An improved process for the homo- and copolymerization of vinyl chloride, wherein the inner wall of a polymeriser and those parts of the apparatus which come into contact with the monomer during polymerization are coated with a special coating agent. This agent comprises an aqueous solution of a modified condensate of phenol with aldehyde and has a specified pH value such that it dissolves at a coating temperature and precipitates said condensate when heated on the inner wall of the polymerizer or the like. Since this agent forms a uniform and tough thin film on the inner wall of the polymerizer and the like, it has an excellent effect of inhibiting adhesion of a polymer.
