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Cite this: RSC Adv., 2020, 10, 37743

One-pot synthesis of poly(ionic liquid)s with 1,2,3triazolium-based backbones via clickable ionicliquid monomers†
Ruka Hirai, Tatsuki Hibino, Takaichi Watanabe, Takashi Teranishi
and Tsutomu Ono *Clickable a-azide-u-alkyne ionic liquid monomers were developed and subsequently applied to the onepot synthesis of ionically conducting poly(ionic liquid)s with 1,2,3-triazolium-based backbones througha click chemistry strategy. This approach does not require the use of solvents, polymerisation mediators,
or catalysts. The obtained poly(ionic liquid)s were characterized by NMR, diﬀerential scanningcalorimetry, thermogravimetric analysis, and impedance spectroscopy analysis. Moreover, these

Received 17th September 2020
Accepted 7th October 2020

poly(ionic liquid)s were cross-linked via N-alkylation with a dianion quarternizing agent to achieveenhanced ionic conductivity and mechanical strength. The resulting free-standing ﬁlms showeda Young's modulus up to 4.8 MPa and ionic conductivities up to 4.60  108 S cm1 at 30  C. This facile

DOI: 10.1039/d0ra07948k

synthetic strategy has the potential to expand the availability of poly(ionic liquid)s and promote thersc.li/rsc-advancesdevelopment of functional materials.

Introduction
Poly(ionic liquid)s (PILs) are a type of polyelectrolyte in which
the repeat unit is an ionic liquid (IL). PILs exhibit the unique
physicochemical properties of low-molecular-weight ILs (e.g.
high ionic conductivity, thermal stability, and chemical
stability) as well as polymeric properties (e.g. mechanicalstability, processability, and macromolecular tunability). So far
various kinds of PIL materials including cross-linked PILs, PIL
block copolymers, and PIL-based ion gels1–3 have been developed as IL-based so materials, since they oﬀer advantages forvarious applications including dye-sensitised solar cells, fuelcells, electrochromic devices, membranes, sensors and actuators, batteries, and supercapacitors.4–10 In addition, a broad
spectrum of PILs with diﬀerent combinations of cations (e.g.
ammonium, pyridinium, imidazolium, phosphonium, and triazolium) and anions (e.g. halides, inorganic uoride, and peruorinated sulfonimides) have been designed to provide
materials with task-specic IL properties.11,12
Recently, 1,2,3-triazolium-based PILs (TPILs) have beendeveloped as a structurally rich family of PILs.13 TPILs are
generally synthesised by combining step-growth or chaingrowth polymerisation methods with copper-catalysed azide–
alkyne cycloaddition click chemistry using diazide and dialkyne

Department of Applied Chemistry, Graduate School of Natural Science, Okayama
University, 3-1-1, Tsushima-naka, Kita-ku, Okayama, 700-8530, Japan. E-mail:tono@okayama-u.ac.jp; Fax: +81-86-251-8083; Tel: +81-86-251-8083† Electronic supplementary
10.1039/d0ra07948k

information(ESI)

available.

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See

DOI:

or a-azide-u-alkyne monomers, followed by 1,2,3-triazole Nalkylation.14 The synthesis of TPILs using click chemistry has
attracted particular attention because the reaction is eﬃcientand orthogonal, which oﬀers unprecedented opportunities tobroaden the functionality of macromolecular design for polymer solid electrolytes. Moreover, Puguan et al. recently reported
that PILs with backbones based on 1,2,3-triazole (backbone
TPILs) with oxyethylene spacers exhibit the highest ionic
conductivities (104 S cm1 at 30  C) among known backbone
PILs.15 This nding suggests that the design and characterization of a broad library of backbone TPILs is important forrealizing innovative functional materials, thus necessitating thedevelopment of simple synthetic strategies for backbone TPILs.
Over the last few years, various types of TPILs with tailored
structures, including ionenes, poly(acrylate)s, poly(vinyl ester)s,poly(styrene)s, and polypeptoids have been developed.16–20
However, to the best of our knowledge, the synthesis of backbone TPILs using clickable IL monomers has not been reported.
In this study, we synthesised backbone TPILs via the polyaddition of clickable a-azide-u-alkyne IL monomers witha 1,2,3-triazolium cation and iodide(I) or bis(triuoromethanesulfonyl)imide (Tf2N) counter anions. Here,polyaddition was achieved using thermal azide–alkyne cycloaddition (TAAC), a type of one-step click chemistry that does not
require the use of solvents, polymerisation mediators, or catalysts. Moreover, the 1,2,3-triazole-based backbones of the obtained TPILs could be N-alkylated using a difunctionalised
quarternizing agent to produce cross-linked TPILs with twice
the number of IL moieties in the polymer backbone anda higher mechanical strength than the precursor TPILs. We

