New series of AB2-type hyperbranched polytriazoles derived from the same polymeric intermediate: Different endcapping spacers with adjustable bulk and convenient syntheses via click chemistry under copper(I) catalysis

Article abstract of DOI:10.1002/pola.24625

In this article, according to the concept of "suitable isolation group," six new AB₂-type polytriazoles containing azo-chromophore moieties, derived from the same hyperbranched polymer intermediate, were successfully prepared through click reac

Full text of DOI:10.1002/pola.24625

New Series of AB2-Type Hyperbranched Polytriazoles Derived from the
Same Polymeric Intermediate: Different Endcapping Spacers with
Adjustable Bulk and Convenient Syntheses via Click Chemistry under
Copper(I) Catalysis
ZHONG’AN LI,1 WENBO WU,1 GUOFU QIU,1 GUI YU,2 YUNQI LIU,2 CHENG YE,2 JINGUI QIN,1 ZHEN LI1
1Department of Chemistry, Hubei Key Lab on Organic and Polymeric Opto-Electronic Materials,
Wuhan University, Wuhan 430072, China
2Organic Solids Laboratories, Institute of Chemistry, The Chinese Academy of Sciences, Beijing 100080, China
Received 1 October 2010; accepted 7 February 2011
DOI: 10.1002/pola.24625
Published online 15 March 2011 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: In this article, according to the concept of ‘‘suitable
isolation group,’’ six new AB2-type polytriazoles containing
azo-chromophore moieties, derived from the same hyper-
branched polymer intermediate, were successfully prepared
through click reaction under copper(I) catalysis by modifying
the synthetic route, in which different isolation groups in differ-
ent size were introduced to the periphery of the hyperbranched
polymers as end-capping moieties. With the different end-cap-
ping groups, these hyperbranched polymers, P1–P6, exhibited
different solubility and processability; also, their nonlinear opti-
cal properties were modified accordingly, realizing the adjust-
ment of the properties of hyperbranched polymers through the
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structural design.
2011 Wiley Periodicals, Inc. J Polym Sci
Part A: Polym Chem 49: 1977–1987, 2011
KEYWORDS: functionalization of polymers; hyperbranched polymers;
nonlinear optics
INTRODUCTION Dendritic macromolecules (i.e., dendrimers,
dendronized polymers, and hyperbranched polymers) are
poised to make significant contributions in several areas of
the physical and biological sciences and engineering.1–20
Especially, hyperbranched polymers, with similarly unique
properties to dendrimers, have attracted much attention in
recent years, due to their convenient preparation via a sin-
gle-step reaction by a one-pot procedure in large scale.12–20
Thanks to the efforts of scientists, many different synthetic
approaches were explored for the syntheses of hyper-
branched polymers. As a powerful synthetic tool, the new
‘‘click’’ chemistry reactions21–29 were also applied to the con-
struction of new functional hyperbranched polymers. How-
ever, the reported successful examples were relatively scarce
and most of them took an A2þB3 approach.30,31 To construct
hyperbranched polymers with the controlled structure more
like dendrimers, it might be better to prepare hyperbranched
polymers from AB2 monomers, although it was difficult for
AB2 monomers to yield soluble polymers through the Cu(I)-
catalyzed click polymerizations due to the self-oligomeriza-
tion.31 Fortunately, by modifying the synthetic procedure and
using end-capping groups, we have successfully prepared
two soluble azo chromophore-containing AB2-type hyper-
branched polytriazoles (HP1 and HP2; the synthetic route
was shown in Scheme 1) as new second-order nonlinear
optical (NLO) polymeric materials. But their processability
was bad, and the prepared thin films were not good enough,
which was not beneficial to their possible practical applica-
tions.32 Thus, we would like to improve the processability by
further modifying their structure. Also, to further confirm
the reproducibility and reliability of the controllable syn-
thetic process for the hyperbranched polymers from AB2
monomers through the Cu(I)-catalyzed click polymerization,
additional study was still needed.
On the other hand, from 2006, on the basis of the literature
and according to the site isolation principle, and with an
attempt to partially resolve the challenge in the second-order
NLO polymeric materials (to efficiently translate the large b
values of the organic chromophores into high macroscopic
NLO activities of polymers), we prepared different kinds of
NLO polymers, in which the size of the isolation groups in
NLO chromophore moieties (generally azo chromophores)
was changed from small to larger. The experimental results
demonstrated that the macroscopic nonlinearity of NLO poly-
mers could be boosted several times higher by bonding
‘‘suitable isolation group’’ to the NLO chromophore moi-
eties.33–45 Interestingly, we also found that the introduction
Additional Supporting Information may be found in the online version of this article. Zhong’an Li and Wenbo Wu contributed equally to this work.
Correspondence to: Z. Li (E-mail: lizhen@whu.edu.cn)
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Journal of Polymer Science Part A: Polymer Chemistry, Vol. 49, 1977–1987 (2011) 2011 Wiley Periodicals, Inc.
NONLINEAR OPTICAL HYPERBRANCHED POLYMERS, LI ET AL.
