Synthesis and properties of novel nonlinear optical polyester containing nitrophenylazocatecholic group

Article abstract of DOI:10.1080/15421406.2013.808544

A new Y-type polyester (3) containing nitrophenylazocatecholic groups as NLO chromophores, which are parts of the polymer backbone was prepared. Polyester 3 is soluble in common organic solvents such as acetone and dimethylsulfoxide. It shows a thermal st

Full text of DOI:10.1080/15421406.2013.808544

This article was downloaded by: [Moskow State Univ Bibliote]
On: 06 January 2014, At: 06:01
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Molecular Crystals and Liquid Crystals
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/gmcl20
Synthesis and Properties of Novel
Nonlinear Optical Polyester Containing
Nitrophenylazocatecholic Group
Hak Jin Kim a , Mi Young Song a , Byeongman Jeon a & Ju-Yeon Lee a
a Institute of Basic Science, Department of Chemistry and Nano
System Engineering , Inje University , Gimhae , Korea
Published online: 13 Sep 2013.
To cite this article: Hak Jin Kim , Mi Young Song , Byeongman Jeon & Ju-Yeon Lee (2013) Synthesis
and Properties of Novel Nonlinear Optical Polyester Containing Nitrophenylazocatecholic Group,
Molecular Crystals and Liquid Crystals, 581:1, 76-82
To link to this article: http://dx.doi.org/10.1080/15421406.2013.808544
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &
Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Mol. Cryst. Liq. Cryst., Vol. 581: pp. 76–82, 2013
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2013.808544
Synthesis and Properties of Novel Nonlinear
Optical Polyester Containing
Nitrophenylazocatecholic Group
HAK JIN KIM, MI YOUNG SONG, BYEONGMAN JEON,
AND JU-YEON LEE∗
Institute of Basic Science, Department of Chemistry and Nano System
Engineering, Inje University, Gimhae, Korea
A new Y-type polyester (3) containing nitrophenylazocatecholic groups as NLO chro-
mophores, which are parts of the polymer backbone was prepared. Polyester 3 is soluble
in common organic solvents such as acetone and dimethylsulfoxide. It shows a thermal
stability up to 280◦C from thermogravimetric analysis with glass-transition temperature
(Tg) obtained from differential scanning calorimetry near 86◦C. The second harmonic
generation (SHG) coefficient (d33) of poled polymer film at the 1064 nm fundamental
wavelength is around 4.42 × 10−9 esu. The dipole alignment exhibits a thermal stability
even at 4◦C higher than Tg, and no SHG decay was observed below 90◦C due to the
partial main-chain character of polymer structure, which is acceptable for NLO device
applications.
Keywords Differential scanning calorimetry (DSC); dipole alignment; NLO;
polyester; SHG coefficient; thermogravimetric analysis (TGA)
Introduction
Nonlinear optical (NLO) polymers have been extensively studied over the past decade
because of their potential applications in electro-optic and photonic devices such as mod-
ulators and switches, due to their larger optical nonlinearity, lower dielectric constants,
ultrafast response time and easier processability [1–3]. One of the current tasks is to design
novel NLO polymers having optimized properties. In the developments of NLO polymers
for electro-optic device applications, stabilization of electrically induced dipole alignment
is one of important criteria [4]; in this context, two approaches to minimize the random-
ization have been proposed, namely the use of cross-linking method [5] and the utilizing
high glass-transition temperature (Tg) polymers [6]. Polyesters containing amino-sulfone
azobenzene chromophores in the main chain exhibit strong and stable reversible birefrin-
gence [7]. NLO polyesters with azobenzene mesogens in the main chain show high thermal
and temporal stabilities [8]. Polyesters having cyanophenylazoaniline moiety in the side
chain display good temporal stability of second-order nonlinearity [9]. In general, poly-
mers with the NLO chromophores in the main chain have good thermal stability of dipole
∗Address correspondence to Ju-Yeon Lee, Institute of Basic Science, Department of Chemistry
and Nano System Engineering, Inje University, 607 Obang-dong, Gimhae 621-749, Korea. Tel.:
+82-55-320-3221; Fax: +82-55-321-9718. E-mail: chemljy@inje.ac.kr
[454]/76

