Functionalization of multiwalled carbon nanotubes with polyesters via bergman cyclization and

Article abstract of DOI:10.1002/pola.24365

In this work, pristine multiwalled carbon nanotubes (MWNTs) were functionalized by utilizing the free radicals generated through Bergman cyclization of enediyne containing compounds 3. Polyesters were subsequently grafted from the surface of MWNTs through

Full text of DOI:10.1002/pola.24365

Functionalization of Multiwalled Carbon Nanotubes with Polyesters via
Bergman Cyclization and ‘‘Grafting from’’ Strategy
JIANGUO MA,1,2 XIN CHENG,1 XIAOWEI MA,1 SHENG DENG,1 AIGUO HU1
1Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering,
East China University of Science and Technology, Shanghai 200237, China
2Faculty of Chemistry Biology and Materials Science, East China Institute of Technology, Jiangxi 344000, China
Received 14 August 2010; accepted 30 August 2010
DOI: 10.1002/pola.24365
Published online 13 October 2010 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: In this work, pristine multiwalled carbon nanotubes
(MWNTs) were functionalized by utilizing the free radicals gen-
erated through Bergman cyclization of enediyne containing
compounds 3. Polyesters were subsequently grafted from the
surface of MWNTs through ring-opening polymerization of e-
caprolactone or lactide initiated by free hydroxy groups gener-
ated after hydrolysis of ester groups. Functionalized MWNTs
were characterized with a variety of techniques, including TGA,
NMR, IR, UV–vis, TEM, and Raman spectroscopy. After surface
modification, MWNTs showed good solubility in common or-
ganic solvents and polymer solutions. Fabrication of MWNTs
polymer nanocomposites was revealed through electrospin-
C
V
ning with polycaprolactone.
2010 Wiley Periodicals, Inc.
J Polym Sci Part A: Polym Chem 48: 5541–5548, 2010
KEYWORDS: Bergman cyclization; carbon nanotubes; electro-
spinning; functionalization; modification; nanocomposites;
polyesters
INTRODUCTION Recent years have witnessed great interests
and extensive explorations on carbon nanotubes (CNTs),
including single-walled carbon tubes and multiwalled carbon
nanotubes (MWNTs), due to their unique mechanical and
electrical properties. Potential applications of CNTs in com-
posite materials,1–4 nanoelectronics,5,6 sensors,7–9 biomedical
delivery,10,11 and photovoltaic devices12 were revealed in
various aspects. Pristine CNTs have poor solubility and dis-
persibility in common solvents because of their bundled
structure originated from strong van der Waals forces and
p–p stacking, which seriously limited the researches and
applications of CNTs in many fields. Consequently, surface
modifications on CNTs to make them more rational and con-
trollable in manipulation are critically important. Two strat-
egies namely covalent13–15 and noncovalent modification16–18
were typically applied, while covalent functionalization was
considered as a more efficient way due to the bundled CNTs
can be exfoliated layer by layer and easily dispersed in vari-
ous media through this method. Many work on covalent
modification of CNTs were reported in recent years, includ-
ing cycloaddition,19–24 coupling reaction,25,26 electrochemical
functionalization,27–29 ozonolysis,30–32 fluorination,33–35 free
radicals addition,36–39 etc. Herein, we wish to report our
work on surface functionalization of MWNTs with diradicals
generated via Bergman cyclization followed by ring-opening
polymerization of caprolactone (CL) and lactide (LA).
heated or shined with UV light. Diradical intermediates are
generated during these processes. During past decades, a
variety of naturally occurring enediyne containing antibiotics
were identified and their strong cytotoxicity was proved to
be associated with in situ triggered Bergman cyclization. Fol-
lowing this finding, great deals of researches were intrigued
in synthesizing biosimilar compounds for potential applica-
tions in antitumor medicines.41–44 In addition, Bergman cy-
clization has been applied to polymer and material science
in generating ill-defined polynaphthalene in mesoporous
silica channels,45 initiating free radical polymerizations,46,47
preparing carbon-enriched materials for thin-film lithogra-
phy,48 generating precursors for glassy carbon.49 Smith and
coworkers50 found that diradicals from bis-o-diynyl arene
(BODA) precursors react with carbon nano-onion and greatly
improved the solubility of these carbonous materials.
Recently, we applied Bergman cyclization in preparation of
soluble-conjugated polymers and mesoporous carbon materi-
als.51–53 The high reactivity of diradical intermediates gener-
ated through Bergman cyclization is essential in construction
of these nanostructures. In this work, we synthesized a sim-
ple enediyne containing compound 3 and conducted thermal
Bergman cyclization in the presence of MWNTs. The hydroxy
functionality introduced onto MWNTs was then allowed to
initiate ring-opening polymerization of CL or LA to graft
these polyesters from MWNTs. The solubility of functional-
ized MWNT in common organic solvents and polycaprolac-
tone (PCL) matrix were greatly improved.
