Controlled polymerization of carbazole-based vinyl and methacrylate monomers at ambient temperature: A comparative study through ATRP, SET, and SET-RAFT polymerizations

Article abstract of DOI:10.1002/pola.24518

The polymerization of N-vinylcarbazole (NVK) and carbazole methacrylate (CMA) was carried out using controlled radical polymerization methods such as atom transfer radical polymerization (ATRP), single electron transfer (SET)-LRP, and single electron tran

Full text of DOI:10.1002/pola.24518

Controlled Polymerization of Carbazole-Based Vinyl and Methacrylate
Monomers at Ambient Temperature: A Comparative Study Through
ATRP, SET, and SET-RAFT Polymerizations
NEELAMEGAN HARIDHARAN, RAGHAVACHARI DHAMODHARAN
Department of Chemistry, Indian Institute of Technology Madras, Chennai 600036, India
Received 10 November 2010; accepted 24 November 2010
DOI: 10.1002/pola.24518
Published online 3 January 2011 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: The polymerization of N-vinylcarbazole (NVK) and
carbazole methacrylate (CMA) was carried out using controlled
radical polymerization methods such as atom transfer radical
polymerization (ATRP), single electron transfer (SET)-LRP, and
single electron transfer initiation followed by reversible addition
fragmentation chain transfer (SET-RAFT). Well-controlled poly-
merization with narrow molecular weight distribution (Mw/Mn) <
1.25 was achieved in the case of NVK by high-temperature ATRP
while ambient temperature SET-RAFT polymerization was rela-
tively slow and controlled. In the case of CMA, SET-RAFT is
found to be more suitable for the ambient temperature polymer-
ization. The polymerization rate followed first order kinetics with
respect to monomer conversion and the molecular weight of the
polymer increased linearly with conversion. The controlled na-
ture of the polymerization is further demonstrated by the syn-
thesis of diblock copolymers from PNVK and PCMA
macroinitiators using
a new flavanone-based methacrylate
(FMA) as the second monomer. All the polymers exhibited fluo-
rescence. The excimer bands in the homopolymers of PNVK and
PCMA were very broad, which may be attributed to the carba-
zole–carbazole overlap interaction. The scanning electron mi-
croscopy analysis of the block copolymer reveals interesting
C
V
morphological features.
2011 Wiley Periodicals, Inc. J Polym
Sci Part A: Polym Chem 49: 1021–1032, 2011
KEYWORDS: atom transfer radical polymerization; block copoly-
mer; fluorescence; fluorescent polymers; reversible addition
fragmentation chain transfer; single electron transfer
INTRODUCTION Carbazole and other carbazole-related poly-
mers attract attention because of their unusual physical
properties such as electrophotographic micro filming, electro
photographic printing plates, laser printing, light emitting
fluorescent material,1 and photovoltaic devices.2 Carbazole-
based polymers are most frequently used as polymeric hosts
because of hole transporting properties and large band
gap.3,4 The most important requirement for all photoconduc-
tive material is extreme purity. Even traces of impurities can
act as traps and have a drastic influence on both the yield
and carrier mobility. Therefore, the preparation of carbazole-
based polymer with utmost purity and in a controlled man-
ner is essential for practical applications. Percec et al.,3
reported a series of fluorescent and electrically conducting
organic crystals and polymers including N-vinylcarbazole
(NVK) and carbazole-based methacrylate for the self-organi-
zation of supramolecular helical dendrimers that in turn
form complex electronic materials. Percec also reported on a
series of halogen carbazole-based polymers in early 1980’s
and investigated their thermal properties.5,6
under cationic and free radical polymerization at higher tem-
perature.7–10 Bottle et al.,11 demonstrated the mechanism of
initiation in the free radical polymerization of NVK. However,
the polymer obtained by conventional free radical polymer-
ization does not provide control over the molecular weight
and the polydispersity index (PDI) values. The syntheses of
poly(N-vinylcarbazole) (PNVK) through controlled living rad-
ical polymerization have been attemped by many groups.
Nowakowsha et al.,12 reported the block copolymerization of
NVK along with sodium styrenesulphonate at higher temper-
ature under nitroxide mediated polymerization (NMP)13
method and the polymer obtained showed higher polydisper-
sity values. Hua et al.,14 reported the polymerization of full-
erene bonded NVK with C60-Cl as the initiator at higher tem-
perature by atom transfer radical polymerization (ATRP).
This produced polymers with high polydispersity values.
Mori et al.,15 reported the synthesis of poly (N-ethyl-3-vinyl-
carbazole) and its block copolymers with styrene via RAFT.
These polymerizations were performed at higher tempera-
ture and no control in molecular weight distribution was
reported. Mori et al.,16 recently reported the synthesis of
xanthate-mediated radical polymerization of NVK with good
control in molecular weight and polydispersity values. They
NVK, which is the first and the most widely studied poly-
meric photoconductor has been polymerized successfully
Additional Supporting Information may be found in the online version of this article. Correspondence to: R. Dhamodharan (E-mail: damo@iitm.ac.
in)
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Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 49, 1021–1032 (2011) 2011 Wiley Periodicals, Inc.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
also reported that the polymerization of NVK initiated by
AIBN (free-radical polymerization) produces polymers with
broader PDI values of >2.0. However, by utilizing the proper
chain transfer agent (CTA) and performing the polymeriza-
tion by RAFT well-defined polymers were produced.