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report the above mentioned facile synthetic methodology toobtain TPILs with clickable a-azide-u-alkyne IL monomers
trough click chemistry and cross-linked TPILs via subsequent
quarternizing reaction. Then, we investigate the eﬀect of theamount of cross-linking agent on the mechanical strength aswell as the ionic conductivity of the resultant cross-linked
TPILs.

Experimental
Materials
Diisopropylethylamine (DIPEA, 97%), benzyl azide (94%), copper(II) acetate (Cu(OAc)2, 97%), Super-dehydrated acetonitrile(99.8%), N,N-dimethylformamide (99.5%), and sodium azide(98%) were purchased from FUJIFILM Wako Pure Chemical
Corp.
5-Chloro-1-pentyne(96%),
lithiumbis(triuoromethanesulfonyl)imide (LiTf2N, 98%), and 1,4-diiodobutane (98%) were purchased from Tokyo Chemical Industry Co.,
Ltd. 6-Iodo-1-hexyne (97%) was purchased from Aldrich. All
chemicals were used as received.
Characterization methods
1

H NMR (400 MHz), 13C NMR (100 MHz), and 19F NMR (376.5
MHz) spectra were recorded on a Varian 400-MR spectrometerin DMSO-d6 using solvent peaks (2.5 ppm) as internal references. Gel permeation chromatography (GPC) was carried out at
40  C using a chromatograph (HLC-8120 GPC, Tosoh Ltd.)
connected to a refractive index detector and columns (TSK
guard column Super AW-H, TSKgel Super AWM-H, TSKgel
Super HM-H, and TSKgel Super H4000). The eluent was 60 mM
LiTf2N in N,N-dimethylformamide (DMF) at a ow rate of 0.3
mL min1. The weight-average molecular weight (Mw), numberaverage molecular weight (Mn), and molecular weight dispersity(Mw/Mn) were calculated from a calibration curve based onpolystyrene standards. Diﬀerential scanning calorimetry (DSC)
measurements were carried out under nitrogen using a DSC
6100 instrument (Seiko Instruments Inc.) at a heating rate of
10  C min1. Glass transition temperature (Tg) values were
measured during the second heating cycle. Thermogravimetricanalysis (TGA) was performed under nitrogen using a DTG-60
instrument (Shimadzu Co.) at a heating rate of 10  C min1.
Scanning electron microscopy (SEM) and energy dispersive Xray spectroscopy (EDX) analyses were performed using a JMTIT100LV instrument (JEOL Ltd.) operated at 15.0 kV. Before
observation, the samples were coated with Au. The mechanicalproperties of cross-linked TPILs 5a–d were evaluated using an
automatic recording universal testing instrument (EZ Test EZSX 500 N, Shimadzu Co.) at room temperature. The sample
lms were cut into dumbbell-shaped specimens with a length,
width, and thickness of 35, 2, and 0.4 mm, respectively. The
specimens were tested at a cross-head rate of 10 mm min1
using an initial gauge length of 15 mm. The swelling behaviourof the cross-linked TPILs was evaluated by measuring theweights of cross-linked TPILs 5a–d aer immersion in [Bmim][Tf2N]. At 1, 2, 3, 6, 9, 12, 24, 36, 48, 72, 96, and 110 h aer the
onset of the experiment, the samples were removed from the37744 | RSC Adv., 2020, 10, 37743–37748

