Synthesis and electro-optic properties of novel X-type polyurethane containing nitrophenylazonitroresorcinoxy group with highly enhanced thermal stability of dipole alignment

Article abstract of DOI:10.1002/pola.27070

Novel X-type polyurethane 4 containing 4-(4-nitrophenylazo)-6- nitroresorcinoxy groups as nonlinear optical (NLO) chromophores, which are parts of the polymer main chains, was prepared and characterized. Polyurethane 4 is soluble in common organic solvent

Full text of DOI:10.1002/pola.27070

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
Synthesis and Electro-Optic Properties of Novel X-Type Polyurethane
Containing Nitrophenylazonitroresorcinoxy Group with Highly Enhanced
Thermal Stability of Dipole Alignment
Hak Jin Kim,1 Ji-Hyang Lee,1 Ju-Yeon Lee2
1Institute of Basic Science, Department of Nano System Engineering, Inje University, 607 Obang-dong, Gimhae 621-749, Korea
2Institute of Basic Science, Department of Chemistry and Nano System Engineering, Inje University, 607 Obang-dong, Gimhae
621-749, Korea
Correspondence to: J.-Y. Lee (E-mail: chemljy@inje.ac.kr)
Received 19 October 2013; accepted 10 December 2013; published online 26 December 2013
DOI: 10.1002/pola.27070
ABSTRACT: Novel X-type polyurethane 4 containing 4-(4-nitro-
phenylazo)-6-nitroresorcinoxy groups as nonlinear optical
(NLO) chromophores, which are parts of the polymer main
chains, was prepared and characterized. Polyurethane 4 is solu-
ble in common organic solvents such as acetone and N,N-
dimethylformamide. It shows thermal stabilities up to 270 ꢀC
from thermogravimetric analysis with glass transition tempera-
ture obtained from differential scanning calorimetry of about
5.37 3 1029 esu. Polymer 4 exhibits a thermal stability up to
Tg, and no significant SHG decay is observed below 135 ꢀC,
C
V
which is acceptable for NLO device applications. 2013 Wiley
Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52,
760–766
KEYWORDS: atomic force microscopy (AFM); differential scan-
ning calorimetry (DSC); NLO; polyurethane; second harmonic
generation (SHG); thermal stability; thermogravimetric analysis
(TGA)
134 ꢀC. The second harmonic generation (SHG) coefficient (d33
)
of poled polymer film at 1064 nm fundamental wavelength is
exhibit large second-order nonlinearity with good
thermal stability.27,28 Polymers with H-type NLO chromo-
phores exhibit a thermal stability and large optical nonli-
nearity.22 Physically crosslinked systems via hydrogen bonds
have the advantages such as homogeneity and good process-
ability relative to chemically crosslinked systems, which suf-
fer from significant optical loss and poor solubility. Recently,
we prepared novel Y-type polyurethanes containing dioxyni-
trostilbene,29 dioxynitroazobenzene,30 and dioxybenzylidene-
malononitrile as NLO chromophores.31,32 The resulting
polymers exhibit enhanced thermal stability of second har-
monic generation (SHG), which stems from the stabilization
of dipole alignment of the NLO chromophore at high
temperature.
INTRODUCTION Nonlinear optical (NLO) materials have
attracted much attention in the past two decades because of
their vast applications in the field of electro-optic technology
such as telecommunications, optical data storage, and optical
information processing.1–9 Among them, the organic NLO
polymers seem to be superior because of their higher NLO
activity, faster response time, low cost, wide response wave
band, high optical damage threshold, and good processability
to form electro-optic devices. A potential NLO polymer must
contain highly polarizable conjugated electronic systems and
has to be mechanically very strong and thermally stable. In
the manufacturing of NLO polymers for electro-optic device
applications, stabilization of electrically induced dipole align-
ment is one of the most challenging task; in this context, sev-
eral approaches to minimize the randomization have been
proposed such as the use of crosslinked systems,10–15 the
utilization of polyimides16–21 with high glass transition tem-
perature (Tg), and H-shape polymers.22 A polyurethane
matrix forms strong hydrogen bonding between urethane
linkages, which increases rigidity preventing the relaxation
of induced dipoles.23,24 Polyurethanes functionalized with
hemicyanine25 and thiophene ring26 in side chain show an
enhanced thermal stability of aligned dipoles. Polyurethanes
having dipole moments aligning transverse to the main chain
In this work reported here, we have prepared novel polyur-
ethane containing 4-(4-nitrophenylazo)-4-nitroresorcinoxy
groups as NLO chromophores. We selected the latter as NLO
chromophores because they are expected to have higher
optical nonlinearities and thermal stability due to a quadru-
ple conjugation and planarity of the dipole moments. Azo-
benzene groups have advantages to be aligned by an
external electric field to obtain an asymmetric arrangement
of chromophores required for the second-order nonlinearity.
