Synthesis and electro-optic activities of novel polycarbonates bearing tricyanopyrroline-based nonlinear optical chromophores with excellent thermal stability of dipole alignment

Article abstract of DOI:10.1016/j.polymer.2013.09.042

Two series of novel electro-optic (EO) polycarbonates incorporating two kinds of tricyanopyrroline-based nonlinear optical (NLO) chromophores were designed and synthesized. These new polycarbonates were prepared through the facile copolymerization of diol

Full text of DOI:10.1016/j.polymer.2013.09.042

Polymer 54 (2013) 6349e6356
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Synthesis and electro-optic activities of novel polycarbonates bearing
tricyanopyrroline-based nonlinear optical chromophores with
excellent thermal stability of dipole alignment
,
,
,
,
,
Guowei Deng a b, Heyan Huang a b, Peng Si a b, Huajun Xu a b, Jialei Liu a, Shuhui Bo a
*
,
Xinhou Liu a, Zhen Zhen a, Ling Qiu a
,
*
a Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences,
Beijing 100190, PR China
b University of Chinese Academy of Sciences, Beijing 100049, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 July 2013
Received in revised form
2 September 2013
Accepted 21 September 2013
Available online 1 October 2013
Two series of novel electro-optic (EO) polycarbonates incorporating two kinds of tricyanopyrroline-based
nonlinear optical (NLO) chromophores were designed and synthesized. These new polycarbonates were
prepared through the facile copolymerization of diol NLO chromophores and bisphenol A bis(chlor-
oformate), and the successful preparations were demonstrated by 1H NMR and Fourier transform
infrared (FT-IR) spectra. These polycarbonates possessed good thermal stabilities and also showed higher
glass transition temperatures (Tg) in the range of 156e165 ꢀC. After corona poling, the EO coefficients
(r33) of two poled polycarbonates films were up to 52 pm/V (PC-DTCPC-Ph-2) and 46 pm/V (PC-DTCPC-
FPh-2) at the wavelength of 1310 nm. The higher Tgs endow the polycarbonates’ poled films with good
temporal stability of poling-induced dipole alignment, and the resulting poled films of PC-DTCPC-Ph-2
and PC-DTCPC-FPh-2 could retain 95% and 93% of the initial EO activities at 85 ꢀC for more than
500 h respectively.
Keywords:
Electro-optic materials
Polycarbonate
Temporal stability
Crown Copyright Ó 2013 Published by Elsevier Ltd. All rights reserved.
1. Introduction
Polycarbonate has been used extensively as the host materials in
the guest-host organic EO materials due to its low crystallization
During the recent decades, the organic electro-optic (EO) ma-
terials are being intensively investigated due to their potential
application in high-speed EO devices with very broad bandwidth
and low driving voltage, etc, and these materials have been seemed
as the promising materials to replace the currently used inorganic
materials (LiNbO3) in high-speed EO modulators [1e7]. To fulfill the
device’s requirements, the organic EO materials should possess
large EO activity, low optical loss, good processability, mechanical
strength and temporal stability of the dipole orientation [8e13]. To
make organic EO materials suitable for applications, much effort
has been expended in developing chromophores and EO polymers
[1,3,14]. Although the microscopy nonlinear optical (NLO) proper-
ties (mb) of chromophores have been greatly enhanced [1,3,6], a
strong need remains for improving the EO activity and thermal
stability of the processed materials to fulfill requirements for device
fabrication processes and long-term operation. [8,15e18].
tendency, good solubility in halogenated solvents, good optical
properties and fairly high glass transition temperature (Tg) [19,20].
Good poling efficiency is also guaranteed owing to its high dielec-
tric constant and compatibility with large mb chromophores [21].
However, the dipolar interactions between chromophores, aggre-
gation formation and thermal relaxation of the poling-induced
order usually hinder the guest-host system’s practical application
[14]. One of the effective approaches to solve above problems is
covalent attachment of NLO chromophores onto polymer back-
bones, which offers many advantages over the simple guest-host
materials [22,23]. However, so far there are only few researches
that provide approaches to tether chromophores to the poly-
carbonate backbone and most of them are based on the post-
functionalization. [20,24].
Our previous work reported that stable covalently attached EO
polycarbonates can be prepared through directly copolymerization
of the bisphenol A, diol-functionalized NLO chromophores and
bisphenol A bis (chloroformate) [25]. The proposed preparation
strategy offered very mild polymerization condition that the fragile
chromophores could tolerate. What’s more, through controlling the
* Corresponding authors. Tel.: þ86 10 82543528.
E-mail addresses: boshuhui@mail.ipc.ac.cn (S. Bo), qiuling@mail.ipc.ac.cn,
tipcqiuling@163.com (L. Qiu).
