Synthesis of block and graft copolymers of styrene by raft polymerization, using dodecyl-based trithiocarbonates as initiators and chain transfer agents

Article abstract of DOI:10.1002/pola.26466

A series of dodecyl-based monofunctional trithiocarbonate chain transfer agents (CTAs) were successfully synthesized, toward the reversible addition-fragmentations chain transfer (RAFT) polymerization of styrene. The CTAs were used as initiators for RAFT

Full text of DOI:10.1002/pola.26466

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Synthesis of Block and Graft Copolymers of Styrene by RAFT
Polymerization, Using Dodecyl-Based Trithiocarbonates as
Initiators and Chain Transfer Agents
Kannukaran Ponnusamy, Rajendran Prakash Babu, Raghavachari Dhamodharan
Department of Chemistry, Indian Institute of Technology Madras, Chennai 600 036, Tamil Nadu, India
Correspondence to: R. Dhamodharan (E-mail: damo@iitm.ac.in)
Received 25 October 2012; accepted 31 October 2012; published online 4 December 2012
DOI: 10.1002/pola.26466
ABSTRACT: A series of dodecyl-based monofunctional trithiocar-
bonate chain transfer agents (CTAs) were successfully synthe-
sized, toward the reversible addition-fragmentations chain
transfer (RAFT) polymerization of styrene. The CTAs were used
as initiators for RAFT polymerization, in the absence of the con-
ventional free radical initiator, at higher temperature. Polysty-
rene (PS) of narrow polydispersity index (PDI) is synthesized.
Subsequently, poly(styrene-b-benzyl methacrylate) diblock and
poly(styrene-b-benzyl methacrylate-b-2-vinyl pyridine) triblock
copolymers were synthesized from the PS macro-RAFT agent by
simply heating with the second and third monomer, respec-
tively. These experiments suggest that it should be possible to
control the RAFT polymerization initiated by a CTA through the
adjustment of the temperature of polymerization in such manner
that initiation is tailored to proceed at faster rate (at higher tem-
perature) in comparison to propagation (lower temperature). For
the specific CTAs studied in this work, the polymerization rate of
styrene was high in the case of the reinitiating cyano (CN)-sub-
stituted group (R group) compared to the other groups studied.
The results further show that 4-cyano pentanoic acid group is
superior to the other R groups used for the RAFT polymerization
of styrene, especially based on the polydispersity at a given con-
version as well as the variation in the expected and experimental
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number-average-molecular weights.
2012 Wiley Periodicals,
Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 1066–1078
KEYWORDS: benzyl methacrylate; chain transfer agents; diblock
copolymer; graft copolymer; homopolymer; p-chloromethyl
styrene; polystyrene; RAFT polymerization; triblock copolymer;
trithiocarbonates; 2-vinyl pyridine
INTRODUCTION Controlled/‘‘living’’ radical polymerization
techniques is a versatile tools for the synthesis of a verity of
polymers with controlled molecular weight, molecular
weight distribution (MWD), and well-defined macromolecu-
lar architectures.1–5 Some of the efficient methods used
nowadays frequently are nitroxide-mediated polymerization6
(NMP), atom transfer radical polymerization2,7 (ATRP), re-
versible addition-fragmentations chain transfer5,8 (RAFT),
single electron transfer9 (SET), and single electron transfer-
reversible addition-fragmentation chain transfer (SET-
RAFT).10ꢀ12 Among these methods, ATRP and RAFT have
emerged as the most successful techniques due to their
applicability to a wide range of monomers and mild reac-
tions conditions.2,13 Recently, RAFT polymerization has
gained importance over the other methods mainly because
of its compatibility with a wide range of functional groups
such as acid, amide, amine, and epoxy containing mono-
mers.14–18 Various RAFT agents (dithioesters,5,19 dithiocarba-
mates,20,21 trithiocarbonates,22–27 and xanthats28,29) have
been effectively used as transfer agents to controlled molecu-
lar weights, MWD, and molecular architecture of polymeric
material prepared from a wide range of monomers. Trithio-
carbonate22–27-based chain transfer agents (CTAs) have been
found to be effective for most of the RAFT polymerization of
the vinyl monomers. The RAFT polymerization of styrene,
ethyl acrylate, 2-hydroxyethyl acrylate, and acrylic acid were
carried out successfully using S-1-dodecyl-S0-(a,a0-dimethyl-
a00-acetic acid)-trithiocarbonate (DDMAT) as a CTA and poly-
mers with narrow disparity (PDI ꢁ 1.16) were obtained.30
The ambient-temperature RAFT polymerization of styrene
and its functional derivatives, for example, 4-vinylbenzyl
chloride, N,N-diethyl vinylbenzylamine, and 4-vinylbenzyl
alcohol were carried out using (2,4,6-trimethylbenzoyl)
diphenylphosphine oxide as the photoinitiator along with
DDMAT under mild long wave UV–visible radiation or radia-
tion of longer wavelength.31 The temperature-responsive bio-
tinylated polymers poly(N-isopropylacrylamide) and water-
soluble poly[N-(2-hydroxypropyl)methacrylamide] have been
prepared in one step via RAFT polymerization using biotinyl-
ated trithiocarbonate as the RAFT agent.32 The temperature
responsive poly(DMA-b-NIPAAm) was successfully prepared,
in a controlled manner, at room temperature, by RAFT
Additional Supporting Information may be found in the online version of this article.
