Noncovalent side-wall functionalization of single-walled carbon nanotubes

Article abstract of DOI:10.1021/ma021417n

A family of poly[(m-phenylenevinylene)-co-(p-phenylenevinylene)]s, functionalized in the synthetically accessible C-5 position of the meta-disubstituted phenylene rings have been designed and synthesized: they are essentially poly{(5-alkoxy-m-phenylenevinylene)-co-[(2,5-dioctyloxy-p-phenylene)-vinylene]} (PAmPV) derivatives. A range of these PAwPV polymers have been prepared both (1) by the polymerization of O-substituted 5-hydroxyisophthaldehydes and (2) by chemical modifications carried out on polymers bearing reactive groups at the C-5 positions. PAmPV polymers solubilize SWNT bundles in organic solvents by wrapping themselves around the nanotube bundles. PAmPV derivatives which bear tethers or rings form pseudorotaxanes with rings and threads, respectively. The formation of the polypseudorotaxanes has been investigated in solution by NMR and UV/vis spectroscopies, as well as on silicon oxide wafers in the presence of SWNTs by AFM and surface potential microscopy. Wrapping of these functionalized PAmPV polymers around SWNTs results in the grafting of pseudorotaxanes along the walls of the nanotubes in a periodic fashion. The results hold out the prospect of being able to construct arrays of molecular switches and actuators.

Full text of DOI:10.1021/ma021417n

Macromolecules 2003, 36, 553-560
553
Articles
Noncovalent Side-Wall Functionalization of Single-Walled Carbon
Nanotubes
Alexa n d er Sta r ,† Yi Liu , Kevin Gr a n t, Lu d ek Rid va n , J . F r a ser Stod d a r t,*
Da vid W. Steu er m a n , Mich a el R. Dieh l, Ak r a m Bou k a i, a n d J a m es R. Hea th
Department of Chemistry and Biochemistry, University of California, Los Angeles,
405 Hilgard Avenue, Los Angeles, California 90095-1569
Received September 3, 2002; Revised Manuscript Received November 21, 2002
ABSTRACT: A family of poly[(m-phenylenevinylene)-co-(p-phenylenevinylene)]s, functionalized in the
synthetically accessible C-5 position of the meta-disubstituted phenylene rings have been designed and
synthesized: they are essentially poly{(5-alkoxy-m-phenylenevinylene)-co-[(2,5-dioctyloxy-p-phenylene)-
vinylene]} (PAmPV) derivatives. A range of these PAmPV polymers have been prepared both (1) by the
polymerization of O-substituted 5-hydroxyisophthaldehydes and (2) by chemical modifications carried
out on polymers bearing reactive groups at the C-5 positions. PAmPV polymers solubilize SWNT bundles
in organic solvents by wrapping themselves around the nanotube bundles. PAmPV derivatives which
bear tethers or rings form pseudorotaxanes with rings and threads, respectively. The formation of the
polypseudorotaxanes has been investigated in solution by NMR and UV/vis spectroscopies, as well as on
silicon oxide wafers in the presence of SWNTs by AFM and surface potential microscopy. Wrapping of
these functionalized PAmPV polymers around SWNTs results in the grafting of pseudorotaxanes along
the walls of the nanotubes in a periodic fashion. The results hold out the prospect of being able to construct
arrays of molecular switches and actuators.
In tr od u ction
own when it comes to mechanical strength and photo-
bleaching properties. The coiled morphologies of the
polymer chains help them wrap themselves around the
nanotubes when they are suspended in dilute solutions
of the polymer.
The small dimensions and remarkable physical prop-
erties of single-walled carbon nanotubes (SWNTs) ren-
der them unique materials with a wide range of
potential applications.1 However, their lack of solubility
in solvents presents a considerable impediment toward
harnessing their applications.2 Although the covalent
functionalization of the sidewalls of SWNTs leads to
soluble samples and opens up the possibility of attaching
other molecules to nanotubes,3,4 all the covalent chemi-
cal approaches disrupt the extended π-networks on their
surfaces, diminishing both their mechanical and elec-
tronic properties. On the other hand, a noncovalent
supramolecular approach which involves polymer wrap-
ping5-8 of the nanotubes preserves their unique proper-
ties.
