Direct synthesis of carboranylpolystyrene and their applications for oxidation resistance of graphene oxides and catalyst support

Article abstract of DOI:10.1016/j.jorganchem.2015.07.034

Radical polymerization reaction of carborane monomer closo-1-R-2-(4-vinylbenzyl)-1,2-C₂B₁₀H₁₀ (R = Me (1), Ph (2)) produced carboranyl-functionalized polystyrenes, poly(1-R-2-(4-vinylbenzyl)-1,2-closo-C₂B₁₀H₁₀) (R = Me (3), Ph (4)), in a yield of 56.3% and 85.0%, respectively. The polymers 3 and 4 were used to coat graphene oxides (GO) and the resulting products exhibited high oxidation resistance property when compared with pristine GO. Polymer 3 was also used to stabilize palladium nanoparticles (Pd-NPs) to form catalyst composite Pd-NPs/3. Composite Pd-NPs/3 was found to be efficient catalyst for selective oxidation of glycerol. All new compounds were fully characterized.

Full text of DOI:10.1016/j.jorganchem.2015.07.034

Journal of Organometallic Chemistry 798 (2015) 80e85
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Direct synthesis of carboranylpolystyrene and their applications for
oxidation resistance of graphene oxides and catalyst support
,
Yinghuai Zhu a *, Wenguang Zhao a, Narayan S. Hosmane b
a Institute of Chemical and Engineering Sciences (ICES), 1 Pesek Road, Jurong Island, Singapore 627833, Singapore
b Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois 60115-2862, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Radical polymerization reaction of carborane monomer closo-1-R-2-(4-vinylbenzyl)-1,2-C2B10H10
(R ¼ Me (1), Ph (2)) produced carboranyl-functionalized polystyrenes, poly(1-R-2-(4-vinylbenzyl)-1,2-
closo-C2B10H10) (R ¼ Me (3), Ph (4)), in a yield of 56.3% and 85.0%, respectively. The polymers 3 and 4
were used to coat graphene oxides (GO) and the resulting products exhibited high oxidation resistance
property when compared with pristine GO. Polymer 3 was also used to stabilize palladium nanoparticles
(Pd-NPs) to form catalyst composite Pd-NPs/3. Composite Pd-NPs/3 was found to be efficient catalyst for
selective oxidation of glycerol. All new compounds were fully characterized.
Received 30 March 2015
Received in revised form
6 July 2015
Accepted 20 July 2015
Available online 23 July 2015
Keywords:
Carborane
© 2015 Elsevier B.V. All rights reserved.
Functional polystyrene
Pd (0) nanoparticles
Graphene oxides
Oxidation resistance
Selective oxidation
1. Introduction
high toxic CuI-based catalyst was used [19,20]. Similar to other click
reactions, the inherent drawbacks such as contamination of CuI
Polymers incorporating carborane units exhibit unique proper-
ties due to inherent chemical inertness, high hydrophobicity,
electron deficient, thermal and radiation stability of carborane
cages [1e17]. For example, silicone polymers with closo-carborane,
C2B10H12, incorporated in its backbone show promising oxidative
stability at high temperatures [1e3]. This type of polymers could
find many new applications, other than oxidation resistance re-
agents, in the near future including those in electrochromic device
[12], neutron detector [14] and boron neutron capture therapy [18].
Various methods such as Sonogashira-Hagihara polycondensation
[5,8], Stille coupling reaction [11,12] and click-grafting [19], have
been used to synthesize carborane-containing polymers. Due to
high oxidative and thermal stability of closo-carborane cage, the
closo-carborane appended polystyrenes are expected to show
improved thermal and oxidative stability when compared with
pristine polystyrenes. Therefore, such polymers have good poten-
tial as catalyst supports for oxidative coupling reactions. However,
in click-grafting method in which carborane cages were attached to
polystyrene chain by an azide-alkyne click cycloaddition reactions,
catalyst species even after completion of the reaction may limit
their further applications such as in drug delivery. Removal of
remaining metal species from polymer products is particularly
challenging because they could be trapped in polymers folds. In
this work, carborane-appended polystyrenes, poly(1-R-2-(4-
vinylbenzyl)-1,2-closo-C2B10H10) (R ¼ Me (3), Ph (4)), were syn-
thesized by direct radical polymerization reactions.
