A membrane including a polyarylnitrile copolymer is presented. The polyarylnitrile copolymer includes structural units having a formula (I) and at least one terminal group having a formula (II): wherein “a” is 0, 1, 2, or 3; “m” is an integer having a value of 35 to 150; R1 is independently at each occurrence a hyrogen atom, a halogen atom, a nitro group, a cyano group, a C1-C12 aliphatic radical, a C3-C12 cycloaliphatic radical, or a C3-C12 aromatic radical; R2 and R3 are independently a C1-C12 aliphatic radical, a C3-C12 cycloaliphatic radical, or a C3-C12 aromatic radical; L is an oxygen atom or a sulfur atom; and Ar is independently at each occurrence a residue of an aromatic diol or a residue of an aromatic dihalide.