The creation of polymer-nanotube composites holds
out much promise, both for reinforcing the polymers and
extending their applications in electronic device set-
tings. Recently, such a scenario has been demonstrated5
in the case of the conjugated luminescent polymer poly-
{(m-phenylenevinylene)-co-[(2,5-dioctyloxy-p-phenylene)-
vinylene]} (PmPV), filled with either SWNTs or multi-
walled carbon nanotubes. Compared with the pristine
polymer, these nanotube/PmPV composites have exhib-
ited large increases (by nearly 8 orders of magnitude)
in electrical conductivity with little loss in photolumi-
nescence and electroluminescence yields. Moreover, the
composite is far more robust than the polymer on its
We have also reported7 on the use of PmPV for
wrapping around SWNTs. Complexes (SWNT/PmPV)
are formed on account of stabilizing noncovalent bond-
ing interactions, presumably as a result of π-π stacking
and van der Waals interactions between PmPV and the
surfaces of the SWNTs. The nature of the interaction
of PmPV, as well as that of poly{(2,6-pyridinylene-
vinylene)-co-[(2,5-dioctyloxy-p-phenylene)vinylene]}
(PPyPV) (Scheme 1), with SWNTs has been investigated
and compared.8 Optoelectronic devices have also been
fabricated with these complexes. It is clear that nonco-
valent functionalization of carbon nanotubes can be
achieved without disrupting the primary structure of
the nanotubes themselves. To this extent, noncovalent
functionalization has potentially a virtue that all forms
of covalent functionalization lack.
In this paper, we report on the synthesis and char-
acterization of a variety of polymers functionalized in
the synthetically accessible C-5 position on the meta-
disubstituted phenylene ring, affording poly{(5-alkoxy-
m-phenylenevinylene)-co-[(2,5-dioctyloxy-p-phenylene)-
vinylene]} (PAmPV) derivatives. The new polymers
were all examined for their interactions with SWNTs.
They provide a ready means to change the physical
properties of nanotubes, such as their solubilities, as
well as the possibility of functionalizing them. PAmPV
derivatives, bearing tethers or rings that form pseu-
dorotaxanes with matching rings or threads represent
† Present address: Nanomix Inc., Emeryville, CA 94608.
* Corresponding Author: Telephone: (310) 206-7078. Fax:
(310) 206-1843. E-mail: stoddart@chem.ucla.edu.
10.1021/ma021417n CCC: $25.00 © 2003 American Chemical Society
Published on Web 01/04/2003

554 Star et al.
Macromolecules, Vol. 36, No. 3, 2003
Sch em e 1. Syn th esis of P oly{(m -p h en ylen evin ylen e)-co-[(2,5-d ioctyloxy-p-p h en ylen e)vin ylen e]}, or P m P V (X )
CH), P oly{(2,6-p yr id in ylen evin ylen e)-co-[(2,5-d ioctyloxy-p-p h en ylen e)vin ylen e]}, or P P yP V (X ) N) by Wittig
P olym er iza tion of Dip h osp h on iu m Sa lt 1 fr om Isop h th a ld eh yd e a n d 2,6-P yr id in ed ica r ba ld eh yd e, Resp ectively
Sch em e 2. Syn th esis of
P oly{(5-a lk oxy-m -p h en ylen evin ylen e)-co-[(2,5-
d ioctyloxy-p-p h en ylen e)vin ylen e]} or P Am P V
P olym er s by (a ) P olym er iza tion a n d (b) P olym er
Mod ifica tion
Sch em e 3. Syn th esis of 5-Hyd r oxyisop h th a ld eh yd e
(2a )a
a
Reagents and conditions: (a) LiAlH4, THF, reflux, 96%;
(b) K2Cr2O7, DMSO, 100 °C, 35%.
published procedure.10 Starting from the commercially
available 5-hydroxydiethylisophthalate (4), reduction
(LiAlH4/THF) gave (96%) 3,5-bishydroxymethylphenol
(5) which was oxidized, on treatment with a Me2SO
solution of potassium dichromate,11 to afford the key
monomer 2a . O-Alkylations of 2a could be performed
(Scheme 4) under relatively mild conditions, i.e., K2CO3
in DMF at room temperature using both bromides and
iodides as the alkylating agents. Alternatively, O-
alkylated 5-hydroxyisophthaldehydes could be obtained
by alkylation of 5-hydroxydiethylisophthalate (4); e.g.,
the Boc-protected derivative 2e was synthesized (Scheme
5) using this approach: 4 was alkylated with 6-azidoto-
sylhexanol and then the product was reducedsthe azide
to an amino function and the ester to alcoholsswith
LiAlH4/THF to afford 6 wherein the amino function was
protected with a Boc group prior to its being oxidized
(PCC/CH2Cl2) to the functionalized dialdehyde 2e. A
range of different O-alkylated 5-hydroxyisophthalde-
hydes (2b-e), including aliphatic alcohols, azides, and
protected amines, undergo (Schemes 4 and 5) bis-Wittig-
style polymerizations smoothly. However, the parent
phenol 2a did not afford polymers without it first being
protected12 as a methoxymethyl (MOM) ether 2f, which
did undergo (Scheme 6) the polymerization to give the
polymer 3f, from which the MOM-protecting groups
could be readily removed to afford 3a .
