Selenium-substituted carbonates as mediators for controlled radical polymerization

Article abstract of DOI:10.1002/pola.26648

A series of selenium-substituted carbonates, S,Se-dibenzyl dithioselenocarbonate (DTSC), S,Se-dibenzyl thiodiselenocarbonate (TDSC), and Se,Se-dibenzyl triselenocarbonate (TSC), were synthesized and used as mediators in radical polymerization. The results indicate that these selenium-substituted carbonates can control the polymerization of styrene (St) and methyl acrylate, as evidenced by the number-average molecular weight that increased linearly with the monomer conversion, molecular weights that agreed well with the predicted values, and successful chain extensions. The treatment of the resultant polystyrene by hydrogen peroxide generated polymers with approximately half-reduced molecular weights, and the absence of carbonate groups and vinyl double bond-terminated chain ends. The polymerization with these selenium-substituted carbonates was the same polymerization mechanism as their analogue, the widely used S,S-dibenzyl trithiocarbonate. This work provided a flexible protocol to incorporate selenium into the polymer chain backbone. Specifically, the treatment of these polymers by oxidation produced clickable vinyl-terminated chain ends, which provided possibilities for further functionalization, for example, via a thiol-ene click reaction.

Full text of DOI:10.1002/pola.26648

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Selenium-Substituted Carbonates as Mediators for Controlled Radical
Polymerization
Jindong Zeng, Zhengbiao Zhang, Jian Zhu, Nianchen Zhou, Zhenping Cheng, Xiulin Zhu
Department of Polymer Science and Engineering, Jiangsu Key Laboratory of Advanced Functional Polymer Design and
Application, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou, 215123,
People’s Republic of China
Correspondence to: J. Zhu (E-mail: chemzhujian@suda.edu.cn) or X. Zhu (E-mail: xlzhu@suda.edu.cn)
Received 30 October 2012; accepted 4 February 2013; published online 15 March 2013
DOI: 10.1002/pola.26648
ABSTRACT: A series of selenium-substituted carbonates, S,Se-
dibenzyl dithioselenocarbonate (DTSC), S,Se-dibenzyl thiodisele-
nocarbonate (TDSC), and Se,Se-dibenzyl triselenocarbonate
(TSC), were synthesized and used as mediators in radical poly-
merization. The results indicate that these selenium-substituted
carbonates can control the polymerization of styrene (St) and
methyl acrylate, as evidenced by the number-average molecular
weight that increased linearly with the monomer conversion, mo-
lecular weights that agreed well with the predicted values, and
successful chain extensions. The treatment of the resultant poly-
styrene by hydrogen peroxide generated polymers with approxi-
mately half-reduced molecular weights, and the absence of
carbonate groups and vinyl double bond-terminated chain ends.
The polymerization with these selenium-substituted carbonates
was the same polymerization mechanism as their analogue, the
widely used S,S-dibenzyl trithiocarbonate. This work provided a
flexible protocol to incorporate selenium into the polymer chain
backbone. Specifically, the treatment of these polymers by oxida-
tion produced “clickable” vinyl-terminated chain ends, which pro-
vided possibilities for further functionalization, for example, via a
C
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thiol-ene click reaction. 2013 Wiley Periodicals, Inc. J. Polym.
Sci., Part A: Polym. Chem. 2013, 51, 2606–2613
KEYWORDS: living polymerization; Radical polymerization; re-
dox-responsive; reversible addition-fragmentation chain trans-
fer (RAFT) polymerization; selenium
organoselenium compounds, and organotellurium compounds
show similar activities in these radical-based carbon–carbon
bond formation reactions.15–17 Because of this property, these
organochalcogen compounds are widely used in the radical po-
lymerization reaction. Among the reported LRP techniques, the
organic chalcogenides have been one of the most “magic” medi-
ators. Sulfur-based organic compounds, especially the dithiocar-
bonyl compounds, have been widely used in the well-developed
RAFT polymerization.5,6,18 Similarly, organotellurium com-
pounds can be used as an effective mediator to control the poly-
merization of styrene (St), acrylates, and even less-active vinyl
monomers.7–9,19 The investigation of radical polymerization
behavior mediated by organoselenium compounds is still under
development.20–22 We recently found that P,P-diphenyl phosphi-
nodiselenoic acid benzyl ester can be used as the mediator in
the radical polymerization of styrene under UV irradiation.23
Polymers with controlled molecular weights and narrow molec-
ular weight distributions were obtained.
