Figure 4.

(A) Substitution of Pfp esters with bisamine cross-linkers and/or short oligo mPEG amines affording hydrophilic nanogels/water-soluble polymer chains. (B) DLS characterization of the resulting cross-linked nanogels and non-cross-linked polymers in PBS derived from poly(Pfp-Nb)₅₀-b-poly(mPEG-Nb)₅₀ precursor micelles, as well as their response upon lowering the pH to endosomal levels of pH 5. Note that only the ketal-cross-linked nanogels disassemble into single polymer chains exclusively. (C) TEM images of soluble polymer chains and nondegradable ether-cross-linked nanogels (1) and their derived counted size distributions (2). (D) DLS monitoring of ketal-cross-linked particle stability at extracellular pH and degradation at endolysosomal pH. Particle scattering intensity (1), particle size (2), and size distribution (3) decrease over time under mild acidic conditions (100 mM acetate buffer, pH 5.0), while the ketal-cross-linked particle’s integrity is guaranteed under neutral conditions (PBS, pH 7.4) for 24 h (compare also Figures S22–S24).