Macrobicyclic hexa-amine cage ligands are known to completely encapsulate transition metals inside the ligand cavity. Recent work has shown that a five-coordinate bromido complex [Cu(AMME-N3S3sar)Br]+ was observed, featuring a novel tetradentate (N2S2) coordinated form of the cage ligand in DMSO. Reduction to its monovalent state results in no change in the geometry of the complex. The electrochemistry of this complex in the presence of an alkyl halide showed that this complex has a low activation to convert these alkyl halides to their corresponding incipient radicals. Further polymerization kinetics with methyl acrylate showed that the molecular weight was uncontrolled, implying that deactivation was negligible. Therefore, this copper/ligand complex with an alkyl halide initiator only acts as an initiation source. This led us to use this Cu/AMME-N3S3sar complex to initiate MA polymerizations at room temperature in the presence of a RAFT agent. The results showed that the molecular weight distribution was controlled and followed ideal ‘living’ radical behavior, in which the molecular weight polydispersity for a range of different molecular weight targets was less than 1.1.