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

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 (M_n = 47-50 kDa, M_w = 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.