Bergman cyclization40 is a ring formation reaction of ene-
diyne (1,5-diyn-3-ene) containing compounds when they are
Correspondence to: A. Hu (E-mail: hagmhsn@ecust.edu.cn)
C
V
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 5541–5548 (2010) 2010 Wiley Periodicals, Inc.
FUNCTIONALIZATION OF MULTIWALLED CARBON NANOTUBES, MA ET AL.
5541

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 1 Synthesis of enediyne-containing ester 3.
RESULTS AND DISCUSSION
pound 3 was slowly added to a boiling suspension of
MWNTs in N-methylpyrolinone (NMP) through a peristalsis
pump. Surface functionalized MWNTs were obtained with
good solubility in various solvents for further modification.
In a control experiment, ‘‘mix-in-once’’ strategy was explored.
After heating a mixture of 3 and MWNTs for 3 days, a black
gum was formed, which was indispersible in any solvent.
This experiment further confirmed the superiority of slow
addition method for minimizing side reactions.
Surface Functionalization of MWNTs
Structural diversity of enediyne compounds allows introduc-
tion of various functional groups onto MWNTs for further
modifications. In this study, compound 3 was chosen due to
its structural feature and facial preparation. Differential scan-
ning calorimetry (DSC) study showed that this compound
undergoes thermal Bergman cyclization when it was heated
53
ꢀ
up to 150 C. The acetyl groups are important for efficient
surface functionalization. We found that without this protec-
tion, hydroxy groups could quench free radicals generated
by Bergman cyclization and seriously affect the grafting den-
sity of enediyne compounds onto MWNTs and solubility of
functionalized MWNTs in common organic solvents. After
Bergman cyclization, the acetyl groups could be easily
removed to release free hydroxy groups for further function-
alization (Schemes 1 and 2).
Grafting Polyester from MWNTs
PCL and polylactide were grafted from MWNTs initiated with
free hydroxyl groups on the surface of MWNTs. By mixing
surface functionalized MWNTs-OH (5) with monomers and
catalysts, the polymerizations were run at 110 ꢀC with
strictly removal of water. Due to the polyesters grafted onto
the sidewall of MWNTs exfoliate the bundles of CNTs, the
functionalized MWNTs can be easily dispersed in many com-
mon organic solvents such as NMP, CH2Cl2, N,N-dimethylfor-
mamide, and tetrahydrofuran (THF). The black and homoge-
neous solutions of functionalized MWNTs in these solvents
are stable for long time.
Functionalization of MWNTs Through
‘‘Slow Addition’’ Method
Slow addition strategy was especially attractive for thermal
triggered reaction to minimize the concentration of highly re-
active intermediates and lower the possibility of side reac-
tions, such as radical–radical coupling reactions. Hawker and
coworkers54,55 used this technique to synthesize polymeric
nanoparticles through intramolecular chain collapse of ben-
zocyclobutenes (BCB)-containing random copolymers. Sakel-
lariou et al.56 prepared polymer functionalized MWNTs via
slow addition of BCB-containing compounds into a hot sus-
pension of MWNTs. In this work, a degassed solution of com-
Characterization with TGA Analysis
As one of the most important methods for characterization of
functionalized CNTs, thermal gravimetric analysis (TGA) can be
used to analyze the amount of surface bounded groups grafted
to the carbonous materials according to different thermal sta-
bility of these two parts. The TGA curves of functionalized
MWNTs-PCL (6) and MWNTs-PLA (7) are shown in Figure 1.
Figure 1(A) shows TGA scan curves of pristine MWNTs,
SCHEME 2 Surface functionaliza-
tion of MWNTs and ring-opening
polymerization of CL and LA.
5542
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
FIGURE 1 TGA (10 ꢀC/min, in air)
of (A) pristine MWNTs (a),
MWNTs-OH (5) (b), MWNTs-PCL
(6) (c), and PCL (d). (B) Pristine
MWNTs (a), MWNTs-OH (5) (b),
MWNTs-PLA (7) (c), and PLA (d).
MWNTs-OH (5), MWNTs-PCL (6), and PCL. In comparison with
pristine MWNTs, the thermal degradation of MWNTs-PCL (6)
is divided into twoꢀ stages, the weight loss in the temperature
range of 150–350 C is related to the degradationꢀof the PCL
parts, while the weight loss between 350 and 550 C is attrib-
uted to carbon-rich moieties like substituted naphthalene on
the surface of MWNTs. The contents of these two parts are ap-
proximate 40% and 18%, respectively. Similarly, TGA curves
for MWNTs-PLA (7) cases are shown in Figure 1(B). The
weight losses in the temperature range of 120–320 ꢀC and
320–550 ꢀC are related to the weight losses of PLA and car-
bon-rich moieties on the sidewalls of the MWNTs, which are
about 43% and 17%, respectively.