INTRODUCTION In past decades, the growing demand for func-
tionalized, structurally well-defined, polymeric materials has
been a driving force for the development of living/controlled
radical polymerization (LRP) techniques. There are three repre-
sentative LRP techniques, namely, atom transfer radical poly-
merization (ATRP),1,2 stable free radical polymerization
(SFRP),3,4 and reversible addition-fragmentation chain transfer
(RAFT) polymerization,5,6 which have been well-developed and
widely used in the synthesis of polymers with predetermined
structures. New LRP techniques are still being developed in the
pursuit of effective and versatile processes for the tailored syn-
thesis of polymers. Organotellurium-mediated living radical po-
lymerization (TERP),7–9 organobismuthine-mediated living
radical polymerization (BIRP),10,11 iodine-mediated radical po-
lymerization (IRP), 12,13 and reversible chain transfer catalyzed
polymerization (RTCP), 13,14 and so forth, have been developed
in recent years by adding different organic compounds as effec-
tive mediators.
Organoselenium compounds play important roles in biologi-
cal systems.24–26 Selenium-containing organic compounds
have been widely used in pharmacochemistry as antioxidants
The reaction between organochalcogen compounds and alkyl
radicals has been widely used in the synthesis of small organic
molecules. Many of the sulfur-containing compounds,
Additional Supporting Information may be found in the online version of this article.
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sodium/benzophenone ketyl under nitrogen before use.
Other chemicals were purchased from Shanghai Chemical
(China) and used as received. CSe2 was prepared by the
reaction of Se with an excess of CH2Cl2, in accordance with
the literature.33 S,S-dibenzyl trithiocarbonate (TTC) was pre-
pared in accordance with the literature.34
Synthesis of S,Se-Dibenzyl dithioselenocarbonate (DTSC)
A NaSeH solution was prepared by the reaction of NaBH4 (0.76
g, 20 mmol) with elemental selenium (0.78 mg, 10 mmol) in
anhydrous ethanol (30 mL) at 0 ꢀC for 30 min under an argon
atmosphere.35 For this solution, sodium hydroxide (0.45 g, 10
mmol) was added. The mixture was stirred for 15 min at 50
ꢀC, then carbon disulfide (5 mL) in THF (30 mL) was added.
The reaction was allowed for 3 h under stirring. Then, the mix-
ture was cooled to room temperature. After that, benzylchlor-
ide (2.55 g, 20 mmol) was added. The mixture was stirred for
an additional 3 h. Finally, the mixture was extracted with Et2O
and washed with water. The organic phase was dried over
anhydrous Na2SO4, filtered, and evaporated in a vacuum. The
residue was chromatographed on silica gel using hexane as an
eluent to give DTSC with a yield of 55.0%.
SCHEME 1 Illustrations of chemical structures of TTC, DTSC,
TDSC, and TSC.
glutathioneperoxidase (GPx) activity.27–29 Because of such
properties, in recent years selenium-containing polymers
have received attention for use as bio-related materials. For
example, Zhang and coworker synthesized selenide-contain-
ing block copolymers and investigated their dual redox re-
sponsive disassembly. The results indicated that their dual
redox responsiveness were superior to corresponding sul-
fide-containing block copolymers.30,31 A coordination respon-
sive selenium-containing block copolymer micelle system
was successfully fabricated by Xu et al.32
1H NMR (CDCl3, d, ppm) : 4.64 (s, 2H), 4.70 (s, 2H), 7.25–
7.40 (m, 10H); LCMS (ESI) m/z: calcd for C15H14S2Se,
337.9702; found: 338.9775 (1 H1). IR (C@S) 1060 cm21
.
