Hierarchical self-assembly of miktoarm star copolymers with pathway complexity

• Published in: Polymer chemistry 2021-03, Vol.12 (1), p.1476-1486
• Main Authors: Xiao, Jie, He, Qun, Yang, Minjun, Li, Haoquan, Qiu, Xiandeng, Wang, Binghua, Zhang, Bin, Bu, Weifeng
• Format: Article
• Language: English
• Subjects: Chloroform; Complexity; Copolymers; Coronas; Functional materials; Methanol; Micelles; Photon correlation spectroscopy; Polyethylene glycol; Polymer chemistry; Polystyrene resins; Self-assembly; Solvents; Stars; Structural hierarchy; Toluene; Vesicles
• ISSN: 1759-9954; 1759-9962
• DOI: 10.1039/d0py01170c

The hierarchical self-assembly of molecular building blocks provides promising opportunities toward the exploration of functional soft materials with structural programmability. Here, we report the hierarchical self-assembly behaviors of amphiphilic miktoarm star copolymers with pathway complexity. In our experiments, supramolecular miktoarm star copolymers with a cluster core of [α-SiW 12 O 40 ] 4− and four polystyrene- block -poly(ethylene glycol) cations ( PS n - b + -PEG m , n = 17, 26, 39, 57, 81; m = 45, SEW-1-5 ) are used as a model of amphiphilic miktoarm stars. When dispersed in the selective THF/methanol and toluene/methanol mixture solvents, the miktoarm stars of SEW-2-5 self-assemble to form bundled fibers, sheet-like assemblies, and hollow spheres. These complex structures are packed by reverse cylindrical or spherical micelles having [α-SiW 12 O 40 ] 4− / PEG 45 cores and PS n coronas, wherein the micelle building blocks are originally formed by SEW-2-5 in the nonselective solvents THF and toluene. These hierarchically self-assembled structures do not resemble micelle-like nano-objects formed by amphiphilic copolymers in selective solvents. The mechanism behind such unconventional aggregates is presumably due to intra- and inter-micelle van der Waals attractions occurring under poor solvent conditions for the PS n coronas. The difference is that SEW-3-5 self-assemble into normal vesicles with a PS n core and a [α-SiW 12 O 40 ] 4− / PEG 45 corona in the chloroform/methanol mixture solvent. The reverse cylinders, rices, and spheres originally fabricated from SEW-3-5 in chloroform experience molecular reorganization for such normal vesicles in the present selective solvents. Moreover, SEW-1 forms normal lamellae in all the methanol based mixture solvents. The results presented herein not only enable us to reconsider the self-assembly behaviors of amphiphilic miktoarm stars in solution, but also provide opportunities for constructing advanced functional materials with high-level structural hierarchy. The self-assembly of amphiphilic miktoarm star copolymers shows hierarchical pathway complexity from molecular building blocks to miktoarm stars to micellar nano-objects to complex hierarchical assemblies.