonium hydrogensulfate (240 mg, 0.7 mmol) as phase transfer catalyst, toluene (14
mL), and the solution of sodium trithiocarbonate in water (12 mL, 3.5 mmol) were introduced
into a round-bottom flask. The mixture was stirred at 60 °C for 72 h. The organic phase was
extracted with diethyl ether, washed with water (4 × 50 mL), dried over MgSO4, filtered and
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solvent was evaporated. The crude product was purified by column chromatography (diameter =
15 cm; height = 1 m) on silica gel, using a 1:1, v:v, cyclohexane:dichloromethane mixture, then
pure dichloromethane, then a 1:3, v:v, ethyl acetate:dichloromethane mixture as an eluent, to
give several fractions, one consisting in 1.2 g of a red solid (yield = 47 %). The fraction of
DR19-based polytrithiocarbonate recovered for subsequent RAFT polymerization of styrene
displayed the following macromolecular characteristics: Mn, MM-RAFT = 2690 g.mol-1, Mw/Mn =
1.20.
RAFT polymerization of styrene (4). A mixture of the prepared multifunctional
macromolecular RAFT agent (515 mg, 1.92 × 10-4 mol, Mn = 2685 g.mol-1, Mw/Mn = 1.20) and
AIBN in solution in dichloromethane (3.84 mL, 5.19 x 10-5 mol) was stirred for 5 min. After
evaporating the dichloromethane, distilled styrene (51.9 mL, 4.54 × 10-1 mol) was added. The
mixture was stirred for 30 min and subsequently poured into six tubes sealed with Rotaflo .
Oxygen was removed by five freeze-vacuum-thaw cycles. The tubes were immersed into an oil
bath thermostated at 70°C. Samples were withdrawn at regular time intervals (4 h, 8 h, 18 h and
48 h), quenched by cooling in water and exposed to air. After evaporating styrene under vacuum,
the crude sample was weighed to determine the monomer conversion. The crude polymer was
purified by dissolving into a minimum volume of dichloromethane prior to precipitation into
cold methanol (below 0 °C). The purified polymer was subsequently dried under vacuum and
characterized by SEC.
Techniques for chemical characterizations. Nuclear Magnetic Resonance (NMR)
Spectroscopy. 1H and 13C NMR spectra were recorded on a Bruker ARX 250 instrument or a
Bruker AC 200 instrument. Chloroform-d (CDCl3) or dimethyl sulfoxyde-d6 (DMSO-d6) were
used as the solvent. Size Exclusion Chromatography (SEC). The number-average molar mass
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(Mn), the weight-average molar mass (Mw) and the molar mass distributions (polydispersity
index = Mw/Mn) were determined by size exclusion chromatography using tetrahydrofuran
(THF) as eluent at a flow rate of 1 mL min-1. The SEC apparatus was a Triple Detector Array
(TDA, model 302 from Viscotek) equipped with both a refractive index detector and a
viscosimeter (online measurement of the intrinsic viscosity [η] by a Wheaston bridge) and three
Polymer Laboratories Mixed C columns (5 µm) thermostated at 40°C. The average molar masses
were derived from a universal calibration curve (Log([η].M) = f(Elution volume)) based on
polystyrene standards from Polymer Standards Service (separation limits: 260 – 2 × 106 g.mol-1).
The sample concentrations ranged from 7 to 10 mg/mL. The refractive index increment of the
macromolecular RAFT agent was measured online (dn/dc = 0.23 L.g-1). Thermal analysis.
Melting points were measured on a TA Instruments DSC 2920-Modulated DSC operating at 5
°C/min under nitrogen. UV-Visible spectroscopy. UV-Visible spectrophotometric analysis of the
polymers was performed in dichloromethane solution using a BIO-TEK Instruments UVIKON
923 spectrophotometer.
