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Effects of the N-alicyclic cation and backbone structures on the performance of poly(terphenyl)-based hydroxide exchange membranes

Pham, Thanh Huong LU ; Olsson, Joel LU and Jannasch, Patric LU (2019) In Journal of Materials Chemistry A 7(26). p.15895-15906
Abstract

Hydroxide ion conducting poly(terphenyl alkylene)s functionalized with piperidine-based quaternary ammonium cations were synthesized via superacid-catalyzed polyhydroxyalkylations. By employing different synthetic strategies, we have systematically varied the structures of the cation and the backbone polymer to study the effects on morphology, stability and hydroxide conductivity. Two monomers were initially prepared by attaching 4-benzylpiperidine groups to trifluororacetophenone and m-terphenyl, respectively, through Suzuki coupling reactions. Polymerizations followed by quaternizations were then carried out to obtain poly(terphenyl alkylene)s with approximately the same ionic contents. These contained either m- or... (More)

Hydroxide ion conducting poly(terphenyl alkylene)s functionalized with piperidine-based quaternary ammonium cations were synthesized via superacid-catalyzed polyhydroxyalkylations. By employing different synthetic strategies, we have systematically varied the structures of the cation and the backbone polymer to study the effects on morphology, stability and hydroxide conductivity. Two monomers were initially prepared by attaching 4-benzylpiperidine groups to trifluororacetophenone and m-terphenyl, respectively, through Suzuki coupling reactions. Polymerizations followed by quaternizations were then carried out to obtain poly(terphenyl alkylene)s with approximately the same ionic contents. These contained either m- or p-terphenyl backbone units, and were tethered with monocyclic N,N-dimethylpiperidinium (DMP) or spirocyclic 6-azonia-spiro[5,5]undecane-6-ium (ASU) cations placed on either the stiff terphenyl or the more flexible alkylene units along the backbone. Polymer chain flexibility and functionalization with DMP cations were found to promote ionic clustering and conductivity. Hence, a membrane based on a m-terphenyl backbone tethered with DMP on pendant phenyl groups achieveda hydroxide conductivity of 146 mS cm-1 at 80 oC. While the thermal stability was significantly higher forASU-functionalized HEMs, the alkaline stability was highest for the ones carrying DMP cations, which showed less than 5% ionic loss after 720 h in 2 M NaOH at 90 oC. After 168 h at 120 oC, 1H NMR analysis suggested that the DMP cation degraded by a combination of β-Hofmann elimination and methyl substitution. Overall, the results of the study demonstrated that the structural features of the present polymers provided high alkaline stability, most probably due to aryl ether-free backbones, and that all the β-protons of the DMP and ASU cations were placed in 6-membered rings. 

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Journal of Materials Chemistry A
volume
7
issue
26
pages
12 pages
publisher
Royal Society of Chemistry
external identifiers
  • scopus:85068499908
ISSN
2050-7488
DOI
10.1039/C9TA05531B
language
English
LU publication?
yes
id
dec9dfe7-f951-4026-9e01-f773ff7e621b
date added to LUP
2019-06-06 20:20:18
date last changed
2019-08-14 04:39:24
@article{dec9dfe7-f951-4026-9e01-f773ff7e621b,
  abstract     = {<p>Hydroxide ion conducting poly(terphenyl alkylene)s functionalized with piperidine-based quaternary ammonium cations were synthesized via superacid-catalyzed polyhydroxyalkylations. By employing different synthetic strategies, we have systematically varied the structures of the cation and the backbone polymer to study the effects on morphology, stability and hydroxide conductivity. Two monomers were initially prepared by attaching 4-benzylpiperidine groups to trifluororacetophenone and <i>m</i>-terphenyl, respectively, through Suzuki coupling reactions. Polymerizations followed by quaternizations were then carried out to obtain poly(terphenyl alkylene)s with approximately the same ionic contents. These contained either <i>m</i>- or <i>p</i>-terphenyl backbone units, and were tethered with monocyclic <i>N,N</i>-dimethylpiperidinium (DMP) or spirocyclic 6-azonia-spiro[5,5]undecane-6-ium (ASU) cations placed on either the stiff terphenyl or the more flexible alkylene units along the backbone. Polymer chain flexibility and functionalization with DMP cations were found to promote ionic clustering and conductivity. Hence, a membrane based on a <i>m</i>-terphenyl backbone tethered with DMP on pendant phenyl groups achieveda hydroxide conductivity of 146 mS cm<sup>-1</sup> at 80 <sup>o</sup>C. While the thermal stability was significantly higher forASU-functionalized HEMs, the alkaline stability was highest for the ones carrying DMP cations, which showed less than 5% ionic loss after 720 h in 2 M NaOH at 90 <sup>o</sup>C. After 168 h at 120 <sup>o</sup>C, <sup>1</sup>H NMR analysis suggested that the DMP cation degraded by a combination of β-Hofmann elimination and methyl substitution. Overall, the results of the study demonstrated that the structural features of the present polymers provided high alkaline stability, most probably due to aryl ether-free backbones, and that all the β-protons of the DMP and ASU cations were placed in 6-membered rings. </p>},
  author       = {Pham, Thanh Huong and Olsson, Joel and Jannasch, Patric},
  issn         = {2050-7488},
  language     = {eng},
  number       = {26},
  pages        = {15895--15906},
  publisher    = {Royal Society of Chemistry},
  series       = {Journal of Materials Chemistry A},
  title        = {Effects of the <i>N</i>-alicyclic cation and backbone structures on the performance of poly(terphenyl)-based hydroxide exchange membranes},
  url          = {http://dx.doi.org/10.1039/C9TA05531B},
  volume       = {7},
  year         = {2019},
}