1977

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 1 Synthetic route to HP1 and HP2. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
of ‘‘suitable isolation group’’ to the chromophore moieties
would lead to the improved solubility and processability of
the resultant chromophore-containing polymers.42–45
balance the processability and NLO properties of the result-
ant hyperbranched polymers.56,57
Therefore, to deepen the exploration of the fundamental
architectural design parameters, to study the relationship
between the structure and properties of hyperbranched
NLO polymers, and to obtain more information concerning
the Cu(I)-catalyzed click polymerization behavior of AB2
monomers, according to the concept of ‘‘suitable isolation
group,’’ we would like to use isolation spacers in different
size, instead of NLO chromophores used previously for the
synthesis of HP2, to end-cap the azido end groups of the
prepared reactive hyperbranched polymeric intermediate
(HP-N3, its structure shown in Chart S1 in the Supporting
Information), to improve the film-forming ability of the re-
sultant hyperbranched polymers (P1–P6, their structure
shown in Chart S2 in the Supporting Information), as well
as other optical and physical properties (Scheme 2). To
facilitate the comparison of the resultant hyperbranched
polymer at the same level and investigate the synthetic
flexibility of the Cu(I)-catalyzed click polymerization of
AB2 monomers, the reaction mixture of polymeric interme-
diate, HP-N3, was divided into six portions without purifi-
cation, and to each portion, different end-capping moieties
(one of Compound 1–6, Scheme 3) were added to react
with the terminal alkyne groups, to yield hyperbranched
polymers P1–P6 with similar structure to those of HP1
and HP2 (Scheme 1). The obtained six hyperbranched
polymers exhibited different solubility and interesting NLO
properties, in accordance with the different end-capping
groups. Herein, we would like to present the syntheses,
characterization, and properties of these new hyper-
branched polymers in detail.
As we know, unlike linear polymers bearing only two end-
groups, the number of end groups in hyperbranched poly-
mers are very large, and the end-groups frequently become
the primary interface between the hyperbranched polymers
and the environment.12–20 As a result, some properties of
hyperbranched polymers (e.g., solubility, processability,
chemical reactivity, glass transition temperature) were domi-
nated by the nature of their large amount of end groups in
the periphery,46–52 similar to those in dendrimers.8 For
example, the recent work of Bunz and coworkers demon-
strated that hyperbranched polymer with large amount of
end-groups was a universal conjugated polymer platform,
and through postfunctionalization strategies, different func-
tional groups end-capped hyperbranched polymer intermedi-
ate to afford new properties.47 Baek et al. designed and
synthesized a series of novel AB2-type of hyperbranched
polymers, and they also explored the structure–property–
processing relationships with respect to tailoring the end-
group functionality.48–50 Thus, we wondered if it was possi-
ble to improve the processability of HP1 and HP2 by chang-
ing the end-capping groups. Considering that there should
be strong electronic interactions among the highly polar, azo
chromophore moieties near the interface in the hyper-
branched polymers, the introduced end-capping groups
could decrease the dipole–dipole interactions and benefit the
poling-induced noncentrosymmetric alignment of chromo-
phore moieties due to the isolation principle.53–55 According
to our experience in the dendrimers and dendronized NLO
polymers, there might be suitable end-capping group to
1978
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ARTICLE
SCHEME 2 Synthetic route to P1–P6. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
M2 were prepared as reported previously.32 Oct-1-yne (1)
EXPERIMENTAL
and ethynylbenzene (2) were purchased from Alfa-Aesar. All
other reagents were used as received.
Materials
Tetrahydrofuran (THF) was dried over and distilled from K-
Na alloy under an atmosphere of dry nitrogen. Triethylamine
(Et3N) was distilled under normal pressure and kept over
potassium hydroxide. Compounds S2, S5–S7 were synthe-
sized according to the literature method.58–60 Chromophore
Instrumentation
1H NMR spectra were measured on a Varian Mercury300 or
Bruker ARX 400 spectrometer using tetramethylsilane (d ¼
0 ppm) as internal standard. The Fourier transform infrared
SCHEME 3 Synthetic route to 3–6.
NONLINEAR OPTICAL HYPERBRANCHED POLYMERS, LI ET AL.
1979

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
(FTIR) spectra were recorded on a PerkinElmer-2 spectrom-
eter in the region of 3000–400 cmꢀ1 on NaCl pellets. UV–
visible spectra were obtained using a Shimadzu UV-2550
spectrometer. Gel permeation chromatography (GPC) was
used to determine the molecular weights of polymers. GPC
analysis was performed on a Waters HPLC system equipped
with a 2690D separation module and a 2410 refractive index
detector. Polystyrene standards were used as calibration
standards for GPC. DMF was used as an eluent, and the flow
rate was 1.0 mL/min. Thermal analysis was performed on
NETZSCH STA449C simultaneous thermal analyzer at a heat-
ing rate of 10 ꢁC/min in nitrogen at a flow rate of 50 cm3/
min for thermogravimetric analysis and the thermal transi-
tions of the polymers. The thickness of the films was meas-
ured with an Ambios Technology XP-2 profilometer.
ness. The crude product was purified by column chromatog-
raphy on silica gel.
S8
Compound S5 (0.80 g, 2.58 mmol), 2-methylbut-3-yn-2-ol
(0.67 g, 8.00 mmol). The crude product was purified by
column chromatography on silica gel using ethyl acetate/
petroleum ether (2/1, V/V) as eluent to afford white solid
(0.47 g, 87.5%).
1H NMR (300 MHz, CDCl3, 298 K) d (ppm): 1.60 (s, 6H,
ACH3), 5.06 (s, 2H, AOCH2Ph), 6.89 (d, J ¼ 9.2 Hz, 2H, ArH),
7.3–7.5 (m, 7H, ArH).
S9
Compound S6 (3.60 g, 11.0 mmol), 2-methylbut-3-yn-2-ol
(3.7 g, 44.0 mmol). The crude product was purified by
column chromatography on silica gel using ethyl acetate/
petroleum ether (2/1, V/V) as eluent to afford buff oil
(2.50 g, 69.4 %).
Synthesis of 4-(Hexyloxy)-N,N-diphenylaniline (S3)
Diphenylamine (S1; 1.69 g, 10.0 mmol), 1-(hexyloxy)-4-iodo-
benzene (S2; 4.56 g, 15.0 mmol), potassium carbonate
(K2CO3; 5.52 g, 40.0 mmol), copper powder (1.28 g, 20.0
mmol), and 18-crown-6 (18-C-6; 0.31 g, 1.0 mmol) were dis-
solved in 1, 2-dichlorobenzene (20 mL) and refluxed for
48 h. Hot reaction mixture was filtered, and the solvent was
removed by vacuum distillation. The crude product was puri-
fied by column chromatography on silica gel using dichloro-
methane/petroleum (1/5) as eluent to afford white powder
S3 (1.96 g, 58.0%).
