An object is to provide a fluorine-containing polymer film. The object can be achieved by a fluorine-containing polymer film having a thermal shrinkage of 0.4% or less after being heated at 90° C. for 1 hour, and having a relative permittivity of 3 to 50 at 25° C. at 1000 Hz, or a fluorine-containing polymer film having a crystallinity of 50% or more and an elongation at break of 400% or more.

An object is to provide a fluorine-containing polymer film. The object can be achieved by a fluorine-containing polymer film having a thermal shrinkage of 0.4% or less after being heated at 90° C. for 1 hour, and having a relative permittivity of 3 to 50 at 25° C. at 1000 Hz, or a fluorine-containing polymer film having a crystallinity of 50% or more and an elongation at break of 400% or more.

A fluororesin having a tensile strength retention ratio of 50% or more, the tensile strength retention ratio being calculated by the following formula from the tensile strength of the fluororesin after a heat treatment obtained by conducting a heat treatment at 130° C. for 40,000 hours, and the tensile strength of the fluororesin before the heat treatment. Tensile strength retention ratio (%)=(tensile strength of fluororesin after heat treatment (MPa))/(tensile strength of fluororesin before heat treatment (MPa))×100.

A fluororesin having a tensile strength retention ratio of 50% or more, the tensile strength retention ratio being calculated by the following formula from the tensile strength of the fluororesin after a heat treatment obtained by conducting a heat treatment at 130° C. for 40,000 hours, and the tensile strength of the fluororesin before the heat treatment. Tensile strength retention ratio (%)=(tensile strength of fluororesin after heat treatment (MPa))/(tensile strength of fluororesin before heat treatment (MPa))×100.

Provided is a binder for a battery, including a fluorine-containing copolymer, wherein the fluorine-containing copolymer comprises a repeating unit (a) based on vinylidene fluoride and at least one repeating unit (b) selected from the group consisting of a repeating unit (bl) represented by a specific structural formula (bl) and a repeating unit (b2) represented by a structural formula (b2), and the fluorine-containing copolymer has a molar ratio of the repeating unit (a) to the repeating unit (b), (a)/(b), of 95/5 to 5/95.

Provided is a binder for a battery, including a fluorine-containing copolymer, wherein the fluorine-containing copolymer comprises a repeating unit (a) based on vinylidene fluoride and at least one repeating unit (b) selected from the group consisting of a repeating unit (bl) represented by a specific structural formula (bl) and a repeating unit (b2) represented by a structural formula (b2), and the fluorine-containing copolymer has a molar ratio of the repeating unit (a) to the repeating unit (b), (a)/(b), of 95/5 to 5/95.

The invention relates to a composition comprising at least one electroactive fluorinated terpolymer, and at least one second polymer compatible with the electroactive fluorinated terpolymer and having a glass transition temperature lower than that of the electroactive fluorinated terpolymer. The invention also relates to a method for producing said composition, and to a device such as an actuator comprising a substrate and a film of the above-mentioned composition.

The invention relates to a composition comprising at least one electroactive fluorinated terpolymer, and at least one second polymer compatible with the electroactive fluorinated terpolymer and having a glass transition temperature lower than that of the electroactive fluorinated terpolymer. The invention also relates to a method for producing said composition, and to a device such as an actuator comprising a substrate and a film of the above-mentioned composition.

The present invention aims to provide a method of producing a fluoropolymer, especially a fluoropolymer essentially including a tetrafluoroethylene or chlorotrifluoroethylene unit, at a higher polymerization rate with improved efficiency, the method being capable of improving the moldability in extrusion molding and suppressing discoloration. The method of producing a fluoropolymer of the present invention includes producing a fluoropolymer by polymerizing tetrafluoroethylene or chlorotrifluoroethylene in the presence of a peroxydicarbonate. The peroxydicarbonate is represented by the formula:
R—O—C(═O)—O—O—C(═O)—O—R
wherein R's may be the same as or different from each other and individually represent a C4 alkyl group or alkoxy alkyl group.

The present invention aims to provide a method of producing a fluoropolymer, especially a fluoropolymer essentially including a tetrafluoroethylene or chlorotrifluoroethylene unit, at a higher polymerization rate with improved efficiency, the method being capable of improving the moldability in extrusion molding and suppressing discoloration. The method of producing a fluoropolymer of the present invention includes producing a fluoropolymer by polymerizing tetrafluoroethylene or chlorotrifluoroethylene in the presence of a peroxydicarbonate. The peroxydicarbonate is represented by the formula:
R—O—C(═O)—O—O—C(═O)—O—R
wherein R's may be the same as or different from each other and individually represent a C4 alkyl group or alkoxy alkyl group.