Multiple Morphologies and Characteristics of “Crew-Cut” Micelle-like Aggregates of Polystyrene-b-poly(acrylic acid) Diblock Copolymers in Aqueous Solutions

Abstract

Crew-cut micelle-like aggregates of various morphologies prepared from polystyrene-b-poly(acrylic acid), PS-b-PAA, diblock copolymers under near-equilibrium conditions, were studied by transmission electron microscopy (TEM). The insoluble block (PS) contents in the copolymers ranged from 80 to 98 wt %. In spherical micelles, the micelle cores, formed by aggregation of the PS blocks, were generally monodisperse. A comparison between star and crew-cut micelles showed that the latter are distinguished by a low density of corona chains on the core surface and a low degree of stretching of the PS blocks in the cores. As the PAA content in block copolymer decreased, the morphology of the aggregates changed progressively from spheres to cylinders, to bilayers (both vesicles and lamellae), and eventually to compound micelles consisting of an assembly of inverted micelles surrounded by a hydrophilic surface. The compound micelles are believed to be a new morphology for block copolymers. The addition of homopolystyrene to the diblocks changed the morphologies from bilayers or cylinders to spheres. The present system provides the first instance in which all these multiple aggregate morphologies have been observed directly in block copolymers in a low molecular weight solvent with changing copolymer composition. It is believed that this is the only way so far to prepare stable nanosize glassy vesicles of block copolymers which form spontaneously and can be isolated in water and studied directly by electron microscopy.

pH Dependence of the morphology of aqueous micelles formed by polystyrene-block-poly(2-vinylpyridine)-blockpoly( ethylene oxide) copolymers

“…2 agree with the formation of monodispersed micelles. The apparent diffusion coefficient of these micelles is independent of concentration, at least in the dilute regime, which is in agreement with 'kinetically frozen' micelles of an extremely low critical micellar concentration [9]. Moreover, the angular dependence of the apparent diffusion coefficient confirms that the micelles are spherical [10].…”

Self‐assembly and responsiveness of polypeptide‐based block copolymers: How “Smart” behavior and topological complexity yield unique assembly in aqueous media

“…For example, vesicles have been observed for PB 40 b-PLGA 100 containing ca. 85 wt % glutamate (in the range where spherical micelles would be expected).…”

“…Pioneering research on pH and salt responsiveness involved synthetic polyelectrolytes such as poly(acrylic acid) and poly(vinyl pyridine) coupled to neutral, hydrophobic blocks (i.e., poly(butadiene)), where changes in pH or salt concentration impacted the ionic nature of the hydrophilic block. [36][37][38][39][40] Common examples of temperature responsiveness are a result of the incorporation of blocks that contain a lower critical solution temperature (LCST) such as poly(N-isopropyl acrylamide) 41 or poly(propylene oxide) 11 or the incorporation of polypeptides where the secondary structure transitions with temperature (i.e., a-helix to b-sheet). 42 Polypeptide-based block copolymers offer many advantages in the realm of responsive block copolymer self-assembly such as biocompatibility and enhanced biofunctionality.…”

Formation and stability of micelles and vesicles

“…PS content) at constant head group area (i.e. PAA content) [6]. Shinkai and coworkers [7•] synthesized some remarkable tetracationic amphiphiles bearing a calix [4]arene core.…”