C
V
2013 Wiley Periodicals, Inc.
760
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 760–766

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
tial scanning calorimeter DSC in a nitrogen atmosphere. A TA
ꢀ
Q50 thermogravimetric analyzer with a heating rate of 10 C
min21 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 chroma-
tography (GPC; styragel HR5E4E columns; tetrahydrofuran
(THF) solvent). AFM images were recorded with a Park Sci-
ence Instrument Autoprobe CP, operated in a contact mode,
which measures topography. Viscosity values were obtained
using a Cannon-Fenske viscometer.
Film Preparation and SHG Measurements
Polymer films were prepared from a 10-wt % polymer solu-
tion in DMF deposited on an indium-tin oxide (ITO) covered
glass. Before film casting, the polymer solution was filtered
R
V
through 0.45-mm Teflon membrane filter. The films were
spin-cast at room temperature in the range 1000–1200 rpm.
The films were dried for 12 h under vacuum at 60 ꢀC. The
alignment of the NLO chromophore of the polymers was car-
ried out using a corona poling method. The poling was per-
formed in a wire-to plane geometry under in situ conditions.
The discharging wire to plane distance was 10 mm. As the
FIGURE 1 Main Chain NLO polymers (a), side chain NLO poly-
mers (b), and X-type NLO polymers (c).
Furthermore, these 4-(4-nitrophenylazo)-6-nitroresorcinoxy
groups can be incorporated into novel X-type NLO polyur-
thanes [see Fig. 1(c)]. The structure of NLO chromophores
and these X-type NLO polyurethanes have not yet been
described in the literature. Thus, we formulated new promis-
ing NLO polyurethane, in which the pendant NLO chromo-
phores are components of the polymer backbone. This X-
type NLO polymer is expected to have the merits of both
main chain [Fig. 1(a)] and side chain [Fig. 1(b)] NLO poly-
mers, namely stable dipole alignment and good solubility.
After confirming the structure of the resulting polymer, we
investigated its properties such as Tg, thermal stability, sur-
face morphology of polymer films, and SHG activity.
ꢀ
temperature was raised gradually to 5–10 C higher than Tg,
a corona voltage of 6.5 kV was applied and the temperature
was maintained for 30 min. The films were cooled to room
temperature in the presence of the electric field. Finally, the
electric field was removed. The refractive index of the sam-
ple was measured using the optical transmission tech-
nique.33 The transmittance of thin film gives information on
the thickness, refractive index, and extinction coefficient of
the film. Thus, we can determine these parameters by ana-
lyzing the transmittance. SHG measurement was carried out
1 day after poling. A continuum PY61 mode-locked Nd:YAG
laser (k 5 1064 nm) with pulse width of 40 ps and repeti-
tion rate of 10 Hz was used as the fundamental light source
and Y-cut quartz was used as reference. A poled polymer
film was mounted on the rotator coupled to a step motor.
The output signals from the photodiode and photomultiplier
tube (PMT) were detected as a function of the incident
angle. A 3-mm-thick Y-cut quartz crystal (a piece of quartz
plate whose plane is perpendicular to the crystalline y-axis
and the thickness of the plate is 3 mm and d11 5 0.3 pm
V21) was used as a reference for determining the relative
intensities of the SH signals generated from the samples. The
Maker Fringe pattern was obtained by measuring the SHG
signal at 0.5ꢀ intervals using a rotation stage. SHG coeffi-
cients (d33) were derived from the analysis of measured
Maker-fringes.34
EXPERIMENTAL
Materials
Reagent-grade chemicals were purchased from Aldrich or
AlfaAesar and purified by either distillation or recrystalliza-
tion before use. All glassware was thoroughly dried under
vacuum with a hot air gun before use. 4-(4-Nitrophenylazo)
resorcinol, 2-chloroethyl vinyl ether, and bismuth(III) tri-
fluoromethanesulfonate were used as supplied. 3,30-Dime-
thoxy-4,40-biphenylenediisocyanate was recrystallized from
ethyl acetate. N,N-Dimethylformamide (DMF) was purified by
drying with anhydrous calcium sulfate, followed by distilla-
tion under reduced pressure.
