Vinyl polymerization initiated by ceric ion-methyl cellosolve redox system in aqueous nitric acid

Polymerizations of methyl methacrylate (MMA) and acrylonitrile (AN) were carried out in aqueous nitric acid at 30°C with the redox initiator system ammonium ceric nitrate–methyl cellosolve (MC). A short induction period was observed, as well as the attainment of a limiting conversion for polymerization reactions. The consumption of ceric ion was first order with respect to Ce(IV) concentration in the concentration range (0.5–3.0) × 10−3 M Ce(IV), and the point at higher concentration deviated from the graph. Plots of the inverse of the pseudo‐first order rate constant for ceric ion consumption, [k′]−1, versus [MC]−1 gave straight lines with non‐zero intercepts for both monomer systems, suggesting complex formation between Ce(IV) and MC. Complex formation between Ce(IV) and reducing agent was also detected by a shift in the absorption maximum of Ce(IV), using a Beckman spectrophotometer. The rates of polymerizations increased with increase in Ce(IV), MC and monomer concentrations; however, at higher concentration of AN (0.2187 M) a steep fall in Rp was observed for AN polymerization. The orders with respect to Ce(IV), MC and monomer for MMA polymerization were found to be 0.22, 0.35 and 1.73 respectively. The orders with respect to Ce(IV), MC and monomer for AN polymerization were found to be 0.56, 0.30 and 1.30 respectively. Maintaining constant nitrate ion in the reaction medium did not significantly change the rate of polymerization with [Ce(IV)], but a fall in RCe was observed. A kinetic scheme involving oxidation of MC by Ce(IV) via complex formation, whose decomposition gives rise to a primary radical, initiation, propagation, and termination of the polymeric radicals by bimolecular interaction, is proposed. An oxidative termination of primary radicals by Ce(IV) is also included.