Similarly, the peaks at 1.6 and 5.2 ppm in spectra (a) of Fig-
ure 2(B) are corresponding to the protons of methyl and
methine groups in PLA chains, respectively. All these charac-
teristic peaks are clearly seen in spectra of functionalized
MWNTs, indicative of successful surface functionalization.
The protons corresponding to enediyne parts, however, were
barely seen in the spectra. It is because all these protons are
very close to MWNTs, the motion of these protons was seri-
ously restricted, and NMR signals were broadened and weak-
ened accordingly.57 The shielding effect of peripheral polyes-
ter groups is also responsible for this signal weakening.
Characterization with Raman Spectroscopy
Figure 3 shows D band (1346 cmꢁ1), G band (1580 cmꢁ1),
and 2D band (2706 cmꢁ1) of pristine MWNTs, MWNTs-PCL
(6), and MWNTs-PLA (7), respectively. G band is the E2g
model corresponding to the movement in the opposite direc-
tion of two neighboring carbon atoms in a graphitic sheet
and it is related to the benzenoid framework of the MWNTs.
D band is an A1g breathing mode assigned to the defects in
the curved graphite sheet, sp3 carbon, or other impurities of
1
Characterization with H NMR Spectroscopy
After surface modification, MWNTs showed good solubility in
a variety of solvents, like THF, CHCl3, and hexane. Thus, solu-
tion 1H NMR spectroscopy was used to characterize surface
functionalities. In Figure 2(A), the characteristic peaks at 1.3,
1.6, 2.3, and 4.0 ppm in spectra (a) were assigned to the
protons of methylene groups in PCL chains, respectively.
FIGURE 2 1H NMR spectra of (A) PCL (a) and MWNTs-PCL (6) (b). (B) PLA (a) and MWNTs-PLA (7) (b).
FUNCTIONALIZATION OF MULTIWALLED CARBON NANOTUBES, MA ET AL.
5543

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
(6) (c) in Figure 4(A) both indicated CAH stretching vibra-
tions at 2916 cmꢁ1 that did not present in the spectrum of
pristine MWNTs, which are assigned to the methylene
groups of the enediyne moieties and PCL polymers on the
sidewall of MWNTs. In addition, the presence of the carbonyl
groups and CAOAC stretching vibration of ester groups in
Figure 4(A) (c) at approximately 1725 and 1162 cmꢁ1
proved that PCL polymers were grafted onto MWNTs. Simi-
larly, the IR spectrum in Figure 4(B) (b, c) indicated CAH
stretching vibrations of methylene groups, carbonyl groups
and CAOAC stretching vibration of ester groups at 2917,
1747, and 1176 cmꢁ1, respectively. The results also con-
firmed the attachment of PLA on MWNTs.
Characterization with UV–vis Spectroscopy
FIGURE 3 Raman spectra of pristine MWNTs (a), MWNTs-PCL
(6) (b), MWNTs-PLA (7) (c).
The UV–vis absorption spectra of functionalized MWNTs and
pristine MWNTs dispersed in CHCl3 are shown in Figure 5.
The results demonstrated a broad absorption signal decreas-
ing from 280 to 800 nm corresponding to the pristine
MWNTs and polymer-grafted MWNTs. Comparing the spectra
of MWNTs-PCL (6) (b), MWNTs-PLA (7) (c) with pristine
MWNTs (a), it is clear that the van Hove singularities from
490 to 800 nm are completely lost in spectra b and c, which
is due to significant numbers of sp2-hybridized carbons were
converted to sp3 hybridization. The difference in this region
between pristine MWNTs and functionalized MWNTs indi-
cates the covalent modification of nanotubes. Moreover, spec-
tra b illustrates that the curve of MWNTs-PCL (6) shows ab-
sorbance peaks at approximately 280 and 350 nm, which
are assigned to the p-p* transition of aryl ring on the surface
of MWNTs and carbonyl groups in PCL. A broad absorbance
peak is also shown up in the spectrum of MWNTs-PCL (6)
from 350 to 490 nm, which is corresponding to the fused
naphthalene ring structures of oligomers on the nanotubes
originated from Bergman cyclization of compound 3. Similar
trend are shown in the spectrum of MWNTs-PLA (7) (c) in-
dicative of the presence of naphthalene ring structures and
carbonyl groups.
