Facile synthesis of thiol-terminated poly(styrene-ran-vinyl phenol) (PSVPh) copolymers via reversible addition-fragmentation chain transfer (RAFT) polymerization and their use in the synthesis of gold nanoparticles with controllable hydrophilicity

Article abstract of DOI:10.1016/j.polymer.2010.01.033

A facile approach to prepare thiol-terminated poly(styrene-ran-vinyl phenol) (PSVPh) copolymers and PSVPh-coated gold nanoparticles is reported with the goal of creating stabilizing ligands for nanoparticles with controlled hydrophilicity. Dithioester-ter

Full text of DOI:10.1016/j.polymer.2010.01.033

Polymer 51 (2010) 1244–1251
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Polymer
journal homepage: www.elsevier.com/locate/polymer
Facile synthesis of thiol-terminated poly(styrene-ran-vinyl phenol) (PSVPh)
copolymers via reversible addition-fragmentation chain transfer (RAFT)
polymerization and their use in the synthesis of gold nanoparticles with
controllable hydrophilicity
,c,
Chang-Uk Lee a, Debashish Roy d, Brent S. Sumerlin d, Mark D. Dadmun b
*
a Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996, USA
b Department of Chemistry, University of Tennessee, Knoxville, TN 37996, USA
c Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA
d Department of Chemistry, Southern Methodist University, Dallas, TX 75275-0314, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A facile approach to prepare thiol-terminated poly(styrene-ran-vinyl phenol) (PSVPh) copolymers and
PSVPh-coated gold nanoparticles is reported with the goal of creating stabilizing ligands for nano-
particles with controlled hydrophilicity. Dithioester-terminated poly(styrene-ran-acetoxystyrene)
copolymers were synthesized via RAFT polymerization using cumyl dithiobenzoate as a chain transfer
agent. These copolymers were converted to thiol-terminated PSVPh copolymers by a one step hydrazi-
nolysis reaction using hydrazine hydrate to simultaneously convert dithioester-terminal and acetoxy-
pendant groups to thiol-terminal and hydroxyl-pendant groups, respectively. Spectroscopic observations
including NMR and IR confirm end- and pendant-group conversion. PSVPh-coated gold nanoparticles
were synthesized in the presence of a mixture of thiol-terminated PSVPh and PSVPh copolymers con-
taining disulfides as stabilizing ligands in a water/toluene, two-phase system. The size and size distri-
bution of core gold nanoparticles were determined by TEM and image analysis. The hydrodynamic radius
of PSVPh-coated gold nanoparticles was also determined by dynamic light scattering experiment, which
confirms the particle analysis by TEM. This procedure provides a facile technique to control the polarity
and hydrophilicity of metal nanoparticle surfaces and could prove critical in advancing the control of
nanoparticle placement in biological and hierarchically ordered systems, such as diblock copolymers.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 24 September 2009
Received in revised form
11 January 2010
Accepted 14 January 2010
Available online 25 January 2010
Keywords:
RAFT Polymerization
Thiol-terminated polymers
Gold nanoparticles
1. Introduction
forming aggregates during nanoparticles synthesis, and can be used
to control the size of nanoparticles [4].
Thiol-terminated polymers or polymers containing disulfides
have been of great interest in polymer science for biological, elec-
tronic, and optical applications, since they can bind with metals
such as gold and silver by specific interactions [1,2]. For example,
thiol-terminated polymers stabilize gold nanoparticles due to the
strong interactions between sulfur and gold due to their soft
character [3]. Thus, successful preparation of thiol-terminated
polymers enables the incorporation of the versatile functionalities
of polymers onto the surfaces of metal nanoparticles. Furthermore,
the thiol-functionalized polymers prevent gold nanoparticles from
Incorporation of functionalized gold nanoparticles in a polymer
matrix have attracted much attention, in that controlled dispersion
of nanoparticles can lead to tailored structures of nanocomposites,
and thus result in a material that is useful in specific applications of
nanocomposites, including chemical sensors, catalysts, or
substrates in electronic devices [5,6] For example, Krasteva et al.
[7]. developed chemical sensors using layer-by-layer self-assembly
of multilayers composed of gold nanoparticles and three kinds of
dendrimers; hydrophobic polyphenylene (PPh) dendrimer, hydro-
philic poly(amidoamine) (PAMAM) dendrimers, and amphiphilic
poly(propylene imine) (PPI) dendrimers. Each film of the Au/den-
drimer nanocomposites was tested as a chemical sensor by dosing
with vapors of toluene, 1-propanol, or water. Au/PPh sensors
showed the highest resistance when exposed to toluene vapor, Au/
PAMAM with 1-propanol, and Au/PPI with water. The increased
* Corresponding author. Department of Chemistry, University of Tennessee,
Knoxville, TN 37996, USA. Tel.: þ1 865 974 6582.
E-mail address: dad@utk.edu (M.D. Dadmun).