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polymerization using 4,40-azobis[2-(imidazolin-2-yl)propane]
dihydrochloride (VA-044) as the initiator and S-ethyl-S0-(a,a0-
dimethyl-a00-acetic acid)-trithiocarbonate as the CTA, and the
polymers obtained were reported to be narrow dispersed.33
The RAFT polymerization of 4-vinylbenzaldehyde was car-
ried out, at 70 ꢂC, using AIBN as the initiator and a trithio-
carbonate CTA (DDMAT). The resulting polymers were
shown to exhibit well-defined molecular weight and narrow
polydispersity index (PDI < 1.2).34 The polystyrene (PS) and
poly(acrylic acid) were synthesized, in a controlled manner,
using DDMAT as the CTA, resulting in a trithiocarbonate end
group on each of these polymers. The RAFT-generated poly-
mers were immobilized onto the surface of the gold nano-
rods with or without the use of reducing agents.35 The first
and somewhat sketchy report on the RAFT polymerization of
tioned here that the addition of AIBN or any conventional
free radical initiator in RAFT polymerization is a more prac-
tical approach to reduce the temperature of polymerization
because it enables the generation of relatively larger concen-
tration of the chain initiators. However, this in principle can
result in homopolymers and block copolymers with the ini-
tiator fragment (in the case of AIBN, it is isobutyronitrile end
group whose concentration could be slightly less than twice
the concentration of the initiator taking into consideration the
initiator efficiency factor). In thermal RAFT polymerizations,
where the CTA functions as both the initiator and the CTA,
pure homo and block copolymers can be obtained as the poly-
merization would involve only the insertion between the RAS
bonds in the CTA. Trithiocarbonate-based CTAs are easy to
synthesize compared to dithiobenzoates, and the yields
obtained are very high. As the dodecyl-based trithiocarbonates
showed less unfavorable odor compared to that of dithioben-
zoates, they have gained more importance these days, as CTAs
in RAFT polymerization.24,32,44,45 The crystalline nature of the
dodecyl-based CTAs provide an additional advantage for its
easier handling in RAFT polymerization. Recently, it was found
that the water-soluble polymers synthesized using trithiocar-
bonate-based CTA exhibited less cytotoxicity than those based
on dithiobenzoate.46
ꢂ
styrene at 110 C, in bulk, using 2-phenylpropan-2-yl benzo-
dithioate CTA, without the conventional free radical initiator,
was reported by Chiefari et al.5 The RAFT polymerization
methods is quite different from photoiniferter and thermal
iniferter methods.36 In thermal iniferter or photoiniferter po-
lymerization, the results obtained suggested that these poly-
merization proceed via living radical polymerization mecha-
nism. Mayo et al. have already reported that in the
polymerization of styrene at higher temperature (in the
range 156–190 ꢂC), styrene acts as a self-initiator.37 The
It is reported that the R group of a RAFT agent plays an im-
portant role in styrene RAFT polymerization kinetics38
whereas, in our hands, the effect of R group (from a pyraz-
ole-based dithiocarbamate CTA) on the RAFT polymerization
kinetics of styrene is negligible.47 To the best of our knowl-
edge, there is no report available on the kinetics of RAFT po-
lymerization of styrene using dodecyl-based trithiocarbonates
at higher temperature. The aforementioned factors prompted
us to study the effect of various R groups, in dodecyl-based tri-
thiocarbonates, on RAFT polymerization of styrene at higher
temperature. We demonstrate the synthesis by RAFT polymer-
ization of styrene and block copolymer of P(S-b-BnMA), P(S-b-
2-VP) as well as graft copolymers via RAFT polymerization in
an ‘‘R group’’ approach. It may be noted that in the literature,
PS comb polymers were prepared by using dithiobenzoate-
attached P(S-co-p-CMS), and the resultant polymers showed
multimodal GPC peaks.48 In this new methodology, we have
ꢂ
RAFT polymerization of styrene at 140 C in bulk as well as
in t-butanol (solution) using a,a0-dimethylacetic acid trithio-
carbonate CTA was reported by Lai et al.30 They reported
the synthesis of oligomeric PS with a number average molec-
ular weight (Mn) of 6709 and a PDI of 1.16. Subsequently,
Postma et al.38 reported the thermal RAFT polymerization of
styrene using n-butyl-based trithiocarbonates with the R
group ‘‘phthalimidomethyl,’’ in the absence of the conven-
tional free radical initiator. They observed that the molecular
weights of the polymers obtained were close to the expected
values, and the PDI values were low (PDI < 1.2), at higher
monomer conversion.38,39 The synthesis of copolymers of
styrene and L-proline-functionalized styrene, in bulk, by
thermal RAFT polymerization at 110 ꢂC was carried out
using S-1-dodecyl-S0-(1-phenyl ethyl) trithiocarbonate
(DPET) as the CTA, without the use of the conventional free
radical initiator.40 The polymerizations were observed to
proceed in a controlled manner as the PDI values of the
polymers were less than 1.15. These are the only reports
available in the literature on thermal RAFT polymerization
carried out in the absence of the conventional free radical
initiator at higher temperature. The block copolymer poly
(methyl acrylate-b-isobutyl vinyl ether) was synthesized
using S-1-isobutoxyethyl-S0-ethyl trithiocarbonate as the CTA
in a controlled manner by RAFT polymerization.41 The
block copolymer of poly(styrene-b-2-vinyl pyridine) and poly
(styrene-b-4-vinyl pyridine) was synthesized using benzyl
dithiobenzoate as CTA at 110 ꢂC with AIBN as initiator.42
Poly(ethylene glycol)-b-poly(styreneboroxole) sugar respon-
sive block copolymers, for insulin delivery applications, were
also successfully synthesized by RAFT polymerization (using
attached
4-cyano-4-(dodecylsulfanylthiocarbonyl)sulfanyl
pentanoic acid (CDSTSP) as pendant groups to P(S-co-p-CMS)
and synthesize the graft copolymer P(S-co-p-CMS)-g-PS by the
thermal RAFT polymerization method.
EXPERIMENTAL
Materials
Styrene (Aldrich, 99.9%) and benzyl methacrylate (Aldrich,
96%) were purified by passing through a column packed
with activated basic alumina, which removes the inhibitor
and any other acidic impurities. 2,20-Azobis (isobutyronitrile)
(AIBN, 98%) and 4, 40-azobis (4-cyanopentanoic acid) (75%)
purchased from Aldrich was recrystallized from methanol
and was placed in the refrigerator (ꢃ4 ꢂC). All the other
chemicals used in this study were purchased from Alfa Aesar,
Merck, and Lancaster. 2-Vinyl pyridines (Sigma Aldrich, 95%)
ꢂ
AIBN as the initiator, in THF, at 75 C) using a trithiocarbon-
ate-based CTA (PEG-attached DDMAT).43 It may be men-
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SCHEME 1 Synthesis of monofunctional dodecyl-based trithiocarbonate CTAs.
were vacuum distilled before use, and all other chemicals were
used without further purification. All the solvents used in this
study were purified using standard laboratory procedures.
S-1-Dodecyl-S0-((2-ethoxycarbonyl)-ethyl)
Trithiocarbonate
The synthesis of S-1-dodecyl-S0-((2-ethoxycarbonyl)-ethyl)
trithiocarbonate (DECET) was performed as described in the
synthesis of DPET except that ethyl a-bromopropionate (1.9
mL, 14.7 mmol) was used in the place of 1-phenylethyl bro-
mide. The crude product was separated using chromatogra-
phy on silica with 1–2% ethyl acetate in hexane as the elu-
ent to provide DECET as a dark yellow color solid and BDT
as a yellow color solid.
