The polymerization of acrylonitrile in aqueous solution. Part I. The reaction catalyzed by Fenton's reagent at 25°C.

Abstract

AbstractAn apparatus is described for following dilatometrically the polymerization of acrylonitrile in aqueous solution initiated by ferrous salts and hydrogen peroxide. A steady rate (Rp) is rapidly established which ultimately decreases rapidly but does not fall to zero after the initiator is consumed. From measurements of the concentration of the ferrous ion surviving the reaction, the effect of cupric, fluoride, and ferric ions on this, on Rp, on the final phases of this reaction, and on the corresponding reaction with methyl methacrylate, it is concluded that polyacrylonitrile radicals are oxidatively terminated by cupric and ferric ions, but polymethyl methacrylate radicals are not. When this linear termination is suppressed, Rp is proportional to [m1]2 at low monomer concentrations and linearly dependent on [m1] at high concentrations. The transition from one state of affairs to the other occurs at a monomer concentration which first decreases and then increases as the initiation rate (Ri) increases. These results are believed to be general for all modes of initiation and include all previous data, reconciling conflicting information. A qualitative interpretation of these results is given in terms of the fairly rapid attainment of a constant number of polymer particles on which monomer is weakly adsorbed, a proportion of which are at any given moment inert, the remainder growing by consuming adsorbed monomer. Initiation, propagation, and mutual termination in the aqueous phase all play a significant part.