0032-3861/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2010.01.033

C.-U. Lee et al. / Polymer 51 (2010) 1244–1251
1245
resistance results from the increase of interparticle distances as
dendrimers absorb analyte vapor and swell the polymer chains.
Furthermore, incorporation of nanoparticles in block copoly-
mers as a matrix has been of recent interest, as the microphase-
separated morphologies of block copolymers can lead to highly
ordered placement of nanoparticles [8–10]. For example, Kramer
and co-workers[11] reported sequestering either polystyrene (PS)-
coated gold nanoparticles or gold nanoparticles coated with a 1:1
mixture of PS and poly(2-vinyl pyridine) (PVP) chains in poly(-
styrene-b-2-vinyl pyridine) (PS-b-P2VP) diblock copolymers, which
microphase-separated into lamellar phases. In this work, PS-coated
gold nanoparticles located at the center of the PS domains in the
diblock copolymers. On the other hand, PS/PVP-coated gold nano-
particles were dispersed at the interface of PS lamellar domains and
PVP lamellar domains in the diblock copolymers.
Recent theoretical and experimental studies reveal that the
morphologies of nanocomposites composed of nanoparticles and
block copolymers can be designed by controlling entropic contri-
butions to the nanoparticles placement by varying particle size, and
by controlling enthalpic contributions between the polymer and
nanoparticles by varying particle coatings [12,13]. For example,
Wiesner and co-workers[14] prepared nanocomposites composed
of silica nanoparticles and poly(isoprene-block-ethylene oxide) (PI-
b-PEO) block copolymers. They reported that the final morphol-
ogies of the nanocomposites were determined by the morphologies
of block copolymers when the diameter of the particles was rela-
as well as optimal mechanical, thermal, and electrical properties of
the resultant nanocomposites. Therefore, we plan to utilize this
fundamental understanding to design optimal ligands for gold
nanoparticles based on PSVPh, to enable their efficient dispersion
in diblock copolymer matrices and bio-based materials by maxi-
mizing the extent of non-covalent interactions between the
nanoparticle ligands and polymer matrix.
For example, such ligands will provide a mechanism to inves-
tigate the ability to tune enthalpic attractions between the gold
nanoparticles and one phase of the diblock copolymer on the
accessible nanocomposite morphologies. The correlation of
morphology with the extent of non-covalent enthalpic attractions
between a nanoparticle and a component of a diblock copolymer
has not been previously examined and yet can potentially provide
a heretofore inaccessible avenue to novel diblock nanocomposite
loadings and morphologies.
However, the synthesis of thiol-terminated PSVPh copolymers
(PSVPh-SH) as well as gold nanoparticles coated with PSVPh
copolymers has not been previously reported. This may result from
the difficulty in synthesizing polymers with both thiol-terminal
and hydroxyl-pendant groups. In this study, we suggest a simple
and useful strategy to prepare PSVPh-SH copolymers via reversible
addition-fragmentation chain transfer (RAFT) polymerization
[20–22]. A common chain transfer agent in the RAFT process is
a thiocarbonylthio compound, which can lead to degenerative
transfer with propagating polymeric radicals [23]. Subsequently,
intermediate radicals are fragmented to polymers with thio-
carbonylthio end groups and a new radical [23,24]. The overall
RAFT process results in polymers with thiocarbonylthio end groups,
which can be converted to thiols by hydrolysis [23,25]. This
conversion of dithioesters to thiols has opened a facile pathway to
synthesize thiol-terminated polymers and to stabilize gold nano-
particles by utilizing the thiol-terminated polymers as a stabilizing
ligand [26–29].
We report here our attempts to synthesize thiol-terminated
PSVPh ligands using controlled free radical techniques. Atom
transfer radical polymerization was attempted first, where the
hydrazinolysis to the thiol and pendant –OH groups were sequen-
tially implemented. These methods proved disappointing, and we
then turned to RAFT polymerization, where a facile method to
synthesize thiol-terminated PSVPh copolymers via RAFT polymer-
ization, and subsequent hydrazinolysis using hydrazine hydrate
was identified. Subsequently, gold nanoparticles coated with these
PSVPh copolymers were synthesized by using thiol-terminated
PSVPh copolymers and PSVPh copolymers containing disulfides as
a stabilizing ligand.
tively small compared with radius of gyration of PEO chains (Rg,PEO
)
in the block copolymers. On the other hand, larger particles than
the PEO chains altered nanocomposite morphologies from lamellar
to onion-like or cylindrical phases. This change in morphology is
ascribed to the loss of entropy of PEO chains as they attempt to
circumvent the large particles, which becomes too great to main-
tain the initial morphologies of the block copolymers without
particles [12]. Additionally, Kim et al. [4]. reported controlling the
sequestration of polystyrene-coated gold nanoparticles in poly(-
styrene-b-2-vinylpyridine) diblock copolymers (PS-b-P2VP) by
varying the chain density of polystyrene attached on gold nano-
particles. They reported that gold nanoparticles with low PS chain
density (less than 1.3 chains/nm2) located at the interface between
PS and P2VP domains due to a favorable interaction between a bare
gold and P2VP chains, while gold nanoparticles with high chain
density located in PS domains.