On the other hand, graphene oxide (GO) has been known for
more than one and a half century [21], it has many intriguing
properties and potential applications [22]. However, GO possesses
thermal and oxidative instability and some of the carbon atoms are
oxidized to carbonaceous gases at elevated temperature (~210 ꢀC)
[21]. Sandoval et al. reported that nitrogen-doped grephene oxide
exhibits increased thermal stability against oxidation by air [22].
Relatively critical conditions such as high temperature (500 ꢀC and
800 ꢀC) and corrosive gas (NH3) were used [22] in the process. Since
closo-carborane-appended polymers have the potential resistance
toward oxidation at high temperatures, polymers 3 and 4 were
used to improve stability of GOs. In addition to its application in
oxidation resistance, polymer 3 was also used as catalyst support.
Palladium nano-particles were supported on polymer 3 to form a
catalyst composite. The palladium-based catalysts play important
* Corresponding author.
E-mail address: zhu_yinghuai@ices.a-star.edu.sg (Y. Zhu).
http://dx.doi.org/10.1016/j.jorganchem.2015.07.034
0022-328X/© 2015 Elsevier B.V. All rights reserved.

Y. Zhu et al. / Journal of Organometallic Chemistry 798 (2015) 80e85
81
roles in many organic transformations including CeC coupling re-
actions that have been well-investigated and documented [23e27].
We have been using Pd catalysts in biomass conversions to value
added chemicals via selective oxidation reactions [28] and
demonstrated their promising catalytic activity. Dihydroxyacetone
(DHA) is being the most popularly used ingredient in current
sunless tanners approved by the US Food and Drug Administration
(FDA) [29]. Commercially available, high-priced DHA is generally
produced in an atom-inefficient fermentation process [29]. The
inherent drawbacks make the existing technology not efficient
from the ecological, energetic, economical, and chemical stand-
point. Heterogeneous catalysts possess obvious advantages in
product isolation and, therefore, received growing interest for their
use [30]. It has been known for a long time that supported platinum
catalysts can be used for catalytic alcohol oxidation to aldehydes or
ketones in aqueous media. Nonetheless, the deactivation of these
catalysts in such reactions is a serious problem [31]. The fact that
carboranyl-appended polystyrene with high oxidation stability are
prepared in our laboratory, we report herein the synthesis and
application of catalyst composite for selective oxidation of biomass-
based glycerol to 1,3-dihydroxyacetone.
Scheme 1. Syntheses of carboranylpolystyrene and Pd NPs supported composites.
2. Results and discussion
Carborane-appended styrene monomers 1 and 2 were prepared
by substitution reactions between in situ generated lithium salts of
[closo-1-R-1,2-C2B10H10
and 81.7% yields, respectively (Scheme 1). The 1H, 13C, and 11B NMR
spectra are similar to those found for other related structures. In 13
]
ꢁ anion and 4-vinylbenzyl chloride in 71.2%
C
NMR spectra, unsaturated C]C bonds show double peaks in the
region of 114.31e114.56 ppm. In 11B NMR spectra, 1 and 2 gave
different resonance patterns. Compound 1 shows a 1:1:2:2:4
splitting pattern, while 2 exhibits a 2:4:4 resonance peaks. This
could be due to the presence of different substituted moieties,
methyl verses phenyl, on carborane cages. In the IR spectra, strong
absorptions at
n
¼ 2562 cmꢁ1 and 2565 cmꢁ1 are attributed to nBH
as shown in Fig. 1. Direct polymerization of carboranyl styrene
monomers were carried out in toluene media. In order to avoid the
risk of violent decomposition during the polymerization, benzoyl
peroxide was not used, instead the safer azobisisobutyronitrile
(AIBN) was chosen to be an initiator. Polymers 3 and 4, poly(closo-
1-R-2-(4-vinylbenzyl)-1,2-C2B10H10) (R ¼ Me (3), Ph (4)) were ob-
tained with Mw of 5795 (DPI ¼ 2.37) and 3029 (DPI ¼ 1.79),
respectively. The lower Mw of 4 could be due to steric effect of
phenyl substituent on the cage carbon. The 1H, 13C, and 11B NMR
spectra appear normal as broad peaks with the disappearance of
the vinyl (CH]CH2) groups when compared to those of the cor-
responding monomers, thus confirming the success of radical po-
lymerizations. As found for monomers, strong absorptions around
Fig. 1. FT-IR spectra of 1-Me-1,2-closo-C2B10H11, 1, 3, and Pd NPs on 3.
