Preparation and characterization of novel side-chain azobenzene polymers containing tetrazole group

Article abstract of DOI:10.1016/j.reactfunctpolym.2015.09.007

A novel methacrylate monomer containing azobenzene chromophore and tetrazole moiety, 4′-(2-methacryloxyethyl)methylamino-4-(5-chlorotetrazol-1-yl)azobenzene (MACA), was synthesized and polymerized to form homopolymer (PMACA) via reversible addition-fragme

Full text of DOI:10.1016/j.reactfunctpolym.2015.09.007

Preparation and characterization of novel side-chain azobenzene polymers
containing tetrazole group
Xiaoqiang Xue, Jing Yang, Wenyan Huang, Hongjun Yang, Bibiao Jiang
PII:
S1381-5148(15)30045-6
DOI:
Reference:
doi: 10.1016/j.reactfunctpolym.2015.09.007
REACT 3564
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Revised date:
Accepted date:
30 April 2015
26 June 2015
24 September 2015
Please cite this article as: Xiaoqiang Xue, Jing Yang, Wenyan Huang, Hongjun Yang,
Bibiao Jiang, Preparation and characterization of novel side-chain azobenzene polymers
containing tetrazole group, (2015), doi: 10.1016/j.reactfunctpolym.2015.09.007
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ACCEPTED MANUSCRIPT
Article type: Full Paper
Preparation and Characterization of Novel Side-Chain
Azobenzene Polymers Containing Tetrazole Group
Xiaoqiang Xue, Jing Yang, Wenyan Huang, Hongjun Yang, Bibiao Jiang*
Jiangsu Key Laboratory of Material Surface Science and Technology, School of Material
Science and Engineering, Changzhou University, Changzhou, Jiangsu, 213164, People's
Republic of China
*Corresponding author. Tel.: 8651986330328;
E-mail: jiangbibiao@cczu.edu.cn
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Abstract
A novel methacrylate monomer containing azobenzene chromophore and tetrazole moiety,
4′-(2-methacryloxyethyl)methylamino-4-(5-chlorotetrazol-1-yl)azobenzene (MACA), was
synthesized and polymerized to form homopolymer (PMACA) via reversible addition-
fragmentation chain transfer (RAFT) polymerization using 2-cyanoprop-2-yl dithiobenzoate
(CPDB) as the RAFT agent and azobisisobutyronitrile (AIBN) as an initiator in dimethyl
formamide (DMF) solution. Meanwhile, block copolymers (PMMA-b-PMACAs) were
successfully obtained by RAFT polymerization of MACA using PMMA as the macro-RAFT
agent and AIBN as an initiator. Gel permeation chromatography (GPC) characterization
indicated that polymers with well-controlled molecular weights and narrow molecular weight
distributions (Mw/Mns <1.30) were obtained. The structures of these polymers were
1
characterized by H NMR and FT-IR spectra. Thermal and photoisomerization behaviors of
the polymers indicated that these polymers were amorphous state with good heat stability and
photoisomeriztion performance. Relationship between the electrochemical behavior of block
copolymer (PMMA-b-PMACA) and the photoisomerization of azobenzene was investigated
by cyclic voltammetry (CV) in chloroform solution, which showed that the oxidation peak of
copolymer shifted from 1.0V to 0.6V during azobenzene isomerization from trans to cis form.
Furthermore, surface relief gratings (SRGs) formed on the films of PMMA-b-PMACAs were
also investigated with illumination of a linearly polarized Kr+ laser beam. The diffraction
efficiency of the SRGs was 1.22 (PMMA-b-PMACA1), 2.38 (PMMA-b-PMACA2) and 3.02
(PMMA-b-PMACA3), respectively, which increased with the azobenzene contain for the
copolymers.
Keywords: Azobenzene; Reversible addition-fragmentation chain transfer (RAFT)
polymerization; tetrazole; photoisomerization behavior
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1. Introduction
In recent years, polymeric materials containing azobenzene chromophore have drawn
widespread attention due to their unique optical trans-cis-trans isomerization [1-4], which can
be potentially applied in many fields, such as optical data storage [5,6], liquid crystal display
[7-9], photoinduced birefringence [10], and holographic surface relief grating [11,12]. As well
known, the photoresponsive behavior of azobenzene polymers is based on reversible trans-
cis-trans photoisomerization of the azobenzene chromophore and possibly large-scale mass
movement of the rigid azobenzene chromophore [11-15]. The trans-cis isomerization
behavior of azobenzene was adjusted by the substituting groups [16]. With different
substituting groups on azobenzene ring, azobenzene chromophore can be separated into three
spectroscopic classes: azobenzene type, aminoazobenzene type and pseudo-stilbene type [17].
Among them, pseudo-stilbene azobenzene, which was substituted at the 4 and 4’ positions
with an electron-donor and an electron-acceptor groups, can be useful in optical isomerization
applications due to the strong asymmetric electron distribution. The heterocyclic azobenzene
groups were widely used as electron-acceptor because of their special push-pull
chromophores as corresponding aryl analogues [18]. Based on this, azobenzene polymers
containing heterocyclic groups are of great interest for their good film forming ability and
potential applications in second-order molecular NLO properties [19], photo-responsive
amphiphilic materials [20], photo-induced birefringence [21] and so on.
In this paper, a special heterocyclic substituting group, tetrazole, was introduced into the 4-
position of azobenzene. The tetrazole compound showed characteristic property for their
considerable energy and nitrogen content. It showed many significant applications in the
fields of biomedical, ecological and agricultural sciences [21,22]. “Living”/controlled free
radical polymerizations (LFRP) were used to synthesize polymers with predetermined
structure. This unique technique offered a powerful tool to design azobenzene polymers with
well-defined architectures, such as homopolymers [23,24], block copolymers [25-27], star
polymers [28-30], graft copolymers [31] and so on. The typical LFRP systems included atom
transfer radical polymerization (ATRP) [32-35], reversible addition-fragmentation chain
transfer (RAFT) polymerization [36-39], nitroxide-mediated radical polymerization (NMP)
[40-42], and so on. Many references reported successfully synthesizing well-defined
azobenzene homopolymers and copolymers by LFRP technology [24-29]. As the alternative
selection, RAFT polymerization was a much better technique to synthesize well defined
polymers containing heterocyclic group for its wide range monomer suitability [21,23].
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Following these basis, we reported the synthesis and characterization of novel methacrylate
monomer with the tetrazole and azobenzene groups, 4′-(2-metharyloxyethyl)methylamino-4-
(5-chlorotetrazol-1-yl)azobenzene (MACA), and incorporated into polymeric backbones by
the RAFT technique. The homopolymer (PMACA) and diblock copolymers (PMMA-b-
PMACA) were obtained with well-defined molecular weights and relatively narrow molecular
weight distributions. Photo-responsive surface relief gratings (SRGs) behaviors of these
polymers were investigated. Particularly, electrochemical behavior of azobenzene polymers
with their cis and trans form was investigated by cyclic voltammetry (CV).
