Synthesis of copolymer grafts containing sulfoalkyl and hydrophilic groups in polymer electrolyte membranes

Kazuyuki Enomoto, Shuichi Takahashi, Rosiah Rohani, Yasunari Maekawa

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

Proton exchange type polymer electrolyte membranes (PEM) consisting of ion conducting alkylsulfonic acid and hydrophilic groups such as a hydroxyl group were successfully synthesized by radiation-induced graft polymerization of vinyl acetate (VAc) into a poly(ethylene-co-tetrafluoroethylene) (ETFE) film, followed by saponification and alkylsulfonation with 1,3-propanesulfone. In contrast to the typical S N2 reactions in a solution, the base-catalyzed nucleophilic ring-opening reactions of hydroxyl groups of poly(vinylalcohol) grafts with 1,3-propanesultone in solid state ETFE films hardly proceeds in the hydrophilic solvents, but it does proceed in hydrophobic toluene with a weak base (triethylamine) to yield ETFE-grafted poly(vinylalcohol-co-vinylsulfopropyl ether) (PEM-OH) with various values of ion-exchange capacity (IEC) and molar ratio of hydroxyl to sulfo groups in the grafts. The relative-humidity (RH) dependence of the proton conductivity of the sulfonated membrane was compared with that of poly(styrenesulfonic acid)-grafted ETFE (PEM-PSSA) with a similar IEC (~1.3mmolg -1) at 80°C. The PEM-OH showed a conductivity of 1.0×10 -3Scm -1 under 30% RH, which is higher than those of PEM-PSSA. Further, the PEM-OH with higher IEC (1.9mmolg -1) prepared with a grafting degree of 82% and a sulfonation degree of 41% showed 3.8×10 -3Scm -1 under 30% RH at 80°C. The conductivity is higher than that of PEMs based on sulfonated polyimide and poly(ether sulfone) with a similar IEC. Furthermore, the tensile strength of PEM-OH was 48MPa with the elongation at break of 422%, which are better than those of Nafion. These results strongly indicate that the radiation-grafted PEM with hydroxyl groups is a promising material with excellent mechanical and electrochemical properties, which are important characteristics for a fuel cell operating at a high temperature and low humidity.

Original languageEnglish
Pages (from-to)36-41
Number of pages6
JournalJournal of Membrane Science
Volume415-416
DOIs
Publication statusPublished - 1 Oct 2012

Fingerprint

Graft copolymers
Electrolytes
copolymers
Polymers
electrolytes
membranes
Membranes
Transplants
polymers
synthesis
Ion Exchange
Ion exchange
Humidity
Hydroxyl Radical
humidity
Atmospheric humidity
Ethylene
ethylene
Grafts
ions

Keywords

  • Graft polymerization
  • Low relative humidity
  • Polymer electrolyte membranes
  • Proton conductivity
  • Sulfoalkylation

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Materials Science(all)
  • Biochemistry
  • Filtration and Separation

Cite this

Synthesis of copolymer grafts containing sulfoalkyl and hydrophilic groups in polymer electrolyte membranes. / Enomoto, Kazuyuki; Takahashi, Shuichi; Rohani, Rosiah; Maekawa, Yasunari.

In: Journal of Membrane Science, Vol. 415-416, 01.10.2012, p. 36-41.

Research output: Contribution to journalArticle

Enomoto, Kazuyuki ; Takahashi, Shuichi ; Rohani, Rosiah ; Maekawa, Yasunari. / Synthesis of copolymer grafts containing sulfoalkyl and hydrophilic groups in polymer electrolyte membranes. In: Journal of Membrane Science. 2012 ; Vol. 415-416. pp. 36-41.
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N2 - Proton exchange type polymer electrolyte membranes (PEM) consisting of ion conducting alkylsulfonic acid and hydrophilic groups such as a hydroxyl group were successfully synthesized by radiation-induced graft polymerization of vinyl acetate (VAc) into a poly(ethylene-co-tetrafluoroethylene) (ETFE) film, followed by saponification and alkylsulfonation with 1,3-propanesulfone. In contrast to the typical S N2 reactions in a solution, the base-catalyzed nucleophilic ring-opening reactions of hydroxyl groups of poly(vinylalcohol) grafts with 1,3-propanesultone in solid state ETFE films hardly proceeds in the hydrophilic solvents, but it does proceed in hydrophobic toluene with a weak base (triethylamine) to yield ETFE-grafted poly(vinylalcohol-co-vinylsulfopropyl ether) (PEM-OH) with various values of ion-exchange capacity (IEC) and molar ratio of hydroxyl to sulfo groups in the grafts. The relative-humidity (RH) dependence of the proton conductivity of the sulfonated membrane was compared with that of poly(styrenesulfonic acid)-grafted ETFE (PEM-PSSA) with a similar IEC (~1.3mmolg -1) at 80°C. The PEM-OH showed a conductivity of 1.0×10 -3Scm -1 under 30% RH, which is higher than those of PEM-PSSA. Further, the PEM-OH with higher IEC (1.9mmolg -1) prepared with a grafting degree of 82% and a sulfonation degree of 41% showed 3.8×10 -3Scm -1 under 30% RH at 80°C. The conductivity is higher than that of PEMs based on sulfonated polyimide and poly(ether sulfone) with a similar IEC. Furthermore, the tensile strength of PEM-OH was 48MPa with the elongation at break of 422%, which are better than those of Nafion. These results strongly indicate that the radiation-grafted PEM with hydroxyl groups is a promising material with excellent mechanical and electrochemical properties, which are important characteristics for a fuel cell operating at a high temperature and low humidity.

AB - Proton exchange type polymer electrolyte membranes (PEM) consisting of ion conducting alkylsulfonic acid and hydrophilic groups such as a hydroxyl group were successfully synthesized by radiation-induced graft polymerization of vinyl acetate (VAc) into a poly(ethylene-co-tetrafluoroethylene) (ETFE) film, followed by saponification and alkylsulfonation with 1,3-propanesulfone. In contrast to the typical S N2 reactions in a solution, the base-catalyzed nucleophilic ring-opening reactions of hydroxyl groups of poly(vinylalcohol) grafts with 1,3-propanesultone in solid state ETFE films hardly proceeds in the hydrophilic solvents, but it does proceed in hydrophobic toluene with a weak base (triethylamine) to yield ETFE-grafted poly(vinylalcohol-co-vinylsulfopropyl ether) (PEM-OH) with various values of ion-exchange capacity (IEC) and molar ratio of hydroxyl to sulfo groups in the grafts. The relative-humidity (RH) dependence of the proton conductivity of the sulfonated membrane was compared with that of poly(styrenesulfonic acid)-grafted ETFE (PEM-PSSA) with a similar IEC (~1.3mmolg -1) at 80°C. The PEM-OH showed a conductivity of 1.0×10 -3Scm -1 under 30% RH, which is higher than those of PEM-PSSA. Further, the PEM-OH with higher IEC (1.9mmolg -1) prepared with a grafting degree of 82% and a sulfonation degree of 41% showed 3.8×10 -3Scm -1 under 30% RH at 80°C. The conductivity is higher than that of PEMs based on sulfonated polyimide and poly(ether sulfone) with a similar IEC. Furthermore, the tensile strength of PEM-OH was 48MPa with the elongation at break of 422%, which are better than those of Nafion. These results strongly indicate that the radiation-grafted PEM with hydroxyl groups is a promising material with excellent mechanical and electrochemical properties, which are important characteristics for a fuel cell operating at a high temperature and low humidity.

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