Synthesis and photoresponsive behaviors of novel poly(arylene ether)s with di-azobenzene pendants

Article abstract of DOI:10.1016/j.reactfunctpolym.2011.01.011

Novel poly(arylene ether)s containing di-azobenzene moieties (diazo-PAEs) were synthesized from a new di-azobenzene monomer, bis(4-((4-cyanophenyl) diazenyl)phenyl)5,5′-carbonylbis(2-fluorobenzenesulfonate). These polymers show good thermal stability, wit

Full text of DOI:10.1016/j.reactfunctpolym.2011.01.011

Reactive & Functional Polymers 71 (2011) 553–560
Contents lists available at ScienceDirect
Reactive & Functional Polymers
journal homepage: www.elsevier.com/locate/react
Synthesis and photoresponsive behaviors of novel poly(arylene ether)s
with di-azobenzene pendants
Jingjing Zhang a, Haibo Zhang a, Xingbo Chen a,b, Jinhui Pang a, Yuxuan Zhang a, Yongpeng Wang a,
Qidai Chen c, Songhao Pei d, Weixian Peng d, Zhenhua Jiang a,
⇑
a Alan G. MacDiarmid Institute, Jilin University, Changchun 130012, China
b State Key Lab for Ceramic Fibers Composites, National University of Defense Technology, Changsha, Hunan 410073, China
c State Key Lab on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012, China
d College of Physics, Jilin University, Changchun 130012, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel poly(arylene ether)s containing di-azobenzene moieties (diazo-PAEs) were synthesized from a new
di-azobenzene monomer, bis(4-((4-cyanophenyl)diazenyl)phenyl)5,50-carbonylbis(2-fluorobenzenesulf-
onate). These polymers show good thermal stability, with glass transition temperatures and 5%
weight-loss temperatures above 160 °C and 406 °C, respectively. Upon irradiation with a 532 nm neo-
dymium dope yttrium aluminum garnet (Nd:YAG) laser beam, these polymers present a high remnant
value, and no fatigue phenomena were observed after several cycles of inscription–erasure–inscription
sequences. By exposing diazo-PAE films to an interference pattern of laser beams (355 nm) at modest
intensity (approximately 80 mW/cm2), stable surface relief gratings (SRGs) can be formed.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 26 October 2010
Received in revised form 21 January 2011
Accepted 24 January 2011
Available online 1 February 2011
Keywords:
Poly(arylene ether)s
Di-azobenzene
Photoinduced birefringence
Surface relief gratings
1. Introduction
(Tgs) of the polymers and can be removed by heating the polymers
above their Tgs or can be erased optically. Although the under-
Polymers containing azobenzene units in main chains or as pen-
dant groups along the backbone have been attracting a great deal
of attention because of their potential applications in optical data
storage, optical switches, and electro-optical modulators [1–7].
Azo-polymers have many attractive features, especially their un-
ique reversible photoisomerization and the anisotropy of the azo-
benzene chromophores. The photoisomerization can cause
significant changes in the bulk properties, surface properties and
polarity of the polymers. One of the attractive phenomena is pho-
toinduced birefringence in films when they are irradiated by line-
arly polarized light. When excited by linearly polarized laser light,
the chromophores undergo trans–cis-trans-isomerization accom-
panied by molecular reorientation. Through the hole-burning
mechanism, an excess of chromophores occurs in the direction per-
pendicular to the laser polarization. This molecular reorientation
induces birefringence, and this reorientation can be reversed by
irradiation with circularly polarized light or depolarized light [8].
Another active field of azo-polymer research is the investigation
of surface relief gratings (SRGs) formed directly on the polymer
films by exposing the films to an interfering laser beam [9,10].
These SRGs are stable below the glass transition temperatures
standing of the mechanism responsible for SRG formation is still
evolving, this phenomenon has already been explored in various
azobenzene-containing systems, including amorphous polymers
[11], liquid crystalline polymers [12,13], molecular glasses [14–
16], and supramolecular polymers [17,18].
