The design, synthesis, and nonlinear optical properties of novel X-type polyurethane containing dicyanovinylnitroresorcinoxy group with enhanced SHG thermal stability

Article abstract of DOI:10.1002/pola.26405

Novel X-type polyurethane 5 containing 4-(2′,2′-dicyanovinyl)- 6-nitroresorcinoxy groups as nonlinear optical (NLO) chromophores, which constitute parts of the polymer backbone, was prepared and characterized. Polyurethane 5 is soluble in common organic solvents such as acetone and N,N-dimethylformamide. It shows thermal stability up to 280 C from thermogravimetric analysis with a glass transition temperature (T_g) obtained from differential scanning calorimetry thermogram of around 120 C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer film at 1064-nm fundamental wavelength is around 6.12 × 10^-9 esu. The dipole alignment exhibits a thermal stability even at 5 C higher than T_g, and there was no SHG decay below 125 C due to the partial main chain character of the polymer structure, which is acceptable for NLO device applications.

Full text of DOI:10.1002/pola.26405

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
The Design, Synthesis, and Nonlinear Optical Properties of Novel X-Type
Polyurethane Containing Dicyanovinylnitroresorcinoxy Group with
Enhanced SHG Thermal Stability
Mi Young Song, Byeongman Jeon, Hak Jin Kim, Ju-Yeon Lee
Institute of Basic Science, Department of Chemistry, Inje University, 607 Obang-dong, Gimhae 621-749, Korea
Correspondence to: J.-Y. Lee (E-mail: chemljy@inje.ac.kr)
Received 7 September 2012; accepted 2 October 2012; published online 29 October 2012
DOI: 10.1002/pola.26405
ABSTRACT: Novel X-type polyurethane
5
containing 4-(20,20-
dipole alignment exhibits a thermal stability even at 5 ꢀC
higher than Tg, and there was no SHG decay below 125 ꢀC
dicyanovinyl)-6-nitroresorcinoxy groups as nonlinear optical
(NLO) chromophores, which constitute parts of the polymer
backbone, was prepared and characterized. Polyurethane 5 is
soluble in common organic solvents such as acetone and
N,N-dimethylformamide. It shows thermal stability up to 280
ꢀC from thermogravimetric analysis with a glass transition
temperature (Tg) obtained from differential scanning calorime-
try thermogram of around 120 ꢀC. The second harmonic gen-
eration (SHG) coefficient (d33) of poled polymer film at 1064-
nm fundamental wavelength is around 6.12 ꢁ 10ꢂ9 esu. The
due to the partial main chain character of the polymer struc-
C
V
ture, which is acceptable for NLO device applications.
2012
Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 51:
275–281, 2013
KEYWORDS: atomic force microscopy (AFM); differential scan-
ning calorimetry (DSC); NLO; polyurethane; second harmonic
generation (SHG); thermogravimetric analysis (TGA); thermal
stability
INTRODUCTION Nonlinear optical (NLO) materials based on
organic compounds have been extensively studied over the
past decade because of their potential applications in elec-
tro-optic and photonic devices such as modulators and
switches, due to their larger optical nonlinearity, lower
dielectric constants, ultrafast response time, and easier proc-
essability.1–5 Among the organic materials, the NLO polymers
are considered candidate materials, mainly because they
offer many advantages such as light weight, low cost, ultra-
fast response, wide-response wave band, high optical
damage threshold, and good processability to form optical
devices. 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, stabili-
zation of electrically induced dipole alignment is one of im-
portant considerations; in this context, two approaches to
minimize the randomization have been adopted, namely the
use of crosslinked systems6–11 and the utilization of poly-
mers with high glass transition temperature (Tg) such as pol-
yimides.12–18 A polyurethane matrix forms extensive hydro-
gen bonding between urethane linkages, with increased
rigidity preventing the relaxation of induced dipoles. Polyur-
ethanes functionalized with hemicyanine19 and thiophene
ring20 in side chain show an enhanced thermal stability of
aligned dipoles. Polyurethanes with dipole moments aligning
transverse to the main chain show large second-order nonli-
nearity with good thermal stability.21,22 Physically cross-
linked systems via hydrogen bonds have the advantages
such as homogeneity and good processability relative to
chemically crosslinked systems, which suffer from significant
optical loss and poor solubility. Recently, we prepared novel
Y-type polyurethanes containing dioxybenzylidenemalononi-
trile23 and dioxybenzylidenecyanoacetate24 as NLO chromo-
phores. The resulting polymers exhibit enhanced thermal
stability of second harmonic generation (SHG), which
stemmed from the stabilization of dipole alignment of the
NLO chromophores.