2. Experimental section
2.1. Materials
Methyl methacrylate (MMA; analytical grade; Shanghai Chemical Reagent Co. Ltd,
Shanghai, China) was washed with an aqueous solution of sodium hydroxide (5 wt %) three
times and then washed with deionized water until neutralization. After being dried with
anhydrous magnesium sulfate, the monomer was distilled twice under reduced pressure, and
o
kept below 0 C. Azobisisobutyronitrile (AIBN; 99%, Shanghai Chemical Reagent Co. Ltd,
Shanghai, China) was recrystallized three times from ethanol and dried in vacuum at room
temperature overnight. Dimethyl formamide (DMF; analytical reagent; Shanghai Chemical
Reagent Co. Ltd, Shanghai, China) was purified by vacuum distillation over anhydrous
calcium hydroxide (CaH2). Chloroform (analytical reagent), tetrahydrofuran (THF; analytical
reagent) and triethylamine (TEA; analytical reagent) were purchased from Shanghai Chemical
Reagent Co. Ltd. (Shanghai, China) and used after distillation. 5-Chloro-1-phenyl-1H-
tetrazole (98%; Aldrich) and N-(2-hydroxyethyl)-N-methylaniline (Tokyo Kasei Kogyo Co.,
Ltd, Japan) were used as received. Other reagents were used without further purification. 2-
Cyanoprop-2-yl dithiobenzoate (CPDB; >98%) was synthesized according to the method
described in the literature [43].
2.2.
Synthesis
of
4′-(2-metharyloxyethyl)methylamino-4-(5-chloro-tetrazol-1-
yl)azobenzene (MACA)
The novel methacrylate monomer (MACA) containing azobenzene chromophore and
tetrazole moiety was synthesized following the synthetic pathway as shown in scheme 1.
(Scheme 1. is here)
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2.2.1. 5-Chloro-1-(4-nitrophenyl)tetrazole (1)
The compound 1 was synthesized according to the literature [44]: 5-chloro-1-phenyl-1H-
tetrazole (10.0 g, 56.0 mmol) was added slowly to fuming nitric acid (30 mL) in a 100 mL
o
flask under vigorous stirring. The reaction was heated at 100 C for 5 min. Subsequently, the
hot mixture was poured onto a large excess of ice. The thick yellow precipitate was filtered
off, washed with water several times, and dried in vacuum at room temperature.
Recrystallization from ethanol gave the target product 1 (10.0 g, 79.2%) as yellow plates. The
1
characteristic analytical data involved are as follows: H NMR (400 MHz, CDCl3, ppm):
13
8.46-8.56(d, 2H, ArH), 7.86-8.02 (d, 2H, ArH). C NMR (100 MHz, CDCl3, ppm): 148.75,
137.13, 125.46 and 125.17 (aromatic carbons), 145.47 (tetrazole carbon). IR (KBr, cm-1):
3116, 3087, 3066, 2871, 1928, 1612, 1598, 1529, 1500, 1443, 1429, 1417, 1400, 1379, 1356,
1322, 1306, 1267, 1251, 1117, 1103, 1072, 1031, 1012, 982, 962, 858, 751, 728, 712, 688.
577, 516, 488, 442. Anal. calcd for C7H4ClN5O2: C 37.27, H 1.79, N 31.04; found: C 37.03, H
1.74, N 31.05. m. p.: 98.1 oC.
2.2.3. 1-(4-Aminophenyl)-5-chlorotetrazole (2)
Compound 2 was synthesized according to the following procedure [45]: a mixture of iron
powder (2.30 g, 60.0 mmol) and ammonium chloride solution (5.30 g, 100 mmol) in 50 mL of
distilled water was first prepared in a 500 mL flask under vigorous stirring. Then a 200 mL
methanolic solution of compound 1 (4.50 g, 20.0 mmol) was added dropwise into this mixture
over 10 min at room temperature. The resultant mixture was stirred under gentle reflux for 5 h.
The inorganic residue was filtered and the methanol was evaporated under vacuum. The
desired product precipitating out from the solution was collected by filtration, washed with
water, dried under vacuum, and then recrystallized three times from methanol. The pure
product 2 (3.00 g, yield: 76.9%) was obtained as pale plates. The characteristic data involved
1
are as follows: H NMR (400 MHz, DMSO-d6, ppm): 7.26-7.30 (d, 2H, ArH), 6.66-6.72 (d,
2H, ArH), 5.79 (s, 2H, ArH). 13C NMR (100 MHz, CDCl3, ppm): 148.83, 122.74, 114.99 and
125.17 (aromatic carbons), 145.76 (tetrazole carbon). IR (KBr, cm-1): 3416, 3321, 3212, 2965,
2931, 2855, 1887, 1642, 1604, 1511, 1455, 1422, 1407, 1312, 1289, 1258, 1245, 1180, 1143,
1112, 1088, 1040, 1006, 981, 832, 722. Anal. calcd for C7H6ClN5: C 42.98, H 3.09, N 35.8;
found: C 42.47, H 3.04, N 35.16. m. p.: 143.1 oC.
2.2.4. 4′-(2-Hydroxyethyl)methylamino-4-(5-chloro-tetrazol-1-yl)azobenzene (3)
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Compound 2 (1.95 g, 10.0 mmol) was dissolved in concentrated HCl (4 mL) and deionized
o
o
water (16 mL) at 70 C. The mixture was stirred at 0-5 C in an ice bath, and then aqueous
solution (2 mL) of sodium nitrite (0.70 g) was added slowly. The mixture was stirred at 0-5 oC
for 30 min. A solution of N-(2-hydroxyethyl)-N-methylaniline (1.50 g, 10.0 mmol) in acetic
acid (5 mL) and deionized water (5 mL) was cooled to 0 oC and added into the above mixture
o
under vigorous stirring at 0-5 C. The pH of final mixture was adjusted to pH 5-6 using a
o
NaOH (40%) solution. It was stirred for further 3 h at 0-5 C. Then the reaction solution was
added to a large amount of NaOH solution (40%) under stirring, and a red-orange precipitate
formed. The desired precipitate was collected by filtration, washed with deionized water
several times, and dried under vacuum. The crude products were recrystallized three times
from ethanol to afford pure azobenzene-containing product 3 as red-orange crystal (3.00 g,
1
yield: 83.8%). The characteristic data involved are as follows: H NMR (400 MHz, CDCl3,
ppm): 7.98-8.07 (d, 2H, ArH), 7.80-7.96 (d, 2H, ArH), 7.57-7.73 (d, 2H, ArH), 6.73-6.90 (d,
2H, ArH), 3.83-3.96 (m, 2H, -CH2-O), 5.59-3.70 (m, 2H, N-CH2-), 3.18 (s, 3H, N-CH3), 1.67
13
(s, 1H, OH). C NMR (100 MHz, CDCl3, ppm): 154.24, 152.55, 143.75, 132.27, 125.77,
125.07, 123.44, and 111.72 (aromatic carbons), 145.55 (tetrazole carbon), 60.33 (-NCH2CH2-
OH)). 54.62 (-NCH2CH2-OH), 39.33 (-NCH3). IR (KBr, cm-1): 3443, 2951, 2931, 2855, 1599,
1558, 1516, 1501, 1500, 1428, 1416, 1396, 1372, 1328, 1308, 1277, 1246, 1192, 1139, 1104,
1085, 1039, 1029, 1004, 957, 845, 830. Anal. calcd for C16H16ClN7O: C 53.71, H 4.51, N
27.40; found: C 53.31, H 4.34, N 27.51. m. p.: 145.9 oC.
