Polysulfobetaine-based diblock copolymer nano-objects via polymerization-induced self-assembly

A zwitterionic polysulfobetaine-based macromolecular chain transfer agent (PSBMA38) was prepared by reversible addition–fragmentation chain transfer (RAFT) solution polymerization of [2-(methacryloyloxy)ethyl] dimethyl(3-sulfopropyl) ammonium hydroxide (SBMA) in an aqueous solution containing 0.5 M NaCl at 70 °C. This PSBMA38 macro-CTA was then utilized for the RAFT aqueous dispersion polymerization of a water-miscible monomer, 2-hydroxypropyl methacrylate (HPMA). The growing PHPMA block became hydrophobic in situ, leading to polymerization-induced self-assembly. Systematic variation of the mean degree of polymerization of the PHPMA block and the copolymer concentration enabled access to pure phases of spheres, worms or vesicles, as judged by transmission electron microscopy and dynamic light scattering studies. A detailed phase diagram was constructed and the thermo-responsive behavior of selected PSBMA38-PHPMAX nanoparticles was investigated. Finally, the salt tolerance of PSBMA38-PHPMA400 vesicles was compared to that of PGMA71-PHPMA400 vesicles; the former vesicles exhibit much better colloidal stability in the presence of 1 M MgSO4.