In this work, the synthesis of polypeptoid-block-polypeptide copolymers (block copolypept(o)ides) based on bifunctional initiators is described, which introduces a distinct chemical entity at the connection between both blocks. With a view towards redox-sensitive block copolypept(o)ides, a cystamine-based initiator was used to synthesize polysarcosine macroinitiators with degrees of polymerization (X-n) between 100 and 200 displaying monomodal molecular weight distributions and dispersities (D) around 1.1 as determined by size exclusion chromatography. Block copolypept(o)ides with a poly(gamma-t-butyloxycarbonyl-L-glutamate) (PGlu((OBu)-Bu-t)) block (X-n = 25 or 50) were synthesized by controlled N-carboxyanhydride polymerization. Resulting block copolymers possess monomodal molecular weight distributions, dispersities around 1.2 and were applied to degradation studies. While block copolypept(o) ides are stable at 10 x 10(-6) M, they degrade over time at GSH concentrations of 10 x 10(-3) and 100 x 10(-3) M. Furthermore, these disulfide-containing block copolymers form PeptoMicelles, which degrade at intracellular GSH concentrations while remaining stable at extracellular GSH levels.