Thus, nanoparticles coated with polymers of versatile func-
tionalities can be a key material to achieve desired morphologies,
and thus properties, of nanocomposites by tailoring enthalpic
parameters within nanocomposite systems. Nanoparticles with
polar functionality are of particular interest to form supramole-
cular, non-covalent intermolecular interactions between the
nanoparticles and polymer matrices. For instance, the incorpora-
tion of metal nanoparticles into bio-responsive and biomaterials
will require exquisite control of the polarity the nanoparticles
surface in order to control their dispersion and placement in these
promising matrices. Unfortunately, the synthesis of nanoparticles
that afford this control is nontrivial, and requires the ability to
tune the distribution and content of polar functionalities within
the stabilizer ligand.
2. Experimental
2.1. Gel permeation chromatography (GPC)
The molecular weight of the synthesized polymers were deter-
mined using gel permeation chromatography on a PL-GPC 120
(Polymer Laboratories, Varian Inc., Amherst, MA, USA) with two
PLgel 5 micron mixed-B columns with a calibration of polystyrene
standards with narrow molecular weight distribution in tetrahy-
drofuran (THF) as the elution solvent.
In our recent work, we have shown that the extent of inter-
molecular hydrogen bonding between the PSVPh matrix and
nanoscale additives can be optimized by controlling the composi-
tion of poly(styrene-ran-vinyl phenol) random copolymers
(PSVPh). These results have been shown to be broadly applicable,
having been applied to the dispersion of liquid crystalline polymers
[15], multi-walled nanotubes [16], single-walled nanotubes [17,18],
and montmorillinite clays in a polymer matrix [19]. The improved
extent of non-covalent interactions results in optimized dispersion
2.2. Nuclear Magnetic Resonance (NMR)
The analysis of the structure of the terminal and pendant groups
of the synthesized copolymers was conducted by collecting the 1H
NMR spectra of copolymers dissolved in deuterated chloroform
using a Bruker spectrometer operating at 300 MHz. Samples for
NMR were prepared by dissolving 7 mg of polymers in 1 mL of

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C.-U. Lee et al. / Polymer 51 (2010) 1244–1251
deuterated chloroform. Each copolymer sample was scanned 1024
times to clearly obtain peaks generated from end groups of the
copolymers with low molecular weight.
were purchased from Aldrich, and utilized as received without
further purification. Styrene (monomer, 9.7 g, 93.3 mmol,
51 equiv.), 4-acetoxystyrene (2.7 g, 16.6 mmol, 9 equiv.), CDB (chain
transfer agent, 500 mg, 1.84 mmol), AIBN (30 mg, 0.1 equiv.), and
anhydrous dioxane (solvent, 3 g) were added to a two-neck, round
bottom flask. All reactants were degassed by freeze and thaw
repeated 3 times. Polymerization was then conducted under
nitrogen in an oil bath at 65 ꢁC for 15 h. After 15 h, the resultant
solution was quenched in liquid nitrogen to stop polymerization,
and polymers were purified by precipitating in petroleum ether. A
reddish polymer powder was obtained after filtration, and dried
under vacuum at 70 ꢁC for 24 h. The molecular weight of the
resultant copolymers was determined by gel permeation chroma-
tography (GPC), exhibiting a number average molecular weight
(Mn) of 5100 (g/mol), weight average molecular weight (Mw) of
6400 (g/mol), and PDI of 1.25.
2.3. Infrared (IR) spectroscopy
The structure of the synthesized copolymers was also charac-
terized by Fourier transform infrared spectroscopy (Varian 4100 FT-
IR). Copolymer samples were scanned 16 times with the range of
400–4000 cmꢀ1 wavenumber at 4 cmꢀ1 resolution. Spectroscopic
information was corrected for KBr background information.
Samples for IR were prepared by mixing 5 mg of copolymers with
95 mg of potassium bromide (KBr) and compressing this mixture
into an IR pellet.
2.4. Transmission electron microscopy (TEM) of gold nanoparticles
The synthesized gold nanoparticles were characterized by
transmission electron microscopy (TEM, Hitachi H800) with an
acceleration voltage of 100 KeV. To examine the gold nanoparticles
coated with either PSVPh or poly(styrene-ran-acetoxystyrene)
copolymers by TEM, a dilute solution of the gold nanoparticles in
toluene (5 mg/mL) was prepared. One drop of this solution was
placed on porous carbon films supported by copper grids [32].
These films were dried in air to evaporate the solvent. Size and size
distribution were determined by analyzing TEM images of the gold
nanoparticles using Image J software by assuming that particles are
spheres. The range of particle area was set to be from 3 to 100 nm2.