1H NMR (300 MHz, CDCl3, 298 K) d (ppm): 0.86 (t, J ¼ 6.6
Hz, 3H, ACH3), 1.2–1.4 (m, 6 H, A(CH2)3A), 1.68(s, 6H,
ACH3), 1.86 (m, 2H, ACH2A), 4.28 (t, J ¼ 7.2 Hz, ANCH2A),
7.25 (m, 1H, ArH), 7.31 (d, J ¼ 8.1 Hz, 1H, ArH), 7.33–7.54
(m, 3H, ArH), 8.06 (d, J ¼ 7.2 Hz, 1H, ArH), 8.19 (s, 1H,
ArH).
S10
Compound S4 (1.70 g, 4.00 mmol), 2-methylbut-3-yn-2-ol
(0.67 g, 8.00 mmol). The crude product was purified by
column chromatography on silica gel using ethyl acetate/
petroleum ether (2/1, V/V) as eluent to afford yellow oil
(1.48 g, 86.7%).
1H NMR (300 MHz, CDCl3, 298 K) d (ppm): 0.91 (t, J ¼ 7.2
Hz, 3H, ACH3), 1.34 (m, 4H, ACH2CH2A), 1.46 (m, 2H,
ACH2A), 1.80 (m, 2H, ACH2A), 3.93 (t, J ¼ 6.6 Hz, 2H,
AOCH2A), 6.81 (d, J ¼ 8.7 Hz, 2H, ArH), 6.94 (br, s, 2H,
ArH), 7.04 (br, s, 6H, ArH), 7.20 (br, s, 4H, ArH).
1H NMR (300 MHz, CDCl3, 298 K) d (ppm): 0.91 (t, J ¼ 6.6
Hz, 3H, ArH), 1.35 (m, 4H, ACH2CH2A), 1.46 (m, 2H,
ACH2A), 1.60 (s, 6H, ACH3), 1.77 (m, 2H, ACH2A), 3.93 (t,
J ¼ 6.0 Hz, 2H, AOCH2A), 6.82 (d, J ¼ 8.7 Hz, 2H, ArH), 6.89
(d, J ¼ 8.7 Hz, 2H, ArH), 6.97–7.07 (m, 5H, ArH), 7.21 (d, J ¼
9.2 Hz, 4H, ArH).
Synthesis of 4-Bromo-N-(4-(hexyloxy)phenyl)-
N-phenylaniline (S4)
Compound S3 (1.71 g, 4.95 mmol) was dissolved in N,N,-di-
methyl formamide (DMF; 10 mL) without light and stirred
under nitrogen at 0 ꢁC. Then N-bromosuccinimide (NBS;
0.97 g, 5.44 mmol) in DMF (5 mL) was slowly added to the
above solution using dropping funnel and stirred at room
temperature for 1 day. The reaction was terminated with
hydrochloric acid (6 mL, 2 M), extracted with dichloro-
methane, and dried with anhydrous Na2SO4. The result
product S4 was not further purified and used in the next
reaction (2.00 g, 95.2%).
S11
Compound S7 (5.00 g, 12.1 mmol), 2-methylbut-3-yn-2-ol
(2.03 g, 24.2 mmol). The crude product was purified by col-
umn chromatography on silica gel using ethyl acetate/petro-
leum ether (2/1, V/V) as eluent to afford white solid (4.80 g,
95.2%).
1H NMR (400 MHz, CDCl3, 298 K) d (ppm): 0.78 (t, J ¼ 7.2
Hz, 6H, ACH3), 1.04–1.14 (m, 16H, A(CH2)4A), 1.69 (s, 6H,
ACH3), 1.96 (m, 4H, ACH2CA), 7.34 (m, 3H, ArH), 7.43 (m,
2H, ArH), 7.63 (d, J ¼ 8.0 Hz, 1H, ArH), 7.70 (m, 1H, ArH).
General Procedure for the Synthesis of S8–S11
A mixture of the compounds S4–S7 (1.00 equiv), 2-methyl-
but-3-yn-2-ol (2.00ꢂ4.00 equiv), cuprous iodide (CuI; 5 mol
%), triphenylphosphine (PPh3; 5 mol %), and tetrakis(triphe-
nylphosphine)palladium (Pd(PPh3)4; 1ꢂ3 mol %) was care-
fully degassed and charged with nitrogen. THF (the concen-
tration of S4–S7 was about 0.1 M)/Et3N (1/1, V/V) was then
added. For compound S5, the reaction was stirred at room
temperature overnight, and for other compounds S4 and S6–
S7, the reaction was refluxed for 30 h. The reaction was ter-
minated with water and extracted with CHCl3, washed with
water, dried over anhydrous Na2SO4, and evaporated to dry-
General Procedure for the Synthesis
of End-Capping Groups 3–6
To a solution of one of the compounds S8–S11 (1.00 equiv)
in isopropanol NaOH or KOH (1.50ꢂ3.00 equiv) was added.
The mixture was refluxed at 80 ꢁC for 3 h, then extracted
with chloroform, washed with brine, dried over anhydrous
Na2SO4, and evaporated to dryness. The crude product was
purified by column chromatography on silica gel.
1980
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
3
pitation from its DMF or THF solution into methanol to
afford the resultant product.
Compound S8 (0.21 g, 0.80 mmol), NaOH (0.064 g, 1.60
mmol). The crude product was purified by column chroma-
tography on silica gel using chloroform/petroleum ether (1/
2, V/V) as eluent to afford buff solid (0.16 g, 96.1%).
