A method for preventing the polymerization of vinylidene chloride (1,1-dichloroethylene) during the manufacture thereof by the caustic dehyrochlorination at elevated temperatures of crude 1,1,2-trichloroethane which comprises admixing and maintaining in intimate association with the reaction mixture and its reaction products from about 50 to about 1500 ppm by weight of an amine having a boiling point between about 50. degree. C and 160. degree. C.