(500e800 ꢀC) in corrosive ammonia [22]. In comparison, the GOs
were also coated with commercially available polystyrene (Mw
35000, SigmaeAldrich) and then subjected to TGA analysis (Fig. 2).
It was observed that the polystyrene-GOs composite started to lose
weight at a temperature of 210 ꢀC in air. The maximum weight loss
temperature is around 292 ꢀC. This temperature is significantly
lower than that for carboranylpolystyrene-GOs composite. This
results suggested that the attachment of carborane cages is crucial
to improve the thermal and oxidative stability of GOs. Although the
real reason is not yet clear, it was proposed that a thermally stable
film was generated in situ from the carborane cages in the contin-
uous heating process, and the resulting film protected GOs to
improve their stability.
n
¼ 2560 cmꢁ1 that are assigned as BH stretching mode of vibra-
tions (nBH) were also observed in the FT-IR spectra of the resulting
polymers.
The GOs were coated with carboranylpolystyrene polymers by
dipping into their corresponding solutions. The resulting compos-
ites were heated to 1000 ꢀC in a stream of nitrogen gas to produce
ceramic-coated GOs-based thermosets. In TGA analysis, the ther-
mosets showed improved thermal stability at high temperatures in
airflow of 100 mL/min as shown in Fig. 2. On the other hand, the
pristine GOs burned completely at 221 ꢀC in airflow (100 ml/min).
Under the same conditions, thermosets 3-GOs and 4-GOs started
losing weights at 536 ꢀC and 552 ꢀC, respectively, and thus showed
significantly improved thermal and oxidative stability at >300 ꢀC in
airflow. The combustion temperature is comparable to that of
previously reported nitrogen-doped GOs (520 ꢀC and 579 ꢀC), that
were prepared under the harsh conditions of high temperatures
Palladium (0) nanoparticles were prepared in situ by reducing
palladium acetate with phenylboronic acid and then supported on
carborane-appended polystyrene 3 following the literature proce-
dure [32]. The synthesized catalyst composite was analyzed using
ICP, XPS as well as TEM to identify the loading amount, chemical
oxidation state and particle size of the supported palladium spe-
cies. As shown in TEM images (Fig. 3), the produced Pd particles are
small crystalline in nanometric size with an average size of around
4.7 nm and a relatively narrow size distribution (Fig. 4(A), deter-
mined from the measurement of ~100 particles). The uniform
nanoparticles were well dispersed on the polymer support. The
samples for XPS analysis were prepared in a glove-box as described

82
Y. Zhu et al. / Journal of Organometallic Chemistry 798 (2015) 80e85
Fig. 2. TGA spectra of GO, Poly(methylcarbonylstyrene) (3)-GO, Poly(methylcarbonylstyrene) (4)-GO and polystyrene-GO by burning in air.
elsewhere [33e37]. The XPS spectrum of the samples (see Fig. 4(B))
showed typical Pd (0) absorptions at 335.68 and 341.08 eV for 3d5/2
It should be pointed out that the support could be separated
conveniently by filtration and reused at least 3 times with the yield
of 49%, 47% and 50% for the glycerol oxidation reaction under the
same conditions. To investigate the leached Pd, the samples of the
filtrate plus washings obtained from above standard reactions were
subjected to ICP analysis that showed the concentrations of Pd were
to be less than 5.0 ppm. In addition, the standard reaction was
conducted with the recovered filtrate, but no product could be
isolated. The results suggested that the supported Pd NPs, rather
than the leached Pds, provided the active centers. The detailed
mechanistic study of the reaction is currently underway in our
laboratories.
and 3d3/2, respectively, with
literature values for Pd (0) [33e37].
