Full text of DOI:10.1002/1521-3927(20001101)21:16<1162::AID-MARC1162>3.0.CO;2-9

1162
Macromol. Rapid Commun. 2000, 21, 1162–1165
Communication: The ATRP (atom-transfer radical poly-
merization) process was used to synthesize C60 end-
capped polystyrene. GPC data demonstrated that fullerene
(C60) was chemically bonded to polystyrene, and C60 was
most likely monosubstituted. Matrix-assisted laser desorp-
tion/ionization-time of flight (MALDI-TOF) mass spec-
trometry (MS) analysis (with 1,8-dihydroxy-9(10H)-
anthracenone (dithranol)/silver trifluoroacetate as the
matrix) of this copolymer proved that C60 was monosub-
stituted.
MALDI-TOF mass spectrometry characterization of C60
end-capped polystyrene prepared by ATRP
Xianfeng Shen, Xiaoran He, Guangqiang Chen, Peng Zhou, Lan Huang*
College of Chemistry and Molecular Engineering, Peking University, 100871, Beijing, P.R. China
Introduction
bromide (1-PEBr), 2,29-bipyridine (bpy) were used as re-
ceived.
Polymeric C60 derivatives are highly intriguing in that
they have extraordinary properties on conducting, mag-
[
1, 2]
netic, photochemical, electrical,
and microtribologi-
[3]
[2]
Synthesis of bromo-terminated polystyrene
cal aspects. Various possibilities have been reported
on the synthesis of these derivatives during recent years. The polymerization was carried out according to a procedure
[7]
However, many of the derivatives are crosslinked and reported by Wang. A reddish brown mixture of styrene, 1-
non-processable due to multisubstitution. In order to PEBr, CuBr (1 molar equiv. relative to 1-PEBr), and bpy (1
molar equiv. relative to CuBr) was degassed in a glass tube
by several freeze-thaw cycles under vacuum, then the tube
was sealed off and immersed in an oil bath at 1108C. After
improve the processability, it is necessary to obtain the
monosubstituted products. So far, reports on monosubsti-
tuted products are based on the reaction of functional
polymers with C60, for example, azido-terminated poly-
8
h reaction time, the solution was very sticky. It was dis-
solved in trichloromethane (CHCl ) and filtered. Under stir-
3
[4]
[5]
styrene, amino-terminated polystyrene, and TEM-
POL-terminated polystyrene (TEMPOL = 4-hydroxy-
ring, the solution was added dropwise into an excess of
methanol. The polymers were isolated by filtration, washed
with methanol, and dried. The data of the polymerization
were summarized in Tab. 1, and the general synthetic route
is shown in Scheme 1.
[6]
2,2,6,6-tetramethylpiperidinyloxy).
With the introduction and development of atom-transfer
[7]
radical polymerization (ATRP), this simple and effective
method has gained increasing interest. In this paper, we
give an account of the synthesis of C60 end-capped poly-
styrene (PS-C60) by ATRP. To determine the structure of
the copolymer, we used MALDI-TOF MS, since it is a fast
and simple technique for qualitative chain-end analyses.
Recently, several groups reported on the characterization
Tab. 1. GPC analysis of polystyrene synthesized by ATRP.
—
—
Sample Reaction
time in h
M
n
M
w
PD
Conversion
in %
PS-I
PS-II
20
20
2060
2550
2980
3580
1.45
1.40
64.9
84.5
[8–10]
of polymers by means of MALDI MS.
Synthesis of C60 end-capped polystyrene
Experimental part
The reaction was carried out by mixing bromo-terminated
polystyrene, fullerene (C60), CuBr and bpy in a glass tube
with toluene. An excess of C60 was used according to Weis.
Materials
[5]
Styrene and toluene were distilled before use. Copper(I) In all reactions, a ratio of 1.5:1 C60/bromo-terminated poly-
bromide (CuBr), fullerene (C60, 99.9 wt.-%), 1-phenylethyl mer was used. The solution was degassed by freeze-thaw
Macromol. Rapid Commun. 2000, 21, No. 16
i WILEY-VCH Verlag GmbH, D-69451 Weinheim 2000
1022-1336/2000/1611–1162$17.50+.50/0

