Macromolecules
ARTICLE
minimize the negative ion mobility effect induced by cross-
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linking. Evidently, the x-PEꢀN(CH3)3 Clꢀ membrane (D-6-
+
+
b), containing 28.1 mol % of C6N(CH3)3 Clꢀ units, possesses
the structure that results in the best combination of high Clꢀ ion
concentration and mobility.
All four PEꢀN(CH3)3 Clꢀ (B-4-b), PEꢀN(iso-C3H7)3 Clꢀ
+
+
(B-4-c), x-PEꢀN(CH3)3 Clꢀ (D-6-b), x-PEꢀN(iso-C3H7)3 Clꢀ
(D-6-c) membranes display close ionic conductivities in 2 N HCl
and 2 N HClꢀ0.2 N CuCl solutions. In addition, the solution in the
cathode side remains colorless during the measurement in 2 N
HClꢀ0.2 N CuCl solution, indicating no Cu2+ species diffusion
through the membrane. The bulky R groups may significantly
reduce the association between Cu species and amino groups,
therefore providing selective Clꢀ ion diffusion throughout the
membranes. This explanation is also in agreement with a phenom-
+
+
enon observed in PEꢀNH3 Clꢀ (B-4-a) and x-PEꢀNH3 Clꢀ
(D-6-a) membranes, with the ionic conductivity in 2 N HClꢀ0.2 N
CuCl solution gradually decreasing with the measurement time;
this is because the Cu species slowly consumes the ammonium salt.
+
+
’ CONCLUSION
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A new class of high performance polyethylene-based anion
exchange membranes has been developed, which contains flex-
ible ammonium chloride (ꢀNR3 Clꢀ) groups and a cross-
+
linking PE network structure. The combination of direct metal-
locene-mediated copolymerization and effective functional
group interconvertions in film form allows us to prepare a wide
range of well-defined x-PEꢀNR3 Clꢀ membranes with good
+
mechanical strength and relatively low thickness (50ꢀ70 μm;
without backing material). A systematic structureꢀproperty
study on both PEꢀNR3 Clꢀ and x-PEꢀNR3 Clꢀ membranes
+
+
was performed in order for us to understand the PE structure0s
+
effect (concentration of ꢀNR3 Clꢀ groups, R in the quaternary
ammonium group, cross-linking density, etc.) on the water uptake
and ionic conductivity. The most desirable x-PEꢀNR3 Clꢀ mem-
+
+
brane contains 28.1 mol % ꢀN(CH3)3 Clꢀ groups in the flexible
side chains and possesses a fully cross-linked hydrophobic PE
matrix (formed by 0.2 mol % BSt units). This membrane offers an
excellent combination of desirable properties, including adequate
water swelling, high thermal stability, and exceptionally high ionic
conductivities of 119.6 mS/cm in 2 N HCl solution and 78.8 mS/cm
in 2 N HClꢀ0.2 N CuCl solution (one order higher than all
commercially available AEM membranes).
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’ ASSOCIATED CONTENT
64, 1469.
S
Supporting Information. Membrane evaluation proce-
b
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dure. This material is available free of charge via the Internet at
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: chung@ems.psu.edu.
(38) Chung, T. C. Prog. Polym. Sci. 2002, 27, 39.
(39) Ruggeri, G.; Aglietto, M.; Petragnani, A.; Ciardelli, F. Eur.
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43, 7147.
’ ACKNOWLEDGMENT
The authors gratefully acknowledge the financial support of
this work by the U.S. Department of Energy (Contract No. DE-
FG36-06GO16036).
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dx.doi.org/10.1021/ma200836d |Macromolecules 2011, 44, 5937–5946