Redox-Responsive Dynamic-Covalent Assemblies: Stars and Miktoarm Stars

Dynamic-covalent macromolecular stars were prepared by cross-linking block copolymers containing reactive maleic anhydride units with a disulfide-containing diamine. Here we report the synthesis of disulfide-cross-linked star polymers obtained by the arm-first process. Well-defined block copolymers containing a reactive poly(styrene-alt-maleic anhydride) (P(S-alt-MAn)) segment and an inert polystyrene or poly(N-isopropylacrylamide) segment were obtained by reversible addition-fragmentation chain transfer (RAFT) polymerization. Facile ring-opening of the pendant anhydride groups in the block copolymers by a disulfide-linked diamine cross-linker led to core-cross-linked stars with redox-responsive cores. The reductive cleavage of the disulfide linkages in the cross-linked cores resulted in star dissociation into linear arms with pendant thiol groups. Oxidation of the pendant thiol units of the resulting unimers in the presence of air led to reassembly or self-healing of the stars without the need for an externally added oxidizing agent.