"Click" synthesis of thermally stable au nanoparticles with highly grafted polymer shell and control of their behavior in polymer matrix

Article abstract of DOI:10.1002/pola.24782

Thermally stable core-shell gold nanoparticles (Au NPs) with highly grafted polymer shells were synthesized by combining reversible addition-fragmentation transfer (RAFT) polymerization and click chemistry of copper-catalyzed azide-alkyne cycloaddition (CuAAC). First, alkyne-terminated poly(4-benzylchloride-b-styrene) (alkyne-PSCl-b-PS) was prepared from the alkyne-terminated RAFT agent. Then, an alkyne-PSCl-b-PS chain was coupled to azide-functionalized Au NPs via the CuAAC reaction. Careful characterization using FT-IR, UV-Vis, and TGA showed that PSCl-b-PS chains were successfully grafted onto the Au NP surface with high grafting density. Finally, azide groups were introduced to PSCl-b-PS chains on the Au NP surface to produce thermally stable Au NPs with crosslinkable polymer shell (Au-PSN₃-b-PS 1). As the control sample, PS-b-PSN₃-coated Au NPs (Au-PSN₃-b-PS 2) were made by the conventional "grafting to" approach. The grafting density of polymer chains on Au-PSN₃-b-PS 1 was found to be much higher than that on Au-PSN₃-b-PS 2. To demonstrate the importance of having the highly packed polymer shell on the nanoparticles, Au-PSN ₃-b-PS 1 particles were added into the PS and PS-b-poly(2- vinylpyridine) matrix, respectively. Consequently, it was found that Au-PSN ₃-b-PS 1 nanoparticles were well dispersed in the PS matrix and PS-b-P2VP matrix without any aggregation even after annealing at 220 °C for 2 days. Our simple and powerful approach could be easily extended to design other core-shell inorganic nanoparticles.

Full text of DOI:10.1002/pola.24782

‘‘Click’’ Synthesis of Thermally Stable Au Nanoparticles with Highly
Grafted Polymer Shell and Control of Their Behavior in Polymer Matrix
JONGMIN LIM,1 HYUNSEUNG YANG,1 KWANYEOL PAEK,1 CHUL-HEE CHO,1 SEYONG KIM,2 JOONA BANG,2 BUMJOON J. KIM1
1Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701,
Republic of Korea
2Department of Chemical and Biological Engineering, Korea University, Seoul 136-701, Republic of Korea
Received 9 April 2011; accepted 16 May 2011
DOI: 10.1002/pola.24782
Published online 8 June 2011 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: Thermally stable core–shell gold nanoparticles
(Au NPs) with highly grafted polymer shells were synthesized
by combining reversible addition-fragmentation transfer
(RAFT) polymerization and click chemistry of copper-catalyzed
azide-alkyne cycloaddition (CuAAC). First, alkyne-terminated
poly(4-benzylchloride-b-styrene) (alkyne-PSCl-b-PS) was pre-
pared from the alkyne-terminated RAFT agent. Then, an
alkyne-PSCl-b-PS chain was coupled to azide-functionalized Au
NPs via the CuAAC reaction. Careful characterization using FT-
IR, UV–Vis, and TGA showed that PSCl-b-PS chains were suc-
cessfully grafted onto the Au NP surface with high grafting
density. Finally, azide groups were introduced to PSCl-b-PS
chains on the Au NP surface to produce thermally stable Au
NPs with crosslinkable polymer shell (Au-PSN3-b-PS 1). As the
control sample, PS-b-PSN3-coated Au NPs (Au-PSN3-b-PS 2)
were made by the conventional ‘‘grafting to’’ approach. The
grafting density of polymer chains on Au-PSN3-b-PS 1 was
found to be much higher than that on Au-PSN3-b-PS 2. To
demonstrate the importance of having the highly packed poly-
mer shell on the nanoparticles, Au-PSN3-b-PS 1 particles were
added into the PS and PS-b-poly(2-vinylpyridine) matrix,
respectively. Consequently, it was found that Au-PSN3-b-PS 1
nanoparticles were well dispersed in the PS matrix and PS-b-
P2VP matrix without any aggregation even after annealing at
220 ꢀC for 2 days. Our simple and powerful approach could be
easily extended to design other core–shell inorganic nanopar-
C
V
ticles. 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym
Chem 49: 3464–3474, 2011
KEYWORDS: block copolymers; click chemistry; grafting density;
nanocomposites; nanoparticles; polymer coated Au nanopar-
ticles; reversible addition fragmentation chain transfer (RAFT)
INTRODUCTION Polymer–inorganic hybrid materials have
been the subject of intense research recently because of their
potentials in various applications, including high perform-
ance optical and energy devices,1,2 microelectronics,3,4 data
storage,5,6 and highly selective membranes.7,8 Incorporation
of inorganic nanoparticles into polymer matrices can com-
bine the functionality of nanoparticles with easy processabil-
ity of polymers. However, achieving the ordered structure or
dispersing the nanoparticles within the polymer matrix is
usually challenging, particularly because of the inherent
immiscibility between inorganic particles and organic materi-
als.9 To address these issues, there have been some
approaches to control the interaction between nanocrystals
and polymer chains within a matrix by manipulating the
interface between the nanoparticle surface and the polymer
matrix. One of the most powerful methods to improve the
chemical affinity of nanoparticles is to design the proper
polymeric ligands that can be grafted on the surfaces of inor-
ganic particles. For example, tuning the surface properties of
nanoparticles by end-attaching ligands such as organic small
molecules,10–15 a single type or a mixture of homopoly-
mers,16–24 random copolymers,25 and block copolymers7,26,27
to the nanoparticle surface can position the particles pre-
cisely at the interface between two different polymers. In
this manner, the particles would have surfactant-like proper-
ties in a block copolymer or polymer matrix.25,28 In the
block copolymer matrix, the interaction between the polymer
shell on the particles and the chains in the block copolymer
matrix determines not only the dispersion of particles in the
matrix but also controls their location within the matrix.
