Multi-block poly(arylene ether)s containing pre-choloromethylated bisphenol: Anion conductive ionomers

Article abstract of DOI:10.1039/c3ta10857k

We report a simple method for the preparation of anion conductive ionomers (ACIs) using chloromethylated bisphenol A, without the use of chloromethyl methyl ether (CMME) (carcinogenic). Aminated multi-block poly(arylene ether)s (AMBPEs) were obtained by nucleophilic aromatic substitution, followed by polymer condensation then amination. The reported ACIs exhibited a 2.74 milliequivalent per g ion-exchange capacity (IEC) and hydroxide ion conductivity of 56 mS cm^-1.

Full text of DOI:10.1039/c3ta10857k

Journal of
Materials Chemistry A
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Multi-block poly(arylene ether)s containing
pre-choloromethylated bisphenol: anion
Cite this: J. Mater. Chem. A, 2013, 1,
6134
conductive ionomers†
Received 28th February 2013
Accepted 12th April 2013
*
Amaranadh Jasti and Vinod K. Shahi
DOI: 10.1039/c3ta10857k
www.rsc.org/MaterialsA
We report a simple method for the preparation of anion conductive Chloromethyl groups were introduced at the specic positions
ionomers (ACIs) using chloromethylated bisphenol A, without the of the uorenyl groups by the Friedel–Cras reaction by using
use of chloromethyl methyl ether (CMME) (carcinogenic). Aminated CMME. However, the carcinogenic and potentially harmful to
multi-block poly(arylene ether)s (AMBPEs) were obtained by nucle- human health nature of CMME is a serious drawback of the
ophilic aromatic substitution, followed by polymer condensation reported method.16–19 These ACIs were achieved by chlor-
then amination. The reported ACIs exhibited a 2.74 milliequivalent omethylation of a block co-polymer, while functionalization of
per g ion-exchange capacity (IEC) and hydroxide ion conductivity of the monomer is expected to result in a relatively higher degree
56 mS cmꢀ1
.
of functionalization. To avoid this problem, we report a method
for the synthesis of aminated multiblock poly(arylene ether)s by
using a functionalized (2,20-bischloromethyl) bisphenol A
(CMBPA) monomer as a novel ACI forming candidate.
The CMBPA monomer was prepared by introducing the
chloromethyl groups by the in situ chloromethylation of
bisphenol A (BPA). The BPA monomer was treated with potas-
sium carbonate such that it underwent an electrophilic substi-
tution reaction through the formation of two phenoxide anions,
which act as electron donating groups. The formed phenoxide
monomer was treated in situ with the chloromethylating agent,
Fuel cells have been considered as a source for clean or
renewable energy, because of their low emission levels with
high efficiency and promising stationary, automotive and
mobile applications.1 Most research efforts have been directed
toward the development of polymer electrolyte fuel cells
(PEFCs) using proton conducting ionomers (PCIs) (preferen-
tially peruorosulfonic acid polymers such as Naon). Signi-
cant drawbacks of PEFCs such as fuel loss, low durability, and
costly electro-catalysts restricts their wide spread commerciali-
zation.2–4 As an alternative, there is a growing interest in alka-
line membrane fuel cells (AMFCs) that utilize ACIs which show
facile fuel oxidation in alkaline media, better oxygen reduction
at the cathode and with less precious transition metal based
electro-catalysts (Co, Ni, Pd, etc.).5,6 Thus, ACIs with good ion
conductivity are urgently required.
