ABC triblock copolymers with a poly(ethylene glycol) (PEG) midblock have attractive properties for biomedical applications because of PEG's favorable properties regarding biocompatibility and hydrophilicity. However, easy strategies to synthesize polymers containing a PEG midblock are limited. In this study, the successful synthesis of a heterofunctional PEG macroinitiator containing both an azoinitiator and an atom transfer radical polymerization (ATRP) initiator is demonstrated. This novel PEG macroinitiator allows the development of elegant synthesis routes for PEG midblock-containing ABC copolymers that does not require protection of initiating sites or polymer end-group postmodification. Polymers with outer blocks composed of different monomers were synthesized to illustrate the versatility of this macroinitiator. N-Isopropylacrylamide (NIPAM) was included to obtain thermosensitive polymers, 2-(dimethylamino)ethyl methacrylate (DMAEMA) provided pH-sensitive properties, and 2-hydroxyethyl acrylate (HEA) functioned as a noncharged hydrophilic block that also allows for postmodifications reactions. This synthesis approach can further contribute to the design of high-precision polymers with tailorable block compositions and polymer topologies, which is highly attractive for applications in nanotechnology.