There are two principle pathways for producing inorganic
core–polymeric shell type nanoparticles. In the ‘‘grafting to’’
approach [Scheme 1(a)], presynthesized ligands with func-
tional end groups that interact favorably with the nanopar-
ticle surfaces are simply bound to the vacant sites during
the particle formation step.29,30 The presynthesized ligands
can also substitute other ligands that were originally on the
particle surface via the ligand exchange step.31,32 A wide
range of presynthesized polymers with great control in the
molecular weight, polydispersity, and molecular structure, is
Correspondence to: J. Bang (E-mail: joona@korea.ac.kr) or B. J. Kim (E-mail: bumjoonkim@kaist.ac.kr)
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SCHEME 1 Comparison of the (a) grafting-to and (b) click approach for controlling grafting density of polymers on Au NPs.
accessible for the grafting to approach. However, the main li-
mitation of this method rests with the fact that the achieva-
ble polymer surface density on the nanoparticles is low
because of the steric hindrance that prevents additional
polymers to approach the surfaces. On the other hand, the
‘‘grafting from’’ method can overcome this drawback and
induce much higher grafting density of the polymer ligands
on nanoparticle surfaces. However, it should be noted that
this approach typically requires more complex procedures to
synthesize polymer-coated nanoparticles and allows much
less control in the polymer ligand characteristics, such as the
molecular weight, the polydispersity, and the molecular
structure. More importantly, most of the radical polymeriza-
tion procedures, including the controlled radical polymeriza-
tion process, typically require the temperature to be above
tions.40 This simple and robust reaction can produce
intended products in very high yields with almost no
byproduct, and it also works well under mild conditions.41
In addition, several research groups have suggested the use
of the click chemistry approach for the functionalization of
2D and 3D substrates, including the functionalization of
nanoparticles.42–48 For example, Fleming et al.45 synthesized
azide-functionalized Au NPs coupled with various alkyne
derivatives. Boisselier et al. demonstrated the click addition
of hydrophilic polyethyleneoxide (PEO) on Au NPs using
CuSO4 as a catalyst under a mixture of water and tetrahy-
drofuran (THF). Very recently, Drockenmuller et al.46
reported the synthesis of PEO- or poly(caprolactone)-coated
Pt nanoparticles by click chemistry. These examples showed
that the surfaces of Au NPs could be effectively decorated
by polymers using the CuAAC reaction. However, most
work on the click synthesis of polymer coated Au NPs
were limited to using water-soluble polymers including
PEO and poly(N-isopropylacrylamide) (PNIPAM) as the
surface ligands because of the solubility issues. Another
important problem was that the copper catalyst in the click
reaction results in aggregation of nanoparticles and/or low
yield.44,45
ꢀ
60 C. At this temperature, many metallic nanoparticles (i.e.,
gold, silver, platinum) stabilized by thiol-functionalized
ligands become thermally unstable and form aggregates
because of the breakage of particle surface–ligand bond-
ings.33 Therefore, an alternative strategy is still necessary to
produce polymer-coated nanoparticles with a high grafting
density.
Emerged as the premier example of ‘‘click’’ chemistry,34,35
copper-catalyzed azide-alkyne cycloaddition (CuAAC) is a
technique that has been extensively used in copolymer syn-
thesis,36,37 surface functionalization,38,39 and bioconjuga-
Herein, we combine the CuAAC reaction with the ‘‘grafting-
to’’ approach to produce inorganic nanoparticles with a
densely packed polymer shell [Scheme 1(b)]. Properly
CLICK SYNTHESIS OF THERMALLY STABLE Au NPs, LIM ET AL.
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designed diblock copolymer of polystyrene (PS) and
poly(4-benzylchloride) (PSCl) with an alkyne end group
was first synthesized by reversible addition-fragmentation
transfer (RAFT) polymerization (Scheme 2). Subsequently,
it was coupled to azide-functionalized Au NPs (Au-N3) by
the CuAAC reaction to produce Au NPs with a highly
grafted polymer shell. To achieve an efficient click reaction
between hydrophobic polymers and Au-N3 without aggre-
gation of nanoparticle, the ratio of THF/water in the reac-
tion was carefully optimized so that all reagents including
catalyst and salt were dissolved and the reaction could be
completed. We chose PS-b-poly(azidostyrene) (PS-b-PSN3)
diblock copolymers as ligands for two reasons. First, PS-b-
PSN3 diblock copolymer shell on Au NPs could be easily
crosslinked to enhance the thermal stability of the Au NPs
as shown in the previous report.49 Second, previous exam-
ples of nanoparticle surface functionalization using the
CuAAC reaction were mostly limited to hydrophilic sys-
tems. Because PS-b-PSN3 diblock copolymers have
extremely low solubility in water, it can be demonstrated
that our approach to produce polymer-coated Au NPs with
highly grafted PS-b-PSN3 shells was very versatile and
could be easily extended to other hydrophobic systems. In
addition, we discussed the behavior of the Au NPs with
highly packed polymer shell in homopolymer and diblock
copolymer matrix.
SCHEME 2 Synthesis scheme for thermally stable Au NPs with densely packed diblock copolymer shell via the click reaction.
Synthesis procedure for (a) Au-N3, (b) alkyne-PSCl-b-PS block copolymers, and (c) Au-PSN3-b-PS 1 nanoparticles via the CuAAC
reaction. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
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RESULTS AND DISCUSSION
that Au NPs were completely functionalized by azide end
groups.
Synthesis of Thermally Stable Au NPs with Highly
Grafted Polymer Shell via Click Chemistry and
RAFT Polymerization
Au-N3 nanoparticles were synthesized following the proc-
esses shown in Scheme 2(a). First, 11-bromo-1-undecane-
Azide groups on the Au NP surface enabled further function-
alization via CuAAC reaction with alkyne derivatives. There-
fore, two different alkyne end-functionalized PS (alkyne-PS 1
and alkyne-PS 2) and alkyne-terminated PSCl-b-PS block
copolymers (alkyne-PSCl-b-PS) were prepared by RAFT poly-
merization, as shown in Scheme 2(b). Alkyne-terminated
RAFT chain transfer agent 6 was designed and prepared
according to the modified literature procedure to ensure the
functionality required for the click chemistry.52,53 The molec-
ular weight (Mn) and polydispersity index (PDI) of alkyne-
PSCl-b-PS were found to be 8.8 kg/mol and 1.1, respectively,
with PSCl (Mn ¼ 3.3 kg/mol) and PS (Mn ¼ 5.5 kg/mol)
blocks. Two additional alkyne-PS 1 and alkyne-PS 2 were
synthesized to have different Mn. The Mn and PDI of alkyne-
PS 1 were 4.5 kg/mol and 1.07, respectively, and the Mn and
PDI of alkyne-PS 2 were 12 kg/mol and 1.1, respectively.
