Development of new nonlinear optical polymers based on epoxy- amine oligomers with Bi-chromophore fragments in the side chain

Article abstract of DOI:10.1016/j.polymer.2018.07.007

For the first time bichromophore nonlinear optically active compounds, 3,5-bis [2- (N-ethyl-4- (4′-nitrophenylazo) anilino) ethoxy] benzyl alcohol, DF1, and 3,5-bis [6- (N-methyl-4- (4′-nitrophenylazo) anilino) hexaoxy] benzyl alcohol, DF2, have been synthesized. The synthesis of the epoxy-amine oligomers containing DF1 and DF2 dendritic fragments in the side chain was preceded by molecular design which demonstrated that the hexyl groups, binding the chromophores to the branching center in DF2, are able to provide greater mobility of the chromophores compared to the ethyl groups in DF1, thus determining the preference of the former from the viewpoint of NLO activity. Bi-chromophore compounds were introduced into the side chain of epoxy amine oligomers using the esterification reaction under mild conditions by the Steglich method. As a result, oligomers OAB-DF1 (Tg = 122 °C) and OAB-DF2 (Tg = 107 °C) were obtained with good yields, the degree of functionalization was 60 mol% and 45 mol%, respectively. The values of the NLO coefficients, d₃₃, were measured by second harmonic generation technique; they are equal to 29 pm/V for OAB-DF1 and 40 pm/V for OAB-DF2.

Full text of DOI:10.1016/j.polymer.2018.07.007

Polymer 149 (2018) 253e265
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Development of new nonlinear optical polymers based on epoxy-
amine oligomers with Bi-chromophore fragments in the side chain
Gulshat N. Nazmieva, Tatiana А. Vakhonina, Nataliya V. Ivanova, Anastasiya V. Sharipova,
*
Olga D. Fominykh, Maxim A. Smirnov, Marina Yu Balakina , Oleg G. Sinyashin
Arbuzov Institute of Organic and Physical Chemistry, FRC Kazan Scientific Center of RAS, Arbuzov str., 8, Kazan, 420088, Russian Federation
a r t i c l e i n f o
a b s t r a c t
0
Article history:
Received 19 March 2018
Received in revised form
For the first time bichromophore nonlinear optically active compounds, 3,5-bis [2- (N-ethyl-4- (4 -
0
nitrophenylazo) anilino) ethoxy] benzyl alcohol, DF1, and 3,5-bis [6- (N-methyl-4- (4 -nitrophenylazo)
anilino) hexaoxy] benzyl alcohol, DF2, have been synthesized. The synthesis of the epoxy-amine oligo-
mers containing DF1 and DF2 dendritic fragments in the side chain was preceded by molecular design
which demonstrated that the hexyl groups, binding the chromophores to the branching center in DF2,
are able to provide greater mobility of the chromophores compared to the ethyl groups in DF1, thus
determining the preference of the former from the viewpoint of NLO activity.
Bi-chromophore compounds were introduced into the side chain of epoxy amine oligomers using the
esterification reaction under mild conditions by the Steglich method. As a result, oligomers OAB-DF1
(Tg ¼ 122 C) and OAB-DF2 (Tg ¼ 107 C) were obtained with good yields, the degree of functionalization
was 60 mol% and 45 mol%, respectively. The values of the NLO coefficients, d33, were measured by second
harmonic generation technique; they are equal to 29 pm/V for OAB-DF1 and 40 pm/V for OAB-DF2.
27 June 2018
Accepted 2 July 2018
Available online 3 July 2018
Keywords:
Epoxy-amine oligomers
Bi-chromophore compounds
Nonlinear optical coefficients
ꢀ
ꢀ
©
2018 Elsevier Ltd. All rights reserved.
1
. Introduction
exceeded, detrimental dipole-dipole interactions (DDI) may cause
the chromophores partial aggregation, resulting in the decrease of
the quadratic NLO response [2,8].
In recent decades, there is intense interest of researchers in
organic polymeric materials exhibiting nonlinear optical (NLO)
response to the applied electric field. Primarily, this is due to the
possibility of using these materials in telecommunications, digital
signal processing, THz generators and photonic devices [1e6]. The
quadratic NLO response of polymer materials originates at the
molecular level due to organic chromophores introduced into the
polymer matrix either as guest molecules or as fragments cova-
lently attached to the bearing chain [2e6]. For the manifestation of
a quadratic NLO activity, the chromophores should be non-
centrosymmetrically organized in the polymer material what is
achieved by their orientation in the applied static electric field [3,6].
The optimal value of NLO response and its relaxation stability are
the key characteristics that must be ensured when developing such
materials [3,7]. Polymer quadratic susceptibility determining the
NLO characteristics depends on the chromophores concentration in
a matrix; when some threshold value of chromophores content is
Over the past decade, new approaches have been developed to
avoid this undesirable effect and to ensure the optimal macroscopic
chromophores order in the polymer matrix. In particular, re-
searchers focus on the following approaches: the use of linear
polymers with bichromophore fragments in the side chain [9], the
use of branched polymers containing NLO chromophores as pe-
ripheral groups [10e13] and of dendronized polymers [6,14e20], or
the combination of the latter two strategies consisting in the
introduction via covalent coupling of dendritic NLO fragments into
the hyperbranched polymers [21]. The structure of such materials
provides spatial separation of chromophores, limiting their unde-
sirable DDI. The second approach involves the use of dendrimers
with a spherical form or dendronized linear polymers having in the
side chain chromophore-containing dendrons of different genera-
tions and structure; most of the works are devoted to the synthesis
of either multichromophore dendrimers [22e25] or dendritic
chromophores with isolating groups [26e28]. The synthesis and
electrooptic (EO) properties of dendronized polymers based on
polyimide with multichromophore dendrons of the second gener-
ation are presented in Refs. [29,30]; at the chromophores content
*
Corresponding author.
E-mail address: mbalakina@yandex.ru (M.Y. Balakina).
https://doi.org/10.1016/j.polymer.2018.07.007
032-3861/© 2018 Elsevier Ltd. All rights reserved.
0