Recently, Brar and Kour,17 reported the polymerization of
NVK by ATRP at 90 ꢀC using N-2-bromoethyl carbazole as
the initiator to produce polymers with control over molecu-
lar weight and polydispersity. Very recently, a well-defined
xanthate-mediated diblock copolymer comprising of NVK
was reported by RAFT polymerization.18 The polymerization
of NVK, at ambient temperature, is still not reported. In view
of the literature reports, the polymerization of carbazole-
based vinyl and methacrylate monomers through various
controlled radical polymerization (CRP) methods to get con-
trol over the polymerization, at ambient temperature,
assumes significance.
where one of the solvents is water, thereby providing an effi-
cient method for the elaboration of large diversity of reac-
tion media in SET-LRP. Very recently, the SET-LRP of acryl-
ates demonstrating control in the presence of air was also
reported.39 The SET–LRP of methacrylates is about 5–10
times slower than the SET–LRP of acrylates under identical
conditions, and the synthesis of most of the methacrylates is
yet to be explored.40 A well controlled copolymerization of
methacrylic acid with MMA is also reported.41 Nguyen and
Percec42 recently demonstrated on intelligent methodology
involving a simple method for the activation of Cu(0) wire
for the dramatic acceleration of SET-LRP of methyl acrylate
which results in excellent control over molecular weight dis-
tribution and high chain end functionality. A report sug-
gested that Cu(0)/N,N,N1,N11,N111–pentamethyldiethylenetri-
amine (PMDETA) catalyzed SET–LRP of MMA can be
conducted using 2-cyanoprop-2-yl 1-dithionaphthalate as an
initiator.43
Some of the efficient controlled radical polymerization meth-
ods used nowadays are ATRP,19 single electron transfer
(SET),20–24 and radical addition fragmentation chain transfer
(RAFT),25 which provide good versatility and functional
group compatibility. ATRP is one of the widely used method
for the synthesis of well-defined block copolymers with pre-
dictable molecular weight and narrow molecular weight dis-
tributions. For the purpose of optimizing control, Cu(II) can
be used in ATRP along with Cu(I). However, the solubility of
Cu(II) is seriously limited in the organic solvents even with
the use of suitable ligands.
The first example of using single electron transfer initiation
and propagation through the SET–RAFT44 was provided by
our group. We reported on the polymerization of styrene at
ambient temperature that was very slow.44 In a subsequent
step, we also showed that diblock copolymers could be syn-
thesized from the macroinitiators. The polymerization at
lower temperatures would be advantageous for a variety of
reasons that include minimization of thermal cross linking,
chain transfer, thermal self-initiation, and other side reac-
tions.45 The ambient temperature initiation of polymerization
by SET followed by controlled propagation through the CTA
via the RAFT mechanism for the propagation (SET–RAFT)
method is expected to have wider applicability especially for
monomers that polymerize very rapidly by free/living radical
polymerization. The SET–RAFT method is a simple and alter-
native method of polymer synthesis with control, under am-
bient conditions. We have reported, recently, that cyclohexyl
methacrylate is polymerized with control, at ambient tem-
perature, by SET–RAFT.46
Recently, several articles have appeared elucidating the utili-
zation of the principles developed in SET-LRP toward syn-
thesizing well-defined macromolecules including novel
photoresist material26 with controlled compositions thereby
advancing the controlled radical polymerization methodol-
ogy. SET-LPR of methyl acrylate, vinyl chloride, and methac-
rylate (in fluoroalcohol, carbon tetrachloride, sulphonyl ha-
lide and in acetic acid medium) has been reported.27–30 The
successful controlled polymerization of water soluble mono-
mers in specific solvents have been reported.31 The implica-
tions of monomer and initiator structure on the electron
transfer step of SET-LRP have been reported.32 A review on
SET-LRP has also appeared.33 The SET–LRP method is less
susceptible to side reactions and radical termination as
some functions of the process occur via outer sphere elec-
tron transfer in contrast to the normal ATRP, which is
accepted to occur via inner sphere election transfer. In ATRP,
the activation of R–X by Cu(I) and subsequent generation of
Cu(II) is accompanied via a halogen-bridged transition state.
The reported ultrafast synthesis of acrylates, at room tem-
perature, showed excellent control over molecular weight
and polydispersity as well as perfect retention of chain end
functionality.34,35 The SET-LRP of methyl acrylate in various
solvents, mediating different degrees of disproportionation
of Cu(I)Br, has also been reported.36 Percec et al.,37 demon-
strated the novel development of self organizable dendritic
macromolecules through the combination of SET-LRP and
click chemistry. Percec et al.,38 demonstrated on intelligent
methodology involving the use of binary mixture of solvents
Based on the above literature reports, it is evident that de-
velopment of mild methods to polymerize carbazole-based
monomers in a controlled manner is important. This gains
even more importance if the carbazole moiety with the semi-
conducting property can be present along with methacrylate
monomer with its unique optical properties.
In this work, we compare the polymerization of NVK and
CMA under ATRP, SET, and SET–RAFT condition at ambient
and higher temperature. This is the first report on the poly-
merization of carbazole-based monomers via SET and SET–
RAFT, at ambient temperature. This article also reports on
the block copolymerization with a novel fluorescent, flava-
none-based monomer. The summary of the objectives of the
work is presented in Schemes 1 and 2.