MWNTs.58 The intensity ratio of these two bands ID/IG was
typically used as an index of graphitization of carbonous
materials. It is expected that the ratio ID/IG increased when
more defects are introduced during surface functionalization
of MWNTs. In comparison of the Raman spectra of the pris-
tine MWNTs and functionalized MWNTs in Figure 3, it clear
that the ratios ID/IG of MWNTs-PCL and MWNTs-PLA both
slightly decrease. Possible causes for this phenomenon are:
(1) the attack of radicals to MWNTs may selectively take
place at imperfect sites of MWNTs that mainly consisted of
sp3 carbons or on the outer layer of CNTs,59 the functionali-
zation would thus not introduce more defects to MWNTs;
(2) The increase of intensity of D bands might also be offset
by a simultaneous removal of some amorphous carbon
atoms during modification.60–62
Characterization with Fourier Transform Infrared
Spectroscopy (FTIR)
FTIR spectra of MWNTs-PCL and MWNTs-PLA are shown in
Figure 4. The spectra of MWNTs-OH (5) (b) and MWNTs-PCL
FIGURE 4 FTIR spectra of (A) pristine MWNTs (a), MWNTs-OH (5) (b), MWNTs-PCL (6) (c), and PCL (d). (B) pristine MWNTs (a),
MWNTs-OH (5) (b), MWNTs-PLA (7) (c), and PLA (d).
5544
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
MWNTs-PLA (7) in common organic solvents, we explored
fabrication of MWNTs polymer nanocomposites through
electrospinning with a biocompatible and biodegradable
polymer, PCL. An ink-like solution was obtained after stirring
a mixture of functionalized MWNTs, PCL, and THF for a
ꢀ
while at 40 C, which was stable even after long time stand-
ing. Then, the composite fibers were obtained by electro-
spinning. TEM images (Fig. 7) show that all MWNTs are well
distributed in PCL fibers. The axes of MWNTs are parallel to
the direction of PCL fibers. Cheng and coworkers63 studied
the alignment of MWNTs in electrospun nanofibers, this phe-
nomenon was proved to be the main factor for enhancing
the strength of polymer fibers by adding CNTs. The uniform-
ity of functionalized MWNTs in polymer nanofibers is
another evidence of the effectiveness of our functionalization
method.
FIGURE 5 UV–vis spectra of pristine MWNTs (a), MWNTs-PCL
(6) (b), MWNTs-PLA (7) (c) in CHCl3.
EXPERIMENTAL
Characterization with Transmission Electron
Micrographs
Materials
Functionalized MWNTs were characterized using transmis-
sion electron micrographs (TEM). The samples were drop
coated on to a copper grid and viewed through TEM. A sub-
stantial amount of amorphous organic layer on the surface
of MWNTs was identified in the TEM images (Fig. 6). The in-
homogeneous layer on the sidewall of tubes was attributed
to polymers of CL or LA initiated by hydroxyl groups from
oligomers of compound 3, which are originated from Berg-
man cyclization of enediyne compound 3 with sp2 carbons of
the CNTs.
THF, triethylamine, and NMP were dried with sodium or cal-
cium hydride (CaH2) under an atmosphere of nitrogen before
use. MWNTs were provided by the Chengdu Organic Chemi-
cals, Chinese Academy of Science, they were prepared
through CVD methods. e-CL (99%, Acros Organic) was dried
over CaH2, distilled under reduced pressure, and stored over
activated 4 Å molecular sieves. LA was synthesized according
to literature procedure.65 PCL (Mn ꢂ 1 ꢃ 105) was obtained
from Shenzhen BrightChina, Industrial. 4-(2-(2-(Trimethylsi-
lyl)ethynyl)phenyl)-but-3-yn-1-ol (1) was synthesized
according to literature procedure.66 Stannous (II) 2-ethylhex-
anoate (SnOct2) (Sigma) and other reagents were commercial
chemicals and used as received. All reactions were per-
formed with dried Schlenk techniques under nitrogen atmos-
phere unless otherwise noted.
Electrospun Fibers of Functionalized MWNTs
in PCL Complex
As a nanofiber assembly technique, electrospinning fabricate
polymer nanofibers with ultra-low diameters by utilizing an
electrostatic field of several KV/cm. With this technique,
CNTs and modified CNTs were electrospun with various
polymers, like polyacryloylnitrile, polyethyleneoxide, and poly-
ureathane.22,63,64 It was found that the mechanical and ther-
mal properties of the composite polymer fibers were greatly
improved by formation of nanocomposites with modified
CNTs. Considering the good solubility MWNTs-PCL (6) and
Characterization
1H NMR (400 MHz) and 13C NMR (100 MHz) spectra were
recorded in chloroform-d (CDCl3) on an Ultra Shield 400
spectrometer (Bruker BioSpin AG, Magnet System 400 MHz/
54 mm). Mass spectra were generated with Micromass LCT
(ESI-TOF). FTIR was recorded from KBr pallets on a Nicolet
FIGURE 6 TEM images of MWNTs-PCL (6) (left) and MWNTs-PLA (7) (right).
FUNCTIONALIZATION OF MULTIWALLED CARBON NANOTUBES, MA ET AL.
5545

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 7 TEM images of electrospun fibers with embedded MWNTs-PCL (6) (left) and MWNTs-PLA (7) (right).