Instrumentation
Preparation of 2,4-Di-(2’-vinyloxyethoxy)-40-
Infrared (IR) spectra were obtained with a Varian FTIR-1000
IR spectrophotometer. H NMR spectra were obtained with a
nitroazobenzene (1)
1
4-(4-Nitrophenylazo)resorcinol (25.9 g, 0.10 mol), anhydrous
potassium carbonate (82.9 g, 0.60 mol), and 2-chloroethyl
vinyl ether (32.0 g, 0.30 mol) were dissolved in 400 mL of
dry DMF under nitrogen. The mixture was refluxed in an oil
bath kept at 90 ꢀC for 24 h under nitrogen. The resulting
solution was cooled to room temperature, diluted with 300
Varian VNMRS 500-MHz NMR spectrometer. UV–visible
absorption spectra were obtained with a SECOMAM Model
UVIKON XS 99-90289 spectrophotometer. Elemental analyses
were performed using a Perkin-Elmer 2400 CHN elemental
analyzer. Tg values were measured using a TA 2920 differen-
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 760–766
761

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
mL of water, and extracted with 300 mL of diethyl ether
three times. The organic layer was washed with saturated
aqueous sodium chloride solution and dried with anhydrous
magnesium sulfate. Rotary evaporation of diethyl ether gave
crude product, which was purified by column chromatogra-
phy (ethyl acetate/hexane 5 1/2 by volume). Thus, obtained
product was washed with 10% aqueous ethanol and dried in
methanol 5 1/2 by volume) gave 1.69 g (75% yield) of pure
product 3.
1H NMR (DMSO-d6) d 3.78–3.82 (t, 2H, AOACH2A), 3.84–
3.88 (t, 2H, AOACH2A), 4.37–4.40 (t, 2H, Ph-OACH2A),
4.43–4.46 (t, 2H, Ph-OACH2A), 5.02–5.04 (t, 1H, AOH),
5.05–5.07 (t, 1H, AOH), 7.17 (s, 1H, aromatic), 8.05–8.08 (d,
2H, aromatic), 8.28 (s, 1H, aromatic), 8.42–8.45 (d, 2H, aro-
matic). IR (KBr) 3320 (m, OAH), 2943 (m, CAH), 1610 (vs,
a
vacuum oven yielded 30.3
g (76% yield) of pure
product 1.
N@N), 1519, 1344 (vs, N@O) cm21
C16H16N4O8: C, 48.98; H, 4.11; N, 14.28. Found: C, 48.92; H,
. Anal. Calcd for
1H NMR (DMSO-d6) d 4.02–4.49 (m, 12H, 2 CH2@, 2
AOACH2ACH2AOA), 6.56–6.63 (m, 2H, 2 @CHAOA), 6.70–
6.74 (m, 1H, aromatic), 6.89–6.91 (m, 1H, aromatic), 7.71–
7.74 (d, 1H, aromatic), 7.95–7.98 (d, 2H, aromatic), 8.40–
8.43 (d, 2H, aromatic). IR (KBr) 3082 (w, @CAH), 2934 (m,
CAH), 1600 (vs, N@N), 1583 (s, C@C), 1515, 1332 (vs,
N@O), 1180 (m, N@N) cm21. Anal. Calcd for C20H21N3O6: C,
60.15; H, 5.30; N, 10.52. Found: C, 60.24; H, 5.26; N, 10.45.
4.06; N, 14.22.
Synthesis of Polyurethane 4
A representative polyaddition reaction procedure was as fol-
lows. Dimethoxy-4,40-biphenylenediisocyanate (2.96 g, 0.01
mol) was added slowly to a solution of 3.92 g of diol 3 (0.01
mol) in 25 mL of anhydrous DMF. The resulting solution was
degassed by a freeze-thaw process under vacuum and placed
ꢀ
in an oil bath kept at 80 C. After heating 15 h with stirring,
Preparation of 2,4-Di-(2’-hydroxyethoxy)-40-
nitroazobenzene (2)
the polymerization tube was opened and the viscous poly-
mer solution was poured into 400 mL of cold water. The
precipitated polymer was collected and reprecipitated from
DMSO into methanol. The polymer was further purified by
extraction in a Soxhlet extractor with methanol and dried
under vacuum to give 6.19 g (90% yield) of polymer 4.