RESULTS AND DISCUSSION
To explore the controlled radical polymerization of NVK
and carbazole methacrylate (CMA) via SET-RAFT and also to
compare the same with the other controlled radical
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SCHEME 1 Structure of the monomers and the chain transfer agents utilized for the polymerization. [Color figure can be viewed in
the online issue, which is available at wileyonlinelibrary.com.]
polymerization methods such as ATRP and SET, CMA was
synthesized and characterized. CMA was synthesized based
on the literature procedure reported by Percec and co-
workers.47 In addition, carboxylic acid end functionalized tri-
thiocarbonate CTA (shown in Scheme 1) was also synthe-
sized and characterized. In addition, flavanone methacrylate
(FMA) was also synthesized and characterized for block
copolymerization and to introduce fluorescence property.
The structures of the compounds were characterized by 1H,
13C, DEPT, and MASS spectroscopies (Supporting Informa-
tion). The H NMR spectra of the monomers and the CTA are
1
shown in Figure 1. The 1H spectrum of the CMA in CDCl3
shows a peak at 1.9 ppm that corresponds to methyl pro-
tons, peaks at 5.5 and 6.2 ppm that correspond to ethylenic
protons, peaks around 7.1–8.2 ppm that corresponds to aro-
matic protons and peaks at 2.2, 4.2, and 4.4 ppm that corre-
spond to methylene protons, respectively. The 1H spectrum
of the FMA in CDCl3 shows a peak at 1.9 ppm that
SCHEME 2 Pictorial representa-
tion for the polymerization of N-
vinylcarbazole and carbazole
methacrylate performed under
various CRP methods namely
ATRP, single electron transfer
(SET), and SET-radical addition
fragmentation chain transfer
(RAFT).
[Color
figure
can
be viewed in the online
issue, which is available at
wileyonlinelibrary.com.]
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FIGURE 1 The 1H NMR spectra of the carbazole methacrylate, flavanone methacrylate, and the CTA.
corresponds to methyl protons, peaks at 5.7 and 6.2 ppm
that correspond to ethylenic protons, peaks around 6.8–7.9
ppm that correspond to aromatic protons, peaks around 2.7
ppm that correspond to methylene protons of cyclohexyl
ring and a peak around 5.4 ppm that corresponds to
methine protons of the ring, respectively. The 1H spectrum
of the CTA in CDCl3 shows five prominent peaks at 0.9, 1.45,
1.7–1.75, 1.79, and 3.3 ppm, integrating to three and two
protons, respectively. These peaks correspond to protons
from the ACH3, ACH2, and C(CH3)2A groups and confirm
the structure of the CTA. The 13C NMR spectra, DEPT correla-
tion spectra, and the mass spectra of the above discussed
compounds (shown in the Supporting Information) provide
additional evidence for the structures.
ization data are given in the Experimental section. From the
results obtained by ATRP and SET (Tables 1 and 2 of Sup-
porting Information), it was clear that the ambient tempera-
ture polymerization of NVK via ATRP and SET–LRP method
was possible under the conditions explored but the rate of
polymerization was very slow. The ATRP of NVK at ambient
temperature produces only oligomers (Supporting Informa-
tion Table 1 entries 1–4). However, increase in the tempera-
ture results in reasonable conversion with polymers of
higher molecular weight and lower polydispersity values but
the number average molecular weight as assessed by gel
permeation chromatography [Mn(GPC)] values obtained are
higher than expected values (Supporting Information Table 1
entries 5–7). Similarly, polymerization was performed
through SET method using Cu (0) and the following ligands:
bipyridyl, PMDETA, and Me6TREN. For a target degree of
polymerization (DP) of 200, the polymerization of NVK with
Cu(0)/bipyridyl results in no significant conversion even
At first, the polymerization of NVK and CMA were investi-
gated through the ATRP and SET methods, which were
performed in solution condition at ambient and higher tem-
perature. The detailed synthetic procedure and the polymer-
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TABLE 1 Experimental Data from the Polymerization of Carbazole-Based Monomers Under Various SET - RAFT Conditions at
Ambient Temperature
Initiator/CTA/
Cu(0)/L
LIGAND
(L)
DMSO
(ml)
Time
(h)
Mn
Mn
Monomer
Entry
DP
% Conv.
(GPC)
(Exp.)
