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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