<p>Anionic polymerizations of vinyl monomers are powerful synthetic platforms for making well-defined materials. However, these reactions are extremely sensitive to moisture and oxygen, require the use of highly purified reagents, must be run at low temperatures, and use hazardous and difficult-to-handle alkyl lithium initiators. Together, these drawbacks limit the practicality of these polymerizations and impede their widespread usage. On this basis, the development of a user-friendly anionic polymerization process for methacrylates is a grand challenge. Here we report an anionic polymerization of methacrylates mediated by CO₂ that can be run at elevated temperatures and uses an easy-to-handle solid initiator. The reversible addition of CO₂ to the enolate chain end efficiently tempers the reactivity of the anion, giving polymers with narrow molar mass distributions and excellent molecular weight targeting at elevated temperatures. Our scalable and more user-friendly CO₂-mediated method improves the accessibility and safety of anionic polymerizations and facilitates the production of a variety of polymeric materials.</p><p></p>