Polymeric nanocomposite comprising gold nanoparticles and bilaterally sulfur-functionalized polystyrene

Article abstract of DOI:10.1002/pola.27562

Anionic polymerization technique has been utilized to synthesize a bilaterally sulfur-functionalized polystyrene, SCH3-polystyrene-SH. The synthesis scheme consists of (1) initiation of 4-vinylbenzylmethyl sulfide with sec-butyllithium to form a living sulfur-containing initiator, (2) polymerization of styrene, and (3) termination of growing polystyrene chain with ethylene sulfide. The resulting bilaterally sulfur-functionalized polystyrene is used to make polystyrene/gold nanoparticles (AuNPs) nanocomposite with AuNPs formed in situ in polymer solution through reduction of AuClO₄. The effects of the polymer/Au molar ratio as well as the molecular weight of polymer on the size and dispersion of formed AuNPs have been studied, and the superiority of bilaterally functionalized polymer to unilaterally functionalized polymer has been demonstrated. The polystyrene/AuNPs composite has been characterized by GPC, ¹H-NMR, ¹³C-NMR, EDS, TEM, UV-Vis, and DSC.

Full text of DOI:10.1002/pola.27562

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Polymeric Nanocomposite Comprising Gold Nanoparticles and Bilaterally
Sulfur-Functionalized Polystyrene
Ying-Shian Liou, Hsin-Chih Tsai, Cheng-Yang Yeh, Raymond Chien-Chao Tsiang
Department of Chemical Engineering, National Chung Cheng University, Chiayi 621, Taiwan, Republic of China
Correspondence to: R.C.-C. Tsiang (E-mail: chmcct@ccu.edu.tw)
Received 2 September 2014; accepted 11 January 2015; published online 3 March 2015
DOI: 10.1002/pola.27562
ABSTRACT: Anionic polymerization technique has been utilized
to synthesize bilaterally sulfur-functionalized polystyrene,
on the size and dispersion of formed AuNPs have been stud-
ied, and the superiority of bilaterally functionalized polymer to
unilaterally functionalized polymer has been demonstrated.
The polystyrene/AuNPs composite has been characterized by
a
SCH3-polystyrene-SH. The synthesis scheme consists of (1) ini-
tiation of 4-vinylbenzylmethyl sulfide with sec-butyllithium to
form a living sulfur-containing initiator, (2) polymerization of
styrene, and (3) termination of growing polystyrene chain with
ethylene sulfide. The resulting bilaterally sulfur-functionalized
polystyrene is used to make polystyrene/gold nanoparticles
(AuNPs) nanocomposite with AuNPs formed in situ in polymer
solution through reduction of AuClO4. The effects of the poly-
mer/Au molar ratio as well as the molecular weight of polymer
GPC, 1H-NMR, 13C-NMR, EDS, TEM, UV-Vis, and DSC.
2015
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Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem.
2015, 53, 1268–1277
KEYWORDS: anionic polymerization; dispersions; living polymer-
ization; nanocomposites; nanoparticles
devices. Stabilized AuNPs in aqueous solution or in polymer
matrix were achieved previously by other researchers, using
starch,37 PVP,38 PEG,39 poly(tert-butyl acrylate),40 PMMA,41
and polysilane,42 with a typical AuNP particle size in the
range of 10 to 50 nm.
INTRODUCTION Polymeric nanocomposites consisting of a
polymer matrix and metal nanoparticles have gained consid-
erable interests owing to their potential use as biosensors,
biomolecules, and optical and electrical materials. The prepa-
ration methods for such composites with good particle dis-
persion have been broadly investigated in the past few
years, and particle stabilization is often required in order to
alleviate the particle aggregation and get monodispersed
particles. Several methods exist for stabilizing monodis-
persed metal nanoparticles, such as the methods using (1)
ligands;1–8 (2) self-assembled polymeric monolayers, con-
taining thiol or other functional group, on the particle sur-
face;9–15 (3) protective linear polymers,16–24 or linear block
copolymers;25,26 and (4) copolymers of special architectures
such as star, micelle, graft copolymer, and dendrimer.27–30
Generally, the dispersity and the particle size of nanopar-
ticles are affected by various factors, such as the kinds of
ligands and polymer, the molecular weight and structure of
polymer, and the molar ratio of functional group/
polymer.31–36
In our work reported hereunder, anionic technique is
employed for synthesis of polystyrene/gold nanoparticles
(PS/AuNPs) composites comprising thiol and thiomethyl-
terminated PS (i.e., SCH3-polystyrene-SH) and in situ formed
AuNPs. The purpose is to compare the stabilizing capability
of a bilaterally functionalized PS with that of a unilaterally
functionalized PS, as well as to study the resulting composite
which contains smaller monodispersed AuNPs.