Film Preparation. Electrical Poling, and NLO Measurements. The studied thin films were
obtained from polymer solutions by the spinning technique. Polymers were dissolved in 1-1-2
trichloroethane and spread on the carefully cleaned glass substrates. The typically used angular
rotation speeds were 2000 tours/min, for both spreading and drying processes. After deposition
the films were additionally dried in an oven at 80°C for about 2 hrs in order to remove the
remaining solvent. The typical film thicknesses, measured with α tallystep, depending on
polymer concentration and spinning speed, ranged between 100 and 200 nm. Chromophores
were oriented by the corona poling technique and the SHG measurements were performed using
a set-up described in supporting information.
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Results and Discussion
In the present work, we propose the synthesis of a new multifunctional macromolecular RAFT
agent containing NLO chromophores (DR19) incorporated along the chain via polyaddition [56]
involving sodium trithiocarbonate and the dibromo derivative of the NLO chromophore (see
Scheme 1, product 3). The controlled insertion of polystyrene blocks into the DR19-based
multifunctional macromolecular RAFT agent was carried out by controlled radical
polymerization of styrene (Scheme 1, step 4). The polar orientation of chromophores was
obtained by the corona poling technique and the second order NLO properties were measured by
the optical SHG. This technique measures the fast, electronic origin second-order NLO
χ (p2p) (−2
ω;ω,ω) = 2dpp
(2)
sp
χ
(−2ω;ω,ω) = 2dsp
susceptibility tensor pp and sp components (
,
) where ω is the
fundamental beam frequency. It allows to determine also the electronic parts of other second-
order NLO susceptibilities of the studied material, including the electro-optic coefficient r.
In the present case the RAFT methodology was judiciously chosen for two reasons: a simple
modification (i.e. esterification) of the NLO chromophore was required for its incorporation into
the multifunctional macro-molecular RAFT agent and the RAFT mechanism can be
implemented under mild polymerization temperature (70°C) avoiding the chromophore
degradation.
For that purpose, an aqueous solution of trithiocarbonate disodium 1 was first obtained
according to literature [57]. The chromophore DR19 was treated with 2-bromopropionyl bromide
to afford the purified dibromo-compound 2 with a yield of 68%. The multifunctional
macromolecular RAFT Agent 3 (MM-RAFT) containing DR19 units in the main chain was
9

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prepared by polycondensation of the dibromo-DR19 2 with trithiocarbonate disodium 1 in the
presence of TBAHS as a phase transfer catalyst (Scheme 1).
OH
HO
NEt3, THF
O
O
N
N
Br
Br
N
N
Br
+
Br
3 days, room T.
O
O
O
N
N
DR19
NO2
NO2
TBAHS
Toluene / H2O
S
S
+
O
O
O
O
S
S
N
N
Br
N
N
Br
NaS
SNa
3 days, 55°C
O
O
O
O
(1)
n
(2)
(3)
N
N
NO2
NO2
RAFT polymerization of styrene (4)
T = 70°C, AIBN
S
O
O
S
S
N
N
m
m
O
O
n
N
NO2
Scheme 1. General synthetic scheme for the synthesis of NLO polystyrene by controlled radical
polymerization of styrene (4) via a DR19-based multifunctional macromolecular RAFT agent
(3).
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The polycondensation proceeded after mixing the monomers at 55°C for 3 days. The crude
product was then purified by column chromatography to afford a low-dispersity DR19-based
polytrithiocarbonate. The macromolecular characteristics of the resulting polymer 3 were
estimated by size exclusion chromatography (SEC) using universal calibration. A fraction with a
dispersity of 1.20 and number-average molar mass of 2690 g.mol-1 was used as macromolecular
RAFT agent for the controlled insertion of styrene via controlled radical polymerization. Styrene
was then polymerized at 70°C in bulk with 3 as a multifunctional macromolecular RAFT agent
(Scheme 1, Table 1) and 2,2‘-Azobis(2-methylpropionitrile) (AIBN) as initiator.
Table 1. Bulk Polymerization of Styrene mediated by RAFT Polymerization Using the DR 19-
based Polytrithiocarbonate as Multifunctional Macromolecular Transfer Agent (MM-RAFT):
characteristics of the recovered polymers containing the DR19 dye.
