Carbon black functionalized with hyperbranched polymers: Synthesis, characterization, and application in reversible CO2 capture

Article abstract of DOI:10.1039/c3ta10699c

The functionalization of carbon black by grafting of hyperbranched polymers from the surface via self-condensing atom transfer radical polymerization (SC-ATRP) is reported. The surfaces of the pristine carbon black were modified with ATRP initiators using two different methods. The first method uses acid oxidation to place COOH groups on the carbon black surface, followed by the esterification to give ATRP initiators bound to the carbon black surface. Alternatively, ATRP initiators bearing both azido and bromine groups were placed directly on the carbon black surface by nitrene chemistry. The hyperbranched poly(p-chloromethylstyrene) (PCMS) was grafted from the ATRP initiator modified carbon black surfaces using the inimer of p-chloromethylstyrene, and CuCl/CuCl₂/N,N,N′,N″,N″- pentamethyldiethylenetriamine (PMDETA) as the catalytic system in N,N-dimethylformamide (DMF). In addition, a one-pot two-step method was developed to graft crosslinked polymers from the carbon black surfaces. The polymerization process was well controlled and the fraction of the grafted polymers on carbon black could be adjusted by changing the polymerization time. The resulting samples were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The hyperbranched polymers on the carbon black surfaces were quaternized to give an ammonium group on the polymer, and a chloride counterion was subsequently exchanged to give a hydroxide counterion. Under these basic conditions, the ATRP initiators should be attached to the surface using nitrene chemistry rather than acid oxidation, to avoid the hydrolysis of the ester groups that link the grafted polymers to the carbon black surface. The ammonium hydroxide functionalized carbon black materials were utilized for the reversible absorption and desorption of CO₂ from ambient air, providing improved absorption/desorption kinetics compared with the commercially available Excellion membrane.

Full text of DOI:10.1039/c3ta10699c

Journal of
Materials Chemistry A
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PAPER
Carbon black functionalized with hyperbranched
polymers: synthesis, characterization, and application in
Cite this: J. Mater. Chem. A, 2013, 1,
6810
reversible CO2 capture†
Hongkun He,a Mingjiang Zhong,a Dominik Konkolewicz,a Karin Yacatto,b
Timothy Rappold, Glenn Sugar, Nathaniel E. David and Krzysztof Matyjaszewski
b
b
b
a
*
The functionalization of carbon black by grafting of hyperbranched polymers from the surface via self-
condensing atom transfer radical polymerization (SC-ATRP) is reported. The surfaces of the pristine carbon
black were modified with ATRP initiators using two different methods. The first method uses acid
oxidation to place COOH groups on the carbon black surface, followed by the esterification to give ATRP
initiators bound to the carbon black surface. Alternatively, ATRP initiators bearing both azido and bromine
groups were placed directly on the carbon black surface by nitrene chemistry. The hyperbranched poly(p-
chloromethylstyrene) (PCMS) was grafted from the ATRP initiator modified carbon black surfaces using the
inimer of p-chloromethylstyrene, and CuCl/CuCl2/N,N,N0,N00,N00-pentamethyldiethylenetriamine (PMDETA)
as the catalytic system in N,N-dimethylformamide (DMF). In addition, a one-pot two-step method was
developed to graft crosslinked polymers from the carbon black surfaces. The polymerization process was
well controlled and the fraction of the grafted polymers on carbon black could be adjusted by changing
the polymerization time. The resulting samples were characterized by transmission electron microscopy
(TEM), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The hyperbranched
polymers on the carbon black surfaces were quaternized to give an ammonium group on the polymer, and
a chloride counterion was subsequently exchanged to give a hydroxide counterion. Under these basic
conditions, the ATRP initiators should be attached to the surface using nitrene chemistry rather than acid
oxidation, to avoid the hydrolysis of the ester groups that link the grafted polymers to the carbon black
surface. The ammonium hydroxide functionalized carbon black materials were utilized for the reversible
absorption and desorption of CO2 from ambient air, providing improved absorption/desorption kinetics
compared with the commercially available Excellion membrane.
Received 15th February 2013
Accepted 25th April 2013
DOI: 10.1039/c3ta10699c
www.rsc.org/MaterialsA
many useful properties, such as high electrical conductivity, low
thermal expansion, environmental stability, and low cost,
Introduction
Carbon black is a particulate form of elemental carbon
produced by thermal decomposition or incomplete combustion
of gaseous or liquid hydrocarbons under controlled condi-
tions.1 Carbon black consists of structurally complex particles
with predominantly spherical or ellipsoidal shapes formed by
aggregation of graphitic layer planes with both amorphous and
crystalline substructures.2 The structure of carbon black differs
from other forms of bulk carbon such as graphite, charcoal,
cokes, and diamond in that carbon blacks are particulates made
of aggregates with complex compositions.3 Carbon black has
generating many applications in a variety of elds, including
reinforcing agents in rubber applications, pigments in plastics,
inks, and coatings.4 Many of these applications involve
dispersing carbon black into either polymeric systems or
solvents, but since crude carbon black is difficult to disperse in
solvents, the surface modication of carbon black is oen used
to improve the dispersibility. For instance, crude carbon black
is difficult to disperse in water, whereas carbon black can be
dispersed in aqueous phase via the adsorption of surfactants.5
Furthermore, attaching polymers to the surface of carbon black
markedly improves the dispersibility in solvents and compati-
bility in polymer matrices. In addition, surface graing can
introduce various functional groups onto the surface, including
photosensitive, bioactive, and amphiphilic groups.6
aCenter for Macromolecular Engineering, Department of Chemistry, Carnegie Mellon
University, 4400 Fih Avenue, Pittsburgh, Pennsylvania 15213, USA. E-mail: km3b@
andrew.cmu.edu
There are two methods to covalently bond polymers to the
surface of carbon black, the “graing onto” and “graing from”.
