This application provides nanoparticles and methods of making nanoparticles using pre-functionalized poly(ethylene glycol)(also referred to as PEG) as a macroinitiator for the synthesis of diblock copolymers. Ring opening polymerization yields the desired poly(ester)-poly (ethylene glycol)-targeting agent polymer that is used to impart targeting capability to therapeutic nanoparticles. This “polymerization from” approach typically employs precursors of the targeting agent wherein the reactivity of functional groups of the targeting agent is masked using protecting groups. Also described is a “coupling to” that utilized the poly(ethylene glycol)-targeting agent conjugate where the targeting agent remains in its native un-protected form. This method uses “orthogonal” chemistry that exhibit no cross reactivity towards functional groups typically found within targeting agents of interest.