Sulfonated Poly(arylene ether sulfone) Multi-Block Copolymers with Selectively Cross-Linked Domains for Proton Exchange Membranes

A facile design of sulfonated poly(arylene ether sulfone) multi-block copolymer membranes with selectively cross-linked hydrophobic domains is reported for proton exchange membranes. The cross-linkable linear multi-block copolymers are prepared via coupling telechelic hydrophilic disulfonated oligomers (BPS100) and telechelic hydrophobic oligomers (PPA0) containing cross-linkable allyl-derivatized phenolphthalein moieties. The cross-linked membranes are prepared through UV-initiated thiol-ene cross-linking reactions between allyl-functionalized hydrophobic blocks with pentaerythritol tetrakis(3-mercaptopropionate) as a cross-linker. With highly cross-linked hydrophobic blocks and flexible hydrophilic blocks, the selectively cross-linked multiblock copolymer membranes exhibit remarkably improved dimensional stability and proton conductivity compared to the cross-linked random copolymers. The cross-linked membrane with the longest hydrophilic block length shows a remarkable proton conductivity of 123 mS/cm with a suppressed volume swelling ratio of 25% at 25 °C. At the highest ion exchange capacity level (2.25 meq/g) and the longest block length, the cross-linked multi-block copolymer membrane outperforms Nafion over the full relative humidity range.