“Graing onto” involves the synthesis of a polymer with a
reactive end-group and then attaching the polymer to the
bKilimanjaro Energy, 630 Tennessee St, San Francisco, California 94158, USA
† Electronic supplementary information (ESI) available: Experimental details,
additional experimental data, IR spectrum, GPC traces, NMR spectra, and SEM
images. See DOI: 10.1039/c3ta10699c
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surface of carbon black using the reactive end-group. One amino)ethyl methacrylate (DMAEMA)19 and temperature-
limitation of the graing-onto approach is that the polymers responsive poly(N-isopropylacrylamide) (PNIPAAm),20 from the
already graed onto the surface hinder the approach of the surface of carbon black. A comb-structured polymer-graed
subsequent polymers, placing a limit on the attainable graing carbon black was synthesized by a combination of SI-ATRP of 2-
density.7 “Graing from” involves the modication the surface hydroxyethyl methacrylate and ring-opening polymerization of
with initiators, followed by the growth of polymers from the 3-caprolactone.21
surface. Since small molecules have much less steric hindrance
than polymers, it is easier to create densely graed surfaces by onto the surface of carbon black makes the resulting hybrid
this approach.8
materials useful for various applications. One of the most
The possibility of introducing various functional polymers
Both techniques have been used to functionalize carbon important potential applications is to mitigate the effects of
black surfaces. One interesting example used the “graing climate change associated with rising carbon dioxide (CO2)
onto” approach used the carbon black surface to trap poly- level in the atmosphere.22 Various strategies have been
meric radicals generated by the thermal dissociation of developed, including carbon capture and sequestration (CCS),
nitroxide-terminated polymers, obtained by nitroxide-medi- which focuses on the capture of CO2 emitted from burning
ated radical polymerization (NMP).9 This method was used to fossil fuels.23 Recently, “CO2 air capture” has emerged as a
introduce various polymers onto the carbon black surfaces, promising methodology that captures CO2 directly from air.24
including polystyrene, poly(4-acetoxystyrene), poly(4-hydroxy- One of the most environmentally promising methods for CO2
styrene), (4-acetoxystyrene)-block-polystyrene, poly(4-hydroxy- air capture is the humidity swing proposed by Lackner et al.25
styrene)-block-polystyrene, and polycaprolactone,2a,9,10 as well In the humidity swing, CO2 is captured under dry conditions,
as poly(4-vinylpyridine), poly(styrene-co-maleic anhydride), and released under humid conditions by the interchange of
and poly(styrene-co-(4-vinylpyridine)).11 In addition, carbon carbonate and bicarbonate anions. Under dry conditions, the
black has been functionalized by polymeric radicals formed bicarbonate ion is favored, and one carbonate ion absorbs
by thermal decomposition of azo- and peroxy-functional one CO2 and one water molecule to give two bicarbonate ions,
molecules, as well as macroradicals derived from the redox and the reverse reaction occurs under wet conditions. In
reaction between polymers having hydroxyl groups and ceric addition, a hydroxide functionalized resin undergoes a one-
ions.11
time absorption of CO2 to generate the bicarbonate ion,
Similarly, polymers have been graed from carbon black which participates in the humidity swing. Resins bearing
using anionic,12 cationic,13 and radical polymerization.14 For quaternary ammonium hydroxide groups have been used to
example, hydroxymethyl groups were introduced onto pristine reversibly capture CO2 from ambient air utilizing the
carbon black surfaces by reacting the unsaturated hydrogen humidity swing.25a,b However, these resins generally have a
atoms present in the polycondensed aromatic rings of carbon relatively low surface area and dense structures, implying that
black with formaldehyde under alkaline conditions.13b These higher capacities and faster kinetics could be achieved by
hydroxymethyl groups were used as initiating sites in the increasing the surface area and gas diffusion rates. Recently,
graing of multihydroxyl hyperbranched polyethers from the our group investigated porous polymers and high surface area
carbon black surface by cationic ring-opening polymerization of supports, including carbon black, in the humidity swing.25c,d
3-ethyl-3-(hydroxymethyl)-oxetane.13b Unlike cationic or anionic These porous materials showed an order of magnitude
reactions, radical polymerization is tolerant towards various improvement in the kinetics of CO2 absorption and desorp-
functional groups and impurities. However, conventional tion, and a 2–4 fold improvement in the amount of CO2
radical polymerization offers minimal control over molecular absorbed per cycle.25c,d
weights and molecular weight distributions of the polymers.
Carbon black is a promising candidate as the support
Therefore, reversible-deactivation radical polymerization material for CO2 capture, since there are several potential
(RDRP) can be used to gra polymers with controlled molecular advantages for polymer-graed carbon black: (1) carbon black
weight and topology from the carbon black surface.15 Atom has a large specic surface area in the range of 50 m2 gꢀ1 to
transfer radical polymerization (ATRP) is a versatile RDRP 1000 m2 gꢀ1
; (2) carbon black is inexpensive and available in
26
method, which has been used to prepare polymers with large quantities, which facilitates industrial applications;27 (3)
complex architectures as well as polymer brushes on organic/ carbon black has high chemical and thermal stability, since it
inorganic substrates.16
contains 97–99% of elemental carbon;28 and (4) well-dened
Previously, poly(n-butyl acrylate) (poly(n-BA)) was graed polymers can be graed from carbon black and a desired
from carbon black surfaces bearing ATRP initiating sites, giving percentage of polymer graing can be achieved by controlled
hybrid particles that showed excellent dispersibility and surface-initiated polymerization. This paper gives various
stability in good solvents for poly(n-BA).8 Subsequently, a block procedures for the self-condensing atom transfer radical
of tert-butyl acrylate (t-BA) was grown from poly(n-BA) func- polymerization (SC-ATRP) of p-chloromethylstyrene (CMS),
tionalized carbon black, yielding a water-dispersible carbon giving hyperbranched polymers graed from the carbon black
black composite aer cleavage of the tert-butyl groups to form surface. This paper also outlines how the hyperbranched
poly(acrylic acid) graed segments.17 ATRP has also been used polymers can be functionalized to quaternary ammonium
to gra polystyrene (PS), poly(methyl methacrylate) (PMMA),18 hydroxide groups, which can reversibly capture CO2 through
and responsive polymers, such as pH-responsive 2-(dimethyl- the humidity swing.
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Results and discussion
1
Functionalization of carbon black with ATRP initiators
ATRP initiators have to be anchored onto the surface of carbon
black to use the “graing from” approach. There are three
commonly used methods to covalently bind ATRP initiators
onto carbon materials (including carbon black, carbon nano-
onions, CNTs, and graphene): acid oxidation,29 nitrene chem-
istry,30 and Pschorr-type arylation.31
The acid oxidation method was initially used to modify the
carbon black surface with an ATRP initiator. As shown in Scheme
1a, the carboxyl group modied carbon black (CB-COOH) was
prepared by acid oxidation. Then, an acyl chloride group modi-
ed carbon black (CB-COCl) was prepared by reacting CB-COOH
with SOCl2. Finally, the CB-COCl was reacted with 2-hydroxyethyl
2-bromoisobutyrate (HEBiB) to form carbon black modied with
ATRP initiators (CB-Br). The Br content in CB-Br was 0.63 mmol
gꢀ1, as determined by elemental analysis. TGA curves(Fig. 1) were
obtained from 50 to 570 ꢁC under a ow of nitrogen at a heating
Fig. 1 TGA curves of CB, CB-COOH, and CB-Br.
rate of 10 C minꢀ1. The pristine carbon black (CB) remained
ꢁ
stable to 570 ꢁC, with only 1.7% weight loss. The CB-COOH
sample had no distinguishable main weight loss region, and had
17.8% weight loss below 570 ꢁC. The CB-Br sample had a weight
loss region between 200 and 400 ꢁC, and had 33.0% weight loss
below 570 ꢁC. The calculated amount of the ATRP initiator from
the difference in weight loss between CB-Br and CB-COOH
samples was 15.2%, which corresponds to 0.79 mmol gꢀ1, which
is in acceptable agreement with the value measured by elemental
analysis. The TEM images of the pristine carbon black in Fig. 2a
and b show the typical structure of carbon black with the smallest
structural unit having a diameter of tens of nanometers, with
many aggregates (from several tens to several hundreds of
nanometers), and some agglomerates larger than 1 mm.
