Controlled\nFabrication of Distinct Nanostructures\nfrom Discrete Oligourethanes via Thermal Annealing

The self-assembly of sequence-defined polymers (SDPs)\nenables the\nformation of a diverse array of nanostructures; however, the construction\nof complex hierarchical structures via thermal annealing from SDPs\nremains relatively unexplored. In this study, two series of oligourethanes,\n2Cit-<i>p</i>B<sub><i>n</i></sub>-OH and 2Cit-<i>m</i>B<sub><i>n</i></sub>-OH, were synthesized to\ninvestigate their thermal annealing behaviors. Nanorod clusters were\ngenerated from 2Cit-<i>p</i>B<sub>6</sub>-OH in a mixture\nof 1,4-dioxane and toluene, whereas 2Cit-<i>p</i>B<sub>8</sub>-OH formed nanosheets after thermal annealing. Upon modifying the\nstructure of the repeating units, 2Cit-<i>m</i>B<sub>6</sub>-OH self-assembled into ultrathin nanosheets, transitioning from\nnanospheres after thermal annealing in a mixture of isopropanol and\ncyclohexane, while “flower” micelles were produced from\n2Cit-<i>m</i>B<sub>8</sub>-OH. Interestingly, when isopropanol\nwas replaced with a mixture of isopropanol and tetrahydrofuran (THF),\nuniform nanotubes were generated by 2Cit-<i>m</i>B<sub>6</sub>-OH under the same thermal annealing conditions. Additionally, a\ndiscrete amphiphile (2Cit-<i>m</i>B<sub>4</sub>-(<i>S</i>)DPEG) was synthesized, leading to the formation of uniform\nnanosheets in aqueous solution after thermal annealing. This work\nhighlights the significant effects of sequence and repeating unit\nstructure of SDPs on their self-assembly behaviors and presents a\nnovel strategy for the controlled fabrication of unique nanostructures\nfrom SDPs.