Controlled polymerization methods are crucial for the synthesis of well-defined materials, which aids in the study of polymer structure-property relationships and synthesis of advanced, functional materials. Anionic polymerization is widely considered the premier strategy for achieving polymers with narrow molar mass distributions and high chain-end fidelities. However, the high operational barriers to this method has limited its implementation by non-experts and industrial scale productions. Herein, this thesis discusses new strategies for addressing the operational barriers of anionic polymerization of methacrylates, such as the need for low temperatures and unstable, pyrophoric reagents. Chapter 1 provides an overview of previous state-of-the-art anionic polymerization methods and emerging strategies for tempering chain-end reactivity. Chapter 2 describes how we leveraged CO2-protected initiators to synthesize well-defined polymethacrylates at elevated temperatures under an atmosphere of CO2. Chapter 3 details our development of the first anionic reversible addition-fragmentation chain-transfer (RAFT) polymerization using substoichiometric amounts of reactive initiators. Chapter 4 expands upon our initial work and provides a better understanding of CO2-mediated anionic polymerization under milder conditions.