In this work, we have prepared a novel polyurethane con-
taining 4-(20,20-dicyanovinyl)-6-nitroresorcinoxy groups as
NLO chromophores. We selected the latter because they are
expected to have a large dipole moment due to a quadruple
conjugation. Furthermore, these 4-(20,20-dicyanovinyl)-6-
nitroresorcinoxy groups can be incorporated into novel X-
type NLO polyurethane [see Fig. 1(c)]. The structure of NLO
chromophores and this X-type NLO polyurethane has not yet
been described in the literature. Thus, we formulated a new
type of NLO polyurethane, in which the pendant NLO chro-
mophores 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
C
V
2012 Wiley Periodicals, Inc.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2013, 51, 275–281
275

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
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 covered glass.
Prior to film casting, the polymer solution was filtered
R
through 0.45 lm TeflonV 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
ꢀ
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.25 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 ¼ 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 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 ¼ 0.3 pm/V) was used as a refer-
ence for determining the relative intensities of the SH signals
generated from the samples. The Maker Fringe pattern was
FIGURE 1 Main chain NLO polymers (a), side chain NLO poly-
mers (b), and X-type NLO polymers (c).
polymers, namely stable dipole alignment and good solubil-
ity. After confirming the structure of the resulting polymer,
we investigated its properties: Tg, thermal stability, surface
morphology of polymer films, and second harmonic genera-
tion activity.
EXPERIMENTAL
Materials
Reagent-grade chemicals were purchased from Aldrich and
purified by either distillation or recrystallization before use.
2-Chloroethyl vinyl ether and 2,4-dihydroxybenzaldehyde
were used as received. Malononitrile was recrystallized from
water and distilled from phosphorus pentoxide. 1,6-Hexam-
ethylene diisocyanate was purified by distillation under
reduced pressure. Piperidine was dried with calcium hydride
and fractionally distilled. N,N-Dimethylformamide (DMF) was
purified by drying with anhydrous calcium sulfate, followed
by distillation under reduced pressure.
ꢀ
obtained by measuring the SHG signal at 0.5 intervals using
a rotation stage. SHG coefficients (d33) were derived from
the analysis of measured Maker fringes.26
Preparation of 2,4-(20-Vinyloxyethoxy)benzaldehyde (1)
2,4-Dihydroxybenzaldehyde (13.8 g, 0.10 mol), anhydrous
potassium carbonate (82.9 g, 0.60 mol), and 2-iodoethyl
vinyl ether (49.5 g, 0.25 mol) were dissolved in 400 mL of
dry DMF under nitrogen. The mixture was refluxed in an oil
Instrumentation
Infrared (IR) spectra were obtained with a Varian FTIR-1000
IR spectrophotometer. H 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. Elemental analyses
were performed using a Perkin-Elmer 2400 CHN elemental
analyzer. Tg values were measured using a TA 2920 differen-
tial scanning calorimeter DSC in a nitrogen atmosphere. A TA
1
ꢀ
bath kept at 80 C for 15 h under nitrogen. The resulting so-
lution was cooled to room temperature, diluted with 300 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 magne-
sium sulfate. Rotary evaporation of diethyl ether gave crude
product, which was recrystallized from 1-butanol yielded
ꢀ
Q50 thermogravimetric analyzer with a heating rate of 10 C
minꢂ1 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-
ꢀ
25.0 g (yield 90%) of pure product 1. M.p.: 68–69 C.
1H NMR (acetone-d6) d 4.03–4.35 (m, 12H, 2 CH2¼¼, 2
AOACH2ACH2AOA), 6.50–6.62 (m, 4H, 2 ¼¼CHAOA, aro-
matic), 7.82–7.86 (d, 1H, aromatic), 10.35 (s, 1H, ACHO). IR
276
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2013, 51, 275–281

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
SCHEME 1 Synthetic route to and structure of polymer 5.