PDI
1
200
200
200
200
200
200
200
300
100
200
200
200
200
200
300
200
300
0:1:2:2
1:1:2:2
2:1:2:2
1:0.5:2:2
1:1:1:1
1:1:2:2
1:1:2:2
1:2:2:2
1:1:1:1
0:1:2:2
1:1:2:2
2:1:2:2
1:0.5:2:2
1:1:1:1
1:2:2:2
1:1:2:2
1:0.5:2:2
PMDETA
PMDETA
PMDETA
PMDETA
PMDETA
PMDETA
PMDETA
PMDETA
PMDETA
PMDETA
PMDETA
PMDETA
PMDETA
PMDETA
PMDETA
Me6TREN
Me6TREN
0.5
0.5
0.5
0.5
0.5
0.1
0.3
0.1
0.3
0.5
0.5
0.5
0.3
0.3
0.3
0.2
0.3
24
24
24
24
20
20
30
20
24
24
24
24
24
22
20
20
22
NIL
5
NIL
NIL
NIL
2
3,500
5,600
4,800
5,000
3,600
6,500
NIL
1,900
3,000
3,500
2,300
1,150
4,200
NIL
1.21
1.25
1.20
1.19
1.22
1.23
NIL
3
8
4
9
5
6
6
3
7
11
NIL
69
NIL
46
58
52
54
23
34
41
8
9
25,800
NIL
20,300
NIL
1.26
NIL
10
11
12
13
14
15
16
17
32,000
39,000
36,000
36,000
23,000
22,800
39,000
27,000
34,100
30,500
31,700
20,300
19,900
36,100
1.26
1.32
1.29
1.25
1.21
1.22
1.23
after 10 h. Under similar condition, the use of Me6TREN
results in low conversion of 5% after 20 h (Supporting Infor-
mation Table 2 entries 2 and 6).
mation. The results illustrate that the SET polymerization
proceeds with moderate rate resulting in polymers with
broader polydispersity values (Supporting Information Table
2 entries 8 and 15). From the above results, it can be
inferred that the polymerization of both vinyl and methacry-
late-based carbazole monomers produce polymers with
broader polydispersity values, at ambient temperature, via
ATRP and SET, except when the ATRP is carried out at
higher temperature.
In the case of CMA, the polymerization was performed at
ambient temperature via ATRP and SET under various
monomer concentrations and with different ligands and the
solvent medium. The results obtained are given in the
Tables 1 and 2 of the Supporting Information. The ATRP
when performed using 1:1 ratio of Cu(I)Br/PMDETA in 25%
v/v of chlorobenzene produces good conversion but the pol-
ydispersity values are higher (Supporting Information Table
1 entry 10). When PMDETA was replaced by Me6TREN a
marginal improvement in polydispersity values was
obtained in chlorobenzene, but the Mn(GPC) values were
greater than the expected ones (Supporting Information Ta-
ble 1 entry 13). Similarly, the polymerization was performed
by the SET method at ambient temperature using Cu(0) and
the ligands bipyridyl or PMDETA or Me6TREN. The results
obtained are given in the Table 2 of the Supporting Infor-
To explore whether SET–LRP offers a milder way to produce
carbazole-based polymers, the use of a CTA (SET–RAFT)
under the SET-LRP conditions was explored. The polymeriza-
tion of both the monomers was carried out by SET–RAFT
using the trithiocarbonate-based CTA (Scheme 1) at ambient
temperature. The polymerizations were performed in solu-
tion, at ambient temperature. The results obtained are given
in the Table 1. The detailed synthetic procedure for the poly-
merization through SET-RAFT is given in the Experimental
section. Under these conditions, CMA undergoes faster rate
TABLE 3 GPC and Monomer Conversion with Time for the
Polymerization of Carbazole-Based Methacrylate (CMA) Via
SET – RAFT
TABLE 2 GPC and Monomer Conversion with Time for the
Polymerization of NVK Via SET – RAFT. [NVK]/{(RX)}/[CTA]/
Cu(0)/PMDETA, 200:1:1:2:2 at RT in DMSO
S. No.
Time (h)
% Conv.
Mn (Exp.)
Mn (GPC)
PDI
S. No.
Time (h)
% Conv.
Mn (Exp.)
Mn (GPC)
PDI
1
2
3
4
5
10
20
30
40
50
9
23
35
43
57
7,900
20,300
31,000
37,900
50,200
10,100
24,600
34,100
42,000
56,000
1.19
1.21
1.22
1.22
1.25
1
2
3
4
5
15
30
45
60
75
2
7
800
2,700
5,000
7,700
10,100
1,900
4,000
1.20
1.21
1.23
1.22
1.23
13
20
26
6,500
10,300
15,000
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FIGURE 2 Kinetics plot of
% conversion versus molecular
weight (Mn) and PDI (right) showing the polymerization of
N-vinylcarbazole at RT via single electron transfer (SET)-RAFT
in the ratio 200:1:1:2:2. [NVK]/[RX]/[CTA]/Cu(0)/[PMDETA] in
DMSO.
FIGURE 4 GPC traces for kinetics of N-vinylcarbazole obtained
with an increase in polymerization time under single electron
transfer-radical addition fragmentation chain transfer (SET-
RAFT) using CTA. [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com.]
of polymerization than NVK. The slower rate of polymeriza-
tion observed in the case of NVK is due to steric hindrance
to propagation. It can be observed from the data presented
in Table 1 that the molecular weight of the PNVK formed is
less (only oligomers are formed) while PCMA of high molec-
ular weight is easily formed, but the agreement between
expected molecular weight and that from GPC is less.
The detailed kinetic data from the polymerization of NVK
and CMA are given in the Tables 2 and 3.
The plot showing the evolution of the molecular weight and
PDI with time of polymerization as well as monomer conver-
sion is shown in Figures 2 and 3. It is evident from the data
that as the polymerization time increases the percentage of
monomer conversion and molecular weight increases line-
arly, which is in tune with typical living radical polymeriza-
tion and the Mn(GPC) and the Mn (expected) values are in
good agreement. The lower PDI values that remain almost
From these results, discussed above, it may inferred that
SET–RAFT method is a useful and simple tool for the synthe-
sis of carbazole-based methacrylate polymers. However, in
certain cases, SET-RAFT method gives poorer conversion
compared with SET-LRP, which may be attributed to the
presence of CTA that not only enables control but slows
down the polymerization as well.