Synthesis of Dodecyl-Based Trithiocarbonate Chain
Transfer Agents
The general procedure used in the synthesis of the CTAs as
shown in the Scheme 1(a,b). The detailed synthetic proce-
dure associated with the synthesis of the docecyl-based tri-
thiocarbonate CTAs and the summary of the results from the
structural characterization studies are given below (1H NMR
and 13C NMR spectra are given in the Supporting Informa-
tion Figs. S1–S5).
1
Yield of DECET ¼ 56%. DECET, H NMR (CDCl3, d ppm, 400
MHz): d ¼ 4.8 (q, 1H, ASCHA), 4.2 (q, 2H, AOCH2A), 3.38
(t, 2H, ASCH2A), 1.7 (quintet, 2H, ASCH2ACH2A), 1.6 (d,
3H, ASCH(CH3)), 1.2–1.48 (remaining CH2 signals), 0.90 (t,
3H, ACH2CH3). 13C NMR (CDCl3, d ppm, 100 MHz): d ¼ 222
(C¼¼S), 170 (C¼¼O), 62, 48, 37, 32, 29 (overlapping signals),
28, 23, 17, 14.
S-1-Dodecyl-S0-(1-phenyl ethyl) Trithiocarbonate
A 250-mL, three-neck, round-bottom (RB) flask (fitted with
septum and reflux condenser with N2 bubbler) was charged
with 60 mL of heptane and a solution of potassium t-butox-
ide (1.644 g, 14.7 mmol) in 15 mL of THF. The temperature
of the reaction mixture was maintained between 5 and 15
ꢂC. n-Dodecylthiol (3.5 mL, 14.7 mmol) was added over 10
min to the RB flask, and the mixture was stirred for 45 min.
To this white slurry, carbon disulfide (CS2) (0.88 mL, 14.7
mmol) was added over 15 min, and it was stirred for a fur-
ther period of 1 h. After allowing the mixture to warm to 20
ꢂC, it was stirred for an additional period of 4.5 h. Then, 1-
phenyl ethylbromide (2 mL, 14.7 mmol) was slowly added,
and the mixture was stirred for 24 h. It was then poured
into water and extracted with ethyl acetate. The combined
extracts were dried with anhydrous magnesium sulfate and
filtered, and the solvent was removed by using a rotary
evaporator. The crude product was separated using chroma-
tography on silica with n-hexane as the eluent to provide
DPET as a dark yellow color liquid and bis(dodecyl) trithio-
carbonate (BDT) as a yellow color solid.
S-1-Dodecyl-S0-(2-cyanoethyl) Trithiocarbonate
NaOH (0.50 g, 12.5 mmol) was dissolved with stirring and
gentle heating in a mixture of dodecanethiol (3.0 mL, 2.5 g,
and 12.5 mmol), acetone (40 mL), water (5 mL), and tetra-
propylammonium bromide (0.27 g, 0.10 mmol). The result-
ing solution was cooled in an ice bath and treated with car-
bon disulfide (0.75 mL, 0.95 g, 12.5 mmol). After 20 min,
2-bromopropanenitrile (1.0 mL, 0.167 g, 12.5 mmol) was
added, and the mixture was stirred at room temperature for
12 h. The solution was evaporated to a quarter of the origi-
nal volume. After cooling, the water phase was separated
from the organic phase and washed with dichloromethane
(DCM) (3 ꢄ 50 mL). The combined organic phases were
dried over anhydrous sodium sulfate. After filtration, the sol-
vent was removed under reduced pressure and dried in vac-
uum, yielding a bright yellow liquid (50%). The compound
1
was characterized by H NMR and 13C NMR.
Yield of DPET ¼ 53%. DPET-1H NMR (CDCl3, d ppm, 400
MHz): d ¼ 7.3–7.5 (m, 5H, Ar-H), 5.4 (q, 1H, ASCHA), 3.4 (t,
2H, ASCH2A), 1.85 (d, 3H, ASCH(CH3)), 1.7 (quintet, 2H,
ASCH2ACH2A), 1.3–1.5 (remaining CH2 signals), 0.96 (t, 3H,
ACH2CH3). 13C NMR (CDCl3, d ppm, 100 MHz): d ¼ 224
(C¼¼S), 140, 128.6, 127.7, 127.6, 50, 36.7, 32, 29 (overlap-
ping signals), 28, 23, 21, 14. Yield of BDT ¼ 28%. BDT-1H
NMR (CDCl3, d ppm, 400 MHz): d ¼ 3.4 (t, 2H, ASCH2A), 1.7
(quintet, 2H, ASCH2ACH2A), 1.2–1.47 (remaining CH2 sig-
nals), 0.90 (t, 3H, ACH2CH3). 13C NMR (CDCl3, d ppm, 100
MHz): d ¼ 225 (C¼¼S), 37, 32, 29 (overlapping signals), 28,
22.6, 13.5.
1H NMR (CDCl3, d ppm, 400 MHz): d ¼ 4.8 (q, 1H, ASCHA);
3.3 (t, 2H, ASCH2A); 2.8 (t, 2H, ASCH2ACH2A); 1.8 (d, 3H,
ASCH(CH3); 1.4 (m, 18H remaining CH2 signals); 0.8 (t, 3H,
ACH2CH3). 13C NMR (CDCl3, d ppm, 100 MHz): d ¼ 221.9
(C¼¼S); 120.0 (CN); 47.4; 39.2; 37.4; 31.9; 30.6; 29.6; 29.4;
29.3; 29.2; 29.1; 28.9; 27.9; 22.7; 16.6; 14.1.
4-Cyano-4 -(dodecylsulfanylthiocarbonyl)sulfanyl
Pentanoic Acid
The initial steps in the synthesis of CDSTSP were similar to
that described in the synthesis of DPET. The preliminary
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product formed in this case (by the reaction of the potas-
sium salt of n-dodecylthiol with carbon disulfide was an yel-
low slurry, which was reacted in portions with iodine (2.0 g,
7.9 mmol) over a 30-min period and stirred at room temper-
ature for 14 h. Distilled water was added, and the separated
organic phase was washed with a solution of sodium thiosul-
fate and brine solution. The organic layer was dried with an-
hydrous sodium sulfate and filtered. The solvent was evapo-
rated to provide 3.7 g of BDSTD as a yellow color solid.
BDSTD-1H NMR (CDCl3, d ppm, 400 MHz): d ¼ 3.3 (t), 3.1
(minor triplet), 2.6 (minor triplet), 1.62 (quintet), 1.18–1.4
(remaining CH2 signals), 0.80 (t).
until a constant weight was obtained. The conversion of sty-
rene was determined gravimetrically. The polymerization
reaction was followed kinetically. The polymer molecular
weight and PDI was characterized by GPC.