EXPERIMENTAL
Reagents and Materials
Styrene was purchased from Alfa Aesar and stirred with cal-
cium hydride (CaH2) and freshly distilled at reduced pres-
sure before used. Cyclohexane was distilled from calcium
hydride under N2. sec-Butyllithium (1.6M in cyclohexane)
was used as received. 4-Vinylbenzyl chloride was acquired
from Aldrich with 90% purity. Sodium thiomethoxide
(NaSCH3) was purchased from Acros with a purity of
95%. Ethylene sulfide was purified by passing through an
alumina column and stored under nitrogen. Hydrogen
Among all metal particles, AuNPs have gained extensive
investigation because of their good electrical and thermal
conductivity, outstanding corrosion resistance, and strong
catalytic activity of AuNPs as well as their good biocompati-
bility with cardiovascular stents, medical and drug delivery
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ular weight distribution were determined by gel permeation
chromatography(GPC) calibrated with polystyrene standards.
Synthesis of PS/AuNPs Composites
Synthesized polymer samples (0.1 g or 0.3 g) were dissolved
in a 250 mL flask containing 10 mL HAuCl4ꢀH2O solution
(prepared in cyclohexane as described in Reagents and Mate-
rials section) under nitrogen. The solution was stirred at
room temperature for an hour. Then, 1 mL solution of lith-
ium triethylborohydride in THF was added slowly and drop-
wisely. The color of the solution changed from golden-yellow
to brown, purple, and dark red gradually owing to the reduc-
tion of Au13 to gold nanoparticles (AuNPs). After reaction
for half an hour, the solution was poured into methanol for
SCHEME 1 Preparation of Sulfur-containing Momoner, 4-
Vinylbenzyl methyl sulfide. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
tetrachloroaurate(III), (HAuCl4ꢀH2O) was purchased from
Alfar Aesar and dissolved in THF to make a solution of
0.01 g/cm3 concentration before use.
Preparation of Sulfur-Containing Momoner, 4-Vinylbenzyl
Methyl Sulfide
The reaction scheme is shown in Scheme 1. A 250 mL glass
reactor was purged with nitrogen before the addition of
0.5 g NaSCH3 and 50 mL anhydrous methanol. Then, 0.8 mL
4-vinylbenzyl chloride was added and the temperature was
raised to reflux temperature. The reaction underwent for
24 h before filtration. The filtrate was put into a rotary evap-
orator to remove methanol. The collected solids was then
dissolved in ethyl ether and washed with deionized water to
remove any residual salts. Afterwards, ethyl ether was
removed in a rotary evaporator resulting in a yellowish tur-
bid oil liquid. This liquid product was purified via column
chromatography in a glass tube filled with silica gel using a
mixed solvent consisting of hexane and ethyl ether at a
weight ratio of 20:1 as an eluent. The purified eluate was
dehydrated by MgSO4 and dried in a rotary evaporator to
remove any residual solvent. The resulting 4-vinylbenzyl
methyl sulfide appeared as clear yellowish oil and the yield
was approximately 50%.
Synthesis of Unilaterally and Bilaterally
Sulfur-Functionalized Polymers
The reaction scheme is shown in Scheme 2(a,b). A 250 mL
glass reactor was purged with nitrogen before the addition
of 100 mL cyclohexane. Then, sec-butyllithium and 4-
Vinylbenzyl methyl sulfide monomer prepared earlier were
added in equimolar quantities under room temperature. The
reaction lasted 1 h and yellowish living chains were formed.
Styrene was next added and the color changed from light-
yellow to red. Polymerization was completed after 2 h. Then,
half of the solution was terminated in methanol to form the
thioether functionalized polystyrene (SCH3-polystyrene). The
remaining half of the solution was added by ethylene sulfide
and one hour later quenched by methanol to form the bilat-
erally sulfur-containing (thioether and thiol) polystyrene
(SCH3-polystyrene-SH). Finally, the solution was poured into
an excessive amount of methanol for polymer precipitation
and the precipitated polymer was dried under vacuum at 40
ꢁC. The number-averaged molecular weight (Mn) and molec-
SCHEME 2 (a) Synthesis of unilaterally sulfur-functionalized
polymer. (b) Synthesis of bilaterally sulfur-functionalized poly-
mer. [Color figure can be viewed in the online issue, which is
available at wileyonlinelibrary.com.]