The information for all polymers is summarized in Table 1.
thiol
2 was synthesized via a two-step reaction from
11-bromo-1-undecene. Then, the unique peak [acetyl group
(2.3 ppm)] of compound 1 completely disappeared. Instead,
a peak at 2.49 ppm appeared because of the presence of
the thiol group at the end of compound 2 (Fig. 1). Using
compound 2 as ligand, bromine-functionalized Au NPs (Au-
Br) were successfully prepared by the Brust method. The
NMR spectrum of Au-Br in Figure 1(d) shows the peak
around 3.4 ppm, a signature of the bromine end group. It
was noted that compared to the sharp peak from the mole-
cule 2, NMR peaks of the Au NPs were significantly broad-
ened because of the ligand attached at the particle sur-
face.50,51 The Au-Br nanoparticles were then stirred in a
solution containing NaN3 to convert the Br-termini on the
Au NP surface into the azide (N3) group via nucleophilic
substitution. It was found that the core size and shape of
Au-N3 particles were not affected during this reaction, and
the particle core diameter was 2.51 nm as shown in the
transmission electron microscope (TEM) image of Figure
2(a). The presence of azide functional groups on the Au NP
surface was evidenced by NMR and FTIR measurements. In
the NMR spectrum, a broad peak that previously appeared
around 3.4 ppm shifted completely to 3.24 ppm because of
azide substitution [Fig. 1(e)]. The FTIR spectrum in Figure
3(a) shows a strong signal at 2100 cmꢁ1, which is a signa-
ture of the azide groups. Therefore, it can be concluded
The previous examples of grafting polymers on Au NPs using
the CuAAC reaction suffered from low yield and/or nanopar-
ticle aggregation mainly because of the different solubilities
of the different reagents including the polymers, the Au NPs,
the catalyst, and the salts.44,45,48 This could also cause a seri-
ous problem of lowering the grafting density of the polymer
shell on the Au NPs and limit the usefulness of the CuAAC
reaction on the nanoparticles. To overcome such problems,
the CuAAC reaction conditions in this system were first opti-
mized by coupling two model polymers, alkyne-PS 2 and PS-
b-PSN3 polymers, without using Au NPs. In this case, the cor-
responding copolymers could be readily recovered and the
molecular weight could be easily traced via size exclusion
FIGURE 1 NMR spectra of (a) 11-bromo-1-undecene, (b) 11-(bromoundecyl)thioacetate, (c) 11-bromo-1-undecanthiol, (d) Au-Br,
and (e) Au-N3. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
CLICK SYNTHESIS OF THERMALLY STABLE Au NPs, LIM ET AL.
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FIGURE 2 TEM images of Au NPs and the corresponding histograms of their size distribution: (a) Au-N3 (2.51 6 1.19 nm), (b) Au-
PS (2.79 6 1.03 nm), (c) Au-PSN3-b-PS 1 (click; 2.37 6 1.01 nm), and (d) Au-PSN3-b-PS 2 (grafting-to; 2.48 6 0.74 nm). Scale bar is
20 nm.
chromatography (SEC). To monitor the efficiency of the
CuAAC reaction, the PS-b-PSN3 polymer was designed to be
monodisperse with only a few units of the azide group per
each chain. The total Mn of PS-b-PSN3 was 5.4 kg/mol. It
should be noted that there are, on average, four units of the
azide group per each chain (PSN3 Mn ¼ 0.7 kg/mol). After
surveying the reaction efficiency with a variety of Cu
catalysts, such as CuBr, CuI, CuSO4, salts, and solvents, it was
found that the system of CuSO4/sodium ascorbate/(THF/
water) gave the best results with a reaction yield close to
completion. It should be noted that the solvent mixture ratio
(THF/water) was an important parameter because sodium
ascorbate requires water to be dissolved. However, both PS-
b-PSN3 and alkyne-PS 2 showed extremely low solubility in
water. Figure 4 shows the SEC curves of the polymers after
the CuAAC reaction between PS-b-PSN3 and a slight excess
amount of alkyne-PS 2 under different THF-to-water ratio.
The SEC curve in Figure 4(c) shows a peak at 12 kg/mol for
alkyne-PS 2, which indicates that no reaction occurred. As
the ratio of THF to water increased from 1:8 to 1:4 and to
1:1, the peak at the lower retention time (Mn ¼ 56 kg/mol)
appeared. Interestingly, this number of Mn ¼ 56 kg/mol cor-
responded approximately to the total molecular weights for
one PS-b-PSN3 chain (Mn ¼ 5.4 kg/mol) and four alkyne-PS
2 chains (Mn ¼ 12 kg/mol). The number of alkyne-PS
2 chains was consistent with the average number of azide
TABLE 1 Characteristics of Polymers Used in This Study
FIGURE 3 FTIR spectra of synthesized Au NPs. (a) Au-N3, (b)
Au-PS, (c) Au-PSCl-b-PS, and (d) Au-PSN3-b-PS 1. In (a), the
peak at ꢂ2100 cmꢁ1 represents the presence of the azide group
on the Au NP surface. In (b) and (c), after the click reaction
between the azide group on the Au NPs and the alkyne group
at the end of alkyne-PSCl-b-PS chain, the peak at ꢂ2100 cmꢁ1
disappeared, which indicates the efficient click reaction. In (d),
the azide peak reappeared after azidation of PSCl-b-PS polymer
brushes on the Au NPs, (PS-Cl ! PS-N3). [Color figure can be
viewed in the online issue, which is available at
wileyonlinelibrary.com.]
Polymer
Mn (kg/mol)
PDI
Alkyne-PS 1
Alkyne-PS 2
Alkyne-PSCl-b-PS
PS-b-PSN3
PS-b-PSN3-SH
PS
4.5
12
1.07
1.10
1.10
1.09
1.07
1.07
1.10
8.8
5.4
8.7
56.5
380
PS-b-P2VP
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ARTICLE
NP surface via click reaction of terminal alkynes in PS chains
with the azides on the Au NPs. Figure 3(d) shows that the
azide peak for the Au-PSN3-b-PS 1 particles reappeared. This
clearly indicates that the chlorine groups in PSCl units were
successfully replaced with azide groups by reacting PS-b-
PSCl chains on the Au NPs with NaN3, producing Au-PSN3-b-
PS 1.
All synthesized Au NPs were analyzed by TEM to obtain the
core size and the grafting density of polymers on the Au
NPs. The information for all Au NPs is listed in Table 2. Fig-
ure 2 represents the TEM images of four different Au NPs.
The core diameters of (a) Au-N3, (b) Au-PS, and (c) Au-PSN3-
b-PS 1 were almost all around 2.5 nm, which indicates that
the particle size was not affected by the CuAAC reaction.
