Vinyl polymerization with Fe(III)–thiourea as initiator system. Part II. Kinetics: Predominant primary radical termination

The rate of polymerization Rp of methyl methacrylate initiated by Fe(CIO4)3 and thiourea (TU) in tert‐butyl alcohol is indepenent of [Fe(III)] and [TU] in the concentration range studied. In contrast to Rp, the degree of polymerization DP changes markedly with the change in the initiator concentration. DP is overwhelmingly lower than is expected in a standard radical polymerization at the same Rp. Further, Rp is proportional to the square of the monomer concentration. Initiation efficiency is less than one. Independent experiments proved that in the azobisisobutyronitrile‐initiated polymerization the Rp and DP are negligibly affected by [Fe(CIO4)3] or [TU], though high [TU] brings about high induction periods. The results of Fe(III)‐TU‐initiated polymerization have been interpreted in terms of the predominant termination of polymer radicals by primary radicals.