Ladder-type aromatic block copolymers containing sulfonated triphenylphosphine oxide moieties as proton conductive membranes

•Ladder-type ionomers with sulfonated triphenylphosphine oxide moiety were prepared.•The ionomers had high molecular weights, leading to tough and flexible membranes.•The ionomer membranes showed high proton conductivity with good mechanical stability.

The synthesis and characterization of ladder-type aromatic block copolymers containing sulfonated triphenylphosphine oxide moieties (LadP-SPE) are reported. Through aromatic nucleophilic substitution polycondensation and Pd-catalyzed intrapolymer Heck reaction, the target copolymers LadP-SPE with high molecular weight (Mn = 47-50 kDa, Mw = 289-579 kDa) and different ion exchange capacity (IEC) values (1.04, 1.84 and 2.22 meq g−1, by titration) were prepared. By solution casting method, all the copolymers gave transparent and bendable membranes. The membrane with IEC = 2.22 meq g−1 exhibited high proton conductivity in wide range of relative humidity (RH) at 80 °C (ca. 1.6 mS cm−1 at 20% RH and 351.2 mS cm−1 at 95% RH). Moreover, the stiff ladder structure strengthened the molecular chain which contributed to the membrane with high IEC value and water uptake to have desirable mechanical stability up to 90% RH at 80 °C.

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