Radical polymer containing a polytriphenylamine backbone: Its synthesis and electrochemical performance as the cathode of lithium-ion batteries

Article abstract of DOI:10.1002/cplu.201402268

A novel radical monomer containing triphenylamine and the 2,2,6,6-tetramethylpiperidinyl-N-oxy (TEMPO) radical has been synthesized. The corresponding linear homopolymer of 4-carboxy-N,N-diphenylaniline-2,2,6,6-tetramethylpiperidin-1-yloxy (PTPA-TEMPO) wa

Full text of DOI:10.1002/cplu.201402268

DOI: 10.1002/cplu.201402268
Full Papers
Radical Polymer Containing a Polytriphenylamine
Backbone: Its Synthesis and Electrochemical Performance
as the Cathode of Lithium-Ion Batteries
Chang Su,[a] Fang Yang,[b] Lihuang Xu,*[a] Xiaogang Zhu,[b] Huihui He,[b] and Cheng Zhang*[b]
A novel radical monomer containing triphenylamine and the
2,2,6,6-tetramethylpiperidinyl-N-oxy (TEMPO) radical has been
synthesized. The corresponding linear homopolymer of 4-car-
boxy-N,N-diphenylaniline-2,2,6,6-tetramethylpiperidin-1-yloxy
(PTPA-TEMPO) was then prepared by chemical oxidative poly-
merization. The chemical structure and electrochemical proper-
ties of the prepared polymers were characterized by Fourier
transform infrared spectroscopy, ultraviolet–visible spectrosco-
py, scanning electron microscopy, cyclic voltammetry, and gal-
vanostatic charge–discharge testing by the simulated lithium-
ion half-cell method. The results demonstrated that the as-syn-
thesized functional polymers exhibited an initial discharge ca-
pacity of up to 140 mAhgÀ1 with two well-defined plateaus at
the potential of 3.8 and 2.7 V versus Li/Li+. Furthermore, the
PTPA-TEMPO electrode showed superior cycling and rate per-
formances. The improved electrochemical performances were
attributed to the construction of the novel linear radical molec-
ular structure with PTPA as the conductive polymer backbone,
which improved the long-range charge-carrier transportation
and facilitated the Li+-ion insertion–extraction process in the
aggregated polymer bulk during the charge–discharge pro-
cess.
Introduction
Studies on rechargeable secondary batteries composed of
a radical polymer have become of great interest in recent
years owing to their rapid electron transfer, high charge ca-
pacity, and an output voltage of 3.6 V against a lithium
anode.[1,2] The studied radical polymers generally have an
oxygen-centered nitroxide radical, 2,2,6,6-tetramethylpiperidin-
yl-N-oxy (TEMPO), as the pendant group, which contains a reso-
nance structure and usually displays two redox couples.
During the charge–discharge process, TEMPO can be reversibly
oxidized to the corresponding oxoammonium cation (p-type
doping) and reduced to the corresponding aminoxy anion (n-
Since then, various studies have focused on the properties
of radical polymers themselves and conductive agents rather
independently, to increase the energy density of radical batter-
ies and improve the battery performance.[5,6] In most of those
efforts, nitroxide radicals are attached generally to polymers
with an aliphatic or nonconducting type of backbone, such as
polymethacrylate,[7] polynorbornene,[8] cellulose,[9] poly(p-tert-
butylaminoxy-styrene),[10] and poly(vinyl ether).[11] However, the
above nitroxide radical polymers are derivatives of convention-
al plastics, which are insulators, thus resulting in electron trans-
fer among the polymer molecules by means of hopping be-
tween the pendant redox sites (short-range conductivity),
which are isolated in the polymer and the long-range conduc-
tivity is limited.[1] As a result, a relatively high proportion of the
conducting agent, even up to 60–80 wt%, is required in the
fabrication of the composite electrode to improve the long-
range conductivity and the utilization rate of nitroxide radical
contained in the electroactive polymer. This leads the actual
redox capacity of the composite electrodes to decrease seri-
ously and extensive studies to use them as active materials for
batteries to be impeded. The intrinsic conductivity of most rad-
ical polymers is rather low owing to the insulating backbone,
so a combination of a stable radical with a conductive polymer
is regarded as an effective way to produce a new radical poly-
mer with an improvement of electron migration. A few
TEMPO-containing polyacetylenes and polythiophenes have
been synthesized and used as a cathode-active material in a re-
chargeable battery.[3,12] Unfortunately, degradation of the un-
stable conducting polymer backbone enforced by the pres-
ence of the radical moiety is observed, which hinders the im-
provement of the electrochemical properties of the TEMPO-
type
doping).[3]
Poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl
methacrylate) (PTMA) has been one of the nitroxide radical
polymers most typically employed as the cathode-active mate-
rial since first being proposed by Nakahara et al. in 2002.[4] As
reported,[4] PTMA applied to the cathode in lithium-ion batter-
ies exhibited an outstanding cathode performance: high ca-
pacity, high charging and discharging rate performance, long
cycle life, and processing compatibility.