Paper[Bmim][Tf2N] bath and their weights were recorded. Subsequently, the samples were reimmersed in the same bath. Thechanges in sample weight were plotted as a function of
immersion time, with the initial sample weight dened as
100 wt%. Ionic conductivities were measured using an impedance analyser (Model 4294A, Keysight). Samples were preparedusing the following methods. TPIL 3 was pressed using a hot
press (IMC-1A45, Imoto Machinery Co., Ltd.), and the thickness
was controlled by employing a 114 mm thick polytetrauoroethylene (PTFE) spacer. TPIL 4 in acetonitrile was cast onto a Cu
electrode and annealed at 80  C under vacuum. Another Cu
electrode was then placed on top of the polymer lms using
a 114 mm thick PTFE spacer to prepare a measurement cell.
Cross-linked TPILs 5a–d were coated (Quick Coater CC701,
Sanyu Electron Co., Ltd.) with Au to prepare measurement cells.
Frequency sweeps were then performed isothermally at 107 to
40 Hz by applying a sinusoidal potential of 1 V over a temperature range of 130 to 20  C in steps of 10  C.
Synthesis of chlorinated-1,2,3-triazole21
DIPEA (2 mmol, 0.345 mL) was added to 65 mL of dry acetonitrile solution containing Cu(OAc)2 (1 mmol, 0.182 g), 5-chloro-1pentyne (20 mmol, 2.12 mL), and benzyl azide (20 mmol, 2.50mL) under stirring. The reaction mixture was stirred in the dark
at room temperature for 24 h, and then the solvent was evaporated. The crude product was puried by column chromatography (hexane/ethyl acetate ¼ 4 : 1) to give chlorinated-1,2,3triazole as a slightly yellow solid (3.48 g, 14.8 mmol, 74%). 1H
NMR (400 MHz, DMSO-d6, d): 7.96 (s, 1H), 7.40–7.28 (m, 5H),
5.55 (s, 2H), 3.67 (t, J ¼ 6.5 Hz, 2H), 2.75 (t, J ¼ 7.5 Hz, 2H), 2.04
(quin, J ¼ 7.0 Hz, 2H). 13C NMR (100 MHz, DMSO-d6, d): 145.9,
136.1, 128.6, 127.9, 127.8, 122.1, 52.8, 44.5, 31.7, 22.3.
Synthesis of azido-1,2,3-triazole
A solution of chlorinated-1,2,3-triazole (20 mmol, 4.71 g) andsodium azide (24 mmol, 1.56 g) in DMF (25 mL) was stirred at
50  C for 24 h. The crude reaction mixture was quenched withsaturated NH4Cl aq. and then extracted with ethyl acetate (3 
100 mL). The resulting organic layer was washed with water (2 
100 mL) and saturated brine (2  100 mL), and dried with
MgSO4. The solvent was then evaporated to give azido-1,2,3triazole as a yellow liquid (3.98 g, 14.8 mmol, 82%). 1H NMR(400 MHz, DMSO-d6, d): 7.95 (s, 1H), 7.40–7.25 (m, 5H), 5.55 (s,2H), 3.38 (t, J ¼ 6.5 Hz, 2H), 2.68 (t, J ¼ 7.9 Hz, 2H), 1.85 (quin, J¼ 7.2 Hz, 2H). 13C NMR (100 MHz, DMSO-d6, d): 146.2, 136.1,
128.6, 127.9, 127.7, 122.0, 52.8, 50.1, 28.0, 22.1.
Synthesis of a-azide-u-alkyne IL monomer 1
A solution of azido-1,2,3-triazole (10 mmol, 2.1 mL) and 6-iodo1-hexyne (15 mmol, 2.0 mL) in dry acetonitrile (20 mL) was
stirred in the dark at 50  C for 120 h. Following solvent evaporation, the crude product was precipitated ve times with
diethyl ether. Aer drying under vacuum, 1 was recovered as anorange viscous liquid (2.35 g, 5.22 mmol, 52%). 1H NMR (400
MHz, DMSO-d6, d): 8.90 (s, 1H), 7.48–7.42 (m, 5H), 5.85 (s, 2H),
4.56 (t, J ¼ 7.7 Hz, 2H), 3.48 (t, J ¼ 6.7 Hz, 2H), 2.92 (t, J ¼ 7.9 Hz,

