Catalytic chain transfer polymerization for molecular weight control in microemulsion polymerization

Catalytic chain transfer using low-spin cobalt(II) complexes is applied in the microemulsion polymerization of methyl and n-butyl methacrylate. In the presence of a catalytic chain transfer agent the rate of polymerization decreases with an increasing cobalt(II) catalyst loading. The course of the polymerization can be captured by the Morgan-Kaler model extended with radical desorption and aqueous phase termination. Proper molecular weight control (i.e. a molecular weight distribution with a dispersity of ∼2) is achieved, however, proves to be strongly dependent on the balance of cobalt(II) molecules and propagating radicals. The presence of a cobalt(II) catalyst enhances the likelihood of homogeneous nucleation, which decreases the colloidal stability in the methyl methacrylate microemulsion polymerizations. The n-butyl methacrylate microemulsion polymerizations on the other hand, display good colloidal stability and a remarkable increase in the nucleation efficiency.