To continue expanding the use of Single Electron Transfer-Living Radical Polymerization (SET-LRP) in applications at the interface between macromolecular science, biomacromolecules, biology and medicine, it is essential to develop novel initiators that do not compromise the structural stability of synthesized polymers in biological environments. Here, we report that stable 2-bromopropionyl peptoid-type initiators such as 1,4-bis(2-bromopropionyl)piperazine and 4-(2-bromopropionyl)morpholine are an alternative that meets the standards reached by the well-known secondary and tertiary alpha-haloester-type initiators in terms of excellent control over molecular weight evolution and distribution as well as polymer chain ends. SET-LRP methodologies in organic, aqueous, and biphasic organic aqueous media were evaluated for this purpose.