Solution Self-Assembly of Coil-Crystalline Diblock Copolypeptoids: The Effects of Linear and Branched <i>N</i>-Alkyl Substituents

We synthesized two types of amphiphilic diblock copolypeptoids, i.e., poly(N-methyl glycine)-b-poly(N-octyl glycine) (PNMG-b-PNOG) and poly(N-methyl glycine)-b-poly(N-2-ethyl-1-hexyl glycine) (PNMG-b-PNEHG), to investigate the influence of N-substituent (side chain) structure on the hierarchical self-assembly of diblock copolypeptoids in solution. With linear aliphatic N-substituent, the board-like PNOG blocks crystallize into a highly ordered lamellar structures, resulting in the hierarchical self-assembly of PNMG-b-PNOG into 3D microflowers comprised of stacked nanoribbons. By contrast, the PNEHG blocks bearing bulky branched aliphatic N-substituents are rod-like and prefer to stack into a columnar hexagonal liquid-crystalline mesophase, which drives PNMG-b-PNEHG to self-assemble into 2D hexagonal nanosheets in solution. These results show that the N-substituent architecture (i.e., linear versus branched) has a tremendous impact on the solution self-assembly of diblock copolypeptoids, which can serve as an effective strategy to tune the geometry and hierarchical structure of polypeptoid-based nanomaterials.