Dynamic-covalent nanostructures prepared by Diels-Alder reactions of styrene-maleic anhydride-derived copolymers obtained by one-step cascade block copolymerization

Macromolecular star formation by Diels-Alder chemistry resulted in dynamic nanomaterials capable of reversibly demonstrating the properties of both linear and highly branched macromolecules. Well-defined block copolymers of maleic anhydride (MAn) and styrene [poly(styrene-alt-MAn)-b-polystyrene (P(S-alt-MAn)-b-PS)] were prepared via a one-pot cascade approach by reversible addition-fragmentation chain transfer (RAFT) polymerization. Subsequent ring opening of the anhydride groups in the P(S-alt-MAn) segments by amidation with furfurylamine led to the formation of block copolymers with pendant furan functionality. Diels-Alder reactions of the furan-functional block copolymer with a bismaleimide crosslinker resulted in core-crosslinked stars by an arm-first approach. Star-like structures were also prepared by first allowing the furan-functional block copolymers to pre-assemble into polymeric micelles in a solvent selective for the polystyrene block. Subsequent addition of a bismaleimide and heating to allow the Diels-Alder reaction resulted in core-crosslinked micelles with similar structures to the polymeric stars prepared by the arm-first approach. Regardless of the synthetic approach employed, the thermoreversibility of the Diels-Alder linkages within the cores rendered the stars/crosslinked micelles dynamic-covalent, as demonstrated by their ability to reversibly dissociate back to the individual arms on heating.