Polymers functionalized with selenium can be easily prepared
by using organoselenium compounds as regulators in radical
polymerization. At the same time, the structures of the poly-
mers can be tailored with the characteristic properties of LRP.
As a premise, a full understanding of the polymerization
behavior mediated by organoselenium is important for the
potential application of selenium-containing polymers. In this
article, a series novel selenium-substituted carbonates, includ-
ing S,Se-dibenzyl dithioselenocarbonate (DTSC); S,Se-dibenzyl
thiodiselenocarbonate (TDSC); and Se,Se-dibenzyl triselenocar-
bonate (TSC) were designed and synthesized, as shown in
Scheme 1. These selenium-substituted carbonates were used
as mediators in radical polymerization. The polymerization
behavior and mechanism were explored and discussed. The
results demonstrate that the polymers mediated by these sele-
nium-substituted carbonates contained selenium-substituted
carbonate moiety in the middle of the polymer chain, similar
to their sulfur analogies, which favor their potential redox-
responsive behavior.
Synthesis of TDSC
Benzyl mercaptan (0.13 g, 1 mmol) was dissolved in triethyl-
amine (1.0 mL) under stirring. Then, a mixture of CSe2 (0.17 g,
1 mmol) and benzylchloride (0.13 g, 1 mmol) was added at 0
ꢀC during 30 min under an argon atmosphere. After stirring
for 3 h at room temperature, the reaction mixture was
extracted with Et2O and washed with water. The organic phase
was dried over anhydrous Na2SO4, filtered, and evaporated in
a vacuum. The residue was chromatographed on silica gel
using hexane as an eluent to give TDSC a yield of 45.5%.
1H NMR (CDCl3, d, ppm) : 4.60–4.72 (s, 4H), 7.25–7.40 (m,
10H). LCMS (ESI) m/z: calcd for C15H14SSe2, 385.9147;
found: 386.9224 (1 H1). IR (C5Se) 850 cm21, 872 cm21
.
Synthesis of TSC
The CSe2 (0.53 g, 3 mmol) was mixed with benzylchloride
(0.52 g, 4 mmol) and K2CO3 (0.62 g, 5 mmol) in DMSO/H2O
(v/v 5 4:1, 30 mL) at room temperature.36 The solution was
stirred at 0 ꢀC for 30 min under an argon atmosphere. The
reaction mixture was extracted with Et2O and washed with
water. The organic phase was dried over anhydrous Na2SO4,
filtered, and evaporated in a vacuum. The residue was chro-
matographed on silica gel using hexane as an eluent to give
TSC a yield of 37.5%.
EXPERIMENTAL
Materials
All chemicals (analytical grade) were purchased from Shang-
hai Chemical Reagents (China). Styrene was washed with an
aqueous solution of sodium hydroxide (5 wt %) three times
and then with deionized water until neutralization. Styrene
was dried with anhydrous magnesium sulfate, then distilled
under reduced pressure and kept in a refrigerator under 0
ꢀC. 2,20-Azoisobutyronitrile (AIBN, 98%) was recrystallized
from ethanol and kept in a refrigerator under 4 ꢀC. Diethyl
ether (Et2O) and tetrahydrofuran (THF) were distilled from
1H NMR (CDCl3, d, ppm) 4.72 (s, 4H), 7.25–7.40 (m, 10H).
LCMS (ESI) m/z: calcd for C15H14Se3, 433.8591; found:
434.8664 (1 H1). IR (C@Se) 852 cm21
.
