Reversible addition-fragmentation chain transfer polymerization of vinyl acetate under high pressure

Article abstract of DOI:10.1002/pola.27582

In this work, high molecular weight polyvinyl acetate (PVAc) (M_n,GPC = 123,000 g/mol, M_w/M_n = 1.28) was synthesized by reversible addition-fragmentation chain transfer polymerization (RAFT) under high pressure (5 kbar), using benzoyl peroxide and N,N-dimethylaniline as initiator mediated by (S)-2-(ethyl propionate)-(O-ethyl xanthate) (X1) at 35 C. Polymerization kinetic study with RAFT agent showed pseudo-first order kinetics. Additionally, the polymerization rate of VAc under high pressure increased greatly than that under atmospheric pressure. The "living" feature of the resultant PVAc was confirmed by ¹H NMR spectroscopy and chain extension experiments. Well-defined PVAc with high molecular weight and narrow molecular weight distribution can be obtained relatively fast by using RAFT polymerization at 5 kbar.

Full text of DOI:10.1002/pola.27582

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Reversible Addition-Fragmentation Chain Transfer Polymerization of Vinyl
Acetate Under High Pressure
Jing Chen, Xiaoning Zhao, Lifen Zhang, Zhenping Cheng, Xiulin Zhu
Suzhou key Laboratory of Macromolecular Design and Precision Synthesis, Jiangsu Key Laboratory of Advanced Functional Poly-
mer Design and Application, Department of Polymer Science and Engineering, College of Chemistry, Chemical Engineering and
Materials Science, Soochow University, Suzhou 215123, China
Correspondence to: Z. P. Cheng (E-mail: chengzhenping@suda.edu.cn), or L. F. Zhang (zhanglifen@suda.edu.cn)
Received 27 September 2014; accepted 28 January 2015; published online 5 March 2015
DOI: 10.1002/pola.27582
ABSTRACT: In this work, high molecular weight polyvinyl ace-
tate (PVAc) (Mn,GPC 5 123,000 g/mol, Mw/Mn 5 1.28) was synthe-
sized by reversible addition-fragmentation chain transfer
polymerization (RAFT) under high pressure (5 kbar), using ben-
zoyl peroxide and N,N-dimethylaniline as initiator mediated by
(S)-2-(ethyl propionate)-(O-ethyl xanthate) (X1) at 35 ꢀC. Poly-
merization kinetic study with RAFT agent showed pseudo-first
order kinetics. Additionally, the polymerization rate of VAc
under high pressure increased greatly than that under atmos-
pheric pressure. The “living” feature of the resultant PVAc was
confirmed by 1H NMR spectroscopy and chain extension
experiments. Well-defined PVAc with high molecular weight
and narrow molecular weight distribution can be obtained rela-
C
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tively fast by using RAFT polymerization at 5 kbar.
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KEYWORDS: high pressure; kinetics (polym.); living radical poly-
merization (LRP); reversible addition fragmentation chain trans-
fer polymerization (RAFT); vinyl acetate
sively.26–31 Stenzel et al.27 first used xanthate as the chain
transfer agent for RAFT polymerization of VAc. They found
that there should be alkoxy Z-group conjugated with carbon–
sulfur double bond to obtain stability and the R-group
should be a good leaving group with a comparable reactivity
toward the monomer like VAc. RAFT/MADIX showed good
controllability on the polymerization of VAc; but to synthe-
size high molecular weight PVAc still remains as a great
challenge.28–33
INTRODUCTION The past decades have witnessed the great
development of the controlled/“living” radical polymerization
(LRP) with a variety of monomers.1–9 Among these mono-
mers, vinyl acetate (VAc) has gained extensive attention due
to the wide applications of this kind of polymer poly(vinyl
acetate) (PVAc) in different areas, such as paints, adhesives,
additives to pharmaceuticals, and so on.10–13 Furthermore,
the largest volume water-soluble polymer poly(vinyl alcohol)
is also made commercially available by the hydrolysis of
PVAc. As an unconjugated monomer, the polymerization of
VAc can only follow the radical mechanism. However, the
very high reactivity of the propagating radicals makes VAc
one of the most challenging monomers for LRP, which usu-
ally results in relatively broad molecular weight distributions
and limitation of controlled molecular weights for the result-
ant PVAcs. Up to now, various LRP methods have been
applied for the polymerization of VAc, such as atom transfer
radical polymerization (ATRP),14,15 degenerative transfer
with alkyl iodides,16–18 iodine transfer radical poly-
merization,19 organotellurium-mediated chain transfer poly-
The use of high pressure reported in organic chemistry
expands our horizons and extends to the synthesis of poly-
mers.34 Actually, high pressure can facilitate to increase the
propagation rate coefficient of the polymerization kp by sev-
eral orders of magnitude and to decrease the overall activa-
tion volumes of 16–21 cm3 mol21 34
Under high pressure,
.
