Controlled radical polymerization (CRP) is typically performed under inert conditions, requiring rigorous deoxygenation procedures such as inert gas purging or freeze–pump–thaw cycles, as oxygen acts as an inhibitor by quenching free radicals. To overcome oxygen inhibition, strategies such as enzymatic cascade catalysis have been explored, where molecular oxygen is converted into radicals to initiate polymerization. However, the reliance on enzymes increases system complexity and limits compatibility with hydrophobic monomers due to the aqueous medium requirement. In this work, we present a novel strategy that utilizes oxygen to initiate and regulate polymerization. By leveraging the homolytic substitution reactions between oxygen and trialkylboranes, carbon-based radicals are generated, serving as effective initiators for radical processes. We have successfully applied this oxygen-initiated system to RAFT polymerization and ATRP. Furthermore, we exploit the side reaction where radicals react with oxygen to form peroxy radicals, directly incorporating oxygen as a monomer into the polymer backbone. This approach enables the design of polyperoxides as novel polymers that can act as biological prodrugs, generating reactive oxygen species (ROS) for potential applications such as cancer therapy. This work demonstrates a versatile and innovative use of oxygen in CRP, expanding its utility in both polymerization control and functional material design.