The PAmPV polymers were obtained (Table 1A) in
yields of 60-80% as a result of reacting the bis-Wittig
reagent, generated on treatment of the bisphosphonium
salt 1 with NaOEt in ethanolic THF containing the
O-substituted 5-hydroxyisophthaldehydes 2b-f. In com-
mon with Wittig reactions of this type, the new olefinic
bonds materialize as a mixture of cis and trans geom-
etries. However, the cis double bonds can be isomerized
to trans ones, giving the all-trans polymers, by heating
the crude polymers in PhMe under reflux in the pres-
ence of iodine as a catalyst. Although, this step pro-
ceeded quantitatively in all cases, one can anticipate a
problem when the substituted 5-hydroxyisophthalde-
hyde monomers react with iodine.13 Theoretically, such
PAmPV polymers could be prepared using the Wittig-
Horner reaction which relies on the use of bisphospho-
nates to produce olefinic bonds with exclusively the all-
trans configurations. Indeed, the parent PmPV polymer
two different types of polypseudorotaxanes.9 In this
article, we also describe the synthesis of self-assembling
pseudorotaxane-containing PAmPV polymers based on
the two different recognition motifss(i) one involving
hydrogen-bonding interactions between secondary di-
alkylammonium centers (e.g., dibenzylammonium ions)
and suitable crown ethers (e.g., benzo[24]crown-8) and
(ii) the other involving π-π stacking, [C-H‚‚‚O], and
[C-H‚‚‚π] interactions between π-electron-deficient hosts
(e.g., cyclobis(paraquat-p-phenylene) and π-electron-rich
guests (e.g., 1,5-bis(hydroxyethoxyethoxy)naphthalene).
Wrapping these functionalized polymers around SWNTs
results, in essence, in the grafting of pseudorotaxanes
along the walls of SWNTs in a periodic fashion.
Resu lts a n d Discu ssion
P r ep a r a tion a n d Ch a r a cter iza tion of F u n ction a l
P Am P V P olym er s. The polymers carrying functional
groups and arms have been prepared either (1) by using
a functionalized monomer directly or (2) by carrying out
subsequent reactions on the polymers. Whereas the first
method produces polymers with functional groups present
in all the repeating units, the second approach generates
randomly substituted polymers where the degree of
substitution depends on the efficiencies of the reactions
bringing about the modifications. We chose to introduce
functionality into the PmPV polymer (X ) CH in
Scheme 1) at the synthetically accessible C-5 position
on the meta-substituted phenylene rings along the
polymer backbone.
The PAmPV polymers 3 were prepared (Scheme 2)
from the precursors 2 by a bis-Wittig reaction with the
common bisphosphonium salt 1 whose synthesis was
described previously.8 A range of PAmPV polymers 3
have been prepared either (1) by polymerization of the
O-substituted 5-hydroxyisophthaldehydes 2 or (2) by
modifications of polymers bearing reactive groups at
their C-5 positions. 5-Hydroxyisophthaldehyde (2a ) was
synthesized (Scheme 3) by employing a variation of a

Macromolecules, Vol. 36, No. 3, 2003
Single-Walled Carbon Nanotubes 555
Sch em e 4. Syn th esis of th e F u n ction a l P Am P V P olym er s 3b-d a
a
Reagents and conditions: (a) RI or RBr, K2CO3, DMF, room temperature, 60-75%; (b) (i) 1, EtONa, EtOH/THF, 60%; (ii) I2
(cat), PhMe, reflux, 100%.
Sch em e 5. Syn th esis of P Am P V P olym er 3ea
Sch em e 7. P olym er Mod ifica tion sa
a
Reagents and conditions: (a) (i) 6-azido-1-(p-toluenesulfo-
nyloxy)hexane, K2CO3, DMF, 90%; (ii) LiAlH4, THF, reflux,
61%; (b) (i) Boc2O, NaHCO3, Na2CO3, 67%; (ii) PCC, CH2Cl2,
60%; (c) (i) 1, EtONa, EtOH/THF, 60%; (ii) I2 (cat), PhMe,
reflux, 100%.
Sch em e 6. Syn th esis of th e P h en ol-Con ta in in g
P Am P V P olym er 3a a
a
Reagents and conditions: (a) ClCH2OMe, Me2CO, K2CO3,
78%; (b) (i) 1, EtONa, EtOH/THF, 84%; (ii) I2 (cat), PhMe,
reflux, 100%; (c) HCl, iPrOH/THF, 92%.
a
Reagents and conditions: (a) diethyl acetylenedicarboxy-
late, PhMe, reflux, 90%; (b) CBr4, PPh3, THF, 0 °C to room
temperature, 92-94%; (c) N-(tert-butoxycarbonyl)-L-cysteine
methyl ester, Et3N, CHCl3, room temperature, 88-91%; (d)
thioacetic acid, Et3N, CHCl3, room temperature, 95%; (e)
thioctic acid, DCC, DMAP, CH2Cl2, room temperature, 93%.