Typical Procedures for RAFT Polymerization of Styrene
A dry 1.0 mL ampule was filled with styrene (0.5 mL, 4.37
mmol), DTSC (7.4 mg, 0.022 mmol), and AIBN (0.72 mg,
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TABLE 1 The polymerization of styrene in the presence of selenocarbonates in bulk at 60 ꢀC
a
Entry
Mediator
[St]0:[Mediator]0:[AIBN]0
Time (h)
Conv. (%)
Mn,GPC
Mn,th
Mw/Mn
1
2
3
4
5
6
7
8
9
DTSC
DTSC
DTSC
TDSC
TDSC
TSC
200:1:0.2
500:1:0.2
200:1:0.5
200:1:0.2
200:1:0.5
500:1:0.5
200:1:0.5
200:1:0.5
200:1:0.5
36
38
9
56.4
44.1
29.8
24.0
19.9
31.9
39.1
31.2
50.3
10,500
25,300
7,200
5,800
4,500
18,800
10,300
7,000
9,700
117,00
22,900
6,200
5,000
4,200
16,600
8,300
6,400
10,500
1.16
1.22
1.23
1.24
1.22
1.26
1.24
1.26
1.26
20
10
10
23
9
TSC
TTC
TTC
14
a
M
n,th 5 ([St]0/[selenocarbonate or thiocarbonate]0) 3 MSt 3 Conversion 1 Mselenocarbonate or thiocarbonate.
0.0044 mmol). The solution was deoxygenated by three
standard freeze-pump-thaw cycles. The ampoule was then
flame-sealed and placed into an oil bath, which was thermo-
set at the desired temperature. At timed intervals, the
ampule was immersed in ice water and then opened. The
contents were dissolved in 1 mL of THF and then precipi-
tated into 200 mL of methanol. The polymer was obtained
by filtration and dried at room temperature under a vacuum
to a constant weight. The conversion of styrene was deter-
mined gravimetrically.
solutions were determined on
spectrophotometer.
a
Shimadzu RF540
RESULTS AND DISCUSSION
The selection of a proper mediator in LRP was a prominent
factor toward both the polymerization controllability and the
functionality of obtained polymers. Organoselenium com-
pounds can control the radical polymerization of styrene.20–
23
The obtained polystyrene contained seleno-functionalized
end groups, which favor these polymers for potential bio-
related applications. In the current work, three selenium-
substituted thiocarbonates, DTSC, TDSC, and TSC, were syn-
thesized in moderate yields. The radical polymerizations of
styrene and methacrylate in the presence of these selenocar-
bonates were investigated.
Oxidative Hydrolysis of Polystyrene (PS)
A solution of PS (Mn,GPC 5 10,300, Mw/Mn 5 1.17, 0.05 g) and
hydrogen peroxide (30% in aqueous, 0.23 g) in THF (2 mL)
was stirred at room temperature under an argon atmos-
phere.20 After a week, the solution was poured into metha-
nol to precipitate. The polymer was collected by filtration
and dried at room temperature under a vacuum to constant
weight.
The polymerizations of styrene in the presence of these syn-
thesized selenocarbonates were investigated at 60 C in bulk
ꢀ
with AIBN as initiator. As shown in Table 1, the PS with mo-
lecular weights ranging from 4500 to 25,300 with a narrow
molecular weight distribution (Mw/Mn < 1.26) were obtained
in various conditions. The GPC traces of these polymers
were unimodal (Supporting Information Figs. S1–S4). GPC-
determined molecular weights were close to theoretical
ones, which revealed that molecular weights of PS can be
controlled both by the molar ratio of styrene to selenocar-
bonate and by the conversion. DTSC, TDSC, and TSC pro-
duced comparable polymerization results as did their
thiocarbonate analogue (i.e., TTC).
Typical Chain Extension Procedure
The procedure of the chain extension experiment was similar
to the polymerization procedure described above, except the
mediator was replaced by the obtained polystyrene.
