Method for producing fluorine-containing polymer, aqueous dispersion liquid of fluorine-containing polymer, and polymer composition

A method for producing a fluorinated polymer, which comprises polymerizing at least one specific compound selected from a compound represented by the formula (1) and a compound represented by the formula (2) in an aqueous medium to obtain an aqueous medium in which a specific polymer is present, and then in the aqueous medium in which the specific polymer is present, polymerizing at least one fluorinated monomer selected from tetrafluoroethylene, chlorotrifluoroethylene and vinylidene fluoride to produce a fluorinated polymer (provided that when tetrafluoroethylene is polymerized, tetrafluoroethylene is copolymerized so that the content of units based on tetrafluoroethylene in the fluorinated polymer is less than 99 mass % to all units in the fluorinated polymer):

• CXY═CR1—COO-(L-O)n—R2 formula (1):
• CXY═CR3—(O)m—CH2—Z—R4 formula (2):
• the symbols in the formula (1) and the formula (2) are as follows:
• X and Y are each independently a hydrogen atom, a halogen atom or a methyl group;
• R1 is a hydrogen atom, a halogen atom or a C1-3 alkyl group;
• R2 is an alkyl group, an alkyl group having at least one —CH2— in the alkyl group replaced with —CO—, or a group of the following formula (3);
• R3 is a hydrogen atom, a halogen atom, a C1-3 alkyl group or —CO—OCH3;
• R4 is an alkyl group;
• L is an alkylene group;
• Z is —CO—O—* or —O—CO—*, provided that * represents the binding position to R4;
• m is 0 or 1, and n is an integer of at least 1;
• —CO—CR1═CXY formula (3):
• in the formula (3), X, Y and R1 are respectively as defined for X, Y and R1 in the formula (1).

A fluorinated polymer aqueous dispersion, which comprises an aqueous medium, particles of a fluorinated polymer having units based on at least one fluorinated monomer selected from tetrafluoroethylene, chlorotrifluoroethylene and vinylidene fluoride (provided that when tetrafluoroethylene is polymerized, tetrafluoroethylene is copolymerized so that the content of units based on tetrafluoroethylene in the fluorinated polymer is less than 99 mass % to all units in the fluorinated polymer) and having a volume based cumulative 50% particle size of from 20 to 3000 nm, and a specific polymer having at least one type of units selected from units based on a compound represented by the formula (1) and units based on a compound represented by the formula (2), contained as particles in the aqueous medium or contained in particles containing the fluorinated polymer, and contains substantially no emulsifier:

• CXY═CR1—COO-(L-O)n—R2 formula (1):
• CXY═CR3—(O)m—CH2—Z—R4 formula (2):
• the symbols in the formula (1) and the formula (2) are as follows:
• X and Y are each independently a hydrogen atom, a halogen atom or a methyl group;
• R1 is a hydrogen atom, a halogen atom or a C1-3 alkyl group;
• R2 is an alkyl group, an alkyl group having at least one —CH2— in the alkyl group replaced with —CO—, or a group of the following formula (3);
• R3 is a hydrogen atom, a halogen atom, a C1-3 alkyl group or —CO—OCH3;
• R4 is an alkyl group;
• L is an alkylene group;
• Z is —CO—O—* or —O—CO—*, provided that * represents the binding position to R4;
• m is 0 or 1, and n is an integer of at least 1;
• —CO—CR1═CXY formula (3):
• in the formula (3), X, Y and R1 are respectively as defined for X, Y and R1 in the formula (1).

A polymer composition comprising a fluorinated polymer having units based on at least one fluorinated monomer selected from tetrafluoroethylene, chlorotrifluoroethylene and vinylidene fluoride (provided that when tetrafluoroethylene is polymerized, the content of units based on tetrafluoroethylene in the fluorinated polymer is less than 99 mass % to all units in the fluorinated polymer), and a specific polymer having at least one type of units selected from units based on a compound represented by the formula (1) and units based on a compound represented by the formula (2), and contains substantially no emulsifier:

• CXY═CR1—COO-(L-O)n—R2 formula (1):
• CXY═CR3—(O)m—CH2—Z—R4 formula (2):
• the symbols in the formula (1) and the formula (2) are as follows:
• X and Y are each independently a hydrogen atom, a halogen atom or a methyl group;
• R1 is a hydrogen atom, a halogen atom or a C1-3 alkyl group;
• R2 is an alkyl group, an alkyl group having at least one —CH2— in the alkyl group replaced with —CO—, or a group of the following formula (3);
• R3 is a hydrogen atom, a halogen atom, a C1-3 alkyl group or —CO—OCH3;
• R4 is an alkyl group;
• L is an alkylene group;
• Z is —CO—O—* or —O—CO—*, provided that * represents the binding position to R4;
• m is 0 or 1, and n is an integer of at least 1;
• —CO—CR1═CXY formula (3):
• in the formula (3), X, Y and R1 are respectively as defined for X, Y and R1 in the formula (1).