A diazo initiator and a chain transfer agent (CTA), both containing a pentafluorophenyl (PFP) activated ester, were synthesized. In a RAFT polymerization using the functionalized chain transfer agent (PFP-CTA), methyl methacrylate (MMA), diethylene glycol monomethyl ether methacrylate (DEGMA), poly(ethylene glycol) monomethyl ether methacrylate (PEGMA), and lauryl methacrylate (LMA) could successfully be polymerized into homopolymers and diblock copolymers with good control over molecular weight, very high conversions, and narrow molecular weight distributions. Polymers derived from the PFP−CTA possessed an activated ester at the α-end of the polymer chain, which could be reacted with amines with high conversions. The terminal ω-dithioester group of each polymer chain could quantitatively be removed by treating the polymer with an excess of AIBN, leaving the α-PFP ester functionality intact. Accordingly, the pentafluorophenyl ester diazo compound could successfully be employed to functionalize RAFT polymers with a PFP ester at their ω-end. As a consequence, functionalization of both end groups was possible and led to telechelic polymers, exhibiting an active ester at both ends of the polymer chain. As an example, a high molecular weight PMMA was prepared by polycondensation with ethylenediamine.