D
¼ 5.4 eV, that is consistent with the
The prepared composite made of palladium nanoparticles sup-
ported on polymer 3 were examined as catalysts in the selective
oxidation reaction of glycerol to produce 1,3-dihydroxy acetone
(DHA). Trichloroisocyanuric acid (TCCA) has been recognized as one
of the sustainable oxidants. TCCA is readily available, low toxic and
less corrosive, and thus it has been widely utilized in organic re-
actions other than its use in the water purification and sanitization
[38,39]. TCCA was also used as oxidant for the conversion process.
Under these reaction conditions, DHA was obtained in 52% yield
that is slightly higher than that for carbon supported PteBi catalyst
which gave a 44.8% yield [40]. The PteBi catalyst was reported to
afford higher activity than others such as Pd/carbon and Pd/TiO2
[40,41]. For comparison, polystyrene supported Pd catalyst was also
prepared and examined for the glycerol oxidation reaction. As
shown in Fig. 5, Pd nanoparticles in the catalyst of nano-Pd/
polystyrene aggregate heavily. A DHA yield of 27% was obtained
with the catalyst under similar conditions. The low activity could be
due to catalyst aggregation.
3. Conclusions
Carborane-appended styrene monomers were synthesized in
high yields. The monomers were able to conduct radical polymer-
ization reactions in the presence of AIBN initiator to produce
carborane-appended polystyrenes. Carboranylpolystyrene-coated
graphene oxides showed higher combustion temperature when
compared to that with pristine GOs. Both the thermal and oxidation
stability of the GOs have been improved significantly. In addition, it
Fig. 3. TEM images of nano-Pd/3.

Y. Zhu et al. / Journal of Organometallic Chemistry 798 (2015) 80e85
83
Fig. 4. Size histogram (A) and XPS spectrum (B) of supported Pd nanoparticles.
Fig. 5. TEM images of nano-Pd/polystyrene.
has been concluded that the well-dispersed, polymer-supported
palladium nanoparticle composite was found to be efficient catalyst
for the glycerol oxidation reaction. It is expected that our protecting
methodology and prototype catalyst will find broader applications
in both academia and industry.
chromatography (GPC) was performed in DMF (0.8 ml/min) on an
Agilent 1200 Chromatograph equipped with an RI detector. A
combination of 2ꢂ PLgel 5
mm Mixed-columns was used. The mo-
lecular weights were calibrated with commercial polystyrene
standards. Thermogravimetric analysis (TGA) was performed with
a TA Instruments Q2960 from 35 to 1000 ꢀC at a heating rate of
10 ꢀC/min under a nitrogen or airflow (100 ml/min). Transmission
electron microscopy (TEM) measurements were carried out on a
JEOL Tecnai-G2, FEI analyzer at 200Kv. Inductively coupled plasma
(ICP) analysis was determined using a VISTA-MPX, CCD Simulta-
neous ICP-OES analyzer. X-Ray photoelectron spectrometer (XPS)
was performed with an ESCALAB 250 analyzer.
