The synthesis of hybrid bioconjugates via the ring-opening polymerization (ROP) of N-carboxyanhydrides (NCAs) using a synthetic macroinitiator is described. Poly(n-butyl acrylate), polystyrene, and poly(N-isopropyl acrylamide) are synthesized (polydisperity index,D < 1.1) using reversible addition-fragmentation chain transfer (RAFT) as the synthetic tool. A phthalimidomethyl trithiocarbonate RAFTchain transfer agentis used to prepare well-defined, end-functional polymers, which after deprotection result in amine terminal macroinitiators. The subsequent initiating systems could successfully be chain extended with epsilon-benzyloxycarbonyl-l-lysine or -benzyl-l-glutamate as the NCAs to produce a library of polymer-polypeptide conjugates. In doing so, a novel procedure for directly synthesizing bioconjugates via a non-modular route without the need for excessive purification and isolation steps is described.