254
G.N. Nazmieva et al. / Polymer 149 (2018) 253e265
5
8 wt% the EO coefficient r33 ¼ 32 pm/V is measured. Along with
N-methylaniline was purified by distillation on a water jet pump
from a flask equipped with a needle reflux condenser, selecting the
multichromophore dendronized polymers, polymers containing
modified dendrons carrying one chromophore and several isolating
groups located in the branches of the dendron have been developed
ꢀ
25
fraction with T
b
¼ 76 C/10 mm. Hg; n
D
¼ 1.5710.
0
4,4 -Methylenediisocyanate (MDI) was purified by recrystalliza-
tion from hexane according to the technique [47].
[
10e13,31e33]; pentafluorophenyl, adamantyl, carbazole bulk
groups, as well as various branched alkyl fragments have been used
as isolating groups [15,31]. However, despite the positive effect
resulting in the decrease of detrimental DDI, the introduction of
isolating groups may lead to an undesirable reduction in the NLO
activity of the material, if it results in the decrease in the concen-
tration of chromophores; besides, it may cause the complication of
the poling process because of the large volume of the dendritic
chromophore-containing groups [31].
The new approach aimed at the development of NLO materials
exploits linear block copolymers with dendritic chromophore-
containing fragments; in such copolymers linear polymer blocks
are responsible for solubility and good film-forming properties, and
the dendritic block - for the manifestation of the NLO effect [34]. In
Refs. [35,36] the study of linear-diblock copolymer [poly(styrene-b-
1,3-Dicyclohexylcarbodiimide (DCC) was purified by fractional
distillation under reduced pressure on the oil pump, selecting the
ꢀ
fraction with T
b
¼ 95e100 C/0.1 mm. Hg.
Bisphenol A diglycidyl ether (DGEBA) from ACROS Organics with
99% substance content, 4-Dimethylaminopyridine from ACROS Or-
ganics with 99% substance content, N-ethyl, -N-hydroxyethylaniline
from ACROS Organics with a substance content of 96%, 6-
chlorohexane-1-ol from ACROS Organics with a substance content
95%, 1,3-dichloropropane-2-ol from ACROS Organics with a sub-
stance content of 99%, were used without preliminary purification.
4-Nitrobenzenediazonium tetrafluoroborate was synthesized ac-
cording to the procedure described in Ref. [48].
2.2. Synthesis of bi-chromophore compounds
4
-vinylpyridine)] and linear-dendritic (poly(methyl methacrylate)-
0
dendron) block copolymer with chromophores coupled via
hydrogen bonding was described.
2.2.1. Synthesis of 3,5- bis[2- (N-ethyl-4- (4 -nitrophenylazo)
anilino) ethoxy] benzyl alcohol (DF1)
For the development of NLO materials epoxy-amine oligomers
and polymers are widely used due to the easy synthesis, relatively
high glass transition temperature (about 130 C), good film-
For the synthesis of dendritic compound DF1 the procedure was
elaborated with the account of those described in Refs. [43,49,50].
ꢀ
forming properties, and processability of the resulting materials.
The synthesis of epoxy amine oligomers is based on the poly-
addition reaction between the epoxy and amino groups, diglycidyl
esters of various structures and aniline being most often used as
monomers After further modification of the polymer, for example,
azo-coupling reaction with various diazotizing agents, one obtains
NLO polymers with aniline as a donor moiety of the chromophore,
that is chromophores donor group becomes the part of the polymer
backbone [37e42]. Such polymers exhibited rather high values of
the NLO coefficient: up to 60 pm/V when a chromophore with nitro
group is used [42] and up to 66 pm/V in the case of a chromophore
with a tricyanovinylene acceptor group [37]. As already noted, the
value of the NLO coefficient depends on many factors, in particular,
on the effectiveness of poling, which, in its turn, is determined by
the local mobility of the chromophore groups in the polymer ma-
trix. The introduction of chromophores into the main chain of the
polymer matrix somewhat limits the mobility of NLO-active units.
This has led to the assumption that the introduction of chromo-
phores into the side chain of the polymer through the spacer
groups will increase the mobility of chromophores, which, in turn,
will allow to perform more effective poling. The introduction of
NLO-active fragments into the side chain of the oligomer requires
the presence of reactive groups. Earlier on the basis of diglycidyl
ether of bisphenol A (DGEBA) and p-aminobenzoic acid (p-ABA), we
synthesized a new reactive polyether polyol OAB [43,44], into
which using polymer-analogous reactions various NLO-units were
incorporated. The bi-chromophore fragments of various structures
were shown to be effective in the search for new NLO-active moi-
eties with improved physical-chemical properties [45,46]. Here we
use epoxy-amine oligomers with bichromophore moiety in the side
chain for the development of polymer NLO material.
2.2.1.1. N-ethyl-N (2-chloroethyl) aniline. The procedure described
in Ref. [49] was used to prepare N-ethyl-N (2-chloroethyl) aniline. A
solution of POCl (3.30 g, 0.021 mol) in 10 mL of THF was added
3
dropwise to a solution of N-ethyl-N- (2-hydroxyethyl) aniline
(5.00 g, 0.03 mol) in THF under intensive stirring at room temper-
ature for one hour. The reaction mixture was stirred for 4 h. The
solvent was evaporated, the residue was diluted with an aqueous
solution of NaHCO
3
2 2
, the product was extracted with CH Cl (20 mL).
The extract was dried over MgSO
4
, filtered, and the solvent was
distilled off in a vacuum of a water jet pump. The product was
purified by vacuum distillation, selecting the fraction with
ꢀ
T
b
¼ 65e73 C/0.4 mm Hg. Yield: 3.5 g (60%), a liquid of a yellow
color was obtained.
1
H NMR (400 MHz, acetone d
6
;
d
, ppm; J, Hz): 1.14 (t, 3H, -CH
3
,
J ¼ 7.1), 3.45 (q, 2H, N-CH
2
-CH
3
, J ¼ 7.1), 3.66 (s, 4H, -N-CH
2
CH -Cl),
2
6.63 (t, 1Н, p-Ar-H(-N), J ¼ 8.9), 6.72 (d, 2Н, o-Ar-H(-N), J ¼ 8.9), 7.17
(t, 2Н, m-Ar-H(-N), J- 8.9).
2.2.1.2. Synthesis of 3,5-bis[2-(N-ethylanilino)ethoxy] benzyl alcohol.
A mixture of N-ethyl-N- (2-chloroethyl) aniline (4.04 g, 0.022 mol),
3,5-dihydroxybenzyl alcohol (1.40 g, 0.010 mol), anhydrous potas-
sium carbonate (10 g), potassium iodide (0.5 g) and 30 mL of
ꢀ
acetone was heated at 56 C under an argon atmosphere with
intense stirring for 48 h. The reaction mixture was poured into
500 mL of water, the product was extracted with CH Cl (20 mL).
2 2
The extract was concentrated to 5 mL and precipitated with pe-
ꢀ
troleum ether. The precipitate was filtered off and dried at 70 C in a
vacuum oven for 48 h and purified by recrystallization. Yield 1.3 g
ꢀ
1
(30%), transparent crystals were obtained, T
NMR (400 MHz, acetone d , ppm; J, Hz): 1.21 (t, 6Н, -СН
3.48 (m, 4H, N-CH -CH ), 3.71 (t, 4H, N-CH CH
-O, J ¼ 7.1), 4.11 (t,
H, N-CH CH -OH), 6.32 (s, 1Н, V-Ar-
-O, J ¼ 5.9), 4.59 (s, 2H, Ar-CH
Н(СН ОН)), 6.47 (s, 2Н, o-Ar-Н(СН ОН)), 6.78 (t, 2Н, V-Ar-Н(N), J
m
¼ 110 C (toluene). H
6
;
d
3
, J ¼ 7.0),
2
3
2
2
4
2
2
2
2
. Materials and methods
2
2
7.3), 6.94 (d, 4Н, o-Ar-Н(N), J 7.9), 7.28 (t, 4Н, m-Ar-Н(N), J 7.3).
2.1. Materials
2.2.1.3. Synthesis of DF1. Into the solution of 3,5-bis [2- (N-ethyl-
Solvents used in the work, THF, DMF, hexane, cyclohexanone,
acetone, chloroform, methylene chloride, ethyl acetate, butanol,
anilino) ethoxy] benzyl alcohol (0.11 g, 0.253 mmol) in 3 mL of DMF
the estimated quantity of 4-nitrobenzenediazonium tetra-
fluoroborate (0.13 g, 0.558 mmol) was introduced under stirring.
After 10 and 30 min in two portions sodium acetate (0.04 g,
were purified by standard procedures. p-Aminobenzoic acid was
ꢀ
recrystallized twice from water, Т
m
¼ 191 С.