Aqueous hydrochloric acid (1.5 mol L21, 30 mL) was slowly
added to a solution of compound 1 (3.99 g, 10 mmol) in 50
mL of dry DMF with stirring under nitrogen at room temper-
ꢀ
ature. The mixture was stirred at 50 C for 6 h under nitro-
gen. The resulting solution was cooled to room temperature
and poured into 100 mL of ice water, stirred, separated by
suction, and washed with 50 mL of water. The obtained
product was dried in a vacuum oven to give 2.78 g (80%
yield) of pure 2.
Inherent viscosity (ginh): 0.30 dL g21 (c, 0.5 g dL21 in DMSO
1
ꢀ
at 25 C). H NMR (DMSO-d6) d 3.75–4.05 (m, 8H, 2 AOCH3,
AOACH2A), 4.36–4.72 (m, 6H, AOACH2A, 2 Ph-OACH2A),
6.65–6.74 (m, 1H, aromatic), 6.86–7.34 (m, 6H, aromatic),
7.65–7.74 (s, 1H, aromatic), 7.91–8.05 (m, 1H, aromatic),
8.16–8.31 (m, 2H, aromatic), 8.52–8.66 (d, 1H, aromatic),
8.91–9.05 (d, 2H, NAH). IR (KBr) 3432 (s, NAH), 2952 (m,
CAH), 1730 (s, C@O), 1609 (s, N@N), 1520, 1343 (vs, N@O)
cm21. Anal. Calcd for (C32H28N6O12)n: C, 55.82; H, 4.10; N,
12.20. Found: C, 55.91; H, 4.16; N, 12.28.
1H NMR (DMSO-d6) d 3.74–3.78 (t, 2H, AOACH2A), 3.79–
3.83 (t, 2H, AOACH2A), 4.12–4.16 (t, 2H, Ph-OACH2A),
4.24–4.28 (t, 2H, Ph-OACH2A), 4.92–4.96 (t, 2H, 2 AOH),
6.65–6.69 (d, 1H, aromatic), 6.84 (s, 1H, aromatic), 7.70–7.73
(d, 1H, aromatic), 7.96–7.99 (d, 2H, aromatic), 8.39–8.42 (d,
2H, aromatic). IR (KBr) 3325 (m, OAH), 2948 (m, CAH),
1600 (vs, N@N), 1519, 1337 (vs, N@O) cm21. Anal. Calcd for
RESULTS AND DISCUSSION
C16H17N3O6: C, 55.33; H, 4.93; N, 12.10. Found: C, 55.25; H,
4.98; N, 12.15.
Synthesis and Characterization of Polymer
Compound 1 was prepared by the reaction of 2-chloroethyl
vinyl ether with 4-(4-nitrophenylazo)resorcinol. Compound 2
was prepared by acid-catalyzed hydrolysis of 2 in DMF. Com-
pound 2 was reacted with nitric acid and bismuth(III) tri-
fluoromethanesulfonate in anhydrous 1,2-dichloroethane
according to a literature procedure35 to yield compound 3.
Diol 3 was condensed with 3,30-dimethoxy-4,40-biphenylene-
diisocyanate in a dry DMF solvent to yield novel polyur-
ethane 4 containing 4-(4-nitrophenylazo)-6-nitroresorcinoxy
group as NLO chromophore. The synthetic route for polymer
4 is presented in Scheme 1. The resulting polymer was puri-
fied by Soxhlet extraction with methanol as a solvent. The
polymerization yield was 90%. The chemical structure of the
polymer was identified using 1H NMR, IR spectra, and ele-
mental analysis. Elemental analysis results fit the polymer
structures. 1H NMR spectrum of the polymer 4 has a signal
broadening due to polymerization, but the chemical shifts
are consistent with the proposed polymer structure. The
Preparation of 2,4-Di-(2’-hydroxyethoxy)-
5-nitro-40-nitroazobenzene (3)
Compound 2 (2.0 g, 5.76 mmol) was dissolved in 40 mL of
dry 1,2-dichloroethane under nitrogen. To the resulted solu-
tion was added bismuth (III) trifluoromethanesulfonate (0.30
g, 0.46 mmol) and 60-wt % nitric acid (60%, 0.91 g, 8.64
mmol). The mixture was refluxed in an oil bath kept at 75
ꢀC for 8 h under nitrogen. The resulting solution was cooled
to room temperature, neutralized with 5 g of anhydrous
sodium bicarbonate, diluted with 100 mL of water with stir-
ring, extracted with 50 mL of diethyl ether three times, and
separated. Rotary evaporation of solvent gave product, which
was dissolved in 50 mL of dichloromethane, washed with
water (100 mL) and saturated aqueous sodium bicarbonate
(50 mL), dried with anhydrous sodium carbonate, filtered,
and concentrated by rotary evaporator. The combined prod-
uct was purified by column chromatography (ethyl acetate/
762
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 760–766

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
SCHEME 1 Synthetic route to and structure of polymer 4.
