Preparation and utilization of catalyst-functionalized single-walled carbon nanotubes for ring-opening metathesis polymerization

Article abstract of DOI:10.1021/ma0359584

Single-walled carbon nanotubes were oxidatively shortened and functionalized with ruthenium-based olefin metathesis catalysts. These catalyst-functionalized nanotubes were shown to be effective in the ring-opening metathesis polymerization of norbornene, resulting in rapid polymerization from the catalyst sites on the nanotube. It was found that high polymer molecular weights could be reached, and the molecular weight increased linearly with polymerization time. The resulting polynorbornene-functionalized nanotubes were found to exhibit solubility in organic solvents, whereas the starting materials and catalyst-functionalized nanotubes were completely insoluble. The polymerized materials were characterized by NMR, IR, DSC, AFM, and TEM.

Full text of DOI:10.1021/ma0359584

Macromolecules 2004, 37, 4755-4760
4755
Preparation and Utilization of Catalyst-Functionalized Single-Walled
Carbon Nanotubes for Ring-Opening Metathesis Polymerization
Yu a n qin Liu a n d Alex Ad r on ov*
Department of Chemistry and the Brockhouse Institute for Materials Research, McMaster University,
Hamilton, Ontario L8S 4M1, Canada
Received December 19, 2003; Revised Manuscript Received April 28, 2004
ABSTRACT: Single-walled carbon nanotubes were oxidatively shortened and functionalized with
ruthenium-based olefin metathesis catalysts. These catalyst-functionalized nanotubes were shown to be
effective in the ring-opening metathesis polymerization of norbornene, resulting in rapid polymerization
from the catalyst sites on the nanotube. It was found that high polymer molecular weights could be
reached, and the molecular weight increased linearly with polymerization time. The resulting polynor-
bornene-functionalized nanotubes were found to exhibit solubility in organic solvents, whereas the starting
materials and catalyst-functionalized nanotubes were completely insoluble. The polymerized materials
were characterized by NMR, IR, DSC, AFM, and TEM.
In tr od u ction
monomers, rather than full-length polymers), loss of
reactivity due to steric crowding on the nanotube surface
is not an issue and should result in higher grafting
density. Additionally, this approach benefits from its
modular nature, where the preparation of a single
initiator-functionalized nanotube sample can be used for
the polymerization of a wide variety of monomers. We,
It is now well established that the unique structural
and electronic properties of carbon nanotubes position
them as one of the leading materials for a wide array
of potential nanotechnological applications.1,2 As part
of the ongoing progress toward expanding their utility,
the preparation of carbon nanotube derivatives, through
chemical modification, has been the subject of intense
recent interest. One of the main goals of this work is
the improvement of nanotube solubility in various
organic and aqueous solvents, as well as their miscibility
1
2-14
and others,
have already shown that it is possible
to polymerize various monomers using atom transfer
radical polymerization (ATRP), resulting in nanotube
structures for which the solubility is controlled by the
nature of the attached polymers.
3
4
with bulk materials, such as polymers. It has been
identified that one of the most promising approaches
to the realization of both of these goals is the covalent
In an attempt to expand this general polymerization
strategy, we have undertaken the investigation of
nonradical approaches to polymer growth. One such
approach is ring-opening metathesis polymerization
5
functionalization of carbon nanotubes with polymers.
The resulting materials would combine the high me-
chanical strength and electronic conductivity of carbon
nanotubes with the solubility and processability of
appended macromolecules, allowing them to be homo-
geneously dispersed in bulk polymers without the
danger of phase separation. Such nanotube-loaded
materials may become useful as conducting layers
within a host of organic electronic devices, such as light-
emitting diodes, photovoltaics, and thin-film transistors.