It is worth noting that an alternative way to synthesize CB-Br
from CB-COCl can be used. In this procedure, ethylene glycol is
rst reacted with the CB-COCl to introduce the hydroxyl groups
to the surface, and then 2-bromopropionyl bromide is added to
introduce the initiator groups onto the carbon black surfaces by
acylation. This method has been used for the functionalization
of CNTs.32 However, some coupling may occur between different
carbon black particles during the reaction of ethylene glycol
with CB-COCl, which could be more signicant than that
observed for the CNT case, due to the close packing of the
neighboring spherical particles in contrast to the loosely packed
cylindrical tubes. Therefore, in order to avoid the potential
Fig. 2 TEM images of crude carbon black (a and b) and CB-Br (c and d).
coupling between particles, ethylene glycol was rst reacted
with 2-bromopropionyl bromide to produce HEBiB, which was
then added to CB-COCl.
Similarly, a compound containing both the azido group and
the bromine group, 1-(azidomethyl)-4-(1-bromoethyl)benzene
(AMBEB) was synthesized from CMS (Scheme 1b) to prepare
Scheme 1 Functionalization of carbon black with ATRP initiator by acid oxidation method (a) and nitrene chemistry method (b).
6812 | J. Mater. Chem. A, 2013, 1, 6810–6821
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ATRP initiator modied carbon black by nitrene chemistry (CB-
N-Br). This compound does not contain an ester bond, which
should increase its stability under basic conditions compared to
ATRP initiators tethered to the carbon black surface by ester
bonds.30 AMBEB was used as an initiator for the polymerization
of styrene, demonstrating its feasibility in ATRP (Fig. S1
and S2†).
The surface of carbon black was modied with ATRP initi-
ators by mixing CB with AMBEB in DMF and heated to 160 ꢁC.
The azide groups decomposed at high temperature to generate
the highly reactive nitrene radicals that can covalently bond
to the carbon surfaces via the [2 + 1] cycloaddition of nitrenes
to the p-electron systems,33 generating the nitrene modied
carbon black (CB-N-Br). The Br content in the CB-N-Br was
1.84 mmol gꢀ1 as determined by elemental analysis. This value
Fig. 5 Photographs of CB-N-Br dispersion in different solvents after sonication.
From left to right: THF, DMF, anisole, methanol, and water.
in THF, DMF, anisole, methanol, and water with ultra-
sonication (Fig. 5).
is nearly three times larger than that of CB-Br (0.63 mmol gꢀ1
)
2
Graing hyperbranched polymers from carbon black
surfaces
2.1 Direct graing of hyperbranched polymers. Hyper-
prepared by acylation of carboxyl group modied carbon black,
which shows the higher graing efficiency of the nitrene
method. The TGA curves in Fig. 3 show that the CB-N-Br branched or highly branched polymers have a three-dimensional
ꢁ
sample had a weight loss of 33.9% below 570 C. The amount dendritic architecture that creates potential applications in
of ATRP initiator was 32.2%, determined from the weight loss various areas due to their unique structural, chemical and
difference between CB-N-Br and CB, which corresponds to ca. physical properties.34 As a synthetic method for hyperbranched
1.52 mmol gꢀ1, in acceptable agreement with the value polymers, the self-condensing vinyl polymerization (SCVP) of
measured by elemental analysis. The morphology of CB-N-Br, AB* inimer bearing both the vinyl group (A) and the initiating
as shown in the TEM images in Fig. 4, was similar to that of group (B*) was rst exemplied via a cationic polymerization of
pristine carbon black, and the dispersibility of CB-N-Br was 3-(1-chloroethyl)-ethenylbenzene.35 SCVP of AB* inimer has also
much better than crude CB, since it could be easily dispersed been performed by ATRP with p-chloromethylstyrene (CMS)36 for
the synthesis of hyperbranched homopolymers37 or copolymers
with styrene,38 pentauorostyrene,39 N-cyclohexylmaleimide,40
and chlorotriuoroethylene.41
In this study, hyperbranched poly(p-chloromethylstyrene)
(PCMS) was graed from carbon black surfaces by SC-ATRP of
CMS (Scheme 2). The polymerization of CMS was conducted
with a CuCl/CCl2/PMDETA catalytic system in the presence of
carbon black modied with ATRP initiator. DMF was used as
the solvent in order to improve the dispersibility of carbon
black. NMR was used to determine the conversion of the CMS by
measuring the decrease of the vinyl signal relative to the DMF
peak as the internal standard (Fig. S3†). Fig. 6a illustrates that
there was a nearly linear kinetics in the semilogarithmic plot.
Nevertheless, some factors may inuence the polymerization
process: the initiators are immobilized on the surfaces, thus the
chance of radical coupling between neighboring growing chains
is increased; some of the initiator sites may not be accessible to
Fig. 3 TGA curves of CB and CB-N-Br.
the catalyst/ligand due to the steric hindrance in the agglom-
erated carbon black particles. During polymerization, the
propagating polymeric radicals could be trapped by the poly-
condensed aromatic rings, and the quinonic and phenolic
oxygens on carbon black.8 In addition, since the inimer, CMS,
can initiate polymerization, some unattached polymers could
also be formed in solution.
In order to determine the amount of the free (unattached)
polymers in solution, samples were drawn from the reaction
solution, with one part of the sample directly dried under
vacuum to remove the solvent and monomer, and the residual
solid was measured by TGA to obtain the value for weight loss,
Fig. 4 TEM images of CB-N-Br.
which corresponds to the total amount of the free and graed
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Fig. 6 (a) The plot of ln([M]0/[M]) and conversion vs. time, (b) GPC traces of free polymer in the reaction solution of CB-g-PCMS, and (c) TGA curves of CB-Br (1), CB-g-
PCMS after (2) and before (3) washing with THF for [CB-Br]0/[CMS]0/[CuCl]0/[CuCl2]0/[PMDETA]0 ¼ 1/400/0.95/0.05/1, DMF/CMS ¼ 1/2 (v/v), 100 ꢁC. (d) TEM image of
CB-g-PCMS.
polymer present in the composite. The other part was washed
thoroughly with THF and separated by high-speed centrifuga-
tion until there was no free polymer detected in the upper
solution by gel permeation chromatography (GPC) (Fig. S5†),
and the separated solid was dried under vacuum and measured
by TGA to obtain the weight loss of the graed polymer. The
TGA results (Fig. 6c) showed that the weight losses of CB-g-
PCMS before and aer washing were 60.1% and 42.1%,
respectively. The content of the polymers on CB-g-PCMS was
Scheme 2 Grafting of hyperbranched PCMS from bromine group modified
53.0 wt%, aer deducting the initial weight loss of CB-Br of
33.0%. The ratio of free polymer to the graed polymer was
carbon black.