(KBr) 3100, 3082 (w, ¼¼CAH), 2954, 2875 (m, CAH), 1674
yellow product was recrystallized fromꢀethyl acetate to give
(vs, C¼¼O), 1615 (vs, C¼¼C), 1575 (s, C¼¼C) cmꢂ1
.
6.13 g (yield 86%) of 3. M.p.: 148–149 C.
1H NMR (acetone-d6) d 2.78–2.84 (m, 2H, AOH), 3.87–3.98
(m, 4H, 2 ACH2AOH), 4.18–4.29 (m, 4H, 2 AOACH2A),
6.73–6.82 (m, 2H, aromatic), 8.18–8.26 (d, 1H, aromatic),
8.43 (s, 1H, -Ph-CH¼¼). IR (KBr) 3394 (s, OAH), 3043 (w,
¼¼CAH), 2953 (m, CAH), 2220 (m, CN), 1607, 1576 (vs,
C¼¼C) cmꢂ1. Anal. Calcd for C14H14N2O4: C, 61.31; H, 5.14; N,
10.21. Found: C, 61.38; H, 5.23; N, 10.12.
Preparation of 2,4-Di-(2’-
vinyloxyethoxy)benzylidenemalononitrile (2)
Piperidine (0.13 g, 1.5 mmol) was added to a solution of
2,4-di-(20-vinyloxyethoxy)benzaldehyde 1 (8.35 g, 30 mmol)
and malononitrile ꢀ(2.18 g, 33 mmol) in 170 mL of 1-butanol
with stirring at 0 C under nitrogen. After stirring for 4 h at
ꢀ
ꢀ
0 C, the reaction mixture was cooled to –10 C for crystalli-
zation. The product was filtered and washed successively
with cold 1-butanol (80 mL), water (30 mL), and cold 1-bu-
tanol (20 mL). The obtained pale yellow product was recrys-
tallized from 1-butanol to give 8.81g (yield 90% of 2. M.p. ¼
Synthesis of Polymer 4
A representative polyaddition reaction procedure was as fol-
lows. Hexamethylenediisocyanate (1.68 g, 0.01 mol) was
added slowly to a solution of 2.74 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
ꢀ
70–71 C.
1H NMR (DMSO-d6) d 4.02–4.40 (m, 12H, 2 CH2¼¼, 2
AOACH2ACH2AOA), 6.45–6.71 (m, 4H, 2 ¼¼CHAOA, aro-
matic), 8.17–8.34 (t, 2H, aromatic). IR (KBr) 3117, 3037 (w,
¼¼CAH), 2943, 2887 (m, CAH), 2222 (s, CN), 1611 (s, C¼¼C),
1566 (vs, C¼¼C) cmꢂ1. Anal. Calcd for C18H18N2O4: C, 66.25;
H, 5.56; N, 8.58. Found: C, 66.38; H, 5.65; N, 8.46.
ꢀ
in an oil bath kept at 80 C. After heating 15 h with stirring,
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 3.89 g (88% yield) of polymer 4.
Preparation of 2,4-Di-(2’-
hydroxyethoxy)benzylidenemalononitrile (3)
Inherent viscosity (ginh) ¼ 0.32 dL gꢂ1 (c ¼ 0.5 g dLꢂ1 in
DMSO at 25 ꢀC). 1H NMR (DMSO-d6) d 1.05–1.42 (d, 8H,
A(CH2)4A), 2.83–3.01 (s, 4H, 2 ANHACH2A), 4.08–4.39 (m,
8H, 2 AOACH2ACH2AOA), 5.67 (s, 2H, 2 NAH), 6.74–8.24
(m, 4H, aromatic). IR (KBr) 3328 (m, NAH), 2935 (m, CAH),
2225 (m, CN), 1697 (s, C¼¼O), 1610 (s, C¼¼C) cmꢂ1. Anal.
Calcd for (C22H26N4O6)n: C, 59.72; H, 5.92; N, 12.66. Found:
C, 59.83; H, 5.98; N, 12.58.
