Preparation of neutrally colorless, transparent polynorbornenes with multiple redox-active chromophores via ring-opening metathesis polymerization toward electrochromic applications

Article abstract of DOI:10.1002/pola.24760

A new electrochromic norbornene derivative containing triphenylamine groups (NBDTPAC8) was synthesized using norbornene amine and bromotriphenylamine. NBDTPAC8 was used in ring-opening metathesis polymerization to obtain poly(NBDTPAC8) using different Gru

Full text of DOI:10.1002/pola.24760

Preparation of Neutrally Colorless, Transparent Polynorbornenes with
Multiple Redox-Active Chromophores via Ring-Opening Metathesis
Polymerization Toward Electrochromic Applications
WEI-REN LIAN,1 KUN-LI WANG,2 JYH-CHIANG JIANG,1 DER-JANG LIAW,1 KUEIR-RARN LEE,3 JUIN-YIH LAI3
1Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan
2Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, Taipei 10608, Taiwan
3R&D Center for Membrane Technology, Department of Chemical Engineering, Chung Yuan University, Chung-Li 32023, Taiwan
Received 5 March 2011; accepted 30 April 2011
DOI: 10.1002/pola.24760
Published online 31 May 2011 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: A new electrochromic norbornene derivative contain-
ing triphenylamine groups (NBDTPAC8) was synthesized using
norbornene amine and bromotriphenylamine. NBDTPAC8 was
used in ring-opening metathesis polymerization to obtain poly
(NBDTPAC8) using different Grubbs’ catalysts and followed by
hydrogen reduction to obtain poly(HNBDTPAC8). The glass tran-
sition temperatures (Tg) of poly(NBDTPAC8) and hydrogenated
poly(HNBDTPAC8) were 132 and 89 ꢀC, respectively. Poly
(HNBDTPAC8) film exhibited a fluorescence maximum around
416 nm with a quantum yield of up to 60%. Hydrogenated poly
(HNBDTPAC8) film showed excellent transparency (up to 93%).
Poly(HNBDTPAC8) showed cyclic voltammetric and electrochro-
mic behaviors similar to those of poly(NBDTPAC8). The cyclic
voltammogram of a poly(HNBDTPAC8) film cast onto an indium
tin oxide (ITO)-coated glass substrate exhibited three reversible
oxidation redox couples at 0.69, 0.94 and 1.38 V versus Ag/Agþ
in an acetonitrile solution. The electrochromic characteristics of
poly(HNBDTPAC8) showed excellent stability and reversibility,
with multi-staged color changes from its colorless neutral form
to green, light blue and dark blue upon the application of poten-
tials ranging from 0 to 1.60 V. The color switching time and
bleaching time of the poly(HNBDTPAC8) film were 6.2 s and 4.3
C
V
s at 1175 nm and 6.6 s and 4.4 s at 970 nm, respectively. 2011
Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 3248–
3259, 2011
KEYWORDS: functionalization of polymers; redox polymers;
ROMP; simulations; synthesis; transparency
INTRODUCTION Electrochromism (EC) results from the gen-
eration of different electronic absorption bands that corre-
spond to changes between at least two states. In most cases,
EC occurs by reduction–oxidation (redox) reactions.1 Non-
redox EC is also possible for some polarizable molecules that
exhibit a spectroscopic shift on the application of a strong
electric field, which is known as the Stark effect.2 Devices
that make use of electrochromic technology include smart
windows,3 electrochromic displays,4 and electrochromic
mirrors.5
organic solvents, which limit their widespread applica-
tion.17,18 In addition, polyimides intrinsically exhibit color
due to their strong charge transfer complex. Colored poly-
mers are not preferred as electrochromic materials, and
native color is one of the disadvantages for the practical use
of these kinds of polymers in optical devices. Colorless elec-
trochromic polymers are generally important, but their use
is not common.19–21 A large difference in transmittance
between colorless and colored states is desirable for electro-
chromic materials, because it provides high contrast.
The electrochromic effect occurs in many inorganic materi-
als, such as transition metal oxides6 and mixed-valence metal
complexes,7 as well as in organic materials, such as
polyimides,8,9 polyamides,10 and conjugated polymers.11–14
Inorganic electrochromic materials suffer from processing
and performance problems.15 For example, inorganic oxides
typically require more than 60 s to switch states.16
On the other hand, it is well known that norbornene-based
polymers are colorless, amorphous, and readily solution-
processable polymers with high thermal stability and optical
transparency.22–25 Ring-opening metathesis polymerization
(ROMP) offers an effective way to polymerize norbornene
monomers with different side chain substitutes.26 Grubbs’
ruthenium (Ru) carbene complexes efficiently catalyze ROMP
under ambient conditions, with a high tolerance for polar
functional groups.27–32 Thus, the use of a Ru-based catalyst
in ROMP is a promising route to prepare polynorbornenes
Normally, most polyamides and polyimides have traditionally
been difficult to process by spin coating because of their
high glass transition temperatures and poor solubility in
Additional Supporting Information may be found in the online version of this article. Correspondence to: D.-J. Liaw (E-mail: liawdj@mail.ntust.edu.
tw or liawdj@gmail.com or liawdj@ntu.edu.tw or liawdj@yahoo.com.tw)
C
V
Journal of Polymer Science Part A: Polymer Chemistry, Vol. 49, 3248–3259 (2011) 2011 Wiley Periodicals, Inc.