RAFT Polymerization of Styrene Using DCET, DSCPA, and
DPET as Initiator and Chain Transfer Agent at Higher
Temperature
A stock solution of 2.0 mL (1.818 g, 17 mmol) of styrene
and 0.0288 g (0.087 mmol) of DCET was prepared in poly-
merization ampoules. After the mixture was degassed under
vacuum, pure nitrogen gas was introduced into the tube,
which was subsequently immersed in an oil bath thermo-
stated at 140 ꢂC (initiation; stirred for 30 min followed by
lowering of temperature) and 90 ꢂC (propagation). At the
end of the reaction, each ampoule was quenched in cold
water and opened. The reaction mixture was diluted with
THF and precipitated into excess of methanol. At the end of
the reaction, each ampoule was quenched in cold water and
opened. The reaction mixture was diluted with THF and pre-
cipitated into a large amount of methanol. The polymer was
dried at room temperature in vacuum for at least 24 h until
a constant weight was obtained. The conversion of styrene
was determined gravimetrically. The polymerization reaction
was followed kinetically. Samples were withdrawn at differ-
ent reaction times. The polymer molecular weight and PDI
was characterized by GPC.
A solution of 4,40-azobis(4-cyanopentanoic acid) (3.10 g,
0.01108 mol) and the BDSTD (3.6335 g, 0.0066 mol) in ethyl
acetate (50 mL) was heated to reflux for 22 h. After the re-
moval of the volatiles in vacuo, the crude product was
washed with water and was crystallized from heptane, to
afford CDSTSP (4.162 g) as a pale yellow solid.
CDSTSP-1H NMR (CDCl3, d ppm, 400 MHz): d ¼ 10.7 (broad,
1H, ACOOH), 3.25 (t, 2H, ASCH2A), 2.26–2.68 (m, 4H,
ACH2CH2A), 1.81 (s, 3H, ACH3), 1.6 (m, 2H, ASCH2ACH2A),
1.1–1.4 (remaining CH2 signals), 0.80 (t, 3H, ACH2CH3). 13C
NMR (CDCl3, d ppm, 100 MHz): d ¼ 217.6 (C¼¼S), 177
(ACOOH), 120 (ACN), 47, 38, 34, 32.1, 30 (overlapping CH2
signals), 28, 26, 23.8, 21, 15.
2 -{[(Dodecylsulfanyl)carbonothioyl]sulfanyl}propanoic
Acid
RAFT Polymerization of Styrene Using DCET and DPET as
Initiator and Chain Transfer Agent at 150 8C
The initial part associated with the synthesis of 2-{[(dodecyl-
sulfanyl)carbonothioyl]sulfanyl}propanoic acid (DSCPA) was
similar to that used for DCET. In this case, 2-bromopropanoic
acid (1.13 mL, 1.91 g, 12.5 mmol) was added instead of 2-
bromopropanenitrile. The product obtained (a precipitate)
was filtered and recrystallized from petroleum ether to give
the desired trithiocarbonate (ꢂDSCPA) as fine yellow platelets
(3.33 g, 76%), Mp. 77.8–78.8 C.
A stock solution of 2.0 mL (1.818 g, 17 mmol) of styrene and
0.0288 g (0.087 mmol) of DCET was prepared in polymeriza-
tion ampoules. After the mixture was degassed by under vac-
uum, pure nitrogen gas was introduced into the tube, which
was subsequently immersed in an oil bath thermostated at
150 ꢂC. At the end of the reaction, each ampoule was
quenched in cold water and opened. The reaction mixture
was diluted with THF and precipitated into excess of metha-
nol. The polymer was dried at room temperature in vacuum
for at least 24 h, until a constant weight was obtained. The
conversion of styrene was determined gravimetrically. The po-
lymerization reaction was followed kinetically. Samples were
withdrawn at different reaction times. The polymer molecular
weight and PDI was characterized by GPC.
1H NMR (CDCl3, d ppm, 400 MHz): d ¼ 4.8 (q, 1H, ASCH);
3.3 (t, 2H, ASCH2); 2.8 (t, 2H, ASCH2); 1.85 (d, 3H, ASCH
(CH3)); 1.65 (q, 2H, ASCH2CH2); 1.3 (m, 16H, remaining CH2
signals); 0.8 (t, 3H, ACH2CH3). 13C NMR (CDCl3, d ppm, 100
MHz): d ¼ 221.9 (C¼¼S); 177.0 (COOH); 47.4; 39.2; 37.4;
31.9; 30.6; 29.6; 29.4; 29.3; 29.2; 29.1; 28.9; 28.5; 27.9; 22.7;
16.6; 14.1.
Synthesis of Linear Block Copolymers P(S-b-BnMA)
Using Polystyrene Macro-RAFT Agent
RAFT polymerization of Styrene Using DPET as Initiator
and Chain Transfer Agent
A stock solution of 2.0 mL (2.08 g, 11.8 mmol) of benzyl
methacrylate and 0.1774 g (0.039 mmol) of PS macro-RAFT
agent was prepared in polymerization ampoules. After the
mixture was degassed under vacuum, pure nitrogen gas was
introduced into the tube, which was subsequently immersed
A stock solution of 2.0 mL (1.818 g, 17 mmol) of styrene
and 0.0745 g (0.00435 mmol) of DPET was prepared, and
aliquots of 3.0 mL were placed in polymerization ampoules.
After the mixture was degassed under vacuum, pure nitro-
gen gas was introduced into the tube, which was subse-
quently immersed in an oil bath thermostated at 100 ꢂC.
Samples were withdrawn at different reaction times. At the
end of the reaction, each ampoule was quenched in cold
water and opened. The reaction mixture was diluted with
THF and precipitated into excess of methanol. The polymer
was dried at room temperature in vacuum for at least 24 h,
ꢂ
in an oil bath thermostated at 110 C. At the end of the reac-
tion, each ampoule was quenched in cold water and opened.
The reaction mixture was diluted with THF and precipitated
into excess of methanol. The polymer was dried at room
temperature in vacuum for at least 24 h, until a constant
weight was obtained. The conversion of block copolymer
P(S-b-BnMA) was determined gravimetrically. The polymer
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SCHEME 2 Chemical structure of the monomers and CTAs used in the polymer synthesis.
molecular weight and MWD or PDI was determined by gel
permeation chromatography (GPC).
under vacuum, pure nitrogen gas was introduced into the
tube, which was subsequently immersed in an oil bath ther-
mostated at 120 ꢂC. After a preset reaction time, the glass
tube was immersed into cold water and opened, diluted with
10 mL of THF, and precipitated into 400 mL of methanol.
The copolymer obtained by filtration was then dried under
vacuum, at room temperature for 24 h. The polymer molecu-
lar weight and MWD or PDI was determined by GPC.