Synthesis and Properties of Novel NLO Polyester
[455]/77
Figure 1. Main chain NLO polymers (a), side chain NLO polymers (b), and Y-type NLO polymers
(c).
alignments, but they often do not dissolve in organic solvents, and their intractability make
them unusable to fabricate stable noncentrosymmetric films. Side chain NLO polymers
have the advantages such as good solubility and homogeneity, but they often suffer from
poor stability of dipole alignments at high temperatures. Recently we reported novel NLO
polyesters containing dioxynitrostilbene [10] or tricyanovinylthiazole [11], which showed
enhanced thermal stability of dipole alignments. In this work reported here, we prepared
new Y-type polyester containing nitrophenylazocatecholic groups as NLO chromophores.
We selected the latter as NLO chromophores because they are expected to have high optical
nonlinearities. Furthermore, these nitrophenylazocatecholic groups constitute novel Y-type
NLO polyesters (Fig. 1c), and these Y-type NLO polyesters have not yet been reported in
the literature. Thus, we synthesized a new type of NLO polyester, in which the pendant
NLO chromophores are parts of the polymer backbones. This Y-type NLO polymer is
expected to have the advantages of both main-chain and side-chain NLO polymers, namely
stable dipole alignment and good solubility. After confirming the structure of the resulting
polymer, we investigated its thermal and nonlinear optical properties. We now report the
results of the initial phase of the work.
Experimental
Materials
Synthetic method of polymer 3 is summarized in Scheme 1. The polymer was further
purified by extraction in a Soxhlet extractor with methanol and dried under vacuum, yielding
4.20 g (88% yield) of polymer 3. Inherent viscosity (ηinh) = 0.31 dL/g (c, 0.5 g/dL in DMSO
at 25◦C). 1H NMR (DMSO-d6) δ 4.35–4.67 (m, 8H, 2 -O-CH2-CH2-O-), 7.32–7.37 (s, 1H,
aromatic), 7.58–7.61 (s, 1H, aromatic), 7.67–8.08 (d, 7H, aromatic), 8.31–8.43 (m, 2H,

78/[456]
H. J. Kim et al.
Scheme 1. Synthetic scheme and structure of polymer 3.
aromatic). IR (KBr) 2928 (m, C-H), 1722 (vs, C O), 1592 (s, N N), 1520, 1344 (s, N O)
cm−1. Anal. Calcd for (C24H19N3O8)n: C, 60.38; H, 4.01; N, 8.80. Found: C, 60.46; H,
4.08; N, 8.72.
Measurements
Infrared (IR) spectra were obtained with a Varian FT IR-1000 IR spectrophotometer.
1H NMR spectra were obtained with a Varian VNMRS 500 MHz NMR spectrometer.
UV-visible absorption spectra were obtained with a SECOMAM Model UVIKON XS
99-90289 spectrophotometer. Tg values were measured using a TA 2920 differential scan-
ning calorimeter (DSC) in a nitrogen atmosphere. A TA Q50 thermogravimetric analyzer
(TGA) with a heating rate of 10◦C/min up to 800◦C was used for the thermal degradation of
polymers under nitrogen. The number-average molecular weight (Mn) and weight-average
molecular weight (Mw) of the polymers were estimated using gel permeation chromatog-
raphy (GPC; styragel HR5E4E columns; THF solvent). The refractive index of the sample
was measured using the optical transmission technique [12]. Second harmonic generation
(SHG) measurements were made using a Maker fringe technique [13]. SHG coefficients
(d33) were derived from the analysis of measured Maker-fringes.
Results and Discussion
Synthesis and Characterization of Polymer 3
Polyester 3 was synthesized through the reaction of monomer 2 containing NLO chro-
mophore with stoichiometric amounts of terephthaloyl chloride in pyridine. The synthetic

Synthesis and Properties of Novel NLO Polyester
[457]/79
route for polymer 3 is presented in Scheme 1. The chemical structure of the resulting poly-
1
mer was confirmed by H NMR, IR spectra, and elemental analysis. The chemical shifts
in 1H NMR spectrum of the polymer are consistent with the proposed polymer structure.
The IR spectrum of polymer 3 shows strong carbonyl peak near 1722 cm−1 indicating the
presence of ester bond. The spectrum also shows strong absorption peak near 1592 cm−1
due to azo group and absorptions at 1520 and 1344 cm−1 due to nitro group indicating
the presence of nitroazobenzene unit. These results are consistent with the proposed struc-
ture, indicating that the NLO chromophores remained intact during the polymerization.
The number average molecular weight (Mn) of the polymer 3, determined by GPC, was
16,500 (Mw/Mn = 1.92). The structural feature of this polymer is that it has pendant NLO
chromophores, which are parts of the polymer main chains. Thus the resulting polymer 3 is
mid type of side-chain and main-chain NLO polymer, and is expected to have both of their
merits. The polymer 3 is soluble in common solvents such as acetone, DMF, and DMSO,
but is not soluble in methanol and diethyl ether. The inherent viscosity value is 0.31 dL/g.
Polymer 3 shows strong absorption near 385 nm due to the nitrophenylazocatecholic NLO
chromophore.
Thermal Properties of Polymer
The thermal behavior of the polymer was investigated by TGA and DSC to determine the
thermal degradation pattern and glass transition temperature. Polymer 3 shows a thermal
stability up to 280◦C from its TGA thermogram. The 5% weight loss degradation temper-
ature of polymer 3 is near 285◦C. Tg value of the polymer 3 measured by DSC is around
86◦C. This Tg value is lower than that of the polyester containing dioxynitrostilbene, which
is near 110◦C [10]. The lower Tg value of polymer 3 is probably due to the easier cis-trans
isomerization of diazo linkage than that of carbon-carbon double bond.
Nonlinear Optical Properties of Polymer
The NLO properties of polymer 3 were studied by the SHG method. To induce noncen-
trosymmetric polar order, the spin-coated polymer film was corona-poled. As the tem-
perature was raised gradually to 5–10◦C higher than Tg, a corona voltage of 6.5 kV was
applied and this temperature was maintained for 30 min. The film was cooled to room
temperature in the presence of the electric field. Finally, the electric field was removed.
After electric poling, the NLO chromophores were aligned and the UV-visible absorption
of polymer 3 exhibits a slight blue shift and a decrease in absorption due to birefringence.
SHG measurements were performed at a fundamental wavelength of 1064 nm using a mode
locked Nd-YAG laser. In 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 3. The SHG values were compared with
those obtained from a Y-cut quartz plate. SHG coefficients (d33, d31) were derived from
the analysis of measured Maker-fringes with the Pascal fitting program according to the
literature procedure [13]. Nonlinear optical properties of polymer 3 are summarized in
Table 1. The values of d33 and d31 for polymer 3 are 4.42 × 10−9 esu and 1.49 × 10−9 esu,
respectively. This d33 value is lower than that of polyester containing 3,4-dioxynitrostilbene
group, which has near 3.59 × 10−8 esu [10]. The lower optical nonlinearity of the polymer
3 is probably due to the easier cis-trans isomerization of diazo linkage. Since the second

80/[458]
H. J. Kim et al.
Figure 2. Angular dependence of SHG signal for a poled film of polymer 3.
harmonic wavelength is at 532 nm, which is not in the absorptive region of the resulting
polyester, there is not resonant contribution to this d33 value.
To evaluate the high-temperature stability of the polymer, we studied the temporal
stability of the SHG signal. Figure 3 shows the dynamic thermal stability study of the
NLO activity of a film of polymer 3. To investigate the real time NLO decay of the SHG
signal of the poled polymer film as a function of temperature, in situ SHG measurement
was performed at a heating rate of 4◦C/min from 30 to 180◦C. The polymer film exhibits a
thermal stability even at 4◦C higher than Tg and no significant SHG decay is observed below
90◦C. The SHG thermal stability of polymer 3 is lower than that of polyester containing
3,4-dioxynitrostilbene group, which may stem from the easier cis-trans isomerization of
diazo linkage and/or lower Tg value. In general, main-chain NLO polymers have good
thermal stability of dipole alignments, and side-chain NLO polymer systems have good
solubility. The SHG thermal stability of polymer 3 up to 90◦C is due to the stabilization of
dipole alignment of NLO chromophore, which stems from the partial main chain character
of the polymer structure. Thus, we made new NLO polyester with stable dipole alignment
and good solubility.
Table 1. Nonlinear optical properties of polymer 3
Film thicknessc
a
b
b
λmax
(nm)
d33
d31
Polymer
(esu)
(esu)
(μm)
n
3
385
4.42 × 10−9
1.49 × 10−9
0.50
1.724
aPolymer film after poling.
bSHG coefficients (d33) were derived from the analysis of measured Maker-fringes [13].
cFilm thickness was determined by the optical transmission technique [12].

Synthesis and Properties of Novel NLO Polyester
[459]/81
Figure 3. Normalized SHG signal of polymer 3 as a function of temperature at a heating rate of
4◦C/min.
Conclusions
A novel Y-type NLO polyester 3 with pendant NLO chromophores as parts of the polymer
backbones was prepared and characterized. This Y-type polymer 3 is soluble in common
organic solvents and shows a thermal stability up to 280◦C with Tg value around 86◦C. The
SHG coefficient (d33) of corona-poled polymer film is 4.42 × 10−9 esu. Polymer 3 exhibits
SHG stability even at 4◦C higher than Tg and no significant SHG decay is observed below
90◦C. This enhanced thermal stability of optical nonlinearity stems from the stabilization
of dipole alignment of the NLO chromophores, which constitute parts of the polymer main
chains.
Acknowledgment
This research was supported by Basic Science Research Program through the National
Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and
Technology (No. 2012-0007485).
References
[1] Burland, D. M., Miller, R. D., & Walsh, C. (1994). Chem. Rev., 94, 31.
[2] Cho, Y. J., Kim, M. S., & Lee, J. Y. (2011). Mol. Cryst. Liq. Cryst., 539, 102.
[3] Ikeda, T., Tadaki, Y., Funajima, R., Tatewaki, Y., & Okada, S. (2011). Mol. Cryst. Liq. Cryst.,
539, 142.
[4] Rau, I. (2008). Mol. Cryst. Liq. Cryst., 485, 862.
[5] Lee, J. W., & Kawatsuki, N. (2009). Mol. Cryst. Liq. Cryst., 498, 59.
[6] Tsutsumi, N., Morishima, M., & Sakai, W. (1998). Macromolecules, 31, 7764.
[7] Xu, Z. S., Drnoyan, V., Natansohn, A., & Rochon, R. (2000). J. Polym. Sci. Part A: Polym.
Chem., 38, 2245.
[8] Sandhya, K. Y., Pillai, C. K. S., Sato, M., & Tsutsumi, N. (2003). J. Polym. Sci. Part A: Polym.
Chem., 41, 1527.

82/[460]
H. J. Kim et al.
[9] Nemoto, N., Miyata, F., Nagase, Y., Abe, J., Hasegawa, M., & Shirai, Y. (1996). Macromolecules,
29, 2365.
[10] Lee, J. Y., Jung, W. T., & Lee, W. J. (2006). Polym. Int. 58, 248.
[11] Cho, Y. J., Kim, M. S., & Lee, J. Y. (2011). Mol. Cryst. Liq. Cryst., 539, 109.
[12] Cisneros, J. I. (1998). Appl. Opt., 37, 5262.
[13] Herman, W. N., & Hayden, L. M. (1995). J. Opt. Soc. Am. B., 12, 416.