The redox aqueous polymerization of acrylonitrile under pressure

Effect of pressure (atmospheric to 20 X 10⁶ Pa) on the K₂S₂O₈–Na₂S₂O₄ initiated aqueous polymerization of acrylonitrile has been studied at 25°C. The conversion and rate of the polymerization tend to rise initially with increase of pressure and fall subsequently to a limiting value. The initial rise in the rate is consistent with an increase of k_p or a decrease in k_t due to high pressure. The ultimate tendency of the rate to fall is possibly due to a decrease in the diffusion rate of the monomer from the aqueous phase to the growing polymer radical site. The molecular weight shows a more or less similar trend except that the fall in the molecular weight begins at a lower pressure range than the same in the rate or conversion. This is explained on the basis of enhanced monomer transfer reaction. These observed kinetic characteristics are not sensitive to the appearance of heterogeneity in the system due to insoluble polymer phase in as much as homogeneous reaction systems in DMF or DMSO essentially exhibit the same features. The rate is proportional to the square root of the product of K₂S₂O₈] and Na₂S₂O₄] and varies linearly as the first power of the monomer concentration.