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Paper2H), 2.83 (t, J ¼ 2.7 Hz, 1H), 2.23 (td, J ¼ 7.3, 2.8 Hz, 2H), 2.01–
1.90 (m, 4H), 1.50 (quin, J ¼ 7.4 Hz, 2H). 13C NMR (100 MHz,DMSO-d6, d): 143.2, 132.7, 129.1, 128.9, 128.8, 128.6, 83.5, 71.4,
56.1, 50.7, 49.3, 27.1, 26.1, 24.5, 20.4, 17.3. Elemental analysis(%): calculated C, 48.0; H, 5.2; N, 18.7; found C, 46.8; H, 5.2; N,
17.6.
Synthesis of a-azide-u-alkyne IL monomer 2
A solution of 1 (8.50 mmol, 3.83 g) and LiTf2N (9.35 mmol, 2.68g) in water (25 mL) was stirred in the dark at 40  C for 24 h. The
reaction mixture was precipitated ve times in water to yieldaer drying under vacuum 2 as a slightly yellow viscous liquid(4.36 g, 7.22 mmol, 85%). 1H NMR (400 MHz, DMSO-d6, d): 8.90(s, 1H), 7.45–7.41 (m, 5H), 5.85 (s, 2H), 4.56 (t, J ¼ 7.5 Hz, 2H),
3.48 (t, J ¼ 6.9 Hz, 2H), 2.92 (t, J ¼ 7.7 Hz, 2H), 2.83 (t, J ¼ 2.7 Hz,
1H), 2.23 (td, J ¼ 7.2, 2.8 Hz, 2H), 2.01–1.90 (m, 4H), 1.50 (quin, J¼ 7.3 Hz, 2H). 13C NMR (100 MHz, DMSO-d6, d): 143.4, 132.5,
129.1, 128.9, 128.7, 128.4, 119.5 (q, J ¼ 320 Hz, 2C), 83.4, 70.8,
56.3, 50.0, 49.5, 26.9, 25.8, 24.3, 19.9, 17.0. Elemental analysis(%): calculated C, 39.8; H, 3.8; N, 16.2; found C, 39.5; H, 3.8; N,
16.2. 19F NMR (376.5 MHz, DMSO-d6, d): 78.5 (6F).
Synthesis of TPIL 3
IL monomer 1 (100 mg, 0.22 mmol) was stirred at 110  C for
24 h. The resulting polymer was precipitated in acetone andthen dried under vacuum to yield 3 as a dark brown material(90 mg, 90%). 1H NMR (400 MHz, DMSO-d6, d): 8.89 (bs, 1H),
7.88 (s, 1H), 7.48–7.39 (m, 5H), 5.84 (bs, 2H), 4.73–4.20 (m, 4H),
3.06–2.85 (m, 2H), 2.79–2.58 (m, 2H), 2.39–2.10 (m, 2H), 2.04–
1.87 (m, 2H), 1.74–1.53 (m, 2H).