A number of reports have demonstrated the feasibility
of attaching amine- and alcohol-functionalized polymeric
structures to the surface of single-walled carbon nano-
tubes (SWNTs) through amidation and esterification
with the carboxylic acid moieties at the ends and defect
sites of shortened SWNTs. Using this “grafting to”
(
ROMP) using ruthenium alkylidene catalysts.15 This
polymerization method has attracted significant atten-
tion due to its versatility, effectiveness, and functional
group tolerance, allowing for a variety of monomers
bearing polar, apolar, and charged functional groups to
1
6
be successfully polymerized. It has recently been
shown that extremely narrow polydispersities and
excellent control over polymer molecular weight and
architecture can be achieved if appropriate ligands are
utilized, where high ligand dissociation rates result in
1
7,18
rapid initiation of polymerization.
have made ROMP a useful methodology for the func-
All of these factors
tionalization of surfaces such as Si and SiO2.1
9,20
In fact,
successful ROMP from the surface of SWNTs, where the
ruthenium alkylidene catalysts were physisorbed on the
nanotube surface using pyrene molecules as anchors has
6
approach, SWNT conjugates with poly(ethylene imine),
7
8
poly(styrene), poly(ethylene oxide), poly(vinyl carba-
2
1
9
10
already been demonstrated. Although this strategy
resulted in successful polymerization and the production
of polymer-coated SWNTs, it was shown that high
molecular weight polymers tended to desorb from the
nanotube surface, as evidenced by a decrease in the
nanotube coating thickness when the polymerization
zole), and poly(vinyl alcohol) have been prepared. An
alternative method that has recently been exploited by
our group involves a “grafting from” approach that
requires the attachment of polymerization initiators to
the nanotubes followed by reaction with appropriate
monomers.11 Since this strategy involves the reaction
2
1
time exceeded 5-10 min.
of nanotubes with small molecules (initiators and
As an alternative to this supramolecular polymer
functionalization, we report here the covalent attach-
ment of ROMP catalysts to the ends and defect sites of
shortened SWNTs, and their subsequent utilization in
the controlled polymerization of norbornene monomers.
*
To whom correspondence should be addressed. Address:
Department of Chemistry, McMaster University, 1280 Main St.
W., Hamilton, Ontario L8S 4M1, Canada. Tel: (905) 525-9140 ext.
3514. Fax: (905) 521-2773. E-mail: adronov@mcmaster.ca.
2
1
0.1021/ma0359584 CCC: $27.50 © 2004 American Chemical Society
Published on Web 06/02/2004

4
756 Liu and Adronov
Sch em e 1
Macromolecules, Vol. 37, No. 13, 2004
Sch em e 2
We demonstrate that it is possible to graft high molec-
ular weight polymers to the nanotube surface, allowing
for the modification of nanotube properties.
F igu r e 1. IR spectra of compounds 1 (A), 5 (B), 7 (C), and 8
(D).
Resu lts a n d Discu ssion
the insolubility of the products formed in each of these
synthetic steps, their characterization was limited to
infrared (IR) spectroscopy. Figure 1 illustrates the IR
spectra for the shortened, but unfunctionalized, SWNTs
(A) as well as the norbornene-functionalized (B) and
catalyst-functionalized (C) structures. The IR spectrum
of the shortened nanotubes (Figure 1A) depicts the
SWNTs, purchased from Carbon Nanotechnologies
Inc., were initially shortened by sonication in H2SO4/
HNO3 for 2 h. This procedure resulted in carboxylic acid-
functionalized nanotubes having lengths in the range
1
1
of 330 nm. The acid groups were converted to acid-
chlorides using thionyl chloride (Scheme 1) and were
then treated with pentaerythritol, resulting in the
introduction of three primary alcohol functionalities for
every reacted acid group of the nanotube. The triol-
functionalized nanotubes (3) were then treated with the
acid-chloride derivative of 5-norbornene-2-carboxylic
acid (4) to produce the norbornene-functionalized nano-
tubes (5) which could subsequently be reacted with
ben zyliden e-bis(t r icycloh exylph osph in e)dich lor o-
ruthenium (1st generation Grubbs catalyst, 6), resulting
in the formation of catalyst-functionalized nanotubes,
-
1
expected CdO stretch at 1748 cm corresponding to
the carboxylic acid groups introduced as a result (Scheme
2) of the shortening process. The large IR band observed
-
1
-1
at 3400 cm
and the weak one at 1632 cm
are
attributed to the asymmetric bending and scissoring
vibrations, respectively, due to trace amounts of water
1
1
present in the KBr pellet used for the measurement.
