Patent ID: 8236887

Claim:
A fluorine-containing polymer having an ionic group which has a number average molecular weight of from 500 to 1,000,000 and is represented by the formula (2): MI N (2) in which the structural unit MI is a structural unit derived from a fluorine-containing ethylenic monomer and represented by the formula (MI): wherein X 1 and X 2 are the same or different and each is H or F; X 3 is H, F, CH 3 or CF 3 ; X 4 and X 5 are the same or different and each is H, F or CF 3 ; Rf x is an organic group, in which —Y a (Y a is: is a moiety forming a heteroaromatic ring together with at least one nitrogen atom, and the whole or a part of its hydrogen atoms may be replaced by the same or different organic groups; Rd is H or a monovalent organic group; X is a counter anion) is directly bonded to a fluorine-containing alkyl group having 1 to 40 carbon atoms or a fluorine-containing alkyl group having 2 to 100 carbon atoms and ether bond; a is an integer of from 0 to 3; b and c are the same or different and each is 0 or 1, the structural unit N is a structural unit derived from a monomer copolymerizable with the fluorine-containing ethylenic monomer providing the structural unit MI, and the structural unit MI and the structural unit N are contained in amounts of from 0.1 to 100% by mole and from 0 to 99.9% by mole, respectively.