Synthesis of TPIL 4
IL monomer 2 (100 mg, 0.17 mmol) was stirred at 110  C for
24 h. The resulting polymer was precipitated in ethyl acetate
and then dried under vacuum to yield 4 as a brown sticky
material (92 mg, 92%). 1H NMR (400 MHz, DMSO-d6, d): 8.89
(bs, 1H), 7.88 (s, 1H), 7.48–7.39 (m, 5H), 5.85 (bs, 2H), 4.74–4.24(m, 4H), 3.07–2.85 (m, 2H), 2.78–2.57 (m, 2H), 2.41–2.10 (m,2H), 2.07–1.86 (m, 2H), 1.74–1.51 (m, 2H). 19F NMR (376.5 MHz,DMSO-d6, d): 78.5 (6F).
Synthesis of cross-linked TPILs 5a–d
1,4-Diiodobutane (0.5, 1.0, 1.5, or 2.0 equiv.) was added toa solution of TPIL 3 (800 mg, 1.78 mmol triazole groups, 1.0
equiv.) in DMF (3.0 mL). The mixture was stirred at room
temperature for 30 min. Subsequently, the reaction mixture wasinjected into a mould consisting of two glass plates with anuorinated ethylene propylene lm and a PTFE spacer witha thickness of 1 mm. Heating at 110  C in an oven for 12 hyielded a brown lm. The iodide-containing lm was added to
a 5 wt% LiTf2N solution in acetonitrile/water (3 : 1) at 50  C for
48 h. The resulting lm was washed with acetonitrile/water(3 : 1) and dried at 100  C under vacuum.

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Results and discussion
a-Azide-u-alkyne IL monomers 1 and 2 were prepared in threeor four steps (Scheme S1†). The successful synthesis of eachcompound was conrmed by 1H and 13C NMR spectroscopy(Fig. S1–S4†), and the purities of the IL monomers were evaluated by elemental analysis. 1H NMR spectrum of IL monomer 1(Fig. S3†) clearly showed the synthesis of a-azide-u-alkyne IL
monomer with a 1,2,3-triazolium cation. Indeed, besides thedisappearance of the signal at 8.0 ppm attributed to the 1,2,3triazole moiety, new signals were conrmed at 8.9 ppm for the
1,2,3-triazolium proton and at 2.8 and 3.5 ppm for propargyl
and azidomethylene chain ends, respectively. TPILs 3 and 4
were obtained by polymerisation of IL monomers 1 and 2 at
110  C for 24 h via TAAC (Scheme 1) as a dark brown material
and brown sticky material, respectively. The successful
synthesis of both samples was conrmed by 1H NMR spectroscopy (Fig. S5 and S6†). All of the 1H NMR peaks were broad
due to shorter relaxation time of the high-molecular-weight
polymer. In both cases, 1H NMR conrmed the polymerisation of IL monomers by the appearance of the proton signals of
the 1,2,3-triazole ring at 7.9 ppm as well as the absence of
signals corresponding to propargyl and azidomethylene chain
ends. Only TPIL 4 could be characterised by gel permeation
chromatography (GPC) using a 60 mM solution of LiTf2N in
N,N-dimethylformamide (DMF) as ref. 22 This analysis revealed
a number-average molar mass of 28 000 g mol1 with a molecular weight dispersity of 3.3 for TPIL 4 (Fig. S7†).
The solubilities of IL monomers 1 and 2 and TPILs 3 and 4
were investigated in water and common organic solvents (Table
S1†). IL monomer 1 was water-soluble but IL monomer 2 waswater-insoluble. This trend is in agreement that halide ishydrophilic anion and Tf2N is hydrophobic anion.23 Both the IL
monomers were soluble in all the examined organic solvents,
except for diethyl ether (Et2O). TPILs 3 and 4 were insoluble inmethanol (MeOH) and dichloromethane (CH2Cl2), but only
TPIL 4 was soluble in acetone and CH3CN. This solubility of
TPIL 4 allows easy processing as membranes and coating using
solvents that can be easily eliminated by evaporation or solvent
extraction.
Cross-linked PILs 5a–d were prepared in two steps (Scheme1). First, a mixture of TPIL 3, 1,4-diiodobutane as a cross-linking
agent, and DMF was injected into a mould and heated at 110  C
for 12 h to yield cross-linked TPILs with I anions. The amount ofcross-linking agent was varied from 0.5 to 2.0 equiv. relative tothe triazole groups in TPIL 3. Then, the cross-linked TPILs with I
anions were added to a mixture of LiTf2N and acetonitrile/water(3 : 1) at 50  C for 48 h to yield 5a–d as slightly yellow lms
(Fig. 1). In comparison with TPIL 4, these lms were freestanding and unchanged shape at high temperature. A
conversion of 87.9 mol% for the anion exchange process wasconrmed by scanning electron microscopy-energy-dispersive
X-ray spectroscopy (SEM-EDX) (Fig. S8†).
The thermal properties of TPILs 3 and 4 and cross-linked
TPILs 5a–d were characterised by diﬀerential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) (Table 1).