In Figure 1B, the carbonyl stretch at 1737 cm
-
1
is
clearly indicative of the ester bond formation between
the norbornene and the alcohol of the SWNTs in
compound 5. In addition, the appearance of the C-H
7
(Scheme 2). This product was isolated by filtration
-
1
through a 200 nm-pore diameter Teflon membrane,
followed by extensive washing with methanol, dichlo-
romethane, and hexanes to remove any unreacted
catalyst. The isolated nanotubes (7) can be considered
as nanotube-based macroinitiators for ROMP. Due to
stretching frequencies at 2883 and 2968 cm
cor-
respond to the added alkyl groups in the transformation
from 1 to 5. Spectroscopic evidence for the conversion
of 5 to 7 is more subtle, but can be gathered from an
increase in the intensity of the CdC stretch at 1660

Macromolecules, Vol. 37, No. 13, 2004
Ring-Opening Metathesis Polymerization 4757
Sch em e 3
cm- relative to the carbonyl stretch at 1741 cm-1
1
.
However, the definitive evidence for the preparation of
the SWNT macroinitiator 7 was derived from its ability
to promote ROMP. Addition of norbornene to a suspen-
sion of 7 in degassed chloroform or heptane resulted in
a rapid polymerization from the surface of the nano-
tubes (Scheme 3). Typical polymerization times ranged
from 5 to 180 min. The polymerization products were
isolated by filtration through a 200 nm pore-diameter
Teflon membrane, followed by thorough washing with
dichloromethane, THF, and methanol. The IR spectrum
of a typical polymerized product (2 h polymerization
time) is depicted in Figure 1D. The significant intensity
F igu r e 2. Raman spectra of shortened nanotubes (A) and
polynorbornene-functionalized nanotubes (B).
-
1
of the C-H stretches at 2856 and 2926 cm is indica-
tive of the increased number of alkyl groups within the
product as a result of norbornene polymerization and
is consistent with the IR of polynorbornene itself. It
should be noted that any free polymer that may be
formed in solution is easily removed by the filtration/
washing step of the workup. Control experiments, where
the polymerization was carried out in the presence of
SWNTs, but with unattached catalyst 6, resulted in no
detectable attachment of polymers to the nanotubes, as
evidenced by the absence of any change in the IR
spectrum of the isolated nanotube product from that of
the starting material.
Figure 2 illustrates the Raman spectra of the short-
ened, unfunctionalized nanotubes and the polymerized
nanotubes (8). In both cases, the characteristic absorp-
tions of the nanotubes are clearly observable at ca. 260
-
1
and 1590 cm , corresponding to the radial breathing
F igu r e 3. Samples of shortened, unfunctionalized nanotubes
1 (A), Grubbs catalyst-functionalized nanotubes 7 (B), and
polymerized nanotubes 8 (C) in THF.
2
2
1
modes (RBM) and the tangential G band, respectively.
-
In addition, the broad disorder band at 1300 cm
3
indicates the presence of sp hybridized C atoms, which
are known to occur at defect sites in the nanotube
structure. The strong similarity between the two
Raman spectra indicates that the functionalization and
polymerization processes did not significantly alter the
nanotube structure.
2
3
It was found that the solubility of the polymerized
nanotubes was influenced by the appended polymers.
Prior to the polymerization step, the catalyst-function-
alized nanotubes were completely insoluble in all or-
ganic solvents. However, after polymerization, the
nanotubes became slightly soluble in THF, chloroform,
and dichloromethane (Figure 3). Utilizing the previously
published specific extinction coefficient for SWNTs (ꢀ500
F igu r e 4. 1H NMR spectra of polynorbornene (A) and
polynorbornene-functionalized nanotubes (B).
two spectra are nearly identical, indicating that nor-
bornene monomers were, indeed, polymerized with the
use of the nanotube macroinitiators.
