Double-Hydrophilic Polyphosphonate-Block-Polyamine Copolymers via Living Anionic Polymerization

We report the first synthesis of polyphosphonate-block-polysulfonamide (PEtPPn-b-PMeSA) copolymers via living anionic polymerization. Sequential polymerization of ethyl ethylene phospholane and cyanobenzenesulfonyl-activated aziridine monomers, including stereochemically defined aziridines, afforded well-defined block copolymers with tunable block lengths and controlled degrees of polymerization. However, due to the largely insoluble polysulfonamide block a desulfonylation step had to be conducted, with the subsequent desulfonylation yielding water-soluble double hydrophilic block copolymers (DHBCs) bearing free amine functionalities. Furthermore, a reverse block sequence was achieved by introducing an intermediate epoxide unit to facilitate the ring-opening polymerization of the phospholane monomer, which was otherwise inaccessible directly from the aziridine chain end due to insufficient nucleophilicity. The assembly behavior of the resulting block copolymers in an aqueous medium with pH as an external trigger was investigated using dynamic light scattering (DLS) and transmission electron microscopy (TEM). DLS indicated self-assembly for both atactic and isotactic DHBCs at different pH values. TEM revealed micellar structures for the isotactic systems, while the atactic analogues showed no discernible micellar-like morphology. Circular dichroism (CD) spectroscopy of the block copolymers bearing isotactic blocks confirmed secondary-structure formation, with the strongest chiroptical response observed for equimolar block compositions, whereas asymmetric block ratios yielded substantially reduced CD intensities. In summary, this report extends the chemical space of DHBCs to polyphosphonate-block-polyamine systems by anionic polymerization, which can be used as building blocks for future macromolecular architectures and potentially in biomedical applications.