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Scheme 1

Fig. 1Paper

Synthesis of TPILs 3 and 4 and cross-linked TPILs 5a–d using clickable IL monomers.

Photographs of TPIL 4 (left) and cross-linked TPIL 5a (right).

whereas TPIL 4 and cross-linked TPILs 5a–d with Tf2N anions
started to degrade near 300  C (Fig. 2). This behaviour is
attributed to the diﬀerence in the nucleophilicities of theseanions.
The mechanical properties of cross-linked TPILs 5a–d were
evaluated by tensile tests under ambient conditions, andrepresentative stress–strain curves are shown in Fig. 3. TPIL 4
was a sticky material but cross-linked TPILs 5a–d were freestanding lms with a Young's modulus in the range of 0.8–

TPIL 4 with Tf2N anions showed a lower glass transition
temperature value (Tg ¼ 7.4  C) than TPIL 3 with I anions (Tg ¼
38.3  C). This diﬀerence can be explained by the sizes of theanions, as the larger Tf2N anion has a greater ability to hinderinteractions between polymer chains, thus decreasing both thechain packing density and Tg.24 Cross-linked TPILs 5a–d showed
higher Tg values (19.0–22.0  C) than TPIL 4 with Tf2N anions
owing to immobilisation of the polymer chains. However, theamount of cross-linking agent did no signicantly aﬀect Tg.
This is probably because Tg would depend on the mobility ofpolymer chains forming a cross-linked network. The TGA curves
showed that TPIL 3 with I anions started to degrade near 200  C,
Fig. 2

Table 1

TGA curves of TPILs 3, 4 and cross-linked TPILs 5a–d.

Physical properties of TPILs 3, 4 and cross-linked TPILs 5a–d

Polymer

RatioaTgb [ C]

Td10c [ C]

Young's modulusd [MPa]sDC at 30  Ce [S cm1]sNf [S cm1]

Bf [K]

T0f [K]

3
4
5a
5b
5c
5d

0
0
0.5
1.0
1.5
2.0

38.3
7.4
22.0
19.0
20.5
21.4

243
302
320
327
327
311

—
—
0.90  0.025
4.79  0.45
2.34  0.27
0.77  0.09—
1.16  108
1.66  109
1.89  1098.49  1094.60  108

0.71
0.41
0.020
0.019
0.019
0.025

1468
1089
978
987
968
858

277
241
241
240
237
241

a
Molar ratio of diiodide to triazole groups. b Obtained by DSC. c Obtained by TGA. d Obtained from tensile tests. e Obtained using an impedance
analyser. f Obtained from VFT ts of the experimental data using eqn (1).

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Paper

Fig. 3Stress–strain curves of cross-linked TPILs 5a–d.

