Effect of stable radicals on the mechanism of microemulsion radical copolymerization of butyl acrylate and acrylonitrile

The oil-in-water microemulsion copolymerization of butyl acrylate and acryl onitrile initiated by water (ammonium peroxodisulfate - APS) and oil (diben zoyl peroxide, DBP)- soluble radical initiators in the presence of a radica l scavenger [an oil soluble 3-stearoyloxy-2,2,6,6-tetramethyl piperidine-1- oxyl (STPO) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) and a water soluble po tassium nitrosodisulfonate (FS) were investigated. The addition of a small amount of a radical scavenger (RS) led to the appearance of an inhibition p eriod and the decrease of both the rate of polymerization and particle size . The inhibition period (IP) and the maximum rate of polymerization (R-pmax ) increased in the following order; IP FS < DPPH < STPO and R-pmax. DPPH < STPO much less than FS, respectively, The increase in the molecular weight was ascribed to the decrease in both the rare of initiation and the radical flux into particles. The short- stopping of particle growth favors the nuc leation of a larger number of monomer-swollen micelles. The selective react ion of growing chains with the stable radicals in certain distinct phases l eads to the formation of polymers with narrower molecular weight distributi on. (C) 1999 Elsevier Science Ltd. All rights reserved.