Method for producing fluorine-containing polymer and composition

A method for producing a fluorine-containing polymer containing a repeating unit represented by the following formula (1) and a repeating unit represented by the following formula (2), the method comprising:

• a step for synthesizing a fluorine-containing monomer, the step comprising:
• reacting a diol represented by the following formula (3) with at least one selected from the group consisting of unsaturated carboxylic acids, esters of the unsaturated carboxylic acids, acid halides of the unsaturated carboxylic acids, and anhydrides of the unsaturated carboxylic acids, to obtain a composition containing a fluorine-containing monomer represented by the following formula (4) as a main reaction product and a fluorine-containing monomer represented by the following formula (5) as a minor reaction product;
• a step for purifying the obtained composition containing the fluorine-containing monomer, the step comprising:
• removing the fluorine-containing monomer of formula (5) from the composition to adjust an amount of the fluorine-containing monomer of formula (5), expressed in parts per million based on a mass of the fluorine- containing monomer of formula (4), to 500 ppm or less;
• and
• a polymerization step, the step comprising:
• performing a polymerization reaction of the composition obtained after the fluorine-containing monomer purification to give a fluorine-containing polymer containing a repeating unit of formula (1) and a repeating unit of formula (2),
• wherein R1 and R2 are each independently a hydrogen atom, a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, an iso-butyl group, a sec-butyl group, or a t-butyl group;
• R3 and R4 are each independently a hydrogen atom, a methyl group, or an ethyl group;
• R5 is a hydrogen atom or a trifluoromethyl group;
• and R6 is a hydrogen atom, a chlorine atom, a methyl group, or a trifluoromethyl group.