In recent years, azobenzene chromophores have been intro-
duced into some high-Tg aromatic polymers such as azo-PI and
azo-PU because this strategy is helpful to improve the stability of
azobenzene chromophores for optical storage applications
[11,19,20]. Poly(arylene ether)s (PAEs) are high-performance ther-
moplastics that are well known for their excellent thermal,
mechanical, and environmental stabilities. These materials can be
used in a wide range of demanding applications from aerospace
to microelectronics [21]. Functionalized poly(arylene ether)s have
received much attention due to their potential applications in pro-
ton-exchange membranes, light-emitting materials, and optical
materials [22–25]. In our previous work, we synthesized some
photoresponsive azo-poly(arylene ether)s by direct copolymeriza-
tion and investigated their corresponding optical properties [26–
28]. These azo-PAEs display photoinduced birefringence behavior
with a high remnant value, and stable SRGs can be formed on
them. However, most azo-PAEs have relatively low molecular
weights and intrinsic viscosities below 0.3 dL/g due to the low
reactivity of azo-monomers. In this work, we synthesized a new
⇑
Corresponding author. Tel./fax: +86 0431 85168886.
E-mail address: jiangzhenhua@mail.jlu.edu.cn (Z. Jiang).
1381-5148/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.reactfunctpolym.2011.01.011

554
J. Zhang et al. / Reactive & Functional Polymers 71 (2011) 553–560
bifluoride monomer with two azobenzene units, bis(4-((4-cyano-
phenyl)diazenyl)phenyl)5,50-carbonylbis(2-fluorobenzenesulfo-
nate) (monomer 2). From this monomer, novel poly(arylene ether)s
with di-azobenzene pendants (diazo-PAEs) were prepared by
nucleophilic aromatic substitution polymerization. The thermal
and optical properties of the diazo-PAEs were also investigated.
and removal of the toluene, the polycondensation reaction was
continued for 10 h at 150 °C. Then, the viscous solution was slowly
poured into water and stirred vigorously. The threadlike polymer
was pulverized, and the resulting powders were washed several
times with hot deionized water and ethanol and dried at 110 °C
under vacuum for 24 h (yield: 92%).
2.3. Polymer film preparation
2. Experimental
Copolymer films were prepared by the following procedure.
Homogeneous solutions of diazo-PAEs in cyclohexanone
2.1. Materials
(10 wt.%) were filtered through 0.8 lm syringe filter membranes.
To fabricate SRGs, thin films were obtained via spin-coating the
solution onto clean glass substrates. The thickness was controlled
4-Aminobenzonitrile and 4,40-(hexafluoroisopropylidene)
diphenol (6F-BPA) were purchased from Alfa Aesar. 4,40-Difluo-
robenzophenone was purchased from Shanghai Chemical
Factory. 4-((4-Hydroxyphenyl)diazenyl)benzonitrile, 1,4-phen-
ylenebis((4-fluorophenyl)methanone) (PBFM) and sodium 5,
50-carbonylbis(2-fluorobenzenesulfonate) were synthesized accor-
ding to the protocols reported in the literature [25,29]. All other
reagents and solvents were obtained commercially and were puri-
fied by conventional methods. K2CO3 was dried at 120 °C for 24 h
before polymerization.
to be approximately 1.0
the photoinduced birefringence experiment, films approximately
8.0 m thick were obtained by solvent-casting on glass substrates.
lm by adjusting the spinning rate. For
l
After drying under vacuum for 48 h to drive off the residual sol-
vent, the films were stored in a desiccator until use.
2.4. Measurements
FT-IR spectra (KBr pellet) were recorded on a Nicolet Impact
410 FT-IR spectrophotometer. Gel permeation chromatography
(GPC) was carried out using a Waters 410 instrument with tetrahy-
drofuran (THF) as the eluent and polystyrene as the calibration
standard. The inherent viscosity was determined using an Ubbe-
lohde viscometer in a thermostatic container with a polymer con-
centration of 0.5 g/dL in DMAc at 25 °C. A Bruker 510 instrument
was used to record 1H (500 MHz) and 13C (125 MHz) NMR spectra.
Glass transition temperatures (Tgs) were determined by DSC (Mod-
el Mettler DSC821e) at a heating rate of 20 °C/min under a nitrogen
atmosphere. Thermo-gravimetric analysis was performed on a Per-
kin Elmer Pyris 1 TGA analyzer at a heating rate of 10 °C/min under
a nitrogen atmosphere. Polarized optical microscopy (POM) was
performed on a Leica DLMP with a Linkam THMSE 600 hot stage.
UV–visible absorption spectra were recorded on a UV2501-PC
spectrophotometer.
2.2. Synthesis
2.2.1. Synthesis of 5,50-carbonylbis(2-fluorobenzene-1-sulfonyl
chloride) (1)
Dry sodium 5,50-carbonylbis(2-fluorobenzenesulfonate) (25.34 g,
60 mmol) was mixed with chlorosulfonic acid (63 mL, 540 mmol)
under a nitrogen atmosphere. The reaction temperature was kept
at 100 °C for 4 h. Then, the mixture was poured into ice-water,
neutralized with NaHCO3 and extracted with dichloromethane.