signal at 8.91–9.05 ppm of 1N NMR spectrum of polymer 4
assigned to the amine proton indicates the formation of ure-
thane linkage. The IR spectrum of polymer 4 shows strong
carbonyl peaks near 1730 cm21 indicating the presence of
urethane bond. The spectrum also shows strong absorption
peak near 1609 cm21 due to azo group and absorptions at
1520 and 1343 cm21 due to nitro group indicating the pres-
ence of nitroazobenzene unit. These results are consistent
with the proposed structure, indicating that the NLO chro-
mophores remained intact during the polymerization. The
molecular weights were determined using GPC with polysty-
rene as the standard and THF as the eluent. Mn of the poly-
mer 4, determined using GPC, is 16,500 g mol21 (Mw/
Mn 5 1.86). The polymer 4 is soluble in common solvents
such as acetone, DMF, and DMSO, but is not soluble in meth-
obtained the well-defined X-type polyurethane 4, we investi-
gated its properties.
Thermal Properties of Polymer
The thermal behavior of the polymer was investigated using
TGA and DSC to determine the thermal degradation pattern
and glass transition temperature. The results are summar-
ized in Table 1. The TGA and DSC thermograms of the poly-
mer 4 are shown in Figures 2 and 3, respectively. Polymer 4
has a thermal stability up to 270 ꢀC according to its TGA
thermogram. The initial weight loss in the polymer begins at
about 270 ꢀC in TGA thermogram, which is also shown in
DSC thermogram. The ꢀTg value of the polymer 4 measured
using DSC is near 134 C. This Tg value is higher than that of
the Y-type polyurethane containing nitrophenylazoresorcinol,
anol and diethyl ether. The inherent viscosity is 0.30 dL g21
.
30
ꢀ
which is near 102 C. The TGA and DSC studies show that
the decomposition temperature of the polymer 4 is much
higher than the corresponding Tg value. This indicates that
high-temperature poling for a short term is feasible without
damaging the NLO chromophore.
Polymer 4 shows strong absorption near 382 nm due to the
4-(4-nitrophenylazo)26-nitroresorcinoxy group NLO chromo-
phore. The striking feature of this polymerization system is
that it gives unprecedented X-type NLO polymers, in which
the pendant NLO chromophores are part of the polymer
backbone. These X-type NLO polymers are expected to have
the advantages of both main-chain and side-chain NLO poly-
mers. Thus, we obtained a new type of NLO polyurethane
with side-chain and main-chain characteristics. Having
Nonlinear Optical Properties of Polymer
The NLO properties of polymers were studied using the SHG
method. To induce noncentrosymmetric polar order, the
spin-coated polymer films were corona-poled. As the
TABLE 1 Thermal Properties of Polymer 4
Degradation Temperature (ꢀC)b
Polymer
5 wt % Loss
20 wt % Loss
40 Wt % Loss
Residue at 800 ꢀC (%)b
a
Tg (ꢀC)
4
134
102
278
276
306
296
391
332
39.6
43.3
c
PU
a
b
Determined from DSC curves measured with a TA 2920 differential
scanning calorimeter with a heating rate of 10 ꢀC min21 under nitrogen
atmosphere.
Determined from TGA curves measured with a TA Q50 thermogravi-
metric analyzer with
a
heating rate of 10 ꢀC min21 under nitrogen
atmosphere.
c
Y-type polyurethane containing nitrophenylazoresorcinol.30
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 760–766
763

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
FIGURE 2 TGA thermogram of polymer 4 obtained at a heating
rate of 10 ꢀC min21 under nitrogen.