Magna 5700 FTIR spectrometer. UV–vis analyses were per-
formed on a UV-2550PC spectrometer from CHCl3 solutions
at room temperature. TEM images were collected on a JEOL-
200CX TEM system (LRTEM, 120 kV). TGA were conducted
on a TG/WRT-2P. Raman spectra were recorded using a
Renishaw in Via þ Reflex Raman spectrometer.
Purification of MWNTs
MWNTs were purified according to literature procedure.14
As-received MWNTs (150 mg) were sonicated for 30 min
and washed with aqueous HF for three times, and then
refluxed in 6 M nitric acid for 24 h. After cooled to room
temperature, the reaction mixture was first rinsed with
deionized water and then filtered through a 0.2-lm poly-
tetrafluoroethylene (PTFE) membrane. The residue was
Synthesis
ꢀ
4-(2-(2-(Trimethylsilyl)ethynyl)phenyl)but-3-ynyl
Acetate (2)
anneꢀaled at 250 C for 2 h under air followed by heating to
450 C for 2 h under nitrogen.
Compound 1 (2.42 g, 10 mmol) was added with acetic anhy-
dride (3.09 g, 30 mmol), and the mixture was stirred over-
night at 80 C. After cooled to room temperature, the excess
Synthesis of MWNTs-3 (4)
ꢀ
Purified MWNTs (100 mg) in NMP (10 mL) was sonicated
for 30 min, and the solution was heated to reflux in a
Schlenk flask with vigorous stirring. In another Schlenk flask,
compound 3 (300 mg) was dissolved in NMP (12 mL) and
slowly added via a peristalsis pump to the above suspension
of MWNTs under nitrogen. After addition, the reaction mix-
ture was refluxed for 3 days. The mixture was then filtered
using a 0.2-lm PTFE membrane and washed with a large
excess of diethyl ether and THF. The residue was dried at
90 ꢀC for 24 h under vacuum and surface-grafted MWNTs
(135 mg) were obtained.
acetic anhydride was removed under reduced pressure and a
dark orange oil was obtained without further purification
(2.85 g, 100%).
1H NMR (CDCl3, d): 7.42 (Ph-H, 2H), 7.20 (Ph-H, 2H), 4.25
(ACCACH2ACH2A, 2H), 2.78 (ACCACH2ACH2A, 2H), 2.06
(AOACOACH3, 3H), 0.24 (ASiACH3, 9H). 13C NMR (CDCl3,
d): 169.8, 131.2, 127.3, 125.3, 102.7, 97.3, 88.7, 80.1, 61.8,
20.0, 19.2, 0.9. MS (ESIþ): Anal. Calcd for C17H20O2Si:
307.1130 [(M þ Na)þ]. found: 307.1129 [(M þ Na)þ].
4-(2-Ethynylphenyl)but-3-ynyl Acetate (3)
Synthesis of MWNTs-OH (5)
To a solution of compound 2 (2.56 g, 9 mmol) in THF (40
mL) was added tetrabutylammonium fluoride (11.77 g, 5
equiv. to trimethylsilyl group). After stirred for 1.5 h at room
temperature under nitrogen, the solution was passed
through a short silica gel column and eluted with ethyl ace-
tate. The crude product was subsequently purified by col-
umn chromatography using ethyl acetate/petroleum ether
(1/25) as elute (Rf ¼ 0.85) to give pure product as a dark
yellow oil (1.81 g, 95%). Note: This reaction was run in dark
environment.
To a mixture of 4 (120 mg) in THF (25 mL) and methanol
(5 mL), a solution of KOH (0.45 g, 8 mmol) in deionized
water (5 mL) was added. After refluxed overnight, the reac-
tion mixture was filtered using a 0.2-lm PTFE membrane
and washed with a large excess of deionized water, ethanol,
ꢀ
and THF. The residue was dried at 90 C for 72 h under vac-
uum to give 5 (104 mg).
In the synthesis of 6 and 7, all glasswares and needles were
ꢀ
dried in an oven at 180 C for 24 h prior to use and all reac-
tions were performed under a dry nitrogen atmosphere.
1H NMR (CDCl3, d): 7.42 (Ph-H, 2H), 7.24 (Ph-H, 2H), 4.26
(ACCACH2ACH2A, 2H), 3.26 (ACCAH, 1H), 2.80
(ACCACH2ACH2A, 2H). 13C NMR (CDCl3, d): 170.6, 131.7,
127.4, 126.1, 124.3, 89.6, 81.2, 80.5, 62.1, 20.6, 19.8. MS
(ESIþ): Anal. Calcd for C14H12O2: 235.0735 [(M þ Na)þ].
Found: 235.0728 [(M þ Na)þ].