The resulting product was recrystallized from toluene to afford
pure white crystals. Yield: 75%, mp: 135 °C (determined by DSC);
IR (KBr, cmꢀ1): 1385, 1175 (–SO2Cl); 1H NMR (DMSO-d6, d, ppm):
8.06 (d, J = 6.9 Hz, 2H), 7.73 (m, 2H), 7.34 (t, J = 9.5 Hz, 2H).
2.2.2. Synthesis of bis(4-((4-cyanophenyl)diazenyl)phenyl)5,
50-carbonylbis(2-fluorobenzenesulfonate) (2)
4-((4-Hydroxyphenyl)diazenyl)benzonitrile (14.06 g, 63 mmol)
and triethylamine (9.1 mL, 63 mmol) were dissolved in 300 mL
dry dichloromethane in a 1000 mL three-necked flask under a
nitrogen atmosphere. The solution of 5,50-carbonylbis(2-fluoroben-
zene-1-sulfonyl chloride) (12.46 g, 30 mmol) in 300 mL dry dichlo-
romethane was added dropwise into the above mixture, which was
then stirred for 12 h at room temperature. After washing with
water/acid/water, the dichloromethane was evaporated, and the
product was recrystallized from 1,4-dioxane. Orange-red crystals
were obtained (21.5 g). Yield: 88%, mp: 233 °C (determined by
DSC); MALDI-TOF-MS: C39H22F2N6O7S2 m/z = 790.1 (M+ + H); IR
(KBr, cmꢀ1): 2231 (–CN), 1363, 1196 (Ar–SO3–Ar); 1H NMR
(DMSO-d6, d, ppm): 8.22 (m, 2H), 8.10–8.07 (m, 6H), 8.01–7.96
(m, 8H), 7.84 (t, J = 9.1 Hz, 2H), 7.44 (d, J = 7.7 Hz, 4H); 13C NMR
(DMSO-d6, d, ppm): 190.91, 162.76, 160.65, 154.68, 151.82,
140.40, 134.72, 134.34, 133.20, 125.80, 124.13, 123.93, 123.52,
119.71, 119.12, 114.59.
2.5. Optical measurements
The experimental setups for the photoinduced birefringence
experiments and SRG formation have been described by our group
previously [26], and only a few details are given here. Photoin-
duced birefringence was evaluated using a pump–probe optical
configuration. The polarization direction of the pump laser
(532 nm 47 mW/cm2) made a 45° angle with respect to the probe
beam (632.8 nm He:Ne laser) polarization. The films were placed
between two crossed polarizers (P and A) in the path of the probe
laser beam. A birefringence
resulted in transmission of the 632.8 nm probe beam through
Dn induced by the 532 nm pump laser
polarizer A. The birefringence (
D
n) value was calculated using It =
Io ꢀ sin2(
pDnd/k), where It is the transmitted probe light intensity
at time t, d is the sample thickness, k is the wavelength of the probe
light and Io is the transmitted probe light intensity for the given
polarizer/analyzer orientation (in the absence of the sample). The
holographic gratings were optically inscribed on the spin-coated
films with p-polarized interfering laser beams. A frequency-tripled,
Q-switched, single-mode neodymium dope yttrium aluminum gar-
net nanosecond laser with a 355 nm wavelength and a 10 ns pulse
width (Spectra-physics) was utilized as the recording light source.
The output laser light was split into two beams of equal intensity
(approximately 40 mW/cm2), each with a diameter of approxi-
mately 10 mm. The surface topology of the films was observed
using a Nanoscope atomic force microscope (AFM) in tapping
mode.
