Role of Solvophobic\nSequences in Amphiphilic Hyperbranched\nPolymers during Self-Assembly and Photoresponsiveness

Self-assembly of amphiphilic molecules is a simple and\neffective\nmethod for creating various nanoscale shapes such as spheres, rods,\ncylinders, and vesicles. The arrangement of amphiphilic molecules\nduring self-assembly is influenced by various factors. These factors\ninclude the balance between hydrophobic and hydrophilic components,\n length of solvophobic segments, amphiphile structure, temperature,\nand concentration. This study explores how the sequence of grafted\nsolvophobic segments influences the self-assembled morphology and\nstimuli-responsive behavior. Herein, the desired amphiphiles were\nprepared by reacting the peripheral alkyne-terminated hyperbranched\npolyester core with two distinct azide-functionalized amphiphiles\nusing Cu-catalyzed click transformations. The solvophobic sequences\nof these two amphiphiles differed by azide functionality positioning.\nFor the Set-1 amphiphile, the azide group presented at the hydrophilic\nchain ends, while for the Set-2 amphiphile, it was the opposite. Furthermore,\nthe solvophobic segments of these two amphiphiles were connected via\na photoresponsive azobenzene spacer. Despite the similar hydrophobic/hydrophilic\nbalance, the self-assembly of these two HBP-amphiphiles exhibited\ndisparities in morphologies and photoresponsive behavior. HBP-1 amphiphile\n(HBP-OEG-Azo-C12) is self-assembled into a vesicular structure, whereas\nthe HBP-2 amphiphile (HBP-C12-Azo-OEG) is self-assembled into spherical\nmicelles. The photoresponsiveness of these two amphiphiles was investigated\nby assessing the release of guest molecules. A photophysical study\nrevealed that the vesicular morphology of HBP-1 exhibits controlled\nrelease of guest molecules, while self-assembled HBP-2 initiates burst\nreleases. Spectroscopic and microscopic imaging techniques were employed\nto gain insight into the mechanism for these differences. The sequence\nof grafted solvophobic units appears to influence the geometry of\nthe self-segregated segments and the stability of the self-assembled\nstructure, resulting in different morphologies and responsive functions.