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J.R. Nykaza et al. / Polymer xxx (2014) 1e10
importance for applications, such as gas separations and energy
storage for the former type and fuel cells and water purification for
the latter type. Recently, there have been several fundamental in-
vestigations on conductivityemorphology relationships in PIL
block copolymers [1e5]. For fluorinated counterions (e.g., TFSI),
morphology type [1,3], the extent of long-range order [1,4], the
strength of micro-phase separation [2,3], and the glass transition
temperature of the PIL microdomain [3,5] have all shown to have a
significant impact on ion conductivity in PIL block copolymers.
More recently, the transport of other counterions, which are of
interest for this present investigation, such as bromide and hy-
droxide, in PIL block copolymers has been explored, where these
counterions are facilitated by a water-mediated transport mecha-
nism. The conductivity of these counterions is of interest for alka-
line exchange membrane (AEM) fuel cells and water purification
applications [9]. Recent work in our laboratory [9] synthesized and
investigated the bromide and hydroxide conductivity in a PIL
diblock copolymer poly(MMA-b-MEBIm-Br) or poly(methyl meth-
acrylate-b-1-[(2-methyacryloyloxy)ethyl]-3-butylimidazolium
bromide). In this previous work, the PIL block copolymer with
1.27 meq/g. Similar to the work of Elabd and coworkers [9], the
block copolymer showed a higher conductivity compared to its
analogous random copolymer.
Several of the recent observations in water-assisted ion trans-
port in anion exchange block copolymers, such as ion conductivity
higher in a block copolymer compared to its random copolymer,
has previously been observed in cation exchange block copolymers
(e.g., sulfonated block copolymers) [18]. However, the recent
observation of ion transport higher in a block copolymer compared
to its analogous homopolymer is unique and is of interest to explore
further [9]. In this study, a PIL block copolymer was synthesized
with a similar chemistry to a former study, poly(MMA-b-MEBIm-
Br), however, the PIL chemistry was modified to incorporate a
longer alkyl side-chain length (from C ¼ 2 to C ¼ 11). This should
lower the glass transition temperature of the PIL domain and
therefore produce more flexible films under dry conditions at room
temperature. We are interested in the properties and conductivity
of these new materials, particularly the conductivity of the block
copolymer compared to its homopolymer.
In this paper, a PIL diblock copolymer with a long alkyl side-
chain was synthesized, poly(MMA-b-MUBIm-Br), at various com-
positions comprising of a PIL component (1-[(2-methacryloyloxy)
undecyl]-3-butylimidazolium bromide) (MUBIm-Br) and a non-
ionic component (MMA). Poly(MMA-b-MUBIm-Br) was synthe-
sized via post-functionalization from its non-ionic precursor
PIL diblock copolymer, poly(MMA-b-BrUMA) (BrUMA ¼ 11-
bromoundecyl methacrylate), which was synthesized via the
reverse addition fragmentation chain transfer (RAFT) polymeriza-
tion technique. An analogous PIL homopolymer, poly(MUBIm-Br),
was synthesized by conventional free radical polymerization for
comparison. The thermal, mechanical, and conductivity properties
of these PILs were investigated in this study.
1
7.3 mol% MEBIm-Br composition or 1.4 meq/g ion exchange ca-
ꢀ1
pacity (IEC) showed a high bromide conductivity of 5.67 mS cm at
8
ꢁ
0
C and 90% RH. The bromide conductivity of this PIL block
copolymer was over an order of magnitude higher than its analo-
gous PIL random copolymer (at the same IEC and water content)
ꢁ
over a temperature range of 30e80 C at high humidity (90% RH).
This was a product of the strong micro-phase separation (lamellae)
in the PIL block copolymer, where no microphase separation was
evident in the PIL random copolymer. Surprisingly, the bromide ion
conductivity in this PIL block copolymer was higher than its anal-
ogous PIL homopolymer, which had a higher IEC (3-fold) and water
content (2-fold) than the block copolymer. It is not clear why the
bromide ion conductivity was higher in the block copolymer
compared to the homopolymer as this has not been evidenced
before in water-assisted ion transport in block copolymers to the
authors’ knowledge [18]. Similar conductivity trends were also
observed for hydroxide ion conductivity in these PIL polymers as
well, where the PIL block copolymer had a hydroxide conductivity
2. Experimental
2.1. Materials
4-Cyano-4-(phenylcarbonothioylthio)pentanoic acid (chain
transfer agent (CTA), >97%, HPLC), tetrahydrofuran (THF, ꢂ99.9%),
N, N-dimethylformamide (DMF, 99.9%, HPLC), methanol (99.9%,
ꢀ1
ꢁ
of 25.46 mS cm at 80 C and 90% RH at a low water content.