2.2.3. Synthesis of di-azobenzene functionalized poly(arylene ether)s
(diazo-PAEs) (3)
Monomer 2, PBFM, 6F-BPA, K2CO3, N,N-dimethylacetamide
(DMAc) and toluene were added to a 100 mL three-necked flask
equipped with a mechanical stirrer, a Dean–Stark trap, a con-
denser, a thermometer and a nitrogen inlet. Under a nitrogen
atmosphere, the mixture was heated to 130–140 °C and main-
tained at that temperature for 3 h to dehydrate the system by
means of a Dean–Stark trap through toluene. After dehydration

J. Zhang et al. / Reactive & Functional Polymers 71 (2011) 553–560
555
–CO–, which further confirmed the successful preparation of dia-
zo-PAEs 3b–d despite the existence of bulky pendant groups in
monomer 2. UV–vis absorption spectra of diazo-PAEs (3a–d) in
DMF solution were recorded (Fig. 1). The characteristic absorption
3. Results and discussion
3.1. Synthesis of monomers
bands due to p–
pꢂ and n–pꢂ, the intramolecular charge-transfer of
A novel aromatic difluoride monomer containing di-azobenzene
groups was designed and synthesized by a two-step reaction, as
shown in Scheme 1. First, we prepared monomer 1 via an acid-
chloride reaction from sodium 5,50-carbonylbis(2-fluorobenzene-
sulfonate) and chlorosulfonic acid. Then, monomer 2 was prepared
from monomer 1 and 4-((4-hydroxyphenyl)diazenyl)benzonitrile
by esterification. After recrystallization from 1,4-dioxane, orange-
red crystals of monomer 2 were obtained with a yield of 88%.
The structure of monomer 2 was determined by MS, FT-IR and
NMR. As shown in Fig. S1 (in the Supporting information), the
assignments of the 1H NMR and 13C NMR signal peaks of monomer
2 correspond well to the expected structure.
azobenzene chromophores at around 350 nm and 445 nm, respec-
tively, can be observed in the spectra of 3b–d. The high-energy band
at 350 nm is attributed to the trans-isomer, whereas the low-energy
band at 445 nm is derived from the metastable cis-isomer. The
absorption intensity of the p–
pꢂ electronic transition of azobenzene
chromophores clearly increases with monomer 2 content.
3.3. Thermal properties of diazo-PAEs
DSC and TGA measurements were carried out to investigate the
thermal properties of diazo-PAEs. Fig. S3 in the Supporting infor-
mation shows the DSC curves of polymers 3a–d, and the experi-
mental data are listed in Table 1. The diazo-PAEs 3a–d had glass
transition temperatures above 160 °C, and no other thermal
change except the glass transition was observed below the decom-
position temperature, indicating the amorphous nature of diazo-
PAEs. The TGA curves and the data for diazo-PAEs are shown in
Fig. S4 (in Supporting information) and Table 1, respectively. The
temperatures at 5% weight loss (TGA-5%) of 3a–d were all above
406 °C, indicating excellent thermal stability. From the TGA curve
of pure PAE 3a, only one degradation step with the maximum
weight loss at 550 °C was observed. Compared to the TGA curve
of 3a, the TGA curves of copolymers 3b–d exhibited another degra-
dation step with the maximum weight loss at 408 °C. This extra
degradation step can be attributed to the thermal degradation of
azobenzene moieties. The 5% weight-loss temperatures of diazo-
PAEs decreased from 516 to 406 °C for azobenzene contents from
0% to 60%.
3.2. Synthesis of diazo-PAEs
Aromatic poly(aryl ether)s containing pendent di-azobenzene
groups (diazo-PAEs) were synthesized by a typical nucleophilic
substitution polycondensation reaction from bis(4-((4-cyano-
phenyl)diazenyl)phenyl)5,50-carbonylbis(2-fluorobenzenesulfonate)
(monomer 2), 4-phenylenebis((4-fluorophenyl)methanone) (PBFM),
and 4,40-(hexafluoroisopropylidene)diphenol (6F-BPA), as shown in
Scheme 2. The copolymerization was carried out in DMAc under a
nitrogen atmosphere with potassium carbonate as a base catalyst.
Toluene was used to dehydrate the reaction system. All obtained
polymers showed good solubility in common organic solvents
such as chloroform, tetrahydrofuran, N,N-dimethylformamide,
N-methyl-2-pyrrolidone and cyclohexanone. From Table 1, it is evi-
dent that the number average molecular weights and intrinsic vis-
cosities of the polymers both decreased with increasing
azobenzene content due to the lower reactivity of monomer 2. All
polymers had number average molecular weights above 1.0 ꢁ 104,
indicating high molecular weights. The structures of the diazo-PAEs
were confirmed using FT-IR, UV–vis and 1H NMR spectra. In 1H NMR
spectra (Fig. S2 in the Supporting information), diazo-PAEs 3b–d
showed characteristic signals corresponding to the protons of the
di-azobenzene groups at around 8.2 (protons H-8) and 7.9–8.1 (pro-
tons H-7, H-10, H-11, H-12) ppm, which correspond well with the
expected structures. In the FT-IR spectra of 3b–d, the characteristic
absorption bands at 2229, 1246, 1379 and 1660 cmꢀ1 were attrib-
uted to the stretching vibrations of –CN, Ar–O–Ar, Ar–SO3–Ar and
3.4. Photoisomerization behavior of diazo-PAEs
The photoisomerization behavior of the diazo-PAEs 3b–d in
DMF solutions was investigated by UV–vis spectroscopy after irra-
diation with 360 nm UV light. As shown in Fig. 2A, UV–vis spectra
of 3b were recorded over different time intervals until the photo-
stationary state was reached (irradiated for 105 s). After irradiation
with 360 nm UV light, the absorption intensity of the trans-form of
azobenzene at 350 nm decreases rapidly, while the intensity of the
cis-form of azobenzene at 445 nm slightly increases with the irra-
diation time, indicating the trans-to-cis photoisomerization of the
Scheme 1. Synthesis of monomers 1 and 2.

