A kinetic model of persulfate–bisulfite-initiated acrylonitrile polymerization

The molecular weight distribution has been derived for a homopolymer polymerized in a continuous-feed reactor under homogeneous conditions. The derived equations are then compared with data obtained on polymers of acrylonitrile–co(vinyl acetate) prepared under heterogeneous conditions with the potassium peroxydisulfate–sodium bisulfite–iron redox system. The termination reaction is assumed to be effected completely by recombination of active radicals with no disproportionation. The only transfer reaction considered is the transfer-to-activator reaction The transfer and termination reactions produce polymers with different acid groups as endgroups. Each molecule, on the average, contains one sulfonate group, whereas the concentration of sulfate groups depends upon the extent of the transfer-to-activator reaction. The basic dye acceptance of the polymer depends on the number of acid groups in the polymer and hence on the activator and catalyst concentrations. Analysis of the basic dye acceptance and conversion data at a variety of catalyst and activator concentrations yields the following parameters at 50°C: kp/k = 1.01 (1./mole sec)1/2, ktr/kp = 0.2063, and k1 [see eq. (1)] = 50.7 l./mole sec. Owing to the heterogeneous nature of the polymerization, the weight-average molecular weight of the polymer depends only on the activator concentration and the conversion and not directly on the catalyst concentration as predicted.