estimated to be 3.3/1 (w/w) from the weight losses. The free
polymer was also characterized by GPC. The samples were
drawn from the reaction solution and the carbon black in the polymer. If the ATRP initiator is attached by the acid oxidation
solution was separated by high-speed centrifugation. The method, the resulting material is not suitable for the CO2
polymers in the supernatant were characterized by GPC using capture applications, since the ester bonds on the surface can
linear polystyrene standards and the results are shown in be hydrolyzed in the presence of KOH solutions. Therefore, the
Fig. 6b. The results show that the apparent molecular weights ATRP initiator modied carbon black prepared by the nitrene
increased with reaction time with high dispersity (Mw/Mn) chemistry method is preferred for such CO2 adsorption/
values in the range of 2.0–2.6, resulting from the hyperbranched desorption applications, since there are no ester bonds linking
nature of the polymers synthesized by SCVP. The peaks of it to the surface, making it stable under strongly basic
oligomers were initially observed in the polymerization process, conditions.
but their intensities gradually decreased compared to those of
higher molecular weight polymer as conversion increased.
Therefore, SC-ATRP of CMS was also conducted in the
presence of CB-N-Br using the same reaction conditions. The
The morphology of the samples was studied by TEM. The conversion of the CMS was measured (Fig. S4†) and the semi-
carbon blacks graed with hyperbranched polymers showed logarithmic plot showed a nearly linear dependence on time
better dispersibility and more single particles in the TEM image (Fig. 7a). The apparent molecular weights increased with reac-
(Fig. 6d), although there were still aggregates. A polymer layer tion time and then decreased, and the Mw/Mn values of the free
can be observed on the carbon black surfaces, revealing the polymers were all near 2 (Fig. 7b and Table 1), which was due to
effective surface functionalization by controlled graing of the continuous generation of new polymer chains initiated by
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Fig. 7 (a) The plot of ln([M]0/[M]) and conversion vs. time, (b) GPC traces, (c) TGA curves of CB-N-g-PCMS at different polymerization time, and (d) the plot of Fpolymer
vs. conversion for [CB-N-Br]0/[CMS]0/[CuCl]0/[CuCl2]0/[PMDETA]0 ¼ 1/400/0.95/0.05/1, DMF/CMS ¼ 1/2 (v/v), 100 ꢁC. (e) TEM image of CB-N-g-PCMS.
Table 1 Data obtained from GPC and GPC-MALLS measurements of hyperbranched polymers formed at different polymerization time, and TGA measurements of CB-
N-g-PCMS. [CB-N-Br]0/[CMS]0/[CuCl]0/[CuCl2]0/[PMDETA]0 ¼ 1/400/0.95/0.05/1, DMF/CMS ¼ 1/2 (v/v), 100 ꢁC
Conv.a
Mn,GPC
Mw,GPC
Mw,GPC/Mn,GPC
Mw,MALLS
Mw,MALLS/Mw,GPC
fw
Fpolymer
b
c
d
e
f
Entry
Time (h)
1
2
3
4
5
6
4
12
24
48
72
96
1.4%
7.1%
15.8%
34.5%
43.6%
48.6%
1810
2600
3260
3010
2610
2200
3840
5230
6720
6500
5380
4310
2.12
2.01
2.06
2.16
2.06
1.96
8720
35 800
40 600
35 400
35 600
23 800
2.3
6.9
6.0
5.4
6.6
5.5
0.574
0.560
0.534
0.482
0.455
0.343
0.132
0.153
0.192
0.271
0.312
0.481
a
The conversion of the CMS in the polymerization measured by NMR. b Number-average molecular weight determined by GPC analysis in THF with
linear polystyrene as the standard. c Weight-average molecular weight determined by GPC analysis in THF with linear polystyrene as the standard.
d
Weight-average molecular weight determined by GPC-MALLS. e The weight loss of the polymer-graed carbon black samples measured by TGA.
The fraction of the polymers to the carbon black in the polymer-graed carbon black samples.
f
benzyl chloride groups and thermal self-initiation of CMS.42 Gel polymer increased as the polymerization progressed. This
permeation chromatography coupled with a multi angle laser sharp increase in the Fpolymer could be due to the increase in the
light scattering detector (GPC-MALLS) was used to determine number of benzyl chloride groups on the surface at higher
the absolute molecular weight of the hyperbranched PCMS. conversion, which increases the likelihood of both monomers
Because hyperbranched polymers have a smaller hydrodynamic and polymers growing from this surface.45 The TEM image
volume than their linear counterparts with the same molecular (Fig. 7e) of CB-N-g-PCMS at 96 h showed the presence of poly-
weight, this leads to longer retention time in GPC and smaller mers graed around carbon black particles, and the free poly-
apparent molecular weight measured by GPC.43 The weight- mers seen as grey dots on the grid.
average molecular weight values obtained by light scattering
The degree of branching (DB) is an important parameter that
(Mw,MALLS) were larger than those obtained by standard GPC characterizes the molecular structure of hyperbranched poly-
analysis by a factor of 2.3–6.9 (Table 1), conrming the existence mers.36d,46 In order to obtain the DB value of a polymer, nuclear
of branched polymers.44
magnetic resonance (NMR) is commonly used to quantify the
The samples of CB-N-g-PCMS taken from the reaction solu- peaks characteristic for different structures. However, PCMS
tion were also washed thoroughly with THF and measured by does not show appropriate signal integrals when using CDCl3 in
TGA (Fig. 7c). As shown in Table 1, the weight losses increased the 1H NMR spectrum due to the signal overlap. This issue was
gradually with polymerization time. The fraction of the poly- recently resolved by Komber et al. based on the aromatic solvent
mers attached to the carbon black (Fpolymer) were calculated induced shis (ASIS) effect.47 When measuring the hyper-
1
based on the weight losses. Fig. 7d shows that Fpolymer branched polymers with C6D6 and CD2Cl2 as the solvent by H
increased linearly with conversion until 72 h and a sharp NMR, respectively, the corresponding characterized proton
increase at 96 h, demonstrating that the amount of graed regions show sufficient signal separation. The signal integration
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of the terminal (T), vinyl-type linear (LV), condensation-type
linear (LC), and dendritic (D) units can be obtained. Therefore,
DB can be calculated based on the following equation:48
DB ¼ 2I(D)/(2I(D) + I(LV) + I(LC))
(1)
For a linear polymer, DB ¼ 0; for a perfect dendrimer, DB ¼
1.36a The polymers formed in the sample of CB-N-g-PCMS at 96 h
have 23.3% T units, 23.3% D units, 40.0% LC units, and 13.5%
LV units, and a DB of 0.43 (Fig. S6†), indicating a highly
branched structure for PCMS. The DB is lower than those
prepared by polycondensation of AB2 monomers, due to the
lower activity of the primary chloride groups compared to the
secondary ones.34a It should be noted that the free polymers
were precipitated into methanol before the NMR measurement,
which removed the low-molecular-weight fractions which have
a larger amount of T units.47a
Fig. 8 Plot of ln([M]0/[M]) and conversion vs. time. [CB-Br]0/[DVB]0/[CuCl]0/
[CuCl2]0/[PMDETA]0 ¼ 1/50/4/0.2/4.2, DMF/DVB ¼ 4/0.22 (v/v), at 100 ꢁC.