Synthesis of MWNTs-PCL (6)
Compound 5 (25 mg) in a Schlenk flask was dried by three
azeotropic distillations of dry toluene, and then dry toluene
(2 mL) was added and sonicated for 30 min before adding
ꢀ
CL (0.15 mL). The flask was put into a 110 C oil bath with
5546
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
REFERENCES AND NOTES
vigorous stirring for about 10 min, Sn(Oct)2 (70 lL, 2 wt %
to CL) in dry toluene (1.5 mL) was added, and the reaction
mixture was refluxed at 110 C under nitrogen for 24 h. Af-
1 Byrne, M. T.; McNamee, W. P.; Gun’ko, Y. K. Nanotechnology
ꢀ
2008, 19, 415707 (8 pp).
ter cooled to room temperature, the mixture was filtered
using 0.2-lm PTFE membrane and collected by washing
with copious amount of THF, and then the residues were
dried at 80 ꢀC for 24 h under vacuum to give grafted
MWNTs (6) as a black powder (34 mg).
2 Banerjee, S.; Wong, S. S. Nano Lett 2002, 2, 49–53.
3 Zhu, J.; Kim, J. D.; Peng, H. Q.; Margrave, J. L.; Khabashesku,
V. N.; Barrera, E. V. Nano Lett 2003, 3, 1107–1113.
4 Byrne, M. T.; Gun’ko, Y. K. Adv Mater 2010, 22, 1672–1688.
5 Zhao, J. J.; Park, H. K.; Han, J.; Lu, J. P. J Phys Chem B 2004,
108, 4227–4230.
Synthesis of MWNTs-PLA (7)67
6 Zhang, W.; Shaikh, A. U.; Tsui, E. Y.; Swager, T. M. Chem
Compound 5 (20 mg) in a Schlenk flask was dried by three
azeotropic distillations of dry toluene, and then dry toluene
(2 mL) was added and sonicated for 30 min before adding
LA (0.76 g), The flask was put into a 110 ꢀC oil bath with
vigorous stirring for about 5 min, Sn(Oct)2 (65 lL, 2 wt %
to LA) in dry toluene (1.2 mL) was added, and the reaction
mixture was refluxed at 110 ꢀC under nitrogen for 24 h.
After cooled to room temperature, the mixture was filtered
using 0.2-lm PTFE membrane and collected by washing
with cꢀopious amount of THF, and then the residue was dried
at 60 C for 24 h under vacuum to give grafted MWNTs (7)
as a black powder (33 mg).
Mater 2009, 21, 3234–3241.
7 Yan, H.; Zhou, H. J.; Yu, P.; Su, L.; Mao, L. Q. Adv Mater
2008, 20, 2899–2906.
8 Nakayama-Ratchford, N.; Bangsaruntip, S.; Sun, X. M.;
Welsher, K.; Dai, H. J. J Am Chem Soc 2007, 129, 2448–2449.
9 Tu, W. W.; Lei, J. P.; Ju, H. X. Chem Eur J 2009, 15, 779–784.
10 Georgin, D.; Czarny, B.; Botquin, M.; Mayne-L’Hermite, M.;
Pinault, M.; Bouchet-Fabre, B.; Carriere, M.; Poncy, J. L.; Chau,
Q.; Maximilien, R.; Dive, V.; Taran, F. J Am Chem Soc 2009,
131, 14658–14659.
11 Kam, N. W. S.; Liu, Z.; Dai, H. J. J Am Chem Soc 2005, 127,
Electrospinning was carried out using a syringe and a stain-
less steel needle with flat tip at an applied voltage of 22 kV.
A grounded aluminum plate located at a distance of 25 cm
from the tip of the needle was used as a fiber-collecting
device. The fibers were electrospun with a mixture solution
of functionalized MWNTs/PCL/THF at weight ratio of
0.01:0.1:1.
12492–12493.
12 Yun, D. Q.; Feng, W.; Wu, H. C.; Li, B. M.; Liu, X. Z.; Yi, W.
H.; Qiang, J. F.; Gao, S.; Yan, S. L. Synth Met 2008, 158,
977–983.
13 Shi, J. H.; Yang, B. X.; Goh, S. H. Eur Polym J 2009, 45,
1002–1008.
14 Ke, G.; Guan, W. C.; Tang, C. Y.; Guan, W. J.; Deng, F. Bio-
macromolecules 2007, 8, 322–326.
CONCLUSIONS
15 Palacin, T.; Le Khanh, H.; Jousselme, B.; Jegou, P.; Filor-
amo, A.; Ehli, C.; Guldi, D. M.; Campidelli, S. J Am Chem Soc
2009, 131, 15394–15402.
In conclusion, we have demonstrated a new method of modi-
fication of pristine MWNTs utilizing diradicals produced by
Bergman cyclization. Further attachment of PCL and PLA
polymers were revealed by initiating ring-opening polymer-
ization of CL or LA with hydroxyl groups on the surface of
MWNTs. Two kinds of polymer functionalized MWNTs were
obtained. They showed good solubility in organic solvent
such as THF, CHCl3, CH2Cl2, and NMP. All the functionalized
MWNTs were characterized with TGA, IR, TEM, NMR, UV–vis,
and Raman spectroscopy. Results confirmed the occurrence
of sidewall modification of MWNTs. When the functionalized
MWNTs were combined with PCL fibers using electrospin-
ning technique, uniformly distributed MWNTs in polymer
fibers were found in TEM images. More applications for
functionalization of carbon nanomaterials via Bergman cycli-
zation are under investigation.
