Ionic Conductivity and Assembled Structures of Imidazolium Salt-Based Block Copolymers with Thermoresponsive Segments

Kazuhiro Nakabayashi; Yu Sato; Yuta Isawa; Chen-Tsyr Lo; Hideharu Mori

doi:10.3390/polym9110616

Ionic Conductivity and Assembled Structures of Imidazolium Salt-Based Block Copolymers with Thermoresponsive Segments

Polymers (Basel). 2017 Nov 15;9(11):616. doi: 10.3390/polym9110616.

Authors

Kazuhiro Nakabayashi^{1

2}, Yu Sato³, Yuta Isawa⁴, Chen-Tsyr Lo⁵, Hideharu Mori^{6

7}

Affiliations

¹ Department of Polymer Science and Engineering, Graduate School of Science and Engineering, Yamagata University, 4-3-16, Jonan, Yonezawa 992-8510, Japan. nakabayashi.k@yz.yamagata-u.ac.jp.
² Department of Organic Materials Science, Graduate School of Organic Materials Science, Yamagata University, 4-3-16, Jonan, Yonezawa 992-8510, Japan. nakabayashi.k@yz.yamagata-u.ac.jp.
³ Department of Polymer Science and Engineering, Graduate School of Science and Engineering, Yamagata University, 4-3-16, Jonan, Yonezawa 992-8510, Japan. txa16692@st.yamagata-u.ac.jp.
⁴ Department of Organic Materials Science, Graduate School of Organic Materials Science, Yamagata University, 4-3-16, Jonan, Yonezawa 992-8510, Japan. tkh21629@st.yamagata-u.ac.jp.
⁵ Department of Organic Materials Science, Graduate School of Organic Materials Science, Yamagata University, 4-3-16, Jonan, Yonezawa 992-8510, Japan. ct.lo@yz.yamagata-u.ac.jp.
⁶ Department of Polymer Science and Engineering, Graduate School of Science and Engineering, Yamagata University, 4-3-16, Jonan, Yonezawa 992-8510, Japan. h.mori@yz.yamagata-u.ac.jp.
⁷ Department of Organic Materials Science, Graduate School of Organic Materials Science, Yamagata University, 4-3-16, Jonan, Yonezawa 992-8510, Japan. h.mori@yz.yamagata-u.ac.jp.

Abstract

Ionic liquid-based block copolymers composed of ionic (solubility tunable)⁻nonionic (water-soluble and thermoresponsive) segments were synthesized to explore the relationship between ionic conductivity and assembled structures. Three block copolymers, comprising poly(N-vinylimidazolium bromide) (poly(NVI-Br)) as a hydrophilic poly(ionic liquid) segment and thermoresponsive poly(N-isopropylacrylamide) (poly(NIPAM)), having different compositions, were initially prepared by RAFT polymerization. The anion-exchange reaction of the poly(NVI-Br) in the block copolymers with lithium bis(trifluoromethanesulfonyl)imide (LiNTf₂) proceeded selectively to afford amphiphilic block copolymers composed of hydrophobic poly(NVI-NTf₂) and hydrophilic poly(NIPAM). Resulting poly(NVI-NTf₂)-b-poly(NIPAM) exhibited ionic conductivities greater than 10^-3 S/cm at 90 °C and 10^-4 S/cm at 25 °C, which can be tuned by the comonomer composition and addition of a molten salt. Temperature-dependent ionic conductivity and assembled structures of these block copolymers were investigated, in terms of the comonomer composition, nature of counter anion and sample preparation procedure.

Keywords: RAFT polymerization; block copolymer; ion conductivity; polymeric ionic liquid; thermoresponsive polymer.