P1
End-capping group 1 (26 mg, 0.234 mmol). P1 was obtained
as red powder (96 mg, 86.1%). Mw ¼ 2.09 ꢃ 105, Mw/Mn ¼
1.64 (GPC, polystyrene calibration). IR (thin film), t (cmꢀ1):
1H NMR (400 MHz, CDCl3, 298 K) d (ppm): 3.03 (s, 1H,
ACBCH), 5.10 (s, 2H, AOCH2Ph), 6.93 (dd, J ¼ 2.0, 6.8 Hz,
2H, ArH), 7.36–7.50 (m, 7H, ArH).
1
1517, 1340 (ANO2). H NMR (400 M Hz, DMSO-d6, 298 K) d
(ppm): 0.5–0.8 (ACH3), 0.9–1.2 (ACH2A), 1.3–1.5 (ACH2A),
1.8–2.2 (ACH2A), 2.6–2.9 (ACH2CA), 3.5–3.9 (ANCH2A),
3.9–4.2 (AOCH2A), 4.3–4.6 (ANCH2A), 6.5–6.8 (ArH), 7.2–
8.0 (ArH). UV–vis (THF, 0.02 mg/mL): kmax (nm): 459.
4
Compound S9 (1.17 g, 3.51 mmol), NaOH (0.21 g, 5.25
mmol). The crude product was purified by column chroma-
tography on silica gel using chloroform/petroleum ether (1/
2, V/V) as eluent to afford yellow solid (0.75 g, 77.6%).
P2
End-capping group 2 (24 mg, 0.234 mmol). P2 was obtained
as red powder (100 mg, 90.9%). Mw ¼ 2.02 ꢃ 105, Mw/Mn
¼ 1.48 (GPC, polystyrene calibration). IR (thin film), t
(cmꢀ1): 1513, 1343 (ANO2). 1H NMR (400 M Hz, DMSO-d6,
298 K) d (ppm): 1.7–2.1 (ACH2A), 2.6–2.9 (ACH2CA), 3.5–
3.9 (ANCH2A), 3.9–4.2 (AOCH2A), 4.3–4.7 (ANCH2A), 6.5–
7.0 (ArH), 7.1–7.9 (ArH), 8.4–8.6 (C¼¼CH). UV–vis (THF, 0.02
mg/mL): kmax (nm): 458.
1H NMR (300 MHz, CDCl3, 298 K) d (ppm): 0.86 (t, J ¼ 7.2
Hz, 3H, ACH3), 1.2–1.4 (m, 6 H, A(CH2)3A), 1.86 (m, 2H,
ACH2A), 3.06 (s, 1H, ACBCH), 4.28 (t, J ¼ 7.2 Hz,
ANCH2A), 7.26 (m, 1H, ArH), 7.32 (d, J ¼ 8.1 Hz, 1H, ArH),
7.42 (d, J ¼ 9.0 Hz, 1H, ArH), 7.51 (m, 1H, ArH), 7.57 (d, J ¼
8.7 Hz, 1H, ArH), 8.06 (d, J ¼ 8.1 Hz, ArH), 8.26 (s, 1H, ArH).
5
P3
Compound S10 (1.03 g, 2.41 mmol), NaOH (0.19 g, 4.80
mmol). The crude product was purified by column chroma-
tography on silica gel using chloroform/petroleum ether (1/
2, V/V) as eluent to afford yellow solid (0.65 g, 73.3%).
End-capping group 3 (49 mg, 0.234 mmol). P3 was obtained
as red powder (118 mg, 90.4%). Mw ¼ 2.14 ꢃ 105, Mw/Mn
¼ 1.49 (GPC, polystyrene calibration). IR (thin film), t
(cmꢀ1): 1517, 1343 (ANO2). 1H NMR (400 M Hz, DMSO-d6,
298 K) d (ppm): 1.7–2.2 (ACH2A), 2.6–2.9 (ACH2CA), 3.5–
3.9 (ANCH2A), 3.9–4.2 (AOCH2A), 4.3–4.7 (ANCH2A), 4.9–
5.2 (AOCH2Ph), 6.5–7.0 (ArH), 7.1–7.9 (ArH), 8.3–8.5
(C¼¼CH). UV–vis (THF, 0.02 mg/mL): kmax (nm): 459.
1H NMR (300 MHz, CDCl3, 298 K) d (ppm): 0.91 (br, s, 3H,
ACH3), 1.34 (br, s, 4H, ACH2CH2A), 1.46 (br, s, 2H, ACH2A),
1.78 (m, 2H, ACH2A), 3.00 (s, 1H, ACBCH), 3.93 (t, J ¼ 6.6
Hz, 2H, AOCH2A), 6.83 (d, J ¼ 8.1 Hz, 2H, ArH), 6.89 (d, J ¼
8.1 Hz, 2H, ArH), 6.98–7.1 (m, 5H, ArH), 7.21–7.31 (m, 4H,
ArH).
P4
End-capping group 4 (84 mg, 0.234 mmol). P4 was obtained
as red powder (103 mg, 71.4 %). Mw ¼ 2.53 ꢃ 105, Mw/Mn
¼ 1.53 (GPC, polystyrene calibration). IR (thin film), t
(cmꢀ1): 1517, 1340 (ANO2). 1H NMR (400 MHz, CDCl3, 298
K) d (ppm): 0.6–0.9 (ACH3), 1.0–1.4 (ACH2A), 1.6–2.2
(ACH2A), 2.6–3.0 (ACH2CA), 3.4–4.5 (ANCH2A and
AOCH2A), 6.4–6.9 (ArH), 7.0–8.0 (ArH and C¼¼CH), 8.3–8.5
(ArH). UV–vis (THF, 0.02 mg/mL): kmax (nm): 455.
6
Compound S11 (1.00 g, 2.40 mmol), KOH (0.40 g, 7.14
mmol). The crude product was purified by column chroma-
tography on silica gel using chloroform/petroleum ether (1/
2, V/V) as eluent to afford yellow oil (0.72 g, 83.9%).