Sample
1
2
3
4
5
Time (h)
0
4
8
18
48
Conversion (%)
Mn (theoretical) b (g.mol-1)
Mn (SEC) (g.mol-1)
Mw/Mn
0
2.6
5.9
13.5
31030
21550
1.35
5.0
16.4
37040
27370
1.42
2.3
-
8000
3820
1.85
14.0
1.6
15080
12340
1.29
7.0
2690
1.20
-
c
Wt-%DR19
NDR19
2.6
2.0
1.9
a Experimental conditions: [Styrene] = 8.7 mol.L-1; [AIBN]0 = 1 × 10-3 mol.L-1; [MM-RAFT] = 3.7 × 10-3
mol.L-1; T = 70°C. b The theoretical molar mass of the styrene-based polymer was calculated as follows:
[
Styrene 0
]
Mn,theoretical = Mn,MM−RAFT
+
×conversion
× (1−e−k t
)
d
[MM −RAFT
]
0 + 0.6× AIBN 0
[
]
with kd the dissociation rate constant of the initiator (kd,AIBN,70°C = 4.72 × 10-5 s-1) [58], the factor 0.6
corresponds to the AIBN efficiency for bulk polymerization (reference [59]) and the factor indicating the
termination mechanism was considered equal to 1 as termination proceeds exclusively by combination for
c
styrene polymerization. Wt-%DR19 and NDR19 are respectively the weight percent of DR19 dye versus
copolymer mass and the average number of DR19 per copolymer chain. The molar concentration of
DR19 was calculated from the UV-visible absorbance (Abs) of the copolymer solution measured in
methylene chloride inside a cell of 1 cm2 using the Beer-Lambert law with εDR19 = 36 000 mol.L-1cm-1 at
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472 nm. The weight percent of DR19 in the polymer was calculated as follows:
100×
[
DR19
]
mol × MDR19
Wt − %DR19
=
with MDR19 = 330 g.mol-1 and [Polymer]wt = 0.1 g.L-1.
[
Copolymer wt
]
The low polymerization rate of styrene polymerization carried out at 70 °C in the presence of
the multifunctional RAFT agent was probably due to retardation phenomenon has already
observed in some cases with trithiocarbonate RAFT agents [60].
The polymerization of styrene was controlled as highlighted by the linear evolution of molar
masses (Mn) versus conversion (Figure 1) together with dispersity below 1.5. The higher value
of dispersity at low conversion is characteristic of CRP mechanism [61] and this phenomenon is
probably emphasized by the use of a relatively polydisperse multifunctional macromolecular
transfer agent.
40000
1.9
1.7
1.5
1.3
1.1
35000
30000
25000
20000
15000
10000
5000
0
0
0.05
0.1
0.15
0.2
Conversion
Figure 1. Evolution of Mn (plain) and Mw/Mn (empty) versus conversion for the polymerization
of styrene mediated by the DR19-based polytrithiocarbonate as “multifunctional
macromolecular” RAFT agent. [AIBN]0 = 1 × 10-3 mol.L-1; [MM-RAFT] = 3.7 × 10-3 mol.L-1; T
= 70°C. The plain line corresponds to the theoretical Mn.
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The experimental Mn determined by a universal calibration were always below the theoretical
Mn as displayed in Figure 1. The number of chains created by the initiator was considered for
the calculation of the theoretical Mn (see Table 1), so the negative deviation indicates that other
source than initiator is able to produce polymer chains. Thermal initiation of styrene
polymerization for such long polymerization time can be a source of additional radicals.
These results showed that well-defined polystyrene blocks were inserted into the
“multifunctional macromolecular” RAFT agent, hence suggesting a homogeneous distribution of
the DR19 units along the polymer backbone. The polymers were analyzed by UV-visible
absorption spectroscopy and we observed a maximum wavelength (λmax) at 455 nm in
dichloromethane, which corresponds to the λmax of DR19. The weight fraction of DR19 in the
functional polymer could then be determined from the measured absorbance of these solutions at
455 nm (Table 1). The DR19 weight fraction logically decreased with the increase of styrene
conversion, corresponding to the increase of styrene content through the controlled growth of PS
blocks within the polymer.