FIGURE 3 DSC thermogram of polymer 4 obtained at a heating
rate of 10 ꢀC min21 under nitrogen.
ꢀ
temperature was raised gradually to 5–10 C higher than Tg,
changed after poling, resulting in numerous hills and valleys
in the surface structure, which means that the NLO chromo-
phores are aligned in the poling direction [Fig. 5(b)].
a corona voltage of 6.5 kV was applied and this temperature
was maintained for 30 min. The films were cooled to room
temperature in the presence of the electric field. Finally, the
electric field was removed. The poling was confirmed from
UV–visible spectra. Figure 4 shows the UV–visible absorption
spectra of the polymer 4 before and after poling. After elec-
tric poling, the dipole moments of the NLO chromophores
were aligned and UV–visible absorption of polymer 4 exhib-
its a decrease in absorption due to birefringence. From the
absorbance change, the order parameter of the poled films
can be estimated, which is related to the poling efficiency.
The estimated order parameter value U is equal to 0.32
The refractive index of the sample was measured using the
optical transmission technique.33 The transmittance of thin
film gives information on the thickness, refractive index, and
extinction coefficient. Thus, we could determine these
for polymer
4 (U 5 1 2 A1/A0, where A0 5 0.9933 and
A1 5 0.6716 are the absorbances of the polymer film before
and after poling, respectively).
The poling was also confirmed by atomic force microscopy
(AFM). Figure 5 shows AFM scans of the spin-coated film of
polymer 4 before and after poling. AFM images show that
the surface of the film sample is quite flat and broad before
poling [Fig. 5(a)]. However, this film was dramatically
FIGURE 4 UV–visible absorption spectra of a film of polymer 4
FIGURE 5 AFM images of spin-coated film of polymer 4: (a)
before and after poling.
before corona-poling; (b) after corona-poling.
764
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 760–766

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
FIGURE 6 Angular dependence of SHG signal for a poled film
of polymer 4.
FIGURE 7 Normalized SHG signal of polymer 4 as a function
of temperature at a heating rate of 4 ꢀC min21
.
parameters by analyzing the transmittance. SHG measure-
ments were performed at a fundamental wavelength of 1064
nm with a mode-locked Nd-YAG laser and optical parametric
oscillator. In order to determine the microscopic second-
order susceptibility of the polymer, the angular SHG depend-
ence was recorded. Figure 6 shows the angular dependence
of SHG signal for a poled sample of polymer 4. The SHG val-
ues were compared with those obtained from a Y-cut quartz
plate. To calculate the d31 and d33 values, both s-polarized
and p-polarized IR laser were directed at the samples. The
NLO properties of polymer 4 are summarized in Table 2.
SHG coefficients (d33) were derived from the analysis of
measured Maker-fringes with the Pascal fitting program
according to the literature procedure.34 The values of d31
and d33 for polymer 4 are 1.76 3 1029 and 5.37 3 1029
esu, respectively. This d33 value is higher than that of the Y-
type polyurethane 4 containing nitrophenylazoresorcinol,
which is near 4.92 3 1029 esu.30 As the second harmonic
wavelength is at 532 nm, which is not in the absorptive
region of the resulting polyurethane, there is little resonant
contribution to this d33 value. In the isotropic model, the
ratio of d33/d31 is predicted to be about 3. Our d33/d31 value
of 3.05 is in good agreement with the predicted value.
shows the dynamic thermal stability study of the NLO activity
of a film of polymer 4. 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 min21 from 30 to 200 ꢀC. The polymer
film exhibits a thermal stability up to Tg, and no significant
SHG decay is observed below 135 ꢀC. This SHG thermal stabil-
ity is higher than that of the Y-type polyurethane containing
nitrophenylazoresorcinol, which is near 100 C. In Figure 8,
we present the temporal stability of the polymer film in which
there was no negligible decay of the SHG signal over hundreds
of hours. We measured normalized SHG signal of polymer 4 as
a function of baking time at 80 ꢀC, which is enough for electro-
optic device applications. In general, side-chain NLO polymers
lose the thermal stability of dipole alignment below Tg. Stabili-
zation of dipole alignment is a characteristic of main-chain
NLO polymers. The polymer also shows good long-term ther-
mal stability of d33 except for the small activity loss within a
few days after poling. The enhanced thermal stability of SHG
of polymer 4 at high temperature is due to the stabilization of
dipole alignment of NLO chromophores, 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 the advantages of both main-chain and side-chain NLO
26
ꢀ
To evaluate the high-temperature stability of the polymer, we
studied the temporal stability of the SHG signal. Figure 7
TABLE 2 Nonlinear Optical Properties of Polymer 4
Uc
Film Thicknessd (mm)
d31 (esu)
n
a
b
b
Polymer
kmax (nm)
d33 (esu)
4
382
5.37 3 1029
4.91 3 1029
0.32
0.52
1.76 3 1029
n1 5 1.715
n2 5 1.741
n1 5 1.716
n2 5 1.743
PUe
399
0.13
0.52
1.64 3 1029
a
d
Polymer film after corona poling.