2.2.5.
4′-(2-Metharyloxyethyl)methylamino-4-(5-chlorotetrazol-1-yl)azobenzene
(MACA)
Compound 3 (1.78 g, 5.0 mmol), freshly distilled THF (50 mL), and freshly distilled
triethylamine (1.07 g, 10.5 mmol) was added to a 250 mL three-necked flask. The solution
was stirred in an ice bath. Methacryloyl chloride (0.960 mL, 10.0 mmol) diluted in dry THF
(10 mL) was added to the cool stirred mixture dropwise. The reaction mixture was vigorously
stirred for 3 h at 0-5 oC and then at room temperature overnight. The mixture was filtered, and
the filtrate was evaporated under vacuum. The remaining yellow mixture was dissolved in
dichloromethane and washed with 5% Na2CO3 aqueous solution and deionized water three
times, then dried with anhydrous MgSO4 overnight. The final crude product was purified by
column chromatography (silica gel, EtOAc / petroleum ether = 1:3) to yield saffron solid
1
(1.32 g, 62.1%). The characteristic analytical data involved are as follows: H NMR (400
MHz, CDCl3, ppm): 8.02-8.11(d, 2H, ArH), 7.88-7.98 (d, 2H, ArH), 7.67-7.76 (d, 2H, ArH),
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6.81-6.90 (d, 2H, ArH), 6.08 (s, 1H, =CH), 5.58 (s, 1H, =CH), 4.30-4.48 (m, 2H, -CH2-O),
13
3.73-3.87 (m, 2H, N-CH2-), 3.16 (s, 3H, N-CH3), 1.92 (s, 3H, C-CH3). C NMR (100 MHz,
CDCl3, ppm): 167.27 (OC=O), 154.19, 152.00, 143.75, 132.27, 125.75, 125.06, 123.44, and
111.58 (aromatic carbons), 145.52 (tetrazole carbon), 135.96 (-CH(CH3)=CH2), 126.23 (-
CH(CH3)=CH2), 61.71 (-NCH2CH2O-), 50.84 (-NCH2CH2O-). 39.03 (-NCH3), 18.34 (-
CH(CH3)=CH2). IR (KBr, cm-1): 2955, 2922, 2854, 1706, 1602, 1557, 1519, 1501, 1450,
1421, 1397, 1378, 1335, 1315, 1294, 1245, 1212, 1170, 1150, 1138, 1106, 1068, 1031, 1018,
1004, 976, 950, 849, 822, 748, 710, 698. Anal. calcd for C20H20ClN7O2: C 56.41, H 4.73, N
23.02; found: C 56.27, H 4.58, N 23.38. m. p.: 127.6 oC.
The 1H NMR spectrum of MACA is shown in Figure 1.
(Figure 1. is here)
2.3. Preparation of the homopolymers (PMACA1, PMACA2, PMACA3) by RAFT
polymerization
The general procedure was as following: MACA (0.425 g, 1.0 mmol), AIBN (1.10 mg,
0.0067 mmol), CPDB (4.40 mg, 0.02 mmol) was dissolved in freshly distilled DMF (2 mL)
and added to a dry 5 mL ampule tube. The contents were purged with argon for 15 min to
eliminate the oxygen. The ampule was flame-sealed and dropped into a preheated oil bath
maintained at 70 oC. After 6 h polymerization, the ampule was opened, and the contents were
diluted with THF (5 mL) and precipitated into methanol (250 mL). The precipitation process
was carried out three times. The polymer (PMACA1) was dried to a constant weight at room
temperature in vacuum. The conversion of PMACA1 was determined by gravimetry. Other
polymers (PMACA2, PMACA3) were prepared in the same way with different
polymerization time. The characteristic analytical data involved are as follows: 1H NMR (400
MHz, CDCl3, δ): 8.3-7.4 (ArH), 7.2-6.4 (ArH), 4.4-3.7 (COOCH2C-), 3.7-3.4 (ArNCH2C-),
3.1-2.6 (ArNCH3), 2.0-1.3 (-CH2-), 1.3-0.2 (-CCH3). IR (KBr, cm-1): 2951, 2844, 1706, 1602,
1518, 1435, 1380, 1245, 1004, 847, 748.
2.4. Preparation of the macro-RAFT agent (PMMA)
The macro-RAFT agent (PMMA) was prepared as following: a dry 2 mL ampule tube with
a stir bar was filled with MMA (1.0 mL, 9.46 mmol), CPDB (25.1 mg, 0.114 mmol), AIBN
(3.10 mg, 0.019 mmol) and freshly distilled DMF (0.5 mL). After purged with argon for 15
o
min, the ampule was flame-sealed. The polymerization was performed in an oil bath at 60 C
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for 12 h. Afterwards, the seal of ampule was opened, and the contents were diluted with THF
(5 mL) and precipitated into methanol (250 mL). The polymer (PMMA) was obtained by
filtration and dried to a constant weight at room temperature in vacuum. The conversion was
83.1% (0.7858 g) determined by gravimetry. The polymer molecular weight determined by
GPC (Mn (GPC)) was 8300 g/mol ( Mw/Mn = 1.14). The characteristic analytical data involved
1
are as follows: H NMR (400 MHz, CDCl3, ppm): 8.1-7.9 (ArH), 7.5-7.3 (ArH), 3.9-3.4 (-
13
OCH3), 2.2-1.3 (-CH2-), 1.3-0.4 (-CCH3). C NMR (100 MHz, CDCl3, ppm): 179.5-176.0
(OC=O), 55.0-52.3 (-CH2-C), 52.1-51.5 (OCH3), 45.6-44.2 (-C(CH3)CH2), 19.4-15.8 (C-CH3).