A variety of ACIs based on polystyrenes,7 poly(phenylene
oxide)s,8 poly(ether-imide),9 poly(arylene ether)s,10–13 radiation-
graed uorinated polymers,14 and organic–inorganic hybrid
composites,15 have been investigated. These ACIs are typically
prepared by chloromethylation using CMME. Recently, Wata-
nabe et al., reported ACIs based on poly(arylene ether sulfone
ketone)s containing quaternized uorenyl groups.10,11
which was
a
mixture of paraformaldehyde, trimethyl-
chlorosilane and a Lewis acid (SnCl4).20
The AMBPE was synthesized by a nucleophilic substitution
polymerization of 4,40-diuorophenyl sulfone (5.5 mmol), 4,40-
diuorobenzophenone (5.5 mmol) and (2,20-bischloromethyl)
bisphenol A (11.5 mmol), inthe presence of potassium carbonate
in dry N,N0-dimethylacetamide (DMAc). The amination was
achieved by treating with trimethylamine solution (35%) for 24 h
at room temperature (Scheme 1). This method avoids the gela-
tion of poly(arylene ether)s as reported previously.10 The func-
tionalized CMBPA monomer was prepared by using optimised
conditions, which ruled out the possibility of self-crosslinking
(which is due to excess addition of paraformaldehyde and SnCl4
in the Friedel–Cras alkylation reaction). We optimised the
conditions to avoid the unwanted Friedel–Cras alkylation
reaction leading to self-crosslinking by using a mixture of para-
formaldehyde (185 mmol), trimethylchlorosilane (185 mmol)
Electro-Membrane Processes Division, CSIR-Central Salt and Marine Chemicals
Research Institute, G.B. Marg, Bhavnagar-364002, Gujarat, India. E-mail: vkshahi@
csmcri.org; Fax: +91 278 2567562 ext. 6970; Tel: +91-278-2567760 ext. 7340
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c3ta10857k
ꢁ
and anhydrous stannic chloride (0.183 mmol) at 80 C, as the
chloromethylation reagent. AMBPE membranes are named as
AMBPE-X, where X is the degree of chloromethylation (DCM).
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Scheme 1 Synthesis of aminated multi-block poly(arylene ether)s containing functionalized bisphenol A groups.
1H NMR spectra of the BPA and CMBPA (D2O exchange) are which correspond to DCMs of 76%, 60%, 45% and 32%,
compared in (Fig. 1(a) and (b)). A new peak at 4.70 ppm for respectively.
CMBPA was attributed to the presence of the –CH2Cl group
The molecular weight of the ionomers was measured by
(denoted as d), in addition to the new broad peak at 4.98 ppm GPC. The number average molecular weight (Mn) ranged
(attributed to D2O exchange). If a –CH2OH group was formed between 4.5 and 8.7 ꢂ 104 g molꢀ1, while the weight average
then the peak at 4.70 ppm would have disappeared with molecular weight (Mw) varied from 1.1 ꢂ 105 to 2.0 ꢂ 105
g
exchange of D2O. Aer the chloromethylation, the chemical molꢀ1, for different ACIs with respective IEC values. In spite of
shi values for the aromatic protons shied from the range of the high molecular weight, ACIs showed high solubility in many
6.8–7.2 ppm to 6.6–7.06 ppm (assigned as a, b and c in Fig. 1(b)). organic solvents due to the highly functionalized bisphenol
The peak at 1.58 ppm corresponds to the –C(CH3)2 (gem- moieties.
dimethyl) group (denoted as e in Fig. 1(b)).
Water uptake (WU) and ion conductivity (s) (summarized in
AMBPE copolymer was conrmed by the peaks with Fig. 2) are important properties for fuel cell applications. The
chemical shi values 1.71 and 1.65 ppm, which correspond to WU values were estimated from the weight of dry and wet
–C(CH3)2 (denoted as b and b0 in Fig. 1(c)). The peak at 2.94 membrane (immersed in water at 30 ꢁC for 48 h). The
ppm (assigned as a in Fig. 1(c)) corresponds to the methyl membrane with the highest IEC value showed maximum water
protons of the trimethyl ammonio groups and the peak at 4.77 uptake (approximately 170%) (Fig. 2(a)). Furthermore, IEC and
ppm (assigned as c, d and e in Fig. 1(c)) corresponds to the WU values are comparable with other ACIs based on the ami-
four methylenes of the trimethyl ammonio groups. The nated ammonio groups, reported in the literature.10,21,22 WU and
aromatic protons of the diphenyl sulfone, CMBPA and IEC values varied proportionally, depending on the overlapping
benzophenone moieties correspond to the peaks with chem- of hydrated regions caused by the distribution of the ion con-
ical shi values between 6.76–7.80 ppm (denoted as f to o in ducting groups in the matrix. In spite of the 170% water uptake
Fig. 1(c)).