Large-scale experiments were conducted using the same
conditions to obtain sufficient amounts of samples for the
measurement of the specic surface areas of the polymer-graf-
ted carbon black. The polymerization was stopped at 56%
monomer conversion. The resulting sample was washed thor-
oughly with THF and dried under vacuum before performing
nitrogen adsorption measurements. The Brunauer–Emmett–
Teller (BET) specic surface area of the CB-N-g-PCMS is 21 m2
gꢀ1. The crude carbon black had a surface area of 223 m2 gꢀ1
,
and the loss of surface area aer the polymerization is mainly
due to the graed polymer partially lling the micro-/meso
pores. The TGA result showed the graed polymers account for
52.3 wt% of the total mass of the sample. This equals to 24.9 mg
mꢀ2 of the carbon black surfaces. Assuming the density of
PCMS is the same as that for polystyrene, 1.05 cm3 gꢀ1, the
average thickness of the graed polymers on carbon black
surfaces is about 23.7 nm.
2.2 One-pot two-step graing of crosslinked hyper-
branched polymers. As discussed previously, the ATRP initiator
modied carbon black prepared by the acid oxidation method
contains ester bonds, which are not stable under alkaline
conditions. Therefore, crosslinking the polymer with divinyl-
benzene (DVB) reduces the probability of cleaving the polymers
from the surface. However, since this process could lead to
crosslinking between different carbon black particles,
enhancing aggregation, the synthesis has to be carefully
controlled to minimize the extent of inter-particle crosslinking.
A model reaction with only the crosslinker was conducted to
investigate the crosslinking process. The crosslinked polymer
shell was formed on the carbon black surfaces by polymeriza-
tion of DVB from the bromine groups of CB-Br, as shown in
Fig. 9 The evolution of morphology of carbon black with DVB crosslinked shells
at different conversions and the corresponding TEM images: 5 h (a), 25 h (b),
and 72 h (c).
Scheme 3. Fig. 8 shows a nearly linear kinetic curve for the
entire polymerization. The change of the morphology of the
materials at different reaction time, 5 h, 25 h, and 72 h, was
observed by TEM (Fig. 9). The polymer layer was very thin at a
conversion of 2.5%, and cannot be easily observed in the TEM
images. When the conversion increased to 11.6%, the polymer
layer became thicker, and could be clearly seen in the TEM
images. When the conversion further increased to 23.9%, the
polymer layer was very thick, and in some areas, the polymer
layer even formed a continuous network.
Aer conducting this model reaction, the one-pot two-step
method was used to gra crosslinked polymers from the surface
of the carbon black (Scheme 4). The CB-Br was rst reacted with
DVB to form a crosslinked polymer shell, and then CMS was
added to the same pot to continue this reaction, forming the
Scheme 3 Preparation of carbon black with divinylbenzene (DVB) crosslinked
shells.
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Scheme 4 One-pot two-step method for the grafting of crosslinked polymers from carbon black.
Fig. 11 Plot of ln([M]0/[M]) and conversion vs. time for step two of the one-pot
two-step method for the grafting of crosslinked polymers. [CB-Br]0/[DVB]0/
[CMS]0/[CuCl]0/[CuCl2]0/[PMDETA]0 ¼ 1/50/400/4/0.2/4.2, DMF/DVB ¼ 4/0.22
(v/v), 100 ꢁC.
Fig. 10 TEM images of CB-g-DVB (a and b) and CB-g-xPCMS (c and d).
crosslinked hyperbranched polymers from carbon black. In the
rst step of this reaction, the conversion of DVB was stopped at
14.3%, which was high enough to form a crosslinked coating
without signicant inter-particle crosslinking, as observed in
the TEM images of CB-g-DVB (Fig. 10a and b). In the second
step, the reaction was stopped when the total conversion of CMS
and DVB reached 40.5%, as shown in the kinetic plot (Fig. 11).
The TEM images (Fig. 10c and d) of the resulting sample of CB-
g-xPCMS show that the polymer layer on the carbon black was
very thick, and some small aggregates were formed by inter-
particle crosslinking of polymer shells of neighboring particles.
The SEM images in Fig. 12 show that aer drying, the carbon
black particles aggregated to form a layer with rough and
porous surfaces. The surfaces of CB-g-xPCMS were smoother
than the CB-g-DVB surfaces, since the former has more graed
Fig. 12 SEM images of CB-g-DVB (a) and CB-g-xPCMS (b).
one-pot synthesis, where the gold core was rst protected with a
crosslinked polymer shell of ethylene glycol dimethacrylate
(EGDMA), and then linear polymer brushes of poly(n-butyl
acrylate) were graed from the shell.49
3
Functionalized carbon black for CO2 capture
3.1 Introduction of quaternary ammonium hydroxide
polymers that decreased the surface roughness of the carbon groups onto functionalized carbon black surfaces. The benzyl
blacks. In one previous report, a similar strategy was success- chloride groups in the hyperbranched PCMS were transformed
fully used for preparing core/shell Au nanoparticles through a into quaternary ammonium hydroxide groups, which allowed
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aggregates, which appear as dark agglomerates in the TEM
images. However, for CB-N-g-PCMS-OHꢀ, the polymer layer can
be easily observed on the particle surfaces, which caused most
of the particles to be separated from each other, leading to fewer
and smaller aggregates. Also, the dispersibility of the func-
tionalized carbon black improved due to the presence of graed
polymer layer.
The morphologies of the samples were also characterized by
SEM. As shown in Fig. 14a and b, the pristine carbon black
aggregated, while the smaller single particles (several tens of
nanometers) are difficult to discern due to the limited resolution
of SEM. The surface structure can be clearly observed for CB-N-
Br-OH sample (Fig. 14e and f). The surface structure become
blurred and cannot be easily observed for CB-N-g-PCMS-OHꢀ
sample, due to the presence of polymer layers on the surfaces
(Fig. 14c and d). In order to conduct SEM measurement for these
samples, they were coated with a thin conducting layer by
sputtering with Au to minimize the charging effects. In
comparison, the same samples without Au coating were also
characterized by SEM (Fig. S7 and S8†), which showed that for
CB-N-Br-OH, the SEM images were nearly the same as that with
Au coating because carbon black without polymer graing has
sufficiently high electrical conductivity; whereas for CB-N-g-
PCMS-OHꢀ, it became clear and there was less charging effects
aer Au coating due to the enhancement of conductivity.