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with colorless, transparent, and easily solution-processable
properties.
meation chromatography (GPC). Five Waters (Ultrastyragel)
columns 300 ꢁ 7.7 mm (guard, 500, 103, 104, and 105 Å in
a series) were used for GPC analysis with THF (1 mL minꢂ1
)
Triphenylamine (TPA) derivatives have shown excellent ther-
mal, electrochemical stability, electron-donating ability, and
optoelectronic properties.33 They have been used as
advanced materials for polymer memories,34–41 electrolumi-
nescence,42 chemosensor application,43,44 and electro-optical
devices.45 However, the oxidation of TPA may undergo the
undesirable radical cation dimerization of the TPA moieties
to produce tetraphenylbenzidine.46 The addition of electron-
donating substituents, such as an alkyl group at the para-
position of the phenyl group of the TPA structure, could
prevent coupling reactions and afford stable coloration.47
Because of their noticeable change in coloration, TPA deriva-
tives are regarded as good electrochromic materials.48–51 To
the best of our knowledge, there has been no report about
electrochromic materials based on polynorbornene deriva-
tives with TPA pendant groups.
as an eluent. The eluents were monitored with a refractive
index detector (RI 2000). Polystyrene was used as a stand-
ard. Cyclic voltammetry (CV) was performed with a CHI
model 619A with indium tin oxide (ITO) used as a working
electrode and a platinum wire as an auxiliary electrode at a
scan rate of 50 mV sꢂ1 against an Ag/Agþ reference elec-
trode in a solution of 0.1 M tetrabutylammonium perchlorate
(TBAP)/acetonitrile (CH3CN). The spectroelectrochemical cell
was composed of a 1-cm cuvette, ITO as a working electrode,
a platinum wire as an auxiliary electrode, and a Ag/Agþ ref-
erence electrode. The UV–vis spectra of the polymer films or
solutions were recorded on a JASCO V-550 spectrophotome-
ter at room temperature in air. Elemental analyses were per-
1
formed on a PerkinElmer 2400 C, H, and N analyzer. H and
13C NMR spectra were recorded on a Bruker DRX-500 instru-
ment operating at 500 MHz for protons and 125 MHz for
carbon. The melting temperature (Tm) and glass transition
temperature (Tg) were measured on a DuPont 9000 differen-
tial scanning calorimeteꢂr1(TA Instruments TA 910) at a heat-
In this study, we prepared a colorless, transparent polynor-
bornene derivative containing electron-donating 2,4,4-trime-
thylpentan-2-yl substituted TPA with high molecular weights
and low polydispersity indices via ROMP and then per-
formed hydrogenation to afford saturated polynorbornene.
The introduction of electron-donating 2,4,4-trimethylpentan-
2-yl substituent is expected to prevent coupling reactions
and lower the oxidation potentials/switching voltage.13 The
basic properties of unsaturated polynorbornene and satu-
rated polynorbornene, such as solubility, thermal properties,
optical properties, electrochemical properties, and electro-
chromic properties, are discussed in this investigation.
ing rate of 10 ꢀC min
under a steady flow of nitrogen.
Thermogravimetric data were obtained on a PerkinElmer
TG/DTA (Diamond TG/DTA). Experiments were performed
on 3–5-mg samples at a heating rate of 10 ꢀC minꢂ1 under
nitrogen- or air-flow conditions (20 cm3 minꢂ1).
Synthesis of 4-Bromo-N,N-bis(4-(2,4,4-trimethylpentan-2-
yl)phenyl)benzene-amine
Sodium tert-butoxide (8.2 g, 86 mmol), DPPF (0.27 g, 4.9 ꢁ
10ꢂ2 mmol), dibromobenzene (8.7 g, 36 mmol), bis(4-(2,4,4-
trimethylpentan-2-yl)phenyl)amine (9.4 g, 24 mmol), and pal-
ladium acetate (0.11 g, 4.8 ꢁ 10ꢂ1 mmol) were dissolved in
100 mL of dry toluene. The mixture was heated, stirred at 120
ꢀC for 7 h, and kept under a nitrogen atmosphere. Thereafter,
the solvent was evaporated under reduced pressure. The
product was purified by silica gel column chromatography by
hexane and recrystallized from n-hexane to afford white crys-
tals, 4-bromo-N,N-bis(4-(2,4,4-trimethylpentan-2-yl)phenyl)-
benzeneamine (Scheme 1, OTPA) at a 60% yield; mp 101–102
EXPERIMENTAL
Materials
Dicyclopentadiene and allyl amine were purchased from
Merck. Palladium acetate, sodium tert-butoxide, tri-tert-butyl-
phosphine, and 1,4-dibromobenzene were purchased from
Aldrich and used without further purification. Catalysts Ru
(G1), Ru (G2), and Ru (G3) were obtained from Sigma-Aldrich,
and 2,6-di-tert-butyl-4-methylphenol, p-toluenesulfonylhydra-
zide, and 1,10-bis(diphenylphosphino)-ferrocene (DPPF) were
purchased from Acros. The synthesis of 5-(amino methyl)
bicyclo[2.2.1] hept-2-ene (NBMA, bp: 60–61 ꢀC/11 mmHg)
was accomplished via the Diels–Alder reaction of freshly
cracked cyclopentadiene and allyl amine according to the pub-
lished literature.52,53 Bis(4-(2,4,4-trimethylpentan-2-yl)phe-
nyl)amine was purchased from OUCHI SHINKO and was
ꢀC by DSC (10 C minꢂ1). IR (KBr pellet, cmꢂ1): 3041 (CAH,
ꢀ
aromatic stretching), 1045 (CABr, aryl bromide).