16 Ostojic, G. N.; Ireland, J. R.; Hersam, M. C. Langmuir 2008,
24, 9784–9789.
17 Richard, C.; Doan, B. T.; Beloeil, J. C.; Bessodes, M.; Toth,
E.; Scherman, D. Nano Lett 2008, 8, 232–236.
18 Assali, M.; Leal, M. P.; Fernandez, I.; Baati, R.; Mioskowski,
C.; Khiar, N. Soft Mater 2009, 5, 948–950.
19 Brunetti, F. G.; Herrero, M. A.; Munoz, J. D.; Diaz-Ortiz, A.;
Alfonsi, J.; Meneghetti, M.; Prato, M.; Vazquez, E. J Am Chem
Soc 2008, 130, 8094–8100.
20 Delgado, J. L.; de la Cruz, P.; Langa, F.; Urbina, A.; Casado,
J.; Navarrete, J. T. L. Chem Commun 2004, 1734–1735.
21 Li, J. X.; Grennberg, H. Chem Eur J 2006, 12, 3869–3875.
22 Zhang, W.; Sprafke, J. K.; Ma, M. L.; Tsui, E. Y.; Sydlik, S.
A.; Rutledge, G. C.; Swager, T. M. J Am Chem Soc 2009, 131,
8446–8454.
The support of National Natural Science Foundation of
China (20874026, 20704013), Shanghai Pujiang Program
(07PJ14024), Shuguang Project (07SG33), New Century Excel-
lent Talents in University, and Shanghai Leading Academic Dis-
cipline Project (B502) is gratefully acknowledged. A. Hu thanks
Prof. Xiaoyong Deng and Prof. Zheng Jiao of Shanghai University
for their kindly help in TEM.
23 Zhou, L.; Gao, C.; Zhu, D.; Xu, W.; Chen, F. F.; Palkar, A.;
Echegoyen, L.; Kong, E. S.-W. Chem Eur J 2009, 15, 1389–1396.
24 Gao, C.; He, H.; Zhou, L.; Zheng, X.; Zhang, Y. Chem Mater
2009, 21, 360–370.
FUNCTIONALIZATION OF MULTIWALLED CARBON NANOTUBES, MA ET AL.
5547

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
25 Cheng, F. Y.; Adronov, A. Chem Mater 2006, 18, 5389–5391.
47 Rule, J. D.; Moore, J. S. Macromolecules 2005, 38, 7266–7273.
26 Shi, D. L.; Guo, Y.; Dong, Z. Y.; Lian, J.; Wang, W.; Liu, G.
48 Chen, X. H.; Tolbert, L. M.; Hess, D. W.; Henderson, C.
K.; Wang, L. M.; Ewing, R. C. Adv Mater 2007, 19, 4033–4037.
Macromolecules 2001, 34, 4104–4108.
27 Zhang, Y. J.; Shen, Y. F.; Li, J. H.; Niu, L.; Dong, S. J.;
49 Smith, D. W.; Shah, H. V.; Perera, K. P. U.; Perpall, M. W.;
Ivaska, A. Langmuir 2005, 21, 4797–4800.
Babb, D. A.; Martin, S. J. Adv Funct Mater 2007, 17, 1237–1246.
28 Marcoux, P. R.; Hapiot, P.; Batail, P.; Pinson, J. New J Chem
50 Rettenbacher, A. S.; Perpall, M. W.; Echegoyen, L.; Hudson,
2004, 28, 302–307.
J.; Smith, D. W. Chem Mater 2007, 19, 1411–1417.
29 Goldsmith, B. R.; Coroneus, J. G.; Khalap, V. R.; Kane, A. A.;
51 Yang, X.; Li, Z.; Zhi, J.; Ma, J.; Hu, A. Langmuir 2010, 26,
Weiss, G. A.; Collins, P. G. Science 2007, 315, 77–81.
11244–11248.
30 Banerjee, S.; Wong, S. S.
J Phys Chem B 2002, 106,
52 Miao, C. C.; Zhi, J.; Sun, S. Y.; Yang, X.; Hu, A. G. J Polym
12144–12151.
Sci Part A: Polym Chem 2010, 48, 2187–2193.
31 Lau, C. H.; Cervini, R.; Clarke, S. R.; Markovic, M. G.; Mati-
sons, J. G.; Hawkins, S. C.; Huynh, C. P.; Simon, G. P. J Nano-
part Res 2008, 10, 77–88.