G.N. Nazmieva et al. / Polymer 149 (2018) 253e265
255
0
.506 mmol) was added. The reaction mixture was stirred at room
(m, 4Н, O-CH
10 J 7.4), 3.96 (t, 4H, O-CH
6.37 (t, 1Н, p-Ar-Н(СН ОН), J 7.4), 6.68 (d, 2H, o-Ar-Н(СН
2
-CH
2
-C
4
H
8
N) 2.92 (s, 6H, -CH
-C 10-, J 6.5), 4.69 (s, 2Н, Ar-CH
ОН), J 7.2),
3
), 3.34 (t, 4H, N-CH
2
-
temperature for 3 h. The reaction mass was precipitated into water,
the precipitate was filtered off, dried in a vacuum oven, and the
product was purified by recrystallization. Yield: 0.105 g (56%), dark
C
5
H
2
5
H
2
OH),
2
2
6.92 (d, 4Н, o-Ar-Н(N), J 8.7), 7.88 (d, 4H, o-Ar-Н(N¼N), J 8.7), 7.92
ꢀ
1
red crystals, M
ppm; J, Hz): 1.26 (t, 6Н, -СН
H, N-CH CH -O, J 7.1), 4.16 (t, 4H, NCH
CH -OH), 6.40 (c, 1Н, V-Ar-Н(СН ОН)), 6.75 (s, 2Н, o-Ar-Н(СН
.92 (d, 4Н, -Ar-Н(N), J 8.3), 7.88 (d, 4Н,
Н, m-Ar-Н(N¼N), J 8.3), 8.33 (d, 4Н,
p
¼ 172 C (toluene). Н NMR (400 MHz, THF-d
, J 7.0), 3.64 (m, 4H, N-CH -CH ), 3.85 (t,
CH -O, J 5.8), 4.71 (s, 2H, Ar-
ОН)),
8
; d,
(d, 4H, m-Ar-Н(N), J 8.7), 8.33 (d, 4Н, m-Ar-Н(N¼N), J 8.7).
3
2
3
45 52 8 7
C H N O , Calculated %: С 64.04; Н 6.82; N 14.57. Obtained, %: С
4
2
2
2
2
63.70; Н 6.87; N 15.05.
2
2
2
6
4
о
о
-Ar-Н(N¼N), J 8.3), 7.92 (d,
2.3. Synthesis of oligomers
о
-Ar-Н(N), J 8.3).
2.3.1. Synthesis of epoxy-amine oligomers
0
2.2.2. Synthesis of 3,5-bis [2- (N-methyl-4- (4 -nitrophenylazo)
Epoxy amine oligomers based on DGEBA and p-aminobenzoic
anilino) hexaoxy] benzyl alcohol (DF2)
.2.2.1. Synthesis of N-methyl-N (6-chlorohexyl) aniline. A solution
of POCl (2.3 g, 0.015 mol) was added dropwise to 10 mL of a cooled
solution of 6- (N-methyl-N-phenylamino) hexane-1-ol (6.20 g,
acid, OAB, were prepared using a polyaddition reaction in bulk
according to the procedure described in Ref. [44]. The yield of the
oligomer was 96%. The IR spectrum of the oligomer contains ab-
sorption bands corresponding to the polyhydroxyaminoether
2
3
ꢁ1
ꢁ1
ꢁ1
0
.030 mol) in 10 mL of THF with stirring for one hour. The reaction
structures: 3357 cm (-OH, broad band), 2967 cm , 2936 cm
,
ꢀ
ꢁ1
ꢁ1
ꢁ1
ꢁ1
mixture was heated to 60 C with stirring for 4 h. The reaction
mixture was concentrated by evaporating THF, washed with water
until neutral reaction, and the product was extracted with diethyl
2874 cm
(CH
2
); 1602 cm , 1510 cm
(Ph); 1668 cm (CO);
ꢁ1
ꢁ1
1247 cm , 1042 cm (COC).
ether (30 mL). The extract was dried over MgSO
concentrated by distilling off the solvent in a vacuum of a water jet
4
, filtered and
2.3.2. Synthesis of epoxy-amine NLO polymers with bi-
chromophore fragments in the side chain
pump. The product was purified by vacuum distillation on an oil
2.3.2.1. One-step functionalization of the OAB oligomer with bi-
chromophore dendritic fragment DF1. A solution of OAB (0.05 g,
0.1 mmol) in 10 mL of THF was poured into a flat bottom flask
equipped with a magnetic stirrer. Then DMAP (0.009 g, 0.7 mmol),
DCC (0.03 g, 0.13 mmol), DF1 (0.08 g, 0.1 mmol) were introduced in
the pointed sequence into the solution of the oligomer with stir-
ring. The reaction mixture was stirred at room temperature for
22 h. The dicyclohexylurea precipitate formed during the reaction
was filtered off, and the reaction mixture was precipitated into
hexane. The oligomer was purified by two-fold precipitation from
the THF solution to hexane. The isolated oligomer was dried in a
vacuum oven to constant weight. Yield 0.1 g (83%), red powder.
ꢀ
pump, selecting the fraction with T
b
¼ 75e85 C/0.4 mm Hg, yield
2
2
1
1
.75 g (26%), a yellow oily liquid, n
acetone d , ppm; J, Hz): 1.30 (m, 2H, Cl-C
m, 4H, Cl-C -CH -СН -CH -СН N), 1.70 (m, 2H, Cl-СН
N-), 2.93 (s, 3H N-CH ), 3.35 (t, 2H, -CH -N-, J 7.9), 3.48 (t, 2H,
ClCH -, J 7.5), 6.66 (t,1H, p-Ar-H(-N(CH ), J 7.3), 6.80 (d, 2H, o-Ar-H(-
N(CH ), J 8.4) 7.20 (t, 2H, m-Ar-H(-N(CH ), J 8.4). Obtained, %: С
0.79; Н 7.32; N 5.94, Cl 15.47. C13 20NCl, Calculated, %: С 69.2; Н
.93; N 6.2, Cl 15.7.
D
¼ 1.538. H NMR (400 MHz,
-CH -C -N-), 1.53
- CH
6
;
d
H
3 6
2
2 4
H
(
2
H
4
2
2
2
2
2
2
-
C
H
4 8
3
2
2
3
3
3
7
8
H
2.2.2.2. Synthesis of 3,5-bis [2- (N-methylanilino) hexaoxy] benzyl
alcohol. A mixture of N-methyl-N- (2-chlorohexyl) aniline (1.5 g
.007 mol), 3,5-dihydroxy-benzyl alcohol (0.42 g 0.003 mol),
0
2.3.2.2. Two-step functionalization of the OAB oligomer with DF1
fragment. The first step: DMAP (0.05 g, 0.4 mmol), DCC (0.28 g,
1.4 mmol) and 3,5-bis [2-(N-ethylanilino) ethoxy] benzyl alcohol
(0.21 g,1.3 mmol) were added in calculated amounts to a solution of
OAB (0.5 g, 1.1 mmol) in 30 mL of THF under stirring with a mag-
netic stirrer. The reaction proceeded for 22 h at room temperature.
The dicyclohexylurea precipitate formed during the reaction was
filtered off, and the reaction mixture was precipitated into hexane.
The oligomer was purified by double reprecipitation from THF to
hexane and dried in a vacuum oven to constant weight. Yield 0.39 g
(62%), white powder.
Second stage: 4-nitrobenzenediazonium tetrafluoroborate
(0.13 g, 0.24 mmol) was added in portions to a solution of the
oligomer (0.3 g, 0.4 mmol) in 15 mL of THF at stirring with a mag-
netic stirrer, after 10 and 30 min sodium acetate (0.08 g, 0.96 mmol)
was added in two portions. The reaction was carried out with
stirring at room temperature for 6 h. The reaction mixture was
precipitated into hexane. The oligomer was purified by double
reprecipitation from THF solution to hexane and dried in a vacuum
oven to constant weight. Yield 0.25 g (83%), light red powder.
anhydrous potassium carbonate (4 g), potassium iodide (2.23 g)
ꢀ
and 20 mL of DMF was heated at 80 C under argon atmosphere
with intense stirring for 40 h. The reaction mixture was poured into
2
00 mL of water and extracted with CH
2 2
Cl (15 mL). The extract was
dried over MgSO , filtered, and the product was purified by column
4
chromatography (eluent - hexane: chloroform: ethyl acetate in a
ratio of 1: 1: 1.5). Yield 0.55 g (35%), an oily liquid of a yellow-green
1
color. H NMR (400 MHz, acetone d
6
;
d
,ppm; J, Hz): 1.42 (m, 4H, O-
-CH -CH -CH CH N), 1.79
N) 2.92 (с, 6H, -CH ), 3.34 (t, 4H, N-CH
10 J 7.4), 3.96 (t, 4H, O-CH -C 10-, J 6.5), 4.28 (m, 1H, -OH), 4.69
s, 2Н, Ar-CH OH), 6.43 (t, 1Н, p-Ar-Н(СН ОН), J 7.4), 6.61 (d, 2H, o-
Ar-Н(СН ОН), J 7.4), 6.67 (t, 2Н, p-Ar-Н(N), J 8.7), 6.75 (d, 4H, o-Ar-
Н(N), J 8.7), 7.22 (t, 4H, m-Ar-Н(N), J 8.7). Obtained, %: С 71.79; Н
C
(
H
3 6
-CH
m, 4Н, O-CH
2
-C
2
H
4
-N-), 1.64 (m, 8H, O-C
-CH -C
2
H
4
2
2
2
2
2
2
4
H
8
3
2
-
C
5
H
2
5
H
(
2
2
2
9
5
.34; N 5.24, C33
H
46
N
2
O
3
, Calculated, %: С 76.4; Н 8.9; N 5.4. ESI:
þ
20 [
М
].
2.2.2.3. Synthesis of DF2. A calculated amount of 4-
nitrobenzenediazonium tetrafluoroborate (0.52 g, 0.002 mol) was
added to a solution of 3,5-bis [2- (N-methylanilino) hexaoxy]
benzyl alcohol (0.54 g, 0.001 mol) in 15 mL of THF. After 10 and
2.3.2.3. Functionalization of OAB oligomer with DF2 fragment.
A sample of OAB (0.144 g, 0.3 mmol) was dissolved in 15 mL of THF.
DMAP (0.028 g, 2.2 mmol), DCC (0.082 g, 0.4 mmol), DF2 dendritic
fragment of (0.25 g, 0.3 mmol) was introduced into the solution of
the oligomer in the indicated sequence. The reaction was carried
out for 72 h; then the mixture was filtered from the formed pre-
cipitate, dicyclohexylurea, and the oligomer was precipitated into
hexane. The oligomer was purified by two-fold precipitation from
the THF solution to hexane and dried in a vacuum oven to constant
3
0 min in two portions sodium acetate (0.17 g, 0.002 mol) was
added. The reaction mixture was stirred at room temperature for
h. The reaction mass was precipitated in hexane (75 mL). The
3
resulting precipitate of burgundy-red color was filtered and
washed several times with water. The product was dried in a vac-
uum oven to constant weight. The yield of the product was 0.5 g
1
(
C
60%). H NMR (400 MHz, acetone d
6
;
d
, ppm; J, Hz): 1.42 (m, 4H, O-
-CH -CH -CH CH N), 1.79
H
3 6
-CH
2
-C
2
H
4
-N-), 1.64 (m, 8H, O-C
2
H
4
2
2
2
2