1H NMR (300 MHz, CDCl3, 298 K) d (ppm): 0.76 (t, J ¼ 6.6
Hz, 6H, ACH3), 0.9–1.2 (m, 16H, A (CH2)4A), 1.94 (t, J ¼ 8.7
Hz, 4H, ACH2CA), 3.14 (s, 1H, ACBCH), 7.32 (s, 3H, ArH),
7.49 (m, 2H, ArH), 7.67 (m, 2H, ArH).
P5
End-capping group 5 (86 mg, 0.234 mmol). P5 was obtained
as red powder (130 mg, 80.2 %). Mw ¼ 2.33 ꢃ 105, Mw/Mn
¼ 1.71 (GPC, polystyrene calibration). IR (thin film), t
Synthesis of Hyperbranched Polymers P1–P6
Chromophore M2 (540 mg, 1.17 mmol) was dissolved in
DMF (60 mL) under an atmosphere of nitrogen, then the
aqueous solution of CuSO4 (1.5 mL, 0.04 M) and sodium
ascorbate (NaAsc; 1.5 mL, 0.08 M) was added, respectively.
After the reaction was stirred for 16 h at room temperature,
the reaction solution was divided into six equitable portions
in air. Then the prepared six end-capping groups 1–6 (0.234
mmol) were added, respectively, into the above six portion
of reaction mixture, and at the same time, another batch of
CuSO4 (85 lL, 0.04 M) and NaAsc (85 lL, 0.08 M) was also
added in each portion. The reaction mixture continued to
stir for 12 h. After that a large amount of methanol was
poured into the mixture. Then, the resultant mixture was fil-
tered, washed with acetone, and further purified by repreci-
1
(cmꢀ1): 1517, 1340 (ANO2). H NMR (400 M Hz, CDCl3, 298
K) d (ppm): 0.7–1.0 (ACH3), 1.2–1.5 (ACH2A), 1.6–2.0
(ACH2A), 2.0–2.2 (ACH2A), 2.7–3.0 (ACH2CA), 3.5–4.2
(ANCH2A and AOCH2A), 4.3–4.7 (ANCH2A), 6.4–7.2 (ArH),
7.3–7.9 (ArH and C¼¼CH). UV–vis (THF, 0.02 mg/mL): kmax
(nm): 457.
P6
End-capping group 6 (64 mg, 0.234 mmol). P6 was obtained
as red powder (128 mg, 80.0 %). Mw ¼ 2.06 ꢃ 105, Mw/Mn
¼ 1.81 (GPC, polystyrene calibration). IR (thin film), t
1
(cmꢀ1): 1513, 1340 (ANO2). H NMR (400 M Hz, CDCl3, 298
K) d (ppm): 0.5–0.7 (ACH3), 0.8–1.1 (ACH2A), 1.6–2.2
(ACH2A), 2.8–3.0 (ACH2CA), 3.6–4.2 (ANCH2A and
NONLINEAR OPTICAL HYPERBRANCHED POLYMERS, LI ET AL.
1981

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 1 Polymerization Results and Characterization Data of Polymers
f
g
d33
d33(1)
No.
Yield (%)
Mw ꢃ 105
Mw/Mn
Tg (ꢁC)
ls (lm)
(pm/V)
(pm/V)
Nh
Tp
a
a
b
c
Td (ꢁC)
d
Te (ꢁC)
e
i
P1
P2
P3
P4
P5
P6
HP2
a
86.1
90.9
90.4
71.4
80.2
80.0
80.8
2.09
2.02
2.13
2.53
2.33
2.06
2.59
1.64
1.48
1.49
1.53
1.71
1.81
1.57
112
NA
144
140
155
125
117
292
297
281
284
300
301
254
e
105
135
165
140
140
120
130
0.58
1.28
0.55
0.41
0.41
0.46
0.48
74.9
40.0
84.6
89.1
74.9
63.7
124.4
13.4
7.8
0.517
0.527
0.442
0.422
0.356
0.361
92
131
121
109
105
88
16.6
18.0
15.1
13.4
22.7
93
Determined by GPC in DMF on the basis of a polystyrene calibration.
Film thickness.
b
f
Glass transition temperature (Tg) of polymers detected by the DSC
Second harmonic generation (SHG) coefficient.
g
analyses under argon at a heating rate of 10 ꢁC/min.
c
The nonresonant d33 values calculated by using the approximate two-
The 5% weight loss temperature of polymers detected by the ther-
level model.
h
mogravimetric analyses under nitrogen at a heating rate of 10 ꢁC/min.
d
The effective loading density of chromophores.
i
The best poling temperature.
The onset temperature for decay. NA ¼ not obtained.
AOCH2A), 4.3–4.6 (ANCH2A), 6.5–6.9 (ArH), 7.3–8.0 (ArH
and C¼¼CH). UV–vis (THF, 0.02 mg/mL): kmax (nm): 456.
SHG signal of a Y-cut quartz crystal (Iq) was tested as the
reference. Then, the heating of the oven was stopped, and
the power of the laser was turned off.
Preparation of Polymer Thin Films
The polymers were dissolved in DMF (concentration ꢂ5 wt
%, for P1 and P3) or THF (concentration ꢂ3 wt %, for P4–
P6), and the resultant solutions were filtered through sy-
ringe filters. The polymer solutions were spin-coated onto
indium-tin-oxide (ITO)-coated glass substrates, which were
cleaned by N, N-dimethyformamide, acetone, distilled water,
and THF sequentially in ultrasonic bath before use. Residual
solvent was removed by heating the polymer films in a vac-
uum oven at 40 ꢁC. For P2, its thin films were prepared by
drop-coating method, due to its poor film-forming ability.