1H NMR (500 MHz, CDCl3): d (ppm) ¼ 0.81 (s, 18H, H1);
1.42 (s, 12H, H3); 1.79 (s, 4H, H2); 6.91–6.92 (d, J ¼ 7.70 Hz,
2H, H6); 6.98–7.00 (d, J ¼ 7.13 Hz, 4H, H5); 7.25–7.27 (d, J
¼ 7.32 Hz, 4H, H4); 7.29–7.31 (d, J ¼ 7.50 Hz, 2H, H7). 13C
NMR (CDCl3): (ppm) ¼ 31.74 (Ce), 31.94 (Ca), 32.20 (Cb),
38.19 (Cd), 57.15 (Cc), 113.67 (Cj), 123.93 (Ch), 124.27 (Ck),
127.04 (Cg), 131.90 (Cl), 144.53 (Ci), 144.93 (Cf), 147.37
(Cm). ELEM ANAL. Calcd. for C34H46BrN : C, 74.43%; H, 8.45%;
N, 2.55%. Found: C, 74.33%; H, 8.47%; N, 2.46%.
ꢀ
recrystallized by ethanol (mp: 105–106 C). The polymeriza-
tion solvent, tetrahydrofuran (THF), was dried over sodium
metal and distilled before use. Solvents such as xylene and
benzene were purified by normal procedures and handled
under a moisture-free atmosphere.
Measurements
Synthesis of Norbornene Monomer with Triphenylamine
Side Groups
High-resolution mass spectrum was recorded using a VG
Platform Electrospray electronspray ionization (ESI)/MS
apparatus in ESI mode. Weight-average (Mw) and number-
average (Mn) molecular weights were determined by gel per-
Palladium acetate (4 mg, 2 ꢁ 10ꢂ2 mmol), NBMA (0.16 g,
1.3 mmol), 4-bromo-N,N-bis(4-(2,4,4-trimethylpentan-2-yl)
phenyl)benzenamine (Scheme 1, OTPA) (1.59 g, 2.90 mmol),
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 1 Synthesis of the norbornene monomer (NBDTPAC8) containing triphenylamine structures.
tri-tert-butylphosphine (10 mg, 4 ꢁ 10ꢂ2 mmol), and sodium
tert-butoxide (0.78 g, 8 mmol) were dissolved in 100 mL of
dry toluene. The reaction mixture was warmed to 110 ꢀC for 5
h and kept under a nitrogen atmosphere. After the completion
of the reaction, the solvent was removed under reduced pres-
sure, and the residual was extracted with ether/water. The col-
lected organic layer was dried over magnesium sulfate
(MgSO4) overnight and then filtered to remove MgSO4. After
removing the solvent of the filtrate, the residue was purified
by silica gel column chromatography (hexane) to obtain a
white solid. Yields: 50%; mp: 120–122 ꢀC by DSC (10 ꢀC
minꢂ1). IR (KBr pellet, cmꢂ1): 3040 (CAH, aromatic stretch-
ing), 1620 (C¼¼C, cyclic alkene).
in 4 mL of anhydrous THF and then degassed via freeze-
pump-thaw cycles. A catalyst solution was prepared by dis-
solving Ru (G3) (0.3 mg, 4 ꢁ 10ꢂ4 mmol) in 0.5 mL of anhy-
drous THF in an argon-filled drybox. After degassing the
monomer solution completely, the catalyst solution was
injected into the monomer solutꢀion by a syringe. The poly-
merization was performed at 25 C for 1 h. The reaction was
terminated by the addition of a small amount of ethyl vinyl
ether (0.2 mL). Poly(NBDTPAC8) was obtained by precipita-
tion in excess methanol and was further purified by dissolv-
ing in benzene and reprecipitating in methanol. Poly
(NBDTPAC8) dissolved in benzene was filtered, frozen, and
dried. The yield of poly(NBDTPAC8) was 80%. The polymer-
izations of monomer NBDTPAC8 with the catalysts Ru (G1)
and Ru (G2) were performed in the same manner. IR (KBr
pellet, cmꢂ1): 1292 (CAN, aromatic amine), 1610 (C¼¼C,
cyclic alkene), 3036 (CAH, aromatic stretching).
1H NMR (500 MHz, THF-d8): d (ppm) ¼ 0.55–0.60 (t, J ¼ 7.11
Hz, 1H, Hn6n), 0.68–0.80 (s, 72H, H15), 1.23–1.35 (m, 5H, Hx7s
,
H
H
H
x7a, Hn7s, Hn7a, and Hx6x), 1.38–1.42 (m, 50H, H13, Hx5, and
x6n), 1.69–1.77 (s, 16H, H14), 1.84–1.91 (t, J ¼ 7.33 Hz, 1H,
n6x), 2.52–2.61 (s, 1H, Hn5), 2.73–2.78 (s, 1H, Hn1), 2.77–2.88
1H NMR (500 MHz, THF-d8): d (ppm) ¼ 0.64–3.17 (m, 7H,
H1 and H4–7), 0.75–1.73 (m, 68H, H13–15), 3.42–3.75 (d, 2H, J
¼ 8.65 Hz, H8), 5.31–5.42 (m, 2H, H2–3), 6.79–7.14 (m, 24H,
(m, 3H, Hx4, Hx1, and Hn4), 3.34–3.47 (m, 2H, Hn8), 3.62–3.72
(m, 2H, Hx8), 5.72–5.74 (t, J ¼ 7.90 Hz, 1H, Hn2), 6.07–6.08 (m,
2H, Hx2, and Hx3), 6.11–6.13 (t, J ¼ 7.85 Hz, 1H, Hn3) 6.85–
7.28 (m, 48H, H9–12). 13C NMR (THF-d8): d (ppm) ¼ 25.50
(C13), 27.88 (Cx7), 28.00 (Cn7), 30.76 (C20) 31.08 (C21), 31.19
(Cx5), 32.26 (C15), 33.09 (Cn6), 38.85 (Cn4), 39.00 (Cn5), 43.02
(Cx4), 43.33 (Cn1), 46.01 (Cx1), 50.88 (Cx6), 57.98 (Cn8), 58.02
(C14), 58.21 (Cx8), 122.60 (C9), 123.80 (C11), 126.00 (C10),
H
9–12). 13C NMR (THF-d8): d (ppm) ¼ 24.03 (C13), 27.32–
46.32 (C1, C4AC7, C15, C20, and C21), 55.76 (C8), 58.01 (C14),
122.21–129.03 (C2–3 and C9AC12), 142.32–146.78 (C16AC19).