Aqueous hydrochloric acid (1.5 M, 30 mL) was slowly added
to a solution of 2,4-di-(20-vinyloxyethoxy)benzylidenemalono-
nitrile (2) (8.48 g, 0.026 mol) in 60 mL of dry THF with stir-
ring under nitrogen at 0 ꢀC. The mixture was stirred at 80
ꢀC for 8 h under nitrogen. The resulting solution was
extracted with diethyl ether (80 mL) three times. The or-
ganic layer was washed successively with saturated sodium
chloride, sodium hydrogen carbonate, and water, followed by
drying with anhydrous magnesium sulfate. Rotary evapora-
tion of diethyl ether gave crude product. The obtained pale
Synthesis of Polymer 5
Polymer 4 (4.42 g, 0.01 mol) was dissolved in 22 mL of
DMF at room temperature and stirred for 30 min. The
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2013, 51, 275–281
277

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
TABLE 1 Thermal Properties of Polymers 4–5
Degradation
Temperature (ꢀC)b
a
Tg
5 wt %
Loss
20 wt %
Loss
40 wt %
Loss
Residue at
800 ꢀC (%)b
Polymers
(ꢀC)
4
5
a
117
120
293
301
359
362
413
416
26.2
26.7
Determined from DSC curves measured with a TAꢂ12920 differential
scanning calorimeter with a heating rate of 10 ꢀC min under nitrogen
atmosphere.
b
Determined from TGA curves measured with a TA Q50 thermogravi-
metric analyzer with
atmosphere.
a
heating rate of 10 ꢀC minꢂ1 under nitrogen
reaction mixture was cooled with ice bath, added 4 mL of
sulfuric acid, and stirred for 30 min. A mixture of nitric acid
(9 mL) and sulfuric acid (9 mL) were added dropwise to the
solution and stirred for 24 h at 0 ꢀC. The reaction mixture
was poured to 500 mL of ice water, and the precipitated
polymer was separated with suction. The polymer was fur-
ther purified by extraction in a Soxhlet extractor with metha-
nol and dried under vacuum, yielding 4.38 g (90% yield) of
polymer 5.
Inherent viscosity (ginh) ¼ 0.30 dL gꢂ1 (c ¼ 0.5 g dLꢂ1 in
DMSO at 25 ꢀC). 1H NMR (DMSO-d6) d 1.08–1.48 (d, 8H,
A(CH2)4A), 2.88–3.03 (s, 4H, 2 ANHACH2A), 4.08–4.45 (m,
8H, 2 AOACH2ACH2AOA), 5.68 (s, 2H, 2 NAH), 6.75–8.26
(m, 3H, aromatic). IR (KBr) 3332 (m, NAH), 2935 (m, CAH),
2223 (m, CN), 1697 (s, C¼¼O), 1609 (s, C¼¼C) 1568, 1276 (s,
N¼¼O) cmꢂ1. Anal. Calcd. for (C22H25N5O8)n: C, 54.21; H,
5.17; N, 14.36. Found: C, 54.32; H, 5.11; N, 14.28.
FIGURE 2 AFM images of spin-coated film of polymer 5: (a)
before corona poling; (b) after corona poling.