556
J. Zhang et al. / Reactive & Functional Polymers 71 (2011) 553–560
Scheme 2. Synthesis of diazo-PAEs 3–d.
Table 1
Properties of diazo-PAEs.
ga (dL/g)
Mn ꢁ 104
Mw/Mn
Tg (°C)
Td5 (°C)
Td10 (°C)
Modulation-depth (nm)
b
c
d
Polymer
Azo (mol.%)
3a
3b
3c
3d
0
20
40
60
0.66
0.48
0.38
0.50
3.89
1.62
1.23
1.04
2.06
1.69
1.74
1.41
161
170
163
161
516
501
426
406
534
528
513
464
–
238
258
283
a
b
c
Inherent viscosity was determined using an Ubbelohde viscometer in a thermostatic container with a polymer concentration of 0.5 g/dL in DMAc at 25 °C.
Glass transition temperatures were determined by DSC.
5% Weight-loss temperatures were detected at a heating rate of 10 °C/min in nitrogen with a gas flow rate of 100 mL/min.
10% Weight-loss temperatures were detected at a heating rate of 10 °C/min in nitrogen with a gas flow rate of 100 mL/min.
d
the absorbances at 350 nm at time 0, time t and the photostation-
ary state, respectively), confirming that the trans-to-cis photoiso-
merizations of 3b–d obey first-order kinetics, as reported
previously [30]. The slope of the plots of ln ((A1 ꢀ At)/(A1 ꢀ A0))
against time gives the first-order rate constants (kP) for the trans-
to-cis photoisomerization of diazo-PAEs. The rate constants of the
photoisomerization of diazo-PAEs were 0.0210, 0.0253 and
0.0309 sꢀ1 for 3b, 3c and 3d, respectively. Copolymer 3b shows
the lowest trans-to-cis photoisomerization rate due to the steric
hindrance of the polymer chain configuration [19]. With increases
in the content of rigid 1,4-phenylenebis((4-fluorophenyl)metha-
none), the motion of the azobenzene chromophores becomes diffi-
cult, which further restricts the photoisomerization process.
3.5. Photoinduced surface relief grating formation of diazo-PAEs
The formation of photoinduced surface relief gratings is one of
the most interesting properties of azo-polymers. Compared with
other technologies used to produce topographic gratings, this
Fig. 1. UV–vis spectra of diazo-PAEs 3a–d in DMF solution.
photo-fabrication approach can be easily completed by a single-
step all-optical process. Generally, a 488 nm laser beam is used
azobenzene chromophores. Diazo-PAEs 3c and 3d displayed simi-
lar photoisomerization behaviors.
to fabricate SRGs on azo-polymers [14]. In this study, a 355 nm
light was chosen because diazo-PAEs are photoactive to UV light
around 350 nm. Compared to a 488 nm laser beam, a shorter wave-
length laser beam (355 nm) offers the opportunity to explore the
use of these polymers for high-density information storage [26].
Spin-coated films of diazo-PAEs 3b–d with smooth surfaces were
obtained on glass substrates and were used for inscription experi-
The trans-to-cis photoisomerization rates of diazo-PAEs in DMF
solution were analyzed using the UV absorption at 350 nm. The
photoisomerization kinetics of diazo-PAEs 3b–d were further stud-
ied and are presented in Fig. 2B. It can be seen that ln ((A1 ꢀ At)/
(A1 ꢀ A0)) is linearly dependent on time (where A0, At and A are
1

J. Zhang et al. / Reactive & Functional Polymers 71 (2011) 553–560
557
Fig. 2. (A) Changes in the UV–vis absorption spectrum of 3b in DMF solution at 25 °C with different irradiation times under 360 nm light irradiation. (B) First-order trans-to-
cis isomerization kinetics of 3b, 3c and 3d.
ments. The interference pattern of laser beams at 355 nm was pro-
duced by two p-polarized beams with incident angles of +11.5° and
ꢀ11.5°. The films were subsequently exposed to two polarized
interfering laser beams of equal intensity (approximately 40 mW/
cm2) for 30 s, and SRGs were sufficiently formed on the films.