ANAL. Calcd. for (C76H103N3)n: C, 86.22%; H, 9.81%; N,
3.97%. Found: C, 86.55%; H, 9.65%; N, 3.80%.
Synthesis of Poly(HNBDTPAC8) Using Hydrogenated Agent
The polymer poly(NBDTPAC8) (1.26 g, 1.2 mmol) was
dissolved in 8 mL of xylene in a Schlenk tube. To the above so-
lution, 1.64 g (8.8 mmol) of hydrogenating agent, p-toluenesul-
fonhydrazide (7.3 equiv relative to the repeating unit), and a
trace amount of 2,6-di-tert-butyl-4-methylphenol (inhibitor)
were added. The polymer solution with hydrogenating agent
was then degassed three times via a freeze-pump-thaw cycle
127.92 (C12), 133.85 (Cn2), 134.21 (Cx2 and Cx3), 137.94 (Cn3
)
and 142.37, 144.31, 144.94 and 146.49 (C16, C17, C18 and C19).
ELEM ANAL. Calcd. for C76H103N3: C, 86.22%; H, 9.81%; N,
3.97%. Found: C, 86.35%; H, 9.75%; N, 3.90%. High resolution
electrospray ionization mass (HRESIMS): m/z 1058.8272
[MþH]þ (calcd for C76H104N3þ, 1058.8230, þ3.59 ppm).
Synthesis of Poly(NBDTPAC8) Using Ring-Opening
Metathesis Polymerization
ꢀ
and sealed. The solution was stirred at 120 C for 12 h until
The monomer, norbornene derivative containing triphenyl-
amine groups (NBDTPAC8; 0.42 g, 0.4 mmol), was dissolved
the evolution of nitrogen stopped. The hydrogenated polymer
poly(HNBDTPAC8) was obtained by precipitation in excess
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FIGURE 1 (A) 1H NMR spectrum of OTPA (with CDCl3 as the solvent) and (B) 13C NMR spectrum of OTPA (with CDCl3 as the
solvent).
methanol and was further purified by dissolving in benzene
and reprecipitating in methanol. Poly(HNBDTPAC8) dissolved
in benzene was filtered, frozen, and dried. The yield of hydro-
genated polymer poly(HNBDTPAC8) was 90%. IR (KBr pellet,
cmꢂ1): 1282 (CAN, aromatic amine), 3040 (CAH, aromatic
stretching).
shown in Figure 2(A). Elemental analysis and the NMR spec-
tra clearly confirm that the compounds OTPA and NBDTPAC8
are consistent with the proposed structures. The ROMP of
NBDTPAC8 using different Grubbs’ catalysts is shown in
Scheme 2. The polymerization using different Grubbs’
catalysts was performed for 1 h. After the polymerization was
finished, the vinylic proton peaks of NBDTPAC8 at 5.70–6.13
ppm disappeared in the 1H NMR spectrum of poly
(NBDTPAC8), as shown in Figure 3(A). Then, new vinyl pro-
tons appeared as broad signals between 5.11 and 5.55 ppm
due to the double bond in the polymer main chain. The cis/
trans ratio of this polymer is roughly estimated to be 35/65
from the broad signals. The broad signal is due to the compli-
cated overlap of vinylic protons of the cis and transconfigura-
tions in the ring-opened poly(NBDTPA). The 13C NMR spec-
trum of poly(NBDTPAC8) is complex, with many overlapping
multiple or broad unresolved peaks, and it is impossible to
interpret them in terms of microstructural detail, as is often
the case for polymers produced by ROMP.54 In the 13C NMR
spectrum [Fig. 3(B)], the weak unresolved signals at 30–42
ppm are ascribed to the cyclic norbornene structure of the
polymer. The weak unresolved signals are due to the possibil-
ity of head–tail additions and cis- and trans-vinylene forms.
Poly(NBDTPAC8) was reduced using a hydrogenating agent to
obtain poly(HNBDTPAC8). The 1H and 13C NMR spectra of
poly(HNBDTPAC8) are shown in Figure 4. In Figure 4(A), the
aromatic resonance signals of poly(HNBDTPAC8) between d
(ppm) 6.71 and 7.41 still appear, which indicates that the
remaining TPA side groups and the resonance signals of ole-
finic protons of poly(NBDTPAC8) between d (ppm) 5.11 and
1H NMR (500 MHz, THF-d8): d (ppm) ¼ 0.75–2.70 (m, 11H,
H
1–7), 0.77–1.77 (m, 68H, H13–15), 3.48–3.78 (d, 2H, J ¼ 8.75
Hz, H8), 6.74–7.37 (m, 24H, H9–12). 13C NMR (THF-d8): d
(ppm) ¼ 21.44–21.95 (C2 and C3), 26.12 (C13), 30.23–43.11
(C1, C4AC7, C15, C20, and C21), 54.73 (C8), 58.04 (C14),
127.76–131.21 (C9AC12), 142.08–147.11 (C16AC19). ANAL.
Calcd. for (C76H105N3)n: C, 86.06%; H, 9.98%; N, 3.96%.
Found: C, 85.85%; H, 9.88%; N, 4.27%.