[a] C. Su, Prof. L. Xu
College of Chemical Engineering
Shenyang University of Chemical Technology
11# Street, Shenyang 110142 (P.R. China)
E-mail: xulihuanss@163.com
[b] F. Yang, X. Zhu, H. He, Prof. C. Zhang
State Key Laboratory Breeding for Green Chemistry Synthesis Technology
College of Chemical Engineering and Materials Science
Zhejiang University of Technology
Chaowang Road 18, Hang Zhou 310014 (P.R. China)
E-mail: czhang@zjut.edu.cn
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cplu.201402268.
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based active polymer, as well the further exploration of the de-
tails of the charge–discharge process or of the influence of the
conductive backbone on the electrochemical properties of
TEMPO.
Polytriphenylamine (PTPA), as well its derivatives, contains
triphenylamine radical units and belongs to another family of
radical polymers, which exhibited a reversible radical redox re-
action during the charge and discharge processes.[13,14] As
a result, triphenylamine-based polymeric materials have been
explored recently as the electrode material applied in the
energy storage field, such as supercapacitors and lithium-ion
batteries.[14–16] As reported,[14] the electrochemical and cell per-
formance of PTPA as the cathode material was studied by a si-
mulated three-electrode method. The results indicated that the
PTPA-based electrode had not only superior high power capa-
bility but also high energy density at prolonged cycling and
a well-defined voltage plateau of 3.8 V, which could contribute
to the p-conjugated triphenylamine substructure and reversi-
ble redox radical nature of PTPA. As a solution, to design
a novel molecular structure containing both PTPA and TEMPO
moieties would be promising to produce a new functional ma-
terial with improved cell performance.
Figure 1. FTIR spectra of samples of PTPA and PTPA-TEMPO.
amine and TEMPO moieties have been contained in the PTPA-
TEMPO polymer, and have not been destroyed during the
polymerization process.
The UV/Vis spectra (normalized absorbance) were further
measured in N,N-dimethylformamide (DMF; 10À3 gLÀ1) to ex-
plore the characteristics of PTMA, PTPA, and PTPA-TEMPO. As
depicted in Figure 2 curve (b), the PTPA exhibits only one
Herein, a novel and linear radical polymer was constructed
with PTPA as the conductive polymer backbone and TEMPO as
the pendant groups. The structure and electrochemical proper-
ties of the prepared polymer were investigated systematically
as cathode materials for Li-ion batteries. Furthermore, the pos-
sible relationships of the structure characteristics of PTPA-
TEMPO and the improved electrochemical properties of the
material are discussed in detail. Thanks to the construction of
the novel linear radical molecular structure with PTPA as the
conductive polymer backbone, we found that the PTPA-
TEMPO-based electrode had remarkably improved charge–dis-
charge performance compared with the as-prepared PTPA-
based material and was promising as an advanced cathode
material.
Figure 2. UV/Vis spectra of a) PTMA, b) PTPA, and c) PTPA-TEMPO.