high molecular weight polymer can be obtained with accessi-
ble industrial polymerization process while the propagation
of free radicals was enhanced and termination was sup-
pressed.35 As reported by Penelle et al., poly(methyl methac-
rylate) (PMMA) has extremely high molecular weight
(>1,000,000 g/mol) and narrow molecular weight distribu-
tion (Mw/Mn 5 1.03) under high pressure (5 kbar).36 Later,
Fukuda and coworkers37 synthesized PMMA with a number-
average molecular weight Mn of 3,600,000 g/mol and a
molecular weight distribution of 1.24 via normal ATRP at 5
merization,20
organostibine-mediated
chain
transfer
polymerization,21 cobalt-mediated radical polymerization
(CMRP),22–25 and reversible addition-fragmentation chain
transfer (RAFT)26,27 polymerization. Among the above poly-
merization methods, RAFT/MADIX (macromolecular design
via the interchange of xanthates) was explored exten-
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SCHEME 1 The synthetic routes of xanthates with different Z- or R- groups, (a) X1, (b) X2, and (c) X3.
kbar. Recently, Matyjaszewski and coworkers38 applied acti-
vators generated by electron transfer for ATRP to high poly-
merization system and obtained high molecular weight
polystyrene with Mn more than 1,000,000 g/mol and molec-
ular weight distribution less than 1.25 at 6 kbar at room
temperature. However, to the best of our knowledge, there
have been no reports on the polymerization of unconjugated
monomers (e.g., VAc) under high pressure.
ethanol (40 mL, 0.645 mol), and CS2 (20 mL, 0.332 mol).
Finally, X1 (Scheme 1) was obtained by the reaction of
potassium O-ethyl xanthate (9.50 g, 59.3 mmol) and ethyl-2-
bromo-propionate (9.48 g, 52.4 mmol) in ethanol (30 mL)
under stirring at room temperature and purified by column
chromatography using hexane/ethyl acetate (95:5 v/v) as
the eluent. The yellow colored oily product X1 (7.83 g,
67.3% yield) was characterized by 1H NMR: 1H NMR (300
MHz, CDCl3, d): 4.66 (q, 1H; CH), 4.40 (q, 2H; C(O)OCH2),
4.23 (q, 2H;C(S)OCH2), 1.59 (d, 3H;CH3CH), 1.44 (t, 3H;
C(S)OCH2CH3), and 1.31 (t, 3H; C(O)OCH2CH3).
Whether can we realize the controlled polymerization of VAc
under high pressure to obtain high molecular weight and low
molecular weight distribution PVAc? To investigate the possi-
bility, in this contribution, we combine the advantages of high
pressure polymerization and controlled polymerization of VAc
with MADIX to demonstrate the RAFT polymerization of VAc
under high pressure at lower temperature (35 ꢀC) for the first
time, using benzoyl peroxide (BPO) and N,N-dimethylaniline
(DMA) as the redox initiators and (S)-2-(ethyl propionate)-(O-
ethyl xanthate) (X1) as the model RAFT agent.
Synthesis of (S)22-(Benzyl)-(O-methxypheny
xanthate) (X2)
X2 was synthesized according to the method reported by the
literature.40 Briefly, the product X2 (Scheme 1) was prepared
by the mixture of potassium O-methxypheny xanthate
(12.88 g, 57.9 mmol) and benzyl bromide (9.01 g, 52.7
mmol) in ethanol (30 mL) under stirring for 16 h at room
temperature. The resultant white precipitate was filtered off,
washed with diethyl ether and deionized water. Finally, a yel-
low colored powdered product (X2) (5.92 g, 41.0% yield)
EXPERIMENTAL
1
Materials
was obtained. The product X2 was characterized by H NMR:
1H NMR (300 MHz, DMSO-d6, d) 7.44 (m, 5H; Ar H), 6.96 (m,
4H; CH3AAr H), 5.10 (s, 2H; CH2), 3.76 (s, 3H; CH3).