Ta ble 1. Selected P Am P V P olym er s
polymer
fwb
yield (%)
Mn / PDI
n
(A) Polymers (3a -f) Prepared by Polymerization of
O-Substituted 5-Hydroxyisophthaldehydes (2a -f)a
cally modified PAmPV derivatives. As a general rule,
treatment of these derivatives with either strong acid
or strong base resulted in insoluble products. For
example, attempts (1) to reduce the azido group in
polymer 3b and (2) to remove the Boc protecting group
from polymer 3e were unsuccessful. Those reactions
which could be carried out successfully are summarized
in Scheme 7. These reactions were followed by 1H NMR
spectroscopy (see Table 2 in Supporting Information).
Changes in the molecular weights of the polymers were
assessed by GPC (Table 1B). Polymer 3b was found to
undergo a 1,3-dipolar cycloaddition with diethylacety-
lenedicarboxylate almost quantitatively to afford poly-
mer 3g. The hydroxymethyl groups in polymers 3c and
3d could be converted easily and efficiently into the
corresponding polymers 3h and 3i, respectively, with
bromomethyl functions. These bromides react well with
good nucleophiles, such as the thiol group in L-cysteine
to give, respectively, the polymers 3j and 3k and
thioacetic acid to give the polymer 3l. However, it should
be noted that the brominations (CBr4/Ph3P) of polymers
PmPV8
3a c
3b
3d
3e
460.69
476.69
601.86
576.85
675.98
520.74
60
0
11 900/1.6
-
26
-
40
45
25
20
77
73
77
84
23 900/1.7
26 000/1.8
16 960/1.6
10 400/1.7
3f
(B) Selected PAmPV Polymers Prepared by
Polymer Modificationsd
3a
3g
3i
3l
3m
476.69
772.02
639.75
634.95
665.00
92
90
94
95
93
8700/2.2
21 700/1.6
4900/2.24
5500/1.7
18
28
8
9
21
14 000/1.8
a
Reagents and conditions: (i) 1, EtONa, EtOH/THF, 60%; (ii)
b
I2 (catalytic), PhMe, reflux, 100%. See Schemes 4-6. Formula
weight of the polymer repeating unit. c No polymerization was
d
observed for the unprotected monomer. See Schemes 6 and 7.
has been prepared13,14 with a high degree of polymeri-
zation using the Wittig-Horner approach.
We have carried out (Scheme 7) a number of different
reactions on PmPV derivatives to obtain further chemi-

556 Star et al.
Macromolecules, Vol. 36, No. 3, 2003
Sch em e 8. Syn th esis of
Diben zo[24]cr ow n -8-Con ta in in g P Am P V P olym er 3n a
a
Reagents and conditions: (a) (i) 2-Formyldibenzo-[24]-
crown-8, PhMe, reflux; (ii) NaBH4, MeOH; (iii) Boc2O, NaH-
CO3, Na2CO3, the total yield for the 3 steps is 67%; (iv) PCC,
CH2Cl2, 60%; (b) (i) 1, EtONa, EtOH/THF, 53%; (ii) I2 (cat),
PhMe, reflux, 100%.
F igu r e 1. 1H NMR spectra (500 MHz, CD3CN/CDCl3) of
dibenzo[24]crown-8-containing polymer (3n ) before (a) and
after (b) addition of dibenzoammonium hexafluorophosphate.
3c and 3d are accompanied by losses in molecular
weight: see Table 1, parts A and B, which show, for
example, that conversion of 3d into 3i is accompanied
by a decrease from 45 to 8 in the polymer repeating unit.
A more promising approach to polymer modification is
the esterification of the phenol-containing polymer 3a ,
using mild activated-coupling conditions with carboxylic
acids, such as thioctic acid where polymer 3m was
obtained without any degradation of the polymer chain
having occurred (Table 1B). It is worth noting that this
polymer could be used to assist in the anchoring of
SWNT/PAmPV bundles onto gold surfaces.
Sch em e 9. Syn th esis of th e Na p h th a len e-Con ta in in g
P Am P V P olym er 3p a
Design a n d Syn th esis of P olyp seu d or ota xa n es.
The approach we have used for the grafting of pseu-
dorotaxanes onto PAmPV polymers has been to attach
neutral recognition units to the C-5 position of 5-hy-
droxyisophthaldehyde (2a ) and then carry out polymer-
izations with the bis-Wittig reagent derived from the
bisphosphonium salt 1. Two pseudorotaxanes were
targetedsone involving the tethering of dibenzo[24]-
crown-8 (DB24C8) macrocycles to the polymer backbone
for threading by dibenzylammonium (DBA+) ions15 and
the other involving a polyether chain incorporating a
1,5-dioxynaphthalene ring system for encircling by
cyclobis(paraquat-p-phenylene).16
a
Reagents and conditions: (a) PPh3, CBr4, THF, 26%; (b)
THP, TsOH, CH2Cl2, 85%; (c) 2a , K2CO3, DMF, 58%; (d) HCl,
THF, 83%; (e) (i) 1, EtONa, EtOH/THF, 53%; (ii) I2 (cat), PhMe,
reflux, 100%.