To date, there are only few reports of water-assisted ion con-
ductivity in PIL block copolymers. However, several recent reports
have investigated water-assisted ion transport in block copolymers
for alkaline fuel cells [9,19e21]. Watanabe and coworkers [19]
investigated hydroxide ion conductivity in aromatic multiblock
copolymers of poly(arylene ether)s containing covalently attached
quaternary ammonium cations. A high hydroxide ion conductivity
2
HPLC), acetonitrile (anhydrous, 99.8%), calcium hydride (CaH ,
95%), lithium bromide (LiBr, ꢂ99%), 11-bromo-1-undecanol
(98%), 1-butylimidazole (98%), magnesium sulfate (anhydrous,
Ò
ReagentPlus , 99%), triethylamine (ꢂ99.5%), methacryloyl chloride
(97%, stabilized with 200 ppm monomethyl ether hydroquinone
(MEHQ)), dichloromethane (ACS reagent, ꢂ99.5%, contains 50 ppm
ꢀ
1
ꢁ
of 144 mS cm at 80 C in liquid water for the block copolymer
with an IEC of 1.93 meq/g was measured, which was w3 times
higher than its analogous random copolymer at an IEC of 1.88 meq/
g. The higher conductivity in the block copolymer compared to the
random copolymer was attributed to a strong micro-phase sepa-
ration observed in the block copolymer via electron microscopy.
Coughlin and co-workers [20] synthesized and investigated the
morphology and conductivity of the block copolymer poly(styrene-
b-vinyl benzyl trimethylammonium hydroxide), PS-b-[PVBTMA]
6 6
amylene stabilizer), dimethyl sulfoxide-d (DMSO-d , 99.9% atom%
3
D, contains 0.03% v/v TMS) and chloroform-d (CDCl , 99.96 atom %
D, contains 0.03% v/v TMS) were used as received from Sigmae
Aldrich. Azobisisobutyronitrile (AIBN, 98%, SigmaeAldrich) was
purified by recrystallization twice from methanol. Methyl meth-
acrylate (MMA, 99%, SigmaeAldrich) was purified by distillation
over CaH
with resistivity ca. 16 M
2
at a reduced pressure. Ultrapure deionized (DI) water
cm was used as appropriate.
U
ꢀ
1
ꢁ
[
OH]. A hydroxide conductivity of 12.55 mS cm at 80 C and 90%
2.2. Synthesis of 11-bromoundecyl methacrylate monomer
RH was measured for the block copolymer with an IEC of 1.36 meq/
g. Differences in hydroxide conductivity were observed between
block copolymers of varying IEC, which was attributed to differ-
ences in morphology type and d-spacing observed with small-
angle X-ray scattering. Knauss and coworkers [21] synthesized
bromide and hydroxide conducting poly(phenylene oxide) block
and random copolymers and measured a bromide and hydroxide
A typical synthesis method for the bromine terminated mono-
mer, 11-bromoundecyl methacrylate (BrUMA), which has been
synthesized in a previous publication [22], is shown in Scheme 1(1)
and includes adding 37.4 g (148.89 mmol) of 11-bromo-1-undecanol
and 80 mL of dichloromethane to a three-neck 500 mL flask in an ice
bath. Under nitrogen, a mixture of 15.24 g (150.61 mmol) of trie-
thylamine and 40 mL of dichloromethane was slowly added to the
flask, followed by a slow addition of a mixture of 15.75 g
ꢀ1
ꢁ
ꢀ1
ꢁ
conductivity of 26 mS cm (90 C; 95% RH) and 84 mS cm (80 C;
5% RH), respectively, for the block copolymer with an IEC of
9
Please cite this article in press as: Nykaza JR, et al., Polymerized ionic liquid diblock copolymers with long alkyl side-chain length, Polymer
2014), http://dx.doi.org/10.1016/j.polymer.2014.04.003
(