The fluorine-containing copolymer of the present invention includes: a structural unit (A) represented by the following formula (1); and at least one selected from the group consisting of a structural unit (B) represented by the following formula (2), a structural unit (C) represented by the following formula (3), and a structural unit (D) represented by the following formula (4): ##STR00001## in the formula (1), R.sub.ff.sup.1 to R.sub.ff.sup.4 each independently represent a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms, and R.sub.ff.sup.1 and R.sub.ff.sup.2 are optionally linked to form a ring; ##STR00002## in the formula (2), R.sup.1 to R.sup.3 each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 7 carbon atoms, R.sup.4 represents a perfluoroalkyl group having 1 to 7 carbon atoms, the perfluoroalkyl group optionally has a ring structure, one or some of the fluorine atoms are optionally substituted by a halogen atom other than a fluorine atom, and one or some of fluorine atoms in the perfluoroalkyl group are optionally substituted by a halogen atom other than a fluorine atom; ##STR00003## in the formula (3), R.sup.5 to R.sup.8 each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 7 carbon atoms, the perfluoroalkyl group optionally has a ring structure, one or some of the fluorine atoms are optionally substituted by a halogen atom other than a fluorine atom, and one or some of fluorine atoms in the perfluoroalkyl group are optionally substituted by a halogen atom other than a fluorine atom; and ##STR00004## in the formula (4), Z represents an oxygen atom, a single bond, or OC(R.sup.19R.sup.20)O, R.sup.9 to R.sup.20 each independently represent a fluorine atom, a perfluoroalkyl group having 1 to 5 carbon atoms, or a perfluoroalkoxy group having 1 to 5 carbon atoms, one or some of the fluorine atoms are optionally substituted by a halogen atom other than a fluorine atom, one or some of fluorine atoms in the perfluoroalkyl group are optionally substituted by a halogen atom other than a fluorine atom, one or some of fluorine atoms in the perfluoroalkoxy group are optionally substituted by a halogen atom other than a fluorine atom, s and t are each independently 0 to 5, and s+t represents an integer of 1 to 6 (when Z is OC(R.sup.19R.sup.20)O, s+t is optionally 0).

The present invention is a copolymer having a structure represented by a general formula (1) [in the formula, R.sup.1 is a fluorine atom, or a perfluoroalkyl group or perfluoroalkoxy group having 1 to 10 carbon atoms which may have O between carbon atoms; R.sup.2 and R.sup.3 each independently represent a hydrogen atom, a halogen atom, an aliphatic hydrocarbon group having 1 to 30 carbon atoms which may have a substituent, or an aryl group which may have a substituent; the R.sup.2 and R.sup.3 may be linked with each other to form a ring; the aliphatic hydrocarbon group may contain one or more selected from the group consisting of O, Si(CH.sub.3).sub.2, CO, and NH between carbon atoms; x and y are positive numbers satisfying a relationship of x+y=1; and a filled circle represents a bond].

##STR00001##

A method for producing a fluorinated polymer which does not require an emulsifier as an essential component while an aqueous medium with little environmental burden is used. A method for producing a fluorinated polymer, which includes polymerizing a fluorinated monomer selected from tetrafluoroethylene, chlorotrifluoroethylene and vinylidene fluoride, in an aqueous medium in the presence of a first polymer having units based on a compound represented by formula (1): CXYCR.sup.1-L-R.sup.2.

A method for producing a fluorinated polymer which does not require an emulsifier as an essential component while an aqueous medium with little environmental burden is used. A method for producing a fluorinated polymer, which includes polymerizing a fluorinated monomer selected from tetrafluoroethylene, chlorotrifluoroethylene and vinylidene fluoride, in an aqueous medium in the presence of a first polymer having units based on a compound represented by formula (1): CXYCR.sup.1-L-R.sup.2.

A method for producing a fluoropolymer which includes polymerizing a fluoromonomer in an aqueous medium in the presence of a fluorine-containing diacyl peroxide represented by the formula (1): XRf.sup.aC(O)OOC(O)Rf.sup.bY (wherein X and Y are each independently H or F; and Rf.sup.a and Rf.sup.b are each independently a C1-C6 linear or branched perfluoroalkylene group optionally containing an ether bond) and a fluorine-containing carboxylic acid represented by the following formula (2): Z.sup.2Rf.sup.cCOOH (wherein Z.sup.2 is H or F; and Rf.sup.c is a C1-C3 linear or branched perfluoroalkylene group optionally containing an ether bond when Z.sup.2 is H, and Rf.sup.c is a C1 or C2 linear or branched perfluoroalkylene group optionally containing an ether bond when Z.sup.2 is F) to provide a fluoropolymer.