Controlled-Growth Free-Radical Polymerization of Methacrylate Esters: Reversible Chain Transfer versus Reversible Termination

Several processes for controlled growth free radical polymerization are contrasted with respect to reaction mechanism and their particular advantages and limitations. Kinetic simulation is used to examine relationships between reaction conditions, the significance of various side reactions, and the evolution of molecular the weight distribution. Expressions used to calculate molecular weights and polydispersities for the various mechanisms are reported Alkoxyamine-initiated polymerizations of methacrylate esters give only low conversions (10-40%, dependent on particular nitroxide and reaction conditions). Polymerization ceases due to a build up in the nitroxide concentration and the initially formed alkoxyamine is ultimately converted to an unsaturated macromonomer. The conversion, molecular weight and polydispersity are determined by the rate and equilibrium constants and combination:disproportionation ratio associated with the nitroxide - propagating radical reaction. Polymerization of methacrylate monomers in the presence of methacrylate macromonomers provides a viable method for controlled growth polymerization to high conversions. However, narrow polydispersities are difficult to achieve by solution polymerization due to a slow rate of exchange between dormant and active propagating species.