RESULTS AND DISCUSSION
Synthesis and Characterization
The norbornene derivative (NBDTPAC8) was successfully syn-
thesized by the Buchwald–Hartwig reaction with 4-bromo-
N,N-bis(4-(2,4,4-trimethylpentan-2-yl)-phenyl)benzenamine
(Scheme 1, OTPA) and 5-(amino methyl)bicyclo[2.2.1]hept-2-
ene. The synthesis procedures of norbornene monomer
(NBDTPAC8) containing TPA structures are outlined in
Scheme 1. OTPA and NBDTPAC8 (Scheme 1) were character-
1
ized by elemental analysis, H and 13C NMR and two-dimen-
1
sional NMR techniques. The H NMR and 13C NMR spectra of
the OTPA and NBDTPAC8 are shown in the Figures 1 and 2,
respectively. The ratio of NBDTPAC8 endoisomers and
exoisomers was calculated to be 10:1 from the NMR spectrum
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 2 (A) 1H NMR and (B) 13C NMR spectra of NBDTPAC8 in THF-d8. [Color figure can be viewed in the online issue, which is
available at wileyonlinelibrary.com.]
5.55 disappear completely. The 1H and 13C NMR spectra of
poly (HNBDTPAC8) are consistent with the proposed struc-
ture shown in Figure 4.
The ROMP of NBDTPAC8 using Ru (G1) was attempted but
suffered from poor initiation and lower activity.55 Ru (G2)
exhibited good activity with respect to the polymerization of
SCHEME 2 Preparation of polynorbornenes, poly(NBDTPAC8), and poly(HNBDTPAC8).
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ARTICLE
FIGURE 3 (A) 1H NMR and (B) 13C NMR spectra of poly(NBDTPAC8) in THF-d8. [Color figure can be viewed in the online issue,
which is available at wileyonlinelibrary.com.]
NBDTPAC8, but the obtained polymer had an uncontrolled
molecular weight and broad PDI due to slower initiation and
faster propagation rates.56 It is widely known that Ru (G3)
exhibits better control due to faster initiation and inhibits
side reactions such as back-biting.57 We found that Ru (G3)
promoted higher activity than Ru (G1) and Ru (G2). The
polymerization of NBDTPAC8 by Grubbs’ catalysts was
performed in a nonliving fashion, as shown in Table 1. The
molecular weight of the ring-opened polynorbornene was
determined by GPC using polystyrene as the standard.
The number-average molecular weights of poly(NBDTPAC8)
obtained by Ru (G1), Ru (G2) and Ru (G3) were 0.66,
2.55, and 3.30 ꢁ 105 with yields of 15, 73, and 80%,
respectively.
Basic Properties
Poly(NBDTPAC8) and poly(HNBDTPAC8) are both highly
soluble in common organic solvents, such as toluene, xylene,
benzene, chlorobenzene, and 1,2-dichlorobenzene, as well as
in low boiling-point solvents, such as THF and ether, even in
n-hexane at room temperature. However, they are insoluble
in polar solvents, such as acetonitrile (CH3CN), dimethyl sulf-
oxide (DMSO), N,N-dimethylacetamide, N,N-dimethylforma-
mide, and N-methyl-2-pyrrolidinone, at room temperature.
The excellent solubility in common organic solvents makes
the hydrogenated ring-opened polynorbornene poly
(HNBDTPAC8) a potential candidate for practical applications
by spin-coating, dip-coating, or inject-printing processes to
obtain thin films for optoelectronic devices. Poly(NBDTPAC8)
FIGURE 4 (A) 1H NMR and (B) 13C NMR spectra of poly(HNBDTPAC8) in THF-d8. [Color figure can be viewed in the online issue,
which is available at wileyonlinelibrary.com.]
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
ꢂ1; THF). However, there are no UV–vis absorption bands
TABLE 1 The Molecular Weights and the Thermal Properties of
L
for NBMA at 250ꢃ350 nm (1 ꢁ 10ꢂ5 mol Lꢂ1; THF). This
means that the UV–vis absorption at 315 nm of poly
(NBDTPAC8) can be ascribed to a p–p* transition resulting
from the conjugated TPA structure8 and is not related to the
cyclic norbornene structure. The UV–vis absorption of poly
(NBDTPAC8) in the solid state (thickness 3 lm) also shows
a similar absorbance peak with a slight red shift at 322 nm.
This suggests the existence of interchain interactions in the
solid-state polymer.12 The optical absorption of poly
(HNBDTPAC8) is similar to that of poly(NBDTPAC8). In Fig-
ure 5(B), the hydrogenated poly(HNBDTPAC8) film shows
excellent transparency (up to 93%; thickness 3 lm). The
onset wavelength of solid-state poly(NBDTPAC8) observed
from the UV–vis transmittance spectrum is approximately
390 nm, through which the energy gap of poly(NBDTPAC8)
is estimated to be 3.2 eV.
Poly(NBDTPAC8) Polymerized by Ru (G1), Ru (G2), and Ru (G3)
Ru Catalyst Yielda (%) [M]/[I]
M
n(GPC) ꢁ 10ꢂ5b PDIb Tg (ꢀC)
c
Ru (G1)
Ru (G2)
Ru (G3)
a
15
73
80
1,000 0.66
1,000 2.55
1,000 3.30
1.35 135
1.68 132
1.33 132
Yield was determined gravimetrically.
b
Determined by gel permeation chromatography (GPC) in THF using
polystyrene as a standard.
c
Tg was determined by DSC at a heating rate of 10 ꢀC minꢂ1
.
was not indefinitely stable in air atmosphere. When stored
under ambient condition for weeks, poly(NBDTPAC8)
became insoluble, whereas the poly(NBDTPAC8) stored
under N2 remained soluble. This is due to the oxidation and
degradation of the unsaturated C¼¼C double bonds in poly
(NBDTPAC8).58 Interestingly, the monomer NBDTPAC8, poly
(NBDTPAC8), and poly(HNBDTPAC8) were soluble in chloro-
form at room temperature, but the color of the solution
quickly changed to dark green under atmospheric conditions.