Interestingly, the TEM images in Figure 2 provide qualitative
support for the increase in the shell thickness by polymer
ligands. In this case, the interparticle distance between Au
NPs dispersed on the carbon film on the TEM grid was sig-
nificantly larger for Au-PS and Au-PSN3-PS 1 than for Au-N3
particles, which indicates that the PS shell on the Au particle
core was much thicker and consistent with the previous
report.54 The areal density of polymer chains grafted onto
the Au NPs is an important parameter to determine the effi-
ciency of the click reaction on the synthesis of polymer-
coated Au NPs. The areal chain density (R) of each Au NP
was calculated based on the gold core size from TEM and
the weight fraction of gold and polymer ligands in the core–
shell Au NPs from thermogravimetric analysis (TGA). The
details of the method were described in the Experimental
section. The R of Au-PS was estimated to be 2.23 chains/
nm2, which was much higher than what can be obtained
from the ‘‘grafting-to’’ method using PS chains with a similar
molecular weight synthesized by RAFT polymerization.55 In
the ‘‘grafting-to’’ method case, R values were always less
than 1.6 chains/nm2 because of the secondary position of
thiol groups. For a higher molecular weight polymer ligand,
such as alkyne-PSCl-b-PS (Mn ¼ 8.8 kg/mol), the R of Au-
PSN3-b-PS 1 was estimated to be 1.22 chains/nm2. To prove
the significance of the click reaction on Au-PSN3-b-PS 1 par-
ticles, another sample of PS-b-PSN3-coated Au NPs (Au-PSN3-
b-PS 2) was made by the conventional grafting-to approach
as the control sample.17,25,49 Thiol-terminated PS-b-PSN3
(PS-b-PSN3-SH) was synthesized by RAFT polymerization to
have the Mn of 8.7 kg/mol and the PDI of 1.07, respectively.
It was noted that the Mn of this polymer was similar to that
FIGURE 4 SEC curves of the polymers after the CuAAC reaction
between PS-b-PSN3 chains and alkyne-PS 2 chains under differ-
ent THF/water ratio. (a) THF:water ¼ 1:1 (v/v), (b) THF:water ¼ 4:1
(v/v), and (c) THF:water ¼ 8:1 (v/v).
groups in a PS-b-PSN3 chain (four units of the azide group in
each chain). Additionally, there was no peak between the
two peaks of Mn ¼ 12 and 56 kg/mol, which indicates the
completion of the CuAAC reaction between two different
polymers.
These conditions were used for the main CuAAC reaction
between Au-N3 particles and alkyne polymers. As a result,
two different particles of PS-coated Au NPs (Au-PS) and PS-
b-PSN3-coated Au NPs (Au-PSN3-b-PS 1) were synthesized.
For the case of Au-PSN3-b-PS 1, additional azide substitution
was performed on PS-b-PSCl-coated Au NPs. To monitor the
efficiency of the CuAAC reaction and the extent of attach-
ment of the polymers on Au NPs, FTIR spectra of each type
of Au NPs were taken (Fig. 3). Comparison between Au-N3
and polymer-coated Au NPs revealed that the strong signal
of the azide group at 2100 cmꢁ1 disappeared after the
CuAAC reaction. Although additional peaks above 3000 cmꢁ1
in Figure 3(b,c) appeared due to the C–H stretching vibration
of the aromatic ring, alkyl stretching vibrations between
2800 and 3000 cmꢁ1 of the polymer-coated Au NPs were
consistent with the pristine Au-N3. This indicates that the
structures of the compounds were not affected by surface
attachment. PS chains were successfully grafted on the Au
TABLE 2 Size and Grafting Density of Polymer-Grafted Au NPs by the Click Chemistry
Approach and the Grafting-to Approach
Particle
Particle Core
(Core þ Shell)
Grafting Density
R (chains/nm2)
Diameter (nm)
Diameter (nm)
Method
Au-N3
2.51
2.79
2.37
2.48
5.20
9.14
8.36
7.79
7.79
2.23
1.22
0.90
–
Au-PS
Click
Au-PSN3-b-PS 1
Au-PSN3-b-PS 2
Click
Grafting-to
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FIGURE 5 TEM images and the
corresponding absorption spectra
of Au NPs in the PS homopolymer
matrix. Au-N3 (a), Au-PS (b), and
Au-PSN3-b-PS 1 (c) were dispersed
in PS (Mn ¼ 56,500) films, respec-
tively. Both Au-PSN3-b-PS
1 and
Au-PS particles after the click reac-
tion were well dispersed in the PS
matrix with the absorption peak at
512 nm, but Au-N3 nanoparticles
showed red-shifted absorption
spectra at 550 nm (d), which indi-
cates the aggregation of Au-N3
nanoparticles. Scale bar is 50 nm.
of alkyne-PSCl-b-PS (Mn ¼ 8.8 kg/mol) used in the polymer
shell of Au-PSN3-b-PS 1. The synthesized Au-PSN3-b-PS 2
showed similar core size of 2.5 nm [Fig. 2(d)], but the R
value of Au-PSN3-b-PS 2 particles was much lower (ꢂ0.9
chains/nm2) than that of Au-PSN3-b-PS 1 particles.
the solution state. In contrast, Au-N3 particles in the matrix
showed red-shifted absorption spectra at 550 nm, which con-
firmed the aggregation of Au-N3 nanoparticles as found in
the TEM image. Therefore, it can be concluded that the
CuAAC reaction between the Au particle surface and the
alkyne polymer chains was successfully performed to form
densely packed polymer chains as the shell on the Au NP sur-
face. The presence of well-packed polymer chains was further
evidenced by the thermal stability test shown in Figure 6. To
enhance the thermal stability, azide groups that can be easily
crosslinked by thermal annealing and/or UV irradiation were
introduced into Au-PSN3-b-PS 1 particles. Two different Au-
PS and Au-PSN3-b-PS 1 nanoparticles were embedded in the
PS matrix and annealed at the elevated temperature of 200
ꢀC for 24 h. It is well known that because of fragile bonding
between the sulfur atoms at the end of the polymer chain
and Au atoms on the particle, Au NPs become unstable and
aggregate above 60 ꢀC.33,58 Therefore, after annealing at the
elevated temperature of 200 ꢀC, TEM images in Figure 6(a)
show that the Au-PS particles became aggregated, showing a
dramatic increase in the particle size from 2.5 to 8.5 nm. In
contrast, the size of Au-PSN3-b-PS 1 particles remained
Investigation on Behavior of Polymer-Coated Au NPs
in a Polymer Matrix
The morphology of Au NPs in a PS matrix was examined by
TEM to investigate the effect of the polymer shell. The blend
sample of Au NPs and PS matrix was prepared by mixing
both Au NPs (ꢂ10 wt %) and PS (Mn ¼ 56.5 kg/mol, PDI ¼
1.07) in toluene and stirred for several hours. The solutions
were drop- or spun-cast on NaCl substrates and the solvent
was evaporated slowly at room temperature under ambient
conditions without further thermal annealing. To characterize
the samples by TEM, the films on NaCl were transferred onto
the TEM grid by floating them onto water. Figure 5 repre-
sents TEM images of three different Au NPs [(a) Au-N3, (b)
Au-PS, and (c) Au-PSN3-b-PS 1] dispersed in PS films. The
Au-PSN3-b-PS 1 and Au-PS particles after click reaction were
well dispersed in the PS matrix, whereas the Au-N3 nanopar-
ticles aggregated because of incompatibility between the par-
ticles and the PS matrix. The morphology of the thin films
observed by TEM was further supported by UV–Vis absorp-
tion measurements [Fig. 5(d)]. The wavelengths of light
absorbed by gold nanoparticles are highly sensitive to the
particle size and distance between neighboring particles.56
When Au NPs come into close contact, the absorption wave-
length is red-shifted because induced dipoles can further
dampen the electron oscillation.57 UV–Vis absorption spectra
of both Au-PS and Au-PSN3-b-PS 1 in the PS matrix exhibited
the peak at 512 nm, which was consistent with the peak in
ꢀ
unchanged after annealing at 200 C for 24 h, thus indicating
that the PSN3-b-PS chains were closely packed enough to
form the crosslinked shell on the Au NP surface.
