Chiral nanostructures of isosorbide- and isomannide-based polyurethanes

Owing to their special optical and chemical properties, polymers with helical nanostructures are good candidates for constructing building blocks for various applications in analytical and biomedical science. While the chirality of conjugated polymers has been well studied, there are few reports on the chirality of polyurethanes (PUs). In particular, direct morphological observations of their chiral nanostructures are rare. In this work, PUs were synthesized using isosorbide (ISO) and isomannide (ISOM), derived from renewable feedstocks, as chiral building segments and 1,4-phenylenediisocyanate (4,4′-MDI) and para-phenylenediisocyanate (PPDI), which have rigid structures, as hard segments. The molecular structures and thermal properties of the PUs were characterized, as well as the nanostructures formed following their deposition on solid surfaces. Polymers with 4,4′-MDI segments had plate-like structures, whereas those with PPDI segments had rod-like structures, with ISO-PPDI-PU and ISOM-PPDI-PU exhibiting helical nanostructures, as confirmed by transmission electron microscopy and atomic force microscopy.