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SCHEME 3 In situ formation of AuNPs in polymer matrix.
TABLE 1 Codes of Composite Samples
MW: 3200
MW: 6700
Neat Polymer
SCH3-PS (PSC4)
SCH3-PS-SH (PSC4S)
SCH3-PS (PSC6)
SCH3-PS-SH (PSC6S)
polymer/Au ratio
2
6
PSC4-1
PSC4-3
PSC4S-1
PSC4S-3
PSC6-1
PSC6-3
PSC6S-1
PSC6S-3
RESULTS AND DISCUSSION
precipitation. The collected products were dried in a vacuum
oven. The formation of PS/AuNPs is shown in Scheme 3.
Synthesis of Composite Samples
After the synthesis of unilaterally functionalized polystyrene
(SCH3-PS) and bilaterally functionalized polystyrene (SCH3-
PS-SH), hydrogen tetrachloroaurate(III) (HAuCl4ꢀ3H2O) solu-
tion was reduced in these two polymer sample solutions to
form PS/AuNPs nanocomposites. By varying the polymer/
HAuCl4 weight ratio and the molecular weight of polymers, a
total of eight composite samples were made as shown in
Table 1.
Measurements
The molecular structure of SCH3-polystyrene and SCH3-poly-
styrene-SH were determined by 1H-NMR and 13C-NMR spec-
tra (BRUKER AMX 400 spectrometer) from samples
dissolved in CDCl3 at 25 ꢁC. The molecular weight and
molecular weight distribution of both polymers were deter-
mined by the Waters GPC equipped with the Waters M-486
absorbance (UV) and the Waters 410 differential refractive
index (RI) detectors. The GPC was operated with three Water
Styragel HR Columns (HR5, HR4, and HR3) at a steady flow
rate of 1 mL/min with the sample concentration of 0.1% in
THF solvent. Transmission electron microscopy (TEM)
images of nanocomposites were analyzed with a JEOL JEM-
2100 instrument operated at an accelerating voltage at 200
kV. TEM samples were prepared either from a dip-coated
film or a drip-formed film on carbon-coated Cu grids. UV-Vis
spectra of various samples were recorded with a Shimadzu
UV-Visible spectrophotometer (model UV2101-PC). The deg-
radation behavior of the nanocomposite was determined
with a thermogravimetric analyzer (TGA2050, TA Instru-
Molecular Weight Analysis
All composite samples contain polystyrene of either 3200 or
6700 molecular weights. Characteristics are shown in Table
2, the low PDI values indicate a clean anionic synthesis
(Figs. 1 and 2).
Identification of Functionalized Sample
Structure by NMR
The 500 MHz 1H-NMR spectra of SCH3-PS and SCH3-PS-SH
were compared in Figure 3(a–c). In addition to the 6.5 to 7.3
ppm chemical shift (d) of benzene rings, the thiol group of
SCH3-PS-SH exhibits peaks f and g in 2.6 to 2.8 ppm clearly.
However, the peak of SCH3 can not be seen probably due to
the too low proton concentration of thiomethyl group (as
compared with other protons). Therefore, the corroboration
of the existence of SCH3 has to resort to 13C NMR
spectroscopy.
ꢁ
ments) with a heating rate of 10 C/min from room temper-
ature to 800 ꢁC under a dry nitrogen flow rate of 10 mL/
min. The thermal properties were analyzed with a differen-
tial scanning calorimeter (Dupont TA Instrument Co.22910
Modulated DSC). The samples were heated from room tem-
perature to 150 ꢁC at a heating rate of 10 ꢁC/min with dry
nitrogen as the effluent gas (60 mL/min).
