Vesicles DOI: 10.1002/smll.200600733 Real-Time Hierarchical Self-Assembly of Large Compound Vesicles from an Amphiphilic Hyperbranched Multiarm Copolymer** Yiyong Mai, Yongfeng Zhou,* and Deyue Yan* Supramolecular self-assembly has displayed great potential for preparing ordered and delicate structures from the mi- croscopic through to the macroscopic scale. [1] However, the level of complexity of the present man-made assembly sys- tems pales in comparison to what nature flaunts all around us. [2] The need for increased complexity will push chemical self-assembly further forward. In recent years, the pioneer- ing research from the groups of Whitesides, Safinya, Nolte, amongst others, has shown that hierarchical self-assembly, a ubiquitous material-building strategy in nature, may be an excellent and promising laboratory tool for building systems with increasing levels of complexity. [3] As defined by White- sides et al., hierarchical self-assembly is the formation of an ordered structure through a set of interactions that decreas- es in strength—that is, through a hierarchy of interactions. [3a] Up to now, some delicate and impressive hierarchical self- assembly systems have been reported, including hexagonal plates, three-layer tubules, helical fibers and strands, multi- layer films, and so on. [3] However, most of them are limited on the microscopic or submicroscopic scales, and can hardly be observed in real time. Herein, we report a vivid hierarch- ical self-assembly on the mesoscopic scale by displaying se- quential real-time morphology transformations in the prepa- ration of large compound vesicles (LCVs). LCVs are complex aggregates analogous to aggregated soap bubbles. Since they were first prepared and defined by Eisenberg et al., LCVs have attracted much attention due to their potential applications in controllable drug release. [4] But so far, all reported LCVs are self-aggregated from linear block copolymers and limited to the microscopic scale. [4] As a result, they can only be detected by electron microscopy, which is unsuitable for studying real-time trans- formations of three-dimensional morphologies. [5] Therefore, the dynamic formation process of LCVs has remained un- clear. This work, for the first time, reports the preparation of giant LCVs (10–100 mm) from a hyperbranched multiarm copolymer. In addition, the real-time formation process of the LCVs was observed under an optical microscope taking advantage of their particularly large size. The employed copolymer, HBPO-star -PEO, has a hydro- phobic hyperbranched poly(3-ethyl-3-oxetanemethanol) (HBPO) core and many hydrophilic poly(ethylene oxide) (PEO) arms (Figure1). Previously, we found that the HBPO-star -PEOs with longer PEO arms or larger hydro- philic fractions (f EO = 0.69–0.86) can self-organize into giant polymer vesicles (5–200 mm) in water. [6] Compared with the reported vesicles prepared by self-assembly of well-defined linear block copolymers or dendrimers, [1a–d,4,7] it is the first report of giant vesicles prepared by relatively ill-defined hy- perbranched polymers. The self-assembly process involved directly placing the polymer into deionized water (polymer concentration: 10mgmL 1 ) under stirring at room tempera- ture. The polymer vesicles were proved to possess a bilayer- or monolayer-walled structure with an inner layer of HBPO cores and outer shells of PEO arms (see Figure S3 in the Supporting Information) due to the microphase separation of the amphiphilic HBPO-star -PEO molecules, which is driven by hydrophobic interactions and hydrogen bonding. The detailed evidence for the self-assembly mechanism has been reported elsewhere. [6] Herein, we find that the HBPO- star -PEO molecules with very short PEO arms (f EO = 0.46, Figure 1) displayed an interesting hierarchical self-assembly behavior: The copolymer first self-assembles into giant vesi- cles, and then the sticky vesicles become interconnected to- gether as a result of successive hydration and membrane Figure 1. Molecular structure of the HBPO-star-PEO hyperbranched multiarm copolymer with a HBPO core (in black) and many short PEO arms (bounded between the two dashed circles in gray) [*] Dr. Y. Mai, Dr. Y. Zhou, Prof. Dr. D. Yan College of Chemistry and Chemical Engineering State Key Laboratory of Metal Matrix Composites Shanghai Jiao Tong University 800 Dongchuan Road Shanghai, 200240 (P. R. China) Fax: (+ 86)21-54741297 E-mail: yfzhou@sjtu.edu.cn dyyan@sjtu.edu.cn [**] This work was financially supported by National Natural Science Foundation (nos. 50503012, 50633010), National Basic Research Program (2007CB808000), and Rising-Star Foundation of Shang- hai Science and Technique Committee (No. 06 A14028). Supporting information for this article is available on the WWW under http://www.small-journal.com or from the author. 1170 # 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim small 2007 , 3, No.7, 1170 – 1173 communications