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

Sequence-controlled methacrylic multiblock copolymers via sulfur-free RAFT emulsion polymerization

Translating the precise monomer sequence control achieved in nature over macromolecular structure (for example, DNA) to whole synthetic systems has been limited due to the lack of efficient synthetic methodologies. So far, chemists have only been able to synthesize monomer sequence-controlled macromolecules by means of complex, time-consuming and iterative chemical strategies such as solid-state Merrifield-type approaches or molecularly dissolved solution-phase systems. Here, we report a rapid and quantitative synthesis of sequence-controlled multiblock polymers in discrete stable nanoscale compartments via an emulsion polymerization approach in which a vinyl-terminated macromolecule is used as an efficient chain-transfer agent. This approach is environmentally friendly, fully translatable to industry and thus represents a significant advance in the development of complex macromolecule synthesis, where a high level of molecular precision or monomer sequence control confers potential for molecular targeting, recognition and biocatalysis, as well as molecular information storage