Characterization
The number-average molecular weight (Mn) and molecular
weight distribution (Mw/Mn) of the resulting polymers were
determined using a Waters 1515 gel permeation chromato-
graph (GPC) equipped with
a refractive-index detector
(Waters 2414), using HR 1, HR 2, and HR 4 (7.8 3 300
mm2, 5 lm bead size) columns with molecular weights rang-
ing from 102 to 5 3 105 g/mol. THF was used as the eluent
at a flow rate of 1.0 mL/min at 30 ꢀC. GPC samples were
injected using a Waters 717 plus autosampler and calibrated
The polymerization profiles in the presence of these seleno-
carbonates were investigated. Figure 1 shows the polymer-
ization kinetics in the presence of different selenocarbonates
with the molar ratio of [St]0:[selenocarbonates]0:
[AIBN]0 5 200:1:0.5. For comparison, polymerizations in the
presence of a thiocarbonate, TTC, were also examined. Linear
kinetics were found in all of these polymerizations. Figure 1
shows the polymerization rates of styrene in the presence of
these mediators: the kpapp s of the polymerization of styrene
with TTC, DTSC, TDSC, and TSC were 0.056, 0.045, 0.041,
1
with PS standards purchased from Waters. The H NMR and
13C NMR spectrum of the polymer was recorded on an
INOVA 400 MHz nuclear magnetic resonance instrument
using CDCl3 as the solvent and tetramethylsilane (TMS) as
an internal standard. The UV–vis absorption spectra in THF
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FIGURE 1 ln([M]0/[M]) versus time for the polymerization of
styrene in the presence of selenocarbonate or thiocarbonate in
bulk at 60 ꢀC. [St]0: [selenocarbonate or thiocarbonate]0:
[AIBN]0 5 200:1:0.5, St 5 0.2 mL.
FIGURE 2 Dependence of Mn and Mw/Mn on the conversion of
styrene in the presence of selenocarbonate or thiocarbonate in
bulk at 60 ꢀC. [St]0: [selenocarbonate or thiocarbonate]0:
[AIBN]0 5 200:1:0.5.
and 0.029 h21, respectively. That is, when more sulfur atoms
in TTC were replaced by selenium atoms, the polymerization
rates were lower. This is explained by the different electronic
properties between the selenium and sulfur. The molecular
orbital of selenium, which is more flexible than that of sulfur,
favors a radical coupling reaction. The ab initio calculation
results also showed that the energy barriers for both alkyl
radical addition and fragmentation with organoselenium
compounds were less than those of the sulfur analogue,
which implies that the addition and fragmentation reactions
between alkyl radical and organoselenium compounds were
faster than those of sulfur analogue.16 The selenium substi-
tuted compounds showed a much larger transfer reaction
methyne adjacent to a sulfur or selenium atom was shown
at d 5 4.5–5.0 ppm in all these samples, which implies the
existence of sulfur or selenium functionalized groups in PS.
However, the chemical shifts of polymers mediated by TSC,
TDSC, DTSC, and TTC showed some difference due to the dif-
ferent functional groups [Fig. 3(b)]. For the polymer medi-
ated by TTC, the chemical shifts at 4.52–4.77 ppm were
obtained, which agrees with the literature.37 PS mediated by
TSC functionalized showed resonance peak values of 4.66
rate than the sulfur one, that is, 8 3 106 compared with 6 3
105
M
s21 15
. Thus, the possibility of side reactions, such as
21
the cross-termination between the propagating radical and
the intermediate radical, and the self-termination of the in-
termediate radical, would also increase in the case of seleno-
carbanate-mediated polymerization due to high reactivities.
The combination effect of the faster addition-fragmentation
reaction, along with the faster transfer reaction and higher
side reactions of selenium compounds, resulted in a poly-
merization rate slower than that of the sulfur one. The more
selenium atoms in these compounds, the slower polymeriza-
tion rate was observed. The molecular weights of the
obtained PS in these cases linearly increased with the con-
version as shown in Figure 2. The molecular weights deter-
mined by GPC were closed to the theoretical values with
narrow molecular weight distributions, in the range of 1.10–
1.30. These results imply that these seleno-substituted thio-
carbonate mediators can control the polymerization of sty-
rene. The controllability was comparable with the widely
used thiocarbonate, TTC.
FIGURE 3 1H NMR spectra of PS obtained with three seleno-
carbonate: TSC, TDSC, and DTSC or thiocarbonate, TTC in
CDCl3 (a). Full spectrum of PS-TSC (Mn,GPC 5 10,300, Mw/
Mn 5 1.24); (b) Enlarged spectra in the range of 4.0 to 5.2 ppm
1
The obtained PS was characterized by H NMR spectroscopy.