4.8 MPa. As the amount of cross-linking agent (molar ratio of
diiodide to triazole groups) increased from 0 to 1.0, the Young's
modulus of the cross-linked TPILs signicantly increased andreached the highest value (4.79 MPa) at the molar ratio of 1.0.
This is because a polymer network with a higher cross-link
density are formed as increasing the amount of cross-linking
agent in this region. On the other hand, as the amount ofcross-linking agent (the molar ratio) increased from 1.0 to 2.0,
the Young's modulus of the cross-linked TPILs decreased. In thecase of 5c and 5d, the molar amounts of iodide in the crosslinking agent are much higher than the amount of 1,2,3-triazole groups in TPILs. Hence, it is likely that only one end of
most of the cross-linking agents reacts with a triazole groups,
causing dangling chains and leading to a polymer network witha lower cross-link density.25 Based on this assumption, thecross-link densities of the cross-linked TPILs can be summarised as follows: 5a < 5d < 5c < 5b. This order is consistent withthe cross-link density trend estimated from the swelling
behaviour of the cross-linked TPILs. In particular, fasterswelling speeds were shown as the cross-link density of thematerial decreased (Fig. 4).
The temperature dependence of the DC conductivity (sDC) of
TPILs 3 and 4 and cross-linked TPILs 5a–d were evaluated by
impedance spectroscopy analysis over the range of 40 to 107 Hz.
The data were collected at temperatures from 20 to 130  C withsteps of 10  C. The sDC values of above mentioned specimens
were plotted as a function of inverse temperature (Fig. 5). As
generally observed for polymeric materials, the temperature

Fig. 4 Swelling behaviour of cross-linked TPILs 5a–d prepared with
diﬀerent amount of cross-linking agent as a function of immersion
time.

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RSC AdvancesFig. 5 Direct current conductivity versus inverse temperature for
TPILs 3 and 4 and cross-linked TPILs 5a–d. The solid lines are the VFT
ﬁts of the experimental data obtained using the sN, B, and T0
parameters listed in Table 1.

evolution of the sDC above Tg follows the Vogel–Fulcher–Tammann (VFT) relation describing the correlation between the
charge transport capability of the ionic moieties and themolecular mobility of the polymer chains. Thus, the experimental data were tted to the VFT equation:
B
sDC ¼ sN exp(1)
T  T0where sN is the ionic conductivity in the limit of high temperature, B is a tting parameter related to the activation energy ofionic conduction, and T0 is the Vogel temperature. The tted
values are summarised in Table 1.
The ionic conductivity of TPIL 4 with Tf2N anions was higher
than that of TPIL 3 with I anions. This diﬀerence is mainly
caused by a lower Tg value of the TPIL 4 than TPIL 3, in addition
to another possible reason related to the lower dissociationenergy of the ion pairs in TPIL 4 owing to the delocalisation of
the Tf2N anion. The sDC values increased from 1.7  109 to 4.6
 108 S cm1, with the order: 5a < 5b < 5c < 5d. As the Tg valuesof these four samples were comparable, higher sDC withincreasing of molar ratio of diiodide could originate from thehigher concentration of mobile Tf2N anions as well as theenhanced mobility of Tf2N anions by increasing of the dangling
chains number. Similarly, the sDC value of cross-linked TPIL 5d
at 30  C was higher than that of TPIL 4.

Conclusions
We developed new clickable a-azide-u-alkyne IL monomers anda simple method to synthesise backbone TPILs via TAAC ofthese monomers. This synthesis method allows the preparationof TPILs in the absence of solvents, polymerisation mediators,
or catalysts, and the resultant TPILs showed ionic conductivity.
As the TPILs possessed 1,2,3-triazole-based backbones, Nalkylation using a difunctionalised quarternizing agent resulted
in cross-linked TPILs that theoretically could contain twice thenumber of IL moieties in their polymer backbones comparedwith the precursor TPILs. Further, the Young's modulus of thecross-linked TPILs was tuned by changing the molar amount of
the cross-linking agent. We believe that our strategy for synthesising backbone TPILs oﬀers opportunities to broaden the

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PIL family and develop innovative functional materials applicable to carbon dioxide separation membranes, fuel cells,
electrochromic devices, sensors, and actuators.

Conﬂicts of interest
There are no conicts to declare.

Acknowledgements
Financial support for this work was provided by the JSPS Grantsin-Aid for Scientic Research (KAKENHI) (Grant No.
JP18H03854 and JP19K15340). We also acknowledge Prof. T.
Uchida for the EDX measurements.

Notes and references
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