Synthesis of Linear Block Copolymers P(S-b-2-VP) Using
Polystyrene Macro-RAFT Agent
A stock solution of 1.5 mL (1.46 g, 13.9 mmol) of 2-vinyl
pyridine and 0.0625 g (0.0195 mmol) of PS macro-RAFT
agent was prepared in polymerization ampoules. After the
mixture was degassed under vacuum, pure nitrogen gas was
introduced into the tube, which was subsequently immersed
Synthesis of CDSTSP-Anchored P(S-co-p-CMS)
ꢂ
in an oil bath thermostated at 120 C. At the end of the reac-
Poly(styrene-co-chloromethyl styrene) (0.7 g, ꢃ0.87 mmol)
was added to a RB flask containing 30 mL of THF and potas-
sium carbonate (0.4501 g, 3.3 mmol), and the suspension
was stirred gently for 10 min at room temperature. CDSTSP
(0.656 g, 1.62 mmol) was dissolved in 20 mL of THF in a
beaker and was then transferred to the RB flask. Tetra-n-
butyl ammonium iodide (0.60 g, 1.62 mmol) was added to
the RB flask, and the temperature was raised to 60 ꢂC and
maintained for 12 h. After cooling the reaction mixture, it
was concentrated and then rinsed with water and acetone.
The CTA-anchored polymer was redissolved in THF and pre-
cipitated in methanol. The yellow solid was dried under vac-
uum, at room temperature for 12 h.
tion, each ampoule was quenched in cold water and opened.
The reaction mixture was diluted with THF and precipitated
into excess of hexane. The polymer was dried at room tem-
perature in vacuum for at least 24 h, until a constant weight
was obtained. The conversion of block copolymer P(S-b-2-
VP) was determined gravimetrically. The polymer molecular
weight and MWD or PDI was determined by GPC.
Synthesis of Linear Block Copolymers P(S-b-BnMA-b-2-
VP) Using P(S-b-BnMA) Macro-RAFT Agent
A stock solution of 1.5 mL (1.46 g, 13.9 mmol) of 2-vinyl
pyridine and 0.052 g of P(S-b-BnMA) macro-RAFT agent was
prepared in polymerization ampoules, in DMF. After the mix-
ture was degassed under vacuum, pure nitrogen gas was
introduced into the ampoules, which was ꢂ subsequently
immersed in an oil bath thermostated at 120 C. At the end
of the prescribed time of reaction, each ampoule was
quenched in cold water and opened. The reaction mixture
was diluted with THF and precipitated into excess of hexane.
The polymer was dried at room temperature in vacuum for
at least 24 h, until a constant weight was obtained. The con-
version of block copolymers P(S-b-BnMA-b-2-VP) was deter-
mined gravimetrically. The polymer molecular weight and
MWD or PDI was determined by GPC.
Synthesis of P(S-co-p-CMS)-g-PS
Poly(styrene-co-p-chloromethyl styrene) macro-RAFT agent
(0.02 g) and styrene (4 mL, 35 mmol) was added to a dry
glass tube. After the mixture was degassed under vacuum,
pure nitrogen gas was introduced into the tube, which was
subsequently immersed in an oil bath thermostated at 110
ꢂC. After 2 h, the glass tube was immersed into cold water,
opened, diluted with THF, and precipitated into methanol.
The graft copolymers obtained by filtration were then dried
under vacuum, at room temperature for 24 h. The polymer
molecular weight and MWD or PDI was determined by GPC.
Synthesis of P(S-co-p-CMS) Using NMP Method
Characterization
The general procedure for the polymerization is as follows:
styrene (3.7 mL, 32 mmol), p-chloromethyl styrene (p-CMS)
(1.2 mL, 8.0 mmol), and TEMPO (0.0302 g, 0.10 mmol) were
added to a dry glass tube. After the mixture was degassed
Molecular weights and MWD or the PDI of the polymers
were determined by GPC measurements. GPC were per-
formed at room temperature on a Water GPC system with
Water 515 HPLC pump, three Phenomenox columns in series
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TABLE 1 Data for the Polymerizations of Styrene with
Dodecyl-Based Trithiocarbonate as CTAs in Bulk,
at 100 6 2 8C ([Styrene]0:[CTA]0 5 400:1)
RAFT Polymerization of Styrene with Monofunctional
Dodecyl-Based Trithiocarbonates
The thermal RAFT polymerization of styrene was carried out
in bulk, at 100 6 2 ꢂC, with dodecyl-based trithiocarbonate
CTAs with various R groups and [styrene]0:[CTA]0 ¼ 400:1.
The 1H NMR spectra of all the PS homopolymers showed
Time
(h)
Mn
Mn
CTAs
DPET
% Conversion (expected) (GPC)
PDI
signals at 3.25 (ASC(S)SCH2C11H23
)
and 4.6–5.0
3.0
28.9
47.3
52.6
23.4
30.1
38.3
46.6
23.1
38.9
49.5
28.0
36.5
48.8
12,420
20,100
22,300
10,100
13,200
15,150
22,560
10,000
16,575
21,000
12,100
15,600
20,700
9,100
1.38
(ACH(Ph)SC(S)SC12H25) ppm, corresponding to the presence
of active trithiocarbonate end functional groups. Further, it
also demonstrated the presence of the reinitiating R group
in all the cases suggesting that the initiation was by the ther-
mal homolysis of the CTA than a Mayo type mechanism.37
The 1H NMR spectra of all the polymer samples are shown
in Supporting Information Figures S6–S8. The expected mo-
lecular weight (Mn,ex) was calculated from the monomer con-
version (which in turn was determined by the mass of the
polymer formed), the initial ratio of the monomer to the
CTA, the molecular weight of styrene (Mw,st) and the molecu-
lar weight of the CTA (Mw,CTA), as follows:
9.0
14,900 1.42
16,200 1.45
14.0
2.0
DCET
6,920
1.48
4.0
10,940 1.37
12,100 1.38
15,550 1.39
8.0
10.0
2.0
DECET
7,830
1.38
6.0
11,120 1.41
18,300 1.43
10,800 1.41
14,400 1.41
18,500 1.44
12.0
CDSTSP 4.0
8.0
10.0
Mn;th ¼ ½Stꢅ0ꢄMw;st ꢄ conversion=½CTAꢅ0þMw;CTA
It is clear from the data presented in the Table 1 that the Mn
(GPC) is less than Mn (expected) for all the polymerizations,
and the PDI is between 1.37 and 1.48. This suggests that the
polymerizations are not well controlled. It is also very clear
from the Table 1 that, in CDSTSP-mediated thermal RAFT po-
lymerization of styrene, the Mn, GPC values are very close to
the Mn, expected values, in comparison with the other CTAs.
