NOVELTY - A polymer blend has ion conductivity of 10-3 second/cm or more at room temperature in water and comprises a polymer (a) which is a sulfonated poly(arylene sulfone) comprising repeating units, and a polymer (b) which is not a sulfonated poly(arylene sulfone) and which is chemically compatible with polymer (a). The polymers are optionally present in the same solvent or solvent mixture without any precipitation for 1 hour.    USE - Polymer blend is used for manufacturing polymer membrane used in electrochemical conversion/storage device e.g. fuel cell and battery/capacitor, dialysis, electrolysis, ion exchange, and reverse osmosis applications (all claimed).    ADVANTAGE - The polymer blend has high ion-exchange capacity, stability and ion-conductivity even at low relative humidity, and can be economically manufactured.    DETAILED DESCRIPTION - A polymer blend has ion conductivity of 10-3 second/cm or more at room temperature in water and comprises a polymer (a) which is a sulfonated poly(arylene sulfone) comprising repeating units of formula: -(-SO2-Ar'(SO3M)o-)n, and a polymer (b) which is not a sulfonated poly(arylene sulfone) and which is chemically compatible with polymer (a). The polymers are optionally present in the same solvent or solvent mixture without any precipitation for 1 hour.    n=10-10000;    Ar'=aryl or heteroaryl with 5-18 ring atoms;    M=cation, preferably proton;and    o=0-4.    INDEPENDENT CLAIMS are included for the following:    (1) basic polymer comprising 20 repeating units chosen from formulae (VII)-(XI);    (2) preparation of polymer blends, which involves combining polymer (a) and polymer (b) in aprotic solvent or solvent mixture directly without any neutralization of components, mixing until a solution is obtained, and removing the solvent by evaporation;    (3) homogeneous solution of acidic polymer and basic polymer; and    (4) preparation of polymer membrane, which involves combining polymer (a) and polymer (b), mixing until a homogeneous solution is obtained, and directly casting the polymer membrane from the homogeneous solution.