Provided is a polymer scale deposition-preventive agent. It includes (A)
a condensation reaction product of an aldehyde compound and a hydroxynaphthalene
compound and (B) a soluble methoxyl group-substituted cellulose ether. The agent
is formed into a film having an adequate polymer scale deposition-preventive property
in a single-step application. The time for the application process is shortened
to improve productivity. Polymer scales can be prevented from adhering to the inner
wall surfaces of the polymerization vessel even if a plenty number of batches for
polymerization are repeated.