To further prove the importance of our approach for the syn-
thesis of Au NPs with highly packed polymer shells via the
combined ‘‘click’’ method and RAFT polymerization, polymer
nanocomposites consisting of Au-PSN3-b-PS 1 nanoparticles
and lamellar-forming PS-b-poly(2-vinylpyridine) (PS-b-P2VP
matrix; Mn ¼ 380 kg/mol) were prepared on NaCl substrates
and annealed at the elevated temperature of 220 ꢀC under
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FIGURE 6 TEM images represent two different nanoparticles (Au-PS and Au-PSN3-b-PS 1) in the PS matrix annealed at the elevated
temperature of 200 ꢀC for 24 h. (a) The Au-PS particles were aggregated and the particle size dramatically increased from 2.5 to 8.5 nm.
In contrast, the size of Au-PSN3-b-PS 1 particles shown in (b) was unchanged because of the presence of azide crosslinkable groups in
Au-PSN3-b-PS 1 particles, thus indicating that the PSN3-b-PS chains were packed closely enough to form the crosslinked shell on the
AuNP surface. Scale bar is 50 nm.
high vacuum (ꢂ10ꢁ7 Torr). Figure 7 shows cross-sectional
TEM images of PS-b-P2VP containing Au-PSN3-b-PS 1 nano-
particles. These images revealed the well-ordered lamellar
phase of PS-b-P2VP containing the Au NPs without any
aggregation. The particles were found to be within PS do-
main (seen as the brighter area) and at the PS/P2VP inter-
face as shown in the TEM image and the corresponding his-
togram. It was reported that, because of the favorable
interaction between bare Au surfaces and the P2VP matrix,
the R value is an important parameter for controlling the
location of the polymer-coated Au NPs within the block co-
polymer matrix.17 According to the previous report,54 the R
value of Au-PSN3-b-PS 1 is above the critical areal chain den-
sity that causes the transition of particles from the PS do-
main to the PS/P2VP interface. However, it should be noted
that because of the presence of the azide shell between the
PS shell and the Au NP surface, the R effect on the location
of our Au-PSN3-b-PS 1 nanoparticles cannot be directly inter-
preted by the previous results.59 We believe that well-dis-
persed Au-PSN3-b-PS 1 particles in both the PS and the PS-
b-P2VP matrices with extremely high thermal stability
proved the importance of our approach for the synthesis of
Au NPs with highly grafted polymer shells via combining the
click method and RAFT polymerization.
EXPERIMENTAL
Synthesis of Au-N3 Nanoparticles
Synthesis of 11-(Bromoundecyl)thioacetate (1)
11-Bromo-1-undecene (2.0 g, 8.58 mmol), thioacetic acid
(3.1 mL, density ¼ 1.065 g/mL, 42.9 mmol), and azobisiso-
butyronitrile (AIBN) (704 mg, 4.29 mmol) were dissolved in
FIGURE 7 (a) Cross-sectional TEM images of lamellar forming PS-b-P2VP block copolymer containing thermally stable PS-coated
gold nanoparticles (Au-PSN3-b-PS 1, R ¼ 1.22 chains/nm2) prepared by the click approach. Mn of PS-b-P2VP ¼ 380 kg/mol. Sam-
ples were annealed at 220 ꢀC for 2 days. Scale bar is 100 nm. (b) Histogram of particle positions from the corresponding TEM
micrograph. Interfaces of the PS domain are at -0.25 and þ0.25, and data are averaged at a given position relative to zero.
CLICK SYNTHESIS OF THERMALLY STABLE Au NPs, LIM ET AL.
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
toluene (50 mL) under Ar atmosphere. The mixture was
stirred at the reflux temperature for 4 h. The resulting mix-
ture was diluted with Et2O (200 mL) and the separated or-
ganic layer was washed with water (ꢃ3) and brine, dried
over MgSO4, and concentrated in vacuo. The crude product
was purified by column chromatography on silica gel using
hexane:CH2Cl2 (2:1) as the eluent to yield product 1 (2.31 g,
solid was separated by filtration, washed with cold water,
and dried. Finally, the products were recrystallized from hex-
ane with gentle stirring to give bright yellow solid crystals
(34.8 g, 71%). 1H NMR (CDCl3, 500 MHz) d 9.90 (br s, 1H),
4.87 (q, J ¼ 7.6 Hz, 1H), 3.37 (t, J ¼ 7.3 Hz, 2H), 1.66–1.72
(m, 2H), 1.64 (d, J ¼ 7.6 Hz, 3H), 1.40–1.47 (m, 2H), 0.94
(t, J ¼ 7.3 Hz, 3H).
1
87%) as a colorless oil. H NMR (CDCl3, 500 MHz) d 3.40 (t,
Alkynation of Trithiocarbonate RAFT Agent (6)
J ¼ 6.7 Hz, 2H), 2.86 (t, J ¼ 7.3 Hz, 2H), 2.32 (s, 3H), 1.82–
Trithiocarbonate RAFT agent (4 g, 16.76 mmol) and DMAP
(1.02 g, 8.38 mmol) were dissolved in DCM (200 mL) under
N2 atmosphere. Propargyl alcohol (1.94 mL, 33.52 mmol)
was then added, and the mixture was stirred for 15 min at
room temperature. Finally, N,N0-dicyclohexylcarbodiimide
(3.448 g, 16.76 mmol) in DCM (20 mL) was added and
allowed to remain at room temperature for 36 h. The reac-
tion product was washed several times with water. After
washing, the product was separated by column chromatogra-
phy. The final product was a yellow oil 6 (4.5g, 97%). 1H
NMR (CDCl3, 500 MHz) d 4.82 (q, J ¼ 7.3 Hz, 1H), 4.71 (t, J
¼ 2.9 Hz, 2H), 3.34 (t, J ¼ 7.3 Hz, 2H), 2.49 (t, J ¼ 2.4 Hz,
1H), 1.62–1.70 (m, 2H), 1.59 (d, J ¼ 7.3 Hz, 3H), 1.36–1.45
(m, 2H), 0.91 (t, J ¼ 7.3 Hz, 3H).