4. Experimental
All synthetic procedures and operations were carried out in an
argon atmosphere using standard Schlenk techniques or a glove
box. Organic solvents such as toluene and hexane were dried using
standard procedures and distilled under argon before use [42]. 1-
Me-closo-1,2-C2B10H11 and 1-Ph-closo-1,2-C2B10H11 were obtained
from KatChem s. r. o., Czech Republic. Palladium acetate, sodium
borohydride and other chemicals were purchased from Sigma-
eAldrich. The 1H, 13C and 11B NMR spectra were recorded on a
Bruker Fourier-Transform multinuclear NMR spectrometer at 400,
100.6 and 128.4 MHz, relative to external Me4Si (TMS) and BF3$OEt2
standards. Infrared (IR) spectra were measured using a BIO-RAD
spectrophotometer with KBr pellets technique and presented in
the sequence of signal strength as strong (s), medium (m) and weak
(w), and peak pattern as single (s), multiple (m) and broad (br). The
mass spectral (MS-ESI) analyses were carried out on a Thermo
Finnigan MAT XP95 analyzer using ESI model. Gel permeation
4.1. Synthesis of closo-1-Me-2-(4-vinylbenzyl)-1,2-C2B10H10 (1)
A modified literature method was used to prepare compounds 1
and 2 [43]. In brief, a solution of 3.17 g (20.0 mmol) of 1-Me-1,2-
C2B10H11 dissolved in 100 mL diethyl ether was cooled to ꢁ78 ꢀC
and 14.00 mL (22.4 mmol) of n-BuLi (1.6 M in n-hexane) was added
with syringe. After stirring for half an hour at ꢁ78 ꢀC, the mixture
was allowed to warm to room temperature with constant stirring
for 6 h, followed by the addition of 3.40 mL (26.8 mmol) of 4-
vinylbenzyl chloride with a syringe at 0 ꢀC. The reaction was then
allowed to continue at room temperature for another 15 h followed

84
Y. Zhu et al. / Journal of Organometallic Chemistry 798 (2015) 80e85
by refluxing for 4 h before cooling to room temperature. The hy-
drolysis of the resulting mixture was carried out at room temper-
ature with 10 mL of water. The organic phase was isolated using a
separating funnel, and the aqueous phase was extracted with
2 ꢂ 40 mL diethyl ether. The combined organic phase was dried
with MgSO4 and filtered, the filtrate was dried under reduced
pressure and the resulting residue was recrystallized with n-
pentane to obtain 3.91 g waxy solid (1) in 71.2% yield. MS (ESI) for
85.0%) of polymer 4 was isolated from 1.20 g of 2. GPC analytic data:
Mw 3029 Da, Mw/Mn 1.79. 1H NMR (CDCl3, ppm),
¼ 7.66e6.54 (br,
9H, C6H5 and C6H4), 2.97e0.87 (m, br, 15H, Ccage-CH2, eCH-CH2e,
10H10). 13C NMR (CDCl3, ppm),
¼ 131.37e127.28 (m), (C6H5 and
d
B
d
C6H4), 81.60 and 82.43 (Ccage), 40.52 (CH2eC6H4). 11B NMR (CDCl3,
ppm),
d
¼ ꢁ5.32 (br), ꢁ11.74 (br). IR (KBr pellet, cmꢁ1), 3055(m, s),
3021(m, s), 2924(s, s), 2851(w, s), 2579(vs, s), 1958(w, s), 1902(w, s),
1609(w, s), 1581(w, s), 1511(m, s), 1495(s, s), 1445(s, s), 1425(s, s),
1319(w s), 1261(w, s), 1157(w, s), 1112(w, s), 1070(m, s), 1026(w, s),
933(w, s), 881(m, s), 857(m, s), 818(m, s), 757(s, s), 729(m, s),
691(vs, s), 650(m, s), 594(m, s), 565(m, s), 492(m, s).