The plots of number-average-molecular weight (Mn) versus
monomer conversion are shown in Figure 1. As shown in
Supporting Information S9, the Mn increases linearly with
the monomer conversion. Although, before polymerization,
high pure nitrogen was used to continuously purge each po-
lymerization ampoule for at least 5–10 min and the CTA
used for polymerization reaction were very pure in nature,
the PDI values obtained are high. This suggests one of the
following: that the initiation step is (not faster than propaga-
tion or even equal to it) slower than the propagation step or
(guard column, 500, 103, and 104 Å; 5 -mm particle size) and a
‘‘Waters’’ 2487 dual k absorbance UV detector and 2414 RI de-
tector with Empower software data analysis package supplied
by Waters. THF was used as a solvent at a flow rate of 1 mL
minꢀ1. Narrow molecular weight PS standards were used for
calibrating the GPC. JASCO FTIR 410 (Japan) infrared spec-
trometer was used for recording IR spectra in the thin-film
form (the polymer was cast on a CsCl disc from a dilute solu-
tion in THF). A Bruker AV 400 and 500 (400 and 500 MHz for
proton) NMR spectrometer was used to record 1H and 13C
spectra and CDCl3 was used as the solvent. Thermal analysis
was performed using a TGA (TGA7 from Perkin Elmer, Q500
Hi-Res TGA from TA instruments), DSC (DSC7 from Perkin
Elmer, Q200 MDSC from TA instrꢂuments) thermal analysis sys-
ꢂ
tem between ambient and 800 C, at a heating rate of 10 C
minꢀ1 under flowing nitrogen atmosphere (50 mL minꢀ1).
RESULTS AND DISCUSSION
Synthesis of Monofunctional Trithiocarbonates
The dodecyl-based monofunctional trithiocarbonate CTAs were
synthesized from dodecane thiol using the reported procedures
as well as by following newer methods such as the use of potas-
sium t-butoxide as base, in heptane-THF solvent mixture. The
general synthetic procedure followed is given below in the form
of Scheme 1. The list of CTAs synthesized is presented in
Scheme 2. It is important to mention here that the synthesis of
monofunctional dodecyl-based trithiocarbonate CTAs with
different R groups (DPET, CDSTSP) have already been reported
in literature49,50 but the synthetic conditions reported in this
article is different. During the synthesis of the aforementioned
dodecyl-based monofunctional trithiocarbonates, BDT was
formed as a byproduct. The CTA CDSTSP was synthesized by
utilizing the previously reported procedure51 with slight modi-
fications and the synthetic methodology is given in Scheme 1.
FIGURE 1 Molecular weight versus monomer conversion for
the thermal RAFT polymerization of styrene, in bulk, at 100 ꢂC.
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SCHEME 3 The mechanism of the thermal RAFT polymerization.
the initial stages of the polymerization proceed by conven-
tional free radical polymerization and that controlled radical
polymerization assumes significance after a certain degree of
monomer conversion. The data for the CTAs DECT and
DECET, which produce more reactive initiating radicals in
comparison to DPET and CDSTSP CTAs, clearly suggest that
the initial stages of monomer conversion is dominated by
conventional free radical polymerization mechanism.
significant role for them in terms of polymerization rate or
control of polymerization as investigated for styrene mono-
mer via thermal RAFT method at higher temperature. How-
ever in the case of 4-cyano pentanoic acid as the R group,
the polymerization rate of styrene was higher compared to
all the other R groups studied, and its homolysis appears to
be best suited for the RAFT polymerization of styrene.
Among the dodecyl-based CTAs, the 1-cyano ethyl (R group;
DCET) gives polymers with low PDI compared to the others,
The ln([M0]/[Mt]) versus time of polymerization plots are
shown in Supporting Information Figure S9. This suggests a
first order dependence of the rate of polymerization with the
concentration of the monomer, except during the initial
stages of the polymerization. The curvature observed during
the initial stages of the polymerization suggests that the po-
lymerization might be taking place by the conventional free
radical polymerization during the initial stages. During the
initial stages of the polymerization, the monomer is present
in very large excess in comparison to the CTA concentration
and hence uncontrolled free radical addition might be taking
place (kt1 >> kt2 and kt3) as shown in Scheme 3.
whereas, in the case 4-cyano pentanoic acid
R group
(CDSTSP), the Mn, GPC values are very close to the Mn,
expected values. The GPCs of the homopolymers as a func-
tion of the time of polymerization are shown in Supporting
Information Figure S10. This suggests that the molecular
weight increases with the time of polymerization for all the
CTAs suggesting in turn the occurrence of controlled radical
polymerization during the periods investigated.
It could be concluded from these studies that the thermal
RAFT polymerization of styrene, initiated by the homolysis of
the CTAs, did not proceed to the degree of control that was
expected. This was perhaps due to the relatively slower rate of
The apparent rate constant of propagation of styrene
decreases in the following order CDSTSP (kapp ¼ 0.053 hꢀ1
)
)
> DCET (kapp ¼ 0.042 hꢀ1) ꢃDECET (kapp ¼ 0.041 hꢀ1
TABLE 2 Data for the Polymerizations of Styrene with DCET
and DPET as the CTAs and the Initiator, in Bulk at 150 6 2 8C
([Styrene] 0:[CTA] 0 5 200:1)
ꢃDPET (kapp ¼ 0.037 hꢀ1). In the range of conversion stud-
ꢂ
ied at 100 C, there is some induction period (during which
the conventional free radical polymerization appears to be
taking place) following which controlled radical polymeriza-
tion assumes significance, for all the CTAs used here. Similar
effect was observed in the RAFT polymerization of styrene
(degree of polymerization ¼ 50) mediated with 2-dodecyl-
sulfanylthiocarbonylsulfanyl-2-methylpropionic acid 3-azido-
propyl ester as a CTA and AIBN as the initiator, in DMF at 70
ꢂC, and the reason for the same was not addressed by the
authors.52 The thermal RAFT polymerization of styrene, at
140 ꢂC, mediated by DDMAT produces oligomers with low
PDI value (PDI ꢃ1.16) at higher conversion (ꢃ75%).5 The
analysis of the results reported here further indicates that
induction period is the largest for DPET, which produces the
most stable R radical, suggesting that the chain transfer con-
stant may be the lowest in this case. Further, among the R
groups (1-phenyl ethyl, 1-cyano ethyl and (2-ethoxy car-
bonyl) ethyl) investigated, there seems to be no specific and
Time
(min)
Mn
Mn
CTAs
DCET
% Conversion
(expected)
(GPC)
PDI
30
32
45
53
56
64
73
41
49
51
58
66
72
6,300
3,600
4,500
5,500
6,100
6,900
7,400
5,200
5,900
6,500
7,100
7,600
8,400
1.20
1.33
1.26
1.23
1.29
1.30
1.24
1.29
1.30
1.31
1.29
1.41
60
9,900
90
11,300
12,000
13,600
15,500
8,900
120
150
180
30
DPET
60
10,600
11,100
12,500
14,100
15,300
90
120
150
180
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FIGURE 2 Dependence of molecular weight versus monomer conversion (a), ln([M]0/[M]t) versus time (b) for the thermal RAFT po-
lymerization of styrene, using different CTAs in bulk at 150 ꢂC.