The degree of circularity, a measure of the degree that the particles
approach a circle was set to be from 0.8 to 1.0 for PSVPh-coated gold
nanoparticles.
2.8. Hydrazinolysis of dithioester-terminated poly(styrene-ran-
acetoxystyrene) to PSVPh copolymers
The one step hydrazinolysis reaction was conducted to convert
both dithioester-terminal and acetoxy-pendant groups to thiol and
hydroxyl groups respectively. In a typical hydrazinolysis reaction,
1.2 g of dithioester-terminated poly(styrene-ran-acetoxystyrene)
copolymers was completely dissolved in 23 mL of dioxane, and
then 10 mL of hydrazine hydrate (NH2NH2xH2O) was added drop-
wise into the polymer solution. This mixture was vigorously stirred
under nitrogen gas flow for 5 days at room temperature. The
polymer was then precipitated in cold methanol, and filtered. The
resultant, white polymer powder was obtained after drying in air
overnight, followed by drying under vacuum at 80 ꢁC for 24 h. After
hydrazinolysis, it was found by spectroscopy and GPC that the final
product is the mixture of thiol-terminated PSVPh copolymers and
PSVPh copolymers containing disulfides.
2.5. Dynamic light scattering (DLS) of copolymers and gold
nanoparticles
The hydrodynamic radius (Rh) of the synthesized copolymers
and the PSVPh-coated gold nanoparticles in toluene at 25 ꢁC were
measured using dynamic light scattering in toluene (PD 5000,
Precision Detectors Inc., Bellingham, MA, USA). A laser of 683 nm
wavelength was used as a light source, and light scattered by the
sample was detected at 65ꢁ. Copolymer or gold nanoparticle solu-
tions in toluene were prepared with the concentration of 5 mg/mL
for copolymers and 2.7 mg/mL for nanoparticles. These solutions
were filtered using Millipore PTFE membrane filters with pore size
of 0.2 micron [29], and centrifuged at 14,000 rpm for 30 min, before
they were injected into the DLS sample holder. Each sample was
scanned 120 times, and the mean Rh was determined by averaging
the Rh values from at least 10 different experiments.
2.9. Synthesis of PSVPh-coated gold nanoparticles using thiol-
terminated polymers and disulfide containing polymer mixtures
Gold nanoparticles with surfaces that are coated with PSVPh
copolymers were synthesized using a mixture of thiol-terminated
PSVPh copolymers and PSVPh copolymers containing disulfides as
the stabilizing ligand. This synthesis procedure was developed to
mimic the process reported by Brust et al. [32]. and Bockstaller et al.
[33,34], which is a water-toluene, two phase synthesis procedure.
In this reaction, hydrogen tetrachloroaurate(III) hydrate, sodium
borohydride, and tetraoctylammonium bromide (Sigma–Aldrich)
were used as received. An aqueous solution of hydrogen tetra-
chloroaurate (HAuCl43H2O, 9 mg in 3 mL water, 8.83 mmol/L) was
mixed with a solution of tetraoctylammonium bromide in toluene
(N(C8H17)4Br, 110 mg in 8 mL toluene, 25 mmol/L), which is a phase
transfer agent in this reaction [34]. This mixture was vigorously
stirred for 3 h until the tetrachloroaurate was completely trans-
ferred from the aqueous phase to the toluene layer, which can be
verified by the appearance of the reddish color of the toluene layer.
The organic phase was separated from the two-phase (water/
toluene) system. Thiol-terminated PSVPh copolymers and PSVPh
copolymers containing disulfides (125 mg, 0.025 mmol) were then
added to the separated toluene layer, and 2 mL of THF was added to
this polymer solution. Addition of THF was needed to increase the
solubility of PSVPh copolymers containing polar-pendant groups in
toluene. An aqueous solution of sodium borohydride (NaBH4,
75.6 mg in 2 mL water, 1 mol/L) and 5 drops of hydrazine was
quickly added while this mixture was vigorously stirred. With the
addition of reductant, a color change of the solution was observed
from yellow-red to dark-purple. This mixture was stirred for 17 h,
2.6. Synthesis of cumyl dithiobenzoate (CDB)
Cumyl dithiobenzoate was prepared by a method derived from
that of Oae et al. [30]. Dithiobenzoic acid[31] (11.1 g, 72.0 mmol)
and a-methylstyrene (10.4 g, 88.0 mmol) excess) were dissolved in
carbon tetrachloride (40 mL), and the resulting solution was purged
with nitrogen and stirred at 70 ꢁC for 5 h. The crude product was
obtained as a dark-purple oil in 69% yield and was subsequently
purified by column chromatography (neutral alumina packing,
hexanes as eluent).
2.7. Synthesis of dithioester- terminated poly(styrene-ran-
acetoxystyrene) copolymers via RAFT polymerization
Styrene, 4-acetoxystyrene, anhydrous 1,4-dioxane, 2,20-azobi-
sisobutyronitrile (AIBN), petroleum ether, and hydrazine hydrate

C.-U. Lee et al. / Polymer 51 (2010) 1244–1251
1247
and the organic phase was then separated. This separated solution
3.2. Synthesis for PSVPh-SH copolymers via RAFT polymerization,
was evaporated to 1 mL using a rotary evaporator. The final product
was precipitated in cold methanol, and the dark brown product was
filtered. Any unbound PSVPh copolymer ligands were removed by
washing with a mixture of ethanol and THF (5:1) once briefly, and
ethanol several times. The final PSVPh-coated gold nanoparticles
were dried under vacuum at 70 ꢁC for 6 h.
followed by hydrazinolysis
To improve the efficiency and facility of the synthesis the thiol-
terminated PSVPh copolymers, we implemented a one step hydra-
zinolysis to convert both dithioester-terminal and acetoxy-pendant
groups of dithioester-terminated poly(styrene-ran-acetoxystyrene)
copolymers to thiol-terminal and hydroxyl-pendant groups,
respectively. This strategy can be rationalized in that the labile
dithioester groups can be converted to thiol groups by hydrolysis
using a nucleophile such as an amine [22]. Furthermore, acetoxy-
pendant groups of the copolymers can be converted to hydroxyl
groups using NH2NH2 [36]. Thus, we prepared dithioester-termi-
nated poly(styrene-ran-acetoxystyrene) copolymers via RAFT
polymerization, and selected hydrazine hydrate as a reducing agent
for the one step hydrazinolysis reaction. Fig. 1 shows the overall
synthesis reaction to prepare PSVPh-SH copolymers. As can be seen,
dithioester-terminated poly(styrene-ran-acetoxystyrene) copoly-
mers were synthesized using cumyl dithiobenzoate as a chain
transfer agent via RAFT polymerization. One step hydrazinolysis
using hydrazine hydrate then followed the polymerization.
The formation of dithioester-terminal and acetoxy-pendant
groups of the poly(styrene-ran-acetoxystyrene) copolymers after
RAFT polymerization was confirmed by NMR. Fig. 2 (A) shows the
1H NMR spectrum of the dithioester-terminated copolymers. In this
figure, the aromatic protons in the dithioester end groups are
present at a chemical shift of 7.8 ppm [20,21]. The methine proton
next to the dithioester chain ends is evidenced by peaks at 4.8 ppm
[20]. Additionally, a chemical shift of around 2.3 ppm indicates the
presence of 3 methyl protons in the acetoxy-pendant groups of the
copolymers. Furthermore, the mole fraction of acetoxy groups in
2.10. Synthesis of thiol-terminated PSVPh copolymers by ATRP
followed by thiolation or hydrazinolysis
We first attempted to synthesize thiol-terminated PSVPh
copolymers via atom transfer radical polymerization (ATRP) fol-
lowed by thiolation or hydrolysis. Our attempts were conducted
with two different approaches starting with different monomers.
First, the synthesis of thiol-terminated PSVPh was attempted by
first synthesizing bromine-terminated poly(styrene-ran-acetox-
ystyrene) copolymers via ATRP, and followed by subsequent indi-
vidual hydrazinolysis and thiolation reactions. The details of these
reactions are provided as supplemental information.
Additionally, the synthesis of PSVPh-SH copolymers was
attempted by first synthesizing bromine-terminated poly(styrene-
ran-4-tert-butoxystyrene) copolymers via ATRP, followed by the
thiolation of the copolymers to thiol-terminated poly(styrene-ran-4-
tert-butoxystyrene) copolymers, and the subsequent hydrazinolysis
of the thiol-terminated poly(styrene-ran-4-tert-butoxystyrene) to
PSVPh-SH. The details of this reaction are also provided as supple-
mental information.
3. Results and discussion
3.1. Attempts to synthesize thiol-terminated PSVPh copolymers via
atom transfer radical polymerization (ATRP)
the
dithioester-terminated
poly(styrene-ran-acetoxystyrene)
copolymers was calculated to be 19.7% [37].
Fig. 2 (B) shows the 1H NMR spectrum of PSVPh-SH copolymers
after hydrazinolysis. In this figure, the peak around 7.8 ppm asso-
ciated with the aromatic protons in the dithioester chain end
disappears. The peak indicating methine protons next to the end
groups also disappears. This NMR data therefore indicates that the
dithioester-terminal groups of the copolymers were converted to
thiol-end groups by hydrazinolysis. Additionally, this conversion of
dithioester chain ends to thiols was confirmed by color change of
The synthesis of thiol-terminated poly(styrene-ran-vinyl phenol)
copolymers was first attempted starting with bromine-terminated
poly(styrene-ran-acetoxystyrene) copolymers. Our experimental
results indicate that the conversion of the acetoxy groups of the
copolymer to hydroxyl groups and the conversion of the bromine-
end groups of this copolymer to thiol-end groups were not
successful. NMR data suggests that the hydrazinolysis of the copol-
ymers using hydrazine hydrate results in a loss of end groups of the
copolymers, and the acetoxy groups of the copolymers are not stable
under thiolation using thiourea and NaOH. The details of these
experimental results are described in the supporting information.
Thus, the synthesis of PSVPh-SH was next attempted starting with
poly(styrene-ran-4-tert-butoxystyrene) copolymers with bromine-
end groups, which was selected as it is expected that the ether bonds
of the tert-butoxystyrene groups will be more stable under thiolation
than the ester bonds of the acetoxystyrene groups [35].
the copolymers after hydrazinolysis (reddish-pink
/ clear).
Furthermore, the acetoxy proton peaks around 2.3 ppm disappear,
which indicates that the acetoxy-pendant groups were converted
to hydroxyl groups. Therefore, this NMR data indicates that both
dithioester and acetoxy groups were converted to thiol and
hydroxyl groups by this one step hydrazinolysis reaction.
IR further confirmed the formation of hydroxyl-pendant groups
by the reduction of acetoxy groups. Fig. 3 shows the IR spectrum of
the
dithioester-terminated
poly(styrene-ran-acetoxystyrene)
The results of this study indicate that the conversion of the
bromine-end groups of poly(styrene-ran-4-tert-butoxystyrene) to
thiol-end groups by thiolation was complete. However, the
conversion of the tert-butoxy groups of the thiol-terminated
poly(styrene-ran-4-tert-butoxystyrene) copolymers to hydroxyl
groups was not successful. Furthermore, NMR data suggests that
the hydrazinolysis impacts the thiol-end group of the thiol-termi-
nated copolymers. The details of these experimental results are also
presented and discussed in the supporting information section.
While incomplete conversion of the hydrazinolysis reaction may
result from insufficient reaction time and/or insufficient amount of
HCl for hydrazinolysis, it was determined that the synthesis for
PSVPh-SH copolymers via RAFT polymerization followed by
hydrazinolysis would be a more facile approach and thus became
the focus of our studies.
before hydrazinolysis and the thiol-terminated PSVPh copolymers
after hydrazinolysis. It is clearly shown in Fig. 3 that the peaks
around 3100–3700 cmꢀ1 denoting hydroxyl (O–H) group stretching
vibration in PSVPh copolymers are present after hydrazinolysis, but
were absent in the dithioester-terminated poly(styrene-ran-ace-
toxystyrene) copolymers. Additionally, the peaks around 1200 and
1760 cmꢀ1, which indicate C–O and C]O group stretching vibration
in the acetoxystyrene pendant groups before hydrazinolysis
respectively, became very weak or disappeared after hydrazinol-
ysis, further verifying that the acetoxy-pendant group is reduced to
hydroxyl groups by the hydrazinolysis reaction.
Fig. 4 shows the GPC curves of the copolymers before and after
hydrazinolysis. As can be seen in this Figure, a peak indicating
a component with higher molecular weight than the original
copolymer is observed at around 13,000 (g/mol) after the 5day

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C.-U. Lee et al. / Polymer 51 (2010) 1244–1251
CH
H2C
CH
H2C
CH3
S
C
C
S
+
+
CH3
OCOCH3
CH2
S
C
AIBN, 65 °C
Dioxane
CH3
CH
CH2
CH
S
CH3
O
O
C
CH3
CH
NH2NH2
Dioxane
CH3
CH3
CH2
CH
CH2
SH
OH
Fig. 1. Overall scheme for the synthesis of thiol-terminated PSVPh copolymers via RAFT polymerization, followed by one step hydrazinolysis using hydrazine hydrate.
hydrazinolysis reaction, in addition to the original peak indicating
the starting material around 5800 (g/mol). The appearance of the
higher molecular weight peak at double the molecular weight of
the starting polymers suggests the formation of disulfides during
the hydrazinolysis reaction [38]. Thiols can be easily oxidized, and
two oxidized thiols can readily link together to form corresponding
disulfides [2,38]. This characteristic of thiols has been previously
observed in thiol-terminated polymers. For example, Kim et al.
[38]. suggested the formation of a disulfide linkage during the
hydrazinolysis reaction to convert dithioester-terminated poly(-
styrene-ran-2-vinyl pyridine) (PS-r-P2VP) copolymers to thiol-
terminated PS-r-P2VP copolymers using hexylamine in dry THF
under nitrogen flow. To further analyze the formation of these
larger molecular weight materials, the GPC curve of PSVPh copol-
ymers after hydrazinolysis was deconvoluted and analyzed to
determine the fraction of thiols and disulfides, as shown in Fig. 4.
