Composition including addition condensation product of aromatic compound and carbonyl compound and thiol compound, method for producing composition, scale adhesion prevention agent, reaction apparatus, polymer, and method for producing polymer

A reaction apparatus for polymerization of monomers, comprising a reactor configured to be able to store solution including the monomers, wherein

• the reactor includes a covering layer arranged on at least part of an inner wall surface that is a surface on a side contacting the solution,
• the covering layer includes an addition condensation product of an aromatic compound and a carbonyl compound,
• the addition condensation product includes:
• a first type of addition condensation product having a first average molecular weight;
• and
• a second type of addition condensation product having a second average molecular weight;
• the second average molecular weight is greater than the first average molecular weight, and
• a ratio of a mass of the second type of addition condensation product to a mass of the first type of addition condensation product is 0.75 to 1000.