AQUEOUS POLYMERIZATION OF METHYL-METHACRYLATE INITIATED BY CERIC ION REDUCING AGENT SYSTEMS IN SULFURIC-ACID MEDIUM

Polymerization of methyl methacrylate (MMA) was carried out in aqueous sulfuric acid medium at 30 degrees C using ammonium eerie sulfate (AC S)/methyl ethyl ketone (MEK) and ammonium eerie sulfate/acetone as red ox initiator systems. A short induction period was observed with both the initiator systems, as well as the attainment of limiting conversio n for polymerization reactions. The rate of eerie ion consumption, R(C e), was first order with respect to Ce(IV) concentration in the concen tration range (0.5-5.5) X 10(-3)M, and 0.5 order with respect to reduc ing agent concentration in the concentration ranges (0.0480-0.2967M) a nd (0.05-0.3912M) for Ce(IV)-MEK and Ce(IV)-acetone initiator systems, respectively. A fall in R(Ce) was observed at higher reducing agent c oncentrations. The plots of R(Ce) versus reducing agent concentrations raised to the half power yielded straight lines passing through the o rigin, indicating the absence of complex formation between reducing ag ents and Ce(IV). The addition of sodium sulfate to maintain constant s ulfate ion concentration in the reaction medium could bring down the R (Ce) values in the present reaction systems. The rate of polymerizatio n of MMA, R(p), increased with increase in Ce(IV), reducing agent, and monomer concentrations for the Ce(IV)-MEK initiator. The rate of poly merization of MMA is independent of Ce(IV) concentration and increased with an increase in reducing agent and monomer concentrations for the Ce(IV)-acetone initiator. At higher concentrations of reducing agent (0.4-0.5M), a steep fall in R(p), values was observed with both the in itiator systems. The orders with respect to Ce(IV), MEK, and MMA using the Ce(IV)-MEK initiator were found to be 0.23, 0.2, and 1.29, respec tively. The orders with respect to Ce(IV), acetone, and MMA using the Ce(IV)-acetone initiator were found to be zero, 0.42, and 1.64, respec tively. Maintaining constant [SO42-] in the reaction medium could brin g down R(p) values for the Ce(IV)-MEK initiator system. On the other h and, a rise in R(p) values with an increase in [Na2SO4] could be obser ved when constant [SO42-] was maintained in the reaction medium for th e Ce(IV)-acetone initiator system. A kinetic scheme involving direct a ttack of Ce(IV) on reducing agent, production of radicals, 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. (C) 1996 John Wiley & Sons, Inc.