Self-assembled polymer nanoparticles have tremendous potential in biomedical and environmental applications. For all applications, tailored polymer chemistries are critical. In this study, we demonstrate a precursor approach in which an activated, organic solvent-soluble block polymer precursor is modified through mild postpolymerization modifications to access new polymer structures. We synthesized and characterized poly(isoprene)- block-poly(di-Boc acrylamide) diblock polymers. This activated-acrylamidebased polymer was then reacted with amines or reductants in the absence of catalysts to yield the hydrophilic blocks polyacrylamide, poly(hydroxypropylene), and poly(N-ethyl acrylamide). The resulting amphiphilic block polymers self-assembled in water to form polymersomes, as confirmed by cryo-electron microscopy and confocal microscopy. The approach also enables simple functionalization with specialized ligands, which we demonstrated by tagging polymers with an amino-fluorophore and imaging by confocal microscopy. We expect that the methodologies established in this study will open doors to new and useful solution nanostructures with surface chemistries that can be optimized for various applications.