Film thickness was determined using the optical transmission
b
SHG coefficients (d33) were derived from the analysis of measured
technique.33
e
Maker-fringes.34
c
Y-type polyurethane containing nitrophenylazoresorcinol.30
Order parameter U 5 1 2 A1/A0, where A0 and A1 are the absorbances
of the polymer film before and after corona poling, respectively.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 760–766
765

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
5 W. Wu, Z. Zhu, G. Qiu, C. Ye, J. Qin, Z. Li, J. Polym. Sci. Part
A: Polym. Chem. 2012, 50, 5124–5133.
6 M. Y. Song, B. Jeon, H. J. Kim, J.-Y. Lee, J. Polym. Sci. Part
A: Polym. Chem. 2013, 51, 275–281.
7 B. Kolli, S. P. Mishra, A. K. Palai, T. Kanai, M. P. Joshi, S. R.
Mohan, T. S. Dhami, L. M. Kukreja, A. B. Samui, J. Polym. Sci.
Part A: Polym. Chem. 2013, 51, 836–843.
8 F. Yu, A. M. Spring, L. Li, F. Qiu, K. Yamamoto, D. Maeda, M.
Ozawa, K. Odoi, S. Yokoyama, J. Polym. Sci. Part A: Polym.
Chem. 2013, 51, 1278–1284.
9 G. Deng, Bo,S., T. Zhou, H. Huang, J. Wu, J. Liu, X. Liu, Z. Zhen,
L. Qiu, J. Polym. Sci. Part A: Polym. Chem. 2013, 51, 2841–2849.
10 N. Tsutumi, S. Yoshizaki, W. Sakai, T. Kiyotsukuri, Macro-
molecules 1995, 28, 6437–6442.
11 K. S. Han, S. K. Park, S. Y. Shim, W. S. Jahng, N. J. Kim,
Bull. Korean Chem. Soc. 1998, 19, 1165–1168.
12 C. Zhang, C. Wang, J. Yang, L. R. Dalton, S. Sun, H. Zhang,
W. H. Steier, Macromolecules 2001, 34, 235–243.
FIGURE 8 Normalized SHG signal of polymer 4 as a function
of baking time at 80 ꢀC in air.
13 T.-D. Kim, J. Luo, Y. Tian, J.-W. Ka, N. M. Tucker, M. Haller,
J.-W. Kang, A. K.-Y. Jen, Macromolecules 2001, 39, 1676–1680.
polymers, namely stabilization of dipole alignment and good
solubility.
14 Y.-L. Liu, C.-Y. Hsieh, J. Polym. Sci. Part A: Polym. Chem.
2006, 44, 905–913.
15 Y. Mori, K. Nakaya, X. Piao, K. Yamamoto, A. Otomo, S.
Yokoyama, J. Polym. Sci. Part A: Polym. Chem. 2012, 50, 1254–1260.
CONCLUSIONS
16 T. Chen, A. K. Y. Jen, Y. Cai, Macromolecules 1996, 29, 535–539.
17 D. Yu, A. Gharavi, L. Yu, Macromolecules 1996, 29, 6139–6142.
Novel X-type polyurethane 4 with pendant NLO chromo-
phores, which are parts of the polymer backbone, was pre-
pared and characterized. The resulting X-type NLO
polyurethane 4 is soluble in common organic solvents. Poly-
18 H. Saadeh, A. Gharavi, D. Yu, L. Yu, Macromolecules 1997,
30, 5403–5407.
19 N. Tsutsumi, M. Morishima, W. Sakai, Macromolecules
1998, 31, 7764–7769.