Linear and non linear optical properties have been measured on thin films spin-coated from
1,1,2-trichloroethane (100 g.L-1). Regarding linear optical properties, UV-visible absorption
spectra (Figure 2) revealed that the films had a maximum absorption wavelength λmax of 458
nm. Extinction coefficients and the real parts of ordinary (no) and extraordinary (ne) thin film
refractive indices for the three studied concentrations are also displayed in Figure 2.
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Figure 2. Wavelength dependence of the extinction coefficients k (solid lines, LHS) and indices
of refraction (RHS) for studied thin films. Closed figures show ordinary (no) and open
extraordinary (ne) index of refraction, respectively. The highest curve and triangles correspond to
the most concentrated films (7.0 wt %) whereas the lowest and diamonds to the less concentrated
(2.3 wt %).
First, increasing the chromophore concentration leads to higher extinction coefficients values,
as expected. Moreover, the observed Fabry-Perrot interference patterns behind the optical
absorption spectra (λ > 600 nm) are fingerprints of a good thin film thickness homogeneity and
low roughness (see supporting information).
The NLO properties of thin films were evaluated as follows. The films were poled by corona
poling at 110 °C. Their second-order NLO susceptibilities, dsp and dpp, measured by the optical
second harmonic generation are reported in Table 2 for the two series of films at different
chromophore concentrations.
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For weight concentrations of DR19 lower than 7 %, the second harmonic generation (SHG)
coefficients (dsp and dpp) increase linearly with the chromophore concentration (see also Figure
SI-3 in Supporting Information). This observation is in favor of the absence (or limited) of
aggregation in synthesized functional polymers [5, 62]. More precisely, very few studies
previously reported the introduction of chromophores parent to DR19 into a polystyrene matrix
in this range of DR19 weight concentrations. For instance, the Disperse red 1 (DR1)
chromophore embedded into a polystyrene matrix led to a low dpp value of 0.85 pm.V-1
characteristic of an aggregation phenomenon (see Supporting Information).8
Table 2: Second -order NLO susceptibilities dsp and dpp values of two thin polymer films (1
and 2) containing the DR19 chromophore at different weight fractions. The precision in d
coefficient is ±10%.
Wt- % DR19
2.3
5.0
7.0
dsp 1 (pm.V-1)
dpp 1 (pm.V-1)
a1 = dpp1/dsp1
dsp 2 (pm.V-1)
a2 = dpp2/dsp2
dpp 2 (pm.V-1)
12.9
34.6
2.7
14.9
58.6
3.9
28.6
76.8
2.7
7.8
13.7
3.6
17.7
4.2
3.7
28.8
49.5
74.7
In Table 2 we also listed the values of the ratio of two tensor components: a = dpp / dsp .
Within the experimental accuracy, the values are close to 3, as usually observed in poled
polymers. This result is a finger print of a moderate poling and agrees well with value predicted
from gaz model of non-interacting chromophores.
15

ACCEPTED MANUSCRIPT
Conclusions
In summary, we demonstrated that our chosen strategy based on controlled radical
polymerization via a macromolecular multifunctional RAFT agent allows the synthesis of well-
defined NLO polymers. More precisely, NLO chromophores are homogeneously distributed
along the polymer backbone. Moreover, in spite of the non polar character of the polystyrene
matrix, quite high dsp and dpp values have been obtained, without any aggregation evidence.
These values are similar to the ones observed with poly(methyl methacrylate) (PMMA) matrix
showing a similar DR19 chromophore loading amount ( 10 wt-%). To conclude, the present
synthetic strategy allows the controlled NLO chromophores insertion along the polymer
backbone and solves the problem of aggregation in non polar matrices. Because of the versatility
of the strategy, we offer a promising route to incorporate more efficient chromophores in a well-
defined manner in other matrices such as PMMA for instance. More generally, this approach can
be used in other fields where avoiding aggregation remains a key issue.
Acknowledgments
Authors F. K. and I. R. acknowledge the support of European Social Fund through the
Sectorial Operation Programme Increasing Economical Competitivity, under POS CCE nr. 634,
SMIS 12575. This work was supported by the French National Agency (ANR), within
LUVORGAN project.