256
G.N. Nazmieva et al. / Polymer 149 (2018) 253e265
weight. Yield 0.35 g (91%), burgundy-red powder.
was established by conformational search by Monte-Carlo method
51] with MMFF94s force field [52] in the presence of chloroform,
[
2
.4. Experimental equipment
ε ¼ 4.8, the GB/SA continuum model [53] being used for the account
of solvent effect. Stable unique conformations were obtained
within the energy window of 5 kcaL/mol above the global
minimum.
IR-spectra of linear oligomers and cross-linked polymers were
recorded on a Bruker Tensor 27 spectrometer, the samples being
films cast from THF on KBr glass plates or tablets with KBr.
The Molecular dynamics (MD) simulations at various tempera-
tures were performed for the chosen characteristic conformations
of the studied oligomers to get the information about the local
mobility of chromophore groups and chain segments at the room
1
Н NMR spectra were registered on an AVANCE 600 Bruker
spectrometer. 13C NMR spectra were registered on an AVANCE 500
Bruker spectrometer; the spectra for the studied oligomers are
presented in Figures S1-S3.
g
temperature and at that close to T . The calculations were per-
UV/vis spectra were recorded in THF on a Lambda 35 Perkin
Elmer spectrometer.
formed using MacroModel program package [54].
To study the local mobility in the polymer systems with the
account of steric hindrances due to the environment we have
performed modeling in the so called amorphous cell with OPLS3
force field, parametrized on the basis of high-level quantum-
chemical calculations [55]. The oligomers size was chosen with the
account of experimental data on molecular-mass distribution [56],
provided by GPC; for both considered systems the oligomers con-
tained six alternating DF-free and DF-containing monomer units;
the number of oligomers was 15 in both studied systems OAB-DF1
and OAB-DF2. The oligomers number was selected to obtain the
cell size not smaller than the cut-off radius for non-covalent in-
teractions, for the case under study it is 9 Å.
The system was relaxed using Multistage Simulation Workflow
implemented in Materials Science suite [57]. The initial condensed
phase model is processed using a series of NVE, NVT, and finally
target temperature NPT simulations to predict the amorphous
system density and structure. Compressive relaxation protocol was
used before starting the simulations to increase the density of the
system. The analysis of local motions in polymer chains was per-
formed in two ways: at different temperatures by MD or by simu-
lated annealing in the temperature range from 360 to 450 K.
Thermophysical properties were generated from a set of mo-
lecular dynamics simulations on a model system over a range of
temperatures starting from 600 K and going down to 200 K in the
NPT ensemble. The densities are obtained from MD simulations at a
set of temperatures. To obtain the thermochemical properties we
used a bilinear fit, in which a linear regression is performed on the
low temperature (glassy) region and the high temperature
OAB oligomer molecular weight was determined by gel-
permeating chromatography (GPC) analysis on
LC10AVP series chromatograph (Japan) equipped with an RID-
0AVP refractometer and SPD-M10AVP diode matrix detectors,
a Shimadzu
1
DGU14U degasser unit, LC-10AD pump and CTO-10A column oven,
using a Phenomenex column (USA) with a size of 7.8 ꢂ 300 mm
filled with the Phenogel sorbent with a pour size of 500 Å; THF was
ꢀ
used as the eluent and the analyses were performed at 40 C,
elution rate was 1 mL/min.
Electrospray ionization mass spectra (ESI) were registered on
AmazonX mass spectrometer (Bruker Daltonik GmbH, Bremen,
Germany). The measurements were carried out in the regime of
detection of positive ions in the range m/z from 100 to 2800. The
voltage on the capillary was 4500 V. The nitrogen gas with a tem-
ꢀ
perature of 300 C and a flow rate of 10 L/min was used as the
dehydrating gas. A solution of isopropanol/water (80:20) was used
as the eluent, and the elution rate was 0.2 mL/min. The compound
ꢁ
6
was dissolved in acetonitrile at a concentration of 10 g/L. The
volume of the sample to be injected is 20 L. Data was processed
using DataAnalysis 4.0 (Bruker Daltonik GmbH, Bremen, Germany).
Glass transition temperature (T ) and thermal stability of the
m
g
obtained oligomers were determined by DSC (the sample heating
ꢀ
rate 10 С/min) and TGA techniques on a Netzsch STA 449 F3
(
Jupiter, Germany) device.
The film thickness was measured with a Linnik MII-4M micro-
interferometer and by AFM technique on a MultiMode V scanning
probe microscope (Veeco) in the intermittent-contact mode.
(rubbery) region of the plot of density against temperature. The
2.5. Film fabrication and poling
glass transition temperature is the temperature at which the two
regression lines or the two asymptotes meet.
Polymer films were spin-cast on glass plates from 7% solution of
polymer in cyclohexanone (~5000 rpm for 60e90 sec); the samples
were kept in vacuum desiccator at room temperature for 10e16 h
followed by a soft baking at 50 С for two hours.
3. Results and discussion
ꢀ
3.1. Modeling of OAB-DF1 and OAB-DF2 oligomers
Polymer films were poled at the corona-triode setup in the
corona discharge field, voltage 6.5e7 kV, poling time ~20 min, the
distance from the tungsten needle electrode to the surface of the
film being 1 cm. The field was applied to the films heated up to
Molecular modeling of DF1, DF2 compounds and OAB-DF1,
OAB-DF2 oligomers (Fig. 1) was performed by Monte-Carlo tech-
nique and a set of unique conformations was obtained; the con-
formers are distinguished, differing by the mutual arrangement of
the chromophore groups, for which electric characteristics (dipole
g
temperatures close to T or somewhat higher.
2
.6. Measurements of NLO characteristics
moments,
) were calculated by the semiempirical method AM1.
Long tether groups connecting chromophores with the
m, polarizabilities, a, and molecular hyperpolarizabilities,
b
Polymer NLO characteristics were measured by the second
harmonic generation (SHG) technique on an automated unit with
-quartz (х-cut) plate as a standard; the fundamental beam was
branching center are shown to provide the structures with small
angles between chromophores in DF2 promoting optimal quadratic
NLO response [60]. Besides, according to the MD study of separate
dimers at various temperatures the use of long tether groups leads
to an increase in the mobility of azochromophores, i.e. we can as-
sume that they provide more effective poling. To study the local
mobility in the polymer systems with the account of steric hin-
drances due to the environment we have performed modeling in
the so called amorphous cell. Both studied polymer systems were
a
3
þ
provided by pulse Nd :YAG laser (
5 ns, power density at the sample 10 kW/sm ). The accuracy of the
estimation of NLO coefficient, d33, is 15%.
l
¼ 1064 nm, pulse duration
2
1
2.7. Molecular modeling
The structure of the oligomers (dimers) OAB-DF1 and OAB-DF2

G.N. Nazmieva et al. / Polymer 149 (2018) 253e265
257
Fig. 1. Monomeric units of model oligomers with chromophore-containing dendritic fragments.
packed, as a result of packing realistic polymer density was ach-
ieved; the resulted packed polymer OAB-DF2 is presented in Fig. 2.
At the first stage of modeling the glass transition temperatures,
chromophores belonging to the same DF, are arranged in different
ways: some of them are codirected, others are oppositely directed
(Fig. S4), what is in agreement with our earlier observations, drawn
from conformational search performed for a separate oligomer
[58]. In the starting structure the oligomers contained DFs with
almost codirected chromophore dipole moments. The fact that in
the course of packing in a cell the chromophores in DF acquired
various mutual arrangements gives evidence of sufficient flexibility
of tether groups, providing the chromophores mobility.
T
g
, were estimated by multistage simulations in the temperature
ꢀ
range from 200 to 600 K, resulting in 423 K (150 C) for OAB-DF1
and 394 K (121 C) for OAB-DF2 (Fig. 3). Both T
ꢀ
g
values are in rather
good agreement with those measured by DSC, reproducing well the
experimentally observed tendency in decreasing T with tether
group elongation; experimental results are given in Table 1. It is
interesting to note, that T for OAB-DF2 is much lower than that for
g
g
After equilibrating OAB-DF2 system in the course of multistage
simulation, to estimate the effect of temperature on the chromo-
phores mobility we performed MD study in the range of temper-
OAB-DF1, this observation also can be explained by long, rather
flexible, tether groups in DF2 fragment, providing polymer soft-
ening at lower temperature.
g
atures from 380 to 430 K, this range contains the T for OAB-DF2.
When considering the oligomers in a cell, one can see, that
We analyzed the chromophores motion in a large number of olig-
omers at three temperatures e 380 K, 400 and 430 K - and revealed
that the chromophores start active motion at temperatures higher
than 400 K. Another approach to the description of local mobility
was also used, consisting in the analysis of torsion angles change
with time in the course of simulated annealing of the system after
its equilibration; the simulated annealing protocol is presented in
Table S1. The dependence of
phore immediate reorientation, and the angle
h
angle, responsible for the chromo-
, describing the
b
motion of the chromophore-containing branch as a whole (see
Fig. 1 for angles notation), on temperature for a number of oligo-
mers is presented in Figure S5 and S6. The analysis of these de-
pendencies shows that the appreciable chromophores local
mobility starts at the temperature of about 400 K and becomes
more pronounced at higher temperatures up to 450 K. Thus sum-
marizing the data of MD and Simulated annealing, we can conclude
that to achieve effective chromophores alignment the poling tem-
g
perature some 30 K higher than T seems to be appropriate.
3.2. Synthesis of NLO-active bi-chromophore compounds
As molecular sources of NLO activity, we first synthesized the bi-
chromophore compounds DF1 and DF2 (Scheme 1) having an ar-
Fig. 2. OAB-DF2 polymer, packed in amorphous cell.
omatic branching center, to which the azochromophores are

258
G.N. Nazmieva et al. / Polymer 149 (2018) 253e265
Fig. 3. The dependence of specific volume on temperature for OAB-DF1 (a) and OAB-DF2 (b) polymers.
Table 1
Physical-chemical properties of oligomers, functionalized with chromophore-containing dendritic fragments.
Nꢀ
oligomer
yield, %
Functionalization degree by 1Н NMR spectrum, mol%
lmax, nm
T
ꢀ
C
T
ꢀ
10%
, C
g
,
1
2
3
OAB
OAB-DF1
OAB-DF2
96
83
91
e
e
98
122
107
167
255
230
60
45
460
496
Scheme 1. Synthesis of DF1 and DF2.
attached via ethyl or hexyl groups. Synthesis of compounds was
carried out according to the method, in the development of which
the synthetic approaches described in Refs. [49,50] were taken into
The signals of the aromatic protons of the branch center at the o-
and p-positions are manifested in the weak-field region, at
6.38 ppm and 6.75 ppm, the protons of the azobenzene moiety are
manifested by signals of 6.92 ppm, 7.88 ppm, 7.92 ppm and
8.33 ppm in the form of doublets equal to the integral intensity. The
protons of the methylene groups of the ethylene bridge are man-
ifested by two triplets in the region of 3.85 ppm and 4.16 ppm. The
ratio of the integrated intensities of all aromatic (19H) and methyl
(6H) protons in the spectrum is 3: 1, which corresponds to the
ꢀ
account. DF1 was obtained as dark-red powder with T
m
¼ 172 С.
The compound DF2 was obtained as a burgundy-red powder with
ꢀ
T
m
¼ 120 C, which is readily soluble in polar organic solvents such
as DMF, THF, DMSO, acetone, etc. The structure of the obtained
compounds was confirmed by spectral methods. Thus, in Fig. 4, the
1
H NMR spectrum of DF1 is shown.

