Method of preventing scale adhesion to surfaces of polymerization tank with phenol-aldehyde coating

A method of polymerizing vinyl chloride wherein when the vinyl chloride monomer is polymerized in an aqueous medium or is subjected to mass polymerization, a coating agent is previously applied to the surfaces of parts of a polymerizing apparatus that will come into contact with said monomer so that the produced vinyl chloride polymer is prevented from adhering to said surfaces, characterized in that a coating fluid containing a reaction product having a molecular weight of 1,000 to 50,000 obtained previously by the condensation reaction of a dihydroxybiphenyl and an aldehyde in the presence of an acid catalyst is applied to said surfaces, wherein said reaction product is one represented by the following formula:

• ##STR2## wherein R represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a cycloalkyl group, an aryl group, or an aralkyl group, X represents a carboxyl group, an alkyl group, or a cycloalkyl group, m is an integer of 1 or 2, and n is an integer of from 2 to 500, said coating fluid being applied as a solution in which said reaction product is dissolved in a concentration of 0.1 to 10 wt. % in an aqueous solution of an alkali metal hydroxide and whose pH is adjusted to 8 to 3 with an inorganic acid or an organic acid.