FIGURE 3 Kinetics plot of
%
conversion versus molecular
FIGURE 5 GPC traces for kinetics of carbazole methacrylate
obtained with an increase in polymerization time under single
electron transfer-radical addition fragmentation chain transfer
(SET-RAFT) using CTA. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
weight (Mn) and PDI (right) showing the polymerization of car-
bazole methacrylate at RT via single electron transfer-radical
addition fragmentation chain transfer (SET-RAFT) in the ratio
300:1:2:2:2. [CMA]/[RX]/[CTA]/Cu(0)/[PMDETA] in DMSO.
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FIGURE 6 GPC traces of PCMA and PNVK macroinitiator [single electron transfer-radical addition fragmentation chain transfer
(SET-RAFT) at ambient temperature] and block copolymer P(CMA-b-FMA) and P(NVK-b-FMA) (ATRP) [FMA]/MI/Cu(I)Br/PMDETA at
RT in DMF. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
FIGURE 7 Fluorescence emission spectra of homo polymer and the block copolymer in THF; 10ꢁ5 mole/L (excited at 340 and
350 nm). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
FIGURE 8 UV–vis absorption spectra of the monomers, homo and the block copolymers (A) and absorption-emission spectra of
PCMA (B). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
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FIGURE 9 Scanning electron microscopy (SEM) images of the block copolymers P(CMA-b-FMA) and P(NVK-b-FMA) in THF at the
concentration of 10 mg/mL.
constant throughout the polymerization may be attributed to
less competitive termination reactions in the presence of
CTA and the Cu(II).
increase in the time of polymerization as shown in Figures 4
and 5.
The living nature of SET-RAFT polymerization was further
confirmed by synthesizing diblock copolymers from the
homopolymers macroinitiators. A flavanone-based monomer
(4-oxo-2-phenyl chroman-7yl-methacrylate) (FMA) was used
Furthermore, the living nature of the polymers are evident
by the evolution of GPC chromatogram with the polymeriza-
tion time, which shows the shift in molecular weight with an
TABLE 4 Summary of the Observations Made from the Controlled Radical Polymerization of Carbazole-Based Monomers
S. No. System Polymerization Observation
1.
2.
Ethyl bromoisobutyrate,
ATRP
ATRP
No Polymerization at RT; only
N-vinylcarbazole, Cu(I)Br, PMDETA, RT
oligomers obtained
Ethyl bromoisobutyrate,
N-vinylcarbazole, Cu(I)Br, bpy, 80 ꢀC
Polymerization observed at higher temperature
(80 ꢀC) with a conversion of 58% and narrow
PDI (< 1.25)
3.
4.
Ethyl bromoisobutyrate,
SET-LRP
Polymerization observed at RT, with a conversion
of 10% and broader PDI (1.38–1.42)
N-vinylcarbazole, Cu(0), PMDETA, RT
Ethyl bromoisobutyrate, N-vinylcarbazole,
SET-RAFT
Polymerization observed at RT, with lower
conversion of 8% and narrow PDI (1.19–1.25)
Cu(0), PMDETA, RT
5.
6.
7.
Ethyl bromoisobutyrate, (3-(9H-carbazol-9-yl)propyl
methacrylate, Cu(I)Br, Me6TREN, RT
ATRP
Polymerization observed at RT, with a conversion
of 64% and less control in PDI (1.29–1.35)
Ethyl bromoisobutyrate, (3-(9H-carbazol-9-yl)propyl
methacrylate, Cu(0), Me6TREN, RT
SET-LRP
Polymerization observed at RT, with a conversion
of 84% and broader PDI (1.3–1.42)
Ethyl bromoisobutyrate, (3-(9H-carbazol-9-yl-)propyl SET-RAFT
methacrylate, Cu(0), PMDETA, RT
Polymerization observed at RT, with a conversion
of 69% and narrow PDI (1.21–1.32)
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FIGURE 10 GPC curves showing the polymerization of N-vinylcarbazole and CMA under various CRP methods namely ATRP, sin-
gle electron transfer (SET)-LRP and newly developed SET-radical addition fragmentation chain transfer (RAFT). [Color figure can
be viewed in the online issue, which is available at wileyonlinelibrary.com.]
for this purpose. The block copolymerization was performed
via conventional ATRP, at ambient temperature, using
Cu(I)Br/PMDETA catalytic system. The evolution of GPC
chromatogram with the time for block copolymerization
shows the shift toward higher molecular weight region
[P(NVK-b-FMA) and P(CMA-b-FMA)] as shown in Figure 6. It
is clear from this result that a halogen end group is present
in the macroinitiators.
P(NVK-b-FMA) and P(CMA-b-FMA), are shown in Figure 7(b).