Since all our initial attempts to introduce crown ether
rings onto the side chains of PAmPV polymers were
unsuccessful, we decided to incorporate the DB24C8
appendages into a dialdehyde monomer 2n prior to
polymerization (Scheme 8). The synthesis of the mono-
mer relied upon starting with a formylated DB24C8
derivative17 which was treated with the amine 6 to
produce an imine which was reduced in situ to an amine
that was Boc-protected, before being subjected to the
polymerization conditions. The molecular weight of the
resulting polymer 3n was determined by GPC and found
to be 12 300 (Mn) with a polydispersity index (PDI) of
1.8. Although the peaks in the 1H NMR spectrum
(Figure 1a) of the polymer were broadened sufficiently
to obscure all the coupling constant information, they
could still be assigned unequivocally to protons in the
polymer. Significant movement of signals in the region
δ 3.0-4.6 was evident when DBA‚PF6 was added to the
solution of the PAmPV polymer 3n in CDCl3, indicating
(Figure 1b) the formation of polypseudorotaxanes in the
solution.
monomer 2p which was synthesized in four steps from
1,5-dihydroxyethoxyethoxynaphthalene18 (7). Compound
7 was monobrominated to give 8 which was converted
to its THP-protected derivative 9 before being used to
alkylate (K2CO3/DMF) 5-hydroxyisophthaldehyde (2a )
at room temperature. Deprotection of the product 2o
yielded the monomer 2p which was subjected to the
usual polymerization conditions to give the polymer 3p
with Mn ) 14,050, corresponding to a repeating unit of
1
18. The H NMR spectrum recorded in CDCl3/CD3CN
is shown in Figure 2c. Upon addition of CBPQT‚4PF6,
with the 1H NMR spectra shown in Figure 2a, the
polypseudorotaxane is formed: the signals (Figure 2b)
for protons in CBPQT4+ are broadened and shifted
together with those for the 1,5-dioxynaphthalene ring
system. The signal broadening is probably related in
part to slow complexation-decomplexation of CBPQT4+
with the side chains tangling from the polymer back-
bone. UV/vis spectroscopy provides (Figure 3) further
evidence for polypseudorotaxane formation. In common
with other PAmPV polymers 3a -3m (see Table 3 in
The 1,5-dioxynaphthalene-containing PAmPV poly-
mer 3p was obtained (Scheme 9) by polymerizing the

Macromolecules, Vol. 36, No. 3, 2003
Single-Walled Carbon Nanotubes 557
F igu r e 2. 1H NMR spectra (500 MHz, CD3CN/CDCl3) of 1,5-
dihydroxyethoxyethoxynaphthalene-containing polymer (3p )
before (c) and after (b) addition of cyclobis(paraquat-p-phe-
nylene) (CBPQT4+), the spectrum of which is presented above
(a).
F igu r e 4. Scanning electron microscopy (SEM) images of (a)
the CHCl3-soluble complex of SWNTs, wrapped with PAmPV
(3a ), and (b) the EtOH-soluble complex of SWNTs, wrapped
with the sodium salt of 3a .
and other organic solvents. In the case of the derivative
3a containing phenolic residues, the sodium phenoxide
derived polymer was found to solubilize the bundles in
protic solvents, e.g., EtOH. Figure 4 provides an ex-
ample of a scanning electron microscopy (SEM) image
of bundles of SWNTs coated with the PAmPV derivative
3a . Other derivatives, namely 3d , 3e, 3g, 3i, and 3l,
afforded (see Figures 6 and 7 in Supporting Information)
similar images, all suggestive of the solubilization of the
nanotube bundles in CHCl3. However, in the case of the
sodium salt of 3a , EtOH affords an image (Figure 4b)
commensurate with it having solubilized the bundles.
SWNTs wrapped with the PAmPV polymer 3a contain-
ing reactive phenolic hydroxyl groups were also exam-
ined for their ability to react with dicarboxylic acids as
cross-linking agents. When the CHCl3 soluble composite
was treated with dodecanedioic acid, an insoluble cross-
linked resin was formed. The SEM images (Figure 8 in
Supporting Information) of this composite resin show
that the SWNT bundles are included in the polymer
network.
Although the polypseudorotaxane formed between the
PAmPV derivative 3n and DBA‚PF6 in CHCl3 (Scheme
10) can also solubilize SWNTs on sonication only 1 min
after sonication is halted, the SWNTs start to precipi-
tate out of solution. Presumably, the introduction of
positive charges on the sidearms of the polymer decrease
the solubility of the polypseudorotaxane composite in
CHCl3.