1.88 (m, 2H), 1.53–1.59 (m, 2H), 1.27–1.43 (m, 14H).
Synthesis of 11-Bromo-1-undecanethiol (2)
Compound 1 (1.0 g, 3.23 mmol) was dissolved in anhydrous
methanol. Acetyl chloride (2.3 mL, 32.3 mmol) was then
added dropwise to the solution under Ar atmosphere and at
ꢀ
0 C. The subsequent solution was allowed to warm to room
temperature for 3 h, and the resulting mixture was diluted
with Et2O (60 mL). The separated organic layer was washed
with water (ꢃ3) and brine, dried over MgSO4. The combined
organic layer was concentrated under vacuum to give prod-
1
uct 2 (786 mg, 91%) as a colorless oil. H NMR (CDCl3, 500
MHz) d 3.38 (t, J ¼ 6.8 Hz, 2H), 2.49 (q, J ¼ 7.6 Hz, 2H),
1.82–1.88 (m, 2H), 1.53–1.62 (m, 2H), 1.20–1.45 (m, 14H).
Synthesis of Bromoundecanethiolate Au NPs (Au-Br, 3)
The Au NPs were synthesized according to the Schiffrin–
Brust method using 0.5 mmol of HAuCl4ꢄ3H2O (aqueous so-
lution, 20 mL), 0.5 mmol of thiol compound 2, 0.5 mmol of
tetraoctylammonium bromide, and 5 mmol of NaBH4.60 Syn-
thesized Au NPs were washed three times with methanol to
remove residual ligands and reducing agents.
Synthesis of Alkyne-PSCl-b-PS (8)
Alkyne PSCl-b-PS block copolymers were synthesized by
RAFT polymerization [Scheme 2(b)]. 4-Vinylbenzylchloride
monomer (Aldrich), alkyne-terminated RAFT agent 6, and
AIBN were added into a glass ampoule. The reactants were
degassed by three freeze–thaw cycles. The inhibitors in the
monomers were removed by an alumina column prior to
polymerization, which was performed under vacuum at 70
ꢀC for 24 h. Poly(4-benzylchloride) was then precipitated
by cold methanol. Poly(4-benzylchloride), styrene monomer,
and AIBN (mol of alkyne-terminated RAFT agent:mol of
AIBN ¼ 10:1) in benzene were added into a glass ampoule
for sequential polymerization under vacuum. After 24 h
reaction at 70 ꢀC, the products were precipitated in cold
methanol, filtered, and dried. The total Mn and PDI of PS-b-
PSN3 were determined by SEC, which was calibrated by PS
standards. Details of the synthesized polymers are given in
Table 1.
Azidation of the Au NPs (Au-N3, 4)
The Au NPs (70 mg) 3 in dichloromethane (DCM) (15 mL)
were added to a solution of NaN3 (175 mg) in DMSO (15
mL). The solution was stirred for 2 days under N2 atmos-
phere at room temperature. After water was added, the
black organic layer was isolated and dried over MgSO4. The
Au NPs were washed with methanol and dried under
vacuum.
Synthesis of Alkyne-Terminated RAFT Chain
Transfer Agent
Synthesis of Trithiocarbonate RAFT Agent (5)
Trithiocarbonate RAFT Agent 5 was synthesized according to
modified literature procedures.61 50% aqueous NaOH solu-
tion (16 g, 200 mmol) was added to a mixture of 1-butane-
thiol (18 g, 200 mmol) and water (30 mL), followed by
10 mL acetone and resulted in a colorless solution. The
solution was stirred at room temperature for 0.5 h. Carbon
disulfide (13.5 mL, 1.27 g/mL, 225 mmol) was added to the
resulting solution to obtain a clear orange solution. The reac-
tion mixture was stirred for 0.5 h and then cooled in an ice
bath. The 2-bromopropionic acid (31.14 g, 205.0 mmol) was
added dropwise, followed by 16 g of 50% aqueous NaOH
solution at a rate to keep the temperature of the bath below
‘‘Click’’ Reactions Between Au-N3 with Alkyne-PSCl-b-PS (9)
The Au-N3 particles 4 and alkyne-PSCl-b-PS 8 were dissolved
in THF. CuSO4 (2 equiv. per alkyne polymers in water)
was added at room temperature, followed by the dropwise
addition of sodium ascorbate (5 equiv. per alkyne polymers
in water). Argon gas was bubbled through the reaction
mixture over 10 min. Final ratio of water to THF was kept at
1:4 to optimize the click reaction. The mixture was stirred
under Ar for 2 days at room temperature. Then, DCM and
aqueous ammonia solution were added to separate and draw
residual copper into the aqueous solution. The organic layer
was washed twice with water, dried with MgSO4, and the
solvent was evaporated under vacuum. The resulting solid
was redispersed in CH2Cl2 and precipitated in ethanol and
methanol. It was subsequently centrifuged at 18,000 rpm
ꢀ
30 C. After the completion of the exothermic reaction, water
(80 mL) was added and then the reaction was stirred at
room temperature for 24 h. Then, 10 M aqueous HCl
(30 mL) was added slowly at 0 ꢀC until solidification. The
several times using
a
gradient mixture of DCM and
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ARTICLE
cyclohexane to remove unreacted polymers and residuals.
Then, Au-PSCl-b-PS (172.6 mg) and sodium azide (220 mg)
were dissolved in DMF and stirred for 24 h. Finally, Au NPs
were purified by centrifugation.
This work was supported by the National Research Founda-
tion of Korea Grant funded by the Korean Government
(2009-0085070, 2009-0088551, 2010-0011033, and 2010-
0016304).
Characterization
NMR spectra were obtained by Bruker AMX 500. FTIR spec-
tra were taken on a Bruker IFS66V/S & HYPERION 3000.
The Mn and PDI of synthesized polymers were obtained by
SEC using a Waters 1515 pumpꢀand a Waters 2414 differen-
tial refractometer in THF at 35 C with a flow rate of 1 mL/
min. SEC was calibrated by PS standards. TGA was per-
REFERENCES AND NOTES
1 Beecroft, L. L.; Ober, C. K. Chem Mater 1997, 9, 1302–1317.
2 Sanchez, C.; Lebeau, B.; Chaput, F.; Boilot, J. P. Adv Mater
2003,15,1969–1994.
