Oxidation resistant membranes

A membrane (M) comprising a poly(arylene ether nitrile) polymer (P) having structural units of Formulae (I) and (II);

• (I) and (III), or (I), (II) and (III):
• wherein
• Q is a direct bond or O;
• X is a direct bond or O;
• Z is a direct bond or O;
• R1, R2, R3, R4, R5, R5′, R6 and R6′ are independently selected from H, halogen, nitro and OR, wherein R is selected from C1-C6 alkyl and C6-C12 aryl;
• and
• m, n and o are independently selected from 0 or 1.