13C-NMR spectra of polystyrene and SCH3-PS are compared
in Figure 3(c). All peaks in both spectra are nearly the same
except that the spectrum of SCH3-polystyrene has a distinct
peak at 26 ppm. In order to prove that this peak is the char-
acteristic peak of SCH3 in polymer, we have checked in Fig-
ure 4 the 13C-NMR spectrum of dimethyl sulfide. Dimethyl
sulfide has a characteristic chemical shift (d) at 18 ppm. The
TABLE 2 GPC Analysis of Sample Polymers
Sample
Mn
PDI
GPC Figure
PSC4
PSC6
3200
6700
1.08
1.06
Figure 1
Figure 2
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FIGURE 1 GPC of the sample PSC4 (molecular weight 5 3200).
minute peak shift from 18 ppm to 26 ppm arises from the
effect of bonded polystyrene.
(20 mesh, 3 mm) and completely evaporating the solvent,
TEM images were taken and are shown in the following. The
AuNPs are black particles, the polymer appears as the dark
material encompasses AuNPs and the exposed substrate
after solvent evaporation appears as the light background.
All AuNPs are distributed in polymer portion and the sub-
strate portion does not have any gold particles, thus indicat-
ing that all gold nanoparticles are being covered with the
polymer.
EDS Elemental Analysis
The existence of thiomethyl group in polymers can be also
verified by the energy dispersive X-ray Spectrometer (EDS).
Shown in Figure 5, the main element contained in sample
PSC4 is carbon and sulfur amounts to 0.95 wt %. Further-
more, this weight percentage is approximately equal to the
predicted number (1.08%, based on the measured molecular
weight of PS), thus indicating little oligomerization of 4-
vinylbenzyl methyl sulfide and existence of a single thio-
methyl group on the SCH3-PS polymer chain head. The small
difference between 1.08 wt % and 0.95 wt % may be attrib-
uted to the unexactness of equimolarity of s-BuLi and 4-
vinylbenzyl methyl sulfide during the initiator preparation.
The effect of thiomethyl group and thiol group, the molecular
weight of polymer and the polymer/Au weight ratio on the
size of the formed AuNPs are studied in the following.
Effect of the Amount of Polymer on Formation of AuNPs
As observed from TEM images of sample PSC4-1 (Fig. 7) and
PSC4-3 (Fig. 8), insufficient sulfur atoms resulting from the
less amount of polymer cause serious AuNPs aggregation in
PSC4-1. In sample PSC4-3 (Fig. 8), individual single AuNPs of
about 10 nm particle size are observed in the polymer/
AuNPs composite.
Similarly, EDS spectrum also verifies the existence of thiol
group at the end of SCH3-PS-SH. As shown in Figure 6, the
weight percentage of sulfur is 2.10 wt %, approximately
equal to the predicted number (2.16%, based on the meas-
ured molecular weight of PS), thus indicating little oligomeri-
zation of ethylene sulfide and a single thiol functional group
at the end of SCH3-PS-SH polymer chain.
The same effect is observed for PSC4S. As shown in Figures
9 and 10, less particle aggregation of AuNPs occurs in
PSC4S-3 composite than in PSC4S-1.
Gold Nanoparticles in Composites
When Au13 solution is reduced by Super-Hydride
in the
Size analysis data (bar chart) in Figure 11 show that PSC4S-
1 composite contains about 75% of AuNPs with a size
inbetween 2 and 5 nm, and the largest particle is nearly
10 nm. On the other hand, PSC4S-3 composite consists of
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presence of SCH3-PS or SCH3-PS-SH, polymer-coated gold
nanoparticles will form. After dripping sample solutions (all
at 0.3 mg/mL concentration) on a carbon-coated copper grid
FIGURE 2 GPC of the sample PSC6 (molecular weight 5 6700).
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FIGURE 4 13C-NMR chart of dimethyl sulfide.
more smaller AuNPs because of better stabilization provided
by the larger amount of sulfur atoms contained in the
polymer.
Effect of Molecular Weight of Polymer on Formation of
AuNPs
When an equal weight of PSC6 is substituted for PSC4, the
AuNPs aggregation become worse. This occurs because the
longer polymer chain of PSC6 leads to a fewer number of
sulfur atoms and thus the lower stabilizing effect on AuNPs.
Both PSC6-1 and PSC6-3 result in severe particle aggregation
and the size of formed AuNP are 60 nm and 45 nm, respec-
tively. However, the thiol group in PSC6S provides additional
stabilizing effect to compensate the adverse effect of molecu-
lar weight, and effectively alleviates aggregation of AuNPs in
nanocomposite. Therefore, the particle sizes of AuNPs in
PSC4S-1 or PSC6S-1 are compared here in Figure 12. As
expected, PSC6S-1 contains larger AuNPs than PSC4S-1
because of the higher molecular weight.