The emission spectra of the FMA shows two main peaks at
the shorter wavelength region around 405 and 430 nm and
the secondary peaks at the longer wavelength region around
460–485 nm, which may be attributed to the flavanone moi-
ety. The emission spectra of both the block copolymers are
dominated by the NVK and CMA moieties, respectively, con-
sistent with their compositions. In general, the emission
peaks are negative Stoke’s shifted, less sharp, broad and
structureless. The emission spectra of the block copolymers
are higher in intensity when compared with the homopoly-
mers, which may be attributed to the combination of
fluorescence emission from both the moieties. The band
gap energy (E) of the materials50,51 (PNVK and PCMA) was
determined from its UV–Vis absorption spectra, which are
estimated to be 3.5 and 3.49 eV, respectively, as shown in
Figure 8. The energy values obtained correlate well with
most of the semiconducting materials and hence the more
flexible PCMA, which forms a very good film, is likely to be a
processable semiconductor.
The carbazole group exhibits fluorescence and this property
was also used to monitor the polymerization. The fluores-
cence emission spectra of the monomers and the block
copolymers were recorded in THF at the concentration of
10ꢁ5 moles/L. These are shown in Figure 7. The emission
spectra of CMA shows two main peaks at the shorter wave-
length region around 380 nm and the secondary peaks at
the longer wavelength region around 420–490 nm, which
may be attributed to the sandwich excimer48 [fully over-
lapped structure of neighbouring carbazolyl chromophore;
Fig. 7(a)] and the second excimer (partially overlapped
structure).
The scanning electron microscopy (SEM) images of the block
copolymers P(NVK-b-FMA) and P(CMA-b-FMA), spin coated
from THF, are shown in Figure 9. Both the block copolymers
exhibit a microfibre like array that could arise from the rigid
NVK block.
The excimer band in the homopolymers (data not shown)
are very broad and this may be attributed to the carbazole–
carbazole overlap interaction within the polymer chain as
well as among the polymer chain.49 The fluorescence emis-
sion spectra of the FMA and the block copolymers, namely
CARBAZOLE-BASED VINYL AND METHACRYLATE MONOMERS, HARIDHARAN AND DHAMODHARAN
1029

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
The overall comparison of the polymerization of carbazole-
based vinyl and methacrylate monomers via ATRP, SET, and
the SET-RAFT method are illustrated in Table 4. The GPC
traces of the PNVK and PCMA synthesized from these meth-
ods are shown in Figure 10. In principle, the polymerization
of PNVK and PCMA through SET-RAFT have some advantages
including the possibilities of minimum number of dead
chains along with halogen end polymers and trithiocarbonyl
end group, easy conversion of halogen end group to a tri-
thiocarbonyl end group, control in the rate of polymerization
which polymerize faster in SET and ATRP condition and also
less competitive termination by CTA.
Synthesis of 4-Oxo-2-phenylchroman-7yl-methacrylate
(FMA)
The reactant (7-hydroxy flavanone), triethylamine, and THF
were added to a 250 mL RB flask with a magnetic stirrer.
The flask was purged with dry N2 gas, sealed and placed on
a salt ice-bath (ꢁ15 ꢀC). Methacryloyl chloride was then
added slowly to the reaction mixture through a syringe. The
ester formation reaction was allowed to continue, overnight, at
ambient temperature. The intermediate product was isolated
from the precipitated triethylamine salt and the solvent. The
final product was dissolved in DCM, rinsed with water, and
dried with anhydrous MgSO4. The product was then character-
1
ized by H NMR, 13C NMR, DEPT, and mass spectroscopies.
Yield: 72%; 1H NMR (400 MHz, CDCl3, d, ppm): 1.92 (s, 3H,
ACH3 adjacent to AC¼¼CA group), 6.23 (s, 1H, ethylene pro-
ton adjacent to AC¼¼O group), 5.6 (s, 1H, ethylene proton cis
to AC(¼¼O)AO-group), 5.758 (s, 1H, ethylene proton trans to
AC(¼¼O)AO-group), 7.83 (s, 1H, aromatic proton), 7.3 (m,
5H, aromatic proton), 6.76 (s, 1H, aromatic proton), 6.73 (d,
1H, aromatic proton), 5.3 (dd, 1H, aliphatic ACHA proton),
2.73–2.97 (dd, 2H, aliphatic proton). 13C NMR (100 MHz,
CDCl3, d, ppm): 17.29 (aliphatic CH3carbon), 137.4, 134.3
(ethylene carbon adjacent to AC¼¼O group), 161.3.39,
155.876, 125.034, 153.367, 117.713, 114.6, 110.132 (aro-
matic carbon), 163.633 (carboxyl carbon), 189.7 (carbonyl
carbon), 43.3, 78.9 (aliphatic carbon). DEPT (400 MHz,
CDCl3, d, ppm): The presence of CH3 protons around 17.2
ppm and ACH2 protons around 43.3 and 127.3 ppm and
ACH proton around 78.8, 110.13, 114.647, 125.162, and
127.845 is clearly identified. TOF-MS (m/z): The peak
appearing at m/z 309 (C19H16O4: molecular ions) confirmed
the structure of the monomer.
EXPERIMENTAL
Materials
NVK (98% Aldrich), copper(I) bromide, copper(I) chloride,
copper powder (Cu(0)), 1-butane thiol, 2-bromo isobutyric
acid, carbazole, NVK, 3-bromo-1-propanol, methacryolyl
chloride, 7-hydroxy flavanone, ethyl bromoisobutyrate, tris
(2-amino ethyl)amine, PMDETA, formic acid, and formalde-
hyde were purchased from Aldrich and were used as
received. Me6TREN was synthesized by using the available
literature report.52 Triethyl amine, tetrahydrofuran, anisole,
dimethyl sulphoxide, ethyl acetate, and hexane were distilled
and dried before use.
