Seeded Heterogeneous Polymerization of Acrylonitrile

Results are reported of an extensive study at 50 °C of the kinetics of seeded heterogeneous polymerization of acrylonitrile (a monomer which is water soluble but insoluble in its polymer). K₂S₂0₈ or γ-irradiation initiation were used, runs using the latter also yielding relaxation kinetics after removal from the radiation source; since free radical loss processes are likely to be similar in all three types of system, these studies permit more inferences to be made than are possible with, e.g., chemical initiation alone. It is thus shown that (i) data can be interpreted by a general kinetic scheme developed for compartmentalized polymerization, (ii) the locus of polymerization is the particle surface, (iii) the average number of free radicals per particle is high (≃250), (iv) radical capture efficiency by the particles is 100%, and (v) for the free radical fluxes used here, all loss of free radical activity is pseudo first order, consistent with the rate-determining step occurring in association with the particle and being the inhibition of propagation due to environmental constraints (e.g., when the propagating free radical grows in such a way as to become completely surrounded with glassy polymer).