FIGURE 3 (a) 1H-NMR spectrum of SCH3-PS. (b) 1H-NMR spec-
trum of SCH3-PS-SH. (c) Comparison between 13C-NMR charts
of polystyrene and SCH3-PS. [Color figure can be viewed in
the online issue, which is available at wileyonlinelibrary.com.]
FIGURE 5 EDS of PSC4. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
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FIGURE 8 TEM images of PSC4-3 (magnification 20 K).
PSC6S-3 all AuNPs have sizes between 3 and 4 nm. Appa-
rently, although the larger amount of sulfur atom in the
small molecular weight PSC4S helps generate smaller AuNPs,
it is the large molecular weight of PSC6S that narrows the
particle size distribution and create uniform AuNPs.
FIGURE 6 EDS of PSC4S. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
Uniformity of AuNPs Dispersion
A comparison between Figures 8 and 10 indicates clearly
that an unilaterally thiomethyl-functionalized PS composite
contains inevitably some aggregated AuNPs while a bilater-
ally sulfur-functionalized PS having both thiomethyl and thiol
end groups shows better particle-dispersing capability. Fur-
thermore, the size of AuNPs is smaller in the bilaterally
sulfur-functionalized PS composite. Nevertheless, the size
uniformity of the dispersed AuNPs varies with the molecular
weight of polymer. As observed clearly from the TEM images
(Figs. 13 and 14), the AuNPs are more uniformly dispersed
in PSC6S-3 composite than in PSC4S-3 composite, even
though PSC6S-3 causes larger AuNPs particle size. It has
been found that a significant amount of tiny 1nm AuNPs
exist together with large particles in PSC4S-3 while in
The exact dispersion of these AuNPs in composite material
has also been quantified by skewness (b) based on TEM
images. A negative b value indicates that the vast majority of
the particles are in the right hand side of the mean location.
A positive b indicates that most of the particle are in the left
hand side of the mean location. If b is zero, particle sizes are
evenly dispersed. Skewness can be calculated by the
equation:43
ꢀ
ꢁ
ꢀ
ꢁ
b
q
Nqi2Nqmean
X
q
b5
ðq21Þðq22Þ
r
i51
FIGURE 7 TEM images of PSC4-1 (magnification 20 K).
FIGURE 9 TEM images of PSC4S-1 (magnification 80 K).
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FIGURE 12 Size comparison of AuNPs in PSC4S-1 and PSC6S-
1. [Color figure can be viewed in the online issue, which is
available at wileyonlinelibrary.com.]
FIGURE 10 The TEM image of PSC4S-3 (magnification 80 K).
In this equation, q represents the number of squares of a
grid which is put into the TEM image, and a proper choice
of q is necessary for meaningfully and correctly determining
the b value. Nqi represents the amount of particles in each
square and Nqmean is the average number of Nqi.
groups are amine and thiol, and trisodium citrate was used as
the reducing agent to convert Au13 to AuNPs. In the presence
of polystyrene with a molecular weight of 3770 and 6500,
uniformly dispersed AuNPs were formed with the particle
size being about 26 nm and 23 nm, respectively. In addition,
Shan et al. reported their work on monodispersed gold nano-
particles (16–100 nm) stabilized by polyelectrolyte-
functionalized ionic liquid and claimed that smaller AuNPs
could be made by using a boron hydride reducing agent.45
TEM images of PSC4S-3 (Fig. 15) and PSC6S-3 (Fig. 16) at a
low magnification of 40 K were gridded into nine quadrats,
and the calculated b’s are very small, 20.81152 and
0.32197, respectively. Because skewness is inversely related
to dispersion of particles in a matrix, our small b correlates
good particle dispersion with less aggregation of AuNPs.
In this work, our samples PSC4S-3 (molecular weight of
polystyrene is 3200) and PSC6S-3 (molecular weight of poly-
styrene is 6700) contain not only uniformly dispersed AuNPs
but with a smaller particle size of 2 to 3 nm and 4 to 5 nm,
respectively (as shown in Figs. 15 and 16). Because smaller
AuNPs have better light absorptivity and higher catalytic
activity and Hvolbæk et al. found particularly the necessity
Relatively Smaller Particle Size Compared with
Previous AuNPs
Yockell- Lelie`vre et al. reported their work on the synthesis of
polystyrene-capped AuNPs using ATRP polymerization and
end functionalization techniques.44 The chain end functional
FIGURE 11 Size comparison of AuNPs in PSC4S-1 and PSC4S-
3. [Color figure can be viewed in the online issue, which is
available at wileyonlinelibrary.com.]