Fig. 3 shows a typical AFM plane and three-dimensional images
of the surface relief structures on the diazo-PAE 3b film. Clear sinu-
soidal surface relief gratings with regular spacing were observed.
AFM section analysis revealed a modulation depth of ca. 238 nm
and a grating spacing of ca. 898 nm, as determined by the interfer-
ence pattern. From Table 1, the following general trend can be ob-
served: under the same irradiation conditions (Irradiation energy:
approximately 80 mW/cm2 and time: 30 s), the relief depth of the
gratings increases with the molar fraction of azobenzene units. In
addition, the modulation depth could be also adjusted by the irra-
diation time and the irradiation energy. The grating spacing is
equal to the period of the interference pattern ( ) and can be con-
trolled by adjusting the angle h between the two interfering beams,
according to the equation = k/2sin(h/2), where k is the wave-
K
K
length of the writing beams [5].
3.6. Thermal stability of the SRGs of 3b
Another important requirement of SRGs is shape stability in
terms of long-term storage and durability at high temperature
[31]. The thermal stability of SRGs formed on the diazo-PAE 3b film
(238 nm) was investigated by polarized optical microscopy (POM).
No obvious change in these SRGs was observed when they was
heated from room temperature to 170 °C (Tg of 3b) or maintained
at 170 °C for 30 min. When the temperature was increased to
Fig. 3. Images of the typical SRGs formed on diazo-PAE 3b films: (A) AFM plane view of the SRGs (10 ꢁ 10
l
m2); (B) typical AFM 3-D view of the SRGs (10 ꢁ 10 m2); and (C)
l
section analysis of the SRGs.

558
J. Zhang et al. / Reactive & Functional Polymers 71 (2011) 553–560
Fig. 4. Images of the typical SRGs formed on diazo-PAE 3b film after heating at 220 °C for 90 min: (A) AFM plane view of the SRGs (10 ꢁ 10
the SRGs (10 ꢁ 10
m2); and (C) section analysis of the SRGs.
l
m2); (B) typical AFM 3-D view of
l
220 °C, SRGs on the diazo-PAE 3b film became slightly blurry, and
after heating at this temperature for 90 min, the SRGs almost dis-
appeared. The surface morphology of the diazo-PAE 3b film was
further investigated by AFM, as shown in Fig. 4. Although the sur-
face modulation depth decreased from 238 nm to approximately
6 nm after heating at 220 °C for 90 min, the SRGs on the diazo-
PAE 3b film still retained a good shape. The excellent stability of
SRGs formed on diazo-PAEs will favor their used on future practical
applications.
investigated by exposing diazo-PAE casting-films to a linearly
polarized laser beam (‘writing’ beam) at room temperature. The
measured photoinduced birefringence curves of 3b–d as a function
of time are shown in Fig. 5A. The moment at which the pump laser
was switched on or off is marked with a letter. For copolymer 3b,
before irradiation, no optical anisotropy is observed because of
the homogeneously random alignment of the azobenzene chro-
mophores. Under irradiation with a linearly polarized 532 nm laser
beam (approximately 47 mW/cm2, at point A), birefringence sig-
nals were induced immediately and reached approximately
0.1030 due to the alignment of the azobenzene chromophores per-
pendicular to the pump laser polarization direction through multi-
ple trans–cis-trans-isomerization cycles of the azo moieties. The
birefringence value exhibited a slight decay after the pump laser
was switched off (at point B) because of the thermal isomerization
3.7. Photoinduced birefringence of diazo-PAEs
Photoinduced birefringence is another important feature of
azo-polymers that makes them suitable for optical storage applica-
tions. Herein, the photoinduced birefringence of diazo-PAEs was
Fig. 5. (A) Typical behavior of the photoinduced birefringence of diazo-PAEs 3b–d at room temperature: at point A, the writing laser was turned on; at point B, the writing
laser was turned off; and at point C, the circularly polarized light was turned on. (B) Normalized photoinduced birefringence of the 10–50 s regions.