Results and Discussion
Material characterization
sharp absorption peak at 356 nm, which is attributed to the p–
p* electron transition of PTPA,[18,19] whereas curve (a) displays
an absorption of 460 nm (n–p*) resulting from the pendants of
the nitroxide radical along the PTMA polymer chain.[20] In con-
trast, two distinct absorption peaks are observed in the UV/Vis
spectra of PTPA-TEMPO. The absorption peak at 375 nm is still
ascribed to p–p* transition from the triphenylamine units, and
another peak at 475 nm corresponds to the n–p* transition ab-
sorption of the pendants of the nitroxide radical along the
polymer chain. In particular, the absorption peaks of nitroxide
radical moieties in the PTPA-TEMPO redshift from the 465 nm
of PTMA to 475 nm, thus implying that the site-to-site electron
hopping process of the nitroxide radical by self-exchange reac-
tions in PTPA-TEMPO becomes easier than that of PTMA. Fur-
thermore, it can be observed that the p–p* electron transition
of triphenylamine units for the PTPA-TEMPO also has a clear
redshift relative to PTPA, which indicates the extended electron
Figure 1 shows the FTIR spectra of the as-prepared PTPA and
PTPA-TEMPO. By comparison with the typical FTIR spectrum of
PTPA,[14] the main characteristic peaks of the PTPA can be
found in both of the samples, and involve the fundamental vi-
brations of triphenylamine moieties for C=C ring stretching at
1594 cmÀ1, CÀC stretching at 1490 cmÀ1, and CÀH bending at
1328 cmÀ1. The absorption peaks at 1276 and 820 cmÀ1 corre-
spond to the CÀN stretching of the tertiary amine and a CÀH
out-of-plane vibration from 1,4-disubstituted benzene rings, re-
spectively. Besides, a number of new bands can be clearly ob-
served in the spectrum of PTPA-TEMPO, in which the absorp-
tion peak at 1708 cmÀ1 is ascribed to C=O (ester carbonyl)
whereas the absorption peak at 1176 cmÀ1 is the stretching of
gCÀOÀC existing in the ester linkage. In particular, the absorption
peak at 1365 cmÀ1 is attributed to nitroxide radical groups in
the polymers.[17] These results indicate that both triphenyl-
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delocalization and the improved electron transportation in the
polymers. This phenomenon can be explained as follows: the
introduction of TEMPO units as the terminating group results
in the molecular structure changing from a cross-linked struc-
ture to a linear structure, which relieves the steric torsion be-
tween triphenylamine units in PTPA and leads to improved
p conjugation and electron transportation along the polymer
chain. The improved electron transportation in the linear PTPA
chain and a radical electron hopping process among the pend-
ant nitroxide radical moieties will be of benefit to the charge-
carrier transportation type changing from short-range conduc-
tion to long-range conduction, which is crucial for high-rate
performance lithium batteries.
The morphologies of the PTPA and PTPA-TEMPO are shown
in Figure 3. As can be seen, the PTPA has a dense aggregation
structure with a size of several micrometers (Figure 3a). Com-
Figure 4. Cyclic voltammograms of a) PTPA-TEMPO, b) PTPA, and c) PTMA in
0.1m LiClO4/CH3CN versus Ag/AgCl at a scan rate of 10 mVsÀ1
.
sponding oxoammonium cations or the p-type doping of the
material.[21] The corresponding difference in separation of the
oxidation and reduction peak potentials is estimated as 0.18 V.
