This invention relates to the reduction of polymer buildup on the inner surfaces of a polymerization reactor by applying a polymer buildup resistant coating to the inner surfaces thereof, the method or process of applying said coating being the subject of this invention. An approximate monolayer coating on the inner surfaces of the reactor results from applying thereto an aqueous or organic solvent solution of the coating material by means of vinyl chloride in vapor form. The coating material is an organic compound or polymer which is capable of resisting polymer buildup thereon. As examples of such coating materials, there may be named the polyaromatic amines, self-condensed polyhydric phenols, tannic acid and tannates, various dyes, such as nigrosine, and the like, etc. When using vinyl chloride to apply the coating material, the same reaches the inner reactor surfaces in the form of a mist. When polymerizing olefinic monomers, such as vinyl halides, vinylidene halides, and vinylidene monomers having at least one terminal CH.sub.2 .dbd.C