To further explore the topological properties of the
hybrid materials, we utilized atomic force microscopy
(AFM). Sample preparation involved spin-coating sev-
eral drops of the nanotube solution onto a mica sub-
strate. Prior to polymerization, the initiator-function-
alized nanotubes were indistinguishable from typical
unfunctionalized structures, associating in small bundles
2
24
)
28.6 cm /mg), we were able to estimate the nanotube
concentration to be ca. 19 mg/L. Although quite low, this
level of solubility nevertheless allowed for the use of
solution NMR in the characterization of the polymerized
structures. Figure 4 depicts the 1H NMR spectra of
polynorbornene and the polymerized nanotubes 8. The

4
758 Liu and Adronov
Macromolecules, Vol. 37, No. 13, 2004
F igu r e 5. AFM images of nanotubes before (A) and after (B) polymerization. Two close-ups of individual structures, (C) and (D),
illustrate that the polymer density can be localized near the ends of the tubes in some cases (C) and along the entire wall of the
tubes in others (D). Profile traces at different points along the features are given below the AFM images (C) and (D).
F igu r e 7. Plot of the molecular weight and polydispersity of
polynorbornene cleaved from the SWNTs as a function of
polymerization time.
Further characterization of the polymerized nano-
tubes was done using transmission electron microscopy
(
TEM), as depicted in Figure 6. Again, solutions of 8 in
THF were drop-cast onto a holey carbon-coated copper
grid and allowed to air-dry. Low magnification TEM
images highlighted the presence of sheets and fibers of
amorphous carbon in which, upon close inspection, it
was possible to discern the presence of SWNTs. It
appeared as though the nanotubes were embedded
within a matrix of amorphous carbon, which corre-
sponds to the polymer coating on the SWNTs. In some
areas, it was also possible to observe portions of single
nanotubes spanning the gap between two regions of
polymer (Figure 6, inset).
F igu r e 6. TEM image of polymerized nanotubes. The inset
is a blow-up of the region within the box, showing a single
nanotube bridging the gap between two polymer regions
(arrow).
with diameters in the range of 1-3.5 nm (Figure 5A).
However, after polymerization, larger features were
observable, corresponding to SWNTs that are sur-
rounded by domains of polymer (Figure 5B). In some
cases, it was possible to observe larger polymer domains
near the ends of the nanotubes, likely because most of
the initiators were attached to the carboxylic acid groups
mainly located at the open nanotube ends (Figure 5C).
Other structures seemed to have polymer regions evenly
distributed along the entire length of the nanotube,
likely due to polymer wrapping or the attachment of
polymerization catalysts at defect sites along the side
walls of the nanotubes (Figure 5D). Height profiles for
the polymerized structures indicated that the height of
the features increased to 8-15 nm as a result of the
appended polymer structures (see the profile traces
below images C and D of Figure 5). However, it is not
possible to ascertain whether the observed features
contain individual nanotubes or bundles of tubes.
To determine the effect of polymerization time on
polymer molecular weight, we analyzed the polymers
produced in a series of polymerizations that ranged from
5 to 180 min in duration. Nanotube bound polymers
were cleaved by saponification of the ester linkages with
KOH/18-crown-6 in THF for 48 h at room temperature.
The SWNTs were separated from the cleaved polymer
by filtration through a 200 nm pore-diameter mem-
brane, leaving the pure polymer in the filtrate. SEC
analysis of the isolated polymers revealed a linear
increase in molecular weight with increasing polymer-
ization time (Figure 7). The polydispersities of the
samples were found to remain relatively constant at all
polymerization times.