Comparably, there are some differences for the CV curves of
PTPA-TEMPO, in which one pair of reduction and oxidation
peaks appearing at 1.03 and 0.91 V can be assigned to the
redox reaction of triphenylamine units of PTPA-TEMPO and an-
other pair of weak redox peaks at 0.83 and 0.76 V results from
the p-type doping of nitroxide radical (from the nitroxide radi-
cals to the oxoammonium cations). Furthermore, the corre-
sponding peak-to-peak separations exhibited by the PTPA-
TEMPO electrode are 0.12 and 0.07 V, respectively, which are
relatively narrower than those of the PTPA and PTMA electro-
des, thus implying the good oxidation/reduction reversibility
of the produced active materials as cathode. Notably, a third
couple of redox peaks with weak intensity appears near À0.2 V
for PTPA-TEMPO (as shown in the inset of Figure 4a), which
can be attributed to the redox couple of the n-type doping of
nitroxide radical (from the aminoxy anion to the nitroxyl radi-
cals) and does not occur in the CV curves of both PTMA and
PTPA at the same position. It can be assumed that the intro-
duction of stable conjugated PTPA as the main chain of
TEMPO-containing polymer works as an electrocatalysis func-
tion, which promotes the redox reaction between the radical
and aminoxy anion (n-type doping process), thereby leading
to the appearance of a third pair of redox peaks. This electro-
catalysis phenomenon is similar to that in previous reports,[22,23]
which indicated that the battery performance of the sulfur-
containing organic compound dimercaptan can be clearly im-
proved by the introduction of polyaniline, owing to the elec-
trocatalysis effect of polyaniline.
Figure 3. SEM images of powder samples: a) PTPA and b) PTPA-TEMPO.
paratively, when TEMPO as a functional terminating group is
introduced into PTPA, the morphology of the obtained PTPA-
TEMPO is different from that of PTPA under the same experi-
mental conditions. As shown in Figure 3b, PTPA-TEMPO exhib-
its a loosely assembled spherical structure consisting of many
small particles of size about 100 nm with good dispersion. This
structural feature of PTPA-TEMPO may provide sufficient sur-
face area and ionic channels for the contact of electrode-active
material and electrolyte, and as a result, the much more elec-
trode-active material is utilized effectively during the charge–
discharge process and the electrochemical properties of PTPA-
TEMPO are clearly improved. All of these factors are very im-
portant to prepare a good cathode material for Li-ion batter-
ies.
Electrochemical performance
Figure 4 shows the cyclic voltammetry (CV) profiles of PTPA,
PTMA, and PTPA-TEMPO measured in 0.1m lithium perchlo-
rate/acetonitrile solution. The PTPA electrode shows a couple
of anodic and cathodic peaks at about 1.11 and 0.75 V with
a potential separation of about 0.36 V, which corresponds to
the charge–discharge reaction of the triphenylamine radical
redox couple of PTPA. The approximately symmetrical peaks
suggest a good insertion–extraction reversibility of the pro-
duced PTPA cathode-active material. PTMA displays a pair of
redox potentials at 0.90 and 0.72 V versus Ag/AgCl, which are
assigned to the oxidation of the nitroxide radicals to the corre-
Charge–discharge performance
The charge–discharge behaviors of the as-prepared polymers
as the cathode of lithium batteries have been investigated sys-
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tematically by the simulated lithium-ion half-cell method to es-
timate the cell performance more realistically. The initial
charge–discharge profiles of the polymer electrodes at
20 mAgÀ1 between 2.5 and 4.2 V are shown in Figure 5. The
in the ester linkage, which leads to the increase of the charge–
discharge voltages of the PTPA part in PTPA-TEMPO.[10] As
a result of that, the redox couple of TEMPO is relatively weaker
than that of PTPA in the CV curves of PTPA-TEMPO (as shown
in Figure 4a). It can be considered that the capacity contribu-
tion from the TEMPO part in PTPA-TEMPO polymer (mainly ob-
tained by the redox reaction process from the oxoammonium
cations to the nitroxide radicals) is relatively less than that of
the PTPA part, which results in the total higher voltage plat-
form at about 3.8 V. This high voltage platform is favorable for
producing a promising cathode material with high energy den-
sity.
We further investigated the cycling stability of the as-pre-
pared polymers as cathode materials of Li-ion batteries, as
shown in Figure 6. It was found that PTPA-TEMPO electrodes
Figure 5. Initial charge–discharge profiles of the polymeric electrode materi-
als at a constant current of 20 mAgÀ1 between 2.5 and 4.2 V in LiPF6 in eth-
ylene carbonate (EC)/dimethyl carbonate (DMC) (1:1, v/v) electrolyte versus
Li/Li+.