C
d
12H22B10
:
m/z
¼
272.18 [Mꢁ2H]þ. 1H NMR (CDCl3, ppm),
¼ 7.34e7.06 (m, 4H, C6H4), 6.64 (m, 1H, CH]CH2), 5.68e5.23 (q,
2H, CH]CH2), 3.40 (s, 2H, CH2eC6H4), 2.72e1.14 (m, br, 13H, Ccage
-
CH3, B10H10). 13C NMR (CDCl3, ppm),
d
¼ 137.34, 136. 11, 134.44,
130.51 and 126.38 (C6H5), 114.56 and 114.53 (CH]CH2), 77.51 and
74.80 (Ccage), 40.95 (CH2eC6H4), 23.70 (Ccage-CH3). 11B NMR (CDCl3,
4.5. Ceramic coating of graphene oxide (GO) with polymer 3, 4 and
polystyrene to protect against oxidation
ppm),
d
¼ ꢁ4.19 (1B, 1JBH ¼ 195 Hz), ꢁ5.55 (1B, 1JBH ¼ 153 Hz), ꢁ8.67
1
1
(2B, JBH ¼ 80 Hz), ꢁ9.36 (2B, JBH ¼ 98 Hz), ꢁ10.33 (4B,
1JBH ¼ 152 Hz). IR (KBr pellet, cmꢁ1), 2930(m, s), 2608(vs, s),
2565(vs, s), 1825(w, s), 1629(m, s), 1510(s, s), 1432 (s, s), 1288(w, s),
1154 (w, s), 1113(m, s), 1017(s, s), 991(s, s), 947(w, s), 910(s, s),
851(m, s), 822(s, s), 728(s, s), 654(w, s), 549(s, s), 455(w, s).
A 60 mg of polymer was taken into a 25 mL round-bottom flask
and dissolved in 2.0 mL of dichloromethane. The GOs (60 mg) were
then dipped into this solution and dried under N2. The coated GOs
were subsequently heated from 10 ꢀC/min to 1000 ꢀC in a stream of
N2 gas (100 mL/min). Upon cooling to room temperature, the
ceramic polymer coated GOs were again heated from 10 ꢀC/min to
1000 ꢀC in a flow of O2 gas (100 mL/min). The TGA results are
shown in Fig. 2.
4.2. Synthesis of closo-1-Ph-2-(4-vinylbenzyl)-1,2-C2B10H10 (2)
Compound 2 was prepared using the same procedure as
described above in 4.1. A 5.50 g (81.7% yield) of 2 was obtained from
4.43 g (20.0 mmol) of 1-Ph-1,2-C2B10H11, 14.00 mL (22.4 mmol) of
n-BuLi (1.6 M in n-hexane) and 3.40 mL (26.8 mmol) of 4-
4.6. Synthesis of polymer 3-supported palladium catalyst (Pd NPs/3
and Pd NPs/Polystyrene)
vinylbenzyl chloride. MS (ESI) for
C
17H24B10
:
m/z
¼
336.85
[Mþ4H]þ. 1H NMR (CDCl3, ppm),
d
¼ 7.64e6.69 (m, 9H, C6H5 and
This catalyst was prepared according to a literature method with
a slight modification [32]. Accordingly, 80 mg of 3, 8 mg of PdAc2,
0.12 g of phenylboronic acid and 15 mL deionized (DI)-water were
taken into a round-bottom flask equipped with magnetic stirring
bar. The reaction mixture was heated to 80 ꢀC for 1.5 h. The aqueous
layer was removed by decantation. The Pd-supported polymer 3
was washed with hexane (5 ꢂ 10 mL) and water (5 ꢂ 15 mL) fol-
lowed by in vacuo drying at 50 ꢀC. The isolated catalyst composite
was subjected to analysis by TEM, XPS and ICP.
C6H4), 6.62 (m, 1H, CH]CH2), 5.67e5.15 (q, 2H, CH]CH2), 3.03 (s,
2H, CH2eC6H4), 2.82e0.84 (m, br, 10H, B10H10). 13C NMR (CDCl3,
ppm),
d
¼ 137.10, 136. 18, 134.67, 130.51, 130.87, 130.82, 130.23,
129.06 and 126.14 (C6H5 and C6H4), 114.34 and 114.31 (CH]CH2),
83.71 and 82.01 (Ccage), 40.67 (CH2eC6H4). 11B NMR (CDCl3, ppm),
d
¼ ꢁ3.41(2B, 1JBH ¼ 154 Hz), ꢁ9.83 (4B, 1JBH ¼ 103 Hz), ꢁ10.33 (4B,
1JBH ¼ 207 Hz). IR (KBr pellet, cmꢁ1), 3039(w, s), 2956(w, s),
2926(m, s), 2855(w, s), 2583(vs, s), 2562(vs, s), 1908(w, s), 1833(w,
s), 1724(w, s), 1628(m, s),1508(m, s), 1491(m, s),1443(m, s), 1407(m,
s), 1358(m, s), 1285(w, s), 1162(w, s), 1115(m, s), 1073(m, s), 996(m,
s), 911(s, s), 830(m, s), 756(m, s), 691(s, s), 584(m, s), 492(m, s).