The typical spectrum for PS obtained from TSC was shown
in Figure 3(a). Supporting Information Figures S5–S7 show
other spectra. The characteristic resonance of protons at
of
PS-TSC
(Mn,GPC 5 10,300,
Mw/Mn 5 1.24),
PS-TDSC
(Mn,GPC 5 5800, Mw/Mn 5 1.24), PS-DTSC (Mn,GPC 5 10,500, Mw/
Mn 5 1.17), and PS-TTC (Mn,GPC 5 9700, Mw/Mn 5 1.26).
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FIGURE 4 GPC curves before and after chain extension using selenocarbonate–mediated PS as the macro-mediators at 60 ꢀC of 17 h
in bulk. Macro-mediators and reaction conversion: (a) PS-DTSC, [St]0:[PS-DTSC]0:[AIBN]0 5 800:1:0.5, conversion 5 33.5%. (b) PS-
TDSC, [St]0:[PS-TDSC]0:[AIBN]0 5 800:1:0.5, conversion 5 36.7%. (c) PS-TSC, [St]0:[PS-TSC]0:[AIBN]0 5 800:1:0.5, conversion 5 33.5%.
FIGURE 5 H2O2-oxidative homolysis of PS obtained from the selenocarbonates and thiocarbonates mediated polymerizations.
7 days, 25 ꢀC.
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SCHEME 2 Reaction route for the oxidative elimination of PS-TSC by H2O2.
ppm and 4.96 ppm. The PS from TDSC and DTSC mediated
polymerizations showed signals at 4.57–4.92 ppm and 4.53–
4.85 ppm, respectively. These results imply the successful
incorporation of selenium into the polymers.
original PS, and kept a similar Mw/Mn. These results indicate
that organosulfur and organoselenium functional groups
were located in the middle of the polymer chain, and the po-
lymerization mediated by selenocarbonates was via a RAFT
mechanism, similar to that mediated by thiocarbonates.
Chain extension investigations using these obtained polymers
as the macro-mediators were also performed. The results are
shown in Figure 4. Molecular weights of chain-extended poly-
mers were increased in all these results, that is, from 4600 to
28,900 in PS-DTSC, from 4600 to 29,300 in PS-TDSC, and from
8800 to 30,300 in PS-TSC. The GPC traces of these chain-
extended polymers showed one peak, which implies a high
degree of functional groups in original macro-mediators. In the
case of PS-TSC, the chain-extended polymer showed a slightly
broader molecular weight distribution than the macro-media-
tor, from 1.25 to 1.43, which implies that the controllability of
the selenocarbonates for styrene was slightly decreased after
the complete substitution of sulfur by selenium.
The vinyl group can be introduced into the polymer chain end
after the oxidative hemolysis, as shown in Scheme 2, according
to the literature.20,23 In this work, the structures of oxidized PS
were characterized by the 1H NMR spectrum. The typical spec-
trum for oxidized PS obtained from TSC is shown in Figure 6.
Other spectra are shown in Supporting Information Figures S8
and S9. The signals at about d 5 6.02–6.22 ppm (2H, integra-
tion5 I6.02–6.22 5 2.00) were ascribed to the vinyl protons at
the polymer chain end after the fragmentation of the triseleno-
carbonate group. The signals at about d 5 0.9–2.4 ppm (3H,
integration 5 I0.90–2.40 5 156.63) were ascribed to the protons
of the ethenyl of styrene units. As shown in Figure 6, no signals
arising from selenocarbonate moieties were found, indicating
that the selenocarbonate group was eliminated by treatment
with hydrogen peroxide. Furthermore, signals of the vinyl dou-
ble bond were found, which implies that the vinyl-terminated
PS were obtained after treatment, in agreement with the litera-
ture.20,23 The molecular weight calculated from the NMR spec-
trum, Mn,NMR, was calculated to be 5500 by the equation
Organosulfur and organoselenium compounds can be frag-
mented under oxidization conditions.20,23,30 To determine
the position of these functional groups in a polymer chain
and the exact polymerization mechanism, the polymers were
oxidized by the H2O2 solution at room temperature. Figure 5
shows the molecular weights and polydispersities of the
polymers before and after oxidation. GPC traces of the
treated PS shifted to about half the molecular weight of the
Mn,NMR 5 104 3 [(I0.9–2.40/3) /(I6.02–6.22/2) 1 1], which was
close to half the value of the molecular weight (10,700) of
the original PS. This result further confirmed that the sele-
nocarbonate moiety was located at the middle of polymer
chain, complying with the trithiocarbnate mediated PS.37–
39
This oxidative homolysis of the PS removed the labile
selenocarbonate moieties from the PS backbone. It gener-
ated a “clickable” vinyl-terminated PS, which provided a
protocol for further modification via the thio-ene click
reaction.40–42
The above results confirmed that the control polymerization
mediated by the selenocarbonates proceeded with the same
mechanism of thiocarbnate as reported.5,38,39,43 The mecha-
nism is shown in Scheme 3.