IR (KBr, cm-1): 2994, 2951, 1730, 1487, 1448, 1387, 1273, 1246, 1194, 1148, 1063, 987, 912,
841, 750.
2.5. Preparation of the block copolymers (PMMA-b-PMACAs)
The synthetic routes of the block copolymers (PMMA-b-PMACAs) were shown in Scheme
2. PMMA-b-PMACAs were synthesized with similar procedures for PMACA except that
PMMA was used as macro-RAFT agent instead of CPDN. MACA (0.425 g, 1.0 mmol),
AIBN (0.550 mg, 0.0033 mmol), PMMA (0.166 g, 0.02 mmol) and freshly distilled DMF (3
mL) were charged in a dry 5 mL ampule tube with a stir bar, and then stirred for 10 min until
a homogeneous solution was formed. After purged with argon for 15 min, the ampule was
flame-sealed, and put in an oil-bath at 70 oC for 24 h. The reactant was diluted by THF (5 mL),
precipitated into methanol (250 mL), and the purification process was carried out three times.
The final product (PMMA-b-PMACA3) was dried to a constant weight at room temperature
in vacuum. Other block copolymers were prepared using similar procedures. The
1
characteristic analytical data involved are as follows: H NMR (400 MHz, CDCl3, ppm): 8.3-
7.5 (ArH), 7.0-6.4 (ArH), 4.3-3.6 (COOCH2C-), 3.6-3.4 (ArNCH2C- and -OCH3), 3.1-2.6
(ArNCH3), 2.1-1.3 (-CH2-), 1.3-0.2 (-CCH3). 13C NMR (100 MHz, CDCl3, ppm): 178.6-176.5
(OC=O), 167.35-167.15, 155.0-150.5, 144.0-142.5, 133.0-131.0, 127.0-121.0, 112.5-111.0
(aromatic carbons), 146.0-144.5 (tetrazole carbon), 61.8-61.6 (-NCH2CH2O-), 54.9-52.2 (-
NCH2CH2O- and -CH2-C), 52.1-51.5 (OCH3), 45.7-44.1 (-C(CH3)CH2), 39.5-38.0 (ArNCH3),
19.4-15.8 (C-CH3). IR (KBr, cm-1): 2993, 2951, 2840, 1730, 1602, 1518, 1435, 1381, 1246,
1146, 991, 845, 750.
(Scheme 2. is here)
2.6. Preparation of the PMMA-b-PMACA film and optical characterization.
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A CHCl3 solution of the PMMA-b-PMACA1 (0.05 g/mL) was filtered through 0.2 μm pore
size filter, and the thin film was obtained via spin-coating the solution onto clean glass slide at
3500 rpm. The thickness of homogeneous thin films was measured to be about 332 nm by
Ambios Technology XP-2 Stylus Profiler and subsequently dried under vacuum for 24 h at
room temperature. The other polymers films were also obtained using the same method , and
the thicknesses were 312 nm (PMMA-b-PMACA2) and 350 nm (PMMA-b-PMACA3),
respectively. The films were allowed to store in a desiccator for further study. The procedure
for SRGs fabrication could be found in a related reference [4].
2.6. Characterizations
1H NMR spectra of the polymers were recorded on an INOVA 400 MHz nuclear magnetic
resonance instrument, using CDCl3 or DMSO-d6 as the solvent and tetramethylsilane (TMS)
13
as the internal standard. C NMR spectra were run on the same instrument operating at 100
MHz at room temperature and the chemical shifts were recorded under similar conditions.
The molecular weights (Mns) and molecular weight distributions (Mw/Mns) of the polymers
were determined with a Waters 1515 gel permeation chromatographer (GPC) equipped with
refractive index detector, using HR1, HR3, and HR4 column with molecular weight range
100-500,000 calibrated with PS or PMMA standard samples. THF was used as the eluent at a
flow rate of 1.0 mL min-1 operated at 30 oC. Elemental analysis of C, H and N were measured
with an EA1110 CHNO-S instrument. The UV absorption spectra of the samples in
chloroform solution were determined on a shimadzu-RF540 spectrophotometer at room
temperature. Thermal analysis of the polymers and melting points (m. p.) of all the
compounds were performed by differential scanning calorimetry (DSC) using a TA
o
instruments DSC2010 with a heating/cooling rate of 10 C min-1 under a continuous nitrogen
flow. FT-IR spectra were recorded on a Perkin-Elmer 2000 FT-IR spectrometer.
Thermogravimetric analysis (TGA) was performed at a heating rate of 20 o C/min from room
o
temperature to 750
C under a continuous nitrogen flow of 50 mL min-1 with a TA
Instruments SDT-2960TG/DTA. Cyclic voltammograms were performed on a CHI631B
electrochemical workstation at a constant scan of 0.1 V/s. Measurements were carried out in a
conventional three-electrode cell. The working electrode was an argentum electrode and
counter electrode was an argentum mesh. The 0.1 mmol polymers were dissolved in 10 mL
chloroform containing 0.1 M tetra-n-butylammonium hexafluorophosphate ((n-Bu)4NPF6) as
the supporting electrolyte.
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3. Results and discussion
3.1. Polymer synthesis
RAFT polymerization of the synthesized monomer (MACA) was carried out using CPDB
o
as RAFT agent and AIBN as initiator in DMF at 70 C, and homopolymers (PMACA1,
PMACA2 and PMACA3) were obtained under different reaction time with a molar ratio of
[MACA]0 : [CPDB]0 : [AIBN]0 = 300 : 3 : 0.5. As showed in Table 1, after 3 h, 6 h and 12 h
polymerization, PMACA1, PMACA2 and PMACA3 were obtained with the monomer
conversions of 15.2 %, 23.5 % and 62.7 %, respectively. The molecular weight distributions
(Mw/Mns) measured by GPC were relatively narrow (Mw/Mn ≤ 1.30) and the number-average
molecular weights measured by GPC (Mn (GPC)) increased with monomer conversions, which
indicated that the polymerization was conducted under a controlled manner. However, there
were slightly discrepancies between the molecular weights (Mn (GPC)s) obtained by GPC and
the theoretical values (Mn (th)s), which may be due to the incomplete usage of RAFT agent
(CPDB) and the poly(methyl methacrylate) (PMMA) standards used for GPC calibration
[46,47].
(Table 1. is here)
The film forming property is very important for the photo-responsive materials of
azobenzene polymers [11]. We find that PMACA showed poor film forming abilities. Thus,
the block copolymers containing MACA and MMA as structural units were designed to
improve forming properties of azobenzene polymers. However, the attempt for preparing
block copolymer using PMACA as macro-RAFT agent for MMA polymerization was failed,
and the obtained block copolymers have broader molecular weight distributions (Mw/Mn >
1.50) with still several homopolymer (PMACA) chains, possibly due to the presence of
“dead” polymer chains in the original polymer [12]. Thus, the alternative way was used here,
e.g. by using PMMA as the macro-RAFT agent to conduct RAFT polymerization of MACA.
