Crystallization of Precise Side-Chain Giant Molecules with Tunable Sequences and Functionalities

Side-chain giant molecules, constructed from giant monomers by precision synthesis, are viewed as a size-amplified analogue of conventional linear polymers. The molecular accuracy in terms of composition, sequence, topology, and functionality makes these precise macromolecules an ideal platform to investigate the interplay of various molecular parameters in their hierarchical assembly processes. In this study, we studied the crystallization of two sets of amphiphilic side-chain giant molecules with elegantly designed chain sequences and functionalities. When crystallizing from dilute solutions, they form well-defined two-dimensional (2D) crystals with a unique sequence-independent feature. In-depth structural characterization suggested a sandwich-like configuration with head-to-head packing of the side-chain components. Interestingly, the chain stem orientation is supposed to be perpendicular to the normal direction of the nanosheet crystals, which was distinct from the classic folded-chain model of conventional linear polymers. Besides, by intentionally altering the functional groups of the non-crystalline moieties to be non-ionic, cationic, or anionic, we proposed that the solvation effect played a key role in inhibiting the crystal stacking along the surface normal direction and thus in stabilizing the 2D crystals. Our findings revealed the unique crystallization behavior of precise side-chain giant molecules and might provide a strategy to engineer 2D nanomaterials with pre-programmed compositions and functions.