FIGURE 13 The TEM image (magnification 40 K) PSC4S-3.
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FIGURE 16 UV-Vis spectra of samples PSC4-1and PSC6-1 con-
taining different AuNP sizes. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
FIGURE 14 The TEM image (magnification 40 K) PSC6S-3.
of having an AuNPs size less than 5 nm to achieve catalytic
activity on the oxidation reaction of carbon monoxide,46 our
composite material containing uniformly dispersed small
AuNPs are of significant importance in potential applications.
blue shift. Similar comparison of the band shift also corrobo-
rate the smaller AuNPs in PSC4S-3 than in PSC4S-1. Thus, it
is corroborated that a higher polymer/Au ratio leads to the
formation of smaller AuNPs.
Analogously, at the same polymer/Au ratio, the effect of
polymer molecular weight on the size of formed AuNPs can
be corroborated by examining the band shift. Shown in Fig-
ure 16 is the UV-Vis spectra of PSC4-1 and PSC6-1. It clearly
proves that a smaller molecular weight causes a blue shift.
This observation coincides with our previous saying that at
the same polymer/Au ratio polymer with a smaller molecu-
lar weight contains more sulfur atom and generates smaller
AuNPs. Similar comparison of the band shift also corroborate
the smaller AuNPs in PSC4S-3 than in PSC6S-3.
UV-Vis Spectroscopic Analysis
AuNPs typically have a surface plasmon resonance band at
520 to 540 nm in its UV-Vis absorption spectrum, and the
absorption band shifts with the particle size. AuNPs of a
smaller size have a band shift towards low wavelength (blue
shift) and AuNPs of a larger size have a band shift towards
high wavelength (red shift). Therefore, a comparison of UV-Vis
spectra enables us to examine the size difference of AuNPs.
As seen in Figure 15, because PSC4-3 contains higher poly-
mer/Au ratio than PSC4-1during the in situ reduction of
Au13, AuNPs formed have a smaller size and thus exhibit a
Thermal Characteristics by DSC
The glass transition temperature (Tg) has been measured by
DSC under nitrogen at aꢁ heating rate of 10 ꢁC/min from
room temperature to 200 C.
FIGURE 15 UV-Vis spectra of samples PSC4-1 and PSC4-3 con-
taining different AuNP sizes. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
FIGURE 17 DSC analyses of PSC6 neat polymer and corre-
sponding composites. [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com.]
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material containing well-dispersed AuNPs of 3 to 4 nm size
have been successfully prepared. Composites have generally
10 to 13 ꢁC increase in Tg compared with the neat polymer,
and composites comprising bilaterally functionalized polymer
have higher Tg’s than those comprising unilaterally functional-
ized polymer.
ACKNOWLEDGMENTS
Financial support provided by the National Science Council of
the Republic of China under the program NSC9101-2120-M-
194-006 is greatly appreciated.
REFERENCES AND NOTES
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3 Gonsalves, M. M. Pereira, J. Mol. Catal. A 1996, 113, 209–221.
As shown in Figure 17, while Tg of the neat PSC6 polymer is
82.5 C, the PSC6-1 and PSC6-3 composites have Tg’s at 90.7
and 92.4 ꢁC, correspondingly. Conceivably, the bonding of
ꢁ
4 J. H. Youk, M. K. Park, J. Locklin, R. Advincula, J. Yang, J.
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AuNPs thwarts the movement of polymer molecules and
ꢁ
thus increases Tg by approximately 8 to 9 C. Analogously, a
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comparison of bilaterally functionalized PSC6S with its corre-
sponding composites PSC6S-1 and PSC6S-3 (shown in Fig.
18)ꢁshows a significantly increased Tg of approximate 10 to
13 C for the composites. While the neat polymers, PSC6 and
PSC6S, have equal Tg’s, the composite comprising a bilater-
ally functionalized polymer has a higher Tg than that com-
prising an unilaterally functionalized polymer (e.g., PSC6S-1
vs. PSC6-1, and PSC6S-3 vs. PSC6-3). This observation could
be attributed to the smaller AuNPs size (caused by bilater-
ally sulfur-functional groups as described in the previous
section) which generates more surface area for bonding
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