PMMA was firstly prepared by RAFT polymerization of MMA using CPDB as RAFT agent.
The Mn (GPC) and Mw/Mn of PMMA was 8300 g/mol and 1.14 (determined by GPC),
respectively, which was showed in the Table 1. Diblock copolymers (PMMA-b-PMACAs)
with different azo-containing compositions were obtained by adjusting the polymerization
o
time ([MACA]0 : [PMMA]0 : [AIBN]0 = 300 : 3 : 0.5, AIBN as initiator in DMF at 70 C).
The results of block copolymers were summarized in Table 1, and these block copolymers
were prepared with predetermined molecular weights and narrow molecular weight
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distributions. Most of all, the obtained block copolymers showed good solubility in CHCl3,
and good film forming ability. The GPC curves of the polymers in Figure 2 indicated that
almost the entire macro-RAFT agent (PMMA) was transferred into block copolymers. It
suggested that the macro-RAFT agent (PMMA) was an efficient RAFT agent for the chain-
extension polymerization of MACA.
(Figure 2. is here)
3.2. Structural characterization of polymers
1
To confirm the molecular structures, polymers were characterized by FT-IR, H NMR and
13C NMR spectra. The FT-IR spectra of these polymers were given in Figure 3. For
comparison, the spectra of MACA, PMMA (Mn (GPC) = 8300 g/mol, Mw/Mn = 1.14), and the
block polymer (PMMA-b-PMACA3, Mn (GPC) = 10200 g/mol, Mw/Mn = 1.28) were shown in
the same figure. The FT-IR spectrum of the monomer, MACA, showed the characteristic
signal at 1706 and 1602 cm-1 due to the stretching vibrations of carbonyl and azobenzene
group. The FT-IR spectrum of PMMA showed the characteristic carbonyl peek at 1730 cm-1
[48-52]. After chain-extension, PMMA-b-PMACA3 showed strong absorption of the
stretching vibration of carbonyl group and azobenzene group at 1730 and 1602 cm-1,
respectively. The peak at 1706 cm-1 corresponding to carbonyl group of MACA was merged
with the 1730 cm-1 peak in the FT-IR spectrum of copolymer. The FT-IR spectra confirmed
the structure of block copolymer.
(Figure 3. is here)
1
Figure 4 showed the H NMR spectroscopy of PMMA, PMACA3, and PMMA-b-
PMACA3, respectively. In spectrum of PMMA, the chemical shifts at the range from 3.4 to
3.9 ppm and 0.4 to 2.2 ppm were due to protons in the PMMA chains [53]. The weak signals
at the range from 7.3 to 8.1 ppm were attributed to the aromatic protons in CPDB structure,
which confirmed that the RAFT agent was attached on the end of the PMMA chain. In the 1H
NMR spectroscopy of PMACA3, the characteristic signals corresponding to the aromatic
protons of azobenzene group were observed at the range of 6.4-7.0 ppm and 7.5-8.3 ppm. The
signals from 0.2 to 4.4 ppm were assigned to the methenyl and methyl protons in the polymer
chain. However, the resonances of characteristic signals of the aromatic protons at CPDB
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moieties were overlapped by the phenyl groups of polymer, and thus these cannot be
discernable in this spectroscopy.
1
In the H NMR spectroscopy of PMMA-b-PMACA3 (Figure 4, PMMA-b-PMACA3), the
characteristic signals corresponding to all protons in PMMA-b-PMACA3 were in accordance
with theoretical chemical shifts. For example, the chemical shifts at 6.4-7.0 ppm (“a” in
Figure 4 (PMMA-b-PMACA3)) and 7.5-8.3 ppm (“b” in Figure 4 (PMMA-b-PMACA3))
were ascribed to the aromatic protons of azobenzene group, and the signals of methyl protons
(“d” in Figure 4 (PMMA-b-PMACA3)) in the PMMA were observed from 3.4 ppm to 3.6
ppm. Furthermore, the molecular weight of the block copolymer (Mn (NMR)) could be
1
calculated from the ratio of the characteristic signals in the H NMR spectroscopy from
equation (1).
I7.5-8.0
6
I
M
MMMA
Mn(NMR)MPMMA(
/
3.4-3.6) PMMAMMACA (1)
3
where I7.5-8.0 is the integral of the signals at 7.5-8.0 ppm (“a” in Figure 4 (PMMA-b-
PMACA3)), and I3.4-3.6 is the integral of the signals at 3.4-3.6 ppm (“d” in Figure 4 (PMMA-
b-PMACA3)).
The calculated molecular weights (Mn (NMR)) listed in Table 1 were close to those theoretical
value, which further confirmed the well-defined structure of the obtained block copolymers.
(Figure 4. is here)
13
To further demonstrate the polymer structures, the C NMR spectroscopy of PMMA and
PMMA-b-PMACA3 were shown in Figure 5. The chemical shifts of the carbonyl carbons (-
OC=O) adjacent to the MMA main chain could be found between 179.5 and 176.0 ppm (“a”)
in 13C NMR spectrum of PMMA, and the visible shifts from 52.1 to 51.5 ppm (“b”)
corresponded to the methyl carbons (OCH3). In the aliphatic carbons region, three broad
peaks (55.0-52.3 ppm, 45.6-44.2 ppm and 19.4-15.8 ppm) were also related to the MMA main
chain, which were in good agreement with PMMA. In the 13C NMR spectroscopy of PMMA-
b-PMACA3 (Figure 5 PMMA-b-PMACA3), the characteristic signals corresponding to all
carbons in PMMA-b-PMACA3 were in accordance with the polymer chemical shifts. The
aromatic carbons in azobenzene group were observed in chemical shifts including 167.35-
167.15 ppm, 155.0-150.5 ppm, 144.0-142.5 ppm, 133.0-131.0 ppm, 127.0-121.0 ppm and
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112.5-111.0 ppm. The most important were the tetrazole carbon (“c”) signals at the range
from 146.0 to 144.5 ppm, which could not be confirmed through in the 1H NMR spectroscopy.