It was also possible to measure the glass transition
temperature of the polynorbornene before and after
cleavage from the nanotubes. The nanotube bound

Macromolecules, Vol. 37, No. 13, 2004
Ring-Opening Metathesis Polymerization 4759
polymers were found to exhibit a Tg of 37 °C. After
cleavage, the Tg was found to decrease to 27 °C, which
Sh or ten in g a n d P u r ifica tion of SWNTs. A 250 mL flask
charged with SWNTs (100 mg) and a H SO /HNO (v/v: 3/1)
2 4 3
120 mL) solution was sonicated for 2 h. Then the suspension
was diluted in a 1000 mL beaker with distilled water (800 mL).
After cooling to room temperature, the dilute solution was
filtered through a 100-nm pore diameter polycarbonate mem-
brane. The black material collected on the membrane was
(
is very similar to previously reported literature values
for polynorbornene.25 The higher Tg observed for the
nanotube-bound polymers is due to their decreased
mobility as a result of nanotube attachment and is
consistent with our earlier observations with PMMA-
added to a 250 mL flask and stirred with H
/1, 50 mL) for 30 min at room temperature. Another 50 mL
of H SO /H O (v/v: 9/1) was added and the suspension was
2 4 2 2
SO /H O (v/v:
1
1
functionalized nanotubes, as well as other literature
9
reports of surface-bound polymers.26
2
4
2
2
sonicated for 5 min. After dilution using distilled water (800
mL) in a 1000 mL beaker, the suspension was filtered again.
The SWNT mat was washed thoroughly using NaOH solution
Con clu sion s
We have demonstrated that it is possible to function-
alize shortened SWNTs with ruthenium alkylidene
catalysts by utilizing the acid groups formed at the ends
and defect sites of nanotubes as a result of the shorten-
ing process. The catalyst-functionalized nanotubes are
effective initiators of norbornene polymerization. The
polymerizations were shown to result in the formation
of polynorbornene-functionalized nanotubes, which had
a slightly improved solubility in organic solvents. The
polymer molecular weights were shown to increase
linearly with time, and the polydispersities were found
to be consistent with expected values for the catalysts
used. Future work will involve the attachment of “third-
generation” ruthenium-based olefin metathesis cata-
lysts1 that will result in narrower polydispersities, and
will allow for the preparation of block copolymers.
Sidewall functionalization of SWNTs with ROMP cata-
lysts will also be investigated.
(10 mmol, 250 mL) and distilled water until the pH of the
filtrate was 7. Then the nanotubes were washed with an HCl
solution (2.0 M, 50 mL) before drying under vacuum overnight.
The product was obtained as a black solid (70.0 mg, 70% yield).
IR (KBr pellet): ν ) 1748 (m), 1632 (m).
Syn th esis of Tr iol-F u n ction a lized SWNTs (3). Short-
ened and purified SWNTs (44.0 mg) were added to thionyl
chloride (10.0 mL, 137 mmol) in a 25 mL flame dried flask.
The suspension was stirred under Ar at 70 °C for 48 h to
convert the acid groups to acid chlorides. The residual thionyl
chloride was evaporated in vacuo. Pentaerythritol (0.5 g, 3.7
mmol) and THF (10 mL) were then added into the flask. The
suspension was stirred at 70 °C for another 36 h. The reaction
mixture was then filtered through a 200-nm pore diameter
Teflon membrane, followed by washing with CH
2 2
Cl (300 mL),
7
THF (100 mL), and methanol (100 mL). The recovered residue
was finally dried under vacuum overnight, yielding 50 mg of
product. IR (KBr pellet): ν ) 3442 (s), 2929 (w), 2871 (w), 1752
(w), 1656 (m).
Syn th esis of Nor bor n en e-F u n ction a lized SWNTs (5).
The mixture of 5-norbornene-2-carboxylic acid (3.0 mL, 24.5
mmol) and thionyl chloride (8 mL, 109.7 mmol, 4.5 eq.) in a
flame-dried 25 mL flask was stirred at reflux under Ar for 24
h. It was then cooled, evaporated to dryness, and used directly.