PTPA shows initial charge–discharge capacities of 104.3/
97 mAhgÀ1 with a typical discharge voltage plateau in the
range of 3.5–4.1 V at the initial cycle, which is almost in accord
with the reports.[24] The coulombic efficiency from the above
results is approximately 93%. For PTMA, the charge–discharge
curves present one clear discharge voltage platform at about
3.6 V with an initial charge–discharge capacity of 86.8/
84 mAhgÀ1, which corresponds to 96.8% of the coulombic effi-
ciency. Comparatively, under the same conditions, the PTPA-
TEMPO electrode exhibits an initial charge–discharge capacity
of up to 146.6/140 mAhgÀ1 and 95.4% of the coulombic effi-
ciency, with two clear discharge voltage platforms at about 3.8
and 2.7 V, respectively. The higher discharge voltage platform
is attributed to the stacking up of the voltage platforms of
both PTMA and PTPA. The lower plateau at 2.7 V corresponds
to the n-type doping process with the redox couples changing
from the nitroxide radical to the aminoxy anion. This character-
istic has been presented in some reports,[3,12] but the emerging
reason for this voltage platform has not been mentioned.
Therein, it is considered to be caused by the electrocatalytic
function of the introduced PTPA to nitroxide radical pendants.
The improved specific capacity for PTPA-TEMPO can be at-
tributed to the introduction of the conjugated conductive
polymer backbone (PTPA), which is itself an electroactive mate-
rial and can be partly responsible for the improvement of total
capacity. Furthermore, the second voltage platform occurring
at 2.7 V, as a result of the redox process of the second electron
caused by the electrocatalysis function of the PTPA backbone
to nitroxide radical pendants, is also ascribed to the increased
discharge capacity. Notably, the voltage platform of the PTPA-
TEMPO electrode at high voltage is clearly higher than that of
either PTPA or PTMA, which can be ascribed to the electron-
withdrawing effect of the C=O bond (ester carbonyl) existing
Figure 6. Cycling stability of the polymeric electrode materials at a constant
current of 20 mAgÀ1 between 2.5 and 4.2 V in LiPF6 in EC/DMC (1:1, v/v)
electrolyte versus Li/Li+.
show a similar stable cycling performance to PTPA. After
50 cycles, the discharge capacity of PTPA decreases from its ini-
tial 97 mAhgÀ1 to 84 mAhgÀ1, with about 14% loss of capacity.
The discharge capacity of PTPA-TEMPO drops from its initial
140 mAhgÀ1 to 125 mAhgÀ1, with only about 11% loss of ca-
pacity, which is even lower than the initial capacity of PTPA. As
reported,[25] the stability of the micromorphology and chemical
structure of polymeric materials has a great influence on the
charge–discharge cycling stability. The above results demon-
strate that the structures of the PTPA-TEMPO electrodes are rel-
atively stable, and during the electrochemical Li+-ion inser-
tion–extraction process, the micromorphology and chemical
structure of the polymeric materials are destroyed less, which
makes the charge–discharge process quite reversible.
The rate performances of the polymer electrodes were fur-
ther examined at different current rates of 50, 100, 300, and
500 mAgÀ1. Compared with the parent PTPA, the PTPA-TEMPO
electrode displays an improved rate capability with an en-
hanced current rate from 50 to 500 mAgÀ1, as shown in
Figure 7. The specific capacities for PTPA-TEMPO are 128.1,
122.0, 113.5, and 105.3 mAgÀ1, with a 10 times increase in the
current from 50 to 500 mAgÀ1, which are still higher than that
of PTPA at high current rate, although the decay rate of capaci-
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nitroxide radical to the aminoxy anion. Also, the PTPA-TEMPO
cathode presented good cycling stability with over 89% of the
initial capacity after 50 cycles. Furthermore, the rate per-
formance of the PTPA-TEMPO composite cathodes was im-
proved, which was ascribed to both the introduction of the
PTPA backbone in the TEMPO-based polymer and the con-
struction of the linear molecular structure, which enhanced the
long-range electron migration and Li+-ion insertion–extraction
process in the aggregated polymer bulk during the charge–dis-
charge process. All the results indicated that the designed
PTPA-TEMPO as composite cathode is a promising candidate
for potential applications in organic radical batteries.