spectrum of polymer 5 shows strong absorption peak near
2223 cm–1 indicating the presence of nitrile group. The spec-
trum also shows a strong carbonyl peak near 1697 cm–1
indicating the presence of urethane bond, and two strong
absorption bands due to the nitro group in the NLO chromo-
phore appeared near 1568 and 1276 cm–1. These results are
consistent with the proposed structure, indicating that the
RESULTS AND DISCUSSION
Synthesis and Characterization of Polymer
Compound 1 was prepared by reaction of 2-iodoethyl vinyl
ether with 2,4-dihydroxybenaldehyde. Compound 2 was pre-
pared by condensation of 1 with malononitrile. Compound 2
was hydrolyzed to yield acetaldehyde and diol 3. Compound
3 was obtained in high yield and was purified by recrystalli-
zation in ethyl acetate for polymerization. Diol 3 was poly-
added with 1,6-hexamethylenediisocyanate in a dry DMF
solvent to yield polyurethane 4. Polymer 4 was reacted with
nitric acid and sulfuric acid in anhydrous DMF to yield novel
polyurethane 5 containing 4-(20,20-dicyanovinyl)-6-nitroresor-
cinoxy groups as NLO chromophores. The polymerization
yield was 90%. The synthetic route for polymer 5 is pre-
sented in Scheme 1. The resulting polymer was purified by
Soxhlet extraction with methanol as a solvent. The chemical
structure of the polymer was identified using 1H NMR, IR
spectra, and elemental analysis. Elemental analysis results fit
the polymer structure. 1H NMR spectrum of the polymer
showed a signal broadening due to polymerization, but the
chemical shifts are consistent with the proposed polymer
structure. The signal at 5.68 ppm assigned to the amine
proton indicates the formation of urethane linkage. The IR
FIGURE 3 Angular dependence of SHG signal for a poled film
of polymer 5.
278
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2013, 51, 275–281

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
TABLE 2 Nonlinear Optical Properties of Polymers 4–5
Uc
Film Thicknessd (lm)
d31 (esu)
n
a
b
b
Polymers
kmax (nm)
d33 (esu)
4
5
a
377
376
5.85 ꢁ 10ꢂ9
6.12 ꢁ 10ꢂ9
0.39
0.43
0.51
0.52
2.03 ꢁ 10ꢂ9
2.10 ꢁ 10ꢂ9
1.623
1.628
c
Polymer film after corona poling.
Order parameter U ¼ 1 ꢂ A1/A0, where A0 and A1 are the absorbances
b
SHG coefficients (d33) were derived from the analysis of measured
of the polymer film before and after corona poling, respectively.
Maker-fringes.26
Film thickness was determined using the optical transmission technique.25
d
NLO chromophores remained intact during the nitration. The
molecular weights were determined using GPC with polysty-
rene as the standard and THF as the eluent. Mn of the poly-
¼ 1.4559 and A1 ¼ 0.8344 are the absorbances of the poly-
mer film before and after poling, respectively).
The poling was also confirmed by atomic force microscopy
(AFM). Figure 2 shows AFM scans of the spin-coated film of
polymer 5 before and after poling. AFM images show that
the surface of the film sample is quite flat and broad before
poling [Fig. 2(a)]. However, this film was dramatically
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. 2(b)].
mer 5 determined using GPC, is 15,800 g molꢂ1 (Mw/Mn
¼
1.95). The polymer 5 is soluble in common solvents such as
acetone, DMF, and DMSO, but is not soluble in methanol and
diethyl ether. The inherent viscosity is 0.30 dL gꢂ1. Polymer
5 shows strong absorption near 376 nm due to the 4-(20,20-
dicyanovinyl)-6-nitroresorcinoxy group NLO chromophore.
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 back-
bone. These X-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. Having obtained
the well-defined X-type polyurethane 5, we investigated its
properties.
The refractive index of the sample was measured using the
optical transmission technique.25 The transmittance of thin
film gives information on the thickness, refractive index, and
extinction coefficient. Thus, we could determine these pa-
rameters by analyzing the transmittance. SHG measurements
were performed at a fundamental wavelength of 1064 nm
using a mode locked Nd-YAG laser and optical parametric os-
cillator. To determine the microscopic second-order suscepti-
bility of the polymers, the angular SHG dependence was
recorded. Figure 3 shows the angular dependence of SHG
signal for a poled sample of polymer 5. The SHG values 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 5 are summarized in Table 2. SHG
coefficients (d33) were derived from the analysis of mea-
sured Maker-fringes with the Pascal fitting program accord-
ing to the literature procedure.26 The values of d31 and d33
for polymer 5 are 2.10 ꢁ 10ꢂ9 and 6.12 ꢁ 10ꢂ9 esu,
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. Polymer 5 has a thermal stability up to 280
ꢀC according to its TGA thermogꢀram. The initial weight loss
in the polymer begins at ca. 280 C. The Tg value of the poly-
mer 5 measured using DSC is near 120 ꢀC. This Tg valueꢀ is
higher than that of the polyurethane 4, which is near 117 C.