0032-3861/$ e see front matter Crown Copyright Ó 2013 Published by Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.polymer.2013.09.042

6350
G. Deng et al. / Polymer 54 (2013) 6349e6356
feed ratio, such a copolymerization strategy could well quantify the
content of chromophores and guarantee the reproducibility of
properties compared to the post-functionalization. The electron-
withdrawing ability of the tricyanopyrroline (TCP) acceptor has
been demonstrated stronger than the tricyanofurane (TCF) moiety
used in the previously work [26e31], which offered new strategies
to prepare novel EO polymers with better performances. However,
to the best of our knowledge, the EO polycarbonates incorporating
TCP-based chromophores have never been reported. Also, cova-
lently attached polymers based on TCP-based chromophores rarely
utilize the copolymerization strategy due to their fragile properties.
Herein, we reported the details of synthesis of two series of novel
polycarbonates containing the TCP-based chromophores through
copolymerization of diol-functionalized TCP-based chromophores
and bisphenol A bis(chloroformate). The bisphenol A was added as
another monomer to adjust the concentrations of chromophores.
The successful synthesis of the polycarbonates has been demon-
strated by the 1H NMR and FT-IR. The synthesized polycarbonates
exhibited good film forming property and thermal stability. After
corona poling, the poled polycarbonates films exhibited desired EO
activities at the wavelength of 1310 nm, and the maximum r33
values reached to 52 pm/V and 46 pm/V for PC-DTCPC-Phs and PC-
DTCPC-FPhs respectively. Owing to the Y shape structure charac-
terization, the resultant polycarbonates possess many advantages
of some other such Y type EO polymers [32e34], especially the
good temporal stability of EO activities. The obtained poled films of
PC-DTCPC-Ph-2 and PC-DTCPC-FPh-2 kept over 92% of the initial r33
values at 85 ꢀC for over 500 h. The excellent temporal stability of EO
activities endowed the new polycarbonates with potential appli-
cation in EO device fabrication.
ethanol,
p-bis(2-tert-butyldimethylsiloxyethyl)amimobenzalde-
hyde (3.8 g, 8.8 mmol) was added, and the mixture was refluxed for
1 h with stirring and then cooled to room temperature. The pure
chromophore TCPC was filtered and washed with cool ethanol.
Yield: 60%. 1H NMR (400 MHz, CD3COCD3),
d (ppm): 8.53 (d,
J ¼ 15.2 Hz,1H), 7.73 (d, J ¼ 8.8 Hz, 2H), 6.93 (d, J ¼ 15.2 Hz,1H), 6.87
(d, J ¼ 8.8 Hz, 2H), 3.81 (t, J ¼ 6.0 Hz, 4H), 3.71 (t, J ¼ 5.6 Hz, 4H), 0.88
(s, 18H), 0.03 (s, 12H); MS (MALDI-TOF): m/z calcd for
C32H45N5O3Si2: 603.9, found: 603.0.
2.3. Synthesis of compound 2a
TCPC (500 mg, 0.83 mmol) and potassium carbonate (286 mg,
2.1 mmol) was added to 50 mL of dry acetonitrile. The mixture was
heated to reflux for 5 min under the protection of N2. And then,
benzyl bromide (220 mg, 1.29 mmol) was added. The reaction
mixture was refluxed for another 30 min. The inorganic salts were
filtered. After removal of the solvent, the residue was purified by
column chromatography using hexane/acetone (5:1) as eluent to
give the product as green solid, yield: 52%. 1H NMR (400 MHz,
CDCl3),
d
(ppm): 8.56 (d, J ¼ 15.2 Hz, 1H), 7.60 (d, J ¼ 8.5 Hz, 2H),
7.42e7.28 (m, 3H), 7.20 (d, J ¼ 7.2 Hz, 2H), 7.08 (d, J ¼ 15.2 Hz, 1H),
6.80 (d, J ¼ 8.7 Hz, 2H), 5.33 (s, 2H), 3.83 (t, J ¼ 5.2 Hz, 4H), 3.71 (t,
5.2 Hz, 4H), 0.87 (s, 18H), 0.02 (s, 12H). 13C NMR (100 MHz, CDCl3),
d
(ppm): 167.62, 155.81, 154.32, 151.12, 144.53, 135.25, 134.35,
129.88, 129.07, 127.56, 125.32, 113.85, 112.89, 112.59, 112.36, 97.79,
61.27, 54.57, 45.12, 26.65, 19.03, ꢁ4.59. MS (MALDI-TOF): m/z calcd
for C39H51N5O3Si2: 694.0, found: 693.6.
2.4. Synthesis of DTCPC-Ph
2. Experimental
To a solution of compound 2a (300 mg, 0.43 mmol) in 30 mL
acetone, 2 mL 1N HCl was added, and the mixture was stirred at
room temperature for 6 h. After the solvent was removed, the crude
product was purified by column chromatography using hexane/
acetone (2:1) as eluent to give the product as green solid yield: 90%.