(Figure 5. is here)
3.3. Thermal properties of the polymers
Thermal properties of the polymers were evaluated by differential scanning calorimetry
(DSC). The second DSC heating curves of PMMA and copolymers (PMMA-b-PMACA1,
PMMA-b-PMACA2 and PMMA-b-PMACA3) were given in Figure 6. The DSC
o
characterizations were carried out with a heating/cooling rate of 10 C min-1 under a
continuous nitrogen flow. From Figure 6, all of the polymers showed glass transition
o
temperature (Tg). The Tg of PMMA was about 123 C, and the Tg of PMMA-b-PMACA1,
o
o
o
PMMA-b-PMACA2 and PMMA-b-PMACA3 were 133 C, 134 C and 141 C, respectively.
o
o
PMACA3 had a much higher Tg (140 C) than PMMA (123 C), which meant that
introduction of rigid azobenzene chromophore into PMMA chain obviously improved the Tg
of the polymers. As shown in Figure 5, there was only one glass transition point observed in
all the block copolymers, and the polymers with higher PMACA content showed higher
values of Tg. That indicated that PMMA and PMACA segments displayed the phase mixing at
the broad molecular region. The glass transition temperature of PMMA-b-PMACA3 (141 oC)
is a little higher than PMACA3, because the molecular weight of PMACA in block copolymer
(11300 g/mol) is a little higher than that of PMACA3 (10200 g/mol). Moreover, there was no
melting point observed in these DSC curves of polymers, which indicated that all the
polymers were amorphous. Figure 6 showed the wide-angle X-ray diffraction (WAXD)
results of PMMA and PMMA-b-PMACA. There is no sharp peak observed, which indicated
that these polymers were amorphous.
Thermal properties of the polymers were also evaluated by the thermogravimetric analysis
(TGA) under a continuous nitrogen flow [54], and the results were shown in Figure 8. PMMA
was thermally stable up to 216 oC with about 5% weight loss, and lost 10% of its weight at the
temperature of 252 oC, which could be attributed to the missing of the methyl carbons (OCH3).
o
Similarly, PMMA-b-PMACA3 has 5% weight degradation at the temperature of 196 C,
which was lower than that of PMMA, and the reason may be due to unstable ester structure
and aliphatic segment (-OCH2CH2N(CH3)). There was about 25% of weight loss at the first
o
stage (215 C). Due to introduction of azobenznene and tetrazole groups, the weight loss of
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o
PMMA-b-PMACA3 slowed down, and about 26% of carbon remained at 750 C. The
remainder mass increased with the higher PMACA content in PMMA-b-PMACAs.
(Figure 6. is here)
(Figure 7. is here)
(Figure 8. is here)
3.4. Photoisomeriztion behavior
As well known, azobenzene polymers exhibit photoisomeriztion behavior, which undergoes
isomerization from trans- to cis-forms under 365 nm UV irradiation [55]. Here,
photoisomeriztion of PMMA-b-PMACA in chloroform solution was studied under irradiation
with 365 nm UV light. The UV-vis absorption spectra were recorded at different time
intervals until photo-stationary state was reached. The representative results for PMMA-b-
PMACA3 (Mn (GPC) = 19600 g/mol, Mw/Mn = 1.25) were given in Figure 9. As shown in
Figure 9, PMMA-b-PMACA3 showed absorption at 430 nm before UV exposure, which was
due to the characteristic intense of π-π* transition (trans-form azobenzene). After irradiation
with 365 nm UV light, the trans-form of the azobenzene changed to the cis-form, which
showed characteristic absorption peak at 513 nm. It should be indicated that the absorption
(430 nm) of trans-form azobenzene slightly increased upon UV irradiation in the beginning
period of irradiation (3 minutes), which may be due to the bulky tetrazole substitution on the
azobenzene. After UV irradiation of 3 minutes, the trans- form content of azobenzene reached
a peak (Figure 9 A). With further increased irradiation time, the absorption of trans-form
azobenzene at 430 nm decreased remarkable, and the intensity of the cis- form azobenzene
(513 nm) increased rapidly. Furthermore, during the tran-cis isomerization, the absorption
peak at 430 nm decreased too much, and embedded into the shoulder of and 513 nm peak
spectra, which resulted in the appearance of a “red-shift” peak from 413 to 513 nm [56].
(Figure 9. is here)
The electrochemical behavior of polymers in solution before and after UV irradiation was
investigated using the cyclic voltammetry (CV). The typical CV curves of PMMA-b-
PMACA3 in chloroform solution before and after UV irradiation was showed in Figure 10.
Before UV irradiation, the azobenzene stay in the trans form, and an oxidation peak at 1.0V
was showed in the CV curve. After the 365 nm light irradiated for 80 min, almost all of the
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azobenzene shifted to the cis form (from Figure 9), and the oxidation peak in CV curve
obviously shifted to 0.6V. Thus, the electrochemical behavior can be adjusted by the UV
irradiation, which may find their applications in photo electronic materials [57].
(Figure 10. is here)
3.5 Photoinduced surface relief gratings
The obtained PMMA-b-PMACAs with good film-forming property were investigated for
the surface relief grating (SRG) ability. Thin films of PMMA-b-PMACAs via spin-coating on
the clean glass were obtained, and the thicknesses were 332 nm (PMMA-b-PMACA1), 312
nm (PMMA-b-PMACA2) and 350 nm (PMMA-b-PMACA3), respectively. Then, the SRG
measurement was performed with linearly polarized Kr+ laser beam (413.1 nm, 200 mW/cm2)
at room temperature [4], and characterized by the inscription rates and the saturation levels of
SRGs formation, which were detected using atomic force microscopy (AFM, NT-MDT
SOLVER P47-PRO). Figure 11 showed AFM three-dimensional (A) and plane (B) images of
the alternate surface relief structures with regular spaces fabricated on the PMMA-b-
PMACA1 film surfaces after Kr+ laser irradiation for 1600 s at room temperature. AFM
images showed that the surface modulation depth was about 145.4 nm, and the grating
spacing was about 1.45 µm, which was used as photoinduced data storage. When the polymer
film was exposed to the writing beam for 1600 s, the rates of gratings formation were probed
by measuring the first-order diffraction efficiency of the SRG. The increase of the diffraction
efficiency of SRG with the irradiation time was shown in Figure 12. For the PMMA-b-
PMACA1 sample, the diffraction efficiency rapidly increased to about 1.22% until saturation
level at 1600 s. Moreover, the diffraction efficiency of SRG was affected by the azobenzene
contain for the PMMA-b-PMACAs. From the Figure 12, the diffraction efficiency of the
SRGs was 1.22 (PMMA-b-PMACA1), 2.38 (PMMA-b-PMACA2) and 3.02 (PMMA-b-
PMACA3), respectively, which increased with the azobenzene contain of the copolymers.
(Figure 11. is here)
(Figure 12. is here)
4. Conclusion
A
novel
methacrylate
monomer
(4’-(2-methacryloxyethyl)methylamino-4-(5-
chlorotetrazol-1-yl)azobenzene, MACA) containing azobenzene chromophore and tetrazole
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moiety was successfully synthesized and polymerized to form homopolymers PMACAs and
block copolymers (PMMA-b-PMACAs) via RAFT technology. These obtained polymers with
controlled molecular weights and narrow molecular weight distributions (Mw/Mns <1.30) were
1
confirmed by H NMR spectroscopy and gel permeation chromatography (GPC). These
copolymers showed moderate trans-cis isomerization behavior, as most of the azobenzene
polymers. Cyclic voltammetry results of copolymer showed that the oxidation peak of
copolymer shifted from 1.0V to 0.6V when azobenzene isomerization from trans to cis form.
