Patent ID: 7833644

Claim:
An electrolytic membrane formed of a polymer comprising at least one recurring unit selected from the group consisting of a recurring unit of the following formula (A), and a recurring unit of the following formula (B), and having a reduced viscosity, measured in a methanesulfonic acid solution having a concentration of 0.5 g/100 ml at 25° C., of 0.05 to 200 dl/g, and having a degree (f) of orientation in the in-plane direction, calculated on the basis of the following expressions (I) and (II), of 0 to 0.3 and a degree (f) of orientation in the thickness direction, calculated on the basis of the expressions (I) and (II), of 0.5 to 1, < cos 2 ⁢ ϕ >= ∫ 0 π 2 ⁢ F ⁡ ( ϕ ) ⁢ sin ⁢ ⁢ ϕ ⁢ ⁢ cos 2 ⁢ ϕ ⁢ ⁢ ⅆ ϕ ∫ 0 π 2 ⁢ F ⁡ ( ϕ ) ⁢ sin ⁢ ⁢ ϕ ⁢ ⁢ ⅆ ϕ ( I ) f = 1 2 ⁢ ( 3 < cos 2 ⁢ ϕ > - 1 ) ( II ) wherein φ is an angle that an X-ray diffraction plane forms with an orientation axis and F is a diffraction intensity.