RESULTS AND DISCUSSION
Synthesis
End-capping groups 3–6 (Scheme 3), containing a terminal
alkyne group, were synthesized according to the literature
methods,61 whereas 1 and 2 were purchased from Alfa-
Aesar. As mentioned in the introduction part, the previous
literature has reported that the Cu(I)-catalyzed click poly-
merizations of the AB2 monomers failed to yield soluble
polymers, due to the self-oligomerization.31 Thus, the poly-
merization process should be handled very carefully. As
shown in Scheme 2, AB2-type polytriazoles P1–P6 could be
successfully prepared by adjusting the synthetic procedure
of the click reaction. At the first stage of the polymerization
process, the hyperbranched polymer intermediate HP-N3,
which possessed a large amount of unreacted azido groups
in the periphery, was synthesized, similar to that of HP2
reported in our previous work.32 At the second stage, the
reaction solution of HP-N3 was divided into six similar por-
tions, and the end-capping group (one of 1–6) and another
batch of catalysts were added into each portion, respectively,
to react with the peripheric azido groups in HP-N3. Gener-
ally, under normal polymerization process, six click reactions
would be needed to carry out; however, here, the prepara-
tion of these six hyperbranched polymers P1–P6 could be
achieved simultaneously through the postfunctional strategy
by using the same hyperbranched polymer intermediate. To
the best of our knowledge, this ‘‘one to six’’ route handled in
air with the usage of click reaction has not been reported
before, and its unique aspects should arise from the near-
perfect reliability of the Cu(I)-catalyzed click reaction
between azides and alkynes,21–28 which was not so sensitive
to water and oxygen. So, this route might not be suitable for
other reactions to prepare end-capping hyperbranched poly-
mers, such as Suzuki reaction, which should be protected
from oxygen, but perhaps only suitable for click reaction,
NLO Measurement of Poled Films
The second-order optical nonlinearity of the polymers was
determined by in situ second harmonic generation (SHG)
experiment using a closed temperature-controlled oven with
optical windows and three needle electrodes. The films were
kept at 45ꢁ to the incident beam and poled inside the oven,
and the SHG intensity was monitored simultaneously. Poling
conditions were as follows: temperature: different for each
polymer (Table 1); voltage: 7.7 kV at the needle point; gap
distance: 0.8 cm. The SHG measurements were carried out
with a Nd:YAG laser operating at a 10 Hz repetition rate and
an 8 ns pulse width at 1064 nm. A Y-cut quartz crystal
served as the reference.
General NLO Test Procedure
after the film was placed in the oven, the oven was heated
under the control of one computer, and the temperature
increased from room temperature to the predetermined one
(generally 10 ꢁC above the glass transition temperature). At
the same time, one beam of laser irradiated on the film to
produce the SHG signal, which was measured by an optical
power meter detector (Beijing Bingsong Photon Technologi-
cal Corporation, China). The detector was connected to a
computer, and there was a light filter in front of the detector,
only the light with the wavelength of 532 nm could be
collected. After the maximum signal (Is) was captured, the
1982
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
P1–P3 were conducted in DMSO-d6, whereas those of P4–P6
measured in chloroform-d, due to their good solubility. From
the 1H NMR spectra, it was easy to ensure the success of
polymerization. For example, in all the 1H NMR spectra,
there was a separate peak observed at 2.8 ppm, which
should be ascribed to the methylene groups bonding to the
carbon atom of the new formed triazole rings. Although in
the 1H NMR spectrum of M2, those methylene groups
bonded to terminal alkyne moieties appeared at about
2.5 ppm. Also, a new peak at 4.5 ppm appeared, which
should be assigned to the methylene groups bonding to the
nitrogen atom of the new formed triazole rings. Further-
more, in the spectra of P2 and P3, the triazole protons
became visible at about 8.4 ppm. The resonances associated
with end-capping groups could be also observed, for exam-
ple, many peaks in the region of 0.5ꢂ2.0 ppm (A(CH2)5CH3)
in the spectra of P1 and P4–P6; one separate peak at 5.1
ppm (AOCH2Ph) in the spectrum of P3; one separate peak
at 8.4 ppm (8-ArH in carbazole) in the spectrum of P4.
FIGURE 1 The 1H NMR spectra of hyperbranched polymers P1–
P3, conducted in DMSO-d6. The solvent peaks were marked
with asterisks (*). [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com.]
The molecular weights of P1–P6 were determined by GPC
with DMF as an eluent and polystyrene standards as cali-
bration standards. As shown in Table 1 and experimental
section, these six hyperbranched polymers possessed high
molecular weights (up to 2.53 ꢃ 105). Thus, the polymeriza-
tion method reported here was successful in constructing
hyperbranched polymeric structures with high molecular
weights and good solubility from AB2 monomers through the
click reaction. Moreover, as derived from the same interme-
diate HP-N3, they possessed similar molecular weights,
which would facilitate the comparison of their properties on
the same level, indicating the superiority of the synthetic
route used in this article. The temperature for 5 wt % loss
has often been used as a degradation temperature (Td) to
estimate thermal stability of a synthetic polymer. Here, as
due to its several advantage (quantitative yields, mild reac-
tion conditions, broad tolerance toward functional groups,
low susceptibility to side reactions, and simple product isola-
tion). Thus, the overall synthetic route was very simple and
efficient, in which different functional end-capping groups
could be easily introduced. So, our preliminary results con-
firmed the reproducibility and reliability of the controllable
synthetic process for the hyperbranched polymers from AB2
monomers through the Cu(I)-catalyzed click polymerization
by modifying the synthetic procedure and using end-capping
groups.32 Moreover, it should be pointed out that the size of
end-capping groups was adjusted from small (Hx) to larger
(Flu); thus, we could investigate the influence of different
end-capping isolation groups in different size on the proper-
ties of the resultant hyperbranched polymers at the same
level, because all the polymers P1–P6 were derived from the
same hyperbranched polymer intermediate HP-N3.