The TGA and DSC studies show that the decomposition
temperature of the polymer 5 is higher than the correspond-
ing 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 using the SHG
method. To induce noncentrosymmetric polar order, the
spin-coated polymer films were corona poled. As the temper-
ꢀ
ature was raised gradually to 5–10 C higher than Tg, 6.5 kV
of corona voltage was applied, and this temperature was
maintained for 30 min. The poling was confirmed by UV–
visible spectra. After electric poling, the dipole moments of
the NLO chromophores were aligned and UV–visible absorp-
tion of polymer 5 exhibits a decrease in absorption due to
birefringence. From the absorbance change, the order param-
eter of the poled film could be estimated, which is related to
the poling efficiency. The estimated order parameter value U
was equal to 0.43 for polymer 5 (U ¼ 1 ꢂ A1/A0, where A0
FIGURE 4 Normalized SHG signal of polymer 5 as a function
of temperature at a heating rate of 4 ꢀC minꢂ1
.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2013, 51, 275–281
279

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
polymer is that it exhibits a SHG thermal stability even at
ꢀC higher than Tg, and no SHG decay is observed below
5
125 ꢀC. This enhanced thermal stability of optical nonli-
nearity stems from the stabilization of dipole alignment of
the NLO chromophores, which constitute part of the poly-
mer backbone and partly by hydrogen bonds between the
neighboring urethane linkages. We are now in the process
of extending the polymerization system to the synthesis of
other type of NLO polymers and the results will be
reported elsewhere.
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. 2012-0007485).
FIGURE 5 Normalized SHG signal of polymer 5 as a function
of baking time at 80 ꢀC in air.
REFERENCES AND NOTES
respectively. This d33 value is higher than that of the polyur-
ethane 4, which is 5.85 ꢁ 10ꢂ9 esu. As the second harmonic
wavelength is at 532 nm, which is not in the absorptive
region of the resulting polyurethane, there was not resonant
contribution to this d33 value. In the isotropic model, the ra-
tio of d33/d31 is predicted to be about 3. Our d33/d31 value
of 2.91 is in good agreement with the predicted value.
1 Marks, T. J.; Ratner, M. A. Angew. Chem. Int. Ed. Engl. 1995,
34, 155–173.
2 Lee, S. K.; Cho, M. J.; Jin, J.-I.; Choi, D. H. J. Polym. Sci. Part
A: Polym. Chem. 2007, 45, 531–542.
3 Centore, R.; Riccio, P.; Carella, A.; Quatela, A.; Schutzmann,
S.; Stella, F.; De Matteis, F. J. Polym. Sci. Part A: Polym. Chem.
2007, 45, 2719–2725.
To evaluate the high-temperature stability of the polymer, we
studied the temporal stability of the SHG signal. Figure 4
shows the dynamic thermal stability study of the NLO activ-
ity of a film of polymer 5. To investigate the real time NLO
decay of the SHG signal of the poled polymer film as a func-
tion of temperature, in situ SHG meꢂas1urements were per-
formed at a heating rate of 4 ꢀC min from 30 to 200 ꢀC.
The polymer film exhibited a thermal stability even at 5 ꢀC
higher than Tg, and no significant SHG decay was observed
below 125 ꢀC. Figure 5 shows the temporal stability of the
polymer film in which there was no negligible decay of the
SHG signal over hundreds of hours. In general, side chain
NLO polymers lose the thermal stability of dipole alignment
below Tg. Stabilization of dipole alignment is a characteristic
of main-chain NLO polymers. The enhanced thermal stability
of second harmonic generation of polymer 5 is due to the
stabilization of dipole alignment of NLO chromophore, which
stems from the partial main-chain character of the polymer
structure and partly by hydrogen bonds between the neigh-
boring urethane linkages. Thus, we obtained a new type of
NLO polyurethane having the advantages of both main chain
and side chain NLO polymers, namely stabilization of dipole
alignment and good solubility.
4 Li, Z.; Dong, S.; Li, P.; Li, Z.; Ye, C.; Qin, J. J. Polym. Sci. Part
A: Polym. Chem. 2008, 46, 2983–2993.
