Highly ordered ion-conducting block copolymers by hydrophobic block modification

Abstract

Block copolymer-based AEMs provide advanced materials with tunable properties through manipulation of both the ionic domains for high conductivity and the hydrophobic domains for mechanical integrity. Herein, we describe the ionic conductivity and self-assembly behavior of cationic block copolymers based on quaternized vinyl benzyl chloride (QAVBC) by tuning the hydrophobic block composition with hexyl methacrylate (HMA), lauryl methacrylate (LMA), stearyl methacrylate (SMA), and 4-butylstyrene monomers (BS). The block copolymers showed self-assembly of highly-ordered microstructures as confirmed by small angle X-ray scattering and transmission electron microscopy. A non-ionic block copolymer composed of PVBC₁₀₀-b-PBeS₁₈₃ showed less ordered phase separation compared to the quaternized PQAVBC₁₀₀-b-PBeS₁₈₃ sample. The PQAVBC₁₀₀-b-PBeS₁₀₇ and PLMA₆₈-b-PQAVBC₁₂₉ samples with long-range ordered microstructures had approximately three times higher conductivity than that of the less-ordered non-block copolymer based quaternized poly(arylene ether ketone) with a similar ion exchange capacity (∼2.8 meq. g⁻¹). Moreover, the robust anionic PQAVBC₄₄-b-PBS₂₀₂ block copolymer immersed in liquid water had an ionic conductivity three orders of magnitude greater than the samples under 95% relative humidity conditions due to the increased water uptake of the material under liquid conditions.