3.2 CO2 capture results. The CO2 absorption/desorption
characteristics of these materials are shown in Table 2 and
Fig. 15. The material was rst saturated with CO2, before being
exposed to humid conditions to release the CO2 from the
material in a closed system, followed by a reduction in the
humidity to trigger the capture of the CO2. In all cases a low
humidity of approximately 5 parts per thousand (ppt) and a
high humidity of approximately 20 ppt was used, which corre-
sponds to approximately 20% and 90% relative humidity,
respectively.25c Excellion membrane, a commercially available
extruded polyethylene membrane containing crosslinked
chloromethylated polystyrene resin with quaternary ammo-
nium hydroxide groups,25a,c was selected as the reference
material. When subject to the humidity swing, the Excellion
membrane showed a swing size of 1.3 ꢂ 10ꢀ1 mmol gꢀ1, an
Scheme
5
Synthetic procedures for the quaternization and ion-exchange
reactions.
Fig. 13 TEM images of CB-N-g-PCMS-OHꢀ (a) and CB-N-Br-OH (b).
the material to be used for CO2 capture by the humidity swing.
The CB-N-g-PCMS was rst quaternized using trimethylamine
in ethanol and then ion-exchanged with KOH in methanol
(Scheme 5). The elemental analysis showed that the Cl content
was 13.28% for CB-N-g-PCMS, and it decreased to 1.24% aer
quaternization and ion-exchange over a one day period. Exten-
sion of the ion exchange process to 7 days decreased the Cl
content to 1.11%, indicating that the one day ion-exchange
procedure was sufficient.
A control sample with no polymer graing (CB-N-Br-OH) was
prepared using CB-N-Br as the feed by the same treatment (rst
with trimethylamine, followed by KOH). The TEM images of the
two samples with or without graing of polymers (Fig. 13) show
different morphologies. For CB-N-Br-OH, no graed polymer
layer was observed on the particle surfaces, and there were more
Fig. 14 SEM images of crude carbon black (a and b), CB-N-g-PCMS-OHꢀ (c and d), and CB-N-Br-OH (e and f).
6818 | J. Mater. Chem. A, 2013, 1, 6810–6821
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1
1
1
Table 2 The CO2 capture results of Excellion membrane and carbon black samples. The overall rate is determined by:
¼
þ
overall rate absorption rate desorption rate
Swing size
(mmol gꢀ1
Absorption rate
(mmol gꢀ1 min)
Desorption rate
Overall rate
Entry
Material
)
(mmol gꢀ1 minꢀ1
)
(mmol gꢀ1 minꢀ1
)
1 (ref. 25c)
2
Excellion membrane
CB
1.3 ꢂ 10ꢀ1
4.0 ꢂ 10ꢀ3
4.5 ꢂ 10ꢀ3
2.1 ꢂ 10ꢀ3
0
0
0
0
3
CB-N-Br-OH
0
0
0
0
4 (ref. 25c)
5
CB-N-g-PCMS-OHꢀ
CB-g-xPCMS-OHꢀ
1.4 ꢂ 10ꢀ1
1.4 ꢂ 10ꢀ1
1.8 ꢂ 10ꢀ2
2.0 ꢂ 10ꢀ2
1.2 ꢂ 10ꢀ2
1.5 ꢂ 10ꢀ2
7.2 ꢂ 10ꢀ3
8.6 ꢂ 10ꢀ3
Fig. 15 Absorption/desorption profiles for Excellion membrane (a), CB-N-g-PCMS-OHꢀ (b), and CB-g-xPCMS-OHꢀ (c).
absorption rate of 4.0 ꢂ 10ꢀ3 mmol gꢀ1 minꢀ1, a desorption oxidation followed by esterication, or by reaction of azide
rate of 4.5 ꢂ 10ꢀ3 mmol gꢀ1 minꢀ1, and an overall rate of 2.1 ꢂ functionalized ATRP initiators with the carbon black surface
10ꢀ3 mmol gꢀ1 minꢀ1. The reversibility of the CO2 absorption/ using nitrene chemistry. ATRP was then conducted using a CMS
desorption based on the interchange of quaternary ammonium inimer and CuCl/CuCl2/PMDETA catalytic system in DMF at 100
carbonate and bicarbonate groups under humidity swing has ꢁC. To maximize the stability of the polymer graed carbon
been demonstrated previously.25c,d
black under basic conditions, the nitrene chemistry approach is
Whenthepolymer-graed carbon black, CB-g-xPCMS-OHꢀ, was preferred to the acid oxidation method. Crosslinked hyper-
subjectedtothehumidityswing, thereweremarkedimprovements branched polymers can be graed from the carbon black as an
in the kinetics. As shown in the absorption and desorption traces in alternative method for synthesizing functionalized surfaces that
Fig. 15, it displayed an absorption rate of 2.0 ꢂ 10ꢀ2 mmol gꢀ1 are stable under basic conditions. These crosslinked materials
minꢀ1, a desorption rate of 1.5 ꢂ 10ꢀ2 mmol gꢀ1 minꢀ1, an overall can be prepared in a one-pot two-step method, where the
rate of 8.6 ꢂ 10ꢀ3 mmol gꢀ1 minꢀ1, and a swing size of 1.4 ꢂ 10ꢀ1 crosslinked shell was rst formed on carbon black using DVB,
mmol gꢀ1. This carbon black sample with polymer graing has followed by the polymerization of CMS to form a crosslinked
nearly the same swing size as the Excellion membrane but a 3-fold hyperbranched outer layer. The morphologies of all the hyper-
increase in the absorption/desorption rates. In contrast, the crude branched PCMS graed carbon blacks were characterized by
carbon black and CB-N-Br-OH without polymer graing showed no TEM and SEM, which conrmed the formation of the functional
absorption/desorption when subjected to the humidity swing, polymer layer on carbon black. TGA results revealed that the
since they contain nearly no quaternary ammonium hydroxide ratio of the graed polymers to carbon black increased with
groups. Thus, the polymer graing is vital for enhancing CO2 polymerization time. The untethered hyperbranched polymers
capture because the polymer layer on the carbon black can greatly formed in the polymerization solution were characterized by 1H
increase the number of accessible hydroxide groups and enhance NMR spectroscopy, GPC, and GPC-MALLS. The hyperbranched
the dispersibility of carbon black in solvents. Moreover, the CO2 polymers on the carbon black surfaces were subsequently
capture results for the CB-N-g-PCMS-OHꢀ (ref. 25c) and CB-g- quaternized and ion-exchanged to generate quaternary ammo-
xPCMS-OHꢀ samples have the same swing sizes (1.4 ꢂ 10ꢀ1 mmol nium hydroxide groups, which were utilized for the reversible
gꢀ1) and very close absorption/desorption rates (the overall rates capture and release of CO2 from ambient air. The crosslinked
are 7.2 ꢂ 10ꢀ3 and 8.6 ꢂ 10ꢀ3 mmol gꢀ1 minꢀ1, respectively). This and uncrosslinked carbon blacks graed with polymeric
implies that forming a crosslinked shell on carbon black has quaternary ammonium hydroxide groups showed a 3- to 4-fold
minimal inuence on the swing size but can induce a slight increasing of the absorption/desorption kinetics compared with
increase of the CO2 absorption/desorption rates.
the Excellion membrane.