To explore the feasibility of these selenocarbonates for differ-
ent monomers, the polymerization of methyl acrylate (MA) in
the presence of selenocarbonats were also investigated. Table
2 shows the polymerization results using different mediators
under various conditions. Poly(methyl acrylate) (PMA) with a
molecular weight in the range of 11,800 to 50,300 was
obtained from moderate to high conversions (51.0–98.8%).
FIGURE 6 1H NMR spectrum of PS-TSC after oxidative homoly-
sis. (Mn,GPC 5 7400 g/mol, Mw/Mn 5 1.19) with CDCl3 as the
solvent.
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SCHEME 3 The reaction scheme for the RAFT polymerization using these selenocarbonate compounds as the mediator.
The GPC-determined molecular weights (Mn,GPC) were close to
the predicted values (Mn,th). The polymers showed narrow
molecular weight distributions, that is 1.09–1.38, except for
1.77 of polymers obtained using TSC as the mediator, which
in this case should be due to the high possibility of side
reactions.
of styrene and MA can be controlled using these selenocar-
bonates, and the controllability of these mediators is similar
to their sulfur analogue, TTC. Well-defined polymers with
seleno-functionalized structures in the middle of the chain
can be prepared. This work provided an alternative and easy
method to synthesize selenium-containing polymers with con-
trolled structure, which may have potential application in bio-
related materials. From another perspective, since the treat-
ment of these polymers by oxidation produced “clickable”
vinyl-terminated chain ends, it can provide possibility for fur-
ther functionalization, for example, via a thiol-ene click
reaction.
CONCLUSIONS
In this work, a series of selenocarbonates, DTSC, TDSC, and
TSC, were synthesized and utilized as mediators for the poly-
merization of styrene and methyl acrylate. The polymerization
TABLE 2 The polymerization of MA in the presence of selenocarbonates at 60 ꢀC in toluene solution
Entry
Mediator
Polymerization ratio
Time (h)
Con. (%)
Mn,GPC
Mn,th
Mw/Mn
1
2
3
4
5
6
7
8
TTC
500:1:0.2
200:1:0.5
200:1:0.5
1000:1:0.2
200:1:0.5
200:1:0.5
200:1:1
15
5
51.0
70.1
55.9
58.8
98.8
<1.0
75.8
81.5
24,300
14,600
11,800
50,300
23,000
–
21,900
12,100
9,600
52,600
17,000
–
1.13
1.12
1.13
1.09
1.38
–
TTC
DTSC
DTSC
TDSC
TSC
10
12
24
24
24
26
TSC
16,400
16,900
13,000
14,000
1.77
1.73
TSC
200:1:1
MA/toluene 5 2/1, v/v.
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ACKNOWLEDGMENTS
19 E. Mishima, T. Tamura, S. Yamago, Macromolecules 2012,
45, 298922994.
The financial support from the National Nature Science Foun-
dation of China (No. 21074082), the Priority Academic Pro-
gram Development (PAPD) of Jiangsu Higher Education
Institutions, and the Program of Innovative Research Team of
Soochow University is gratefully acknowledged.
20 T. S. Kwon, S. Kondo, H. Kunisada, Y. Yuki, Polym. J. 1998,
30, 559–565.
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