In the case of the PAmPV derivative 3p and CBPQT‚
4PF6 (Scheme 10), a solvent mismatch (SWNT bundles
wrapped with 3p are soluble in CHCl3 but not in MeCN,
whereas CBPQT‚4PF6 is soluble in MeCN but not in
CHCl3) has prevented us from studying the solubiliza-
tion of SWNTs with this polypseudorotaxane. Indeed,
the polymer-wrapped SWNTs which are soluble in
F igu r e 3. UV-vis spectra of the 1,5-dihydroxyethoxyethoxy-
naphthalene-containing polymer (3p ) before (dashed line, a)
and after (solid line, b) addition of cyclobis(paraquat-p-phe-
nylene) (CBPQT4+). UV-vis spectra of a charge-transfer band
of the pseudorotaxane formed by 1,5-dihydroxyethoxyethoxy-
naphthalene and CBPQT4+ presented as (c) a dashed and
dotted line.
Supporting Information), polymer 3p absorbs strongly
at just above 400 nm. It does not absorb in the 520-
540 nm region where the 1,5-dioxynaphthalene/CB-
PQT4+ charge-transfer band is expected.19 However,
addition of CBPQT‚4PF6 to the polymer solution pro-
duces a shoulder centered on 520 nm, indicating the
threading of CBPQT4+ cyclophanes onto the 1,5-dihy-
droxynaphthalene-containing polyether sidearms on the
polymer 3p . This polypseudorotaxane formation can also
be detected by the naked eye since the color of the
polymer solution changes from greenish-yellow to or-
ange on addition of CBPQT‚4PF6.
In ter a ction of P Am P V P olym er s w ith Sin gle-
Wa lled Ca r bon Na n otu bes (SWNTs). The polymers
were tested for their abilities to solubilize bundles of
SWNTs. We have shown that the PAmPV derivatives
3a -p form stable solutions with the bundles in CHCl3

558 Star et al.
Macromolecules, Vol. 36, No. 3, 2003
Sch em e 10. P olyp seu d or ota xa n e F or m a tion fr om
P olym er s 3n a n d 3p
CHCl3 precipitate their SWNTs on addition of an MeCN
solution of CBPQT‚4PF6. The precipitation may be
another example where addition of positive charge to
the sidearms of the polymer is the cause or it may
simply be a solvent effect.
On account of solvent constraints, the traditional
observation of a CT band resulting from the threading
of the CBPQT4+ by the 1,5-dioxynaphthalene-containing
polyether side chains on the PAmPV derivative 3p could
not be performed in the presence of SWNTs, the reason
being that, on the addition of MeCN or Me2CO the
SWNTs precipitate from solution. Scanning probe mi-
croscopy provides an alternative means to investigate
this triply supramolecular bundle. In particular, tapping
mode atomic force microscopy (AFM) and surface po-
tential (SP) microscopy were informative. Dilute solu-
tions of the polymer 3p and SWNTs in CHCl3 were spin-
coated onto silicon oxide wafers that were pre-patterned
with alignment markers. After the supramolecular
bundles had been characterized by AFM and SP, the
wafers were placed in a 0.1 mM solution of CBPQT‚4PF6
in MeCN for 12 h.20 Individual bundles were identifiable
as a result of their fixed proximity to the alignment
markers. A series of AFM images is shown in Figure 5,
starting with the topography (Figure 5a) of the su-
pramolecular bundle and its corresponding SP (Figure
5b). After exposure of the wafer to the MeCN solution
of CBPQT‚4PF6, while there was no change in the
topography, there was a significant change in the SP.
It is evident from a comparison of the images portrayed
in Figure 5, parts b and c, that the addition of the
CBPQT‚4PF6 solution affects the dipole density of the
bundle. Although this observation does not prove that
CBPQT4+ has threaded onto the 3p polymer-coated
bundles, we believe that the tetracationic cyclophane
has become associated in some way with the bundles.
F igu r e 5. Atomic Force Microscopy (AFM) tapping mode
images of an SWNT bundle wrapped with the polymer 3p ,
which is soluble in CHCl3, and treated subsequently with
cyclobis(paraquat-p-phenylene) (CBPQT4+). (a) Topography of
a bundle of SWNTs wrapped with the polymer 3p on a silicon
oxide substrate after spin-coating. (b) Surface potential of this
same sample. (c) Surface potential of the same SWNT polymer-
wrapped bundle after a 12 h exposure to a MeCN solution of
CBPQT‚4PF6. The feature on the left represents the alignment
marker in the 4 × 4 µm images.
attached to the polymer of threaded complexes. The
results conjure up the prospect of developing arrays of
molecular actuators and switches in the future.