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Electronic Supplementary Information
Well-Defined Second-Order Nonlinear Optical Polymers by Controlled
Radical Polymerization, via Multifunctional Macromolecular Chain Transfer
Agent: Design, Synthesis, and Characterizations.
Anne-Lise Roy, a Chong Bui, a Ileana Rau, d François Kajzar, d,e Bernadette Charleux, c Maud
Save, b David Kreher, a,f André-Jean Attias* a
a UMR 7610 CNRS – UPMC, Laboratoire de Chimie des Polymères, 3 rue Galilée, 94200 Ivry, France. E-mail:
andre-jean.attias@upmc.fr.
b IPREM Equipe de Physique et Chimie des Polymères, UMR 5254 CNRS, Université de Pau et des Pays de
L’Adour, Hélioparc, 2 Avenue du Président Angot, 64053 Pau Cedex, France.
c Chemistry, Catalysis, Polymers and Processes (UMR 5265), Université de Lyon, Bât. F308, B.P. 2077, 43 Bd du
11 Nov. 1918, 69616 Villeurbanne Cedex, France,
d
University POLITEHNICA of Bucharest, Faculty of Applied Chemistry and Materials Science, Dept. of General
Chemistry, 1 Polizu Street, 011061 Bucharest, Romania,
e
Institut des Sciences et Technologies Moléculaires d’Angers, MOLTECH Anjou – UMR CNRS 6200, Angers
University, 2 bd Lavoisier, 49045 Angers Cedex, France
f ENSTA – Synthèse Organique et Réactivité, Ecole Polytechnique – UMR CNRS 7652, 91128 Palaiseau Cedex,
France
Experimental
Figure SI-1 shows the propagation length dependence of the scattered light from the planar
waveguide made of studied films.
10 mm
10 mm
10 mm
Figure SI-1. Propagation length dependence of scattered light from planar waveguide at 830
nm.
The derived optical propagation losses are listed in Table SI-1. The propagation losses increase
with the chromophore concentration, as it is already observed in Figure SI-1, where the
attenuation of the propagated light is the largest for the most concentrated film.
Chromophore
concentration
Propagation
(dB/cm)
2.3
6.8
5
1
7.1
12.
losses
0
7
Table SI-1: Propagation losses in studied films at 830 nm

ACCEPTED MANUSCRIPT
We observe increase of propagation losses with concentration . Most likely it is due to two
factors:
(i)
residual absorption of chromophores (measurements are done at 830
nm, thus not very far from the absorption band) and absorption of
harmonics of O-H and C-H vibrations
(ii)
Light scattering by aggregates
(iii)
Residual impurities
It is well known that strong dipole-dipole interaction of dipolar CT chromophores leads to their
aggregation, thus to large propagation losses. However the aggregation effect strongly increases
with the chromophore concentration. If it was the case of propagation losses we should observe
much larger propagation losses at higher chromophore concentration. We observe a less than
proportional increase, what is in favour of second point.
Impurities may contribute to the scattering losses too. Although our polymers were carefully
purified, we cannot exclude their presence in. They may either absorb and/or scatter light..
Chromophores were oriented by the corona poling technique :1
To remember, usually in corona poling method, a high voltage (6-8 kV) applied to a needle
electrode distant by 1.5 to 2.5 cm from the thin film surface creates the ionization of the
surrounding atmosphere. The second bottom electrode is planar (usually ITO covered glass plate,
on which is deposited the poled film). The substrate supporting the thin film is put on a heating
block and the film is heated close to the glass transition temperature to increase the orientational
mobility of poled chromophores. Depending on the sign of the potential applied to the needle
electrode, positive or negative charges are created and cover the thin film surface, creating a large
electric field between the thin film surface and the bottom electrode. Usually the poling time is
short, a few minutes and the created polar order is afterwards frozen by cooling the film to room
temperature. More details can be found in reference 3.