Triol-functionalized SWNTs (3) (48 mg) were added to the
5-norbornene-2-carboxylic acid chloride along with 10 mL of
Exp er im en ta l Section
Gen er a l. Single-walled carbon nanotubes (SWNTs) were
purchased from Carbon Nanotechnologies, Inc. (Houston, TX).
N-(4-Hydroxyphenyl)glycine was purchased from Aldrich and
2
purified by recrystallization in distilled H O. Pentaerythritol,
octyl aldehyde, 5-norbornene-2-carboxylic acid, acryloyl chlo-
ride, thionyl chloride, 18-crown-6, triethylamine, benzylidene-
bis(tricyclohexylphosphine)dichlororuthenium (Grubbs cata-
lyst, 1st generation), and norbornene were all purchased from
Aldrich and used without further purification. All other
reagents and solvents were purchased from commercial sup-
pliers and used as received. FTIR was performed on a Bio-
Rad FTS-40 instrument. All samples were prepared as pellets
using spectroscopic grade KBr in a Carver press at 15 000 psi.
Laser Raman spectroscopy was performed on a Bruker RFS
2 2
CH Cl , 1 mL of anhydrous DMF, and 1 mL of triethylamine.
The suspension was stirred at 50 °C under Ar for 48 h. The
product was isolated by filtration through a 200 nm-pore
diameter Teflon membrane, followed by washing with metha-
2 2
nol (300 mL), THF (100 mL), and CH Cl (200 mL). The
recovered residue was then dried under vacuum overnight,
yielding 53 mg of product. IR (KBr pellet): ν ) 2968 (m), 2883
(w), 1737 (s), 1660-1530 (br, m), 1451 (w).
Syn th esis of Ca ta lyst-F u n ction a lized SWNTs (7). The
norbornene-functionalized SWNTs (5) (51 mg), benzylidene-
bis(tricyclohexylphosphine)dichlororuthenium catalyst (6) (20.0
1
00 instrument equipped with a YAG laser and a Ge high-
sensitivity detector. AFM was done using a Digital Instru-
ments NanoScope IIIa Multimode AFM, with samples pre-
pared by spin casting (4000 rpm) sample solutions or
suspensions on freshly cleaved mica substrates. The images
were recorded with standard tips in tapping mode at a scan
rate of 0.5 Hz. TEM analysis was performed using a Philips
CM12 operating at 120 keV. NMR was performed on a Bruker
-2
mg, 2.4 × 10 mmol), and heptane (10.0 mL) were added into
a 25 mL flask. The suspension was sonicated for 5 min and
then stirred at room temperature for 12 h. The product was
isolated by filtration through a 200-nm pore diameter Teflon
membrane, followed by washing with methanol (200 mL), CH
2
-
2
Cl (200 mL), and hexanes (200 mL). The recovered residue
2
00 MHz instrument in CDCl
3
. Differential scanning calorim-
was then dried under vacuum overnight. The resulting SWNT
macroinitiator was isolated as a black powder (54 mg). IR (KBr
pellet): ν ) 2937 (s), 2860 (m), 1741 (m), 1660 (w), 1451 (w),
1204 (w).
Gen er a l P r oced u r e for Rin g-Op en in g Meta th esis P o-
lym er iza tion u sin g th e SWNT Ma cr oin itia tor . Approxi-
mately 3.0 mg of the SWNT macroinitiator (7) was dispersed
etry (DSC) was performed on a TA 2100 Modulated Dif-
ferential Scanning Calorimeter with a temperature gradient
of 15°/min. Ultrasonication was done in a Banson Ultrasonics
B1510 bath sonicator. Filtration was done through either a
1
00-nm pore diameter polycarbonate membrane (Millipore),
or a 200-nm pore diameter Teflon membrane (Millipore).
