ma8b00284_si_001.pdf (1.59 MB)
Structurally Well-Defined Anion Conductive Aromatic Copolymers: Effect of the Side-Chain Length
journal contribution
posted on 2018-04-25, 18:54 authored by Ryo Akiyama, Naoki Yokota, Kanji Otsuji, Kenji MiyatakeFor improving the
alkaline stability and other properties of aromatic
semiblock copolymer [QPE-bl-11a(C1)] membranes containing
benzyltrimethylammonium groups, several novel hydrophilic monomers
with different side-chain lengths and substitution positions were
designed and synthesized for the polymerization. The pendant-type
preaminated copolymers PE-bl-11s were quaternized
using iodomethane to obtain the target QPE-bl-11s
with well-defined chemical structure. In TEM analyses, QPE-bl-11a(C3) and QPE-bl-11a(C5) membranes
with propyl and pentyl side-chains, respectively, showed more developed
phase-separated morphology with greater hydrophilic domains (ca. 10–20
nm in width) than that of the C1 equivalent. The phase separation
was more distinct and larger for the QPE-bl-11a membranes
linked with p-phenylene groups in the hydrophilic
part than for the QPE-bl-11b membranes with m-phenylene groups. In particular, QPE-bl-11b(C5) membrane exhibited considerably smaller hydrophilic/hydrophobic
domains compared to those of the other membranes. After the alkaline
stability test in 1 M KOH aqueous solution at 60 °C for 1000
h, the remaining conductivity was better as increasing the side-chain
length: 34% for QPE-bl-11a(C1), 54% for QPE-bl-11a(C3), and 72% for QPE-bl-11a(C5)
at 60 °C. The results suggest that the pendant alkyl chains could
improve the alkaline stability and the main-chain bond position could
improve morphology, water utilization, and mechanical properties of
QPE-bl-11 membranes. An H2/O2 fuel cell with QPE-bl-11 membrane showed 139 mW
cm–2 of the maximum power density at 0.28 A cm–2 of the current density.