Structural Characterization
The polymers were characterized by spectroscopic methods,
and all gave satisfactory data (see Experimental Section, the
Supporting Information and Table 1 for the detailed analysis
data). Supporting Information Figure S1 showed the IR spec-
tra of P1–P6, the absorption bands associated with the nitro
groups were at about 1520 and 1340 cmꢀ1. It was easily
seen that the peak at 2095 cmꢀ1, associated with azido
groups, disappeared, indicating that the end-capping reaction
conducted completely, thanks to the powerful click reaction.
Actually, in the polymerization process, we could monitor
the reaction by using the IR spectra of the reaction mixture,
and when the absorption peak of the azido groups at about
2095 cmꢀ1 disappeared, the reaction should be terminated.
FIGURE 2 The 1H NMR spectra of hyperbranched polymers P4–
P6, conducted in chloroform-d. The solvent peaks were marked
with asterisks (*). [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com.]
In all the 1H NMR spectra of the polymers (Figs. 1 and 2),
the chemical shifts were consistent with the polymer struc-
tures as demonstrated in Scheme 2. The 1H NMR spectra of
NONLINEAR OPTICAL HYPERBRANCHED POLYMERS, LI ET AL.
1983

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 3 The Maximum Absorption Wavelength of Polymers
(0.02 mg/mL) (kmax, nm)
THF
1,4-dioxane
CHCl3
DMF
DMSO
HP2
P1
P2
P3
P4
P5
P6
464
459
458
459
455
456
457
470
464
463
467
457
453
454
465
452
475
470
468
469
469
469
469
484
476
474
475
475
476
476
455
453
452
451
The UV–vis absorption spectra of the hyperbranched polymers
in different solvents were tested, and their maximum absorp-
tion wavelength for the p–p* transition of the azo moieties in
them were listed in the Experimental section and Table 3. Fig-
ure 4 showed the UV–vis spectra of the hyperbranched poly-
mers in chloroform. Our previous work has demonstrated that
the [1,2,3]-triazole rings surrounding the chromophore moi-
eties could act as suitable isolation moieties, leading to the
effective site-isolation effect.62,63 Here, similar results were
obtained, and better effective site-isolation effect could be
achieved in P1–P6 than that in HP2. As shown in Table 3, all
of P1–P6 exhibited blue-shifted maximum absorption wave-
length in comparison with HP2 in each solvent, for example,
the blue-shifted extent was as large as 14 nm in chloroform in
the case of P6. As demonstrated in Scheme 1, there were also
many newly formed triazole rings present in the interior
architecture of HP2, and the only difference among P1–P6
and HP2 was the different end-capping moieties introduced to
their periphery: in HP2, azo chromophores were utilized as
the end-capping groups (Scheme 1), whereas in P1–P6, differ-
ent isolation groups in different size (1–6) acted as the end-
FIGURE 3 Thermogravimetric analysis thermograms of P1–P6,
measured in nitrogen at a heating rate of 10 ꢁC/min. [Color fig-
ure can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
shown in Figure 3, all of the Td values for P1–P6 were
ꢁ
higher than 280 C, demonstrating that these polymers were
thermally stable, much better than HP2. The glass transition
temperature (Tg) of the polymers were also investigated and
summarized in Table 1. Most of P1–P6 demonstrated higher
Tgs than HP2, confirmed the importance of the introduced
peripheral groups. Also, the high Tgs would lead to the better
thermal stabilities of their NLO effects.
The solubility of the hyperbranched polytriazoles in various
solvents was summarized in Table 2. It was reported that
the solubility properties of dendritic mocromolecules was
dominated by their periphery, and here, really, six hyper-
branched polymers exhibited different solubility in organic
solvents, due to their different end-capping isolation groups.
As shown in Table 2, all the polymers were soluble in DMF
and DMSO at room temperature, however, they displayed dif-
ferent solubility in other three solvents, including THF, 1,4-
dioxane and chloroform. For example, in comparison with
P1–P3, P4–P6 showed much better solubility in chloroform.
TABLE 2 The Solubility of Polymers in Different
Organic Solvents
THF
1,4-dioxane
CHCl3
DMF
DMSO
P1
P2
P3
P4
P5
P6
þꢀ
–
þꢀ
ꢀ
–
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
ꢀꢀ
–
–
–
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
FIGURE 4 UV–vis spectra of polymers in chloroform (0.02 mg/
mL). [Color figure can be viewed in the online issue, which is
available at wileyonlinelibrary.com.]
(þþ): soluble at room temperature; (þꢀ): partially soluble; (ꢀ): slight
soluble; (ꢀꢀ): insoluble.
1984
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
capping ones (Chart S2). Thus, in comparison with that of
HP2, the blue-shifted maximum absorption wavelengths of
P1–P6 should be attributed to the presence of lots of end-cap-
ping bulky groups, which nearly connected the primary inter-
face between the hyperbranched polymers and the environ-
ment. This was reasonable. As mentioned in the introduction
part, some properties of hyperbranched polymers were domi-
nated by the nature of their large amount of end groups in the
periphery,46–52 similar to those in dendrimers,6 the different
absorption behavior of P1–P6 just proved this point on one
aspect.
NLO Properties
To evaluate the NLO activity of the polymers, their poled
thin films were prepared. In our previous work,32 both of
HP1 and HP2 exhibited bad processability, and they could
not form high-quality thin films through spin-coating. In this
article, by the introduction of different bulky groups into
the periphery of the hyperbranched polymers according
to the concept of ‘‘suitable isolation group,’’ we expected that
the processability of P1–P6 should be improved. Fortunately,
the obtained results were consistent with our original idea.