Polymer molecular weight and polydispersity index (PDI) were
estimated by gel permeation chromatography (GPC) using a
Waters 2695 Separations Module equipped with a Waters 2996
Photodiode Array Detector, a Waters 2414 Refractive Index
Detector, a Waters 2475 Multi λ Fluorescence Detector, and
four Polymer Labs PLgel individual pore size columns. Poly-
styrene standards were used for calibration, and tetrahydro-
furan (THF) was used as the eluent at a flow rate of 1.0 mL/
min. The concentrations of the soluble polymer functionalized
SWNTs were calculated from UV/vis absorption results ob-
tained using a Varian Cary 50 Bio UV-visible spectropho-
tometer.
in 10 mL of CHCl
was degassed by bubbling with nitrogen for 5 min, and a
3
by sonication for 5 min. The suspension
-
3
solution of norbornene (0.5 g, 5.3 × 10 mol) in 5 mL of CHCl
3
was added. The suspension was then stirred at room temper-
ature for 5-180 min. The product was filtered through a 200
nm-pore diameter Teflon membrane, and washed with CH -
2
Cl (300 mL), THF (300 mL), and methanol (100 mL). The
2
recovered residue was then dried under vacuum overnight. IR
(KBr pellet): ν ) 2926 (s), 2856 (m), 1741 (m), 1648 (w), 1467
1
(w), 969 (w). H NMR (200 MHz, CDCl
3
): δ 0.91-1.19 (br),
1.19-1.48 (br), 1.64-1.97 (br), 2.20-2.55 (br), 2.70-2.90 (br),
5.12-5.40 (m).

4
760 Liu and Adronov
Macromolecules, Vol. 37, No. 13, 2004
Gen er a l P r oced u r e for Clea va ge of P olyn or bor n en e
(9) Wu, W.; Zhang, S.; Li, Y.; Li, J . X.; Liu, L. Q.; Qin, Y. J .;
fr om th e P olym er ized SWNTs. A sample of the polynor-
bornene-functionalized SWNTs (8) (51.0 mg) was suspended
in THF (50.0 mL) followed by the addition of ground KOH (0.2
g, 3.6 mmol) and 18-crown-6 (1.0 g, 3.8 mmol). The solution
was then stirred at room temperature for 48 h. The reaction
mixture was filtered through a 200-nm pore diameter Teflon
membrane, followed by washing with THF (250 mL). This
resulted in a black residue, composed of SWNTs, remaining
on the membrane, with the filtrate containing the cleaved
polynorbornene. The filtrate was concentrated to approxi-
mately 2 mL and precipitated into hexanes (100 mL). The
precipitate was then filtered and dried under vacuum over-
night, allowing the recovery of the cleaved polynorbornene as
a white solid (20 mg). IR (KBr pellet): ν ) 2956-2837 (br,
Guo, Z. X.; Dai, L. M.; Ye, C.; Zhu, D. B. Macromolecules
2
003, 36, 6286-6288.
(
(
(
(
(
(
(
(
(
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Sun, Y. P. Macromolecules 2003, 36, 7199-7204.
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16) Louie, J .; Grubbs, R. H. Organometallics 2002, 21, 2153-
m), 1660-1567 (br, m), 1470-1420 (br, m), 1351 (m), 1281 (w),
2
164.
1
1
250 (w), 1109 (s), 967 (m), 840 (w). H NMR (200 MHz,
17) Love, J . A.; Morgan, J . P.; Trnka, T. M.; Grubbs, R. H. Angew.
Chem., Int. Ed. 2002, 41, 4035-4037.
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CDCl
3
): δ 0.91-1.19 (br), 1.19-1.48 (br), 1.64-1.97 (br), 2.20-
2
.55 (br), 2.70-2.90 (br), 5.12-5.40 (m).
1
743-1746.
Ack n ow led gm en t. This work was supported by
(19) J uang, A.; Scherman, O. A.; Grubbs, R. H.; Lewis, N. S.
Langmuir 2001, 17, 1321-1323.
grants from the Natural Science and Engineering
Research Council of Canada (NSERC), the Canada
Foundation for Innovation, the Ontario Innovation
Trust, as well as McMaster University. Support in the
form of a Premier’s Research Excellence Award is also
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