Emulsion polymerization of lower alkyl acrylates

Abstract

IT IS well-known from papers [1-3] tha t the acrylate latexes have particularly valuable properties as bases for coatings. However, they possess insufficient colloidal stability which hinders their application in this field. As compared with rubber, acrylate latexes are more sensitive to low temperatures and mechanical effects. With polymerization to an extent considered to be conventional for rubber latexes, simultaneous feed of monomers in the react ion mixture, in the case of acrylic monomers, often produces coagulated masses owing to the lack of stability of the system [4]. Most of the investigations of emulsion polymerization were carried out with monomers sparingly soluble in water, styrene, isoprene, chloroprene, with simultaneous feeding of the monomers, i.e. in the presence of a monomer emulsion during the synthesis of latex [5-6]. In these studies the solubility in water of the methyl methacrylate used was 1 .5~ at 30 °, whereas the solubility of methacrylate from which film-forming latexes are often made, was 5.2~/~ at 2o°c [17].* The colloidal stability of latexes is often determined by the degree of saturation of polymer particles by the adsorption layer of the emulsifying agent [1922] a n d increases with increase of concentration during synthesis. As has been established by one of the authors, the increase of the proportion of ionogen emulsifying agent (Nekal) during polymerization of methyl acrylate or copolymerization of methyl methacrylate with divinyl exceeds 1 .5-2~ of the monomer and increases coagulation during the synthesis [4, 23]. We assumed tha t this anomaly is due to the ready solubility of lower alkyl acrylates in water and to polarity of the polymer chains formed. In view of this, the process may proceed differently, according to the monomer content in the system, i.e. whether in the sYnthesis there is a monomer emulsion and its saturated moleeuls~ solution, or the monomer emulsion is absent and its concentration in the solution remains below saturation.