P1–P6 exhibited different processability, caused by their dif-
ferent peripheral groups: P1–P3 could not form good films
just as HP2 (the films of P2 were prepared through drop-
coating); however, P4–P6 showed much better processability
while the end-capping groups were much bulky. This con-
firmed that the introduction of bulky isolation groups to the
periphery of the hyperbranched polymers really improved
their processability as found in our previous cases.42–45
FIGURE 5 (A) Comparison of the d33 values of the polymers,
using P1 as reference. (B) Comparison of the calculated d33 val-
ues, which were obtained by using the tested d33 values of the
polymers divided by the concentration of the active chromo-
phore moieties of the polymers, using that of P1 as reference.
groups in comparison with other groups. However, the
enhanced extent was not larger as high as those in our pre-
vious work: compared with that of P1 with Hx as isolation
groups, the d33 value of P4 with Car as isolation groups was
only enhanced 14.2 pm/V. This was understandable: the
formed triazole rings in the polymerization process have
already acted as good isolation groups to isolate the chromo-
phore moieties effectively and contribute to the decrease of
the strong interactions.62,63 Thus, further adjusting the size
of periphery groups would not improve the poling efficiency
of the resultant polymers in a large degree, but on the
contrary, reduce the loading density of the chromophore
moieties (leading to the decrease of d33 values). Thus, we
used the tested d33 values divided by the molar concentra-
tions of the active chromophore moieties (Table 1), and
compared the calculated results again with that of P1 as the
reference (curve B in Fig. 5). Now, the curve still demon-
strated that the isolation groups (Car) in P4 were the suita-
ble ones (1.46 times that of P1). P5 showed a similar value
as P4 (curve B of Fig. 5). The nonplanar structure of triphe-
nylamine moieties in P5 could suppress the strong electronic
interactions of the peripheral chromophores much efficiently
as Car, but because of the bigger bulk of Tri in comparison
with Car, the concentrations of the active chromophore moi-
eties in P5 decreased in a relatively larger degree, leading to
the smaller d33 value as presented in curve A of Fig. 5. After
deducting the influence of the concentration of the active
chromophore moieties, the calculated value of P5 was
similar as that of P4. However, further increasing the bulk
of the isolation group, the poling efficiency might decrease
according to the concept of ‘‘suitable isolation group,’’ result-
ing in the decreased NLO effect.
The most convenient technique to study the second-order
NLO activity was to investigate the second harmonic genera-
tion (SHG) processes characterized by d33, an SHG coeffi-
cient. The method for the calculation of the SHG coefficients
(d33) for the poled films has been reported in our previous
articles.64–69 From the experimental data, the d33 values of
P1–P6 were calculated at 1064-nm fundamental wavelength.
Here, according to the concept of ‘‘suitable isolation groups’’:
for a given chromophore moiety and given linkage position,
there should be a suitable isolation group present to boost
its microscopic b value to possible higher macroscopic NLO
property efficiently, we introduced different isolation groups
from small size (Hx) to larger one (Flu), to end-cap the pe-
ripheral azide groups in the polymer intermediate HP-N3,
and study whether there might be suitable end-capping
groups to balance the processability and NLO properties of
the resultant hyperbranched polymers. As shown in Table 1,
these AB2-type hyperbranched polymers P1–P6 exhibited
different d33 values while the size of end-capping groups
enlarged. P2 demonstrated a lowest d33 value (40.0 pm/V).
This should be due to the big film thickness (up to 1.28 lm),
which directly led to its bad poling efficiency.
To study their NLO results more visually, the curve A in
Figure 5 showed the comparison of the d33 values of the
polymers, using P1 as reference. It was easily seen that the
d33 values were not always increasing as the isolation groups
enlarging, and Car moieties were much suitable isolation
NONLINEAR OPTICAL HYPERBRANCHED POLYMERS, LI ET AL.
1985

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
temporal stabilities, with their onset temperatures for decays
of 109 and 105 ꢁC, respectively. Thus, the results indicated
the importance of the adjustment of peripheral groups,
which provided a new approach to yield hyperbranched
polymers with excellent temporal stability.
CONCLUSIONS
In this article, six new AB2-type polytriazoles containing azo-
chromophores, derived from the same hyperbranched poly-
mer intermediate, were successfully prepared through click
reaction under copper(I) catalysis, by modifying the synthetic
route. Because of the near-perfect reliability of click reaction,
the bulky groups in different size could be easily introduced to
end-cap the peripheral azide groups in the polymer intermedi-
ate HP-N3, to yield P1–P6 with different solubility, process-
ability, and optic-physical properties. The NLO effects of P1–
P6 were different, well in accordance with the different size of
end-capping groups, and Car moieties were demonstrated to
be the suitable isolation groups. Also, the end-capping groups
could influence the temporal stabilities of P1–P6, and the
highest onset temperatures for decays were up to 131 ꢁC.
These results, coupled with their good NLO effects, made them
good candidates for the practical photonic applications.
FIGURE 6 Decay curves of SHG coefficient of P1–P6 and HP2
as a function of temperature.
All the tested d33 values of P1–P6 were not higher than that
of HP2, this should be attributed to the decrease of the load-
ing density of chromophore moieties (the labeled part in the
structure of hyperbranched polymers in Scheme 2) of in
these polymers. After a large amount of bulky groups intro-
duced in the periphery of P1–P6, their effective chromo-
phore density reduced dramatically. For example, the effec-
tive chromophores density of P4 was only 0.422, whereas
that of HP2 was up to 0.703. But, the processability and
solubility of the hyperbranched polymers with bulky groups
introduced in the periphery (i.e., P4–6) was improved in a
large degree. Thus, there should be a balance between the
NLO performance and the processability. By utilizing the
concept of ‘‘suitable isolation group,’’ the balanceable point
could be found. Therefore, according to the practical require-
ments, we could regulate the performance of the designed
polymers by adjusting the subtle structure according to the
concept of ‘‘suitable isolation group.’’
The authors are grateful to the National Science Foundation of
China (no. 21034006) and the program of NCET for financial
support.
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