value, gel-like properties were not observed and the membranes
Under optimised reaction conditions, 76% DCM (estimated were mechanically robust due to the high molecular weights of
by the integral peak ratio of d and e using eqn (1)) was obtained. the ionomers.21
AMBPE membranes are considered to contain hydrophilic
2AðHdÞ
DCM ¼
(1)
morphology, where hydrophilic domains contribute toward
the IEC/conductivity. The hydroxide ion conductivity of the
AMBPE membranes were measured in deionized water at 30
ꢁC by an impedance technique discussed in the ESI.†
Hydroxide ion conductivity for different AMBPE membranes
were found to be 56, 40, 25, and 12 mS cmꢀ1 corresponding
to 2.74, 2.28, 1.86 and 1.19 milliequivalent per g IEC values.
To the best of our knowledge, the AMBPE-76 membrane
AðHeÞ
where A (Hd) is the integral area of the Hd peak (–CH2Cl), and A
(He) is the integral area of the He peak (–C(CH3)2 group)
(Fig. 1(b)). For the CMBPA monomer, varied DCMs of 60%, 45%
and 32% were achieved under various conditions. For the
AMBPE membranes, ion exchange capacities (IEC) were
obtained as 2.74, 2.28, 1.86 and 1.19 milliequivalent per g,
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Fig. 1 1H NMR spectra of (a) BPA, (b) CMBPA (76% DCM, D2O exchange) and (c) AMBPE-76 (IEC ¼ 2.74 milliequivalent per g).
(IEC
¼
2.74 milliequivalent per g) showed the highest
In summary, multi-block poly(arylene ether)s containing
hydroxide ion conductivity (56 mS cmꢀ1 at 30 ꢁC) reported functionalized BPA were synthesized via an in situ chlor-
thus far for anion conducting ionomers in the litera- omethylation, followed by polymer condensation then amina-
ture.8–10,12,13,19,23 While the conductivꢁity for AMBPE-76 was tion. The proposed reaction route avoided the use of CMME
measured at about 85 mS cmꢀ1 at 70 C. Moreover, hydroxide (carcinogenic and hazardous), which is a commonly used
ion conductivity for the AMBPE membranes followed Arrhe- reagent in the chloromethylation reaction. By cleverly optimis-
nius-type temperature dependent behaviour at elevated ing the reaction conditions, a DCM of up to 76% was achieved,
ꢁ
temperatures (except at 70 and 80 C) (Fig. 2(b)). The apparent which corresponded to 2.74 milliequivalent per g IEC aer
activation energy estimated from the slope was between 5.9– amination, resulting in the development of highly charged
12.2 kJ molꢀ1 and depended on the IEC. The activation energy ACIs. High hydroxide ion conductivities of up to 56–85 mS cmꢀ1
of AMBPE was similar to or slightly lower than those of at temperatures 30–70 ꢁC were obtained, which also revealed an
reported anion exchange membranes. These membranes Arrhenius-type temperature dependent behaviour for AMBPE
exhibit much higher conductivity possibly due to highly membranes and activation energies of 5.9–12.2 kJ molꢀ1. The
functionalized blocks which exhibit more ion exchangeable design concept of ACIs is based on a multi-block copolymer
sites. These results suggest a multi-block structure with highly structure with highly functionalized hydrophilic blocks. This
ionized hydrophilic blocks is effective for improved hydroxide enabled the introduction of more functional groups, which
conductivity and IEC.
were responsible for high conductivity and IEC.
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4 T. J. Peckham and S. Holdcro, Adv. Mater., 2010, 22, 4667–
4690.
