Aqueous latex polymerization of acrylonitrile. Kinetics, particle numbers and particle sizes

Abstract

Unseeded latex polymerization of acrylonitrile has been studied in water at 50 °C using potassium persulphate as initiator. Volume changes were monitored dilatometrically and particle size distributions were determined by transmission electron microscopy. The particle number density in each run became constant before the earliest sample could be taken for analysis. The same value [1.56 (s= 0.21)× 10¹² cm^–3] was found for four different initial concentrations of monomer and initiator. The rate of polymerization was proportional to the average particle radius. This deduction was confirmed by the observation that plots of (amount of polymer)^2/3 against time are linear. The process was first order in the concentration of monomer and of order 0.5 in concentration of initiator. The ‘exposure’, an adjusted time variable, is introduced and used. It is intended to facilitate analysis of cases in which the extent of reaction is not small enough to use the ‘initial rate’ approach and in which the integrated rate law is inconvenient.