initiation in comparison to the rate of propagation as well as
due to competing conventional free radical monomer addition
during the initial stages of the polymerization. To address this
concern, the thermal properties of the CTAs were analyzed
using TGA and DSC, under nitrogen atmosphere, to study the
suitable temperature required to cleave the C-S bond. The TGA
results are shown in Supporting Information Figure S11. This
suggested that a temperature range 120–150 ꢂC may be suita-
ble for the initiation of the polymerization. The DSC studies
did not indicate any other specific physical transitions in the
CTAs, other than melting (where relevant, as shown in Sup-
porting Information Fig. S12)
temperature range 120–150 ꢂC may be appropriate for the
homolysis of the CTAs, the thermal RAFT polymerization of
ꢂ
styrene was performed at 150 C, in the bulk, with DCET and
DPET as the CTA for a [styrene] : [CTA] ratio of 200:1. The
0
0
monomer conversion and the polymer molecular weight and
MWD were determined for various periods. The conversion
data, molecular weight, and PDI are listed in Table 2.
It is very clear from the experimental data in Table 2 that
the Mn (GPC) is less than Mn (expected) for the two CTAs
(DCET and DPET) suggesting that the mechanism of thermal
polymerization may not be very different from what was
observed at 100 ꢂC, that is, the occurrence of conventional
free radical polymerization during the initial stages of the
polymerization followed by the controlled radical
ꢂ
Based on the thermal RAFT polymerization results at 100 C
and the thermal analysis of the CTAs, which suggested that a
FIGURE 3 GPC traces of polystyrene obtained with increase in time of polymerization using CTAs DCET (a) and DPET (b) in bulk,
at 150 ꢂC.
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TABLE 3 Data for the Polymerizations of Styrene with DSCPA,
DCET, and DPET as CTAs and the initiator, in Bulk, at 140 8C
ln([M]0/[M]t) versus time, are both good indications of the
controlled nature of the polymerization. The monomer con-
version with time [Fig. 2(b)] suggests that the conventional
free radical polymerization kinetics might be dominating the
first 1 h of the polymerization while controlled polymeriza-
tion kinetics starts beyond 1 h. The GPC traces of the poly-
mers obtained as a function of time of polymerization are
shown in Figure 3. The shifting of the peak maximum with
time again suggests that the chain ends are active and that
the polymerizations are controlled.
(30-min Time Period) and at 90 6 2 8C ([Styrene]0:[CTA]0
5
200:1)
Time (h)
at 90 ꢂC
%
Mn
Mn
CTAs
DCET
Conversion
(expected)
(GPC)
PDI
2.0
3.0
4.0
5.0
6.0
7.0
2.0
3.0
4.0
5.0
6.0
7.0
2.0
3.0
4.0
5.0
6.0
7.0
25
29
38
45
50
58
37
41
48
54
60
65
27
34
37
40
43
48
4,900
6,400
8,200
9,700
10,800
12,400
8,100
8,900
10,400
11,600
12,900
13,900
6,000
7,400
8,100
8,700
9,300
10,400
3,600
4,700
5,900
7,100
8,300
10,100
6,000
7,800
9,900
11,300
12,300
14,100
7,300
9,500
11,100
12,900
13,600
15,100
1.20
1.27
1.26
1.28
1.29
1.35
1.32
1.33
1.21
1.24
1.28
1.27
1.20
1.18
1.19
1.24
1.49
1.61
Based on the results of the thermal RAFT polymerization
carried out at 100 and 150 ꢂC and with the view to have
greater control over the thermal RAFT polymerization of sty-
rene, the initial part of the polymerization was carried out at
higher temperature (140 ꢂC) for shorter period while the
later part of the polymerization was carried out at lower
temperature (90 ꢂC) for a relatively larger duration. Thus,
the thermal RAFT polymerization of styrene was performed
(for shorter duration at 140 ꢂC and longer duration at 90
ꢂC), as described earlier, in the bulk, with a [styrene]0:[CTA]0
of 200:1. The monomer conversion and the polymer molecu-
lar weight and MWD after various periods were determined
and the same are listed in Table 3.
DPET
DSCPA
It can be seen from these data that the Mn (GPC) is less than
Mn (expected) for the CTAs DCET and DPET although the dif-
ference appears to be very narrow in the case of DPET. The
PDI remained narrow in most cases and is in the range 1.2–
1.3. The plots of number-average-molecular weight (Mn) ver-
sus monomer conversion and ln([M]0/[M]t) versus time are
shown in Figure 4(a,b). The linearity of the Mn GPC versus
monomer conversion suggests that the polymerization
proceeds in a controlled manner. The monomer conversion
versus time plot [Fig. 4(b)] suggests that the thermal RAFT
polymerization initiated by DPET proceeds without any
induction time for controlled polymerization suggesting that
polymerization. However, the PDI values are relatively less in
comparison suggesting that higher temperature favors the
chain initiation kinetics better than the chain propagation
during the initial stages of the polymerization. The Mn (GPC)
versus monomer conversion and the ln([M]0/[M]t) versus
time curves for these cases are shown in Figure 2(a,b). The
linearity of the Mn GPC versus monomer conversion and the
FIGURE 4 Dependence of molecular weight versus monomer conversion (a) ln([M]0/[M]t) versus time (b) for the thermal RAFT po-
lymerization of styrene, using different CTAS in bulk at 140 and 90 ꢂC.
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FIGURE 5 GPC traces of polystyrene obtained with increase in time of polymerization using CTAs (a) DSCPA (a), DCET (b), and
DPET (c) bulk, at 140 and 90 ꢂC.
the conditions identified are best suited for controlled poly-
merization of styrene. The GPC data for these polymeriza-
tions are shown in Figure 5. A control experiment was per-
formed with another DSCPA as the CTA. The structure of
DSCPA is similar to DCET in terms of radical stability and
these results are also shown in Table 3 and Figure 5. These
SCHEME 4 Synthetic route followed for the preparation of diblock and triblock copolymers from the homopolymer of styrene via
thermal RAFT polymerization at high temperature.