However, when the samples were dissolved in chloroform
and stored in the dark, the color of the samples remained
unchanged. The 1H NMR spectrum of the color-changed
NBDTPAC8 in chloroform showed that the chemical shifts at
1.8ꢃ1.9, 2.5ꢃ2.6, 3.3ꢃ3.5, and 3.6ꢃ3.7 ppm disappeared,
and 6.8ꢃ7.3 ppm became broader. This means that the
newly prepared monomer and polymers are unstable in
chloroform under light. We propose that these phenomena
are related to carbon–chlorine single bond cleavages and the
generation of free radicals, which interact with NBDTPAC8
under light.
Thermal Properties
The thermogravimetric behavior of poly(NBDTPAC8) and
poly(HNBDTPAC8) obtained by Ru (G3) were tested. The
thermogravimetric spectra of poly(NBDTPAC8) and hydro-
genated poly(HNBDTPAC8) in nitrogen are shown in Figure
6. The unsaturated poly(NBDTPAC8) and saturated poly
(HNBDTPAC8) showed 10% weight-loss temperatures
(Td10%) at 374 and 418 ꢀC under nitrogen, respectively.
Under air, the unsaturated poly(NBDTPAC8) and saturated
poly(HNBDTPAC8) showed 10% weight-loss temperatures
(Td10%) at 366 and 407 ꢀC, respectively. The saturated poly
(HNBDTPAC8) is more stable than the unsaturated poly
(NBDTPAC8), with a 10% increases in decomposition tem-
perature to about 44 and 41 ꢀC under nitrogen and air,
respectively. In many applications, the instability of the un-
saturated polymers with respect to thermal degradation is a
concern.59,60 In Table 1, the polynorbornenes obtained by
the three different Grubbs’ ruthenium catalysts had glass
transition temperatures (Tg) between 132 and 135 ꢀC, and
no remarkable difference was observed. The glass transition
The optical absorption and emission spectra of NBMA,
NBDTPAC8, and poly(NBDTPAC8) were investigated by UV–
vis and photoluminescence spectroscopy. In Figure 5(A), the
UV–vis absorption of NBDTPAC8 and poly(NBDTPAC8) ex-
hibit strong absorption at 311 and 315 nm (1 ꢁ 10ꢂ5 mol
FIGURE 5 (A) Normalized UV–vis spectra of NBMA (1 ꢁ 10ꢂ5 mol Lꢂ1; THF), NBDTPAC8 (1 ꢁ 10ꢂ5 mol Lꢂ1; THF), poly(NBDTPAC8)
(1 ꢁ 10ꢂ5 mol Lꢂ1; THF) and poly(NBDTPAC8) film and (B) transparent spectra and film states of hydrogenated poly(HNBDTPAC8)
(thickness 3 lm). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
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FIGURE 6 TGA curves for poly(NBDTPAC8) and hydrogenated
poly(HNBDTPAC8) measured under nitrogen. Temperature was
raised at a rate of 10 ꢀC minꢂ1. [Color figure can be viewed in
the online issue, which is available at wileyonlinelibrary.com.]
temperatures (Tg) of poly(NBDTPAC8) and hydrogenated
poly(HNBDTPAC8) were 132 and 89 ꢀC, respectively. The
ꢀ
prepared polynorbornenes have higher Tgs (132 C) than the
polymers containing TPA moieties with a polynorbornene
backbone (23ꢂ120 ꢀC).61,62 A decrꢀease in Tg caused by
hydrogenation was approximately 45 C. The rotation around
the hydrogenated carbon–carbon single bond clearly made
the mobility of the polymer chain easier.63
FIGURE 8 Sketch map of the studied structure (M1) and opti-
mized structure determined by DFT/B3LYP/6-31G*. [Color figure
can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
Electrochemical Properties
The electrochemical behaviors of poly(NBDTPAC8) and poly
(HNBDTPAC8) were investigated by CV conducted on films
cast on ITO-coated glass substrates as the working electrode
in dry CH3CN solution containing 0.1 M of TBAP as the electro-
lyte. The oxidative and reductive cycles of poly(NBDTPAC8)
and poly(HNBDTPAC8) are shown in Figure 7. Poly
(NBDTPAC8) showed three reversible oxidation redox couples
at E1/2 values of 0.70, 0.93, and 1.39 V. Poly(HNBDTPAC8)
showed three similar reversible oxidation redox couples at E1/
values of 0.69, 0.94, and 1.38 V. Both poly(NBDTPAC8) and
2
poly(HNBDTPAC8) showed color changes from colorless to
green, then to light blue, and finally to dark blue at applied
potentials above 0.80, 1.15, and 1.50 V in the oxidative scan,
respectively. From the oxidation potential relative to ferro-
cene/ferrocenenium, which corresponds to ꢂ4.8 eV for ferro-
cene below the vacuum level,64 we can approximately calcu-
late the HOMO energy levels of poly(NBDTPAC8) and
poly(HNBDTPAC8). The LUMO levels of poly(NBDTPAC8) and
poly(HNBDTPAC8) were calculated according to the following
equation: LUMO ¼ HOMO þ Eg. The HOMO and LUMO energy
levels of poly(NBDTPAC8) are ꢂ4.75 and ꢂ1.59 eV, respec-
tively. The electrochromic characteristics will be discussed
below.
Theoretical Study of Oxidation Mechanism of
Polynorbornene Derivatives
The electrochromic phenomenon is based on the redox
behavior of a polymer; that is, it is based on the removal of
electrons from the polymer and the capture of electrons by
the polymer. We have reported the mechanism based on mo-
lecular orbital theory.8,10,11,14 The first electron is removed
from the HOMO of the polymer to form a single occupied
FIGURE 7 Cyclic voltammograms of poly(HNBDTPAC8) and
poly(NBDTPAC8) in films cast on indium tin oxide (ITO)-coated
glass substrates in CH3CN containing 0.1 M TBAP. The scan-
ning rate is 0.1 V sꢂ1. [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com.]
