In-situ synthesis of cross-linked imidazolium functionalized Poly(styrene-b-isobutylene-b-styrene) for anion exchange membranes

The cross-linked imidazolium functionalized anion-exchange membranes is in-situ prepared via reaction of chloromethylated poly(styrene-b-isobutylene-b-styrene) with 1,1’-(1,6-hexanediyl)bisimidazole and N-methylimidazole. The composite membranes of cross-linked imidazolium poly(styrene-b-isobutylene-b-styrene) with a small amount of modified graphene oxide grafted with octadecyl and propyl phenyl imidazolium could be further prepared. These membranes exhibit significantly high chemical stability and ionic conductivity (σ), marked by low methanol permeability, together with improved dynamic mechanical properties. The ionic conductivity of cross-linked imidazolium poly(styrene-b-isobutylene-b-styrene) reaches 2.09 × 10−2 S cm−1 at 80 °C by introduction of 0.5 wt% loading of modified graphene oxide. This membrane also behaves an excellent chemical stability and σ can remain ca. 82% of the original value after immerged in strong alkaline medium (2 M NaOH) at 60 °C for 500 h, which is almost the same as that (ca. 82%) of commercial Nafion 115 in acid medium (2 M H2SO4) at 60 °C for 500 h. The cross-linked imidazolium poly(styrene-b-isobutylene-b-styrene) is characterized as a promising anion exchange membrane materials in fuel cell for its high ionic conductivity, chemical stability and low methanol permeability.