VAc (>99%, Aldrich) was dried over calcium hydride and
then stored in the refrigerator. BPO (Chemical pure, Sino-
pharm Chemical Reagent) was purified by recrystallization.
DMA (>99%, Sinopharm Chemical Reagent) was used as
received. Ethyl 2-bromoisobutyrate (>98%) and ethyl 2-
bromopropionate (>98%) were purchased from Acros and
used as received. Benzyl bromide (>99%) was purchased
from Sinopharm Chemical Reagent. p-Cresol (Chemical pure,
Sinopharm Chemical Reagent) was purified twice by recrys-
tallization. Ethanol (analytical reagent), tetrahydrofuran
(THF, analytical reagent), n-heptane (analytical reagent),
ethyl acetate (EA, analytical reagent), and all other chemicals
were obtained from Shanghai Chemical Reagents (Shanghai,
China) and used as received unless mentioned.
Synthesis of (S)22-(Ethyl isobutyrate)-(O-ethyl
xanthate) (X3)
X3 was prepared according to the method reported by litera-
ture.30 Similarly, X3 (Scheme 1) was obtained by the reaction
of potassium O-ethyl xanthate (9.50 g, 59.3 mmol) and ethyl
2-bromoisobutyrate (10.26 g, 52.6 mmol) in ethanol (30 mL)
under stirring at room temperature and purified by column
chromatography using hexane/ethyl acetate (40:1 v/v) as
the eluent. A yellow colored oily product (X3) (7.10 g, 57.1%
yield) was obtained. The product X3 was characterized by
1H NMR: 1H NMR (300 MHz, CDCl3, d) 4.56 (q, 2H;
C(O)OCH2), 4.13 (q, 2H; C(S)OCH2), 1.55 (s, 6H; C(CH3)2),
1.31 (t, 6H;CH2CH3,CH2CH3).
Synthesis of (S)-2-(Ethyl propionate)-(O-ethyl
xanthate) (X1)
X1 was synthesized according to the method reported by lit-
erature.30,39 First, the intermediate potassium O-ethyl xan-
thate was prepared by the reaction of KOH (5.63 g, 0.1 mol),
General Procedures for the Polymerization of VAc
A typical solution RAFT polymerization with a molar ratio of
[VAc]0/[CTA]0/[DMA]0/[BPO]0 5 20,000/2/1/1
was
as
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TABLE 1 RAFT Polymerization of VAc at 1 bar and 5 kbar
a
b
Entry
R
Time (h)
Conv. [%]
Mn,th (g/mol)
Mn,GPC (g/mol)
Mw/Mn
1
10,000/2/1/1
20,000/2/1/1
20,000/2/1/1
20,000/2/1/1
10,000/2/1/1
20,000/2/1/1
20000/2/1/1
20,000/4/1/1
20,000/8/1/1
10,000/4/1/1
10,000/4/1/1
24
6
10.8
NA
46,700
NA
35,800
NA
1.46
NA
2
3
24
48
3
6.6
56,700
290,500
154,400
NA
49,400
101,900
92,800
NA
1.52
1.73
1.48
NA
4
33.8
35.9
NA
5
6
3
7
5.5
5.5
5.5
6
37.4
22.6
18.6
20.5
12.2
322,200
97,300
40,300
45,000
27,200
123,000
67,200
47,000
30,500
32,500
1.28
1.32
1.27
1.40
1.53
8
9
10c
11d
6
a
b
c
Polymerization conditions: R 5 [VAc]0/[CTA]0/[DMA]0/[BPO]0,
V
VAc 5
Mn,th 5 [VAc]0/[CTA]03MVAc 3 Conv. 1 MCTA.
V
EA 5 2.5 mL; X1 was used as the CTA except entries 10 and 11, T 5 35
Determined by GPC with poly(methyl methacrylate) calibration.
RAFT polymerization of VAc using X2 as the CTA.
RAFT polymerization of VAc using X3 as the CTA.
ꢀC. Entries 1–4 polymerized at 1 bar, and entries 5–11 polymerized at 5
kbar.
d
follows: A mixture was obtained by adding DMA (0.17 mg,
1.36 3 1023 mmol), BPO (0.33 mg, 1.36 3 1023 mmol), X1
(0.60 mg, 2.72 3 1023 mmol), EA (2.5 mL), and VAc
(2.5 mL, 27.2 mmol) to a dried ampoule (10 mL) (under
atmospheric pressure) or a bag made by polyperfluorinated
ethylene propylene film (under high pressure). The solution
was bubbled with argon for about 20 min to eliminate the
dissolved oxygen. Then, thꢀe ampoule was flame-sealed and
placed in an oil bath at 35 C. The bag was sealed by plastic-
envelop machine and placed in a water bath with high pres-
sure (5 kbar). The high pressure reaction system (HPP
L2–600/0.6, Tianjin, China) was purchased from Tianjin Hua-
tai Sen Miao Biological Engineering Technology. The reactor
includes a hydraulic piston-cylinder unit with pressure reac-
tion vessel equipped with a temperature controller and a
pressure sensor using water as the medium of pressure con-
ductivity. The ampoule or a bag was opened after the desired
polymerization time under atmospheric pressure and high
pressure, respectively. The mixture was dissolved in 2 mL of
THF and precipitated into 250 mL of hexane. The polymers
were isolated by filtration and dried under vacuum at room
temperature until a constant weight was achieved. The con-
version of the monomer was determined gravimetrically.
refractive-index detector (TOSOH), using TSKgel guardcol-
umn SuperMP-N (4.6 mm 3 20 mm) and two TSKgel
SupermultiporeHZ-N (4.6 mm 3 150 mm) with measurable
molecular weight ranging from 5 3 102 to 1 3 106 g/mol.
THF was used as the eluent at a flow rate of 0.35 mL/min
and 40 ꢀC. GPC samples were injected using a TOSOH plus
autosampler and calibrated with linear poly(methyl methac-
1
rylate) standards purchased from TOSOH. The H NMR spec-
tra were recorded on an Inova 300 MHz nuclear magnetic
resonance (NMR) instrument using CDCl3 or dimethyl
sulfoxide (DMSO) as the solvent and tetramethylsilane as the
internal standard at the ambient temperature.
RESULTS AND DISCUSSION
Polymerization of VAc at 1 bar and 5 kbar
To investigate the effect of pressure on the polymerization of
VAc in the presence of different structures of xanthates X1,
X2, and X3, the polymerization was conducted at a lower
temperature (35 ꢀC) using EA as the solvent under atmos-
pheric and high pressure, respectively, and the results are
summarized in Table 1.
It is found from Table 1 that the polymerization of VAc
under high pressure was successful, and the polymerization
rate increased with the decrease of molar ratio of monomer
to initiator, both under atmospheric pressure (1 bar) (entry
1, 10.8% of monomer conversion for [VAc]0/[DMA]0/
[BPO]0 5 1000/1/1 versus entry 3, 6.6% of conversion for
[VAc]0/[DMA]0/ [BPO]0 5 2000/1/1) and high pressure (5
kbar) (entry 5, 35.9% of monomer conversion for [VAc]0/
[DMA]0/[BPO]0 5 1000/1/1 versus entry 6, no polymer
obtained for [VAc]0/[DMA]0/[BPO]0 5 2000/1/1). It results
from the decrease of initiator concentration in the case of
higher molar ratio of monomer to initiator as expected. At
the same time, the polymerization rate decreased with
increasing of the amount of CTA (entries 7–9), demonstrated
Chain extension of PVAc Macro-RAFT agent
A predetermined quantity of DMA/BPO, PVAc, and VAc was
dissolved in predetermined quantity of EA, and the polymer-
ization temperature was kept at 35 ꢀC. The rest procedure
was the same as described above, except for the chain trans-
fer agent (CTA) which was replaced by the macro-RAFT
agent PVAc.
Characterization
The number-average molecular weight (Mn,GPC) and molecu-
lar weight distribution (Mw/Mn) results of the resultant poly-
mers were determined using
a TOSOH HLC-8320 gel
permeation chromatograph (GPC) equipped with
a
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of xanthates with different Z- and R-groups can also be used
as the CTAs under high pressure.
Polymerization Kinetics of VAc
To further investigate the polymerization behaviors under
atmospheric and high pressure, the polymerization kinetics
was carried out under both pressures with molar ratio of
[VAc]0/[CTA]0/[DMA]0/[BPO]0 5 20,000/4/1/1 at 35 ꢀC.
From Figure 1(a), it can be seen that an induction period
was observed both under atmospheric and high pressures.
This suggests that it needed a certain time to generate initia-
tor species and establish a dynamic equilibrium between the
CTA and propagating radicals during the polymerization. In
addition, a much longer induction period (ꢁ21.5 h) was
observed under atmospheric pressure than that (ꢁ4.2 h)
under high pressure. After the induction period, a linear
relationship between ln([M]0/[M]) and polymerization time
was observed in Figure 1(a), which demonstrated that con-
stant propagating radicals maintained in both cases.
FIGURE 1 ln([M]0/[M]) as a function of time (a) and number-
average molecular weight (Mn,GPC) and molecular weight distri-
bution (Mw/Mn) versus monomer conversion (b) for the RAFT
polymerization of VAc at 1 bar and 5 kbar. Polymerization con-
ditions: [VAc]0/[X1]0/[DMA]0/[BPO]0 5 20,000/4/1/1, VVAc 5 VEA 5
2.5 mL, T 5 35 ꢀC. [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com.]
by monomer conversion decreasing from 37.4%, 22.6% to
18.6% when the molar ratio of [VAc]0/[CTA]0 increases from
2000/2, 2000/4 to 2000/8. This contributed to retardation
phenomena of RAFT polymerization.41–50 In addition, by
comparison of entry 1 and entry 5, it is discernible that the
polymerization rate under high pressure (35.9% of monomer
conversion after 3 h) was much faster than that under
atmospheric pressure (10.8% of monomer conversion after
24 h). To the best of our knowledge, till now, the reported
high molecular weight PVAc (Mn,GPC 5 119,400 g/mol,
Mw/Mn 5 1.37) could be obtained by photoinduced CMRP51
and photoinduced electron transfer-RAFT polymerization
(PVAc, Mn,GPC 5 101,400 g/mol, Mw/Mn 5 1.24),52 respec-
tively. From entry 7 in Table 1, high molecular weight PVAc
up to 123,000 g/mol with narrow molecular weight distribu-
tion (Mw/Mn 5 1.28) could be obtained at 5 kbar in this
work. Besides X1, from entries 10 and 11, other two kinds
FIGURE 2 ln([M]0/[M]) as a function of time (a) and number-
average molecular weight (Mn,GPC) and molecular weight distri-
bution (Mw/Mn) versus monomer conversion (b) for the RAFT
polymerization of VAc with different molar ratios of [VAc]0/
[X1]0/[DMA]0/[BPO]0 at
5
kbar. Polymerization conditions:
[VAc]0/[X1]0/[DMA]0/[BPO]0 5 20,000/x/1/1 (x 5 2, 4, 8),
V
VAc 5
VEA 5 2.5 mL, T 5 35 ꢀC. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
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intermediate radical by decreasing the termination rate.53
Both of the two factors could be suppressed to a larger
extent than the reaction between two macroradicals just like
the situation under atmospheric pressure. From Figure 2(b),
the molecular weights of PVAc increased linearly with mono-
mer conversion (below 30%), and the molecular weight dis-
tributions remained less than 1.5. However, the molecular
weights deviated the linear increase with the monomer con-
version when the conversion was more than 40%, and the
Mw/Mn values increased correspondingly. This may due to
the active monomer radicals which caused chain transfer
and chain termination reactions of PVAc.
Analysis of Chain End and Chain Extension of PVAc
The end group of the PVAc (Mn,GPC 5 29,800 g/mol,
Mw/Mn 5 1.12) obtained at 5 kbar was confirmed by 1H
NMR, as shown in Figure 3. Peaks (e, e00, f, f00, g, and g00)
were the characteristic repeating unit of the VAc as assigned
in Figure 3. The remaining peaks are from the X1 mediator.
All of the 2-ethyl propionate protons (a, b, c, d) were
observed at around 1.42, 4.66, 3.89, and 1.16 ppm, respec-
tively. In addition, O-ethyl protons (h, i) were observed at
4.11 and 1.25 ppm, respectively. The peak of the methine
proton f" of the terminal VAc group close to O-ethylxanthate
group was observed at around 6.61 ppm.
FIGURE 3 1H NMR spectrum (300 MHz, CDCl3) of PVAc pre-
pared in the solution polymerization of VAc at 5 kbar. Polymer-
ization condition: [VAc]0:[X1]0:[AIBN]0 5 20,000:4:1:1, VVAc 5 VEA
5 2.5 mL, T 5 35 ꢀC, time 5 4 h, conversion 5 6.6%.
Furthermore, an extraordinary increase of the polymerization
rate under high pressure was discernable from Figure 1(a).
To further confirm the living feature of PVAc, the chain-
extension experiments were conducted at 35 ꢀC. When the
PVAc prepared at 5 kbar was used as the macro-RAFT agent,
from Figure 4, there has been a peak shift from the original
PVAc (Mn,GPC 5 22,900 g/mol, Mw/Mn 5 1.27) to the chain-
extended PVAc (Mn,GPC 5 73,500 g/mol, Mw/Mn 5 1.41) at 1
It was further quantitatively calculated by the apparent rate
app
constant kpappðRp52d½Mꢂ=dt5kp½Pn ꢂ½Mꢂ5kp ½MꢂÞ from the
•
slopes of the kinetic plots, which was 0.243 h21 in the case
of 5 kbar and 0.0164 h21 in the case of 1 bar, respectively.
The former is 15.2 times of the latter. The reason for these
differences should be attributed to the fact that the propaga-
tion of free radicals was enhanced, and termination was sup-
pressed under high pressure.35 High pressure may make the
formation of the stable carbon centered radicals easily and
enhance their reactivity.38 The evaluation of the molecular
weight and molecular weight distribution with conversion is
shown in Figure 1(b). Both the polymer molecular weights
linearly increased with the monomer conversion. At the
same time, it can be seen that narrower molecular weight
distributions were obtained in the case of high pressure.
bar for 28
h
and PVAc (Mn,GPC 5 68,700 g/mol,
Mw/Mn 5 1.48) at 5 kbar for 5 h, respectively. The GPC
traces of the chain-extended PVAc showed unimodal
To further confirm the retardation phenomena as discussed
in Table 1, the polymerization kinetics with the three molar
ratios of [VAc]0/[X1]0 5 20,000/2, 20,000/4, 20,000/8 was
investigated at 5 kbar. As shown in Figure 2(a), all the poly-
merization kinetics was first order with the monomer con-
centration, indicating almost constant propagating radicals
during the polymerization. Similarly, we can calculate the
apparent rate constant kpapp values to directly judge the
change of the polymerization rate in three cases. A kpapp
0.299 h21 for the case of 20,000/2, 0.243 h21 for the case
20,000/4, and 0.170 h21 for the case of 20,000/8, was
obtained, respectively, fully confirming the rate retardation
in the presence of larger amount of CTAs even if under high
pressure. Philipp Vana explained that the pressure may not
only make the addition reaction diffusion-controlled and
retard it but also compensated the amount of the stable
FIGURE 4 GPC traces of PVAc before and after chain exten-
sion, using PVAc prepared by the RAFT polymerization of VAc
at 1 bar (a) and 5 kbar (b) as the macro-RAFT agents. The poly-
merization condition: [VAc]0/[PVAc]0/[DMA]0/[BPO]0 5 20,000/2/
1/1, VVAc 5 VEA 5 2.5 mL, T 5 35 ꢀC. [Color figure can be viewed
in the online issue, which is available at wileyonlinelibrary.
com.]
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15 H. Tang, M. Radosz, Y. Shen, AIChE J. 2009, 55, 737–746.
distribution. All of these evidences confirmed the features of
the controlled/living polymerization under high pressure
when using DMA/BPO as the initiator and X1 as the
xanthate.
16 D. Greszta, D. Mardare, K. Matyjaszewski, Macromolecules
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CONCLUSIONS
19 K. Koumura, K. Satoh, M. Kamigaito, Y. Okamoto, Macro-
molecules 2006, 39, 4054–4061.
In summary, high pressure can enhance the polymerization
rate significantly (15.2 times) in comparison with that under
atmospheric pressure. It is more important that PVAc with
high molecular weight up to 123,000 g/mol and narrow
molecular weight distribution (Mw/Mn 5 1.28) can be easily
obtained via RAFT polymerization under high pressure
(5 kbar).
20 Y. Kwak, A. Goto, T. Fukuda, Y. Kobayashi, S. Yamago, Mac-
romolecules 2006, 39, 4671–4679.
21 S. Yamago, B. Ray, K. Iida, J. Yoshida, T. Tada, K.
Yoshizawa, Y. Kwak, A. Goto, T. Fukuda, J. Am. Chem. Soc.
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ACKNOWLEDGMENTS
The financial support from the National Natural Science Foun-
dation of China (No. 21174096, 21274100, 21234005), the
Specialized Research Fund for the Doctoral Program of Higher
Education (No. 20123201130001), the Project of Science and
Technology Development Planning of Suzhou (No. ZXG201413,
SYG201430), the Project of Science and Technology Develop-
ment Planning of Jiangsu Province (No. BK20141192), and the
Project Funded by the Priority Academic Program Develop-
ment of Jiangsu Higher Education Institutions (PAPD) is grate-
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