Synthesis of 2-(butylthio-carbonothioylthio)-2-
methylpropanoic Acid
A 250 mL 3-necked round bottom (RB) flask (fitted with
septum and reflux condenser (with N2 bubbler) was charged
with 60 mL of acetone and a solution of sodium hydroxide
(0.022 mol) in 15 mL of acetone/water mixture. The temper-
ature of the mixture was maintained between 5 and 15 ꢀC.
1-butane thiol (0.022 mol) was added over 10 min to the RB
flask and the mixture was stirred for 45 min. To this white
slurry, carbon disulfide (0.022 mol) was added over 15 min
and it was stirred for an additional period of 1 h, following
which it was allowed to warm to 20 ꢀC and stirred for fur-
ther period of 1 h. a0-bromoisobutyric acid (0.022 mol) was
then slowly added and the mixture was stirred for 24 h. The
reaction mixture was then poured in to water, which was
then followed by extraction with ethyl acetate. The combined
extracts were dried with anhydrous magnesium sulphate fil-
tered and the solvent was removed. The crude product was
recrystalized several times with hexane to provide pure 2-
Synthesis of (3-(9H-carbazol-9-yl-)propyl
Methacrylate (CMA)
The reactant (3-(9H-carbazol-9-yl-)propan-1-ol), triethylamine
and pyridine were added to a 250 mL RB flask equipped with
a magnetic stir bar. The flask was purged with dry N2 gas,
sealed and cooled to 8 ꢀC. Methacryloyl chloride was then
added slowly to the reaction mixture through a syringe. The
ꢀ
ester formation was allowed to continue, for 1 h at 10 C and
2 h, at room temperature. The intermediate product was iso-
lated from the precipitated amine salt and washed succes-
sively with NaOH (5% solution in water). The final product
was dissolved in DCM, rinsed with water and dried with anhy-
drous MgSO4. The product was recrystalized twice from meth-
anol to give white crystals. The product was then character-
(butylthio-carbonothioylthio)-2-methylpropanoic acid as
yellow color solid.
a
1
ized by H NMR, 13C NMR DEPT and mass spectroscopies.
Yield of CTA: 73%
Yield: 55%; 1H NMR (400 MHz, CDCl3, d, ppm): 1.88 (s, 3H,
ACH3 protons), 2.15 (quintet, 2H, ACH2 protons), 4.06 (t, 2H,
ACH2 protons), 4.33 (t, 2H, ACH2 protons), 5.51 (s, 1H, ethyl-
ene proton), 6.04 (s, 1H, ethylene proton), 7.15 (t, 2H, aromatic
proton), 7.32 (d, 2H, aromatic proton), 7.35 (t, 1H, aromatic pro-
ton), 7.9 (d, 1H, aromatic proton). 13C NMR (100 MHz, CDCl3, d,
ppm): 17.3, 27.9, 38.5, 60.8 (aliphatic CH3 and CH2 carbon),
139.2 (ethylene carbon adjacent to AC¼¼O group), 128.342,
135.292 (ethylene carbon), 135.1, 124.7, 121.9, 119.3, 113.0,
1H NMR (400 MHz, CDCl3, d, ppm): 0.92 (t, 3H, ACH3, 1.42
(sextet, 2H, ACH2, 1.6 (quintet, 2H, ACH2, 1.7 (s, 6H,
AC(CH3)2, 3.2 (t, 2H, SACH2). 13C NMR (100 MHz, CDCl3, d,
ppm): 220.8 (C¼¼S), 178.8 (C¼¼O), 55.6(SAC (CH3)2), 36.7
(SACH2), 25.2 (CH3)2, 13.6 ACH3 carbon. DEPT (400 MHz,
CDCl3, d, ppm): The presence of CH3 protons around 25.2
and 13.6 ppm and ACH2 protons around 36.7, 29.8, and
24.9 ppm is clearly identified.
1030
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
107.3 (aromatic carbon), 166.12 (carbonyl carbon). TOF-MS (m/
z): The peak appearing at m/z 293 and 295 (C19H19NO2: molec-
ular ions) confirms the structure of the monomer.
then added and the solution was stirred until the copper com-
plex formed. Polymerization was performed for the desired pe-
riod of time at ambient temperature (30 C). The product was
ꢀ
purified by passing through Al2O3 column and then precipi-
tated in to methanol. The resulting polymers were character-
ized by H NMR and GPC measurements.
Polymerization of NVK or 3-(9H-carbazol-9-yl)propyl
Methacrylate (CMA) via ATRP
1
The copper halide catalyst and the monomer (NVK or CMA as
the case may be) were added to a flame dried Schlenk tube
equipped with a magnetic stirring bar. The flask was then sealed
with a rubber septum and it was evacuated and back filled with
argon, twice. The ligand was then added and the solution was
stirred until the copper complex formed. After the complex for-
mation, the initiator/macro initiator was added and the mixture
was stirred at room temperature. After the predetermined time
interval, the polymerization was stopped by dilution with THF.
