Achieving Continuous Anion Transport Domains Using Block Copolymers Containing Phosphonium Cations

Triblock and diblock copolymers based on isoprene (IP) and chloromethylstyrene (CMS) were synthesized by sequential polymerization using reversible addition-fragmentation chain transfer radical polymerization (RAFT). The block copolymers were quaternized with tris(2,4,6-trimethoxyphenyl)phosphine (Ar₃P) to prepare soluble ionomers. The ionomers were cast from chloroform to form anion exchange membranes (AEMs) with highly ordered morphologies. At low volume fractions of ionic blocks, the ionomers formed lamellar morphologies, while at moderate volume fractions (≥30% for triblock and ≥22% for diblock copolymers) hexagonal phases with an ionic matrix were observed. Ion conductivities were higher through the hexagonal phase matrix than in the lamellar phases. Promising chloride conductivities (20 mS/cm) were achieved at elevated temperatures and humidified conditions.