Figure 7. Rate performances of the polymer electrodes in the voltage range
from 2.5 to 4.2 V at various current rates of 50, 100, 300, and 500 mAgÀ1
.
Experimental Section
ty is comparatively high. In addition, PTPA and PTPA-TEMPO
present a quickly recovered ability of capacity, as the current
rate gets back to 50 mAgÀ1. The possible reasons for the im-
proved high rate capability can be partly ascribed to the novel
molecular structure design, in which introduction of the conju-
gated PTPA as the conductive molecular backbone improves
the long-range charge transportation of the nitroxide free radi-
cal in the aggregated polymer (as indicated in the UV/Vis spec-
tra), which leads to the rapid charge-transportation ability of
PTPA-TEMPO and the higher rate performance. Furthermore,
the introduction of the nitroxide radical as the terminating
group into triphenylamine units leads to the molecular struc-
ture of PTPA changing from a cross-linked structure to a linear
structure, which, as well as the tiny particle morphology of
PTPA-TEMPO, will be convenient for Li+-ion insertion–extrac-
tion during the charge–discharge process, which is also re-
sponsible for the high rate capability. Thus, the novel PTPA-
TEMPO polymer would be a good potential candidate for cath-
ode materials of high-power lithium batteries.
Materials
Diphenylamine (98%), 4-fluorobenzonitrile (99%), and 4-hydroxy-
2,2,6,6-tetramethylpiperidine 1-oxyl free radical (99%) were pur-
chased from Energy Chemical Reagent Co. Sodium hydride (60%),
N-methylpyrrolidone (NMP, 99.9%, electronic grade), and N,N-dime-
thylformamide (DMF, 99.9%, HPLC grade) were purchased from
Aladdin. All other reagents were received as analytical grade and
used without further purification.
Syntheses
Synthesis of PTPA-TEMPO: The synthesis of the monomer (TPA-
TEMPO) is shown in Scheme 1.
Synthesis of 4-cyano-N,N-diphenylaniline: Diphenylamine (5.1 g)
and sodium hydride (1.5 g) were firstly dissolved in DMF (50 mL).
Then 4-fluorobenzonitrile (4.5 g) was added to the above solution.
The reaction was performed under a nitrogen atmosphere for 12 h
at 1108C. The resulting solution was extracted with dichlorome-
thane and dried by anhydrous MgSO4. The obtained 4-cyano-N,N-
diphenylaniline (1) was isolated by column chromatography as
a yellow powder with 61.1% (4.98 g) yield.
Conclusion
A novel and linear 2,2,6,6-tetra-
methylpiperidinyl-N-oxy
(TEMPO)-based
polytriphenyl-
amine (PTPA) derivative, with
PTPA as molecular backbone
and TEMPO as pendant groups,
has been synthesized successful-
ly by chemical oxidation poly-
merization. Compared to PTPA,
PTPA-TEMPO exhibited two clear
voltage plateaus with a higher
discharge
capacity
of
140 mAhgÀ1 during the charge–
discharge process, which was at-
tributed to the electrocatalytic
function of PTPA as a molecular
backbone that promoted the n-
type doping process with the
redox couple changing from the Scheme 1. Synthesis route to PTPA-TEMPO.
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1H NMR (CDCl3, 500 MHz): d=6.94 (d, 2H), 7.20 (d, 4H), 7.25 (d,
2H), 7.39 (t, 4H), 8.05 ppm (d, 2H); MS (EI): m/z (%): 270.12.
(DMC) (EC/DMC=1:1, v/v) as the electrolyte. Charge–discharge
measurements were performed on a LAND CT2001 apparatus
using a constant current density at room temperature.
Synthesis of 4-carboxy-N,N-diphenylaniline: Potassium hydroxide
(2.1 g) and 4-cyano-N,N-diphenylaniline (1.0 g) were firstly dis-
solved in a mixture of deionized water (30 mL) and glacial acetic
acid (20 mL) in a predried three-necked flask and heated at reflux
(858C) for 48 h. The reaction mixture was then cooled and hydro-
chloric acid (1m) was added dropwise to the reaction solution until
the pH value of the reaction solution was adjusted to about 1. The
white precipitate was then isolated by fitration and washed with
a large amount of water. The obtained white powder of 4-carboxy-
N,N-diphenylaniline (2) was dried in vacuum at 608C for 24 h to
give an 82% (0.82 g) yield.
Acknowledgements
We thank the National Natural Science Foundation of China
(NSFC, No. 51003095, No. 51103132) and Research on Public Wel-
fare Technology Application Projects of Zhejiang Province, China
(2010C31121) for financial support. This work was also supported
by the analysis and testing foundation of Zhejiang University of
Technology.
1H NMR (CDCl3, 500 MHz): d=7.00 (t, 2H), 7.17 (m, 6H), 7.34 (t,
4H), 7.92 (d, 2H), 10.43 ppm (s, 1H; sharp COOH); MS (EI): m/z (%):
288.
Keywords: batteries · cathodes · electrochemistry · lithium ·
polymers
Synthesis of 4-carboxy-N,N-diphenylaniline-2,2,6,6-tetramethyl-
piperidin-1-yloxy (TPA-TEMPO): 4-Hydroxy-2,2,6,6-tetramethyl-
piperidine-1-oxyl free radial (1.6 g) and 4-carboxy-N,N-diphenylani-
line (2.0 g) were dissolved in dichloromethane (50 mL) in a predried
three-necked flask, then 1-(3-dimethylaminopropyl)-3-ethylcarbodi-
imide hydrochloride (0.4 g) as dehydrating agent and 4-dimethyl-
aminopyridine (1.6 g) as acylating catalyst were added, with stirring
for 24 h at room temperature. The reaction mixture was then sepa-
rated by vacuum filtration. The filtrate was washed with saturated
brine three times and the organic phase was dried over sodium
sulfate. The ester was purified by column chromatography using
silica gel and petroleum ether/ethyl acetate to afford the title com-
pound as a pink powder with 61.8% (1.9 g) yield.
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Chemical polymerization of TPA-TEMPO: The polymers of 4-car-
boxy-N,N-diphenylaniline-2,2,6,6-tetramethylpiperidin-1-yloxy
(PTPA-TEMPO) and triphenylamine (PTPA) were prepared by chemi-
cal oxidative polymerization of TPA-TEMPO and TPA in chloroform
(20 mL) by using ferric chloride as oxidant. The solution was stirred
24 h at room temperature under N2. After completion of the solu-
tion polymerization reaction, the mixture was poured into metha-
nol to deposit the polymer product, which was then isolated by fil-
tration and washed with methanol several times. Finally, the poly-
mer product was isolated by filtration and dried in vacuum at
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Characterization and electrochemical measurements
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.
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Received: August 19, 2014
Published online on && &&, 0000
&
ChemPlusChem 0000, 00, 0 – 0
www.chempluschem.org
6
ꢀ 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

FULL PAPERS
Energy saving: A linear radical polymer
with polytriphenylamine (PTPA) as the
conductive polymer backbone and
2,2,6,6-tetramethylpiperidinyl-N-oxy
(TEMPO) as pendant groups has been
synthesized as an energy storage mate-
rial. PTPA-TEMPO exhibited superior
electrochemical performance as the
cathode of lithium batteries (see figure)
and was promising as an advanced
cathode material.
C. Su, F. Yang, L. Xu,* X. Zhu, H. He,
C. Zhang*
&& – &&
Radical Polymer Containing
a Polytriphenylamine Backbone: Its
Synthesis and Electrochemical
Performance as the Cathode of
Lithium-Ion Batteries
ChemPlusChem 0000, 00, 0 – 0
www.chempluschem.org
7
ꢀ 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