5 Y. Zha, M. L. D. Miller, Z. D. Johnson, M. A. Hickner and
G. N. Tew, J. Am. Chem. Soc., 2012, 134, 4493–4496.
6 N. Li, Q. Zhang, C. Wang, Y. M. Lee and M. D. Guiver,
Macromolecules, 2012, 45, 2411–2419.
7 K. Kneifel, Desalination, 1980, 34, 77–95.
8 L. Wu, T. Xu, D. Wu and X. Zheng, J. Membr. Sci., 2008, 310,
577–585.
9 G. Wang, Y. Weng, D. Chu, D. Xie and R. Chen, J. Membr. Sci.,
2009, 326, 4–8.
10 M. Tanaka, M. Koike, K. Miyatake and M. Watanabe,
Macromolecules, 2010, 43, 2657–2659.
11 M. Tanaka, K. Fukasawa, E. Nishino, S. Yamaguchi,
K. Yamada, H. Tanaka, B. Bae, K. Miyatake and
M. Watanabe, J. Am. Chem. Soc., 2011, 133, 10646–
10654.
12 Z. Zhao, J. Wang, S. Li and S. Zhang, J. Power Sources, 2011,
196, 4445–4450.
13 J. Zhou, M. Unlu, J. A. Vega and P. A. Kohl, J. Power Sources,
2009, 190, 285–292.
14 J. R. Varcoe and R. C. T. Slade, Electrochem. Commun., 2006,
8, 839–843.
Fig. 2 (a) Hydroxide ion conductivity and water uptake as a function of IEC at 30
ꢁC: (:) conductivity; (C) water uptake. (b) Temperature dependence of
hydroxide ion conductivity for AMBPE membranes bearing various IECs.
15 Y. Wu, C. Wu, T. Xu, X. Lin and Y. Fu, J. Membr. Sci., 2009,
329, 236–245.
16 US Department of Health Human Services, Public Health
Service, National Toxicology Program. Report on Carcinogens,
12th edn, 2011, http://ntp.niehs.nih.gov/ntp/roc/twelh/
roc12.pdf.
Acknowledgements
17 M. C. Lin and N. Takai, J. Membr. Sci., 1994, 88, 77–83.
18 S. Laskin, M. Kusschner, R. T. Drew, V. P. Capiello and
N. Nelson, Arch. Environ. Health, 1971, 23, 135–136.
19 T. Xu, Z. Liu, Y. Li and W. Yang, J. Membr. Sci., 2008, 320,
232–239.
Financial assistance was received from the Ministry of New and
Renewable Energy (MNRE), Government of India and is grate-
fully acknowledged for sponsoring project no. 102/79/2010-NT.
Instrumental support was received from the Analytical Science
Division, CSIR-CSMCRI and is gratefully acknowledged.
20 E. Avram, E. Butuc, C. Luca and I. Druta, J. Macromol. Sci.,
Part A: Pure Appl. Chem., 1997, 34, 1701–1714.
21 M. R. Hibbs, M. A. Hickner, T. M. Alam, S. K. McIntyre,
C. H. Fujimoto and C. J. Cornelius, Chem. Mater., 2008, 20,
2566–2573.
Notes and references
1 W. Vielstich, Handbook of Fuel Cells, Wiley, Chichester,
England, 2009.
2 M. A. Hickner, H. Ghassemi, Y. S. Kim, B. R. Einsla and 22 J. Zhou, M. Unlu, J. A. Vega and P. A. Kohl, J. Power Sources,
J. E. McGrath, Chem. Rev., 2004, 104, 4587.
3 C. H. Park, C. H. Lee, M. D. Guiver and Y. M. Lee, Prog. Polym.
Sci., 2011, 36, 1443–1498.
2009, 190, 285–292.
23 M. Tanaka, M. Koike, K. Miyatake and M. Watanabe, Polym.
Chem., 2011, 2, 99–106.
This journal is ª The Royal Society of Chemistry 2013
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