Thioether-Mediated Degenerative Chain-Transfer Cationic Polymerization: A Simple Metal-Free System for Living Cationic Polymerization

Article abstract of DOI:10.1021/acs.macromol.5b01341

Cationic degenerative chain-transfer polymerization of vinyl ethers and p-alkoxystyrenes was investigated using a series of thioethers as a reversible chain-transfer agent via the equilibrium between a growing carbocationic species and the resulting sulfonium intermediate in the presence of a small amount of triflic acid (TfOH) as a cationogen. The stable thioether, which was easily prepared from isobutyl vinyl ether (IBVE) and n-butanethiol, efficiently controls the molecular weight of the resulting poly(IBVE) up to M_n ～ 1 × 10⁵ with narrow molecular weight distributions (MWDs) (M_w/M_n ～ 1.2). Upon increasing the bulkiness of the alkyl substituents in the thiols (R-SH; R: n-Bu < s-Bu < t-Bu) or those in the monomers (CH₂=CHOR′, R′: ethyl < isobutyl < cyclohexyl), the MWDs became broader due to the slower formation of the sulfonium intermediate for the degenerative chain-transfer reaction. For p-methoxystyrene, thioethers derived from bulkier alkylthiols or more electron-rich thiophenols are more effective. A silyl-protected difunctional dithioether produced telechelic polymers possessing hydroxyl groups at both chain ends and stable thiol linkers in the middle of the polymer chains. These polymers were subsequently used in chain-extension reactions in conjunction with diisocyanates and diols as chain extenders to be converted into high molecular weight polymers linked via urethane linkages. (Figure Presented).

Full text of DOI:10.1021/acs.macromol.5b01341

Article
pubs.acs.org/Macromolecules
Thioether-Mediated Degenerative Chain-Transfer Cationic
Polymerization: A Simple Metal-Free System for Living Cationic
Polymerization
Mineto Uchiyama, Kotaro Satoh,* and Masami Kamigaito*,†
†
,†,‡
†
Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
‡
Precursory Research for Embryonic Science and Technology, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi,
Saitama 332-0012, Japan
*
S Supporting Information
ABSTRACT: Cationic degenerative chain-transfer polymer-
ization of vinyl ethers and p-alkoxystyrenes was investigated
using a series of thioethers as a reversible chain-transfer agent
via the equilibrium between a growing carbocationic species
and the resulting sulfonium intermediate in the presence of a
small amount of triflic acid (TfOH) as a cationogen. The
stable thioether, which was easily prepared from isobutyl vinyl
5
ether (IBVE) and n-butanethiol, efficiently controls the molecular weight of the resulting poly(IBVE) up to M ∼ 1 × 10 with
n
narrow molecular weight distributions (MWDs) (M /M ∼ 1.2). Upon increasing the bulkiness of the alkyl substituents in the
w
n
thiols (R−SH; R: n-Bu < s-Bu < t-Bu) or those in the monomers (CH CHOR′, R′: ethyl < isobutyl < cyclohexyl), the MWDs
2
became broader due to the slower formation of the sulfonium intermediate for the degenerative chain-transfer reaction. For p-
methoxystyrene, thioethers derived from bulkier alkylthiols or more electron-rich thiophenols are more effective. A silyl-
protected difunctional dithioether produced telechelic polymers possessing hydroxyl groups at both chain ends and stable thiol
linkers in the middle of the polymer chains. These polymers were subsequently used in chain-extension reactions in conjunction
with diisocyanates and diols as chain extenders to be converted into high molecular weight polymers linked via urethane linkages.
INTRODUCTION
relatively weak protonic acid generating a nucleophilic
counteranion that can form a covalent bond via an addition
reaction with a monomer. In these Lewis-acid-catalyzed living
cationic polymerizations, the contamination of metal residues is
generally inevitable.
■
Living polymerization is one of the most effective and useful
methods for not only controlling the molecular weight of
synthetic polymers but also enabling the synthesis of complex
polymeric architectures such as block, end-functional, telechelic,
1
Another living cationic polymerization, which is based on a
dissociation−combination mechanism, was achieved using
triflic acid (TfOH) in combination with thioethers in the
and star polymers by design. Recently, there has been great
progress in controlled/living polymerization techniques, most
of which are based on the transient reversible deactivation of
the propagating chain end into a dormant species, and as such,
IUPAC recommends the name reversible deactivation polymer-
36,37
1
990s (Scheme 1A).
Although the superstrong acid, TfOH,
generates a free carbocation via a reaction with vinyl ether, it is
immediately converted into a stable and dormant sulfonium ion
in the presence of the added thioethers. The formed sulfonium
chain ends can transiently dissociate into the carbocationic
species, which then induces the living cationic polymerization
via a dissociation−combination mechanism. Although this
system is free from metal, it needs one molecule of TfOH
per polymer chain and a large molar excess of thioether with
respect to TfOH or the polymer chain.
2
ization (RDP). This class of polymerization has been most
actively studied in radical polymerization systems and can be
classified into at least three different mechanisms, i.e.,
3
4
−7
8−15
dissociation−combination,
atom transfer,
according to the kinetic treatments.
The concept of RDP originates from several living ionic
and degener-
16−23
ative chain transfer,
2
4−27
polymerizations
GTP) of methacrylates
of vinyl ethers and isobutene,
such as group transfer polymerization
2
8,29
(
and living cationic polymerization
30−35
Recently, we reported a new living cationic polymerization
that proceeds via a reversible addition−fragmentation chain-
which were accomplished in
the mid-1980s. Most living cationic polymerizations rely on a
type of atom transfer mechanism, in which the dormant
covalent bonds, such as carbon−halogen and carbon−oxygen
ester bonds, are reversibly activated by Lewis acid catalysts into
38
transfer (RAFT) mechanism, a type of degenerative chain-
transfer polymerization (Scheme 1C). In this cationic RAFT
3
0−35
a carbocationic species (Scheme 1B).
The Lewis acid
Received: June 20, 2015
Revised: July 28, 2015
catalysts are generally metal halides with a few exceptions such
3
4
as iodine, while the dormant species is derived from a
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.macromol.5b01341
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
Scheme 1. Reversible Deactivation Mechanisms for Living Cationic Polymerization
Scheme 2. Thioether-Mediated Degenerative Chain-Transfer Cationic Polymerization
polymerization, similar to the radical RAFT polymeriza-
can be controlled by the proposed degenerative chain-transfer
mechanism. Although a competing degenerative mechanism
has been proposed in living cationic polymerizations involving
C−I bonds in the presence of ammonium salts that generate
less nucleophilic anions such as perchlorates and triflates, it has
1
7−21
tion,
the covalent C−SC(S)Z bond derived from the
thiocarbonylthio compound employed as a chain-transfer agent
is reversibly activated by a very small amount of the growing
carbocationic species originating from TfOH as cationogen.
This system is not only free from metal but also needs only one
chain-transfer agent per chain and very small quantities of
TfOH relative to the RAFT agent (ppm range or smaller). The
key to the cationic RAFT polymerization is a high affinity of the
sulfur atom to the carbocation, which contributes to the
formation of the intermediate and then enables the rapid
interchange reaction between the growing carbocation and the
dormant thiocarbonylthio terminal.
39,40
not been fully elucidated.
In addition, the iodide compound
is less stable and difficult to synthesize and to purify. Here, we
synthesized various adducts of vinyl ether and thiols with
different steric and electronic substituents via a simple addition
reaction followed by purification under mild conditions to use
as chain-transfer agents for controlling the cationic polymer-
ization of various vinyl ethers and p-methoxystyrene in the
presence of a small amount of TfOH as a cationogen.
Furthermore, telechelic polymers were synthesized by prepar-
ing stable difunctional thioether compounds and used in
subsequent chain-extension reactions.
In this study, we developed another novel living cationic
polymerization that proceeds via a degenerative chain-transfer
mechanism using a thioether as a reversible chain-transfer agent
in place of the thiocarbonylthio compound used in conven-
tional RAFT polymerizations (Scheme 2). The thioether is
more easily prepared and possesses a simpler structure with a
more stable C−S bond. If the thioether forms a stable
sulfonium intermediate via reaction with the propagating
carbocationic species and the resulting intermediate rapidly
dissociates into the carbocation and thioether via an
interchange reaction, the chain length of the resulting polymer
RESULTS AND DISCUSSION
■
Thioether-Mediated Cationic Polymerization of IBVE
via a Degenerative Chain-Transfer Mechanism. The
thioether or thioacetal 1 was easily synthesized by the reaction
of isobutyl vinyl ether (IBVE) and n-butanethiol in the
presence of a small amount of p-toluenesulfonic acid as a
catalyst. It is stable and can be distilled and handled in air.
B
DOI: 10.1021/acs.macromol.5b01341
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
a
Table 1. Cationic Polymerization of IBVE with Various Transfer Agents
b
c
d
c
e
entry
1
transfer agent (IBVE-X)
[M] /[I]
time
conv (%)
Mn
M (calcd)
M /Mn
Ctr
0
0
n
w
none
−
25
1 min
1 min
1 min
1 min
45 min
1 h
98
93
95
92
99
99
91
98
94
93
91
90
89
24600
3300
3.58
1.18
1.23
1.27
1.19
1.24
1.68
1.84
1.93
1.90
1.52
1.18
1.82
f
2
−Sn-Bu (1)
2500
4800
3
50
5100
5.31
f
4
100
500
1000
50
10600
56500
117400
4600
9400
g
5
g
50300
100400
4800
6
7
8
9
−Ss-Bu (2)
−St-Bu (3)
1 min
2 min
1 min
1 min
1 min
25 s
1.81
1.31
1.23
1.32
2.41
7.68
1.55
50
6100
5100
−SC H Cl (4)
50
5500
5000
6
4
10
11
12
13
−SC H (5)
50
4900
4900
6
5
−SC H OCH (6)
50
5300
4800
6
4
3
−SC(S)SEt (7)
50
5000
4700
−OCH (8)
50
30 s
5800
4800
3
a
b
Polymerization condition: [M] /[transfer agent] /[TfOH] = 500/10/0.05 mM in n-hexane/CH Cl /Et O (80/10/10) at −40 °C. Determined
by H NMR. Determined by SEC. M (calcd) = MW(IBVE) × ([M] /[transfer agent] ) × conv + MW(transfer agent). Chain transfer constant.
IBVE] /[1] /[TfOH] = 500/20 or 5/0.05 in n-hexane/CH Cl /Et O (80/10/10) at −40 °C. [IBVE] /[1] /[TfOH] = 600/1.2 or 0.6/0.03 in
0
0
0
2
2
2
1
c
d
e
n
0
0
f
g
[
0
0
0
2
2
2
0
0
0
n-hexane/CH Cl /Et O (80/10/10) at −78 °C.
2
2
2
The cationic polymerization of IBVE was then examined
using 1 as a possible chain-transfer agent in conjunction with a
trace amount of TfOH as a cationogen ([IBVE] /[1] /
0
0
[
TfOH] = 500/10/0.05 mM) in a solvent mixture of n-
0
hexane/CH Cl /Et O (80/10/10 vol %) at −40 °C. The
2
2
2
polymerization proceeded rapidly and was complete within 1
min. Irrespective of the very fast polymerization, the obtained
polymers showed controlled number-average molecular weights
(
M ) that agreed well with the calculated values assuming that
n
one thioether generates one polymer chain and were
characterized by relatively narrow molecular weight distribu-
tions (MWDs) (M /M ∼ 1.2) (entry 3 in Table 1 and Figure
w
n
S1 in the Supporting Information). To confirm the molecular
weight control by the thioether, feed ratios of IBVE to 1 were
changed ([M] /[1] = 25−1000). The M values were directly
Figure 1. M , M /M , and SEC curves for monomer-addition
n w n
0
0
n
experiment in cationic polymerization of IBVE in the presence of 1
in n-hexane/CH Cl /Et O (80/10/10 vol %) at −40 °C: [M] /
proportional to [M] /[1] and were in good agreement with
0
0
2
2
2
0
the theoretical values (entries 2−6 in Table 1 and Figure S2) in
all cases. Even at a high feed ratio targeting a 1000-mer of
IBVE, a high molecular weight was obtained that agreed well
[
M] /[1] /[TfOH] = 500/10/0.05 mM.
add 0 0
5
with the expected molecular weight (Mn ∼ 1 × 10 )
the products decreased due to an increase in the cationogen
and thereby the polymer chain (Figures S3 and S4).
accompanied by a narrow MWD (entry 6 in Table 1). These
results indicate that the thioether, which is easy to prepare and
to handle, efficiently works as a degenerative chain-transfer
agent in the metal-free cationic polymerization of IBVE in the
presence of a small amount of TfOH.
Almost all the polymers obtained using a small amount of
TfOH ([1] /[TfOH] = 10/0.05 mM) had thioacetal ω-chain
0
0
ends (Figure S4), which are polymeric analogues of 1 and are
dormant species. The MALDI-TOF-MS spectrum also revealed
that nearly one series of peaks each separated by the molar
mass of the IBVE units (100.2 Da) are observable and can be
assigned to the thioether-ended polymers (Figure 2A). It also
indicates the high stability of the thioether terminal even during
the work-up procedures and MALDI-TOF-MS analysis unlike
the thioester terminals obtained by the cationic RAFT
Furthermore, a fresh feed of IBVE was added to the reaction
mixture after the initial charge of monomer was almost
completely polymerized. The additional portion of IBVE was
also consumed smoothly. As shown in Figure 1, even after the
monomer addition, the M of the obtained polymers increased
n
in direct proportion to the monomer conversion and agreed
well with the calculated values. The MWDs remained similarly
38
polymerization of IBVE. Upon increasing the concentration
of TfOH, the acetal terminals originating from the methanol
used for quenching the polymerization became visible in both
narrow (M /M ∼ 1.2). Thus, the 1/TfOH initiating system
w
n
mediates the cationic polymerization in a living manner without
any significant irreversible termination and chain-transfer
reactions during the chain propagation, even after the
monomer is almost depleted.
1
the H NMR and MALDI-TOF-MS spectra (Figure 2B). A
further increase of [TfOH] makes these peaks larger (Figure
0
2C). These results indicate that the concentration or number of
cationic propagating species increased as [TfOH]0 was
increased and that the cationic propagating species is
terminated as the acetal group upon quenching with methanol.
Thus, TfOH works as a cationogen and generates the
carbocationic species that interchanges with the thioether
Mechanistic Investigation To Elucidate the Effect of
Triflic Acid on the Resulting Polymers. To elucidate the
mechanism of the thioether-mediated cationic polymerization,
the concentration of TfOH ([TfOH] ) was changed, keeping
0
all other parameters constant. As [TfOH] increased, the M of
0
n
C
DOI: 10.1021/acs.macromol.5b01341
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
Figure 2. Effects of [TfOH] on MALDI-TOF-MS spectra of the polymers obtained in the polymerization of IBVE at [M] /[1] /[TfOH] = 500/
0
0
0
0
1
0/0.05−10.0 mM in n-hexane/CH Cl /Et O (80/10/10 vol %) at −78 °C.
2
2
2
Figure 3. M , M /M , and SEC curves for cationic polymerization of IBVE in the presence of various aliphatic thioethers in n-hexane/CH Cl /Et O
n
w
n
2
2
2
(
80/10/10 vol %) at −40 °C: [M] /[thioether] /[TfOH] = 500/10/0.05 mM.
0
0
0
chain end via the sulfonium intermediate, resulting in
controlled molecular weights and the retention of chain-end
groups via a degenerative chain-transfer mechanism.
sec-butanethiol (2), and tert-butanethiol (3), and were
employed to polymerize IBVE (entries 3, 7, and 8 in Table
1, respectively). In all cases, the polymerization proceeded
Various Thioethers and Related Compounds for the
Cationic Polymerization of IBVE. To elucidate the thioether
structure that can effectively control the cationic polymerization
via a degenerative chain-transfer mechanism, various thioethers
and related compounds were employed for the cationic
polymerization of IBVE under the same conditions.
smoothly and was complete in 1−2 min. The M of the
n
polymers obtained with a bulkier thioether 2 increased almost
linearly with IBVE conversion and were close to the theoretical
values assuming that one thioether generates one polymer
chain (Figure 3). The bulkiest thioether 3 with tert-butanethiol
resulted in higher molecular weights than the calculated values.
Furthermore, the MWDs became broader as the thioether
substituent bulkiness increased. These results indicate that a
First, a series of thioethers of different bulkiness were
synthesized from various butanethiols, i.e., n-butanethiol (1),
D
DOI: 10.1021/acs.macromol.5b01341
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
bulky substituent around the thioether retards the formation of
the sulfonium ion for the effective degenerative chain-transfer
mechanism, resulting in higher and uncontrolled molecular
weights and broader MWDs.
chain-transfer reactions. The least bulky thioether 1 with n-
butanethiol is therefore effective for at least the cationic
polymerization of IBVE via a degenerative chain-transfer
mechanism.
Another series of thioethers (4, 5, 6) were prepared from
IBVE and thiophenols with electron-withdrawing and -donating
substituents and used for the cationic polymerization of IBVE
under the same conditions (entries 9, 10, and 11 in Table 1).
1
The H NMR analysis of the obtained polymers all showed
the presence of thioether ω-chain ends, which is characterized
by a methine proton (b′) adjacent to a sulfur atom and the
corresponding butanethiol moiety (f) (Figure 4). The M
n
The M determined by SEC were all in good agreement with
n
the calculated values, although the MWDs were relatively broad
for 4 and 5 (M /M ∼ 1.9) (Figure S5). However, the MWD
w
n
of the polymers prepared with 6, which has an electron-
donating p-methoxy group on the thiophenol, was narrower
(
M /M ∼ 1.5). These results suggest that a more electron-
w
n
donating substituent on the thioether group results in a more
stable sulfonium intermediate, which results in a faster
degenerative chain-transfer reaction.
To evaluate the rate of the degenerative chain-transfer
process, the chain-transfer constants (C ) were calculated for
tr
the various chain-transfer agents under the same conditions
used in Table 1 according to this simple equation M /M = 1 +
w
n
1
/X + (2 − c)/(cC ), where X is the number-average degree
n
tr
n
3
of polymerization and c is the monomer conversion.
A relatively large C was obtained with 1 (C = 5.31, entry
tr
tr
3
), which gave the narrowest MWD among the various
thioethers examined, whereas it was lower than that with the
trithiocarbonate RAFT agent (7; C = 7.68, entry 12)
tr
38,41
previously reported by us.
A similar oxygen ether or acetal
compound (8) that is the adduct of methyl vinyl ether and
methanol resulted in a higher molecular weight, a broader
MWD (M /M ∼ 1.8), and, thus, a low constant (C = 1.55,
w
n
tr
entry 13). Thus, the sulfur atom is necessary for the effective
degenerative chain-transfer process via the formation of the
sulfonium intermediate.
1
Figure 4. H NMR spectra (in CDCl at 55 °C) of poly(IBVE)
3
obtained in the same experiments as for Figure 3. (A) M (NMR) =
n
However, the thioether is no longer effective in the radical
mechanism as indicated by the control experiments for the
radical copolymerization of IBVE and methyl acrylate (MA) in
the presence of 2,2-azobis(4-methoxy-2,4-dimethyl-
2
200, M (SEC) = 2700, M /M = 1.27, conversion = 35%. (B)
n w n
M (NMR) = 2700, M (SEC) = 3000, M /M = 1.82, conversion =
3
conversion = 37%.
n
n
w
n
8%. (C) M (NMR) = 5500, M (SEC) = 6000, M /M = 1.67,
n n w n
valeronitrile) (V-70), where copolymers with uncontrolled
5
[
M (NMR)] determined from the integration ratios of the
high molecular weight (M
n
> 10 ) and broad MWDs (M
/M
w
n
n
repeat units (e) to the ω-end (b′) were close to those obtained
∼ 2.5) were obtained (Figure S6). This is in sharp contrast with
the trithiocarbonate (7), which controlled the molecular weight
even in the radical copolymerization (Figure S7).
Cationic Polymerization of Other Vinyl Ethers. To
confirm the versatility of this polymerization system for other
vinyl ethers, ethyl (EVE) and cyclohexyl vinyl ether (CHVE)
by SEC [M (SEC)] in all cases, indicating that the resulting
n
38
polymers all possessed the thioether chain ends irrespective of
the bulkiness of the substituents. This again shows that less
controlled molecular weights with bulkier substituents are not
due to irreversible side reactions but due to slower degenerative
a
Table 2. Cationic Polymerization of Various Vinyl Ethers with Thioethers
b
c
d
c
n
entry
monomer
EVE
transfer agent (IBVE-X)
time (s)
conv (%)
Mn
M (calcd)
M /M
n
w
1
2
3
4
5
6
7
8
9
−Sn-Bu (1)
−Ss-Bu (2)
−St-Bu (3)
−Sn-Bu (1)
−Ss-Bu (2)
−St-Bu (3)
−Sn-Bu (1)
−Ss-Bu (2)
−St-Bu (3)
30
30
15
12
2
97
96
94
99
98
99
94
93
92
4700
4000
4800
6600
8900
37200
3700
3200
3200
3700
3700
3600
6400
6400
6400
5200
5100
5100
1.11
1.38
1.71
1.63
2.47
4.05
1.37
1.52
2.19
CHVE
CEVE
2
40
30
30
a
Polymerization condition: [monomer] /[transfer agent] /[TfOH] = 500/10/0.05 in n-hexane/CH Cl /Et O (80/10/10) (EVE and CHVE) or
0
0
0
2
2
2
b
1
[
monomer] /[transfer agent] /[TfOH] = 500/10/0.50 toluene/CH Cl /Et O (80/10/10) (CEVE) at −40 °C. Determined by H NMR.
0
0
0
2
2
2
c
d
Determined by SEC. M (calcd) = MW(monomer) × ([M] /[transfer agent] ) × conv + MW(transfer agent).
n
0
0
E
DOI: 10.1021/acs.macromol.5b01341
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
Figure 5. SEC curves of the obtained polymers for cationic polymerization of various monomers in the presence of various aliphatic thioethers in the
same experiments as for Tables 1 and 2.
a
Table 3. Cationic Polymerization of pMOS with Thioethers
b
c
d
c
entry
transfer agent
TfOH (mM)
time
conv (%)
Mn
M (calcd)
n
M /M
w
n
1
2
3
4
5
6
7
8
9
none
0.05
0.50
0.05
0.50
0.05
0.50
0.05
0.50
0.05
0.05
0.50
0.05
0.05
0.05
40 min
5 min
30 h
90
90
0
119800
58800
2.02
2.05
IBVE-Sn-Bu (1)
IBVE-Ss-Bu (2)
IBVE-St-Bu (3)
IBVE-SC H Cl (4)
24 h
0
30 h
1
80 h
1
140 h
42 h
5
99
91
97
96
94
93
95
5500
5100
5700
5200
6500
6000
5100
6800
6300
6700
6700
6600
6500
6600
1.55
1.47
1.35
1.31
1.41
1.28
1.27
30 min
14 h
6
4
1
1
1
1
1
0
1
2
3
4
IBVE-SC H (5)
6 5
IBVE-SC H OCH (6)
1 h
6
4
3
pMOS-SC H ClI (9)
80 min
1 h
6
4
pMOS-SC H (10)
6
5
pMOS-SC H OCH (11)
6 h
6
4
3
a
b
1
Polymerization condition: [M] /[transfer agent] /[TfOH] = 500/10/0.05 or 0.50 mM in CH Cl /Et O (90/10) at 0 °C. Determined by H
0
0
0
2
2
2
c
d
NMR. Determined by SEC. M (calcd) = MW(pMOS) × ([M] /[transfer agent] ) × conv + MW(transfer agent).
n
0
0
with different bulkiness were polymerized using 1, 2, and 3
under the same conditions used for IBVE (Table 2).
mediate difficult to form due to steric repulsion, which results
in poorer control over the molecular weight.
Another vinyl ether with a chlorine containing substituent,
These alkyl vinyl ethers were similarly and quantitatively
polymerized within 1 min. The molecular weights and MWDs
depended on the bulkiness of the substituents in both the
monomers and the thioethers. As shown in Figure 5, the
MWDs became narrower as the substituents in the monomers
and thioethers became smaller. Thus, the narrowest MWD was
obtained (M /M = 1.11) with 1 for EVE. However, for
i.e., 2-chloroethyl vinyl ether (CEVE), was also examined using
1
, 2, and 3 under the same conditions (entries 7−9 in Table 2).
Although the MWDs were slightly broader than those of IBVE,
the molecular weight can be controlled by the thioethers
(
Figure S8).
Thus, thioethers or thioacetals are effective for the controlled
w
n
cationic polymerization of various vinyl ethers via a
degenerative chain-transfer mechanism triggered by a small
amount of triflic acid. The steric hindrance around the ether
group of the monomer and the thioether group of the chain-
transfer agent is crucial for control because the sulfonoium ion
intermediate is surrounded by two vinyl ether units and one
thiol substituent.
CHVE, i.e., the bulkiest monomer around the ether oxygen, the
MWD obtained, even with 1, was relatively broad (M /M ∼
w
n
1.6). Furthermore, the bulkiest thioether, 3, derived from tert-
butanethiol resulted in much higher and uncontrolled
molecular weights. These results indicate that bulky sub-
stituents around the thioacetals make the sulfonium inter-
F
DOI: 10.1021/acs.macromol.5b01341
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
Figure 6. Time−conversion curve and SEC curves of the obtained polymers in cationic polymerization of pMOS in the presence of aromatic
thioethers in CH Cl /Et O (90/10 vol %) at 0 °C: [pMOS] /[thioether] /[TfOH] = 500/10/0.05 mM.
2
2
2
0
0
0
Figure 7. SEC curves of (A) silyl-protected telechelic poly(IBVE), (B) deprotected telechelic poly(IBVE), (C) products obtained with with 2 equiv
of 1,4-phenylene diisocyanate, and (D) products obtained via further reaction with 1 equiv of 1,4-butanediol.
Cationic Polymerization of p-Methoxystyrene. To
further expand the scope of the thioether-mediated degener-
ative cationic polymerization, a styrene derivative with an
electron-donating group, p-methoxystyrene (pMOS), was
polymerized using various thioethers in the presence of a
trace amount of TfOH in a CH Cl /Et O (90/10 vol %)
ion than that for IBVE which results in a more stable
carbocationic species. Especially in the case where pMOS is
polymerized in combination with a less bulky thioether such as
1 and 2, the equilibrium is highly shifted to the sulfonium
intermediate, which makes the dissociation into the carboca-
tionic species more difficult, resulting in almost no polymer-
ization. However, the bulkier thioether, 3, with a tert-butyl
group, promotes the dissociation of the sulfonium ion into the
carbocationic species due to steric hindrance to induce an
effective degenerative chain-transfer reaction for controlling the
molecular weight in the cationic polymerization of pMOS.
A series of aromatic thioethers, i.e., adducts of pMOS and p-
chloro (9), nonsubstituted (10), and p-methoxy (11)
thiophenols, were also used in the cationic polymerization of
pMOS to investigate the electronic effects on the controllability
of the polymerizations. The polymerizations all proceeded
quantitatively even in the presence of a lower amount of TfOH
([TfOH]0 = 0.05 mM) when employing any aromatic
thioethers. The polymerizations proceeded at almost the
same rate in the presence of 9 and 10, whereas the
polymerization became slower using 11 that bears a more
2
2
2
mixture at 0 °C (Table 3).
Without thioethers, the polymerization proceeded very
quickly and reached 90% conversion within 5 min, resulting
4
in high molecular weight polymers (M > 5 × 10 ). Almost no
n
polymerization occurred with 1 and 2, which were effective for
IBVE, even in the presence of a larger amount of TfOH
(
[TfOH] = 0.50 mM) (Figure S9). The polymerization of
0
pMOS using 3 with a bulky tert-butyl group occurred slowly to
give polymers with controlled molecular weights closer to the
calculated values and tert-butanethiol moiety at the chain end
(Figure S10). These results can be attributed to the difference
in the stability of the carbocationic species derived from styrene
derivatives and vinyl ether. The equilibrium between the
carbocationic species of pMOS and its resulting sulfonium
intermediate is expected to be shifted more to the sulfonium
G
DOI: 10.1021/acs.macromol.5b01341
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
electron-donating methoxy substituent. This substituent results
in a more stable sulfonium intermediate and therefore a lower
concentration of the propagating cationic species in the
polymerization equilibrium. As shown in Figure 6, with all
aromatic thioethers, the SEC curves are relatively narrow and
shifted to high molecular weight. Furthermore, the Mn
increased directly with the monomer conversion and were
close to the calculated values (entries 9, 10, and 11 in Table 3).
The MWDs were narrower using aromatic thioethers derived
from nonsubstituted (10) or p-methoxy-substituted (11)
thiophenols than from an electron-withdrawing p-chloro-
substituted thioether (12). Similar results were obtained with
adducts of IBVE and a series of thiophenols (4−6) for the
cationic polymerization of pMOS (Figure S11).
Thus, the cationic polymerization of pMOS can also be
controlled via a thioether-mediated degenerative chain-transfer
mechanism using appropriate thioethers, particularly those
derived from thiophenols. These results indicate that for the
design of thioethers for good polymerization control it is crucial
to consider both the steric and electronic nature of the
thioether.
Difunctional Dithioethers for Telechelic Polymers and
Postpolymerization Reactions. One of the most notable
features of thioether-based chain-transfer agents is their high
stability and accessibility in comparison to other initiators or
reversible chain-transfer agents for living cationic polymer-
izations thus far reported. To evaluate the applicability of the
thioether-mediated polymerization for precision polymer
design and synthesis, a difunctional dithioether (12) was
synthesized from a dithiol and functionalized vinyl ether and
was used for the synthesis of telechelic polymers followed by a
postpolymerization reaction.
1
Figure 8. (A) H NMR spectrum (in CDCl
at 55 °C) of silyl-
3
protected poly(IBVE) obtained in the polymerization of IBVE with
difunctional dithioether at [M] /[12] /[TfOH] = 500/10/0.05 mM
0
0
0
in n-hexane/CH Cl /Et O (80/10/10 vol %) at −78 °C and (B) the
2
2
2
telechelic poly(IBVE) obtained polymers by deprotection with TBAF.
(
A) M (NMR) = 3200, M (SEC) = 2900, M /M = 1.22, F (α) =
n n w n n
1
.81. (B) M (NMR) = 3000, M (SEC) = 2700, M /M = 1.23, F (α)
n
n
w
n
n
=
1.80.
The difunctional dithioether with silyl-protected hydroxyl
groups was easily synthesized from the lithium salt of 1,4-
butanedithiol and 2 equiv of the hydrogen chloride adduct of
tert-butyldimethylsiloxyethyl vinyl ether. As with the mono-
thioethers above, the polymerization also proceeded smoothly,
resulting in polymers with controlled molecular weights and
narrow MWDs (M /M < 1.2) (Figure 7A). The M agreed
ends were obtained via the difunctional dithioether-mediated
cationic polymerization.
The chain extension reaction using the hydroxyl groups of
the telechelic poly(IBVE) was carried out in conjunction with
1,4-phenylene diisocyanate via the formation of urethane
linkages. The telechelic poly(IBVE) was first reacted with 2
equiv of 1,4-phenylene diisocyanate in the presence of
dibutyltin dilaurate (DBTDL) as a catalyst in n-hexane at 20
°C to be converted into diisocyanate chain ends. After 2 h, 1
equiv of 1,4-butanediol as the chain extender was further added
to the reaction solution. During these reactions, the SEC curves
shifted to high molecular weight, and the precursor telechelic
poly(IBVE) peak decreased (Figure 8D). These results indicate
that the telechelic poly(IBVE) was efficiently converted into
high molecular weight polyurethane via the reaction between
the hydroxyl and isocyanate groups. This success is owed
primarily to the high functionality of the telechelic polymers as
well as the high stability of the mid thioether groups. This
approach for telechelic polymers based on difunctional
compounds is not suitable for the other living cationic
polymerizations, which are based on less stable covalent
bonds. Thus, the thioether-mediated cationic polymerization
system offers a different approach for precision polymer
synthesis of novel well-defined polymer architectures.
w
n
n
well with the calculated values, assuming that one dithioether
forms one polymer chain (Figure S12).
The polymers obtained with the difunctional dithioether
1
were analyzed by H NMR spectroscopy (Figure 8A). The
spectrum showed the main signals of the IBVE repeating units
and the characteristic signals derived from the difunctional
dithioether, such as the methyl protons (i) of the protected silyl
groups, methyl protons (f) at the initiating α-end, and
methylene (k) and methine (b′) protons adjacent to the sulfur
atoms in the middle of polymer chain. The α-end functionality
(1.81) was close to two, indicating that this difunctional
dithioether works as a difunctional reversible chain-transfer
agent for the living cationic polymerization of IBVE.
The silyl groups were then deprotected and converted to the
hydroxyl groups using tetrabutylammonium fluoride (TBAF) in
THF at 40 °C. There were almost no changes in the SEC
curves (Figure 7B), indicating that the mid thioacetal group is
1
stable even during the deprotection. The H NMR spectrum
CONCLUSIONS
after the deprotection showed that the silyl groups completely
disappeared and that the adjacent methylene signals (g) slightly
shifted upfield (Figure 7B) whereas almost no changes were
observed for the other signals. The functionality of the α-end
group (1.80) remained almost the same. These results indicate
that telechelic polymers with hydroxyl groups at both chain
■
A series of thioethers, which can be easily synthesized and are
easy to handle, effectively mediate the degenerative cationic
chain-transfer polymerization of vinyl ethers and p-alkoxystyr-
enes in conjunction with a trace amount of triflic acid to result
in polymers with a controlled molecular weight and stable
H
DOI: 10.1021/acs.macromol.5b01341
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
thioether chain ends with high fidelity. This system is not only
reduced pressure (1.13 mmHg, bp = 46 °C) to give 1 as colorless
liquid (4.0 g, 21 mmol, 30% yield).
The experimental details for the other thioethers (2−6, 9−12) are
described in the Supporting Information.
based on a novel relevant degenerative chain-transfer
34,36−39,42−48
mechanism but is also metal-free
and can be
distinguished from other controlled or living cationic polymer-
izations thus far reported. Thus, this study offers a novel
synthetic route to prepare well-defined polymers and can be
used for bioapplications in which the polymers should be metal-
free.
Cationic Polymerization with Thioether. The cationic polymer-
ization of IBVE was carried out by the syringe technique under dry
nitrogen in baked glass tubes equipped with a three-way stopcock. A
typical example for the polymerization procedure is given below. The
reaction was initiated by addition of TfOH (0.30 mL of 0.50 mM in
−4
Et O, 1.5 × 10 mmol) via dry syringe into monomer solution (2.70
2
mL) containing IBVE (0.20 mL, 1.53 mmol) and 1 (0.05 mL of 564
mM in toluene, 0.03 mmol) in the n-hexane/CH Cl mixture (80/10)
EXPERIMENTAL SECTION
■
2
2
Materials. Isobutyl vinyl ether (IBVE) (TCI, 95%), ethyl vinyl
ether (EVE) (TCI, 98%), cyclohexyl vinyl ether (CHVE) (Aldrich,
at −40 °C. In predetermined intervals, the polymerization was
terminated with methanol (1.0 mL) containing a small amount of
triethylamine. The monomer conversion was determined from the
concentration of residual monomer measured by 1H NMR with
toluene as an initial standard (25 s, 90%). The quenched reaction
mixture was washed with distilled water to remove initiator residues,
evaporated to dryness under reduced pressure, and vacuum-dried to
9
8%), 2-chloroethyl vinyl ether (CEVE) (TCI, 97%), p-methoxystyr-
ene (pMOS) (TCI, 95%), acetaldehyde dimethylacetal (8) (Aldrich,
5%), and 1,4-butanediol (TCI, 99%) were distilled over calcium
hydride under reduced pressure before use. Trifluoromethanesulfonic
acid (TfOH) (TCI, >98.0%), n-butanethiol (Aldlich, 99%) 2-
butanethiol (sec-butanethiol) (TCI, 93%), 2-methyl-2-propanethiol
9
give the product polymers (M = 5000, M /M = 1.18).
n w n
(
tert-butanethiol) (Aldrich, 99%), benzenethiol (TCI, 98%), 4-
chlorobenzenethiol (TCI, 98%), 4-methoybenzenethiol (TCI, 96%),
,4-butanedithiol (TCI, 95%), p-toluenesulfonic acid monohydrate
Radical Copolymerization of IBVE and MA. The polymer-
ization was carried out by syringe techniques under dry argon or
nitrogen in baked glass tubes equipped with three-way stopcock. A
typical example for radical copolymerization of IBVE and MA is given
below. In a 25 mL round-bottomed flask was placed IBVE (1.77 mL,
1
(
(
TCI, 98%), sodium hydrate (TCI, 60%), hydrogen chloride solution
Aldrich, 1.0 M in Et O), dibutyl dilaurate (TCI, 95%), and 1,4-
2
1
3.6 mmol), MA (1.25 mL, 13.6 mmol), 1 (0.48 mL of 564 mM in
phenylene diisocyanate (TCI, 98%) were used as received. 2,2-
Azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70) (Wako, 95%) was
purified by washing with acetone at −15 °C and was evaporated to
dryness under reduced pressure. S-1-Isobutoxyethyl S′-2-ethyltrithio-
toluene, 0.27 mmol), toluene (1.94 mL), and solution of V-70 (1.36
mL of 50 mM solution in toluene, 0.068 mmol) at room temperature.
The total volume of the reaction mixture was 6.80 mL. After mixing,
the solution was charged in eight glass tubes, and the tubes were sealed
by flame under a nitrogen atmosphere. The tubes ware immersed in
thermostatic oil bath at 20 °C. In predetermined intervals, the
polymerization was terminated by cooling of the reaction mixtures to
49
50
carbonate (7), 1-(isobutoxy)ethyl chloride (IBVE-HCl), and 2-
51
(tert-butyldimethylsiloxy)ethyl vinyl ether were synthesized accord-
ing to the literature. Toluene (KANTO, >99.5%; H O <10 ppm), n-
hexane (KANTO, >96%; H O <10 ppm), diethyl ether (KANTO,
>
H O <0.005%) were dried and deoxygenized by passage through
column of Glass Contour Systems before use.
Synthesis of Butyl(1-isobutoxyethyl)thioether (1). 1 was
synthesized by the following two methods.
a. Method 1. The synthesis was carried out by reaction between
IBVE (14.6 mL, 112 mmol) and n-butanethiol (24.0 mL, 224 mmol)
in the presence of trace amount of p-toluenesulfonic acid monohydrate
2
2
−
78 °C. The monomer conversion was determined from the
99.5%; H O <50 ppm), and dichloromethane (KANTO, >99.5%;
2
1
concentration of residual monomer measured by the H NMR using
EtOAc as internal standard (20 h, IBVE: 41%, MA: 95%). The
quenched reaction mixture was evaporated to dryness under reduced
2
pressure and vacuum-dried to give the product polymers (Mn
63 300, M /M = 2.53).
=
1
w
n
Deprotection of Silyl-Protected Telechelic Polymer. The
deprotection of silyl-protected telechelic polymer was carried out
under a dry nitrogen atmosphere in 50 mL round-bottom flask
equipped with a three-way stopcock. For a typical example, a THF
solution of TBAF (1.0 M, 5.20 mL, 5.2 mmol) was added to the silyl-
protected telechelic poly(IBVE) (0.15 g, M = 2900, M /M = 1.22,
(
45 mg, 0.26 mmol) in dry CH Cl (31.4 mL) at −40 °C for 1 h. After
2
2
the reaction, the solution was diluted with Et O and washed with 5 wt
%
2
NaHCO aqueous solution and water. The solvent was removed by
3
n
w
n
evaporation. The remaining liquid was distilled under reduced pressure
1.13 mmHg, bp = 46 °C) to give 1 as colorless liquid (16.7 g, 87.6
0
.05 mmol). The mixture was stirred for 20 h at 40 °C. The reaction
(
was quenched by adding methanol (5.0 mL). The reaction solution
1
mmol, 78% yield). H NMR (CDCl ): 0.92 (m, 9H, OCH CH(CH )
and SCH CH CH CH ), 1.42 (se, 3H, SCH CH CH CH , J = 7.3
Hz), 1.73 (d, 3H, CH CH, J = 6.4 Hz), 1.54−1.62 (m, 5H, CH CH
and SCH CH CH CH ), 1.85 (m, 1H, OCH CH(CH ) ), 2.58 (m,
3
2
3 2
was diluted with CHCl , washed with distilled water, and then dried
3
2
2
2
3
2
2
2
3
vic
under vacuum to give telechelic polymers with hydroxyl groups at both
3
3
chain ends (0.15 g, M = 2700, M /M = 1.23).
n
w
n
2
2
2
3
2
3 2
Chain Extension Reaction. The chain extension reaction via the
formation of urethane linkages was carried out under a dry nitrogen
atmosphere in baked 25 mL glass tubes equipped with a three-way
stopcock. For a typical example, toluene solution of 1,4-phenylene
diisocyanate (1.88 mL of 36.3 mM solution in toluene, 0.068 mmol)
was added to the mixture solution of telechelic poly(IBVE) (93.5 mg,
M = 2700, M /M = 1.23, 0.034 mmol), DBTDL (0.54 mL of 12.7
2
H, SCH CH CH CH ), 3.19 and 3.42 (dd, 2H, OCH CH(CH ) , J
2 2 2 3 2 3 2 vic
=
6.4 and 6.9 Hz, Jgem = −9.2 Hz), 4.67 (q, 1H, CH CH, J = 6.4 Hz).
3
1
3
C NMR (CDCl , rt): 13.9 (SCH CH CH CH ), 19.7 (OCH CH-
3
2
2
2
3
2
(
(
(
CH ) ), 22.4 (SCH CH CH CH ), 22.5 (CH CH), 27.6
3 2 2 2 2 3 3
SCH CH CH CH ), 28.5 (OCH CH(CH ) ), 32. 4
2
2
2
3
2
3 2
SCH CH CH CH ), 73.8 (OCH CH(CH ) ), 81.3 (CH CH).
2
2
2
3
2
3
2
3
n
w
n
b. Method 2. The other method is based on the reaction between
sodium butanethiolate and the HCl adduct of IBVE (IBVE-HCl).
According to the reported method, IBVE-HCl was prepared by
adding 1.0 M Et O solution of hydrogen chloride (77 mL, 77 mmol)
dropwise into Et O solution of IBVE (9.1 mL, 70 mmol) at −78 °C.
Sodium butanethiolate was prepared from 1-butanethiol (7.5 mL, 70
mmol) and sodium hydride (2.8 g, 70 mmol) in dry Et O (40 mL).
Into the Et O solution of sodium butanethiolate was added dropwise
the IBVE-HCl solution (70 mmol) at 0 °C over 40 min. After stirring
−4
mM solution in n-hexane, 6.8 × 10 mmol), and n-hexane (1.0 mL).
The mixture was stirred for 2 h at 20 °C. Then, 1,4-butanediol (0.13
mL of 260 mM solution in THF, 0.034 mmol) was added to the
reaction solution. After 2 h, the reaction was quenched by adding
50
2
2
methanol to give the poly(IBVE) linked via urethane linkages (M =
w
20 400, M /M = 3.03).
w
n
2
Measurements. Monomer conversion was determined from the
1
2
concentration of residual monomer measured by H NMR spectros-
1
copy with toluene or 1,2-dichlororbenzene as an internal standard. H
for 1 h at 0 °C and then 1 h at ambient temperature, the reaction was
NMR spectra were recorded on a JEOL ECS-400 spectrometer,
operating at 400 MHz. MALDI-TOF-MS spectra were measured on a
Shimazu AXIMA-CFR Plus mass spectrometer (linear mode) with
dithranol as the ionizing matrix and sodium trifluoroacetate as the ion
quenched by diluting with Et O. The solution was washed with 5 wt %
2
NaHCO3 aqueous solution, brine, and water. The solvent was
removed by evaporation. The remaining liquid was distilled under
I
DOI: 10.1021/acs.macromol.5b01341
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
source. The number-average molecular weight (M ) and the molecular
(20) Moad, G.; Rizzardo, E.; Thang, S. H. Aust. J. Chem. 2012, 65,
985−1076.
n
weight distribution (M /M ) of the product polymer were determined
w
n
by size-exclusion chromatography (SEC) in THF at 40 °C on two
(21) Destarac, M. Polym. Rev. 2011, 51, 163−187.
(22) Yamago, S. Chem. Rev. 2009, 109, 5051−5068.
(23) Hurtgen, M.; Detrembleur, C.; Jerome, C.; Debuigne, A. Polym.
Rev. 2011, 51, 188−213.
polystyrene gel column [TSKgel MultiporeH -M (7.8 mm i.d. × 30
XL
cm)] connected to a JASCO PU-2080 precision pump and JASCO RI-
2
031 detector. The columns were calibrated against 10 standard
polystyrene samples (Varian; M = 575−2 783 000, M /M = 1.02−
(24) Litvinenko, G.; Mu
1266.
25) Matyjaszewski, K. ACS Symp. Ser. 1997, 665, 12−24.
(26) Muller, A. H. E.; Zhuang, R.; Yan, D.; Litvinenko, G.
Macromolecules 1995, 28, 4326−4333.
27) Muller, A. H. E.; Yan, D.; Litvinenko, G.; Zhuang, R.; Dong, H.
̈
ller, A. H. E. Macromolecules 1997, 30, 1253−
p
w
n
1
.23).
(
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.macro-
mol.5b01341.
̈
■
*
S
(
̈
Macromolecules 1995, 28, 7335−7338.
(28) Webster, O. W. Adv. Polym. Sci. 2004, 167, 1−34.
(29) Webster, O. W.; Hertler, W. R.; Sogah, D. Y.; Farnham, W. B.;
Additional experimental procedures and supplementary
data (PDF)
RajanBabu, T. V. J. Am. Chem. Soc. 1983, 105, 5706−5708.
(30) Sawamoto, M. Prog. Polym. Sci. 2000, 25, 403−452.
(
(
31) Puskas, J. E.; Kaszas, G. Prog. Polym. Sci. 2000, 25, 403−452.
32) Goethals, E. J.; Du Prez, F. Prog. Polym. Sci. 2007, 32, 220−246.
AUTHOR INFORMATION
Corresponding Authors
E-mail: satoh@apchem.nagoya-u.ac.jp (K.S.).
E-mail: kamigait@apchem.nagoya-u.ac.jp (M.K.).
■
(33) Aoshima, S.; Kanaoka, S. Chem. Rev. 2009, 109, 5245−5287.
(34) Miyamoto, M.; Sawamoto, M.; Higashimura, T. Macromolecules
*
1984, 17, 265−268.
*
(35) Faust, R.; Kennedy, J. P. Polym. Bull. 1986, 15, 317−323.
(36) Cho, C. G.; Feit, B. A.; Webster, O. W. Macromolecules 1990, 23,
Notes
1
(
2
(
918−1923.
37) Cho, C. G.; Feit, B. A.; Webster, O. W. Macromolecules 1992, 25,
081−2085.
38) Uchiyama, M.; Satoh, K.; Kamigaito, M. Angew. Chem., Int. Ed.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported in part by a Grant-in-Aid for Scientific
Research (A) (No. 26248032) for K.S. by the Japan Society for
the Promotion of Science and Program for Leading Graduate
Schools “Integrative Graduate Education and Research
Program in Green Natural Sciences”.
2
015, 54, 1924−1928.
(39) Cramail, H.; Deffieux, A.; Nuyken, O. Makromol. Chem., Rapid
Commun. 1993, 14, 17−27.
(40) Cramail, H.; Deffieux, A. Macromolecules 1994, 27, 1401−1406.
(
41) The estimated C values of 5.31 for 1 and 7.68 for 7 are the
tr
smallest limits, and the actual C values are even larger. The C values
tr
tr
obtained at middle stage of the polymerizations are 11.19 for 1 (conv
48%, M = 3000, M /M = 1.32) and 13.2 for 7 (conv = 55%, M =
REFERENCES
■
=
n
w
n
n
(
1) Controlled and Living Polymerization: From Mechanisms to
3
400, M /M = 1.23). The lower C at higher conversions is due to
w n tr
Materials; Mu
̈
ller, A. H. E., Matyjaszewskiz, K., Eds.; Wiley-VCH:
some side reactions because the equation (M /M = 1 + 1/X + (2 −
w
n
n
Weinheim, 2009.
2) Jenkins, A. D.; Jones, R. G.; Moad, G. Pure Appl. Chem. 2010, 82,
c)/(cC )) assumes no side reactions.
tr
(
4
(
(
3
(
(
1
(
(
3
(
1
(
4
(
(
42) Aoshima, H.; Uchiyama, M.; Satoh, K.; Kamigaito, M. Angew.
Chem., Int. Ed. 2014, 53, 10932−10936.
43) Sawamoto, M.; Fujimori, J.; Higashimura, T. Macromolecules
987, 20, 916−920.
44) Nuyken, O.; Kro
45) Cramail, H.; Deffieux, A. Macromol. Chem. Phys. 1994, 195,
17−227.
46) Van Meirvenne, D.; Haucourt, N.; Goethals, E. J. Polym. Bull.
990, 23, 185−190.
47) Sugihara, S.; Tanabe, Y.; Kitagawa, M.; Ikeda, I. J. Polym. Sci.,
Part A: Polym. Chem. 2008, 46, 1913−1918.
48) Kanazawa, A.; Hashizume, R.; Kanaoka, S.; Aoshima, S.
Macromolecules 2014, 47, 1578−1585.
49) Kumagai, S.; Nagai, K.; Satoh, K.; Kamigaito, M. Macromolecules
010, 43, 7523−7531.
50) Kamigaito, M.; Maeda, Y.; Sawamoto, M.; Higashimura, T.
Macromolecules 1993, 26, 1643−1649.
51) Higashimura, T.; Ebara, K.; Aoshima, S. J. Polym. Sci., Part A:
Polym. Chem. 1989, 27, 2937−2950.
83−491.
3) Goto, A.; Fukuda, T. Prog. Polym. Sci. 2004, 29, 329−385.
(
1
4) Hawker, C. J.; Bosma, A. W.; Harth, E. Chem. Rev. 2001, 101,
661−3688.
5) Studer, A.; Schulte, T. Chem. Rec. 2005, 5, 27−35.
6) Sciannamea, V.; Jer me, R.; Detrembleur, C. Chem. Rev. 2008,
(
(
̈
ner, H. Makromol. Chem. 1990, 191, 1−16.
́ ̂
o
2
(
1
(
08, 1104−1126.
7) Grubbs, R. B. Polym. Rev. 2011, 51, 104−137.
8) Kamigaito, M.; Ando, T.; Sawamoto, M. Chem. Rev. 2001, 101,
689−3746.
9) Kamigaito, M.; Ando, T.; Sawamoto, M. Chem. Rec. 2004, 4,
59−175.
10) Ouchi, M.; Terashima, T.; Sawamoto, M. Chem. Rev. 2009, 109,
(
(
2
(
963−5050.
11) Matyjaszewski, K.; Xia, J. Chem. Rev. 2001, 101, 2921−2990.
(
2
(
1
12) Tsarevsky, N. V.; Matyjaszewski, K. Chem. Rev. 2007, 107,
270−2299.
13) di Lena, F.; Matyjaszewski, K. Prog. Polym. Sci. 2010, 35, 959−
021.
(
(
14) Rosen, B. M.; Percec, V. Chem. Rev. 2009, 109, 5069−5119.
(
15) Haddleton, D. M.; Limer, A. Prog. React. Kinet. Mech. 2004, 29,
1
(
87−241.
16) David, G.; Boyer, C.; Tonnar, J.; Ameduri, B.; Lacroix-
Desmazes, P.; Boutevin, B. Chem. Rev. 2006, 106, 3936−3962.
17) Moad, G.; Rizzardo, E.; Thang, S. H. Aust. J. Chem. 2005, 58,
79−410.
18) Moad, G.; Rizzardo, E.; Thang, S. H. Aust. J. Chem. 2006, 59,
69−692.
19) Moad, G.; Rizzardo, E.; Thang, S. H. Aust. J. Chem. 2009, 62,
402−1472.
(
3
(
6
(
1
J
DOI: 10.1021/acs.macromol.5b01341
Macromolecules XXXX, XXX, XXX−XXX