Exp er im en ta l Section
Ma ter ia ls a n d In str u m en ta tion . Chemicals were pur-
chased from Aldrich and used as received. Syntheses of 2,5-
bis(methyltriphenylphosphonium chloride)-1,4-bis(octyloxy)-
benzene (1) have previously been reported by us.8 Cyclobis(para-
quat-p-phenylene) (CBPQT4+) was synthesized according to the
literature procedures.16 Sodium ethoxide was freshly prepared
prior to use from Na metal and anhydrous EtOH. Solvents
were dried, distilled, and stored under argon. UV/visible
spectra were obtained using a Varian Cary 100 Bio spectro-
photometer. Absorption measurements of polymeric sample
Con clu sion s
The noncovalent functionalization of bundles of car-
bon nanotubes with conducting polymers that have the
capacity to form pseudorotaxanes represents the opera-
tion of supramolecular forces at three different levels
of superstructure, viz., (1) the aggregation of the nano-
tubes into bundles, (2) the wrapping of the bundles by
the polymer, and (3) the formation through the sidearms

Macromolecules, Vol. 36, No. 3, 2003
Single-Walled Carbon Nanotubes 559
9.97 (s, 0.08H, CHO end groups), 7.91 (d, 1H, J ) 8.6 Hz, Ar-
H, NP), 7.87 (d, 1H, J ) 8.4 Hz, Ar-H, NP), 7.51-7.44 (m,
1H), 7.37 (t, 1H, J ave ) 8.0 Hz, Ar-H, NP), 7.33 (t, 1H, J ave
)
8.2 Hz, Ar-H, NP), 7.28 (s, 1H), 7.17-7.04 (m, 5H), 6.88 (d,
1H, J ) 7.6 Hz, Ar-H, NP), 6.83 (d, 1H, J ) 7.6 Hz, Ar-H,
NP), 6.85-6.70 (m, 2H), 4.37 (t, 2H, J ) 4.6 Hz, -OCH2CH2O-
), 4.29 (t, 4H, J ) 4.6 Hz, -OCH2CH2O-), 4.12 (t, 2H, J ) 4.6
Hz, -OCH2CH2O-), 4.07 (t, 4H, J ) 6.0 Hz, -OCH2(CH2)6-
CH3), 3.99 (t, 4H, J ) 4.6 Hz, -OCH2CH2O-), 3.78-3.72 (m,
4H, -OCH2CH2O-), 2.02 (brs, 1H, -OH), 1.89 (p, 4H, J )
6.8 Hz, -OCH2CH2(CH2)5CH3), 1.54 (p, 4H, J ) 6.8 Hz,
-O(CH2)2CH2(CH2)4CH3), 1.38-1.27 (m, 16H, -O(CH2)3(CH2)4-
CH3), 0.85 (t, 6H, J ) 6.8 Hz, -O(CH2)7CH3). 13C NMR (100
MHz, CDCl3): δ ) 154.38 (Ar-C, NP), 154.27 (Ar-C, NP),
151.17, 139.6, 128.9, 126.85 (Ar-C, NP), 126.79 (Ar-C, NP),
125.22 (Ar-CH, NP), 125.15 (Ar-CH, NP), 124.1, 114.8,
114.56 (Ar-CH, NP), 114.55 (Ar-CH, NP), 108.7, 105.80 (Ar-
CH, NP, 2 overlapping), 72.60 (-OCH2CH2O-), 70.18 (OCH2-
CH2O), 70.10 (-OCH2CH2O-), 69.78 (-OCH2(CH2)6CH3),
69.61 (-OCH2CH2O-), 68.02 (OCH2CH2O-, 2 overlapping),
67.90 (-OCH2CH2O-), 61.86 (-OCH2CH2O-), 31.85, 29.51,
29.49, 29.44, 26.27, 22.68, 14.12. Anal. Calcd for C50H66O8
(795.05): C, 75.53; H, 8.37. Found: C, 74.92; H, 8.40.
Molecu lar Weigh t Deter m in ation s. The molecular weights
and polydispersity (PDI) of 3n (Mw ) 22 100; DPI ) 1.8) and
3p (Mw ) 24 720; PDI ) 1.76) were determined in THF by
using a size-exclusion chromatograph (SEC) equipped with a
UV detector. The SEC system was calibrated by using poly-
styrene standards prior to use. The GPC measurements of 3n
show that its number-average molecular weight (Mn) is 12 300,
corresponding to 11 repeating units. The GPC measurements
of 3p show that the number-average molecular weight (Mn) is
14 045, corresponding to 18 repeating units. The presence of
solutions were carried out in CHCl3 with concentrations of 1.0
× 10-4 and 1 × 10-5 M relative to repeating units in a polymer.
Molecular weights of polymers were determined by using a
Dynamax solvent delivery module system, a Styragel HR3
column, and a Dynamax PDA-2 diode array detector, at a flow
rate of 1.0 mL/min. All molecular weights were measured
against polystyrene standards in THF. Proton and carbon
nuclear magnetic resonance spectra (1H NMR and 13C NMR)
spectra were recorded on a Bruker ARX400 or ARX500 at 25
°C, using the deuterated solvent as lock and the residual
solvent as internal standard. Elemental analyses were per-
formed by Quantitative Technologies Inc.
