VINYL POLYMERIZATION INITIATED BY CERIC ION METHYL 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 ceric nitrate-methyl cellosolve (MC). A short induction period was observed, as well as the attainment of a limitin g conversion for polymerization reactions. The consumption of ceric io n was first order with respect to Ce(IV) concentration in the concentr ation range (0.5-3.0) x 10(-3) M Ce(IV), and the point at higher conce ntration deviated from the graph. Plots of the inverse of the pseudo-f irst order rate constant for ceric ion consumption, [k']-1, versus [MC ]-1 gave straight lines with non-zero intercepts for both monomer syst ems, suggesting complex formation between Ce(IV) and MC. Complex forma tion 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 (0.218 7 M) a steep fall in R(p) was observed for AN polymerization. The orde rs 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 r eaction medium did not significantly change the rate of polymerization with [Ce(IV)], but a fall in R(Ce) was observed. A kinetic scheme inv olving oxidation of MC by Ce(IV) via complex formation, whose decompos ition gives rise to a primary radical, initiation, propagation, and te rmination of the polymeric radicals by bimolecular interaction, is pro posed. An oxidative termination of primary radicals by Ce(IV) is also included.