Precision Synthesis and Distinct Assembly of Double-Chain Giant Surfactant Regioisomers

The delicate influence of minute structural difference, such as regiochemistry, on self-assembly and phase behaviors has been commonly observed in small molecules but rarely in synthetic polymers. Herein, we report the precision synthesis of a series of double-chain giant surfactant regioisomers and their distinct phase structures and phase behaviors. These giant surfactants possess a hydroxyl-functionalized cubic T9 polyhedral oligomeric silsesquioxane head and two polystyrene tails tethered at para-, meta-, and orthoconfigurations and were prepared following the sequential click method. As revealed by temperature-dependent small angle X-ray scattering and bright-field transmission electron microscopy, their order disorder transition temperatures decrease in the order of ortho-, meta-, and para-isomers, while order order transitions were observed in the meta-isomer from lamellae to double gyroids and in the ortho-isomer from double gyroids to hexagonal cylinders upon increasing temperature. The mechanisms are elucidated by the influence of the tethering positions on the different free energy contributions, i.e., the interfacial energy, the head-to-head interaction, and the entropic energy of the tails. The distinct assembly behaviors of the three regioisomers are unusual in macromolecules yet resemble small molecules. It opens an avenue to fine-tune the macromolecular assembly at the level of molecular precision.