PREPARATION OF POLYNORBORNENES, LIAN ET AL.
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 2 Atomic Charge Distribution of Selected Atoms in Ground State, First Oxidation State, Second Oxidation State, Third
Oxidation State, and the Charge Difference of DQ1, DQ2, and DQ3 for M1
G. S.a
Ox1b
Ox2c
Ox3d
DQ1e
DQ2f
DQ3g
12 N
13 C
15 C
20 C
23 C
30 C
33 N
41 C
44 C
51 C
101 N
109 C
119 C
a
ꢂ0.4782
0.1687
ꢂ0.3517
0.1186
ꢂ0.3161
0.1595
ꢂ0.2231
0.1981
0.1834
0.1956
ꢂ0.3234
0.0370
0.1167
0.0374
ꢂ0.3147
0.0431
0.0447
ꢂ0.3252
0.2399
ꢂ0.2343
0.1701
0.1402
0.1537
ꢂ0.2609
0.0997
0.1330
0.1026
ꢂ0.2927
0.0884
0.0872
0.1266
ꢂ0.0501
0.0537
0.0752
0.0612
0.0175
0.0482
0.0359
ꢂ0.0325
0.0404
0.0827
0.0363
0.0377
0.0356
0.0409
0.0046
0.0101
0.0101
0.0182
0.0735
0.0443
ꢂ0.0063
0.0473
0.0473
0.0411
0.0421
ꢂ0.0092
0.0804
ꢂ0.0112
ꢂ0.0280
ꢂ0.0432
ꢂ0.0419
0.0625
0.0627
0.0164
0.0652
0.0220
0.0452
0.0425
ꢂ0.2814
0.1128
ꢂ0.2277
0.1880
0.1121
0.1733
0.1599
0.1775
ꢂ0.4451
ꢂ0.0432
0.1555
ꢂ0.3968
ꢂ0.0073
0.1230
ꢂ0.0503
ꢂ0.4447
ꢂ0.0343
ꢂ0.0351
ꢂ0.0099
ꢂ0.3620
0.0020
0.0026
e
f
G. S.: ground state.
DQ1 ¼ atomic charge difference of Ox1 and G. S.
DQ2 ¼ atomic charge difference of Ox2 and Ox1.
DQ3 ¼ atomic charge difference of Ox3 and Ox2.
b
c
Ox1: losing one electron.
Ox2: losing two electrons.
Ox2: losing three electrons.
g
d
molecular orbital (SOMO), and the second electron is
removed from the SOMO to form the second oxidation state,
and so on. All theoretical calculations in this study were per-
formed using the quantum mechanical package Gaussian
0365 based on the molecular orbital approach. The equilib-
rium structure of the polymers was determined using DFT
with the B3LYP functional and the 6-31G* basis set. The stud-
ied model compound (M1) structure and structure optimized
by B3LYP/6-31G* are plotted in Figure 8; the redox behavior
of poly(NBDTPAC8) was selected for study. The electronic
states of the neutral and oxidized structures of M1 were
simulated, and the main results are summarized in Table 2
(see detailed distribution in Table S1 in the Supporting Infor-
mation). The main atomic charge differences were located on
the 12N, 13C, 15C, 20C, 23C, 30C, 33N, 41C, 44C, 51C, 101N,
109C, and 119C atoms. For the first oxidation (losing first
electron), the 12N, 15C, 20C, 23C, 30C, 33N, 41C, 51C, 101N,
109C, and 119C atoms contributed 12.7, 5.4, 7.5, 6.1, 1.8, 4.8,
3.6, 4.0, 8.3, 3.6, and 3.8% of an electron, respectively,
whereas the 13C and 44C received 5.0 and 3.3% of an elec-
tron. For the second oxidation, the 12N, 13C, 15C, 20C, 23C,
30C, 33N, 41C, 51C, 101N, 109C, and 119C atoms contributed
3.6, 4.1, 0.46, 1.0, 1.0, 1.8, 7.4, 4.4, 4.7, 4.7, 4.1, and 4.2% of
an electron, respectively, whereas the 44C received 0.6% of
an electron. For the third oxidation, the 13C, 33N, 41C, 44C,
51C, 101N, 109C, and 119C atoms contributed 8.0, 6.3, 6.3,
1.6, 6.5, 2.2, 4.5, and 4.2% of an electron, respectively,
whereas the 12N, 15C, 20C, 23C, and 30C received 0.9, 1.1,
2.8, 4.3, and 4.2% of an electron. The electron density con-
tours of the ground state and oxidation states are plotted by
Gauss View in Figure 9, which illustrates the electron density
distribution of the HOMO (ground state) and SOMO (first oxi-
dized state) of the M1. The electron density distribution of
the HOMO state is mainly located on the TPA moiety, and the
HOMO-1 state has a similar electron density distribution to
that of the HOMO state but located on the other TPA moiety.
As for the SOMO state, the electron density distribution is
mainly located on the di(triphenylamino)amine moiety. The
model compound (M2) structure and optimized structure
studied by B3LYP/6-31G* are plotted (see detailed data in
the Supporting Information); these conditions were chosen to
study the oxidative behavior of poly(HNBDTPAC8) at the mo-
lecular level. The oxidative behavior of poly(NBDTPAC8) is
similar to that of poly(HNBDTPAC8). This suggests that the
redox behaviors of poly(NBDTPAC8) and poly(HNBDTPAC8)
are almost the same. The calculation results support the elec-
trochemical experimental results.