Concerning our setup, in order to increase the chromophore rotational mobility, the films were
heated to the glass transition temperature. Than a high voltage of 6-8 kV was applied to the
needle electrode, distant by about 15 mm from the poled film (Figure SI-2). The corona
discharge ionizes the air around the electrode and depending on the sign of the applied electric
field to the needle electrode those of the same sign are repelled and deposited on the film surface
creating a large (~ 2-3 MV/cm) electric field inside. As said before, the bottom electrode usually
is a thin layer of ITO, but the conductivity of BK7 glass used here is sufficient, so the glass
substrate itself acts as electrode. The metallic grid, located between the film and the needle
electrode (Figure SI-2) serves to control the poling current (for details see reference 2).
mA
mA
HV
NEEDLE
ELECTRODE
METALLIC
GRID
mA
mA
HV
++++++++++++++++++++++++++
THIN FILM
ELECTRODE
SUBSTRATE
HEATING BLOCK
Figure SI-2. Schematic representation of the corona poling set up (note 3)

ACCEPTED MANUSCRIPT
The optical absorption spectra of thin films were collected using a UV-VIS Perkins Elmer
spectrophotometer, model lambda 16. The thin film propagation losses were determined by
imaging the scattered light from the planar waveguide. Its refractive indices were measured by m-
lines technique using standard Metricon prism coupler system.
The SHG measurements were performed using a set-up described in reference 4 (cf. also Rau and
5
Kajzar ). The light source is a Q switched Neodymium doped Yttrium Aluminium Garnet
(Nd:YAG) laser, operating at 1 064.2 nm fundamental wavelength with pulse duration of 13
nanoseconds and 10 Hz repetition rate. The sample was mounted on a goniometer and rotated
along an axis perpendicular to the beam propagation direction, coinciding with it. The SHG
intensities were collected as function of the incidence angle. The input polarization was set by
using a half wave plate, whereas the generated harmonic field polarization by a polarizer in fixed
position, selecting p harmonic beam. In order to get the two nonzero tensor components for poled
(2)
XXZ
(2)
χ
= 2dsp
χ
= 2d
ZZZ
films with point symmetry ∞mm:
and
pp , the measurements were done in
s-p and p-p fundamental – harmonic beam polarization. Here Z is the direction perpendicular to
the film and X is within in the laboratory reference frame, respectively. For the f and h
fundamental –harmonic beam polarization configuration the SHG intensity is given (cf reference
4 as well as the work of Swalen and Kajzar.6 )
2
32π 3
c2
χ
(−2ω;ω,ω)
ffh
(2)
2
ϕ ffh
2
ei∆ −1 Iω2
(1)
ffh
ω
I2
(θ
) =
Tfh (θ
)Afh (
θ
)
∆ε
where Tfh (θ) and Afh (θ) are, respectively, incidence angle dependent factors arising from
transmission and boundary conditions, Iω is the incident light intensity and ∆ϕ is the phase
mismatch between the fundamental and harmonic beam in the studied film, given by
4
π l
f
f
∆ϕ ffh
=
ϕω
−
ϕ 2h
=
(
nωf cosθω − n2 cosθ2h
)
(2)
ω
ω
ω
λω
f (h)
θω
(2ω)
where ω(2ω) refers to the fundamental (harmonic) frequency, respectively.
are
propagation angles in nonlinear medium for f(h) polarization of the beam with frequency ω(2ω),
respectively.
The effective χ(2)
susceptibilities in Eq. (1), for a given fundamental –harmonic beam
IJK
polarization configurations contain the projection factors and are given by
(2)
ssp
χ
(−2ω
;
ω
,
ω
) = 2dsp sin 2θωs cosθ2s
(3)
ω
for s-p fundamental harmonic beam polarization, and
(2)
ppp
p
p
p
p
χ
(−2ω;ω,ω )
) = 2d pp sin2 θωp sinθ2 + 2ds(p cosθωp (cosθω + 2sinθω cosθ2
(4)
ω
ω
where we took account of the usually used notations for the second order NLO susceptibility
tensor components: ) = 2dsp (−2 and
χ X(2X)Z (−2
χ Z(2Z)Z (−2
) = 2d pp (−2 . Equations (3) - (4) show that the determination of both
ω
;
ω
,
ω
ω;ω,ω)
ω
;
ω
,
ω
ω;ω,ω)

ACCEPTED MANUSCRIPT
tensor components requires two independent measurements in s-p and p-p fundamental –
harmonic beams polarization configurations. First measurements gives the off diagonal value
(2)
χ s(p2) . The second (p-p) configuration measurements will yield the diagonal
χ
susceptibility,
pp
(2)
injecting the previously determined value of
χ
into Eq. (4).
sp
The SHG intensities were calibrated with SHG measurements performed on an y-cut slab of α-
quartz. For the calibration we used the value reported by Choy and Byer (d11 = 0.5 pm/V).7
As detailed in the article, for weight concentrations of DR19 lower than 7 %, the second
harmonic generation (SHG) coefficients (dsp and dpp) increase linearly with the chromophore
concentration (see Figure SI-3). Moreover, even taking into account of the experimental
uncertainty (± 10 %) we observe a chromophore concentration dependence of both dsp and dpp
coefficients. This observation is in favor of the absence (or limited) of aggregation in synthesized
functional polymers.
Figure SI-3. Second -order NLO susceptibilities dsp and dpp of the thin polymer films containing
the DR19 chromophore at different weight concentrations fractions. The precision in d coefficient
determination is ±10%. Evolution of (dsp and dpp) NLO coefficients of polymers as a function of
the DR19 loading density.
Calculation procedure of dpp value for reference 8 of the article (Banach, M. J.; Alexander, M.
D.; Caracci, S.; Vaia, R. A. Chemistry of Materials 1999, 11, 2554-2561):
In this precedent study, very small electro-optic coefficient r33 of 0.4 pm/V was measured by the
modulated ellipsometry technique at 780 nm wavelength, in thin film of polystyrene containing
10 wt% concentration of disperse red 1 (DR1) chromophore. The relationship between the
electro-optic (EO) χ(2)(−ω;ω,0) susceptibility and the electro-optic coefficient rpp (Burland, D.;
Miller, R.; Walsh, C. Chem. Rev. 1994, 94, 31) is as follows:
n4'
χ (p2p) (−
ω
;
ω
,0) =
rpp (−ω;ω,0)
2
where n is the index of refraction at ω frequency and taking n = 1.62 (cf. Fig 2 of the article) one
gets χ (p2p) (−
ω
;
ω
,0) = 1.7 pm/V. Assuming that both susceptibilities EO and SHG are close
,0) ), dpp was calculated to be 0.85 pm.V-1.
(2)
pp
(2)
pp
(
χ
(−2ω
;
ω
,
ω
) ≈
χ
(−ω;ω

ACCEPTED MANUSCRIPT
1 Comizzoli, B. J. Electrochem. Soc.: Solid Science and Technology 1987, 134: 424.
2 Kajzar, F.; Lee, K.-S.; Jen, A; K.-Y. Advances in Polymer Science 2002, 161, 1.
3
from F. Kajzar and J.-M. Nunzi, Molecule Orientation Techniques, in Beam Shaping and Control with Nonlinear
Optics, F. Kajzar and R. Reinisch, Eds, NATO ASI Series, Series B : Physics, vol. 369, Plenum Press, New York
1998, pp. 101-132)
4 Rau, I.; Armatys, P.; Chollet, P.-A.; Kajzar, F.; Andraud, C.; Bretonnière, Y. Linear and nonlinear optical properties
of a new guest host system, Nonl. Opt. Quant. Opt., 35, 57-67, (2007).
5 I. Rau and F. Kajzar, Second harmonic generation an its applications, Nonl. Opt. Quant. Opt.,38, 99-140(2008)
6
J. Swalen and F. Kajzar. Introduction, in Organic Thin Films for Waveguiding Nonlinear Optics, F. Kajzar and J.
Swalen Eds, Gordon & Breach Sc. Publ., Amsterdam 1996, pp. 1-44
7 Choy, M.; Byer, R. L. Phys. Rev. B. 1976, 14, 1693.