Viscosity effects in the free-radical polymerization of methyl methacrylate

Methyl methacrylate has been polymerized in the presence of poly(methyl methacrylate) by using a free-radical initiator. The efficiency of the initiator is shown to be independent of the viscosity. At high viscosities, chain termination was influenced by the rate of translational diffusion of the polymer radicals. The dependence of the polymerization rate on viscosity is less than that predicted by a simple kinetic scheme. It appears that only those radicals which are above a certain size have their chain termination reactions controlled by the solution viscosity. This limiting size decreases as the viscosity increases.