Electrochromic Characteristics
FIGURE 9 Electronic density contours of the frontier orbitals
(M1) for optimized structure at ground state and first oxidation
state. [Color figure can be viewed in the online issue, which is
available at wileyonlinelibrary.com.]
For the electrochromic investigations, poly(NBDTPAC8) and
poly(HNBDTPAC8) were cast onto ITO-coated glass slides,
and a homemade electrochemical cell was built from a
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ARTICLE
FIGURE 10 Absorption spectral change of poly(NBDTPAC8) thin film (in CH3CN with 0.1 M TBAP as the supporting electrolyte) (A)
Eappl: (a) 0.00, (b) 0.70, (c) 0.75, (d) 0.80, (e) 0.90, (f) 1.00, (g) 1.10, and (h) 1.15 V. (B) Eappl: (a) 0.00, (h) 1.15, (i) 1.20, (j) 1.30, (k)
1.40, (l) 1.45, (m) 1.50, and (n) 1.60 V.
commercial UV–visible cuvette. The cell was placed in the
optical path of the sample light beam in a UV–vis-NIR spec-
trophotometer, which allowed us to acquire electronic
absorption spectra in situ under potential control in a 0.1 M
TBAP/CH3CN solution. The results for the poly(NBDTPAC8)
film (thickness about 3 lm) are presented in Figure 10 as a
series of UV–vis-NIR absorbance curves correlated to elec-
trode potentials. When the applied potentials were increased
positively from 0 to 0.80 V [Fig. 10(A)], the new bands rose
at 970 and 1175 nm due to the first oxidation. When the
potential was increased to 1.15 V, corresponding to the sec-
ond oxidation step, the peak at 970 nm still increased, and
another peak at 1175 nm disappeared. Meanwhile, the film
changed from its neutral colorless state to green and then to
a light blue as shown in Figure 10(A) due to the oxidations.
By applying an even more positive potential bias up to 1.50
V, corresponding to the third oxidation step as shown in Fig-
ure 10(B), the peak at 970 nm gradually decreased in inten-
sity and the peak at 450 nm decreased. As the oxidation con-
tinued, the poly(NBDTPAC8) film continued to exhibit a color
change from light blue to dark blue. The observed UV–vis-
NIR absorption changes in the poly(NBDTPAC8) film at vari-
ous potentials are fully reversible and are associated with
strong color changes. The poly(HNBDTPAC8) film showed
similar spectral changes. For electrochromic switching stud-
ies, polymer films were cast onto ITO-coated glass slides in
the same manner as that described above. Although the films
were switched, the absorbance at the given wavelength was
monitored as a function of time by UV–vis-NIR spectroscopy.
The switching data for poly(NBDTPAC8) are shown in Figure
11. The switching time was calculated at 90% of the full
switch because of the difficulty in perceiving any further
color changes with the naked eye beyond this point. The
thin poly(NBDTPAC8) film at 0.80 V required 6.2 s to
switch and 4.3 s to bleach at 1175 nm. At 970 nm, the thin
poly(NBDTPAC8) film at 0.80 V required 6.6 s to switch and
FIGURE 11 Current consumption and potential step absorptom-
etry of poly(NBDTPAC8) (in CH3CN with 0.1 M TBAP as the sup-
porting electrolyte) by applying a potential step (0.00–0.80 V).
[Color figure can be viewed in the online issue, which is avail-
able at wileyonlinelibrary.com.]
PREPARATION OF POLYNORBORNENES, LIAN ET AL.
3257

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
12 Wu, H. Y.; Wang, K. L.; Liaw, D. J.; Lee, K. R.; Lai, J. Y. J
4.4 s to bleach. Poly(HNBDTPAC8) showed electrochromic
stability similar to that of poly(NBDTPAC8). Over continuous
cyclic scans between 0.00 and 0.80 V, the poly(NBDTPAC8)
and poly(HNBDTPAC8) films exhibited good electrochromic
stability.
Polym Sci Part A: Polym Chem 2010, 48, 1469–1476.
13 Chen, W. H.; Wang, K. L.; Liaw, D. J.; Lee, K. R.; Lai, J. Y.
Macromolecules 2010, 43, 2236–2243.
14 Chen, W. H.; Wang, K. L.; Hung, W. Y.; Jiang, J. C.; Liaw, D.
J.; Lee, K. R.; Lai, J. Y.; Chen, C. L. J Polym Sci Part A: Polym
Chem 2010, 48, 4654–4667.
CONCLUSIONS
A new class of electrochromic polymer based on polynorbor-
nenes containing electroactive chromophores was designed
and prepared via ROMP to obtain poly(NBDTPAC8) and was
followed by hydrogenation to obtain poly(HNBDTPAC8). Poly
(NBDTPAC8) and hydrogenated poly(HNBDTPAC8) exhibited
similar electrochemical and electrochromic behaviors
with high contrast and electrochromic reversibility. Poly
(HNBDTPAC8) shows greater thermal stability than poly
(NBDTPAC8) does, whereas poly(NBDTPAC8) exhibits
15 Yuan, Y. F.; Xia, X. H.; Wu, J. B.; Gui, J. S.; Chen, Y. B.;
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higher glass transition temperature than does poly
20 Tajima, K.; Yamada, Y.; Bao, S.; Okada, M.; Yoshimura, K. J
(HNBDTPAC8). Both polynorbornenes are colorless and
transparent in their neutral state and exhibit higher glass
transition temperatures than do general polynorbornenes.
These excellent characteristics suggest that the prepared col-
orless polynorborenes are good candidates for electrochro-
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The authors thank the National Science Council of the Republic
of China for the financial support for this work. The HRESIMS
spectrum was obtained at instrument centers of National Tai-
wan University. The assistances of the Shoou-ling Huang and
Shu-Yun Sun are gratefully appreciated.
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