Synthesis of novel Y-type nonlinear optical polyurethane containing tricyanovinylthiophene with high thermal stability of dipole alignment

Article abstract of DOI:10.1080/15421400902950196

A novel Y-type polyurethane 7 containing 1-(2,4-dioxyethoxy)phenyl-2-{5-(1, 2,2- tricyanovinyl)-2-thiophenyl)}ethenyl groups as nonlinear optical (NLO)- chromophores, which are components of the polymer backbones, was prepared. Polyurethane 7 is soluble in common organic solvents such as DMF and DMSO. It showed a thermal stability up to 280°C in TGA thermogram and the T _g value obtained from DSC thermogram was around 163°C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer film at 1560nm fundamental wavelength was around 3.72×10^-9 esu. The dipole alignment exhibited a thermal stability up to near T_g, and there was no SHG decay below 150°C due to the partial main-chain character of the polymer structure, which is acceptable for nonlinear optical device applications. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/15421400902950196

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Synthesis of Novel Y-
Type Nonlinear Optical
Polyurethane Containing
Tricyanovinylthiophene with
High Thermal Stability of
Dipole Alignment
Han-Na Jang a , Hyo Jin No a & Ju-Yeon Lee a
a Institute of Basic Science, Department of
Chemistry, Inje University , Gimhae, Korea
Published online: 25 Jun 2009.
To cite this article: Han-Na Jang , Hyo Jin No & Ju-Yeon Lee (2009) Synthesis of Novel
Y-Type Nonlinear Optical Polyurethane Containing Tricyanovinylthiophene with High
Thermal Stability of Dipole Alignment, Molecular Crystals and Liquid Crystals, 504:1,
204-211, DOI: 10.1080/15421400902950196
To link to this article: http://dx.doi.org/10.1080/15421400902950196
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Mol. Cryst. Liq. Cryst., Vol. 504, pp. 204–211, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400902950196
Synthesis of Novel Y-Type Nonlinear Optical
Polyurethane Containing Tricyanovinylthiophene
with High Thermal Stability of Dipole Alignment
Han-Na Jang, Hyo Jin No, and Ju-Yeon Lee
Institute of Basic Science, Department of Chemistry, Inje University,
Gimhae, Korea
A novel Y-type polyurethane 7 containing 1-(2,4-dioxyethoxy)phenyl-2-{5-(1,2,2-
tricyanovinyl)-2-thiophenyl)}ethenyl groups as nonlinear optical (NLO)-
chromophores, which are components of the polymer backbones, was prepared.
Polyurethane 7 is soluble in common organic solvents such as DMF and DMSO.
It showed a thermal stability up to 280ꢀC in TGA thermogram and the Tg value
obtained from DSC thermogram was around 163ꢀC. The second harmonic genera-
tion (SHG) coefficient (d33) of poled polymer film at 1560 nm fundamental wave-
length was around 3.72 Â 10À9 esu. The dipole alignment exhibited a thermal
stability up to near Tg, and there was no SHG decay below 150ꢀC due to the partial
main-chain character of the polymer structure, which is acceptable for nonlinear
optical device applications.
Keywords: differential scanning calorimetry (DSC); NLO; polyurethane; relaxation of
dipole alignment; SHG coefficient; thermogravimetric analysis (TGA)
INTRODUCTION
Recently there has been an extensive effort to synthesize novel
nonlinear optical (NLO) materials because of their potential applica-
tions in the field of electro-optic devices [1–3]. Among them, NLO
polymers are considered promising materials, mainly because they offer
many advantages such as light weight and good processability to form
optical devices. In the developments of NLO polymers, stabilization of
This work was supported by the 2009 Korea Research Foundation Grant funded by
the Korean Government (#2009-007052).
Address correspondence to Ju-Yeon Lee, Institute of Functional Materials Depart-
ment of Chemistry, Inje University 607 Obang-dong, Gimhae 621-749, Korea. E-mail:
chemljy@inje.ac.kr
204

Synthesis of Novel Y-Type NLO Polyurethane
205
electrically induced dipole alignment is one of important considerations
[4]. Two approaches to minimize the randomization have been pro-
posed, that is to use crosslinking method [5–6] and to utilize high Tg
polymers such as polyimides [7–8]. Polyurethane matrix forms exten-
sive hydrogen bond between urethane linkage and increases rigidity
preventing the relaxation of induced dipoles. Polyurethanes with a
NLO chromophore, whose dipole moment is aligned transverse to
the main chain backbone, showed enhanced thermal stability [9–10].
A polyurethane with a thiophene ring having a tricyanovinyl group
in the polymer side chain showed enhanced thermal stability
[11–12]. In general, main-chain NLO polymers exhibit good thermal
stability of dipole alignments, but they often do not dissolve in organic
solvents. Side-chain NLO polymers have the advantages such as good
solubility and high level of NLO chromophore, but they often suffer
from poor stability of dipole alignments at high temperatures.
Recently we reported novel NLO polyurethanes containing dioxyni-
trostilbenyl group [13] and dioxybenzylidenemalononitrile [14] with
enhanced thermal stability of dipole alignments. In this work we
have prepared novel polyurethane containing 1-(2,4-dioxyethoxy)
phenyl)-2-{5-(1,2,2-tricyanovinyl)-2-thiophenyl)}ethenyl groups as NLO-
chromophores. We selected the latter because they have a large
dipole moment. Furthermore, 1-(2,4-dioxyethoxy)phenyl)-2-{5-(1,2,2-
tricyanovinyl)-2-thiophenyl)}ethenyl group constitutes a novel Y-type
NLO polyurthane (see Fig. 1b), in which the structure of NLO chromo-
phore, and this Y-type NLO polyurethane is not described in the
literature. Thus we made a new type of NLO polyurethane, in which
the pendant NLO-chromophores are components of the polymer back-
bones. These mid-type NLO polymers are expected to have the advan-
tages of both main-chain and side-chain NLO polymers namely stable
FIGURE 1 Side chain NLO polymers (a) and Y-type NLO polymers (b).

206
Han-Na Jang et al.
dipole alignment and good solubility. After confirming the structure of
the resulting polymer, we investigated its properties such as thermal
stability and second harmonic generation (SHG) activity (d33). We now
report the results of the initial phase of the work.
EXPERIMENTAL
Materials
Synthetic method of polymer 7 is summarized in Scheme 1. Polymer 7:
ginh ¼ 0.30 dL=g (c, 0.5 g=dL in DMSO at 25ꢀC). 1H NMR (DMSO-d6) d
3.73–4.13 (m, 8H, -O-CH2-, 2 –OCH3), 4.21–4.68 (m, 6H, -O-CH2-,
2-O-CH2-OCO-), 6.59–6.75 (m, 1H, aromatic), 7.02–7.88 (m, 11H, aro-
matic), 8.18–8.35 (d, 1H, aromatic), 8.53–8.71 (d, 1H, N-H), 8.95–9.12
(s, 1H, N-H). IR (KBr) 3397 (s, N-H), 2939 (m, C-H), 2219 (m, CN),
1687 (s, C ¼ O), 1595 (s, C ¼ C) cmꢁ1. Anal. Calcd for (C37H29N5O8S)n:
C, 63.15; H, 4.15; N, 9.95; S, 4.56. Found: C, 63.24; H, 4.18; N, 9.88; S,
4.62.
Measurements
IR, 1H NMR, and UV-Vis spectra were taken on a Shimadzu FT
IR-8201PC infrared spectrophotometer, Varian 300 MHz NMR
SCHEME 1 Synthetic scheme and structure of polymer 7.

Synthesis of Novel Y-Type NLO Polyurethane
207
spectrometer, and Shimadzu UV-3100S spectrophotometer, respectively.
Elemental analyses were performed using a Perkin-Elmer 2400 CHN
elemental analyzer. Tg values were measured on a TA 2920 differen-
tial scanning calorimeter (DSC) in a nitrogen atmosphere. TA Q50
thermogravimetric analyzer (TGA) with a heating rate of 10ꢀC=min
up to 800ꢀC was used for the thermal degradation study of polymers
under nitrogen. The number average molecular weight (Mn) and
weight average molecular weight (Mw) of the polymer were estimated
by gel permeation chromatography (GPC) (columns styragel HR5E4E;
solvent THF). The alignment of the NLO-chromophore of the polymer
was carried out by corona poling method. The refractive index of the
polymer sample was measured by the optical transmission technique
[15]. Second harmonic generation (SHG) measurements were made
using a Maker fringe technique [16].
RESULTS AND DISCUSSION
Synthesis and Characterization of Polymer 7
Synthetic method of polyurethane 7 is summarized in Scheme 1.
Polymer 6 was prepared by the polyaddition reaction between a diol
5 and 3,30-dimethoxy-4,40-biphenylenediisocyanate. Polymer 6 was
reacted with tetracyanoethylene in anhydrous DMF [11–12] to yield
polyurethane
7
containing 1-(2,4-dioxyethoxy)phenyl)-2-{5-(1,2,2-
tricyanovinyl)-2-thiophenyl)}ethenyl group as a NLO-chromophore.
The chemical structure of the polymer was confirmed by 1H NMR,
IR spectra, and elemental analysis. Elemental analysis results fit
1
the polymer structure. H NMR spectrum of the polymer showed a
signal broadening due to polymerization, but the chemical shifts are
consistent with the proposed polymer structure. The IR spectrum of
polymer 7 showed strong absorption peak near 2219 cmꢁ1 indicating
the presence of nitrile group. The IR spectrum of the same polymer
sample also showed a strong carbonyl peak near 1687 cmꢁ1 indicating
the presence of urethane bond. These results are consistent with the
proposed structure, indicating that the tricyanovinyl groups are intro-
duced well to thiophene ring. The number average molecular weight
(Mn) of the polymer 7, determined by GPC, was 18200 (Mw=Mn ¼ 1.93).
The polymer 7 was soluble in common solvents such as DMF and
DMSO, but was not soluble in methanol and diethyl ether. The inher-
ent viscosity value was 0.30 dL;g. Polymer 7 showed strong absorption
near 581 nm by the NLO-chromophore 1-(2,4-dioxyethoxy)phenyl)-
2-{5-(1,2,2-tricyanovinyl)-2-thiophenyl)}ethenyl group. The striking
feature of this polymerization system is that it gives unprecedented

208
Han-Na Jang et al.
Y-type NLO polymer, in which the pendant NLO chromophores are
parts of the polymer backbones. These mid-type NLO polymers are
expected to have the advantages of both main-chain and side-chain
NLO polymers. Thus, we obtained a new type of NLO polyurethane
with side-chain and main-chain characteristics.
Thermal Properties of Polymer
The thermal behavior of the polymer was investigated by TGA and
DSC to determine the thermal degradation pattern and Tg. Polymer
7 showed a thermal stability up to 280ꢀC according to its TGA thermo-
gram. The Tg value of the polymer 4 measured by DSC was around
163ꢀC. The TGA and DSC studies showed that the decomposition
temperature of the polyurethane 7 was higher than the corresponding
Tg value. This indicates that high-temperature poling for a short term
is feasible without damaging the NLO chromophore.
Nonlinear Optical Properties of Polymer
The NLO properties of polymer were studied by the SHG method. To
induce noncentrosymmetric polar order, the spin-coated polymer films
were corona-poled. As the temperature was raised gradually to 165ꢀC,
6.5 kV of corona voltage was applied and this temperature was main-
tained for 30 min. The UV-Vis absorption spectra of the polymers
before and after the poling were recorded. After electric poling, the
dipole moments of the NLO-chromophores were aligned and UV-Vis
spectrum of polymer 7 exhibited a slight blue shift and a decrease in
absorption due to birefringence. From the absorbance change, the
order parameter of the poled film could be estimated, which is related
to the poling efficiency. The estimated order parameter value U of
polymer 7 was equal to 0.25. SHG measurements were performed at
a fundamental wavelength of 1560 nm using a mode locked Nd-YAG
laser. NLO properties of polymer 7 are summarized in Table 1. In
TABLE 1 Nonlinear Optical Properties of Polymer 7
Polymer kmaxa(nm)
581
aPolymer film.
d33b(esu)
Uc
d31b(esu)
Film thicknessd (mm)
n
7
3.72 ꢂ 10ꢁ9 0.25 1.19 ꢂ 10ꢁ10
0.50
1.56
bSHG coefficients (d33) were derived from the analysis of measured Maker-fringes [16].
cOrder parameter U ¼ 1ꢁA1=A0, where A0 and A1 are the absorbances of the polymer
film before and after corona poling, respectively.
dFilm thickness was determined by the optical transmission technique [15].

Synthesis of Novel Y-Type NLO Polyurethane
209
FIGURE 2 Angular dependence of SHG signal in a poled film of polymer 7.
order to determine the microscopic second-order susceptibility of the
polymer, the angular SHG dependence was recorded. Figure 2 shows
the angular dependence of SHG signal in a poled polymer 7. The
SHG values were compared with those obtained from a Y-cut quartz
plate. SHG coefficients (d33) were derived from the analysis of mea-
sured Maker-fringes with Pascal fitting program according to the lit-
erature procedure [16]. The preliminary measured values of d33 and
d31 for polymer 7 were 3.72 ꢂ 10ꢁ9 and 1.19 ꢂ 10ꢁ10 esu, respectively.
Since the second harmonic wavelength was at 780 nm, which is not in
the absorptive region of the resulting polymer, there was not resonant
contribution to this d33 value.
To evaluate the high-temperature stability of the polymers, we stu-
died the temporal stability of the SHG signal. In Figure 3, we present
the dynamic thermal stability study of the NLO activity of the film 7.
To investigate the real time NLO decay of the SHG signal of the poled
polymer film as a function of temperature, in situ SHG measurements
were performed at a heating rate of 3.5ꢀC=min from 25ꢀC to 250ꢀC.
The polymer film exhibited a thermal stability up to near Tg and no
significant SHG decay was observed below 150ꢀC, as shown in
Figure 3. In general, side chain NLO polymers lose thermal stability
of dipole alignment below Tg. Stabilization of dipole alignment is a
characteristic of main chain NLO polymer. The enhanced thermal
stability of SHG of polymer 7 is due to the stabilization of dipole

210
Han-Na Jang et al.
FIGURE 3 Normalized SHG signal of polymer 7 as a function of temperature
at a heating rate of 3.5ꢀC=min.
alignment of NLO chromophore, which stems from the partial main
chain character of the polymer structure and partly by hydrogen
bonds between the neighboring urethane linkages. Thus, we obtained
a new type of NLO polyurethane having both of the merits of main
chain- and side-chain NLO polymers namely stabilization of dipole
alignment and good solubility.
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