The areas under the two Gaussian curves are used to estimate that
the final product of the hydrazinolysis is composed of 52% disul-
fides and 48% thiols. It should be emphasized that this estimation is
not precise as the use of the area under the curves does not take
into account the mass-sensitive response of the RI detector.
the hydrazinolysis reaction after 5 days was used to determine its
suitability to act as a ligand in the formation of gold nanoparticles,
and the optimization of this hydrazinolysis procedure is currently
ongoing in our lab.
3.3. Synthesis of gold nanoparticles stabilized by a mixture of thiol-
terminated PSVPh and PSVPh copolymers containing disulfides
It has been demonstrated that polymers containing disulfides,
as well as thiol-terminated polymers, are effective stabilizing
ligands in the synthesis of gold nanoparticles, and thus the product
of the hydrazinolysis reaction was used to synthesize gold nano-
particles. For instance, disulfides have been utilized in recent
experimental studies to stabilize metal nanoparticles such as gold
and silver, or to functionalize the surfaces of gold nanoparticles
[29,39,40]. Lee and co-workers [39] reported the preparation of
gold or silver nanoparticles in the presence of n-octadecyl disul-
fides, (C18S)2, as a stabilizing agent. They observed that the size and
size distribution of gold nanoparticles that were synthesized using
n-octadecanethiols, C18SH were similar to those of nanoparticles
synthesized using n-octadecyl disulfides as the ligand, suggesting
that disulfides can effectively stabilize gold surfaces, comparable to
that of thiols. Additionally, Mangeney et al. [40]. functionalized gold
nanoparticles with poly(acrylamide)s containing disulfide-
terminal groups. They found that the surfaces of the gold colloids
could effectively be coated with those polymers due to strong
This ratio could certainly be optimized by limiting the reaction
time of the hydrazinolysis to shorter time than 5 days. This was
attempted, where the hydrazinolysis reaction was performed for 1
and 18 h. However, it was found that neither 1 h nor 18 h was
sufficient to completely hydrolyze the acetoxy-pendant groups to
hydroxyl groups, as evidenced by NMR studies. Thus, the product of

C.-U. Lee et al. / Polymer 51 (2010) 1244–1251
1249
After hydrazinolysis (Experiment)
Disulfides (Deconvolution)
Thiols (Deconvolution)
Before hydrazinolysis (Experiment)
14.0
14.5
15.0
15.5
16.0
16.5
17.0
Retention time (mins)
Fig. 4. GPC curves of copolymers before and after hydrazinolysis. Deconvoluted curves
from the SH-PSVPh copolymer data are also shown.
size and size distribution of the gold nanoparticles, which were
determined using Image J software (1.34 s) by counting 459 parti-
cles, where an average diameter of 5.7 nm with standard deviation
of 2.2.was found As can be seen in Figs. 5 and 6, the size of the gold
nanoparticles was well-controlled in the presence of the mixture of
thiol-terminated PSVPh and PSVPh copolymers containing disul-
fide bridges. This data indicates that polymers containing disulfides
mixed with thiol-terminated polymers can be utilized to stabilize
gold nanoparticles and to control their size. While this is in
agreement with previous work, where disulfides or thiols are
effective at passivating gold nanoparticles during particle synthesis,
our results indicate that mixtures of thiol and disulfides effectively
stabilize gold nanoparticles, suggesting that any competition
between the thiol and disulfide does not inhibit the nanoparticle
stabilization process.
Fig. 2. 1H spectrum of (A) dithioester-terminated poly(styrene-ran-acetoxystyrene)
from RAFT polymerization and (B) of thiol-terminated PSVPh copolymers after
hydrazinolysis.
interactions between the gold and the sulfur from disulfide-
terminal groups.
Therefore gold nanoparticles coated with PSVPh-SH and PSVPh
copolymers containing disulfides were synthesized in a water-
toluene two-phase system using the mixture of thiol-terminated
PSVPh and disulfides that resulted from the hydrazinolysis. These
gold nanoparticles were characterized by TEM to analyze their size
and size distribution. Fig. 5 shows a representative TEM image of
the PSVPh-coated gold nanoparticles. Additionally, Fig. 6 shows the
This is not surprising, as the adsorption of a polymer with the
adsorbing group in the middle of the polymer chain has been
shown to adsorb much more slowly than the comparable end-
3
~ 1200 cm-1
Before hydrazinolysis
C-O stretching
After hydrazinolysis
~ 1760 cm-1
2
1
0
C=O stretching
~ 3100 - 3700 cm-1
O-H stretching
500
1000 1500 2000 2500 3000 3500 4000
Wavenumber (cm-1)
Fig. 3. IR spectrum of dithioester-terminated poly(styrene-ran-acetoxystyrene) before
Fig. 5. Representative TEM image of gold nanoparticles coated with PSVPh copoly-
hydrazinolysis and PSVPh-SH copolymers after hydrazinolysis.
mers. (Scale bar: 100 nm).

