VINYL POLYMERIZATION INITIATED BY CERIC ION-ETHYL CELLOSOLVE REDOX SYSTEM IN AQUEOUS NITRIC-ACID

Polymerizations of methyl methacrylate (MMA) and acrylonitrile (AN) we re carried out in aqueous nitric acid at 30 degrees C with the redox i nitiator system ammonium eerie nitrate-ethyl cellosolve (EC). A short induction period was observed as well as the attainment of a limiting conversion for polymerization reactions. The consumption of eerie ion was first order with respect to Ce(IV) concentration in the concentrat ion range (0.2-0.4) x 10(-2) M, and the points at higher and lower con centrations show deviations from a linear fit. The plots of the invers e of pseudo-first-order rate constant for eerie ion consumption, (k(1) )(-1) vs [EC](-1), gave straight lines for both the monomer systems wi th nonzero intercepts supporting complex formation between Ce(IV) and EC. The rate of polymerization increases regularly with [Ce(IV)] up to 0.003 M, yielding an order of 0.41, then falls to 0.0055 M and again shows a rise at 0.00645 M for MMA polymerization. For AN polymerizatio n, R(p) shows a steep rise with [Ce(IV)] up to 0.001 M, and beyond thi s concentration R(p) shows a regular increase with [Ce(IV)], yielding an order of 0.48. In the presence of constant [NO3-], MMA and AN polym erizations yield orders of 0.36 and 0.58 for [Ce(IV)] variation, respe ctively. The rates of polymerization increased with an increase in EC and monomer concentrations: only at a higher concentration of EC (0.5 M) was a steep fall in R(p) observed for both monomer systems. The ord ers with respect to EC and monomer for MMA polymerization were 0.19 an d 1.6, respectively. The orders with respect to EC and monomer for AN polymerization were 0.2 and 1.5, respectively. A kinetic scheme involv ing oxidation of EC by Ce(IV) via complex formation, whose decompositi on gives rise to a primary radical, initiation, propagation, and termi nation of the polymeric radicals by biomolecular interaction is propos ed. An oxidative termination of primary radicals by Ce(IV) is also inc luded.