53 Cheng, X.; Ma, J.; Zhi, J.; Yang, X.; Hu, A. Macromolecules
2010, 43, 909–913.
54 Mackay, M. E.; Dao, T. T.; Tuteja, A.; Ho, D. L.; van Horn, B.;
32 Hemraj-Benny, T.; Bandosz, T. J.; Wong, S. S. J Colloid
Kim, H. C.; Hawker, C. J. Nat Mater 2003, 2, 762–766.
Interface Sci 2008, 317, 375–382.
55 Harth, E.; Van Horn, B.; Lee, V. Y.; Germack, D. S.; Gonzales,
C. P.; Miller, R. D.; Hawker, C. J. J Am Chem Soc 2002, 124,
8653–8660.
33 Plank, N. O. V.; Forrest, G. A.; Cheung, R.; Alexander, A. J. J
Phys Chem B 2005, 109, 22096–22101.
34 Stevens, J. L.; Huang, A. Y.; Peng, H. Q.; Chiang, L. W.; Kha-
56 Sakellariou, G.; Ji, H.; Mays, J. W.; Hadjichristidis, N.; Bas-
bashesku, V. N.; Margrave, J. L. Nano Lett 2003, 3, 331–336.
karan, D. Chem Mater 2007, 19, 6370–6372.
35 Valentini, L.; Puglia, D.; Armentano, I.; Kenny, J. M. Chem
57 Holzinger, M.; Abraha, J.; Whelan, P.; Graupner, R.; Ley, L.;
Hennrich, F.; Kappes, M.; Hirsch, A. J Am Chem Soc 2003, 125,
8566–8580.
Phys Lett 2005, 403, 385–389.
36 Martinez-Rubi, Y.; Guan, J.; Lin, S.; Scriver, C.; Sturgeon, R.
E.; Simard, B. Chem Commun 2007, 5146–5148.
58 Chen, C. L.; Liang, B.; Ogino, A.; Wang, X. K.; Nagatsu, M. J
Phys Chem C 2009, 113, 7659–7665.
37 Ying, Y. M.; Saini, R. K.; Liang, F.; Sadana, A. K.; Billups, W.
E. Org Lett 2003, 5, 1471–1473.
59 Georgakilas, V.; Bourlinos, A.; Gournis, D.; Tsoufis, T.; Tra-
palis, C.; Mateo-Alonso, A.; Prato, M. J Am Chem Soc 2008,
130, 8733–8740.
38 Chang, J. Y.; Wu, H. Y.; Hwang, G. L.; Su, T. Y. J Mater
Chem 2008, 18, 3972–3976.
60 Yang, D. Q.; Rochette, J. F.; Sacher, E. J Phys Chem B 2005,
39 Chattopadhyay, J.; Chakraborty, S.; Mukherjee, A.; Wang,
R.; Engel, P. S.; Billups, W. E. J Phys Chem C 2007, 111,
17928–17932.
109, 7788–7794.
61 Huang, W. J.; Lin, Y.; Taylor, S.; Gaillard, J.; Rao, A. M.;
Sun, Y. P. Nano Lett 2002, 2, 231–234.
40 Bergman, R. G. Acc Chem Res 1973, 6, 25–31.
62 Chen, G. X.; Kim, H. S.; Park, B. H.; Yoon, J. S. J Phys Chem
41 Basak, A.; Bag, S. S.; Basak, A. Bioorg Med Chem 2005, 13,
B 2005, 109, 22237–22243.
4096–4102.
63 Ge, J. J.; Hou, H.; Li, Q.; Graham, M. J.; Greiner, A.;
Reneker, D. H.; Harris, F. W.; Cheng, S. Z. D. J Am Chem Soc
2004, 126, 15754–15761.
42 Lewis, K. D.; Matzger, A. J. J Am Chem Soc 2005, 127,
9968–9969.
43 Kovalenko, S. V.; Alabugin, I. V. Chem Commun 2005,
64 Ko, F.; Gogotsi, Y.; Ali, A.; Naguib, N.; Ye, H.; Yang, G. L.;
1444–1446.
Li, C.; Willis, P. Adv Mater 2003, 15, 1161–1165.
44 Joshi, M. C.; Bisht, G. S.; Rawat, D. S. Bioorg Med Chem
65 Hyon, S.-H.; Jamshidi, K.; Ikada, Y. Biomaterials 1997, 18,
Lett 2007, 17, 3226–3230.
1503–1508.
45 Bhongale, C. J.; Yang, C.-H.; Hsu, C.-S. Chem Commun
66 Scott, E. E.; Donnelly, E. T.; Welker, M. E. J Organomet
2006, 2274–2276.
Chem 2003, 673, 67–76.
46 Rule, J. D.; Wilson, S. R.; Moore, J. S. J Am Chem Soc
2003, 125, 12992–12993.
67 Choi, I. S.; Langer, R. Macromolecules 2001, 34, 5361–5363.
5548
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA