Synthesis of 1,2,4-triazolium salt-based polymers and block copolymers by RAFT polymerization: Ion conductivity and assembled structures

Article abstract of DOI:10.1016/j.polymer.2016.04.062

Well-defined 1,2,4-triazolium-based polymers were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of N-vinyl-1,2,4-triazolium salts, i.e., N-vinyl-4-ethyl-1,2,4-triazolium bromide (NVETri-Br) and N-vinyl-(4-ethoxyethyl)-1,2,4-triazolium bromide (NVEtOETri-Br). Reasonable control of the polymerization of these monomers was attained using a trithiocarbonate-type chain transfer agent (CTA), producing poly(N-vinyl-1,2,4-triazolium bromide)s with controlled molecular weights (M_n,SEC > 20000) and low values (M_w/M_n < 1.1). Nonionic (water-soluble)-ionic (solubility tunable) block copolymers were achieved by RAFT polymerization of N-vinyl-1,2,4-triazolium salts using hydrophilic macro-CTAs derived from N-vinyl pyrrolidone (NVP) and N-vinyl-1,2,4-triazole (NVTri). The anion exchange reaction of the poly(NVETri-Br) segment in the block copolymers with lithium bis(trifluoromethanesulfonyl)imide (LiNTf₂) proceeded selectively to afford amphiphilic block copolymers composed of hydrophobic poly(NVETri-NTf₂) and hydrophilic nonionic segment, poly(NVP) or poly(NVTri). The ionic conductivity of poly(NVP)₃₃-b-poly(NVETri-NTf₂)₆₇ was 4.3 × 10^-5 S/cm at 25 °C, which was remarkably higher than that of poly(NVETri-NTf₂) (1.7 × 10^-5 S/cm). At 90 °C, poly(NVP)-b-poly(NVETri-NTf₂) exhibited high ionic conductivities of 3.1-2.3 × 10^-4 S/cm under the ambient humidity conditions, depending on the comonomer composition (NVP content = 12-33%). We believe that this represents the first report on controlled synthesis of 1,2,4-triazolium-based polymers and block copolymers that exhibit high characteristic ion-conducting properties, depending on the structure of the substituent group, counter anion, comonomer structure, and composition.

Full text of DOI:10.1016/j.polymer.2016.04.062

Accepted Manuscript
Synthesis of 1,2,4-triazolium salt-based polymers and block copolymers by RAFT
polymerization: Ion conductivity and assembled structures
Kazuhiro Nakabayashi, Akiko Umeda, Yu Sato, Hideharu Mori
PII:
S0032-3861(16)30344-5
10.1016/j.polymer.2016.04.062
JPOL 18649
DOI:
Reference:
To appear in: Polymer
Received Date: 1 March 2016
Revised Date: 22 April 2016
Accepted Date: 26 April 2016
Please cite this article as: Nakabayashi K, Umeda A, Sato Y, Mori H, Synthesis of 1,2,4-triazolium
salt-based polymers and block copolymers by RAFT polymerization: Ion conductivity and assembled
structures, Polymer (2016), doi: 10.1016/j.polymer.2016.04.062.
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ACCEPTED MANUSCRIPT
Synthesis of 1,2,4-Triazolium Salt-Based Polymers and Block Copolymers by
RAFT Polymerization: Ion Conductivity and Assembled Structures
Graphic Abstract

ACCEPTED MANUSCRIPT
Synthesis of 1,2,4-Triazolium Salt-Based Polymers and
Block Copolymers by RAFT Polymerization: Ion
Conductivity and Assembled Structures
†
†
†
*†‡
Kazuhiro Nakabayashi , Akiko Umeda , Yu Sato , Hideharu Mori
†
‡
Department of Polymer Science and Engineering, Department of Organic Device Engineering,
Graduate School of Science and Engineering, Yamagata University, 4-3-16, Jonan, Yonezawa,
92-8510, Japan
9
*
To whom correspondence should be addressed. e-mail: h.mori@yz.yamagata-u.ac.jp
Phone:+81-238-26-3765, Fax: +81-238-26-3092
Keywords: Polymeric ionic liquid, ion conductivity, RAFT polymerization, block copolymer, triazolium
1

ACCEPTED MANUSCRIPT
Abstract: Well-defined 1,2,4-triazolium-based polymers were synthesized by reversible
addition-fragmentation chain transfer (RAFT) polymerization of N-vinyl-1,2,4-triazolium salts, i.e.,
N-vinyl-4-ethyl-1,2,4-triazolium bromide (NVETri-Br) and N-vinyl-(4-ethoxyethyl)-1,2,4-triazolium
bromide (NVEtOETri-Br). Reasonable control of the polymerization of these monomers was attained
using a trithiocarbonate-type chain transfer agent (CTA), producing poly(N-vinyl-1,2,4-triazolium
bromide)s with controlled molecular weights (Mn,SEC > 20000) and low Ð values (M /M < 1.1).
w
n
Nonionic (water-soluble)-ionic (solubility tunable) block copolymers were achieved by RAFT
polymerization of N-vinyl-1,2,4-triazolium salts using hydrophilic macro-CTAs derived from N-vinyl
pyrrolidone (NVP) and N-vinyl-1,2,4-triazole (NVTri). The anion exchange reaction of the
poly(NVETri-Br) segment in the block copolymers with lithium bis(trifluoromethanesulfonyl)imide
(
LiNTf ) proceeded selectively to afford amphiphilic block copolymers composed of hydrophobic
2
poly(NVETri-NTf ) and hydrophilic nonionic segment, poly(NVP) or poly(NVTri). The ionic
2
-5
o
conductivity of poly(NVP) -b-poly(NVETri-NTf ) was 4.3 × 10 S/cm at 25 C, which was
3
3
2 67
-5
o
remarkably higher than that of poly(NVETri-NTf ) (1.7
×
10
S/cm). At 90 C,
2
-4
poly(NVP)-b-poly(NVETri-NTf
2
) exhibited high ionic conductivities of 3.1–2.3 × 10 S/cm under the
ambient humidity conditions, depending on the comonomer composition (NVP content = 12–33 %). We
believe that this represents the first report on controlled synthesis of 1,2,4-triazolium-based polymers
and block copolymers that exhibit high characteristic ion-conducting properties, depending on the
structure of the substituent group, counter anion, comonomer structure, and composition.
2

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1
. INTRODUCTION
The field of polymeric ionic liquids, which are macromolecules obtained by polymerizing ionic liquid
monomers, has considerably extended in the past few decades, owing to their great interest in polymer
science as well as in practical applications.[1-4] Many researchers have focused on the manipulation of
their attractive properties, such as ionic conductivity and CO -absorbing property, by adjusting the
2
structures of the cation (e.g., imidazolium, pyridinium, and tetraalkylammonium) and the anion (e.g.,
halide, tetrafluoroborate, hexafluorophosphate), in addition to the structure of the polymer backbone.
Among the various polymeric ionic liquids, imidazolium salt-based polymers are the most popular
cationic components, which include polymers having imidazolium moieties in the side chains, such as
poly(N-vinylimidazolium salt) derivatives.[5-8]
Recently, growing attention has been paid to triazolium-based polymers as a new member of the
polymeric ionic liquids family.[4, 9] Triazole belongs to a versatile class of five-membered heterocyclic
azole compounds having three isomers, including 1,2,3-triazole, 1,2,4-triazole, and 1,3,4-triazole
derivatives, depending on the relative positions of the three nitrogen atoms. Among then, 1,2,3-triazole
derivatives and their viny monomers, which can be utilized as precursors for 1,2,3-triazolium units, have
gained great interest, driven by the remarkable development of the copper-catalyzed azide-alkyne
cycloaddition as a representative click reaction.[10, 11] Based on the versatility of the click reaction,
various 1,2,3-triazolium-based polymers have been prepared via post-quaternization of 1,2,3-triazole
units in the polymers[12, 13] or direct polymerization of 1,2,3-triazolium-containing monomers[14]
originating from the 1,2,3-triazole derivatives. In addition to main-chain type polymers,[15-17] a variety
of
polymers
having
1,2,3-triazolium
side
chains
have
been
developed
from
C-vinyl-1,2,3-triazolium,[14] vinyl ester,[12] and acrylate[13, 18] derivatives. 1,2,3-Triazolium-based
ion conducting networks comprise an intriguing subclass of such triazolium-based polymers.[19] Other
interesting systems involve antimicrobial polymethacrylates and their copolymers based on quaternized
thiazole and 1,2,3-triazole side-chains.[20-22] However, to the best of our knowledge, the direct
3

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controlled radical polymerization of N-vinyltriazolium salt monomers (e.g., N-vinyl-1,2,3-triazolium
salts and N-vinyl-1,2,4-triazolium salts) has never been reported.
The 1,2,4-triazolium ring, another nitrogen-rich heterocyclic ionic liquid, has also gained increased
interest due to its various attractive physicochemical and thermal properties,[23-26] as well as its
potential electrochemical and energetic applications.[27-30] For example, Luo et al. demonstrated high
ionic conductivity, wide electrochemical window, and good thermal stability of 1,2,4-triazolium
methanesulfonate, which would be a suitable candidate for high temperature proton exchange
membrane fuel cell electrolytes.[31] Vestergaard et al. also reported the availability of molten mixtures
of 1,2,4-triazolium chloride-aluminum chloride, exhibiting high conductivity in a wide range of
temperature range, as secondary battery electrolytes.[27] Despite the many characteristic functions and
properties of 1,2,4-triazolium-containing ionic liquids, research on 1,2,4-triazolium-based polymers has
been rather limited. Shreeve et al. developed 1,2,4-triazolium-based energetic polymers via free radical
polymerization of N-vinyl-1,2,4-triazolium salts or by protonation of poly(N-vinyl-1,2,4-triazole),
respectively.[32] Very recently, Yuan’s group demonstrated that poly(N-vinyl-1,2,4-triazolium)
obtained by free radical polymerization exhibited unique behavior in loading metal ions.[33] Miller et al.
reported the synthesis of 1,2,4-triazolium-based covalently crosslinked polyester networks by Michael
addition polymerization.[34] Another example is the preparation of proton-conducting membranes
based on incorporating a proton conductor, 1,2,4-triazolium methanesulfonate, into the Nafion
membrane.[35]
To further exploit the intriguing properties of 1,2,4-triazolium units for the development of advanced
polymeric materials, in this study, we focus on N-vinyl-1,2,4-triazolium salts (NVTri-X) as a new
family of triazolium-based monomers (Scheme 1). Two monomers, N-vinyl-4-ethyl-1,2,4-triazolium
bromide (NVETri-Br) and N-vinyl-(4-ethoxyethyl)-1,2,4-triazolium bromide (NVEtOETri-Br), were
selected, which were prepared by quaternization of N-vinyl-1,2,4-triazole (NVTri), as shown in Scheme
2
. Similar to N-vinylimidazolium salts (NVIm-X), 1,2,4-triazolium-containing monomers belong to the
class of non-conjugated N-vinyl monomers having a cationic heterocyclic ring. The reactivity of the
4

ACCEPTED MANUSCRIPT
monomers and the various properties of the resulting polymers can be tuned as a function of the
structure of the substituted group at the 4-position and the nature of the counteranion. Both NVTri-X
and NVIm-X are ionic and azolium-based monomers, whereas NVTri and NVIm can be recognized as
nonionic precursors and azole-based monomers (Scheme 1). Triazole, possessing an electron-rich
aromatic ring, undergoes a proton-transfer mechanism similar to that of imidazole.[36] It was reported
that the proton in 1,2,4-triazole is more readily transferred than that in imidazole due to the alternating
single-double bond structure and the three nitrogens in the triazole.[35, 37] Electrochemical stability of
1
,2,4-triazole and efficient promotion of proton conductivity were also demonstrated,[37] which are
crucial for fuel cell applications. Poly(NVTri) composed of the 1,2,4-triazole unit is a water-soluble
polymer possessing a pyridine-type isolated nitrogen atom that tends to form hydrogen bonds with water
molecules, and its solubility is distinctly different from that of other water-insoluble poly(vinylazole)s
containing sequences of two or more nitrogen atoms in the heterocycle, such as
poly(N-vinyl-1,2,3-triazole) and poly(N-vinyl-1,3,4-triazole).[38, 39] Hence, 1,2,4-triazolium-based
polymers may offer many attractive functions and properties compared to imidazolium- and
1
,2,3-triazolium analogues.
Scheme 1. Structures of N-vinyl azoles (NVIm: N-vinylimidazole, NVTri: N-vinyl-1,2,4-triazole) and
N-vinyl azolium salts (NVIm-X: N-vinylimidazolium salt, NVTri-X: N-vinyl-1,2,4-triazolium salt).
5

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Ionic liquid-based block copolymers have continued to attract widespread interest because of their
characteristic ionic conductivity and the ability to self-assemble into hierarchical structures. A variety of
block copolymers with imidazolium salts having various substituent groups and counterions have been
developed as promising candidates for diverse applications.[40-42] For example, atom transfer radical
polymerization,[43, 44] reversible addition-fragmentation chain transfer (RAFT) polymerization,[45-48]
and cobalt-mediated radical polymerization[49, 50] of imidazolium-containing monomers have been
utilized to synthesize block copolymers having imidazolium-containing segments. In particular, much
effort has been devoted to exploring the structure-morphology-property correlation, including the ionic
conductivity and nanostructured morphologies of self-assembled architectures.[51-54] In some systems,
the block copolymers exhibited increased ionic conductivity relative to statistical copolymer analogues
or homopolymers; this is attributed to the confinement blocks within the ordered nanodomains.
6

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Scheme 2. RAFT Polymerization of N-vinyl-4-ethyl-1,2,4-triazolium bromide (NVETri-Br) and
N-vinyl-(4-ethoxyethyl)-1,2,4-triazolium bromide (NVEtOETri-Br) using different chain transfer agents
(CTAs).
In this study, we initially investigated the RAFT polymerization of two 1,2,4-triazolium-based
monomers (NVETri-Br and NVEtOETri-Br), which were prepared from NVTri (Scheme 2). In previous
studies, we reported RAFT polymerization of NVTri, which is a nonionic N-vinyl monomer having a
basic aromatic heterocycle.[38] RAFT polymerization of NVTri afforded well-defined amphiphilic
block copolymers[38] and star block copolymers[55] comprising poly(NVTri) as a hydrophilic segment
and poly(N-vinylcarbazole) as a hydrophobic segment with characteristic optoelectronic properties. We
also developed controlled RAFT polymerization of NVIm-X, which were prepared by quaternization of
NVIm, using xanthate-type chain transfer agents (CTAs).[45] The RAFT polymerization of NVIm-X
afforded various imidazolium-based polymers involving thermoresponsive-ionic liquid block
copolymers, star, and star-block copolymers.[45, 56] As a distinction from previous related studies
using imidazolium-based and 1,2,4-triazole-based N-vinyl monomers (NVIm-X [45, 56] and NVTri [38,
5
5]), this contribution represents the first report of the controlled radical polymerization of
N-vinyl-1,2,4-triazolium salts (NVTri-X), leading to the production of a new class of functional polymer
electrolyte having characteristic ion conductivity.
We also describe the synthesis of well-defined block copolymers composed of two different N-vinyl
monomers, in which the ionic segment was obtained by RAFT polymerization of NVETri-Br, as shown
in Scheme 3. Poly(N-vinyl pyrrolidone) and poly(NVTri) were selected as non-ionic water-soluble
segments. The solubility of the poly(NVTri-X) segment in the block copolymers can be tuned by
-
-
changing the structure of the counteranion (Br and bis(trifluoromethanesulfonyl)imide ((SO CF ) N =
2
3 2
-
Tf N ) to hydrophilic and hydrophobic ions, respectively) via anion exchange reactions. Hence, the
2
resulting block copolymers are regarded as nonionic (water-soluble)-ionic (solubility tunable) block
7

ACCEPTED MANUSCRIPT
copolymers that can be transformed from double hydrophilic block copolymers into amphiphilic block
copolymers via anion exchange. Herein, we evaluate the ion conductivity and assembled structures of
the resulting block copolymers.
2
2
2
. EXPERIMENTAL SECTION
.1.Materials
,2-Azobis(isobutyronitrile) (AIBN, Kanto Chemical, 97%) was purified by recrystallization from
methanol. N-vinyl pyrrolidone (NVP, Wako Pure Chemical, > 98 %) was purified by distillation under
vacuum. N-Vinyl-1,2,4-triazole (NVTri) was obtained by the reaction of 1H-1,2,4-triazole with a excess
of vinyl acetate in the presence of trifluoroacetic acid, hydroquinone, and mercury(II) acetate.[38, 57]
Bromoethane (Kanto Chemical, > 98 %), 2-bromoethyl ethyl ether (Tokyo Chemical Industry, > 95 %),
lithium bis(trifluoromethanesulfonyl)imide (LiNTf , Tokyo Chemical Industry, > 98 %), and methanol
2
(anhydrous MeOH, Kanto Chemical, 99.8%) were used as received. Other materials were used
without further purification.
Eight different chain transfer agents (CTAs) were employed in this study, as shown in Scheme 2.
O-Ethyl-S-(1-phenylethyl) dithiocarbonate (CTA 1),[58-60] O-ethyl-S-propionic acid dithiocarbonate
(CTA 2),[61] O-ethyl-S-(1-ethoxy carbonyl) ethyl dithiocarbonate (CTA 3),[62, 63] and
O-ethyl-S-(cyanomethyl) dithiocarbonate (CTA 4),[64] were synthesized by the reaction of potassium
ethyl xanthogenate with corresponding bromide (1-bromoethyl benzene for CTA 1, 2-bromopropionic
acid for CTA 2, ethyl 2-bromopropionate for CTA 3, bromoacetonitrile for CTA 4, respectively),
according to a procedure reported in the literature. Benzyl 1-pyrrolecarbodithioate (CTA 5) was also
synthesized
according
to
the
procedure
reported
previously.[65,
66]
2
-(Dodecylthiocarbonothioylthio)-2-methylpropanoic acid (CTA 6, Aldrich, >98%), 2-cyano-2-propyl
dodecyl
trithiocarbonate
(CTA
7,
Aldrich,
>97%),
and
4
-cyano-4-[(dodecyl-sulfanylthiocarbonyl)sulfanyl]pentanoic acid (CTA 8, Aldrich, >98%) were used
as received.
8

ACCEPTED MANUSCRIPT
2
.2.Synthesis of N-Vinyl-1,2,4-triazolium Salts
Two N-viny-1,2,4-triazolium salts having different substituent groups, NVETri-Br and NVEtOETri-Br,
were synthesized by the reaction of NVTri with corresponding alkyl bromides according to the method
used for the synthesis of N-vinylimidazolium salts, with slight modifications (Scheme 1).[6] In a typical
experiment, NVTri (2.50 g, 26.3 mmol) and 3-bromoethane (14.1 g, 0.13 mol) were placed in a flask
o
equipped with a magnetic stirring bar, and the mixture was refluxed at 50 C for five days. During the
reaction, the product precipitated from the reaction mixture. After washing the resulting precipitate
several times with ethyl acetate by decantation, the product was isolated by filtration and dried under
o
vacuum overnight at room temperature to afford NVETri-Br as a white solid (2.9 g, 54%). T = 85 C.
m
1
H NMR (DMSO-d ): δ 1.49 (t, 3H, -CH -CH ), 4.29 (q, 2H, -CH -CH ), 5.58 (d, 1H, CH =CH-), 6.07
6
2
3
2
3
2
1
3
(
d, 1H, CH =CH-), 7.50 (dd, 1H, CH =CH-), 9.35 (s, 1H , N-CH-N), 10.37 (s, 1H, N-CH-N) ppm. C
2
2
NMR (DMSO-d ): δ 14.20 (-CH -CH ), 43.36 (-CH -CH ), 110.01 (CH =CH-), 129.24 (CH =CH-),
6
2
3
2
3
2
2
1
41.60 (N-CH-N), 144.69 (N-CH-N) ppm. Anal. Calcd for C H BrN : C, 35.3; H, 4.9; N, 20.6. Found:
6 10 3
C, 35.3; H, 5.0; N, 20.5.
The same procedure was employed for the synthesis of NVEtOETri-Br. The mixture of NVTri (2.50 g,
o
2
6.3 mmol) and 2-bromoethylethyl ether (12.1 g, 78.9 mmol) was refluxed at 70 C for 5 days, followed
by the decantation with ethyl acetate. NVEtOETri-Br was obtained as a white solid (9.3g, 71%). T =
m
o
1
7
2 C. H NMR (DMSO-d ): δ 1.11 (t, 3H, -CH -CH ), 3.49 (q, 2H, -CH -CH ), 3.77 (t, 2H,
6 2 3 2 3
-
CH -CH -), 4.46 (t, 2H, -CH -CH -), 5.58 (d, 1H, CH =CH-), 6.07 (d, 1H, CH =CH-), 7.57 (dd, 1H,
2 2 2 2 2 2
1
3
CH =CH-), 9.29 (s, 1H, N-CH-N), 10.28 (s, 1H, N-CH-N) ppm. C NMR (DMSO-d ): δ 14.51
2
6
(
-CH
2
-CH
3
), 47.86 (-N-CH
2
-), 65.54 (-O-CH
2
-), 66.51 (-O-CH
2
-), 110.04 (CH
2
2
=CH), 129.17 (CH =CH),
1
8 3
41.88 (N-CH-N), 145.16 (N-CH-N) ppm. Anal. Calcd for C H14BrN O: C, 38.7; H, 5.7; N, 16.9.
Found: C, 38.3; H, 5.84; N, 16.9.
1
13
H and C NMR spectra of NVETri, NVETri-Br, and NVEtOETri-Br are shown in Figures S1-S5
Supporting Information).
(
9

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2
.3.General Polymerization Procedure
All polymerizations were carried out with AIBN as the initiator in a degassed sealed tube. A
representative example is as follows: NVETri-Br (0.20 g, 1.00 mmol), CTA 7 (6.9 mg, 0.02 mmol),
AIBN (1.6 mg, 0.01 mmol), and methanol (0.5 mL, [M] = 2.0 mol/L) were placed in a dry glass
0
ampule equipped with a magnetic stirring bar, and then the solution was degassed by three
o
freeze-evacuate-thaw cycles. After the ampule was flame-sealed under vacuum, it was stirred at 60 C
for 24 h. The reaction was stopped by rapid cooling with liquid nitrogen. For the determination of the
1
monomer conversion, the H NMR spectrum of the polymerization mixture collected just after the
polymerization was measured in DMSO-d at room temperature, and the integration of the monomer
6
C=C-H resonance at around 6.1 ppm was compared with the sum of N-CH-N peak intensity of the
triazolium ring in the polymer and the monomer at around 10.4–11.3 ppm. Conversion determined by
this method was >99%. The crude polymer was purified by reprecipitation into a large excess of
o
acetone/chloroform (7/3 vol%), and the resulting product was dried under vacuum at 60 C to afford
1
poly(NVETri-Br) as a pale yellow solid: yield 0.195 g, 95 %. H NMR (DMSO-d
6
): δ 1.2-1.9 (br, 3H,
-CH in the
side chain), 4.5-5.4 (br, 1H, CH in the polymer main chain), 9.2-9.8 (br, 1H, N-CH-N), 10.4-11.3 (br,
CH
3
in the side chain), 1.9-3.1 (br, 2H, CH
2
in the polymer main chain), 3.9-4.5 (br, 2H, CH
2
3
1
3
1
H, N-CH-N) ppm. C NMR (DMSO-d ): δ 12.5-15.2 (CH ), 35.3-38.9 (CH -CH), 42.6-45.9
6 3 2
(
CH -CH ), 53.6-57.5 (CH -CH), 141.8-144.7 (N-CH-N), 144.7-146.9 (N-CH-N) ppm. Anal. Calcd for
2 3 2
C H BrN ・1/2H O: C, 33.8; H, 5.2; N, 19.7. Found: C, 34.0; H, 5.3; N, 19.3.
6
10
3
2
Similar procedure was applied for the polymerization of NVEtOETri-Br. In the case, monomer
1
conversion was determined by the H NMR spectrum (DMSO-d ) by comparing the peak integration of
6
the monomer C=C-H resonance at around 6.1 ppm to the sum of N-CH-N peak intensity of the
triazolium ring in the polymer and the monomer at around 10.1-11.0 ppm. After the polymerization, the
crude polymer was purified by dialysis (Spectra Pore; MWCO 1000Da) with methanol. After 2 days,
o
the solution was concentrated, and dried under vacuum at 60 C to afford poly(NVEtOETri) as a pale
1
0

ACCEPTED MANUSCRIPT
1
yellow solid. H NMR (DMSO-d
6 3 2
): δ 0.9-1.4 (br, 3H, CH in the side chain), 1.8-3.0 (br, 2H, CH in the
polymer main chain), 3.4-3.7 (br, 2H, CH -CH in the side chain), 3.7-4.1 (br, 2H, -CH -CH -), 4.2-4.6
2
3
2
2
(
br, 2H, -CH -CH -), 4.7-5.5 (br, 1H, CH in the polymer main chain), 8.8-9.5 (br, 1H, N-CH-N),
2 2
1
3
1
4
0.1-11.0 (br, 1H, N-CH-N) ppm. C NMR (DMSO-d ): δ 15.0-16.7 (CH ), 36.4-38.7 (CH -CH),
6 3 2
7.3-50.1 (N-CH -CH ), 54.1-57.8 (CH -CH), 65.6-66.3 (-O-CH -), 66.3-67.3 (-O-CH -), 140.3-144.8
2
2
2
2
2
(N-CH-N), 144.8-147.7 (N-CH-N) ppm. Anal. Calcd for C
8
H14BrN
3
O・1H
2
O: C, 36.1; H, 6.1; N, 15.8.
Found: C, 36.7; H, 6.1; N, 16.1.
1
13
H and C NMR spectra of poly(NVETri-Br) and poly(NVEtOETri-Br) are shown in Figures S2-5
(see Supporting Information). Both poly(NVETri-Br) and poly(NVEtOETri-Br) were soluble in water,
methanol, DMSO, and insoluble in acetone, ethyl acetate, THF, diethyl ether, hexane. Additionally,
poly(NVEtOETri-Br) was soluble in DMF and chloroform. The solubilities of these polymers in various
solvents are summarized in Table S1 (Supporting Information).
2
.4.Synthesis of Block Copolymers
A representative example of the synthesis of the block copolymer composed of NVP and NVETri-Br is
as follows: NVP (5.3 mL, 5.6 g, 50 mmol), CTA 3 (0.22 g, 1.0 mmol), and AIBN (0.08 g, 0.5 mmol)
were placed in a dry ampule, and then the solution was degassed by three freeze-evacuate-thaw cycles.
o
After the ampule was flame-sealed under vacuum, it was stirred at 60 C for 50 min. After the product
was purified by precipitation into diethyl ether, the product was dried under vacuum to afford
poly(NVP) as a pale yellow solid (5.5 g, yield = 99%, Mn,NMR = 7000 g/mol, M /M = 1.07), which was
w
n
employed as a macro-CTA. The xanthate-terminated poly(NVP) (0.14 g, 0.02 mmol), AIBN (1.6 mg,
.01 mmol), NVETri-Br (0.20 g, 1.0 mmol), and methanol (0.7 mL) were placed in a dry ampule. After
the solution was degassed by three freeze-evacuate-thaw cycles, the polymerization was conducted at 60
0
o
1
C for 24 h (conversion determined by H NMR spectroscopy = 97%). The reaction mixture was
purified by reprecipitation into a large excess of acetone/chloroform (7/3 vol%), and isolated by
filtration to give a block copolymer, poly(NVP)-b-poly(NVETri-Br) as a pale yellow solid (0.206 g,
1
1

ACCEPTED MANUSCRIPT
6
0%). The block copolymer was soluble in water, methanol, DMSO, and insoluble in DMF, acetone,
ethyl acetate, THF, chloroform, diethyl ether, hexane. The copolymer composition was determined
1
using H NMR spectroscopy (CD OD) by a comparison of peaks associated with the two comonomers;
3
the peak at 4.8-5.4 ppm attributed to the methine proton (1H) of the main chain in NVETri-Br unit and
the peak at 1.9-2.1 ppm corresponded to the methylene proton (2H) of the NVP units.
In the case of the block copolymer obtained at [NVP] /[macro-CTA] /[AIBN] = 25/2/1, the product
0
0
0
was purified by dialysis (Spectra Pore; MWCO 1000Da) with methanol and then by reprecipitation into
a large excess of acetone/diethylether (6/4 vol%).
For the synthesis of the block copolymer composed of NVTri and NVETri-Br, initially NVTri (3.8 g,
4
0 mmol), CTA 7 (0.14 g, 0.4 mmol), and AIBN (0.03 g, 0.2 mmol), and methanol (20 mL) were placed
in a dry ampule, and then the solution was degassed by three freeze-evacuate-thaw cycles. After the
o
ampule was flame-sealed under vacuum, it was stirred at 60 C for 6 h. After the product was purified
by precipitation into diethyl ether, the product was dried under vacuum to afford poly(NVTri) as a pale
yellw solid (1.4 g, yield = 41%, Mn,NMR = 5100 g/mol, M /M = 1.09), which was employed as a
w
n
macro-CTA. The trithiocarbonate-terminated poly(NVTri) (0.10 g, 0.02 mmol), AIBN (1.6 mg, 0.01
mmol), NVETri-Br (0.20 g, 1.0 mmol), and methanol (0.8 mL) were placed in a dry ampule. After the
o
solution was degassed by three freeze-evacuate-thaw cycles, the polymerization was conducted at 60 C
1
for 24 h (conversion determined by H NMR spectroscopy = 97%). The reaction mixture was purified
by reprecipitation into a large excess of acetone/chloroform (7/3 vol%), and isolated by filtration to give
a block copolymer, poly(NVTri)-b-poly(NVETri-Br) as a pale yellow solid (0.304 g, 99%). The block
copolymer was soluble in water, methanol, DMSO, and insoluble in DMF, ethyl acetate, THF,
1
chloroform, diethyl ether, hexane. The copolymer composition was determined using H NMR
spectroscopy (DMSO-d
.0-9.7 ppm attributed to the N-CH-N proton (1H) of the triazolium ring in NVETri-Br unit and the
peak at 7.4-8.2 ppm corresponded to the N=CH-N protons (2H) of the NVTri units.
6
) by a comparison of peaks associated with the two comonomers: the peak at
9
1
2

ACCEPTED MANUSCRIPT
1
H NMR spectra and the solubilities of the block copolymers are shown in Figures S6-8 and Table S2,
respectively (Supporting Information).
2
.5.Anion Exchange Reactions
The anion exchange to replace Br with NTf was carried out according to the method used for the
-
-
2
exchange reaction of poly(N-vinylimidazolium bromide), with slight modifications.[6]
Poly(NVETri-NTf ) was synthesized by adding an aqueous solution (1.2 mL) of lithium
bis(trifluoromethanesulfonyl)imide (LiNTf , 0.6 g, 2.1 mmol) dropwise to a solution of
2
2
poly(NVETri-Br) (0.1 g, 0.5 monomer unit mmol) dissolved in distilled water (2.0 mL). The mixture
was then stirred at room temperature for 30 min. The precipitate was isolated by filtration, and the
residual solid was washed with distilled water. Subsequently, the product was dried under vacuum at 60
o
C overnight to afford poly(NVETri-NTf ) as a pale yellow solid (0.19g, 94%). Anal. Calcd for
2
C H F N O S : C, 23.8; H, 2.5; N, 13.9; S, 15.9. Found: C, 24.3; H, 2.7; N, 13.9; S, 15.3.
8
10
6
4
4 2
The anion exchange reaction of poly(NVEtOETri-Br) was conducted using the same procedure to
afford poly(NVEtOETri-NTf ) as a pale yellow solid (95%). Anal. Calcd for C10 : C, 26.8;
H, 3.2; N, 12.5; S, 14.3. Found: C, 26.3; H, 3.2; N, 12.2; S, 14.8.
2
14 6 4 5 2
H F N O S
-
-
The same method was employed for anion exchange to replace Br with NTf2 in the block
copolymers, poly(NVP)-b-poly(NVETri-Br) and poly(NVTri)-b-poly(NVETri-Br).
2
.6.Instrumentation
1
13
H (400 MHz) and C NMR (100 MHz) spectra were recorded with a JEOL JNM-ECX400.
Elemental analysis was carried out on a Perkin-Elmer 2400 II CHNS/O analyzer. For the determination
of the number-average molecular weight (M ) and molecular weight distribution (M /M ) of the
,2,4-triazolium-based polymers, the SEC measurement was conducted using special SEC columns
n
w
n
1
applicable for cationic polymers in acetonitrile/water (50/50 vol%) containing 0.05 M NaNO as an
3
eluent, similar to the case of poly(N-vinylimidazolium bromide)s.[45, 56] The SEC was performed on a
1
3

ACCEPTED MANUSCRIPT
system consisting of a Tosoh DP-8020 pump, a Viscotek TDA model-301 triple detector array (RI,
Viscosity, and RALLS; wavelength = 670 nm) at a flow rate of 1.0 mL/min. The column set was as
follows: two consecutive columns [Tosoh TSK-GELs (exclusion limited molecular weight):
6
4
G5000PW -CP (1 x 10 ), G3000PW -CP (9 x 10 ), 30 cm each] and a guard column
XL
XL
[
TSK-guardcolumn PW -CP, 4.0 cm]. Poly(ethylene oxide) standards were employed for calibration.
XL
Dynamic Light Scattering (DLS) was performed using a Zetasizer Nano (Sysmex) with a He-Ne laser.
Thermogravimetric analysis (TGA) was performed on a SEIKO TGA/6200 at a heating rate of 10
o
C/min under nitrogen atmosphere. Differential scanning calorimetry (DSC) analysis was conducted
o
using a Seiko EXSTAR 6000 DSC 6200 at a heating rate of 10 C /min under a nitrogen atomsphere.
Tapping mode scanning force microscopy (SFM) observation was performed with an Agilent AFM
5
500, using micro-fabricated cantilevers with a force constant of approximately 34 N/m. The samples
were prepared by the drop casting of polymer methanol solutions onto mica substrates.
Ionic conductivity in plane direction of a membrane was determined using an electrochemical
5
impedance spectroscopy technique over the frequency from 5 to 10 Hz (Hioki 3532-80) at 25, 55, and
o
9
0 C under the ambient humidity conditions. A two-point-probe conductivity cell with two platinum
plate electrodes was fabricated. The cell was placed under a thermo-controlled chamber. Ionic
conductivity (σ) was calculated from:
σ = d/(L w R)
s
s
where d is the distance between the two electrodes, L and w are the thickness and width of the
s
s
membrane, and R is the resistance value measured.
3
. RESULTS AND DISCUSSION
.1.RAFT Polymerization of N-Vinyl-1,2,4-triazolium Salts
3
Driven by our interest to probe the effects of the structures of the azolium component and the
substituent group on the polymerization behavior and resulting polymer properties, we synthesized two
N-viny-1,2,4-triazolium salts having different substituent groups, NVETri-Br and NVEtOETri-Br, by
1
4

ACCEPTED MANUSCRIPT
the reaction of NVTri with corresponding alkyl bromides (Scheme 2). Compared to the synthesis of
N-vinylimidazolium bromides,[6] a higher reaction temperature and a longer reaction time (50 and 70
o
C for 5 days) were employed for the synthesis of the 4-substituted N-vinyl-1,2,4-triazolium bromides.
Both NVETri-Br and NVEtOETri-Br can be regarded as nonconjugated N-vinyl monomers with
cationic units, in which the nature of triazolium moiety, the counter ion, and the structure of the alkyl
chain may affect the polymerization behavior.
Initially, various CTAs for conducting RAFT polymerization of NVETri-Br were tested with AIBN as
o
an initiator at [M]
0
/[CTA]
0
/[AIBN]
0
= 100/2/1 at 60 C for 24 h. Methanol was selected as a
polymerization solvent due to its good solvency for the monomers and the resulting polymers. The
results are summarized in Table 1. Under the conditions, suitable systems could be identified. The
polymerization of NVETri-Br with the trithiocarbonate-type CTAs (CTA 6, CTA 7, and CTA 8)
proceeded homogeneously to afford polymers having low Ð values (M /M = 1.09–1.10) with almost
w
n
1
quantitative conversions (>95%, as determined by H NMR spectroscopy). The SEC traces of
poly(NVETri-Br)s prepared with the trithiocarbonate-type CTAs were unimodal with no evidence of
high and low molecular weight species (Figure S9, Supporting Information), and observed molecular
weights were comparable to the theoretical values. In contrast, the molecular weights distributions were
somewhat broader for poly(NVETri-Br)s obtained via polymerization with the xanthate-type mediating
agents (CTA 1, CTA 3, and CTA 4, M /M > 1.4). Relatively low monomer conversions (<30%) were
w
n
obtained when using CTA 2 and CTA 5. We also investigated RAFT polymerization of NVETri-Br at a
higher CTA-to-initiator ratio ([CTA] /[AIBN] = 4), but no significant effect was detected (Figure S9,
0
0
Table S3, Supporting Information). Similarly, RAFT polymerization of NVEtOETri-Br with the
trithiocarbonate-type CTAs (CTA 6, CTA 7, and CTA 8) showed well-controlled molecular weights and
w n
low Ð values (M /M = 1.09–1.10, Figure S10, Supporting Information) with quantitative conversions,
as shown in Table 1.
<
insert Table 1>
1
5

ACCEPTED MANUSCRIPT
Table 2 summarizes the results of the polymerization of two 1,2,4-triazolium-based monomers,
NVETri-Br and NVEtOETri-Br, using the trithiocarbonate-type CTA 7 at different [M] /[CTA] ratios
0
0
between 25 and 200. The polymerizations of NVETri-Br reached more than 95% conversion after 24 h
o
at 60 C in all cases, and the molecular weights increased with the [M] /[CTA] ratio while low Ð
0
0
values (M /M = 1.07–1.34) were maintained up to a [M] /[CTA] ratio of 200 (Figure 1a). Figure 2
w
n
0
0
1
shows the H NMR spectra of poly(NVETri-Br) and poly(NVEtOETri-Br) obtained with CTA 7. The
1
molecular weights of poly(NVETri-Br) could be estimated from relative integration of the H NMR
signal of the polymer backbone proton (triazolium ring at around 10.7 ppm) to the end group proton
(methylene group in the trithiocarbonate group at around 1.2 ppm), as shown in Figure 2a. The values
matched reasonably well with the theoretical molecular weights, which were apparently higher than the
observed values determined by the SEC measurements. The end groups of the poly(NVETri-Br)s
obtained at different [M] /[CTA 7] ratios and with other CTAs (CTA 1, 5, 6, and 8) were also detected
0
0
1
by H NMR spectroscopy (Figures S11 and S12, Supporting Information).
<
insert Table 2>
1
6

ACCEPTED MANUSCRIPT
(
a) [
M] /[CTA 7] =
0
0
200 100
50 25
11
12 13 14 15 16 17 18
Elution Time (min)
(
b) [
M] /[CTA 7] =
0
0
200 100
50 25
11
12 13 14 15 16 17 18
Elution Time (min)
Figure 1. SEC traces of (a) poly(NVETri-Br) and (b) poly(NVEtOETri-Br) obtained by RAFT
polymerization with CTA 7 at different monomer-to-CTA ratios.
Similarly, the control exhibited by the polymerization of NVEtOETri-Br with CTA 7 was satisfactory,
in terms of the molecular weight controlled by the monomer/CTA molar ratio with low Ð values (Table
2
). The unimodal SEC trace shifts toward the higher molecular weight region with an increase in the
[
M] /[CTA] ratio, as shown in Figure 1b. Reasonable agreement between the theoretical and
0
0
1
experimental molecular weights determined by SEC analysis and H NMR measurement (Figure 2b) is
seen until [M] /[CTA] ratio of 50. In this system, the conversion decreased markedly at a high
0
0
0 0
monomer-to-CTA ratio ([M] /[CTA] = 200), which may be due to relatively slow polymerization rate
1
7

ACCEPTED MANUSCRIPT
of NVEtOETri-Br. Nevertheless, efficient control of the molecular weights of the 1,2,4-triazolium-based
polymers, poly(NVETri-Br) and poly(NVEtOETri-Br), could be achieved, regardless of the structure of
the substituent group, by adjusting the [M] /[CTA] ratio.
0
0
(
a)
DMSO
a
b
NC
f
S
S
h
H O
n
9
2
g
N
S
d
N
Br
f
N
c
e
e
c, d
10
g
a
2
b
h
12
8
6
4
0
ppm
(b)
a
b
i
NC
S
S
n
9
N
S
d
N
c
h
g
Br
f
N
e, f
g
O
h
e
c, d
10
a
2
i
b
12
8
6
4
0
ppm
1
Figure 2. H NMR spectra (DMSO-d ) of (a) poly(NVETri-Br) and (b) poly(NVEtOETri-Br) obtained
6
by RAFT polymerization with CTA 7 at [M] /[CTA 7] /[AIBN] = 100/2/1.
0
0
0
Kinetic studies of the polymerization of NVETri-Br and NVEtOETri-Br were carried out in the
presence of the trithiocarbonate-type CTA 7 with AIBN in methanol at 60 °C. As illustrated in Figure
3
a and d, the rate of polymerization of NVETri-Br was notably faster than that of NVEtOETri-Br. In
both cases, after the short induction period of less than 4 h, the kinetic plots followed a
pseudo-first-order profile up to high conversions. A similar induction period is often observed during
1
8

ACCEPTED MANUSCRIPT
RAFT polymerization of N-vinylimidazolium bromides[45] and several N-vinyl monomers.[60, 63,
6
7-71] Nevertheless, a controlled polymerization process is indicated by the linear increase in the
number-average molecular weights, M , vs the monomer conversion and low Ð values (M /M < 1.1,
n
w
n
Figure 3b and e). In both cases, the SEC traces of the 1,2,4-triazolium-based polymers are unimodal and
clearly shift toward the higher region with time, and no shoulder peak is apparent in the high molecular
weight region, even in the last stage of the polymerization (Figure 3c and f). The structure of the
substituent group in the 1,2,4-triazolium unit did not affect the controlled behavior of the polymerization,
whereas the polymerization rate was influenced by the substituent group, presumably steric reason. All
these results verified the controlled nature of the polymerization of N-vinyl-1,2,4-triazolium bromides
with CTA 7 under the conditions.
1
9

ACCEPTED MANUSCRIPT
(
a) 100
(d)100
5
5
4
3
2
1
0
8
6
4
2
0
0
0
0
0
4
3
2
1
0
80
60
40
20
0
Conversion
ln([M] /[M] )
Conversion
ln([M] /[M] )
0
t
0
t
0
5
10
15
20
0
5
10
15
20
Time (h)
Time (h)
(
b)
(e1)6000
1
.5
1.5
1.4
1.3
1.2
1.1
1
M (theory)
1
0000
M (theory)
n
n
M (NMR)
M (NMR)
14000
12000
10000
n
n
1.4
M (SEC)
M (SEC)
8
6
4
2
000
000
000
000
0
n
n
M /M (SEC)
M /M (SEC)
w
n
w
n
1
1
1
1
.3
.2
.1
8
000
6000
4
2
000
000
0
0
20
40
60
80
100
0
20
40
60
80
100
Conversion (%)
Conversion (%)
(c)
(f)
12 h 6 h 4 h 3.7 h 3.3 h
18 h 12 h 6 h 4.5 h 3.5 h
13
14
15
16
17
18
13
14
15
16
17
18
Elution Time (min)
Elution Time (min)
Figure 3. (a, d) Time-conversion and first-order-kinetic plots for RAFT polymerization of (a-c)
o
NVETri-Br and (d-f) NVEtOETri-Br at [M] /[CTA] /[AIBN] = 100/2/1 in methanol at 60 C. (b, e)
0
0
0
Conversion vs M and M /M plots. SEC traces of (c) poly(NVETri-Br) and (f) poly(NVEtOETri-Br).
n
w
n
2
0

ACCEPTED MANUSCRIPT
3
.2.Synthesis of Triazolium-based Block Copolymers
We synthesized two series of block copolymers composed of two different N-vinyl monomers, in which
one segment is composed of the 1,2,4-triazolium-based polymer formed by controlled RAFT
polymerization of NVETri-Br (Scheme 3). As another component, a representative N-vinyl monomer,
NVP, was initially selected, which afforded an important water-soluble polymer. Owing to the many
desirable properties, such as low toxicity, chemical stability, and good biocompatibility, poly(NVP) has
been employed in various fields, such as biomedical and cosmetic applications. Recently, much
attention has been paid to controlled radical polymerization of NVP, as it offers the possibility to
produce various functional polymers with specific architectures, such as block and graft copolymers,
star and branched polymers, and hybrids.[40, 42, 72] Since xanthate-type CTAs have proven for
controlling the polymerization of NVP and other nonconjugated N-vinyl monomers,[40, 42, 72] in this
study we selected the xanthate-type CTA 3 for the synthesis of poly(NVP) macro-CTA. Then, the
xanthate-terminated poly(NVP) was employed as a macro-CTA for the synthesis of a nonionic-ionic
block copolymer (Scheme 3a).
(a)
N
O
N
Br
S
O
N
,
AIBN
O
m
n
n
N
N
N
O S
o
O
Methanol, 60 C, 24 h
N
Br
N
(
b)
N
N
Br
N
NC
S
S
,
AIBN
m
n
n
N
N
9
o
N
S
Methanol, 60 C, 24 h
N
N
N
Br
N
N
N
Scheme 3. Synthesis of block copolymers by RAFT polymerization of NVETri-Br using (a) poly(NVP)
macro-CTA prepared with CTA 3 and (b) poly(NVTri) macro-CTA prepared with CTA 7.
2
1

ACCEPTED MANUSCRIPT
Polymerization of NVETri-Br was initially conducted in the presence of the xanthate-terminated
poly(NVP) (Mn,NMR = 7000, M /M = 1.07) in methanol at 60 °C for 24 h. The polymerization
w
n
conditions and results are presented in Table 3. When the polymerization was carried out with an
1
[
NVETri-Br] /[macro-CTA] of 25, the conversion determined by H NMR spectroscopy was 93%,
0
0
whereas the polymer was recovered in moderate yield (42%) by precipitation in acetone/chloroform (7/3
vol%). During the purification process, unreacted poly(NVP) macro-CTA and the monomer (and some
oligomers) could be removed, which may contribute relatively lower polymer yield. As shown in Figure
4
a, formation of the block copolymer was evidenced by the SEC chromatograms of the starting
poly(NVP) macro-CTA and resulting block copolymer, illustrating a clear increase in the molecular
weight, while the Ð value remained at M /M ≈ 1.4. No significant macro-CTA impurity was detected
w
n
1
in the block copolymer. The H NMR spectrum (DMSO-d ) of the product exhibits peaks corresponding
6
to the triazolium units at 9.2–9.8 and 10.4–11.3 ppm (Figure 5b), suggesting that chain extension
1
proceeds with consequent formation of the block copolymer, poly(NVP)-b-poly(NVETri-Br). H NMR
analysis of the block copolymer in CD OD permitted evaluation of the comonomer composition via
3
comparison of the peaks associated with the two comonomers (Figure S7, Supporting Information). As
shown in Table 3, the comonomer composition could be tuned by adjusting the
[
NVETri-Br] /[macro-CTA] ratio and the molecular weights of the poly(NVP) macro-CTAs. However,
0 0
the molecular weights determined from the comonomer composition and the molecular weights of the
macro-CTA were inconsistent with the theoretical and experimental molecular weights determined by
SEC measurement. Note that SEC analysis of these ionic-nonionic block copolymers was challenging
since these species are prone to hydrophilic and electrostatic interactions with the stationary phase. In
this study, the use of special SEC columns applicable to cationic polymers and SEC measurement in
3
acetonitrile/water (50/50 vol%) containing 0.1 M NaNO as an eluent facilitated estimation of the
molecular weights and the Ð value of the cationic block copolymers by SEC. However, the presence of
nonionic poly(NVP) in the block copolymers may lead to difficulty in accurate determination of the
molecular weights. Another possible reason for the discrepancy between Mn,NMR and Mn,SEC as well as
2
2

ACCEPTED MANUSCRIPT
the theoretical values is partial chain extension from the xanthate-terminated poly(NVP) to NVETri-Br,
suggesting that this process is not perfectly controlled. Synthesis of the block copolymer by RAFT
polymerization using an opposite order, i.e., polymerization of NVP using xanthate-terminated
poly(NVETri-Br), was also unsuccessful (Figure S13, Supporting Information). Nevertheless, the
nonionic-ionic (pyrrolidone/1,2,4-triazolium)-based block copolymers with tunable comonomer
compositions were successfully produced by the polymerization of NVETri-Br with the
xanthate-functionalized poly(NVP) and subsequent purification process.
(a)
macro-CTA
12
13 14 15 16 17 18 19 20
Elution Time (min)
(b)
macro-CTA
13
14
15
16
17
18
19
Elution Time (min)
Figure 4. SEC traces of (a) poly(NVP)-b-poly(NVETri-Br) and poly(NVP) macro-CTA (Mn,NMR = 7000,
Mn,SEC = 1100, M /M = 1.07, and (b) poly(NVTri)-b-poly(NVETri-Br) and poly(NVTri) macro-CTA
w
n
(
Mn, NMR = 5100, Mn,SEC = 1300, M /M = 1.09). In both cases, the block copolymers were synthesized
w n
by the polymerization at [NVETri-Br] /[macro-CTA] /[AIBN] = 50/2/1.
0
0
0
2
3

ACCEPTED MANUSCRIPT
Novel 1,2,4-triazole/1,2,4-triazolium-based block copolymers comprising poly(NVTri) as a
water-soluble segment and poly(NVETri-Br) as an ionic segment were synthesized by RAFT
polymerization (Scheme 3b). Note that water-solubility of non-ionic poly(NVTri) is ascribed to the
presence of a pyridine-type isolated nitrogen atom in the heterocycle, which is in accord with the
tendency
of
nonionogenic
poly(vinyl
azole)s,
including
poly(vinylimidazole)s
and
poly(vinyltriazole)s.[38, 39] In this case, RAFT polymerization of NVETri-Br was conducted in the
presence of the trithiocarbonate-terminated poly(NVTri) macro-CTA (Figure S14, Supporting
Information) in methanol at 60 °C for 24 h. For preparation of block copolymers having pre-determined
comonomer compositions and molecular weights, the monomer to CTA ratio was varied in the range of
1
[
NVETri-Br] /[macro-CTA] = 25–100. Under the given conditions, the conversions determined by H
0
0
NMR spectroscopy were more than 95%, and the polymers were recovered in high yields (78–99%)
after precipitation in acetone/chloroform mixed solvent (Table 3). The structure of the resulting block
1
copolymer was confirmed by H NMR measurement (Figure 5c). Peaks corresponding to poly(NVTri)
6
and poly(NVETri-Br) were clearly observed in the spectrum acquired in DMSO-d . Integration of the
appropriate peaks facilitated elucidation of the compositions of NVTri and NVETri-Br, and the
1
molecular weights calculated from H NMR were comparable to the theoretical compositions, as shown
in Table 3. Figure 4b shows a complete shift of the SEC trace of the parent poly(NVTri) to the higher
molecular mass region without residual macro-CTA impurity, indicating successful chain extension
from the trithiocarbonate-terminated poly(NVTri) macro-CTA to NVETri-Br. With an increase of the
[
NVETri-Br]/[macro-CTA] ratio, the molecular weight increased with maintaining unimodal SEC peaks
/M < 1.2, Figure S14, Supporting Information), which is indicative of the formation of the
,2,4-triazole/1,2,4-triazolium-based block copolymers with controlled comonomer compositions.
(M
w
n
1
3
.3.Anion Exchange Reactions
2
4

ACCEPTED MANUSCRIPT
-
-
Anion exchange to replace Br with NTf
2
was carried out according to the method used for the synthesis
of poly(N-vinylimidiazolium salt)s with slight modifications (Scheme 4).[6] Poly(NVETri-NTf ) was
2
synthesized by initially dissolving poly(NVETri-Br) in distilled water, after which an aqueous solution
of LiN(SO CF ) (LiNTf ) was added dropwise to the polymer solution at room temperature. After
2
3 2
2
stirring the mixture at room temperature for 30 min, the precipitate, which was formed by the anion
exchange reaction, was isolated by filtration, and the residual solid was washed with distilled water. As
expected, the resulting poly(NVETri-NTf
2
) was insoluble in H
2
O but soluble in methanol, DMSO, DMF,
1
acetone, ethyl acetate, and THF (Table S1, Supporting Information). As shown in Figure 5a, the H
2
NMR spectrum of poly(NVETri-NTf ) exhibits peaks at 9.0–9.4 and 9.8–10.2 ppm attributed to the
triazolium ring, which were notably shifted from the peaks at 9.2–9.8 and 10.4–11.3 ppm corresponding
to the original poly(NVETri-Br). In the case of poly(NVEtOETri-Br), similar chemical shifts of the
peaks at 8.8–9.5 and 10.1–11.0 ppm were observed for the NVEtOETri-Br repeating unit to 8.7–9.4 and
1
3
9
.8–10.2 ppm in the NVEtOETri-NTf repeating unit (Figure S16a, Supporting Information). The C
2
NMR spectrum of poly(NVETri-NTf ) clearly shows four peaks in the range of 114–125 ppm,
2
2
attributed to the trifluoromethyl group in the NTf unit, whereas these peaks were not apparent in the
1
3
profile of poly(NVETri-Br) (Figure S17a, Supporting Information). The C NMR spectrum of
poly(NVEtOETri-NTf ) also exhibited four new peaks at 115–125 ppm (Figure S16b, Supporting
2
Information), indicating successful incorporation of the NTf unit. The elemental analyses of the
2
products, poly(NVETri-NTf ) and poly(NVEtOETri-NTf ), obtained after the anion exchange reaction
2
2
also indicated that the observed values including sulfur content were well agreement with the theoretical
1
13
values (see experimental section). The H and C NMR results and elemental analyses suggested
quantitative anion exchange to generate the targeted hydrophobic 1,2,4-triazolium-based polymers,
2
poly(NVTri-NTf )s.
2
5

ACCEPTED MANUSCRIPT
Scheme 4. Anion exchange of (a) poly(NVETri-Br), (b) poly(NVP)-b-poly(NVETri-Br), and (c)
poly(NVTri)-b-poly(NVETri-Br).
The thermal stability of poly(NVTri-Br) and poly(NVTri-NTf ) was investigated under nitrogen
2
atmosphere by TG analysis. Figure 6 illustrates initiation of rapid decomposition around 220 °C for
o
pristine poly(NVETri-Br) and poly(NVEtOETri-Br) (Td10 = 221 and 230 C, respectively), and the
o
residual weight at 300 C was less than 30%. In contrast, the poly(NVETri-NTf ) and
2
poly(NVEtOETri-NTf ) species obtained after the anion exchange reaction exhibited higher stability
2
o
(
Td10 > 320 C). Thus, anion exchange to generate the NTf form led to improve thermal stability at
2
elevated temperature in both cases. Glass transition temperature (T ) of poly(NVETri-Br) and
g
poly(NVETri-NTf ) were evaluated by DSC analysis (Figure S18, Supporting Information). The T s of
2
g
o
poly(NVETri-Br) and poly(NVETri-NTf
2
) were observed at 70 and 13 C, respectively. The lower T
g
of
poly(NVETri-NTf ) might result from an increase of the free volume by the larger NTf anions.
2 2
2
6

ACCEPTED MANUSCRIPT
(
a)
a
H O
f
b
2
n
N
c
DMSO
a
c, d
N
d
Br
e
f
N
b
e
n
N
N
N
NTf2
1
2
10
8
8
8
6
6
6
4
2
0
ppm
(
b)
DMSO
A
a
H O
b
B
N
2
A, f
m
n
b, e
N
c, d
O
B, C, D, E, a
C
D
d
N
Br
f
N
E
c
e
m
n
N
N
O
N
N
NTf2
12
10
4
2
0
ppm
DMSO Acetone
(
c)
H O
2
A
a
b
B
A, B, a
m
f
n
e
b
N
N
c, d
D
N
d
Br
N
c
C, D
N
f
N
C
e
n
m
N
N
N
N
N
N
NTf
2
12
10
4
2
0
ppm
1
Figure 5. H NMR spectra (DMSO-d ) of (a) poly(NVETri-Br) and poly(NVETri-NTf ), (b)
6
2
poly(NVP)-b-poly(NVETri-Br)
and
poly(NVP)-b-poly(NVETri-NTf2),
and
(c)
poly(NVTri)-b-poly(NVETri-Br) and poly(NVTri)-b-poly(NVETri-NTf2).
2
7

ACCEPTED MANUSCRIPT
(
a)100
NTf2
8
6
4
2
0
0
0
0
0
Br
100
200
300
400
500
o
Temperature ( C)
(
b)1
00
NTf2
80
60
40
20
0
Br
100
200
300
400
500
o
Temperature ( C)
Figure 6. TG analysis of (a) poly(NVETri-X) and (b) poly(NVEtOETri-X); X = Br and NTf2.
Anion exchange was also conducted for the block copolymers, poly(NVP)-b-poly(NVETri-Br) and
poly(NVTri)-b-poly(NVETri-Br), under the same conditions used for the homopolymer,
1
poly(NVETri-Br). The H NMR spectrum of the exchanged pyrrolidone/1,2,4-triazolium-based block
copolymer measured in DMSO-d clearly shows peaks corresponding to poly(NVETri-NTf ) (Figure
6
2
5
b), which were evidently shifted relative to the peaks of the original poly(NVETri-Br), in addition to
the unchanged peaks attributed to the poly(NVP) segment. Successful incorporation of the NTf unit
2
into the pyrrolidone/1,2,4-triazolium-based block copolymer was also confirmed by the presence of the
1
3
2
four peaks at 115–125 ppm in C NMR spectrum of poly(NVP)-b-poly(NVETri-NTf ), corresponding
2
8