5 Kolli, B.; Mishra, S. P.; Joshi, M. P.; Mohan, S. R.; Dhami, T.
S.; Samui, A. B. J. Polym. Sci. Part A: Polym. Chem. 2012, 50,
1572–1578.
6 Tsutumi, N.; Yoshizaki, S.; Sakai, W.; Kiyotsukuri, T. Macro-
molecules 1995, 28, 6437–6442.
7 Han, K. S.; Park, S. K.; Shim, S. Y.; Jahng, W. S.; Kim, N. J.
Bull. Korean Chem. Soc. 1998, 19, 1165–1168.
8 Zhang, C.; Wang, C.; Yang, J.; Dalton, L. R.; Sun, S.; Zhang,
H.; Steier, W. H. Macromolecules 2001, 34, 235–243.
9 Kim, T.-D.; Luo, J.; Tian, Y.; Ka, J.-W.; Tucker, N. M.; Haller,
M.; Kang, J.-W.; Jen, A. K.-Y. Macromolecules 2001, 39,
1676–1680.
10 Liu, Y.-L.; Hsieh, C.-Y. J. Polym. Sci. Part A: Polym. Chem.
2006, 44, 905–913.
11 Mori, Y.; Nakaya, K.; Piao, X.; Yamamoto, K.; Otomo, A.;
Yokoyama, S. J. Polym. Sci. Part A: Polym. Chem. 2012, 50,
1254–1260.
12 Yu, D.; Gharavi, A.; Yu, L. Macromolecules 1995, 28,
784–786.
13 Chen, T.; Jen, A. K. Y.; Cai, Y. Macromolecules 1996, 29,
535–539.
14 Yu. D.; Gharavi, A.; Yu, L. Macromolecules 1996, 29,
6139–6142.
15 Saadeh, H.; Gharavi, A.; Yu, D.; Yu, L. Macromolecules
1997, 30, 5403–5407.
CONCLUSIONS
We synthesized novel X-type polyurethane 5 with pendant
NLO chromophores, which are part of the polymer main
chain. This X-type NLO polyurethane is soluble in common
organic solvents. The resulting polymer 5 shows a thermal
stability uꢀp to 280 ꢀC from TGA thermograms with Tg value
near 120 C. The SHG coefficient (d33) of corona-poled poly-
mer film is 6.12 ꢁ 10ꢂ9 esu. The striking feature of this
16 Tsutsumi, N.; Morishima, M.; Sakai, W. Macromolecules
1998, 31, 7764–7769.
17 Liu, J.-G.; Nakamura, Y.; Shibasaki, Y.; Ando, S.; Ueda, M.
J. Polym. Sci. Part A: Polym. Chem. 2007, 45, 5606–5617.
18 Hoang, M, A.; Kim, M. H.; Cho, M. J.; Kim, K. H.; Kim, K. N.;
Jin, J.-I.; Choi, D. H. J. Polym. Sci. Part A: Polym. Chem. 2008,
46, 5064–5076.
280
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2013, 51, 275–281

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
19 Moon, K. J.; Shim, H. K.; Lee, K. S.; Zieba, J.; Prasad, P. N.
Macromolecules 1996, 29, 861–867.
23 Lee, J.-Y.; Bang, H.-B.; Kang, T.-S.; Park, E.-J. Eur. Polym. J.
2004, 40, 1815–1822.
20 Woo, H. Y.; Shim, H.-K.; Lee, K.-S. Polym. J. 2000, 32, 8–14.
24 Lee, J.-Y.; Park, E.-J.; Lee, H.; Rhee, B. K. Polym. Bull. 2002,
48, 233–241.
21 Tsutumi, N.; Matsumoto, O.; Sakai, W.; Kiyotsukuri, T. Mac-
romolecules 1996, 29, 592–597.
25 Cisneros, J. I. Appl. Opt. 1998, 37, 5262–5270.
22 Tsutumi, N.; Matsumoto, O.; Sakai, W. Macromolecules
1997, 30, 4584–4589.
26 Herman, W. N.; Hayden, L. M. J. Opt. Soc. Am. B 1995, 12,
416–427.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2013, 51, 275–281
281