Gen er a l P olym er iza tion P r oced u r e. A solution of NaO-
Et in EtOH (1 M, 2.5 mL) was added dropwise to a solution of
2,5-dioctyloxy-1,4-bis(triphenylphosphonium) dichloride (1) (1
mmol) and substituted 5-hydroxyisophthaldehyde (2) (1 mmol)
in a mixture of anhydrous EtOH (10 mL) and THF (10 mL) at
ambient temperature. The reaction mixture was stirred for an
additional 24 h and then evaporated to dryness. The residue
was dissolved in a minimum amount of CHCl3 (1 mL), and
the crude polymer was precipitated out by addition of MeOH
(20 mL) as a yellow resin, which was filtered and dried. A
sample of the crude polymer (50 mmol) and I2 (0.5 mg) was
refluxed in PhMe (15 mL) for 4 h. The solvent was evaporated
off under vacuum, and the polymer was precipitated from
CHCl3 by the addition of an excess of MeOH. The polymer was
filtered and dried to afford PAmPV (3) as a yellow resin.
Typical yields are 60-80%. See Table 1.
1
the aldehyde end groups is evident from H NMR spectroscopy.
The degree of polymerization of 3p was estimated as n ≈ 25
by NMR end group analysis.
P r ep a r a t ion of t h e SWNT/P olym er Com p lex. The
SWNTs were produced by the HiPco method and used as
received from Rice University. SWNTs (0.3 mg) were added
to a solution of the polymer in CHCl3 solution (1 mg in 5 mL).
Sonication (30 min) in a water bath (Branson model 1510, 40
kHz) gave a stable transparent solution.
P r ep a r a tion of th e SWNT/P olym er Sa m p les P r ior to
Atom ic F or ce Micr oscop y (AF M). After sonication, 1 drop
of the SWNT/PAmPV solution was placed on a freshly cleaved
1 cm2 mica wafer, which was subsequently washed with 5
drops of CHCl3 while spinning at 750 rpm to wash off excess
of the polymer. AFM images were collected in tapping mode.
Ack n ow led gm en t. This work was supported by the
Office of Naval Research and by the National Science
Foundation.
3n . Following the general polymerization procedure, this
polymer was obtained from 1 (0.96 g, 1.0 mmol) and 2n (0.81
g, 1 mmol) as a yellow sticky solid (0.74 g, 65%). Data for 3n
Su p p or tin g In for m a tion Ava ila ble: Text giving experi-
mental procedures for 5-hydroxyisophthaldehyde (2a ), O-
alkylated 5-hydroxyisophthaldehyde (2b-p ), and PAmPV
polymers (3a -m ), tables giving 1H NMR and UV-vis spectral
data of PAmPV polymers (3a -m ) and figures giving SEM
images of SWNTs/PAmPV complexes. This material is avail-
able free of charge via the Internet at http://pubs.acs.org.
1
follow. H NMR (500 MHz, CDCl3): δ ) 7.52 (s, 1H), 7.42 (s,
1H), 7.19-7.06 (m, 5H), 6.96 (s, 2H), 6.79 (brs, 4H, Ar-H,
crown), 6.68 (brd, 3H, Ar-H, crown), 4.33 (brs, 2H, >NCH2-
Ar), 4.12 (brs, 8H, R-H crown), 4.07-4.03 (m, 6H, -OCH2-
(CH2)5-), 3.90 (brs, 8H, â-H crown), 3.82 (brs, 8H, γ-H
crown), 3.19 (brd, 2H, -O(CH2)5CH2N<), 1.88-1.85 (m, 6H,
-OCH2CH2-), 1.54-1.28 (m, 26H, -CH2-), 1.45 (s, 9H, t-Bu),
0.85 (brt, 6H, -O(CH2)7CH3). 13C NMR (100 MHz, CDCl3): δ
) 160.0, 159.0, 151.17, 148.95, 148.88, 148.0, 139.6, 131.5,
128.9, 127.0, 124.1, 121.4, 113.99, 113.67, 110.8, 79.5, 71.25,
69.93, 69.62, 69.46, 69.34, 67.90, 53.0, 31.85, 29.71, 29.51,
29.44, 29.34, 28.51, 26.76, 26.30, 25.96, 22.67, 14.12. Anal.
Calcd for C68H97NO3 (1136.5): C, 71.86; H, 8.60; N, 1.23.
Found: C, 71.21; H, 8.61; N, 1.25.
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polymer was obtained from 1 (65 mg, 0.07 mmol) and 2n (32
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53%). Data for 3p follow. 1H NMR (400 MHz, CDCl3): δ )

560 Star et al.
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MA021417N