MALDI-TOF mass spectrometry characterization ...
1163
Scheme 1.
Scheme 2.
Tab. 2. GPC analysis of C60-polystyrene synthesized by ATRP.
MALDI-TOF mass spectrometry
—
—
MALDI-TOF MS was performed using a Bruker time-of-
flight mass spectrometer. The instrument was equipped with
nitrogen laser (337 nm), delayed extraction and reflector. It
was operated at an accelerating potential of 20 kV in linear
mode. The MALDI mass spectra represent averages over
100 consecutive laser shots (3 Hz repetition rate). The sam-
ples (10 mg/ml), dithranol matrices (20 mg/ml) and silver tri-
fluoroacetate solution (10 mg/ml) were all prepared in THF.
The ratio of the sample to matrice and silver trifluoroacetate
is 10:10:1. A 2 ll portion of the final solution was deposited
onto the sample target and allowed to dry at room tempera-
ture and ambient atmosphere.
Sample
Reaction
time in h
M
n
M
w
PD
PS-C60(I)
PS-C60(II)
PS-IIcontrol
20
20
20
2960
3340
2340
3890
4400
3680
1.31
1.32
1.57
cycles under vacuum. The tube was sealed off and immersed
in an oil bath at 1108C for 12 h. A control sample using PS-
II was prepared under the same conditions. After filtration,
the solution was added dropwise into an excess of methanol
under stirring. The resulting precipitate was dissolved in tet-
rahydrofuran (THF) to remove unreacted C60, and THF was
then removed by rotary evaporation. The so obtained crude
polymer consists of a mixture of polystyrene and C60-poly-
styrene. Thin layer chromatography (silica) was used to
separate C60-polystyrene from polystyrene; a mixture of
Results and discussion
All samples were dissolved in THF giving golden brown
[5]
[6]
toluene, tetrachloromethane and acetic acid (1:1:0.25) was solutions. According to Weis and Wang, we used the
used as the eluent. C60-polystyrene was received as a brown GPC equipped with a UV detector at 350 nm to demon-
powder with a yield of 35–37%. The data of the reaction are strate that C60 and polystyrene are chemically bonded
summarized in Tab. 2, and the general synthetic route is
shown in Scheme 2.
because polystyrene can be detected only at 254 nm,
while PS-C60 copolymer can be detected at wavelengths
ranging from 300 to 350 nm. Fig. 1 shows the GPC
results utilizing the UV detector. In contrast to the control
sample from PS-II, it becomes clear that C60 and polysty-
rene are chemically bonded. Comparing Tab. 1 and Tab. 2
reveals that the molecular weights of C60 end-capped
polystyrene [PS-C (I,II)] are just similar to their bromo-
Gel permeation chromatography (GPC)
GPC was performed using a Waters apparatus working at
3
58C with stabilized tetrahydrofuran (THF) as the eluent at a
–1
6
0
flow rate of 1 ml N min , equipped with three Styragel col-
umns (HT2, HT3, HT4), and with polystyrene as standard.
terminated precursors [PS-I,II]: each one increased in
Differential refractive index detector and UV detector were about 1000 in molecular weight. This means that most
used respectively. likely one bromo-terminated polystyrene molecule

1164
X. Shen, X. He, G. Chen, P. Zhou, L. Huang
Fig. 1. GPC curves of PS-C60(I,II) and control PS-II measured
with a UV detector at 350 nm (A: PS-C60(I), B: PS-C60(II), C:
control PS-II).
reacted with one C60 molecule resulting in monosubsti-
tuted C60
.
With respect to MALDI-TOF studies, it was reported
[8]
by Charleux that no polymer has a single, narrow molar
mass distribution, although MALDI-TOF mass spectra
should give results similar to those by means of GPC. In
order to compare with C60-polystyrene, samples of mix-
tures of polystyrene [PS-(I,II)] and powdered C60 were
studied using MALDI-TOF. It is shown in Fig. 2 that C60
can be obviously observed at m/z = 720, and we attributed Fig. 2. MALDI-TOF mass spectra obtained with dithranol/sil-
ver trifluoroacetate matrix for polystyrene samples PS-I,II
two principle ion series of polystyrene which can be dis-
tinguished and assigned as:
mixed with C60
.
linkage was easily broken in the process of analysis. No
bromo end group could be detected with the dithranol/sil-
ver trifluoroacetate matrix.
MALDI-TOF spectra of the C60-polystyrene samples
presented in Tab. 2 are shown in Fig. 3. With the structure
of series B and the existence of methyl group fragments
in the high laser energy field, we tentatively attribute that
the bromo-terminated polystyrene subsequently reacted
with C60 under rearrangement of 1CH
Interestingly, no polymer with bromo end group was namically most stable isomer. The principle ion series of
detected. It may be probable that the covalent bromo-
60-polystyrene can be distinguished and assigned as:
3
to the thermody-
C

MALDI-TOF mass spectrometry characterization ...
1165
+
Tab. 3. MALDI-TOF experimental molar masses of Ag -
ionized samples (dithranol/silver trifluoroacetate matrix).
Observed masses
Identified
series
Samples including
the series
1
1
2
358, 1462, 1566 ...
373, 1477, 1581 ...
302, 2406, 2510 ...
series A
series B
series C
PS-I, PS-II
PS-I, PS-II
PS-C60(I), PS-C60(II)
Conclusion
C
60 end-capped polystyrene was successfully synthesized
by the ATRP method. MALDI-TOF mass spectrometry
characterization of the samples with dithranol/silver tri-
fluoroacetate as the matrix demonstrates that C60 was
monosubstituted. However, the mechanism of the frag-
mentation needs further research.
Acknowledgement: This work was financially supported by
the NCSF (projects 59703001, 59843008).
Received: June 28, 1999
Revised: January 31, 2000
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Fig. 3. MALDI-TOF mass spectra obtained with dithranol/sil-
ver trifluoroacetate matrix for C60-polystyrene samples PS-
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One further series is evident but has not been assigned
yet. Still the bromo end group can not be detected this
way. But from the MALDI data, we can be sure that C60
was monosubstituted since the data are in agreement with
each other. Tab. 3. shows the corresponding masses for
the three series A, B and C.
[
10] C. B. Jasieczek, D. M. Haddleton, A. J. Shooter, A. Buzy,
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