• isobutyronitrile;
  • partition;
  • styrene;
  • miniemulsion polymerization;
  • 2,2′-azobis(isobutyronitrile)


Isobutyronitrile has been selected as a stable substitute for the 2-cyano-2-propyl radical originating from 2,2′-azobis(isobutyronitrile) to study the behavior of this radical in miniemulsion polymerization. The partition of isobutyronitrile between styrene monomers/polymers and water has been investigated by carrying out equilibrium experiments under different conditions. Prediction based on a published kinetic model using the newly measured partition coefficient has also been compared with published experimental data and prediction based on the partition coefficient of 2,2′-azobis(isobutyronitrile). The partition coefficients for isobutyronitrile were found to be 10.98 for the styrene/water system and 4.34 for the polystyrene/water system, respectively. The partition coefficient was found to be unaffected by selected conditions. The model prediction based on the partition coefficient of isobutyronitrile agreed well with the published experimental data, thus, indicating that the partition coefficient of the primary radical should be used in theoretical calculations rather than that of the initiator. © 2011 American Institute of Chemical Engineers AIChE J, 58: 3135–3143, 2012