Composition containing addition condensation product, method for producing same, use of same, polymerization vessel, and method for producing polymer

A method for producing a composition that comprises an addition condensation product of an aromatic compound with a carbonyl compound and a solvent, the method comprising:

• causing an addition condensation reaction of the aromatic compound with the carbonyl compound in a reaction solvent in presence of a catalyst and a surfactant whose amount is 0.01 equivalents or greater relative to the aromatic compound (excluding the addition condensation product) to obtain the addition condensation product, wherein
• the addition condensation product is an aromatic compound multimer in which two or more composition units derived from the aromatic compound are each bonded via one composition unit derived from the carbonyl compound, the surfactant is a surfactant satisfying an HLB value in a range of 15 to 50 both inclusive as calculated in accordance with “HLB value calculation method using an organic conceptual diagram method by Fujita, Oda, et al.”, the composition comprising the addition compound includes the solvent in an amount of 95% by mass or less, and the composition is in a solution state with a viscosity of 2.0 mPa's or greater at 25° C., or in a gel-like state at 25° C.,
• wherein said aromatic compound is not a phenol other than a naphthol.