Ionic Functionalization of Polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene via Friedel-Crafts Bromoalkylation and Its Application for Anion Exchange Membranes

摘要

Polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) based anion exchange membranes (AEMs) were synthesized via Friedel-Crafts alkylation on the polystyrene block using a bromoalkylated tertiary alcohol and trifluoromethanesulfonic acid catalyst. This simple one-step bromoalkylation and following quaternization of the aromatic polymer allowed to control ion exchange capacity (IEC) and cation tether length conveniently by changing the amount and the structure of bromoalkylated tertiary alcohol substrate. A series of SEBS-based AEMs with different quaternary ammonium concentrations and tether lengths were systemically investigated by comparing IECs, water uptakes, and OH~- conductivities. SEBS-C_3-TMA-0.8 (tether length, n=3; 80% of polystyrene functionalization) had the highest IEC (1.62 mequiv./g), and OH~- conductivity of 93 mS/cm at 80 °C in water. Polymer structure made of all carbon-carbon bond backbone and tethered side chain provided remarkable chemical stability under alkaline conditions. The IEC and OH~- conductivity of SEBS membranes remain unaffected after immersing in 1 M NaOH at 80°C for 500 h.