ma5b01457_si_001.pdf (4.51 MB)
Polyethylene-Based Block Copolymers for Anion Exchange Membranes
journal contribution
posted on 2015-09-22, 00:00 authored by Yifan Li, Ye Liu, Alice
M. Savage, Frederick L. Beyer, Soenke Seifert, Andrew M. Herring, Daniel M. KnaussBlock copolymer membranes with a
semicrystalline polyethylene component
were prepared by anionic polymerization and postpolymerization functionalization
reactions. Polybutadiene-b-poly(4-methylstyrene)
(PB-b-P4MS) precursors with four different block
compositions and 92–95% 1,4-content in the polybutadiene block
were produced by living anionic polymerization in a nonpolar solvent.
The polybutadiene block was subsequently hydrogenated to prepare a
polyethylene block, and the hydrogenated block copolymers were then
brominated at the arylmethyl group of the P4MS block. Subsequent quaternization
reaction with trimethylamine led to the anion exchange membranes.
The degree of crystallinity in the polyethylene block was determined
by differential scanning calorimetry to be approximately 24–27%.
The postpolymerization modification reactions were examined by 1H NMR and IR spectroscopy. The amount of quaternary ammonium
groups was quantified by ion exchange capacity (IEC) measurements.
Membranes with IEC’s ranging from 1.17 to 1.92 mmol/g were
prepared. The IEC was varied by changing the relative amount of P4MS
in the precursor block copolymer, and water uptake and ionic conductivity
were found to increase with increasing IEC. Small-angle X-ray scattering
(SAXS) experiments and transmission electron microscopy (TEM) showed
phase-separated, bicontinuous structures at all compositions. Materials
with higher IEC show improved ionic conductivity as well as lower
activation energy of ion conduction compared to less functionalized
membranes. The hydroxide conductivity of the block copolymer membrane
with an IEC of 1.92 mmol/g reached 73 mS/cm at 60 °C in water.
Tensile measurements indicated excellent mechanical properties of
the semicrystalline membranes for potential use as alkaline fuel cell
membrane materials.
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Keywords
P 4MS blockpolyethylene blockSubsequent quaternization reactionpostpolymerization modification reactionsSAXS1 H NMRAnion Exchange MembranesBlock copolymer membranesion exchange capacitypostpolymerization functionalization reactionsquaternary ammonium groupsfuel cell membrane materialsTEMprecursor block copolymerIECtransmission electron microscopyblock copolymer membraneanion exchange membranessemicrystalline polyethylene componentIRpolybutadiene blockhydrogenated block copolymers
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