On irradiation with a linearly polarized Kr+ laser beam (413.1 nm), The PMMA-b-PMACA1
film could formed the well-defined efficient surface relief grating (SRG) with the 145.4 nm
surface modulation depth and 1.45 µm grating spacing. the diffraction efficiency of the SRGs
were 1.22 (PMMA-b-PMACA1), 2.38 (PMMA-b-PMACA2) and 3.02 (PMMA-b-PMACA3),
respectively, which increased with the azobenzene contain for the copolymers.
Acknowledgements: The financial supports of this work by the National Natural Science
Foundation of China (Nos. 21104006), A Project Funded by the Priority Academic Program
Development of Jiangsu Higher Education Institutions (PAPD), the Program of Innovative
Research Team of Changzhou University (ZMF1002118).
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References
[1] G. Kumar, D. C. Neckers, Chem. Rev. 89 (1989) 1915.
[2] D. Brown, A. Natansohn, P. Rochon, Macromolecules 28 (1995) 6116.
[3] A. Natansohn, P. Rochon, Chem. Rev. 102 (2002) 4139.
[4] X. Q. Xue, J. Zhu, Z. B. Zhang, N. C. Zhou, Y. F. Tu, X. L. Zhu, Macromolecules 43
(2010) 2704.
[5] W. M. Gibons, P. J. Shannon, S. T. Sun, B. J. Swetlin, Nature 351 (1991) 49.
[6] T. G. Pedersen, P. M. Johansen, H. C. Pedersen, J. Opt. A: Pure Appl. Opt. 2 (2000) 272.
[7] D. Hore, A. Natansohn, P. Rochon, J. Phys. Chem. B 107 (2003) 2197.
[8] H. R. Hafiz, F. Nakanishi, Nanotechnology 14 (2003) 649.
[9] A. Bobrovsky1, V. Shibaev, A. Bubnov, V. Hamplová, M. Kašpar, D. Pociecha, M.
Glogarová, Macromol. Chem. Phys. 4 (2011) 342.
[10] L. M. Sáiz, P. A. Oyanguren, M. J. Galante, React. Funct. Polym. 72 (2012) 478.
[11] P. Rochon, E. Batalla, A. Natansohn, Appl. Phys. Lett. 66 (1995) 136.
[12] X. Q. Xue, J. Zhu, Z. B. Zhang, N. C. Zhou, X. L. Zhu, React. Funct. Polym. 70 (2010)
456.
[13] Y. Wu, A. Natansohn, P. Rochon, Macromolecules 37 (2004) 6090.
[14] C. Barrett, P. Rochon, A. Natansohn, J. Chem. Phys. 109 (1998) 1505.
[15] M. S. Ho, C. Barrett, J. Paterson, M. Esteghamatian, A. Natansohn, P. Rochon,
Macromolecules 29 (1996) 4613.
[16] I. Mita, K. Horie, K. Hirao, Macromolecules 22 (1989) 558.
[17] T. Naito, K. Horie, I. Mita, Polym. J. 23 (1991) 809.
[18] U. Caruso, R. Diana, A. Fort, B. Panunzi, A. Roviello, Macromol. Symp. 234 (2006) 87.
[19] A. Facchetti, A. Abbotto, L. Beverina, M. E. van der Boom, P. Dutta, G. Evmenenko, T.
J. Marks, G. A. Pagani, Chem. Mater. 14 (2002) 4996.
[20] J. Wei, Z. Yan, L. Lin, J. S. Gu, Z. Feng, Y. L. Yu, React. Funct. Polym. 73 (2013) 1009.
[21] L. P. Yu, Z. B. Zhang, X. R. Chen, W. Zhang, J. H. Wu, Z. P. Cheng, J. Zhu. X. L. Zhu,
J. Polym. Sci. Part A: Polym. Chem. 46 (2008) 682.
[22] N. V. Tsarevsky, K. V. Bernaerts, B. Dufour, F. E. DuPrez, K. Matyjaszewski,
Macromolecules 37 (2004) 9308.
[23] Y. Y. Zhang, Z. P. Cheng, X. R. Chen, W. Zhang, J. H. Wu, J. Zhu, X. L. Zhu,
Macromolecules 40 (2007) 4809.
[24] M. Jin, Q. X. Yang, R. Lu, T. H. Xu, Y. Y. Zhao, J. Polym. Sci. Part A: Polym. Chem.
42 (2004) 4237.
- 17 -

ACCEPTED MANUSCRIPT
[25] P. Forcen, C. Oriol, R. Sanchez, S. Alcala, Hvilsted, K. Jankova, J. Loos, J. Polym. Sci.
Part A: Polym. Chem. 45 (2007) 1899.
[26] X. Q. Xue, J. Zhu, Z. B. Zhang, Z. P. Cheng, Y. F. Tu, X. L. Zhu, Polymer 51 (2010)
3083.
[27] W. Deng, P. A. Albouy, E. Lacaze, P. Keller, X. G. Wang, M. M. Li, Macromolecules 41
(2008) 2459.
[28] X. Li, X. M. Lu, Q. H. Lu, D. Y. Yan, Macromolecules 40 (2007) 3306.
[29] X. D. Tang, L. C. Gao, N. F. Han, X. H. Fan, Q. F. Zhou, J. Polym. Sci. Part A: Polym.
Chem. 45 (2007) 3342.
[30] K. Gharagozloo-Hubmann, O. Kulikovska, V. Börger, H. Menzel, J. Stumpe, Macromol.
Chem. Phys. 21 (2009) 1809.
[31] X. D. Tang, L. C. Gao, X. H. Fan. Q. F. Zhou, J. Polym. Sci. Part A: Polym. Chem. 45
(2007) 1653.
[32] M. Kato, M. Kamigaito, M. Sawamoto, T. Higashimura, Macromolecules 28 (1995)
1721.
[33] J. S. Wang, K. Matyjaszewski, Macromolecules 28 (1995) 7901.
[34] K. Matyjaszewski, J. Xia, Chem. Rev. 101 (2001) 2921.
[35] X. Q. Xue, W. Zhang, Z. P. Cheng, J. Zhu, X. L. Zhu, J. Polym. Sci. Part A: Polym.
Chem. 46 (2008) 5626.
[36] J. Chiefari, Y. K. Chong, F. Ercole, J. Krstina, J. Jeffery, T. P. T. Le, R. T. A.
Mayadunne, G. F. Meijs, C. L. Moad, G. Moad, E. Rizzardo, S. H. Thang,
Macromolecules 31 (1998) 5559.