G.N. Nazmieva et al. / Polymer 149 (2018) 253e265
259
Fig. 4. 1Н NMR spectrum of DF1.
Fig. 5. 1Н NMR spectrum of DF2.
proposed structure.
groups of the hexyl tether group, which are adjacent to the nitrogen
and oxygen atoms, are manifested by two triplets in the region of
3.85 ppm and 4.16 ppm. The ratio of the integral intensities of all
aromatic (19H) and methyl (2H) protons of the hydroxymethylene
group at the branching center is 9.5: 1, what confirms the proposed
structure.
As an example, in Fig. 6 the UV/vis spectrum of the DF2 is
presented. Two absorption bands are observed in the spectrum; a
band in the short-wavelength region that has two peaks: 286 nm
1
Fig. 5 shows the H NMR spectrum for DF2. The proton signals of
the aromatic branching center at the o- and p-positions relative to
the hydroxymethylene group are manifested as a doublet at
6
.68 ppm (J 7.4) and triplet at 6.37 ppm (J 7.2), the protons of the
azobenzene fragment appear at 6.92 ppm, 7.88 ppm, 7.92 ppm and
.33 ppm in the form of doublets, whose integral intensities are
equal.
The protons of the methylene group at the branching center are
8
revealed as a singlet at 4.61 ppm. The protons of the methylene
corresponding to the electronic
ring and 258 nm corresponding to the n-
more intense symmetric absorption band in the long-wavelength
region with * and
max ¼ 480 nm is due to superimposed n-
* transitions of azobenzene chromophore groups.
p
-
p
* transitions of the aromatic
p
* Ar-O-R transition; a
l
p
p-
p
3.3. Synthesis of epoxy amine oligomers
To create NLO polymers with chromophores in the side chain
based on DGEBA and p-aminobenzoic acid (p-ABA), an oligomer
containing reactive carboxyl groups was obtained, these groups
were shown to have sufficient reactivity [43,44]. The degree of
functionalization of oligomers with DF1 was estimated as 60%;
although, as it was shown in Ref. [59], only amine groups of ami-
nobenzoic acids participate in the oxirane ring cleavage. The reac-
tion proceeds without the formation of by-products, i.e. carboxyl
group does not interact with oxirane ring.
ꢀ
The reaction (Scheme 2) was carried out in bulk at 100 C during
Fig. 6. UV/vis spectrum of DF2.
24 h. After purification by a standard procedure, the OAB oligomer

260
G.N. Nazmieva et al. / Polymer 149 (2018) 253e265
Scheme 2. Synthesis of OAB.
is a cream powder that is readily soluble in polar organic solvents
and has a film-forming ability. Molecular weight for OAB oligomer
was measured by GPC, the GPC curve is given in Figure S7, the
molecular weights data are summarized in Table S2.
When DF2 was introduced into the oligomer, the synthesis time
was increased to 72 h. The resulting product was an amorphous
powder of a dark red color, well soluble in most polar organic
solvents. The degree of functionalization of the OAB-DF2 oligomer,
1
calculated from the H NMR spectrum, was 45 mol %.
3
.4. Functionalization of epoxy-amine oligomer
Fig. 7 shows the UV/vis spectra of oligomers OAB and OAB-DF2.
As it can be seen from the figure, when the oligomer is function-
alized, a new absorption band appears in the visible region of the
Two approaches to the introduction of chromophores into the
polymer matrix are given in the literature: the first, when com-
pounds already containing chromophores in their composition are
used in polymerization or polycondensation reactions; second,
when a polymer is first produced, and then chromophores are
introduced into the polymer chain using various polymer-
analogous reactions. The second approach to the introduction of
chromophores is quite often encountered in the literature. Thus, it
was shown in Refs. [37e42,60e63] that the use of polymer-
analogous reactions upon introduction of chromophores into the
polymer chain makes it possible to increase the yield [40,60] and
the molecular weight [41,62] of the polymer. For the introduction of
chromophores, the reactions of esterification, azo coupling, etc. are
most often used; obviously, chromophores introduced into the
polymer matrix should have reactive groups.
Synthesis of chromophores is quite complex and laborious
process, requiring rather long time, a large amount of solvents to
purify and isolate an individual product. In the work [56], an
approach was proposed that makes it possible to obtain a NLO-
active polymer without resorting to synthesis, purification, and
isolation of the chromophore itself. This approach consisted in
introducing an aniline-containing fragment into the polymer in the
first stage, followed by an azo coupling reaction with diazotizing
agents. Such approach permits avoiding the time-consuming pro-
cess of purifying the chromophore, and also allows one to control
the degree of functionalization of the polymer by introducing a
certain amount of diazotizing agents.
spectrum with
l
max ¼ 480 nm, characteristic for the azochromo-
1
phore fragment. Fig. 6 shows H NMR spectra of epoxy amine
oligomers before and after functionalization with bi-chromophore
DF2. As can be seen, in the spectrum of the oligomer after the
functionalization with the chromophore-containing fragments the
proton signal of the carboxyl group of the OAB oligomer with a
chemical shift of 10.8 ppm disappears, which indicates a suffi-
ciently high degree of the oligomer functionalization.
It should also be noted that new signals emerge from protons of
azobenzene fragments as doublets with chemical shifts of
7.85 ppm, 7.93 ppm, and 8.31 ppm, related to the o- and m-protons
of the azobenzene moiety, signals from phenyl o- and p-protons of
the aromatic branching center of dendritic fragments appear in the
region of 6.7 ppm and 6.3 ppm, respectively, as well as a broadened
signal of 4.9 ppm from the protons of the methylene spacer group
that binds the bi-chromophore fragment to the oligomer chain (see
Fig. 8).
At the same time, the signals confirming the differences in the
structure of the introduced dendritic fragments are clearly man-
ifested. Thus, in the case of oligomers OAB-DF1 the proton signals
of the ethyl tether group are manifested in the region of 4.0 ppm
and 4.2 ppm; the methyl protons at the azochromophore group
appear in the region of 1.1 ppm.
In the case of OAB-DF2, the protons of the methylene groups of
the hexyl tether group, which are adjacent to the nitrogen and
oxygen atoms, are manifested by two triplets in the region of
3.3 ppm and 3.8 ppm, and the signals of other methylene groups of
the tether group - in the form of a broadened multiplet at 1.35 ppm
and 1.20 ppm, which also confirms the structure of the target
products.
Since the OAB oligomer contains reactive hydroxyl groups, it
could be assumed that under the conditions of Steglich esterifica-
tion [ 64] in the presence of DMAP and DCC, a side reaction may
occur between neighboring oligomers. Taking this into account, we
have carried out the search for the most efficient way of obtaining
chromophore-containing OAB oligomers [43,44]. Two methods of
the oligomer functionalization were developed: a two-step tech-
nique, including the introduction of a chromophore fragment
containing an aniline group, which is subsequently diazotized with
the formation of azochromophores, and a one-step technique with
the introduction of obtained chromophore. We have tested these
approaches by the example of azochromophore DR1 [44] and
compound DF1 [43] as NLO-active units. One-step method of
functionalizing the OAB oligomer is found to be preferable in
comparison with the two-stage one in both cases: the degree of
functionalization of the epoxy amine oligomer, calculated on the
Some physical-chemical characteristics of obtained oligomers
are given in Table 1. The T
g
of the OAB-DF1 oligomer increases by
ꢀ
ꢀ
24 C compared to that for the OAB and is 122 C, while the OAB-
ꢀ
DF2 oligomer has a lower T
g
¼ 107 C, which is apparently due to
the plasticizing behavior of hexyl tether group. The DSC curves for
all the oligomers are presented in Fig. S8. The introduction of
chromophores leads to a significant increase in the thermal sta-
bility of the oligomers, so the value of 10% mass loss, T10%, increases
ꢀ
ꢀ
ꢀ
from 167 C for OAB to ~255 C for OAB-DF1 and ~230 C for OAB-
DF2. The TGA curves for all the studied oligomers are presented in
Fig. S9.
1
basis of the H NMR spectra, for the case of DR1 chromophore was
3.5. Creation of network materials based on epoxy-amine oligomers
with NLO-active fragments in the side chain
7
0% and 29%, and for the DF1 compound 60% and 27%, respectively.
Taking into account the results obtained earlier, linking of the
DF2 compound was carried out using the one-step functionaliza-
tion procedure (Scheme 3).
On the basis of the synthesized oligomers cross-linked struc-
tures were obtained using MDI as hardener. Films were spin cast

G.N. Nazmieva et al. / Polymer 149 (2018) 253e265
261
Scheme 3. OAB functionalization by DF1 and DF2.
content in the cross-linked polymer was carried out by extraction
in THF for 10 h; the gel fraction was 78%. Thus, it can be concluded
that isocyanate groups are involved not only in the cross-linking
reactions, but also, apparently, in the side reactions leading to
chain growth. On the other hand, the analysis of the given IR
spectra allows us to assume that not only hydroxyl groups of the
bearing chain participate in the cross-linking reactions (an insig-
ꢁ
1
nificant decrease in the intensity of the corresponding 3325 cm
ꢁ1
band is observed), but the terminal amino (3035 cm ) and epoxy-
ꢁ
1
groups (915 cm ) as well.
The obtained results were used in the selection of optimal
poling regimes.
3.6. NLO properties of the synthesized oligomers
As already mentioned, polymer NLO materials used in EO de-
vices must have the relaxation stability of oriented NLO dipole
chromophores. To increase this stability, cross-linking is often used,
in which both polymer chains and the chromophores themselves
can participate. Reacting with the functional groups of the polymer
chain or chromophore, the cross-linking agents result in the for-
mation of a network structure and thereby limit the local mobility
of the chromophores. The presence of hydroxyl groups in epoxy-
amine oligomers with NLO-active fragments in the side chain
makes it possible to obtain cross-linked polymers by reaction with
MDI as a cross-linking agent.
To study the NLO properties of epoxyamine oligomers thin films
were made, the thickness of which was from 200 to 500 nm, and
the roughness depended on the type of introduced bi-
chromophore fragment. In the process of poling, polymer films
were transferred to the electret state with nonzero macroscopic
polarization, which arises from the orientation of the chromophore
fragments in the applied electric field. Fig. 10 shows the change in
the surface of the OAB-DF2 film after the poling process. It can be
seen that as a result of poling, the film surface roughness
Fig. 7. UV/vis spectrum for OAB oligomer before (1) and after (2) introduction of NLO
active fragment DF2.
from the polymer solution containing the amount of MDI equi-
molar to that of reactive polymer hydroxyl groups. The kinetics of
the polymer curing was studied at various temperatures by IR
spectroscopy analyzing the spectra recorded at regular intervals.
The film curing process was studied in parallel at room temperature
ꢀ
and at 120 C.
The kinetics of the cross-linking was analyzed by the change in
ꢁ1
the isocyanate group absorption intensity at 2274 cm . It has been
found that at room temperature the curing is not complete: after
3
0 h, up to 30% of unreacted isocyanate groups remain in the
ꢀ
sample, while at 120 C, after 45 min from the start of heating, the
isocyanate groups absorption intensity decreases by 90%, and after
3
.5 h the corresponding absorption band completely disappears.
In Fig. 9, the IR spectra of the molecular system (OAB-DF2) þ
MDI are given as an example. Determination of the gel fraction

262
G.N. Nazmieva et al. / Polymer 149 (2018) 253e265
Fig. 8. 1H NMR spectra of epoxy-amine oligomers before (a) and after (b, c) functionalization with DF1, DF2, respectively.
The NLO properties of the obtained materials were studied by
the SHG method. Table 2 shows the characteristics of the obtained
polymer films. The introduction of dendritic type NLO-active frag-
ments into the oligomers makes it possible to increase the con-
centration of chromophore groups, which leads to an increase in
the values of NLO coefficients as compared to the case of OAB-DR1.
As can be seen from Table 2, the poling conditions significantly
affect the NLO response of the polymer film: it is evident by the
example of (OAB-DF1) and (OAB-DF1)þMDI, that performing the
g
poling procedure at temperature Tpol exceeding T makes it possible
to achieve more efficient orientation of the chromophores and, as a
consequence, higher d33 values.
It can be seen from the data in Table 2, that the NLO coefficient of
the OAB-DF2 oligomer is significantly higher (40 pm/V) than
d
33 ¼ 29 pm/V for OAB-DF1 in spite of the lower chromophore
Fig. 9. IR-spectrum variation in the course of cross-linking reaction of OAB-DF2 with
MDI in a polymer film: (1) 20 С, 15 min; (2) 120 С, 45 min; (3) 120 С, 3.5 h.
ꢀ
ꢀ
ꢀ
content (32 wt% and 39 wt%, respectively). Perhaps this is primarily
due to the structure of the dendritic fragment: the presence of
hexyl tether groups contributes to an increased mobility of chro-
mophores allowing for more effective poling. It can be assumed
that an increase in the chromophores concentration in the case of
appreciably increases (up to ~ 30 nm).
Poling of polymer films was carried out in a corona discharge
field. The orientation protocol was developed taking into account
OAB-DF2 will result in the growth of the NLO coefficient value d33
.
the T
g
of the obtained oligomers and polymers. The orientation
It is interesting to compare the values of NLO coefficients of epoxy-
amine oligomers with bi-chromophore fragments, OAB-DF1 and
OAB-DF2, with that containing one azochromophore in the side
chain e OAB-DR1 [44]. The NLO coefficient values for the OAB-DF1
and OAB-DF2 are higher than those for oligomer OAB-DR1
quality of the chromophores was monitored by UV/vis spectros-
copy by comparing the absorption intensities of the film before and
after poling. The value of the order parameter,
under study lies in the range from 0.1 to 0.3.
h, for the samples

G.N. Nazmieva et al. / Polymer 149 (2018) 253e265
263
Fig. 10. OAB-DF2 film surface (a) and film roughness (b) before poling; film surface (c, d) and film roughness (e) after poling.
(
d
33 ¼ 22 pm/V), where chromophore is linked to the chain through
fragments in the design of new polymer materials with quadratic
NLO response. Further optimization of bi-chromophore fragment
content will allow obtaining higher values of NLO coefficient.
NLO coefficient value for the cross-linked polymer (OAB-DF1)þ
MDI is close to that for linear polymer, while d33 for (OAB-DF2)þ
MDI is somewhat lower, than for OAB-DF2, what can be due to
partial cross-linking of polymer chains before the poling stage due
to high reactivity of MDI. T of cross-linked polymers is usually
g
higher, than that for linear polymers, but here they were assumed
equal, what can be another reason for this difference.
ethyl tethering group. It is worth stressing that the d33 coefficient
value for OAB-DF2 is almost double that for OAB-DR1, both having
close chromophore content; this growth seems to be caused by
spatial isolation of azochromophores in the dendritic fragment and
more efficient orientation of chromophores in OAB-DF2 during
poling due to longer tether groups. This assumption is confirmed by
our atomistic modeling [58]. It is interesting to compare the d33
values for OAB-DF1 and OAB-DR1 with the same length of groups
tethering the chromophore to the branching center in the former
and aminobenzoate fragment of the OAB chain in the latter. In these
two cases the weight content of chromophores is quite close (39
and 35 wt%, respectively), however, the number of chromophores
estimated according to the degree of functionalization is almost 1.5
times higher for OAB-DF1 compared to that for OAB-DR1, while d33
coefficient for the former is greater by ca 32% than for the latter. In
both cases the chromophore content is rather high; however, the
structure of the dendritic fragment seems to prevent the chromo-
phores aggregation. These facts support the use of bi-chromophore
The d33 measurements, repeated after 9 months on the same
films showed that the NLO coefficient for linear oligomers
decreased by half, and for cross-linked polymers - by 40%.
4. Conclusions
Here we have synthesized and characterized for the first time
new bi-chromophore compounds: DF1 and DF2 with an aromatic
branching center and different lengths of tether groups, whose
structure realizes the spatial separation of chromophores, mini-
mizing the probability of undesirable DDI between them.
Table 2
New epoxy-amine-based NLO oligomers, containing bi-
chromophore fragments in the side chain were obtained. By the
example of OAB-DF1 two ways of incorporation of the dendritic
fragments into the oligomers side were considered; the advantage
of a one-step process was established, since the degree of func-
tionalization in this case reaches 60 mol% in comparison with
29 mol% when the two-step procedure was used.
Molecular modeling of obtained compounds gave guidelines for
the design of promising NLO materials. It was demonstrated that
hexyl groups, tethering the chromophores to the branching center
Characteristics of the obtained polymer films.
Nꢀ
Polymer
Film thickness, nm
Т
g, ºС
Т
pol, ºС
h
d33, pm/V
1
2
4
5
6
7
OAB-DF1 (39 wt%) 140
122
135
153
0.10 5a
0.30 29
0.20 10
0.30 25
0.30 40
0.21 25
190
122b 125
155
a
(OAB-DF1)þMDI
160
240
OAB-DF2 (32 wt%) 350
(OAB-DF2)þMDI 200
107b 143
142
a
[
T
43].
b
g
for network materials is taken to be equal to T for linear polymers.
g

264
G.N. Nazmieva et al. / Polymer 149 (2018) 253e265
in DF2, are able to provide greater mobility of the chromophores
compared to ethyl groups in DF1, thus DF2 is preferable from the
viewpoint of NLO activity. The glass transition temperatures were
estimated for both studied polymer systems by multistage simu-
through click chemistry under copper (I) catalysis: improved optical trans-
parency and enhanced NLO effects, Chem. Eur J. 18 (2012) 4426e4434.
13] Z. Li, Q. Li, J. Qin, Some new design strategies for second-order nonlinear
optical polymers and dendrimers, Polym. Chem. 2 (2011) 2723e2740.
[14] M.J. Choa, D.H. Choia, P.A. Sullivan, A.J.P. Akelaitis, L.R. Dalton, Recent progress
in second-order nonlinear optical polymers and dendrimers, Prog. Polym. Sci.
[
ꢀ
ꢀ
lations, resulting in 150 C for OAB-DF1 and 121 C for OAB-DF2;
these T values are in good agreement with experimental estima-
33 (2008) 1013e1058.
g
[
15] P.A. Sullivan, A.J.P. Akelaitis, G. McGrew, S.K. Lee, D.H. Choi, L.R. Dalton, Novel
dendritic chromophores for electro-optics: influence of binding mode and
attachment flexibility on electro-optic behavior, Chem. Mater. 18 (2006)
tions by DSC. Molecular modeling of a set of OAB-DF2 oligomers
packed in an amorphous cell allowed to study the local mobility of
chromophores in the polymer side chain and to determine the
temperature at which the chromophores begin active motion, what
can be used for the selection of optimal temperature for performing
344e351.
[
[
[
16] S. Yokoyama, T. Nakahama, A. Otomo, S. Mashiko, Intermolecular coupling
enhancement of the molecular hyperpolarizability in multichromophoric
dipolar dendrons, J. Am. Chem. Soc. 122 (2000) 3174e3181.
17] H. Ma, J. Luo, S.H. Kang, S. Wong, J.W. Kang, A.K.-Y. Jen, et al., Highly fluori-
nated and crosslinkable dendritic polymer for photonic applications, Macro-
mol. Rapid Commun. 25 (2004) 1667e1673.
18] T.D. Kim, J.W. Kang, J. Luo, S.H. Jang, J.W. Ka, N. Tucker, et al., Ultralarge and
termally stable electro-optic activities from supramolecular self-assembled
molecular glasses, J. Am. Chem. Soc. 129 (2007) 488e489.
efficient polymer poling: temperature some 30 K higher than T
g
seems to be appropriate.
NLO characteristics of OAB-DF1 and OAB-DF2 have been
determined. It has been established that oligomers containing in
the side chain bi-chromophore fragments of the dendritic type are
characterized by higher d33 values (29 pm/V for OAB-DF1 and 40
pm/V for OAB-DF2) in comparison with the corresponding values
for oligomers with single azochromophores (21 pm/V for OAB-
DR1).
The increase of the relaxation stability of NLO response of the
epoxy-amine NLO polymers upon cross-linking was established:
for linear oligomers, the value of d33, measured after 9 months, was
halved, and for cross-linked polymers - by 40% compared to the one
determined right after poling.
[19] H. Ma, A.K.-Y. Jen, Functional dendrimers for nonlinear optics, Adv. Mater. 13
(2001) 1201e12055.
[
20] J. Luo, M. Haller, H. Ma, S. Liu, D.T Kim, Y. Tian, et al., Nanoscale architectural
control and macromolecular engineering of nonlinear optical dendrimers and
polymers for electro-optics, J. Phys. Chem. B 108 (2004) 8523e8530.
[21] R. Tang, Z. Lee, Second-order nonlinear optical dendrimers and dendronized
hyperbranched polymers, Chem. Rec. 17 (2017) 71e89.
22] J.Y. Do, J.J. Ju, Polyester dendrimers carrying NLO chromophores: synthesis
[
and optical characterization, Macromol. Chem. Phys. 206 (2005) 1326e1331.
[23] J.Y. Do, S.K. Park, J.-J. Ju, S. Park, M.-H. Lee, Electro-optic materials: hyper-
branched chromophores attached linear polyimide and dendritic polyesters,
Polym. Adv. Technol. 16 (2005) 221e226.
24] R. Tang, H. Chen, S. Zhou, W. Xiang, X. Tang, B. Liu, Y. Dong, H. Zeng, Z. Li,
Dendronized hyperbranched polymers containing isolation chromophores:
design, synthesis and further enhancement of the comprehensive NLO per-
formance, Polym. Chem. 6 (2015) 5580e5589.
[
Acknowledgment
[
[
[
25] X. Shen, H. Liu, Y. Li, S. Liu, Click-together azobenzene dendrons: synthesis
and characterization, Macromolecules 41 (2008) 2421e2425.
26] W. Wu, J. Qin, Z. Li, New design strategies for second-order nonlinear optical
polymers and dendrimers, Polymer 54 (2013) 4351e4382.
27] Z. Li, Z. Li, C. Di, Z. Zhu, Q. Li, Q. Zeng, K. Zhang, Y. Liu, C. Ye, J. Qin structural
control of the side-chain chromophores to achieve highly efficient nonlinear
optical polyurethanes, Macromolecules 39 (2006) 6951e6961.
The authors thank Dr. A. Khamatgalimov for the determination
of glass transition temperature and thermostability of the obtained
polymers.
Appendix A. Supplementary data
[
28] Z. Li, Q. Zeng, Z. Li, S. Dong, Z. Zhu, Q. Li, C. Ye, C. Di, Y. Liu, J. Qin an attempt to
modify nonlinear optical effects of polyurethanes by adjusting the structure of
the chromophore moieties at the molecular level using “click” chemistry,
Macromolecules 39 (2006) 8544e8546.
Supplementary data related to this article can be found at
https://doi.org/10.1016/j.polymer.2018.07.007.
[
29] J.Y. Do, S.K. Park, J.-J. Ju, S. Park, M.-H. Lee, Electro-optic materials: hyper-
branched chromophores attached linear polyimide and dendritic polyesters,
Polym. Adv. Technol. 16 (2005) 221e226.
30] J.Y. Do, S.K. Park, J.-J. Ju, S. Park, M.-H. Lee, Improved electro-optic effect by
hyperbranched chromophore structures in side-chain polyimide, Macromol.
Chem. Phys. 204 (2003) 410e416.
References
[
[
1] X. Piao, X. Zhang, Y. Mori, M. Koishi, A. Nakaya, S. Inoue, I. Aoki, A. Otomo,
S. Yokoyama, Nonlinear optical side-chain polymers post-functionalized with
high-b chromophores exhibiting large electro-optic property, J. Polym. Sci. A
[31] W. Wu, J. Qin, Z. Li, New design strategies for second-order nonlinear optical
polymers and dendrimers, Polymer 54 (2013) 4351e4382.
49 (2011) 47e54.
[
[
[
2] L.R. Dalton, P.A. Sullivan, D.H. Bale, Electric field poled organic electro-optic
materials: state of the art and future prospects, Chem. Rev. 110 (2010) 25e55.
3] D.M. Burland, R.D. Miller, C.A. Walsh, Second-order nonlinearity in poled-
polymer systems, Chem. Rev. 94 (1994) 31e75.
4] L.R. Dalton, A.W. Harper, R. Ghosn, W.H. Steier, M. Ziari, H. Fetterman, et al.,
Synthesis and processing of improved organic second-order nonlinear optical
materials for applications in photonics, Chem. Mater. 7 (1995) 1060e1081.
5] L.R. Dalton, A.W. Harper, A. Ren, F. Wang, G. Todorova, J. Chen, et al., Polymeric
electro-optic modulators: from chromophore design to integration with
semiconductor VLSI electronics and silica fiber optics, Ind. Eng. Chem. Res. 38
[32] Z. Li, Z. Li, C. Di, Z. Zhu, Q. Li, Q. Zeng, K. Zhang, Y. Liu, C. Ye, J. Qin, Structural
control of the side-chain chromophores to achieve highly efficient nonlinear
optical polyurethanes, Macromolecules 39 (2006) 6951e6961.
[33] Z. Li, Q. Zeng, Z. Li, S. Dong, Z. Zhu, Q. Li, C. Ye, C. Di, Y. Liu, J. Qin, An attempt to
modify nonlinear optical effects of polyurethanes by adjusting the structure of
the chromophore moieties at the molecular level using “click” chemistry,
Macromolecules 39 (2006) 8544e8546.
[34] G. Jiang, L. Wang, T. Chen, H. Yu, Synthesis and self-assembly of poly(benzyl
ether)-b-poly(methylmethacrylate) dendritic-linear polymers, Polymer 46
(2005) 81e87.
[
[
(
1999) 8e33.
[35] M. Leolukman, P. Paoprasert, Y. Wang, V. Makhija, D.J. McGee, P. Gopalan,
Influence of architecture, concentration, and thermal history on the poling of
nonlinear optical chromophores in block copolymer domains, Macromole-
cules 41 (2008) 4651e4660.
6] L.R. Dalton, W.H. Steier, B.H. Robinson, C. Zhang, A. Ren, S. Garner, et al., From
molecules to opto-chips: organic electro-optic materials, Mater. J. Chem. 9
(
1999) 1905e1921.
[
7] C. Gao, D. Yan, Hyperbranched polymers: from synthesis to applications, Prog.
Polym. Sci. 29 (2004) 183e275.
8] Y.V. Pereverzev, O.V. Prezhdo, L.R. Dalton, Macroscopic order and electro-optic
[36] M. Leolukman, P. Paoprasert, I. Mandel, S.J. Diaz, D.J. McGee, P. Gopalan,
Linear-dendritic block copolymer hosts for the encapsulation of electro-optic
chromophores via H-Bonding, J. Polym. Sci., Part A: Polym. Chem. 47 (2009)
5017e5026.
[37] X. Wang, J.-I. Chen, S. Marturunkakul, L. Li, J. Kumar, S.K. Tripathy, Epoxy-
based nonlinear optical polymers functionalized with tricyanovinyl chromo-
phores, Chem. Mater. 9 (1997) 45e50.
[
response of dipolar chromophoreepolymer materials, ChemPhysChem
2004) 1821e1830.
5
(
[9] S. Wu, F. Zeng, F. Li, Y. Zhu, J. Li, Synthesis and properties of polysiloxane-
based electrooptic materials, J. Polym. Sci. A: Polym. Chem. 37 (1999)
3
854e3860.
[38] X. Wang, J. Kumar, S.K. Tripathy, L. Li, J.-I. Chen, S. Marturunkakul, Epoxy-
based nonlinear optical polymers from post azo coupling reaction, Macro-
molecules 30 (1997) 219e225.
[39] X. Wang, S. Balasubramanian, L. Li, X. Jiang, D.J. Sandman, M.F. Rubner,
J. Kumar, S.K. Tripathy, Self-assembled second order nonlinear optical
multilayer azo polymer, Macromol. Rapid Commun. 18 (1997) 451e459.
[40] X. Wang, K. Yang, J. Kumar, S.K. Tripathy, K.G. Chittibabu, L. Li, G. Lindsay,
Heteroaromatic chromophore functionalized epoxy-based nonlinear optical
polymers, Macromolecules 31 (1997) 4126e4134.
[
[
[
10] T. Kimura, T. Fukuda, H. Matsuda, A. Komoriya, M. Kazama, M. Kato, et al.,
Branched epoxy copolymers with oligo (benzoate) side chains carrying donor
and acceptor functions in each end, Polym. Adv. Technol. 12 (2001) 231e236.
11] Z. Zhu, Z. Li, Y. Tan, Z. Li, Q. Li, Q. Zeng, et al., New hyperbranched polymers
containing second-order NLO chromophores: synthesis and NLO character-
ization, Polymer 47 (2006) 7881e7888.
12] W. Wu, C. Ye, G. Yu, Y. Liu, J. Qin, Z. Li, New hyperbranched polytriazoles
containing isolation chromophore moieties derived from AB4 monomers

G.N. Nazmieva et al. / Polymer 149 (2018) 253e265
265
[
41] S.V. Shulyndin, T.A. Vakhonina, N.V. Ivanova, E.F. Gubanov, A.N. Ustyugov,
O.D. Fominykh, G.A. Estrina, B.A. Rozenberg, M.B. Zuev, Synthesis and prop-
erties of epoxyamine oligomers and prepolymers with nonlinear-optical
azobenzene chromophores, Polym. Sci. Ser. A 47 (2005) 808e819.
molecular mechanics force fields: potential form, combination rules, and vdW
parameters, J. Am. Chem. Soc. 114 (1992) 7827e7843;
b) T.A. Halgren, V.I. MMFF, MMFF94s option for energy minimization studies,
J. Comput. Chem. 20 (1999) 720e729.
[
42] T.A. Vakhonina, S.M. Sharipova, N.V. Ivanova, O.D. Fominykh, N.N. Smirnov,
A.V. Yakimansky, M.Yu Balakina, O.G. Sinyashin, Nonlinear-optical properties
of epoxyamine-based thin films, Mendeleev Commun. 21 (2011) 75e76.
43] G.N. Nazmieva, T.A. Vakhonina, S.M. Sharipova, N.V. Ivanova, I.R. Nizameev,
M.I. Valitov, N.N. Smirnov, A.V. Yakimanskiy, M.Yu Balakina, Synthesis and
nonlinear optical properties of polyether polyols of azochromophore groups
with different structures, Butlerov Commun 35 (2013) 59e67.
[53] D. Qiu, P.S. Shenkin, F.P. Hollinger, W.C. Still, The GB/SA continuum model for
solvation. A fast analytical method for the calculation of approximate born
radii, J. Phys. Chem. 101 (1997) 3005e3014.
[
[54] MacroModel Version 11.0, Copyright Schrodinger, LLC, New York, 2015.
[55] E. Harder, W. Damm, J. Maple, C. Wu, M. Reboul, J. Xiang, L. Wang, D. Lupyan,
M. Dahlgren, J. Knight, J. Kaus, D. Cerutti, G. Krilov, W. Jorgensen, R. Abel,
R. Friesner, OPLS3: a force field providing broad coverage of drug-like small
molecules and proteins, J. Chem. Theor. Comput. 12 (2016) 281e296.
[56] S.V. Shulyndin, T.A. Vakhonina, G.A. Estrina, B.A. Rozenberg, M.B. Zuev, Syn-
thesis, structure, and properties of bifunctional azobenzene monomers and
polymers on their basis, Polym. Sci. Ser. A 49 (2007) 782e794.
[
[
[
44] G.N. Nazmieva, T.A. Vakhonina, N.V. Ivanova, A.Sh Mukhtarov, N.N. Smirnov,
A.V. Yakimansky, M. Yu Balakina, O.G. Sinyashin, Testing of the ways for
synthesis of new nonlinear optical epoxy-based polymers with azochromo-
phores in the side chain, Eur. Polym. J. 63 (2015) 207e216.
45] Yanling He, Lu Chen, Hua Zhang, Zhuo Chen, Fuyang Huo, Bing Li, Zhen Zhen,
Xinhou Liua, Shuhui Bo, A novel bichromophore based on julolidine chro-
mophores with enhanced transferring efficiency from hyperpolarizability b to
electro-optic activity, J. Mater. Chem. C 6 (2018) 1031e1037.
46] Yanling He, Lu Chen, Liu Fenggang, Zhang Hua, Huo Fuyang, Chen Zhuo,
Liu Jialei, Zhen Zhen, Liu Xinhou, Bo Shuhui, Enhanced electro-optic activity of
two novel bichromophores which are synthesized by Cu(I) catalyzed click-
reaction, Dyes Pigments 139 (2017) 756e763.
[57] Materials Science Suite 2017-1, Schr o€ dinger, LLC, NY, 2017.
[58] A.V. Sharipova, O.D. Fominykh, M.Yu Balakina, Supramolecular organization of
chromophores in nonlinear-optical epoxyamine oligomers with dendrite
chromophore-containing fragments, Butlerov Commun 35 (2013) 10e18.
[59] A.A. Kulkov, Carboxyl-containing Epoxide Oligomers, Ph.D. Thesis, 2006 (in
Russian).
[60] M.J. Cho, D.H. Choi, P.A. Sullivan, A.-J.P. Akelaitis, L.R. Dalton, Recent progress
in second-order nonlinear optical polymers and dendrimers, Prog. Polym. Sci.
33 (2008) 1013e1058.
[47] J.A. Moore, Macromolecular Syntheses, vol. 1, John Wiley & Sons, New York,
1
977, p. 80.
[61] T.A. Chen, A.K.Y. Jen, Y. Cai, Two-step synthesis of side-chain aromatic poly-
imides for second-order nonlinear optics, Macromolecules 29 (1996)
535e539.
[
48] M.W. Dunker, E.R. Starkey, G.L. Jenkins, The preparation of some organic
mercurials from diazonium borofluorides, J. Am. Chem. Soc. 58 (1936)
2
308e2309.
49] P. Che, Y. He, X. Wang, Hyperbranched azo-polymers synthesized by azo-
coupling reaction of an AB monomer and postpolymerization modification,
[62] T.A. Vakhonina, N.V. Ivanova, N.N. Smirnov, A.V. Yakimansky, M.Yu Balakina,
O.G. Sinyashin, Nonlinear-optical properties of methacrylic (co)polymers with
azo chromophores in the side chain, Mendeleev Commun. 24 (2014)
138e139.
[
[
2
Macromolecules 38 (2005) 8657e8663.
50] H. Wang, Y. He, X. Tuo, X. Wang, Sequentially adsorbed electrostatic multi-
layers of branched side-chain polyelectrolytes bearing DonorꢁAcceptor type
azo chromophores, Macromolecules 37 (2004) 135e146.
[63] X. Piao, X. Zhang, Y. Mori, M. Koishi, A. Nakaya, Sh Inoie, I. Aoki, A. Otomo,
Sh Yokoyama, Nonlinear optical side-chain polymers post-functionalized with
high-b chromophores exhibiting large electro-optic property, J. Polym. Sci.,
[
[
51] G. Chang, W.C. Guida, W.C. Still, An internal-coordinate Monte Carlo method
for searching conformational space, J. Am. Chem. Soc. 111 (1989) 4379e4386.
52] a) T.A. Halgren, The representation of van der Waals (vdW) interactions in
Part A: Polym. Chem. 49 (2011) 47e54.
[64] B. Neises, W. Steglich, Simple method for the esterification of carboxylic acids,
Angew. Chem. Int. Ed. 17 (1978) 522e524.