3 Sohn, B. H.; Cohen, R. E. J Appl Polym Sci 1997, 65, 723–729.
4 Buxton, G. A.; Balazs, A. C. Mol Simul 2004, 30, 249–257.
5 Zijlstra, P.; Chon, J. W. M.; Gu, M. Nature 2009, 459, 410–413.
ꢀ
formed on a TA Q50ꢀ0 at a scan rate of 10 C/min from room
temperature to 600 C under N2 atmosphere.
The characterization of Au NPs was carried out using TEM,
NMR, FTIR, GPC, UV–Vis, and TGA. The core size of Au NPs
was analyzed by TEM (Tecnai G220 S-twin or JEOL JEL-3011
HR) images. A carbon-coated TEM grid was dipped into a
dilute solution of Au NPs for several seconds and dried
under air before being examined by TEM. The weight frac-
tion of gold and organic ligands in the core–shell Au NPs
was analyzed by TGA. The weight fraction of polymer
brushes and gold particles were converted to volume frac-
tion using the density of organic ligands and the density of
the gold particles (ꢂ19.3 g/cm3). It should be noted that the
ungrafted organic and/or polymer ligands were washed sev-
eral times by centrifugation. Polymer ligands were carefully
washed several times by centrifugation using the density-
gradient method,62,63 in which the particles were washed
through five different layers of DCM and cyclohexane at vari-
ous ratios with different densities. The unwashed alkyne-ter-
minated polymer after each washing step was monitored by
SEC. The grafting density of polymer ligands on the Au NPs
was estimated by dividing the number of ligands attached on
Au surface by the surface area.
6 Siwick, B. J.; Kalinina, O.; Kumacheva, E.; Miller, R. J. D.;
Noolandi, J. J Appl Phys 2001, 90, 5328–5334.
7 Tsutsumi, K.; Funaki, Y.; Hirokawa, Y.; Hashimoto, T. Lang-
muir 1999, 15, 5200–5203.
8 Zalusky, A. S.; Olayo-Valles, R.; Wolf, J. H.; Hillmyer, M. A.
J Am Chem Soc 2002, 124, 12761–12773.
9 Mackay, M. E.; Tuteja, A.; Duxbury, P. M.; Hawker, C. J.; Van
Horn, B.; Guan, Z. B.; Chen, G. H.; Krishnan, R. S. Science
2006, 311, 1740–1743.
10 Bockstaller, M. R.; Lapetnikov, Y.; Margel, S.; Thomas, E. L.
J Am Chem Soc 2003, 125, 5276–5277.
11 Huang, C. M.; Wei, K. H. Macromolecules 2008, 41,
6876–6879.
12 Kang, H.; Detcheverry, F. A.; Mangham, A. N.; Stoykovich,
M. P.; Daoulas, K. C.; Hamers, R. J.; Muller, M.; de Pablo, J. J.;
Nealey, P. F. Phys Rev Lett 2008, 100, 148303-1–148303-4.
13 Maria, S.; Susha, A. S.; Sommer, M.; Talapin, D. V.; Rogach,
A. L.; Thelakkat, M. Macromolecules 2008, 41, 6081–6088.
14 Li, Q. F.; He, J. B.; Glogowski, E.; Li, X. F.; Wang, J.; Emrick,
T.; Russell, T. P. Adv Mater 2008, 20, 1462–1466.
CONCLUSIONS
15 Lin, Y.; Boker, A.; He, J. B.; Sill, K.; Xiang, H. Q.; Abetz, C.;
Li, X. F.; Wang, J.; Emrick, T.; Long, S.; Wang, Q.; Balazs, A.;
Russell, T. P. Nature 2005, 434, 55–59.
In this work, we developed a simple and powerful route for
creating thermally stable core–shell gold nanoparticles with
highly grafted polymer shells by combining RAFT and click
chemistry. Properly designed diblock copolymer of PS and
PSCl with alkyne end group was coupled to Au-N3 by CuAAC
reaction, in which the reaction conditions such as ratio of
THF/water during reaction was carefully optimized, thereby
achieving good solubility of all reagents including the Cu cat-
alyst and salt. Careful characterization using FTIR, UV–Vis,
and TGA showed that PSN3-b-PS chains were successfully
grafted onto the Au NP surface with high grafting density.
The synthesized Au NPs exhibited good thermal stability
over 220 ꢀC because of the densely grafted and crosslinked
PSN3 blocks in polymer shell. We successfully demonstrated
the importance of our highly packed polymer shell on the
nanoparticles by examining their behavior in homopolymer
and diblock copolymer matrix. We believe that this approach
can be easily extended to design other functional core–shell
nanoparticles.
16 Chung, H.; Ohno, K.; Fukuda, T.; Composto, R. J. Nano Lett
2005, 5, 1878–1882.
17 Kim, B. J.; Bang, J.; Hawker, C. J.; Kramer, E. J. Macromole-
cules 2006, 39, 4108–4114.
18 Kim, B. J.; Chiu, J. J.; Yi, G. R.; Pine, D. J.; Kramer, E. J.
Adv Mater 2005, 17, 2618–2622.
19 Listak, J.; Bockstaller, M. R. Macromolecules 2006, 39,
5820–5825.
20 Spontak, R. J.; Shankar, R.; Bowman, M. K.; Krishnan, A. S.;
Hamersky, M. W.; Samseth, J.; Bockstaller, M. R.; Rasmussen,
K. O. Nano Lett 2006, 6, 2115–2120.
21 Lan, Q.; Francis, L. F.; Bates, F. S. J Polym Sci Part B: Polym
Phys 2007, 45, 2284–2299.
22 Xu, C.; Ohno, K.; Ladmiral, V.; Composto, R. J. Polymer
2008, 49, 3568–3577.
CLICK SYNTHESIS OF THERMALLY STABLE Au NPs, LIM ET AL.
3473

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
23 Chiu, J. J.; Kim, B. J.; Kramer, E. J.; Pine, D. J. J Am Chem
44 Fischler, M.; Sologubenko, A.; Mayer, J.; Clever, G.; Burley,
G.; Gierlich, J.; Carell, T.; Simon, U. Chem Commun 2008,
169–171.
Soc 2005, 127, 5036–5037.
24 van Berkel, K. Y.; Hawker, C. J. J Polym Sci Part A: Polym
Chem 2010, 48, 1594–1606.
45 Fleming, D. A.; Thode, C. J.; Williams, M. E. Chem Mater
2006, 18, 2327–2334.
25 Kim, B. J.; Bang, J.; Hawker, C. J.; Chiu, J. J.; Pine, D. J.;
Jang, S. G.; Yang, S. M.; Kramer, E. J. Langmuir 2007, 23,
12693–12703.