[37] G. Moad, E. Rizzardo, S. H. Thang, polymer 49 (2008) 1079.
[38] A. B. Lowe, C. L. McCormick, Prog. Sci. 32 (2007) 283.
[39] U. Georgi, P. Reichenbach, U. Oertel, L. M. Eng, B. Voit, React. Funct. Polym. 72
(2012) 242.
[40] G. Moad, E. Rizzardo, D. H. Solomon, Macromolecules 15 (1982) 909.
[41] C. J. Hawker, A. W. Bosman, E. Harth, Chem. Rev. 101 (2001) 3661.
[42] M. K. Georges, P. R. N. Veregin, P. M. Kazmaier, G. K. Hamer, Macromolecules 26
(1993) 2987.
[43] Y. K. Chong, J. Kristina, T. P. T. Le, G. Moad, A. Psotma, E. Rizzarid, S. H. Thang,
Macromolecules 36 (2003) 2256.
[44] R. A. W. Johnstone, P. J. Pricet, J. Chem. Soc. Perkin Trans. 1 1069 (1987).
[45] K. Ramadas, N. Srinivasan, Syn. Commun. 22 (1992) 3189.
- 18 -

ACCEPTED MANUSCRIPT
[46] G. Moad, E. Rizzardo, S. H. Thang, Aust. J. Chem. 58 (2005) 379.
[47] J. Krstina, T. P. T. Le, G. Moad, A. Postma, E. Rizzardo, S. H. Thang, Macromolecules
36 (2003) 2256.
[48] A. V. Raghu, G. S. Gadaginamath, N. T. Mathew, S. B. Halligudi, T. M. Aminabhavi,
Reac. Funct. Polym. 67 (2007) 503.
[49] A. V. Raghu, G. S. Gadaginamath, M. Priya, P. Seema, H. M. Jeong,T. M. Aminabhavi,
J. Appl. Polym. Sci. 110 (2008) 2315.
[50] A. V. Raghu, H. M. Jeong, J. H. Kim, Y. R. Lee, Y. B. Cho, K. Sirsalmath, Macromol.
Res. 16 (2008) 194.
[51] K. R. Reddy, A. V. Raghu, H. M. Jeong, Polym. Bull. 60 (2008) 609.
[52] A. V. Raghu, G. S. Gadaginamath, S. S. Jawalkar, S. B. Halligudi and T. M. Aminabhavi,
J. Polym. Sci., Part A:Polym. Chem. 44 (2006) 6032.
[53] X. Q. Xue, F. Li, W. Y. Huang, H. J. Yang, B. B. Jiang, Y. L. Zheng, D. L. Zhang, J. B.
Fang, L. Z. Kong, G. Q. Zhai, J. H. Chen, Macromol. Rapid Commun. 35 (2014) 330.
[54] W. Y. Huang, C. Liu, H. J. Yang, X. Q. Xue, B. B. Jiang, D. L. Zhang, L. Z. Kong, Y.
Zhang, S. Komarneni, Polym. Chem. 5 (2014) 3326.
[55] Z. D. Xu, Y. Zhang, X. H. Fan, X. H. Wan, Q. F. Zhou, Chinese J Polym. Sci. 20 (2002),
99.
[56] H. Z. Cao, W. Zhang, J. Zhu, X. R. Chen, Z. P. Cheng, J. H. Wu, X. L. Zhu, Express
Polym. Lett. 2 (2008) 589.
[57] G. Klopman, N. Doddapaneni, J. Phys. Chem. 78 (1974) 1825.
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Figure captions
Scheme 1. The synthetic route of 4′-(2-metharyloxyethyl)methylamino-4-(5-chlorotetrazol-1-
yl)azobenzene (MACA).
Scheme 2. The synthetic route of block copolymers (PMMA-b-PMACA).
1
Figure 1. H NMR spectrum of 4′-(2-metharyloxyethyl)methylamino-4-(5-chlorotetrazol-1-
yl)azobenzene (MACA) in CDCl3.
Figure 2. The GPC curves of PMMA, PMMA-b-PMACA1, PMMA-b-PMACA2, and
PMMA-b-PMACA3.
Figure 3. The FT-IR spectroscopy of MACA, PMMA (Mn (GPC) = 8300 g/mol, Mw/Mn = 1.14)
and PMMA-b-PMACA3 (Mn (GPC) = 19600 g/mol, Mw/Mn = 1.25).
Figure 4. 1H NMR spectroscopy of PMMA (Mn (GPC) = 8300 g/mol, Mw/Mn = 1.14), PMACA3
(Mn (GPC) = 10200 g/mol, Mw/Mn = 1.28), and PMMA-b-PMACA3 (Mn (GPC) = 19600
g/mol, Mw/Mn = 1.25) in DMSO-d6.
Figure 5. 13C NMR spectroscopy of PMMA (Mn (GPC) = 8300 g/mol, Mw/Mn = 1.14) and
PMMA-b-PMACA3 (Mn (GPC) = 19600 g/mol, Mw/Mn = 1.25) in CDCl3.
Figure 6. Second DSC heating curves of PMMA, PMMA-b-PMACA1, PMMA-b-PMACA2,
PMMA-b-PMACA3, PMACA3.
Figure 7. WAXD spectra of PMMA, PMMA-b-PMACA1 and PMMA-b-PMACA3 at room
temperature.
Figure 8. Thermogravimetric analysis (TGA) of PMMA, PMMA-b-PMACA1 and PMMA-b-
PMACA3.
Figure 9. The UV-vis absorption changes of PMMA-b-PMACA3 during the irradiation with
365 nm UV light in chloroform solution at room temperature. The concentration of
repeating units is 2.50 × 10-6 M. A: initial 3 minutes; B: after 3 minutes.
Figure 10. Cyclic voltammogams of PMMA-b-PMACA3 before and after the irradiation with
365 nm UV light in chloroform solution. The concentration of repeating units is
2.50 × 10-6 M in room temperature containing 0.1 M tetra-n-butylammonium
hexafluorophosphate ((n-Bu)4NPF6) as the supporting electrolyte.
Figure 11. AFM images of the SRG formed on PMMA-b-PMACA1 film: (A) plane view of
the SRG and (B) three-dimensional view of the SRG.
Figure 12. Diffraction efficiency as a function of the irradiation time for the similar thickness
thin film of three samples (PMMA-b-PMACA1, 330 nm; PMMA-b-PMACA2, 312
nm; PMMA-b-PMACA3, 350 nm).
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Table 1. Characteristics of PMMA, PMACAs and PMMA-b-PMACAs
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Figure 1
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Figure 2
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Figure 3
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Figure 4
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Figure 5
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Figure 6
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Figure 7
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Figure 8
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