ꢀ
mer 4 shows a thermal stability up to 270 C from TGA ther-
ꢀ
mogram with Tg value near 134 C. The SHG coefficient (d33
)
20 J.-G. Liu, Y. Nakamura, Y. Shibasaki, S. Ando, M. Ueda, J.
Polym. Sci. Part A: Polym. Chem. 2007, 45, 5606–5617.
of corona-poled polymer film is 5.37 x 1029 esu. Polymer 4
exhibits SHG stability up to 135 ꢀC. This enhanced thermal
stability of optical nonlinearity stems from the stabilization
of dipole alignment of the NLO chromophores, which are
components of the polymer backbone and partly by hydro-
gen bonds between the neighboring urethane linkages. We
are now in the process of extending the polymerization sys-
tem to the synthesis of other type of NLO polymers and the
results will be reported elsewhere.
21 M. A. Hoang, M. H. Kim, M. J. Cho, K. H. Kim, K. N. Kim, J.-I.
Jin, D. H. Choi, J. Polym. Sci. Part A: Polym. Chem. 2008, 46, 5064–
5076.
22 Z. Li, G. Qui, C. Ye, J. Qin, Z. Li, Dyes Pigments 2012, 94,
16–22.
23 C. Zhang, C. Wang, J. Yang, L. Dalton, R. G. Sun, H. Zhang,
W. H. Steier, Macromolecules 2001, 34, 236–243.
24 H. Xie, Z. Liu, X. Huang, J. Guo, Eur. Polym. J. 2001, 37, 497–
505.
25 K. J. Moon, H. K. Shim, K. S. Lee, J. Zieba, P. N. Prasad,
Macromolecules 1996, 29, 861–867.
ACKNOWLEDGMENTS
This research was supported by Basic Science Research Pro-
gram through the National Research Foundation of Korea
(NRF) funded by the Ministry of Education, Science, and Tech-
nology (No. 2010-0020951).
26 H. Y. Woo, H.-K. Shim, K.-S. Lee, Polym. J. 2000, 32, 8–14.
27 N. Tsutumi, O. Matsumoto, W. Sakai, T. Kiyotsukuri, Macro-
molecules 1996, 29, 592–597.
28 N. Tsutumi, O. Matsumoto, W. Sakai, Macromolecules 1997,
30, 4584–4589.
29 J.-Y. Lee, H.-B. Bang, E.-J. Park, W.-J. Lee, B. K. Rhee, S. M.
Lee, Polym. Int. 2004, 53, 1838–1844.
REFERENCES AND NOTES
30 M. S. Kim, M. Y. Song, B. Jeon, J.-Y. Lee, Polym. Int. 2012,
61, 1739–1744.
1 T. J. Marks, M. A. Ratner, Angew. Chem. Int. Ed. Engl. 1995,
34, 155–173.
31 J.-Y. Lee, H.-B. Bang, T.-S. Kang, E.-J. Park, Eur. Polym. J.
2004, 40, 1815–1822.
2 I. Javier, S. R.-F. Yessica, R. Ernesto, G. M.-S. Omar, A. R.-R.
Antonio, A. Valeria, N. Daniele, S. Sergio, M. Alberto, J. Polym.
Sci. Part A: Polym. Chem. 2012, 50, 821–830.
32 J.-Y. Lee, J.-H. Kim, W. T. Jung, Y. G. Park, J. Mater. Sci.
2007, 42, 3936–3943.
3 B. Kolli, S. P. Mishra, M. P. Joshi, S. R. Mohan, T. S. Dhami, A. B.
Samui, J. Polym. Sci. Part A: Polym. Chem. 2012, 50, 1572–1578.
33 J. I. Cisneros, Appl. Opt. 1998, 37, 5262–5270.
34 W. N. Herman, L. M. Hayden, J. Opt. Soc. Am. B 1995, 12, 416–
ꢀ
4 I. Javier, O.-P. Jesus, E.-G. Jair, S. R.-F. Yessica, R. Ernesto,
427.
G. M.-S. Omar, A. R.-R. Antonio, A. Valeria, N. Daniele, S.
Sergio, M. Alberto, J. Polym. Sci. Part A: Polym. Chem. 2012,
50, 1906–1916.
35 W. Zhu, Y. Liu, G. Niu, Q. Wang, J. Li, X. Zhu, Y. Li, H. Xue,
G. Yang, Catal. Commun. 2012, 29, 145–148.
766
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 760–766