46 Drockenmuller, E.; Colinet, I.; Damiron, D.; Gal, F.; Perez, H.;
Carrot, G. Macromolecules 2010, 43, 9371–9375.
26 Kim, J. S.; Jeon, H. J.; Park, J. J.; Park, M. S.; Youk, J. H.
47 Boisselier, E.; Salmon, L.; Ruiz, J.; Astruc, D. Chem Com-
J Polym Sci Part A: Polym Chem 2009, 47, 4963–4970.
mun 2008, 5788–5790.
27 Vestberg, R.; Piekarski, A. M.; Pressly, E. D.; Van Berkel,
K. Y.; Malkoch, M.; Gerbac, J.; Ueno, N.; Hawker, C. J. J Polym
Sci Part A: Polym Chem 2009, 47, 1237–1258.
48 Zhang, T.; Zheng, Z. H.; Ding, X. B.; Peng, Y. X. Macromol
Rapid Commun 2008, 29, 1716–1720.
49 Yoo, M.; Kim, S.; Lim, J.; Kramer, E. J.; Hawker, C. J.; Kim,
28 Kim, B. J.; Fredrickson, G. H.; Bang, J.; Hawker, C. J.;
B. J.; Bang, J. Macromolecules 2010, 43, 3570–3575.
Kramer, E. J. Macromolecules 2009, 42, 6193–6201.
50 Terrill, R. H.; Postlethwaite, T. A.; Chen, C. H.; Poon, C. D.;
Terzis, A.; Chen, A. D.; Hutchison, J. E.; Clark, M. R.; Wignall,
G.; Londono, J. D.; Superfine, R.; Falvo, M.; Johnson, C. S.;
Samulski, E. T.; Murray, R. W. J Am Chem Soc 1995, 117,
12537–12548.
29 Corbierre, M. K.; Cameron, N. S.; Sutton, M.; Laaziri, K.; Len-
nox, R. B. Langmuir 2005, 21, 6063–6072.
30 Corbierre, M. K.; Cameron, N. S.; Lennox, R. B. Langmuir
2004, 20, 2867–2873.
51 Badia, A.; Gao, W.; Singh, S.; Demers, L.; Cuccia, L.; Reven,
31 Luo, S. Z.; Xu, J.; Zhu, Z. Y.; Wu, C.; Liu, S. Y. J Phys Chem
L. Langmuir 1996, 12, 1262–1269.
B 2006, 110, 9132–9139.
52 Li, Z.; Zhang, K.; Ma, J.; Cheng, C.; Wooley, K. L. J Polym
32 Zhu, M. Q.; Wang, L. Q.; Exarhos, G. J.; Li, A. D. Q. J Am
Sci Part A: Polym Chem 2009, 47, 5557–5563.
Chem Soc 2004, 126, 2656–2657.
53 Tao, L.; Kaddis, C. S.; Loo, R. R. O.; Grover, G. N.; Loo,
33 Xiao, X. D.; Wang, B.; Zhang, C.; Yang, Z.; Loy, M. M. T.
J. A.; Maynard, H. D. Chem Commun 2009, 2148–2150.
Surf Sci 2001, 472, 41–50.
54 Kim, B. J.; Fredrickson, G. H.; Kramer, E. J. Macromolecules
34 Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew Chem Int
2008, 41, 436–447.
Ed Engl 2001, 40, 2004–2021.
55 Kim, B. J.; Given-Beck, S.; Bang, J.; Hawker, C. J.; Kramer,
35 Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B.
E. J. Macromolecules 2007, 40, 1796–1798.
Angew Chem Int Ed Engl 2002, 41, 2596–2599.
56 LizMarzan, L. M.; Giersig, M.; Mulvaney, P. Langmuir 1996,
36 Magenau, A. J. D.; Martinez-Castro, N.; Savin, D. A.; Storey,
12, 4329–4335.
R. F. Macromolecules 2009, 42, 8044–8051.
57 Ung, T.; Liz-Marzan, L. M.; Mulvaney, P. J Phys Chem B
37 Pressly, E. D.; Amir, R. J.; Hawker, C. J. J Polym Sci Part A:
2001, 105, 3441–3452.
Polym Chem 2011, 49, 814–819.
58 Ramachandran, G. K.; Hopson, T. J.; Rawlett, A. M.; Nagahara,
38 Collman, J. P.; Devaraj, N. K.; Eberspacher, T. P. A.; Chid-
L. A.; Primak, A.; Lindsay, S. M. Science 2003, 300, 1413–1416.
sey, C. E. D. Langmuir 2006, 22, 2457–2464.
59 Jang, S. G.; Khan, A.; Dimitriou, M.; Kim, B. J.; Lynd, N. A.;
Kramer, E. J.; Hawker, C. J. Soft Matter, in press; DOI: 10.1039/
c1sm05223c.
39 Ru, X.; Zeng, X. H.; Li, Z. M.; Evans, D. J.; Zhan, C. X.; Tang,
Y.; Wang, L. J.; Liu, X. M. J Polym Sci Part A: Polym Chem
2010, 48, 2410–2417.
60 Brust, M.; Walker, M.; Bethell, D.; Schiffrin, D. J.; Whyman,
40 Lee, L. V.; Mitchell, M. L.; Huang, S. J.; Fokin, V. V.; Sharp-
R. J Chem Soc Chem Commun 1994, 801–802.
less, K. B.; Wong, C. H. J Am Chem Soc 2003, 125, 9588–9589.
61 Ferguson, C. J.; Hughes, R. J.; Nguyen, D.; Pham, B. T. T.;
Gilbert, R. G.; Serelis, A. K.; Such, C. H.; Hawkett, B. S. Macro-
molecules 2005, 38, 2191–2204.
41 Hein, J. E.; Fokin, V. V. Chem Soc Rev 2010, 39, 1302–1315.
42 Brennan, J. L.; Hatzakis, N. S.; Tshikhudo, T. R.; Dirvian-
skyte, N.; Razumas, V.; Patkar, S.; Vind, J.; Svendsen, A.; Nolte,
R. J. M.; Rowan, A. E.; Brust, M. Bioconjugate Chem 2006, 17,
1373–1375.
62 Bai, L.; Ma, X. J.; Liu, J. F.; Sun, X. M.; Zhao, D. Y.; Evans,
D. G. J Am Chem Soc 2010, 132, 2333–2337.
43 Ranjan, R.; Brittain, W. J. Macromolecules 2007, 40,
63 Kwon, T.; Min, M.; Lee, H.; Kim, B. J. J Mater Chem, in
6217–6223.
press; DOI:10.1039/C1JM11318F.
3474
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA