Studies on the kinetics of ceric–thiourea-initiated aqueous polymerization of methyl methacrylate. I. Mechanistic features in moderately acid solution

The kinetics of the aqueous polymerization of methyl methacrylate by a ceric-thiourea initiator system in moderately acid solution (pH 2.15) was studied. The rate of polymerization was proportional to 0.41 power of ceric concentration, 0.32 power of thiourea concentration, and 1.18 power of monomer concentration. The degree of polymerization was smaller than expected from the rate of polymerization. Initiation efficiency was less than one. There was no evidence of any ceric ion termination in the concentration range of 2.50 × 10^?4–2.00 × 10^?3M studied. The results are explained in terms of partial primary radical termination; the principal mode of termination, however, was bimolecular.