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

Abstract

The oil-in-water microemulsion copolymerization of butyl acrylate and acrylonitrile initiated by water (ammonium peroxodisulfate - APS) and oil (dibenzoyl peroxide, DBP)- soluble radical initiators in the presence of a radical scavenger [an oil soluble 4-stearoyloxy-2,2,6,6-tetramethyl piperidine-1-oxyl (STPO) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) and a water soluble potassium nitrosodisulfonate (FS) were investigated. The addition of a small amount of a radical scavenger (RS) led to the appearance of an inhibition period and the decrease of both the rate of polymerization and particle size. The inhibition period (IP) and the maximum rate of polymerization ( R p,max) increased in the following order; IP FS<DPPH<STPO and R p,max, DPPH<STPO ≪ FS, respectively. The increase in the molecular weight was ascribed to the decrease in both the rate of initiation and the radical flux into particles. The short- stopping of particle growth favors the nucleation of a larger number of monomer-swollen micelles. The selective reaction of growing chains with the stable radicals in certain distinct phases leads to the formation of polymers with narrower molecular weight distribution.