Method for producing fluoropolymer, method for producing polytetrafluoroethylene, method for producing perfluoroelastomer, and composition

A method for producing a fluoropolymer, the method comprising polymerizing a fluoromonomer in an aqueous medium in the presence of a polymer (1) to obtain a fluoropolymer, wherein

• the polymer (1) is a polymer of a monomer (1) represented by the general formula (1) below and has a number average molecular weight of 0.3×104 or more, in which a content of a dimer and a trimer of the monomer (1) is 1.0% by mass or less based on the polymer (1):
• CF2═CF—R—CZ1Z2-A0 (1)
• wherein R is a linking group;
• Z1 and Z2 are each independently F or CF3;
• and A0 is an anionic group,
• polymerizing the monomer (1) represented by the general formula (1) to obtain a crude composition containing the polymer of the monomer (1);
• and
• removing the dimer and trimer of the monomer (1) contained in the crude composition from the crude composition to obtain the polymer (1) in which the content of the dimer and trimer of the monomer (1) is 1.0% by mass or less based on the polymer (1).