J. Zhang et al. / Reactive & Functional Polymers 71 (2011) 553–560
559
from cis to trans-form and dipole redistribution, which increase
the entropy. However, compared to other azo-polymers
[11,32,33], diazo-PAEs show much smaller birefringence decay
and possess a remnant value greater than 85% of the saturation va-
lue, indicating the excellent stability of the photoinduced orienta-
tion. This stability is mainly attributed to the rigidity of the
aromatic main chain structures of diazo-PAEs, which suppress
the relaxation process of the photoalignment. The remaining pho-
toinduced anisotropy can be erased with a circularly polarized
beam (‘erasing’ beam) (at point C). Copolymers 3c and 3d exhibited
behaviors similar to those described above (shown in Table 2).
From this table, it is evident that the saturation values of diazo-
PAEs 3b–d varied from 0.1030 to 0.3289. The remnant values of
these polymers varied from 0.0875 to 0.2859. The saturation value
and remnant value both increased with increasing azobenzene
content.
To allow qualitative comparison of the birefringence evolution
with irradiation time for different diazo-PAEs, in Fig. 5B, we show
the same evolution, but with the birefringence values normalized
to the saturation value [34]. From the growth curves of the three
copolymers, it can be seen that the order of the birefringence
growth rate was 3d > 3c > 3b. Generally, the growth process of
the photoinduced birefringence is attributable to the multiple
trans–cis-trans-isomerizations of the azobenzene moieties and
the reorientation of azobenzene chromophores through these
isomerization cycles. Therefore, their birefringence growth rates
depend on their photoisomerization rates. As a result, copolymer
3d, which has the fastest photoisomerization rate as discussed in
Section 3.4, shows the highest birefringence growth rate among
these copolymers.
age applications. Indeed, after several irradiation steps with line-
arly polarized and circularly polarized laser beams alternatively
acting on a diazo-PAE 3b film, the saturation values and remnant
values were similar. This result indicates that diazo-PAEs have
excellent reproducibility, without any degradation of the signal
or material fatigue.
4. Conclusions
A series of di-azobenzene functionalized poly(arylene ether)s
(diazo-PAEs) were successfully synthesized via a nucleophilic sub-
stitution polycondensation reaction. These polymers exhibit good
solubility and thermal stability. Upon irradiation with 360 nm UV
light, all diazo-PAEs exhibited obvious photoisomerization behav-
ior in DMF solution due to the existence of azobenzene groups.
After exposure to an interference pattern created by 355 nm laser
beams, diazo-PAE films rapidly formed thermal-stable surface re-
lief gratings, displaying their potential applications in high-density
optical data storage. Upon irradiation with a 532 nm Nd:YAG laser
beam, diazo-PAEs presented large, high-quality, photoinduced
birefringence with a remnant value greater than 85% of the satura-
tion value. Furthermore, multiple writing/erasing experiments
indicate that diazo-PAEs have potential applications in reversible
optical storage.
Acknowledgment
The authors gratefully acknowledge the National Science Foun-
dation of China (50803025) for the financial support.
The complete reversibility of the photoinduced birefringence of
diazo-PAEs is related to fatigue resistance properties. As shown in
Fig. 6, diazo-PAEs are promising for use in reversible optical stor-
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.reactfunctpolym.2011.01.011.
Table 2
Photoinduced birefringence characteristics of diazo-PAEs.
References
Polymer
Saturation value
Remnant value
Remnant value (%)a
3b
3c
3d
0.1030
0.2414
0.3289
0.0875
0.2056
0.2859
85
85
87
[1] W.M. Gibbons, P.J. Shannon, S.T. Sun, B.J. Swetlin, Nature 351 (1991) 49–50.
[2] S. Hvilsted, C. Sanchez, R. Alcala, J. Mater. Chem. 19 (2009) 6641–6648.
[3] H.R. Hafiz, F. Nakanishi, Nanotechnology 14 (2003) 649–654.
[4] G. Iftime, F.L. Labarthet, A. Natansohn, P. Rochon, J. Am. Chem. Soc. 122 (2000)
12646–12650.
[5] A. Natansohn, P. Rochon, Chem. Rev. 102 (2002) 4139–4175.
[6] Y.W. Bai, N.H. Song, J.P. Gao, X. Sun, X.M. Wang, Z.Y. Wang, J. Am. Chem. Soc.
127 (2005) 2060–2061.
a
Remnant value (%) = remnant value/saturation value ꢁ 100%.
[7] Y.L. Yu, M. Nakano, T. Ikeda, Nature 425 (2003) 145.
[8] D.H. Han, X. Tong, Y. Zhao, T. Galstian, Y. Zhao, Macromolecules 43 (2010)
3664–3671.
[9] P. Rochon, E. Batalla, A. Natansohn, Appl. Phys. Lett. 66 (1995) 136–138.
[10] D.Y. Kim, S.K. Tripathy, L. Li, J. Kumar, Appl. Phys. Lett. 66 (1995) 1166–1168.
[11] Y. Wu, A. Natansohn, P. Rochon, Macromolecules 37 (2004) 6090–6095.
[12] J. Isayama, S. Nagano, T. Seki, Macromolecules 43 (2010) 4105–4112.
[13] N. Zettsu, T. Ogasawara, N. Mizoshita, S. Nagano, T. Seki, Adv. Mater. 20 (2008)
516–521.
[14] R. Walker, H. Audorff, L. Kador, H.W. Schmidt, Adv. Funct. Mater. 19 (2009) 1–
9.
[15] M.J. Kim, E.M. Seo, D. Vak, D.Y. Kim, Chem. Mater. 15 (2003) 4021–4027.
[16] E. Ishow, B. Lebon, Y.N. He, X.G. Wang, L. Bouteiller, L. Galmeche, K. Nakatani,
Chem. Mater. 18 (2006) 1261–1267.
[17] J. Gao, Y.N. He, H.P. Xu, B. Song, X. Zhang, Z.Q. Wang, X.G. Wang, Chem. Mater.
19 (2007) 14–17.
[18] J. Vapaavuori, A. Priimagi, M. Kaivola, J. Mater. Chem. 20 (2010) 5260–5264.
[19] X.Q. Xue, J. Zhu, Z.B. Zhang, N.C. Zhou, X.L. Zhu, React. Funct. Polym. 70 (2010)
456–462.
[20] E. Schab-Balcerzak, M. Siwy, M. Kawalec, A. Sobolewska, A. Chamera, A.
Miniewicz, J. Phys. Chem. A 113 (2009) 8765–8780.
[21] J.B. Rose, Polymer 15 (1974) 456–465.
[22] H.B. Zhang, J.H. Pang, D. Wang, X. Li, Z.H. Jiang, J. Membr. Sci. 264 (2005) 56–
64.
[23] X.B. Chen, B.J. Liu, H.B. Zhang, S.W. Guan, J.J. Zhang, Z.H. Jiang, Langmuir 25
(2009) 10444–10446.
[24] J.J. Zhang, H.B. Zhang, X.B. Chen, Y.H. Zhang, X.F. Li, Z.H. Jiang, Mater. Lett. 64
(2010) 337–340.
Fig. 6. Multiple writing-erasing cycles of diazo-PAE 3b at room temperature: at
point A, the writing laser was turned on; at point B, the writing laser was turned off;
and at point C, the circularly polarized light was turned on.

560
J. Zhang et al. / Reactive & Functional Polymers 71 (2011) 553–560
[25] X.B. Chen, J.J. Zhang, H.B. Zhang, Z.H. Jiang, G. Shi, Y.L. Song, Dyes Pigments 77
(2008) 223–228.
[26] X.B. Chen, Y.H. Zhang, B.J. Liu, J.J. Zhang, H. Wang, Z.H. Jiang, J. Mater. Chem. 18
(2008) 5019–5026.
[27] X.Y. Jiang, X.B. Chen, X.G. Yue, J.J. Zhang, S.W. Guan, H.B. Zhang, W.Y. Zhang,
Q.D. Chen, React. Funct. Polym. 70 (2010) 616–621.
[28] X.Y. Jiang, H. Wang, X.B. Chen, X.J. Li, J.X. Mu, S.L. Zhang, React. Funct. Polym.
70 (2010) 699–705.
[29] F. Wang, T.L. Chen, J.P. Xu, Macromol. Chem. Phys. 199 (1998) 1421–1426.
[30] G.S. Kumar, D.C. Neckers, Chem. Rev. 89 (1989) 1915–1925.
[31] N. Zettsu, T. Ubukata, T. Seki, K. Ichimura, Adv. Mater. 13 (2001) 1693–1697.
[32] C. Chun, M. Kim, D. Vak, D.Y. Kim, J. Mater. Chem. 13 (2003) 2904–2909.
[33] R. Fernandez, I. Mondragon, P.A. Oyanguren, M.J. Galante, React. Funct. Polym.
68 (2008) 70–76.
[34] P. Forcén, L. Oriol, C. Sánchez, R. Alcalá, S. Hvilsted, K. Jankova, J. Loos, J. Polym.
Sci. Pol. Chem. 45 (2007) 1899–1910.