The polymer was precipitated by using excess methanol and
dried under vacuum. The copper complex in the polymer was
removed by passing the polymer solution in THF through a neu-
tral alumina column. The solution obtained was used for the
determination of molecular weight and polydispersity.
Methods
1
The H NMR, DEPT, and 13C NMR spectra were recorded on a
Bruker Avance 400 spectrometer (400 MHz for 1H and 100
MHz for 13C). Spectra in solution were recorded in CDCl3, at
room temperature. UV–Visible absorption spectra were meas-
ured on a JASCO UV-Visible 530 spectrometer. The mass spectra
were performed using
a Q-TOF micromass spectrometer
(WATERS) with electrospray ionization. The molecular weight
data were recorded on a WATERS GPC equipped with three
columns of average pore size 103, 104, 105 Å (particle size 5
lm) and connected in series. Tetrahydrofuran (THF) was used
as the eluent, at the flow rate of 1 mL/min. Detection was per-
formed using a refractive index detector (2410 WATERS). Nar-
row molecular weight polystyrene standards were used for cal-
ibration and data analysis was performed using Empower
software (WATERS). Fluorescence spectra were recorded on a
FluoroMax-4 spectrofluorimeter (HORIBA Jobin Yvon) under
the following conditions: excitation wavelength 340 and 360
nm, scan speed ꢁ80 nm/sec, excitation and emission slit width
of 5.0 nm. The high resolution SEM was performed using a FEI
Quanta 200 Scanning Electron Microscopy operating at 30 kV.
Polymerization of NVK or 3-(9H-carbazol-9-yl)propyl
Methacrylate (CMA) via SET
In a dry Schlenk tube, Cu(0) powder (0.011 g, 1.73 ꢂ 10ꢁ4
mol) was taken along with the monomer (NVK or CMA as the
case may be) (1.818 g, 0.0174 mol) and the desired quantity of
DMSO. The tube was purged with nitrogen. The ligand (0.0298
g, 1.72ꢂ 10ꢁ4 mol) was added to the Schlenk tube. It was then
subjected to freeze thaw-cycle. Finally, the initiator, ethyl bro-
moisobutyrate (0.022 g, 8.89ꢂ 10ꢁ5 mol) was added. The poly-
merization was allowed to proceed for prescribed period. After
the polymerization, the solution was diluted with THF and the
polymer was recovered by precipitating in excess of methanol.
It was purified by passing the polymer solution in THF through
CONCLUSIONS
Two novel monomers with fluorescent groups, CMA, and FMA
are synthesized and characterized. SET-RAFT method is a sim-
pler tool to produce methacrylate polymers with carbazole
pendant group [PCMA] under ambient conditions in compari-
son with ATRP and SET-LRP. ATRP at higher temperature (80
ꢀC) is more suitable for the synthesis PNVK Well-controlled po-
lymerization with narrow molecular weight distribution (Mw/
Mn) < 1.25 is achieved. The polymerization rate of CMA fol-
lowed first order kinetics with respect to monomer conversion
and the molecular weight of the polymer increased linearly
with conversion. The controlled nature of the polymerization of
CMA by SET-RAFT is further demonstrated by the synthesis of
a diblock copolymer P(CMA-b-FMA). The pendant group in the
monomers exhibit fluorescence as expected. The excimer bands
in the homopolymers PNVK and PCMA were very broad, which
may be attributed to the carbazole–carbazole overlap interac-
tion. The emission spectra of the block copolymers P(NVK-b-
FMA) and P(CMA-b-FMA) shows higher intensity compared
with the homopolymers, which may be attributed to the combi-
nation of the fluorescence from both the moieties.
1
the alumina column. It was characterized by GPC and H NMR.
Polymerization of NVK or 3-(9H-carbazol-9-yl)propyl
Methacrylate (CMA) via SET-RAFT polymerization
In a dry Schlenk tube, Cu(0) powder (0.011 g, 1.73 ꢂ 10ꢁ4 mol)
was taken along with monomer (NVK or CMA as the case may
be) (1.818 g, 0.0174 mol) and the desired amount of DMSO. It
was purged with nitrogen. The ligand (0.0298 g, 1.72 ꢂ 10ꢁ4
mol) was then added followed by the addition of the CTA (0.023
g, 8.94 ꢂ 10ꢁ5 mol). The Schlenk tube was then subjected to
freeze-thaw cycle. Finally, the initiator, ethyl bromoisobutyrate
(0.023 g, 8.94 ꢂ 10ꢁ5 mol) was added. The polymerization was
allowed to proceed for the prescribed period. After the polymer-
ization, the solution was diluted with THF and the polymer was
recovered by precipitating in excess of methanol. It was purified
by passing a solution of the polymer in THF through alumina
column. It was characterized by GPC and 1H NMR.
Synthesis of Block Copolymers via ATRP
The required quantity of the copper catalyst and the macroini-
tiator [PNVK or PCMA as the case may be from SET-RAFT]
were added to a flame dried Schlenk tube equipped with a
magnetic stirring bar. The flask was then sealed with a rubber
septum and it was evacuated and back filled with argon, twice.
The solvent (DMF) and the degassed monomer (FMA) in DMF
were then added through a cannula. The ligand PMDETA was
The authors thank the Department of Science and Technology,
India for support. This work was supported by the DST, India.
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