1250
C.-U. Lee et al. / Polymer 51 (2010) 1244–1251
Rh,PSVPh-Au
rAu+2Rh,PSVPh
100
80
60
40
20
0
7
Count: 459 particles
Average: 5.7 nm
Standard Dev.: 2.2
6
5
4
3
2
1
0
rAu from TEM
Rh,PSVPh
i
ii
iii
iv
2
3
4
5
6
7
8
9
10 11 12
Fig. 8. Comparison of experimental results from TEM and DLS. (i) average radius of
core Au nanoparticles, rAu from TEM, (ii) Rh of PSVPh, Rh,PSVPh from DLS, (iii)
rAu þ Rh,PSVPh, and (iv) Rh of PSVPh-coated Au nanoparticles, Rh,PSVPh-Au
Diameter (nm)
,
,
.
Fig. 6. Size and size distribution of gold nanoparticles coated with PSVPh copolymers.
functionalized polymer[41] as well as to adsorb fewer chains
[41,42]. Thus, in our system, it is expected that the PSVPh-SH
molecules will adsorb onto the gold nanoparticle much more
quickly and be more plentiful than the disulfide containing PSVPh
molecules, providing a system that can effectively stabilize nano-
particle formation.
This result, however, appears to contradict the GPC data,
which indicate the coupling of thiols to form disulfides, which
should result in, on average, larger polymer chains, and thus an
increase in Rh. However, these two data points can be rational-
ized by considering that the disulfide containing PSVPh will
adsorb at their center point and form brushes that are nearly as
extended as the end-functionalized PSVPh-SH. In fact, theoretical
calculations[42] estimate that the center-adsorbing chain
will extend w90% as far from the surface as a comparable
end-functionalized that is ½ the length, the precise conditions of
our study. Thus, the increased chain length of the potential
adsorbate does not result in an increase in the resultant brush
length. The decrease in the Rh of PSVPh copolymers in toluene
can be explained due to the repulsive interaction between the
pendant, polar –OH moieties in PSVPh copolymers and the non-
polar solvent. It is important to emphasize that this is not the
only mechanism by which the PSVPh can decrease in size, for
instance intramolecular hydrogen bonding among vinyl phenol
groups of a chain may also cause a contraction of the PSVPh
chain.
3.4. Dynamic light scattering of copolymers and gold nanoparticles
The hydrodynamic radii (Rh) of dithioester-terminated poly(-
styrene-ran-acetoxystyrene) copolymers, thiol-terminated PSVPh
copolymers, and PSVPh-coated gold nanoparticles in toluene at
25 ꢁC were determined by dynamic light scattering (DLS). Fig. 7
shows a scheme to illustrate the relationship between the Rh of the
copolymers and of the PSVPh-coated gold nanoparticles. The
average Rh of the copolymers in toluene decreased after hydrazi-
nolysis, where the Rh of the dithioester-terminated poly(styrene-
ran-acetoxystyrene) copolymers was 2.37 nm, and the Rh of the
PSVPh-SH copolymers was 2.15 nm. This DLS data indicates, not
surprisingly, that the PSVPh copolymer chains with ca. 20 mol%
polar, hydroxyl-pendant groups tend to shrink in non-polar
toluene, relative to the poly(styrene-ran-acetoxystyrene) copol-
ymer chains before hydrazinolysis.
To further verify this analysis, the average Rh of the gold
nanoparticles coated with PSVPh copolymers was measured and
found to be 7.2 nm. This DLS data agrees with the DLS and TEM
Fig. 7. Scheme to illustrate hydrodynamic radius of the copolymers before and after hydrazinolysis, and of the PSVPh-coated gold nanoparticles.

C.-U. Lee et al. / Polymer 51 (2010) 1244–1251
1251
data of the PSVPh copolymers, as shown in Fig. 8. The average
Supplementary data
radius of the core gold nanoparticles was determined to be
2.85 nm by TEM analysis. The Rh of the PSVPh copolymers, which
form the corona around the core gold nanoparticles, was deter-
mined to be 2.15 nm. The sum of radius of the core gold and
hydrodynamic diameter of PSVPh copolymers is 7.15 nm, which is
sufficiently close to the Rh of gold nanoparticles coated with PSVPh
copolymer as determined by DLS. (7.2 nm) Therefore, the DLS data
further verifies that the synthesized PSVPh-coated gold nano-
particles are composed of core gold nanoparticles surrounded by
PSVPh copolymer coronas.
Supplementary data associated with this article can be found in
the online version doi:10.1016/j.polymer.2010.01.033.
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This work was financially supported by National Science Foun-
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by the Division of Materials Sciences and Engineering, U.S.
Department of Energy under contract with UT-Battelle, LLC. The
authors would also like to thank Dr. John Dunlap in the Microscopy
Facility at the University of Tennessee, Knoxville for imaging gold
nanoparticles by TEM and helpful discussions regarding particle
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