Conclusions
Acknowledgements
Carbon black with tethered hyperbranched polymers were We thank Joseph P. Suhan for his help on the SEM and TEM
prepared by surface initiated self-condensing ATRP. The ATRP measurements. We acknowledged NSF support (CHE-1039870
initiator was introduced onto the carbon black surfaces by acid and DMR-0969301).
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18 Q. Yang, L. Wang, W.-D. Xiang, J.-F. Zhou and Q.-H. Tan,
J. Polym. Sci., Part A: Polym. Chem., 2007, 45, 3451–3459.
19 T. Q. Liu, S. J. Jia, T. Kowalewski, K. Matyjaszewski,
R. Casado-Portilla and J. Belmont, Macromolecules, 2006,
39, 548–556.
20 (a) J. Cheng, L. Wang, J. Huo, H. Yu, Q. Yang and L. Deng,
J. Polym. Sci., Part B: Polym. Phys., 2008, 46, 1529–1535; (b)
Q. Yang, L. Wang, W. Xiang, J. Zhou and Q. Tan, Polymer,
2007, 48, 3444–3451.
References
1 A. C. Lau, D. N. Furlong, T. W. Healy and F. Grieser, Colloids
Surf., 1986, 18, 93–104.
2 (a) M. Wang, F. Xu, Q. Liu, H. Sun, R. Cheng, H. He,
E. A. Stach and J. Xie, Carbon, 2011, 49, 256–265; (b)
N. Krishnankutty and M. A. Vannice, Chem. Mater., 1995, 7,
754–763.
3 E. M. Dannenberg, L. Paquin and H. Gwinnell, Kirk-Othmer
Encyclopedia of Chemical Technology, 2000.
4 M. Hussain, Y. H. Choa and K. Niihara, J. Mater. Sci. Lett.,
2001, 20, 525–527.
5 Y. N. Lin, T. W. Smith and P. Alexandridis, J. Colloid Interface
Sci., 2002, 255, 1–9.
6 N. Tsubokawa, T. Satoh, M. Murota, S. Sato and H. Shimizu,
Polym. Adv. Technol., 2001, 12, 596–602.
7 X. Li, C.-Y. Hong and C.-Y. Pan, Polymer, 2010, 51,
92–99.
8 T. Q. Liu, S. Jia, T. Kowalewski, K. Matyjaszewski, R. Casado-
Portilla and J. Belmont, Langmuir, 2003, 19, 6342–6345.
9 C. F. Lee, C. C. Yang, L. Y. Wang and W. Y. Chiu, Polymer,
2005, 46, 5514–5523.
21 Q. Yang, L. Wang, J. Huo, J. Ding and W. Xiang, J. Appl.
Polym. Sci., 2010, 117, 824–827.
22 (a) C. D. Thomas, A. Cameron, R. E. Green, M. Bakkenes,
L. J. Beaumont, Y. C. Collingham, B. F. N. Erasmus,
M. F. de Siqueira, A. Grainger, L. Hannah, L. Hughes,
B. Huntley, A. S. van Jaarsveld, G. F. Midgley, L. Miles,
M. A. Ortega-Huerta, A. T. Peterson, O. L. Phillips and
S. E. Williams, Nature, 2004, 427, 145–148; (b) C. W. Jones
and E. J. Maginn, ChemSusChem, 2010, 3, 863–864.
23 (a) S. Choi, J. H. Drese and C. W. Jones, ChemSusChem, 2009,
2, 796–854; (b) D. M. D’Alessandro, B. Smit and J. R. Long,
Angew. Chem., Int. Ed., 2010, 49, 6058–6082; (c) S. Chu,
Science, 2009, 325, 1599–1599.
10 S. Yoshikawa, S. Machida and N. Tsubokawa, J. Polym. Sci.,
Part A: Polym. Chem., 1998, 36, 3165–3172.
11 Q. Yang, L. Wang, W. Xiang, J. Zhou and J. Li, Polymer, 2007,
48, 2866–2873.
12 N. Tsubokawa, H. Tsuchida and K. Kobayashi, Nippon Gomu
Kyokaishi, 1993, 66, 124–129.
13 (a) N. Tsubokawa, Y. Jian and Y. Sone, J. Polym. Sci., Part A:
Polym. Chem., 1988, 26, 2715–2724; (b) Q. Yang, L. Wang,
W. Xiang, J. Zhou and G. Jiang, J. Appl. Polym. Sci., 2007,
103, 2086–2092.
14 (a) S. Hayashi, S. Handa and N. Tsubokawa, J. Polym. Sci.,
Part A: Polym. Chem., 1996, 34, 1589–1595; (b) S. Hayashi,
A. Naitoh, S. Machida, M. Okazaki, K. Maruyama and
N. Tsubokawa, Appl. Organomet. Chem., 1998, 12, 743–748.
15 (a) W. A. Braunecker and K. Matyjaszewski, Prog. Polym. Sci.,
2007, 32, 93–146; (b) K. Matyjaszewski, Macromolecules,
2012, 45, 4015–4039.
24 (a) S. Choi, J. H. Drese, P. M. Eisenberger and C. W. Jones,
Environ. Sci. Technol., 2011, 45, 2420–2427; (b) C. Gebald,
J. A. Wurzbacher, P. Tingaut, T. Zimmermann and
A. Steinfeld, Environ. Sci. Technol., 2011, 45, 9101–
9108.
25 (a) T. Wang, K. S. Lackner and A. Wright, Environ. Sci.
Technol., 2011, 45, 6670–6675; (b) K. S. Lackner, Eur. Phys.
J.: Spec. Top., 2009, 176, 93–106; (c) H. K. He, W. W. Li,
M. J. Zhong, D. Konkolewicz, D. C. Wu, K. Yaccato,
T. Rappold, G. Sugar, N. E. David and K. Matyjaszewski,
Energy Environ. Sci., 2013, 6, 488–493; (d) H. K. He,
M. J. Zhong, D. Konkolewicz, K. Yaccato, T. Rappold,
G. Sugar, N. E. David, J. Gelb, N. Kotwal, A. Merkle and
K. Matyjaszewski, Adv. Funct. Mater., 2013, DOI: 10.1002/
adfm.201300401.
26 L. O. Vasquez, Fuel Cell Research Trends, Nova Publishers,
2007.
