Block-Length-Tunable Sulfonated Polyphenylene- b -Polyimide Multiblock Copolymers with Enhanced Microphase Separation for Proton Exchange Membrane Fuel Cells

A series of sulfonated polyphenylene-b-polyimide (SPP-b-PI) multiblock copolymers were synthesized by coupling hydrophilic SPP oligomers with hydrophobic polyimide oligomers for proton exchange membranes. The block architecture promotes microphase-separated morphologies, in which SPP domains form continuous proton-transport pathways and semi-crystalline PI domains provide a robust hydrophobic framework to suppress swelling and stabilize membrane morphology. By tuning block length, the balance among proton transport, dimensional stability, and durability is regulated. The membrane electrode assembly (MEA) based on the S10-b-(ND)8 membrane shows representative performance, delivering a peak power density of 2.00 W cm–2 at 90 °C, 100% relative humidity (RH), and 150 kPa, compared with 1.59 W cm–2 for Nafion 212. Under 30% RH, it retains 1.31 W cm–2, 32% higher than Nafion 212. The corresponding cell maintains an OCV of ∼1.0 V for 400 h at 90 °C and 50% RH, with a decay rate of 0.111 mV h–1, demonstrating the effectiveness of block-length-regulated microphase-separated morphology in achieving a balance between proton conductivity and membrane durability.