A polymer scale preventive agent for use in the polymerization of a monomer containing
an ethylenic double bond is provided. The agent includes (A) a condensation reaction
product obtained by reacting an aldehyde compound and a hydroxynaphthalene-based
compound in the presence of a reducing agent, and (B) a polymer compound containing
a nitrogen atom. This agent is capable of forming a coating with satisfactory scale
prevention properties on inner wall surfaces of a polymerization vessel with a
single-stage application, enabling the production process time to be shortened
and the productivity and quality of polymeric products improved.
