Poly(2,6-dimethyl-1,4-phenylene oxide)-b-poly(vinylbenzyltrimethylammonium) Diblock Copolymers for Highly Conductive Anion Exchange Membranes

Diblock copolymer membranes of poly(2,6-dimethyl-1,4-phenylene oxide)-b-poly(vinylbenzyltrimethylammonium) (PPO-b-PVBTMA) were prepared as anion exchange membranes. The membranes were produced by growing poly(vinylbenzyl chloride) (PVBC) blocks from a PPO macroinitiator using nitroxide-mediated polymerization to make PPO-b-PVBC copolymers with varying PVBC content, then melt pressing into films, and subsequently reacting with trimethylamine. Phase separation was indicated for the PPO-b-PVBC polymers based on the evidence of two Tgs from differential scanning calorimetry measurements. The melt-processing conditions to form films produced lightly cross-linked materials. The conversion to PPO-b-PVBTMA membranes by reaction with trimethylamine led to materials with varying ion exchange capacities based on the amount of PVBC in the precursor. The water uptake, the dimensional changes with hydration, and the ionic conductivities in the hydroxide and bicarbonate forms were determined. The water uptake was suppressed by the light cross-linking in the hydrophilic PVBTMA component, allowing the films to remain insoluble in aqueous solutions at high IEC values. Membranes with IECs up to 2.9 mequiv/g were flexible under dry and hydrated conditions and showed hydroxide conductivity of 132 ± 3.8 mS/cm at 60 °C.