2.1. Materials and instruments
All the reagents and solvents were purchased from commercial
sources and used without further purification. Bisphenlo A bis(-
chloroformate) was purchased from Tokyo Chemical Industry Co.,
Ltd. 1,2-dichloroethane (DCE) was freshly distilled prior to use. The
protected electron donor p-bis(2-tert-butyldimethylsiloxyethyl)
amimo benzaldehyde and electron acceptor TCP were prepared
according to previous literature [26,35]. 1H NMR and 13C NMR
spectra were determined by Advance Bruker (400 MHz) NMR
spectrometer (tetramethylsilane as internal reference). The FT-IR
spectra were recorded on a Varian 3100 FT-IR spectrometer at a
resolution of 2 cmꢁ1 with a minimum of 64 scans. UVeVis spectra
were obtained using a Hitachi U2001 spectrophotometer. The
number-average molecular weight (Mn) and weight-average mo-
lecular weight (Mw) values of the obtained polycarbonates
were estimated by gel permeation chromatography (GPC), and
tetrahydrofuran (THF) was used as the eluent and polystyrene (PS)
standards were used for the molecular weight calibration. Ther-
mogravimetric analysis (TGA) was determined by TA5000-
2950TGA (TA co) with a heating rate of 10 ꢀC/min under the pro-
tection of nitrogen. Differential scanning calorimetry (DSC) mea-
surements were performed on a TA5000, 2910MDSC with a heating
rate of 10 ꢀC/min under the protection of nitrogen. The thickness of
the films were measured with an Ambios Technology XP-1 profil-
ometer. The index of the films were measured with a Model 2010
prism coupler (Metricon) instrument.
1H NMR (400 MHz, Acetone/DMSO-d6 (5:1)),
d (ppm): 8.57 (s, 1H),
7.78 (s, 2H), 7.37 (t, J ¼ 7.3 Hz, 2H), 7.29 (dd, J ¼ 13.4, 7.2 Hz, 3H), 7.11
(s, 1H), 7.01 (d, J ¼ 8.8 Hz, 2H), 5.30 (s, 2H), 4.79 (s, 2H), 3.74 (s, 8H).
13C NMR (100 MHz, Acetone/DMSO-d6 (5:1)),
d (ppm): 167.69,
156.98, 155.14, 150.41, 144.60, 136.52, 134.57, 129.66, 128.50, 127.11,
125.16, 114.55, 114.40, 113.24, 113.13, 112.12, 96.53, 59.62, 54.89,
45.13. MS(MALDI-TOF): m/z calcd for C27H23N5O3: 465.5, found:
465.7.
2.5. Synthesis of compound 2b
TCPC (500 mg, 0.83 mmol) and potassium carbonate (286 mg,
2.1 mmol) was added to 50 mL of dry acetonitrile. The mixture was
heated to reflux for 5 min under the protection of N2. And then, 3,5-
bis(trifloromethyl) benzyl bromide (396 mg, 1.29 mmol) was
added. The reaction mixture was refluxed for another 30 min. The
inorganic salts were filtered. After removal of the solvent, the res-
idue was purified by column chromatography using hexane/
acetone (5:1) as eluent to give the product as green solid, yield:
52%. 1H NMR (400 MHz, CD3COCD3),
d
(ppm): 8.53 (d, J ¼ 15.2 Hz,
1H), 8.05 (s, 2H), 7.99 (s, 1H), 7.78 (d, J ¼ 8.0 Hz, 2H), 7.08 (d,
J ¼ 15.2 Hz, 1 H), 7.03 (d, J ¼ 9.2 Hz, 2H), 5.54 (s, 2H), 3.94 (t,
J ¼ 5.6 Hz, 4H), 3.84 (t, J ¼ 5.2 Hz, 4H), 0.87 (s,18H), 0.03 (s,12H); 13C
NMR (100 MHz, CD3COCD3), d (ppm): 168.03, 157.28, 154.90, 150.61,
2.2. Synthesis of compound TCP chromophores 1
144.95, 140.52, 134.31, 132.3 (q, 2JC-F ¼ 26 Hz), 128.41, 125.72, 123.0
(p, 1JC-F ¼ 273.7 Hz), 114.37, 112.60, 112.11, 98.09, 61.52, 54.47, 45.02,
30.62, 26.26, 18.83, ꢁ5.31; MS(MALDI-TOF): m/z calcd for
C41H49F6N5O3Si2: 830.0, found: 830.5.
Chromophore TCPC was prepared according to the literature
[26]. To a solution of TCP acceptor (1.84 g, 10 mmol) in 30 mL

G. Deng et al. / Polymer 54 (2013) 6349e6356
6351
2.6. Synthesis of DTCPC-FPh
(s, 2H, aromatic), 8.02 (s, 1H, aromatic), 7.79 (s, 2H, aromatic), 7.35e
6.96 (m, 116.7H, aromatic), 5.31 (s, 2H, FPheCH2e), 4.42 (s, 4H,
NCH2CH2OCOe), 3.90 (s, 4H, NCH2CH2OCOe), 1.65 (s, 85H, eCH3).
IR (KBr pellet, cmꢁ1): 3140 (AreH), 2970 (eCH2e), 2224 (eCN),
1774 (C]O), 1504 (Aromatic CeC), 1230 (CeO). UVeVis (THF): lmax
(nm) ¼ 666.
To a solution of compound 2b (300 mg, 0.36 mmol) in 30 mL
acetone, 2 mL 1N HCl was added, and the mixture was stirred at
room temperature for 6 h. After the solvent was removed, the
crude product was purified by column chromatography using
hexane/acetone (2:1) as eluent to give the product as green solid,
PC-DTCPC-FPh-2: bisphenol A (97 mg, 0.425 mmol), DTCPC-FPh
(100 mg, 0.166 mmol), and bisphenol A bis (chloroformate)
(250 mg, 0.708 mmol). PC-DTCPC-FPh-2 was obtained as green
powder (0.33 g, 92%). GPC: Mw ¼ 8586, Mw/Mn ¼ 1.75. 1H NMR
yield: 92%. 1H NMR (400 MHz, Acetone),
d (ppm): 8.55 (d,
J ¼ 15.2 Hz, 1H), 8.06 (s, 1H), 8.00 (s, 1H), 7.79 (d, J ¼ 8.8 Hz, 2H),
7.12 (d, J ¼ 15.2 Hz, 1H), 7.01 (d, J ¼ 9.1 Hz, 2H), 5.55 (s, 2H), 4.20 (t,
J ¼ 5.2 Hz, 2H), 3.86 (dd, J ¼ 10.4, 5.0 Hz, 4H), 3.81 (t, J ¼ 5.0 Hz, 4H).
(400 MHz, DMSO-d6),
d
(ppm): 8.43 (d, J ¼ 15.1 Hz, 1H, vinylic), 8.07
13C NMR (100 MHz, Acetone),
d
(ppm): 167.92, 157.22, 154.75,
(s, 2H, aromatic), 8.02 (s, 1H, aromatic), 7.79 (s, 2H, aromatic), 7.35e
6.96 (m, 59.4H, aromatic), 5.31 (s, 2H, FPheCH2e), 4.42 (s, 4H,
NCH2CH2OCOe), 3.90 (s, 4H, NCH2CH2OCOe), 1.65 (s, 42.2H, eCH3).
IR (KBr pellet, cmꢁ1): 3140 (AreH), 2970 (eCH2e), 2224 (-CN), 1772
(C]O), 1504 (Aromatic CeC), 1230 (CeO). UVeVis (THF): lmax
(nm) ¼ 666.
2
150.54, 144.98, 140.47, 134.19, 132.32 (q, JC-F ¼ 26 Hz),, 128.29,
1
125.13, 122.92 (p, JC-F ¼ 273.7 Hz), 114.28, 112.60, 111.96, 97.83,
60.01, 54.86, 45.01. MS (MALDI-TOF) m/z calc for C29H21F6N5O3:
601.5, found: 601.7.
2.7. General procedure for the synthesis of polycarbonate
PC-DTCPC-FPh-3: bisphenol A (78 mg, 0.342 mmol), DTCPC-FPh
(150 mg, 0.249 mmol), and bisphenol A bis (chloroformate)
(250 mg, 0.708 mmol). PC-DTCPC-FPh-3 was obtained as green
powder (0.37 g, 95%). GPC: Mw ¼ 6684, Mw/Mn ¼ 1.66. 1H NMR
A solution of bisphenol A, DTCPC and 0.2 mL pyridine were
dissolved in DCE. The solution was heated to general reflux. A so-
lution of bisphenol A bis (chloroformate) in DCE was then added
dropwise, and the reaction mixture was stirred for another 3 h
under reflux. After cooling to room temperature, the solution was
precipitated in MeOH (200 mL), and the precipitates were collected
by filtration. Then the precipitates were re-dissolved in a minimum
quantity of CH2Cl2 and re-precipitated in MeOH. The products were
further purified by extraction in a Soxhlet extractor with ethyl ether
and dried under vacuum.
(400 MHz, DMSO-d6),
d
(ppm): 8.43 (d, J ¼ 15.1 Hz, 1H, vinylic), 8.07
(s, 2H, aromatic), 8.02 (s, 1H, aromatic), 7.79 (s, 2H, aromatic), 7.35e
6.96 (m, 39.8H, aromatic), 5.31 (s, 2H, FPheCH2e), 4.42 (s, 4H,
NCH2CH2OCOe), 3.90 (s, 4H, NCH2CH2OCOe), 1.65 (s, 27.7H, eCH3).
IR (KBr pellet, cmꢁ1): 3140 (AreH), 2970 (eCH2e), 2224 (eCN),
1770 (C]O), 1504 (Aromatic CeC), 1230 (CeO). UVeVis (THF): lmax
(nm) ¼ 665.
PC-DTCPC-Ph-1: bisphenol A (110 mg, 0.482 mmol), DTCPC-Ph
2.8. Preparation of the polymer films
(50 mg, 0.108 mmol), and bisphenol
A bis (chloroformate)
(250 mg, 0.708 mmol). PC-DTCPC-Ph-1 was obtained as green
The synthesized polycarbonates were dissolved in cyclo-
pentanone to form the 15 wt% solution. The solution was filtered
using a 0.2-mm syringe filter to remove large particulates. And then
the solution was spin-coated on indium-tin oxide (ITO) glass sub-
strates. The films were dried in vacuo for 12 h to remove the re-
sidual solvent.
powder (0.30 g, 92%). GPC: Mw ¼ 18,235, Mw/Mn ¼ 2.32. 1H NMR
(400 MHz, DMSO-d6),
d
(ppm): 8.43 (d, J ¼ 15.3 Hz, 1H, vinylic), 7.75
(J ¼ 8.6 Hz, d, 2H, aromatic), 6.91e7.41 (m, 93.5H, aromatic and
vinylic), 5.18 (s, 2H, PheCH2e), 4.41 (s, 4H, NCH2CH2OCOe), 3.90 (s,
4H, NCH2CH2OCOe), 1.64 (s, 63.6H, eCH3). IR (KBr pellet, cmꢁ1):
3140 (AreH), 2970 (eCH2e), 2222 (eCN), 1774 (C]O), 1504 (Aro-
matic CeC), 1230 (CeO). UVeVis (THF): lmax (nm) ¼ 659.
3. Results and discussion
PC-DTCPC-Ph-2: bisphenol A (85 mg, 0.375 mmol), DTCPC-Ph
(100 mg, 0.215 mmol), and bisphenol A bis (chloroformate)
(250 mg, 0.708 mmol). PC-DTCPC-Ph-2 was obtained as green
powder (0.33 g, 94%). GPC: Mw ¼ 9569, Mw/Mn ¼ 1.94. 1H NMR
3.1. Monomers and polymers syntheses
The synthesis of the diol-functionalized NLO chromophores are
illustrated in Scheme 1. The TCP-based NLO chromophores can be
synthesized by the Knoevenagel reaction of TCP with tert-
butyldimethylsiloxyethyl group subistituted p-bis(hydroxyl) ami-
mobenzaldehyde in refluxing ethanol. One of the major advantages
of the TCP-based chromophores is that the secondary amine in the
TCP acceptor offered a reaction site to introduce various of sub-
stituents, which could tune the electronic properties of chromo-
phores, improve solubility and minimize molecular aggregation
[26,28]. Two new modified TCP chromophores 2a and 2b were
obtained through attaching benzyl group and 3,5-bis (tri-
fluoromethyl)benzyl group to the amine of pyrroline ring. After
hydrolysis in acetone in the presence of HCl, the diol-functionalized
TCP-based chromophores DTCPC-Ph and DTCPC-FPh were suc-
cessfully synthesized.
Scheme 2 shows the preparation strategy of new polycarbonates
bearing TCP-based chromophores. Polycondensation of the diol
NLO chromophores and bisphenol A with bisphenol A bis(chlor-
oformate) in solution using pyridine as acid scavenger, afforded the
polycarbonates containing the corresponding NLO chromophores,
where the bisphenol A was used to adjust the chromophores con-
tent. In order to avoid the influence of moisture and trace water in
the solvent, and ensure the chromophores are polymerized in a
(400 MHz, DMSO-d6),
d
(ppm): 8.43 (d, J ¼ 15.3 Hz, 1H, vinylic), 7.75
(J ¼ 8.6 Hz, d, 2H, aromatic), 6.91e7.41 (m, 51.7H, aromatic and
vinylic), 5.18 (s, 2H, PheCH2e), 4.41 (s, 4H, NCH2CH2OCOe), 3.90 (s,
4H, NCH2CH2OCOe), 1.64 (s, 32.4H, eCH3). IR (KBr pellet, cmꢁ1):
3140 (AreH), 2970 (eCH2e), 2222 (eCN), 1770 (C]O), 1504 (Aro-
matic CeC), 1230 (CeO). UVeVis (THF): lmax (nm) ¼ 659.
PC-DTCPC-Ph-3: bisphenol A (61 mg, 0.267 mmol), DTCPC-Ph
(150 mg, 0.323 mmol), and bisphenol A bis (chloroformate)
(250 mg, 0.708 mmol). PC-DTCPC-Ph-3 was obtained as green
powder (0.31 g, 95%). GPC: Mw ¼ 5779, Mw/Mn ¼ 1.99. 1H NMR
(400 MHz, DMSO-d6),
d
(ppm): 8.43 (d, J ¼ 15.3 Hz, 1H, vinylic),
7.75 (J ¼ 8.6 Hz, d, 2H, aromatic), 6.91e7.41 (m, 34.7H, aromatic
and vinylic), 5.18 (s, 2H, PheCH2e), 4.41 (s, 4H, NCH2CH2OCOe),
3.90 (s, 4H, NCH2CH2OCOe), 1.64 (s, 19.8H, eCH3). IR (KBr pellet,
cmꢁ1): 3140 (AreH), 2970 (eCH2e), 2222 (eCN), 1770 (C]O),
1504 (Aromatic CeC), 1230 (CeO). UVeVis (THF): lmax
(nm) ¼ 657.
PC-DTCPC-FPh-1: bisphenol A (116 mg, 0.509 mmol), DTCPC-
FPh (50 mg, 0.083 mmol), and bisphenol A bis (chloroformate)
(250 mg, 0.708 mmol). PC-DTCPC-FPh-1 was obtained as green
1
powder (0.31 g, 94%). GPC: Mw ¼ 16,383, Mw/Mn ¼ 2.12. H NMR
(400 MHz, DMSO-d6),
d
(ppm): 8.43 (d, J ¼ 15.1 Hz, 1H, vinylic), 8.07

6352
G. Deng et al. / Polymer 54 (2013) 6349e6356
Scheme 1. The synthesis route of DTCPCs.
maximum extent, the bisphenol A bis(chloroformate) was used in
an excessive quantity (1.2 equ of (m þ n)). The excess bisphenol A
bis(chloroformate) didn’t damage the obtained polymers and were
removed through the precipitate process. Using the diol-
functionalized chromophores DTCPC-Ph and DTCPC-FPh, two se-
ries of polycarbonates containing different concentrations of NLO
chromophores (PC-DTCPC-Phs and PC-DTCPC-FPhs) were obtained
with 90%e93% yield.
3.2. Characterization
The structure determinations of the EO polycarbonates were
performed by 1H NMR and FT-IR. Fig. 1 and Fig. 2 show the 1H NMR
spectra of PC-DTCPC-Phs and PC-DTCPC-FPhs. In the 1H NMR
spectra, the vinyl proton’s singles of PC-DTCPC-Phs and PC-DTCPC-
FPhs appeared near 8.43 as a doublet peak, which were the same as
the TCP-based chromophores monomer. Due to polymerization, the
Scheme 2. The polymerization strategy of the PC-DTCPCs.

G. Deng et al. / Polymer 54 (2013) 6349e6356
6353
Both FI-IR spectra showed a strong absorption peak near 2220 cmꢁ1
indicating the presence of nitrile group, and typical band of aro-
matic ring at 1504 cmꢁ1. The spectra also showed a strong carbonyl
peak near 1770 cmꢁ1 and a typical band of eCeOeCe group at
1230 cmꢁ1, indicating the presence of carbonate structure. These
FT-IR spectra results further demonstrated the successful prepa-
ration of the designed polycarbonates.
According to the 1H NMR analysis, the molar contents of the NLO
chromophores in the resulting polycarbonates could also be ob-
tained. Table 1 lists the feed ratios and measured ratios of chro-
mophores and comonomers in PC-DICPC-Phs and PC-DTCPC-FPhs.
One disadvantage of attaching NLO chromophores onto the poly-
mer backbone adopting the post-functionalization strategy is that
the degree of substitution may be hard to quantify, which directly
influences the reproducibility of the polymers’ property [6]. Here,
the measured ratios are approximately the same as the feed ratios.
Through controlling the feed ratio, the content of the NLO chro-
mophores in the polycarbonates could be well-controlled, and the
reproducibility of the polymers’ property is guaranteed.
Fig. 1. 1H NMR spectra of PC-DTCPC-Phs.
GPC was used to estimated the molecular weight and molecular
weight distribution on the basis of PS standards (the details were
summarized in Table 1). The molecular weight and molecular
weight distribution were in the range of 5779e18235 and 1.66e
2.32, respectively. Owing to the strong steric effect of bulky chro-
mophores, the molecular weights were greatly influenced by the
chromophores contents. Lower chromophore content could get
larger molecular weight (PC-DTCPC-Ph-1 and PC-DTCPC-FPh-1). As
the increase of the chromophore content, the molecular weight
decreased to lower values (5779 and 6694 for PC-DTCPC-Ph-3 and
PC-DTCPC-FPh-3 respectively). All the polycarbonates can dissolve
in common polar organic solvents, such as cyclopentanone, THF,
DMF, DMSO and halogenated solvents. These polymers also
exhibited well film forming property. High-quality, smooth, ho-
mogenous and highly transparent films were obtained through
spin-coating from the PC-DTCPC-Phs and PC-DTCPC-FPhs.
3.3. UVevis spectra
Fig. 2. 1H NMR spectra of PC-DTCPC-FPhs.
The UVevis spectra of PC-DTCPC-Phs and PC-DTCPC-FPhs are
studied in both solvent and films, and the maximum absorption
single HOeCH2e moved from 3.80 to 4.41. Except the signals of
aromatic protons which were overlapped by the aromatic proton
signals of bisphenol A, the other signals of DTCPC-Ph and DTCPC-
FPh (Figure S1 and Figure S3) could be easily observed in the 1H
NMR spectra of PC-DTCPC-Phs and PC-DTCPC-FPhs. All chemical
shifts are consistent with the proposed polymer structure. The FT-
IR spectra of PC-TCPC-Phs and PC-DTCPC-FPhs are shown in Fig. 3.
wavelengths for the
pep* transition (lmax) are listed in Table 2.
Figure S5 shows the UVevis spectra of EO polycarbonates in THF,
and the lmax of PC-DTCPC-Phs and PC-DTCPC-FPhs are 659 nm and
666 nm, respectively. As the increase of the chromophores content,
the shape of absorption band didn’t changed, which indicated that
there only exist weak interaction between chromophores in the
solution state [36,37]. Fig. 4 shows the UVevis spectra of EO
Fig. 3. FT-IR spectra of PC-DTCPC-Phs (left) and PC-DTCPC-FPhs (right).

6354
G. Deng et al. / Polymer 54 (2013) 6349e6356
Table 1
Characterization and properties of EO polycarbonates.
Feed ratioa
Measured ratiob
Yield (%)
Mw
Mw/Mn
Td (ꢀC)d
Tg (ꢀC)e
c
c
Product
PC-DTCPC-Ph-1
PC-DTCPC-Ph-2
PC-DTCPC-Ph-3
PC-DTCPC-FPh-1
PC-DTCPC-FPh-2
PC-DTCPC-FPh-3
1:9.9
1:4.5
1:2.7
1:13.3
1:6.1
1:3.7
1:10.6
1:5.4
1:3.3
1:14.2
1:7.0
1:4.6
92
94
95
94
92
95
18,235
9569
5779
16,383
8586
6694
2.32
1.94
1.99
2.12
1.75
1.66
329
299
294
343
309
291
155
165
164
156
160
164
a
The ratio of NLO chromophore: the sum of bisphenol A and bisphenol A bis (chloroformate).
Determined by 1H NMR.
b
c
Determined by GPC in THF on the basis of a polystyrene calibration.
d
e
Performed at a heating rate of 10 ꢀC/min under nitrogen atmosphere by DSC.
Defined as weight loss at 5 wt%, which were performed at a heating rate of 10 ꢀC/min under nitrogen atmosphere by TGA.
Table 2
EO properties of poled films and related parameters.
Product
Chromophore
N
b (mmol/g)
lmax (nm)
Film
thickness (mm)
n(1310 nm)
r33 (pm/V)c
contenta (wt %)
THF solution
Film
PC-DTCPC-Ph-1
PC-DTCPC-Ph-2
PC-DTCPC-Ph-3
PC-DTCPC-FPh-1
PC-DTCPC-FPh-2
PC-DTCPC-FPh-3
15
25
35
14
25
33
0.32
0.54
0.75
0.23
0.42
0.55
659
659
657
666
666
665
659
659
650
666
666
668
2.09
2.49
2.18
2.37
1.98
2.63
1.599
1.621
1.654
1.581
1.599
1.608
37
52
34
32
46
35
a
Determined by 1H NMR.
b
Molar concentration (N is defined by molar value of chromophores in 1 g polymer).
Measured by simple reflection technique at 1310 nm.
c
polycarbonates films. The lmax of PC-DTCPC-Ph-1 and PC-DTCPC-
Ph-2 were still 659 nm, but the absorption band became broader
when the chromophore content increased, and the lmax of PC-
DTCPC-Ph-3 even shifted to 650 nm. The broadening of the ab-
sorption band and the shift of lmax maybe caused by the aggrega-
tion of chromophores [38e40]. For PC-DTCPC-FPhs, the absorption
band also broadened as the increase of chromophore content.
These results indicated that when the chromophore content
increased to a high level, there existed chromophore aggregations
in the polymer films, which would influence the macroscopic EO
activities.
PC-DTCPC-FPhs began to decompose at near 220 ꢀC which are more
or less the same as the thermal decomposing behaviors of DTCPC-
Ph and DTCPC-FPh (Figure S6 and Figure S7), indicating that the
decomposition of the polymers were mainly determined by the
chromophores at this temperature range. All the polymers are
thermally stable below 220 ꢀC and these are already enough for the
practical application of EO polymers.
As shown in Fig. 6, the Tgs of PC-DTCPC-Phs and PC-DTCPC-FPhs
were observed in the range of 155e165 ꢀC and 156e164 ꢀC. Owing
to the stronger interchromophore interactions [25], the Tg values
varied depending on the chromophores contents. In both series of
NLO polymers, the Tg values increased as the chromophores
reached a high molar content in the polymer backbone. The
decrease of the molecular weight influenced the Tg of PC-DTCPC-
Ph-3 which exhibited a slightly lower value (164 ꢀC) than PC-
DTCPC-Ph-2 (165 ꢀC). Usually, the Tg greatly influenced the tem-
poral stability of the poling-induced dipole alignment [41,42]. So
the higher Tgs of the resultant polycarbonates ensure the EO ac-
tivities of poled films possess good stability.
3.4. Thermal properties of the polymers
Thermal properties of PC-DTCPC-Phs and PC-DTCPC-FPhs are
evaluated by TGA and DSC. The thermal decomposition behaviors
and glass transition temperature were measured under nitrogen,
and the relevant results are summarized in Table 1. Fig. 5 shows the
TGA thermogram of obtained polymers. Both PC-DTCPC-Phs and
Fig. 4. Normalized UVevis spectra of films of PC-DTCPC-Phs (left) and PC-DTCPC-FPhs (right).

G. Deng et al. / Polymer 54 (2013) 6349e6356
6355
Fig. 5. TGA curves of PC-DTCPC-Phs (left) and PC-DTCPC-FPhs (right).
3.5. EO properties of polymers
chromophores (PC-TCFCs) obtained the maximum r33 values of 45
pm/V when the molar concentration increased to 0.72 (PC-TCFC-2)
[25]. Compared to PC-TCFCs, PC-DTCPC-Phs can get larger macro-
scopic EO activity at a lower concentration due to the TCP-based
chromophores’ better nonlinearity properties (mb) which were
caused by the TCP’s stronger electron accepting ability. In PC-
DTCPC-Phs, when the chromophore’s molar concentration
increased to 0.75 (PC-DTCPC-Ph-3), the r33 value decreased to 34
pm/V. That is because the dipoleedipole electrostatic interaction
would cause the aggregation of the chromophores at high con-
centration and decrease the poling efficiency, which are consistent
with the UVevis spectra analysis results. The theoretical calculation
In order to evaluate the EO activities of PC-DTCPC-Phs and PC-
DTCPC-FPhs, the corona poling method was utilized to realize the
asymmetric alignment of the NLO chromophores in films. Polymer
films obtained through spin-coating were heated to the poling
temperature (near Tg), and then the poling voltage was applied and
the samples were allowed to equilibrate for 20 min. The poling
voltage was removed after the samples cooled to room tempera-
ture. After the thermal evaporation of a thick film of gold on top of
polymer layers, the EO coefficients of the poled films were
measured immediately.
The EO coefficients of the poled films were determined by the
simple reflection technique initially proposed by Teng and Man
[43]. The r33 values were calculated by the following equation:
indicated that the hyperpolarizability
(
b
)
of DTCPC-FPh
(370 ꢂ 10ꢁ30 esu) is larger than DTCPC-Ph (325 ꢂ 10ꢁ30) (the
calculation details are presented in the ESI), which provided the
probability to obtain larger EO activities. The similar structure also
provided PC-DTCPC-FPhs with the similar best poling condition as
PC-DTCPC-Phs except the poling temperature, however, PC-DTCPC-
FPhs only exhibited the maximum r33 of 46 pm/V at the molar
concentration of 0.42 (PC-DTCPC-FPh-2). Such a phenomenon may
be caused by the presence of trifluoro group, which made the
DTCPC-FPh require higher activation energy for aligning the chro-
mophore to the poling direction so that the poling efficiency of PC-
DTCPC-FPhs was greatly influenced. [28].
À
Á
3=2
n2 ꢁ sin2q
3
p
l m
VmIcn2
I
1
r33
¼
(1)
À
Á
n2 ꢁ 2sin2q sin2
q
4
where r33 is the EO coefficient of the poled polymer;
l
is the optical
wavelength;
q is the incidence angle; Ic is the output beam in-
tensity; Im is the amplitude of the modulation; Vm is the modulating
voltage; n is the refractive indices of the polymer films.
In order to investigate the relaxation feature of the poling-
induced chromophores’ dipole alignment, the temporal stability
was studied through monitoring the r33 changes at evaluated
temperature. Fig. 7 shows the long-term temporal stability of poled
PC-DTCPC-Ph-2 and PC-DTCPC-FPh-2 films at 85 ꢀC. After a fast
decay at the beginning because of the recovery of bond angle and
bond length of the oriented chromophores, the PC-DTCPC-Ph-2 and
PC-DTCPC-FPh-2 retained 95% and 93% of the initial r33 values and
stayed almost unchanged for more than 500 h. The excellent long-
Through changing the poling temperature, poling time and
poling voltage, the optimum poling condition were poled at (Tg þ 5)
ꢀC for 20 min under the electric field of 11e11.5 kV. Table 2 lists the
obtained r33 values under the optimum condition and the refractive
indices. The EO coefficients of PC-TCPC-Phs and PC-DTCPC-FPhs
were in the ranges of 35e52 pm/V and 32e46 pm/V, respectively.
The highest r33 value of PC-DTCPC-Phs was determined as 52 pm/V
at the molar concentration of 0.54 (PC-DTCPC-Ph-2). We previously
reported that EO polycarbonates containing TCF-based
Fig. 6. DSC curves of PC-DTCPC-Phs (left) and PC-DTCPC-FPhs (right).

6356
G. Deng et al. / Polymer 54 (2013) 6349e6356
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Acknowledgments
We are grateful to the Directional Program of the Chinese
Academy of Sciences (KJCX2.YW.H02), Innovation Fund of the
Chinese Academy of Sciences (CXJJ-11-M035) and the National
Natural Science Foundation of China (no. 61101054) for financial
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Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.polymer.2013.09.042.