Microemulsion polymerization of butyl acrylate. Effect of radical scavenger and formation of primary radicals

Microemulsion polymerizations of butyl acrylate initiated by dibenzoyl pero xide in the presence of a radical scavenger (RS){stable radicals : an oil s oluble RS : 4-stearoyloxy-2,2,6,6-tetramethyl piperidine-1-oxyl (STPO) and water soluble RS : 4-hydroxy-2,2,6,6-tetramethyl piperidine-1-oxyl (HTPO)}w ere investigated. STPO and HTPO decreased the rate of polymerization and th e decrease was more pronounced with STPO. Inorganic salts and organic addit ives decreased the rate of polymerization. The shift of the maximum rate of polymerization to lower conversion by increasing temperature and addition of several additives was attributed to increase of particle number and decr ease of monomer concentration at the reaction loci. The decrease of the pal -tide size in the presence of RS is attributed to retardation of particle g rowth. A close packed structure at the droplet surface promoted by current additives acts as a barrier for entering radicals. The larger overall activ ation energy in runs with STPO is discussed in terms of a depressed entry o f radicals into microdroplets.