16 (a) J. S. Wang and K. Matyjaszewski, J. Am. Chem. Soc., 1995,
117, 5614–5615; (b) K. Matyjaszewski and J. H. Xia, Chem.
Rev., 2001, 101, 2921–2990; (c) M. Kato, M. Kamigaito,
M. Sawamoto and T. Higashimura, Macromolecules, 1995,
28, 1721–1723; (d) M. Kamigaito, T. Ando and
M. Sawamoto, Chem. Rev., 2001, 101, 3689–3745; (e)
K. Matyjaszewski and N. V. Tsarevsky, Nat. Chem., 2009, 1,
276–288; (f) N. V. Tsarevsky and K. Matyjaszewski, Chem.
Rev., 2007, 107, 2270–2299; (g) S. S. Sheiko, B. S. Sumerlin
and K. Matyjaszewski, Prog. Polym. Sci., 2008, 33, 759–785;
(h) H. Gao and K. Matyjaszewski, Prog. Polym. Sci., 2009,
34, 317–350; (i) V. Coessens, T. Pintauer and
K. Matyjaszewski, Prog. Polym. Sci., 2001, 26, 337–377; (j)
D. Wu, F. Xu, B. Sun, R. Fu, H. He and K. Matyjaszewski,
Chem. Rev., 2012, 112, 3959–4015.
27 The International Carbon Black Association (ICBA), http://
www.carbon-black.org.
28 Z. Jiang, J. Jin, C. Xiao and X. Li, Colloids Surf., A, 2012, 395,
105–115.
29 (a) Y. Zhang, H. He and C. Gao, Macromolecules, 2008, 41,
9581–9594; (b) Y. Zhang, H. He, C. Gao and J. Wu,
Langmuir, 2009, 25, 5814–5824.
30 (a) H. He and C. Gao, Chem. Mater., 2010, 22, 5054–5064; (b)
C. Gao, H. He, L. Zhou, X. Zheng and Y. Zhang, Chem. Mater.,
2009, 21, 360–370.
31 (a) C. A. Dyke and J. M. Tour, J. Am. Chem. Soc., 2003, 125,
1156–1157; (b) H. He and C. Gao, Curr. Org. Chem., 2011,
15, 3667–3691.
32 H. Kong, C. Gao and D. Y. Yan, J. Am. Chem. Soc., 2004, 126,
412–413.
17 T. Q. Liu, R. Casado-Portilla, J. Belmont and
K. Matyjaszewski, J. Polym. Sci., Part A: Polym. Chem., 2005,
43, 4695–4709.
33 M. Holzinger, J. Steinmetz, D. Samaille, M. Glerup,
M. Paillet, P. Bernier, L. Ley and R. Graupner, Carbon,
2004, 42, 941–947.
6820 | J. Mater. Chem. A, 2013, 1, 6810–6821
This journal is ª The Royal Society of Chemistry 2013

View Article Online
Paper
Journal of Materials Chemistry A
34 (a) C. Gao and D. Yan, Prog. Polym. Sci., 2004, 29, 183–275; (b) 40 X. L. Jiang, Y. L. Zhong, D. Y. Yan, H. Yu and D. Z. Zhang,
D. Y. Yan, C. Gao and H. Frey, Hyperbranched Polymers: J. Appl. Polym. Sci., 2000, 78, 1992–1997.
Synthesis, Properties, and Applications, 2010; (c) 41 W. X. Wang, D. Y. Yan, D. Bratton, S. M. Howdle, Q. Wang
D. Konkolewicz, M. J. Monteiro and S. Perrier, and P. Lecomte, Adv. Mater., 2003, 15, 1348–1352.
Macromolecules, 2011, 44, 7067–7087; (d) D. Konkolewicz, 42 F. R. Mayo, J. Am. Chem. Soc., 1953, 75, 6133–6141.
A. Gray-Weale and S. Perrier, Polym. Chem., 2010, 1, 1067– 43 (a) S.-i. Yamamoto, J. Pietrasik and K. Matyjaszewski,
1077; (e) D. Konkolewicz, R. G. Gilbert and A. Gray-Weale,
Phys. Rev. Lett., 2007, 98, 238301.
Macromolecules, 2007, 40, 9348–9353; (b) M. Jikei and
M. Kakimoto, Prog. Polym. Sci., 2001, 26, 1233–1285.
35 J. M. J. Frechet, M. Henmi, I. Gitsov, S. Aoshima, M. R. Leduc 44 F. H. Gong, H. L. Tang, C. L. Liu, B. B. Jiang, Q. Ren and
and R. B. Grubbs, Science, 1995, 269, 1080–1083. Y. Yang, J. Appl. Polym. Sci., 2006, 101, 850–856.
36 (a) K. Matyjaszewski, S. G. Gaynor and A. H. E. Muller, 45 Y. Liu, X. Miao, J. Zhu, Z. Zhang, Z. Cheng and X. Zhu,
Macromolecules, 1997, 30, 7034–7041; (b) K. Matyjaszewski Macromol. Chem. Phys., 2012, 213, 868–877.
and S. G. Gaynor, Macromolecules, 1997, 30, 7042–7049; (c) 46 (a) H. Mori, A. Boker, G. Krausch and A. H. E. Muller,
¨
¨
¨
A. H. E. Muller, D. Y. Yan and M. Wulkow,
Macromolecules, 2001, 34, 6871–6882; (b) K. Matyjaszewski,
S. G. Gaynor, A. Kulfan and M. Podwika, Macromolecules,
1997, 30, 5192–5194; (c) B. I. Voit and A. Lederer, Chem.
Rev., 2009, 109, 5924–5973.
Macromolecules, 1997, 30, 7015–7023; (d) D. Y. Yan,
A. H. E. Muller and K. Matyjaszewski, Macromolecules,
1997, 30, 7024–7033.
¨
37 S. G. Gaynor, S. Edelman and K. Matyjaszewski, 47 (a) H. Komber, U. Georgi and B. Voit, Macromolecules, 2009,
Macromolecules, 1996, 29, 1079–1081.
38 Q. Ren, A. Y. Li, J. Bibiao, D. L. Zhang and J. H. Chen, J. Appl.
Polym. Sci., 2004, 94, 2425–2430.
42, 8307–8315; (b) F. M. Dean and R. S. Varma, Tetrahedron,
1982, 38, 2069–2081.
48 D. Holter, A. Burgath and H. Frey, Acta Polym., 1997, 48, 30–35.
39 C. Cheng, K. L. Wooley and E. Khoshdel, J. Polym. Sci., Part A: 49 H. Dong, M. Zhu, J. A. Yoon, H. Gao, R. Jin and
Polym. Chem., 2005, 43, 4754–4770.
K. Matyjaszewski, J. Am. Chem. Soc., 2008, 130, 12852–12853.
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J. Mater. Chem. A, 2013, 1, 6810–6821 | 6821