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TABLE 4 GPC Data for the Diblock and Triblock Copolymers of BnMA and 2-Vinyl Pyridine
Monomers
Macro-RAFT Agent
Time (h)
% Conversion
Mn (expected)
Mn (GPC)
PDI
BnMA
PS Mn ¼ 4,200, PDI ¼ 1.18
4.0
75
52
43
57,400
14,700
61,200
53,800a
13,500
59,900
1.51
1.32
1.58
2-Vinyl pyridine
PS Mn ¼ 4,200, PDI ¼ 1.18
12.0
11.0
2-Vinyl pyridine
P(S-b-BnMA) Mn ¼ 53,800, PDI ¼ 1.51
a
Molecular weight by MALDI-TOF ¼ 52,800.
data (Mn (GPC) < Mn (expected) and PDI increases with
time) suggest that DSCPA could be a better CTA than DCET
for the controlled radical polymerization of styrene.
mers and one triblock copolymer were synthesized from the
PS macro-RAFT agent as CTA using 2-vinyl pyridine and ben-
zyl methacrylate monomers in bulk and in solution at 110
and 120 ꢂC (Table 4). The thermal RAFT polymerization
method used is shown in Scheme 4.
Diblock and Triblock Copolymers
To demonstrate that the PS synthesized has active thiocarbo-
nylthio end groups for chain extension two diblock copoly-
The GPC traces of the two block copolymers P(S-b-BnMA),
P(S-b-2-VP), and triblock copolymer P(S-b-BnMA-b-2-VP)
thus obtained are shown in Figures 6 and 7. This shows that
the GPC traces of the block copolymers are shifted toward
higher molecular weight while the MWDs are broad relative to
the PS macro-RAFT agent. In the case of P(S-b-BnMA), the mo-
lecular weight is very high in comparison to P(S-b-2-VP),
because the benzyl methacrylate monomer polymerizes faster
compared to 2-vinyl pyridine, and this is also reflected by the
lower PDI of the P(S-b-2-VP). The thermogravimetric analysis
of the homopolymer and the diblock copolymer of P(S-b-
BnMA) shows decomposition around 320 ꢂC, corresponding to
BnMA block and one from 370 to 460 ꢂC, corresponding to the
PS block (in Supporting Information Fig. S13).
Synthesis of Graft Copolymers on P(S-co-p-CMS) Side
Chains via RAFT Method
The utility of the thermal RAFT polymerization toward the
synthesis of graft copolymers was also explored as shown in
Scheme 5. Thus, the random copolymer P(S-co-p-CMS) was
obtained via NMP with the Mn,GPC value of 17,800 and the
PDI value of 1.44. The 1H NMR spectrum of this polymer
confirms its structure (data shown in Supporting Information
FIGURE 7 GPC traces of the polystyrene, P(S-b-BnMA) macro-
RAFT agent, and the triblock copolymer P(S-b-BnMA-b-2-VP).
FIGURE 6 GPC traces of the polystyrene macro-RAFT agent
and the diblock copolymers P(S-b-BnMA) and P(S-b-2-VP).
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SCHEME 5 Synthesis of graft copolymers via RAFT polymerization from P(S-co-p-CMS).
Fig. S14; the chemical shift at 4.5 ppm is characteristic of
chloromethyl protons (CH2Cl) in p-CMS unit. The molar ratio
(F) of S to p-CMS in P(S-co-(p-CMS)) was calculated from the
the temperature for propagation and extending the duration
of propagation should in principle result in the synthesis of
polymers in a controlled manner. This in principle should also
enable the scaled up synthesis of block copolymers of complex
architecture through suitable programming of the polymeriza-
tion temperature, duration, and automatic injection of mono-
mers at the set intervals. For the specific CTAs studied in this
work, the polymerization rate of styrene was high in the case of
the reinitiating group 4-cyano pentanoic acid (R group) com-
pared to the other groups studied. The results further show
that 4-cyano pentanoic acid group is superior to the other R
groups used for the RAFT polymerization of styrene, especially
based on the polydispersity at a given conversion as well as the
variation in the expected and experimental number-average-
molecular weights. The suitability of the method is demon-
strated through the synthesis of diblock, triblock, and graft
copolymers by the thermal RAFT polymerization method.
1
results of H NMR, and the F value was found to be 6.3:1. In
addition to that, it was found that ꢃ22 p-CMS units are pres-
ent in a single random copolymer chain). The CTA CDSTSP
was anchored onto P(S-co-(p-CMS)), and the structure of the
same was confirmed by 1H NMR spectrum (data shown in
the Supporting Information Figure S15; The peak seen at 5.0
ppm is characteristic of A(CO)OCH2Ph protons in P(S-co-p-
CMS). From the 1H NMR, it was concluded that ꢃ4.6 RAFT
agents were anchored on a single P(S-co-p-CMS). The ther-
mal RAFT polymerization of styrene, in bulk, was performed
with the help of the CTA-anchored P(S-co-p-CMS). The result-
ing P(S-co-p-CMS)-g-PS shows bimodal distribution in the
GPC analysis with the Mn,GPC value of 1,13,000 and the PDI
value of 1.26. The bimodal nature of the graft copolymer
obtained may be, because of the chloromethyl group’s chain
transfer effect. However, for styrene graft copolymer synthe-
sis, performing RAFT polymerization in solvent medium or
using azo initiator for the initiation process can lower the
PDI value. As the chain transfer constant value for the R
group, 4-cyano pentanoic acid is high for all types of mono-
mers, this methodology can be utilized for anchoring func-
tional group containing acrylic or methacrylic monomers
directly on styrenic surface under suitable reaction condi-
tions. The GPC traces of P(S-co-p-CMS) and P(S-co-p-CMS)-g-
PS are given in Supporting Information Figure S16.
ACKNOWLEDGMENTS
The financial support of this work by the Department of
Science and Technology (DST), Government of India, is
gratefully acknowledged.
REFERENCES AND NOTES
1 B. M. Rosen, V. Percec, Chem. Rev. 2009, 109, 5069–5119.
2 K. Matyjaszewski, J. Xia, Chem. Rev. 2001, 101, 2921–2990.
3 M. Kamigaito, T. Ando, M. Sawamoto, Chem. Rev. 2001, 101,
3689–3746.
CONCLUSIONS
4 C. J. Hawker, A. W. Bosman, E. Harth, Chem. Rev. 2001, 101,
3661–3688.
The thermal RAFT polymerization of styrene was investi-
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