4.7. Procedures of catalytic oxidation of glycerol
4.3. Synthesis of poly(closo-1-Me-2-(4-vinylbenzyl)-1,2-closo-
C2B10H10) (3)
A 25 mL round-bottom flask was equipped with magnetic stir-
ring bar in which 0.10
g of glycerol (1.34 mmol), 0.05 g
(0.02 mmol Pd) of 3 and 0.33 g (1.43 mmol) of trichloroisocyanuric
acid were added and then made the suspension of the mixture in
6 mL of acetonitrile. This reaction mixture was stirred at room
temperature for 24 h and then evaporated to dryness. The obtained
crude product was purified by flash chromatography (SiO2) eluting
with Et2O/acetone (v/v ¼ 3/2) to give dihydroxyacetone in 52% yield
as the known product as identified by 1H and 13C NMR spectra that
are consistent with the literature data. A same procedure was used
to test Pd NPs/polystyrene to produce DHA in 27% yield.
To a solution of 0.80 g (2.92 mmol) of 1 in 4 mL of anhydrous
toluene AIBN (25 mg; 0.15 mmol) was added under argon. The
mixture was allowed to react at 80 ꢀC for 5 h with constant stirring.
The reaction mixture was first poured into 400 mL of hexane and
then cooled. The precipitated products were collected by filtration
followed by washing with hexane (2 ꢂ 15 mL) and dried in vacuo at
50 ꢀC to isolate the polymer product 3 with consistent weight
(~0.45 g, yield 56.3%). GPC analytic data: Mw 5795 Da, Mw/Mn 2.37.
1H NMR (CDCl3, ppm),
CH2eC6H4), 2.90e0.86 (m, br, 16H, Ccage-CH3, eCHeCH2e, B10H10).
13C NMR (CDCl3, ppm),
¼ 130.52e127.75 (m) (C6H4), 78.02 and
d
¼ 7.01e6.81 (br, 4H, C6H4), 3.37 (br, 2H,
d
Acknowledgment
75.06 (Ccage), 40.87 (CH2eC6H4), 23.65 (Ccage-CH3). 11B NMR (CDCl3,
ppm),
d
¼ ꢁ6.13(br), ꢁ10.56 (br). IR (KBr pellet, cmꢁ1), 3021(m, s),
We thank the Institute of Chemical and Engineering Sciences
(ICES/12-4B4A01), Agency for Science, Technology and Research,
Singapore, and Singapore-MIT Alliance for Research and Technol-
ogy Innovation Centre (NG120510ENG(IGN)) for financial support.
We also thank Ms Wang Zhan at Institute of Chemical and Engi-
neering Sciences, Agency for Science, Technology and Research,
Singapore for XPS analysis. NSH thanks the support from the Na-
tional Science Foundation (Grant #CHE-0906179) and Northern
Illinois University for the Board of Trustees Professorship.
2928(m, s), 2582(vs, s), 1512 (s, s), 1443 (s, s), 1387(m, s), 1319(w, s),
1160(m, s), 1115(m, s), 1019(s, s), 950(m, s), 919(w, s), 856(m, s),
817(s, s), 729(s, s), 647(m, s), 591(m, s), 557(m, s).
4.4. Synthesis of poly(closo-1-Ph-2-(4-vinylbenzyl)-1,2-closo-
C2B10H10) (4)
In a procedure identical that reported above in 4.3, 1.02 g (yield

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A Eur. J. 20 (2014) 11999e12003.
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